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In number theory , Hurwitz's theorem , named after Adolf Hurwitz , gives a bound on a Diophantine approximation . The theorem states that for every irrational number ξ there are infinitely many relatively prime integers m , n such that | ξ − m n | < 1 5 n 2 . {\displaystyle \left|\xi -{\frac {m}{n}}\right|<{\frac {1}{{\sqrt {5}}\,n^{2}}}.}
The condition that ξ is irrational cannot be omitted. Moreover the constant 5 {\displaystyle {\sqrt {5}}} is the best possible; if we replace 5 {\displaystyle {\sqrt {5}}} by any number A > 5 {\displaystyle A>{\sqrt {5}}} and we let ξ = ( 1 + 5 ) / 2 {\displaystyle \xi =(1+{\sqrt {5}})/2} (the golden ratio ) then there exist only finitely many relatively prime integers m , n such that the formula above holds.
The theorem is equivalent to the claim that the Markov constant of every number is larger than 5 {\displaystyle {\sqrt {5}}} . | https://en.wikipedia.org/wiki/Hurwitz's_theorem_(number_theory) |
In mathematics, the Hurwitz class number H ( N ), introduced by Adolf Hurwitz , is a modification of the class number of positive definite binary quadratic forms of discriminant – N , where forms are weighted by 2/ g for g the order of their automorphism group, and where H (0) = –1/12 .
Zagier (1975) showed that the Hurwitz class numbers are coefficients of a mock modular form of weight 3/2. | https://en.wikipedia.org/wiki/Hurwitz_class_number |
In mathematics, Hurwitz determinants were introduced by Adolf Hurwitz ( 1895 ), who used them to give a criterion for all roots of a polynomial to have negative real part.
Consider a characteristic polynomial P in the variable λ of the form:
where a i {\displaystyle a_{i}} , i = 0 , 1 , … , n {\displaystyle i=0,1,\ldots ,n} , are real.
The square Hurwitz matrix associated to P is given below:
The i- th Hurwitz determinant is the i- th leading principal minor (minor is a determinant) of the above Hurwitz matrix H . There are n Hurwitz determinants for a characteristic polynomial of degree n . | https://en.wikipedia.org/wiki/Hurwitz_determinant |
In mathematics , a Hurwitz polynomial (named after German mathematician Adolf Hurwitz ) is a polynomial whose roots (zeros) are located in the left half-plane of the complex plane or on the imaginary axis , that is, the real part of every root is zero or negative. [ 1 ] Such a polynomial must have coefficients that are positive real numbers . The term is sometimes restricted to polynomials whose roots have real parts that are strictly negative, excluding the imaginary axis (i.e., a Hurwitz stable polynomial ). [ 2 ] [ 3 ]
A polynomial function P ( s ) of a complex variable s is said to be Hurwitz if the following conditions are satisfied:
Hurwitz polynomials are important in control systems theory , because they represent the characteristic equations of stable linear systems . Whether a polynomial is Hurwitz can be determined by solving the equation to find the roots, or from the coefficients without solving the equation by the Routh–Hurwitz stability criterion .
A simple example of a Hurwitz polynomial is:
The only real solution is −1, because it factors as
In general, all quadratic polynomials with positive coefficients are Hurwitz.
This follows directly from the quadratic formula :
where, if the discriminant b 2 −4 ac is less than zero, then the polynomial will have two complex-conjugate solutions with real part − b /2 a , which is negative for positive a and b .
If the discriminant is equal to zero, there will be two coinciding real solutions at − b /2 a . Finally, if the discriminant is greater than zero, there will be two real negative solutions,
because b 2 − 4 a c < b {\displaystyle {\sqrt {b^{2}-4ac}}<b} for positive a , b and c .
For a polynomial to be Hurwitz, it is necessary but not sufficient that all of its coefficients be positive (except for quadratic polynomials, which also imply sufficiency). A necessary and sufficient condition that a polynomial is Hurwitz is that it passes the Routh–Hurwitz stability criterion . A given polynomial can be efficiently tested to be Hurwitz or not by using the Routh continued fraction expansion technique. | https://en.wikipedia.org/wiki/Hurwitz_polynomial |
In mathematics, the Hurwitz problem (named after Adolf Hurwitz ) is the problem of finding multiplicative relations between quadratic forms which generalise those known to exist between sums of squares in certain numbers of variables.
There are well-known multiplicative relationships between sums of squares in two variables
(known as the Brahmagupta–Fibonacci identity ), and also Euler's four-square identity and Degen's eight-square identity . These may be interpreted as multiplicativity for the norms on the complex numbers ( C {\displaystyle \mathbb {C} } ), quaternions ( H {\displaystyle \mathbb {H} } ), and octonions ( O {\displaystyle \mathbb {O} } ), respectively. [ 1 ] : 1–3 [ 2 ]
The Hurwitz problem for the field K is to find general relations of the form
with the z being bilinear forms in the x and y : that is, each z is a K -linear combination of terms of the form x i y j . [ 3 ] : 127
We call a triple ( r , s , n ) {\displaystyle \;(r,s,n)\;} admissible for K if such an identity exists. [ 1 ] : 125 Trivial cases of admissible triples include ( r , s , r s ) . {\displaystyle \;(r,s,rs)\;.} The problem is uninteresting for K of characteristic 2, since over such fields every sum of squares is a square, and we exclude this case. It is believed that otherwise admissibility is independent of the field of definition. [ 1 ] : 137
Hurwitz posed the problem in 1898 in the special case r = s = n {\displaystyle \;r=s=n\;} and showed that, when coefficients are taken in C {\displaystyle \mathbb {C} } , the only admissible values ( n , n , n ) {\displaystyle \,(n,n,n)\,} were n ∈ { 1 , 2 , 4 , 8 } . {\displaystyle \;n\in \{1,2,4,8\}\;.} [ 3 ] : 130 His proof extends to a field of any characteristic except 2. [ 1 ] : 3
The "Hurwitz–Radon" problem is that of finding admissible triples of the form ( r , n , n ) . {\displaystyle \,(r,n,n)\;.} Obviously ( 1 , n , n ) {\displaystyle \;(1,n,n)\;} is admissible. The Hurwitz–Radon theorem states that ( ρ ( n ) , n , n ) {\displaystyle \;\left(\rho (n),n,n\right)\;} is admissible over any field where ρ ( n ) {\displaystyle \,\rho (n)\,} is the function defined for n = 2 u v , {\displaystyle \;n=2^{u}v\;,} v odd, u = 4 a + b , {\displaystyle \;u=4a+b\;,} with 0 ≤ b ≤ 3 , {\displaystyle \;0\leq b\leq 3\;,} and ρ ( n ) = 8 a + 2 b . {\displaystyle \;\rho (n)=8a+2^{b}\;.} [ 1 ] : 137 [ 3 ] : 130
Other admissible triples include ( 3 , 5 , 7 ) {\displaystyle \,(3,5,7)\,} [ 1 ] : 138 and ( 10 , 10 , 16 ) . {\displaystyle \,(10,10,16)\;.} [ 1 ] : 137 | https://en.wikipedia.org/wiki/Hurwitz_problem |
In ecological theory, the Hutchinson's ratio is the ratio of the size differences between similar species when they are living together as compared to when they are isolated. It is named after G. Evelyn Hutchinson who concluded that various key attributes in species varied according to the ratio of 1:1.1 to 1:1.4. [ 1 ] Hutchinson concluded that the mean ratio, 1.3, can be understood as the variation of attribute separation needed in order to preserve species coexistence at the same trophic level but in differing niches. [ 2 ]
However, some authors present evidence that this ratio does not depict the structure of animal communities. Rather, Hutchinson's ratio is just a representation of the distribution of entities, both living and non-living, in nature. [ 3 ] A study was conducted by R. Charles MacNally to test whether sympatric species form geometric series, also known as a Hutchinsonian series. The results of this revealed that only a small fraction of the series conformed to the expected ratio of 1.3, questioning the accuracy of Hutchinson's ratio. [ 4 ]
This ecology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hutchinson's_ratio |
In ecological theory, the Hutchinson's ratio is the ratio of the size differences between similar species when they are living together as compared to when they are isolated. It is named after G. Evelyn Hutchinson who concluded that various key attributes in species varied according to the ratio of 1:1.1 to 1:1.4. The mean ratio 1.3 can be interpreted as the amount of separation necessary to obtain coexistence of species at the same trophic level . [ 1 ]
The variation in trophic structures of sympatric congeneric species is presumed to lead to niche differentiation, and allowing coexistence of multiple similar species in the same habitat by the partitioning of food resources. [ 2 ] Hutchinson concluded that this size ratio could be used as an indicator of the kind of difference necessary to permit two species to co-occur in different niches but at the same level of the food web. [ 3 ] The rule's legitimacy has been questioned, as other categories of objects also exhibit size ratios of roughly 1.3.
Studies done on interspecific competition and niche changes in Tits (Parus spp.) [ 4 ] show that when there are multiple species in the same community there is an expected change in foraging when they are of similar size (size ratio 1-1.2). There was no change found among the less similar species. In this paper this was strong evidence for niche differentiation for interspecific competition, and would also be a good argument for Hutchinson's rule.
The simplest and perhaps the most effective way to differentiate the ecological niches of coexisting species is their morphological differentiation (in particular, size differentiation).
Hutchinson showed that the average body size ratio in species of the same genus that belong to the same community and use the same resource is about 1.3 (from 1.1 to 1.4) and the respective body weight ratio is 2. This empirical pattern tells us that this rule does not apply to all organisms and ecological situations. And, therefore, it would be of particular interest to study the size differentiation of closely related species in different communities and reveal cases meeting Hutchinson's rule
M. Eadie. [ 5 ] however, presents evidence that Hutchinson's constant is an artifact of the distribution of the size of animate, as well as inanimate, objects in nature. This distribution or ratio would just represent a log-normal distribution and that the variances of these distributions are small. They argue that the size ratio Hutchinson suggests doesn't tell a lot about the actual structuring of animal communities.
This evolution -related article is a stub . You can help Wikipedia by expanding it .
This ecology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hutchinson's_rule |
In mathematics , the Hutchinson metric otherwise known as Kantorovich metric is a function which measures "the discrepancy between two images for use in fractal image processing " and "can also be applied to describe the similarity between DNA sequences expressed as real or complex genomic signals". [ 1 ] [ 2 ]
Consider only nonempty , compact , and finite metric spaces . For such a space X {\displaystyle X} , let P ( X ) {\displaystyle P(X)} denote the space of Borel probability measures on X {\displaystyle X} , with
the embedding associating to x ∈ X {\displaystyle x\in X} the point measure δ x {\displaystyle \delta _{x}} . The support | μ | {\displaystyle |\mu |} of a measure in P ( X ) {\displaystyle P(X)} is the smallest closed subset of measure 1.
If f : X 1 → X 2 {\displaystyle f:X_{1}\rightarrow X_{2}} is Borel measurable then the induced map
associates to μ {\displaystyle \mu } the measure f ∗ ( μ ) {\displaystyle f_{*}(\mu )} defined by
for all B {\displaystyle B} Borel in X 2 {\displaystyle X_{2}} .
Then the Hutchinson metric is given by
where the sup {\displaystyle \sup } is taken over all real -valued functions u {\displaystyle u} with Lipschitz constant ≤ 1. {\displaystyle \leq \!1.}
Then δ {\displaystyle \delta } is an isometric embedding of X {\displaystyle X} into P ( X ) {\displaystyle P(X)} , and if f : X 1 → X 2 {\displaystyle f:X_{1}\rightarrow X_{2}} is Lipschitz then f ∗ : P ( X 1 ) → P ( X 2 ) {\displaystyle f_{*}:P(X_{1})\rightarrow P(X_{2})} is Lipschitz with the same Lipschitz constant. [ 3 ] | https://en.wikipedia.org/wiki/Hutchinson_metric |
Hutchison Asia Telecom Group or HAT , is a division of Hong Kong-based multinational conglomerate CK Hutchison Holdings . [ 1 ] The division provides telecommunications services to several Asian countries. The division was formerly incorporated as Hutchison Telecommunications International Limited , known as Hutchison Telecom or HTIL in short. It was [ clarification needed ] an offshore company in the Cayman Islands and a listed company in the Stock Exchange of Hong Kong . It operates GSM , 3G and 4G mobile telecommunications services in Indonesia, Sri Lanka and Vietnam under brands 3 , Hutch and Vietnamobile .
Hutchison Telecommunications International was formerly a listed company with a primary listing on the Stock Exchange of Hong Kong (former stock code: 2332) and American depositary shares quoted on the New York Stock Exchange . In May 2010, Hutchison Telecom became a fully owned subsidiary of Hutchison Whampoa and its shares were delisted. [ 2 ] [ 3 ] In 2009, Hutchison Telecom also spun off part of their assets as a separate listed company Hutchison Telecommunications Hong Kong Holdings , which including 3 Hong Kong and Hutchison Global Communications .
In 1999 and 2000, Hutchison Telecom sold its Orange and VoiceStream interests and re-invested the greater part of the proceeds to develop its global third-generation ( 3G ) mobile broadband telecommunications business, based on the European UMTS ( W-CDMA ) 3G standard. [ citation needed ]
In early 2007, Hutchison Telecom made headlines by selling its 67% interest in the Indian mobile phone network Hutch Essar to Vodafone for US$ 13.1 billion (of which $2 billion was debt). [ citation needed ]
In December 2007, minority shareholder of Hutchison Telecommunications International (HTIL), Orascom Telecom , sold the 14.2% stake of HTIL, to HTIL's parent company Hutchison Whampoa , for HK$7.5 billion (approx. US$962 million). [ 4 ] Orascom also reduced the stake from 19.3% to 16.3%, through a private placement of shares to the market in October 2007. [ 5 ]
In 2009, Hutchison sold its controlling stake in Orange Israel to Scailex Corporation . Thus it ended using the Orange brand for providing mobile services. [ citation needed ]
In 2009, it spun off Hutchison Telecommunications Hong Kong Holdings (stock code: 215) to be listed on the Stock Exchange of Hong Kong. [ 6 ]
In 2010, the company was privatized.
In July 2005, Hutchison Telecom acquired a 60% equity stake in PT Hutchison 3 Indonesia ("H3I", formerly known as PT Hutchison CP Telecommunications ("Hutchison CP Telecom" or "HCPT"), PT Cyber Access Communication and PT Telindo Inti Nusa) from the Charoen Pokphand Group Indonesia. In 2006, H3I announced that it retained Siemens to design, build and operate state-of-the-art 2G and 3G nationwide wireless networks. H3I launched its commercial services on 29 March 2007 under the 3 brand.
Indonesia is an extremely attractive wireless market with a sizable population and a relatively low mobile penetration rate. It is an excellent example of Hutchison Telecom's vision and strategy in achieving growth in emerging markets.
At the end of September 2009, H3I's customer base grew to approximately 7.3 million.
In September 2021, it was announced that the latter company would be merged with Ooredoo 's Indosat (who operates IM3 Ooredoo networks) to form Indosat Ooredoo Hutchison (IOH) and was closed the merger on 4 January 2022.
The company's Sri Lankan operation, commonly known as Hutch . CK Hutchison Holdings Limited owns 85% controlling stake of the company while the rest is held by Emirates Telecommunication Group Company PJSC . Initially it was called as "CallLink" and was the second mobile operator in Sri Lanka. Hutchison acquired its services in 1998 with the aim of being a nationwide operator in Sri Lanka . As of September 2018 [update] , Hutch has a network coverage of approximately 90% of the entire island. Hutch announced that they acquired Etisalat on 30 November 2018.
Hutch Sri Lanka operates a GSM / EDGE supported network using 900 / 1800 MHz. In 2012 the company launched HSPA+ services using 2100 MHz. [ 7 ] The company launched 4G via 1800 MHz B3 from 2018 [ 8 ] and 900 MHz B8 from 2019.
In July 2004, Hutchison Telecommunications (Vietnam) S.à r.l. ("Hutchison Telecom Vietnam"), a wholly owned subsidiary of Hutchison Telecom, entered into a business cooperation contract with Hanoi Telecom Joint Stock Company. In February 2005, Hutchison Telecom was granted an investment licence by the government for the project and in January 2007, launched CDMA service under the brand HT Mobile.
While they offered a superior network, the market uptake was greatly hampered by the lack of affordable CDMA handsets, in particular, those with the Vietnamese language option, coupled with the trend of leading manufacturers to scale back handset development for this market.
On 8 March 2008 they received government approval to convert from CDMA technology to GSM. After the successful conversion, it launched GSM services in April 2009 under the new brand "Vietnamobile". The brand surpassed the one million customer mark within six months of launch, mostly in the prepaid segment.
Vietnamobile offers some of the highest growth potential in the region.
Hutchison Essar Limited started operations under the brand name " Orange " in Mumbai. In other states it was marketed under "Hutch" brand. It was then changed to "Hutch" nationwide when they expanded rapidly to become the third largest mobile service provider in India and furthered its market share through the acquisition of BPL, Fascel, Command & Aircel Digilink. On 31 March 2007 Hutchison Essar Limited (in Hutch Essar) sold its 67.1% stake to Vodafone .
Even after selling the Orange plc to Mannesmann AG in February 1999, [ 9 ] [ non-primary source needed ] Hutchison continued to use Orange brand in Israel . [ citation needed ] Recently [ when? ] they have sold the controlling stake in this venture to Scailex Corporation . Thus it ends the story of Orange brand associated with Hutchison Telecom. Though Scailex Corp are still using this [ clarification needed ] brand for their Operations.
In 2000, Hutchison Telecom and CAT Telecom Public Company Limited ("CAT Telecom") entered into a joint venture by establishing Hutchison CAT Wireless MultiMedia Ltd. ("Hutchison CAT") to provide exclusive marketing services for CAT Telecom's CDMA mobile telecommunications in 25 provinces located in the Bangkok Metropolitan Area and in central, east coast and west coast regions of Thailand .
In 2003, Hutchison CAT launched marketing services for CAT Telecom's CDMA mobile services under the brand Hutch, providing high speed voice and data wireless service to customers.
In 2013 Hutch Thailand has ended its CDMA services. [ citation needed ] | https://en.wikipedia.org/wiki/Hutchison_Asia_Telecom |
The Hutter Prize is a cash prize funded by Marcus Hutter which rewards data compression improvements on a specific 1 GB English text file, with the goal of encouraging research in artificial intelligence (AI).
Launched in 2006, the prize awards 5000 euros for each one percent improvement (with 500,000 euros total funding) [ 1 ] in the compressed size of the file enwik9 , which is the larger of two files used in the Large Text Compression Benchmark (LTCB); [ 2 ] enwik9 consists of the first 10 9 bytes of a specific version of English Wikipedia . [ 3 ] The ongoing [ 4 ] competition is organized by Hutter, Matt Mahoney, and Jim Bowery. [ 1 ]
The prize was announced on August 6, 2006 [ 1 ] with a smaller text file: enwik8 consisting of 100MB. On February 21, 2020 it was expanded by a factor of 10, to enwik9 of 1GB, the prize went from 50,000 to 500,000 euros.
The goal of the Hutter Prize is to encourage research in artificial intelligence (AI). The organizers believe that text compression and AI are equivalent problems. Hutter proved that the optimal behavior of a goal-seeking agent in an unknown but computable environment is to guess at each step that the environment is probably controlled by one of the shortest programs consistent with all interaction so far. [ 5 ] However, there is no general solution because Kolmogorov complexity is not computable. Hutter proved that in the restricted case (called AIXI tl ) where the environment is restricted to time t and space l , a solution can be computed in time O (t2 l ), which is still intractable.
The organizers further believe that compressing natural language text is a hard AI problem, equivalent to passing the Turing test . Thus, progress toward one goal represents progress toward the other. They argue that predicting which characters are most likely to occur next in a text sequence requires vast real-world knowledge. A text compressor must solve the same problem in order to assign the shortest codes to the most likely text sequences. [ 6 ]
Models like ChatGPT are not ideal for the Hutter Prize for a variety of reasons, they might take more computational resources than those allowed by the competition (computational and storage space).
The contest is open-ended. It is open to everyone. To enter, a competitor must submit a compression program and a decompressor that decompresses to the file enwik9 (formerly enwik8 up to 2017). [ 3 ] It is also possible to submit a compressed file instead of the compression program. The total size of the compressed file and decompressor (as a Win32 or Linux executable) must be less than or equal 99% of the previous prize winning entry. For each one percent improvement, the competitor wins 5,000 euros. The decompression program must also meet execution time and memory constraints.
Submissions must be published in order to allow independent verification. There is a 30-day waiting period for public comment before awarding a prize. In 2017, the rules were changed to require the release of the source code under a free software license , out of concern that "past submissions [which did not disclose their source code] had been useless to others and the ideas in them may be lost forever." [ 4 ] | https://en.wikipedia.org/wiki/Hutter_Prize |
The Huwood Power Loader was mechanical device of roughly 6 ft by 2 ft by 1 ft dimensions and powered by a 10 hp engine, used to move cut coal from the coal face on to the conveyor. The machine was equipped with winches which used haulage ropes to drag the machine along the coal face and used both horizontal and rotary motions to shift the coal onto the conveyor. Pleasley Colliery , Derbyshire introduced one of the first such loaders in 1950. [ 1 ] [ 2 ] [ 3 ] [ 4 ] | https://en.wikipedia.org/wiki/Huwood_power_loader |
The Huzita–Justin axioms or Huzita–Hatori axioms are a set of rules related to the mathematical principles of origami , describing the operations that can be made when folding a piece of paper. The axioms assume that the operations are completed on a plane (i.e. a perfect piece of paper), and that all folds are linear. These are not a minimal set of axioms but rather the complete set of possible single folds.
The first seven axioms were first discovered by French folder and mathematician Jacques Justin in 1986. [ 1 ] Axioms 1 through 6 were rediscovered by Japanese - Italian mathematician Humiaki Huzita and reported at the First International Conference on Origami in Education and Therapy in 1991. Axioms 1 though 5 were rediscovered by Auckly and Cleveland in 1995. Axiom 7 was rediscovered by Koshiro Hatori in 2001; Robert J. Lang also found axiom 7.
The first 6 axioms are known as Justin's axioms or Huzita's axioms. Axiom 7 was discovered by Jacques Justin . Koshiro Hatori and Robert J. Lang also found axiom 7. The axioms are as follows:
Axiom 5 may have 0, 1, or 2 solutions, while Axiom 6 may have 0, 1, 2, or 3 solutions. In this way, the resulting geometries of origami are stronger than the geometries of compass and straightedge , where the maximum number of solutions an axiom has is 2. Thus compass and straightedge geometry solves second-degree equations, while origami geometry, or origametry, can solve third-degree equations, and solve problems such as angle trisection and doubling of the cube . The construction of the fold guaranteed by Axiom 6 requires "sliding" the paper, or neusis , which is not allowed in classical compass and straightedge constructions. Use of neusis together with a compass and straightedge does allow trisection of an arbitrary angle.
Given two points p 1 and p 2 , there is a unique fold that passes through both of them.
In parametric form, the equation for the line that passes through the two points is :
Given two points p 1 and p 2 , there is a unique fold that places p 1 onto p 2 .
This is equivalent to finding the perpendicular bisector of the line segment p 1 p 2 . This can be done in four steps:
Given two lines l 1 and l 2 , there is a fold that places l 1 onto l 2 .
This is equivalent to finding a bisector of the angle between l 1 and l 2 . Let p 1 and p 2 be any two points on l 1 , and let q 1 and q 2 be any two points on l 2 . Also, let u and v be the unit direction vectors of l 1 and l 2 , respectively; that is:
If the two lines are not parallel, their point of intersection is:
where
The direction of one of the bisectors is then:
And the parametric equation of the fold is:
A second bisector also exists, perpendicular to the first and passing through p int . Folding along this second bisector will also achieve the desired result of placing l 1 onto l 2 . It may not be possible to perform one or the other of these folds, depending on the location of the intersection point.
If the two lines are parallel, they have no point of intersection. The fold must be the line midway between l 1 and l 2 and parallel to them.
Given a point p 1 and a line l 1 , there is a unique fold perpendicular to l 1 that passes through point p 1 .
This is equivalent to finding a perpendicular to l 1 that passes through p 1 . If we find some vector v that is perpendicular to the line l 1 , then the parametric equation of the fold is:
Given two points p 1 and p 2 and a line l 1 , there is a fold that places p 1 onto l 1 and passes through p 2 .
This axiom is equivalent to finding the intersection of a line with a circle, so it may have 0, 1, or 2 solutions. The line is defined by l 1 , and the circle has its center at p 2 , and a radius equal to the distance from p 2 to p 1 . If the line does not intersect the circle, there are no solutions. If the line is tangent to the circle, there is one solution, and if the line intersects the circle in two places, there are two solutions.
If we know two points on the line, ( x 1 , y 1 ) and ( x 2 , y 2 ), then the line can be expressed parametrically as:
Let the circle be defined by its center at p 2 =( x c , y c ), with radius r = | p 1 − p 2 | {\displaystyle r=\left|p_{1}-p_{2}\right|} . Then the circle can be expressed as:
In order to determine the points of intersection of the line with the circle, we substitute the x and y components of the equations for the line into the equation for the circle, giving:
Or, simplified:
where:
Then we simply solve the quadratic equation:
If the discriminant b 2 − 4 ac < 0, there are no solutions. The circle does not intersect or touch the line. If the discriminant is equal to 0, then there is a single solution, where the line is tangent to the circle. And if the discriminant is greater than 0, there are two solutions, representing the two points of intersection. Let us call the solutions d 1 and d 2 , if they exist. We have 0, 1, or 2 line segments:
A fold F 1 ( s ) perpendicular to m 1 through its midpoint will place p 1 on the line at location d 1 . Similarly, a fold F 2 ( s ) perpendicular to m 2 through its midpoint will place p 1 on the line at location d 2 . The application of Axiom 2 easily accomplishes this. The parametric equations of the folds are thus:
Given two points p 1 and p 2 and two lines l 1 and l 2 , there is a fold that places p 1 onto l 1 and p 2 onto l 2 .
This axiom is equivalent to finding a line simultaneously tangent to two parabolas, and can be considered equivalent to solving a third-degree equation as there are in general three solutions. The two parabolas have foci at p 1 and p 2 , respectively, with directrices defined by l 1 and l 2 , respectively.
This fold is called the Beloch fold after Margharita P. Beloch , who in 1936 showed using it that origami can be used to solve general cubic equations. [ 2 ]
Given one point p and two lines l 1 and l 2 that aren't parallel, there is a fold that places p onto l 1 and is perpendicular to l 2 .
This axiom was originally discovered by Jacques Justin in 1989 but was overlooked and was rediscovered by Koshiro Hatori in 2002. [ 3 ] Robert J. Lang has proven that this list of axioms completes the axioms of origami. [ 4 ]
Subsets of the axioms can be used to construct different sets of numbers. The first three can be used with three given points not on a line to do what Alperin calls Thalian constructions. [ 5 ]
The first four axioms with two given points define a system weaker than compass and straightedge constructions : every shape that can be folded with those axioms can be constructed with compass and straightedge, but some things can be constructed by compass and straightedge that cannot be folded with those axioms. [ 6 ] The numbers that can be constructed are called the origami or pythagorean numbers, if the distance between the two given points is 1 then the constructible points are all of the form ( α , β ) {\displaystyle (\alpha ,\beta )} where α {\displaystyle \alpha } and β {\displaystyle \beta } are Pythagorean numbers. The Pythagorean numbers are given by the smallest field containing the rational numbers and 1 + α 2 {\displaystyle {\sqrt {1+\alpha ^{2}}}} whenever α {\displaystyle \alpha } is such a number.
Adding the fifth axiom gives the Euclidean numbers , that is the points constructible by compass and straightedge construction .
Adding the neusis axiom 6, all compass-straightedge constructions, and more, can be made. In particular, the constructible regular polygons with these axioms are those with 2 a 3 b ρ ≥ 3 {\displaystyle 2^{a}3^{b}\rho \geq 3} sides, where ρ {\displaystyle \rho } is a product of distinct Pierpont primes . Compass-straightedge constructions allow only those with 2 a ϕ ≥ 3 {\displaystyle 2^{a}\phi \geq 3} sides, where ϕ {\displaystyle \phi } is a product of distinct Fermat primes . (Fermat primes are a subset of Pierpont primes.)
The seventh axiom does not allow construction of further axioms. The seven axioms give all the single-fold constructions that can be done rather than being a minimal set of axioms.
The existence of an eighth axiom was claimed by Lucero in 2017, which may be stated as: there is a fold along a given line l 1 . [ 7 ] The new axiom was found after enumerating all possible incidences between constructible points and lines on a plane. [ 8 ] Although it does not create a new line, it is nevertheless needed in actual paper folding when it is required to fold a layer of paper along a line marked on the layer immediately below. | https://en.wikipedia.org/wiki/Huzita–Hatori_axioms |
Chemical
Neurological
The Hwang affair , [ 1 ] or Hwang scandal , [ 2 ] or Hwanggate , [ 3 ] is a case of scientific misconduct and ethical issues surrounding a South Korean biologist, Hwang Woo-suk , who claimed to have created the first human embryonic stem cells by cloning in 2004. [ 4 ] [ 5 ] Hwang and his research team at the Seoul National University reported in the journal Science that they successfully developed a somatic cell nuclear transfer method with which they made the stem cells. In 2005, they published again in Science the successful cloning of 11 person-specific stem cells using 185 human eggs. [ 6 ] The research was hailed as "a ground-breaking paper" in science. Hwang was elevated as "the pride of Korea", [ 7 ] "national hero" [of Korea], [ 8 ] and a "supreme scientist", [ 9 ] to international praise and fame. [ 10 ] [ 11 ] Recognitions and honours immediately followed, including South Korea's Presidential Award in Science and Technology, and Time magazine listing him among the "People Who Mattered 2004" [ 12 ] and the most influential people "The 2004 Time 100". [ 13 ]
Suspicion and controversy arose in late 2005, when Hwang's collaborator, Gerald Schatten at the University of Pittsburgh , came to know of the real source of oocytes (egg cells) used in the 2004 study. [ 14 ] The eggs, reportedly from several voluntary donors, were in fact from Hwang's two researchers, which Hwang later denied. The ethical issues made Schatten immediately break ties with Hwang. In December 2005, a whistleblower informed Science of reuse of data. As the journal probed in, it was revealed that there was additional data fabrication . [ 14 ] The SNU immediately investigated the research work and found that both the 2004 and 2005 papers contained fabricated results. Hwang was compelled to resign from the university, [ 15 ] and publicly confessed in January 2006 that the research papers were based on fabricated data. [ 14 ] Science immediately retracted the two papers. [ 16 ]
In 2009, the Seoul Central District Court convicted Hwang for embezzlement and bioethical violations , sentencing him to a two-year imprisonment. [ 17 ] The incident was then recorded as the scandal that "shook the world of science," [ 6 ] and became "one of the most widely reported and universally disappointing cases of scientific fraud in history". [ 18 ]
Hwang Woo-suk was a professor of veterinary biotechnology at the Seoul National University and specialised in stem cell research. In 1993, he devised an in vitro fertilisation method with which he made the first assisted reproduction in cows. [ 19 ] He rose to public notice in 1999 when he announced that he had successfully cloned a dairy cow, named Yeongrong-i , and a few months later, a Korean cow, Jin-i (also reported as Yin-i [ 8 ] ). The following year, he announced the preparation for cloning an endangered Siberian tiger . [ 8 ] It was a failed attempt, but the announcements received widespread media attention in South Korea and contributed to increased public interest in his work. In 2002, he claimed creation of a genetically modified pig that could be used for human organ transplant. [ 6 ] In 2003, he announced the successful cloning of a BSE ( bovine spongiform encephalopathy )-resistant cow. [ 20 ] However, science sceptics raised concern over the absence of research papers for any of his claims. [ 19 ]
In 2004, Hwang announced the first complete cloning of a human embryo. [ 13 ] [ 21 ] The research, published in the 12 March 2004 issue of Science , was reported as "Evidence of a pluripotent human embryonic stem cell line derived from a cloned blastocyst." [ 22 ] For its potential medical value to replace diseased and damaged cells, several scientists had previously tried to clone the human embryo, but none had succeeded. [ 23 ] Hwang's team had developed an improved method of somatic cell nuclear transfer , in which they could transfer the nuclei of somatic (non-reproductive) cells into egg cells that had their nuclei removed. [ 24 ] They used human egg cells and cumulus cells , which are found in ovaries near the developing eggs and are known to be good source of nuclear transfer. After emptying an egg of its nucleus, they transferred the nucleus of the cumulus cell into it. The new egg cell divided normally and grew into a blastocyst , an early embryo characterised by a hollow ball of cells. They isolated the outer trophoblast cells that are destined to become the placenta, discarding the inner cell mass that would form the placenta. When the trophoblast cells were cultured, they could divide and form different tissues, indicating that they were viable stem cells. [ 25 ] The report concluded: "This study shows the feasibility of generating human ES [embryonic stem] cells from a somatic cell isolated from a living person." [ 22 ] It was the first instance of cloning of adult human cells and human embryonic stem cells. [ 25 ]
Hwang publicly reported the research at the annual meeting of the American Association for the Advancement of Science (AAAS) in Seattle on 16 February 2004. [ 24 ] He specified that they used 242 eggs from 16 unpaid volunteers, creating about 100 cells from which 30 embryos were developed. [ 26 ] Since the embryos had adult DNA, the resulting stem cells became clones of the adult somatic cells. From the embryos, the stem cells were collected and grafted into mice in which they could grow into various body parts including muscle, bone, cartilage and connective tissues. [ 23 ] The method ensured that immune rejection would be avoided so that it could be used for the treatment of genetic disorders. As Hwang explained: "Our approach opens the door for the use of these specially developed cells in transplantation medicine." [ 26 ]
Hwang's team reported another successful cloning of human cells in the 17 June 2005 issue of Science , in this case, embryonic stem cells derived from skin cells. [ 27 ] Their study claimed the creation of 11 different stem cell lines that were the exact match of DNA in people having a variety of diseases. The experiment used 185 eggs from 18 donors. [ 28 ] The report explicitly stated that: "Patients voluntarily donated oocytes and somatic cells for therapeutic cloning research and relevant applications but not for reproductive cloning ... no financial reimbursement in any form was paid." [ 27 ]
When the 2004 research was announced, it was received with praise and admiration. Donald Kennedy , editor-in-chief of Science , remarked: "the generation of stem cells by somatic cell nuclear transfer methods involving the same individuals may hold promise for advances in transplantation technology that could help people affected by many devastating conditions." [ 26 ] Michael S. Gazzaniga , neuroscientist and bioethicist at Dartmouth College, who had supported therapeutic cloning, described it as "a major advance in biomedical cloning". [ 29 ] Some American scientists took the news to criticise the US government, arguing that it had weakness in stem cell research and a prohibitive attitude. [ 26 ] [ 30 ] As Helen Pearson reported in Nature , the cloning accomplishment turned Asians into "scientific tigers". [ 24 ]
Time reported that as a consequence of the achievement, "a medical and ethical door that had remained mostly closed was kicked wide open." [ 31 ] Hwang and his colleague Shin Yong Moon were listed by Time at number 84 in its list of most influential people "The 2004 Time 100" in April 2004. [ 13 ]
The critical issue was on bioethics, as the method ultimately wasted many human embryos [ 32 ] and could be used to create full human clones, as John T. Durkin argued in Science : "the developmental events leading from fertilised ovum, to blastula, to embryo, to fetus, to fully formed adult constitute a continuum." [ 33 ] Hwang claimed that the purpose was for medical applications only, and said in Seattle, "Reproductive cloning is strictly prohibited [in South Korea]." [ 30 ] At the time, South Korea was developing its "Bioethics and Biosafety Act" to be enforced in 2005. The regulations proscribed human reproductive cloning and experimental fusion of human and animal embryos; even therapeutic cloning for diseases would require authorised approval. Based on this situation, Sang-yong Song of the Hanyang University, criticised Hwang for not waiting for the forthcoming regulations and social consensus in Korea. [ 34 ] Howard H. Kendler , psychologist at the University of California, had an unbiased viewpoint, [ fact or opinion? ] commenting: "Although individuals will differ in their opinions, a democracy can decide whether the benefits of embryonic stem cell research outweigh any disadvantages. Science can assist in making this decision, but cannot dictate it." [ 35 ]
Hwang attempted to establish a network of bureaucrats. To name his second cloned cow, he solicited President Kim Dae-jung , who named it after a celebrated Korean geisha " Hwang Jini ." [ 6 ] As he announced the cloning of a BSE -resistant cow in 2003, [ 20 ] President Roh Moo-hyun visited his laboratory and was shown a dog healed from its injury using stem cell transfer, to which the president applauded, "this is not a science; this is a magic." [ 6 ] From that point, Hwang received escalated research funding from the government that peaked in 2005 at around US$30 million. [ 3 ] That year, the Korean Ministry of Science and Technology officially honoured him as "Supreme Scientist" for the first time in Korea; the title carried US$15 million. [ 36 ] He was frequently portrayed in Korean media as “the pride of Korea,” and appeared on numerous TV programs and newspaper covers as the face of national scientific achievement. [ 37 ] The government set up the World Stem Cell Hub at Seoul National University Hospital on 19 October 2005, created and directed by Hwang. [ 38 ] [ 39 ] On the day of opening, 3000 people registered for stem cell therapy. [ 6 ]
In the 2004 report, Hwang's team remarked that "we cannot completely exclude the possibility that the cells had a parthenogenetic origin." [ 22 ] Reference to parthenogenesis, the ability of embryo development from egg cells without fertilisation, was relevant because it had been documented that stem cells are capable of such transformation. In 1984, an experiment demonstrated that a genetic mixture ( chimera ) of nuclei from the stem cells, one-cell-stage embryos of mouse could develop into full embryos. [ 40 ] Researchers at the Advanced Cell Technology (ACT) in Worcester, Massachusetts, further showed in 2002 that primate (in this case crab-eating macaque , Macaca fascicularis ) stem cells grew into the blastocyst stage. [ 41 ] The ACT subsequently announced that they had created the human parthenogenetic cells, although the cells could not reach the blastocyst stage. [ 42 ] In 2003, Gerald Schatten of the University of Pittsburgh and his team reported a failed attempt of stem cell cloning in rhesus monkey , as the cell divisions were erratic and produced abnormal chromosomes. [ 43 ] Schatten declared: "This reinforces the fact that the charlatans who claim to have cloned humans have never understood enough cell or developmental biology." [ 44 ]
The Hwang scandal was widely described as “a scandal that shook the world of science,” exposing systemic weaknesses in the regulation of research integrity. [ 45 ]
In response, South Korea implemented a series of research ethics reforms across universities, government agencies, and academic associations. These included stricter institutional review board (IRB) procedures and national guidelines for ethical research practices. [ 46 ]
Although public opinion initially remained sympathetic, most Koreans quickly withdrew their support after Hwang’s admission of misconduct. Online communities supporting him dissolved rapidly, reflecting a collective reassessment of scientific credibility and trust. [ 47 ]
In June 2023, Netflix released the documentary film King of Clones , which covered Hwang Woo-suk and this affair. | https://en.wikipedia.org/wiki/Hwang_affair |
HWiNFO (also known as HWiNFO64 [ 1 ] ) is a system monitoring , system profiling and system diagnostics program for Windows and DOS -based systems. [ 2 ] It is developed by Martin Malik and REALiX.
It was used by NASA during several tests of different microprocessors, including an AMD Ryzen 3 1200 and Intel i5-6600K . [ 3 ] [ 4 ]
This software article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hwinfo |
Hy's law is a rule of thumb that a patient is at high risk of a fatal drug-induced liver injury if given a medication that causes hepatocellular injury (not Hepatobiliary injury ) with jaundice . [ 1 ] The law is based on observations by Hy Zimmerman, a major scholar of drug-induced liver injury. [ 2 ] [ 3 ] [ 4 ] Some have suggested the principle be called a hypothesis or observation. [ 5 ]
Hy's Law cases have three components: [ 2 ]
In Zimmerman's analysis of 116 patients with hepatocellular injury and jaundice due to drug exposure, 76% went on to either require a liver transplant or died. [ 6 ] Other studies have reported a lower but still significant mortality of 10%. [ 7 ] [ 8 ]
This medical treatment –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hy's_law |
HyShot is a research project of The University of Queensland , Australia Centre for Hypersonics , to demonstrate the possibility of supersonic combustion under flight conditions using two scramjet engines, one designed by The University of Queensland and one designed by QinetiQ (formerly the MOD's Defence Evaluation & Research Agency). [ 1 ] [ 2 ]
The project has involved the successful launch of one engine designed by The University of Queensland, and one launch of the scramjet designed by the British company QinetiQ . [ 3 ] Each combustion unit was launched on the nose of a Terrier-Orion Mk70 sounding rocket on a high ballistic trajectory, reaching altitudes of approximately 330 km. The rocket was rotated to face the ground, and the combustion unit ignited for a period of 6–10 seconds while falling between 35 km and 23 km at around Mach 7.6. The system is not designed to produce thrust.
The carrier rocket for the HyShot experiments was composed of a RIM-2 Terrier first stage (6 second burn, 4000 km/h) and an Orion second stage (26 second burn, 8600 km/h, 56 km altitude). A fairing over the payload was then jettisoned. The package then coasted to an altitude of around 300 km. Cold gas nitrogen attitude control thrusters were used to re-orient the payload for atmospheric reentry . The experiments each lasted for some 5 seconds as the payload descended between approximately 35 and 23 kilometers altitude, when liquid hydrogen fuel was fed to the scramjet. Telemetry reported results to receivers on the ground for later analysis. The payload landed about 400 km down range from the launch site, at which time its temperature was still expected to be about 300 degrees Celsius, which may be enough to cause a small brush fire and thereby make spotting and recovery easier even though a radio beacon was in the payload.
The team continue [ when? ] to work as part of the Australian Hypersonics Initiative , a joint program of The University of Queensland , the Australian National University and the University of New South Wales ' Australian Defence Force Academy campus, the governments of Queensland and South Australia and the Australian Defence Department .
The Hyshot program spawned [ when? ] the HyCAUSE (Hypersonic Collaborative Australian/United States Experiment) program [1] : a collaborative effort between the United States’ Defense Advanced Research Projects Agency ( DARPA ) and Australia's Defence Science and Technology Organisation (DSTO), also representing the research collaborators in the Australian Hypersonics Initiative (AHI) [2] .
All tests were conducted at the Woomera Test Range in South Australia .
The Hypersonic International Flight Research Experimentation (HIFiRE) program was created [ when? ] jointly by DSTO (now DSTG) and the Air Force Research Laboratory (AFRL). HIFiRE was formed to investigate hypersonic flight technology, the fundamental science and technology required, and its potential for next generation aeronautical systems. Boeing is also a commercial partner in the project. [ 9 ] This will involve up to ten flights with The University of Queensland involved in at least the first three: [ 10 ] | https://en.wikipedia.org/wiki/HyShot |
Hybricon Corporation is a provider of systems packaging serving the military , aerospace , homeland security , medical and high-end Industrial markets and develops embedded computing systems using OpenVPX , VPX , VXS , VMEbus , VME64X, CompactPCI , rugged MicroTCA, and custom bus structures.
Charles Michael Hayward, who was born in Argentina in 1928, started a consulting business in his basement in 1976, and incorporated as Hybricon Corporation in 1978 as business grew. [ 1 ] They were originally located in Littleton, Massachusetts , and sold wire wrap products by 1979. [ 2 ] In September 2000, Paul R. Freve was appointed as president, after Hayward served for 22 years. [ 3 ]
Hybricon is a member of the PCI Industrial Computer Manufacturers Group (PICMG) through 2008, [ 4 ] VMEbus International Trade Association (VITA), [ 5 ] and member of the OpenVPX Industry Working Standards Group when it formed in 2009. [ 6 ] Hybricon along with Curtiss-Wright were the first to demonstrate a live OpenVPX System at the trade show Milcom in Boston in October 2009. The system included an OpenVPX backplane in a Hybricon SFF-4 Small Form Factor conduction-cooled chassis with Curtiss-Wright Control small form factor 3U cards. [ 7 ]
In 2010, Curtiss-Wright Controls Electronic Systems acquired Hybricon for $19 million in cash.
At the time it was based in Ayer, Massachusetts . It became the engineered packaging business unit. [ 8 ] Hybricon was estimated to have $17 million per year in sales at the time. [ 9 ] By the end of 2010. it announced a thermal management technology called CoolWall. [ 10 ]
In 2015, Atrenne Integrated Solutions acquired the assets of Hybricon from Curtiss-Wright. [ 11 ] [ 12 ] Based in Minneapolis , Atrenne was formed in 2014 from a merger of AbelConn Electronics, CBT Technology, Photo Etch, and SIE Computing Solutions. It was led by Jan Erik Mathiesen at the time. [ 13 ] In April, 2018, Toronto -based Celestica acquired Atrenne, after announcing the agreement in January. [ 14 ] | https://en.wikipedia.org/wiki/Hybricon_Corporation |
CORDIC ( coordinate rotation digital computer ), Volder's algorithm , Digit-by-digit method , Circular CORDIC ( Jack E. Volder ), [ 1 ] [ 2 ] Linear CORDIC , Hyperbolic CORDIC (John Stephen Walther), [ 3 ] [ 4 ] and Generalized Hyperbolic CORDIC ( GH CORDIC ) (Yuanyong Luo et al.), [ 5 ] [ 6 ] is a simple and efficient algorithm to calculate trigonometric functions , hyperbolic functions , square roots , multiplications , divisions , and exponentials and logarithms with arbitrary base, typically converging with one digit (or bit) per iteration. CORDIC is therefore also an example of digit-by-digit algorithms . CORDIC and closely related methods known as pseudo-multiplication and pseudo-division or factor combining are commonly used when no hardware multiplier is available (e.g. in simple microcontrollers and field-programmable gate arrays or FPGAs), as the only operations they require are additions , subtractions , bitshift and lookup tables . As such, they all belong to the class of shift-and-add algorithms . In computer science, CORDIC is often used to implement floating-point arithmetic when the target platform lacks hardware multiply for cost or space reasons.
Similar mathematical techniques were published by Henry Briggs as early as 1624 [ 7 ] [ 8 ] and Robert Flower in 1771, [ 9 ] but CORDIC is better optimized for low-complexity finite-state CPUs.
CORDIC was conceived in 1956 [ 10 ] [ 11 ] by Jack E. Volder at the aeroelectronics department of Convair out of necessity to replace the analog resolver in the B-58 bomber 's navigation computer with a more accurate and faster real-time digital solution. [ 11 ] Therefore, CORDIC is sometimes referred to as a digital resolver . [ 12 ] [ 13 ]
In his research Volder was inspired by a formula in the 1946 edition of the CRC Handbook of Chemistry and Physics : [ 11 ]
where φ {\displaystyle \varphi } is such that tan ( φ ) = 2 − n {\displaystyle \tan(\varphi )=2^{-n}} , and K n := 1 + 2 − 2 n {\displaystyle K_{n}:={\sqrt {1+2^{-2n}}}} .
His research led to an internal technical report proposing the CORDIC algorithm to solve sine and cosine functions and a prototypical computer implementing it. [ 10 ] [ 11 ] The report also discussed the possibility to compute hyperbolic coordinate rotation , logarithms and exponential functions with modified CORDIC algorithms. [ 10 ] [ 11 ] Utilizing CORDIC for multiplication and division was also conceived at this time. [ 11 ] Based on the CORDIC principle, Dan H. Daggett, a colleague of Volder at Convair, developed conversion algorithms between binary and binary-coded decimal (BCD). [ 11 ] [ 14 ]
In 1958, Convair finally started to build a demonstration system to solve radar fix –taking problems named CORDIC I , completed in 1960 without Volder, who had left the company already. [ 1 ] [ 11 ] More universal CORDIC II models A (stationary) and B (airborne) were built and tested by Daggett and Harry Schuss in 1962. [ 11 ] [ 15 ]
Volder's CORDIC algorithm was first described in public in 1959, [ 1 ] [ 2 ] [ 11 ] [ 13 ] [ 16 ] which caused it to be incorporated into navigation computers by companies including Martin-Orlando , Computer Control , Litton , Kearfott , Lear-Siegler , Sperry , Raytheon , and Collins Radio . [ 11 ]
Volder teamed up with Malcolm McMillan to build Athena , a fixed-point desktop calculator utilizing his binary CORDIC algorithm. [ 17 ] The design was introduced to Hewlett-Packard in June 1965, but not accepted. [ 17 ] Still, McMillan introduced David S. Cochran (HP) to Volder's algorithm and when Cochran later met Volder he referred him to a similar approach John E. Meggitt (IBM [ 18 ] ) had proposed as pseudo-multiplication and pseudo-division in 1961. [ 18 ] [ 19 ] Meggitt's method also suggested the use of base 10 [ 18 ] rather than base 2 , as used by Volder's CORDIC so far. These efforts led to the ROMable logic implementation of a decimal CORDIC prototype machine inside of Hewlett-Packard in 1966, [ 20 ] [ 19 ] built by and conceptually derived from Thomas E. Osborne 's prototypical Green Machine , a four-function, floating-point desktop calculator he had completed in DTL logic [ 17 ] in December 1964. [ 21 ] This project resulted in the public demonstration of Hewlett-Packard's first desktop calculator with scientific functions, the HP 9100A in March 1968, with series production starting later that year. [ 17 ] [ 21 ] [ 22 ] [ 23 ]
When Wang Laboratories found that the HP 9100A used an approach similar to the factor combining method in their earlier LOCI-1 [ 24 ] (September 1964) and LOCI-2 (January 1965) [ 25 ] [ 26 ] Logarithmic Computing Instrument desktop calculators, [ 27 ] they unsuccessfully accused Hewlett-Packard of infringement of one of An Wang 's patents in 1968. [ 19 ] [ 28 ] [ 29 ] [ 30 ]
John Stephen Walther at Hewlett-Packard generalized the algorithm into the Unified CORDIC algorithm in 1971, allowing it to calculate hyperbolic functions , natural exponentials , natural logarithms , multiplications , divisions , and square roots . [ 31 ] [ 3 ] [ 4 ] [ 32 ] The CORDIC subroutines for trigonometric and hyperbolic functions could share most of their code. [ 28 ] This development resulted in the first scientific handheld calculator , the HP-35 in 1972. [ 28 ] [ 33 ] [ 34 ] [ 35 ] [ 36 ] [ 37 ] Based on hyperbolic CORDIC, Yuanyong Luo et al. further proposed a Generalized Hyperbolic CORDIC (GH CORDIC) to directly compute logarithms and exponentials with an arbitrary fixed base in 2019. [ 5 ] [ 6 ] [ 38 ] [ 39 ] [ 40 ] Theoretically, Hyperbolic CORDIC is a special case of GH CORDIC. [ 5 ]
Originally, CORDIC was implemented only using the binary numeral system and despite Meggitt suggesting the use of the decimal system for his pseudo-multiplication approach, decimal CORDIC continued to remain mostly unheard of for several more years, so that Hermann Schmid and Anthony Bogacki still suggested it as a novelty as late as 1973 [ 16 ] [ 13 ] [ 41 ] [ 42 ] [ 43 ] and it was found only later that Hewlett-Packard had implemented it in 1966 already. [ 11 ] [ 13 ] [ 20 ] [ 28 ]
Decimal CORDIC became widely used in pocket calculators , [ 13 ] most of which operate in binary-coded decimal (BCD) rather than binary. This change in the input and output format did not alter CORDIC's core calculation algorithms. CORDIC is particularly well-suited for handheld calculators, in which low cost – and thus low chip gate count – is much more important than speed.
CORDIC has been implemented in the ARM-based STM32G4 , Intel 8087 , [ 43 ] [ 44 ] [ 45 ] [ 46 ] [ 47 ] 80287 , [ 47 ] [ 48 ] 80387 [ 47 ] [ 48 ] up to the 80486 [ 43 ] coprocessor series as well as in the Motorola 68881 [ 43 ] [ 44 ] and 68882 for some kinds of floating-point instructions, mainly as a way to reduce the gate counts (and complexity) of the FPU sub-system.
CORDIC uses simple shift-add operations for several computing tasks such as the calculation of trigonometric, hyperbolic and logarithmic functions, real and complex multiplications, division, square-root calculation, solution of linear systems, eigenvalue estimation, singular value decomposition , QR factorization and many others. As a consequence, CORDIC has been used for applications in diverse areas such as signal and image processing , communication systems , robotics and 3D graphics apart from general scientific and technical computation. [ 49 ] [ 50 ]
The algorithm was used in the navigational system of the Apollo program 's Lunar Roving Vehicle to compute bearing and range, or distance from the Lunar module . [ 51 ] [ 52 ] CORDIC was used to implement the Intel 8087 math coprocessor in 1980, avoiding the need to implement hardware multiplication. [ 53 ]
CORDIC is generally faster than other approaches when a hardware multiplier is not available (e.g., a microcontroller), or when the number of gates required to implement the functions it supports should be minimized (e.g., in an FPGA or ASIC ).
In fact, CORDIC is a standard drop-in IP in FPGA development applications such as Vivado for Xilinx, while a power series implementation is not due to the specificity of such an IP, i.e. CORDIC can compute many different functions (general purpose) while a hardware multiplier configured to execute power series implementations can only compute the function it was designed for.
On the other hand, when a hardware multiplier is available ( e.g. , in a DSP microprocessor), table-lookup methods and power series are generally faster than CORDIC. In recent years, the CORDIC algorithm has been used extensively for various biomedical applications, especially in FPGA implementations. [ citation needed ]
The STM32G4 , STM32U5 and STM32H5 series and certain STM32H7 series of MCUs implement a CORDIC module to accelerate computations in various mixed signal applications such as graphics for human-machine interface and field oriented control of motors. While not as fast as a power series approximation, CORDIC is indeed faster than interpolating table based implementations such as the ones provided by the ARM CMSIS and C standard libraries. [ 54 ] Though the results may be slightly less accurate as the CORDIC modules provided only achieve 20 bits of precision in the result. For example, most of the performance difference compared to the ARM implementation is due to the overhead of the interpolation algorithm, which achieves full floating point precision (24 bits) and can likely achieve relative error to that precision. [ 55 ] Another benefit is that the CORDIC module is a coprocessor and can be run in parallel with other CPU tasks.
The issue with using Taylor series is that while they do provide small absolute error, they do not exhibit well behaved relative error. [ 56 ] Other means of polynomial approximation, such as minimax optimization, may be used to control both kinds of error.
Many older systems with integer-only CPUs have implemented CORDIC to varying extents as part of their IEEE floating-point libraries. As most modern general-purpose CPUs have floating-point registers with common operations such as add, subtract, multiply, divide, sine, cosine, square root, log 10 , natural log, the need to implement CORDIC in them with software is nearly non-existent. Only microcontroller or special safety and time-constrained software applications would need to consider using CORDIC.
CORDIC can be used to calculate a number of different functions. This explanation shows how to use CORDIC in rotation mode to calculate the sine and cosine of an angle, assuming that the desired angle is given in radians and represented in a fixed-point format. To determine the sine or cosine for an angle β {\displaystyle \beta } , the y or x coordinate of a point on the unit circle corresponding to the desired angle must be found. Using CORDIC, one would start with the vector v 0 {\displaystyle v_{0}} :
In the first iteration, this vector is rotated 45° counterclockwise to get the vector v 1 {\displaystyle v_{1}} . Successive iterations rotate the vector in one or the other direction by size-decreasing steps, until the desired angle has been achieved. Each step angle is γ i = arctan ( 2 − i ) {\displaystyle \gamma _{i}=\arctan {(2^{-i})}} for i = 0 , 1 , 2 , … {\displaystyle i=0,1,2,\dots } .
More formally, every iteration calculates a rotation, which is performed by multiplying the vector v i {\displaystyle v_{i}} with the rotation matrix R i {\displaystyle R_{i}} :
The rotation matrix is given by
Using the trigonometric identity :
the cosine factor can be taken out to give:
The expression for the rotated vector v i + 1 = R i v i {\displaystyle v_{i+1}=R_{i}v_{i}} then becomes:
where x i {\displaystyle x_{i}} and y i {\displaystyle y_{i}} are the components of v i {\displaystyle v_{i}} . Setting the angle γ i {\displaystyle \gamma _{i}} for each iteration such that tan ( γ i ) = ± 2 − i {\displaystyle \tan(\gamma _{i})=\pm 2^{-i}} still yields a series that converges to every possible output value. The multiplication with the tangent can therefore be replaced by a division by a power of two, which is efficiently done in digital computer hardware using a bit shift . The expression then becomes:
and σ i {\displaystyle \sigma _{i}} is used to determine the direction of the rotation: if the angle γ i {\displaystyle \gamma _{i}} is positive, then σ i {\displaystyle \sigma _{i}} is +1, otherwise it is −1.
The following trigonometric identity can be used to replace the cosine:
giving this multiplier for each iteration:
The K i {\displaystyle K_{i}} factors can then be taken out of the iterative process and applied all at once afterwards with a scaling factor K ( n ) {\displaystyle K(n)} :
which is calculated in advance and stored in a table or as a single constant, if the number of iterations is fixed. This correction could also be made in advance, by scaling v 0 {\displaystyle v_{0}} and hence saving a multiplication. Additionally, it can be noted that [ 43 ]
to allow further reduction of the algorithm's complexity. Some applications may avoid correcting for K {\displaystyle K} altogether, resulting in a processing gain A {\displaystyle A} : [ 57 ]
After a sufficient number of iterations, the vector's angle will be close to the wanted angle β {\displaystyle \beta } . For most ordinary purposes, 40 iterations ( n = 40) are sufficient to obtain the correct result to the 10th decimal place.
The only task left is to determine whether the rotation should be clockwise or counterclockwise at each iteration (choosing the value of σ {\displaystyle \sigma } ). This is done by keeping track of how much the angle was rotated at each iteration and subtracting that from the wanted angle; then in order to get closer to the wanted angle β {\displaystyle \beta } , if β n + 1 {\displaystyle \beta _{n+1}} is positive, the rotation is clockwise, otherwise it is negative and the rotation is counterclockwise:
The values of γ n {\displaystyle \gamma _{n}} must also be precomputed and stored. For small angles it can be approximated with arctan ( γ n ) ≈ γ n {\displaystyle \arctan(\gamma _{n})\approx \gamma _{n}} to reduce the table size.
As can be seen in the illustration above, the sine of the angle β {\displaystyle \beta } is the y coordinate of the final vector v n , {\displaystyle v_{n},} while the x coordinate is the cosine value.
The rotation-mode algorithm described above can rotate any vector (not only a unit vector aligned along the x axis) by an angle between −90° and +90°. Decisions on the direction of the rotation depend on β i {\displaystyle \beta _{i}} being positive or negative.
The vectoring-mode of operation requires a slight modification of the algorithm. It starts with a vector whose x coordinate is positive whereas the y coordinate is arbitrary. Successive rotations have the goal of rotating the vector to the x axis (and therefore reducing the y coordinate to zero). At each step, the value of y determines the direction of the rotation. The final value of β i {\displaystyle \beta _{i}} contains the total angle of rotation. The final value of x will be the magnitude of the original vector scaled by K . So, an obvious use of the vectoring mode is the transformation from rectangular to polar coordinates.
In Java the Math class has a scalb(double x,int scale) method to perform such a shift, [ 58 ] C has the ldexp function, [ 59 ] and the x86 class of processors have the fscale floating point operation. [ 60 ]
The number of logic gates for the implementation of a CORDIC is roughly comparable to the number required for a multiplier as both require combinations of shifts and additions. The choice for a multiplier-based or CORDIC-based implementation will depend on the context. The multiplication of two complex numbers represented by their real and imaginary components (rectangular coordinates), for example, requires 4 multiplications, but could be realized by a single CORDIC operating on complex numbers represented by their polar coordinates, especially if the magnitude of the numbers is not relevant (multiplying a complex vector with a vector on the unit circle actually amounts to a rotation). CORDICs are often used in circuits for telecommunications such as digital down converters .
In two of the publications by Vladimir Baykov, [ 61 ] [ 62 ] it was proposed to use the double iterations method for the implementation of the functions: arcsine, arccosine, natural logarithm, exponential function, as well as for the calculation of the hyperbolic functions. Double iterations method consists in the fact that unlike the classical CORDIC method, where the iteration step value changes every time, i.e. on each iteration, in the double iteration method, the iteration step value is repeated twice and changes only through one iteration. Hence the designation for the degree indicator for double iterations appeared: i = 0 , 0 , 1 , 1 , 2 , 2 … {\displaystyle i=0,0,1,1,2,2\dots } . Whereas with ordinary iterations: i = 0 , 1 , 2 … {\displaystyle i=0,1,2\dots } . The double iteration method guarantees the convergence of the method throughout the valid range of argument changes.
The generalization of the CORDIC convergence problems for the arbitrary positional number system with radix R {\displaystyle R} showed [ 63 ] that for the functions sine, cosine, arctangent, it is enough to perform R − 1 {\displaystyle R-1} iterations for each value of i (i = 0 or 1 to n, where n is the number of digits), i.e. for each digit of the result. For the natural logarithm, exponential, hyperbolic sine, cosine and arctangent, R {\displaystyle R} iterations should be performed for each value i {\displaystyle i} . For the functions arcsine and arccosine, two R − 1 {\displaystyle R-1} iterations should be performed for each number digit, i.e. for each value of i {\displaystyle i} . [ 63 ]
For inverse hyperbolic sine and arcosine functions, the number of iterations will be 2 R {\displaystyle 2R} for each i {\displaystyle i} , that is, for each result digit.
CORDIC is part of the class of "shift-and-add" algorithms , as are the logarithm and exponential algorithms derived from Henry Briggs' work. Another shift-and-add algorithm which can be used for computing many elementary functions is the BKM algorithm , which is a generalization of the logarithm and exponential algorithms to the complex plane. For instance, BKM can be used to compute the sine and cosine of a real angle x {\displaystyle x} (in radians) by computing the exponential of 0 + i x {\displaystyle 0+ix} , which is cis ( x ) = cos ( x ) + i sin ( x ) {\displaystyle \operatorname {cis} (x)=\cos(x)+i\sin(x)} . The BKM algorithm is slightly more complex than CORDIC, but has the advantage that it does not need a scaling factor ( K ). | https://en.wikipedia.org/wiki/Hybrid_CORDIC |
Hybrid Insect Micro-Electro-Mechanical Systems (HI-MEMS) is a project of DARPA , a unit of the United States Department of Defense. Created in 2006, the unit's goal is the creation of tightly coupled machine - insect interfaces by placing micro-mechanical systems inside the insects during the early stages of metamorphosis . [ 1 ] After implantation, the "insect cyborgs" could be controlled by sending electrical impulses to their muscles. [ 2 ] The primary application is surveillance . The project was created with the ultimate goal of delivering an insect within 5 meters of a target located 100 meters away from its starting point. [ 3 ] In 2008, a team from the University of Michigan demonstrated a cyborg unicorn beetle at an academic conference in Tucson, Arizona. The beetle was able to take off and land, turn left or right, and demonstrate other flight behaviors. [ 4 ] Researchers at Cornell University demonstrated the successful implantation of electronic probes into tobacco hornworms in the pupal stage. [ 5 ]
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hybrid_Insect_Micro-Electro-Mechanical_Systems |
Hybrid automatic repeat request ( hybrid ARQ or HARQ ) is a combination of high-rate forward error correction (FEC) and automatic repeat request (ARQ) error-control. In standard ARQ, redundant bits are added to data to be transmitted using an error-detecting (ED) code such as a cyclic redundancy check (CRC). Receivers detecting a corrupted message will request a new message from the sender. In Hybrid ARQ, the original data is encoded with an FEC code, and parity bits are either immediately sent along with the message or only transmitted upon request when a receiver detects an erroneous message. The ED code may be omitted when a code is used that can perform both forward error correction (FEC) in addition to error detection, such as a Reed–Solomon code . The FEC code is chosen to correct an expected subset of all errors that may occur, while the ARQ method is used as a fall-back to correct errors that are uncorrectable using only the redundancy sent in the initial transmission. As a result, hybrid ARQ performs better than ordinary ARQ in poor signal conditions, but in its simplest form this comes at the expense of significantly lower throughput in good signal conditions. There is typically a signal quality cross-over point below which simple hybrid ARQ is better, and above which basic ARQ is better.
The simplest version of HARQ, Type I HARQ , adds both ED and FEC information to each message prior to transmission. When the coded data block is received, the receiver first decodes the error-correction code. If the channel quality is good enough, all transmission errors should be correctable, and the receiver can obtain the correct data block. If the channel quality is bad, and not all transmission errors can be corrected, the receiver will detect this situation using the error-detection code, then the received coded data block is rejected and a re-transmission is requested by the receiver, similar to ARQ. [ 1 ]
In a more sophisticated form, Type II HARQ , the message originator alternates between message bits along with error-detecting parity bits and only FEC parity bits. When the first transmission is received error free, the FEC parity bits are never sent. Also, two consecutive transmissions can be combined for error correction if neither is error free. [ 2 ]
To understand the difference between Type I and Type II Hybrid ARQ, consider the size of ED and FEC added information: error detection typically only adds a couple of bytes to a message, which is only an incremental increase in length. FEC, on the other hand, can often double or triple the message length with error correction parities. In terms of throughput, standard ARQ typically expends a few percent of channel capacity for reliable protection against error, while FEC ordinarily expends half or more of all channel capacity for channel improvement.
In standard ARQ a transmission must be received error free on any given transmission for the error detection to pass. In Type II Hybrid ARQ, the first transmission contains only data and error detection (no different from standard ARQ). If received error free, it's done. If data is received in error, the second transmission will contain FEC parities and error detection. If received error free, it's done. If received in error, error correction can be attempted by combining the information received from both transmissions.
Only Type I Hybrid ARQ suffers capacity loss in strong signal conditions. Type II Hybrid ARQ does not because FEC bits are only transmitted on subsequent re-transmissions as needed. In strong signal conditions, Type II Hybrid ARQ performs with as good capacity as standard ARQ. In poor signal conditions, Type II Hybrid ARQ performs with as good sensitivity as standard FEC.
In practice, incorrectly received coded data blocks are often stored at the receiver rather than discarded, and when the re-transmitted block is received, the two blocks are combined. This is called Hybrid ARQ with soft combining (Dahlman et al., p. 120). While it is possible that two given transmissions cannot be independently decoded without error, it may happen that the combination of the previously erroneously received transmissions gives us enough information to correctly decode. There are two main soft combining methods in HARQ:
Several variants of the two main methods exist. For example, in partial Chase combining only a subset of the bits in the original transmission are re-transmitted. In partial incremental redundancy, the systematic bits are always included so that each re-transmission is self-decodable.
An example of incremental redundancy HARQ is HSDPA : the data block is first coded with a punctured 1/3 Turbo code , then during each (re)transmission the coded block is usually punctured further (i.e. only a fraction of the coded bits are chosen) and sent. The puncturing pattern used during each (re)transmission is different, so different coded bits are sent at each time. Although the HSDPA standard supports both Chase combining and incremental redundancy, it has been shown that incremental redundancy almost always performs better than Chase combining, at the cost of increased complexity. [ 3 ]
HARQ can be used in stop-and-wait mode or in selective repeat mode. Stop-and-wait is simpler, but waiting for the receiver's acknowledgment reduces efficiency. Thus multiple stop-and-wait HARQ processes are often done in parallel in practice: when one HARQ process is waiting for an acknowledgment, another process can use the channel to send some more data.
