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40,779 | https://en.wikipedia.org/wiki/BCH%20code | In coding theory, the Bose–Chaudhuri–Hocquenghem codes (BCH codes) form a class of cyclic error-correcting codes that are constructed using polynomials over a finite field (also called a Galois field). BCH codes were invented in 1959 by French mathematician Alexis Hocquenghem, and independently in 1960 by Raj Chandra Bose and D. K. Ray-Chaudhuri. The name Bose–Chaudhuri–Hocquenghem (and the acronym BCH) arises from the initials of the inventors' surnames (mistakenly, in the case of Ray-Chaudhuri).
One of the key features of BCH codes is that during code design, there is a precise control over the number of symbol errors correctable by the code. In particular, it is possible to design binary BCH codes that can correct multiple bit errors. Another advantage of BCH codes is the ease with which they can be decoded, namely, via an algebraic method known as syndrome decoding. This simplifies the design of the decoder for these codes, using small low-power electronic hardware.
BCH codes are used in applications such as satellite communications, compact disc players, DVDs, disk drives, USB flash drives, solid-state drives, and two-dimensional bar codes.
Definition and illustration
Primitive narrow-sense BCH codes
Given a prime number and prime power with positive integers and such that , a primitive narrow-sense BCH code over the finite field (or Galois field) with code length and distance at least is constructed by the following method.
Let be a primitive element of .
For any positive integer , let be the minimal polynomial with coefficients in of .
The generator polynomial of the BCH code is defined as the least common multiple .
It can be seen that is a polynomial with coefficients in and divides .
Therefore, the polynomial code defined by is a cyclic code.
Example
Let and (therefore ). We will consider different values of for based on the reducing polynomial , using primitive element . There are fourteen minimum polynomials with coefficients in satisfying
The minimal polynomials are
The BCH code with has the generator polynomial
It has minimal Hamming distance at least 3 and corrects up to one error. Since the generator polynomial is of degree 4, this code has 11 data bits and 4 checksum bits. It is also denoted as: (15, 11) BCH code.
The BCH code with has the generator polynomial
It has minimal Hamming distance at least 5 and corrects up to two errors. Since the generator polynomial is of degree 8, this code has 7 data bits and 8 checksum bits. It is also denoted as: (15, 7) BCH code.
The BCH code with has the generator polynomial
It has minimal Hamming distance at least 7 and corrects up to three errors. Since the generator polynomial is of degree 10, this code has 5 data bits and 10 checksum bits. It is also denoted as: (15, 5) BCH code. (This particular generator polynomial has a real-world application, in the "format information" of the QR code.)
The BCH code with and higher has the generator polynomial
This code has minimal Hamming distance 15 and corrects 7 errors. It has 1 data bit and 14 checksum bits. It is also denoted as: (15, 1) BCH code. In fact, this code has only two codewords: 000000000000000 and 111111111111111 (a trivial repetition code).
General BCH codes
General BCH codes differ from primitive narrow-sense BCH codes in two respects.
First, the requirement that be a primitive element of can be relaxed. By relaxing this requirement, the code length changes from to the order of the element
Second, the consecutive roots of the generator polynomial may run from instead of
Definition. Fix a finite field where is a prime power. Choose positive integers such that and is the multiplicative order of modulo
As before, let be a primitive th root of unity in and let be the minimal polynomial over of for all
The generator polynomial of the BCH code is defined as the least common multiple
Note: if as in the simplified definition, then is 1, and the order of modulo is
Therefore, the simplified definition is indeed a special case of the general one.
Special cases
A BCH code with is called a narrow-sense BCH code.
A BCH code with is called primitive.
The generator polynomial of a BCH code has coefficients from
In general, a cyclic code over with as the generator polynomial is called a BCH code over
The BCH code over and generator polynomial with successive powers of as roots is one type of Reed–Solomon code where the decoder (syndromes) alphabet is the same as the channel (data and generator polynomial) alphabet, all elements of . The other type of Reed Solomon code is an original view Reed Solomon code which is not a BCH code.
Properties
The generator polynomial of a BCH code has degree at most . Moreover, if and , the generator polynomial has degree at most .
Each minimal polynomial has degree at most . Therefore, the least common multiple of of them has degree at most . Moreover, if then for all . Therefore, is the least common multiple of at most minimal polynomials for odd indices each of degree at most .
A BCH code has minimal Hamming distance at least .
Suppose that is a code word with fewer than non-zero terms. Then
Recall that are roots of hence of . This implies that satisfy the following equations, for each :
In matrix form, we have
The determinant of this matrix equals
The matrix is seen to be a Vandermonde matrix, and its determinant is
which is non-zero. It therefore follows that hence
A BCH code is cyclic.
A polynomial code of length is cyclic if and only if its generator polynomial divides Since is the minimal polynomial with roots it suffices to check that each of is a root of This follows immediately from the fact that is, by definition, an th root of unity.
Encoding
Because any polynomial that is a multiple of the generator polynomial is a valid BCH codeword, BCH encoding is merely the process of finding some polynomial that has the generator as a factor.
The BCH code itself is not prescriptive about the meaning of the coefficients of the polynomial; conceptually, a BCH decoding algorithm's sole concern is to find the valid codeword with the minimal Hamming distance to the received codeword. Therefore, the BCH code may be implemented either as a systematic code or not, depending on how the implementor chooses to embed the message in the encoded polynomial.
Non-systematic encoding: The message as a factor
The most straightforward way to find a polynomial that is a multiple of the generator is to compute the product of some arbitrary polynomial and the generator. In this case, the arbitrary polynomial can be chosen using the symbols of the message as coefficients.
As an example, consider the generator polynomial , chosen for use in the (31, 21) binary BCH code used by POCSAG and others. To encode the 21-bit message {101101110111101111101}, we first represent it as a polynomial over :
Then, compute (also over ):
Thus, the transmitted codeword is {1100111010010111101011101110101}.
The receiver can use these bits as coefficients in and, after error-correction to ensure a valid codeword, can recompute
Systematic encoding: The message as a prefix
A systematic code is one in which the message appears verbatim somewhere within the codeword. Therefore, systematic BCH encoding involves first embedding the message polynomial within the codeword polynomial, and then adjusting the coefficients of the remaining (non-message) terms to ensure that is divisible by .
This encoding method leverages the fact that subtracting the remainder from a dividend results in a multiple of the divisor. Hence, if we take our message polynomial as before and multiply it by (to "shift" the message out of the way of the remainder), we can then use Euclidean division of polynomials to yield:
Here, we see that is a valid codeword. As is always of degree less than (which is the degree of ), we can safely subtract it from without altering any of the message coefficients, hence we have our as
Over (i.e. with binary BCH codes), this process is indistinguishable from appending a cyclic redundancy check, and if a systematic binary BCH code is used only for error-detection purposes, we see that BCH codes are just a generalization of the mathematics of cyclic redundancy checks.
The advantage to the systematic coding is that the receiver can recover the original message by discarding everything after the first coefficients, after performing error correction.
Decoding
There are many algorithms for decoding BCH codes. The most common ones follow this general outline:
Calculate the syndromes sj for the received vector
Determine the number of errors t and the error locator polynomial Λ(x) from the syndromes
Calculate the roots of the error location polynomial to find the error locations Xi
Calculate the error values Yi at those error locations
Correct the errors
During some of these steps, the decoding algorithm may determine that the received vector has too many errors and cannot be corrected. For example, if an appropriate value of t is not found, then the correction would fail. In a truncated (not primitive) code, an error location may be out of range. If the received vector has more errors than the code can correct, the decoder may unknowingly produce an apparently valid message that is not the one that was sent.
Calculate the syndromes
The received vector is the sum of the correct codeword and an unknown error vector The syndrome values are formed by considering as a polynomial and evaluating it at Thus the syndromes are
for to
Since are the zeros of of which is a multiple, Examining the syndrome values thus isolates the error vector so one can begin to solve for it.
If there is no error, for all If the syndromes are all zero, then the decoding is done.
Calculate the error location polynomial
If there are nonzero syndromes, then there are errors. The decoder needs to figure out how many errors and the location of those errors.
If there is a single error, write this as where is the location of the error and is its magnitude. Then the first two syndromes are
so together they allow us to calculate and provide some information about (completely determining it in the case of Reed–Solomon codes).
If there are two or more errors,
It is not immediately obvious how to begin solving the resulting syndromes for the unknowns and
The first step is finding, compatible with computed syndromes and with minimal possible locator polynomial:
Three popular algorithms for this task are:
Peterson–Gorenstein–Zierler algorithm
Berlekamp–Massey algorithm
Sugiyama Euclidean algorithm
Peterson–Gorenstein–Zierler algorithm
Peterson's algorithm is the step 2 of the generalized BCH decoding procedure. Peterson's algorithm is used to calculate the error locator polynomial coefficients of a polynomial
Now the procedure of the Peterson–Gorenstein–Zierler algorithm. Expect we have at least 2t syndromes sc, …, sc+2t−1. Let v = t.
Factor error locator polynomial
Now that you have the polynomial, its roots can be found in the form by brute force for example using the Chien search algorithm. The exponential
powers of the primitive element will yield the positions where errors occur in the received word; hence the name 'error locator' polynomial.
The zeros of Λ(x) are α−i1, …, α−iv.
Calculate error values
Once the error locations are known, the next step is to determine the error values at those locations. The error values are then used to correct the received values at those locations to recover the original codeword.
For the case of binary BCH, (with all characters readable) this is trivial; just flip the bits for the received word at these positions, and we have the corrected code word. In the more general case, the error weights can be determined by solving the linear system
Forney algorithm
However, there is a more efficient method known as the Forney algorithm.
Let
And the error evaluator polynomial
Finally:
where
Than if syndromes could be explained by an error word, which could be nonzero only on positions , then error values are
For narrow-sense BCH codes, c = 1, so the expression simplifies to:
Explanation of Forney algorithm computation
It is based on Lagrange interpolation and techniques of generating functions.
Consider and for the sake of simplicity suppose for and for Then
We want to compute unknowns and we could simplify the context by removing the terms. This leads to the error evaluator polynomial
Thanks to we have
Thanks to (the Lagrange interpolation trick) the sum degenerates to only one summand for
To get we just should get rid of the product. We could compute the product directly from already computed roots of but we could use simpler form.
As formal derivative
we get again only one summand in
So finally
This formula is advantageous when one computes the formal derivative of form
yielding:
where
Decoding based on extended Euclidean algorithm
An alternate process of finding both the polynomial Λ and the error locator polynomial is based on Yasuo Sugiyama's adaptation of the Extended Euclidean algorithm. Correction of unreadable characters could be incorporated to the algorithm easily as well.
Let be positions of unreadable characters. One creates polynomial localising these positions
Set values on unreadable positions to 0 and compute the syndromes.
As we have already defined for the Forney formula let
Let us run extended Euclidean algorithm for locating least common divisor of polynomials and
The goal is not to find the least common divisor, but a polynomial of degree at most and polynomials such that
Low degree of guarantees, that would satisfy extended (by ) defining conditions for
Defining and using on the place of in the Fourney formula will give us error values.
The main advantage of the algorithm is that it meanwhile computes required in the Forney formula.
Explanation of the decoding process
The goal is to find a codeword which differs from the received word minimally as possible on readable positions. When expressing the received word as a sum of nearest codeword and error word, we are trying to find error word with minimal number of non-zeros on readable positions. Syndrom restricts error word by condition
We could write these conditions separately or we could create polynomial
and compare coefficients near powers to
Suppose there is unreadable letter on position we could replace set of syndromes by set of syndromes defined by equation Suppose for an error word all restrictions by original set of syndromes hold,
than
New set of syndromes restricts error vector
the same way the original set of syndromes restricted the error vector Except the coordinate where we have an is zero, if For the goal of locating error positions we could change the set of syndromes in the similar way to reflect all unreadable characters. This shortens the set of syndromes by
In polynomial formulation, the replacement of syndromes set by syndromes set leads to
Therefore,
After replacement of by , one would require equation for coefficients near powers
One could consider looking for error positions from the point of view of eliminating influence of given positions similarly as for unreadable characters. If we found positions such that eliminating their influence leads to obtaining set of syndromes consisting of all zeros, than there exists error vector with errors only on these coordinates.
If denotes the polynomial eliminating the influence of these coordinates, we obtain
In Euclidean algorithm, we try to correct at most errors (on readable positions), because with bigger error count there could be more codewords in the same distance from the received word. Therefore, for we are looking for, the equation must hold for coefficients near powers starting from
In Forney formula, could be multiplied by a scalar giving the same result.
It could happen that the Euclidean algorithm finds of degree higher than having number of different roots equal to its degree, where the Fourney formula would be able to correct errors in all its roots, anyway correcting such many errors could be risky (especially with no other restrictions on received word). Usually after getting of higher degree, we decide not to correct the errors. Correction could fail in the case has roots with higher multiplicity or the number of roots is smaller than its degree. Fail could be detected as well by Forney formula returning error outside the transmitted alphabet.
Correct the errors
Using the error values and error location, correct the errors and form a corrected code vector by subtracting error values at error locations.
Decoding examples
Decoding of binary code without unreadable characters
Consider a BCH code in GF(24) with and . (This is used in QR codes.) Let the message to be transmitted be [1 1 0 1 1], or in polynomial notation,
The "checksum" symbols are calculated by dividing by and taking the remainder, resulting in or [ 1 0 0 0 0 1 0 1 0 0 ]. These are appended to the message, so the transmitted codeword is [ 1 1 0 1 1 1 0 0 0 0 1 0 1 0 0 ].
Now, imagine that there are two bit-errors in the transmission, so the received codeword is [ 1 0 1 1 1 0 0 0 1 0 1 0 0 ]. In polynomial notation:
In order to correct the errors, first calculate the syndromes. Taking we have and
Next, apply the Peterson procedure by row-reducing the following augmented matrix.
Due to the zero row, is singular, which is no surprise since only two errors were introduced into the codeword.
However, the upper-left corner of the matrix is identical to , which gives rise to the solution
The resulting error locator polynomial is which has zeros at and
The exponents of correspond to the error locations.
There is no need to calculate the error values in this example, as the only possible value is 1.
Decoding with unreadable characters
Suppose the same scenario, but the received word has two unreadable characters [ 1 0 ? 1 1 ? 0 0 1 0 1 0 0 ]. We replace the unreadable characters by zeros while creating the polynomial reflecting their positions We compute the syndromes and (Using log notation which is independent on GF(24) isomorphisms. For computation checking we can use the same representation for addition as was used in previous example. Hexadecimal description of the powers of are consecutively 1,2,4,8,3,6,C,B,5,A,7,E,F,D,9 with the addition based on bitwise xor.)
Let us make syndrome polynomial
compute
Run the extended Euclidean algorithm:
We have reached polynomial of degree at most 3, and as
we get
Therefore,
Let Don't worry that Find by brute force a root of The roots are and (after finding for example we can divide by corresponding monom and the root of resulting monom could be found easily).
Let
Let us look for error values using formula
where are roots of We get
Fact, that should not be surprising.
Corrected code is therefore [ 1 0 1 1 0 0 1 0 1 0 0].
Decoding with unreadable characters with a small number of errors
Let us show the algorithm behaviour for the case with small number of errors. Let the received word is [ 1 0 ? 1 1 ? 0 0 0 1 0 1 0 0 ].
Again, replace the unreadable characters by zeros while creating the polynomial reflecting their positions
Compute the syndromes and
Create syndrome polynomial
Let us run the extended Euclidean algorithm:
We have reached polynomial of degree at most 3, and as
we get
Therefore,
Let Don't worry that The root of is
Let
Let us look for error values using formula where are roots of polynomial
We get
The fact that should not be surprising.
Corrected code is therefore [ 1 0 1 1 0 0 0 1 0 1 0 0].
Citations
References
Primary sources
Secondary sources
Course notes are apparently being redone for 2012: http://www.stanford.edu/class/ee387/
Further reading
Error detection and correction
Finite fields
Coding theory | BCH code | Mathematics,Engineering | 4,207 |
1,250,090 | https://en.wikipedia.org/wiki/Blood%20culture | A blood culture is a medical laboratory test used to detect bacteria or fungi in a person's blood. Under normal conditions, the blood does not contain microorganisms: their presence can indicate a bloodstream infection such as bacteremia or fungemia, which in severe cases may result in sepsis. By culturing the blood, microbes can be identified and tested for resistance to antimicrobial drugs, which allows clinicians to provide an effective treatment.