There are other forward error correction codes that can be used in an HARQ scheme besides Turbo codes, e.g. extended irregular repeat-accumulate (eIRA) code and Efficiently-Encodable Rate-Compatible (E2RC) code, both of which are low-density parity-check codes .
HARQ is used in HSDPA and HSUPA which provide high speed data transmission (on downlink and uplink , respectively) for mobile phone networks such as UMTS , and in the IEEE 802.16-2005 standard for mobile broadband wireless access, also known as "mobile WiMAX" . It is also used in Evolution-Data Optimized and LTE wireless networks.
Type I Hybrid ARQ is used in ITU-T G.hn , a high-speed Local area network standard that can operate at data rates up to 1 Gbit/s over existing home wiring ( power lines , phone lines and coaxial cables ). G.hn uses CRC-32C for Error Detection, LDPC for Forward Error Correction and Selective Repeat for ARQ. | https://en.wikipedia.org/wiki/Hybrid_automatic_repeat_request |
In automata theory , a hybrid automaton (plural: hybrid automata or hybrid automatons ) is a mathematical model for precisely describing hybrid systems , for instance systems in which digital computational processes interact with analog physical processes. A hybrid automaton is a finite-state machine with a finite set of continuous variables whose values are described by a set of ordinary differential equations . This combined specification of discrete and continuous behaviors enables dynamic systems that comprise both digital and analog components to be modeled and analyzed.
A simple example is a room- thermostat -heater system where the temperature of the room evolves according to laws of thermodynamics and the state of the heater (on/off); the thermostat senses the temperature, performs certain computations and turns the heater on and off. In general, hybrid automata have been used to model and analyze a variety of embedded systems including vehicle control systems, air traffic control systems, mobile robots , and processes from systems biology .
An Alur–Henzinger hybrid automaton H {\displaystyle H} comprises the following components: [ 1 ]
So this is a labeled multidigraph .
Hybrid automata come in several flavors: The Alur–Henzinger hybrid automaton is a popular model; it was developed primarily for algorithmic analysis of hybrid systems model checking . The HyTech model checking tool is based on this model. The Hybrid Input/Output Automaton model has been developed more recently. This model enables compositional modeling and analysis of hybrid systems. Another formalism, which is useful to model implementations of hybrid automaton, is the lazy linear hybrid automaton .
Given the expressiveness of hybrid automata it is not surprising that simple reachability questions are undecidable for general hybrid automata. In fact, a straightforward reduction from counter machines to three variables hybrid automata (two variables for storing counter values and one to restrict spending a unit-time per location) proves the undecidability of the reachability problem for hybrid automata. A sub-class of hybrid automata are timed automata [ 2 ] where all of the variables grow with uniform rate (i.e., all continuous variables have derivative 1). Such restricted variables can act as timer variables, called clocks, and permit modeling of real-time systems. Other notable decidable subclasses include initialized rectangular hybrid automata, [ 3 ] one-dimensional piecewise-constant derivatives (PCD) systems, [ 4 ] priced timed automata, [ 5 ] and constant-rate multi-mode systems. [ 6 ] | https://en.wikipedia.org/wiki/Hybrid_automaton |
In telecommunications , a hybrid balance is an expression of the degree of electrical symmetry between two impedances connected to two conjugate sides of a hybrid coil or resistance hybrid . It is usually expressed in dB .
If the respective impedances of the branches of the hybrid that are connected to the conjugate sides of the hybrid are known, hybrid balance may be computed by the formula for return loss .
This article incorporates public domain material from Federal Standard 1037C . General Services Administration . Archived from the original on 2022-01-22. (in support of MIL-STD-188 ).
This article about electric power is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hybrid_balance |
A hybrid bond graph is a graphical description of a physical dynamic system with discontinuities (i.e., a hybrid dynamical system ). Similar to
a regular bond graph , it is an energy-based technique. However, it allows instantaneous switching of the junction structure, which may violate the principle of continuity of power (Mosterman and Biswas, 1998).
This mathematical physics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hybrid_bond_graph |
Hybrid computers are computers that exhibit features of analog computers and digital computers . The digital component normally serves as the controller and provides logical and numerical operations, while the analog component often serves as a solver of differential equations and other mathematically complex problems. [ citation needed ]
The first desktop hybrid computing system was the Hycomp 250, released by Packard Bell in 1961. [ 1 ] Another early example was the HYDAC 2400, an integrated hybrid computer released by EAI in 1963. [ 2 ] In the 1980s, Marconi Space and Defense Systems Limited (under Peggy Hodges ) developed their "Starglow Hybrid Computer", which consisted of three EAI 8812 analog computers linked to an EAI 8100 digital computer, the latter also being linked to an SEL 3200 digital computer. [ 3 ] Late in the 20th century, hybrids dwindled with the increasing capabilities of digital computers including digital signal processors . [ 4 ]
In general, analog computers are extraordinarily fast, since they are able to solve most mathematically complex equations at the rate at which a signal traverses the circuit, which is generally an appreciable fraction of the speed of light. On the other hand, the precision of analog computers is not good; they are limited to three, or at most, four digits of precision. [ citation needed ]
Digital computers can be built to take the solution of equations to almost unlimited precision, but quite slowly compared to analog computers. Generally, complex mathematical equations are approximated using iterative methods which take huge numbers of iterations, depending on how good the initial "guess" at the final value is and how much precision is desired. (This initial guess is known as the numerical "seed".) For many real-time operations in the 20th century, such digital calculations were too slow to be of much use (e.g., for very high frequency phased array radars or for weather calculations), but the precision of an analog computer is insufficient. [ citation needed ]
Hybrid computers can be used to obtain a very good but relatively imprecise 'seed' value, using an analog computer front-end, which is then fed into a digital computer iterative process to achieve the final desired degree of precision. With a three or four digit, highly accurate numerical seed, the total digital computation time to reach the desired precision is dramatically reduced, since many fewer iterations are required. One of the main technical problems to be overcome in hybrid computers is minimizing digital-computer noise in analog computing elements and grounding systems. [ citation needed ]
Consider that the nervous system in animals is a form of hybrid computer. Signals pass across the synapses from one nerve cell to the next as discrete (digital) packets of chemicals, which are then summed within the nerve cell in an analog fashion by building an electro-chemical potential until its threshold is reached, whereupon it discharges and sends out a series of digital packets to the next nerve cell. The advantages are at least threefold: noise within the system is minimized (and tends not to be additive), no common grounding system is required, and there is minimal degradation of the signal even if there are substantial differences in activity of the cells along a path (only the signal delays tend to vary). The individual nerve cells are analogous to analog computers; the synapses are analogous to digital computers. [ citation needed ]
Hybrid computers are distinct from hybrid systems . The latter may be no more than a digital computer equipped with an analog-to-digital converter at the input and/or a digital-to-analog converter at the output, to convert analog signals for ordinary digital signal processing, and conversely , e.g., for driving physical control systems, such as servomechanisms . [ citation needed ]
In 2015, researchers at Columbia University published a paper [ 5 ] on a small scale hybrid computer in 65 nm CMOS technology. This 4th-order VLSI hybrid computer contains 4 integrator blocks, 8 multiplier/gain-setting blocks, 8 fanout blocks for distributing current-mode signals, 2 ADCs, 2 DACs and 2 SRAMs blocks. Digital controllers are also implemented on the chip for executing the external instructions. A robot experiment in the paper demonstrates the use of the hybrid computing chip in today's emerging low-power embedded applications. [ citation needed ] | https://en.wikipedia.org/wiki/Hybrid_computer |
The hybrid difference scheme [ 1 ] [ 2 ] is a method used in the numerical solution for convection–diffusion problems. It was introduced by Spalding (1970). It is a combination of central difference scheme and upwind difference scheme as it exploits the favorable properties of both of these schemes. [ 3 ] [ 4 ]
Source: [ 5 ]
Hybrid difference scheme is a method used in the numerical solution for convection-diffusion problems. These problems play important roles in computational fluid dynamics . It can be described by the general partial equation as follows: [ 6 ]
Where, ρ {\displaystyle \rho } is density , u {\displaystyle \mathbf {u} } is the velocity vector, Γ {\displaystyle \Gamma } is the diffusion coefficient and S ϕ {\displaystyle S_{\phi }} is the source term. In this equation property, ϕ {\displaystyle \phi } can be temperature , internal energy or component of velocity vector u {\displaystyle \mathbf {u} } in x, y and z directions.
For one-dimensional analysis of convection-diffusion problem in steady state and without the source the equation reduces to,
With boundary conditions, ϕ ( 0 ) = ϕ 0 {\displaystyle \phi (0)\,=\phi _{0}} and ϕ ( L ) = ϕ L {\displaystyle \phi (L)\,=\phi _{L}} , where L is the length, ϕ 0 {\displaystyle \phi _{0}} and ϕ L {\displaystyle \phi _{L}} are the given values.
Integrating equation 2 over the control volume containing node N, and using Gauss’ theorem i.e.,
Yields the following result,
Where, A is the cross-sectional area of the control volume.
The equation must also satisfy the continuity equation , i.e.,
Now let us define variables F and D to represent the convection mass flux and diffusion conductance at cell faces,
Hence, equations ( 4 ) and ( 5 ) transform into the following equations:
Where, the lower case letters denote the values at the faces and the upper case letters denote that at the nodes.
We also define a non-dimensional parameter Péclet number (Pe) as a measure of the relative strengths of convection and diffusion,
For a low Peclet number (|Pe|<2) the flow is characterized as dominated by diffusion. For large Peclet number the flow is dominated by convection.
Sources: [ 3 ] [ 7 ]
In the above equations ( 7 ) and ( 8 ), we observe that the values required are at the faces, instead of the nodes. Hence approximations are required to fulfill this.
In the central difference scheme we replace the value at the face with the average of the values at the adjacent nodes,
By putting these values in equation ( 7 ) and rearranging we get the following result,
where,
In the Upwind scheme we replace the value at the face with the value at the adjacent upstream node. For example, for the flow to the right (Pe>0)as shown in the diagram, we replace the values as follows;
And for Pe < 0, we put the values as shown in the figure 3,
By putting these values in equation ( 7 ) and rearranging we get the same equation as equation ( 11 ), with the following values of the coefficients:
Sources: [ 3 ] [ 7 ]
The hybrid difference scheme of Spalding (1970) is a combination of the central difference scheme and upwind difference scheme. It makes use of the central difference scheme, which is second order accurate, for small Peclet numbers (|Pe| < 2). For large Peclet numbers (|Pe| > 2) it uses the Upwind difference scheme, which first order accurate but takes into account the convection of the fluid.
As it can be seen in figure 4 that for Pe = 0, it is a linear distribution and for high Pe it takes the upstream value depending on the flow direction. For example, the value at the left face, in different circumstances is,
Substituting these values in equation ( 7 ) we get the same equation ( 11 ) with the values of the coefficients as follows,
It exploits the favourable properties of the central difference and upwind scheme. It switches to upwind difference scheme when central difference scheme produces inaccurate results for high Peclet numbers. It produces physically realistic solution and has proved to be helpful in the prediction of practical flows. The only disadvantage associated with hybrid difference scheme is that the accuracy in terms of Taylor series truncation error is only first order. | https://en.wikipedia.org/wiki/Hybrid_difference_scheme |
In bioinformatics , hybrid genome assembly refers to utilizing various sequencing technologies to achieve the task of assembling a genome from fragmented, sequenced DNA resulting from shotgun sequencing. Genome assembly presents one of the most challenging tasks in genome sequencing as most modern DNA sequencing technologies can only produce reads that are, on average, 25–300 base pairs in length. [ 1 ] This is orders of magnitude smaller than the average size of a genome (the genome of the octoploid plant Paris japonica is 149 billion base pairs [ 2 ] ). This assembly is computationally difficult and has some inherent challenges, one of these challenges being that genomes often contain complex tandem repeats of sequences that can be thousands of base pairs in length. [ 3 ] These repeats can be long enough that second generation sequencing reads are not long enough to bridge the repeat, and, as such, determining the location of each repeat in the genome can be difficult. [ 4 ] Resolving these tandem repeats can be accomplished by utilizing long third generation sequencing reads, such as those obtained using the PacBio RS DNA sequencer. These sequences are, on average, 10,000–15,000 base pairs in length and are long enough to span most repeated regions. [ 5 ] Using a hybrid approach to this process can increase the fidelity of assembling tandem repeats by being able to accurately place them along a linear scaffold and make the process more computationally efficient.
The term genome assembly refers to the process of taking a large number of DNA fragments that are generated during shotgun sequencing and assembling them into the correct order such as to reconstruct the original genome. [ 6 ] Sequencing involves using automated machines to determine the order of nucleic acids in the DNA of interest (the nucleic acids in DNA are adenine , cytosine , guanine and thymine ) to conduct genomic analyses involving an organism of interest. The advent of next generation sequencing has presented significant improvements in the speed, accuracy and cost of DNA sequencing and has made the sequencing of entire genomes a feasible process. [ 7 ] [ 8 ] There are many different sequencing technologies that have been developed by various biotechnology companies, each of which produce different sequencing reads in terms of accuracy and read length. Some of these technologies include Roche 454 , Illumina , SOLiD , and IonTorrent . [ 9 ] These sequencing technologies produce relatively short reads (50–700 bases) and have a high accuracy (>98%). Third-generation sequencing include technologies as the PacBio RS system which can produce long reads (maximum of 23kb) but have a relatively low accuracy. [ 10 ]
Genome assembly is normally done by one of two methods: assembly using a reference genome as a scaffold, [ 11 ] or de novo [ 12 ] assembly. The scaffolding approach can be useful if the genome of a similar organism has been previously sequenced. This process involves assembling the genome of interest by comparing it to a known genome or scaffold. De novo genome assembly is used when the genome to be assembled is not similar to any other organisms whose genomes have been previously sequenced. This process is carried out by assembling single reads into contiguous sequences ( contigs ) which are then extended in the 3' and 5' directions by overlapping other sequences. The latter is preferred because it allows for the conservation of more sequences. [ 13 ]
The de novo assembly of DNA sequences is a very computationally challenging process and can fall into the NP-hard class of problems if the Hamiltonian-cycle approach is used. This is because millions of sequences must be assembled to reconstruct a genome. Within genomes, there are often tandem repeats of DNA segments that can be thousands of base pairs in length, which can cause problems during assembly. [ 1 ]
Although next generation sequencing technology is now capable of producing millions of reads, the assembly of these reads can cause a bottleneck in the entire genome assembly process. As such, extensive research is being done to develop new techniques and algorithms to streamline the genome assembly process and make it a more computationally efficient process and to increase the accuracy of the process as a whole. [ 10 ]
One hybrid approach to genome assembly involves supplementing short, accurate second-generation sequencing data (i.e. from IonTorrent, Illumina or Roche 454) with long less accurate third-generation sequencing data (i.e. from PacBio RS) to resolve complex repeated DNA segments. [ 15 ] The main limitation of single-molecule third-generation sequencing that prevents it from being used alone is its relatively low accuracy, which causes inherent errors in the sequenced DNA. Using solely second-generation sequencing technologies for genome assembly can miss or lead to the incomplete assembly of important aspects of the genome. Supplementation of third generation reads with short, high-accuracy second generation sequences can overcome these inherent errors and completed crucial details of the genome. This approach has been used to sequence the genomes of some bacterial species including a strain of Vibrio cholerae . [ 16 ] Algorithms specific for this type of hybrid genome assembly have been developed, such as the PacBio corrected Reads algorithm. [ 10 ]
There are inherent challenges when utilizing sequence reads from various technologies to assemble a sequenced genome; data coming from different sequencers can have different characteristics. An example of this can be seen when using the overlap-layout-consensus (OLC) method of genome assembly, which can be difficult when using reads of substantially different lengths. Currently, this challenge is being overcome by using multiple genome assembly programs. [ 1 ] An example of this can be seen in Goldberg et al. where the authors paired 454 reads with Sanger reads. The 454 reads were first assemble using the Newbler assembler (which is optimized to use short reads) generating pseudo reads that were then paired with the longer Sanger reads and assembled using the Celera assembler. [ 17 ]
Hybrid genome assembly can also be accomplished using the Eulerian path approach. In this approach, the length of the assembled sequences does not matter as once a k-mer spectrum has been constructed, the lengths of the reads are irrelevant. [ 1 ] [ 18 ]
The authors of this study developed a correction algorithm called the PacBio corrected Reads (PBcR) algorithm which is implemented as part of the Celera assembly program. [ 10 ] This algorithm calculates an accurate hybrid consensus sequence by mapping higher accuracy short reads (from second generation sequencing technologies) to individual lower accuracy long reads (from third-generation sequencing technologies). This mapping allows for trimming and correction of the long reads to improve the read accuracy from as low as 80% to over 99.9%. In the best example of this application from this paper, the contig size was quintupled when compared to the assemblies using only second-generation reads. [ 10 ]
This study offers an improvement over the typical programs and algorithms used to assemble uncorrected PacBio reads. ALLPATHS-LG (another program that can assemble PacBio reads) uses the uncorrected PacBio reads to assist in scaffolding and for the closing of gaps in short sequence assemblies. Due to computational limitations, this approach limits assembly to relatively small genomes (maximum of 10Mbp). The PBcR algorithm allows for the assembly of much larger genomes with higher fidelity and using uncorrected PacBio reads. [ 10 ]
This study also shows that using a lower coverage of corrected long reads is similar to using a higher coverage of shorter reads; 13x PBcR data (corrected using 50x Illumina data) was comparable to an assembly constructed using 100x paired-end Illumina reads. The N50 for the corrected PBcR data was also longer than the Illumina data (4.65MBp compared to 3.32 Mbp for the Illumina reads). A similar trend was seen in the sequencing of the Escherichia coli JM221 genome: a 25x PBcR assembly had a N50 triple that of 50x 454 assembly. [ 10 ]
This study employed two different methods for hybrid genome assembly: a scaffolding approach that supplemented currently available sequenced contigs with PacBio reads, as well as an error correction approach to improve the assembly of bacterial genomes. [ 16 ] The first approach in this study started with high-quality contigs constructed from sequencing reads from second-generation (Illumina and 454) technology. These contigs were supplemented by aligning them to PacBio long reads to achieve linear scaffolds that were gap-filled using PacBio long reads. These scaffolds were then supplemented again, but using PacBio strobe reads (multiple subreads from a single contiguous fragment of DNA [ 19 ] ) to achieve a final, high-quality assembly. This approach was used to sequence the genome of a strain of Vibrio cholerae that was responsible for a cholera outbreak in Haiti . [ 16 ] [ 20 ]
This study also used a hybrid approach to error-correction of PacBio sequencing data. This was done by utilizing high-coverage Illumina short reads to correct errors in the low-coverage PacBio reads. BLASR (a long read aligner from PacBio) was used in this process. In areas where the Illumina reads could be mapped, a consensus sequence was constructed using overlapping reads in that region. [ 16 ]
One area of the genome where the use of the long PacBio reads was especially helpful was the ribosomal operon. This region is usually greater than 5kb in size and occurs seven time throughout the genome with an average identity ranging from 98.04% to 99.94%. Resolving these regions using only short second generation reads would be very difficult but the use of long third generation reads makes the process much more efficient. Utilization of the PacBio reads allowed for unambiguous placement of the complex repeated along the scaffold. [ 16 ]
This study employs a hybrid genome assembly approach that only uses sequencing reads generated using SOLiD sequencing (a second-generation sequencing technology). [ 13 ] The genome of C. pseudotuberculosis was assembled twice: once using a classical reference genome approach, and once using a hybrid approach. The hybrid approach consisted of three contiguous steps. Firstly, contigs were generated de novo, secondly, the contigs were ordered and concatenated into supercontigs, and, thirdly, the gaps between contigs were closed using an iterative approach. The initial de novo assembly of contigs was achieved in parallel using Velvet, which assembles contigs by manipulating De Bruijn graphs, and Edena, which is an OLC-based assembler [ 13 ]
Comparing the assembly constructed using the hybrid approach to the assembly created using the traditional reference genome approach showed that, with the availability of a reference genome, it is more beneficial to utilize an hybrid de novo assembly strategy as it preserves more genome sequences. [ 13 ]
The authors of this paper present Cerulean, a hybrid genome assembly program that differs from traditional hybrid assembly approaches. [ 21 ] Normally, hybrid assembly involved mapping short high quality reads to long low quality reads, but this still introduces errors in the assembled genomes. This process is also computationally expensive and require a large amount of running time, even for relatively small bacterial genomes. [ 21 ]
Cerulean, unlike other hybrid assembly approaches, doesn’t use the short reads directly, instead it uses an assembly graph that is created in a similar manner to the OLC method or the De Bruijn method. This graph is used to assemble a skeleton graph, which only uses long contigs with the edges of the graph representing the putative genomic connection between the contigs. The skeleton graph is a simplified version of a typical De Bruijn graph, which means that unambiguous assembly using the skeleton graph is more favourable than traditional methods. [ 21 ]
This method was tested by assembling the genome of an ‘’Escherichia coli’’ strain. First, short reads were assembled using the ABySS assembler. These reads were then mapped to the long reads using BLASR. The results from the ABySS assembly were used to create the assembly graph, which were used to generate scaffolds using the filtered BLASR data .
The advantages of cerulean are that it requires minimal resources and results in assembled scaffolds with high accuracy. These characteristics make it better suited for up-scaling to be used on larger eukaryotic genomes, but the efficiency of cerulean when applied to larger genomes remains to be verified. [ 21 ]
The current challenges in genome assembly are related to the limitation of modern sequencing technologies. Advances in sequencing technology aim to develop systems that are able to produce long sequencing reads with very high fidelity but, at this point, these two things are mutually exclusive. [ 1 ] The advent of third-generation sequencing technology is expanding the limits of genomic research as the cost of generating high quality sequencing data is decreasing. [ 22 ]
The idea of using multiple sequencing technologies to facilitate genome assembly may become an idea of the past as the quality of long sequencing reads (hundreds or thousands of base pairs) approaches and exceeds the quality of current second generation sequencing reads. The computational difficulties that are encountered during genome assembly will also become a concept of the past as computation efficiency and performance increases. The development of more efficient sequencing algorithms and assembly programs is needed to develop more effective assembly approaches that can tandemly incorporate sequencing reads from multiple technologies.
Many of the current limitations in genomic research revolve around the ability to produce large amounts of high quality sequencing data and to assemble entire genomes of organisms of interest. Developing more effective hybrid genome assembly strategies is taking the next step in advancing sequence assembly technology and these strategies are guaranteed to become more effective as more powerful technologies emerge. | https://en.wikipedia.org/wiki/Hybrid_genome_assembly |
Hybrid growth disorders refer to reduced growth or overgrowth in an organism that is a hybrid of two different species. [ 1 ] In some sense, it is a type of hybrid dysgenesis when the growth disorder proves deleterious, making it the opposite of heterosis or hybrid vigour . [ 2 ] [ 3 ]
Hybrid growth disorders may be referred to as a growth dysplasia , especially when resulting in overgrowth, although this terminology may be confusing since the term dysplasia is commonly used to imply an impending cancer. [ 4 ] However, a hybrid growth disorder is not caused by cancer.
Hybrid growth disorders are exhibited among a variety organisms, including ligers , tigons , hybrid mice, and hybrid dwarf hamsters. [ 5 ] [ 6 ]
A study on hybrid mice which investigated the possible causes for hybrid growth disorders reveals genomic imprinting to have a major effect. [ 6 ] Paternal imprinting may increase growth to maximize maternal resources allocated to his progeny, while maternal imprinting may suppress growth in favor of ensuring her own survival and equal allocation of resources between offspring. [ 7 ] This suggests that the extent of a disorder depends on the combination of parental species and their respective sexes, as demonstrated by the Vrana study. [ 6 ] The study concludes that hybrid growth disorders most commonly affect the heterozygous sex, as expected by Haldane's rule . [ 8 ] [ 9 ] This would also explain why hybrid growth disorders often appear to affect one sex more than the other.
Similarly, a study of hybrids between dwarf hamster species Phodopus campbelli and Phodopus sungorus suggests that gene imprinting causes abnormal interactions between growth-promoting and growth-repressing genes which regulate placental and embryonic growth. [ 1 ]
This genetics article is a stub . You can help Wikipedia by expanding it .
This developmental biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hybrid_growth_disorders |
The hybrid iguana is a first-generation hybrid , the result of intergeneric breeding between a male marine iguana ( Amblyrhynchus cristatus ) and a female Galapagos land iguana ( Conolophus subcristatus ) on South Plaza Island in the Galápagos Islands , where the territories of the two species overlap.
Hybrid iguanas are dark with light speckles or bands of mottling near the head and a banded body. By contrast, marine iguanas are a solid blackish color, while land iguanas are reddish-yellow; neither are banded. [ 1 ]
The first hybrid iguana was discovered in 1981. In 1997, high ocean temperatures during a severe El Niño season caused failure of the seaweed beds around the Galapagos Islands and about half the marine iguanas starved to death. Others searched inland for plants to eat. There they mated with the land iguanas, producing an unusual number of hybrid iguanas. As of 2003, 20 had been found. Four were known to be alive as of a 2013 census. [ 2 ] DNA testing by a German researcher revealed that marine iguanas were the fathers and land iguanas the mothers. [ 1 ]
A unique set of circumstances on South Plaza Island helps explain why the hybrid iguanas have been observed only there. [ 2 ] Elsewhere in the Galápagos, reproductive isolation between the two species is maintained by separation of breeding in both place and time: there is little overlap between the inland habitat favored by the land iguanas and the coastal habitat of the marine iguana, and the short breeding seasons of the two species normally do not overlap. However, long, narrow South Plaza Island is so small that no place on it is far from the coast, leaving female land iguanas no place to retreat from invasion by the larger, more aggressive male marine iguanas. And on South Plaza there is a slight overlap between the end of the land iguana's breeding season and the beginning of the marine iguana's, so that male marine iguanas forced inland by hunger may occasionally encounter a female land iguana that is still in breeding condition. [ 2 ]
Marine iguanas have sharp claws and are able to grip rock under seawater and eat seaweed, whereas land iguanas lack sharp claws, making them unable to climb the cacti that are their staple foods. Hybrid iguanas have sharp claws and can climb on cacti and also eat seaweed underwater. The hybrid iguana can survive in both sea and land environments. [ 3 ] [ 4 ] Despite the long evolutionary separation between the two parent species, which are assigned to different genera, the offspring are viable, although likely sterile. [ 5 ] The hybrid iguanas have a laterally compressed tail like that of the marine iguanas, though they have not been seen swimming. They also have sharp claws like their marine fathers, which enable them to climb for food rather than waiting for it to drop from a cactus as the land iguanas do. [ 1 ] | https://en.wikipedia.org/wiki/Hybrid_iguana |
Hybrid incompatibility is a phenomenon in plants and animals, wherein offspring produced by the mating of two different species or populations have reduced viability and/or are less able to reproduce. Examples of hybrids include mules and ligers from the animal world, and subspecies of the Asian rice crop Oryza sativa from the plant world. Multiple models have been developed to explain this phenomenon. Recent research suggests that the source of this incompatibility is largely genetic, as combinations of genes and alleles prove lethal to the hybrid organism. [ 1 ] Incompatibility is not solely influenced by genetics , however, and can be affected by environmental factors such as temperature. [ 2 ] The genetic underpinnings of hybrid incompatibility may provide insight into factors responsible for evolutionary divergence between species. [ 3 ]
Hybrid incompatibility occurs when the offspring of two closely related species are not viable or suffer from infertility . Charles Darwin posited that hybrid incompatibility is not a product of natural selection , stating that the phenomenon is an outcome of the hybridizing species diverging, rather than something that is directly acted upon by selective pressures. [ 4 ] The underlying causes of the incompatibility can be varied: earlier research focused on things like changes in ploidy in plants. More recent research has taken advantage of improved molecular techniques and has focused on the effects of genes and alleles in the hybrid and its parents.
The first major breakthrough in the genetic basis of hybrid incompatibility is the Dobzhansky-Muller model , a combination of findings by Theodosius Dobzhansky and Joseph Muller between 1937 and 1942. The model provides an explanation as to why a negative fitness effect like hybrid incompatibility is not selected against. By hypothesizing that the incompatibility arose from alterations at two or more loci , rather than one, the incompatible alleles are in one hybrid individual for the first time rather than throughout the population - thus, hybrids that are infertile can develop while the parent populations remain viable. The negative fitness effects of infertility are not present in the original population. [ 5 ] [ 6 ] In this way, hybrid infertility contributes in some part to speciation by ensuring that gene flow between diverging species remains limited. Further analysis of the issue has supported this model, although it does not include conspecific genic interactions, a potential factor that more recent research has begun to look in to. [ 4 ]
Decades after the research of Dobzhansky and Muller, the specifics of hybrid incompatibility were explored by Jerry Coyne and H. Allen Orr. Using introgression techniques to analyze the fertility in Drosophila hybrid and non-hybrid offspring, specific genes that contribute to sterility were identified; a study by Chung-I Wu which expanded on Coyne and Orr's work found that the hybrids of two Drosophila species were made sterile by the interaction of around 100 genes. [ 7 ] These studies widened the scope of the Dobzhansky-Muller model, who thought it likely that more than two genes would be responsible. [ 5 ] [ 6 ] The ubiquity of Drosophila as a model organism has allowed many of the sterility genes to be sequenced in the years since Wu's study. [ citation needed ]
With modern molecular techniques, researchers have been able to more accurately identify the underlying genetic causes of hybrid incompatibility. This has led to both the development of expansions to the Dobzhansky-Muller model. Recent research has also explored the possibility of external influences on sterility as well.
An extension of the Dobzhansky-Muller model is the "snowball effect"; an accumulation of incompatible loci due to increased species divergence. Since the model posits that sterility is due to negative allelic interaction between the hybridizing species, as species become more diverged it follows that more negative interactions should develop. The snowball effect states that the number of these incompatibilities will increase exponentially over the time of divergence, particularly when more than two loci contribute to the incompatibility. This concept has been exhibited in tests with the flowering plant genus Solanum , with the findings supporting the genetic underpinnings of Dobzhansky-Muller:
"Overall, our results indicate that the accumulation of sterility loci follows a different trajectory from the accumulation of loci for other quantitative species differences, consistent with the unique genetic basis expected to underpin species reproductive isolating barriers. ...In doing so, we uncover direct empirical support for the Dobzhansky-Muller model of hybrid incompatibility, and the snowball prediction in particular." [ 8 ]
Though the primary causes of hybrid incompatibility appear to be genetic, external factors may play a role as well. Studies focused primarily on model plants have found that the viability of hybrids can be dependent on environmental influence. Several studies on rice and Arabidopsis species identify temperature as an important factor in hybrid viability; generally, low temperatures seem to cause negative hybrid symptoms to be expressed while high temperatures suppress them, although one rice study found the opposite to be true. [ 9 ] [ 10 ] [ 11 ] There has also been evidence in an Arabidopsis species that in poor environmental conditions (in this case, high temperatures), hybrids did not express negative symptoms and are viable with other populations. When environmental conditions return to normal, however, the negative symptoms are expressed and the hybrids are once again incompatible with other populations. [ 12 ]
Though a multitude of evidence supports the Dobzhansky-Muller model of hybrid sterility and speciation, this does not rule out the possibility that other situations besides the inviable combination of benign genes can lead to hybrid incompatibility. One such situation is incompatibility by way of gene duplication, or the Lynch and Force model (put forth by Michael Lynch and Allan Force in 2000). When gene duplication occurs, there is a possibility that a redundant gene can be rendered non-functional over time by mutations . From Lynch and Force's paper:
"The divergent resolution of genomic redundancies, such that one population loses function from one copy while the second population loses function from a second copy at a different chromosomal location, leads to chromosomal repatterning such that gametes produced by hybrid individuals can be completely lacking in functional genes for a duplicate pair." [ 12 ]
This hypothesis is relatively recent compared to Dobzhansky-Muller, but has support as well.
A possible contributor to hybrid incompatibility that fits with the Lynch and Force model better than the Dobzhansky-Muller model is epigenetic inheritance. Epigenetics broadly refers to heritable elements that affect offspring phenotype without adjusting the DNA sequence of the offspring. When a particular allele has been epigenetically modified, it is referred to as an epiallele A study found that an Arabidopsis gene is not expressed because it is a silent epiallele, and when this epiallele is inherited by hybrids in combination with a mutant gene at the same locus, the hybrid is inviable. [ 1 ] This fits with the Lynch and Force model because the heritable epiallele, ordinarily not an issue in non-hybrid populations with non-epiallele copies of the gene, becomes problematic when it is the only copy of the gene in the hybrid population. [ 1 ] Study in Capsella shows that dosage of maternal small-interfering RNAs can contribute to hybrid incompatibility between closely related plant species. [ 13 ] | https://en.wikipedia.org/wiki/Hybrid_incompatibility |
Hybrid inviability is a post-zygotic barrier , which reduces a hybrid 's capacity to mature into a healthy, fit adult. [ 1 ] The relatively low health of these hybrids relative to pure-breed individuals prevents gene flow between species. Thus, hybrid inviability acts as an isolating mechanism , limiting hybridization and allowing for the differentiation of species.
The barrier of hybrid inviability occurs after mating species overcome pre-zygotic barriers (behavioral, mechanical, etc.) to produce a zygote . The barrier emerges from the cumulative effect of parental genes ; these conflicting genes interfere with the embryo 's development and prevents its maturation . Most often, the hybrid embryo dies before birth. However, sometimes, the offspring develops fully with mixed traits, forming a frail, often infertile adult. [ 2 ] This hybrid displays reduced fitness, marked by decreased rates of survival and reproduction relative to the parent species. The offspring fails to compete with purebred individuals, limiting genes flow between species. [ 3 ]
In the 1970s, Allan C. Wilson and his colleagues first investigated the evolution of hybrid inviability in tetrapods , specifically mammals , birds , and frogs . [ 4 ] [ 5 ]
Recognizing that hybrid viability decreases with time, the researchers used molecular clocks to quantify divergence time. They identified how long ago the common ancestor of hybridizing species diverged into two lines, and found that bird and frog species can produce viable hybrids up to twenty million years after speciation . In addition, the researchers showed that mammal species can only produce viable hybrids up to two or three million years after speciation.
Wilson et al. (1974) proposes two hypotheses to explain the relatively faster evolution of hybrid inviability in mammals: the Regulatory and the Immunological Hypotheses. Subsequent research finds support for these hypotheses.
The Regulatory Hypothesis accounts for two characteristics of mammals, and explains the general formation of hybrid inviability in mammals, birds, and frogs.
First, mammals display relatively lower protein diversity than frogs. As Wilson et al. (1974) suggests, “mammals that can hybridize with each other differ only slightly at the protein level, whereas frogs that differ substantially in protein sequence hybridize readily.” This analysis suggests that gene divergence is not the only determinate of hybridization in mammals, birds, or frogs.
Second, the evolution of anatomical diversity occurred far faster in mammals than in either birds or frogs. As Fitzpatrick (2004) indicates, “the morphological disparities among bats , mole-rats , and whales are more dramatic than any disparities in birds and frogs.” This anatomical diversity is evidence for the diversification of regulatory systems . This mammalian characteristic suggests that, although mammals are genetically similar, dramatic changes in regulatory genes caused distinct developmental differences. [ 6 ]
The Regulatory Hypotheses specifically attributes hybrid inviability in mammals, birds, and frogs to differences in gene regulation . It proposes that hybrid inviability evolved faster in mammalian taxa because mammals have accumulated significantly more changes in regulatory systems than birds or frogs, and it suggests that organisms with distinctly different systems of gene regulation may not produce viable hybrids.
Wilson et al. (1974) recognizes that the development of embryos in the mammalian placenta requires regulatory compatibility. Both the regulatory genes of the sperm and egg contribute to the expression of other protein-coding genes in the zygote; if certain regulatory genes are not expressed or are expressed at the wrong time, the inter-specific zygote will abort or develop unhealthy traits. Moreover, because the development of the zygote depends on maternal characteristics, such as cytoplasmic determinants, the regulatory traits of the mother may not support the hybrid's developmental needs.
The Immunological Hypothesis proposes that the divergence of certain protein structures associated with mother and child causes hybrid inviability. The hypothesis applies only to mammals, where fertilization and development is internal. In birds and in frogs, fertilization is primarily external, and the mother’s immune system does not interfere with fetal development .
This hypothesis stems from the immunological characteristics of the placenta, where the growing fetus is in constant contact with the fluids and tissues of the mother. Variation within species and variation between species may contribute to fetal-maternal incompatibility, and according to the hypothesis, if the proteins of the fetus varies significantly from the proteins of the placenta, the mother may produce anti-bodies that will attack and abort the fetus. Therefore, if the fetal proteins of the father species are incompatible the mother's placental proteins, the mother's immune system may abort the embryo.
Evidence for the Immunological Hypothesis varies considerably. Wilson et al. (1974) recognizes studies that provide no support to the Immunological Hypotheses. In these experiments, the use of immunological suppressants provided no additional viability to inter-specific hybrids. In contrast, Elliot and Crespi (2006) documents the effects of placental immunology on hybrid inviability, showing that mammals with hemochorial placentas more readily hybridize than mammals with epitheliochorial or endotheliochorial placentas . These different placenta types possess divergent immunological systems, and consequently, they cause varying degrees of hybrid inviability. [ 7 ] | https://en.wikipedia.org/wiki/Hybrid_inviability |
Hybrid masonry is a new type of building system that uses engineered, reinforced masonry to brace frame structures. Typically, hybrid masonry is implemented with concrete masonry panels used to brace steel frame structures. The basic concept is to attach a reinforced concrete masonry panel to a structural steel frame such that some combination of gravity forces, story shears and overturning moments can be transferred to the masonry. The structural engineer can choose from three different types of hybrid masonry (I, II, or III) and two different reinforcement anchorage types (a & b). In conventional steel frame building systems, the vertical force resisting steel frame system is supported in the lateral direction by steel bracing or an equivalent system. When the architectural plans call for concrete masonry walls to be placed within the frame, extra labor is required to ensure the masonry fits around the steel frame. Usually, this placement does not take advantage of the structural properties of the masonry panels. In hybrid masonry, the masonry panels take the place of conventional steel bracing, utilizing the structural properties of reinforced concrete masonry walls.
The system was first introduced by David Biggs, PE in 2007 at the 10th North American Masonry Conference and was based on historical masonry construction [ 1 ] and the practice of anchoring masonry walls in steel frames for out of plane strength. [ 2 ]
There are five different configurations of hybrid masonry. They consist of three different main types with two subsets; however, the first type does not allow both subsets. The three types consist of different constraint conditions within the steel frame and the two subsets are based on the anchoring of the vertical reinforcement in the masonry panel.
Type I hybrid masonry has no direct contact with the surround steel frame. For this reason, there are not two subsets of this configuration. Lateral forces are transmitted to the masonry panel through steel plates that are connected to the floor beams and attached to the wall with a through-bolt. The hole in the plate for the through-bolt is slotted so that gravity loads are not transmitted to the masonry panel; the vertical loads travel solely through the steel frame. Thus, the masonry panel takes only the story shear from the above floors and acts as a one story shear wall.
The steel plates can be designed in two manners. If the design engineer wishes the steel plate to be the weak point, the plate can be designed as a fuse. The fuse would dissipate energy after yielding and be easily replaced after an extreme event. Alternatively, the plate can be designed so it does not yield before the masonry panel experiences significant damage. A strong plate would localize the damage to the masonry.
Type II hybrid masonry is constrained vertically by the steel frame; however, the sides of the panel still have a gap between the steel and the masonry. The vertical contact transfers the gravity load from the beam into the masonry panel, increasing its flexural and shear strength. Instead of the plates transferring the lateral force from the steel to the masonry, shear studs are welded to the bottom side of the beam. Grout is then used to fill the space between the masonry and the steel beam. With this contact, the wall is subject to story shears, gravity loads, as well as overturning moments much like a continuous shear wall.
The two subsets of Type II hybrid masonry are Type IIa and Type IIb. The difference between the two systems are whether the vertical reinforcement is anchored into the base or to the steel beam. In Type IIa, the vertical reinforcement is anchored and can develop tension forces along its length. The vertical reinforcement is not anchored in Type IIb hybrid masonry and consequently the rebar cannot take the force on the tension side of the wall. Instead, the top of the wall undergoes compression. [ 3 ]
Similar Type II hybrid masonry, Type III hybrid masonry has the vertical confinement. In addition to the vertical contact with the beam, contact with the columns is also used for horizontal confinement. Shear studs are welded on the insides of the columns to transfer vertical forces that are the result of axial load in the columns as well as shear in the wall. The wall system resembles infill masonry in terms of confinement in the steel, yet differs in that it is grouted and reinforced, allowing for a more ductile response.
Prof. Ian Robertson at the University of Hawaiʻi -Mānoa (UHM) has developed and tested the steel plate connections between the masonry. The result was a design method of a fuse plate that yields along its entire length, with the aim of creating a ductile energy dissipating fuse. Bolt pullout tests were also performed at UHM to validate the strength of the masonry with through bolts. A research team at Rice University develops computational models for the study of hybrid masonry structural systems. Profs. Larry A. Fahnestock and Daniel P. Abrams are performing full scale experimental tests on hybrid masonry at the Network for Earthquake Engineering Simulation (NEES) site at the University of Illinois at Urbana-Champaign . [ 4 ] | https://en.wikipedia.org/wiki/Hybrid_masonry |
Hybrid navigation is the simultaneous use of more than one navigation system for location data determination, needed for navigation . By using multiple systems at once, the accuracy as a whole is improved. It also allows for a more reliable navigation system, as if one system fails, the other can kick in and provide accurate navigation for the user. [ 1 ] Especially for self-driving cars , the exact and continuous knowledge of the navigating object's location is essential. [ 2 ]
GPS and other satellite based systems ( GLONASS , GALILEO , BEIDOU , QZSS ) provide a way to learn one's location, but these methods require free field conditions in order to receive the radio signal. Various satellite systems are subject to switching-off or reduction of data precision by the company or government that runs them. [ 3 ] They are also prone to intentional or unintentional disturbances. Even passing through a tunnel or a garage interrupts the data flow. In situations where the signal cannot be received reliably, alternate sources of location data are needed. Combining GPS with other methods can avoid these limitations, but each method has its own specific limitations. A hybrid system provides fault tolerance for each underlying method and improves the overall precision of the result. [ 4 ]
The hybrid system needs to decide how to choose among the different methods at any given time. One solution is a triple configuration, allowing 'result voting' for data collecting systems. [ 3 ] [ 5 ]
Alternate systems that supply navigational data include: | https://en.wikipedia.org/wiki/Hybrid_navigation |
Hybrid physical–chemical vapor deposition (HPCVD) is a thin-film deposition technique, that combines physical vapor deposition (PVD) with chemical vapor deposition (CVD).
For the instance of magnesium diboride (MgB 2 ) thin-film growth, HPCVD process uses diborane (B 2 H 6 ) as the boron precursor gas, but unlike conventional CVD, which only uses gaseous sources, heated bulk magnesium pellets (99.95% pure) are used as the Mg source in the deposition process. Since the process involves chemical decomposition of precursor gas and physical evaporation of metal bulk, it is named as hybrid physical–chemical vapor deposition.
The HPCVD system usually consists of a water-cooled reactor chamber, gas inlet and flow control system, pressure maintenance system, temperature control system and gas exhaust and cleaning system.
The main difference between HPCVD and other CVD systems is in the heating unit. For HPCVD, both substrate and solid metal source are heated up by the heating module. The conventional HPCVD system usually has only one heater. The substrate and solid metal source sit on the same susceptor and are heated up inductively or resistively at the same time. Above certain temperature, the bulk metal source melts and generates a high vapor pressure in the vicinity of the substrate. Then the precursor gas is introduced into the chamber and decomposes around the substrate at high temperature. The atoms from the decomposed precursor gas react with the metal vapor, forming thin films on the substrate. The deposition ends when the precursor gas is switched off. The main drawback of single heater setup is the metal source temperature and the substrate temperature cannot be controlled independently. Whenever the substrate temperature is changed, the metal vapor pressure changes as well, limiting the ranges of the growth parameters. In the two-heater HPCVD arrangement, the metal source and substrate are heated up by two separate heaters. Thus it can provide more flexible control of growth parameters.
HPCVD has been the most effective technique for depositing magnesium diboride (MgB 2 ) thin films. Other MgB 2 deposition technologies either have a reduced superconducting transition temperature and poor crystallinity , or require ex situ annealing in Mg vapor. The surfaces of these MgB 2 films are rough and non- stoichiometric . Instead, HPCVD system can grow high-quality in situ pure MgB 2 films with smooth surfaces, which are required to make reproducible uniform Josephson junctions , the fundamental element of superconducting circuits.
From the theoretical phase diagram of Mg-B system, a high Mg vapor pressure is required for the thermodynamic phase stability of MgB 2 at elevated temperature. MgB 2 is a line compound and as long as the Mg/B ratio is above the stoichiometric 1:2, any extra Mg at elevated temperature will be in the gas phase and be evacuated. Also, once MgB 2 is formed, it has to overcome a significant kinetic barrier to thermally decompose. So one does not have to be overly concerned about maintaining a high Mg vapor pressure during the cooling stage of the MgB 2 film deposition.
During the growth process of magnesium diboride thin films by HPCVD, the carrier gas is purified hydrogen gas H 2 at a pressure of about 100 Torr . This H 2 environment prevents oxidation during the deposition. Bulk pure Mg pieces are placed next to the substrate on the top of the susceptor . When the susceptor is heated to about 650 °C, pure Mg pieces are also heated, which generates a high Mg vapor pressure in the vicinity of the substrate. Diborane (B 2 H 6 ) is used as the boron source. MgB 2 films starts to grow when the boron precursor gas B 2 H 6 is introduced into the reactor chamber. The growth rate of the MgB 2 film is controlled by the flow rate of B 2 H 6 /H 2 mixture. The film growth stops when the boron precursor gas is switched off.
To improve the performance of superconducting magnesium diboride thin films in magnetic field, it is desirable to dope impurities into the films. The HPCVD technique is also an efficient method to grow carbon -doped or carbon- alloyed MgB 2 thin films. The carbon-alloyed MgB 2 films can be grown in the same way as the pure MgB 2 films deposition process described above except adding a metalorganic magnesium precursor, bis(methylcyclopentadienyl)magnesium precursor, into the carrier gas. The carbon-alloyed MgB 2 thin films by HPCVD exhibit extraordinarily high upper critical field ( H c2 ). H c2 over 60 T at low temperatures is observed when the magnetic field is parallel to the ab -plane. | https://en.wikipedia.org/wiki/Hybrid_physical–chemical_vapor_deposition |
Hybrid rail , also known as diesel light rail transit ( DLRT ), is a mode of passenger rail service unique to North America that uses lightweight multiple unit trains —typically diesel multiple units (DMUs)—operating on the national rail system . In the United States , these vehicles do not comply with Federal Railroad Administration (FRA) Tier I crashworthiness standards and must operate under shared-use waivers that require temporal separation from freight rail traffic. Hybrid rail differs from conventional commuter rail by offering frequent, all-day service rather than being limited to peak-period operations. However, service frequencies are generally lower than those of urban light rail systems. Although often categorized as a subset of light rail, hybrid rail systems employ mainline railway infrastructure and are closer in function to tram-train , railcar or former interurban operations.
The first hybrid rail system in North America was New Jersey Transit's River Line , which began service in 2004. Since then, similar systems have been introduced in other regions. Hybrid rail aims to deliver rail transit service without the capital costs associated with electrification or fully dedicated rights-of-way . Some systems, such as Ottawa’s O-Train Line 2 , have transitioned to regional rail or been discontinued, such as the Puebla–Cholula Tourist Train in Mexico. Several expansions of existing hybrid rail services are currently planned or under development in the United States.
Hybrid rail combines technical and operational features associated with both light rail and commuter rail, but it remains distinct from either mode. The "hybrid" nomenclature is derived from the modal convergence of both commuter and light rail operational aspects. In practice, it employs lightweight, self-propelled DMUs operating on existing national freight rail infrastructure. [ 1 ] The Federal Railroad Administration (FRA) classifies these services as operating with vehicles that do not meet Tier I crashworthiness standards, requiring temporal separation from freight traffic under shared-use agreements. [ 2 ] This regulatory distinction is based on safety compliance rather than service characteristics. [ 3 ]
Despite this federal designation, some hybrid rail systems are legally or operationally classified as light rail by local or state transit agencies. For instance, New Jersey Transit's River Line and Trinity Metro’s A-train in the Dallas–Fort Worth metropolitan area both use FRA-regulated DMUs with temporal separation but are categorized as light rail in agency planning documents or funding mechanisms. [ 4 ] This reflects a broader ambiguity in U.S. transit taxonomy, where service classification may be influenced more by local policy or funding structures than by regulatory compliance. [ 5 ] The result is a hybrid designation that straddles technical, regulatory, and branding distinctions. [ 6 ]
Hybrid rail is typically deployed in corridors with moderate demand, limited capital budgets, or geographic constraints that make full electrification or dedicated rights-of-way impractical. [ 7 ] The ability to operate on existing freight corridors reduces infrastructure costs and makes hybrid rail suitable for a range of applications; these include suburban shuttles (e.g., Austin's Capital MetroRail and eBART ), interurban -style services (e.g., the River Line in New Jersey), airport or campus connectors (e.g., the former Ottawa O-Train Line 2), and low-density regional corridors. In many cases, hybrid rail functions as a lower-cost alternative to light rail or traditional commuter rail in low-to-medium demand corridors.
Canada and Mexico maintain rail vehicle safety and crashworthiness standards, but differ from the United States' FRA regulations and are generally less stringent. In Canada, crashworthiness is regulated by Transport Canada under the Railway Safety Act, using standards from the Canadian Standards Association and international frameworks such as European EN standards. [ 8 ] Lighter European-style trainsets are permitted following performance-based assessments. [ 9 ] In Mexico, the Agencia Reguladora del Transporte Ferroviario (ARTF) oversees rail safety; however, regulations are less formalized, with equipment approvals typically based on UIC or European standards and governed by technical specifications in procurement contracts rather than a unified national code. [ 10 ] [ 11 ]
Despite regulatory differences, rail operations in Canada and Mexico converge with U.S. standards due to the privatization of national rail infrastructure. In both countries, the majority of the rail network is owned and operated by private freight companies that operate heavy freight-oriented rolling stock. As a result, the implementation of passenger services—particularly hybrid rail with lightweight trains—requires negotiated agreements with host railroads to ensure legal access, operational compatibility, and safety. [ 12 ] This framework distinguishes hybrid rail in these countries from international coutnerparts, as passenger operations must accommodate the priorities and constraints of private freight carriers.
Early forms of regional passenger rail in North America included interurban electric railways and multiple-unit self-propelled railcars, which operated on both dedicated and shared track. These services declined mid-century due to rising automobile use and federal investment in highways . In the postwar period , DMU services remained in operation on rural, branch line , and low-demand corridors, often utilizing Budd Rail Diesel Cars (RDCs). [ 13 ] While DMU services persisted through the 1950s on lower-density routes, the decade marked a broader shift away from regional passenger rail, as many services were discontinued or restructured in response to declining ridership and changing travel patterns by the end of that decade. [ 14 ]
By the 1960s, most regional passenger rail had either been discontinued or consolidated into subsidized commuter rail networks. [ 15 ] In 1966, the Federal Railroad Administration (FRA) established crashworthiness standards for passenger trains operating on the national rail system that favored weight specification for push-pull freight operations. [ 2 ] These Tier I standards required heavy, reinforced vehicles and effectively excluded lightweight multiple units from shared freight corridors. As a result, commuter rail in the U.S. shifted to locomotive-hauled trains, and the domestic market for passenger DMUs diminished. [ 16 ] New or restructured commuter rail services favored high density corridors with high ridership, while branch line and low-demand services were effectively eliminated nationwide. The last domestically manufactured DMU in the United States during the twentieth century was the Budd SPV-2000 , produced in the late 1970s and early 1980s. The model was considered a commercial failure and contributed to the eventual bankruptcy and closure of the Budd Company . [ 17 ]
Outside of North America, lightweight DMU rail systems continued to operate and evolve throughout the mid-to-late twentieth century. In Europe, countries such as Germany , France , and the United Kingdom maintained extensive DMU networks, particularly for regional and rural services. Germany's Schienenbusse and the British Rail Class 101 were designed for low-density routes. [ 18 ] Similarly, in Japan , DMUs such as the KiHa series were widely deployed on non-electrified regional lines, offering reliable and efficient service where electrification was not economically viable. In South America , countries like Argentina and Brazil also utilized lightweight railcars for interurban travel. [ 19 ] These systems often featured simple, single-car or two-car configurations—sometimes referred to as " railcars "—designed for minimal infrastructure needs and lower passenger volumes. The continued development and deployment of DMUs in these regions reflected differing regulatory environments, investment priorities, and operating conditions compared to the United States, Canada and Mexico where regulatory constraints and market conditions led to the near-total disappearance of DMU service by the 1980s.
Amid rising costs associated with operating traditional locomotive-hauled commuter trains, U.S. transit agencies in the 1980s and 1990s began reevaluating the potential of lightweight diesel services as a cost-effective solution for regional and lower-ridership corridors. The emergence and rapid expansion of light rail transit (LRT) systems during this period—beginning with projects in San Diego , Portland , and Sacramento —demonstrated the viability of lower-cost urban rail infrastructure paired with lighter rolling stock. [ 20 ] These systems often used dedicated rights-of-way or shared space with automobiles, offering flexibility and reduced capital costs compared to heavy rail. The success of light rail projects encouraged planners and policymakers to explore whether similar principles could be applied to longer-distance, non-electrified corridors, particularly those on underutilized lines already owned by freight railroads. [ 21 ]
The Southeastern Pennsylvania Transportation Authority (SEPTA) conducted a pilot program in 1993, testing British Rail Class 142 Pacer units on unnelectrified lines of its regional rail network. The goal was to assess the feasibility of using lightweight DMUs for suburban services; however, the Pacers faced challenges adapting to American operating conditions, including differences in platform heights, track standards, and regulatory requirements. Consequently, the pilot did not lead to widespread adoption, and all diesel-hauled regional rail services would be eliminated. By the late 1990s, growing interest in lower-cost regional rail prompted the FRA to develop a waiver process for shared-use operations. [ 22 ] [ 23 ] In 1999, the agency issued formal guidelines allowing non-compliant DMUs to operate under temporal separation from freight trains. [ 24 ]
The first system to launch under this framework was New Jersey Transit's River Line in 2004. [ 25 ] The model was subsequently adopted in other regions, including North County Transit District’s Sprinter ( California , 2008) and Denton County Transportation Authority’s A-train ( Texas , 2011), where capital constraints and moderate demand made traditional commuter rail impractical. By the mid-2000s, hybrid rail was promoted as a cost-effective solution for regions seeking to implement passenger rail service without the capital investment required for electrification or conventional commuter rail. Most systems were developed between 2004 and 2012, targeting corridors with existing freight track, moderate population densities, and constrained budgets.
Internationally, hybrid rail has been used selectively in North America. In Canada, Ottawa’s O-Train Line 2 began operation in 2001 as a diesel light rail demonstration project using Bombardier Talent DMUs on a shared freight alignment. [ 26 ] It remained in service until 2020, when it was closed for conversion to an expanded regional rail corridor. In Mexico, the Puebla–Cholula Tourist Train operated from 2017 to 2021 as a diesel rail service on rehabilitated freight track, connecting the cities of Puebla and Cholula . Though designed for tourism, it functioned as a regional connector consistent with hybrid rail characteristics. The service was discontinued due to low ridership and high operational costs. [ 27 ]
Reception of hybrid rail systems has been mixed. Proponents highlight the mode's ability to restore regional service at a lower cost per mile than commuter rail or light rail, especially in underutilized or freight-shared corridors. [ 28 ] However, ridership has generally remained below original projections, and operational constraints—such as limited frequency, lack of electrification, and temporal separation from freight—have reduced effectiveness in attracting discretionary riders. [ 29 ] For instance, New Jersey's River Line and California’s Sprinter have maintained moderate ridership but failed to catalyze major transit-oriented development . [ 30 ] Texas's A-train similarly underperformed early forecasts, with weekday boardings averaging between 1,200 and 1,500 over its first decade. [ 31 ] Since the early 2010s, new hybrid rail development has slowed considerably, due in part to shifting transportation funding priorities, regulatory complexities, and limited ridership gains from existing systems. New-build systems under construction, such as DART's Silver Line , are functionally more similar to regional rail than hybrid rail. [ 32 ]
Early North American hybrid rail projects relied heavily on equipment derived from European models. A significant enabling factor was the reintroduction of DMUs to the U.S. market, notably by Siemens and Stadler , which began offering modified versions of their European vehicles. [ 33 ] The River Line in New Jersey operates Stadler GTW 2/6 DMUs, a design originally developed for European regional services and modified to meet certain North American regulatory requirements. [ 34 ] Similarly, the Sprinter service in California uses Siemens Desiro Classic DMUs, adapted for FRA-compliant shared-use corridors.
Newer systems such as Trinity Metro's TEXRail and Metrolink's Arrow Line in California use Stadler FLIRT DMUs. [ 35 ] [ 36 ] In Europe, FLIRT trainsets are primarily used for mainline regional and intercity services operating at higher average speeds on dedicated or lightly shared infrastructure. In North America, FLIRT DMUs have been adapted to meet hybrid rail needs. Across most systems, hybrid rail rolling stock maintains lighter axle loads and lower overall vehicle weights than traditional locomotive-hauled commuter trains. Most units offer bidirectional operation and low-floor designs for level boarding, enhancing operational flexibility and reducing infrastructure requirements at terminal stations. While most hybrid rail systems do not operate in mixed street traffic, limited street-running does occur in certain cases, such as the River Line within Camden , New Jersey . This distinguishes some hybrid systems from conventional commuter rail but also from fully segregated light rail operations.
Some hybrid systems, specifically WES Commuter Rail , Union Pearson Express and SMART , utilize high-floor FRA compliant DMUs. WES Commuter Rail, operated by TriMet , uses Colorado Railcar DMUs and SMART operates Nippon Sharyo DMUs built to FRA Tier I standards. These vehicles are significantly heavier and more structurally reinforced than typical European-style DMUs, resulting in performance characteristics more similar to traditional commuter rail equipment. [ 37 ] While not subjected to U.S. FRA standards, the Union Pearson Express in Toronto utilizes high-floor Nippon Sharyo DMUs to enable mixed operations with conventional commuter rail equipment. [ 38 ] | https://en.wikipedia.org/wiki/Hybrid_rail |
Hybrid speciation is a form of speciation where hybridization between two different species leads to a new species, reproductively isolated from the parent species. Previously, reproductive isolation between two species and their parents was thought to be particularly difficult to achieve, and thus hybrid species were thought to be very rare. With DNA analysis becoming more accessible in the 1990s, hybrid speciation has been shown to be a somewhat common phenomenon, particularly in plants. [ 1 ] [ 2 ] In botanical nomenclature , a hybrid species is also called a nothospecies . [ 3 ] Hybrid species are by their nature polyphyletic . [ 4 ]
A hybrid may occasionally be better fitted to the local environment than the parental lineage, and as such, natural selection may favor these individuals. If reproductive isolation is subsequently achieved, a separate species may arise. Reproductive isolation may be genetic, ecological , [ 5 ] behavioral, spatial, or a combination of these.
If reproductive isolation fails to establish, the hybrid population may merge with either or both parent species. This will lead to an influx of foreign genes into the parent population, a situation called an introgression . Introgression is a source of genetic variation, and can in itself facilitate speciation. There is evidence that introgression is a ubiquitous phenomenon in plants and animals, [ 6 ] [ 7 ] even in humans, [ 8 ] where genetic material from Neanderthals and Denisovans is responsible for much of the immune genes in non-African populations. [ 9 ] [ 10 ]
For a hybrid form to persist, it must be able to exploit the available resources better than either parent species, which, in most cases, it will have to compete with. For example : while grizzly bears and polar bears may be able to mate and produce offspring, a grizzly–polar bear hybrid is apparently less- suited in either of the parents' ecological niches than the original parent species themselves. So: although the hybrid is fertile (i.e. capable of reproduction and thus theoretically could propagate) , this poor adaptation would be unlikely to support the establishment of a permanent population. [ 11 ]
Likewise, lions and tigers have historically overlapped in a portion of their range and can theoretically produce wild hybrids: ligers , which are a cross between a male lion and female tiger, and tigons , which are a cross between a male tiger and a female lion; however, tigers and lions have thus far only hybridized in captivity. [ 12 ] In both ligers and tigons, the females are fertile and the males are sterile. [ 12 ] One of these hybrids (the tigon) carries growth-inhibitor genes from both parents and thus is smaller than either parent species [ 12 ] and might in the wild come into competition with smaller carnivores, e.g. the leopard . The other hybrid, the liger, ends up larger than either of its parents: about a thousand pounds (450 kilograms) fully grown. [ 12 ] No tiger-lion hybrids are known from the wild, and the ranges of the two species no longer overlap (tigers are not found in Africa, and while there was formerly overlap in the distribution of the two species in Asia, both have been extirpated from much of their respective historic ranges, and the Asiatic lion is now restricted to the Gir Forest National Park , where tigers are mostly absent). [ 13 ]
Some situations may favor hybrid population. One example is rapid turnover of available environment types, like the historical fluctuation of water level in Lake Malawi , a situation that generally favors speciation. [ 14 ] A similar situation can be found where closely related species occupy a chain of islands . This will allow any present hybrid population to move into new, unoccupied habitats, avoiding direct competition with parent species and giving a hybrid population time and space to establish. [ 15 ] [ 5 ] Genetics, too, can occasionally favor hybrids. In the Amboseli National Park in Kenya, yellow baboons and anubis baboons regularly interbreed. The hybrid males reach maturity earlier than their pure-bred cousins, setting up a situation where the hybrid population may over time replace one or both of the parent species in the area. [ 16 ]
Genetics are more variable and malleable in plants than in animals, probably reflecting the higher activity level in animals. [ citation needed ] Hybrids' genetics will necessarily be less stable than those of species evolving through isolation, which explains why hybrid species appear more common in plants than in animals. [ citation needed ] Many agricultural crops are hybrids with double or even triple chromosome sets. Having multiple sets of chromosomes is called polyploidy . Polyploidy is usually fatal in animals where extra chromosome sets upset fetal development , but is often found in plants. [ 17 ] A form of hybrid speciation that is relatively common in plants occurs when an infertile hybrid becomes fertile after doubling of the chromosome number.
Hybridization without change in chromosome number is called homoploid hybrid speciation. [ 1 ] This is the situation found in most animal hybrids. For a hybrid to be viable, the chromosomes of the two organisms will have to be very similar, i.e., the parent species must be closely related, or else the difference in chromosome arrangement will make mitosis problematic. With polyploid hybridization, this constraint is less acute. [ citation needed ]
Super-numerary chromosome numbers can be unstable, which can lead to instability in the genetics of the hybrid. The European edible frog appears to be a species, but is actually a triploid semi-permanent hybrid between pool frogs and marsh frogs . [ 18 ] In most populations, the edible frog population is dependent on the presence of at least one of the parent species to be maintained, as each individual need two gene sets from one parent species and one from the other. Also, the male sex determination gene in the hybrids is only found in the genome of the pool frog, further undermining stability. [ 19 ] Such instability can also lead to rapid reduction of chromosome numbers, creating reproductive barriers and thus allowing speciation. [ citation needed ]
Hybrid speciation in animals is primarily homoploid . While thought not to be very common, a few animal species are the result of hybridization, mostly insects such as tephritid fruitflies that inhabit Lonicera plants [ 20 ] and Heliconius butterflies, [ 21 ] [ 22 ] as well as some fish , [ 15 ] one marine mammal, the clymene dolphin , [ 23 ] a few birds. [ 24 ] and certain Bufotes toads. [ 25 ]
One bird is an unnamed form of Darwin's finch from the Galapagos island of Daphne Major, described in 2017 and likely founded in the early 1980s by a male Española cactus finch from Española Island and a female medium ground finch from Daphne Major. [ 26 ] Another is the great skua , which has a surprising genetic similarity to the physically very different pomarine skua ; most ornithologists [ who? ] now assume it to be a hybrid between the pomarine skua and one of the southern skuas. [ 27 ] The golden-crowned manakin was formed 180,000 years ago by hybridization between snow-capped and opal-crowned manakins . [ 28 ]
A 2021 DNA study determined that the Columbian mammoth of North America was a hybrid species between woolly mammoths and another lineage, discovered in Krestovka , descended from steppe mammoths . The two populations had diverged from the ancestral steppe mammoth earlier in the Pleistocene. Analysis of genetic material recovered from their remains showed that half of the ancestry of the Columbian mammoths originated from the Krestovka lineage and the other half from woolly mammoths, with the hybridization happening more than 420,000 years ago, during the Middle Pleistocene . This is the first evidence of hybrid speciation obtained from prehistoric DNA. [ 29 ] [ 30 ]
Rapidly diverging species can sometimes form multiple hybrid species, giving rise to a species complex , like several physically divergent but closely related genera of cichlid fishes in Lake Malawi . [ 14 ] The duck genus Anas (mallards and teals) has a very recent divergence history, many of the species are inter-fertile, and quite a few of them are thought to be hybrids. [ 31 ] [ 32 ] While hybrid species generally appear rare in mammals, [ 15 ] the American red wolf appears to be a hybrid species of the Canis species complex, between gray wolf and coyote . [ 33 ] Hybridization may have led to the species-rich Heliconius butterflies , [ 34 ] though this conclusion has been criticized. [ 35 ]
Hybrid speciation occurs when two divergent lineages (e.g., species) with independent evolutionary histories come into contact and interbreed. Hybridization can result in speciation when hybrid populations become isolated from the parental lineages, leading to divergence from the parent populations.
In cases where the first-generation hybrids are viable but infertile, fertility can be restored by whole genome duplication (polyploidy), resulting in reproductive isolation and polyploid speciation. Polyploid speciation is commonly observed in plants because their nature allows them to support genome duplications. Polyploids are considered a new species because the occurrence of a whole genome duplication imposes post-zygotic barriers, which enable reproductive isolation between parent populations and hybrid offspring. Polyploids can arise through single step mutations or through triploid bridges. In single step mutations, allopolyploids are the result of unreduced gametes in crosses between divergent lineages. The F1 hybrids produced from these mutations are infertile due to failure of bivalent pairing of chromosomes and segregation into gametes which leads to the production of unreduced gametes by single division meiosis, which results in unreduced, diploid (2N) gametes. Triploid bridges occur in low frequencies in populations and are produced when unreduced gametes combine with haploid (1N) gametes to produce a triploid offspring that can function as a bridge to the formation of tetraploids. [ 36 ] In both paths, the polyploid hybrids are reproductively isolated from the parents due to the difference in ploidy. Polyploids manage to remain in populations because they generally experience less inbreeding depression and have higher self-fertility. [ 36 ] [ 37 ]
Homoploid (diploid) speciation is another result of hybridization, but the hybrids remain diploid. It is less common in plants than polyploid speciation because, without genome duplication, genetic isolation must develop through other mechanisms. Studies on diploid hybrid populations of Louisiana irises show how these populations occur in Hybrid zones created by disturbances and ecotones (Anderson 1949). Novel niches can allow for the persistence of hybrid lineages. For example, established sunflower ( Helianthus ) hybrid species show transgressive phenotypes and display genomic divergence separating them from the parent species. [ 38 ] | https://en.wikipedia.org/wiki/Hybrid_speciation |
The hybrid sulfur cycle (HyS) is a two-step water-splitting process intended to be used for hydrogen production . Based on sulfur oxidation and reduction , it is classified as a hybrid thermochemical cycle because it uses an electrochemical (instead of a thermochemical) reaction for one of the two steps. The remaining thermochemical step is shared with the sulfur-iodine cycle .