To perform the test, blood is drawn into bottles containing a liquid formula that enhances microbial growth, called a culture medium. Usually, two containers are collected during one draw, one of which is designed for aerobic organisms that require oxygen, and one of which is for anaerobic organisms, that do not. These two containers are referred to as a set of blood cultures. Two sets of blood cultures are sometimes collected from two different blood draw sites. If an organism only appears in one of the two sets, it is more likely to represent contamination with skin flora than a true bloodstream infection. False negative results can occur if the sample is collected after the person has received antimicrobial drugs or if the bottles are not filled with the recommended amount of blood. Some organisms do not grow well in blood cultures and require special techniques for detection.
The containers are placed in an incubator for several days to allow the organisms to multiply. If microbial growth is detected, a Gram stain is conducted from the culture bottle to confirm that organisms are present and provide preliminary information about their identity. The blood is then subcultured, meaning it is streaked onto an agar plate to isolate microbial colonies for full identification and antimicrobial susceptibility testing. Because it is essential that bloodstream infections are diagnosed and treated quickly, rapid testing methods have been developed using technologies like polymerase chain reaction and MALDI-TOF MS.
Procedures for culturing the blood were published as early as the mid-19th century, but these techniques were labour-intensive and bore little resemblance to contemporary methods. Detection of microbial growth involved visual examination of the culture bottles until automated blood culture systems, which monitor gases produced by microbial metabolism, were introduced in the 1970s. In developed countries, manual blood culture methods have largely been made obsolete by automated systems.
Medical uses
Blood is normally sterile. The presence of bacteria in the blood is termed bacteremia, and the presence of fungi is called fungemia. Minor damage to the skin or mucous membranes, which can occur in situations like toothbrushing or defecation, can introduce bacteria into the bloodstream, but this bacteremia is normally transient and is rarely detected in cultures because the immune system and reticuloendothelial system quickly sequester and destroy the organisms. Bacteria can enter the blood from infections such as cellulitis, UTIs and pneumonia; and infections within the vascular system, such as bacterial endocarditis or infections associated with intravenous lines, may result in a constant bacteremia. Fungemia occurs most commonly in people with poorly functioning immune systems. If bacteria or fungi are not cleared from the bloodstream, they can spread to other organs and tissues, or evoke an immune response that leads to a systemic inflammatory condition called sepsis, which can be life-threatening.
When sepsis is suspected, it is necessary to draw blood cultures to identify the causative agent and provide targeted antimicrobial therapy. People who are hospitalized and have a fever, a low body temperature, a high white blood cell count or a low count of granulocytes (a category of white blood cells) commonly have cultures drawn to detect a possible bloodstream infection. Blood cultures are used to detect bloodstream infections in febrile neutropenia, a common complication of chemotherapy in which fever occurs alongside a severely low count of neutrophils (white blood cells that defend against bacterial and fungal pathogens). Bacteremia is common in some types of infections, such as meningitis, septic arthritis and epidural abscesses, so blood cultures are indicated in these conditions. In infections less strongly associated with bacteremia, blood culture may still be indicated if the individual is at high risk of acquiring an intravascular infection or if cultures cannot be promptly obtained from the main site of infection (for example, a urine culture in pyelonephritis or a sputum culture in severe community-acquired pneumonia). Blood culture can identify an underlying microbial cause in cases of endocarditis and fever of unknown origin.
The pathogens most frequently identified in blood cultures include Staphylococcus aureus, Escherichia coli and other members of the family Enterobacteriaceae, Enterococcus species, Pseudomonas aeruginosa and Candida albicans. Coagulase-negative staphylococci (CNS) are also commonly encountered, although it is often unclear whether these organisms, which constitute part of the normal skin flora, are true pathogens or merely contaminants. In blood cultures taken from newborn babies and children, CNS can indicate significant infections. The epidemiology of bloodstream infections varies with time and place; for instance, Gram-positive organisms overtook Gram-negative organisms as the predominant cause of bacteremia in the United States during the 1980s and 1990s, and rates of fungemia have greatly increased in association with a growing population of people receiving immunosuppressive treatments such as chemotherapy. Gram-negative sepsis is more common in Central and South America, Eastern Europe, and Asia than in North America and Western Europe; and in Africa, Salmonella enterica is a leading cause of bacteremia.
Procedure
Collection
Blood cultures are typically drawn through venipuncture. Collecting the sample from an intravenous line is not recommended, as this is associated with higher contamination rates, although cultures may be collected from both venipuncture and an intravenous line to diagnose catheter-associated infections. Prior to the blood draw, the top of each collection bottle is disinfected using an alcohol swab to prevent contamination. The skin around the puncture site is then cleaned and left to dry; some protocols recommend disinfection with an alcohol-based antiseptic followed by either chlorhexidine or an iodine-based preparation, while others consider using only an alcohol-containing antiseptic to be sufficient. If blood must be drawn for other tests at the same time as a blood culture, the culture bottles are drawn first to minimize the risk of contamination. Because antimicrobial therapy can cause false negative results by inhibiting the growth of microbes, it is recommended that blood cultures are drawn before antimicrobial drugs are given, although this may be impractical in people who are critically ill.
A typical blood culture collection involves drawing blood into two bottles, which together form one "culture" or "set". One bottle is designed to enhance the growth of aerobic organisms, and the other is designed to grow anaerobic organisms. In children, infection with anaerobic bacteria is uncommon, so a single aerobic bottle may be collected to minimize the amount of blood required. It is recommended that at least two sets are collected from two separate venipuncture locations. This helps to distinguish infection from contamination, as contaminants are less likely to appear in more than one set than true pathogens. Additionally, the collection of larger volumes of blood increases the likelihood that microorganisms will be detected if present.
Blood culture bottles contain a growth medium, which encourages microorganisms to multiply, and an anticoagulant that prevents blood from clotting. Sodium polyanethol sulfonate (SPS) is the most commonly used anticoagulant because it does not interfere with the growth of most organisms. The exact composition of the growth medium varies, but aerobic bottles use a broth that is enriched with nutrients, such as brain-heart infusion or trypticase soy broth, and anaerobic bottles typically contain a reducing agent such as thioglycollate. The empty space in an anaerobic bottle is filled with a gas mixture that does not contain oxygen.
Many commercially manufactured bottles contain a resin that absorbs antibiotics to reduce their action on the microorganisms in the sample. Bottles intended for paediatric use are designed to accommodate lower blood volumes and have additives that enhance the growth of pathogens more commonly found in children. Other specialized bottles may be used to detect fungi and mycobacteria. In low and middle income countries, pre-formulated culture bottles can be prohibitively expensive, and it may be necessary to prepare the bottles manually. It can be difficult to access the proper supplies and facilities, and in some regions, it may not be possible to perform blood cultures at all.
It is important that the bottles are neither underfilled nor overfilled: underfilling can lead to false negative results as fewer organisms are present in the sample, while overfilling can inhibit microbial growth because the ratio of growth medium to blood is comparatively lower. A 1:10 to 1:5 ratio of blood to culture medium is suggested to optimize microbial growth. For routine blood cultures in adults, the Clinical and Laboratory Standards Institute (CLSI) recommends the collection of two sets of bottles from two different draws, with 20–30 mL of blood drawn in each set. In children, the amount of blood to be drawn is often based on the child's age or weight. If endocarditis is suspected, a total of six bottles may be collected.
Culturing
After the blood is collected, the bottles are incubated at body temperature to encourage the growth of microorganisms. Bottles are usually incubated for up to five days in automated systems, although most common bloodstream pathogens are detected within 48 hours. The incubation time may be extended further if manual blood culture methods are used or if slower-growing organisms, such as certain bacteria that cause endocarditis, are suspected. In manual systems, the bottles are visually examined for indicators of microbial growth, which might include cloudiness, the production of gas, the presence of visible microbial colonies, or a change in colour from the digestion of blood, which is called hemolysis. Some manual blood culture systems indicate growth using a compartment that fills with fluid when gases are produced, or a miniature agar plate which is periodically inoculated by tipping the bottle. To ensure that positive blood cultures are not missed, a sample from the bottle is often inoculated onto an agar plate (subcultured) at the end of the incubation period regardless of whether or not indicators of growth are observed.
In developed countries, manual culture methods have largely been replaced by automated systems that provide continuous computerized monitoring of the culture bottles. These systems, such as the BACTEC, BacT/ALERT and VersaTrek, consist of an incubator in which the culture bottles are continuously mixed. Growth is detected by sensors that measure the levels of gases inside the bottle—most commonly carbon dioxide—which serve as an indicator of microbial metabolism. An alarm or a visual indicator alerts the microbiologist to the presence of a positive blood culture bottle. If the bottle remains negative at the end of the incubation period, it is generally discarded without being subcultured.
A technique called the lysis-centrifugation method can be used for improved isolation of slow-growing or fastidious organisms, such as fungi, mycobacteria, and Legionella. Rather than incubating the blood in a bottle filled with growth medium, this method involves collecting blood into a tube containing an agent that destroys (lyses) red and white blood cells, then spinning the sample in a centrifuge. This process concentrates the solid contents of the sample, including microorganisms if present, into a pellet, which is used to inoculate the subculture media. While lysis-centrifugation offers greater sensitivity than conventional blood culture methods, it is prone to contamination because it requires extensive manipulation of the sample.
Identification
If growth is detected, a microbiologist will perform a Gram stain on a sample of blood from the bottle for a rapid preliminary identification of the organism. The Gram stain classifies bacteria as Gram-positive or Gram-negative and provides information about their shape—whether they are rod-shaped (referred to as bacilli), spherical (referred to as cocci), or spiral-shaped (spirochetes)—as well as their arrangement. Gram-positive cocci in clusters, for example, are typical of Staphylococcus species. Yeast and other fungi may also be identified from the Gram stain. A Gram stain identifying microbial growth from a blood culture is considered a critical result and must immediately be reported to the clinician. The Gram stain provides information about the possible identity of the organism, which assists the clinician in the selection of a more appropriate antimicrobial treatment before the full culture and sensitivity results are complete.
In traditional methods, the blood is then subcultured onto agar plates to isolate the organism for further testing. The Gram stain results inform microbiologists about what types of agar plates should be used and what tests might be appropriate to identify the organism. In some cases, no organisms are seen on the Gram stain despite the culture bottle showing indicators of growth or being reported as positive by automated instruments. This may represent a false positive result, but it is possible that organisms are present but cannot easily be visualized microscopically. Positive bottles with negative Gram stains are subcultured before being returned to the incubator, often using special culture media that promotes the growth of slow-growing organisms.
It typically takes 24 to 48 hours for sufficient growth to occur on the subculture plates for definitive identification to be possible. At this point, the microbiologist will assess the appearance of the bacterial or fungal colonies and carry out tests that provide information about the metabolic and biochemical features of the organism, which permit identification to the genus or species level. For example, the catalase test can distinguish streptococci and staphylococci (two genera of Gram-positive cocci) from each other, and the coagulase test can differentiate Staphylococcus aureus, a common culprit of bloodstream infections, from the less pathogenic coagulase-negative staphylococci.
Microorganisms may also be identified using automated systems, such as instruments that perform panels of biochemical tests, or matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), in which microbial proteins are ionized and characterized on the basis of their mass-to-charge ratios; each microbial species exhibits a characteristic pattern of proteins when analyzed through mass spectrometry.
Because bloodstream infections can be life-threatening, timely diagnosis and treatment is critical, and to this end several rapid identification methods have been developed. MALDI-TOF can be used to identify organisms directly from positive blood culture bottles after separation and concentration procedures, or from preliminary growth on the agar plate within a few hours of subculturing. Genetic methods such as polymerase chain reaction (PCR) and microarrays can identify microorganisms by detection of DNA sequences specific to certain species in blood culture samples. Several systems designed for the identification of common blood culture pathogens are commercially available. Some biochemical and immunologic tests can be performed directly on positive blood cultures, such as the tube coagulase test for identification of S. aureus or latex agglutination tests for Streptococcus pneumoniae, and unlike PCR and MALDI-TOF, these methods may be practical for laboratories in low and middle income countries. It is also possible to directly inoculate microbial identification panels with blood from a positive culture bottle, although this is not as reliable as testing subcultured bacteria because additives from the growth media can interfere with the results.
Even faster diagnosis could be achieved through bypassing culture entirely and detecting pathogens directly from blood samples. A few direct testing systems are commercially available as of 2018, but the technology is still in its infancy. Most panels detect only a limited number of pathogens, and the sensitivity can be poor compared to conventional blood culture methods. Culturing remains necessary in order to carry out full antimicrobial sensitivity testing.
Antibiotic susceptibility testing
Antimicrobial treatment of bloodstream infections is initially empiric, meaning it is based on the clinician's suspicion about the causative agent of the disease and local patterns of antimicrobial resistance. Carrying out antibiotic susceptibility testing (AST) on pathogens isolated from a blood culture allows clinicians to provide a more targeted treatment and to discontinue broad-spectrum antibiotics, which can have undesirable side effects. In traditional AST methods, such as the disk diffusion test, pure colonies of the organism are selected from the subculture plate and used to inoculate a secondary medium. These methods require overnight incubation before results can be obtained. There are automated systems which use pre-formulated antibiotic panels, measure microbial growth automatically, and determine the sensitivity results using algorithms; some of these can provide results in as little as five hours, but others require overnight incubation as well.
Rapid administration of effective antimicrobial drugs is crucial in the treatment of sepsis, so several methods have been developed to provide faster antibiotic sensitivity results. Conventional AST methods can be carried out on young growth from the subculture plate, pellets of microorganisms obtained from concentration and purification of the positive blood culture, or directly from the culture bottle. Because direct testing methods do not isolate the organisms, they do not provide accurate results if more than one microorganism is present, although this is an infrequent occurrence in blood cultures. Another source of error is the difficulty in standardizing the amount of bacteria in the sample (the inoculum), which has a profound effect on the test results.
Genetic testing can be used for rapid detection of certain antimicrobial resistance markers. Methods such as PCR and microarrays, which can be performed directly on positive blood culture samples, detect DNA sequences associated with genes that confer resistance, such as the mecA gene found in methicillin-resistant Staphylococcus aureus or the vanA and vanB genes of vancomycin-resistant enterococci. MALDI-TOF has been explored as a rapid antimicrobial sensitivity testing method; principles involve measuring microbial growth in the presence of antibiotics, identifying the breakdown of antibiotics by microbial enzymes, and detecting protein spectra associated with bacterial strains that exhibit antibiotic resistance. Some of these methods can be performed on pellets from positive blood culture bottles. However, the lack of established methodologies for AST by MALDI-TOF limits its use in clinical practice, and direct AST by MALDI-TOF, unlike genetic testing methods, had not been approved by the Food and Drug Administration as of 2018.
Limitations
Blood cultures are subject to both false positive and false negative errors. In automated culture systems, identification of positive bottles is based on the detection of gases produced by cellular metabolism, so samples with high numbers of white blood cells may be reported as positive when no bacteria are present. Inspection of the growth curve produced by the instrument can help to distinguish between true and false positive cultures, but Gram staining and subculturing are still necessary for any sample that is flagged as positive.
Blood cultures can become contaminated with microorganisms from the skin or the environment, which multiply inside the culture bottle, giving the false impression that those organisms are present in the blood. Contamination of blood cultures can lead to unnecessary antibiotic treatment and longer hospital stays. The frequency of contamination can be reduced by following established protocols for blood culture collection, but it cannot be eliminated; for instance, bacteria can survive in deeper layers of the skin even after meticulous disinfection of the blood draw site. The CLSI defines an acceptable contamination rate as no greater than 3% of all blood cultures. The frequency of contamination varies widely between institutions and between different departments in the same hospital; studies have found rates ranging from 0.8 to 12.5 percent.
When faced with a positive blood culture result, clinicians must decide whether the finding represents contamination or genuine infection. Some organisms, such as S. aureus or Streptococcus pneumoniae, are usually considered to be pathogenic when detected in a blood culture, while others are more likely to represent contamination with skin flora; but even common skin organisms such as coagulase-negative staphylococci can cause bloodstream infections under certain conditions. When such organisms are present, interpretation of the culture result involves taking into account the person's clinical condition and whether or not multiple cultures are positive for the same organism.
False negatives may be caused by drawing blood cultures after the person has received antibiotics or collecting an insufficient amount of blood. The volume of blood drawn is considered the most important variable in ensuring that pathogens are detected: the more blood that is collected, the more pathogens are recovered. However, if the amount of blood collected far exceeds the recommended volume, bacterial growth may be inhibited by natural inhibitors present in the blood and an inadequate amount of growth medium in the bottle. Over-filling of blood culture bottles may also contribute to iatrogenic anemia.
Not all pathogens are easily detected by conventional blood culture methods. Particularly fastidious organisms, such as Brucella and Mycobacterium species, may require prolonged incubation times or special culture media. Some organisms are exceedingly difficult to culture or do not grow in culture at all, so serology testing or molecular methods such as PCR are preferred if infection with these organisms is suspected.