The Hybrid sulphur cycle (HyS)was initially proposed and developed by Westinghouse Electric Corp. in the 1970s, [ 1 ] so it is also known as the "Westinghouse" cycle. Current development efforts in the United States are being led by the Savannah River National Laboratory .
The two reactions in the HyS cycle are as follows: [ 2 ]
Sulfur dioxide acts to depolarize the anode of the electrolyzer . This results in a significant decrease in the reversible cell potential (and, therefore, the electric power requirement) for reaction (2). The standard cell potential for reaction (2) is -0.158 V at 298.15 K, compared to -1.229 V for the electrolysis of water (with oxygen evolution as the anodic reaction). [ 3 ]
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hybrid_sulfur_cycle |
A hybrid vehicle is one that uses two or more distinct types of power, such as submarines that use diesel when surfaced and batteries when submerged. Other means to store energy include pressurized fluid in hydraulic hybrids .
Hybrid powertrains are designed to switch from one power source to another to maximize both fuel efficiency and energy efficiency . In hybrid electric vehicles , for instance, the electric motor is more efficient at producing torque , or turning power, while the combustion engine is better for maintaining high speed. Improved efficiency, lower emissions, and reduced running costs relative to non-hybrid vehicles are three primary benefits of hybridization.
Mopeds , electric bicycles , and even electric kick scooters are a simple form of a hybrid, powered by an internal combustion engine or electric motor and the rider's muscles. Early prototype motorcycles in the late 19th century used the same principle.
The first published prototype of an SHB is by Augustus Kinzel (US Patent 3'884'317) in 1975. In 1994 Bernie Macdonalds conceived the Electrilite [ 3 ] SHB with power electronics allowing regenerative braking and pedaling while stationary. In 1995 Thomas Muller designed and built a "Fahrrad mit elektromagnetischem Antrieb" for his 1995 diploma thesis. In 1996 Jürg Blatter and Andreas Fuchs of Berne University of Applied Sciences built an SHB and in 1998 modified a Leitra tricycle (European patent EP 1165188). Until 2005 they built several prototype SH tricycles and quadricycles . [ 4 ] In 1999 Harald Kutzke described an "active bicycle": the aim is to approach the ideal bicycle weighing nothing and having no drag by electronic compensation.
A SHEPB prototype made by David Kitson in Australia [ 5 ] in 2014 used a lightweight brushless DC electric motor from an aerial drone and small hand-tool sized internal combustion engine , and a 3D printed drive system and lightweight housing, altogether weighing less than 4.5 kg. Active cooling keeps plastic parts from softening. The prototype uses a regular electric bicycle charge port.
Hybrid power trains use diesel–electric or turbo-electric to power railway locomotives, buses, heavy goods vehicles, mobile hydraulic machinery , and ships. A diesel / turbine engine drives an electric generator or hydraulic pump, which powers electric/hydraulic motors—strictly an electric/hydraulic transmission (not a hybrid), unless it can accept power from outside. With large vehicles, conversion losses decrease and the advantages in distributing power through wires or pipes rather than mechanical elements become more prominent, especially when powering multiple drives—e.g. driven wheels or propellers. Until recently most heavy vehicles had little secondary energy storage, e.g. batteries/ hydraulic accumulators —excepting non-nuclear submarines , one of the oldest production hybrids, running on diesel while surfaced and batteries when submerged. Both series and parallel setups were used in World War II-era submarines.
Europe The new Autorail à grande capacité (AGC or high-capacity railcar) built by the Canadian company Bombardier for service in France is diesel/electric motors, using 1500 or 25,000 V on different rail systems. [ 7 ] It was tested in Rotterdam, the Netherlands with Railfeeding, a Genesee & Wyoming company.
China The First Hybrid Evaluating locomotive was designed by rail research center Matrai in 1999 and built in 2000. It was an EMD G12 locomotive upgraded with batteries, a 200 kW diesel generator, and four AC motors.
Japan Japan's first hybrid train with significant energy storage is the KiHa E200 , with roof-mounted lithium-ion batteries . [ 8 ]
India Indian railway launched one of its kind CNG -Diesel hybrid trains in January 2015. The train has a 1400 hp engine which uses fumigation technology. The first of these trains is set to run on the 81 km long Rewari-Rohtak route. [ 9 ] CNG is less-polluting alternative for diesel and petrol and is popular as an alternative fuel in India. Already many transport vehicles such as auto-rickshaws and buses run on CNG fuel.
North America In the US, General Electric made a locomotive with sodium–nickel chloride (Na-NiCl 2 ) battery storage. They expect ≥10% fuel economy. [ 10 ] [ failed verification ]
Variant diesel electric locomotive include the Green Goat (GG) and Green Kid (GK) switching/yard engines built by Canada's Railpower Technologies , with lead acid (Pba) batteries and 1000 to 2000 hp electric motors, and a new clean-burning ≈160 hp diesel generator. No fuel is wasted for idling: ≈60–85% of the time for these types of locomotives. It is unclear if regenerative braking is used; but in principle, it is easily utilized.
Since these engines typically need extra weight for traction purposes anyway the battery pack's weight is a negligible penalty. [ citation needed ] The diesel generator and batteries are normally built on an existing "retired" "yard" locomotive's frame. The existing motors and running gear are all rebuilt and reused. Fuel savings of 40–60% and up to 80% pollution reductions are claimed over a "typical" older switching/yard engine. The advantages hybrid cars have for frequent starts and stops and idle periods apply to typical switching yard use. [ 11 ] "Green Goat" locomotives have been purchased by Canadian Pacific , BNSF , Kansas City Southern Railway and Union Pacific among others.
Railpower Technologies engineers working with TSI Terminal Systems are testing a hybrid diesel–electric power unit with battery storage for use in Rubber Tyred Gantry (RTG) cranes . RTG cranes are typically used for loading and unloading shipping containers onto trains or trucks in ports and container storage yards. The energy used to lift the containers can be partially regained when they are lowered. Diesel fuel and emission reductions of 50–70% are predicted by Railpower engineers. [ 12 ] First systems are expected to be operational in 2007. [ 13 ]
Hybrid systems are regularly in use for trucks, buses and other heavy highway vehicles. Small fleet sizes and installation costs are compensated by fuel savings, [ 14 ] [ needs update ] with advances such as higher capacity, lowered battery cost, etc. Toyota, Ford, GM and others are introducing hybrid pickups and SUVs. Kenworth Truck Company recently introduced the Kenworth T270 Class 6 that for city usage seems to be competitive. [ 15 ] [ 16 ] FedEx and others are investing in hybrid delivery vehicles—particularly for city use where hybrid technology may pay off first. [ 17 ] As of December 2013 [update] FedEx is trialling two delivery trucks with Wrightspeed electric motors and diesel generators; the retrofit kits are claimed to pay for themselves in a few years. The diesel engines run at a constant RPM for peak efficiency. [ 18 ]
In 1978 students at Minneapolis, Minnesota's Hennepin Vocational Technical Center, converted a Volkswagen Beetle to a petro-hydraulic hybrid with off-the shelf components. A car rated at 32 mpg was returning 75 mpg with the 60 hp engine replaced by a 16 hp engine, and reached 70 mph. [ 19 ]
In the 1990s, engineers at EPA's National Vehicle and Fuel Emissions Laboratory developed a petro-hydraulic powertrain for a typical American sedan car. The test car achieved over 80 mpg on combined EPA city/highway driving cycles. Acceleration was 0-60 mph in 8 seconds, using a 1.9-liter diesel engine. No lightweight materials were used. The EPA estimated that produced in high volumes the hydraulic components would add only $700 to the cost. [ 20 ] Under EPA testing, a hydraulic hybrid Ford Expedition returned 32 mpg (7.4 L/100 km) City, and 22 mpg (11 L/100 km) highway. [ 20 ] [ 21 ] UPS currently has two trucks in service using this technology. [ 22 ]
Since 1985, the US military has been testing serial hybrid Humvees [ 23 ] [ 24 ] and have found them to deliver faster acceleration, a stealth mode with low thermal signature , near silent operation, and greater fuel economy.
Ships with both mast-mounted sails and steam engines were an early form of a hybrid vehicle. Another example is the diesel–electric submarine . This runs on batteries when submerged and the batteries can be recharged by the diesel engine when the craft is on the surface.
As of 2022 [update] , there are 550 ships with an average of 1.6 MWh of batteries. The average was 500 kWh in 2016. [ 25 ]
Newer hybrid ship-propulsion schemes include large towing kites manufactured by companies such as SkySails . Towing kites can fly at heights several times higher than the tallest ship masts, capturing stronger and steadier winds.
The Boeing Fuel Cell Demonstrator Airplane has a Proton-Exchange Membrane (PEM) fuel cell/lithium-ion battery hybrid system to power an electric motor, which is coupled to a conventional propeller. The fuel cell provides all power for the cruise phase of flight. During takeoff and climb, the flight segment that requires the most power, the system draws on lightweight lithium-ion batteries.
The demonstrator aircraft is a Dimona motor glider, built by Diamond Aircraft Industries of Austria, which also carried out structural modifications to the aircraft. With a wingspan of 16.3 meters (53 feet), the airplane will be able to cruise at about 100 km/h (62 mph) on power from the fuel cell. [ 26 ]
Hybrid FanWings have been designed. A FanWing is created by two engines with the capability to autorotate and landing like a helicopter. [ 27 ]
When the term hybrid vehicle is used, it most often refers to a Hybrid electric vehicle . These encompass such vehicles as the Saturn Vue , Toyota Prius , Toyota Yaris , Toyota Camry Hybrid , Ford Escape Hybrid , Ford Fusion Hybrid , Toyota Highlander Hybrid , Honda Insight , Honda Civic Hybrid , Lexus RX 400h , and 450h , Hyundai Ioniq Hybrid , Hyundai Sonata Hybrid , Hyundai Elantra Hybrid , Kia Sportage Hybrid , Kia Niro Hybrid , Kia Sorento Hybrid and others. A petroleum-electric hybrid most commonly uses internal combustion engines (using a variety of fuels, generally gasoline or Diesel engines ) and electric motors to power the vehicle. The energy is stored in the fuel of the internal combustion engine and an electric battery set . There are many types of petroleum-electric hybrid drivetrains , from Full hybrid to Mild hybrid , which offer varying advantages and disadvantages. [ 28 ]
William H. Patton filed a patent application for a gasoline-electric hybrid rail-car propulsion system in early 1889, and for a similar hybrid boat propulsion system in mid 1889. [ 29 ] [ 30 ] There is no evidence that his hybrid boat met with any success, but he built a prototype hybrid tram and sold a small hybrid locomotive . [ 31 ] [ 32 ]
In 1899, Henri Pieper developed the world's first petro-electric hybrid automobile. In 1900, Ferdinand Porsche developed a series-hybrid using two motor-in-wheel-hub arrangements with an internal combustion generator set providing the electric power; Porsche's hybrid set two-speed records. [ citation needed ] While liquid fuel/electric hybrids date back to the late 19th century, the braking regenerative hybrid was invented by David Arthurs, an electrical engineer from Springdale, Arkansas, in 1978–79. His home-converted Opel GT was reported to return as much as 75 mpg with plans still sold to this original design, and the "Mother Earth News" modified version on their website. [ 33 ]
The plug-in-electric-vehicle (PEV) is becoming more and more common. It has the range needed in locations where there are wide gaps with no services. The batteries can be plugged into house (mains) electricity for charging, as well being charged while the engine is running.
Some battery electric vehicles can be recharged while the user drives. Such a vehicle establishes contact with an electrified rail, plate, or overhead wires on the highway via an attached conducting wheel or other similar mechanisms (see conduit current collection ). The vehicle's batteries are recharged by this process—on the highway—and can then be used normally on other roads until the battery is discharged. For example, some of the battery-electric locomotives used for maintenance trains on the London Underground are capable of this mode of operation.
Developing an infrastructure for battery electric vehicles would provide the advantage of virtually unrestricted highway range. Since many destinations are within 100 km of a major highway, this technology could reduce the need for expensive battery systems. However, private use of the existing electrical system is almost universally prohibited. Besides, the technology for such electrical infrastructure is largely outdated and, outside some cities, not widely distributed (see Conduit current collection , trams , electric rail , trolleys , third rail ). Updating the required electrical and infrastructure costs could perhaps be funded by toll revenue or by dedicated transportation taxes.
In addition to vehicles that use two or more different devices for propulsion , some also consider vehicles that use distinct energy sources or input types (" fuels ") using the same engine to be hybrids, although to avoid confusion with hybrids as described above and to use correctly the terms, these are perhaps more correctly described as dual mode vehicles:
Hydraulic hybrid and pneumatic hybrid vehicles use an engine or regenerative braking (or both) to charge a pressure accumulator to drive the wheels via hydraulic (liquid) or pneumatic (compressed gas) drive units. In most cases the engine is detached from the drivetrain, serving solely to charge the energy accumulator. The transmission is seamless. Regenerative braking can be used to recover some of the supplied drive energy back into the accumulator.
A French company, MDI , has designed and has running models of a petro-air hybrid engine car. The system does not use air motors to drive the vehicle, being directly driven by a hybrid engine. The engine uses a mixture of compressed air and gasoline injected into the cylinders. [ 37 ] A key aspect of the hybrid engine is the "active chamber", which is a compartment heating air via fuel doubling the energy output. [ 38 ] Tata Motors of India assessed the design phase towards full production for the Indian market and moved into "completing detailed development of the compressed air engine into specific vehicle and stationary applications". [ 39 ] [ 40 ]
Petro-hydraulic configurations have been common in trains and heavy vehicles for decades. The auto industry recently focused on this hybrid configuration as it now shows promise for introduction into smaller vehicles.
In petro-hydraulic hybrids, the energy recovery rate is high and therefore the system is more efficient than electric battery charged hybrids using the current electric battery technology, demonstrating a 60% to 70% increase in energy economy in US Environmental Protection Agency (EPA) testing. [ 41 ] The charging engine needs only to be sized for average usage with acceleration bursts using the stored energy in the hydraulic accumulator, which is charged when in low energy demanding vehicle operation. The charging engine runs at optimum speed and load for efficiency and longevity. Under tests undertaken by the US Environmental Protection Agency (EPA), a hydraulic hybrid Ford Expedition returned 32 miles per US gallon (7.4 L/100 km; 38 mpg ‑imp ) City, and 22 miles per US gallon (11 L/100 km; 26 mpg ‑imp ) highway. [ 20 ] [ 21 ] UPS currently has two trucks in service using this technology. [ 22 ]
Although petro-hydraulic hybrid technology has been known for decades and used in trains as well as very large construction vehicles, the high costs of the equipment precluded the systems from lighter trucks and cars. In the modern sense, an experiment proved the viability of small petro-hydraulic hybrid road vehicles in 1978. A group of students at Minneapolis, Minnesota's Hennepin Vocational Technical Center, converted a Volkswagen Beetle car to run as a petro-hydraulic hybrid using off-the-shelf components. A car rated at 32 mpg ‑US (7.4 L/100 km; 38 mpg ‑imp ) was returning 75 mpg ‑US (3.1 L/100 km; 90 mpg ‑imp ) with the 60 hp engine replaced by a 16 hp engine. The experimental car reached 70 mph (110 km/h). [ 19 ]
In the 1990s, a team of engineers working at EPA's National Vehicle and Fuel Emissions Laboratory succeeded in developing a revolutionary type of petro-hydraulic hybrid powertrain that would propel a typical American sedan car. The test car achieved over 80 mpg on combined EPA city/highway driving cycles. Acceleration was 0-60 mph in 8 seconds, using a 1.9 L diesel engine. No lightweight materials were used. The EPA estimated that produced in high volumes the hydraulic components would add only $700 to the base cost of the vehicle. [ 20 ]
The petro-hydraulic hybrid system has a faster and more efficient charge/discharge cycling than petro-electric hybrids and is also cheaper to build. The accumulator vessel size dictates total energy storage capacity and may require more space than an electric battery set. Any vehicle space consumed by a larger size of accumulator vessel may be offset by the need for a smaller sized charging engine, in HP and physical size.
Research is underway in large corporations and small companies. The focus has now switched to smaller vehicles. The system components were expensive which precluded installation in smaller trucks and cars. A drawback was that the power driving motors were not efficient enough at part load. A British company ( Artemis Intelligent Power ) made a breakthrough introducing an electronically controlled hydraulic motor/pump, the Digital Displacement® motor/pump. The pump is highly efficient at all speed ranges and loads, giving feasibility to small applications of petro-hydraulic hybrids. [ 42 ] The company converted a BMW car as a test bed to prove viability. The BMW 530i gave double the mpg in city driving compared to the standard car. This test was using the standard 3,000 cc engine, with a smaller engine the figures would have been more impressive. The design of petro-hydraulic hybrids using well sized accumulators allows downsizing an engine to average power usage, not peak power usage. Peak power is provided by the energy stored in the accumulator. A smaller more efficient constant speed engine reduces weight and liberates space for a larger accumulator. [ 43 ]
Current vehicle bodies are designed around the mechanicals of existing engine/transmission setups. It is restrictive and far from ideal to install petro-hydraulic mechanicals into existing bodies not designed for hydraulic setups. One research project's goal is to create a blank paper design new car, to maximize the packaging of petro-hydraulic hybrid components in the vehicle. All bulky hydraulic components are integrated into the chassis of the car. One design has claimed to return 130 mpg in tests by using a large hydraulic accumulator which is also the structural chassis of the car. The small hydraulic driving motors are incorporated within the wheel hubs driving the wheels and reversing to claw-back kinetic braking energy. The hub motors eliminate the need for friction brakes, mechanical transmissions, driveshafts, and U-joints, reducing costs and weight. Hydrostatic drive with no friction brakes is used in industrial vehicles. [ 44 ] The aim is 170 mpg in average driving conditions. The energy created by shock absorbers and kinetic braking energy that normally would be wasted assists in charging the accumulator. A small fossil-fuelled piston engine sized for average power use charges the accumulator. The accumulator is sized at running the car for 15 minutes when fully charged. The aim is a fully charged accumulator that will produce a 0-60 mph acceleration speed of under 5 seconds using four wheel drive. [ 45 ] [ 46 ] [ 47 ]
In January 2011 industry giant Chrysler announced a partnership with the US Environmental Protection Agency (EPA) to design and develop an experimental petro-hydraulic hybrid powertrain suitable for use in large passenger cars. In 2012 an existing production minivan was adapted to the new hydraulic powertrain for assessment. [ 20 ] [ 48 ] [ 49 ] [ 50 ]
PSA Peugeot Citroën exhibited an experimental "Hybrid Air" engine at the 2013 Geneva Motor Show . [ 51 ] [ 52 ] The vehicle uses nitrogen gas compressed by energy harvested from braking or deceleration to power a hydraulic drive which supplements power from its conventional gasoline engine. The hydraulic and electronic components were supplied by Robert Bosch GmbH . Mileage was estimated to be about 118 mpg ‑US (2 L/100 km; 142 mpg ‑imp ) on the Euro test cycle if installed in a Citroën C3 type of body. [ 53 ] [ 54 ] PSA Although the car was ready for production and was proven and feasible delivering the claimed results, Peugeot Citroën were unable to attract a major manufacturer to share the high development costs and are shelving the project until a partnership can be arranged. [ 55 ]
Another form of a hybrid vehicle are the human-powered electric vehicles. These include such vehicles as the Sinclair C5 , Twike , electric bicycles , electric skateboards , and Electric motorcycles and scooters
In a parallel hybrid vehicle, an electric motor and an internal combustion engine are coupled such that they can power the vehicle either individually or together. Most commonly the internal combustion engine, the electric motor and gearbox are coupled by automatically controlled clutches. For electric driving, the clutch between the internal combustion engine is open while the clutch to the gearbox is engaged. While in combustion mode the engine and motor run at the same speed.
The first mass-production parallel hybrid sold outside Japan was the 1st generation Honda Insight .
The Mercedes-Benz E 300 BlueTEC HYBRID released in 2012 only in European markets is a very rare mass-produced diesel hybrid vehicle powered by a Mercedes-Benz OM651 engine developing 152 kW (204 hp) paired with a 20 kW (27 hp) electric motor, positioned between the engine and the gearbox, for a combined output of 170 kW (228 hp). The vehicle has a fuel consumption rate of 24–26 km/L (56–62 mpg ‑US ; 67–74 mpg ‑imp ). [ 56 ] [ 57 ] [ 58 ]
These types use a generally compact electric motor (usually <20 kW) to provide auto-stop/start features and to provide extra power assist [ 59 ] during the acceleration, and to generate on the deceleration phase (also known as regenerative braking ).
On-road examples include Honda Civic Hybrid , Honda Insight 2nd generation, Honda CR-Z , Honda Accord Hybrid , Mercedes Benz S400 BlueHYBRID , BMW 7 Series hybrids, General Motors BAS Hybrids , Suzuki S-Cross , Suzuki Wagon R and Smart fortwo with micro hybrid drive.
In a power-split hybrid electric drive train, there are two motors: a traction electric motor and an internal combustion engine. The power from these two motors can be shared to drive the wheels via a power split device, which is a simple planetary gear set. The ratio can be from 100% for the combustion engine to 100% for the traction electric motor, or anything in between. The combustion engine can act as a generator charging the batteries.
Modern versions such as the Toyota Hybrid Synergy Drive have a second electric motor/generator connected to the planetary gear. In cooperation with the traction motor/generator and the power-split device, this provides a continuously variable transmission.
On the open road, the primary power source is the internal combustion engine. When maximum power is required, for example, to overtake, the traction electric motor is used to assist. This increases the available power for a short period, giving the effect of having a larger engine than actually installed. In most applications, the combustion engine is switched off when the car is slow or stationary thereby reducing curbside emissions.
Passenger car installations include Toyota Prius , Ford Escape and Fusion, as well as Lexus RX 400h, RX450h, GS450h, LS600h, and CT200h.
A series- or serial-hybrid vehicle is driven by an electric motor, functioning as an electric vehicle while the battery pack energy supply is sufficient, with an engine tuned for running as a generator when the battery pack is insufficient. There is typically no mechanical connection between the engine and the wheels, and the primary purpose of the range extender is to charge the battery. Series-hybrids have also been referred to as extended range electric vehicle , range-extended electric vehicle, or electric vehicle-extended range (EREV/REEV/EVER).
The BMW i3 with range extender is a production series-hybrid. It operates as an electric vehicle until the battery charge is low, and then activates an engine-powered generator to maintain power, and is also available without the range extender. The Fisker Karma was the first series-hybrid production vehicle.
When describing cars, the battery of a series-hybrid is usually charged by being plugged in—but a series-hybrid may also allow for a battery to only act as a buffer (and for regeneration purposes), and for the electric motor's power to be supplied constantly by a supporting engine. Series arrangements have been common in diesel-electric locomotives and ships. Ferdinand Porsche effectively invented this arrangement in speed-record-setting racing cars in the early 20th century, such as the Lohner–Porsche Mixte Hybrid . Porsche named his arrangement "System Mixt" and it was a wheel hub motor design, where each of the two front wheels was powered by a separate motor. This arrangement was sometimes referred to as an electric transmission , as the electric generator and driving motor replaced a mechanical transmission. The vehicle could not move unless the internal combustion engine was running.
In 1997 Toyota released the first series-hybrid bus sold in Japan. [ 60 ] GM introduced the Chevy Volt series plug-in hybrid in 2010, aiming for an all-electric range of 40 mi (64 km), [ 61 ] though this car also has a mechanical connection between the engine and drivetrain. [ 62 ] Supercapacitors combined with a lithium-ion battery bank have been used by AFS Trinity in a converted Saturn Vue SUV vehicle. Using supercapacitors they claim up to 150 mpg in a series-hybrid arrangement. [ 63 ]
Nissan Note e-power is an example of a series hybrid technology since 2016 in Japan.
Another subtype of hybrid vehicles is the plug-in hybrid electric vehicle . The plug-in hybrid is usually a general fuel-electric (parallel or serial) hybrid with increased energy storage capacity, usually through a lithium-ion battery , which allows the vehicle to drive on all-electric mode a distance that depends on the battery size and its mechanical layout (series or parallel). It may be connected to mains electricity supply at the end of the journey to avoid charging using the on-board internal combustion engine. [ 64 ] [ 65 ]
This concept is attractive to those seeking to minimize on-road emissions by avoiding—or at least minimizing—the use of ICE during daily driving. As with pure electric vehicles, the total emissions saving, for example in CO 2 terms, is dependent upon the energy source of the electricity generating company.
For some users, this type of vehicle may also be financially attractive so long as the electrical energy being used is cheaper than the petrol/diesel that they would have otherwise used. Current tax systems in many European countries use mineral oil taxation as a major income source. This is generally not the case for electricity, which is taxed uniformly for the domestic customer, however that person uses it. Some electricity suppliers also offer price benefits for off-peak night users, which may further increase the attractiveness of the plug-in option for commuters and urban motorists.
A 2009 National Highway Traffic Safety Administration report examined hybrid electric vehicle accidents that involved pedestrians and cyclists and compared them to accidents involving internal combustion engine vehicles (ICEV). The findings showed that, in certain road situations, HEVs are more dangerous for those on foot or bicycle. For accidents where a vehicle was slowing or stopping, backing up, entering, or leaving a parking space (when the sound difference between HEVs and ICEVs is most pronounced), HEVs were twice as likely to be involved in a pedestrian crash than ICEVs. For crashes involving cyclists or pedestrians, there was a higher incident rate for HEVs than ICEVs when a vehicle was turning a corner. However, there was no statistically significant difference between the types of vehicles when they were driving straight. [ 66 ]
Several automakers developed electric vehicle warning sounds designed to alert pedestrians to the presence of electric drive vehicles such as hybrid electric vehicle, plug-in hybrid electric vehicles and all-electric vehicles (EVs) travelling at low speeds. Their purpose is to make pedestrians, cyclists, the blind, and others aware of the vehicle's presence while operating in all-electric mode . [ 67 ] [ 68 ] [ 69 ] [ 70 ]
Vehicles in the market with such safety devices include the Nissan Leaf , Chevrolet Volt , Fisker Karma , Honda FCX Clarity , Nissan Fuga Hybrid/Infiniti M35 , Hyundai ix35 FCEV , Hyundai Sonata Hybrid , 2012 Honda Fit EV , the 2012 Toyota Camry Hybrid , 2012 Lexus CT200h , and all the Prius family of cars.
The hybrid vehicle typically achieves greater fuel economy and lower emissions than conventional internal combustion engine vehicles (ICEVs), resulting in fewer emissions being generated. These savings are primarily achieved by three elements of a typical hybrid design:
Other techniques that are not necessarily 'hybrid' features, but that are frequently found on hybrid vehicles include:
These features make a hybrid vehicle particularly efficient for city traffic where there are frequent stops, coasting, and idling periods. In addition noise emissions are reduced, particularly at idling and low operating speeds, in comparison to conventional engine vehicles. For continuous high-speed highway use, these features are much less useful in reducing emissions.
Hybrid vehicle emissions today are getting close to or even lower than the recommended level set by the EPA (Environmental Protection Agency). The recommended levels they suggest for a typical passenger vehicle should be equated to 5.5 metric tons of CO 2 . The three most popular hybrid vehicles, Honda Civic , Honda Insight and Toyota Prius , set the standards even higher by producing 4.1, 3.5, and 3.5 tons showing a major improvement in carbon dioxide emissions. Hybrid vehicles can reduce air emissions of smog-forming pollutants by up to 90% and cut carbon dioxide emissions in half. [ 71 ]
An increase in fossil fuels is needed to build hybrid vehicles versus conventional cars. This increase is more than offset by reduced emissions when running the vehicle. [ 72 ]
Hybrid CO 2 emissions have been understated when comparing certification cycles to real-world driving. In one study using real-world driving data, it was shown they use on average 120 g of CO 2 per km instead of the 44 g per km in official tests. [ 73 ]
Toyota states that three Hybrid vehicles equal one battery electric vehicle in CO 2 reduction effect from carbon neutrality viewpoint which means reducing CO 2 emissions to zero throughout the entire life cycle of a product, starting from procurement of raw materials, manufacturing, and transportation to use, recycling, and disposal. [ 74 ]
Though hybrid cars consume less fuel than conventional cars, there is still an issue regarding the environmental damage of the hybrid car battery. [ 75 ] [ 76 ] Today, most hybrid car batteries are Lithium-ion , which has higher energy density than nickel–metal hydride batteries and is more environmentally friendly than lead-based batteries which constitute the bulk of petrol car starter batteries today. [ 77 ]
There are many types of batteries. Some are far more toxic than others. Lithium-ion is the least toxic of the batteries mentioned above. [ 78 ]
The toxicity levels and environmental impact of nickel metal hydride batteries—the type previously used in hybrids—are much lower than batteries like lead acid or nickel cadmium according to one source. [ 79 ] Another source claims nickel metal hydride batteries are much more toxic than lead batteries, also that recycling them and disposing of them safely is difficult. [ 80 ] In general various soluble and insoluble nickel compounds, such as nickel chloride and nickel oxide, have known carcinogenic effects in chick embryos and rats. [ 81 ] [ 82 ] [ 83 ] The main nickel compound in NiMH batteries is nickel oxyhydroxide (NiOOH), which is used as the positive electrode. However Nickel Metal Hydride Batteries have fallen out of favour in hybrid vehicles as various lithium-ion chemistries have become more mature to market.
The lithium-ion battery has become a market leader in this segment due to its high energy density, stability, and cost when compared to other technologies. [ 84 ] A market leader in this area is Panasonic with their partnership with Tesla [ 85 ] [ 86 ] [ 87 ] [ 88 ]
The lithium-ion batteries are appealing because they have the highest energy density of any rechargeable batteries and can produce a voltage more than three times that of nickel–metal hydride battery cell while simultaneously storing large quantities of electricity as well. [ 77 ] The batteries also produce higher output (boosting vehicle power), higher efficiency (avoiding wasteful use of electricity), and provides excellent durability, compared with the life of the battery being roughly equivalent to the life of the vehicle. [ 89 ] Additionally, the use of lithium-ion batteries reduces the overall weight of the vehicle and also achieves improved fuel economy of 30% better than petro-powered vehicles with a consequent reduction in CO 2 emissions helping to prevent global warming. [ 90 ]
Lithium-ion batteries are also safer to recycle, with Volkswagen Group pioneering processes to recycle lithium-ion batteries; [ 91 ] this is also being chased by various other large companies, such as BMW , [ 92 ] Audi , [ 93 ] Mercedes-Benz [ 94 ] and Tesla . [ 95 ] The main goal within many of these companies is to combat disinformation about the nature of lithium batteries, primarily that they are not recyclable, which primarily stem from articles discussing the difficulties of recycling. [ 96 ] [ 97 ] [ 98 ]
There are two different levels of charging in plug-in hybrids. Level one charging is the slower method as it uses a 120 V/15 A single-phase grounded outlet. Level two is a faster method; existing Level 2 equipment offers charging from 208 V or 240 V (at up to 80 A, 19.2 kW). It may require dedicated equipment and a connection installation for home or public units. [ 99 ] The optimum charging window for lithium-ion batteries is 3–4.2 V. Recharging with a 120-volt household outlet takes several hours, a 240-volt charger takes 1–4 hours, and a quick charge takes approximately 30 minutes to achieve 80% charge. Three important factors—distance on charge, cost of charging, and time to charge [ 100 ] In order for hybrids to run on electrical power, the car must perform the action of braking in order to generate some electricity. [ citation needed ] The electricity then gets discharged most effectively when the car accelerates or climbs up an incline.
In 2014, hybrid electric car batteries can run on solely electricity for 70–130 miles (110–210 km) on a single charge. [ citation needed ] Hybrid battery capacity currently ranges from 4.4 kWh to 85 kWh on a fully electric car. On a hybrid car, the battery packs currently range from 0.6 kWh to 2.4 kWh representing a large difference in use of electricity in hybrid cars. [ 101 ]
There is an impending increase in the costs of many rare materials used in the manufacture of hybrid cars. [ 102 ] For example, the rare-earth element dysprosium is required to fabricate many of the advanced electric motors and battery systems in hybrid propulsion systems. [ 102 ] [ 103 ] Neodymium is another rare earth metal which is a crucial ingredient in high-strength magnets that are found in permanent magnet electric motors. [ 104 ]
Nearly all the rare-earth elements in the world come from China, [ 105 ] and many analysts believe that an overall increase in Chinese electronics manufacturing will consume this entire supply by 2012. [ 102 ] In addition, export quotas on Chinese rare-earth elements have resulted in an unknown amount of supply. [ 103 ] [ 106 ]
A few non-Chinese sources such as the advanced Hoidas Lake project in northern Canada as well as Mount Weld in Australia are currently under development; [ 106 ] however, the barriers to entry are high [ 107 ] and require years to go online.
Hybrid-electric vehicles (HEVs) combine the advantage of gasoline engines and electric motors. The key areas for efficiency or performance gains are regenerative braking, dual power sources, and less idling. [ 108 ]
Other types of green vehicles include other vehicles that go fully or partly on alternative energy sources than fossil fuel . Another option is to use alternative fuel composition (i.e. biofuels ) in conventional fossil fuel-based vehicles, making them go partly on renewable energy sources.
Other approaches include personal rapid transit , a public transportation concept that offers automated on-demand non-stop transportation, on a network of specially built guideways.
Automakers spend around $US8 million in marketing Hybrid vehicles each year. With combined effort from many car companies, the Hybrid industry has sold millions of Hybrids. [ citation needed ]
Hybrid car companies like Toyota, Honda, Ford, and BMW have pulled together to create a movement of Hybrid vehicle sales pushed by Washington lobbyists to lower the world's emissions and become less reliant on our petroleum consumption. [ citation needed ]
In 2005, sales went beyond 200,000 Hybrids, but in retrospect that only reduced the global use for gasoline consumption by 200,000 gallons per day—a tiny fraction of the 360 million gallons used per day. [ citation needed ] According to Bradley Berman author of Driving Change—One Hybrid at a time , "cold economics shows that in real dollars, except for a brief spike in the 1970s, gas prices have remained remarkably steady and cheap. Fuel continues to represent a small part of the overall cost of owning and operating a personal vehicle". [ 109 ] Other marketing tactics include greenwashing which is the "unjustified appropriation of environmental virtue." [ 110 ] Temma Ehrenfeld explained in an article by Newsweek. Hybrids may be more efficient than many other gasoline motors as far as gasoline consumption is concerned but as far as being green and good for the environment is completely inaccurate.
Hybrid car companies have a long time to go if they expect to really go green. According to Harvard business professor Theodore Levitt states "managing products" and "meeting customers' needs", "you must adapt to consumer expectations and anticipation of future desires." [ 111 ] This means people buy what they want, if they want a fuel efficient car they buy a Hybrid without thinking about the actual efficiency of the product. This "green myopia" as Ottman calls it, fails because marketers focus on the greenness of the product and not on the actual effectiveness.
Researchers and analysts say people are drawn to the new technology, as well as the convenience of fewer fill-ups. Secondly, people find it rewarding to own the better, newer, flashier, and so-called greener car.
In 2019 the term self-charging hybrid became prevalent in advertising, though cars referred to by this name do not offer any different functionality than a standard hybrid electric vehicle provides. The only self-charging effect is in energy recovery via regenerative braking, which is also true of plug-in hybrids , fuel cell electric vehicles and battery electric vehicles. [ 112 ]
In January 2020, using this term has been prohibited in Norway , for misleading advertising by Toyota and Lexus . [ 113 ] "Our claim is based on the fact that customers never have to charge the battery of their vehicle, as it is recharged during the vehicle use. There is no intention to mislead customers, on the contrary: the point is to clearly explain the difference with plug-in hybrid vehicles."
While the adoption rate for hybrids in the US is small today (2.2% of new car sales in 2011), [ 114 ] this compares with a 17.1% share of new car sales in Japan in 2011, [ 115 ] and it has the potential to be very large over time as more models are offered and incremental costs decline due to learning and scale benefits. However, forecasts vary widely. For instance, Bob Lutz , a long-time skeptic of hybrids, indicated he expects hybrids "will never comprise more than 10% of the US auto market." [ 116 ] Other sources also expect hybrid penetration rates in the US will remain under 10% for many years. [ 117 ] [ 118 ] [ 119 ]
More optimistic views as of 2006 include predictions that hybrids would dominate new car sales in the US and elsewhere over the next 10 to 20 years. [ 120 ] Another approach, taken by Saurin Shah, examines the penetration rates (or S-curves) of four analogs (historical and current) to hybrid and electrical vehicles in an attempt to gauge how quickly the vehicle stock could be hybridized and/or electrified in the United States. The analogs are (1) the electric motors in US factories in the early 20th century, (2) diesel-electric locomotives on US railways in the 1920–1945 period, (3) a range of new automotive features/technologies introduced in the US over the past fifty years, and 4) e-bike purchases in China over the past few years. These analogs collectively suggest it would take at least 30 years for hybrid and electric vehicles to capture 80% of the US passenger vehicle stock. [ 121 ]
The EPA expects the combined market share of new gasoline hybrid light-duty vehicles to reach 13.6% for the 2023 model year from 10.2% in the 2022 model year. [ 122 ]
The European Parliament, Council, and European Commission have reached an agreement which is aimed at reducing the average CO 2 passenger car emissions to 95 g/km by 2020, according to a European Commission press release.
According to the release, the key details of the agreement are as follows:
Media related to Hybrid-powered vehicles at Wikimedia Commons | https://en.wikipedia.org/wiki/Hybrid_vehicle |
Hybrid vehicle drivetrains transmit power to the driving wheels for hybrid vehicles . A hybrid vehicle has multiple forms of motive power, and can come in many configurations. For example, a hybrid may receive its energy by burning gasoline, but switch between an electric motor and a combustion engine .
A typical powertrain includes all of the components used to transform stored potential energy . Powertrains may either use chemical, solar, nuclear or kinetic energy for propulsion. The oldest example is the steam locomotive. Modern examples include electric bicycles and hybrid electric vehicles , which generally combine a battery (or supercapacitor ) supplemented by an internal combustion engine (ICE) that can either recharge the batteries or power the vehicle. Other hybrid powertrains can use flywheels to store energy.
Among different types of hybrid vehicles, only the electric/ICE type is commercially available as of 2017. One variety operated in parallel to provide power from both motors simultaneously. Another operated in series with one source exclusively providing the power and the second providing electricity. Either source may provide the primary motive force, with the other augmenting the primary.
Other combinations offer efficiency gains from superior energy management and regeneration that are offset by cost, complexity and battery limitations. Combustion-electric (CE) hybrids have battery packs with far larger capacity than a combustion-only vehicle. A combustion-electric hybrid has batteries that are light that offer higher energy density and are far more costly. ICEs require only a battery large enough to operate the electrical system and ignite the engine. [ 1 ]
Electrical vehicles have a long history combining internal combustion and electrical transmission – as in a diesel–electric power-train – although they have mostly been used for rail locomotives . A diesel–electric powertrain fails the strict definition of hybrid because the electric drive transmission directly replaces the mechanical transmission rather than being a supplementary source of motive power.
One of the earliest forms of hybrid land vehicle was the 'trackless' trolleybus experiment in The United States (New Jersey) that ran from 1935 to 1948, which normally used traction current delivered by wire. The trolleybus was fitted with an internal combustion engine to power the mechanical drivetrain directly, not to generate electricity for the traction motor. This enabled the vehicle to be used for revenue service where there was no contact wire.
Since the 1990s trolleybus hybrids have been introduced with small power plants to provide a low speed capability for emergency and maintenance but not to support general revenue service.
Parallel hybrid systems have both an internal combustion engine and an electric motor that can both individually drive the car or both coupled up jointly giving drive. This is the most common hybrid system as of 2016.
If they are joined at an axis (in parallel) , the speeds at this axis must be identical and the supplied torques will add together (most electric bicycles are of this type). When only one of the two sources is in use, the other must be connected via a one-way clutch or freewheel so it can rotate freely.
With cars the two sources may be applied to the same shaft (for example with the electric motor connected between the engine and transmission), turning at equal speeds and the torques adding up with the electric motor adding or subtracting torque to the system as necessary. (The first two generations of Honda Insight use this system.)
Parallel hybrids can be further categorized by the balance between the different motors are at providing motive power: the ICE may be dominant (engaging the electric motor only in specific circumstances) or vice versa; while in others can run on the electric system alone but because current parallel hybrids are unable to provide electric-only or internal combustion-only modes they are often categorized as mild hybrids (see below).
Parallel hybrids rely more on regenerative braking and the ICE can also act as a generator for supplemental recharging. This makes them more efficient in urban 'stop-and-go' conditions. They use a smaller battery pack than other hybrids. Honda 's early Insight, Civic , and Accord hybrids using IMA are examples of production parallel hybrids. [ 2 ] General Motors Parallel Hybrid Truck (PHT) and BAS Hybrids such as the Saturn Vue and Aura Greenline and Chevrolet Malibu hybrids also employ a parallel hybrid architecture.
An alternative parallel hybrid is the "through the road" type. [ 3 ] [ 4 ] In this system a conventional drivetrain powers one axle, with an electric motor or motors driving another. This arrangement was used by the earliest 'off track' trolleybuses. It in effect provides a complete backup power train. In modern motors batteries can be recharged through regenerative braking or by loading the electrically driven wheels during cruise. This allows a simpler approach to power-management. This layout also has the advantage of providing four-wheel-drive in some conditions. (An example of this principle is a bicycle fitted with a front hub motor, which assists the cyclist's pedal power at the rear wheel.) Vehicles of this type include the Audi 100 Duo II and Subaru VIZIV concept cars, Peugeot 3008 , Peugeot 508 , 508 RXH , Citroën DS5 (all using PSA 's HYbrid4 system), the Volvo V60 plug-in hybrid , the BMW 2 Series Active Tourer , BMW i8 and the second generation Honda NSX .
Series hybrids are also referred to as extended-range electric vehicles (EREV) [ 5 ] or range-extended electric vehicles (REEV), or electric vehicle with extended range (EVER). All series hybrids are EREV, REEV or EVER, but not all EREV, REEV or EVER are series hybrids. Series hybrids with particular characteristics are classified as range-extended battery-electric vehicle (BEVx) by the California Air Resources Board . [ 6 ]
Electric transmissions were invented by 1903. Mechanical transmissions involve costs via their weight, bulk, noise, cost, complexity and drain on engine power with every gear-change, affecting both manual and automatic systems. Unlike ICEs, electric motors typically do not require a transmission.
Compared to parallel hybrids, the mechanical transmission between the engine and wheels is discarded. The engine instead acts as an electric generator, attached to the battery via cable. The linkage is engine to battery to electric motor to wheels. In some cases, the generator also directly links to the motor.
This serial arrangement is common in diesel–electric locomotives and ships (the Russian river ship Vandal , launched in 1903, was the world's first diesel-powered and diesel–electric powered vessel). Ferdinand Porsche successfully used this arrangement in the early 20th century in racing cars, including the Lohner–Porsche Mixte Hybrid . Porsche named the system System Mixte, which had a wheel hub motor arrangement, with a motor in each of the two front wheels, setting speed records.
This approach isolates the engine from demand, allowing it to operate only at its most efficient speed. The engine can be much smaller, since it does not have to accommodate high speed/acceleration. Traction motors are typically powered only by the battery, which can also be charged from external sources.
Nissan 's e-Power line ( Note , [ 7 ] Serena , [ 8 ] Kicks , [ 9 ] X-Trail , [ 10 ] and Qashqai ) [ 11 ] using the engine to drive a generator and the EM57 traction motor. [ 12 ] Mazda 's MX-30 , is optionally equipped with a range extender. [ 13 ] BMW's i3 attached the generator only to the battery. ThunderVolt hybrid transit buses [ 14 ] and transit buses fitted with BAE Systems (formerly Lockheed Martin ) HybriDrive powertrains are also serial hybrids. [ 15 ] [ 16 ]
Electric motors are more efficient than ICEs, with high power-to-weight ratios providing torque over a wide speed range. ICEs are most efficient when turning at a constant speed.
ICEs can run optimally when turning a generator. Series-hybrid systems offer smoother acceleration by avoiding gear changes. Series-hybrids incorporate:
In addition:
The electric motor may be entirely fed by electricity from the battery or via the generator turned by the ICE, or both. Such a vehicle conceptually resembles a diesel–electric locomotive with the addition of a battery that may power the vehicle without running the ICE and acting as an energy buffer that is used to accelerate and achieve greater speed; the generator may simultaneously charge the battery and power the electric motor that moves the vehicle.
When the vehicle is stopped the ICE is switched off without idling, while the battery provides whatever power is needed at rest. Vehicles at traffic lights, or in slow moving stop-start traffic need not burn fuel when stationary or moving slowly, reducing emissions.
Series-hybrids can be fitted with a supercapacitor or a flywheel to store regenerative braking energy, which can improve efficiency by recovering energy otherwise lost as heat through the braking system. Because a series-hybrid has no mechanical link between the ICE and the wheels, the engine can run at a constant and efficient rate regardless of vehicle speed, achieving higher efficiency (37%, rather than the ICE average of 20% [ 17 ] ) and at low or mixed speeds this could result in ~50% increase in overall efficiency (19% vs 29%).
Lotus offered an engine/generator set design that runs at two speeds, giving 15 kW of electrical power at 1,500 rpm and 35 kW at 3,500 rpm via the integrated electrical generator, [ 18 ] used in the Nissan concept Infiniti Emerg-e .
This operating profile allows greater scope for alternative engine designs, such as a microturbine , [ 19 ] rotary Atkinson cycle engine or linear combustion engine . [ 20 ]
The ICE is matched to the electric engine by comparing the output rates at cruising speed . Generally, output rates for combustion engines are provided for instantaneous (peak) output rates, [ 21 ] but in practice these can't be used.
The use of an electric motor driving a wheel directly eliminates the conventional mechanical transmission elements: gearbox, transmission shafts and differential, and can sometimes eliminate flexible couplings .
In 1997, Toyota released the first series-hybrid bus sold in Japan. [ 22 ] Designline International of Ashburton, New Zealand produces city buses with a microturbine powered series-hybrid system. Wrightbus produces series hybrid buses including the Gemini 2 and New Routemaster . Supercapacitors combined with a lithium ion battery bank have been used by AFS Trinity in a converted Saturn Vue SUV vehicle. Using supercapacitors they claim up to 150 mpg in a series-hybrid arrangement. [ 23 ]
Well known automotive series hybrid models include the variant of the BMW i3 that is equipped with a range extender. Another example of a series hybrid automobile is the Fisker Karma . The Chevrolet Volt is almost a series hybrid, but also includes a mechanical link from the engine to the wheels above 70 mph. [ 24 ] [ 25 ]
Series-hybrids have been taken up by the aircraft industry. The DA36 E-Star, an aircraft designed by Siemens , Diamond Aircraft and EADS , employs a series hybrid powertrain with the propeller turned by a Siemens 70 kW (94 hp) electric motor. A power sapping propeller speed reduction unit is eliminated. The aim is to reduce fuel consumption and emissions by up to 25 percent. An onboard 40 hp (30 kW) Austro Engine Wankel rotary engine and generator provides the electricity.
The Wankel was chosen because of its small size, low weight and great power to weight ratio. (Wankel engines also run efficiently at a constant speed of approximately 2,000 RPM which is suited to generator operation. Keeping to a constant/narrow band offsets many of the perceived disadvantages of the Wankel engine in automotive applications. [ 26 ] )
The electric propeller motor uses electricity stored in batteries, with the engines not operating, to take off and climb reducing sound emissions. The powertrain reduces the weight of the plane by 100 kilos relative to its predecessor. The DA36 E-Star first flew in June 2013, making this the first ever flight of a series hybrid powertrain. Diamond Aircraft state that the technology is scalable to a 100-seat aircraft. [ 27 ] [ 28 ]
If the motors are attached to the vehicle body, flexible couplings are required but not if the traction motors are integrated into the wheels . One disadvantage is that the unsprung mass increases and suspension responsiveness decreases, which impacts ride and potentially safety. However the impact should be minimal as electric motors in wheel hubs such as Hi-Pa Drive , may be very small and light having exceptionally high power-to-weight ratios and braking mechanisms can be lighter as the wheel motors brake the vehicle.
Advantages of individual wheel motors include simplified traction control , all wheel drive if required and a lower floor (useful for buses and other specialised vehicles (some 8x8 all-wheel drive military vehicles use individual wheel motors). Diesel–electric locomotives have used this concept (individual motors driving axles of each pair of wheels) for 70 years. [ 29 ] [ full citation needed ]
Other measures include lightweight aluminium wheels to reduce the unsprung mass of the wheel assembly; vehicle designs may be optimized to lower the centre of gravity by locating heavier elements (including battery) at floor level; In a typical road vehicle the power-transmission setup may be smaller and lighter than the equivalent conventional mechanical power-transmission setup, liberating space; the combustion generator set only requires cables to the driving electric motors, increasing flexibility in major component layout spread across a vehicle giving superior weight distribution and maximizing vehicle cabin space and opening up the possibility of superior vehicle designs exploiting this flexibility.
Power-split hybrid or series-parallel hybrid are parallel hybrids that incorporate power-split devices, allowing for power paths from the ICE to the wheels that can be either mechanical or electrical. The main principle is to decouple the power supplied by the primary source from the power demanded by the driver.
ICE torque output is minimal at lower RPMs and conventional vehicles increase engine size to meet market requirements for acceptable initial acceleration. The larger engine has more power than needed for cruising. Electric motors produce full torque at standstill and are well-suited to complement ICE torque deficiency at low RPMs. In a power-split hybrid, a smaller, less flexible, and more efficient engine can be used. The conventional Otto cycle (higher power density, more low-RPM torque, lower fuel efficiency ) is often modified to an Atkinson cycle or Miller cycle (lower power density, less low-rpm torque, higher fuel efficiency; sometimes called an Atkinson-Miller cycle). The smaller engine, using a more efficient cycle and often operating in the favorable region of the brake specific fuel consumption map, significantly contributes to the higher overall efficiency of the vehicle.
Interesting variations of the simple design (pictured at right) found, for example, in the well-known Toyota Prius are the:
The Toyota Hybrid System THS / Hybrid Synergy Drive has a single power-split device (incorporated as a single three-shaft planetary gearset) and can be classified as an Input-Split, since the power of the engine is split at the input to the transmission. This in turn makes this setup very simple in mechanical terms, but has drawbacks of its own. For example, in Generation 1 and Generation 2 HSDs maximum speed is mainly limited by the speed of the smaller electric motor (often functioning as a generator). The Generation 3 HSD separates the ICE-MG1 path from the MG2 path, each with its own, tailored gear ratio (1.1:1 and 2.5:1, respectively, for late Priuses, including the Prius c). The Generation 4 HSD eliminates the second planetary gear set, and places the electric motors on parallel axes, with a combining gear in between these axes, and transfers the combined result to the final drive differential. This is quite similar to Toyota-affiliated Aisin Seiki 's hybrid system, and saves significant space.
General Motors , BMW , and DaimlerChrysler collaborated on a system named "Two-Mode Hybrid" as part of the Global Hybrid Cooperation . The technology was released in the fall of 2007 on the Chevrolet Tahoe Hybrid . The system was also featured on the GMC Graphite SUV concept vehicle at the 2005 North American International Auto Show in Detroit . [ 32 ] BYD Auto 's F3DM sedan is a series-parallel plug-in hybrid automobile, which went on sale in China in 2008. [ 33 ] [ 34 ] [ 35 ]
The Two-Mode Hybrid name highlights the drive-train's ability to operate in all-electric (Mode 1, or Input-Split ) as well as hybrid (Mode 2, or Compound-Split ) modes. The design allows for operation in more than two modes. Two power-split modes are available, along with several fixed-gear (essentially parallel hybrid) regimes. Such a design can be referred to as a multi-regime design. [ 36 ] The Two-Mode Hybrid powertrain design can be classified as a compound-split design, since the addition of four clutches within the transmission allows for multiple configurations of engine power-splitting. In addition to the clutches, this transmission has a second planetary gearset. The objective of the design is to vary the percentage of mechanically vs. electrically transmitted power to cope both with low-speed and high-speed operating conditions. This enables smaller motors to do the job of larger motors when compared to single-mode systems, because the derived electrical peak power is proportional to the width of the continuous variation range. The four fixed gears enable the Two-Mode Hybrid to function like a conventional parallel hybrid under high continuous power regions such as sustained high speed cruising or trailer towing. Full electric boost is available in fixed-gear modes. [ 37 ]
These contain two different energy recovery systems. This is a transversal categorization.
Micro hybrid is a general term given to vehicles that use some type of start-stop system to automatically shut off the engine when idling . Strictly speaking, micro hybrids are not real hybrid vehicles, because they do not rely on two different sources of power. [ 38 ]
Mild hybrids are essentially conventional vehicles with some hybrid hardware, but with limited hybrid features. Typically, they are a parallel hybrid with start-stop and modest levels of engine-assist or regenerative braking. Mild hybrids generally cannot provide all-electric propulsion.
Mild hybrids like the General Motors 2004–2007 Parallel Hybrid Truck (PHT) and the Honda Eco-Assist hybrids are equipped with a three-phase electric motor mounted within the bell-housing between the engine and transmission, allowing the engine to be turned off whenever the truck is coasting, braking, or stopped, yet restart quickly to provide power. Accessories can continue to run on electrical power while the engine is off, and as in other hybrid designs, regenerative braking recaptures energy. The large electric motor spins up the engine to operating-speeds before injecting fuel.
The 2004–2007 Chevrolet Silverado PHT was a full-size pickup truck . Chevrolet was able to get a 10% efficiency improvement by shutting down and restarting the engine on demand and using regenerative braking. The electrical energy was used only to drive accessories such as power steering. The GM PHT used a 42 volt system via three 12 volt vented lead acid batteries connected in series (36V total) to supply the power needed for the startup motor, as well as to power the electronic accessories.
General Motors then introduced their BAS Hybrid system, another mild-hybrid implementation officially released on the 2007 Saturn Vue Green Line . Its "start-stop" functionality operates similarly to the Silverado, although via a belted connection to the motor/generator unit. However the GM BAS Hybrid System can also provide modest assist under acceleration and during steady driving, and captures energy during regenerative (blended) braking. BAS Hybrid offered as much as a 27% improvement in combined fuel efficiency in EPA testing of the 2009 Saturn VUE. [ 39 ] The system can also be found on the 2008–2009 Saturn Aura Green Line and the 2008–2010 Chevrolet Malibu hybrids.
Another way to offer start/stop is by employing a static start engine. Such an engine requires no starter motor, but employs sensors to determine the exact position of each piston, then precisely timing the injection and ignition of fuel to turn over the engine. [ 40 ]
Mild hybrids are sometimes called power-assist hybrids as they use the ICE for primary power, with a torque-boosting electric motor connected to a (largely) conventional power train. The electric motor is mounted between the engine and transmission. It is essentially a large starter motor that operates when the engine needs to be turned over and when the driver "steps on the gas" and requires extra power. The electric motor may also restart the combustion engine and shutting down the main engine at idle, while the enhanced battery system is used to power accessories. [ citation needed ] GM announced Buick LaCrosse and Buick Regal mild-hybrids dubbed Eassist.
Before 2015, Honda 's hybrids, including the Insight , used this design, leveraging their expertise in small, efficient gasoline engines; their system is dubbed Integrated Motor Assist (IMA). IMA hybrids cannot provide propulsion on electric power alone. However, since the amount of electrical power needed is much smaller, system size is reduced.
Another variation is the Saturn Vue Green Line BAS Hybrid system that uses a smaller electric motor (mounted to the side of the engine) and battery pack than the Honda IMA, but functions similarly.
Another variation on this type is Mazda 's e-4WD system, offered on the Mazda Demio sold in Japan. [ 41 ] This front-wheel drive vehicle has an electric motor that can drive the rear wheels when extra traction is needed. The system is disengaged in all other driving conditions, so it does not directly enhance performance or economy but allows the use of a smaller and more economical engine relative to total performance.
Ford has dubbed Honda's hybrids "mild" in their advertising for the Escape Hybrid, arguing that the Escape's full hybrid design is more efficient.
The Genesis G90 and Genesis GV80 Coupe offer mild hybrid options with an electric supercharger . [ 42 ] [ 43 ]
These contain two different energy recovery systems.
The Mercedes-Benz C-Class (W206) , Mercedes-AMG SL 43 (R232) , the Mercedes-AMG CLE 53, the petrol Mercedes C254/X254 , and the Porsche 911 Carrera GTS T-Hybrid have an electrically-assisted turbocharger / MGU-H . [ 44 ] [ 45 ] [ 46 ]
A full hybrid , sometimes also called a strong hybrid , is a vehicle that can run on just the engine, the batteries, or a combination. The Toyota Prius , Toyota Camry Hybrid , Ford Escape Hybrid / Mercury Mariner Hybrid , Ford Fusion Hybrid / Lincoln MKZ Hybrid / Mercury Milan Hybrid , Ford C-Max Hybrid , Ford Maverick Hybrid , Kia Optima Hybrid , Toyota Sienna Hybrid , as well as the General Motors 2-mode hybrid trucks and SUVs, are examples of this type of hybridization as they can operate on battery power alone. A large, high-capacity battery provides battery-only operation. These vehicles have a split power path that allows more flexibility in the drivetrain by inter-converting mechanical and electrical power. To balance the forces from each portion, the vehicles use a differential -style linkage between the engine and motor connected to the head end of the transmission.
The Toyota brand name for this technology is Hybrid Synergy Drive , which is used in the Prius, the Highlander Hybrid SUV and the Camry Hybrid . A computer oversees system operation, determining how to mix the power sources. The Prius operations can be divided into six distinct regimes:–
These contain two different energy recovery systems. An example of dual hybrids are Formula One cars (See Formula One engines#2014–2021 and Formula One engines#2022–2025 ). Other examples are the Porsche 919 Hybrid , and the Infiniti Project Black S which was cancelled.
A plug-in hybrid electric vehicle (PHEV) has two defining characteristics. It:
They are full hybrids, able to run on battery power. They offer greater battery capacity and the ability to recharge from the grid . They can be either parallel or series designs. They are also called gas-optional , or griddable hybrids. Their main benefit is that they can be gasoline-independent for significant distances, with the extended range of an ICE for longer trips. Electric Power Research Institute research found a lower total cost of ownership for PHEVs due to reduced service costs and gradually improving battery technology. The " well-to-wheel " efficiency and emissions of PHEVs compared to gasoline hybrids depends on the grid energy sources (the US grid is 30% coal ; California's grid is primarily natural gas , hydroelectric power , and wind power ).
Prototypes of PHEVs, with larger battery packs that can be recharged from the power grid, were built in the U.S., notably at Andy Frank 's Hybrid Center [ 47 ] at University of California, Davis . One production PHEV, the Renault Kangoo , went on sale in France in 2003. DaimlerChrysler built PHEVs based on the Mercedes-Benz Sprinter van . Light Trucks are offered by Micro-Vett SPA [ 48 ] the so-called Daily Bimodale.
The California Cars Initiative converted the 2004 and newer Toyota Prius to become a prototype of what it calls PRIUS+. With the addition of 140 kg (300 lb) of lead–acid batteries , the PRIUS+ achieved roughly double the gasoline mileage of a standard Prius and could make trips of up to 16 kilometres (10 mi) using only electric power. [ 49 ]
Chinese battery manufacturer and automaker BYD Auto released the F3DM compact sedan to the Chinese fleet market on December 15, 2008, [ 50 ] [ 51 ] later replaced by the BYD Qin plug-in hybrid. [ 52 ] [ 53 ]
General Motors began deliveries of the Chevrolet Volt in the United States in December 2010, [ 5 ] and its sibling, the Opel Ampera, was released in Europe by early 2012. [ 54 ] [ 55 ] As of November 2012 [update] , other plug-in hybrids available in several markets were the Fisker Karma , Toyota Prius Plug-in Hybrid and Ford C-Max Energi .
As of October 2012 [update] , the best selling PHEV is the Volt, with more than 33,000 units of the Volt/Ampera family sold worldwide since December 2010, led by US sales of 27,306, [ 56 ] [ 57 ] followed by the Netherlands with 2,175 Amperas sold through October 2012. [ 58 ] [ 59 ] The Prius Plug-in Hybrid had sold 21,600 units sold worldwide through October 2012, with US sales of 9,623 units, followed by Japan with 9,500 units. [ 57 ] [ 60 ] More recently, the 4xe variants of the Jeep Wrangler and Jeep Grand Cherokee have become the best-selling PHEVs in the U.S., respectively selling 67,429 and 45,684 units in calendar 2023. [ 61 ]
These contain two different energy recovery systems. Examples of such systems include the Mercedes-AMG ONE , is a plug-in dual hybrid. The Mercedes-Benz C-Class (W206) and the Mercedes C254/X254 also have an electrically-assisted turbocharger / MGU-H . [ 62 ] [ 45 ]
There are many ways to create an electric-Internal Combustion Engine (ICE) hybrid. The variety of electric-ICE designs can be differentiated by how the electric and combustion portions of the powertrain connect, at what times each portion is in operation, and what percent of the power is provided by each hybrid component. Two major categories are series hybrids and parallel hybrids , though parallel designs are most common today.
Most hybrids, no matter the specific type, use regenerative braking to recover energy when slowing down the vehicle. This simply involves driving a motor so it acts as a generator.
Many designs also shut off the internal combustion engine when it is not needed in order to save energy. That concept is not unique to hybrids; Subaru pioneered this feature in the early 1980s, and the Volkswagen Lupo 3L is one example of a conventional vehicle that shuts off its engine when at a stop. Some provision must be made, however, for accessories such as air conditioning which are normally driven by the engine. Furthermore, the lubrication systems of internal combustion engines are inherently least effective immediately after the engine starts; since it is upon startup that the majority of engine wear occurs, the frequent starting and stopping of such systems reduce the lifespan of the engine considerably. [ dubious – discuss ] Also, start and stop cycles may reduce the engine's ability to operate at its optimum temperature, thus reducing the engine's efficiency.
Fuel cell vehicles are often fitted with a battery or supercapacitor to deliver peak acceleration power and to reduce the size and power constraints on the fuel cell (and thus its cost); this is effectively also a series hybrid configuration.
A hydraulic hybrid vehicle uses hydraulic and mechanical components instead of electrical. A variable displacement pump replaces the electric motor/generator. A hydraulic accumulator stores energy. The vessel typically carries a flexible bladder of pre-charged pressurized nitrogen gas. Pumped hydraulic fluid is compressed against the bladder storing the energy in the compressed nitrogen gas. Some versions have a piston in a cylinder rather than a pressurized bladder. The hydraulic accumulator is potentially cheaper and more durable than batteries. Hydraulic hybrid technology was originally implemented in Germany in the 1930s. Volvo Flygmotor used petro-hydraulic hybrids experimentally in buses from the early 1980s.
The initial concept involved a giant flywheel (see Gyrobus ) for storage connected to a hydrostatic transmission. The system is under development by Eaton and several other companies, primarily in heavy vehicles like buses, trucks and military vehicles. An example is the Ford F-350 Mighty Tonka concept truck shown in 2002. It features an Eaton system that can accelerate the truck to highway speeds.
The system components were expensive, which precluded installation in smaller trucks and cars. A drawback was that the power motors were not efficient enough at part load. Focus switched to smaller vehicles. A British company, Artemis Intelligent Power , made a breakthrough by introducing an electronically controlled hydraulic motor/pump that is efficient at all ranges and loads, making small applications of petro-hydraulic hybrids feasible. [ 63 ] The company converted a BMW car to prove viability. The BMW 530i gave double the MPG in city driving compared to the standard car. The test used the standard 3,000 cc engine. Petro-hydraulic hybrids allows downsizing an engine to average power usage, not peak power usage. Peak power is provided by the energy stored in the accumulator. [ 64 ]
The kinetic braking energy recovery rate is higher and therefore the system is more efficient than 2013-era battery charged hybrids, demonstrating a 60% to 70% increase in economy in EPA testing. [ 65 ] In EPA tests a hydraulic hybrid Ford Expedition returned 32 mpg ‑US (7.4 L/100 km) in urban driving and 22 mpg ‑US (11 L/100 km) on the highway. [ 66 ]
One research company's goal was to create a fresh design to improve the packaging of gasoline-hydraulic hybrid components. All bulky hydraulic components were integrated into the chassis. One design claimed to reach 130mpg in tests by using a large hydraulic accumulator that is also the structural chassis. The hydraulic driving motors are incorporated within the wheel hubs and reversing to recover braking energy. The aim is 170 mpg in average driving conditions. Energy created by shock absorbers and kinetic braking energy, that normally would be wasted, assists in charging the accumulator. An ICE sized for average power use charges the accumulator. The accumulator is sized to run the car for 15 minutes when fully charged. [ 67 ] [ 68 ] [ 69 ]
In January 2011, Chrysler announced a partnership with the EPA to design and develop an experimental gasoline-hydraulic hybrid powertrain suitable for use in passenger cars. Chrysler adapted an existing production minivan to the powertrain. [ 70 ] [ 71 ] [ 72 ] [ 73 ] [ 74 ]
NRG Dynamix of the U.S.A. claimed its approach reduced cost by one-third compared with electric hybrids and added only 300 lbs (136 kg) to vehicle weight vs. 1,000 lbs (454 kg) for electric hybrids. The company claimed a standard pickup vehicle powered by a 2.3-litre, 4-cylinder engine achieved 14 mpg (16.8 L/100 km) in city driving. Using the petro-hydraulic setup fuel economy reached "the mid 20s". [ 75 ]
Compressed air can power a hybrid car with a gasoline compressor to provide the power. Motor Development International in France was developing such air-powered cars. A team led by Tsu-Chin Tsao, a UCLA mechanical and aerospace engineering professor, collaborated with engineers from Ford to get pneumatic hybrid technology up and running. The system is similar to that of a hybrid-electric vehicle in that braking energy is harnessed and stored to assist the engine as needed during acceleration.
Many land and water vehicles use human power combined with a further power source. Common are parallel hybrids, e.g. a sailboat with oars, motorized bicycles or a human-electric hybrid vehicle such as the Twike . Some series hybrids exist. Such vehicles can be tribrid vehicles , combining three power sources e.g. on-board solar cells, grid-charged batteries and pedals.
Hybrid vehicles can be used in different modes. The figure shows some typical modes for a parallel hybrid configuration.
P stands for Position. If there are multiple electric motors in different locations, may be written as P1 + P3 or P0 + P2.5 + P4.
Location of electric motor(s) in drivetrain:
Often, an aftermarket powertrain can be added to a vehicle. The aftermarket solution is used when the user delivers glider ( rolling chassis ) and the hybrid (two engines) or all-electric (only an electric motor) powertrain kit to the automaker and receives the vehicle with the tech installed. An (electric or hybrid) powertrain can be added to a glider [ 78 ] by an aftermarket installer.
In 2013 a University of Central Florida design team, On the Green , worked to develop a bolt-on hybrid conversion kit to transform an older model vehicle into a gas-electric hybrid. [ 79 ]
A conversion of a 1966 Mustang was demonstrated by an engineer in California. The system replaced the alternator with a 12 kW (30 kW peak) brushless electric motor. Gas mileage and power improved. [ 80 ]
There are hub motors that can be fitted in the wheel, [ 81 ] or between the wheel and brake rotor [ 82 ] of internal combustion vehicles to convert them to hybrid individual wheel drive (IWD). | https://en.wikipedia.org/wiki/Hybrid_vehicle_drivetrain |
A hybridization assay comprises any form of quantifiable hybridization i.e. the quantitative annealing of two complementary strands of nucleic acids , known as nucleic acid hybridization . [ 1 ]
In the context of biochemistry and drug development, a hybridization assay is a type of Ligand Binding Assay (LBA) used to quantify nucleic acids in biological matrices. Hybridization assays can be in solution or on a solid support such as 96-well plates or labelled beads.