History
Early blood culture methods were labour-intensive. One of the first known procedures, published in 1869, recommended that leeches be used to collect blood from the patient. A microbiology textbook from 1911 noted that decontamination of the draw site and equipment could take over an hour, and that due to a lack of effective methods for preserving blood, the cultures would sometimes have to be prepared at the patient's bedside. In addition to subculturing the broth, some protocols specified that the blood be mixed with melted agar and the mixture poured into a petri dish. In 1915, a blood culture collection system consisting of glass vacuum tubes containing glucose broth and an anticoagulant was described. Robert James Valentine Pulvertaft published a seminal work on blood cultures in 1930, specifying—among other insights—an optimal blood-to-broth ratio of 1:5, which is still accepted today. The use of SPS as an anticoagulant and preservative was introduced in the 1930s and 40s and resolved some of the logistical issues with earlier methods. From the 1940s through the 1980s, a great deal of research was carried out on broth formulations and additives, with the goal of creating a growth medium that could accommodate all common bloodstream pathogens.
In 1947, M.R. Castañeda invented a "biphasic" culture bottle for the identification of Brucella species, which contained both broth and an agar slant, allowing the agar to be easily subcultured from the broth; this was a precursor of some contemporary systems for manual blood cultures. E.G. Scott in 1951 published a protocol described as "the advent of the modern blood culture set". Scott's method involved inoculating blood into two rubber-sealed glass bottles; one for aerobes and one for anaerobes. The aerobic bottle contained trypticase soy broth and an agar slant, and the anaerobic bottle contained thioglycollate broth. The lysis-centrifugation method was introduced in 1917 by Mildred Clough, but it was rarely used in clinical practice until commercial systems were developed in the mid-1970s.
Automated blood culture systems first became available in the 1970s. The earliest of these—the BACTEC systems, produced by Johnston Laboratories (now Becton Dickinson)—used culture broths containing nutrients labelled with radioactive isotopes. Microbes that fed on these substrates would produce radioactive carbon dioxide, and growth could be detected by monitoring its concentration. Before this technique was applied to blood cultures, it had been proposed by NASA as a method for detecting life on Mars. Throughout the 1970s and 80s several manufacturers attempted to detect microbial growth by measuring changes in the electrical conductivity of the culture medium, but none of these methods were commercially successful.
A major issue with the early BACTEC systems was that they produced radioactive waste, which required special disposal procedures, so in 1984 a new generation of BACTEC instruments was released that used spectrophotometry to detect CO2. The BacT/ALERT system, which indirectly detects production of CO2 by measuring the decrease in the medium's pH, was approved for use in the US in 1991. Unlike the BACTEC systems available at the time, the BacT/ALERT did not require a needle to be introduced into the bottle for sampling; this reduced the frequency of contamination and made it the first system to provide truly continuous monitoring of blood cultures. This non-invasive measurement method was adopted in 1992 by the BACTEC 9000 series, which used fluorescent indicators to detect pH changes. The Difco ESP, a direct predecessor of the contemporary VersaTREK system which detects gas production by measuring pressure changes, was also first approved in 1992. By 1996, an international study found that 55% of 466 laboratories surveyed were using the BACTEC or BacT/ALERT systems, with other automated systems accounting for 10% of the total.
Notes
References
Bibliography
Microbiology techniques
Blood tests | Blood culture | Chemistry,Biology | 5,383 |
990,343 | https://en.wikipedia.org/wiki/Lindenbaum%E2%80%93Tarski%20algebra | In mathematical logic, the Lindenbaum–Tarski algebra (or Lindenbaum algebra) of a logical theory T consists of the equivalence classes of sentences of the theory (i.e., the quotient, under the equivalence relation ~ defined such that p ~ q exactly when p and q are provably equivalent in T). That is, two sentences are equivalent if the theory T proves that each implies the other. The Lindenbaum–Tarski algebra is thus the quotient algebra obtained by factoring the algebra of formulas by this congruence relation.
The algebra is named for logicians Adolf Lindenbaum and Alfred Tarski.
Starting in the academic year 1926-1927, Lindenbaum pioneered his method in Jan Łukasiewicz's mathematical logic seminar, and the method was popularized and generalized in subsequent decades through work
by Tarski.
The Lindenbaum–Tarski algebra is considered the origin of the modern algebraic logic.
Operations
The operations in a Lindenbaum–Tarski algebra A are inherited from those in the underlying theory T. These typically include conjunction and disjunction, which are well-defined on the equivalence classes. When negation is also present in T, then A is a Boolean algebra, provided the logic is classical. If the theory T consists of the propositional tautologies, the Lindenbaum–Tarski algebra is the free Boolean algebra generated by the propositional variables.
Related algebras
Heyting algebras and interior algebras are the Lindenbaum–Tarski algebras for intuitionistic logic and the modal logic S4, respectively.
A logic for which Tarski's method is applicable, is called algebraizable. There are however a number of logics where this is not the case, for instance the modal logics S1, S2, or S3, which lack the rule of necessitation (⊢φ implying ⊢□φ), so ~ (defined above) is not a congruence (because ⊢φ→ψ does not imply ⊢□φ→□ψ). Another type of logic where Tarski's method is inapplicable is relevance logics, because given two theorems an implication from one to the other may not itself be a theorem in a relevance logic. The study of the algebraization process (and notion) as topic of interest by itself, not necessarily by Tarski's method, has led to the development of abstract algebraic logic.
See also
Algebraic semantics (mathematical logic)
Leibniz operator
List of Boolean algebra topics
References
Algebraic logic
Algebraic structures | Lindenbaum–Tarski algebra | Mathematics | 510 |
2,266,631 | https://en.wikipedia.org/wiki/Finger%20binary | Finger binary is a system for counting and displaying binary numbers on the fingers of either or both hands. Each finger represents one binary digit or bit. This allows counting from zero to 31 using the fingers of one hand, or 1023 using both: that is, up to 25−1 or 210−1 respectively.
Modern computers typically store values as some whole number of 8-bit bytes, making the fingers of both hands together equivalent to 1¼ bytes of storage—in contrast to less than half a byte when using ten fingers to count up to 10.
Mechanics
In the binary number system, each numerical digit has two possible states (0 or 1) and each successive digit represents an increasing power of two.
Note: What follows is but one of several possible schemes for assigning the values 1, 2, 4, 8, 16, etc. to fingers, not necessarily the best. (see below the illustrations.): The rightmost digit represents two to the zeroth power (i.e., it is the "ones digit"); the digit to its left represents two to the first power (the "twos digit"); the next digit to the left represents two to the second power (the "fours digit"); and so on. (The decimal number system is essentially the same, only that powers of ten are used: "ones digit", "tens digit" "hundreds digit", etc.)
It is possible to use anatomical digits to represent numerical digits by using a raised finger to represent a binary digit in the "1" state and a lowered finger to represent it in the "0" state. Each successive finger represents a higher power of two.
With palms oriented toward the counter's face, the values for when only the right hand is used are:
When only the left hand is used:
When both hands are used:
And, alternately, with the palms oriented away from the counter:
The values of each raised finger are added together to arrive at a total number. In the one-handed version, all fingers raised is thus 31 (16 + 8 + 4 + 2 + 1), and all fingers lowered (a fist) is 0. In the two-handed system, all fingers raised is 1,023 (512 + 256 + 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1) and two fists (no fingers raised) represents 0.
It is also possible to have each hand represent an independent number between 0 and 31; this can be used to represent various types of paired numbers, such as month and day, X-Y coordinates, or sports scores (such as for table tennis or baseball). Showing the time as hours and minutes is possible using 10 fingers, with the hour using 4 fingers (0-23) and the minutes using 6 fingers (0-59).
Examples
Right hand
Left hand
When used in addition to the right.
Negative numbers and non-integers
Just as fractional and negative numbers can be represented in binary, they can be represented in finger binary.
Negative numbers
Representing negative numbers is extremely simple, by using the leftmost finger as a sign bit: raised means the number is negative, in a sign-magnitude system. Anywhere between and +511 can be represented this way, using two hands. Note that, in this system, both a positive and a negative zero may be represented.
If a convention were reached on palm up/palm down or fingers pointing up/down representing positive/negative, you could maintain 210 −1 in both positive and negative numbers ( to +1023, with positive and negative zero still represented).
Fractions
Dyadic fractions
Fractions can be stored natively in a binary format by having each finger represent a fractional power of two: . (These are known as dyadic fractions.)
Using the left hand only:
Using two hands:
The total is calculated by adding all the values in the same way as regular (non-fractional) finger binary, then dividing by the largest fractional power being used (32 for one-handed fractional binary, 1024 for two-handed), and simplifying the fraction as necessary.
For example, with thumb and index finger raised on the left hand and no fingers raised on the right hand, this is (512 + 256)/1024 = 768/1024 = 3/4. If using only one hand (left or right), it would be (16 + 8)/32 = 24/32 = 3/4 also.
The simplification process can itself be greatly simplified by performing a bit shift operation: all digits to the right of the rightmost raised finger (i.e., all trailing zeros) are discarded and the rightmost raised finger is treated as the ones digit. The digits are added together using their now-shifted values to determine the numerator and the rightmost finger's original value is used to determine the denominator.
For instance, if the thumb and index finger on the left hand are the only raised digits, the rightmost raised finger (the index finger) becomes "1". The thumb, to its immediate left, is now the 2s digit; added together, they equal 3. The index finger's original value (1/4) determines the denominator: the result is 3/4.
Rational numbers
Combined integer and fractional values (i.e., rational numbers) can be represented by setting a radix point somewhere between two fingers (for instance, between the left and right pinkies). All digits to the left of the radix point are integers; those to the right are fractional.
Decimal fractions and vulgar fractions
Dyadic fractions, explained above, have limited use in a society based around decimal figures. A simple non-dyadic fraction such as 1/3 can be approximated as 341/1024 (0.3330078125), but the conversion between dyadic and decimal (0.333) or vulgar (1/3) forms is complicated.
Instead, either decimal or vulgar fractions can be represented natively in finger binary. Decimal fractions can be represented by using regular integer binary methods and dividing the result by 10, 100, 1000, or some other power of ten. Numbers between 0 and 102.3, 10.23, 1.023, etc. can be represented this way, in increments of 0.1, 0.01, 0.001, etc.
Vulgar fractions can be represented by using one hand to represent the numerator and one hand to represent the denominator; a spectrum of rational numbers can be represented this way, ranging from 1/31 to 31/1 (as well as 0).
Finger ternary
In theory, it is possible to use other positions of the fingers to represent more than two states (0 and 1); for instance, a ternary numeral system (base 3) could be used by having a fully raised finger represent 2, fully lowered represent 0, and "curled" (half-lowered) represent 1. This would make it possible to count up to 242 (35−1) on one hand or 59,048 (310−1) on two hands. In practice, however, many people will find it difficult to hold all fingers independently (especially the middle and ring fingers) in more than two distinct positions.
See also
Chisanbop
References
External links
Binary Counting
Finger-counting
Elementary arithmetic
Binary arithmetic | Finger binary | Mathematics | 1,537 |
67,325,019 | https://en.wikipedia.org/wiki/Andrei%20Gritsan | Andrei V. Gritsan is an American-Siberian particle physicist. He was a member of a team of researchers at the Large Hadron Collider, who, in 2012, announced the discovery of a new subatomic particle, a Higgs boson.
Early life and education
Gritsan was born in Russia and graduated from Novosibirsk State University with his Bachelor of Science degree and master's degree in physics. He then enrolled at the University of Colorado, Boulder in the United States for his PhD.
Career
Gritsan joined the faculty at Johns Hopkins University in 2005 after working at the Lawrence Berkeley National Laboratory. As an assistant professor in the department of physics and astronomy, Gritsan won both the National Science Foundation's Faculty Early Career Development Award and a Sloan Research Fellowship in 2007. A few years later, he worked alongside more than 2,000 other scientists and researchers on the Higgs boson which was the recipient of a Nobel Prize in Physics.
In recognition of his "significant contributions to the discovery and to the characterization of the Higgs Boson at the CERN Large Hadron Collider, and for significant contributions to the measurement of sin2alpha at the SLAC PEP II collider," Gritsan was elected a Fellow of the American Physical Society.
References
External links
Living people
Year of birth missing (living people)
Novosibirsk State University alumni
University of Colorado Boulder alumni
Johns Hopkins University faculty
Fellows of the American Physical Society
21st-century American physicists
Particle physicists
People associated with CERN | Andrei Gritsan | Physics | 311 |
15,809,725 | https://en.wikipedia.org/wiki/The%20Robotic%20Workshop | The Robotic Workshop was a toy kit, much like Lego Mindstorms, that allowed users to build and program robots using a home computer.
Access Software announced The Robotic Workshop in the January 1987 issue of Ahoy! magazine. A review later appeared in the May 1988 issue of Compute! magazine. The kit included over 50 Capsela parts, including two motors, gears, wheels, and sensors. It also included an electronic control unit that plugged into the user port of a , an instruction manual with 50 tutorial projects, and special programming software on a floppy disk. It was later released for Apple II, Atari 8-bit computers, and IBM PC.
External links
Review in Compute!
Robot kits
1987 robots
Robots of the United States | The Robotic Workshop | Technology | 149 |
2,182,805 | https://en.wikipedia.org/wiki/Periodinane | Periodinanes also known as λ5-iodanes are organoiodine compounds with iodine in the +5 oxidation state. These compounds are described as hypervalent because the iodine center has more than 8 valence electrons.
Periodinane compounds
The λ5-iodanes such as the Dess-Martin periodinane have square pyramidal geometry with 4 heteroatoms in basal positions and one apical phenyl group.
Iodoxybenzene or iodylbenzene, , is a known oxidizing agent.
Dess-Martin periodinane (1983) is another powerful oxidant and an improvement of the IBX acid already in existence in 1983. The IBX acid is prepared from 2-iodobenzoic acid and potassium bromate and sulfuric acid and is insoluble in most solvents whereas the Dess-Martin reagent prepared from reaction of the IBX acid with acetic anhydride is very soluble. The oxidation mechanism ordinarily consists of a ligand exchange reaction followed by a reductive elimination.
Uses
The predominant use of periodinanes is as oxidizing reagents replacing toxic reagents based on heavy metals.
See also
Carbonyl oxidation with hypervalent iodine reagents
Dess–Martin oxidation
References
External links
Hypervalent Iodine Chemistry
Oxidizing agents | Periodinane | Chemistry | 283 |
4,625,335 | https://en.wikipedia.org/wiki/Symbiotic%20bacteria | Symbiotic bacteria are bacteria living in symbiosis with another organism or each other. For example, rhizobia living in root nodules of legumes provide nitrogen fixing activity for these plants.
Types of symbiosis
Types of symbiotic relationships are mutualism, commensalism, parasitism, and amensalism.
Endosymbiosis
Endosymbionts live inside other organisms whether that be in their bodies or cells. The theory of endosymbiosis, as known as symbiogenesis, provides an explanation for the evolution of eukaryotic organisms. According to the theory of endosymbiosis for the origin of eukaryotic cells, scientists believe that eukaryotes originated from the relationship between two or more prokaryotic cells approximately 2.7 billion years ago. It is suggested that specifically ancestors of mitochondria and chloroplasts entered into an endosymbiotic relationship with another prokaryotic cell, eventually evolving into the eukaryotic cells that people are familiar with today.
Ectosymbiosis
Ectosymbiosis is defined as a symbiotic relationship in which one organism lives on the outside surface of a different organism. For instance, barnacles on whales is an example of an ectosymbiotic relationship where the whale provides the barnacle with a home, a ride, and access to food. The whale is not harmed, but it also does not receive any benefits so this is also an example of commensalism. An example of ectosymbiotic bacteria is cutibacterium acnes. These bacteria are involved in a symbiotic relationship with humans on whose skin they live. Cutibacterium acnes can cause acne when the skin becomes too oily, but they also reduce the skin's susceptibility to skin diseases caused by oxidative stress.
Symbiotic relationships
Certain plants establish a symbiotic relationship with bacteria, enabling them to produce nodules that facilitate the conversion of atmospheric nitrogen to ammonia. In this connection, cytokinins have been found to play a role in the development of root fixing nodules. It appears that not only must the plant have a need for nitrogen fixing bacteria, but they must also be able to synthesize cytokinins which promote the production of root nodules, required for nitrogen fixation.
Symbiotic bacteria are able to live in or on plant or animal tissue. In digestive systems, symbiotic bacteria help break down foods that contain fiber. They also help produce vitamins. Symbiotic bacteria can live near hydrothermal vents. They usually have a mutual relationship with other bacteria. Some live in tube worms.
Transmission
There are two major modes of transmission for symbiotic bacteria. The first is horizontal transmission in which microbes are acquired from the environment and either the environment or the host population serves as the inoculum for the symbiosis. An example of horizontal transmission is the deep sea tube worm and its symbiont. The second type of transmission is vertical transmission in which the symbiont is passed down from the parent to the offspring and there is no aposymbiotic phase. An example of vertical transmission is seen in Drosophila melanogaster and its Wolbachia spp. symbionts.