Hybridization assays involve labelled nucleic acid probes to identify related DNA or RNA molecules (i.e. with significantly high degree of sequence similarity) within a complex mixture of unlabelled nucleic acid molecules. Antisense therapy , siRNA , and other oligonucleotide and nucleic acid based biotherapeutics can be quantified with hybridization assays.
Signalling of hybridization methods can be performed using oligonucleotide probes modified in-synthesis with haptens and small molecule ligands which act homologous to the capture and detection antibodies. As with traditional ELISA , conjugates to horse radish peroxidase (HRP) or alkaline phosphatase (AP) can be used as secondary antibodies.
In the sandwich hybridization ELISA assay format, the antigen ligand and antibodies in ELISA are replaced with a nucleic acid analyte, complementary oligonucleotide capture and detection probes. [ 2 ]
Generally, in the case of nucleic acid hybridization, monovalent salt concentration and temperature are controlled for hybridization and wash stringency, contrary to a traditional ELISA, where the salt concentration will usually be fixed for the binding and wash steps (i.e. PBS or TBS). Thus, optimal salt concentration in hybridization assays varies dependent upon the length and base composition of the analyte, capture and detection probes.
The competitive hybridization assay [ 3 ] is similar to a traditional competitive immunoassay . Like other hybridization assays, it relies on complementarity, where the capture probe competes between the analyte and the tracer–a labelled oligonucleotide analog to the analyte.
In the hybridization-ligation assay [ 4 ] [ 5 ] a template probe replaces the capture probe in the sandwich assay for immobilization to the solid support. The template probe is fully complementary to the oligonucleotide analyte and is intended to serve as a substrate for T4 DNA ligase -mediated ligation. The template probe has in addition an additional stretch complementary to a ligation probe so that the ligation probe will ligate onto the 3'-end of the analyte. Albeit generic, the ligation probe is similar to a detection probe in that it is labelled with, for example, digoxigenin for downstream signalling. Stringent, low/no salt wash will remove un-ligated products.
The ligation of the analyte to the ligation probe makes the method specific for the 3'-end of the analyte, ligation by T4 DNA ligase being much less efficient over a bulge loop, which would happen for a 3' metabolite N-1 version of the analyte, for example. The specificity of the hybridization-ligation assay for ligation at the 3'-end is particularly relevant because the predominant nucleases in blood are 3' to 5' exonucleases .
One limitation of the method is that it requires a free 3'-end hydroxyl which may not be available when targeting moieties are attached to the 3'-end, for example. Further, more exotic nucleic acid chemistries with oligonucleotide drugs may impact upon the activity of the ligase, which needs to be determined on a case-by-case basis.
The dual ligation hybridization assay (DLA) [ 6 ] extends the specificity of the hybridization-ligation assay to a specific method for the parent compound. Despite hybridization-ligation assay's robustness, sensitivity and added specificity for the 3'-end of the oligonculeotide analyte, the hybridization-ligation assay is not specific for the 5' end of the analyte.
The DLA is intended to quantify the full-length, parent oligonucleotide compound only, with both intact 5' and 3' ends. DLA probes are ligated at the 5' and 3' ends of the analyte by the joint action of T4 DNA ligase and T4 polynucleotide kinase . The kinase phosphorylates the 5'-end of the analyte and the ligase will join the capture probe to the analyte to the detection probe. The capture and detection probes in the DLA can thus be termed ligation probes. As for the hybridization-ligation assay, the DLA is specific for the parent compound because the efficiency of ligation over a bulge loop is low, and thus the DLA detects the full-length analyte with both intact 5' and 3'-ends. The DLA can also be used for the determination of individual metabolites in biological matrices.
The limitations with the hybridization-ligation assay also apply to the dual ligation assay, with the 5'-end in addition to the 3'-end requiring to have a free hydroxyl (or a phosphate group). Further, T4 DNA ligases are incompatible with ligation of RNA molecules as a donor (i.e. RNA at the 5' end of the ligation). Therefore, second generation antisense that comprise 2'-O-methyl RNA, 2'-O-methoxyethyl or locked nucleic acids may not be compatible with the dual ligation assay.
The nuclease hybridization assay, [ 7 ] [ 8 ] also called S1 nuclease cutting assay, is a nuclease protection assay -based hybridization ELISA. The assay is using S1 nuclease , which degrades single-stranded DNA and RNA into oligo- or mononucleotides, leaving intact double-stranded DNA and RNA.
In the nuclease hybridization assay, the oligonucleotide analyte is captured onto the solid support such as a 96-well plate via a fully complementary cutting probe. After enzymatic processing by S1 nuclease, the free cutting probe and the cutting probe hybridized to metabolites, i.e. shortmers of the analyte are degraded, allowing signal to be generated only from the full-length cutting probe-analyte duplex.
The assay is well tolerant to diverse chemistries, as exemplified by the development of a nuclease assay for morpholino oligonucleotides. [ 9 ]
This assay set-up can lack robustness and is not suitable for validation following the FDA's guidelines for bioanalytical method validation . This is demonstrated by an absence of published method that have been validated to the standards outlined by the FDA for bioanalytical methods. | https://en.wikipedia.org/wiki/Hybridization_assay |
In molecular biology , a hybridization probe ( HP ) is a fragment of DNA or RNA , usually 15–10000 nucleotides long, which can be radioactively or fluorescently labeled . HPs can be used to detect the presence of nucleotide sequences in analyzed RNA or DNA that are complementary to the sequence in the probe. [ 1 ] The labeled probe is first denatured (by heating or under alkaline conditions such as exposure to sodium hydroxide ) into single stranded DNA (ssDNA) and then hybridized to the target ssDNA ( Southern blotting ) or RNA ( northern blotting ) immobilized on a membrane or in situ .
To detect hybridization of the probe to its target sequence, the probe is tagged (or "labeled") with a molecular marker of either radioactive or (more recently) fluorescent molecules. Commonly used markers are 32 P (a radioactive isotope of phosphorus incorporated into the phosphodiester bond in the probe DNA), digoxigenin , a non-radioactive, antibody -based marker, biotin or fluorescein. DNA sequences or RNA transcripts that have moderate to high sequence similarity to the probe are then detected by visualizing the hybridized probe via autoradiography or other imaging techniques. Normally, either X-ray pictures are taken of the filter, or the filter is placed under UV light. Detection of sequences with moderate or high similarity depends on how stringent the hybridization conditions were applied—high stringency, such as high hybridization temperature and low salt in hybridization buffers, permits only hybridization between nucleic acid sequences that are highly similar, whereas low stringency, such as lower temperature and high salt, allows hybridization when the sequences are less similar.
Hybridization probes used in DNA microarrays refer to DNA covalently attached to an inert surface, such as coated glass slides or gene chips , to which a mobile cDNA target is hybridized. Depending on the method , the probe may be synthesized using the phosphoramidite method, or it can be generated and labeled by PCR amplification or cloning (both are older methods). In order to increase the in vivo stability of the probe RNA is not used. Instead, RNA analogues may be used, in particular morpholino - derivatives. Molecular DNA- or RNA-based probes are routinely used in screening gene libraries, detecting nucleotide sequences with blotting methods , and in other gene technologies, such as nucleic acid and tissue microarrays .
Within the field of microbial ecology , oligonucleotide probes are used in order to determine the presence of microbial species, genera, or microorganisms classified on a more broad level, such as bacteria , archaea , and eukaryotes via fluorescence in situ hybridization (FISH). [ 2 ] rRNA probes have enabled scientists to visualize microorganisms, yet to be cultured in laboratory settings, by retrieval of rRNA sequences directly from the environment. [ 3 ] Examples of these types of microorganisms include:
In some instances, differentiation between species may be problematic when using 16S rRNA sequences due to similarity. In such instances, 23S rRNA may be a better alternative. [ 6 ] The global standard library of rRNA sequences is constantly becoming larger and continuously being updated, and thus the possibility of a random hybridization event between a specifically-designed probe (based on complete and current data from a range of test organisms) and an undesired/unknown target organism cannot be easily dismissed. [ 7 ] On the contrary, it is plausible that there exist microorganisms, yet to be identified, which are phylogenetically members of a probe target group, but have partial or near-perfect target sites, usually applies when designing group-specific probes.
Probably the greatest practical limitation to this technique is the lack of available automation. [ 8 ]
In forensic science, hybridization probes are used, for example, for detection of short tandem repeats ( microsatellite ) regions [ 9 ] and in restriction fragment length polymorphism ( RFLP ) methods, all of which are widely used as part of DNA profiling analysis. | https://en.wikipedia.org/wiki/Hybridization_probe |
Hybridoma technology is a method for producing large quantities of monoclonal antibodies by fusing antibody producing B cells with myeloma cells (cancerous B cells). This creates hybrid cells, hybridomas, that produce the antibody from their parent B cell whilst maintaining the properties of the parental myeloma cell line being immortal (endlessly reproducing) and having desirable properties for cell culture . The B cells to be used are generally gathered from animals who have been immunized with an antigen against which an antibody targeting it is desired.
After forming hybridomas any non-hybrid cells are killed before screening and monoclonalization to create hybridoma lines that are derived from one parental cell and thus producing the same antibody against the desired target.
The production of monoclonal antibodies was invented by César Milstein and Georges J. F. Köhler in 1975. They shared the Nobel Prize of 1984 for Medicine and Physiology with Niels Kaj Jerne , who made other contributions to immunology. The term hybridoma was coined by Leonard Herzenberg during his sabbatical in Milstein's laboratory in 1976–1977. [ 1 ]
Laboratory animals ( mammals , e.g. mice) are first exposed to the antigen against which an antibody is to be generated. Usually this is done by a series of injections of the antigen in question, over the course of several weeks. These injections are typically followed by the use of in vivo electroporation , which significantly enhances the immune response. Once splenocytes are isolated from the mammal's spleen , the B cells are fused with immortalised myeloma cells. The fusion of the B cells with myeloma cells can be done using electrofusion. Electrofusion causes the B cells and myeloma cells to align and fuse with the application of an electric field. Alternatively, the B-cells and myelomas can be made to fuse by chemical protocols, most often using polyethylene glycol . The myeloma cells are selected beforehand to ensure they are not secreting antibody themselves and that they lack the hypoxanthine-guanine phosphoribosyltransferase (HGPRT) gene, making them sensitive (or vulnerable) to the HAT medium (see below).
Fused cells are incubated in HAT medium ( hypoxanthine - aminopterin - thymidine medium) for roughly 10 to 14 days. Aminopterin blocks the pathway that allows for nucleotide synthesis. Hence, unfused myeloma cells die, as they cannot produce nucleotides by the de novo or salvage pathways because they lack HGPRT. Removal of the unfused myeloma cells is necessary because they have the potential to outgrow other cells, especially weakly established hybridomas. Unfused B cells die as they have a short life span. In this way, only the B cell-myeloma hybrids survive, since the HGPRT gene coming from the B cells is functional. These cells produce antibodies (a property of B cells) and are immortal (a property of myeloma cells). The incubated medium is then diluted into multi-well plates to such an extent that each well contains only one cell. Since the antibodies in a well are produced by the same B cell, they will be directed towards the same epitope, and are thus monoclonal antibodies.
The next stage is a rapid primary screening process, which identifies and selects only those hybridomas that produce antibodies of appropriate specificity. The first screening technique used is called ELISA . The hybridoma culture supernatant, secondary enzyme labeled conjugate, and chromogenic substrate, are then incubated, and the formation of a colored product indicates a positive hybridoma. Alternatively, immunocytochemical, [ 2 ] western blot , and immunoprecipitation-mass spectrometry. Unlike western blot assays, immunoprecipitation-mass spectrometry facilitates screening and ranking of clones which bind to the native (non-denaturated) forms of antigen proteins. [ 3 ] Flow cytometry screening has been used for primary screening of a large number (~1000) of hybridoma clones recognizing the native form of the antigen on the cell surface. [ 4 ] In the flow cytometry-based screening, a mixture of antigen-negative cells and antigen-positive cells is used as the antigen to be tested for each hybridoma supernatant sample. [ 4 ]
The B cell that produces the desired antibodies can be cloned to produce many identical daughter clones. Supplemental media containing interleukin-6 (such as briclone ) are essential for this step. Once a hybridoma colony is established, it will continually grow in culture medium like RPMI-1640 (with antibiotics and fetal bovine serum) and produce antibodies. [ 2 ]
Multiwell plates are used initially to grow the hybridomas, and after selection, are changed to larger tissue culture flasks. This maintains the well-being of the hybridomas and provides enough cells for cryopreservation and supernatant for subsequent investigations. The culture supernatant can yield 1 to 60 μg/ml of monoclonal antibody, which is maintained at -20 °C or lower until required. [ 2 ]
By using culture supernatant or a purified immunoglobulin preparation, further analysis of a potential monoclonal antibody producing hybridoma can be made in terms of reactivity, specificity, and cross-reactivity. [ 2 ]
The use of monoclonal antibodies is numerous and includes the prevention, diagnosis, and treatment of disease. For example, monoclonal antibodies can distinguish subsets of B cells and T cells , which is helpful in identifying different types of leukaemias . In addition, specific monoclonal antibodies have been used to define cell surface markers on white blood cells and other cell types. This led to the cluster of differentiation series of markers. These are often referred to as CD markers and define several hundred different cell surface components of cells, each specified by binding of a particular monoclonal antibody. Such antibodies are extremely useful for fluorescence-activated cell sorting , the specific isolation of particular types of cells.
With the help of monoclonal antibodies, tissues and organs can be classified based on their expression of certain defined markers, which reflect tissue or cellular genesis. Prostate specific antigen , placental alkaline phosphatase , human chorionic gonadotrophin , α-fetoprotein and others are organ-associated antigens and the production of monoclonal antibodies against these antigens helps in determining the nature of a primary tumor. [ 2 ]
Monoclonal antibodies are especially useful in distinguishing morphologically similar lesions, like pleural and peritoneal mesothelioma , adenocarcinoma , and in the determination of the organ or tissue origin of undifferentiated metastases . Selected monoclonal antibodies help in the detection of occult metastases ( cancer of unknown primary origin ) by immuno-cytological analysis of bone marrow, other tissue aspirates, as well as lymph nodes and other tissues and can have increased sensitivity over normal histopathological staining . [ 2 ]
One study [ 5 ] performed a sensitive immuno-histochemical assay on bone marrow aspirates of 20 patients with localized prostate cancer. Three monoclonal antibodies (T16, C26, and AE-1), capable of recognizing membrane and cytoskeletal antigens expressed by epithelial cells to detect tumour cells, were used in the assay. Bone marrow aspirates of 22% of patients with localized prostate cancer (stage B, 0/5; Stage C, 2/4), and 36% patients with metastatic prostate cancer (Stage D1, 0/7 patients; Stage D2, 4/4 patients) had antigen-positive cells in their bone marrow. It was concluded that immuno-histochemical staining of bone marrow aspirates are very useful to detect occult bone marrow metastases in patients with apparently localized prostate cancer.
Although immuno-cytochemistry using tumor-associated monoclonal antibodies has led to an improved ability to detect occult breast cancer cells in bone marrow aspirates and peripheral blood, further development of this method is necessary before it can be used routinely. [ 6 ] One major drawback of immuno-cytochemistry is that only tumor-associated and not tumor-specific monoclonal antibodies are used, and as a result, some cross-reaction with normal cells can occur. [ 7 ]
In order to effectively stage breast cancer and assess the efficacy of purging regimens prior to autologous stem cell infusion, it is important to detect even small quantities of breast cancer cells. Immuno-histochemical methods are ideal for this purpose because they are simple, sensitive, and quite specific. Franklin et al. [ 8 ] performed a sensitive immuno-cytochemical assay by using a combination of four monoclonal antibodies (260F9, 520C9, 317G5 and BrE-3) against tumor cell surface glycoproteins to identify breast tumour cells in bone marrow and peripheral blood. They concluded from the results that immuno-cytochemical staining of bone marrow and peripheral blood is a sensitive and simple way to detect and quantify breast cancer cells.
One of the main reasons for metastatic relapse in patients with solid tumours is the early dissemination of malignant cells. The use of monoclonal antibodies (mAbs) specific for cytokeratins can identify disseminated individual epithelial tumor cells in the bone marrow.
One study [ 9 ] reports on having developed an immuno-cytochemical procedure for simultaneous labeling of cytokeratin component no. 18 (CK18) and prostate specific antigen (PSA). This would help in the further characterization of disseminated individual epithelial tumor cells in patients with prostate cancer. The twelve control aspirates from patients with benign prostatic hyperplasia showed negative staining, which further supports the specificity of CK18 in detecting epithelial tumour cells in bone marrow.
In most cases of malignant disease complicated by effusion, neoplastic cells can be easily recognized. However, in some cases, malignant cells are not so easily seen or their presence is too doubtful to call it a positive report. The use of immuno-cytochemical techniques increases diagnostic accuracy in these cases.
Ghosh, Mason and Spriggs [ 10 ] analysed 53 samples of pleural or peritoneal fluid from 41 patients with malignant disease. Conventional cytological examination had not revealed any neoplastic cells. Three monoclonal antibodies (anti-CEA, Ca 1 and HMFG-2) were used to search for malignant cells. Immunocytochemical labelling was performed on unstained smears, which had been stored at -20 °C up to 18 months. Twelve of the forty-one cases in which immuno-cytochemical staining was performed, revealed malignant cells. The result represented an increase in diagnostic accuracy of approximately 20%. The study concluded that in patients with suspected malignant disease, immuno-cytochemical labeling should be used routinely in the examination of cytologically negative samples and has important implications with respect to patient management.
Another application of immuno-cytochemical staining is for the detection of two antigens in the same smear. Double staining with light chain antibodies and with T and B cell markers can indicate the neoplastic origin of a lymphoma. [ 11 ]
One study has reported the isolation of a hybridoma cell line (clone 1E10), which produces a monoclonal antibody (IgM, k isotype). This monoclonal antibody shows specific immuno-cytochemical staining of nucleoli. [ 12 ]
Tissues and tumours can be classified based on their expression of certain markers, with the help of monoclonal antibodies. They help in distinguishing morphologically similar lesions and in determining the organ or tissue origin of undifferentiated metastases. Immuno-cytological analysis of bone marrow, tissue aspirates, lymph nodes etc. with selected monoclonal antibodies help in the detection of occult metastases. Monoclonal antibodies increase the sensitivity in detecting even small quantities of invasive or metastatic cells. Monoclonal antibodies (mAbs) specific for cytokeratins can detect disseminated individual epithelial tumour cells in the bone marrow. | https://en.wikipedia.org/wiki/Hybridoma_technology |
Hybrizyme is a term coined to indicate novel or normally rare gene variants (or alleles ) that are associated with hybrid zones , geographic areas where two related taxa (e.g. species or subspecies ) meet, mate, and produce hybrid offspring. [ 1 ] The hybrizyme phenomenon is widespread and these alleles occur commonly, if not in all hybrid zones. [ 2 ] Initially considered to be caused by elevated rates of mutation in hybrids, the most probable hypothesis infers that they are the result of negative (purifying) selection . Namely, in the center of the hybrid zone, negative selection purges alleles against hybrid disadvantage (e.g. hybrid inviability or infertility). Stated differently, any allele that will decrease reproductive isolation is favored and any linked alleles (genetic markers) also increase their frequency by genetic hitchhiking . If the linked alleles used to be rare variants in the parental taxa, they will become more common in the area where the hybrids are formed. [ 3 ]
Originally hybrizymes were defined as "unexpected allelic electromorphs associated with hybrid zones", a formal term proposed by renowned conservation geneticist and biogeographer David S. Woodruff in 1988. [ 1 ] By suggesting a new definition for a phenomenon that had been previously widely observed Woodruff's interpretation bypasses the etiological connotation of alternative terms and avoids inappropriate context. Namely, previous studies referred to allozymes that were observed at high frequency in hybrid zones, but are absent or rare in parental taxa as "the rare allele phenomenon". [ 2 ] [ 4 ] [ 5 ] These alleles can have increased frequencies up to a point of the allele becoming the most common one in the hybrid zone, rendering the term "the rare allele phenomenon" deceptive. Despite this, these two terms have been used interchangeably in literature.
Hybrid populations display the hybrizyme phenomenon by having increased frequencies of certain alleles that are rare or non-existent outside of the hybrid zone. The hybrizyme phenomenon is widespread in hybrid zones of species of snails, crickets, lizards, salamanders, rodents, fish and birds. [ 1 ] Intriguingly, the increased frequency of some of these alleles can have a pronounced effect making them 3-20 times more common in hybrids than in non-hybrid populations. [ 6 ]
Early studies focused on detecting electromorphs for loci that code regulatory and non-regulatory enzymes from several functional classes using allozyme electrophoresis and usually involved loci that were polymorphic in parental populations. The phenomenon has also been detected in a broad range of genetic markers such as intron haplotypes, [ 3 ] microsatellites, [ 7 ] ribosomal DNA spacer variants, [ 8 ] and anonymous SNPs. [ 9 ]
Multiple hypotheses have been proposed to explain the mutational (molecular) origin of hybrizymes. They include gene conversion, [ 10 ] transposable element activity, [ 11 ] post-translational modification, mutations. [ 12 ] [ 13 ] [ 14 ] [ 1 ] and intragenic recombination. Some of these hypotheses are rejected by research in the past couple of years, but there is an unambiguous explanation for the mutational origin of hybrizymes. The two hypotheses most often discussed are increased mutation rates and intragenic recombination.
Under the mutational hypothesis, hybrizymes likely arise due to simple point mutations. Sequencing data have indicated this and imply low likelihood that hybrizymes arise as a result of transposition or recombination. Research on pocket gophers and Japanese freshwater crabs confirms that the phenomenon is possibly caused by simple nucleotide substitutions . [ 13 ] [ 12 ] [ 15 ] [ 16 ] However, the hypothesis has several weaknesses. It does not explain why normally rare alleles are restricted to a hybrid zone, why polymorphic loci are affected more or offers a mechanism that explains the high frequency of even the rarest variants. [ 1 ]
Intragenic recombination, under certain circumstances, might create new allelic variants at rates higher than the ones associated with regular mutational processes. Under this hypothesis the variant allele would be a mosaic of the parental alleles. The likelihood of this hypothesis was disputed, through sequencing studies. [ 14 ] [ 13 ] [ 17 ] Although there is yet no specific explanation for hybrizymes, it is not excluded that hybrizymes are generated by the combined effect of recombination and mutation events, with any recombination trace concealed by succeeding mutations. However, research on Acer species implies that high recombination rates are possible due to acceleration of genetic variation after hybridization. [ 8 ] Furthermore, results are found that indicate that recurrent mutation is unlikely and that support the hypothesis of recombination. [ 18 ]
Several hypotheses have been proposed to account the high frequency of hybrizymes in hybrid zones such as genetic drift, elevated rates of nucleotide substitutions. [ 1 ] [ 2 ] [ 19 ] [ 20 ] or positive selection on alleles which are mildly deleterious in parental taxa. Still, some faced a certain degree of unpredictability; specifically under the mutational hypothesis the overall substitution rates are elevated and many variants are expected versus having only one allele reaching high frequency and, at the same time, positive selection on deleterious alleles seems ambiguous.
Selection does not need to be directed to the hybrizyme, but to other genes with which the hybrizyme is linked, placing genetic hitchhiking in perspective. In other words, hybrid zones are maintained primarily by balance between gene flow and hybrid inferiority. In the centre of hybrid zones, the process of constant creation of low-fitness recombinant genotypes will favor any allele that will decrease reproductive isolation, consequently elevating the hybrid fitness. So, a likely mechanism would be negative or purifying selection against poorly fit multilocus genotypes. Therefore, the hybrizymes that increase in frequency could be modifier alleles or genetic markers that increase via hitchhiking. [ 21 ] It is not excluded that the targets of selection are the barrier loci, loci that resist homogenization with the other genome during gene flow among diverging species, making them the most different parts of the genome between divergent populations. [ 22 ]
If allelic variation at these loci is considered, there might be alleles that have differential effect on reproductive isolation or hybrid disadvantage, leading to selection of those who have lower severity. [ 21 ] The exact origin and mechanism that maintains these alleles at a high frequency is still a subject of debate and additional studies, such as Next Generation Sequencing analysis of the genomic regions involved in the phenomenon as a more trustworthy pathway to identify genes that impact the level of reproductive isolation. [ 9 ]
Hybridization might expand the prospect of adaptive radiation to the point where positive selection on recombinant hybrid genotypes surpasses the intrinsic selection against them. Therefore, the selection schemes in hybrid swarms ensures that relatively strong endogenous selection would not quench such potential. [ 23 ] Additionally, partial postzygotic reproductive isolation usually involves multiple genes and segregation and recombination of genes creates broadly varying reproductive compatibility in hybrid populations. Consequently, there will be recurrent removal of disadvantageous alleles for reproductive isolation and relative stabilization of hybrid zones, possibly slowing down the path of complete speciation by reinforcement. [ 24 ] [ 25 ]
With the continual selection against hybrid disadvantage, crossing-over might, over time, interrupt existing linkages and establish new. This generates a shift in selection pressure on loci which are in linkage with these genes and will contribute to further changes in allele frequencies on a genome scale. [ 9 ] The "rare allele phenomenon" might be an indication of this process. Even with the continuous effect of relatively strong endogenous selection against hybrids, a hybrid population might be an example where selection against reproductive isolation results in creating variable recombinant genotypes. [ 24 ] Sometimes, this phenomenon might assist in creating a complex of adaptive traits that lead to adaptive novelty. | https://en.wikipedia.org/wiki/Hybrizyme |
A hyclate ( Latin : hyclas ) is a pharmaceutical term for hydrochloride hemiethanolate hemihydrate [ 1 ] [ 2 ] (· HCl · 1 / 2 EtOH · 1 / 2 H 2 O ), e.g. doxycycline hyclate. [ 3 ] [ 4 ]
This article about a salt (chemistry) is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hyclate |
In mathematics, specifically in graph theory and number theory , a hydra game is a single-player iterative mathematical game played on a mathematical tree called a hydra where, usually, the goal is to cut off the hydra's "heads" while the hydra simultaneously expands itself. Hydra games can be used to generate large numbers or infinite ordinals or prove the strength of certain mathematical theories. [ 1 ]
Unlike their combinatorial counterparts like TREE and SCG , no search is required to compute these fast-growing function values – one must simply keep applying the transformation rule to the tree until the game says to stop.
A simple hydra game can be defined as follows:
Even though the hydra may grow by an unbounded number n {\displaystyle n} of leaves at each turn, the game will eventually end in finitely many steps: if d {\displaystyle d} is the greatest distance between the root and the leaf, and w {\displaystyle w} the number of leaves at this distance, induction on d {\displaystyle d} can be used to demonstrate that the player will always kill the hydra. If d = 1 {\displaystyle d=1} , removing the leaves can never cause the hydra to grow, so the player wins after w {\displaystyle w} turns. For general d {\displaystyle d} , we consider two kinds of moves: those that involve a leaf at a distance less than d {\displaystyle d} from the root, and those that involve a leaf at a distance of exactly d {\displaystyle d} . Since moves of the first kind are also identical to moves in a game with depth d − 1 {\displaystyle d-1} , the induction hypothesis tells us that after finitely many such moves, the player will have no choice but to choose a leaf at depth d {\displaystyle d} . No move introduces new nodes at this depth, so this entire process can only repeat up to w {\displaystyle w} times, after which there are no more leaves at depth d {\displaystyle d} and the game now has depth (at most) d − 1 {\displaystyle d-1} . Invoking the induction hypothesis again, we find that the player must eventually win overall.
While this shows that the player will win eventually, it can take a very long time. As an example, consider the following algorithm. Pick the rightmost leaf (i.e., the newest leaf which will be on the level closest to the root) and set n = 1 {\displaystyle n=1} the first time, 2 {\displaystyle 2} the second time, and so on, always increasing n {\displaystyle n} by one. If a hydra has a single y {\displaystyle y} -length branch, then for y = 1 {\displaystyle y=1} , the hydra is killed in a single step, while it is killed in three steps if y = 2 {\displaystyle y=2} . There are 11 steps required for y = 3 {\displaystyle y=3} . There are 1114111 steps required for y = 4 {\displaystyle y=4} . [ 2 ] y = 5 {\displaystyle y=5} has been calculated exactly. [ 3 ] Let F ( x ) = 2 x ⋅ ( x + 2 ) − 1 {\displaystyle F(x)=2^{x}\cdot (x+2)-1} and F n ( x ) {\displaystyle F^{n}(x)} to be F {\displaystyle F} nested n times. Then H Y D R A ( 5 ) = 2 ⋅ F F 2 ( 3 ) + 1 ( F 2 ( 3 ) + 1 ) + 1 = 2 ⋅ F 22539988369408 ( 22539988369408 ) + 1 {\displaystyle HYDRA(5)=2\cdot F^{F^{2}(3)+1}(F^{2}(3)+1)+1=2\cdot F^{22539988369408}(22539988369408)+1} .
The general solution to the hydra game is as follows: [ 4 ]
Let F i ( x ) {\displaystyle F_{i}(x)} denote the number of steps required to decrement a head of depth n when the heads closer to the roots are all singular (no further "right" branches).
Then F i + 1 ( x ) = F i x ( x + 1 ) {\displaystyle F_{i+1}(x)=F_{i}^{x}(x+1)} and F 1 ( x ) = 2 ⋅ ( x + 1 ) − 1 = 2 x + 1 {\displaystyle F_{1}(x)=2\cdot (x+1)-1=2x+1} .
The answer to h y d r a ( n ) {\displaystyle hydra(n)} is: F 1 ( F 2 ( F 3 ( … F n − 1 ( F n ( 1 ) ) … ) ) ) {\displaystyle F_{1}(F_{2}(F_{3}(\ldots F_{n-1}(F_{n}(1))\ldots )))}
The growth rate of this function is faster than the standard fast-growing hierarchy , as F i ( x ) {\displaystyle F_{i}(x)} alone grows at the rate of the fast-growing hierarchy , and the solution is the nth nesting of F i ( x ) {\displaystyle F_{i}(x)} .
The Kirby–Paris hydra is defined by altering the fourth rule of the hydra defined above.
4 KP : Assume b {\displaystyle b} is the parent of a {\displaystyle a} if a ≠ R {\displaystyle a\neq R} . Attach n {\displaystyle n} copies of the subtree with root a {\displaystyle a} to b {\displaystyle b} to the right of all other nodes connected to b {\displaystyle b} . Return to stage 2. [ 5 ]
Instead of adding only new leaves, this rule adds duplicates of an entire subtree. Keeping everything else the same, this time y = 1 {\displaystyle y=1} requires 1 {\displaystyle 1} turn, y = 2 {\displaystyle y=2} requires 3 {\displaystyle 3} steps, y = 3 {\displaystyle y=3} requires 37 {\displaystyle 37} steps and y = 4 {\displaystyle y=4} requires more steps than Graham's number . This functions growth rate is massive , equal to f ε 0 ( n ) {\displaystyle f_{\varepsilon _{0}}(n)} in the fast-growing hierarchy.
This is not the most powerful hydra. The Buchholz hydra is a more potent hydra. [ 6 ] It entails a labelled tree. The root has a unique label (call it R {\displaystyle R} ), and each other node has a label that is either a non-negative integer or ω {\displaystyle \omega } . [ 7 ]
Surprisingly, even though the hydra can grow enormously taller, this sequence always ends. [ 9 ]
For Kirby–Paris hydras, the rules are simple: start with a hydra, which is an unordered unlabelled rooted tree T {\displaystyle T} . At each stage, the player chooses a leaf node c {\displaystyle c} to chop and a non-negative integer n {\displaystyle n} . If c {\displaystyle c} is a child of the root r {\displaystyle r} , it is removed from the tree and nothing else happens that turn. Otherwise, let p {\displaystyle p} be c {\displaystyle c} 's parent, and g {\displaystyle g} be p {\displaystyle p} 's parent. Remove c {\displaystyle c} from the tree, then add n {\displaystyle n} copies of the modified p {\displaystyle p} as children to g {\displaystyle g} . The game ends when the hydra is reduced to a single node.
To obtain a fast-growing function, we can fix n {\displaystyle n} , say, n = 1 {\displaystyle n=1} at the first step, then n = 2 {\displaystyle n=2} , n = 3 {\displaystyle n=3} , and so on, and decide on a simple rule for where to cut, say, always choosing the rightmost leaf. Then, Hydra ( k ) {\displaystyle \operatorname {Hydra} (k)} is the number of steps needed for the game to end starting with a path of length k {\displaystyle k} , that is, a linear stack of k + 1 {\displaystyle k+1} nodes. Hydra ( k ) {\displaystyle \operatorname {Hydra} (k)} eventually dominates all recursive functions which are provably total in Peano arithmetic, and is itself provably total in P A + ( ε 0 is well-ordered ) {\displaystyle \mathrm {PA} +(\varepsilon _{0}{\text{ is well-ordered}})} . [ 10 ]
This could alternatively expressed using strings of brackets:
For example, with n = 3 {\displaystyle n=3} , ( ( ) ( ( ) ( ) ) ) ⟹ ( ( ) ( ( ) ) ( ( ) ) ( ( ) ) ( ( ) ) ) {\displaystyle (()(()\mathbf {()} ))\implies (()(())(())(())(()))} . Next is a list of values of Hydra ( k ) {\displaystyle \operatorname {Hydra} (k)} :
The Buchholz hydra game is a hydra game in mathematical logic, a single player game based on the idea of chopping pieces off a mathematical tree. The hydra game can be used to generate a rapidly growing function B H ( n ) {\displaystyle BH(n)} , which eventually dominates all provably total recursive functions. It is an extension of Kirby-Paris hydras. What we use to obtain a fast-growing function is the same as Kirby-Paris hydras, but because Buchholz hydras grow not only in width but also in height, B H ( n ) {\displaystyle BH(n)} has a much greater growth rate of f ψ 0 ( ε Ω ω + 1 ) ( n ) {\displaystyle f_{\psi _{0}(\varepsilon _{\Omega _{\omega }+1})}(n)} :
This system can also be used to create an ordinal notation for infinite ordinals, e.g. ψ 0 ( Ω ω ) = + 0 ( ω ) {\displaystyle \psi _{0}(\Omega _{\omega })=+0(\omega )} .
This article incorporates text by Komi Amiko available under the CC BY 4.0 license. | https://en.wikipedia.org/wiki/Hydra_game |
A hydrant is an outlet from a fluid main often consisting of an upright pipe with a valve attached, from which fluid (e.g. water or fuel ) can be tapped.
Depending on the fluid involved, the term may refer to: | https://en.wikipedia.org/wiki/Hydrant |
Hydrastine is an isoquinoline alkaloid which was discovered in 1851 by Alfred P. Durand . [ 1 ] Nitric acid induced hydrolysis of hydrastine yields hydrastinine , which was patented by Bayer as a haemostatic drug in the early 1900's. [ 2 ] It is present in Hydrastis canadensis (thus the name) and other plants of the family Ranunculaceae .
The first attempt for the total synthesis of hydrastine was reported by Sir Robert Robinson and co-workers [ 3 ] in 1931. Following studies [ 4 ] [ 5 ] where the synthesis of the key lactonic amide intermediate (structure 4 in figure) was the most troublesome, the major breakthrough was achieved in 1981 when J. R. Falck and co-workers [ 6 ] reported a four-step total synthesis of hydrastine from simple starting materials. The key step in the Falck synthesis was using a Passerini reaction to construct the lactonic amide intermediate 4.
Starting from a simple phenylbromide variant 1, alkylation reaction with lithium methylisocyanide gives the isocyanide intermediate 2. Reacting isocyanide intermediate 2 with opianic acid 3 initiated the intramolecular Passerini reaction to give the key lactonic amide intermediate 4. The tetrahydro-isoquinolin ring was formed by first a ring-closure reaction under dehydration conditions using POCl3 and then a catalyzed hydrogenation using PtO2 as the catalyst. Finally, hydrastine was synthesized by installing the N-methyl group via reductive amination reaction with formaldehyde . | https://en.wikipedia.org/wiki/Hydrastine |
In chemistry , a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understood.
Hydrates are not inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal " [ 1 ] that are either bound to a metal center or that have crystallized with the metal complex. Such hydrates are also said to contain water of crystallization or water of hydration . If the water is heavy water in which the constituent hydrogen is the isotope deuterium , then the term deuterate may be used in place of hydrate . [ 2 ] [ 3 ]
A colorful example is cobalt(II) chloride , which turns from blue to red upon hydration , and can therefore be used as a water indicator.
The notation " hydrated compound ⋅ n H 2 O ", where n is the number of water molecules per formula unit of the salt, is commonly used to show that a salt is hydrated. The n is usually a low integer , though it is possible for fractional values to occur. For example, in a monohydrate n = 1, and in a hexahydrate n = 6. Numerical prefixes mostly of Greek origin are: [ 4 ]
A hydrate that has lost water is referred to as an anhydride ; the remaining water, if any exists, can only be removed with very strong heating. A substance that does not contain any water is referred to as anhydrous . Some anhydrous compounds are hydrated so easily that they are said to be hygroscopic and are used as drying agents or desiccants .
In organic chemistry, a hydrate is a compound formed by the hydration, i.e. "Addition of water or of the elements of water (i.e. H and OH) to a molecular entity". [ 5 ] For example: ethanol , CH 3 −CH 2 −OH , is the product of the hydration reaction of ethene , CH 2 =CH 2 , formed by the addition of H to one C and OH to the other C, and so can be considered as the hydrate of ethene. A molecule of water may be eliminated, for example, by the action of sulfuric acid . Another example is chloral hydrate , CCl 3 −CH(OH) 2 , which can be formed by reaction of water with chloral , CCl 3 −CH=O .
Many organic molecules, as well as inorganic molecules, form crystals that incorporate water into the crystalline structure without chemical alteration of the organic molecule ( water of crystallization ). The sugar trehalose , for example, exists in both an anhydrous form ( melting point 203 °C) and as a dihydrate (melting point 97 °C). Protein crystals commonly have as much as 50% water content.
Molecules are also labeled as hydrates for historical reasons not covered above. Glucose , C 6 H 12 O 6 , was originally thought of as C 6 (H 2 O) 6 and described as a carbohydrate .
Hydrate formation is common for active ingredients . Many manufacturing processes provide an opportunity for hydrates to form and the state of hydration can be changed with environmental humidity and time. The state of hydration of an active pharmaceutical ingredient can significantly affect the solubility and dissolution rate and therefore its bioavailability . [ 6 ]
Clathrate hydrates (also known as gas hydrates, gas clathrates, etc.) are water ice with gas molecules trapped within; they are a form of clathrate . An important example is methane hydrate (also known as gas hydrate, methane clathrate, etc.).
Nonpolar molecules, such as methane, can form clathrate hydrates with water, especially under high pressure. Although there is no hydrogen bonding between water and guest molecules when methane is the guest molecule of the clathrate, guest–host hydrogen bonding often forms when the guest is a larger organic molecule such as tetrahydrofuran . In such cases, the guest–host hydrogen bonds result in the formation of L-type Bjerrum defects in the clathrate lattice. [ 7 ] [ 8 ]
The stability of hydrates is generally determined by the nature of the compounds, their temperature, and the relative humidity (if they are exposed to air). | https://en.wikipedia.org/wiki/Hydrate |
In chemistry , hydration energy (also hydration enthalpy ) is the amount of energy released when one mole of ions undergoes solvation . Hydration energy is one component in the quantitative analysis of solvation . It is a particular special case of water . [ 1 ] The value of hydration energies is one of the most challenging aspects of structural prediction. [ 2 ] Upon dissolving a salt in water, the cations and anions interact with the positive and negative dipoles of the water. The trade-off of these interactions vs those within the crystalline solid comprises the hydration energy.
If the hydration energy is greater than the lattice energy , then the enthalpy of solution is negative ( heat is released), otherwise it is positive (heat is absorbed). [ 3 ]
The hydration energy should not be confused with solvation energy , which is the change in Gibbs free energy (not enthalpy) as solute in the gaseous state is dissolved. [ 4 ] If the solvation energy is positive, then the solvation process is endergonic ; otherwise, it is exergonic .
For instance, water warms when treated with CaCl 2 (anhydrous calcium chloride ) as a consequence of the large heat of hydration. However, the hexahydrate, CaCl 2 ·6H 2 O cools the water upon dissolution. The latter happens because the hydration energy does not completely overcome the lattice energy, and the remainder has to be taken from the water in order to compensate the energy loss.
The hydration energies of the gaseous Li + , Na + , and Cs + are respectively 520, 405, and 265 kJ/mol. [ 1 ] | https://en.wikipedia.org/wiki/Hydration_energy |
In coordination chemistry , hydration isomerism is a kind of isomerism that is observed in some solids. Hydration isomers have identical formula but differ with respect to the numbers of water ligands .
One example is the pair [CrCl(H 2 O) 5 ]Cl 2 •H 2 O and [Cr(H 2 O) 6 ]Cl 3 . [ 1 ] The former has one water of crystallization but the latter does not.
Another example is the pair of titanium(III) chlorides , [Ti(H 2 O) 6 ]Cl 3 and [Ti(H 2 O) 4 Cl 2 ]Cl(H 2 O) 2 . The former is violet and the latter, with two molecules of water of crystallization, is green. [ 2 ] | https://en.wikipedia.org/wiki/Hydration_isomerism |
The hydration number of a compound is defined as the number of molecules of water bonded to a central ion, often a metal cation. The hydration number is related to the broader concept of solvation number , the number of solvent molecules bonded to a central atom. The hydration number varies with the atom or ion of interest.
In aqueous solution, solutes interact with water molecules to varying degrees. Metal cations form aquo complexes , wherein the oxygen of water bind to the cation. This first coordination sphere is encased in further solvation shells , whereby water bonds to the coordinated water via hydrogen bonding. For charged species , the orientation of water molecules around the solute dependent on its radius and charge, [ 1 ] with cations attracting water’s electronegative oxygen and anions attracting the hydrogens. Uncharged compounds such as methane can also be solvated by water and also have a hydration number. Although solvation shells can contain inner and outer shell solvent-solute interactions, the hydration number generally focuses on the inner shell solvent molecules that directly interact with the solute. Sodium ions
are typically surrounded by 4 to 6 water molecules in their primary hydration shell. This arrangement reflects the ion's charge density and size, leading to strong ion-dipole interactions with water molecules. In contrast, chloride ions generally have a hydration number closer to 6 due to their larger ionic radius and more distributed charge, which allows them to stabilize a larger number of water molecules in their hydration shell.
These hydration characteristics result from the dynamic nature of hydration shells, where water molecules frequently exchange positions between the inner and outer layers, influenced by the strength of ion-water interactions and water-water hydrogen bonding. This behavior has been observed through experimental studies and molecular dynamics simulations. [ 2 ]
A variety of definitions exist for hydration number. One such approach counts the number of water molecules bound to the compound more strongly (by 13.3 kcal/mol or more) than they are bound to other water molecules. [ 3 ] Hydration number estimates are not limited to integer values (for instance, estimates for sodium include 4, 4.6, 5.3, 5.5, 5.6, 6, 6.5, and 8), with some of the spread of estimated values being due to differing detection methods. [ 4 ]
Hydration numbers can be determined by a variety of experimental methods. These include Raman spectroscopy , [ 5 ] neutron and X-ray scattering , [ 6 ] luminescence , [ 7 ] and NMR . [ 8 ] Hydration numbers can change depending on whether the species is locked into a crystall or in solution. The apparent hydration number of a species can vary depending on which experimental method was used. [ 4 ] The hydration number of large alkali metal cations are difficult to characterize. [ 9 ]
NMR is the most informative technique for determining hydration numbers in solution. 1 H and 17 O NMR signals, even for paramagnetic species, can be interpreted to give information on hydration number. Aside from paramagnetism, another complication with NMR is the rate of exchange between bound and unbound water. The second coordination sphere is another aspect to be considered. Finally, ion pairing where the anion enters the solvation shell of the cation must be assessed. [ 10 ]
X-ray crystallography provides definitive information on hydration numbers, especially for cations. Most salts crystallize from water with aquo ligands bonded to the cation. Typical hydration numbers are six for first row transition metal ions and nine for lanthanides. Anions compete with aquo ligands for coordination to the cation. A major question concerns the relationship between structure of such hydrates in the crystal and in aqueous solution. X-ray crystallography provides little insight about the hydration numbers for anions and monocations, much less neutral solutes. In such cases, water is bonded so weakly that crystallization is a major perturbation on stoichiometry.
Ion movement methods involve assessing the resistance to motion hence estimating an effective volume for a solvated ion and from that volume the solvation number. The motion may be from diffusion, mechanically engineered by changes to viscosity or caused by electrical means. Many of these methods give the sum of anion and cation contributions but some can work out values for independent ions. For monoatomic ions, decreasing ionic radius shows decreasing conductivity suggesting that the effective radius of the hydrated ion increases as ionic radius decreases (larger ions are less mobile so their ability to move charge is decreased). Once the mobility of the ions is determined it is possible to estimate diffusion coefficients and from those hydrodynamic radii. The hydrodynamic radii may be used to calculate the number of solvent molecules. [ 11 ]
Even nonpolar entities hydrate and thus can in principle be assigned hydration numbers. For example even methane ( CH 4 ) forms a hydrate called methane clathrate , which are stable under pressure. | https://en.wikipedia.org/wiki/Hydration_number |
In chemistry , a hydration reaction is a chemical reaction in which a substance combines with water . In organic chemistry , water is added to an unsaturated substrate, which is usually an alkene or an alkyne . This type of reaction is employed industrially to produce ethanol , isopropanol , and butan-2-ol . [ 1 ]
Any unsaturated organic compound is susceptible to hydration.
Several million tons of ethylene glycol are produced annually by the hydration of oxirane , a cyclic compound also known as ethylene oxide :
Acid catalysts are typically used. [ 2 ]
The general chemical equation for the hydration of alkenes is the following:
A hydroxyl group (OH − ) attaches to one carbon of the double bond, and a proton (H + ) adds to the other. The reaction is highly exothermic. In the first step, the alkene acts as a nucleophile and attacks the proton, following Markovnikov's rule . In the second step an H 2 O molecule bonds to the other, more highly substituted carbon. The oxygen atom at this point has three bonds and carries a positive charge (i.e., the molecule is an oxonium ). Another water molecule comes along and takes up the extra proton. This reaction tends to yield many undesirable side products, (for example diethyl ether in the process of creating ethanol ) and in its simple form described here is not considered very useful for the production of alcohol.
Two approaches are taken. Traditionally the alkene is treated with sulfuric acid to give alkyl sulphate esters . In the case of ethanol production, this step can be written:
Subsequently, this sulphate ester is hydrolyzed to regenerate sulphuric acid and release ethanol:
This two step route is called the "indirect process".
In the "direct process," the acid protonates the alkene, and water reacts with this incipient carbocation to give the alcohol. The direct process is more popular because it is simpler. The acid catalysts include phosphoric acid and several solid acids . [ 1 ] Here an example reaction mechanism of the hydration of 1-methylcyclohexene to 1-methylcyclohexanol:
Many alternative routes are available for producing alcohols, including the hydroboration–oxidation reaction , the oxymercuration–reduction reaction , the Mukaiyama hydration , the reduction of ketones and aldehydes and as a biological method fermentation .
Acetylene hydrates to give acetaldehyde: [ 3 ] The process typically relies on mercury catalysts and has been discontinued in the West but is still practiced in China. The Hg 2+ center binds to a C≡C bond, which is then attacked by water. The reaction is
Aldehydes and to some extent even ketones, hydrate to geminal diols . The reaction is especially dominant for formaldehyde, which, in the presence of water, exists significantly as dihydroxymethane.
Conceptually similar reactions include hydroamination and hydroalkoxylation , which involve adding amines and alcohols to alkenes.
Nitriles are susceptible to hydration to amides: RCN + H 2 O → RC(O)NH 2 This reaction requires catalysts. Enzymes are used for the commercial production of acrylamide from acrylonitrile . [ citation needed ]
Hydration is an important process in many other applications; one example is the production of Portland cement by the crosslinking of calcium oxides and silicates that is induced by water. Hydration is the process by which desiccants function. | https://en.wikipedia.org/wiki/Hydration_reaction |
Hydraulic Launch Assist ( HLA ) is the name of a hydraulic hybrid regenerative braking system for land vehicles produced by the Eaton Corporation . [ 1 ]
The HLA system recycles energy by converting kinetic energy into potential energy during deceleration via hydraulics , storing the energy at high pressure in an accumulator filled with nitrogen gas . The energy is then returned to the vehicle during subsequent acceleration thereby reducing the amount of work done by the internal combustion engine . This system provides considerable increase in vehicle productivity while reducing fuel consumption in stop-and-go use profiles like refuse vehicles and other heavy duty vehicles. [ 2 ]
The HLA system is called a parallel hydraulic hybrid. In parallel systems the original vehicle drive-line remains, allowing the vehicle to operate normally when the HLA system is disengaged. When the HLA is engaged, energy is captured during deceleration and released during acceleration, in contrast to series hydraulic hybrid systems which replace the entire traditional drive-line to provide power transmission in addition to regenerative braking.
Hydraulic hybrids are said to be power dense , while electric hybrids are energy dense . This means that electric hybrids , while able to deliver large amounts of energy over long periods of time are limited by the rate at which the chemical energy in the batteries is converted to mechanical energy and vice versa . This is largely governed by reaction rates in the battery and current ratings of associated components. Hydraulic hybrids on the other hand are capable of transferring energy at a much higher rate, but are limited by the amount of energy that can be stored. For this reason, hydraulic hybrids lend themselves well to stop-and-go applications and heavy vehicles.
Ford Motor Company included the HLA system in their 2002 F-350 Tonka truck concept vehicle , reported to have lower emissions and better fuel economy than any V-8 diesel truck engine of the time, with HLA designed to eventually improve fuel economy by 25%-35% in heavy truck city driving. [ 3 ]
Eaton, Ford, the US Army, and IMPACT Engineering, Inc. (of Kent, Washington ), built an E-450 shuttle bus as part of the Army's HAMMER (Hydraulic Hybrid Advanced Materials Multifuel Engine Research) project. [ 4 ]
Eaton has been awarded the Texas government’s New Technology Research and Development grant to build 12 refuse vehicles with HLA systems. [ 5 ]
Peterbilt Motors has designed a Model 320 chassis that incorporates the HLA system, [ 6 ] which was featured on the cover of the December 13, 2007, issue of Machine Design . [ 7 ] | https://en.wikipedia.org/wiki/Hydraulic_Launch_Assist |
A hydraulic accumulator is a pressure storage reservoir in which an incompressible hydraulic fluid is held under pressure that is applied by an external source of mechanical energy . The external source can be an engine, a spring , a raised weight , or a compressed gas . [ note 1 ] An accumulator enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand, and to smooth out pulsations. It is a type of energy storage device.
Compressed gas accumulators, also called hydro-pneumatic accumulators, are by far the most common type.
The first accumulators for William Armstrong 's hydraulic dock machinery were simple raised water towers . Water was pumped to a tank at the top of these towers by steam pumps. When dock machinery required hydraulic power, the hydrostatic head of the water's height above ground provided the necessary pressure.
These simple accumulators were extremely tall. For instance, Grimsby Dock Tower , built in 1852, is 309 feet (94 m) tall. Because of their size, they were costly, and so were constructed for less than a decade. Around the same time, John Fowler was working on the construction of the ferry quay at nearby New Holland but could not use similar hydraulic power as the poor ground conditions did not permit a tall accumulator tower to be built. By the time Grimsby was opened, it was already obsolete as Armstrong had developed the more complex, but much smaller, weighted accumulator for use at New Holland. [ 1 ] In 1892 the original Grimsby tower's function was replaced, on Fowler's advice, by a smaller weighted accumulator on an adjacent dock, although the tower remains to this day as a well-known landmark.
Other surviving towers include one adjacent to East Float in Birkenhead , England, and another located at the Bramley-Moore Dock, Liverpool, England. The latter tower is to be renovated as part of plans for the proposed development of the area associated with the construction of a new football stadium for Everton F.C.
A raised weight accumulator consists of a vertical cylinder containing fluid connected to the hydraulic line. The cylinder is closed by a piston on which a series of weights are placed that exert a downward force on the piston and thereby pressurizes the fluid in the cylinder. In contrast to compressed gas and spring accumulators, this type delivers a nearly constant pressure, regardless of the volume of fluid in the cylinder, until it is empty. (The pressure will decline somewhat as the cylinder is emptied due to the decline in weight of the remaining fluid.)
A working example of this type of accumulator may be found at the hydraulic engine house, Bristol Harbour . [ 2 ] The original 1887 accumulator is in place in its tower, an external accumulator was added in 1954 and this system was used until 2010 to power the Cumberland Basin (Bristol) lock gates. The water is pumped from the harbour into a header tank and then fed by gravity to the pumps. The working pressure is 750 psi (5.2 MPa , or 52 bar ) which was used to power the cranes, bridges and locks of Bristol Harbour . [ citation needed ]
The original operating mechanism of Tower Bridge , London , also used this type of accumulator. Although no longer in use, two of the six accumulators may still be seen in situ in the bridge's museum. [ 3 ]
Regent's Canal Dock, now named Limehouse Basin has the remains of a hydraulic accumulator, dating from 1869, a fragment of the oldest remaining such facility in the world, the second at the dock, which was installed later than that at Poplar Dock , originally listed incorrectly as a signalbox for the London and Blackwall Railway , when correctly identified, it was restored as a tourist attraction by the now defunct London Docklands Development Corporation . [ clarification needed ] Now owned by the Canal & River Trust , it is open for large groups on application to the Dockmaster's Office at the basin and on both the afternoons of London Open House Weekend , held on the third weekend of September each year. [ 4 ]
London had an extensive public hydraulic power system from the mid-nineteenth century finally closing in the 1970s with 5 hydraulic power stations, operated by the London Hydraulic Power Company . Railway goods yards and docks often had their own separate system. [ citation needed ]
A simple form of accumulator is an enclosed volume, filled with air. A vertical section of pipe, often enlarged diameter, may be enough and fills itself with air, trapped as the pipework fills.
Such accumulators typically do not have enough capacity to be useful for storing significant power since they cannot be pre-charged with high pressure gas, but they can act as a buffer to absorb fluctuations in pressure. They are used to smooth out the delivery from piston pumps. Another use is as a shock absorber to damp out water hammer ; this application is an integral part of most ram pumps . Loss of air will result in loss of effectiveness. If air is lost over time, the design must include some way to replenish the accumulator.
A compressed gas accumulator consists of a cylinder with two chambers that are separated by an elastic diaphragm, a totally enclosed bladder, or a floating piston. One chamber contains the fluid and is connected to the hydraulic line. The other chamber contains an inert gas (typically nitrogen ), usually under pressure, that provides the compressive force on the hydraulic fluid. Inert gas is used because oxygen and oil can form an explosive mixture when combined under high pressure. As the volume of the compressed gas changes, the pressure of the gas (and the pressure on the fluid) changes inversely.
For low pressure water system use the water usually fills a rubber bladder within the tank (pictured), preventing contact with the tank which would otherwise need to be corrosion resistant. Units designed for high-pressure applications such as hydraulic systems are usually pre-charged to a very high pressure (approaching the system operating pressure) and are designed to prevent the bladder or membrane being damaged by this internal pressure when the system pressure is low. For bladder types this generally requires the bladder to be filled with the gas so that when system pressure is zero the bladder is fully expanded rather than being crushed by the gas charge. To prevent the bladder being forced out of the device when the system pressure is low there is typically either an anti-extrusion plate attached to the bladder that presses against and seals the entrance, or a spring-loaded plate on the entrance that closes when the bladder presses against it.
It is possible to increase the gas volume of the accumulator by coupling a gas bottle to the gas side of the accumulator. For the same swing in system pressure this will result in a larger portion of the accumulator volume being used. If the pressure does not vary over a very wide range this can be a cost effective way to reduce the size of the accumulator needed. If the accumulator is not of the piston type care must be taken that the bladder or membrane will not be damaged in any expected over-pressure situation, many bladder-type accumulators cannot tolerate the bladder being crushed under pressure.
A compressed gas accumulator was invented by Jean Mercier [ 5 ] for use in variable-pitch propellers .
A spring type accumulator is similar in operation to the gas-charged accumulator above, except that a heavy spring (or springs) is used to provide the compressive force. According to Hooke's law the magnitude of the force exerted by a spring is linearly proportional to its change of length. Therefore, as the spring compresses, the force it exerts on the fluid is increased linearly.
The metal bellows accumulators function similarly to the compressed gas type, except that the elastic diaphragm or floating piston is replaced by a hermetically sealed welded metal bellows . Fluid may be internal or external to the bellows. The advantages to the metal bellows type include exceptionally low spring rate, allowing the gas charge to do all the work with little change in pressure from full to empty, a long stroke that allows efficient usage of the casing volume, and the bellows can be built to be resistant to overpressure that would crush a bladder-type separator. The welded metal bellows accumulator provides an exceptionally high level of accumulator performance, and can be produced with a broad spectrum of alloys, resulting in a broad range of fluid compatibility. Other advantages to this type are that it does not face issues with high pressure operation, may be built to be resistant to very high or low temperatures or certain aggressive chemicals, and may be longer lasting in some situations. Metal bellows tend to be much more costly to produce than other common types.
In modern, often mobile, hydraulic systems the preferred item is a gas charged accumulator, but simple systems may be spring-loaded. There may be more than one accumulator in a system. The exact type and placement of each may be a compromise [ clarification needed ] due to its effects and the costs of manufacture.
An accumulator is placed close to the pump with a non-return valve preventing flow back to the pump. In the case of piston-type pumps this accumulator is placed in the ideal location to absorb pulsations of energy from the multi-piston pump . [ citation needed ] It also helps protect the system from fluid hammer . This protects system components, particularly pipework, from both potentially destructive forces.
An additional benefit is the additional energy that can be stored while the pump is subject to low demand. The designer can use a smaller-capacity pump. The large excursions of system components, such as landing gear on a large aircraft, that require a considerable volume of fluid can also benefit from one or more accumulators. These are often placed close to the demand to help overcome restrictions and drag from long pipework runs. The outflow of energy from a discharging accumulator is much greater, for a short time, than even large pumps could generate.
An accumulator can maintain the pressure in a system for periods when there are slight leaks without the pump being cycled on and off constantly. When temperature changes cause pressure excursions the accumulator helps absorb them. Its size helps absorb fluid that might otherwise be locked in a small fixed system with no room for expansion due to valve arrangement.
The gas precharge in an accumulator is set so that the separating bladder, diaphragm or piston does not reach or strike either end of the operating cylinder. The design precharge normally ensures that the moving parts do not foul the ends or block fluid passages. Poor maintenance of precharge can destroy an operating accumulator. A properly designed and maintained accumulator should operate trouble-free for years. [ citation needed ] | https://en.wikipedia.org/wiki/Hydraulic_accumulator |
Hydraulic action , most generally, is the ability of moving water (flowing or waves) to dislodge and transport rock particles. This includes a number of specific erosional processes, including abrasion , at facilitated erosion, such as static erosion where water leaches salts and floats off organic material from unconsolidated sediments, and from chemical erosion more often called chemical weathering .
It is a mechanical process, in which the moving water current flows against the banks and bed of a river, thereby removing rock particles.
A primary example of hydraulic action is a wave striking a cliff face which compresses the air in cracks of the rocks. This exerts pressure on the surrounding rock which can progressively crack, break, splinter and detach rock particles. This is followed by the decompression of the air as the wave retreats which can occur suddenly with explosive force which additionally weakens the rock. Cracks are gradually widened so each wave compresses more air, increasing the explosive force of its release. Thus, the effect intensifies in a ' positive feedback ' system. Over time, as the cracks may grow they sometimes form a sea cave . The broken pieces that fall off produce two additional types of erosion, abrasion (sandpapering) and attrition. In corrasion , the newly formed chunks are thrown against the rock face. Attrition is a similar effect caused by eroded particles after they fall to the sea bed where they are subjected to further wave action. In coastal areas wave hydraulic action is often the most important form of erosion.
Similarly, where hydraulic action is strong enough to loosen sediment along a stream bed and its banks; this will take rocks and particles from the banks and bed of the stream and add this to the stream's load . This process is the result of friction between the moving water and the static stream bed and banks. This friction increases with the speed of the water and once loosened the smaller particles are held in suspension by the force of the flowing water, these suspended particles can scour the sides and bottom of the stream. The scouring action produces distinctive markings on streams beds such as ripple marks , fluting, and crescent marks. [ 1 ] The larger particles and even large rocks are scooted (dragged) along the bottom in a process known as traction which causes attrition, and are often "bounced" along in a process known as saltation where the force of the water temporarily lifts the rock particle which then crashes back into the bed dislodging other particles. [ 2 ]
Hydraulic action also occurs as a stream tumbles over a waterfall to crash onto the rocks below. It usually leads to the formation of a plunge pool below the waterfall due in part to corrosion from the stream's load, but more to a scouring action as vortices form in the water as it escapes downstream. Hydraulic action can also cause the breakdown of river banks since there are water bubbles which enter the banks and collapse them when they expand. | https://en.wikipedia.org/wiki/Hydraulic_action |
Water transportation and distribution networks require hydraulic calculations to determination the flowrate and pressure characteristics at one or several consumption points and the water supply flowrate and pressures needed to meet the design requirements. [ 1 ]
In the context of fire safety , hydraulic calculations are used to determine the flow of an extinguishing medium through a piping network and through discharge devices (e.g., nozzles, sprinklers) to control, suppress, or extinguish fires.
Hydraulic calculations verify that the water flowrate (or water mixed with additives like firefighting foam concentrate) through piping networks for the purpose of suppressing or extinguishing a fire will be sufficient to meet design objectives. The hydraulic calculation procedure is defined in the applicable reference model codes such as that published by the US-based National Fire Protection Association (NFPA), [ 2 ] or the EN 12845 standard, Fixed firefighting system – Automatic sprinkler systems – Design, installation and maintenance . [ 3 ]
Hydraulic calculations indicate that the combination of the two primary components of a water based fire protection system will meet the design objectives to control, suppress, or extinguish a fire:
Requirements for the quantity of water discharge are specified by an applicable model code such as NFPA 13, NFPA 15, EN 12845, BS 9251, [ 4 ] NFPA 750 CP 52, ASIB, and AS2118.1. Property insurance design standards may also apply.
The probable intensity and extent of a fire inside the building are indicated by factors including the building use, the building height, the items contained inside the building and their arrangement. These variables are compared to tables and values expressed in the model codes. The values in these tables are based on fire tests and loss history.
The water available is often determined by means of a water flow test , in which one or more fire hydrants are opened and the water pressures and flowrate are measured. Some municipal water jurisdictions may provide an estimate of available water supplies based on hydraulic models.
In locations where a municipal connection is not possible or practical, the required water may be drawn from an open body of water (e.g., lake, pond, river) or a water storage tank.
Hydraulic calculations determine if the available water supply pressure is adequate to provide the sprinkler system design flowrate. If not, additional water pressure is provided by a fire pump.
Suppression system piping networks are usually arranged in one of 3 configurations: Tree, Loop, or Grid. All of these types of systems utilize large horizontal pipes - "mains" - which deliver large flowrates to smaller pipes - "branch lines" - which are connected to the mains. Sprinklers are installed only on the branch pipes. The mains are supplied with water by connection to a single vertical pipe - "riser" - which is in turn provided with water by connection to water supply piping.
Tree systems includes a single main pipe with several smaller branch lines. As all pipes terminate at a dead end, water flowrate is possible only in one direction.
Looped systems utilize a main that runs a significant distance into a building and is routed back to connect to itself near the riser. Branch lines are connected to this 'loop'. Less water supply pressure is required with this looped main configuration as the hydraulic pressure drop is lower through the main as water can flow in two directions to any sprinkler. The branch lines may terminate in a dead end or may connect at each end to different (usually opposite) points on the looped main. In the latter case, less water supply pressure is required as the hydraulic pressure drop is lower in the branch pipe as water flows from both ends of the branch line to any sprinkler.
Grid systems utilizes two large mains at opposite ends of several branch lines which are connected to the mains at each end. Gridded systems provide multiple paths for the water to travel to any point in the system, reducing pressure losses in the system.
Most design standards require application of the Hazen-Williams method for determining frictional pressure losses through the piping network as water passes through it. Tree and Loop systems are simple enough that the hydraulic calculations could be performed by hand. Because hydraulic calculations for gridded systems require an iterative process to balance the water flow through all possible water paths, these calculations are most often performed by computer software. In practice, most calculations on all types of piping networks are performed by computer software. The sizes of network components can be more readily modified and recalculated on a computer than through a manual process.
The 2013 NFPA 13 handbook includes a supplement which describes some of the application theory and processes applied when performing hydraulic calculations. [ 5 ] | https://en.wikipedia.org/wiki/Hydraulic_calculation |
A chainsaw (or chain saw [ 1 ] ) is a portable handheld power saw that cuts with a set of teeth attached to a rotating chain driven along a guide bar.
Modern chainsaws are typically gasoline or electric and are used in activities such as tree felling , limbing , bucking , pruning , cutting firebreaks in wildland fire suppression , harvesting of firewood , for use in chainsaw art and chainsaw mills , for cutting concrete, and cutting ice. Precursors to modern chainsaws were first used in surgery, with patents for wood chainsaws beginning in the late 19th century.
A chainsaw comprises an engine, a drive mechanism, a guide bar, a cutting chain, a tensioning mechanism, and safety features. Various safety practices and working techniques are used with chainsaws.