Examples of Symbiotic Relationships
Corals
Corals have been found to form characteristic associations with symbiotic nitrogen-fixing bacteria. Corals have evolved in oligotrophic waters which are typically poor in nitrogen. Corals must therefore form a mutualistic relationship with nitrogen fixing organism, in this case the subject of this study, namely Symbiodinium. In addition to this dinoflagellate, coral also form relationships with bacteria, archae and fungi. The problem is that these dinoflagellates are also nitrogen limited and must form a symbiotic relationship with another organism; here it is suggested to be diazotrophs. In addition, cyanobacteria have been found to possess genes that enable them to undergo nitrogen fixation. This particular study goes further to investigate the possibility that in addition to the named dinoflagellate and certain cyanobacteria, endosymbiotic algae and the coral contain enzymes enabling them to both undergo ammonium assimilation.
Due to the small size of the genome of most endosymbionts, they are unable to exist for any length of time outside of the host cell, thereby preventing a long-term symbiotic relationship. However, in the case of the endonuclear symbiotic bacterium Holospora, it has been discovered that Holospora species can maintain their infectivity for a limited time and form a symbiotic relationship with Paramecium species.
Plants and rhizobial bacteria
There is a mutualistic relationship between legumes and rhizobial bacteria enabling the plants to survive in an otherwise nitrogen-poor soil environment. Co-evolution is described as a situation where two organisms evolve in response to one another. In a study reported in Functional Ecology, these scientists investigated whether such a mutualistic relationship conferred an evolutionary advantage to either plant or symbiont. They did not find that the rhizobial bacteria studied had any evolutionary advantage with their host but did find great genetic variation among the populations of rhizobial bacteria studied.
Chemosynthetic Bacteria and Mussels
Symbiotic, chemosynthetic bacteria that have been discovered associated with mussels (Bathymodiolus) located near hydrothermal vents have a gene that enables them to utilize hydrogen as a source of energy, in preference to sulphur or methane as their energy source for production of energy.
Termites and Cellulase-Producing Bacteria
Termites are known by many as pests that feed on wood. However, termites cannot digest the wood alone. Instead, they rely on a non-bacterial protozoan called Trichonympha to help in the digestion process. Trichonympha is an endosymbiont that lives inside termites and also acts as a host to bacterial symbionts. The bacteria inside Trichonympha in termites produces cellulase. Cellulase enzymes are used to break down cellulose which is found in plants' cell walls. The termites, the gut protist Trichonympha, and the cellulase-producing bacteria are all involved in a 3-way obligate symbiotic mutualism. The termites benefit from the other two species because they transform the wood into nutrients that the termites can digest. Additionally, the Trichonympha benefit from the termites because the termites provide a place to live and access to food. The Trichonympha also benefit from the bacteria because they help break down the cellulose in wood that the protist consumes. Finally, the bacteria benefits because it gains a place to live and the nutrients it needs to survive.
Symbiotic Bacteria in Humans
Gut Bacteria
The human gut contains approximately thirty-eight trillion microbes. The gut is a dynamic ecosystem as it is composed of both constant and transient components, meaning some bacteria establishes itself and remains throughout the human’s lifetime and other bacteria is ingested and later leaves in feces. When babies are born, they are born without any bacteria in their intestines. However, as soon as they enter the world, they begin accumulating gut bacteria through food and other means. Most bacteria in the human body are actually good for us and help with carrying out necessary life processes. Gut bacteria in humans often aid in the breakdown of foods and synthesize important vitamins that could not be processed by humans alone. Therefore, humans must be careful when taking antibiotics when they are sick. Antibiotics do not differentiate between the good and bad bacteria in our bodies and therefore, kill both. If not treated carefully, this can lead to issues with the gastrointestinal tract because of an imbalance of bacteria in this microbiome. Therefore, some doctors recommend taking a probiotic when taking antibiotics to restore the good bacteria.
Benefits of Bacterial Symbiosis
Organisms typically establish a symbiotic relationship due to their limited availability of resources in their habitat or due to a limitation of their food source. Triatomine vectors have only one host and therefore must establish a relationship with bacteria to enable them to obtain the nutrients required to maintain themselves.
A use for symbiotic bacteria is in paratransgenesis for controlling important vectors for disease, such as the transmission of Chagas disease by Triatome kissing bugs.
Symbiotic bacteria in legume roots provide the plants with ammonia in exchange for the plants' carbon and a protected home.
References
Symbiosis
Bacteriology | Symbiotic bacteria | Biology | 1,827 |
56,278,061 | https://en.wikipedia.org/wiki/Wash%20copper | A wash copper, copper boiler or simply copper is a wash house boiler, generally made of galvanised iron, though the best sorts are made of copper. In the inter-war years they came in two types. The first is built into a brickwork furnace and was found in older houses. The second was the free-standing or portable type, it had an enamelled metal exterior that supported the inner can or copper. The bottom part was adapted to hold a gas burner, a high pressure oil or an ordinary wood or coal fire. Superior models could have a drawing-off tap, and a steam-escape pipe that led into the flue.
It was used for domestic laundry. Linen and cotton were placed in the copper and were boiled to whiten them. Clothes were agitated within the copper with a washing dolly, a vertical stick with either a metal cone or short wooden legs on it. After washing, the laundry was lifted out of the boiling water using the washing dolly or a similar device, and placed on a strainer resting on a laundry tub or similar container to capture the wash water and begin the drying and cooling process. The laundry was then dried with a mangle and then line-dried.
Coppers could also be used in cooking, used to boil puddings such as a traditional Christmas pudding.
Meticulous care was taken to avoid rust, and grease. In cases of the latter it could be cleaned with paraffin or soft soap. Water was always put in the copper before it was lit. In the case of solid fuel, a small shovel of hot coals would be brought from the main kitchen fire and coke shovelled on top.
See also
Russian stove
Kamado (Japanese)
Furo
Agungi/Buttumak (Korean)
References
External links
Laundry washing equipment
Fire
Heating | Wash copper | Chemistry | 367 |
18,580,879 | https://en.wikipedia.org/wiki/Transport | Transport (in British English) or transportation (in American English) is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipelines, and space. The field can be divided into infrastructure, vehicles, and operations. Transport enables human trade, which is essential for the development of civilizations.
Transport infrastructure consists of both fixed installations, including roads, railways, airways, waterways, canals, and pipelines, and terminals such as airports, railway stations, bus stations, warehouses, trucking terminals, refueling depots (including fuel docks and fuel stations), and seaports. Terminals may be used both for the interchange of passengers and cargo and for maintenance.
Means of transport are any of the different kinds of transport facilities used to carry people or cargo. They may include vehicles, riding animals, and pack animals. Vehicles may include wagons, automobiles, bicycles, buses, trains, trucks, helicopters, watercraft, spacecraft, and aircraft.
Modes
A mode of transport is a solution that makes use of a certain type of vehicle, infrastructure, and operation. The transport of a person or of cargo may involve one mode or several of the modes, with the latter case being called inter-modal or multi-modal transport. Each mode has its own advantages and disadvantages, and will be chosen on the basis of cost, capability, and route.
Governments deal with the way the vehicles are operated, and the procedures set for this purpose, including financing, legalities, and policies. In the transport industry, operations and ownership of infrastructure can be either public or private, depending on the country and mode.
Passenger transport may be public, where operators provide scheduled services, or private. Freight transport has become focused on containerization, although bulk transport is used for large volumes of durable items. Transport plays an important part in economic growth and globalization, but most types cause air pollution and use large amounts of land. While it is heavily subsidized by governments, good planning of transport is essential to make traffic flow and restrain urban sprawl.
Human-powered
Human-powered transport, a form of sustainable transport, is the transport of people or goods using human muscle-power, in the form of walking, running, and swimming. Modern technology has allowed machines to enhance human power. Human-powered transport remains popular for reasons of cost-saving, leisure, physical exercise, and environmentalism; it is sometimes the only type available, especially in underdeveloped or inaccessible regions.
Although humans are able to walk without infrastructure, the transport can be enhanced through the use of roads, especially when using the human power with vehicles, such as bicycles and inline skates. Human-powered vehicles have also been developed for difficult environments, such as snow and water, by watercraft rowing and skiing; even the air can be entered with human-powered aircraft.