A "flexible saw", consisting of a fine serrated link chain held between two wooden handles, was pioneered in the late 18th century ( c. 1783 –1785) by two Scottish doctors, John Aitken and James Jeffray , for symphysiotomy and excision of diseased bone, respectively. [ 2 ] It was illustrated in the second edition of Aitken's Principles of Midwifery, or Puerperal Medicine (1785) in the context of a pelviotomy . [ 3 ] In 1806, Jeffray published Cases of the Excision of Carious Joints , which collected a paper previously published by H. Park in 1782 and a translation of an 1803 paper by French physician P. F. Moreau, with additional observations by Park and Jeffray. [ 4 ] In it, Jeffray reported having conceived the idea of a saw "with joints like the chain of a watch" independently very soon after Park's original 1782 publication, but that he was not able to have it produced until 1790, after which it was used in the anatomy lab and occasionally lent out to surgeons. Park and Moreau described successful excision of diseased joints, particularly the knee and elbow, and Jeffray explained that the chainsaw would allow a smaller wound and protect the adjacent muscles, nerves, and veins. [ 5 ] While symphysiotomy had too many complications for most obstetricians, Jeffray's ideas about the excision of the ends of bones became more accepted, especially after the widespread adoption of anaesthetics. For much of the 19th century the chainsaw was a useful surgical instrument, but it was superseded in 1894 by the Gigli twisted-wire saw , which was substantially cheaper to manufacture, and gave a quicker, narrower cut, without risk of breaking and being entrapped in the bone. [ 6 ]
A precursor of the chainsaw familiar today in the timber industry was another medical instrument developed around 1830, by German precision mechanic and orthopaedist Bernhard Heine . This instrument, the osteotome , had links of a chain carrying small cutting teeth with the edges set at an angle; the chain was moved around a guiding blade by turning the handle of a sprocket wheel. As the name implies, this was used to cut bone. [ 7 ]
One of the earliest patents for an "endless chain saw" comprising a chain of links carrying saw teeth was granted to Frederick L. Magaw of Flatlands, New York in 1883, apparently for the purpose of producing boards by stretching the chain between grooved drums. [ 8 ] [ 9 ] A later patent incorporating a guide frame was granted to Samuel J. Bens of San Francisco on January 17, 1905, his intent being to fell giant redwoods. [ 10 ] The first portable chainsaw was developed and patented in 1918 by Canadian millwright James Shand. [ 11 ] [ 12 ] After he allowed his rights to lapse in 1930, his invention was further developed by what became the German company Festo in 1933. The company, now operating as Festool , produces portable power tools. Other important contributors to the modern chainsaw are Joseph Buford Cox and Andreas Stihl ; the latter patented and developed an electric chainsaw for use on bucking sites in 1926 [ 13 ] and a gasoline-powered chainsaw in 1929, and founded a company to mass-produce them. In 1927, Emil Lerp , the founder of Dolmar , developed the world's first gasoline-powered chainsaw and mass-produced them. [ 14 ]
World War II interrupted the supply of German chainsaws to North America, so new manufacturers sprang up, including Industrial Engineering Ltd (IEL) in 1939, the forerunner of Pioneer Saws Ltd and part of Outboard Marine Corporation , the oldest manufacturer of chainsaws in North America. [ 15 ]
The first one-man chainsaw was introduced in 1950, though it was relatively heavy. By 1959, the average weight was around 12 kg (today, chainsaws typically weigh between 4 and 5 kg, with heavy-duty models ranging from 7 to 9 kg), and it quickly gained attention. [ 16 ]
McCulloch in North America started to produce chainsaws in 1948. The early models were heavy, two-person devices with long bars. Often, chainsaws were so heavy that they had wheels like dragsaws . Other outfits used driven lines from a wheeled power unit to drive the cutting bar. [ 17 ]
Carburetors featuring swivel and floating diaphragms were developed after the war, enabling modern chainsaws to operate in any orientation without the risk of flooding or fuel starvation. Additionally, the use of lighter materials played a crucial role in the advancement of the modern hand-held chainsaw. [ 18 ]
While today's logging operations use a variety of specialized machinery, hand felling with a cable skidder (where tractors and horses may still be utilized) continues to be a viable, cost-effective way to make a living as a logger. [ 19 ]
They are made in many sizes, from small electric saws intended for home and garden use, to large "lumberjack" saws. Members of military engineer units are trained to use chainsaws, as are firefighters to fight forest fires and to ventilate structure fires. [ 20 ]
Three main types of chainsaw sharpeners are used: handheld file, electric chainsaw, and bar-mounted. [ citation needed ]
The first electric chainsaw was invented by Stihl in 1926. [ 21 ] Corded chainsaws became available for sale to the public from the 1960s onwards, [ 22 ] but these were never as successful commercially as the older gas-powered type due to limited range, dependency upon the presence of an electrical socket , plus the health and safety risk of the blade's proximity to the cable. [ 23 ]
For most of the early 21st century petrol driven chainsaws remained the most common type, but they faced competition from cordless lithium battery powered chainsaws from the late 2010s onwards. [ 24 ] Although most cordless chainsaws are small and suitable only for hedge trimming and tree surgery , [ 25 ] Husqvarna and Stihl began manufacturing full size chainsaws for cutting logs during the early 2020s. [ 26 ] Battery powered chainsaws should eventually see increased market share in California due to state restrictions planned to take effect in 2024 on gas powered gardening equipment. [ 27 ] [ 28 ]
A chainsaw consists of several parts:
Chainsaw engines are traditionally either a two-stroke single-cylinder gasoline (petrol) internal combustion engine (usually with a cylinder volume of 30 to 120cc) or an electric motor driven by a battery or electric power cord. In a petrol chainsaw, fuel is generally supplied to the engine by a carburetor at the intake. Two-stroke engines have been preferred for chainsaws due to their higher power-to-weight ratio and simplicity. [ 29 ]
Hydraulic power may be used for chainsaws for underwater use. [ 30 ]
To allow use in any orientation, modern gas chainsaws use a diaphragm carburetor, which draws fuel from the tank using the alternating pressure differential within the crankcase. Early engines used carburetors with gravity fed float chambers , which caused the engine to stall when tilted. The carburetor may need to be adjusted to maintain an appropriate idle speed and air-fuel ratio , such as when moving to a higher/lower altitude or as the air filter clogs. Carburetors are adjusted either by the operator or, in some saws, automatically by an electronic control unit . [ citation needed ]
To prevent vibration induced injury and reduce user fatigue, saws generally have an anti-vibration system to physically decouple the handles from the engine and bar. [ 31 ] This is achieved by constructing the saw in two pieces, connected by springs or rubber in the same way an automobile suspension isolates the chassis from the wheels and road. [ 32 ] In cold weather, carburetor icing can occur, so many saws have a vent between the cylinders and carburetor which may be opened to allow hot air to pass. Cold temperature can also contribute to vibration-induced injury, [ 33 ] and some saws have a small alternator connected to resistive heating elements in the handles and/or carburetor. [ citation needed ]
Typically, a centrifugal clutch and sprocket are used. The centrifugal clutch expands with increasing speed, engaging a drum. On this drum sits either a fixed sprocket or an exchangeable one. The clutch has three jobs: When the engine runs idle (typically 2500–2700 rpm) the chain does not move. When the clutch is engaged and the chain stops in the wood for another reason, it protects the engine. Most importantly, it protects the operator in case of a kickback. Here, the chain brake stops the drum, and the clutch releases immediately. [ citation needed ]
A guide bar, typically an elongated bar with a round end of wear-resistant alloy steel typically 40 to 90 cm (15.5 to 35.5 in) in length, is used. An edge slot guides the cutting chain. Specialized, loop-style bars, called bow bars, were also used at one time for bucking logs and clearing brush, although they are now rarely encountered due to increased hazards of operation.
All guide bars have some elements for operation:
The lower part of the chain runs in the gauge. Here, the lubrication oil is pulled by the chain to the nose. This is basically the thickness of the drive links.
The end of the saw power head has two oil holes, one on each side. These holes must match with the outlet of the oil pump. The pump sends the oil through the hole in the lower part of the gauge. [ citation needed ]
Saw bar producers provide a large variety of bars matching different saws. [ citation needed ]
Through this hole, grease is pumped, typically each tank filling to keep the nose sprocket well lubricated. [ citation needed ]
Here, one or two bolts from the saw run through. The clutch cover is put on top of the bar and it is secured through these bolts. The number of bolts is determined by the size of the saw. [ citation needed ]
Different bar types are available: [ citation needed ]
Usually, each segment in a chain (which is constructed from riveted metal sections similar to a bicycle chain , but without rollers ) features small, sharp, cutting teeth. Each tooth takes the form of a folded tab of chromium-plated steel with a sharp angular or curved corner and two beveled cutting edges, one on the top plate and one on the side plate. Left-handed and right-handed teeth are alternated in the chain. Chains are made in varying pitch and gauge; the pitch of a chain is defined as half of the length spanned by any three consecutive rivets (e.g., 8 mm, 0.325 inch), while the gauge is the thickness of the drive link where it fits into the guide bar (e.g., 1.5 mm, 0.05 inch). The conventional "full complement" chain has one tooth for every two drive links. "Full skip" chain has one tooth for every three drive links. Built into each tooth is a depth gauge or "raker", which rides ahead of the tooth and limits the depth of cut, typically to around 0.5 mm (0.025"). Depth gauges are critical to safe chain operation. If left too high, they cause very slow cutting; if filed too low, the chain becomes more prone to kick back. Low depth gauges also cause the saw to vibrate excessively. Vibration is uncomfortable for the operator and is detrimental to the saw. [ citation needed ]
The tension of the chain that does the cutting is adjusted so that it neither binds on nor comes loose from the guide bar. The tensioner for doing so is either operated by turning a screw or a manual wheel. The tensioner is either in a lateral position underneath the exhaust or integrated into the clutch cover. [ citation needed ]
Lateral tensioners have the advantage that the clutch cover is easier to mount, but the disadvantage that it is more difficult to reach nearby the bar. Tensioners through the clutch cover are easier to operate, but the clutch cover is more difficult to attach. [ citation needed ]
When turning the screw, a hook in a bar hole moves the bar either out (tensioning) or in, making the chain loose. Tension is right when it can be moved easily by hand and not hanging loose from the bar. When tensioning, hold the bar nose up and pull the bar nuts tight. Otherwise, the chain might derail. [ citation needed ]
The underside of each link features a small, metal finger called a "drive link", which locates the chain on the bar, helps to carry lubricating oil around the bar, and engages with the engine's drive sprocket inside the body of the saw. The engine drives the chain around the track by a centrifugal clutch, engaging the chain as engine speed increases under power, but allowing it to stop as the engine speed slows to idle speed. [ citation needed ]
Consistent improvement to overall chainsaw design, including adding safety features , has taken place over the years. These include chain-brake systems, better chain design, and lighter, more ergonomic saws, including fatigue-reducing antivibration systems. [ citation needed ]
As chainsaw carving has become more popular, manufacturers are making special short, narrow-tipped bars (called "quarter-tipped" "nickel-tipped", or "dime-tipped" bars, based on the size of their tips). Some chainsaws are built specifically for carving applications. [ 34 ] Echo sponsors a carving series. [ 35 ]
Today's chainsaws have multiple safety features to protect the operator. These include: [ citation needed ]
Two-stroke chainsaws require about 2–5% of oil in the fuel to lubricate the engine, while the motor in electrical chain-saws is normally lubricated for life. Most modern gasoline-operated saws today require a fuel mix of 2% (1:50). Gasoline that contains ethanol can result in problems for the equipment because ethanol dissolves plastic, rubber, and other material. [ 36 ] This leads to problems, especially on older equipment. A workaround for this problem is to run fresh fuel only and run the saw dry at the end of the work. [ citation needed ]
Separate chain oil or bar oil is used for the lubrication of the bar and chain on all types of chainsaws. The chain oil is depleted quickly because it tends to be thrown off by chain centrifugal force , and it is soaked up by sawdust. On two-stroke chainsaws, the chain oil reservoir is usually filled up at the same time as refueling. The reservoir is normally large enough to provide sufficient chain oil between refueling. Lack of chain oil, or using an oil of incorrect viscosity , is a common source of damage to chainsaws, and tends to lead to rapid wear of the bar, or the chain seizing or coming off the bar. In addition to being quite thick, chain oil is particularly sticky (due to " tackifier " additives) to reduce the amount thrown off the chain. Although motor oil is a common emergency substitute, it is lost even faster, so leaves the chain under-lubricated. [ citation needed ]
The oil is pumped from a small pump to a hole in the bar. From there, the lower ends of each chain drive link take a portion of the oil into the gauge towards the bar nose. The pump outlet and bar hole must be aligned. Since the bar is moving out and inwards depending on the chain length, the oil outlet on the saw side has a banana-style long shape. [ citation needed ]
Chains must be kept sharp to perform well. They become blunt rapidly if they touch soil, metal, or stones. When blunt, they tend to produce powdery sawdust, rather than the longer, clean shavings characteristic of a sharp chain; a sharp saw also needs very little force from the operator to push it into the cut. Specially-hardened chains (made with tungsten carbide ) are used for applications where the soil is likely to contaminate the cut, such as for cutting through roots . [ citation needed ]
A clear sign of a blunt chain is the vibrations of the saw. A sharp chain pulls itself into the wood without pressing on the saw. [ citation needed ]
Since the air intake filter tends to clog up with sawdust, it must be cleaned from time to time but is not a problem during normal operation. [ citation needed ]
Protective clothing is designed to protect operators in the event of a moving chain touching their clothing by snarling the chain and sprocket, by using special synthetic fibers woven into the garment. Despite safety features and protective clothing, injuries can still arise from chainsaw use, from the large forces involved in the work, from the fast-moving, sharp chain, or the vibration and noise of the machinery. [ 37 ]
A common accident arises from "kickback" when a chain tooth at the tip of the guide bar catches on wood without cutting through it. [ 38 ] This throws the bar (with its moving chain) in an upward arc toward the operator, which can cause serious injury or even death. [ citation needed ]
Another dangerous situation occurs when heavy timber begins to fall or shift before a cut is complete. The chainsaw operator may be trapped or crushed. [ 39 ] Similarly, timber falling in an unplanned direction may harm the operator or other workers, or an operator working at a height may fall or be injured by falling timber. [ citation needed ]
Like other hand-held machinery, the operation of chainsaws can cause vibration white finger , [ 40 ] tinnitus , or industrial deafness . These symptoms were very common before vibration dampening using rubber or steel spring was introduced. Heated handles are additional help. Newer, lighter, and easier to wield cordless electric chainsaws use brushless motors, which further decrease noise and vibration compared to traditional petroleum-powered models. [ citation needed ]
The risks associated with chainsaw use mean that protective clothing such as chainsaw boots , chaps, and hearing protectors are normally worn while operating them, and many jurisdictions require that operators be certified or licensed to work with chainsaws. [ where? ] Injury can also result if the chain breaks during operation due to poor maintenance or attempting to cut inappropriate materials. [ citation needed ]
Gasoline-powered chainsaws expose operators to harmful carbon monoxide gas, especially indoors or in partially enclosed outdoor areas. [ 41 ]
Drop starting, or turning on a chainsaw by dropping it with one hand while pulling the starting cord with the other, is a safety violation in most states in the U.S. [ 42 ] Keeping both hands on the saw for stability is essential for safe chainsaw use. [ citation needed ]
Safe and effective chainsaw and crosscut use on federally administered public lands within the United States has been codified since 2016 in the Final Directive for National Saw Program [ 43 ] issued by the United States Forest Service , which specifies the training, testing, and certification process for employees and unpaid volunteers who operate chainsaws within public lands. [ citation needed ]
Chainsaw training is designed to provide working technical knowledge and skills to safely operate the equipment. [ 44 ]
Chainsaws with specially designed bar-and-chain combinations have been developed as tools for use in chainsaw art and chainsaw mills . Specialized chainsaws are used for cutting concrete during construction developments. Chainsaws are sometimes used for cutting ice; for example, ice sculpture and winter swimming in Finland. [ citation needed ]
When fastened into a special guide frame, a chainsaw can be used as a portable sawmill to cut bulk wood into planks or boards. Such usage is called a chainsaw mill or Alaskan sawmill. [ citation needed ]
Special chainsaws can cut concrete, brick, and natural stone . These use similar chains to ordinary chainsaws, but with cutting edges embedded with diamond grit . They may use gasoline or hydraulic power, and the chain is lubricated with water , because of high friction and to remove stone dust. The machine is used in construction, for example, in cutting deep, square holes in walls or floors, in stone sculpture for removing large chunks of stone during pre-carving, by fire departments for gaining access to buildings, and in restoration of buildings and monuments for removing parts with minimal damage to the surrounding structure. More recently, concrete chainsaws with electric motors of 230 volts have also been developed. [ 47 ]
Because the material to be cut is not fibrous, much less kickback occurs. So, the most-used method of cutting is plunge-cutting, by pushing the tip of the blade into the material. With this method, square cuts as small as the blade width can be achieved. Pushback can occur if a block shifts when nearly cut through and pinches the blade, but overall, the machine is less dangerous than a wood-cutting chainsaw. [ citation needed ]
Chainsaws are used for underwater cutting by professional divers. They are usually driven by hydraulic power supplied from the surface and operated by commercial divers using surface-supplied diving equipment. Underwater chainsaw cutting may also be used by public safety divers. [ 30 ]
Hydraulic chainsaws can be used to cut wood, concrete, brick and steel if the appropriate chain is used. Underwater cutting may be done in conditions of moving water and low visibility, which can increase risk, and appropriate safety precautions and suitable procedures are required for safety. [ 30 ]
Underwater wood structures may include bridge pilings, pier, and dock timbers. Chain saws generally include an interlocking safety trigger with hand guard. [ 30 ] | https://en.wikipedia.org/wiki/Hydraulic_chainsaw |
Hydraulic clearance. Flow in narrow clearances are of vital importance in hydraulic system component design. The flow in a narrow circular clearance of a spool valve can be calculated according to the formula below if the height is negligible compared to the width of the clearance, such as most of the clearances in hydraulic pumps , hydraulic motors , and spool valves . Flow is considered to be laminar. The formula below is valid for a spool valve when the spool is steady. [ 1 ]
Concentric spool/valve housing position i.e. the height/radial clearance c is the same all around:
Units as per SI conventions :
Flow Q i = (∆P · π · d · c 3 ) ÷ (12 · ν · ρ · L) where: Q = volumetric flow rate (m^3/sec) ΔP = P1-P2 = pressure drop over the clearance (N/m^2, Pa) d = valve spool diameter (metre) c = clearance height (radial clearance) (metre) ν = kinematic viscosity for the oil (m^2/sec) ρ = density for the oil (kg/m^3) L = clearance length (metre)
As can be seen from the formula, the clearance height c has much more influence on the leakage than the length.
The formula clearly hints of pure laminar flow conditions.
It is also valid for gases.
Contact between the spool and the wall , the value that is generally used for practical calculations:
Flow Q e = 2.5 · Qi
Pistons :
Hydraulic spool valves:
Hydraulic seals :
Hydraulic cylinders :
Understanding and controlling hydraulic clearance is essential for optimizing the performance, efficiency, and longevity of hydraulic systems. | https://en.wikipedia.org/wiki/Hydraulic_clearance |
In science and engineering , hydraulic conductivity ( K , in SI units of meters per second), is a property of porous materials , soils and rocks , that describes the ease with which a fluid (usually water) can move through the pore space , or fracture network. [ 1 ] It depends on the intrinsic permeability ( k , unit: m 2 ) of the material, the degree of saturation , and on the density and viscosity of the fluid. Saturated hydraulic conductivity, K sat , describes water movement through saturated media.
By definition, hydraulic conductivity is the ratio of volume flux to hydraulic gradient yielding a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient.
There are two broad approaches for determining hydraulic conductivity:
The experimental approach is broadly classified into:
The small-scale field tests are further subdivided into:
The methods of determining hydraulic conductivity and other hydraulic properties are investigated by numerous researchers and include additional empirical approaches. [ 2 ]
Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain-size analyses:
where
A pedotransfer function (PTF) is a specialized empirical estimation method, used primarily in the soil sciences , but increasingly used in hydrogeology. [ 3 ] There are many different PTF methods, however, they all attempt to determine soil properties, such as hydraulic conductivity, given several measured soil properties, such as soil particle size , and bulk density .
There are relatively simple and inexpensive laboratory tests that may be run to determine the hydraulic conductivity of a soil: constant-head method and falling-head method.
The constant-head method is typically used on granular soil.
This procedure allows water to move through the soil under a steady state head condition while the volume of water flowing through the soil specimen is measured over a period of time.
By knowing the volume Δ V of water measured in a time Δ t , over a specimen of length L and cross-sectional area A , as well as the head h , the hydraulic conductivity ( K ) can be derived by simply rearranging Darcy's law :
Proof: Darcy's law states that the volumetric flow depends on the pressure differential Δ P between the two sides of the sample, the permeability k and the dynamic viscosity μ as: [ 4 ]
In a constant head experiment, the head (difference between two heights) defines an excess water mass, ρAh , where ρ is the density of water.
This mass weighs down on the side it is on, creating a pressure differential of Δ P = ρgh , where g is the gravitational acceleration.
Plugging this directly into the above gives
If the hydraulic conductivity is defined to be related to the hydraulic permeability as
this gives the result.
In the falling-head method, the soil sample is first saturated under a specific head condition.
The water is then allowed to flow through the soil without adding any water, so the pressure head declines as water passes through the specimen.
The advantage to the falling-head method is that it can be used for both fine-grained and coarse-grained soils.
. [ 5 ] If the head drops from h i to h f in a time Δ t , then the hydraulic conductivity is equal to
Proof: As above, Darcy's law reads
The decrease in volume is related to the falling head by Δ V = Δ hA .
Plugging this relationship into the above, and taking the limit as Δ t → 0 , the differential equation
has the solution
Plugging in h ( t f ) = h f {\displaystyle h(t_{f})=h_{f}} and rearranging gives the result.
In compare to laboratory method, field methods gives the most reliable information about the permeability of soil with minimum disturbances. In laboratory methods, the degree of disturbances affect the reliability of value of permeability of the soil.
Pumping test is the most reliable method to calculate the coefficient of permeability of a soil. This test is further classified into Pumping in test and pumping out test.
There are also in-situ methods for measuring the hydraulic conductivity in the field. When the water table is shallow, the augerhole method, a slug test , can be used for determining the hydraulic conductivity below the water table. The method was developed by Hooghoudt (1934) [ 6 ] in The Netherlands and introduced in the US by Van Bavel en Kirkham (1948). [ 7 ] The method uses the following steps:
where:
where:
The picture shows a large variation of K -values measured with the augerhole method in an area of 100 ha. [ 9 ] The ratio between the highest and lowest values is 25. The cumulative frequency distribution is lognormal and was made with the CumFreq program.
The transmissivity is a measure of how much water can be transmitted horizontally, such as to a pumping well.
An aquifer may consist of n soil layers. The transmissivity T i of a horizontal flow for the i th soil layer with a saturated thickness d i and horizontal hydraulic conductivity K i is:
Transmissivity is directly proportional to horizontal hydraulic conductivity K i and thickness d i . Expressing K i in m/day and d i in m, the transmissivity T i is found in units m 2 /day. The total transmissivity T t of the aquifer is the sum of every layer's transmissivity: [ 8 ]
The apparent horizontal hydraulic conductivity K A of the aquifer is:
where D t , the total thickness of the aquifer, is the sum of each layer's individual thickness: D t = ∑ d i . {\textstyle D_{t}=\sum d_{i}.}
The transmissivity of an aquifer can be determined from pumping tests . [ 10 ]
Influence of the water table When a soil layer is above the water table , it is not saturated and does not contribute to the transmissivity. When the soil layer is entirely below the water table, its saturated thickness corresponds to the thickness of the soil layer itself. When the water table is inside a soil layer, the saturated thickness corresponds to the distance of the water table to the bottom of the layer. As the water table may behave dynamically, this thickness may change from place to place or from time to time, so that the transmissivity may vary accordingly. In a semi-confined aquifer, the water table is found within a soil layer with a negligibly small transmissivity, so that changes of the total transmissivity ( D t ) resulting from changes in the level of the water table are negligibly small. When pumping water from an unconfined aquifer, where the water table is inside a soil layer with a significant transmissivity, the water table may be drawn down whereby the transmissivity reduces and the flow of water to the well diminishes.
The resistance to vertical flow ( R i ) of the i th soil layer with a saturated thickness d i and vertical hydraulic conductivity K v i is:
Expressing K v i in m/day and d i in m, the resistance ( R i ) is expressed in days. The total resistance ( R t ) of the aquifer is the sum of each layer's resistance: [ 8 ]
The apparent vertical hydraulic conductivity ( K v A ) of the aquifer is:
where D t is the total thickness of the aquifer: D t = ∑ d i . {\textstyle D_{t}=\sum d_{i}.}
The resistance plays a role in aquifers where a sequence of layers occurs with varying horizontal permeability so that horizontal flow is found mainly in the layers with high horizontal permeability while the layers with low horizontal permeability transmit the water mainly in a vertical sense.
When the horizontal and vertical hydraulic conductivity ( K h i {\textstyle K_{h_{i}}} and K v i {\textstyle K_{v_{i}}} ) of the i -th {\textstyle i{\mbox{-th}}} soil layer differ considerably, the layer is said to be anisotropic with respect to hydraulic conductivity. When the apparent horizontal and vertical hydraulic conductivity ( K h A {\textstyle K_{h_{A}}} and K v A {\textstyle K_{v_{A}}} ) differ considerably, the aquifer is said to be anisotropic with respect to hydraulic conductivity. An aquifer is called semi-confined when a saturated layer with a relatively small horizontal hydraulic conductivity (the semi-confining layer or aquitard ) overlies a layer with a relatively high horizontal hydraulic conductivity so that the flow of groundwater in the first layer is mainly vertical and in the second layer mainly horizontal. The resistance of a semi-confining top layer of an aquifer can be determined from pumping tests . [ 10 ] When calculating flow to drains [ 11 ] or to a well field [ 12 ] in an aquifer with the aim to control the water table , the anisotropy is to be taken into account, otherwise the result may be erroneous.
Because of their high porosity and permeability, sand and gravel aquifers have higher hydraulic conductivity than clay or unfractured granite aquifers. Sand or gravel aquifers would thus be easier to extract water from (e.g., using a pumping well ) because of their high transmissivity, compared to clay or unfractured bedrock aquifers.
Hydraulic conductivity has units with dimensions of length per time (e.g., m/s, ft/day and ( gal /day)/ft 2 ); transmissivity then has units with dimensions of length squared per time. The following table gives some typical ranges (illustrating the many orders of magnitude which are likely) for K values.
Hydraulic conductivity ( K ) is one of the most complex and important of the properties of aquifers in hydrogeology as the values found in nature:
Table of saturated hydraulic conductivity ( K ) values found in nature
Values are for typical fresh groundwater conditions — using standard values of viscosity and specific gravity for water at 20 °C and 1 atm.
See the similar table derived from the same source for intrinsic permeability values. [ 13 ]
Source: modified from Bear, 1972 | https://en.wikipedia.org/wiki/Hydraulic_conductivity |
A hydraulic cylinder (also called a linear hydraulic motor ) is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. [ citation needed ] It has many applications, notably in construction equipment ( engineering vehicles ), manufacturing machinery , elevators , and civil engineering .
A hydraulic cylinder is a hydraulic actuator that provides linear motion when hydraulic energy is converted into mechanical movement. It can be likened to a muscle in that, when the hydraulic system of a machine is activated, the cylinder is responsible for providing the motion. [ 1 ]
Hydraulic cylinders get their power from pressurized hydraulic fluid , which is incompressible. [ 2 ] Typically oil is used as hydraulic fluid. The hydraulic cylinder consists of a cylinder barrel , in which a piston connected to a piston rod moves back and forth. The barrel is closed on one end by the cylinder bottom (also called the cap) and the other end by the cylinder head (also called the gland) where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder into two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end/head-end).
Flanges , trunnions , clevises , and lugs are common cylinder mounting options. The piston rod also has mounting attachments to connect the cylinder to the object or machine component that it is pushing or pulling.
A hydraulic cylinder is the actuator or "motor" side of this system. The "generator" side of the hydraulic system is the hydraulic pump which delivers a fixed or regulated flow of oil to the hydraulic cylinder, to move the piston. There are three types of pump widely used: hydraulic hand pump, hydraulic air pump, and hydraulic electric pump. The piston pushes the oil in the other chamber back to the reservoir. If we assume that the oil enters from the cap end, during extension stroke, and the oil pressure in the rod end/head end is approximately zero, the force F on the piston rod equals the pressure P in the cylinder times the piston area A :
For double-acting single-rod cylinders, when the input and output pressures are reversed, there is a force difference between the two sides of the piston due to one side of the piston being covered by the rod attached to it. The cylinder rod reduces the surface area of the piston and reduces the force that can be applied for the retraction stroke. [ 3 ]
During the retraction stroke, if the oil is pumped into the head (or gland) at the rod end and the oil from the cap end flows back to the reservoir without pressure, the fluid pressure in the rod end is (Pull Force) / (piston area - piston rod area):
where P is the fluid pressure, F p is the pulling force, A p is the piston face area and A r is the rod cross-section area.
For double-acting, double-rod cylinders, when the piston surface area is equally covered by a rod of equal size on both sides of the head, there is no force difference. Such cylinders typically have their cylinder body affixed to a stationary mount.
Hydraulic cylinders can be used in any machine where high forces are required, one of the most familiar being earth-moving equipment such as excavators, back hoes and tractors to lift or lower the boom, arm, or bucket. [ 4 ] Manufacturing is another popular application where they can be found in hydraulic bending machines , metal sheet shearing machines, particle board or plywood making hot press .
A hydraulic cylinder has the following parts:
The main function of the cylinder body is to contain cylinder pressure. The cylinder barrel is mostly made from honed tubes. [ 5 ] Honed tubes are produced from Suitable To Hone Steel Cold Drawn Seamless Tubes (CDS tubes) or Drawn Over Mandrel (DOM) tubes. Honed tubing is ready to use for hydraulic cylinders without further ID processing. The surface finish of the cylinder barrel is typically 4 to 16 microinch. Honing process and Skiving & Roller burnishing (SRB) process are the two main types of processes for manufacturing cylinder tubes. [ 6 ] The piston reciprocates in the cylinder. The cylinder barrel has features of smooth inside surface, high precision tolerance, durable in use, etc.
The main function of the cap is to enclose the pressure chamber at one end. The cap is connected to the body by means of welding, threading, bolts, or tie rods. Caps also perform as cylinder mounting components [cap flange, cap trunnion, cap clevis]. Capsize is determined based on the bending stress. A static seal / o-ring is used in between cap and barrel (except welded construction).
The main function of the head is to enclose the pressure chamber from the other end. The head contains an integrated rod sealing arrangement or the option to accept a seal gland. The head is connected to the body by means of threading, bolts, or tie rods. A static seal / o-ring is used in between head and barrel.
The main function of the piston is to separate the pressure zones inside the barrel. The piston is machined with grooves to fit elastomeric or metal seals and bearing elements. These seals can be single-acting or double-acting. The difference in pressure between the two sides of the piston causes the cylinder to extend and retract. The piston is attached to the piston rod by means of threads, bolts, or nuts to transfer the linear motion.
The piston rod is typically a hard chrome-plated piece of cold-rolled steel that attaches to the piston and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment. The piston rod is highly ground and polished so as to provide a reliable seal and prevent leakage.
The cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface between the rod and the head. This area is called the seal gland. The advantage of a seal gland is easy removal and seal replacement. The seal gland contains a primary seal, a secondary seal/buffer seal, bearing elements, a wiper/scraper, and a static seal. In some cases, especially in small hydraulic cylinders, the rod gland and the bearing elements are made from a single integral machined part.
The seals are considered/designed to withstand maximum cylinder working pressure, cylinder speed, operating temperature , working medium, and application. Piston seals are dynamic seals, and they can be single-acting or double-acting. [ 7 ] Generally speaking, Elastomer seals made from nitrile rubber , Polyurethane, or other materials are best in lower temperature environments, while seals made of Fluorocarbon Viton are better for higher temperatures. Metallic seals are also available and commonly used cast iron for the seal material. Rod seals are dynamic seals and generally are single-acting. The compounds of rod seals are nitrile rubber , Polyurethane, or Fluorocarbon Viton . Wipers/scrapers are used to eliminate contaminants such as moisture, dirt, and dust, which can cause extensive damage to cylinder walls, rods, seals, and other components. The common compound for wipers is polyurethane. Metallic scrapers are used for sub-zero temperature applications and applications where foreign materials can deposit on the rod. The bearing elements/wear bands are used to eliminate metal to metal contact. The wear bands are designed to withstand maximum side loads. The primary compounds used for wear bands are filled PTFE , woven fabric reinforced polyester resin, and bronze
There are many component parts that make up the internal portion of a hydraulic cylinder. All of these pieces combine to create a fully functioning component. [ 8 ]
There are primarily two main styles of hydraulic cylinder construction used in the industry: tie rod-style cylinders and welded body-style cylinders.
Tie rod style hydraulic cylinders use high strength threaded steel rods to hold the two end caps to the cylinder barrel. They are most often seen in industrial factory applications. Small-bore cylinders usually have 4 tie rods, and large bore cylinders may require as many as 16 or 20 tie rods in order to retain the end caps under the tremendous forces produced. Tie rod style cylinders can be completely disassembled for service and repair, and they are not always customizable. [ 10 ]
The National Fluid Power Association (NFPA) has standardized the dimensions of hydraulic tie-rod cylinders. This enables cylinders from different manufacturers to interchange within the same mountings.
Welded body cylinders have no tie rods. The barrel is welded directly to the end caps. The ports are welded to the barrel. The front rod gland is usually threaded into or bolted to the cylinder barrel. That allows the piston rod assembly and the rod seals to be removed for service.
Welded body cylinders have a number of advantages over tie rod-style cylinders. Welded cylinders have a narrower body and often a shorter overall length enabling them to fit better into the tight confines of machinery. Welded cylinders do not suffer from failure due to tie rod stretch at high pressures and long strokes. [ 11 ] The welded design also lends itself to customization. Special features are easily added to the cylinder body, including special ports, custom mounts, valve manifolds, and so on. [ 10 ]
The smooth outer body of welded cylinders also enables the design of multi-stage telescopic cylinders.
Welded body hydraulic cylinders dominate the mobile hydraulic equipment market such as construction equipment ( excavators , bulldozers, and road graders) and material handling equipment (forklift trucks, telehandlers, and lift-gates). They are also used by heavy industry in cranes, oil rigs, and large off-road vehicles for above-ground mining operations.
The piston rod of a hydraulic cylinder operates both inside and outside the barrel, and consequently both in and out of the hydraulic fluid and surrounding atmosphere.
Wear and corrosion-resistant surfaces are desirable on the outer diameter of the piston rod. The surfaces are often applied using coating techniques such as Chrome (Nickel) Plating, Lunac 2+ duplex, Laser Cladding, PTA welding and Thermal Spraying. These coatings can be finished to the desirable surface roughness (Ra, Rz) where the seals give optimum performance. All these coating methods have their specific advantages and disadvantages. It is for this reason that coating experts play a crucial role in selecting the optimum surface treatment procedure for protecting Hydraulic Cylinders.
Cylinders are used in different operational conditions and that makes it a challenge to find the right coating solution. In dredging there might be impact from stones or other parts, in saltwater environments, there are extreme corrosion attacks, in off-shore cylinders facing bending and impact in combination with salt water, and in the steel industry, there are high temperatures involved, etc. There is no single coating solution that successfully combats all the specific operational wear conditions. Every technique has its own benefits and disadvantages.
Piston rods are generally available in lengths that are cut to suit the application. As the common rods have a soft or mild steel core, their ends can be welded or machined for a screw thread .
The forces on the piston face and the piston head retainer vary depending on which piston head retention system is used.
If a circlip (or any non-preloaded system) is used, the force acting to separate the piston head and the cylinder shaft shoulder is the applied pressure multiplied by the area of the piston head. The piston head and shaft shoulder will separate and the load is fully reacted by the piston head retainer.
If a preloaded system is used the force between the cylinder shaft and piston head is initially the piston head retainer preload value. Once pressure has applied this force will reduce. The piston head and cylinder shaft shoulder will remain in contact unless the applied pressure multiplied by the piston head area exceeds the preload.
The maximum force the piston head retainer will see is the larger of the preload and the applied pressure multiplied by the full piston head area. The load on the piston head retainer is greater than the external load, which is due to the reduced shaft size passing through the piston head. Increasing this portion of shaft reduces the load on the retainer. [ 12 ]
Side loading is unequal pressure that is not centered on the cylinder rod. This off-center strain can lead to bending of the rod in extreme cases, but more commonly causes leaking due to warping the circular seals into an oval shape. It can also damage and enlarge the bore hole around the rod and the inner cylinder wall around the piston head, if the rod is pressed hard enough sideways to fully compress and deform the seals to make metal-on-metal scraping contact. [ 13 ]
The strain of side loading can be directly reduced with the use of internal stop tubes which reduce the maximum extension length, leaving some distance between the piston and bore seal, and increasing leverage to resist warping of the seals. Double pistons also spread out the forces of side loading while also reducing stroke length. Alternately, external sliding guides and hinges can support the load and reduce side loading forces applied directly on the cylinder. [ 14 ]
Mounting methods also play an important role in cylinder performance. Generally, fixed mounts on the centerline of the cylinder are best for straight-line force transfer and avoiding wear. Common types of mounting include:
Flange mounts —Very strong and rigid, but have little tolerance for misalignment. Experts recommend cap end mounts for thrust loads and rod end mounts where major loading puts the piston rod in tension. Three types are head rectangular flange, head square flange or rectangular head. Flange mounts function optimally when the mounting face attaches to a machine support member. [ 15 ]
Side-mounted cylinders —Easy to install and service, but the mounts produce a turning moment as the cylinder applies force to a load, increasing wear and tear. To avoid this, specify a stroke at least as long as the bore size for side mount cylinders (heavy loading tends to make short stroke, large bore cylinders unstable). Side mounts need to be well aligned and the load supported and guided.
Centerline lug mounts —Absorb forces on the centerline, and require dowel pins to secure the lugs to prevent movement at higher pressures or under shock conditions. Dowel pins hold it to the machine when operating at high pressure or under shock loading. [ 15 ]
Pivot mounts —Absorb force on the cylinder centerline and let the cylinder change alignment in one plane. Common types include clevises, trunnion mounts and spherical bearings. Because these mounts allow a cylinder to pivot, they should be used with rod-end attachments that also pivot. Clevis mounts can be used in any orientation and are generally recommended for short strokes and small- to medium-bore cylinders. [ 16 ]
The length of a hydraulic cylinder is the total of the stroke, the thickness of the piston, the thickness of bottom and head and the length of the connections. Often this length does not fit in the machine. In that case the piston rod is also used as a piston barrel and a second piston rod is used. These kinds of cylinders are called telescopic cylinders . If we call a normal rod cylinder single stage, telescopic cylinders are multi-stage units of two, three, four, five, or more stages. In general telescopic cylinders are much more expensive than normal cylinders. Most telescopic cylinders are single acting (push). Double acting telescopic cylinders must be specially designed and manufactured. [ 17 ]
A hydraulic cylinder without a piston or with a piston without seals is called a plunger cylinder. A plunger cylinder can only be used as a pushing cylinder; the maximum force is piston rod area multiplied by pressure. This means that a plunger cylinder in general has a relatively thick piston rod.
A differential cylinder acts like a normal cylinder when pulling. If the cylinder however has to push, the oil from the piston rod side of the cylinder is not returned to the reservoir but goes to the bottom side of the cylinder. In such a way, the cylinder goes much faster, but the maximum force the cylinder can give is like a plunger cylinder. A differential cylinder can be manufactured like a normal cylinder, and only a special control is added.
The above differential cylinder is also called a regenerative cylinder control circuit. This term means that the cylinder is a single rod, double-acting hydraulic cylinder. The control circuit includes a valve and piping which during the extension of the piston, conducts the oil from the rod side of the piston to the other side of the piston instead of to the pump’s reservoir. The oil which is conducted to the other side of the piston is referred to as the regenerative oil.
Position sensing hydraulic cylinders eliminate the need for a hollow cylinder rod. Instead, an external sensing "bar" using Hall Effect technology senses the position of the cylinder’s piston. This is accomplished by the placement of a permanent magnet within the piston. The magnet propagates a magnetic field through the steel wall of the cylinder, providing a locating signal to the sensor. | https://en.wikipedia.org/wiki/Hydraulic_cylinder |
The hydraulic diameter , D H , is a commonly used term when handling flow in non-circular tubes and channels. Using this term, one can calculate many things in the same way as for a round tube. When the cross-section is uniform along the tube or channel length, it is defined as [ 1 ] [ 2 ]
where
More intuitively, the hydraulic diameter can be understood as a function of the hydraulic radius R H , which is defined as the cross-sectional area of the channel divided by the wetted perimeter. Here, the wetted perimeter includes all surfaces acted upon by shear stress from the fluid. [ 3 ]
Note that for the case of a circular pipe,
The need for the hydraulic diameter arises due to the use of a single dimension in the case of a dimensionless quantity such as the Reynolds number , which prefers a single variable for flow analysis rather than the set of variables as listed in the table below. The Manning formula contains a quantity called the hydraulic radius . Despite what the name may suggest, the hydraulic diameter is not twice the hydraulic radius, but four times larger.
Hydraulic diameter is mainly used for calculations involving turbulent flow . Secondary flows can be observed in non-circular ducts as a result of turbulent shear stress in the turbulent flow. Hydraulic diameter is also used in calculation of heat transfer in internal-flow problems. [ 4 ]
In the more general case, channels with non-uniform non-circular cross-sectional area, such as the Tesla valve , the hydraulic diameter is defined as: [ 5 ]
where
This definition is reduced to 4 A P {\displaystyle {\frac {4A}{P}}} for uniform non-circular cross-section channels, and 2 R {\displaystyle 2R} for circular pipes.
For a fully filled duct or pipe whose cross-section is a convex regular polygon , the hydraulic diameter is equivalent to the diameter D {\displaystyle D} of a circle inscribed within the wetted perimeter .
This can be seen as follows: The N {\displaystyle N} -sided regular polygon is a union of N {\displaystyle N} triangles, each of height D / 2 {\displaystyle D/2} and base B = D tan ( π / N ) {\displaystyle B=D\tan(\pi /N)} .
Each such triangle contributes B D / 4 {\displaystyle BD/4} to the total area and B {\displaystyle B} to the total perimeter, giving
for the hydraulic diameter. | https://en.wikipedia.org/wiki/Hydraulic_diameter |
Hydraulic machines use liquid fluid power to perform work. Heavy construction vehicles are a common example. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses, tubes, or pipes.
Hydraulic systems, like pneumatic systems , are based on Pascal's law which states that any pressure applied to a fluid inside a closed system will transmit that pressure equally everywhere and in all directions. A hydraulic system uses an incompressible liquid as its fluid, rather than a compressible gas.
The popularity of hydraulic machinery is due to the large amount of power that can be transferred through small tubes and flexible hoses, the high power density and a wide array of actuators that can make use of this power, and the huge multiplication of forces that can be achieved by applying pressures over relatively large areas. One drawback, compared to machines using gears and shafts, is that any transmission of power results in some losses due to resistance of fluid flow through the piping.
Joseph Bramah patented the hydraulic press in 1795. [ 1 ] While working at Bramah's shop, Henry Maudslay suggested a cup leather packing. [ 2 ] [ clarification needed ] Because it produced superior results, the hydraulic press eventually displaced the steam hammer for metal forging. [ 3 ]
To supply large-scale power that was impractical for individual steam engines, central station hydraulic systems were developed. Hydraulic power was used to operate cranes and other machinery in British ports and elsewhere in Europe. The largest hydraulic system was in London. Hydraulic power was used extensively in Bessemer steel production. Hydraulic power was also used for elevators, to operate canal locks and rotating sections of bridges. [ 1 ] [ 3 ] Some of these systems remained in use well into the twentieth century.
Harry Franklin Vickers was called the "Father of Industrial Hydraulics" by ASME . [ why? ]
A fundamental feature of hydraulic systems is the ability to apply force or torque multiplication in an easy way, independent of the distance between the input and output, without the need for mechanical gears or levers, either by altering the effective areas in two connected cylinders or the effective displacement (cc/rev) between a pump and motor. In normal cases, hydraulic ratios are combined with a mechanical force or torque ratio for optimum machine designs such as boom movements and track drives for an excavator.
Cylinder C1 is one inch in radius, and cylinder C2 is ten inches in radius. If the force exerted on C1 is 10 lbf , the force exerted by C2 is 1000 lbf because C2 is a hundred times larger in area ( S = π r ²) as C1. The downside to this is that you have to move C1 a hundred inches to move C2 one inch. The most common use for this is the classical hydraulic jack where a pumping cylinder with a small diameter is connected to the lifting cylinder with a large diameter.
If a hydraulic rotary pump with the displacement 10 cc/rev is connected to a hydraulic rotary motor with 100 cc/rev, the shaft torque required to drive the pump is one-tenth of the torque then available at the motor shaft, but the shaft speed (rev/min) for the motor is also only one-tenth of the pump shaft speed. This combination is actually the same type of force multiplication as the cylinder example, just that the linear force in this case is a rotary force, defined as torque.
Both these examples are usually referred to as a hydraulic transmission or hydrostatic transmission involving a certain hydraulic "gear ratio".
A hydraulic circuit is a system comprising an interconnected set of discrete components that transport liquid . The purpose of this system may be to control where fluid flows (as in a network of tubes of coolant in a thermodynamic system) or to control fluid pressure (as in hydraulic amplifiers). For example, hydraulic machinery uses hydraulic circuits (in which hydraulic fluid is pushed, under pressure, through hydraulic pumps , pipes, tubes, hoses, hydraulic motors , hydraulic cylinders , and so on) to move heavy loads. The approach of describing a fluid system in terms of discrete components is inspired by the success of electrical circuit theory . Just as electric circuit theory works when elements are discrete and linear, hydraulic circuit theory works best when the elements (passive components such as pipes or transmission lines or active components such as power packs or pumps ) are discrete and linear. This usually means that hydraulic circuit analysis works best for long, thin tubes with discrete pumps, as found in chemical process flow systems or microscale devices. [ 4 ] [ 5 ] [ 6 ]
The circuit comprises the following components:
For the hydraulic fluid to do work, it must flow to the actuator and/or motors, then return to a reservoir. The fluid is then filtered and re-pumped. The path taken by hydraulic fluid is called a hydraulic circuit of which there are several types.
Open-loop: Pump-inlet and motor-return (via the directional valve) are connected to the hydraulic tank. The term loop applies to feedback; the more correct term is open versus closed "circuit". Open center circuits use pumps which supply a continuous flow. The flow is returned to the tank through the control valve's open center; that is, when the control valve is centered, it provides an open return path to the tank and the fluid is not pumped to a high pressure. Otherwise, if the control valve is actuated it routes fluid to and from an actuator and tank. The fluid's pressure will rise to meet any resistance, since the pump has a constant output. If the pressure rises too high, fluid returns to the tank through a pressure relief valve. Multiple control valves may be stacked in series. This type of circuit can use inexpensive, constant displacement pumps.
Closed-loop: Motor-return is connected directly to the pump-inlet. To keep up pressure on the low pressure side, the circuits have a charge pump (a small gear pump) that supplies cooled and filtered oil to the low pressure side. Closed-loop circuits are generally used for hydrostatic transmissions in mobile applications. Advantages: No directional valve and better response, the circuit can work with higher pressure. The pump swivel angle covers both positive and negative flow direction. Disadvantages: The pump cannot be utilized for any other hydraulic function in an easy way and cooling can be a problem due to limited exchange of oil flow. High power closed loop systems generally must have a 'flush-valve' assembled in the circuit in order to exchange much more flow than the basic leakage flow from the pump and the motor, for increased cooling and filtering. The flush valve is normally integrated in the motor housing to get a cooling effect for the oil that is rotating in the motor housing itself. The losses in the motor housing from rotating effects and losses in the ball bearings can be considerable as motor speeds will reach 4000-5000 rev/min or even more at maximum vehicle speed. The leakage flow as well as the extra flush flow must be supplied by the charge pump. A large charge pump is thus very important if the transmission is designed for high pressures and high motor speeds. High oil temperature is usually a major problem when using hydrostatic transmissions at high vehicle speeds for longer periods, for instance when transporting the machine from one work place to the other. High oil temperatures for long periods will drastically reduce the lifetime of the transmission. To keep down the oil temperature, the system pressure during transport must be lowered, meaning that the minimum displacement for the motor must be limited to a reasonable value. Circuit pressure during transport around 200-250 bar is recommended.
Closed loop systems in mobile equipment are generally used for the transmission as an alternative to mechanical and hydrodynamic (converter) transmissions. The advantage is a stepless gear ratio (continuously variable speed/torque) and a more flexible control of the gear ratio depending on the load and operating conditions. The hydrostatic transmission is generally limited to around 200 kW maximum power, as the total cost gets too high at higher power compared to a hydrodynamic transmission. Large wheel loaders for instance and heavy machines are therefore usually equipped with converter transmissions. Recent technical achievements for the converter transmissions have improved the efficiency and developments in the software have also improved the characteristics, for example selectable gear shifting programs during operation and more gear steps, giving them characteristics close to the hydrostatic transmission.
Hydrostatic transmissions for earth moving machines, such as for track loaders, are often equipped with a separate ' inch pedal ' that is used to temporarily increase the diesel engine rpm while reducing the vehicle speed in order to increase the available hydraulic power output for the working hydraulics at low speeds and increase the tractive effort. The function is similar to stalling a converter gearbox at high engine rpm. The inch function affects the preset characteristics for the 'hydrostatic' gear ratio versus diesel engine rpm.
The closed center circuits exist in two basic configurations, normally related to the regulator for the variable pump that supplies the oil:
Load-sensing systems (LS) generate less power losses as the pump can reduce both flow and pressure to match the load requirements, but require more tuning than the CP system with respect to system stability. The LS system also requires additional logical valves and compensator valves in the directional valves, thus it is technically more complex and more expensive than the CP system. The LS system generates a constant power loss related to the regulating pressure drop for the pump regulator :
Power loss = Δ p LS ⋅ Q tot {\displaystyle {\text{Power loss}}=\Delta p_{\text{LS}}\cdot Q_{\text{tot}}}
The average Δ p L S {\displaystyle \Delta p_{LS}} is around 2 MPa (290 psi). If the pump flow is high the extra loss can be considerable. The power loss also increases if the load pressures vary a lot. The cylinder areas, motor displacements and mechanical torque arms must be designed to match load pressure in order to bring down the power losses. Pump pressure always equals the maximum load pressure when several functions are run simultaneously and the power input to the pump equals the (max. load pressure + Δ p LS ) x sum of flow.
Technically the down-stream mounted compensator in a valve block can physically be mounted "up-stream", but work as a down-stream compensator.
System type (3) gives the advantage that activated functions are synchronized independent of pump flow capacity. The flow relation between two or more activated functions remains independent of load pressures, even if the pump reaches the maximum swivel angle. This feature is important for machines that often run with the pump at maximum swivel angle and with several activated functions that must be synchronized in speed, such as with excavators. With the type (4) system, the functions with up-stream compensators have priority, for example the steering function for a wheel loader. The system type with down-stream compensators usually have a unique trademark depending on the manufacturer of the valves, for example "LSC" (Linde Hydraulics), "LUDV" ( Bosch Rexroth Hydraulics) and "Flowsharing" (Parker Hydraulics) etc. No official standardized name for this type of system has been established but flowsharing is a common name for it.
Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in reaction to the load. Hence, a pump rated for 5,000 psi is capable of maintaining flow against a load of 5,000 psi.
Pumps have a power density about ten times greater than an electric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coupling to reduce vibration.
Common types of hydraulic pumps to hydraulic machinery applications are:
Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half of a hydrostatic transmission .
Directional control valves route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. The spool slides to different positions in the housing, and intersecting grooves and channels route the fluid based on the spool's position.
The spool has a central (neutral) position maintained with springs; in this position the supply fluid is blocked, or returned to tank. Sliding the spool to one side routes the hydraulic fluid to an actuator and provides a return path from the actuator to tank. When the spool is moved to the opposite direction the supply and return paths are switched. When the spool is allowed to return to neutral (center) position the actuator fluid paths are blocked, locking it in position.
Directional control valves are usually designed to be stackable, with one valve for each hydraulic cylinder, and one fluid input supplying all the valves in the stack.
Tolerances are very tight in order to handle the high pressure and avoid leaking, spools typically have a clearance with the housing of less than a thousandth of an inch (25 μm). The valve block will be mounted to the machine's frame with a three point pattern to avoid distorting the valve block and jamming the valve's sensitive components.
The spool position may be actuated by mechanical levers, hydraulic pilot pressure, or solenoids which push the spool left or right. A seal allows part of the spool to protrude outside the housing, where it is accessible to the actuator.
The main valve block is usually a stack of off the shelf directional control valves chosen by flow capacity and performance. Some valves are designed to be proportional (flow rate proportional to valve position), while others may be simply on-off. The control valve is one of the most expensive and sensitive parts of a hydraulic circuit.
The hydraulic fluid reservoir holds excess hydraulic fluid to accommodate volume changes from: cylinder extension and contraction, temperature driven expansion and contraction, and leaks. The reservoir is also designed to aid in separation of air from the fluid and also work as a heat accumulator to cover losses in the system when peak power is used. Reservoirs can also help separate dirt and other particulate from the oil, as the particulate will generally settle to the bottom of the tank.
Some designs include dynamic flow channels on the fluid's return path that allow for a smaller reservoir.
Accumulators are a common part of hydraulic machinery. Their function is to store energy by using pressurized gas. One type is a tube with a floating piston. On the one side of the piston there is a charge of pressurized gas, and on the other side is the fluid. Bladders are used in other designs. Reservoirs store a system's fluid.
Examples of accumulator uses are backup power for steering or brakes, or to act as a shock absorber for the hydraulic circuit.
Also known as tractor fluid , hydraulic fluid is the life of the hydraulic circuit. It is usually petroleum oil with various additives. Some hydraulic machines require fire resistant fluids, depending on their applications. In some factories where food is prepared, either an edible oil or water is used as a working fluid for health and safety reasons.
In addition to transferring energy, hydraulic fluid needs to lubricate components, suspend contaminants and metal filings for transport to the filter, and to function well to several hundred degrees Fahrenheit or Celsius.
Filters are an important part of hydraulic systems which removes the unwanted particles from fluid. Metal particles are continually produced by mechanical components and need to be removed along with other contaminants. [ 8 ]
Filters may be positioned in many locations. The filter may be located between the reservoir and the pump intake. Blockage of the filter will cause cavitation and possibly failure of the pump. Sometimes the filter is located between the pump and the control valves. This arrangement is more expensive, since the filter housing is pressurized, but eliminates cavitation problems and protects the control valve from pump failures. The third common filter location is just before the return line enters the reservoir. This location is relatively insensitive to blockage and does not require a pressurized housing, but contaminants that enter the reservoir from external sources are not filtered until passing through the system at least once. Filters are used from 7 micron to 15 micron depends upon the viscosity grade of hydraulic oil.
Hydraulic tubes are seamless steel precision pipes, specially manufactured for hydraulics. The tubes have standard sizes for different pressure ranges, with standard diameters up to 100 mm. The tubes are supplied by manufacturers in lengths of 6 m, cleaned, oiled and plugged. The tubes are interconnected by different types of flanges (especially for the larger sizes and pressures), welding cones/nipples (with o-ring seal), several types of flare connection and by cut-rings. In larger sizes, hydraulic pipes are used. Direct joining of tubes by welding is not acceptable since the interior cannot be inspected.
Hydraulic pipe is used in case standard hydraulic tubes are not available. Generally these are used for low pressure. They can be connected by threaded connections, but usually by welds. Because of the larger diameters the pipe can usually be inspected internally after welding. Black pipe is non-galvanized and suitable for welding .
Hydraulic hose is graded by pressure, temperature, and fluid compatibility. Hoses are used when pipes or tubes can not be used, usually to provide flexibility for machine operation or maintenance. The hose is built up with rubber and steel layers. A rubber interior is surrounded by multiple layers of woven wire and rubber. The exterior is designed for abrasion resistance. The bend radius of hydraulic hose is carefully designed into the machine, since hose failures can be deadly, and violating the hose's minimum bend radius will cause failure. Hydraulic hoses generally have steel fittings swaged on the ends. The weakest part of the high pressure hose is the connection of the hose to the fitting. Another disadvantage of hoses is the shorter life of rubber which requires periodic replacement, usually at five to seven year intervals.
Tubes and pipes for hydraulic n applications are internally oiled before the system is commissioned. Usually steel piping is painted outside. Where flare and other couplings are used, the paint is removed under the nut, and is a location where corrosion can begin. For this reason, in marine applications most piping is stainless steel.
Components of a hydraulic system [sources (e.g. pumps), controls (e.g. valves) and actuators (e.g. cylinders)] need connections that will contain and direct the hydraulic fluid without leaking or losing the pressure that makes them work. In some cases, the components can be made to bolt together with fluid paths built-in. In more cases, though, rigid tubing or flexible hoses are used to direct the flow from one component to the next. Each component has entry and exit points for the fluid involved (called ports) sized according to how much fluid is expected to pass through it.
There are a number of standardized methods in use to attach the hose or tube to the component. Some are intended for ease of use and service, others are better for higher system pressures or control of leakage. The most common method, in general, is to provide in each component a female-threaded port, on each hose or tube a female-threaded captive nut, and use a separate adapter fitting with matching male threads to connect the two. This is functional, economical to manufacture, and easy to service.
Fittings serve several purposes;
A typical piece of machinery or heavy equipment may have thousands of sealed connection points and several different types:
Elastomeric seals (O-ring boss and face seal) are the most common types of seals in heavy equipment and are capable of reliably sealing more than 6,000 psi (41 MPa ) of fluid pressure. | https://en.wikipedia.org/wiki/Hydraulic_drive_system |
A hydraulic drop is a type of local phenomena found in open channel flow . It is a rapid change in the depth of flow from a high stage to a low stage that results in a steep depression in the water surface. It is often caused by an abrupt change in the channel slope.
Another type of local phenomena found in an open channel flow is the hydraulic jump .
Chow, V. T. (2008). Open-channel hydraulics. Caldwell, New Jersey: Blackburn Press.
This fluid dynamics –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydraulic_drop |
Hydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids , principally water and sewage. One feature of these systems is the extensive use of gravity as the motive force to cause the movement of the fluids. This area of civil engineering is intimately related to the design of bridges , dams , channels , canals , and levees , and to both sanitary and environmental engineering .
Hydraulic engineering is the application of the principles of fluid mechanics to problems dealing with the collection, storage, control, transport, regulation, measurement, and use of water. [ 1 ] Before beginning a hydraulic engineering project, one must figure out how much water is involved. The hydraulic engineer is concerned with the transport of sediment by the river, the interaction of the water with its alluvial boundary, and the occurrence of scour and deposition. [ 1 ] "The hydraulic engineer actually develops conceptual designs for the various features which interact with water such as spillways and outlet works for dams, culverts for highways, canals and related structures for irrigation projects, and cooling-water facilities for thermal power plants ." [ 2 ]
A few examples of the fundamental principles of hydraulic engineering include fluid mechanics , fluid flow, behavior of real fluids, hydrology , pipelines, open channel hydraulics, mechanics of sediment transport, physical modeling, hydraulic machines, and drainage hydraulics.
Fundamentals of Hydraulic Engineering defines hydrostatics as the study of fluids at rest. [ 1 ] In a fluid at rest, there exists a force, known as pressure, that acts upon the fluid's surroundings. This pressure, measured in N/m 2 , is not constant throughout the body of fluid. Pressure, p, in a given body of fluid, increases with an increase in depth. Where the upward force on a body acts on the base and can be found by the equation:
where,
Rearranging this equation gives you the pressure head p ρ g = y {\displaystyle {\frac {p}{\rho g}}=y} . Four basic devices for pressure measurement are a piezometer , manometer , differential manometer, Bourdon gauge , as well as an inclined manometer. [ 1 ]
As Prasuhn [ 1 ] states:
The main difference between an ideal fluid and a real fluid is that for ideal flow p 1 = p 2 and for real flow p 1 > p 2 . Ideal fluid is incompressible and has no viscosity. Real fluid has viscosity. Ideal fluid is only an imaginary fluid as all fluids that exist have some viscosity.
A viscous fluid will deform continuously under a shear force by the pascles law, whereas an ideal fluid does not deform.
The various effects of disturbance on a viscous flow are a stable, transition and unstable.
For an ideal fluid, Bernoulli's equation holds along streamlines.
As the flow comes into contact with the plate, the layer of fluid actually "adheres" to a solid surface. There is then a considerable shearing action between the layer of fluid on the plate surface and the second layer of fluid. The second layer is therefore forced to decelerate (though it is not quite brought to rest), creating a shearing action with the third layer of fluid, and so on. As the fluid passes further along with the plate, the zone in which shearing action occurs tends to spread further outwards. This zone is known as the "boundary layer". The flow outside the boundary layer is free of shear and viscous-related forces so it is assumed to act as an ideal fluid. The intermolecular cohesive forces in a fluid are not great enough to hold fluid together. Hence a fluid will flow under the action of the slightest stress and flow will continue as long as the stress is present. [ 3 ] The flow inside the layer can be either vicious or turbulent, depending on Reynolds number. [ 1 ]
Common topics of design for hydraulic engineers include hydraulic structures such as dams , levees , water distribution networks including both domestic and fire water supply, distribution and automatic sprinkler systems, water collection networks, sewage collection networks, storm water management, sediment transport , and various other topics related to transportation engineering and geotechnical engineering . Equations developed from the principles of fluid dynamics and fluid mechanics are widely utilized by other engineering disciplines such as mechanical, aeronautical and even traffic engineers.
Related branches include hydrology and rheology while related applications include hydraulic modeling, flood mapping, catchment flood management plans, shoreline management plans, estuarine strategies, coastal protection, and flood alleviation.
Earliest uses of hydraulic engineering were to irrigate crops and dates back to the Middle East and Africa . Controlling the movement and supply of water for growing food has been used for many thousands of years. One of the earliest hydraulic machines, the water clock was used in the early 2nd millennium BC. [ 4 ] Other early examples of using gravity to move water include the Qanat system in ancient Persia and the very similar Turpan water system in ancient China as well as irrigation canals in Peru. [ 5 ]
In ancient China , hydraulic engineering was highly developed, and engineers constructed massive canals with levees and dams to channel the flow of water for irrigation, as well as locks to allow ships to pass through. Sunshu Ao is considered the first Chinese hydraulic engineer. Another important Hydraulic Engineer in China, Ximen Bao was credited of starting the practice of large scale canal irrigation during the Warring States period (481 BC–221 BC), even today hydraulic engineers remain a respectable position in China.
In the Archaic epoch of the Philippines , hydraulic engineering also developed specially in the Island of Luzon , the Ifugaos of the mountainous region of the Cordilleras built irrigations, dams and hydraulic works and the famous Banaue Rice Terraces as a way for assisting in growing crops around 1000 BC. [ 6 ] These Rice Terraces are 2,000-year-old terraces that were carved into the mountains of Ifugao in the Philippines by ancestors of the indigenous people . The Rice Terraces are commonly referred to as the " Eighth Wonder of the World ". [ 7 ] [ 8 ] [ 9 ] It is commonly thought that the terraces were built with minimal equipment, largely by hand. The terraces are located approximately 1500 metres (5000 ft) above sea level. They are fed by an ancient irrigation system from the rainforests above the terraces. It is said that if the steps were put end to end, it would encircle half the globe. [ 10 ]
Eupalinos of Megara was an ancient Greek engineer who built the Tunnel of Eupalinos on Samos in the 6th century BC, an important feat of both civil and hydraulic engineering. The civil engineering aspect of this tunnel was that it was dug from both ends which required the diggers to maintain an accurate path so that the two tunnels met and that the entire effort maintained a sufficient slope to allow the water to flow.
Hydraulic engineering was highly developed in Europe under the aegis of the Roman Empire where it was especially applied to the construction and maintenance of aqueducts to supply water to and remove sewage from their cities. [ 3 ] In addition to supplying the needs of their citizens they used hydraulic mining methods to prospect and extract alluvial gold deposits in a technique known as hushing , and applied the methods to other ores such as those of tin and lead .
In the 15th century, the Somali Ajuran Empire was the only hydraulic empire in Africa. As a hydraulic empire, the Ajuran State monopolized the water resources of the Jubba and Shebelle Rivers . Through hydraulic engineering, it also constructed many of the limestone wells and cisterns of the state that are still operative and in use today. The rulers developed new systems for agriculture and taxation , which continued to be used in parts of the Horn of Africa as late as the 19th century. [ 11 ]
Further advances in hydraulic engineering occurred in the Muslim world between the 8th and 16th centuries, during what is known as the Islamic Golden Age . Of particular importance was the ' water management technological complex ' which was central to the Islamic Green Revolution . [ 12 ] The various components of this 'toolkit' were developed in different parts of the Afro-Eurasian landmass, both within and beyond the Islamic world. However, it was in the medieval Islamic lands where the technological complex was assembled and standardized, and subsequently diffused to the rest of the Old World. [ 13 ] Under the rule of a single Islamic caliphate , different regional hydraulic technologies were assembled into "an identifiable water management technological complex that was to have a global impact." The various components of this complex included canals , dams , the qanat system from Persia, regional water-lifting devices such as the noria , shaduf and screwpump from Egypt , and the windmill from Islamic Afghanistan . [ 13 ] Other original Islamic developments included the saqiya with a flywheel effect from Islamic Spain, [ 14 ] the reciprocating suction pump [ 15 ] [ 16 ] [ 17 ] and crankshaft - connecting rod mechanism from Iraq , [ 18 ] [ 19 ] and the geared and hydropowered water supply system from Syria . [ 20 ]
In many respects, the fundamentals of hydraulic engineering have not changed since ancient times. Liquids are still moved for the most part by gravity through systems of canals and aqueducts, though the supply reservoirs may now be filled using pumps. The need for water has steadily increased from ancient times and the role of the hydraulic engineer is a critical one in supplying it. For example, without the efforts of people like William Mulholland the Los Angeles area would not have been able to grow as it has because it simply does not have enough local water to support its population. The same is true for many of our world's largest cities. In much the same way, the central valley of California could not have become such an important agricultural region without effective water management and distribution for irrigation. In a somewhat parallel way to what happened in California, the creation of the Tennessee Valley Authority (TVA) brought work and prosperity to the South by building dams to generate cheap electricity and control flooding in the region, making rivers navigable and generally modernizing life in the region.
Leonardo da Vinci (1452–1519) performed experiments, investigated and speculated on waves and jets, eddies and streamlining. Isaac Newton (1642–1727) by formulating the laws of motion and his law of viscosity, in addition to developing the calculus, paved the way for many great developments in fluid mechanics. Using Newton's laws of motion, numerous 18th-century mathematicians solved many frictionless (zero-viscosity) flow problems. However, most flows are dominated by viscous effects, so engineers of the 17th and 18th centuries found the inviscid flow solutions unsuitable, and by experimentation they developed empirical equations, thus establishing the science of hydraulics. [ 3 ]
Late in the 19th century, the importance of dimensionless numbers and their relationship to turbulence was recognized, and dimensional analysis was born. In 1904 Ludwig Prandtl published a key paper, proposing that the flow fields of low-viscosity fluids be divided into two zones, namely a thin, viscosity-dominated boundary layer near solid surfaces, and an effectively inviscid outer zone away from the boundaries. This concept explained many former paradoxes and enabled subsequent engineers to analyze far more complex flows. However, we still have no complete theory for the nature of turbulence, and so modern fluid mechanics continues to be combination of experimental results and theory. [ 21 ]
The modern hydraulic engineer uses the same kinds of computer-aided design (CAD) tools as many of the other engineering disciplines while also making use of technologies like computational fluid dynamics to perform the calculations to accurately predict flow characteristics, GPS mapping to assist in locating the best paths for installing a system and laser-based surveying tools to aid in the actual construction of a system. | https://en.wikipedia.org/wiki/Hydraulic_engineering |
A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery . Common hydraulic fluids are based on mineral oil or water. [ 1 ] Examples of equipment that might use hydraulic fluids are excavators and backhoes , hydraulic brakes , power steering systems, automatic transmissions , garbage trucks , aircraft flight control systems , lifts , and industrial machinery .
Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has zero compressibility .
The primary function of a hydraulic fluid is to convey power. In use, however, there are other important functions of hydraulic fluid such as protection of the hydraulic machine components. The table below lists the major functions of a hydraulic fluid and the properties of a fluid that affect its ability to perform that function: [ 2 ]
The original hydraulics fluid, dating back to the time of ancient Egypt , was water . [ citation needed ] Beginning in the 1920s, mineral oil began to be used more than water as a base stock due to its inherent lubrication properties and ability to be used at temperatures above the boiling point of water. Today most hydraulic fluids are based on mineral oil base stocks.
Natural oils such as rapeseed are used as base stocks for fluids where biodegradability and renewable sources are considered important.
Other base stocks are used for specialty applications, such as for fire resistance and extreme temperature applications. Some examples include: glycol ethers , organophosphate ester , polyalphaolefin , propylene glycol , and silicone oils .
NaK -77, a eutectic alloy of sodium and potassium , can be used as a hydraulic fluid in high-temperature and high-radiation environments, for temperature ranges of 10 to 1,400 °F (−12 to 760 °C). Its bulk modulus at 1,000 °F (538 °C) is 310,000 psi (2.14 GPa), higher than of a hydraulic oil at room temperature. Its lubricity is poor, so positive-displacement pumps are unsuitable and centrifugal pumps have to be used. The addition of caesium shifts the useful temperature range to −95 to 1,300 °F (−71 to 704 °C). The NaK-77 alloy was tested in hydraulic and fluidic systems for the Supersonic Low Altitude Missile . [ 3 ]
Hydraulic fluids can contain a wide range of chemical compounds, including: oils , butanol , esters (e.g. phthalates , like DEHP , and adipates , like bis(2-ethylhexyl) adipate ), polyalkylene glycols (PAG), organophosphate (e.g. tributylphosphate ), silicones, alkylated aromatic hydrocarbons, polyalphaolefins (PAO) (e.g. polyisobutenes ), corrosion inhibitors (incl acid scavengers ), anti- erosion additives, etc.
Environmentally sensitive applications (e.g. farm tractors and marine dredging ) may benefit from using biodegradable hydraulic fluids based upon rapeseed vegetable oil when there is the risk of an oil spill from a ruptured oil line. Typically these oils are available as ISO 32, ISO 46, and ISO 68 specification oils. ASTM standards ASTM-D-6006, Guide for Assessing Biodegradability of Hydraulic Fluids and ASTM-D-6046, Standard Classification of Hydraulic Fluids for Environmental Impact are relevant.
Anti-wear (AW) hydraulic oils are made from a petroleum base fluid and commonly contain the anti-wear additive Zinc dialkyldithiophosphate (ZDDP) . This additive works to protect the hydraulic pump. They come in multiple viscosity grades that have varying applications. For example, AW 46 hydraulic oils can be used to operate the hydraulic systems in off-road equipment such as dump trucks, excavators, and backhoes, while AW 32 hydraulic oils may be more suitable for colder weather applications like in a snow plow's pump. [ 4 ]
Because industrial hydraulic systems operate at hundreds to thousands of PSI and temperatures reaching hundreds of degrees Celsius, severe injuries and death can result from component failures and care must always be taken when performing maintenance on hydraulic systems. [ 5 ]
Fire resistance is a property available with specialized fluids. Water-glycol and polyol-ester are some of these specialized fluids that contain excellent thermal and hydrolitic properties, which aid in fire resistance. [ 6 ]
Brake fluid is a subtype of hydraulic fluid with high boiling point , both when new (specified by the equilibrium boiling point) and after absorption of water vapor (specified by wet boiling point). Under the heat of braking, both free water and water vapor in a braking system can boil into a compressible vapor , resulting in brake failure. [ 7 ] Glycol-ether based fluids are hygroscopic , and absorbed moisture will greatly reduce the boiling point over time. Mineral oil and silicone based fluids are not hygroscopic.
Power steering fluid is a sub type of hydraulic fluid. Most are mineral oil or silicone based fluids, while some use automatic transmission fluid , made from synthetic base oil. [ 8 ] [ 9 ] Automatic transmissions use fluids for their lubrication, cooling and hydraulic properties for viscous couplings .
Use of the wrong type of fluid can lead to failure of the power steering pump. [ 8 ]
As aircraft performance increased in the mid-20th century, the amount of force required to operate mechanical flight controls became excessive, and hydraulic systems were introduced to reduce pilot effort. The hydraulic actuators are controlled by valves; these in turn are operated directly by input from the aircrew (hydro-mechanical) or by computers obeying control laws (fly by wire).
Hydraulic power is used for other purposes. It can be stored in accumulators to start an auxiliary power unit (APU) for self-starting the aircraft's main engines. Many aircraft equipped with the M61 family of cannon use hydraulic power to drive the gun system, permitting reliable high rates of fire.
The hydraulic power itself comes from pumps driven by the engines directly, or by electrically driven pumps . In modern commercial aircraft these are electrically driven pumps; should all the engines fail in flight the pilot will deploy a propeller-driven electric generator called a Ram-Air Turbine (RAT) which is concealed under the fuselage. [ 10 ] This provides electrical power for the hydraulic pumps and control systems as power is no longer available from the engines. In that system and others, electric pumps can provide both redundancy and the means of operating hydraulic systems without the engines operating, which can be very useful during maintenance.
Special, stringent care is required when handling aircraft hydraulic fluid, as it is critical to flight safety that it stay free from contamination. It is also necessary to strictly adhere to authorized references when servicing or repairing any aircraft system. Samples from aircraft hydraulic systems are taken during heavy aircraft maintenance checks (primarily C and D checks) to check contamination. [ 11 ]
Military Spec 1246C is one fluid contamination specification.
The ISO fluid contamination scale assigns a contamination category based on particle size count and distribution. [ 12 ]
The properties of HLP 32 hydraulic oil make it ideal for lubricating machine tools. [ 13 ] [ 14 ]
Source: [ 15 ] [ 16 ]
Source: [ 15 ]
Synthetic hydrocarbon base:
These synthetic fluids are compatible with mineral-base hydraulic fluids and were developed to address the low flash point draw back of mineral based hydraulic fluids. [ 17 ]
Source: [ 15 ] [ 19 ]
Source: [ 20 ]
Commonly used hydraulic oil viscosities fall under the ISO VG (Viscosity Grade) classification system, which is based on the oil's kinematic viscosity at 40 °C (104 °F). The most prevalent grades for general industrial and mobile hydraulic systems are typically:
Additional viscosities such as the following, are also used, but less frequently or for specific low/high-temperature applications. | https://en.wikipedia.org/wiki/Hydraulic_fluid |
Hydraulic head or piezometric head is a measurement related to liquid pressure (normalized by specific weight ) and the liquid elevation above a vertical datum . [ 1 ] [ 2 ] It is usually measured as an equivalent liquid surface elevation, expressed in units of length, at the entrance (or bottom) of a piezometer . In an aquifer , it can be calculated from the depth to water in a piezometric well (a specialized water well ), and given information of the piezometer's elevation and screen depth. Hydraulic head can similarly be measured in a column of water using a standpipe piezometer by measuring the height of the water surface in the tube relative to a common datum. The hydraulic head can be used to determine a hydraulic gradient between two or more points.
In fluid dynamics , the head at some point in an incompressible (constant density) flow is equal to the height of a static column of fluid whose pressure at the base is equal to the total energy per unit volume at that point. As greater energy per unit volume corresponds to a taller column, head increases with energy per unit volume and serves as an alternate measure of it.
Head has dimension of length and is expressed in units such as meters or feet, whereas energy per unit volume has dimensions of energy over volume, and is expressed in units such as Pa or psi. The parallel is made clearer by noting that head can be equivalently considered to have dimensions of energy over weight; the higher a mass of liquid is raised, the greater its potential energy per unit weight. The equivalence of weight and volume follows from the assumption of an incompressible flow, given that these quantities stand in a proportional relationship for constant density.
The hydrostatic pressure at the base of a column of fluid with density ρ {\displaystyle \rho } , height h {\displaystyle h} and gravitational acceleration g {\displaystyle g} , as well as the potential energy per unit volume of a static fluid element at height h {\displaystyle h} above datum, is ρ g h {\displaystyle \rho gh} . The total energy per unit volume is given by Bernoulli's equation in pressure form with static pressure p {\displaystyle p} , velocity v {\displaystyle v} and height z {\displaystyle z} as p + 1 2 ρ v 2 + ρ g z {\displaystyle p+{\frac {1}{2}}\rho v^{2}+\rho gz} . Equating these and dividing by ρ g {\displaystyle \rho g} leads to, h = p ρ g + v 2 2 g + z {\displaystyle h={\frac {p}{\rho g}}+{\frac {v^{2}}{2g}}+z} .
The individual terms can be interpreted as follows:
On Earth, additional height of fresh water adds a static pressure of about 9.8 kPa per meter (0.098 bar/m) or 0.433 psi per foot of water column height.
The static head of a pump is the maximum height (pressure) it can deliver. The capability of the pump at a certain RPM can be read from its Q-H curve (flow vs. height).
Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density.
After free falling through a height h {\displaystyle h} in a vacuum from an initial velocity of 0, a mass will have reached a speed v = 2 g h {\displaystyle v={\sqrt {{2g}{h}}}} where g {\displaystyle g} is the acceleration due to gravity. Rearranged as a head : h = v 2 2 g . {\displaystyle h={\frac {v^{2}}{2g}}.}
The term v 2 2 g {\displaystyle {\frac {v^{2}}{2g}}} is called the velocity head , expressed as a length measurement. In a flowing fluid, it represents the energy of the fluid due to its bulk motion.
The total hydraulic head of a fluid is composed of pressure head and elevation head . [ 1 ] [ 2 ] The pressure head is the equivalent gauge pressure of a column of water at the base of the piezometer, and the elevation head is the relative potential energy in terms of an elevation. The head equation , a simplified form of the Bernoulli principle for incompressible fluids, can be expressed as: h = ψ + z {\displaystyle h=\psi +z} where
In an example with a 400 m deep piezometer, with an elevation of 1000 m, and a depth to water of 100 m: z = 600 m, ψ = 300 m, and h = 900 m.
The pressure head can be expressed as: ψ = P γ = P ρ g {\displaystyle \psi ={\frac {P}{\gamma }}={\frac {P}{\rho g}}} where P {\displaystyle P} is the gauge pressure (Force per unit area, often Pa or psi),
The pressure head is dependent on the density of water, which can vary depending on both the temperature and chemical composition ( salinity , in particular). This means that the hydraulic head calculation is dependent on the density of the water within the piezometer. If one or more hydraulic head measurements are to be compared, they need to be standardized, usually to their fresh water head , which can be calculated as:
where
The hydraulic gradient is a vector gradient between two or more hydraulic head measurements over the length of the flow path. For groundwater , it is also called the Darcy slope , since it determines the quantity of a Darcy flux or discharge. It also has applications in open-channel flow where it is also known as stream gradient and can be used to determine whether a reach is gaining or losing energy.
The hydraulic gradient norm i {\displaystyle i} , a dimensionless quantity (of kind length per length), can be calculated between two points with known head values as a ratio: i = d h d l {\displaystyle i={\frac {dh}{dl}}} where
The hydraulic gradient vector ∇ h {\textstyle \nabla h} can be formulated using the del operator for a spatial gradient . This requires a hydraulic head field , which can be practically obtained only from numerical models, such as MODFLOW for groundwater or standard step or HEC-RAS for open channels. In Cartesian coordinates , this can be expressed as: ∇ h = ( ∂ h ∂ x , ∂ h ∂ y , ∂ h ∂ z ) = ∂ h ∂ x i + ∂ h ∂ y j + ∂ h ∂ z k {\displaystyle \nabla h=\left({\frac {\partial h}{\partial x}},{\frac {\partial h}{\partial y}},{\frac {\partial h}{\partial z}}\right)={\frac {\partial h}{\partial x}}\mathbf {i} +{\frac {\partial h}{\partial y}}\mathbf {j} +{\frac {\partial h}{\partial z}}\mathbf {k} } This vector describes both the magnitude and the direction of the groundwater flow, where negative values indicate flow along the dimension, and zero indicates 'no flow'. As with any other example in physics, energy must flow from high to low, which is why the flow is in the negative gradient. This vector can be used in conjunction with Darcy's law and a tensor of hydraulic conductivity to determine the flux of water in three dimensions.
The distribution of hydraulic head through an aquifer determines where groundwater will flow. In a hydrostatic example (first figure), where the hydraulic head is constant, there is no flow. However, if there is a difference in hydraulic head from the top to bottom due to draining from the bottom (second figure), the water will flow downward, due to the difference in head, also called the hydraulic gradient .
Even though it is convention to use gauge pressure in the calculation of hydraulic head, it is more correct to use absolute pressure (gauge pressure + atmospheric pressure ), since this is truly what drives groundwater flow. Often detailed observations of barometric pressure are not available at each well through time, so this is often disregarded (contributing to large errors at locations where hydraulic gradients are low or the angle between wells is acute.)
The effects of changes in atmospheric pressure upon water levels observed in wells has been known for many years. The effect is a direct one, an increase in atmospheric pressure is an increase in load on the water in the aquifer, which increases the depth to water (lowers the water level elevation). Pascal first qualitatively observed these effects in the 17th century, and they were more rigorously described by the soil physicist Edgar Buckingham (working for the United States Department of Agriculture (USDA)) using air flow models in 1907.
In any real moving fluid, energy is dissipated due to friction ; turbulence dissipates even more energy for high Reynolds number flows. This dissipation, called head loss , is divided into two main categories, "major losses" associated with energy loss per length of pipe, and "minor losses" associated with bends, fittings, valves, etc. The most common equation used to calculate major head losses is the Darcy–Weisbach equation . Older, more empirical approaches are the Hazen–Williams equation and the Prony equation .
For relatively short pipe systems, with a relatively large number of bends and fittings, minor losses can easily exceed major losses. In design, minor losses are usually estimated from tables using coefficients or a simpler and less accurate reduction of minor losses to equivalent length of pipe, a method often used for shortcut calculations of pneumatic conveying lines pressure drop. [ 3 ] | https://en.wikipedia.org/wiki/Hydraulic_head |
A hydraulic jump is a phenomenon in the science of hydraulics which is frequently observed in open channel flow such as rivers and spillways . When liquid at high velocity discharges into a zone of lower velocity, a rather abrupt rise occurs in the liquid surface. The rapidly flowing liquid is abruptly slowed and increases in height, converting some of the flow's initial kinetic energy into an increase in potential energy, with some energy irreversibly lost through turbulence to heat. In an open channel flow, this manifests as the fast flow rapidly slowing and piling up on top of itself similar to how a shockwave forms.
It was first observed and documented by Leonardo da Vinci in the 1500s. [ 1 ] The mathematics were first described by Giorgio Bidone of Turin University when he published a paper in 1820 called Experiences sur le remou et sur la propagation des ondes . [ 2 ]
The phenomenon is dependent upon the initial fluid speed. If the initial speed of the fluid is below the critical speed, then no jump is possible. For initial flow speeds which are not significantly above the critical speed, the transition appears as an undulating wave. As the initial flow speed increases further, the transition becomes more abrupt, until at high enough speeds, the transition front will break and curl back upon itself. When this happens, the jump can be accompanied by violent turbulence, eddying, air entrainment, and surface undulations, or waves .
There are two main manifestations of hydraulic jumps and historically different terminology has been used for each. However, the mechanisms behind them are similar because they are simply variations of each other seen from different frames of reference, and so the physics and analysis techniques can be used for both types.
The different manifestations are:
A related case is a cascade – a wall or undulating wave of water moves downstream overtaking a shallower downstream flow of water as shown in Figure 5. If considered from a frame of reference which moves with the wave front, this is amenable to the same analysis as a stationary jump.
These phenomena are addressed in an extensive literature from a number of technical viewpoints. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] [ 17 ] [ 18 ]
Hydraulic Jump is used sometimes in mixing chemicals. [ 19 ]
Hydraulic jumps can be seen in both a stationary form, which is known as a "hydraulic jump", and a dynamic or moving form, which is known as a positive surge or "hydraulic jump in translation". [ 16 ] They can be described using the same analytic approaches and are simply variants of a single phenomenon. [ 15 ] [ 16 ] [ 18 ]
A tidal bore is a hydraulic jump which occurs when the incoming tide forms a wave (or waves) of water that travel up a river or narrow bay against the direction of the current. [ 16 ] As is true for hydraulic jumps in general, bores take on various forms depending upon the difference in the waterlevel upstream and down, ranging from an undular wavefront to a shock-wave-like wall of water. [ 9 ] Figure 3 shows a tidal bore with the characteristics common to shallow upstream water – a large elevation difference is observed. Figure 4 shows a tidal bore with the characteristics common to deep upstream water – a small elevation difference is observed and the wavefront undulates. In both cases the tidal wave moves at the speed characteristic of waves in water of the depth found immediately behind the wave front. A key feature of tidal bores and positive surges is the intense turbulent mixing induced by the passage of the bore front and by the following wave motion. [ 20 ]
Another variation of the moving hydraulic jump is the cascade. In the cascade, a series of roll waves or undulating waves of water moves downstream overtaking a shallower downstream flow of water.
A moving hydraulic jump is called a surge. The travel of wave is faster in the upper portion than in the lower portion in case of positive surges
A stationary hydraulic jump is the
type most frequently seen on rivers and on engineered features such as outfalls of dams and irrigation works. They occur when a flow of liquid at high velocity discharges into a zone of the river or engineered structure which can only sustain a lower velocity. When this occurs, the water slows in a rather abrupt rise (a step or standing wave ) on the liquid surface. [ 17 ]
Comparing the characteristics before and after, one finds:
The other stationary hydraulic jump occurs when a rapid flow encounters a submerged object which throws the water upward. The mathematics behind this form is more complex and will need to take into account the shape of the object and the flow characteristics of the fluid around it.
In spite of the apparent complexity of the flow transition, application of simple analytic tools to a two dimensional analysis is effective in providing analytic results which closely parallel both field and laboratory results. Analysis shows:
The height of the jump is derived from the application of the equations of conservation of mass and momentum. [ 18 ] There are several methods of predicting the height of a hydraulic jump. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 10 ] [ 15 ] [ 18 ] [ 21 ]
They all reach common conclusions that:
For a known flow rate q , {\displaystyle q,} as shown by the figure below, the approximation that the momentum flux is the same just up- and downstream of the energy principle yields an expression of the energy loss in the hydraulic jump. Hydraulic jumps are commonly used as energy dissipators downstream of dam spillways.
In fluid dynamics, the equation of continuity is effectively an equation of conservation of mass . Considering any fixed closed surface within an incompressible moving fluid, the fluid flows into a given volume at some points and flows out at other points along the surface with no net change in mass within the space since the density is constant. In case of a rectangular channel, then the equality of mass flux upstream ( ρ v 0 h 0 {\displaystyle \rho v_{0}h_{0}} ) and downstream ( ρ v 1 h 1 {\displaystyle \rho v_{1}h_{1}} ) gives:
with ρ {\displaystyle \rho } the fluid density , v 0 {\displaystyle v_{0}} and v 1 {\displaystyle v_{1}} the depth- averaged flow velocities upstream and downstream, and h 0 {\displaystyle h_{0}} and h 1 {\displaystyle h_{1}} the corresponding water depths.
For a straight prismatic rectangular channel, the conservation of momentum flux across the jump, assuming constant density, can be expressed as:
In rectangular channel, such conservation equation can be further simplified to dimensionless M-y equation form , which is widely used in hydraulic jump analysis in open channel flow.
Jump height in terms of flow
Dividing by constant ρ {\displaystyle \rho } and introducing the result from continuity gives
which, after some algebra, simplifies to:
where F r 2 = v 0 2 g h 0 . {\displaystyle Fr^{2}={v_{0}^{2} \over gh_{0}}.} Here F r {\displaystyle Fr} is the dimensionless Froude number , and relates inertial to gravitational forces in the upstream flow. Solving this quadratic yields:
Negative answers do not yield meaningful physical solutions, so this reduces to:
known as Bélanger equation. The result may be extended to an irregular cross-section. [ 18 ]
This produces three solution classes:
This is equivalent to the condition that F r > 1 {\displaystyle \ Fr>1} . Since the g h 0 {\displaystyle \ {\sqrt {gh_{0}}}} is the speed of a shallow gravity wave , the condition that F r > 1 {\displaystyle \ Fr>1} is equivalent to stating that the initial velocity represents supercritical flow (Froude number > 1) while the final velocity represents subcritical flow (Froude number < 1).
Practically this means that water accelerated by large drops can create stronger standing waves ( undular bores ) in the form of hydraulic jumps as it decelerates at the base of the drop. Such standing waves, when found downstream of a weir or natural rock ledge, can form an extremely dangerous "keeper" with a water wall that "keeps" floating objects (e.g., logs, kayaks, or kayakers) recirculating in the standing wave for extended periods.
One of the most important engineering applications of the hydraulic jump is to dissipate energy in channels, dam spillways, and similar structures so that the excess kinetic energy does not damage these structures. The rate of energy dissipation or head loss across a hydraulic jump is a function of the hydraulic jump inflow Froude number and the height of the jump. [ 15 ]
The energy loss at a hydraulic jump expressed as a head loss is:
Δ E = ( h 1 − h 0 ) 3 4 h 0 h 1 {\displaystyle \Delta E={\frac {(h_{1}-h_{0})^{3}}{4h_{0}h_{1}}}} [ 22 ]
In the design of a dam the energy of the fast-flowing stream over a spillway must be partially dissipated to prevent erosion of the streambed downstream of the spillway, which could ultimately lead to failure of the dam. This can be done by arranging for the formation of a hydraulic jump to dissipate energy. To limit damage, this hydraulic jump normally occurs on an apron engineered to withstand hydraulic forces and to prevent local cavitation and other phenomena which accelerate erosion.
In the design of a spillway and apron, the engineers select the point at which a hydraulic jump will occur. Obstructions or slope changes are routinely designed into the apron to force a jump at a specific location. Obstructions are unnecessary, as the slope change alone is normally sufficient. To trigger the hydraulic jump without obstacles, an apron is designed such that the flat slope of the apron retards the rapidly flowing water from the spillway. If the apron slope is insufficient to maintain the original high velocity, a jump will occur.
Two methods of designing an induced jump are common:
In both cases, the final depth of the water is determined by the downstream characteristics. The jump will occur if and only if the level of inflowing (supercritical) water level ( h 0 {\displaystyle h_{0}} ) satisfies the condition:
The hydraulic jump is characterised by a highly turbulent flow. Macro-scale vortices develop in the jump roller and interact
with the free surface leading to air bubble entrainment, splashes and droplets formation in the two-phase flow region. [ 23 ] [ 24 ] The air–water flow is associated with turbulence, which can also lead to sediment transport. The turbulence may be strongly affected by the bubble dynamics. Physically, the mechanisms involved in these processes are complex.
The air entrainment occurs in the form of air bubbles and air packets entrapped at the impingement of the upstream jet flow with the roller. The air packets are broken up in very small air bubbles as they are entrained in the shear region, characterised by large air contents and maximum bubble count rates. [ 25 ] Once the entrained bubbles are advected into regions of lesser shear, bubble collisions and coalescence lead to larger air entities that are driven toward the free-surface by a combination of buoyancy and turbulent advection.
NB: the above classification is very rough. Undular hydraulic jumps have been observed with inflow/prejump Froude numbers up to 3.5 to 4. [ 15 ] [ 16 ]
A number of variations are amenable to similar analysis:
Figure 2 above illustrates an example of a hydraulic jump, often seen in a kitchen sink. Around the place where the tap water hits the sink, a smooth-looking flow pattern will occur. A little further away, a sudden "jump" in the water level will be present. This is a hydraulic jump.
A circular impinging jet creates a thin film of liquid that spreads radially, with a circular hydraulic jump occurring downstream. For laminar jets, the thin film and the hydraulic jump can be remarkably smooth and steady. In 1993, Liu and Lienhard demonstrated the role of surface tension in setting the structure of hydraulic jumps in these thin films. [ 26 ] Many subsequent studies have explored surface tension and pattern formation is such jumps. [ 27 ]
A 2018 study [ 28 ] experimentally and theoretically investigated the relative contributions of surface tension and gravity to the circular hydraulic jump. To rule out the role of gravity in the formation of a circular hydraulic jump, the authors performed experiments on horizontal, vertical and inclined surfaces finding that irrespective of the orientation of the substrate, for same flow rate and physical properties of the liquid, the initial hydraulic jump happens at the same location. They proposed a model for the phenomenon and
found the general criterion for a thin film hydraulic jump to be
where W e {\displaystyle We} is the local Weber number and F r {\displaystyle Fr} is the local Froude number .
For kitchen sink scale hydraulic jumps, the Froude number remains high, therefore, the effective criteria for the thin film hydraulic jump is W e = 1 {\displaystyle We=1} . In other words, a thin film hydraulic jump occurs when the liquid momentum per unit width equals the surface tension of the liquid. [ 28 ] However, this model stays heavily contested. [ 29 ]
Turbidity currents can result in internal hydraulic jumps (i.e., hydraulic jumps as internal waves in fluids of different density) in abyssal fan formation. The internal hydraulic jumps have been associated with salinity or temperature induced stratification as well as with density differences due to suspended materials. When the slope of the bed (over which the turbidity current flows) flattens, the slower rate of flow is mirrored by increased sediment deposition below the flow, producing a gradual backward slope. Where a hydraulic jump occurs, the signature is an abrupt backward slope, corresponding to the rapid reduction in the flow rate at the point of the jump. [ 30 ]
Hydraulic jumps occur in the atmosphere in the air flowing over mountains. [ 31 ] A hydraulic jump also occurs at the tropopause interface between the stratosphere and troposphere downwind of the overshooting top of very strong supercell thunderstorms. [ 32 ] A related situation is the Morning Glory cloud observed, for example, in Northern Australia, sometimes called an undular jump. [ 16 ]
The hydraulic jump is the most commonly used choice of design engineers for energy dissipation below spillways and outlets. A properly designed hydraulic jump can provide for 60-70% energy dissipation of the energy in the basin itself, limiting the damage to structures and the streambed. Even with such efficient energy dissipation, stilling basins must be carefully designed to avoid serious damage due to uplift, vibration, cavitation , and abrasion. An extensive literature has been developed for this type of engineering. [ 7 ] [ 8 ] [ 13 ] [ 15 ]
While travelling down river, kayaking and canoeing paddlers will often stop and playboat in standing waves and hydraulic jumps. The standing waves and shock fronts of hydraulic jumps make for popular locations for such recreation.
Similarly, kayakers and surfers have been known to ride tidal bores up rivers.
Hydraulic jumps have been used by glider pilots in the Andes and Alps [ 31 ] and to ride Morning Glory effects in Australia. [ 33 ] | https://en.wikipedia.org/wiki/Hydraulic_jump |
Hydraulic jump in a rectangular channel , also known as classical jump , is a natural phenomenon that occurs whenever flow changes from supercritical to subcritical flow. In this transition, the water surface rises abruptly, surface rollers are formed, intense mixing occurs, air is entrained, and often a large amount of energy is dissipated. Numeric models created using the standard step method or HEC-RAS are used to track supercritical and subcritical flows to determine where in a specific reach a hydraulic jump will form.
There are common hydraulic jumps that occur in everyday situations such as during the use of a household sink. There are also man-made hydraulic jumps created by devices like weirs or sluice gates. In general, a hydraulic jump may be used to dissipate energy, to mix chemicals, or to act as an aeration device. [ 1 ] [ 2 ]
To produce equations describing the jump, since there is an unknown energy loss, there is a need to apply conservation of momentum . [ 3 ] To develop this equation, a general situation in which there may or may not be an energy loss between upstream and downstream, and there may or may not be some obstacle on which there is a drag force P f is considered. however, for a simple or classic hydraulic jump the force per unit width(P f ) equals 0. From there the momentum equation, and the conjugate depths equation can be derived.
The depth of supercritical flow, y 1 , ‘jumps’ up to its subcritical conjugate depth, y 2 , and the result of this abrupt change in flow conditions is considerable turbulence and Energy Loss, E L . [ 4 ] Figure 1 shows a schematic of typical jump characteristics where E 1 is the energy of the upstream flow, E 2 is the energy of the downstream flow and L j is the length of the hydraulic jump. A series of small surface rollers are formed in a standing wave like the one shown in Figure 1.
Figure 1. Hydraulic Jump Overall Schematic
Hydraulic jumps occur commonly in everyday situations such as during the use of any household sink . The jump can be seen in the form of a circular, stationary wave surrounding the inflow of water. The hydraulic jump occurs at the point where the seemingly still water becomes turbulent. As water hits the sink, it disperses, increasing in depth to a critical radius where the flow (supercritical with low depth, high velocity, and a Froude number greater than 1) must suddenly jump to a greater, subcritical depth (high depth, low velocity, and a Froude number less than 1) that is known to conserve momentum .
Figure 2. Turbulent hydraulic jump can be created in sink (left), viscous hydraulic jump can create advanced shapes (right)
(Images courtesy of John Bush, MIT) [ 5 ]
Hydraulic jumps may also be manmade; as seen in Figure 2, scientists have been experimenting with the effects of viscosity on the hydraulic jump and have been able to create steady asymmetrical forms. [ 6 ] In more practical applications, jumps are created in the environment with specific purposes such as erosion prevention. Erosion in stream beds is often caused by a high velocity water flow which leads to sediment transport. This process can be prevented by decreasing the velocity of the flow into the stream bed with the introduction of a hydraulic jump. Often in these cases, a hydraulic jump is created by devices such as a weir or sluice gate where the turbulent flow enters the stream. The mixture of chemical constituents in a solution is another practical use for hydraulic jumps. Introducing a hydraulic jump rapidly increases the turbulence of the flow, allowing sufficient constituent mixing without the use of any additional mechanisms. The wastewater industry sometimes uses hydraulic jumps as a way to mix solutions, minimizing the need to implement more expensive mechanical mixing systems.
Figure 3. Weir in Riverfront Park, WA (left) and Hydraulic Jump in Coagulation Chamber (right)
Still another use for manmade hydraulic jumps is energy dissipation . One example of an energy dissipating use is a hydraulic jump stilling basin. In these basins, horizontal and sloping aprons are used to dissipate up to 60% of the energy of incoming flow; the basins implement devices such as chute blocks, baffle piers, and dentated ends whose effectiveness in energy dissipation is dependent on the Froude number of the incoming flow. ‘Hydraulic jump stilling basins are not typically suggested for use when dealing with heads greater than 100 meters due to complications caused by turbulences like intermittent cavitation , vibration, uplift, and hydrodynamic loading.’ [ 7 ] Other hydraulic structures such as dams and weirs also use these same energy dissipating principles to reduce the incoming force from turbulent flows that tend to scour or erode downstream areas.
Figure 4. Stilling Basin On Oker River in the Harz-Mointains at Opened Scour Outlet (left) and Stilling Basin for Griggs Dam in Columbus, OH (right)
Momentum is defined as the product of mass times velocity, and like velocity, it is a vector . French Scientist and Philosopher of the early 1600s René Descartes first discovered the concept of momentum but got stuck on the amount of motion (speed) which was not being conserved. Christiaan Huygens , a Dutch Scientist, pointed out that the "quantity of motion" did not need to be a positive value; a negative value meant that it was moving in the opposite direction.
The basic principles behind the momentum function are:
The following derivation is for the momentum function of a simple momentum conserving hydraulic jump in a rectangular channel with constant width.
Conjugate depths are the depths ( y 1 ) upstream and the depth (y 2 ) downstream of the hydraulic jump whose momentum functions are equal for a given unit discharge, q . The depth upstream of a hydraulic jump is always supercritical, and the depth downstream of a hydraulic jump is always subcritical. It is important to note that the conjugate depth is different than the alternate depths for flow which are used in energy conservation calculations.
(1) Beginning with momentum function [ citation needed ] , we equate momentum between locations 1 and 2:
(2) Rearranging terms by moving the q terms to the left and the 1/2 terms to the right, we get:
(3) We then multiply to get a common denominator on the left-hand side and factor the right-hand side:
(4) The ( y 2 − y 1 ) term cancels out:
(5) Divide by y 1 2
(6) Multiply by y 2 and expand right-hand side:
(7) Substitute x for the quantity y 2 / y 1 . We have a quadratic equation in x :
(8) Using the quadratic equation:
(9) Hence, substituting the constant y 2 / y 1 back in for x to get the conjugate depth equation:
Given:
Find:
Solution:
The M-y Diagram for this example is plotted below. To develop the M-y Diagram, we plot the value of M as a function of depth with M on the x-axis and depth on the y-axis since this is more naturally conducive to visualizing the change in momentum with depth. This example is a very basic hydraulic jump situation where the flow approaches at a supercritical depth, y 1 , and jumps to its subcritical conjugate depth, y 2 , in order to obtain the necessary energy to continue moving down the channel with the given flow rate , q .
Figure 6. M-y Diagram
The M-y Diagram is a graphical representation of the conservation of momentum and can be applied over a hydraulic jump to find the upstream and downstream depths. We can see from the above example that the flow approaches supercritically at a depth of y 1 . There is a jump to the subcritical conjugate depth of y 1 which is labeled as y 2 in Figure 6. Figure 6 helps in visualizing how two depths can exist with the same momentum.
There are a few key locations on the M-y diagram which are labeled in Figure 6 above developed based on the information in Example 1. The first location of interest is the critical point labeled with y c and M c in Figure 6. The critical point represents the minimum value of the momentum function available for that particular flow per unit width, q . An increase in q would cause the M function to move to the right and slightly up, giving the flow access to more momentum at its critical point. It follows that a decrease in the q value would move the M function down and to the left, decreasing the momentum available to the flow at its critical value. This is shown graphically Figure 7 below.
Figure 7. Effect of increasing q on depth up- and down-stream of hydraulic jump
From Figure 7, it can also be seen what effect increasing the flow rate, q , will have on the depth up- and down-stream of the jump. Increasing the incoming flow rate (from q = 10 ft 2 /s to 30 ft 2 /s in Figure 7) will result in an increase in the supercritical approach depth and a decrease in the subcritical depth post-jump. This can be seen in Figure 6 by the decrease in depth from y 1,q=30 to y 1,q=10 and the increase in depth between y 2,q=30 and y 2,q=10 . From this analysis of the change in depth due to a change in flow rate, we can also imagine that the energy lost in a jump with a value of q = 10 ft 2 /s would be different from that of a jump with q = 30 ft 2 /s. This is further discussed in Section 5.1.
Although momentum is conserved throughout the hydraulic jump, the energy is not. There is an initial loss of energy when the flow jumps from supercritical to subcritical depths. The resulting loss of energy is equal to the change in specific energy across the jump and is given by the equation for ΔE below. The equation below is based on the condition that y 1 and y 2 are conjugate depths.
When looking at the critical points on the M-y diagram and what their locations tell us about the nature of the hydraulic jump, we mentioned that an increase in q would affect the energy lost in the jump. From Figure 7 we see that increasing the flow rate decreases the difference in the upstream and downstream depth of the jump ( y 2 – y 1 ). From this we can infer that if the momentum is held to be constant, there will be a decrease in the energy lost in the jump if the flow rate is increased.
The efficiency of the jump is determined by the dimensionless parameter E 2 /E 1 which tells us how much of the original energy is remaining after the jump is complete. [ 8 ] The equation for the energy efficiency is given below and shows the heavy dependence that the efficiency has on the Froude number of the upstream flow. Example 2 shows a sample calculation for energy loss and efficiency.
Given:
Find:
Solution:
Length of a hydraulic jump is often hard to measure in the field and during laboratory investigations due to the sudden changes in surface turbulence, in addition to the formation of roller and eddies. [ 9 ] The length of a hydraulic jump is often an important factor to know when considering the design of structures like settling basins .
The equation derived for length is based on experimental data, and relates the length to the upstream Froude number.
Given:
Find:
Solution:
The height of the hydraulic jump, similar to length, is useful to know when designing waterway structures like settling basins or spillways . The height of the hydraulic jump is simply the difference in flow depths prior to and after the hydraulic jump. The height can be determined using the Froude number and upstream energy.
Equations:
Substitute y 2 equation into jump height equation:
Given:
Find:
Solution:
A hydraulic jump can assume several distinct forms depending on the approach Froude number , Fr 1 . [ 11 ] Each of these types has unique flow patterns and flow characteristics, such as the strength and formation of rollers and eddies, that help to determine the amount of energy dissipation that will occur in the jump. The following descriptions of jump types are based on specific ranges of Froude numbers , but these ranges are not precise and that overlap can occur near the endpoints.
For the case when 1 < Fr 1 < 1.7, y 1 and y 2 are approximately equal and only a very small jump occurs. [ 11 ] In this range, the water surface shows slight undulations and because of this, jumps in this range are sometimes known as undular jumps. These surface riffles generally result in very little energy dissipation . As Fr 1 approaches 1.7, a number of small rollers begin to form at the water surface at the jump location, but in general, the downstream water surface remains relatively smooth. Between 1.7 < Fr 1 < 2.5, the velocity remains fairly uniform on either side of the jump and energy loss is low. [ 11 ] [ 12 ] [ 13 ]
An oscillating jump can occur when 2.5 < Fr 1 < 4.5. During this jump, the jet of water at the entrance of the jump (supercritical) fluctuates from the bottom of the channel to the top of the channel at an irregular period. Turbulence created from this jet can be near the channel bottom at one instant and then suddenly transition to the water surface. This oscillation of the jet causes irregular waves to form, which can propagate for long distances downstream of the jump, potentially causing damage and degradation of the channel banks. [ 11 ] [ 12 ] [ 13 ]
When the Froude number falls into this range, the jump forms steadily and at the same location. In a steady jump, turbulence is confined within the jump and the location of the jump is the least susceptible to downstream flow conditions out of the four major types of jumps. Steady jumps are generally well-balanced and the energy dissipation is usually considerable (45-70%). [ 11 ] [ 12 ] [ 13 ]
There is a large difference in conjugate depths in a strong jump. Strong jumps are characterized by a jump action that is very rough resulting in a high energy dissipation rate. At irregular intervals, slugs of water can be seen rolling down the front of the jump face. These slugs enter the high-velocity, supercritical jet and cause the formation of additional waves in the jump. Energy dissipation in strong jumps can reach up to 85%. [ 11 ] [ 12 ] [ 13 ]
In general, a hydraulic jump is formed at a location where the upstream and downstream flow depths satisfy the conjugate depth equation. However, there can be conditions in a channel, such as downstream controls, that can alter where the conjugate depths form. Tailwater depth can play a very influential role on where the jump will occur in the channel, and changes in this depth can shift the jump either upstream or downstream. Figure 6 contains three scenarios of tailwater elevations (y d ): y d is equal to the conjugate depth (y 2 ) of the upstream flow depth (y 1 ), y d is less than the conjugate depth (y 2 ) of the upstream flow depth (y 1 ), and y d is greater than the conjugate depth (y 2 ) of the upstream flow depth (y 1 ). The upstream depth (y 1 ) in all three cases is controlled by a sluice gate and remains constant. Its corresponding conjugate depth (y 2 ) is shown by the dashed line in each of the scenarios.
In the first situation (Scenario A), the jump is formed right at the apron, as it would if there was no downstream control. However, in the next scenario (Scenario B), the downstream tailwater depth has some control imposed on it such that it is less than the conjugate to y 1 . In this case, the jump travels downstream and initiates at a point where the upstream flow depth (y 1 ’) has risen to the conjugate of the new downstream tailwater depth (y d ). This rise from y 1 to y 1 ’ is caused by frictional resistance in the channel; and velocity decrease, the depth increase. In this image, y 1 ’ and y 2 ’ represent the conjugate depths of the hydraulic jump where y 2 ’ assumes the depth of y d . In contrast, in the third setup (Scenario C), there is a downstream control that forces the tailwater elevation to a depth above the original conjugate depth. Here, y d is greater than the required depth so the jump is pushed upstream. In this scenario, the sluice gate inhibits the movement of the jump upstream so that the upstream conjugate cannot be attained. This leads to a situation known as a submerged or drowned hydraulic jump. These scenarios demonstrate how influential the role of tailwater is to jump formation and location. [ 12 ]
Table 1. Hydraulic Jump Classifications [ 14 ]
To help visualize the relationship of the upstream Froude number and the flow depth downstream of the hydraulic jump, it is helpful to plot y 2 /y 1 versus the upstream Froude Number, Fr 1 . (Figure 8) The value of y 2 /y 1 is a ratio of depths that represent a dimensionless jump height; for example, if y 2 /y 1 = 2, then the jump doubles the depth of flow. As the upstream Froude Number increases (moves toward more supercritical flow), the ratio of the downstream depth to the upstream depth also increases, and the graph verifies the existence of a positive linear relationship between the dimensionless jump height and the upstream Froude Number. This implies that a more supercritical upstream flow, y 1 , will produce a larger downstream depth, y 2 , and thus a larger jump. The relationship given in Figure 8 below was developed for a horizontal, rectangular channel with q = 10 ft 2 /s. This graph is limited by the following due to the nature of a hydraulic jump:
Table 2 shows the calculated values used to develop Figure 8. The values associated with a y 1 = 1.5 ft are not valid for use since they violate the above limits. The cusp of the above limits is reached at the critical depth, y c , where all of these values are equal to 1. There will not, however, be a hydraulic jump in the situation where y 1 is equal to y c .
Table 2. Values for Depth and Froude Number over Hydraulic Jump
q = 10 ft, g = 32.2 ft/s 2 , y c = 1.46 ft, y values in ft
Figure 8. Dimensionless Jump Height vs. Upstream Froude Number (Please note that this diagram is not fully correct. Other factors taken into account are width and water velocity
This topic contribution was made in partial fulfillment of the requirements for Virginia Tech, Department of Civil and Environmental Engineering course: CEE 5984 – Open Channel Flow during the Fall 2010 semester. | https://en.wikipedia.org/wiki/Hydraulic_jumps_in_rectangular_channels |
Hydraulic machines use liquid fluid power to perform work. Heavy construction vehicles are a common example. In this type of machine, hydraulic fluid is pumped to various hydraulic motors and hydraulic cylinders throughout the machine and becomes pressurized according to the resistance present. The fluid is controlled directly or automatically by control valves and distributed through hoses, tubes, or pipes.
Hydraulic systems, like pneumatic systems , are based on Pascal's law which states that any pressure applied to a fluid inside a closed system will transmit that pressure equally everywhere and in all directions. A hydraulic system uses an incompressible liquid as its fluid, rather than a compressible gas.
The popularity of hydraulic machinery is due to the large amount of power that can be transferred through small tubes and flexible hoses, the high power density and a wide array of actuators that can make use of this power, and the huge multiplication of forces that can be achieved by applying pressures over relatively large areas. One drawback, compared to machines using gears and shafts, is that any transmission of power results in some losses due to resistance of fluid flow through the piping.
Joseph Bramah patented the hydraulic press in 1795. [ 1 ] While working at Bramah's shop, Henry Maudslay suggested a cup leather packing. [ 2 ] [ clarification needed ] Because it produced superior results, the hydraulic press eventually displaced the steam hammer for metal forging. [ 3 ]
To supply large-scale power that was impractical for individual steam engines, central station hydraulic systems were developed. Hydraulic power was used to operate cranes and other machinery in British ports and elsewhere in Europe. The largest hydraulic system was in London. Hydraulic power was used extensively in Bessemer steel production. Hydraulic power was also used for elevators, to operate canal locks and rotating sections of bridges. [ 1 ] [ 3 ] Some of these systems remained in use well into the twentieth century.
Harry Franklin Vickers was called the "Father of Industrial Hydraulics" by ASME . [ why? ]
A fundamental feature of hydraulic systems is the ability to apply force or torque multiplication in an easy way, independent of the distance between the input and output, without the need for mechanical gears or levers, either by altering the effective areas in two connected cylinders or the effective displacement (cc/rev) between a pump and motor. In normal cases, hydraulic ratios are combined with a mechanical force or torque ratio for optimum machine designs such as boom movements and track drives for an excavator.
Cylinder C1 is one inch in radius, and cylinder C2 is ten inches in radius. If the force exerted on C1 is 10 lbf , the force exerted by C2 is 1000 lbf because C2 is a hundred times larger in area ( S = π r ²) as C1. The downside to this is that you have to move C1 a hundred inches to move C2 one inch. The most common use for this is the classical hydraulic jack where a pumping cylinder with a small diameter is connected to the lifting cylinder with a large diameter.
If a hydraulic rotary pump with the displacement 10 cc/rev is connected to a hydraulic rotary motor with 100 cc/rev, the shaft torque required to drive the pump is one-tenth of the torque then available at the motor shaft, but the shaft speed (rev/min) for the motor is also only one-tenth of the pump shaft speed. This combination is actually the same type of force multiplication as the cylinder example, just that the linear force in this case is a rotary force, defined as torque.
Both these examples are usually referred to as a hydraulic transmission or hydrostatic transmission involving a certain hydraulic "gear ratio".
A hydraulic circuit is a system comprising an interconnected set of discrete components that transport liquid . The purpose of this system may be to control where fluid flows (as in a network of tubes of coolant in a thermodynamic system) or to control fluid pressure (as in hydraulic amplifiers). For example, hydraulic machinery uses hydraulic circuits (in which hydraulic fluid is pushed, under pressure, through hydraulic pumps , pipes, tubes, hoses, hydraulic motors , hydraulic cylinders , and so on) to move heavy loads. The approach of describing a fluid system in terms of discrete components is inspired by the success of electrical circuit theory . Just as electric circuit theory works when elements are discrete and linear, hydraulic circuit theory works best when the elements (passive components such as pipes or transmission lines or active components such as power packs or pumps ) are discrete and linear. This usually means that hydraulic circuit analysis works best for long, thin tubes with discrete pumps, as found in chemical process flow systems or microscale devices. [ 4 ] [ 5 ] [ 6 ]
The circuit comprises the following components:
For the hydraulic fluid to do work, it must flow to the actuator and/or motors, then return to a reservoir. The fluid is then filtered and re-pumped. The path taken by hydraulic fluid is called a hydraulic circuit of which there are several types.
Open-loop: Pump-inlet and motor-return (via the directional valve) are connected to the hydraulic tank. The term loop applies to feedback; the more correct term is open versus closed "circuit". Open center circuits use pumps which supply a continuous flow. The flow is returned to the tank through the control valve's open center; that is, when the control valve is centered, it provides an open return path to the tank and the fluid is not pumped to a high pressure. Otherwise, if the control valve is actuated it routes fluid to and from an actuator and tank. The fluid's pressure will rise to meet any resistance, since the pump has a constant output. If the pressure rises too high, fluid returns to the tank through a pressure relief valve. Multiple control valves may be stacked in series. This type of circuit can use inexpensive, constant displacement pumps.
Closed-loop: Motor-return is connected directly to the pump-inlet. To keep up pressure on the low pressure side, the circuits have a charge pump (a small gear pump) that supplies cooled and filtered oil to the low pressure side. Closed-loop circuits are generally used for hydrostatic transmissions in mobile applications. Advantages: No directional valve and better response, the circuit can work with higher pressure. The pump swivel angle covers both positive and negative flow direction. Disadvantages: The pump cannot be utilized for any other hydraulic function in an easy way and cooling can be a problem due to limited exchange of oil flow. High power closed loop systems generally must have a 'flush-valve' assembled in the circuit in order to exchange much more flow than the basic leakage flow from the pump and the motor, for increased cooling and filtering. The flush valve is normally integrated in the motor housing to get a cooling effect for the oil that is rotating in the motor housing itself. The losses in the motor housing from rotating effects and losses in the ball bearings can be considerable as motor speeds will reach 4000-5000 rev/min or even more at maximum vehicle speed. The leakage flow as well as the extra flush flow must be supplied by the charge pump. A large charge pump is thus very important if the transmission is designed for high pressures and high motor speeds. High oil temperature is usually a major problem when using hydrostatic transmissions at high vehicle speeds for longer periods, for instance when transporting the machine from one work place to the other. High oil temperatures for long periods will drastically reduce the lifetime of the transmission. To keep down the oil temperature, the system pressure during transport must be lowered, meaning that the minimum displacement for the motor must be limited to a reasonable value. Circuit pressure during transport around 200-250 bar is recommended.
Closed loop systems in mobile equipment are generally used for the transmission as an alternative to mechanical and hydrodynamic (converter) transmissions. The advantage is a stepless gear ratio (continuously variable speed/torque) and a more flexible control of the gear ratio depending on the load and operating conditions. The hydrostatic transmission is generally limited to around 200 kW maximum power, as the total cost gets too high at higher power compared to a hydrodynamic transmission. Large wheel loaders for instance and heavy machines are therefore usually equipped with converter transmissions. Recent technical achievements for the converter transmissions have improved the efficiency and developments in the software have also improved the characteristics, for example selectable gear shifting programs during operation and more gear steps, giving them characteristics close to the hydrostatic transmission.
Hydrostatic transmissions for earth moving machines, such as for track loaders, are often equipped with a separate ' inch pedal ' that is used to temporarily increase the diesel engine rpm while reducing the vehicle speed in order to increase the available hydraulic power output for the working hydraulics at low speeds and increase the tractive effort. The function is similar to stalling a converter gearbox at high engine rpm. The inch function affects the preset characteristics for the 'hydrostatic' gear ratio versus diesel engine rpm.
The closed center circuits exist in two basic configurations, normally related to the regulator for the variable pump that supplies the oil:
Load-sensing systems (LS) generate less power losses as the pump can reduce both flow and pressure to match the load requirements, but require more tuning than the CP system with respect to system stability. The LS system also requires additional logical valves and compensator valves in the directional valves, thus it is technically more complex and more expensive than the CP system. The LS system generates a constant power loss related to the regulating pressure drop for the pump regulator :
Power loss = Δ p LS ⋅ Q tot {\displaystyle {\text{Power loss}}=\Delta p_{\text{LS}}\cdot Q_{\text{tot}}}
The average Δ p L S {\displaystyle \Delta p_{LS}} is around 2 MPa (290 psi). If the pump flow is high the extra loss can be considerable. The power loss also increases if the load pressures vary a lot. The cylinder areas, motor displacements and mechanical torque arms must be designed to match load pressure in order to bring down the power losses. Pump pressure always equals the maximum load pressure when several functions are run simultaneously and the power input to the pump equals the (max. load pressure + Δ p LS ) x sum of flow.
Technically the down-stream mounted compensator in a valve block can physically be mounted "up-stream", but work as a down-stream compensator.
System type (3) gives the advantage that activated functions are synchronized independent of pump flow capacity. The flow relation between two or more activated functions remains independent of load pressures, even if the pump reaches the maximum swivel angle. This feature is important for machines that often run with the pump at maximum swivel angle and with several activated functions that must be synchronized in speed, such as with excavators. With the type (4) system, the functions with up-stream compensators have priority, for example the steering function for a wheel loader. The system type with down-stream compensators usually have a unique trademark depending on the manufacturer of the valves, for example "LSC" (Linde Hydraulics), "LUDV" ( Bosch Rexroth Hydraulics) and "Flowsharing" (Parker Hydraulics) etc. No official standardized name for this type of system has been established but flowsharing is a common name for it.
Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in reaction to the load. Hence, a pump rated for 5,000 psi is capable of maintaining flow against a load of 5,000 psi.
Pumps have a power density about ten times greater than an electric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coupling to reduce vibration.
Common types of hydraulic pumps to hydraulic machinery applications are:
Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half of a hydrostatic transmission .
Directional control valves route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. The spool slides to different positions in the housing, and intersecting grooves and channels route the fluid based on the spool's position.
The spool has a central (neutral) position maintained with springs; in this position the supply fluid is blocked, or returned to tank. Sliding the spool to one side routes the hydraulic fluid to an actuator and provides a return path from the actuator to tank. When the spool is moved to the opposite direction the supply and return paths are switched. When the spool is allowed to return to neutral (center) position the actuator fluid paths are blocked, locking it in position.
Directional control valves are usually designed to be stackable, with one valve for each hydraulic cylinder, and one fluid input supplying all the valves in the stack.
Tolerances are very tight in order to handle the high pressure and avoid leaking, spools typically have a clearance with the housing of less than a thousandth of an inch (25 μm). The valve block will be mounted to the machine's frame with a three point pattern to avoid distorting the valve block and jamming the valve's sensitive components.
The spool position may be actuated by mechanical levers, hydraulic pilot pressure, or solenoids which push the spool left or right. A seal allows part of the spool to protrude outside the housing, where it is accessible to the actuator.
The main valve block is usually a stack of off the shelf directional control valves chosen by flow capacity and performance. Some valves are designed to be proportional (flow rate proportional to valve position), while others may be simply on-off. The control valve is one of the most expensive and sensitive parts of a hydraulic circuit.
The hydraulic fluid reservoir holds excess hydraulic fluid to accommodate volume changes from: cylinder extension and contraction, temperature driven expansion and contraction, and leaks. The reservoir is also designed to aid in separation of air from the fluid and also work as a heat accumulator to cover losses in the system when peak power is used. Reservoirs can also help separate dirt and other particulate from the oil, as the particulate will generally settle to the bottom of the tank.
Some designs include dynamic flow channels on the fluid's return path that allow for a smaller reservoir.
Accumulators are a common part of hydraulic machinery. Their function is to store energy by using pressurized gas. One type is a tube with a floating piston. On the one side of the piston there is a charge of pressurized gas, and on the other side is the fluid. Bladders are used in other designs. Reservoirs store a system's fluid.
Examples of accumulator uses are backup power for steering or brakes, or to act as a shock absorber for the hydraulic circuit.
Also known as tractor fluid , hydraulic fluid is the life of the hydraulic circuit. It is usually petroleum oil with various additives. Some hydraulic machines require fire resistant fluids, depending on their applications. In some factories where food is prepared, either an edible oil or water is used as a working fluid for health and safety reasons.
In addition to transferring energy, hydraulic fluid needs to lubricate components, suspend contaminants and metal filings for transport to the filter, and to function well to several hundred degrees Fahrenheit or Celsius.
Filters are an important part of hydraulic systems which removes the unwanted particles from fluid. Metal particles are continually produced by mechanical components and need to be removed along with other contaminants. [ 8 ]
Filters may be positioned in many locations. The filter may be located between the reservoir and the pump intake. Blockage of the filter will cause cavitation and possibly failure of the pump. Sometimes the filter is located between the pump and the control valves. This arrangement is more expensive, since the filter housing is pressurized, but eliminates cavitation problems and protects the control valve from pump failures. The third common filter location is just before the return line enters the reservoir. This location is relatively insensitive to blockage and does not require a pressurized housing, but contaminants that enter the reservoir from external sources are not filtered until passing through the system at least once. Filters are used from 7 micron to 15 micron depends upon the viscosity grade of hydraulic oil.
Hydraulic tubes are seamless steel precision pipes, specially manufactured for hydraulics. The tubes have standard sizes for different pressure ranges, with standard diameters up to 100 mm. The tubes are supplied by manufacturers in lengths of 6 m, cleaned, oiled and plugged. The tubes are interconnected by different types of flanges (especially for the larger sizes and pressures), welding cones/nipples (with o-ring seal), several types of flare connection and by cut-rings. In larger sizes, hydraulic pipes are used. Direct joining of tubes by welding is not acceptable since the interior cannot be inspected.
Hydraulic pipe is used in case standard hydraulic tubes are not available. Generally these are used for low pressure. They can be connected by threaded connections, but usually by welds. Because of the larger diameters the pipe can usually be inspected internally after welding. Black pipe is non-galvanized and suitable for welding .
Hydraulic hose is graded by pressure, temperature, and fluid compatibility. Hoses are used when pipes or tubes can not be used, usually to provide flexibility for machine operation or maintenance. The hose is built up with rubber and steel layers. A rubber interior is surrounded by multiple layers of woven wire and rubber. The exterior is designed for abrasion resistance. The bend radius of hydraulic hose is carefully designed into the machine, since hose failures can be deadly, and violating the hose's minimum bend radius will cause failure. Hydraulic hoses generally have steel fittings swaged on the ends. The weakest part of the high pressure hose is the connection of the hose to the fitting. Another disadvantage of hoses is the shorter life of rubber which requires periodic replacement, usually at five to seven year intervals.
Tubes and pipes for hydraulic n applications are internally oiled before the system is commissioned. Usually steel piping is painted outside. Where flare and other couplings are used, the paint is removed under the nut, and is a location where corrosion can begin. For this reason, in marine applications most piping is stainless steel.
Components of a hydraulic system [sources (e.g. pumps), controls (e.g. valves) and actuators (e.g. cylinders)] need connections that will contain and direct the hydraulic fluid without leaking or losing the pressure that makes them work. In some cases, the components can be made to bolt together with fluid paths built-in. In more cases, though, rigid tubing or flexible hoses are used to direct the flow from one component to the next. Each component has entry and exit points for the fluid involved (called ports) sized according to how much fluid is expected to pass through it.
There are a number of standardized methods in use to attach the hose or tube to the component. Some are intended for ease of use and service, others are better for higher system pressures or control of leakage. The most common method, in general, is to provide in each component a female-threaded port, on each hose or tube a female-threaded captive nut, and use a separate adapter fitting with matching male threads to connect the two. This is functional, economical to manufacture, and easy to service.
Fittings serve several purposes;
A typical piece of machinery or heavy equipment may have thousands of sealed connection points and several different types:
Elastomeric seals (O-ring boss and face seal) are the most common types of seals in heavy equipment and are capable of reliably sealing more than 6,000 psi (41 MPa ) of fluid pressure. | https://en.wikipedia.org/wiki/Hydraulic_machinery |
A hydraulic manifold is a component that regulates fluid flow between pumps and actuators and other components in a hydraulic system. It is like a switchboard in an electrical circuit because it lets the operator control how much fluid flows between which components of a hydraulic machinery. For example, in a backhoe loader a manifold turns on or shuts off or diverts flow to the telescopic arms of the front bucket and the back bucket. The manifold is connected to the levers in the operator's cabin which the operator uses to achieve the desired manifold behaviour. [ 1 ]
A manifold is composed of assorted hydraulic valves connected to each other. It is the various combinations of states of these valves that allow complex control behaviour in a manifold. [ 1 ] [ citation needed ] A hydraulic manifold is a block of metal with flow paths drilled through it, connecting various ports. [ 2 ] Hydraulic manifolds consist of one or more relative large pipes called a "barrel" or "main", with numerous junctions connecting smaller pipes and ports. [ 3 ]
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydraulic_manifold |
A hydraulic modular trailer (HMT) is a special platform trailer unit which feature swing axles , hydraulic suspension , independently steerable axles , two or more axle rows, compatible to join two or more units longitudinally and laterally and uses power pack unit (PPU) to steer and adjust height. [ 1 ] These trailer units are used to transport oversized load , which are difficult to disassemble and are overweight. These trailers are manufactured using high tensile steel , which makes it possible to bear the weight of the load with the help of one or more ballast tractors which push and pull these units via drawbar or gooseneck this combination of tractor and trailer is also termed as heavy hauler .
Typical loads include oil rig modules, bridge sections, buildings , ship sections, and industrial machinery such as generators and turbines also many militaries uses HMT for tank transportation. There is a limited number of manufacturers who produce these heavy-duty trailers because the market share of oversized loads is very thin when we talk about the over all transportation industry. There are self powered units of hydraulic modular trailer which are called SPMT which are used when the ballast tractors can not be applied due to space.
In 1957 the first every hydraulic modular trailers were made by Willy Scheuerle a Germany based trailer specialist which were four axles 32 wheeled modules for Robert Wynn and Sons Ltd, a Shaftesbury -based Guinness Book of Record -winning heavy haulage company. [ 2 ] Wynns were also the first to use pneumatic tires for loads weighing more than 100 tons and also to use hydraulic suspension trailers which were manufactured by Cranes Trailers limited from Dereham . [ 3 ]
In 1962 Cranes Trailers limited developed two four-axle 32-wheel modules for Pickfords , a London based heavy haulage company, with combined payload capacity of 160 tons on a total of eight axles and 64 wheels the modules incorporated hydraulic suspensions and each axle interlinked with mechanical steering system at an operational height varied from 2.9 to 3.11ft. The modules had drawbar coupling which could be coupled at either of both ends or even both for push-pull combination. [ 4 ]
In 1963 Goldhofer developed modular trailers in Europe for heavy haulers. [ 5 ] In the same year, Cometto developed a 300-ton capacity module in 14-axle, seven-row configuration. [ 6 ] Scheuerle also demonstrated its modules at events in 1967 [ 7 ] and later King Truck Equipment Ltd signed an agreement with Scheuerle which gave them exclusive manufacturing rights to produce their trailers in the UK. [ 8 ]
In 1971, King Truck Equipment Ltd demonstrated two units that were custom-built for Pickfords. A single unit was able to carry 150 tons on six axle rows and 48 wheels in total. Who would use them mostly with their Scammell ballast tractors via a drawbar coupling. These trailers had independent suspension and steering abilities via the Petter twin-cylinder diesel engine used as a PPU. [ 9 ]
In the 1970s, many manufacturers started to developed HMTs as the industry believed that the conventional low loaders had various limitations. To comply with new regulations and keeping safety in mind, the industry knew that they needed more axles to distribute the payload and the ultimate solution for the demand would be HMTs. Manufacturers opted hydraulic suspension instead of mechanical leaf springs and air suspension due to its efficient size and adjustable characteristics. Manufacturers chose high-tensile steel instead of aluminum because when it comes to HMTs and oversize loads, the minimizing the weight of the HMT is not relevant when they have their own payload capacity excluding the ballast tractor. The only weak point that existed on a HMT were the tires, [ 10 ] which are still a significant weakness till today, that's the reason why SPMTs have solid tires . HMTs operate at a higher speed then SPMts that's why solid tires are not an option for HMTs.
The number of axles on a HMT is not specified; two-, three-, four-, five-, six-, and eight-axle units are manufactured. Multiple units can be coupled longitudinally and laterally to transport a heavier load; each axle has a lifting capacity ranging from 18 tons to 45 tons. With a steering capacity of 50 to 60 degrees. Some combinations require a trailer operator who controls steering and height adjustments of the trailer via a controller which is modular and can be mounted at the frontend or rear end of the trailer. Huge combinations may also have a cabin for the operator, while typical combinations have a seat attached to the controller. [ citation needed ]
Hydraulic cylinders are used for steering and suspension of the trailer each axle has an individual suspension cylinder, steering rod which is connected to the main steering cylinder which is at the frontend of the trailer which makes all the axles steer at once in the same direction one row of axle consist of two turn tables , two knees, two suspension cylinders and four to eight wheels attached to a high strength metal platform. Steering and suspension cylinders are hydraulically operated using hydraulic fluid through hose pipe from the hydraulic tank, which is located near the PPU. PPU, which powers the steering, suspension to and fro flow of hydraulic fluid from hydraulic tank to suspensions and steering cylinders, puts out about 18 to 25 hp of power and are available in both diesel and petrol variants manufactured by renowned brands like Kohler , Yanmar and Hatz . [ citation needed ]
Multiple units of HMT can be interconnected longitudinally by pins and interconnecting couplings mounted in the centre of the chassis in the front and rear to interconnect them laterally they are bolted on the side wall of the chassis. HMTs can not move themselves, so There are two ways by which a HMT can be coupled with a tractor unit which can push and pull the trailer, these are gooseneck and drawbar.
[ citation needed ]
Gooseneck is the most common coupling used in the industry. A swan shaped coupling is coupled to the trailer and the tractor via connection of trailer pin and tractor fifth wheel . This coupling can be hydraulically adjusted to suit the tractor's height also the steering controls are connected to the coupling. Goosenecks are easy to use and gives benefit to using conventional tractors, [ 11 ] but this coupling has two huge drawbacks. This coupling can not be applied in a two file or side by side HMT configuration which limits the payload. Additionally, it can not be applied in push and pull configuration. Goosenecks are manufactured by the trailers manufactures themselves.
Drawbar is the most efficient and economical coupling which consists of an A-shaped frame with an I-shaped loop which is coupled to the trailer and connected to a ballast tractor via a towing hitch of the tractor. This coupling is widely used in developing countries because of its economical cost. Unlike gooseneck, this coupling can be applied to side by side and push & pull configuration [ 12 ] which, but this coupling can not be connected to a typical tractor, it requires a ballast tractor which has a ballast box instead of a fifth wheel and tow hitches in the rear and front. [ 13 ] Draw bars and tow hitches are manufacture red by companies like jost and Ringfeder. [ citation needed ]
Since 2005 in the United States of America , HMT have extra features and design changes which include widening axles, and half way folding system. Due to different road regulations in different states, almost all manufacturers have adopted the US design and developed a product for the US market. These HMT trailers are named dual lane trailers, which comes from the widening characteristic of the trailer. Dual lane trailers have capability to change its width from 13 feet (4.0 m) to 20 feet (6.1 m) wide to make transport of empty trailers easy and also comply with state regulations when required. [ 14 ] | https://en.wikipedia.org/wiki/Hydraulic_modular_trailer |
A hydraulic power network is a system of interconnected pipes carrying pressurized liquid used to transmit mechanical power from a power source, like a pump , to hydraulic equipment like lifts or motors . The system is analogous to an electrical grid transmitting power from a generating station to end-users. Only a few hydraulic power transmission networks are still in use; modern hydraulic equipment has a pump built into the machine. In the late 19th century, a hydraulic network might have been used in a factory, with a central steam engine or water turbine driving a pump and a system of high-pressure pipes transmitting power to various machines.
The idea of a public hydraulic power network was suggested by Joseph Bramah in a patent obtained in 1812. William Armstrong began installing systems in England from the 1840s, using low-pressure water, but a breakthrough occurred in 1850 with the introduction of the hydraulic accumulator , which allowed much higher pressures to be used. The first public network, supplying many companies, was constructed in Kingston upon Hull , England. The Hull Hydraulic Power Company began operation in 1877, with Edward B. Ellington as its engineer. Ellington was involved in most of the British networks, and some further afield. Public networks were constructed in Britain at London, Liverpool , Birmingham , Manchester and Glasgow . There were similar networks in Antwerp , Melbourne , Sydney , Buenos Aires and Geneva . All of the public networks had ceased to operate by the mid-1970s, but Bristol Harbour still has an operational system, with an accumulator situated outside the main pumphouse, enabling its operation to be easily visualised.
Joseph Bramah , an inventor and locksmith living in London, registered a patent at the London Patent Office on 29 April 1812, which was principally about a provision of a public water supply network, but included a secondary concept for the provision of a high-pressure water main, which would enable workshops to operate machinery. The high-pressure water would be applied "to a variety of other useful purposes, to which the same has never before been so applied". Major components of the system were a ring main, into which a number of pumping stations would pump the water, with pressure being regulated by several air vessels or loaded pistons. Pressure relief valves would protect the system, which he believed could deliver water at a pressure of "a great plurality of atmospheres", and in concept, this was how later hydraulic power systems worked. [ 1 ]
In Newcastle upon Tyne , a solicitor called William Armstrong , who had been experimenting with water-powered machines, was working for a firm of solicitors who were appointed to act on behalf of the Whittle Dene Water Company. The water company had been set up to supply Newcastle with drinking water, and Armstrong was appointed secretary at the first meeting of shareholders. Soon afterwards, he wrote to Newcastle Town Council, suggesting that the cranes on the quay should be converted to hydraulic power. He was required to carry out the work at his own expense, but would be rewarded if the conversion was a success. It was, and he set up the Newcastle Cranage Company, which received an order for the conversion of the other four cranes. Further work followed, with the engineer from Liverpool Docks visiting Newcastle and being impressed by a demonstration of the crane's versatility, given by the crane driver John Thorburn, known locally as "Hydraulic Jack". [ 2 ]
While the Newcastle system ran on water from the public water supply, the crane installed by Armstrong at Burntisland was not located where such an option was possible, and so he built a 180-foot (55 m) tower, with a water tank at the top, which was filled by a 6 hp (4.5 kW) steam engine. At Elswick in Glasgow, charges by the Corporation Water Department for the water used persuaded the owners that the use of a steam-powered crane would be cheaper. [ 2 ] Bramah's concept of "loaded pistons" was introduced in 1850, when the first hydraulic accumulator was installed as part of a scheme for cranes for the Manchester, Sheffield and Lincolnshire Railway . A scheme for cranes at Paddington the following year specified an accumulator with a 10-inch (250 mm) piston and a stroke of 15 feet (4.6 m), which enabled pressures of 600 pounds per square inch (41 bar) to be achieved. Compared to the 80 psi (5.5 bar) of the Newcastle scheme, this increased pressure significantly reduced the volumes of water used. Cranes were not the only application, with hydraulic operation of the dock gates at Swansea reducing the operating time from 15 to two minutes, and the number of men required to operate them from twelve to four. [ 3 ] Each of these schemes was for a single customer, and the application of hydraulic power more generally required a new model.
The first practical installation which supplied hydraulic power to the public was in Kingston upon Hull , in England. The Hull Hydraulic Power Company began operation in 1876. They had 2.5 miles (4.0 km) of pipes, which were up to 6 inches (150 mm) in diameter, and ran along the west bank of the River Hull from Sculcoates bridge to its junction with the Humber . The pumping station was near the north end of the pipeline, on Machell Street, near the disused Scott Street bascule bridge, which was powered hydraulically. There was an accumulator at Machell Street, and another one much nearer the Humber, on the corner of Grimsby Lane. Special provision was made where the pressure main passed under the entrance to Queens Dock. [ 4 ] By 1895, pumps rated at 250 hp (190 kW) pumped some 500,000 imperial gallons (2,300 m 3 ) of water into the system each week, and 58 machines were connected to it. The working pressure was 700 psi (48 bar), and the water was used to operate cranes, dock gates, and a variety of other machinery connected with ships and shipbuilding. The Hull system lasted until the 1940s, when the systematic bombing of the city during the Second World War led to the destruction of much of the infrastructure, [ 5 ] and the company was wound up in 1947, [ 6 ] when Mr F J Haswell, who had been the manager and engineer since 1904, retired. [ 7 ]
The man responsible for the Hull system was Edward B. Ellington , who had risen to become the managing director of the Hydraulic Engineering Company, based in Chester, since first joining it in 1869. At the time of its installation, such a scheme seemed like "a leap in the dark", according to R. H. Tweddell writing in 1895, but despite a lack of enthusiasm for the scheme, Ellington pushed ahead and used it as a test bed for both the mechanical and the commercial aspects of the idea. He was eventually involved on some level in most of the hydraulic power networks of Britain. The success of such systems led to them being installed in places as far away as Antwerp in Belgium, Melbourne and Sydney in Australia, and Buenos Aires in Argentina. [ 8 ]
Independent hydraulic power networks were also installed at Hull's docks - both the Albert Dock (1869), and Alexandra Dock (1885) installed hydraulic generating stations and accumulators. [ 9 ]
The best-known public hydraulic network was the citywide network of the London Hydraulic Power Company . This was formed in 1882, as the General Hydraulic Power Company, with Ellington as the consulting engineer. By the following year another enterprise, the Wharves and Warehouses Steam Power and Hydraulic Pressure Company, had begun to operate, with 7 miles (11 km) of pressure mains on both sides of the River Thames . These supplied cranes, dock gates, and other heavy machinery. Under the terms of the London Hydraulic Power Act 1884 ( 47 & 48 Vict. c. lxxii), the two companies amalgamated to become the London Hydraulic Power Company. Initially supplying 17.75 million gallons (80.7 megalitres) of high-pressure water each day, this had risen to 1,650 million gallons (7,500 megalitres) by 1927, when the company was powering around 8,000 machines from the supply. They maintained 184 miles (296 km) of mains at 700 psi (48 bar), which covered an area reaching Pentonville in the north, Limehouse in the east, Nine Elms and Bermondsey in the south and Earls Court and Notting Hill in the west. [ 10 ]
Five pumping stations kept the mains pressurised, assisted by accumulators. The original station was at Falcon Wharf, Bankside, but this was replaced by four stations at Wapping, Rotherhithe, Grosvenor Road in Pimlico and City Road in Clerkenwell. A fifth station at East India Docks was originally operated by the Port of London Authority , but was taken over and connected to the system. The stations used steam engines until 1953, when Grosvenor Road station was converted to use electric motors, and following the success of this project, the other four were also converted. The electric motors allowed much smaller accumulators to be used, since they were then only controlling the pressure and flow, rather than storing power. While the network supplied lifts, cranes and dockgates, it also powered the cabaret platform at the Savoy Hotel, and from 1937, the 720-tonne three-section central floor at the Earls Court Exhibition Centre , which could be raised or lowered relative to the main floor to convert between a swimming pool and an exhibition hall. [ 11 ] [ 12 ] The London system contracted during the Second World War, due to the destruction of customers' machinery and premises. Following the hostilities, large areas of London were reconstructed, and the re-routing of pressure mains was much more difficult than the provision of an electric supply, so that by 1954 the number of machines had fallen to 4,286. [ 5 ] The company was wound up in 1977.
A system began operating in Liverpool in 1888. [ 13 ] It was an offshoot of the London-based General Hydraulic Power Company, and was authorised by acts of Parliament obtained in 1884 and 1887. [ 14 ] By 1890, some 16 miles (26 km) of mains had been installed, supplied by a pumping station at Athol Street, on the bank of the Leeds and Liverpool Canal . Although water was originally taken from the canal, cleaner water supplied by Liverpool Corporation was in use by 1890, removing the need for a filtration plant. At this time two pumpsets were in use, and a third was being installed. Pressure was maintained by two accumulators, each with an 18-inch (460 mm) diameter piston with a stroke of 20 feet (6.1 m). The Practical Engineer quoted the pressure as 75 pounds per square inch (5.2 bar), [ 15 ] but this is unlikely to be correct by comparison with other systems. A second pumping station at Grafton Street was operational by 1909. [ 16 ] The system ceased operation in 1971. [ 17 ]
Birmingham obtained its system in 1891, when the Dalton Street hydraulic station opened. In an unusual move, J. W. Gray, the Water Department engineer for the city, had been laying pressure mains beneath the streets for some years, anticipating the need for such a system. The hydraulic station used Otto 'Silent' type gas engines, and had two accumulators, with an 18-inch (460 mm) diameter piston, a stroke of 20 feet (6.1 m) and each loaded with a 93-tonne weight. The gas engines were started by a small hydraulic engine, which used the hydraulic energy stored in the accumulators, and all equipment was supplied by Ellington's company. Very few documents describing the details of the system are known to exist. [ 18 ]
The final two public systems in Britain were in Manchester , commissioned in 1894, and Glasgow , commissioned the following year. Both were equipped by Ellington's company, and used the higher pressure of 1,120 psi (77 bar). This was maintained by six sets of triple-expansion steam engines, rated at 200 hp (150 kW) each. Two accumulators with pistons of 18-inch (460 mm) diameter, a stroke of 23 feet (7.0 m), and loaded with 127 tonnes were installed. In Manchester, the hydraulic station was built on the east side of Gloucester Street, [ 19 ] by Manchester Oxford Road railway station . It was later supplemented by stations at Water Street and Pott Street, the latter now under the car parks of the Central Retail Park. [ 20 ] At its peak in the 1930s, the system consisted on 35 miles (56 km) of pipes, which were connected to 2,400 machines, most of which were used for baling cotton. [ 21 ] The system was shut down in 1972. [ 20 ] In Glasgow, the pumping station was at the junction of High Street and Rottenrow. By 1899, it was supplying power to 348 machines, and another 39 were in the process of being completed. [ 19 ] The pipes were 7 inches (180 mm) in diameter, and there were around 30 miles (48 km) of them by 1909, when 202,141 imperial gallons (918.95 m 3 ) of high pressure water were supplied to customers. The system was shut down in 1964. [ 22 ]
All of the British systems were designed to provide power for intermittent processes, such as the operation of dock gates or cranes. The system installed at Antwerp was somewhat different, in that its primary purpose was the production of electricity for lighting. It was commissioned in 1894, and used pumping engines producing a total of 1,000 hp (750 kW) to supply water at 750 psi (52 bar). Ellington, writing in 1895, stated that he found it difficult to see that this was an economical use of hydraulic power, although tests conducted at his works at Chester in October 1894 showed that efficiencies of 59 per cent could be achieved using a Pelton wheel directly coupled to a dynamo. [ 23 ]
Two major systems were built in Australia. The first was in Melbourne , where the Melbourne Hydraulic Power Company began operating in July 1889. [ 24 ] The company was authorised by an Act of the Victorian Parliament passed in December 1887, and construction of the system began, with Coates & Co. acting as consulting engineers, and George Swinburne working as engineering manager. The steam pumping plant was supplied by Abbot & Co. from England. Expansion was rapid, with around 70 machines, mainly hydraulic lifts, connected to the system by the end of 1889, and a third steam engine had to be installed in mid-1890, which more than doubled the capacity of the system. A fourth pumping engine was added in 1891, by which time there were 100 customers connected to the mains. The mains were a mixture of 4-inch (100 mm) and 6-inch (150 mm) pipes. The water was extracted from the Yarra River until 1893, after which it was drawn from the Public Works Department's supply. There were some 16 miles (26 km) of mains by 1897. A second pumping station was added in 1901, and in 1902, 102 million gallons (454 megalitres) of pressurised water were used by customers. [ 25 ]
The system was operated as a commercial enterprise until 1925, after which the business and its assets reverted to the City of Melbourne, as specified by the original act. One of the early improvements made by the City Council was to consolidate the system. The steam pumps were replaced by new electric pumps, located in the Spencer Street power station , which thus supplied both electric power and hydraulic power to the city. The hydraulic system continued to operate under municipal ownership until December 1967. [ 25 ]
In January 1891, a system in Sydney came on-line, having been authorised by act of Parliament in 1888. George Swinburne was again the engineer, and the system was supplying power to around 200 machines by 1894, which included 149 lifts and 20 dock cranes. [ 26 ] The operating company was the Sydney and Suburbs Hydraulic Power Company, [ 27 ] later shortened to the Sydney Hydraulic Power Company. Pressure mains were either of 4-inch (100 mm) or 6-inch (150 mm) diameter, and at its peak, there were around 50 miles (80 km) of mains, [ 28 ] covering an area between Pyrmont , Woolloomooloo , and Broadway . In 1919, most of the 2369 lifts in the metropolitan area were hydraulically operated. [ 26 ] The pumping station, together with two accumulators, was situated in the Darling Harbour district, and the original steam engines were replaced by three electric motors driving centrifugal pumps in 1952. [ 29 ] The scheme remained in private ownership until its demise in 1975, and the pumping station has since been re-used as a tavern. [ 25 ]
Ellington's system in Buenos Aires was designed to operate a sewage pumping scheme in the city. [ 10 ]
Geneva created a public system in 1879, using a 300 hp (220 kW) steam engine installed at the Pont de la Machine to pump water from Lake Geneva, which provided drinking water and a pressurized water supply for the city. The water power was used by about a hundred small workshops having Schmid-type water engines installed. The power of the engines was between 1 and 4 hp (0.75 and 2.98 kW) and the water was supplied at a pressure of 2 to 3 bars (29 to 44 psi). [ 30 ]
Due to increased demand, a new pumping plant was installed, which started operation in 1886. The pumps were driven by Jonval turbines using the water power of the river Rhône . This structure was called Usine des Forces Motrices and was one of the largest structures for generation and distribution of power at the time of construction. By 1897 a total of 18 turbines had been installed, with a combined rating of 3.3MW.
The distribution network used three different pressure levels. The drinking water supply used the lowest pressure, while the intermediate and the high pressure mains served as hydraulic power networks. The intermediate pressure mains operated at 6.5 bars (94 psi) and by 1896 some 51 miles (82 km) of pipework had been installed. It was used for powering 130 Schmid type water engines with a gross power of 230 hp (170 kW). The high pressure network had an operating pressure of 14 bars (200 psi) bar and had a total length of 58 miles (93 km). It was used to power 207 turbines and motors, as well as elevator drives, and had a gross power of 3,000 hp (2,200 kW). [ 31 ]
Many turbines were used for driving generators for electric lighting. In 1887 an electricity generation plant was built next to the powerhouse, which generated 110 V DC with a maximum power of 800 hp (600 kW) and an AC network with a maximum power of 600 hp (450 kW). [ 31 ] The generators were driven by a water turbine supplied from the hydraulic power network. [ 32 ] The hydraulic power network was not in competition with the electric power supply, but was seen as a supplement to it, and continued to supply power to many customer until the economic crisis of the 1930s, when the demand for pressurized water as an energy source declined. The last water engine was decommissioned in 1958. [ 31 ]
In order to avoid excessive pressure build-up in the hydraulic power network, a release valve was fitted beside the main hall of the powerhouse. A tall water fountain, the Jet d'Eau , was ejected by the device whenever it was activated. This typically happened at the end of the day when the factories switched off their machines, making it hard to control the pressure in the system, and to adjust the supply of pressurized water to match the actual demand. [ 33 ] The tall fountain was visible from a great distance and became a landmark in the city. When an engineering solution was found which made the fountain redundant, there was an outcry, and in 1891 it was moved to its current location in the lake, where it operated solely as a tourist attraction, although the water to create it still came from the hydraulic network. [ 34 ]
Two systems were built in New Zealand . The Thames Water Race was built in 1876 to supply water to the Thames goldfields powering stamper batteries, pumps and mine-head lifting equipment. Later, electricity was supplied to the residents of Thames in 1914, and when goldmining ceased the following year, a Francis Turbine and generator made use of the surplus water to generate more electricity for the residents of the town. It was eventually decommissioned in 1946. [ 35 ]
The Oamaru Borough Water Race was designed by Donald McLeod (b.1835). It opened in 1880 after 3 years of construction. With water sourced from the Waitaki River , the race stretched nearly 50 km and comprised an intake structure, a stilling pond, 19 aqueducts and six tunnels. The spare horsepower generated water motors, water engines and turbines in the town of Oamaru for decades and operated for 103 years. Much of the race and its components can still be seen today. [ 36 ]
Bristol Harbour still has a working system, the pumping machinery of which was supplied by Fullerton, Hodgart and Barclay of Paisley , Scotland in 1907. The engine house is a grade II* listed building, constructed in 1887, fully commissioned by 1888, with a tower at one end to house the hydraulic accumulator. [ 37 ] A second accumulator was fitted outside the building (dated 1954) which enables the operation of the system to be more easily visualised.
A number of artefacts, including the buildings used as pumping stations, have survived the demise of public hydraulic power networks. In Hull, the Machell Street pumping station has been reused as a workshop. The building still supports the sectional cast-iron roof tank used to allow the silt-laden water of the River Hull to settle, and is marked by a Blue plaque , to commemorate its importance. [ 6 ] In London, Bermondsey pumping station, built in 1902, is in use as an engineering works, but retains its chimney and accumulator tower, [ 38 ] while the station at Wapping is virtually complete, retaining all of its equipment, which is still in working order. The building is grade II* listed because of its completeness. [ 39 ]
In Manchester, the Water Street pumping station, built in Baroque style between 1907 and 1909, was used as workshops for the City College, [ 40 ] but has formed part of the People's History Museum since 1994. One of the pumping sets has been moved to the Museum of Science and Industry , where it has been restored to working order and forms part of a larger display about hydraulic power. [ 20 ] The pumps were made by the Manchester firm of Galloways. [ 21 ]
Geneva still has its Jet d'Eau fountain, but since 1951 it has been powered by a partially submerged pumping station, which uses water from the lake rather than the city water supply. Two Sulzer pumps, named Jura and Salève, create a fountain which rises to a height of 460 feet (140 m) above the surface of the lake. [ 41 ] | https://en.wikipedia.org/wiki/Hydraulic_power_network |
A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. They generate flow with enough power to overcome pressure induced by a load at the pump outlet. When a hydraulic pump operates, it creates a vacuum at the pump inlet, which forces liquid from the reservoir into the inlet line to the pump and by mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system.
Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement (flow through the pump per rotation of the pump) cannot be adjusted, or variable displacement pumps , which have a more complicated construction that allows the displacement to be adjusted. Hydrodynamic pumps are more frequent in day-to-day life. Hydrostatic pumps of various types all work on the principle of Pascal's law .
Gear pumps (with external teeth) (fixed displacement) are simple and economical pumps. The swept volume or displacement of gear pumps for hydraulics will be between about 1 to 200 milliliters. They have the lowest volumetric efficiency ( η v ≈ 90 % {\displaystyle \eta _{v}\approx 90\%} ) of all three basic pump types (gear, vane and piston pumps) [ 1 ] These pumps create pressure through the meshing of the gear teeth, which forces fluid around the gears to pressurize the outlet side. Some gear pumps can be quite noisy, compared to other types, but modern gear pumps are highly reliable and much quieter than older models. This is in part due to designs incorporating split gears, helical gear teeth and higher precision/quality tooth profiles that mesh and unmesh more smoothly, reducing pressure ripple and related detrimental problems. Another positive attribute of the gear pump, is that catastrophic breakdown is a lot less common than in most other types of hydraulic pumps. This is because the gears gradually wear down the housing and/or main bushings, reducing the volumetric efficiency of the pump gradually until it is all but useless. This often happens long before wear and causes the unit to seize or break down. Hydraulic gear pumps are used in various applications where there are different requirements such as lifting, lowering, opening, closing, or rotating, and they are expected to be safe and long-lasting. [ 2 ]
A rotary vane pump is a positive-displacement pump that consists of vanes mounted to a rotor that rotates inside a cavity. In some cases these vanes can have variable length and/or be tensioned to maintain contact with the walls as the pump rotates. A critical element in vane pump design is how the vanes are pushed into contact with the pump housing, and how the vane tips are machined at this very point. Several type of "lip" designs are used, and the main objective is to provide a tight seal between the inside of the housing and the vane, and at the same time to minimize wear and metal-to-metal contact. Forcing the vane out of the rotating centre and towards the pump housing is accomplished using spring-loaded vanes, or more traditionally, vanes loaded hydrodynamically (via the pressurized system fluid). [ 3 ]
Screw pumps (fixed displacement) consist of two Archimedes' screws that intermesh and are enclosed within the same chamber. These pumps are used for high flows at relatively low pressure (max 100 bars (10,000 kPa)). [ clarification needed ] They were used on board ships where a constant pressure hydraulic system extended through the whole ship, especially to control ball valves [ clarification needed ] but also to help drive the steering gear and other systems. The advantage of the screw pumps is the low sound level of these pumps; however, the efficiency is not high.
The major problem of screw pumps is that the hydraulic reaction force is transmitted in a direction that's axially opposed to the direction of the flow.
There are two ways to overcome this problem:
Types of screw pumps:
Bent axis pumps , axial piston pumps and motors using the bent axis principle, fixed or adjustable displacement, exists in two different basic designs. The Thoma-principle (engineer Hans Thoma, Germany, patent 1935) with max 25 degrees angle and the Wahlmark-principle (Gunnar Axel Wahlmark, patent 1960) with spherical-shaped pistons in one piece with the piston rod, piston rings, and maximum 40 degrees between the driveshaft centerline and pistons (Volvo Hydraulics Co.). These have the best efficiency of all pumps. Although in general, the largest displacements are approximately one litre per revolution, if necessary a two-liter swept volume pump can be built. Often variable-displacement pumps are used so that the oil flow can be adjusted carefully. These pumps can in general work with a working pressure of up to 350–420 bars in continuous work.
By using different compensation techniques, the variable displacement type of these pumps can continuously alter fluid discharge per revolution and system pressure based on load requirements, maximum pressure cut-off settings, horsepower/ratio control, and even fully electro proportional systems, requiring no other input than electrical signals. This makes them potentially hugely power saving compared to other constant flow pumps in systems where prime mover/diesel/electric motor rotational speed is constant and required fluid flow is non-constant. [ 4 ]
A radial piston pump is a form of hydraulic pump. The working pistons extend in a radial direction symmetrically around the drive shaft, in contrast to the axial piston pump.
Q = n ⋅ V stroke ⋅ η vol {\displaystyle Q=n\cdot V_{\text{stroke}}\cdot \eta _{\text{vol}}}
where
P = n ⋅ V stroke ⋅ Δ p η mech {\displaystyle P={n\cdot V_{\text{stroke}}\cdot \Delta p \over \eta _{\text{mech}}}}
where
n mech = T theoretical T actual ⋅ 100 % {\displaystyle n_{\text{mech}}={T_{\text{theoretical}} \over T_{\text{actual}}}\cdot 100\%}
where
n h y d r = Q a c t u a l Q t h e o r e t i c a l ⋅ 100 % {\displaystyle n_{hydr}={Q_{actual} \over Q_{theoretical}}\cdot 100\%}
where | https://en.wikipedia.org/wiki/Hydraulic_pump |
Hydraulic redistribution is a passive mechanism where water is transported from moist to dry soils via subterranean networks. [ 1 ] It occurs in vascular plants that commonly have roots in both wet and dry soils, especially plants with both taproots that grow vertically down to the water table , and lateral roots that sit close to the surface. In the late 1980s, there was a movement to understand the full extent of these subterranean networks. [ 2 ] Since then it was found that vascular plants are assisted by fungal networks which grow on the root system to promote water redistribution. [ 1 ] [ 3 ] [ 4 ]
Hot, dry periods, when the surface soil dries out to the extent that the lateral roots exude whatever water they contain, will result in the death of such lateral roots unless the water is replaced. Similarly, under extremely wet conditions when lateral roots are inundated by flood waters, oxygen deprivation will also lead to root peril. In plants that exhibit hydraulic redistribution, there are xylem pathways from the taproots to the laterals, such that the absence or abundance of water at the laterals creates a pressure potential analogous to that of transpirational pull . In drought conditions, ground water is drawn up through the taproot to the laterals and exuded into the surface soil, replenishing that which was lost. Under flooding conditions, plant roots perform a similar function in the opposite direction.
Though often referred to as hydraulic lift, movement of water by the plant roots has been shown to occur in any direction. [ 5 ] [ 6 ] [ 7 ] This phenomenon has been documented in over sixty plant species spanning a variety of plant types (from herbs and grasses to shrubs and trees) [ 8 ] [ 9 ] [ 10 ] and over a range of environmental conditions (from the Kalahari Desert to the Amazon Rainforest). [ 8 ] [ 9 ] [ 11 ] [ 12 ]
The movement of this water can be explained by a water transport theory throughout a plant. This well-established water transport theory is called the cohesion-tension theory . In brief, it explains the movement of water throughout the plant depends on having a continuous column of water, from the leaves to roots. Water is then pulled up from the roots to the leaves moving throughout the plant's vascular system , all facilitated by the differences in water potential in the boundary layers of the soil and the atmosphere . Therefore, the driving force for moving water through a plant is the cohesive strength of water molecules and a pressure gradient from the roots to the leaves. This theory is still applied when the boundary layer to the atmosphere is closed, e.g. when plant stomata are closed or in senesced plants. [ 13 ] The pressure gradient is developed between soil layers with different water potentials causing water to move by the roots from wetter to drier soil layers in a similar manner as when a plant is transpiring.
It has been understood that hydraulic lift aids the host plant and its neighboring plants in the transportation of water and other vital nutrients. [ 2 ] At that time, the hydraulic lift described as the movement of water and soil nutrients from a vascularized host into the soil during at night mostly. [ 2 ] Then after studies in the 2000s, a more comprehensive word was taken into consideration where it described a bi-directional and passive movement exhibited by the plant roots and further assisted by mycorrhizal networks . [ 2 ] [ 3 ] [ 14 ] A 2015 study then described a "direct transfer of hydraulically redistributed water" between the host and fungi into the surrounding root system. [ 3 ] As mentioned, hydraulic redistribution not only transports water but nutrients as well. [ 14 ] The fungi most likely to form water and nutrient networks are Ectomycorrhizae and Arbuscular mycorrhizae . [ 3 ]
The ecological importance of hydraulically redistributed water is becoming better understood as this phenomenon is more carefully examined. Water redistribution by plant roots has been found influencing crop irrigation, where watering schemes leave a harsh heterogeneity in soil moisture. This influencing process also assist in seedling success. [ 3 ] [ 4 ] The plant roots have been shown to smooth or homogenize the soil moisture. This sort of smoothing out of soil moisture is important in maintaining plant root health. The redistribution of water from deep moist layers to shallow drier layers by large trees has shown to increase the moisture available in the daytime to meet the transpiration demand.
The implications of hydraulic redistribution seem to have an important influence on plant ecosystems . Whether or not plants redistribute water through the soil layers can affect plant population dynamics , such as the facilitation of neighboring species. [ 15 ] The increase in available daytime soil moisture can also offset low transpiration rates due to drought ( see also drought rhizogenesis ) or alleviate competition for water between competing plant species. Water redistributed to the near surface layers may also influence plant nutrient availability. [ 16 ]
Due to the ecological significance of hydraulically redistributed water, there is an ongoing effort to continue the categorization of plants exhibiting this behaviour and adapting this physiological process into land-surface models to improve model predictions.
Traditional methods of observating hydraulic redistribution include Deuterium isotope traces, [ 7 ] [ 9 ] [ 12 ] [ 17 ] sap flow, [ 8 ] [ 11 ] [ 18 ] [ 19 ] and soil moisture. [ 6 ] [ 9 ] In attempts to characterize the magnitude of the water redistributed, numerous models (both empirically and theoretically based) have been developed. [ 20 ] | https://en.wikipedia.org/wiki/Hydraulic_redistribution |
Hydraulic roughness is the measure of the amount of frictional resistance water experiences when passing over land and channel features. [ 1 ] It quantifies the impact of surface irregularities and obstructions on the flow of water.
One roughness coefficient is Manning's n-value . [ 2 ] Manning's n is used extensively around the world to predict the degree of roughness in channels. The coefficient is critical in hydraulic engineering, floodplain management, and sediment transport studies. Flow velocity is strongly dependent on the resistance to flow. [ 3 ] An increase in this n value will cause a decrease in the velocity of water flowing across a surface. [ 4 ]
The value of Manning's n is affected by many variables. Factors like suspended load , sediment grain size , presence of bedrock or boulders in the stream channel, variations in channel width and depth, and overall sinuosity of the stream channel can all affect Manning's n value. For instance, a narrow, rocky channel with irregular obstructions such as large boulders will have a higher n value than a smooth, straight channel with uniform depth.
Biological factors have the greatest overall effect on Manning's n; key influences include bank stabilization by vegetation, height of grass and brush across a floodplain, and stumps and logs creating natural dams are the main observable influences.
Additionally, seasonal changes in vegetation density and growth can cause fluctuations in Manning's n values.
Recent studies have found a relationship between hydraulic roughness and salmon spawning habitat; “bed-surface grain size is responsive to hydraulic roughness caused by bank irregularities, bars, and wood debris… We find that wood debris plays an important role at our study sites, not only providing hydraulic roughness but also influencing pool spacing, frequency of textural patches, and the amplitude and wavelength of bank and bar topography and their consequent roughness. Channels with progressively greater hydraulic roughness have systematically finer bed surfaces, presumably due to reduced bed shear stress , resulting in lower channel competence and diminished bed load transport capacity, both of which promote textural fining”.
Textural fining of stream beds can affect more than just salmon spawning habitats, “bar and wood roughness create a greater variety of textural patches, offering a range of aquatic habitats that may promote biologic diversity or be of use to specific animals at different life stages.” [ 5 ]
This erosion article is a stub . You can help Wikipedia by expanding it .
This hydrology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydraulic_roughness |
A hydraulic seal is a relatively soft, non-metallic ring , captured in a groove or fixed in a combination of rings, forming a seal assembly, to block or separate fluid in reciprocating motion applications. Hydraulic seals are vital in machinery . Their use is critical in providing a way for fluid power to be converted to linear motion.
For example, they are widely used in hydraulic cylinders of excavators, bulldozers, cranes, and many other types of heavy equipment.
Hydraulic seals also play a crucial role in hydraulic lifting equipment, such as lift tables , by ensuring the efficient and safe operation of hydraulic cylinders. [ 1 ]
Hydraulic seals can be made from a variety of materials such as polyurethane , rubber or PTFE . [ 2 ] The type of material is determined by the specific operating conditions or limits due to fluid type, pressure , fluid chemical compatibility or temperature .
For instance, polyurethane seals offer good abrasion and tear resistance, while rubber seals have high elasticity and good sealing performance at low pressures. PTFE is often used in high-temperature environments or when exposed to corrosive fluids.
Hydraulic seals are classified based on their function and working conditions:
Static
A static hydraulic seal is located in a groove and sees no movement - only sealing within its confined space, acting like a gasket . To achieve this the gasket should be under pressure. The pressure is applied by tightening of the bolts.
Examples of static seals include O-rings , flange seals, and cover seals.
Dynamic
This type of seal is exposed to movement.
Rod seal:
Is installed on the piston rod of a hydraulic cylinder.
Prevents leakage of hydraulic fluid to the outside of the sealing system.
Helps prevent contamination from entering the hydraulic system (in conjunction with a wiper seal). [ 3 ] [ 4 ]
Piston seal:
Is installed on the piston head.
Prevents fluid from crossing the area of the piston head.
Ensures that fluid does not leak from the cylinder and adequate pressure is maintained. [ 5 ]
Wiper seal:
Is installed on the outside of the cylinder.
Its main function is to prevent dirt, debris, and other contaminants from entering the hydraulic system.
Other types of dynamic seals include chevron seals, U-cup seals, and labyrinth seals.
The performance of a hydraulic seal depends on several factors, including:
Application : Each application requires a different type of seal and material.
Operating conditions: Temperature, pressure, speed, fluid type, and working environment influence the choice of seal.
Seal profile : Piston seals come in various designs, each with its own advantages. [ 6 ] Selecting the right hydraulic seal requires careful consideration of these factors to ensure optimal sealing performance and service life of the hydraulic system
Specific Applications : Selecting appropriate hydraulic seals for dock leveler [ 7 ] requires careful consideration of factors like load capacity, frequency of use, and environmental conditions. | https://en.wikipedia.org/wiki/Hydraulic_seal |
Hydraulic shock ( colloquial : water hammer ; fluid hammer ) is a pressure surge or wave caused when a fluid in motion is forced to stop or change direction suddenly: a momentum change. It is usually observed in a liquid but gases can also be affected. This phenomenon commonly occurs when a valve closes suddenly at an end of a pipeline system and a pressure wave propagates in the pipe.
This pressure wave can cause major problems, from noise and vibration to pipe rupture or collapse. It is possible to reduce the effects of the water hammer pulses with accumulators , expansion tanks , surge tanks , blowoff valves , and other features. The effects can be avoided by ensuring that no valves will close too quickly with significant flow, but there are many situations that can cause the effect.
Rough calculations can be made using the Zhukovsky (Joukowsky) equation, [ 1 ] or more accurate ones using the method of characteristics .
In the 1st century B.C., Marcus Vitruvius Pollio described the effect of water hammer in lead pipes and stone tubes of the Roman public water supply. [ 2 ] [ 3 ]
In 1772, Englishman John Whitehurst built a hydraulic ram for a home in Cheshire, England. [ 4 ] In 1796, French inventor Joseph Michel Montgolfier (1740–1810) built a hydraulic ram for his paper mill in Voiron . [ 5 ] In French and Italian, the terms for "water hammer" come from the hydraulic ram: coup de bélier (French) and colpo d'ariete (Italian) both mean "blow of the ram". [ 6 ] As the 19th century witnessed the installation of municipal water supplies, water hammer became a concern to civil engineers. [ 7 ] [ 8 ] [ 9 ] Water hammer also interested physiologists who were studying the circulatory system. [ 10 ]
Although it was prefigured in work by Thomas Young , [ 11 ] [ 10 ] the theory of water hammer is generally considered to have begun in 1883 with the work of German physiologist Johannes von Kries (1853–1928), who was investigating the pulse in blood vessels. [ 12 ] [ 13 ] However, his findings went unnoticed by civil engineers. [ 14 ] [ 15 ] Kries's findings were subsequently derived independently in 1898 by the Russian fluid dynamicist Nikolay Yegorovich Zhukovsky (1847–1921), [ 1 ] [ 16 ] in 1898 by the American civil engineer Joseph Palmer Frizell (1832–1910), [ 17 ] [ 18 ] and in 1902 by the Italian engineer Lorenzo Allievi (1856–1941). [ 19 ]
Water flowing through a pipe has momentum. If the moving water is suddenly stopped, such as by closing a valve downstream of the flowing water, the pressure can rise suddenly with a resulting shock wave . In domestic plumbing this shock wave is experienced as a loud banging resembling a hammering noise. Water hammer can cause pipelines to break if the pressure is sufficiently high. Air traps or stand pipes (open at the top) are sometimes added as dampers to water systems to absorb the potentially damaging forces caused by the moving water.
For example, the water traveling along a tunnel or pipeline to a turbine in a hydroelectric generating station may be slowed suddenly if a valve in the path is closed too quickly. If there is 14 km (8.7 mi) of tunnel of 7.7 m (25 ft) diameter full of water travelling at 3.75 m/s (8.4 mph), [ 20 ] that represents approximately 8,000 megajoules (2,200 kWh) of kinetic energy. This energy can be dissipated by a vertical surge shaft into which the water flows [ 21 ] which is open at the top. As the water rises up the shaft its kinetic energy is converted into potential energy, avoiding sudden high pressure. At some hydroelectric power stations, such as the Saxon Falls Hydro Power Plant In Michigan , what looks like a water tower is in fact a surge drum . [ 22 ]
In residential plumbing systems, water hammer may occur when a dishwasher , washing machine or toilet suddenly shuts off water flow. The result may be heard as a loud bang, repetitive banging (as the shock wave travels back and forth in the plumbing system), or as some shuddering.
Other potential causes of water hammer:
Steam hammer can occur in steam systems when some of the steam condenses into water in a horizontal section of the piping. The steam forcing the liquid water along the pipe forms a " slug " which impacts a valve of pipe fitting, creating a loud hammering noise and high pressure. Vacuum caused by condensation from thermal shock can also cause a steam hammer. Steam hammer or steam condensation induced water hammer (CIWH) was exhaustively investigated both experimentally and theoretically more than a decade ago because it can have radical negative effects in nuclear power plants. [ 23 ] It is possible to theoretically explain the 2 millisecond duration 130 bar overpressure peaks with a special 6 equation multiphase thermohydraulic model, [ 24 ] similar to RELAP .
Steam hammer can be minimized by using sloped pipes and installing steam traps .
On turbocharged internal combustion engines , a "gas hammer" can take place when the throttle is closed while the turbocharger is forcing air into the engine. There is no shockwave but the pressure can still rapidly increase to damaging levels or cause compressor surge . A pressure relief valve placed before the throttle prevents the air from surging against the throttle body by diverting it elsewhere, thus protecting the turbocharger from pressure damage. This valve can either recirculate the air into the turbocharger's intake (recirculation valve), or it can blow the air into the atmosphere and produce the distinctive hiss-flutter of an aftermarket turbocharger ( blowoff valve ).
Water hammers have caused accidents and fatalities, but usually damage is limited to breakage of pipes or appendages. An engineer should always assess the risk of a pipeline burst. Pipelines transporting hazardous liquids or gases warrant special care in design, construction, and operation. Hydroelectric power plants especially must be carefully designed and maintained because the water hammer can cause water pipes to fail catastrophically.
The following characteristics may reduce or eliminate water hammer:
One of the first to successfully investigate the water hammer problem was the Italian engineer Lorenzo Allievi .
Water hammer can be analyzed by two different approaches— rigid column theory , which ignores compressibility of the fluid and elasticity of the walls of the pipe, or by a full analysis that includes elasticity. When the time it takes a valve to close is long compared to the propagation time for a pressure wave to travel the length of the pipe, then rigid column theory is appropriate; otherwise considering elasticity may be necessary. [ 25 ] Below are two approximations for the peak pressure, one that considers elasticity, but assumes the valve closes instantaneously, and a second that neglects elasticity but includes a finite time for the valve to close.
The pressure profile of the water hammer pulse can be calculated from the Joukowsky equation [ 26 ]
So for a valve closing instantaneously, the maximal magnitude of the water hammer pulse is
where Δ P is the magnitude of the pressure wave (Pa), ρ is the density of the fluid (kg/m 3 ), a 0 is the speed of sound in the fluid (m/s), and Δ v is the change in the fluid's velocity (m/s). The pulse comes about due to Newton's laws of motion and the continuity equation applied to the deceleration of a fluid element. [ 27 ]
As the speed of sound in a fluid is a = B ρ {\displaystyle a={\sqrt {\frac {B}{\rho }}}} , the peak pressure depends on the fluid compressibility if the valve is closed abruptly.
where
When the valve is closed slowly compared to the transit time for a pressure wave to travel the length of the pipe, the elasticity can be neglected, and the phenomenon can be described in terms of inertance or rigid column theory:
Assuming constant deceleration of the water column ( dv / dt = v / t ), this gives
where:
The above formula becomes, for water and with imperial unit,
For practical application, a safety factor of about 5 is recommended:
where P 1 is the inlet pressure in psi, V is the flow velocity in ft/ s , t is the valve closing time in seconds, and L is the upstream pipe length in feet. [ 28 ]
Hence, we can say that the magnitude of the water hammer largely depends upon the time of closure, elastic components of pipe & fluid properties. [ 29 ]
When a valve with a volumetric flow rate Q is closed, an excess pressure Δ P is created upstream of the valve, whose value is given by the Joukowsky equation:
In this expression: [ 30 ]
The hydraulic impedance Z of the pipeline determines the magnitude of the water hammer pulse. It is itself defined by
where
The latter follows from a series of hydraulic concepts:
Thus, the equivalent elasticity is the sum of the original elasticities:
As a result, we see that we can reduce the water hammer by:
The water hammer effect can be simulated by solving the following partial differential equations.
where V is the fluid velocity inside pipe, ρ {\displaystyle \rho } is the fluid density, B is the equivalent bulk modulus, and f is the Darcy–Weisbach friction factor . [ 31 ]
Column separation is a phenomenon that can occur during a water-hammer event. If the pressure in a pipeline drops below the vapor pressure of the liquid, cavitation will occur (some of the liquid vaporizes, forming a bubble in the pipeline, keeping the pressure close to the vapor pressure). This is most likely to occur at specific locations such as closed ends, high points or knees (changes in pipe slope). When subcooled liquid flows into the space previously occupied by vapor the area of contact between the vapor and the liquid increases. This causes the vapor to condense into the liquid reducing the pressure in the vapor space. The liquid on either side of the vapor space is then accelerated into this space by the pressure difference. The collision of the two columns of liquid (or of one liquid column if at a closed end) causes a large and nearly instantaneous rise in pressure. This pressure rise can damage hydraulic machinery , individual pipes and supporting structures. Many repetitions of cavity formation and collapse may occur in a single water-hammer event. [ 32 ]
Most water hammer software packages use the method of characteristics [ 27 ] to solve the differential equations involved. This method works well if the wave speed does not vary in time due to either air or gas entrainment in a pipeline. The wave method (WM) is also used in various software packages. WM lets operators analyze large networks efficiently. Many commercial and non-commercial packages are available.
Software packages vary in complexity, dependent on the processes modeled. The more sophisticated packages may have any of the following features: | https://en.wikipedia.org/wiki/Hydraulic_shock |
Hydraulic tomography (HT) is a sequential cross-hole hydraulic test followed by inversion of all the data to map the spatial distribution of aquifer hydraulic properties. Specifically, HT involves installation of multiple wells in an aquifer, which are partitioned into several intervals along the depth using packers. A sequential aquifer test at selected intervals is then conducted. During the test, water is injected or withdrawn (i.e. a pressure excitation) at a selected interval in a given well. Pressure responses of the subsurface are then monitored at other intervals at this well and also in other wells. This test produces a set of pressure excitation/response data of the subsurface.
Once a given test has been completed, the pump is moved to another interval and the test is repeated to collect another set of data. The same procedure is then applied to the intervals at other wells. Afterward, the data sets from all tests are processed by a mathematical model to estimate the spatial distribution of hydraulic properties of the aquifer. These pairs of pumping and drawdown data sets at different locations make an inverse problem better posed, because each pair cross-validates the others such that the estimates become less non-unique. In other words, predictions of ground water flow based on the HT estimates will be more accurate and less uncertain than those based on estimates from traditional site-characterization approaches and model calibrations .
This hydrology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydraulic_tomography |
Hydraulics (from Ancient Greek ὕδωρ ( húdōr ) ' water ' and αὐλός ( aulós ) ' pipe ' ) [ 2 ] is a technology and applied science using engineering , chemistry , and other sciences involving the mechanical properties and use of liquids . At a very basic level, hydraulics is the liquid counterpart of pneumatics , which concerns gases . Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation, control, and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, and they cover concepts such as pipe flow , dam design, fluidics , and fluid control circuitry. The principles of hydraulics are in use naturally in the human body within the vascular system and erectile tissue . [ 3 ] [ 4 ]
Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers , canals , lakes , estuaries , and seas . Its sub-field open-channel flow studies the flow in open channels .
Early uses of water power date back to Mesopotamia and ancient Egypt , where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient Central Asia.
In the Persian Empire or previous entities in Persia, the Persians constructed an intricate system of water mills, canals and dams known as the Shushtar Historical Hydraulic System . The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I , [ 5 ] has been referred to by UNESCO as "a masterpiece of creative genius". [ 5 ] They were also the inventors [ 6 ] of the Qanat , an underground aqueduct, around the 9th century BC. [ 7 ] Several of Iran's large, ancient gardens were irrigated thanks to Qanats. [ 8 ]
The Qanat spread to neighboring areas, including the Armenian highlands . There, starting in the early 8th century BC, the Kingdom of Urartu undertook significant hydraulic works, such as the Menua canal . [ 9 ] [ 7 ] [ 10 ]
The earliest evidence of water wheels and watermills date back to the ancient Near East in the 4th century BC, [ 11 ] specifically in the Persian Empire before 350 BCE, in the regions of Iraq , Iran , [ 12 ] and Egypt . [ 13 ]
In ancient China there was Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 – 139 AD), and Ma Jun (200 – 265 AD), while medieval China had Su Song (1020 – 1101 AD) and Shen Kuo (1031–1095). Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron . Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation . [ 14 ] [ 15 ]
In ancient Sri Lanka, hydraulics were widely used in the ancient kingdoms of Anuradhapura and Polonnaruwa . [ 16 ] The discovery of the principle of the valve tower, or valve pit, (Bisokotuwa in Sinhalese) for regulating the escape of water is credited to ingenuity more than 2,000 years ago. [ 17 ] By the first century AD, several large-scale irrigation works had been completed. [ 18 ] Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya , Sri Lanka. The coral on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa (King Dhatusena), Parakrama Samudra (King Parakrama Bahu), Tisa Wewa (King Dutugamunu), Minneriya (King Mahasen)
In Ancient Greece , the Greeks constructed sophisticated water and hydraulic power systems. An example is a construction by Eupalinos , under a public contract, of a watering channel for Samos , the Tunnel of Eupalinos . An early example of the usage of hydraulic wheel, probably the earliest in Europe, is the Perachora wheel (3rd century BC). [ 19 ]
In Greco-Roman Egypt , the construction of the first hydraulic machine automata by Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10 – 80 AD) is notable. Hero describes several working machines using hydraulic power, such as the force pump , which is known from many Roman sites as having been used for raising water and in fire engines. [ 20 ]
In the Roman Empire , different hydraulic applications were developed, including public water supplies, innumerable aqueducts , power using watermills and hydraulic mining . They were among the first to make use of the siphon to carry water across valleys, and used hushing on a large scale to prospect for and then extract metal ores . They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae . [ citation needed ]
Hydraulic mining was used in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold-mine of Las Medulas was one of the largest of their mines. At least seven long aqueducts worked it, and the water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content. [ 21 ] [ 22 ]
In the Muslim world during the Islamic Golden Age and Arab Agricultural Revolution (8th–13th centuries), engineers made wide use of hydropower as well as early uses of tidal power , [ 23 ] and large hydraulic factory complexes. [ 24 ] A variety of water-powered industrial mills were used in the Islamic world, including fulling mills, gristmills , paper mills , hullers , sawmills , ship mills , stamp mills , steel mills , sugar mills , and tide mills . By the 11th century, every province throughout the Islamic world had these industrial mills in operation, from Al-Andalus and North Africa to the Middle East and Central Asia . [ 25 ] Muslim engineers also used water turbines , employed gears in watermills and water-raising machines, and pioneered the use of dams as a source of water power, used to provide additional power to watermills and water-raising machines. [ 26 ]
Al-Jazari (1136–1206) described designs for 50 devices, many of them water-powered, in his book, The Book of Knowledge of Ingenious Mechanical Devices , including water clocks, a device to serve wine, and five devices to lift water from rivers or pools. These include an endless belt with jugs attached and a reciprocating device with hinged valves. [ 27 ]
The earliest programmable machines were water-powered devices developed in the Muslim world. A music sequencer , a programmable musical instrument , was the earliest type of programmable machine. The first music sequencer was an automated water-powered flute player invented by the Banu Musa brothers, described in their Book of Ingenious Devices , in the 9th century. [ 28 ] [ 29 ] In 1206, Al-Jazari invented water-powered programmable automata/ robots . He described four automaton musicians, including drummers operated by a programmable drum machine , where they could be made to play different rhythms and different drum patterns. [ 30 ]
During the mid 16th century, Italian engineer Giuseppe Ceredi advanced the design of the Archimedean screw pump, applying mathematical principles to improve its efficiency for irrigation and drainage and secured a patent for his developments. Ceredi's innovations, documented in Tre discorsi sopra il modo d'alzar acque da' luoghi bassi (1567), led to widespread adoption of the technology throughout Southern Europe. [ 31 ] [ 32 ] In 1619 Benedetto Castelli , a student of Galileo Galilei , published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters," one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e., management of rivers in the Papal States, beginning in 1626. [ 33 ] The science and engineering of water in Italy from 1500-1800 in books and manuscripts is presented in an illustrated catalog published in 2022. [ 34 ]
Blaise Pascal (1623–1662) studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids. His discovery on the theory behind hydraulics led to his invention of the hydraulic press , which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure (or exact change of pressure) at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height, and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force. This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other end in the container, i.e., any change in pressure applied at any point of the liquid is transmitted undiminished throughout the fluids.
A French physician, Poiseuille (1797–1869) researched the flow of blood through the body and discovered an important law governing the rate of flow with the diameter of the tube in which flow occurred. [ 35 ] [ citation needed ]
Several cities developed citywide hydraulic power networks in the 19th century, to operate machinery such as lifts, cranes, capstans and the like. Joseph Bramah [ 36 ] (1748–1814) was an early innovator and William Armstrong [ 37 ] (1810–1900) perfected the apparatus for power delivery on an industrial scale. In London, the London Hydraulic Power Company [ 38 ] was a major supplier its pipes serving large parts of the West End of London , City and the Docks , but there were schemes restricted to single enterprises such as docks and railway goods yards .
After students understand the basic principles of hydraulics, some teachers use a hydraulic analogy to help students learn other things.
For example:
The conservation of mass requirement combined with fluid compressibility yields a fundamental relationship between pressure, fluid flow, and volumetric expansion, as shown below: [ 39 ]
Assuming an incompressible fluid or a "very large" ratio of compressibility to contained fluid volume, a finite rate of pressure rise requires that any net flow into the collected fluid volume create a volumetric change. | https://en.wikipedia.org/wiki/Hydraulics |
Hydrazides in organic chemistry are a class of organic compounds with the formula R−NR 1 −NR 2 R 3 where R is acyl ( R'−C(=O)− ), sulfonyl ( R'−S(=O) 2 − ), phosphoryl ( (R'−) 2 P(=O)− ), phosphonyl ( (R'−O−) 2 P(=O)− ) and similar groups ( chalcogen analogs are included, for example sulfur analogs called thiohydrazides), [ 1 ] R 1 , R 2 , R 3 and R' are any groups (typically hydrogen or organyl ). [ 2 ] Unlike hydrazine and alkylhydrazines, hydrazides are nonbasic owing to the inductive influence of the acyl, sulfonyl, or phosphoryl substituent.
A common sulfonyl hydrazide is p -toluenesulfonyl hydrazide , a white air-stable solid. They are also widely used as organic reagents.
Toluenesulfonyl hydrazide is used to generate toluenesulfonyl hydrazones. When derived from ketones, these hydrazones participate in the Shapiro reaction [ 3 ] and the Eschenmoser–Tanabe fragmentation . [ 4 ] [ 5 ]
2,4,6-Triisopropylbenzenesulfonylhydrazide is a useful source of diimide . [ 6 ]
Acylhydrazines are derivatives of carboxylic acids , although they are typically prepared by the reaction of esters with hydrazine: [ 8 ]
An applied example is a synthesis of sunitinib begins by mixing 5-fluoro isatin slowly into hydrazine hydrate . [ 9 ] After 4 hours at 110 °C, the indole ring structure has been broken into (2-amino-5-fluoro-phenyl)-acetic acid hydrazide with reduction of the ketone at the 3-position. Subsequent annelation in strong acid creates the 1,3-dihydro-2-oxo indole structure required for the drug. | https://en.wikipedia.org/wiki/Hydrazide |
Hydrazine is an inorganic compound with the chemical formula N 2 H 4 . It is a simple pnictogen hydride , and is a colourless flammable liquid with an ammonia -like odour. Hydrazine is highly hazardous unless handled in solution as, for example, hydrazine hydrate ( N 2 H 4 · x H 2 O ).
Hydrazine is mainly used as a foaming agent in preparing polymer foams , but applications also include its uses as a precursor to pharmaceuticals and agrochemicals , as well as a long-term storable propellant for in- space spacecraft propulsion. Additionally, hydrazine is used in various rocket fuels and to prepare the gas precursors used in airbags . Hydrazine is used within both nuclear and conventional electrical power plant steam cycles as an oxygen scavenger to control concentrations of dissolved oxygen in an effort to reduce corrosion. [ 8 ] As of 2000 [update] , approximately 120,000 tons of hydrazine hydrate (corresponding to a 64% solution of hydrazine in water by weight) were manufactured worldwide per year. [ 9 ]
Hydrazines are a class of organic substances derived by replacing one or more hydrogen atoms in hydrazine by an organic group. [ 9 ]
The name "hydrazine" was coined by Emil Fischer in 1875; he was trying to produce organic compounds that consisted of mono-substituted hydrazine. [ 10 ] By 1887, Theodor Curtius had produced hydrazine sulfate by treating organic diazides with dilute sulfuric acid; however, he was unable to obtain pure hydrazine, despite repeated efforts. [ 11 ] [ 12 ] [ 13 ] Pure anhydrous hydrazine was first prepared by the Dutch chemist Lobry de Bruyn in 1895. [ 14 ] [ 15 ] [ 16 ]
The nomenclature is a bi-valent form, with prefix hydr- used to indicate the presence of hydrogen atoms and suffix beginning with -az- , from azote , the French word for nitrogen .
The largest use of hydrazine is as a precursor to blowing agents . Specific compounds include azodicarbonamide and azobisisobutyronitrile , which produce 100–200 mL of gas per gram of precursor. In a related application, sodium azide , the gas-forming agent in airbags , is produced from hydrazine by reaction with sodium nitrite . [ 9 ]
Hydrazine is also used as a long-term storable propellant on board space vehicles, such as the Dawn mission to Ceres and Vesta, and to both reduce the concentration of dissolved oxygen in and control pH of water used in large industrial boilers. The F-16 fighter jet, [ 17 ] Space Shuttle , and U-2 spy plane use hydrazine to fuel their Emergency Start System in the event of an engine stall. [ 18 ]
Hydrazine is a precursor to several pharmaceuticals and pesticides. Often these applications involve conversion of hydrazine to heterocyclic rings such as pyrazoles and pyridazines . Examples of commercialized bioactive hydrazine derivatives include cefazolin , rizatriptan , anastrozole , fluconazole , metazachlor, metamitron, metribuzin , paclobutrazol , diclobutrazole, propiconazole , hydrazine sulfate , [ 19 ] diimide , triadimefon , [ 9 ] and the diacylhydrazine insecticides.
Hydrazine compounds can be effective as active ingredients in insecticides, miticides, nematicides , fungicides, antiviral agents, attractants, herbicides, or plant growth regulators. [ 20 ]
The Italian catalyst manufacturer Acta (chemical company) has proposed using hydrazine as an alternative to hydrogen in fuel cells . The chief benefit of using hydrazine is that it can produce over 200 m W /cm 2 more than a similar hydrogen cell without requiring (expensive) platinum catalysts. [ 21 ] Because the fuel is liquid at room temperature, it can be handled and stored more easily than hydrogen. By storing the hydrazine in a tank full of a double-bonded carbon - oxygen carbonyl , the fuel reacts and forms a safe solid called hydrazone . By then flushing the tank with warm water, the liquid hydrazine hydrate is released. Hydrazine has a higher electromotive force of 1.56 V compared to 1.23 V for hydrogen. Hydrazine breaks down in the cell to form nitrogen and hydrogen which bonds with oxygen, releasing water. [ 21 ] Hydrazine was used in fuel cells manufactured by Allis-Chalmers Corp. , including some that provided electric power in space satellites in the 1960s.
A mixture of 63% hydrazine, 32% hydrazine nitrate and 5% water is a standard propellant for experimental bulk-loaded liquid propellant artillery . The propellant mixture above is one of the most predictable and stable, with a flat pressure profile during firing. Misfires are usually caused by inadequate ignition. The movement of the shell after a mis-ignition causes a large bubble with a larger ignition surface area, and the greater rate of gas production causes very high pressure, sometimes including catastrophic tube failures (i.e. explosions). [ 22 ] From January–June 1991, the U.S. Army Research Laboratory conducted a review of early bulk-loaded liquid propellant gun programs for possible relevance to the electrothermal chemical propulsion program. [ 22 ]
The United States Air Force (USAF) regularly uses H-70, a 70% hydrazine 30% water mixture, in operations employing the General Dynamics F-16 Fighting Falcon fighter aircraft and the Lockheed U-2 "Dragon Lady" reconnaissance aircraft. The single jet engine F-16 utilizes hydrazine to power its Emergency Power Unit (EPU), which provides emergency electrical and hydraulic power in the event of an engine flame out. The EPU activates automatically, or manually by pilot control, in the event of loss of hydraulic pressure or electrical power in order to provide emergency flight controls. The single jet engine U-2 utilizes hydrazine to power its Emergency Starting System (ESS), which provides a highly reliable method to restart the engine in flight in the event of a stall. [ 23 ]
Hydrazine was first used as a component in rocket fuels during World War II . A 30% mix by weight with 57% methanol (named M-Stoff in the German Luftwaffe ) and 13% water was called C-Stoff by the Germans. [ 24 ] The mixture was used to power the Messerschmitt Me 163B rocket-powered fighter plane, in which the German high test peroxide T-Stoff was used as an oxidizer. Unmixed hydrazine was referred to as B-Stoff by the Germans, a designation also used later for the ethanol/water fuel for the V-2 missile . [ 25 ]
Hydrazine is used as a low-power monopropellant for the maneuvering (RCS/Reaction control system) thrusters of spacecraft, and was used to power the Space Shuttle 's auxiliary power units (APUs). In addition, mono-propellant hydrazine-fueled rocket engines are often used in terminal descent of spacecraft. Such engines were used on the Viking program landers in the 1970s as well as the Mars landers Phoenix (May 2008), Curiosity (August 2012), and Perseverance (February 2021).
During the Soviet space program , unsymmetrical dimethylhydrazine (also discovered by Fischer in 1875) was used instead of hydrazine. Together with nitric oxidizers it became known as " devil's venom " due to its highly dangerous nature. [ 26 ]
In all hydrazine mono-propellant engines, the hydrazine is passed over a catalyst such as iridium metal supported by high-surface-area alumina (aluminium oxide), which causes it to decompose into ammonia ( NH 3 ), nitrogen gas ( N 2 ), and hydrogen ( H 2 ) gas according to the three following reactions: [ 27 ]
The first two reactions are extremely exothermic (the catalyst chamber can reach 800 °C in a matter of milliseconds, [ 28 ] ) and they produce large volumes of hot gas from a small volume of liquid, [ 29 ] making hydrazine a fairly efficient thruster propellant with a vacuum specific impulse of about 220 seconds. [ 30 ] Reaction 2 is the most exothermic, but produces a smaller number of molecules than that of reaction 1. Reaction 3 is endothermic and reverts the effect of reaction 2 back to the same effect as reaction 1 alone (lower temperature, greater number of molecules). The catalyst structure affects the proportion of the NH 3 that is dissociated in reaction 3; a higher temperature is desirable for rocket thrusters, while more molecules are desirable when the reactions are intended to produce greater quantities of gas. [ 31 ]
Since hydrazine is a solid below 2 °C, it is not suitable as a general purpose rocket propellant for military applications. Other variants of hydrazine that are used as rocket fuel are monomethylhydrazine , CH 3 NHNH 2 , also known as MMH (melting point −52 °C), and unsymmetrical dimethylhydrazine , (CH 3 ) 2 NNH 2 , also known as UDMH (melting point −57 °C). These derivatives are used in two-component rocket fuels, often together with dinitrogen tetroxide , N 2 O 4 . A 50:50 mixture by weight of hydrazine and UDMH was used in the engine of the service propulsion system of the Apollo command and service module , both the ascent and descent engines of the Apollo Lunar Module and Titan II ICBMs and is known as Aerozine 50 . [ 24 ] These reactions are extremely exothermic, and the burning is also hypergolic (it starts burning without any external ignition). [ 32 ]
There are ongoing efforts in the aerospace industry to find a replacement for hydrazine, given its potential ban across the European Union. [ 33 ] [ 34 ] [ 35 ] Promising alternatives include nitrous oxide -based propellant combinations, with development being led by commercial companies Dawn Aerospace , Impulse Space , [ 36 ] and Launcher . [ 37 ] The first nitrous oxide-based system ever flown in space was by D-Orbit onboard their ION Satellite Carrier in 2021, using six Dawn Aerospace B20 thrusters. [ 38 ] [ 39 ] Another alternative is more safe blends of hydrazine with much lower vapor pressure , hence reduced inhalation hazard. Aerojet Rocketdyne has developed HPB-G28 blend that have 150 times lower vapor pressure, same specific impulse, and 35% higher density specific impulse than neat hydrazine. HPB-G28 can be used with same thrusters and catalysts as hydrazine, but has freezing point of -55°C, making propellant line heating unnecessary. It contains 65% (by mol) hydrazine, 27% hydroxyethylhydrazinuim nitrate (HEHN) and 8% hydrazinium nitrate . [ 40 ]
Potential routes of hydrazine exposure include dermal, ocular, inhalation and ingestion. [ 41 ]
Hydrazine exposure can cause skin irritation/contact dermatitis and burning, irritation to the eyes/nose/throat, nausea/vomiting, shortness of breath, pulmonary edema, headache, dizziness, central nervous system depression, lethargy, temporary blindness, seizures and coma. Exposure can also cause organ damage to the liver, kidneys and central nervous system. [ 41 ] [ 42 ] Hydrazine is documented as a strong skin sensitizer with potential for cross-sensitization to hydrazine derivatives following initial exposure. [ 43 ] In addition to occupational uses reviewed above, exposure to hydrazine is also possible in small amounts from tobacco smoke. [ 42 ]
The official U.S. guidance on hydrazine as a carcinogen is mixed but generally there is recognition of potential cancer-causing effects. The National Institute for Occupational Safety and Health (NIOSH) lists it as a "potential occupational carcinogen". The National Toxicology Program (NTP) finds it is "reasonably anticipated to be a human carcinogen". The American Conference of Governmental Industrial Hygienists (ACGIH) grades hydrazine as "A3—confirmed animal carcinogen with unknown relevance to humans". The U.S. Environmental Protection Agency (EPA) grades it as "B2—a probable human carcinogen based on animal study evidence". [ 44 ]
The International Agency for Research on Cancer (IARC) rates hydrazine as "2A—probably carcinogenic to humans" with a positive association observed between hydrazine exposure and lung cancer. [ 45 ] Based on cohort and cross-sectional studies of occupational hydrazine exposure, a committee from the National Academies of Sciences , Engineering and Medicine concluded that there is suggestive evidence of an association between hydrazine exposure and lung cancer, with insufficient evidence of association with cancer at other sites. [ 46 ] The European Commission 's Scientific Committee on Occupational Exposure Limits (SCOEL) places hydrazine in carcinogen "group B—a genotoxic carcinogen". The genotoxic mechanism the committee cited references hydrazine's reaction with endogenous formaldehyde and formation of a DNA-methylating agent. [ 47 ]
In the event of a hydrazine exposure-related emergency, NIOSH recommends removing contaminated clothing immediately, washing skin with soap and water, and for eye exposure removing contact lenses and flushing eyes with water for at least 15 minutes. NIOSH also recommends anyone with potential hydrazine exposure to seek medical attention as soon as possible. [ 41 ] There are no specific post-exposure laboratory or medical imaging recommendations, and the medical work-up may depend on the type and severity of symptoms. The World Health Organization (WHO) recommends potential exposures be treated symptomatically with special attention given to potential lung and liver damage. Past cases of hydrazine exposure have documented success with pyridoxine ( vitamin B6 ) treatment. [ 43 ]
The odor threshold for hydrazine is 3.7 ppm, thus if a worker is able to smell an ammonia-like odor then they are likely over the exposure limit. However, this odor threshold varies greatly and should not be used to determine potentially hazardous exposures. [ 48 ]
For aerospace personnel, the United States Air Force uses an emergency exposure guideline, developed by the National Academy of Sciences Committee on Toxicology, which is utilized for non-routine exposures of the general public and is called the Short-Term Public Emergency Exposure Guideline (SPEGL). The SPEGL, which does not apply to occupational exposures, is defined as the acceptable peak concentration for unpredicted, single, short-term emergency exposures of the general public and represents rare exposures in a worker's lifetime. For hydrazine the 1-hour SPEGL is 2 ppm, with a 24-hour SPEGL of 0.08 ppm. [ 49 ]
A complete surveillance programme for hydrazine should include systematic analysis of biologic monitoring, medical screening and morbidity/mortality information. The CDC recommends surveillance summaries and education be provided for supervisors and workers. Pre-placement and periodic medical screening should be conducted with specific focus on potential effects of hydrazine upon functioning of the eyes, skin, liver, kidneys, hematopoietic, nervous and respiratory systems. [ 41 ]
Common controls used for hydrazine include process enclosure, local exhaust ventilation and personal protective equipment (PPE). [ 41 ] Guidelines for hydrazine PPE include non-permeable gloves and clothing, indirect-vent splash resistant goggles, face shield and in some cases a respirator. [ 48 ] The use of respirators for the handling of hydrazine should be the last resort as a method of controlling worker exposure. In cases where respirators are needed, proper respirator selection and a complete respiratory protection program consistent with OSHA guidelines should be implemented. [ 41 ]
For USAF personnel, Air Force Occupational Safety and Health (AFOSH) Standard 48-8, Attachment 8 reviews the considerations for occupational exposure to hydrazine in missile, aircraft and spacecraft systems. Specific guidance for exposure response includes mandatory emergency shower and eyewash stations and a process for decontaminating protective clothing. The guidance also assigns responsibilities and requirements for proper PPE, employee training, medical surveillance and emergency response. [ 49 ] USAF bases requiring the use of hydrazine generally have specific base regulations governing local requirements for safe hydrazine use and emergency response.
Hydrazine, H 2 N−NH 2 , contains two amine groups NH 2 connected by a single bond between the two nitrogen atoms. Each N−NH 2 subunit is pyramidal. The structure of the free molecules was determined by gas electron diffraction and microwave spectroscopy . The N–N single bond length is 1.447(2) Å (144.7(2) pm ), the N-H distance is 1.015(2) Å , the N-N-H angles are 106(2)° and 112(2)°, the H-N-H angle is 107°. [ 50 ] The molecule adopts a gauche conformation with a torsion angle of 91(2)° (dihedral angle between the planes containing the N-N bond and the bisectors of the H-N-H angles). The rotational barrier is twice that of ethane . These structural properties resemble those of gaseous hydrogen peroxide , which adopts a "skewed" anticlinal conformation, and also experiences a strong rotational barrier.
The structure of solid hydrazine was determined by X-ray diffraction. In this phase the N-N bond has a length of 1.46 Å and the nearest non-bonded distances are 3.19, 3.25 and 3.30 Å . [ 51 ]
Diverse synthetic pathways for hydrazine production have been developed. [ 9 ] The key step is the creation of the N –N single bond. The many routes can be divided into those that use chlorine oxidants (and generate salt) and those that do not.
Hydrazine can be synthesized from ammonia and hydrogen peroxide with a ketone catalyst, in a procedure called the Peroxide process (sometimes called Pechiney-Ugine-Kuhlmann process, the Atofina–PCUK cycle, or ketazine process). [ 9 ] The net reaction is: [ 52 ]
In this route, the ketone and ammonia first condense to give the imine , which is oxidised by hydrogen peroxide to the oxaziridine , a three-membered ring containing carbon, oxygen, and nitrogen. Next, the oxaziridine gives the hydrazone by treatment with ammonia , which process creates the nitrogen-nitrogen single bond. This hydrazone condenses with one more equivalent of ketone.
The resulting azine is hydrolyzed to give hydrazine and regenerate the ketone, methyl ethyl ketone :
Unlike most other processes, this approach does not produce a salt as a by-product. [ 53 ]
The Olin Raschig process , first announced in 1907, produces hydrazine from sodium hypochlorite (the active ingredient in many bleaches ) and ammonia without the use of a ketone catalyst. This method relies on the reaction of monochloramine with ammonia to create the N –N single bond as well as a hydrogen chloride byproduct: [ 19 ]
Related to the Raschig process, urea can be oxidized instead of ammonia. Again sodium hypochlorite serves as the oxidant. The net reaction is shown: [ 54 ]
The process generates significant by-products and is mainly practised in Asia. [ 9 ]
The Bayer Ketazine Process is the predecessor to the peroxide process. It employs sodium hypochlorite as oxidant instead of hydrogen peroxide. Like all hypochlorite-based routes, this method produces an equivalent of salt for each equivalent of hydrazine. [ 9 ]
Hydrazine forms a monohydrate N 2 H 4 ·H 2 O that is denser (1.032 g/cm 3 ) than the anhydrous form N 2 H 4 (1.021 g/cm 3 ). Hydrazine has basic ( alkali ) chemical properties comparable to those of ammonia : [ 55 ]
(for ammonia K b = 1.78 × 10 −5 )
It is difficult to diprotonate: [ 56 ]
Exposure to extremely strong bases or alkali metals generates deprotonated hydrazide salts. Most explode on exposure to air or moisture. [ 57 ]
Ideally, the combustion of hydrazine in oxygen produces nitrogen and water:
An excess of oxygen gives oxides of nitrogen, including nitrogen monoxide and nitrogen dioxide :
The heat of combustion of hydrazine in oxygen (air) is 19.41 MJ/kg (8345 BTU/lb). [ 58 ]
Hydrazine is a convenient reductant because the by-products are typically nitrogen gas and water. This property makes it useful as an antioxidant , an oxygen scavenger , and a corrosion inhibitor in water boilers and heating systems. It also directly reduces salts of less active metals (e.g., bismuth, arsenic, copper, mercury, silver, lead, platinum, and palladium) to the element. [ 59 ] That property has commercial application in electroless nickel plating and plutonium extraction from nuclear reactor waste . Some colour photographic processes also use a weak solution of hydrazine as a stabilising wash, as it scavenges dye coupler and unreacted silver halides. Hydrazine is the most common and effective reducing agent used to convert graphene oxide (GO) to reduced graphene oxide (rGO) via hydrothermal treatment. [ 60 ]
Hydrazine can be protonated to form various solid salts of the hydrazinium cation [N 2 H 5 ] + , by treatment with mineral acids. A common salt is hydrazinium hydrogensulfate , [N 2 H 5 ] + [HSO 4 ] − . [ 61 ] Hydrazinium hydrogensulfate was investigated as a treatment of cancer-induced cachexia , but proved ineffective. [ 62 ]
Double protonation gives the hydrazinium dication or hydrazinediium, [N 2 H 6 ] 2+ , of which various salts are known. [ 63 ]
Hydrazines are part of many organic syntheses , often those of practical significance in pharmaceuticals (see applications section), as well as in textile dyes and in photography. [ 9 ]
Hydrazine is used in the Wolff–Kishner reduction , a reaction that transforms the carbonyl group of a ketone into a methylene bridge (or an aldehyde into a methyl group ) via a hydrazone intermediate. Upon the catalysis with transition-metals, the hydrazones are used as organometallic reagent equivalents (HOME chemistry) for C-C bond formations. [ 64 ] The production of the highly stable dinitrogen from the hydrazine derivative helps to drive the reaction.
Being bifunctional, with two amines, hydrazine is a key building block for the preparation of many heterocyclic compounds via condensation with a range of difunctional electrophiles . With 2,4-pentanedione , it condenses to give the 3,5-dimethylpyrazole . [ 65 ] In the Einhorn-Brunner reaction hydrazines react with imides to give triazoles .
Being a good nucleophile, N 2 H 4 can attack sulfonyl halides and acyl halides. [ 66 ] The tosylhydrazine also forms hydrazones upon treatment with carbonyls.
Hydrazine is used to cleave N -alkylated phthalimide derivatives. This scission reaction allows phthalimide anion to be used as amine precursor in the Gabriel synthesis . [ 67 ]
Illustrative of the condensation of hydrazine with a simple carbonyl is its reaction with acetone to give the acetone azine . The latter reacts further with hydrazine to yield acetone hydrazone : [ 68 ]
The propanone azine is an intermediate in the Atofina- PCUK process . Direct alkylation of hydrazines with alkyl halides in the presence of base yields alkyl-substituted hydrazines, but the reaction is typically inefficient due to poor control on level of substitution (same as in ordinary amines ). The reduction of hydrazones to hydrazines present a clean way to produce 1,1-dialkylated hydrazines.
In a related reaction, 2-cyanopyridines react with hydrazine to form amide hydrazides, which can be converted using 1,2-diketones into triazines .
Hydrazine is the intermediate in the anaerobic oxidation of ammonia ( anammox ) process. [ 69 ] It is produced by some yeasts and the open ocean bacterium anammox ( Brocadia anammoxidans ). [ 70 ]
The false morel produces the poison gyromitrin which is an organic derivative of hydrazine that is converted to monomethylhydrazine by metabolic processes. Even the most popular edible "button" mushroom Agaricus bisporus produces organic hydrazine derivatives, including agaritine , a hydrazine derivative of an amino acid, and gyromitrin . [ 71 ] [ 72 ]
In the novel The Martian (which was adapted into a feature film ) the main character uses an iridium catalyst to separate hydrogen gas from surplus hydrazine fuel, which he then burns to generate water for survival. | https://en.wikipedia.org/wiki/Hydrazine |
Hydrazine nitrate is an inorganic compound with the chemical formula N 2 H 4 ·HN O 3 . It has usage in liquid explosives as an oxidizer . It exists in two crystalline forms, stable α-type and unstable β-type. The former is usually used in explosives. Its solubility is small in alcohols but
large in water and hydrazine . It has strong hygroscopicity , only slightly lower than ammonium nitrate . [ 1 ]
Hydrazine nitrate has a good thermal stability. Its weight loss rate at 100 °C is slower than that of ammonium nitrate. Its explosion point is 307 °C (50% detonation) and explosion heat is about 3.829 MJ/kg. Because it has no carbon elements, the detonation products are not solid and their average molecular weight is small. [ 1 ]
Hydrazine nitrate is produced by the reaction of hydrazine and nitric acid : [ 2 ] | https://en.wikipedia.org/wiki/Hydrazine_nitrate |
Unsymmetrical dimethylhydrazine
Phenylhydrazine
2,4-Dinitrophenylhydrazine
1,2-Diphenylhydrazine
Tetraphenylhydrazine
Hydrazines (R 2 N−NR 2 ) are a class of chemical compounds with two nitrogen atoms linked via a covalent bond and which carry from one up to four alkyl or aryl substituents. Hydrazines can be considered as derivatives of the inorganic hydrazine (H 2 N−NH 2 ), in which one or more hydrogen atoms have been replaced by hydrocarbon groups. [ 1 ]
Hydrazines can be divided into three groups according to the degree of substitution. Hydrazines belonging to the same group behave similarly in their chemical properties. Monosubstituted hydrazines and so-called asymmetrically disubstituted hydrazines, where (only) two hydrocarbon groups are bonded to the same nitrogen atom are colorless liquids. Aliphatic monosubstituted and asymmetrically disubstituted hydrazines are very water soluble, strongly alkaline and good reducing agents. Aromatic monosubstituted and asymmetrically disubstituted hydrazines are poorly soluble in water, less basic and weaker reducing agents. For the preparation of aliphatic hydrazines, the reaction of hydrazine with alkylating compounds such as alkyl halides is used, or by reduction of nitroso derivatives. Aromatic hydrazines are prepared by reducing aromatic diazonium salts. [ 3 ] [ 4 ]
In symmetric disubstituted hydrazines, a hydrocarbon group is bonded to each of the hydrazine nitrogen atoms. Like asymmetrically disubstituted hydrazines, they are liquids, but their boiling points are typically higher. In particular, the aliphatic compounds are basic and reducing agents and are soluble in water. Aromatic symmetric disubstituted hydrazines are not soluble in water. Symmetrically disubstituted hydrazines are prepared by reducing nitro compounds under basic conditions or by reducing the azines.
Tri- or tetrasubstituted aliphatic hydrazines are water-insoluble weakly basic compounds. The corresponding arylhydrazines are solid colorless substances which are insoluble in water and substantially not basic. They react with concentrated sulfuric acid to form violet or dark blue compounds.
Phenylhydrazine and 2,4-dinitrophenylhydrazine had been used historically in analytical chemistry to detect and identify compounds with carbonyl groups. Phenylhydrazine was used to study the structure of carbohydrates , because the reaction of the sugar's aldehyde groups lead to well crystallizing phenylhydrazones or osazones .
Organohydrazines and their derivatives are numerous, especially when hydrazones are included. | https://en.wikipedia.org/wiki/Hydrazines |
Hydrazoic acid , also known as hydrogen azide , azic acid or azoimide , [ 2 ] is a compound with the chemical formula HN 3 . [ 3 ] It is a colorless, volatile, and explosive liquid at room temperature and pressure. It is a compound of nitrogen and hydrogen , and is therefore a pnictogen hydride . It was first isolated in 1890 by Theodor Curtius . [ 4 ] The acid has few applications, but its conjugate base , the azide ion, is useful in specialized processes.
Hydrazoic acid, like its fellow mineral acids , is soluble in water. Undiluted hydrazoic acid is dangerously explosive [ 5 ] with a standard enthalpy of formation Δ f H o (l, 298K) = +264 kJ/mol. [ 6 ] When dilute, the gas and aqueous solutions (<10%) can be safely prepared but should be used immediately; because of its low boiling point, hydrazoic acid is enriched upon evaporation and condensation such that dilute solutions incapable of explosion can form droplets in the headspace of the container or reactor that are capable of explosion. [ 7 ] [ 8 ]
The acid is usually formed by acidification of an azide salt like sodium azide . Normally solutions of sodium azide in water contain trace quantities of hydrazoic acid in equilibrium with the azide salt, but introduction of a stronger acid can convert the primary species in solution to hydrazoic acid. The pure acid may be subsequently obtained by fractional distillation as an extremely explosive colorless liquid with an unpleasant smell. [ 2 ]
Its aqueous solution can also be prepared by treatment of barium azide solution with dilute sulfuric acid , filtering the insoluble barium sulfate . [ 9 ]
It was originally prepared by the reaction of aqueous hydrazine with nitrous acid :
With the hydrazinium cation [N 2 H 5 ] + this reaction is written as:
Other oxidizing agents, such as hydrogen peroxide , nitrosyl chloride , trichloramine or nitric acid , can also be used to produce hydrazoic acid from hydrazine. [ 10 ]
Hydrazoic acid reacts with nitrous acid:
This reaction is unusual in that it involves compounds with nitrogen in four different oxidation states. [ 11 ]
In its properties hydrazoic acid shows some analogy to the halogen acids, since it forms poorly soluble (in water) lead, silver and mercury(I) salts. The metallic salts all crystallize in the anhydrous form and decompose on heating, leaving a residue of the pure metal. [ 2 ] It is a weak acid (p K a = 4.75. [ 6 ] ) Its heavy metal salts are explosive and readily interact with the alkyl iodides . Azides of heavier alkali metals (excluding lithium ) or alkaline earth metals are not explosive, but decompose in a more controlled way upon heating, releasing spectroscopically-pure N 2 gas. [ 12 ] Solutions of hydrazoic acid dissolve many metals (e.g. zinc , iron ) with liberation of hydrogen and formation of salts, which are called azides (formerly also called azoimides or hydrazoates).
Hydrazoic acid may react with carbonyl derivatives, including aldehydes, ketones, and carboxylic acids, to give an amine or amide, with expulsion of nitrogen. This is called Schmidt reaction or Schmidt rearrangement.
Dissolution in the strongest acids produces explosive salts containing the aminodiazonium ion [H 2 N=N=N] + ⇌ [H 2 N−N≡N] + , for example: [ 12 ]
The ion [H 2 N=N=N] + is isoelectronic to diazomethane H 2 C=N + =N − .
The decomposition of hydrazoic acid, triggered by shock, friction, spark, etc. produces nitrogen and hydrogen:
Hydrazoic acid undergoes unimolecular decomposition at sufficient energy:
The lowest energy pathway produces NH in the triplet state, making it a spin-forbidden reaction. This is one of the few reactions whose rate has been determined for specific amounts of vibrational energy in the ground electronic state, by laser photodissociation studies. [ 13 ] In addition, these unimolecular rates have been analyzed theoretically, and the experimental and calculated rates are in reasonable agreement. [ 14 ]
Hydrazoic acid is volatile and highly toxic. It has a pungent smell and its vapor can cause violent headaches . The compound acts as a non-cumulative poison.
2-Furonitrile , a pharmaceutical intermediate and potential artificial sweetening agent has been prepared in good yield by treating furfural with a mixture of hydrazoic acid ( HN 3 ) and perchloric acid ( HClO 4 ) in the presence of magnesium perchlorate in the benzene solution at 35 °C. [ 15 ] [ 16 ]
The all gas-phase iodine laser (AGIL) mixes gaseous hydrazoic acid with chlorine to produce excited nitrogen chloride , which is then used to cause iodine to lase; this avoids the liquid chemistry requirements of COIL lasers . | https://en.wikipedia.org/wiki/Hydrazoic_acid |
Hydrazones are a class of organic compounds with the structure R 1 R 2 C=N−NH 2 . [ 1 ] They are related to ketones and aldehydes by the replacement of the oxygen =O with the = N−NH 2 functional group . They are formed usually by the action of hydrazine on ketones or aldehydes. [ 2 ] [ 3 ]
Hydrazine, organohydrazines, and 1,1-diorganohydrazines react with aldehydes and ketones to give hydrazones.
Phenylhydrazine reacts with reducing sugars to form hydrazones known as osazones , which was developed by German chemist Emil Fischer as a test to differentiate monosaccharides . [ 4 ] [ 5 ]
Hydrazones are the basis for various analyses of ketones and aldehydes. For example, dinitrophenylhydrazine coated onto a silica sorbent is the basis of an adsorption cartridge. The hydrazones are then eluted and analyzed by high-performance liquid chromatography (HPLC) using a UV detector.
The compound carbonyl cyanide- p -trifluoromethoxyphenylhydrazone (abbreviated as FCCP) is used to uncouple ATP synthesis and reduction of oxygen in oxidative phosphorylation in molecular biology .
Hydrazones are the basis of bioconjugation strategies. [ 7 ] [ 8 ] Hydrazone-based coupling methods are used in medical biotechnology to couple drugs to targeted antibodies (see ADC ), e.g. antibodies against a certain type of cancer cell. The hydrazone-based bond is stable at neutral pH (in the blood), but is rapidly destroyed in the acidic environment of lysosomes of the cell. The drug is thereby released in the cell, where it exerts its function. [ 9 ]
Hydrazones are susceptible to hydrolysis:
Alkyl hydrazones are 10 2 - to 10 3 -fold more sensitive to hydrolysis than analogous oximes . [ 10 ]
When derived from hydrazine itself, hydrazones condense with a second equivalent of a carbonyl to give azines : [ 11 ]
Hydrazones are intermediates in the Wolff–Kishner reduction .
Hydrazones are reactants in hydrazone iodination , the Shapiro reaction , and the Bamford–Stevens reaction to vinyl compounds. Hydrazones can also be synthesized by the Japp–Klingemann reaction via β-keto acids or β-keto-esters and aryl diazonium salts. Hydrazones are converted to azines when used in the preparation of 3,5-disubstituted 1 H - pyrazoles , [ 12 ] a reaction also well known using hydrazine hydrate . [ 13 ] [ 14 ] With a transition metal catalyst , hydrazones can serve as organometallic reagent surrogates to react with various electrophiles. [ 15 ]
In N , N -dialkylhydrazones [ 16 ] the C=N bond can be hydrolysed, oxidised and reduced, the N–N bond can be reduced to the free amine. The carbon atom of the C=N bond can react with organometallic nucleophiles. The alpha-hydrogen atom is more acidic by 10 orders of magnitude compared to the ketone and therefore more nucleophilic. Deprotonation with for instance lithium diisopropylamide (LDA) gives an azaenolate which can be alkylated by alkyl halides. [ 17 ] The hydrazines SAMP and RAMP function as chiral auxiliary . [ 18 ] [ 19 ]
Several methods are known to recover carbonyl compounds from N,N-dialkylhydrazones. [ 20 ] Procedures include oxidative, hydrolytic or reductive cleavage conditions and can be compatible with a wide range of functional groups. | https://en.wikipedia.org/wiki/Hydrazone |
Hydric soil is soil which is permanently or seasonally saturated by water, resulting in anaerobic conditions, as found in wetlands .
Most soils are aerobic . This is important because plant roots respire (that is, they consume oxygen and carbohydrates while releasing carbon dioxide ) and there must be sufficient air—especially oxygen—in the soil to support most forms of soil life . Air normally moves through interconnected pores by forces such as changes in atmospheric pressure , the flushing action of rainwater, and by simple diffusion .
In addition to plant roots , most forms of soil microorganisms need oxygen to survive. This is true of the more well-known soil animals as well, such as ants , earthworms and moles . But soils can often become saturated with water due to rainfall and flooding. Gas diffusion in soil slows (some 10,000 times slower) when soil becomes saturated with water because there are no open passageways for air to travel. When oxygen levels become limited, intense competition arises between soil life forms for the remaining oxygen. When this anaerobic environment continues for long periods during the growing season, quite different biological and chemical reactions begin to dominate, compared with aerobic soils. In soils where saturation with water is prolonged and is repeated for many years, unique soil properties usually develop that can be recognized in the field. Soils with these unique properties are called hydric soils, and although they may occupy a relatively small portion of the landscape, they maintain important soil functions in the environment. [ 1 ]
The plants found in hydric soils often have aerenchyma , internal spaces in stems and rhizomes, that allow atmospheric oxygen to be transported to the rooting zone. [ 2 ] Hence, many wetlands are dominated by plants with aerenchyma; [ 3 ] common examples include cattails, sedges and water-lilies.
A hydric soil is defined by federal law [ 4 ] to mean "soil that, in its undrained condition, is saturated, flooded, or ponded long enough during a growing season to develop an anaerobic condition that supports the growth and regeneration of hydrophytic vegetation". This term is part of the legal definition of a wetland included in the United States Food Security Act of 1985 (P.L. 99-198). This definition is provided in the controlling regulations to the Wetland Conservation Provisions of the FSA of 1985(7 C.F.R 12) and is used by the U.S.D.A. Natural Resources Conservation Service in the administration of the Wetland Conservation Compliance provisions ("Swampbuster") contained in the FSA of 1985. In adopting this definition in 1985, Congress attempted to capture the duration of waterlogged condition of a hydric soil by adding that a hydric soil is waterlogged long enough to support not only the growth of plants adapted to life in anaerobic conditions but also the regeneration of such plants.
Another common definition of a hydric soils is provided by the National Technical Committee of Hydric Soils (NTCHS) as "a soil that formed under conditions of saturation, flooding, or ponding long enough during the growing season to develop anaerobic conditions in the upper part." [ 5 ] The NTCHS hydric soil definition is used by the U.S. Army Corps of Engineers and the Environmental Protection Agency in their joint responsibilities in the administration of Section 404 of the Clean Water Act (1972). | https://en.wikipedia.org/wiki/Hydric_soil |
In chemistry , a hydride is formally the anion of hydrogen (H − ), a hydrogen ion with two electrons. [ 1 ] In modern usage, this is typically only used for ionic bonds, but it is sometimes (and has been more frequently in the past) applied to all compounds containing covalently bound H atoms . In this broad and potentially archaic sense, water (H 2 O) is a hydride of oxygen , ammonia is a hydride of nitrogen , etc. In covalent compounds, it implies hydrogen is attached to a less electronegative element . In such cases, the H centre has nucleophilic character, which contrasts with the protic character of acids. The hydride anion is very rarely observed.
Almost all of the elements form binary compounds with hydrogen , the exceptions being He , [ 2 ] Ne , [ 3 ] Ar , [ 4 ] Kr , [ 5 ] Pm , Os , Ir , Rn , Fr , and Ra . [ 6 ] [ 7 ] [ 8 ] [ 9 ] Exotic molecules such as positronium hydride have also been made.
Bonds between hydrogen and the other elements range from being highly ionic to somewhat covalent. Some hydrides, e.g. boron hydrides , do not conform to classical electron counting rules and the bonding is described in terms of multi-centered bonds, whereas the interstitial hydrides often involve metallic bonding . Hydrides can be discrete molecules , oligomers or polymers , ionic solids , chemisorbed monolayers, [ citation needed ] bulk metals (interstitial), or other materials. While hydrides traditionally react as Lewis bases or reducing agents , some metal hydrides behave as hydrogen-atom donors and act as acids.
Free hydride anions exist only under extreme conditions and are not invoked for homogeneous solution. Instead, many compounds have hydrogen centres with hydridic character.
Aside from electride , the hydride ion is the simplest possible anion , consisting of two electrons and a proton . Hydrogen has a relatively low electron affinity , 72.77 kJ/mol and reacts exothermically with protons as a powerful Lewis base .
The low electron affinity of hydrogen and the strength of the H–H bond ( Δ H BE = 436 kJ/mol ) means that the hydride ion would also be a strong reducing agent
According to the general definition, every element of the periodic table (except some noble gases ) forms one or more hydrides. These substances have been classified into three main types according to the nature of their bonding : [ 6 ]
While these divisions have not been used universally, they are still useful to understand differences in hydrides.
These are stoichiometric compounds of hydrogen. Ionic or saline hydrides [ 12 ] are composed of hydride bound to an electropositive metal, generally an alkali metal or alkaline earth metal . The divalent lanthanides such as europium and ytterbium form compounds similar to those of heavier alkaline earth metals. In these materials the hydride is viewed as a pseudohalide . Saline hydrides are insoluble in conventional solvents, reflecting their non-molecular structures. Ionic hydrides are used as bases and, occasionally, as reducing reagents in organic synthesis . [ 13 ]
Typical solvents for such reactions are ethers . Water and other protic solvents cannot serve as a medium for ionic hydrides because the hydride ion is a stronger base than hydroxide and most hydroxyl anions. Hydrogen gas is liberated in a typical acid-base reaction.
Often alkali metal hydrides react with metal halides. Lithium aluminium hydride (often abbreviated as LAH) arises from reactions of lithium hydride with aluminium chloride .
According to some definitions, covalent hydrides cover all other compounds containing hydrogen. Some definitions limit hydrides to hydrogen centres that formally react as hydrides, i.e. are nucleophilic, and hydrogen atoms bound to metal centers. These hydrides are formed by all the true non-metals (except zero group elements) and the elements like Al, Ga, Sn, Pb, Bi, Po, etc., which are normally metallic in nature, i.e., this class includes the hydrides of p-block elements. In these substances the hydride bond is formally a covalent bond much like the bond made by a proton in a weak acid . This category includes hydrides that exist as discrete molecules, polymers or oligomers, and hydrogen that has been chem-adsorbed to a surface. A particularly important segment of covalent hydrides are complex metal hydrides , powerful soluble hydrides commonly used in synthetic procedures.
Molecular hydrides often involve additional ligands; for example, diisobutylaluminium hydride (DIBAL) consists of two aluminum centers bridged by hydride ligands. Hydrides that are soluble in common solvents are widely used in organic synthesis. Particularly common are sodium borohydride ( NaBH 4 ) and lithium aluminium hydride and hindered reagents such as DIBAL.
Interstitial hydrides most commonly exist within metals or alloys. They are traditionally termed "compounds" even though they do not strictly conform to the definition of a compound, more closely resembling common alloys such as steel. In such hydrides, hydrogen can exist as either atomic or diatomic entities. Mechanical or thermal processing, such as bending, striking, or annealing, may cause the hydrogen to precipitate out of solution by degassing. Their bonding is generally considered metallic . Such bulk transition metals form interstitial binary hydrides when exposed to hydrogen. These systems are usually non-stoichiometric , with variable amounts of hydrogen atoms in the lattice. In materials engineering, the phenomenon of hydrogen embrittlement results from the formation of interstitial hydrides. Hydrides of this type form according to either one of two main mechanisms. The first mechanism involves the adsorption of dihydrogen, succeeded by the cleaving of the H-H bond, the delocalisation of the hydrogen's electrons, and finally the diffusion of the protons into the metal lattice. The other main mechanism involves the electrolytic reduction of ionised hydrogen on the surface of the metal lattice, also followed by the diffusion of the protons into the lattice. The second mechanism is responsible for the observed temporary volume expansion of certain electrodes used in electrolytic experiments.
Palladium absorbs up to 900 times its own volume of hydrogen at room temperatures, forming palladium hydride . This material has been discussed as a means to carry hydrogen for vehicular fuel cells . Interstitial hydrides show certain promise as a way for safe hydrogen storage . Neutron diffraction studies have shown that hydrogen atoms randomly occupy the octahedral interstices in the metal lattice (in an fcc lattice there is one octahedral hole per metal atom). The limit of absorption at normal pressures is PdH0.7, indicating that approximately 70% of the octahedral holes are occupied. [ 14 ]
Many interstitial hydrides have been developed that readily absorb and discharge hydrogen at room temperature and atmospheric pressure. They are usually based on intermetallic compounds and solid-solution alloys. However, their application is still limited, as they are capable of storing only about 2 weight percent of hydrogen, insufficient for automotive applications. [ 15 ]
Transition metal hydrides include compounds that can be classified as covalent hydrides . Some are even classified as interstitial hydrides [ citation needed ] and other bridging hydrides. Classical transition metal hydride feature a single bond between the hydrogen centre and the transition metal. Some transition metal hydrides are acidic, e.g., HCo(CO) 4 and H 2 Fe(CO) 4 . The anions potassium nonahydridorhenate [ReH 9 ] 2− and [FeH 6 ] 4− are examples from the growing collection of known molecular homoleptic metal hydrides. [ 17 ] As pseudohalides , hydride ligands are capable of bonding with positively polarized hydrogen centres. This interaction, called dihydrogen bonding , is similar to hydrogen bonding , which exists between positively polarized protons and electronegative atoms with open lone pairs.
Hydrides containing protium are known as protides .
Hydrides containing deuterium are known as deuterides . Some deuterides, such as LiD , are important fusion fuels in thermonuclear weapons and useful moderators in nuclear reactors .
Hydrides containing tritium are known as tritides.
Mixed anion compounds exist that contain hydride with other anions. These include boride hydrides, carbohydrides , hydridonitrides , oxyhydrides and others.
Protide , deuteride and tritide are used to describe ions or compounds that contain enriched hydrogen-1 , deuterium or tritium , respectively.
In the classic meaning, hydride refers to any compound hydrogen forms with other elements, ranging over groups 1–16 (the binary compounds of hydrogen ). The following is a list of the nomenclature for the hydride derivatives of main group compounds according to this definition: [ 9 ]
According to the convention above, the following are "hydrogen compounds" and not "hydrides": [ citation needed ]
Examples:
All metalloid hydrides are highly flammable. All solid non-metallic hydrides except ice are highly flammable. But when hydrogen combines with halogens it produces acids rather than hydrides, and they are not flammable.
According to IUPAC convention , by precedence (stylized electronegativity), hydrogen falls between group 15 and group 16 elements. Therefore, we have NH 3 , "nitrogen hydride" (ammonia), versus H 2 O, "hydrogen oxide" (water). This convention is sometimes broken for polonium, which on the grounds of polonium's metallicity is often referred to as "polonium hydride" instead of the expected "hydrogen polonide". | https://en.wikipedia.org/wiki/Hydride |
Hydride vapour-phase epitaxy ( HVPE ) is an epitaxial growth technique often employed to produce semiconductors such as GaN, GaAs, InP and their related compounds, in which hydrogen chloride is reacted at elevated temperature with the group-III metals to produce gaseous metal chlorides, which then react with ammonia to produce the group-III nitrides. Carrier gasses commonly used include ammonia , hydrogen and various chlorides .
HVPE technology can significantly reduce the cost of production compared to the most common method of vapor deposition of organometallic compounds ( MOCVD ). [ 1 ] Cost reduction is achieved by significantly reducing the consumption of NH 3 , cheaper source materials than in MOCVD, reducing the capital equipment costs, due to the high growth rate.
Developed in the 1960s, it was the first epitaxial method used for the fabrication of single GaN crystals.
Hydride vapour-phase epitaxy (HVPE) is the only III–V and III–N semiconductor crystal growth process working close to equilibrium. This means that the condensation reactions exhibit fast kinetics: one observes immediate reactivity to an increase of the vapour-phase supersaturation towards condensation. This property is due to the use of chloride vapour precursors GaCl and InCl, of which dechlorination frequency is high enough so that there is no kinetic delay. A wide range of growth rates, from 1 to 100 micrometers per hour, can then be set as a function of the vapour-phase supersaturation. Another HVPE feature is that growth is governed by surface kinetics: adsorption of gaseous precursors, decomposition of ad-species, desorption of decomposition products, surface diffusion towards kink sites. This property is of benefit when it comes to selective growth on patterned substrates for the synthesis of objects and structures exhibiting a 3D morphology. The morphology is only dependent on the intrinsic growth anisotropy of crystals. By setting experimental growth parameters of temperature and composition of the vapour phase, one can control this anisotropy, which can be very high as growth rates can be varied by an order of magnitude. Therefore, we can shape structures with various novel aspect ratios. The accurate control of growth morphology was used for the making of GaN quasi-substrates, arrays of GaAs and GaN structures on the micrometer and submicrometer scales, GaAs tips for local spin injection. Fast dechlorination property is also used for the VLS growth of GaAs and GaN nanowires with exceptional length.
This engineering-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydride_vapour-phase_epitaxy |
Hydrindantin is an organic chemical thought to be involved with the ninhydrin test for amines . [ 2 ]
This article about a ketone is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrindantin |
Hydrion is a trademarked name for a popular line of compound pH indicators , marketed by Micro Essential Laboratory Inc., exhibiting a series of color changes (typically producing a recognizably different color for each pH unit) over a range of pH values. Although solutions are available, the most common forms of Hydrion are a series of papers impregnated with various mixtures of indicator dyes. It is considered a "universal indicator".
This article about chemical compounds is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrion_paper |
HydroCAD is a computer-aided design (CAD) program used by civil engineers for modeling the hydrology and hydraulics (H&H) of stormwater runoff . [ 1 ] Its use as a tool has grown in the U.S. as rules for managing stormwater have become more stringent. Specifically, the National Pollutant Discharge Elimination System (NPDES), last updated in December 2016, regulates point source pollution by municipal governments, industrial facilities and agricultural facilities. The NPDES was introduced in 1972 as part of the Clean Water Act , and is administered by the U.S. Environmental Protection Agency (EPA) in partnership with state environmental agencies. [ 2 ]
H&H software such as HydroCAD is important in the implementation of the Low-Impact Development approach to stormwater management that is gaining popularity throughout the U.S. and Canada. [ 3 ]
The company was founded in 1977 as Applied Microcomputer Systems (AMS), initially developing custom software for technical and scientific applications. In the early years of personal computers, AMS produced various other programming tools for technical professionals.
In 1985, AMS began development of the HydroCAD Stormwater Modeling System as a response to growing hydrology requirements facing civil engineers. The program, ultimately introduced in 1986 for HP workstations, made it possible to conduct complex calculations on desktop computers rather than only on mainframes. It also added new graphical interfaces to improve ease of use.
In 2001, the HydroCAD software was re-written as a native Windows application, using Borland's Delphi programming environment, and released as HydroCAD 6.0.
In 2004, the company officially changed its name to “HydroCAD Software Solutions LLC”. Its headquarters office is on Chocorua Mountain Highway (also known as Route 16) in the town of Tamworth, New Hampshire .
The latest HydroCAD version 10.2 was released in May 2022. Future updates are expected approximately twice a year, allowing HydroCAD to stay current with the ever-expanding market of stormwater storage products (chambers) and flow control devices. [ needs update ] [ 4 ] | https://en.wikipedia.org/wiki/HydroCAD |
Hydroacylation is a type of organic reaction in which an electron-rich [ 1 ] unsaturated hydrocarbon inserts into a formyl C-H bond. With alkenes, the product is a ketone :
With an alkyne instead, the reaction produces an α,β-unsaturated ketone . [ 2 ]
The reaction requires a metal catalyst or a radical initiator . [ 1 ] It is almost invariably practiced as an intramolecular reaction using homogeneous catalysts , often based on rhodium phosphines.
The reaction was discovered in the 1970s as part of a synthetic route to certain prostanoids . [ 3 ] The reaction required tin tetrachloride and a stoichiometric amount of Wilkinson's catalyst :
An equal amount of a cyclopropane was formed as the result of decarbonylation .
The first catalytic application involved cyclization of 4-pentenal to cyclopentanone using (again) Wilkinson's catalyst . [ 4 ] In this reaction the solvent was saturated with ethylene .
Labeling studies establish the following regiochemistry:
In terms of the reaction mechanism , hydroacylation begins with oxidative addition of the aldehydic carbon-hydrogen bond . The resulting acyl hydride complex next binds the alkene. The sequence of oxidative addition and alkene coordination is often unclear. Via migratory insertion , the alkene inserts into either the metal-acyl or the metal-hydride bonds. In the final step, the resulting alkyl-acyl or beta-ketoalkyl-hydride complex undergoes reductive elimination . [ 2 ] A competing side-reaction is decarbonylation of the aldehyde. This process also proceeds via the intermediacy of the acyl metal hydride :
This step can be followed by reductive elimination of the alkane:
Hydroacylation as an asymmetric reaction was demonstrated in the form of a kinetic resolution. [ 5 ] [ 6 ] A true asymmetric synthesis was also described. [ 7 ] [ 8 ] Both conversions employed rhodium catalysts and a chiral diphosphine ligand . In one application the ligand is Me-DuPhos : [ 9 ] | https://en.wikipedia.org/wiki/Hydroacylation |
Hydroalkoxylation is a chemical reaction that combines alcohols with alkenes or alkynes . The process affords ethers .
The reaction converts alkenes to dialkyl or aryl-alkyl ethers:
Similarly, alkynes are converted to vinyl ethers:
As shown, the reaction follows the Markovnikov rule . The process exhibits good atom-economy in the sense that no byproducts are produced. The reaction is catalyzed by bases and also by transition metal complexes. [ 1 ] Usually symmetrical ethers are prepared by dehydration of alcohols and unsymmetrical ethers by the Williamson ether synthesis from alkyl halides and alkali metal alkoxides. [ 2 ]
This catalysis article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydroalkoxylation |
In organic chemistry , hydroamination is the addition of an N−H bond of an amine across a carbon-carbon multiple bond of an alkene , alkyne , diene , or allene . [ 1 ] In the ideal case, hydroamination is atom economical and green . [ 2 ] Amines are common in fine-chemical, pharmaceutical, and agricultural industries. [ 3 ] [ 4 ] [ 5 ] [ 6 ] Hydroamination can be used intramolecularly to create heterocycles or intermolecularly with a separate amine and unsaturated compound . The development of catalysts for hydroamination remains an active area, especially for alkenes. Although practical hydroamination reactions can be effected for dienes and electrophilic alkenes, the term hydroamination often implies reactions metal-catalyzed processes.
Hydroamination is well-established technology for generating fragrances from myrcene . In this conversion, diethylamine adds across the diene substituent, the reaction being catalyzed by lithium diethylamide. [ 7 ] Intramolecular hydroaminations were reported by Tobin J. Marks in 1989 using metallocene derived from rare-earth metals such as lanthanum , lutetium , and samarium . Catalytic rates correlated inversely with the ionic radius of the metal, perhaps as a consequence of steric interference from the ligands. [ 8 ] In 1992, Marks developed the first chiral hydroamination catalysts by using a chiral auxiliary, which were the first hydroamination catalysts to favor only one specific stereoisomer . Chiral auxiliaries on the metallocene ligands were used to dictate the stereochemistry of the product. [ 9 ] The first non-metallocene chiral catalysts were reported in 2003, and used bisarylamido and aminophenolate ligands to give higher enantioselectivity . [ 10 ]
Hydroamination has been examined with a variety of amines, unsaturated substrates, and vastly different catalysts. Amines that have been investigated span a wide scope including primary, secondary, cyclic, acyclic, and anilines with diverse steric and electronic substituents. The unsaturated substrates that have been investigated include alkenes, dienes, alkynes, and allenes. For intramolecular hydroamination, various aminoalkenes have been examined. [ 11 ]
Addition across the unsaturated carbon-carbon bond can be Markovnikov or anti-Markovnikov depending on the catalyst. [ 12 ] When considering the possibly of R/S chirality, four products can be obtained: Markovnikov with R or S and anti-Markovnikov addition with R or S. Although there have been many reports of catalytic hydroamination with a wide range of metals, there are far fewer describing enantioselective catalysis to selectively make one of the four possible products. Recently, there have been reports of selectively making the thermodynamic or kinetic product , which can be related to the racemic Markovnikov or anti-Markovnikov structures (see Thermodynamic and Kinetic Product below).
Hydroamination reactions are atom-efficient processes that generally use readily available and cheap starting materials, therefore a general catalytic strategy is highly desirable. Also, direct catalytic hydroamination strategies have in principle significant benefits over more classical methods to prepare amine containing compounds, including the reduction in the number of synthetic steps required.
[ 13 ]
However, hydroamination reactions pose some tough challenges for catalysis: Strong electron repulsion of the nitrogen atom lone pair and the electron rich carbon-carbon multiple bond, coupled with hydroamination reactions being entropically disfavoured (particularly the intermolecular version), [ 14 ] [ 15 ] results in a large reaction barrier. Regioselectivity issues also hamper the synthetic utility of the resulting products, with Markovnikov addition of the amine being the most common outcome over the less favoured anti-Markovnikov addition (see figure). As a result, there are now numerous catalysts that can be utilised in the hydroamination of alkene, allene and alkyne substrates, including various metal based heterogeneous catalysts, early-transition metal complexes (e.g. titanium and zirconium), late-transition metal complexes (e.g. ruthenium and palladium), lanthanide and actinide complexes (e.g. samarium and lanthanum), as well as Brønsted acids and bases. [ 16 ] [ 17 ] [ 18 ]
Many metal-ligand combinations have been reported to catalyze hydroamination, including main group elements including group 1 metals such as lithium , [ 11 ] group 2 metals such as calcium , [ 19 ] group 13 metals such as aluminum , [ 20 ] indium , [ 21 ] and even bismuth . [ 22 ] In addition to these main group examples, extensive research has been conducted on the transition metals with reports of early, mid, and late metals, as well as first, second, and third row elements. Finally the lanthanides have been thoroughly investigated. Zeolites have also shown utility in hydroamination. [ 11 ]
The mechanism of metal-catalyzed hydroamination has been well studied. [ 11 ] Particularly well studied is the organolanthanide catalyzed intramolecular hydroamination of alkenes. [ 23 ] First, the catalyst is activated by amide exchange, generating the active catalyst (i). Next, the alkene inserts into the Ln-N bond (ii). [ 24 ] Finally, protonolysis occurs generating the cyclized product while also regenerating the active catalyst (iii). Although this mechanism depicts the use of a lanthanide catalyst, it is the basis for rare-earth, actinide , and alkali metal based catalysts.
Late transition metal hydroamination catalysts have multiple models based on the regioselective determining step. The four main categories are (1) nucleophilic attack on an alkene alkyne, or allyl ligand and (2) insertion of the alkene into the metal-amide bond. [ 11 ] Generic catalytic cycles appear below. Mechanisms are supported by rate studies , isotopic labeling , and trapping of the proposed intermediates.
The hydroamination reaction is approximately thermochemically neutral. The reaction however suffers from a high activation barrier , perhaps owing to the repulsion of the electron-rich substrate and the amine nucleophile . The intermolecular reaction also is accompanied by highly negative changing entropy , making it unfavorable at higher temperatures.
[ 14 ] [ 15 ] Consequently, catalysts are necessary for this reaction to proceed. [ 3 ] [ 11 ] As usual in chemistry, intramolecular processes occur at faster rates than intermolecular versions.
In general, most hydroamination catalysts require elevated temperatures to function efficiently, and as such, only the thermodynamic product is observed. The isolation and characterization of the rarer and more synthetically valuable kinetic allyl amine product was reported when allenes was used at the unsaturated substrate. One system utilized temperatures of 80 °C with a rhodium catalyst and aniline derivatives as the amine. [ 25 ] The other reported system utilized a palladium catalyst at room temperature with a wide range of primary and secondary cyclic and acyclic amines. [ 26 ] Both systems produced the desired allyl amines in high yield, which contain an alkene that can be further functionalized through traditional organic reactions.
Strong bases catalyze hydroamination, an example being the ethylation of piperidine using ethene : [ 27 ]
Such base catalyzed reactions proceed well with ethene but higher alkenes are less reactive.
Certain titanium and zirconium complexes catalyze intermolecular hydroamination of alkynes and allenes. [ 3 ] Both stoichiometric and catalytic variants were initially examined with zirconocene bis(amido) complexes. Titanocene amido and sulfonamido complexes catalyze the intra-molecular hydroamination of aminoalkenes via a [2+2] cycloaddition that forms the corresponding azametallacyclobutane, as illustrated in the figure below. Subsequent protonolysis by incoming substrate gives the α-vinyl-pyrrolidine ( 1 ) or tetrahydropyridine ( 2 ) product. Experimental and theoretical evidence support the proposed imido intermediate and mechanism with neutral group IV catalysts.
The addition of hydrogen and an amino group (NR 2 ) using reagents other than the amine HNR 2 is known as a "formal hydroamination" reaction. Although the advantages of atom economy and/or ready available of the nitrogen source are diminished as a result, the greater thermodynamic driving force, as well as ability to tune the aminating reagent are potentially useful. In place of the amine, hydroxylamine esters [ 28 ] and nitroarenes [ 29 ] have been reported as nitrogen sources.
Hydroamination could find applications due to the valuable nature of the resulting amine, as well as the greenness of the process. Functionalized allylamines , which can be produced through hydroamination, have extensive pharmaceutical application, although presently such species are not prepared by hydroamination. Hydroamination has been utilized to synthesize the allylamine Cinnarizine in quantitative yield. Cinnarizine treats both vertigo and motion sickness related nausea . [ 26 ]
Hydroamination is also promising for the synthesis of alkaloids . An example was the hydroamination step used in the total synthesis of (-)-epimyrtine. [ 30 ]
This article incorporates text by David Michael Barber available under the CC BY 2.5 license. | https://en.wikipedia.org/wiki/Hydroamination |
Hydrobiology is the science of life and life processes in water. Much of modern hydrobiology can be viewed as a sub-discipline of ecology but the sphere of hydrobiology includes taxonomy , economic and industrial biology, morphology , and physiology. The one distinguishing aspect is that all fields relate to aquatic organisms. Most work is related to limnology and can be divided into lotic system ecology (flowing waters) and lentic system ecology (still waters).
One of the significant areas of current research is eutrophication . Special attention is paid to biotic interactions in plankton assemblage including the microbial loop , the mechanism of influencing algal blooms , phosphorus load, and lake turnover. Another subject of research is the acidification of mountain lakes. [ 1 ] [ 2 ] Long-term studies are carried out on changes in the ionic composition of the water of rivers, [ 3 ] lakes and reservoirs in connection with acid rain and fertilization . One goal of current research is elucidation of the basic environmental functions of the ecosystem in reservoirs, [ 4 ] which are important for water quality management and water supply.
Much of the early work of hydrobiologists concentrated on the biological processes utilized in sewage treatment and water purification especially slow sand filters. Other historically important work sought to provide biotic indices for classifying waters according to the biotic communities that they supported. This work continues to this day in Europe in the development of classification tools for assessing water bodies for the EU water framework directive. [ 5 ]
A hydrobiologist technician conducts field analysis for hydrobiology. They identify plants and living species, locate their habitat, and count them. They also identify pollutants and nuisances that can affect the aquatic fauna and flora. They take the samples and write reports of their observations for publications.
A hydrobiologist engineer intervenes more in the process of the study. They define the intervention protocols and what samples should be taken. They plan and program the study campaigns, and then summarize their results. In the event of pollution, they propose solutions to improve the biological quality of water within the framework of the regulations in force. In the case of complex programs, hydrobiologists can work in a multidisciplinary team with botanists and zoologists.
The hydrobiologist works on behalf of large public institutions of a scientific and technological nature (CNRS, INRA, IRD, CIRAD, IRSTEA ...), public institutions (Water Agencies, Regional Directorates environment, Higher Council of Fisheries, CEMAGREF ...), companies (EDF, Veolia environment, Suez environment, Saur, ...), local authorities, research departments, and associations (Federations of fishing, Permanent Centers for Environmental Initiatives ...).
The biologist technician usually has a training level bac +2 or bac +3:
- DUT biological engineering options biological and biochemical analyzes (ABB), environmental engineering,
- BTSA water professions
- BTS GEMEAU - water management and control
- BTS and regional controls
- BTSA Agricultural, Biological and Biotechnological Analyzes (ANABIOTEC)
- DEUST analysis of biological media
- Bachelor's degree in biology
The engineer in hydrobiology has a training level bac +5:
- engineering school diploma: INA, ENSA, Polytech Montpellier sciences and water technologies
- master's degree in environmental sciences or biology (training examples)
environmental management and coastal ecology (University of La Rochelle)
biology of organisms and populations (University of Burgundy)
continental and coastal environments sciences Environment, Soils, Waters and Biodiversity (University of Rouen)
operation and restoration of continental aquatic environments (University of Clermont Ferrand), etc.
The following are the research interests of Hydrobiologists: | https://en.wikipedia.org/wiki/Hydrobiology |
In organic chemistry , hydroboration refers to the addition of a hydrogen - boron bond to certain double and triple bonds involving carbon ( C=C , C=N , C=O , and C≡C ). This chemical reaction is useful in the organic synthesis of organic compounds . [ 1 ]
Hydroboration produces organoborane compounds that react with a variety of reagents to produce useful compounds, such as alcohols , amines , or alkyl halides . The most widely known reaction of the organoboranes is oxidation to produce alcohols from alkenes.
The development of this technology and the underlying concepts were recognized by the Nobel Prize in Chemistry to Herbert C. Brown . [ 2 ] [ 3 ]
Much of the original work on hydroboration employed diborane as a source of BH 3 . Usually however, borane dimethylsulfide complex BH 3 S(CH 3 ) 2 (BMS) is used instead. [ 5 ] It can be obtained in highly concentrated forms. [ 6 ]
The adduct BH 3 (THF) is also commercially available as THF solutions. Its shelf life is less than BMS. [ 7 ]
In terms of synthetic results, diborane or the more conveniently handle BMS and borane-THF are equivalent.
The stoichiometry and idealized regiochemistry of hydroboration of terminal alkenes follows:
In reality, each hydroboration step follows 1,2-addition but ca. 4% gives the 2,1 addition (affording the B(CH(CH3)R isomer). [ 1 ] In extreme cases, such as risubstituted alkenes, hydroboration affords. This significant rate difference in producing di- and tri-alkyl boranes is useful in the synthesis of bulky boranes that can enhance regioselectivity.
In terms of regiochemistry, hydroboration is typically anti-Markovnikov , i.e. the hydrogen adds to the most substituted carbon of the double bond. That the regiochemistry is reverse of a typical HX addition reflects the polarity of the B δ+ -H δ− bonds. Hydroboration proceeds via a four-membered transition state: the hydrogen and the boron atoms added on the same face of the double bond. Granted that the mechanism is concerted, the formation of the C-B bond proceeds slightly faster than the formation of the C-H bond. As a result, in the transition state, boron develops a partially negative charge while the more substituted carbon bears a partially positive charge. This partial positive charge is better supported by the more substituted carbon. Formally, the reaction is an example of a group transfer reaction . However, an analysis of the orbitals involved reveals that the reaction is 'pseudopericyclic' and not subject to the Woodward–Hoffmann rules for pericyclic reactivity.
Hydroboration of trisubstituted alkenes places boron on the less substituted carbon. [ 8 ]
Hydroboration of 1,2-disubstituted alkenes, such as a cis or trans olefin, produces generally a mixture of the two organoboranes of comparable amounts, even if the steric properties of the substituents are very different. For such 1,2-disubstituted olefins, regioselectivity can be observed only when one of the two substituents is a phenyl ring. In such cases, such as trans -1-phenylpropene, the boron atom is placed on the carbon adjacent to the phenyl ring. The observations above indicate that the addition of H-B bond to olefins is under electronic control rather than steric control.
Hydroboration of alkynes gives alkenylboranes. The stereochemistry is cis-addition. With terminal alkynes, both H 2 BCH=HR and HB(CH=CHR) 2 are formed. Often the hydroboration of alkynes use bulky boranes such as 9-BBN to give monoalkenylborane products. The alkenylboranes are susceptible to many reactions such as protonolysis to give the alkene and oxidation to give the aldehyde or ketone. [ 9 ]
As honored by the Nobel Prize to Brown, hydroboration is widely practiced because the alkylboranes are susceptible to many reactions.
Treatment of alkylboranes with base and hydrogen peroxide gives alcohols:
The net reaction is hydration.
Because the addition of H-B to olefins is stereospecific, this oxidation reaction will be diastereoselective when the alkene is trisubstituted. [ 10 ] Hydroboration-oxidation is thus an excellent way of producing alcohols in a stereospecific and anti-Markovnikov fashion.
Hydroboration can also lead to amines by treating the intermediate organoboranes with monochloramine or O-hydroxylaminesulfonic acid (HSA). [ 11 ]
Terminal olefins are converted to the corresponding alkyl bromides and alkyl iodides by treating the organoborane intermediates with bromine [ 12 ] or iodine. [ 13 ] Such reactions have not however proven very popular, because succinimide based reagents such as NIS and NBS are more versatile and do not require rigorous conditions as do organoboranes.
etc.
Trialkylboranes react with carbon monoxide to afford homologated products such as 2-bora-1,3-dioxolanes. When the addition of CO is conducted in the presence of a hydride reducing agent, the primary alcohol is produced.
One example of a monoalkylborane is thexylborane (ThxBH 2 ), produced by the hydroboration of tetramethylethylene : [ 14 ]
A chiral example is monoisopinocampheylborane. Although often written as IpcBH 2 , it is a dimer [IpcBH 2 ] 2 . It is obtained by hydroboration of (−)‐α‐pinene with borane dimethyl sulfide . [ 15 ]
Monobromo- and monochloro-borane can be prepared from BMS and the corresponding boron trihalides. The stable complex of monochloroborane and 1,4-dioxane effects hydroboration of terminal alkenes. [ 16 ]
Prominent among hindered dialkylboranes is disiamylborane , abbreviated Sia 2 BH. It also is a dimer. Owing to its steric bulk, it selectively hydroborates less hindered, usually terminal alkenes in the presence of more substituted alkenes. [ 17 ] Disiamylborane must be freshly prepared as its solutions can only be stored at 0 °C for a few hours. Dicyclohexylborane Chx 2 BH exhibits improved thermal stability than Sia 2 BH.
A versatile dialkylborane is 9-BBN . Also called "banana borane", it exists as a dimer. Reactions with 9-BBN typically occur at 60–80 °C, with most alkenes reacting within one hour. Tetrasubstituted alkenes add 9-BBN at elevated temperature. Hydroboration of alkenes with 9-BBN proceeds with excellent regioselectivity. It is more sensitive to steric differences than Sia 2 BH, perhaps because of it rigid C 8 backbone. 9-BBN is more reactive towards alkenes than alkynes. [ 18 ]
For catalytic hydroboration, pinacolborane and catecholborane are widely used. They also exhibit higher reactivity toward alkynes. [ 19 ] Pinacolborane is also widely used in a catalyst-free hydroborations. | https://en.wikipedia.org/wiki/Hydroboration |
In chemistry, a hydrobromide is an acid salt resulting, or regarded as resulting, from the reaction of hydrobromic acid with an organic base (e.g. an amine ). The compounds are similar to hydrochlorides .
Some drugs are formulated as hydrobromides, e.g. dextromethorphan hydrobromide.
This article about a salt (chemistry) is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrobromide |
Hydrocarbon mixtures are a group of various volatile , highly flammable , mixtures used chiefly as nonpolar solvents .
Hydrocarbon mixtures are composed of petroleum ethers and other hydrocarbons . [ 1 ] Petroleum ether should not be confused with the class of organic compounds called ethers ; and equally, going under its alternative name of benzine , it should not be confused with benzene . (Benzine is a mixture of alkanes , such as pentane , hexane , and heptane ; whereas benzene is a cyclic, aromatic hydrocarbon .)
A hydrocarbon is any chemical compound that consists only of the elements carbon (C) and hydrogen (H). They all contain a carbon frame, and have hydrogen atoms attached to the frame. Often the term is used as a shortened form of the term aliphatic hydrocarbon . Most hydrocarbons are combustible . [ 2 ]
Petroleum ether is obtained from petroleum refineries as the portion of the distillate which is intermediate between the lighter naphtha and the heavier kerosene . It has a specific gravity of between 0.6 and 0.8 depending on its composition. [ 3 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrocarbon_mixtures |
Hydrocarbon plants are plants that follow certain metabolic pathways that produce hydrocarbon products similar to petroleum. These
hydrocarbon products are called terpenoids . [ 1 ] The plants that produce terpenoids in large enough quantities
to be harvested can be as big as trees or as small as single-cell algae. The family Euphorbiaceae has been studied in detail by
Dr. Melvin Calvin , Nobel Laureate, and discoverer of the Calvin Cycle .
One particular tree of the genus Hevea , more commonly known as the rubber tree , is probably the most famous hydrocarbon plant,
supplying an estimated one third of the world’s rubber demand. It is still not as quick and cheap to make as petroleum-based rubber,
which is why it does not occupy a larger portion of the market. [ 2 ] Hevea naturally produces a latex substance which can tapped by cutting into the tree, and the latex can then be processed into rubber.
Most hydrocarbon plants are not trees, so this technique of tapping the tree is no longer feasible. Instead of tapping the tree, the hydrocarbons are extracted using various organic solvents . This process is especially useful with single-cell algae, such
as Botryococcus braunii . This algae has two forms, both of which live in brackish water. The first form is a red algae that
produces odd-numbered carbon chains roughly 25-31 atoms in
length. [ 2 ] These carbon chains usually do not possess a large number of double bonds. The
second type of B. braunii is green and produces even-numbered carbon chains that are between 34 and 38 carbons long, with
many double bonds present. While the cause of this difference is not well-studied, the two different algae can be used for discrete
purposes.
Dr. Calvin began his studies of hydrocarbon plants in 1977 by looking at yields of Euphorbia lathyris over two years. While his results were limited, due to growing season complications, [ 3 ] he did find a substantial amount of hydrocarbon products. Once the plant samples were separated using adsorption chromatography and column chromatography , they were analyzed via mass spectrometry , IR spectroscopy , UV spectroscopy , and gas chromatography , 31-and-34-carbon-long alkane chains were found to be present in the hexane layer of the adsorption chromatography [ 3 ]
The PETRO project is a program started in 2011 in an attempt to create petroleum products using plants. The program is composed of ten projects that intend to extract petroleum directly from plants without affecting the U.S. food supply. The goal of the program is to make more oil per acre than what we have now, and with less processing before it gets to the pump. This results in a process that is cleaner, uses less energy, and is more sustainable than the system we have in place presently.
The ten PETRO projects include:
All of these efforts are funded through the ARPA-E program available through the U.S. Department of Energy. The program, headed by Jonathan Burbaum, has received over $37,000,000 of funding since its initial acceptance into the ARPA-E program. | https://en.wikipedia.org/wiki/Hydrocarbon_plant |
Hydrocarbon poisoning is either the swallowing or breathing in of hydrocarbons . [ 1 ] Swallowing hydrocarbons may result in symptoms include coughing or vomiting. [ 1 ] Breathing in hydrocarbons may result in low blood oxygen and shortness of breath . [ 1 ] Complications may include confusion or seizures . [ 1 ]
Hydrocarbons may include gasoline , mineral oil , or paint thinner . [ 1 ] Treatment is supportive care . [ 1 ] Efforts to empty the stomach are not recommended. [ 1 ]
This toxicology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Hydrocarbon_poisoning |
Hydrocarbonoclastic bacteria (also known as hydrocarbon degrading bacteria , oil degrading bacteria or HCB ) are a heterogeneous group of prokaryotes which can degrade and utilize hydrocarbon compounds as source of carbon and energy. Despite being present in most of environments around the world, several of these specialized bacteria live in the sea and have been isolated from polluted seawater.
The taxonomic diversity of hydrocarbon-degrading bacteria has not changed dramatically if we consider the higher taxa, many studies have provided information on 25 kinds of hydrocarbon-degrading bacteria and 25 kinds of fungi isolated from marine environments. [ 1 ] Bacterial genera such as Gordonia , Brevibacterium , Aeromicrobium , Dietzia , Burkholderia and Mycobacterium isolated from oil have been shown to be potential organisms for hydrocarbon degradation. Cerniglia et al. observed that nine cyanobacteria, five green algae, one red alga, one brown alga and two diatoms could oxidise naphthalene. Temperature is crucial because it influences microbial physiology and diversity; the rate of biodegradation generally decreases as the temperature decreases. [ 1 ]
Hydrocarbonoclastic bacteria are diazophilic, i.e. they can live in environments extremely poor in nitrogen compounds, which allows them to distribute themselves throughout the environment. They are extremely useful for environmentally friendly biosanitation; the fastest and most complete degradation occurs under aerobic conditions.
Hydrocarbons occur in marine environments where there are oil spills , which makes us understand that they are nutritionally independent of nitrogen sources, a characteristic due to their ability to fix atmospheric nitrogen. In Lagos in a city in Nigeria, nine bacterial strains Pseudomonas fluorescens , P. aeruginosa , Bacillus subtilis , Bacillus sp., Alcaligenes sp., Acinetobacter lwoffi , Flavobacterium sp., Micrococcus roseus and Corynebacterium sp, isolated from the polluted flow that could degrade crude oil, were detected [ citation needed ] ; in north-east India they were also detected. In the Louisiana incident in the Gulf of Mexico, about 100 strains were detected and studied, revealing that the isolates all belong to the phylum Proteobacteria and three classes ( Alteromonadales , Rhodospirillales and Enterobacteriales ). [ 2 ]
These organisms are normally present in very small numbers, which gives them an advantage over hydrocarbons such as carbon and energy, as they grow and multiply rapidly. Alcanivorax-like bacteria have been detected in oil-affected environments around the world, including the US , Germany , the UK , Spain , Italy , Singapore , China , the western Philippines , Japan , the mid-Atlantic ridge near Antarctica , and from deepwater sediments in the eastern Pacific Ocean . [ 3 ]
Hydrocarbonoclastic bacteria have two fundamental characteristics: (1) specific membrane-bound dioxygenases [ 4 ] and (2) mechanisms for optimizing contact with water-insoluble hydrocarbons. [ 5 ] Microbial biodegradation occurs wherever oil contamination occurs. However, biodegradation rates are slow and as a result there are severe toxic effects on marine life in the water and on the coast. [ 6 ]
The hydrocarbons contained in petroleum have a different behavior in water depending on their chemical nature. This process is called weathering , those with low molecular weight volatilize when they reach the surface.
The rest is attacked by bacteria that are able to do this. These bacteria do not adhere to the oil and do not have a high hydrophobicity of the cell surface. The next stage of degradation involves microorganisms with high cell surface hydrophobicity, which can adhere to residual high molecular weight hydrocarbons. Adhesion is due to hydrophobic fimbriae, fibrils, lipids and proteins of the outer membrane and some small molecules of the cell surface, such as gramicidin S and prodigiosin . [ 7 ]
All petroleum products are derived from crude oil whose major constituents are hydrocarbons, that can be separated into four fractions: saturated , aromatic , resin and asphaltene fractions. The susceptibility of hydrocarbons to microbial degradation can be generally ranked as follows: linear alkanes branched alkanes > small aromatics > cyclic alkanes. [ 8 ] [ 9 ] Some compounds, such as the high molecular weight polycyclic aromatic hydrocarbons ( PAHs ), may not be degraded at all, asphaltenes and resins are considered to be recalcitrant to biodegradation. [ 10 ]
Alkanes are readily biodegraded aerobically in the sea by several different pathways.
The degradation of medium-length ones by Pseudomonas putida starts from the alkane hydroxylase, this enzyme is made up of three components: the membrane-bound oxygenase component and two soluble components called rubredoxin and rubredoxin reductase. [ 11 ]
From the oxidation of the methyl group of n-alkanes by the alkane hydroxylase, n- alkanols are released which are further oxidized by a membrane-bound alcohol dehydrogenase in n- alkanals . The n-alkanals are subsequently transformed into fatty acids and then into acyl CoA , respectively by the aldehyde dehydrogenase and by the acyl-CoA synthetase .
CH 3 − R − CH 3 ⟶ CH 3 − R − CH 2 OH ⟶ CH 3 − R − CHO ⟶ CH 3 − R − COOH ⟶ ( CH 2 OH ) − R − COOH {\displaystyle {\ce {CH3-R-CH3 -> CH3-R-CH2OH -> CH3-R-CHO -> CH3-R-COOH -> (CH2OH)-R-COOH}}}
CH 3 − R − CH 2 OH ⟶ ( CH 2 OH ) − R − CH 2 OH ⟶ ( CH 2 OH ) − R − CHO ⟶ ( CH 2 OH ) − R − COOH {\displaystyle {\ce {CH3-R-CH2OH -> (CH2OH)-R-CH2OH -> (CH2OH)-R-CHO -> (CH2OH)-R-COOH}}}
( CH 2 OH ) − R − COOH ⟶ CHO − R − COOH ⟶ HOOC − R − COOH {\displaystyle {\ce {(CH2OH)-R-COOH -> CHO-R-COOH -> HOOC-R-COOH}}}
This path leads to the release of secondary alcohols . The n-alkanes are oxidized by monooxygenase to secondary alcohols, then to ketones and finally to fatty acids. [ 12 ]
R 1 − ( CH 2 ) ( CH 2 ) − R 2 ⟶ R 1 − ( CH 2 ) ( CHOH ) − R 2 ⟶ R 1 − ( CH 2 ) ( CO ) − R 2 ⟶ R 1 − ( CH 2 ) O ( CO ) − R 2 ⟶ R 1 − COOH + R 2 − COOH {\displaystyle {\ce {R1-(CH2)(CH2)-R2 -> R1-(CH2)(CHOH)-R2 -> R1-(CH2)(CO)-R2 -> R1-(CH2)O(CO)-R2 -> R1-COOH + R2-COOH}}}
Cycloalkanes are degraded by a co-oxidation mechanism, the process leading to the formation of a cyclic alcohol and a ketone. A monooxygenase introduces an oxygen into the cyclic ketone and the cyclic ring is cleaved. [ 13 ]
For aromatic compounds there are different pathways, considering toluene at least five are known, [ 14 ] each of these is present in specific bacterial species, Burkholderia sp. strain JS150 is unique in using multiple pathways for toluene metabolism: [ 15 ]
Oil components that are trapped in marine sediments tend to persist in anaerobic conditions . Some hydrocarbons can be oxidized under anaerobic conditions when nitrate reduction , sulfate reduction, methane production, Fe 3+ reduction or photosynthesis are coupled to hydrocarbon oxidation. [ 16 ]
Anaerobic bacterium strain HD-1 grows on CO 2 in the presence of H 2 or tetradecane. In the absence of H 2 , tetradecane is degraded, and the major metabolic intermediate is 1-dodecene [ 17 ]
The biodegradation of hydrocarbons is limited by a number of chemical, physical and biological factors.
At the moment, most studies of the ecology of hydrocarbonoclastic bacteria refer to a wide group of genera found principally in marine environments. Since each of them is characterized by a different metabolism, these organisms work together in order to degrade all types of hydrocarbon compounds in a very efficient way. They also play a fundamental role in the carbon biogeochemical cycle and several studies show that some species can create intricate relationships with different marine organisms. [ 23 ]
When a release of oil (or whichever kind of hydrocarbon compound) happens in a specific marine area, a lot of bacterial species begin to colonize it, changing the microbial community already present there. Analyzing the dynamics of those communities has led to the discovery of common patterns that are associated with biodegradation, and those information can be useful for the improving of bioremediation methods. Microbial community in situ shuffles since the quantities of nutrients change as the presence of hydrocarbons increases: this ecological situation is able to select only those organisms which can use hydrocarbons as an energy source and possess all the enzymes to do so. In addition, most oil biodegrading species require specific quantities of phosphorus and nitrogen to carry out their catabolic processes. It is possible to state therefore, that hydrocarbonoclastic bacteria rate is limited by the availability of nitrogen and phosphorus mainly. [ 24 ]
Several experiments conducted both in vitro and in situ showed the fundamental role that OHCBs (obligate hydrocarbonoclastic bacteria) play during events like an oil spill. The very first microorganism populations that bloom when hydrocarbons are released are the so-called generalists, which can break (through specific enzymes) the most simple bonds in hydrocarbons (generally they are n-alkane degraders); among them, the most common genus is Alcanivorax (the most important species is Alcanivorax borkumensis ) which can degrade aliphatic hydrocarbon compounds. [ 25 ] Subsequently, specialists replace generalists to degrade stronger and more complex bounds; among them one of the most known genera is Cycloclasticus which can, for example, degrade aromatic hydrocarbons such as PAH (polycyclic aromatic hydrocarbons). [ 26 ]
Up to now, no hydrocarbonoclastic Archaea species have been found, since it appears that they are too sensitive to the effects of an oil spill, as shown by many studies carried out on beaches and coastal waters. [ 27 ] Nevertheless, Archaea species could be used as markers of the ecological status of an environment.
Hydrocarbonoclastic bacteria form just a part of the ecological network during bioremediation and biodegradation processes, which involves many direct and indirect relationships and interactions with other communities and with the surrounding environment too. Such interactions include competition for limiting nutrients, predation by protozoa , lysis by phages and cooperative interactions that can decrease or increase degradation of hydrocarbons. [ 23 ]
Nutrients availability, as well as nutrients recycling, are important aspects of biodegradation communities. As said before, the amount of phosphorus and nitrogen can modify the structure of a microbial populations and consequently the composition of the community that is shaped by the presence of certain molecules in the ecosystem.
Predation and interactions with phages also affect development of a hydrocarbonoclastic bacterial community. It is possible that the increase of the turnover of biomass (which can be obtained by stimulating the activity of bacteriophages lysis or protozoa predation) could benefit hydrocarbonoclastic populations by stimulating biological remediation. [ 28 ] In fact, the presence of oil in the environment can induce prophages [ 29 ] and the subsequent lysis of a huge number of bacteria. [ 30 ] At the same time, nutrients recycling caused by phages' lysis can trigger a bloom of those species who are favored by the presence of both nutrients and hydrocarbons (used as energy resource). On the other hand, the presence of protozoa can create the opposite situation (it has a negative effect on biodegradation), by limiting the growth of bacterial populations in the ecosystem. [ 31 ] That is why interactions with predators are fundamental in marine environments. Nevertheless, in specific occasions, the presence of predators can boost bacterial degradation, as it happens for benzene [ 32 ] or toluene. [ 33 ] Moreover, in a similar way to what happens with phages, the activity of predation does create a nutritional loop , because predators can remineralize nutrients, which increases bacterial growth.
Since hydrocarbonoclastic bacteria can oxidize long carbon compounds, their metabolism includes part of the large family of biotic reactions in the biogeochemical carbon cycle . Hydrocarbons, especially alkanes, are produced by myriad organisms as waste, for defense, as structural elements, and as chemoattractants. [ 34 ] Therefore, this type of biodegradation represents one of the major sinks of hydrocarbon compounds and one of the source of carbon dioxide in marine environments.
In conclusion, hydrocarbonoclastic bacteria can mobilize hydrocarbons from natural sources and use the oxidized carbon atoms and introduce them into their metabolic central pathways. Those oxidized molecules enter the biotic phase of the carbon cycle and can be assimilated by primary and secondary consumers through predation or can assume them after cells' death.
Hydrocarbon-degrading bacteria have many different applications but has specially importance their role in the field of environmental microbiology . [ 35 ]
Marine hydrocarbonoclastic bacteria are powerful tools for bioremediation , as they can degrade and convert contaminant oils because of their catabolic versatility. [ 36 ] In that way, using biotechnology is possible accelerate the cleaning up of a contaminated site such as coastal regions and offshore after an oil spills or human activities' pollution, but also it is possible to contain and mitigate their damage. [ 37 ] They normally bloom after an oil spill or other pollution, and because as they are very versatile metabolically, they can grow on minimal mediums. One example of this is the nitrogen-fixing and heavy oil-degrading bacterium Azospirillum oleiclasticum, which was isolated from an oil production mixture. [ 38 ] But A. oleiclasticum is not the only strain that can grow on oil, a 2013 study discovered that there are at least 125 strains, adapted to grow on minimal medium supplemented with crude oil. The predominant bacterial detected by approaches were the Proteobacteria and the most abundant species were in genera Acinetobacter and Stenotrophomons . [ 39 ]
They are also used in biosynthesis because they are an extraordinary archive of enzymes like mono and dioxygenases, oxidases, dehydrogenases and others. Furthermore, as they are adapted to grow in hydrocarbon-rich environments, they often synthesize characteristic compounds like polymeric storage substances of industrial interest and bio-detergents with high emulsifying activity. One example of this is the use of the oleaginous yeast Yarrowia lipolytica . As this yeast has a versatile lipid metabolism, by its combination with specific bacterial genes it can use specific enzymatic pathways to bioconvert different lipids (petroleum, alkane, vegetable oil, fatty acid), fats and oils into industrially valuable lipid-derived compounds like isoprenoid-derived compounds (carotenoids, polyenic carotenoid ester), wax esters (WE), polyhydroxyalkanoates (PHAs) and free hydroxylated fatty acids (HFAs). [ 40 ] | https://en.wikipedia.org/wiki/Hydrocarbonoclastic_bacteria |
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