Animal-powered
Animal-powered transport is the use of working animals for the movement of people and commodities. Humans may ride some of the animals directly, use them as pack animals for carrying goods, or harness them, alone or in teams, to pull sleds or wheeled vehicles.
Air
A fixed-wing aircraft, commonly called an airplane, is a heavier-than-air craft where movement of the air in relation to the wings is used to generate lift. The term is used to distinguish this from rotary-wing aircraft, where the movement of the lift surfaces relative to the air generates lift. A gyroplane is both fixed-wing and rotary wing. Fixed-wing aircraft range from small trainers and recreational aircraft to large airliners and military cargo aircraft.
Two things necessary for aircraft are air flow over the wings for lift and an area for landing. The majority of aircraft also need an airport with the infrastructure for maintenance, restocking, and refueling and for the loading and unloading of crew, cargo, and passengers. While the vast majority of aircraft land and take off on land, some are capable of take-off and landing on ice, snow, and calm water.
The aircraft is the second fastest method of transport, after the rocket. Commercial jets can reach up to , single-engine aircraft . Aviation is able to quickly transport people and limited amounts of cargo over longer distances, but incurs high costs and energy use; for short distances or in inaccessible places, helicopters can be used. As of April 28, 2009, The Guardian article notes that "the WHO estimates that up to 500,000 people are on planes at any time."
Land
Land transport covers all land-based transport systems that provide for the movement of people, goods, and services. Land transport plays a vital role in linking communities to each other. Land transport is a key factor in urban planning. It consists of two kinds, rail and road.
Rail
Rail transport is where a train runs along a set of two parallel steel rails, known as a railway or railroad. The rails are anchored perpendicular to ties (or sleepers) of timber, concrete, or steel, to maintain a consistent distance apart, or gauge. The rails and perpendicular beams are placed on a foundation made of concrete or compressed earth and gravel in a bed of ballast. Alternative methods include monorail and maglev.
A train consists of one or more connected vehicles that operate on the rails. Propulsion is commonly provided by a locomotive, that hauls a series of unpowered cars, that can carry passengers or freight. The locomotive can be powered by steam, by diesel, or by electricity supplied by trackside systems. Alternatively, some or all the cars can be powered, known as a multiple unit. Also, a train can be powered by horses, cables, gravity, pneumatics, and gas turbines. Railed vehicles move with much less friction than rubber tires on paved roads, making trains more energy efficient, though not as efficient as ships.
Intercity trains are long-haul services connecting cities; modern high-speed rail is capable of speeds up to , but this requires specially built track. Regional and commuter trains feed cities from suburbs and surrounding areas, while intra-urban transport is performed by high-capacity tramways and rapid transits, often making up the backbone of a city's public transport. Freight trains traditionally used box cars, requiring manual loading and unloading of the cargo. Since the 1960s, container trains have become the dominant solution for general freight, while large quantities of bulk are transported by dedicated trains.
Road
A road is an identifiable route, way, or path between two or more places. Roads are typically smoothed, paved, or otherwise prepared to allow easy travel; though they need not be, and historically many roads were simply recognizable routes without any formal construction or maintenance. In urban areas, roads may pass through a city or village and be named as streets, serving a dual function as urban space easement and route.
The most common road vehicle is the automobile; a wheeled passenger vehicle that carries its own motor. Other users of roads include buses, trucks, motorcycles, bicycles, and pedestrians. As of 2010, there were 1.015 billion automobiles worldwide.
Road transport offers complete freedom to road users to transfer the vehicle from one lane to the other and from one road to another according to the need and convenience. This flexibility of changes in location, direction, speed, and timings of travel is not available to other modes of transport. It is possible to provide door-to-door service only by road transport.
Automobiles provide high flexibility with low capacity, but require high energy and area use, and are the main source of harmful noise and air pollution in cities; buses allow for more efficient travel at the cost of reduced flexibility. Road transport by truck is often the initial and final stage of freight transport.
Water
Water transport is movement by means of a watercraft—such as a barge, boat, ship, or sailboat—over a body of water, such as a sea, ocean, lake, canal, or river. The need for buoyancy is common to watercraft, making the hull a dominant aspect of its construction, maintenance, and appearance.
In the 19th century, the first steam ships were developed, using a steam engine to drive a paddle wheel or propeller to move the ship. The steam was produced in a boiler using wood or coal and fed through a steam external combustion engine. Now most ships have an internal combustion engine using a slightly refined type of petroleum called bunker fuel. Some ships, such as submarines, use nuclear power to produce the steam. Recreational or educational craft still use wind power, while some smaller craft use internal combustion engines to drive one or more propellers or, in the case of jet boats, an inboard water jet. In shallow draft areas, hovercraft are propelled by large pusher-prop fans. (See Marine propulsion.)
Although it is slow compared to other transport, modern sea transport is a highly efficient method of transporting large quantities of goods. Commercial vessels, nearly 35,000 in number, carried 7.4 billion tons of cargo in 2007. Transport by water is significantly less costly than air transport for transcontinental shipping; short sea shipping and ferries remain viable in coastal areas.
Other modes
Pipeline transport sends goods through a pipe; most commonly liquid and gases are sent, but pneumatic tubes can also send solid capsules using compressed air. For liquids/gases, any chemically stable liquid or gas can be sent through a pipeline. Short-distance systems exist for sewage, slurry, water, and beer, while long-distance networks are used for petroleum and natural gas.
Cable transport is a broad mode where vehicles are pulled by cables instead of an internal power source. It is most commonly used at steep gradient. Typical solutions include aerial tramways, elevators, and ski lifts; some of these are also categorized as conveyor transport.
Spaceflight is transport outside Earth's atmosphere by means of a spacecraft. It is most frequently used for satellites placed in Earth orbit. However, human spaceflight mission have landed on the Moon and are occasionally used to rotate crew-members to space stations. Uncrewed spacecraft have also been sent to all the planets of the Solar System.
Suborbital spaceflight is the fastest of the existing and planned transport systems from a place on Earth to a distant "other place" on Earth. Faster transport could be achieved through part of a low Earth orbit or by following that trajectory even faster, using the propulsion of the rocket to steer it.
Elements
Infrastructure
Infrastructure is the fixed installations that allow a vehicle to operate. It consists of a roadway, a terminal, and facilities for parking and maintenance. For rail, pipeline, road, and cable transport, the entire way the vehicle travels must be constructed. Air and watercraft are able to avoid this, since the airway and seaway do not need to be constructed. However, they require fixed infrastructure at terminals.
Terminals such as airports, ports, and stations, are locations where passengers and freight can be transferred from one vehicle or mode to another. For passenger transport, terminals are integrating different modes to allow riders, who are interchanging between modes, to take advantage of each mode's benefits. For instance, airport rail links connect airports to the city centres and suburbs. The terminals for automobiles are parking lots, while buses and coaches can operate from simple stops. For freight, terminals act as transshipment points, though some cargo is transported directly from the point of production to the point of use.
The financing of infrastructure can either be public or private. Transport is often a natural monopoly and a necessity for the public; roads, and in some countries railways and airports, are funded through taxation. New infrastructure projects can have high costs and are often financed through debt. Many infrastructure owners, therefore, impose usage fees, such as landing fees at airports or toll plazas on roads. Independent of this, authorities may impose taxes on the purchase or use of vehicles. Because of poor forecasting and overestimation of passenger numbers by planners, there is frequently a benefits shortfall for transport infrastructure projects.
Means of transport
Animals
Animals used in transportation include pack animals and riding animals.
Vehicles
A vehicle is a non-living device that is used to move people and goods. Unlike the infrastructure, the vehicle moves along with the cargo and riders. Unless being pulled/pushed by a cable or muscle-power, the vehicle must provide its own propulsion; this is most commonly done through a steam engine, combustion engine, electric motor, jet engine, or rocket, though other means of propulsion also exist. Vehicles also need a system of converting the energy into movement; this is most commonly done through wheels, propellers, and pressure.
Vehicles are most commonly staffed by a driver. However, some systems, such as people movers and some rapid transits, are fully automated. For passenger transport, the vehicle must have a compartment, seat, or platform for the passengers. Simple vehicles, such as automobiles, bicycles, or simple aircraft, may have one of the passengers as a driver. Recently, the progress related to the Fourth Industrial Revolution has brought a lot of new emerging technologies for transportation and automotive fields such as Connected Vehicles and Autonomous Driving. These innovations are said to form future mobility, but concerns remain on safety and cybersecurity, particularly concerning connected and autonomous mobility.
Operation
Private transport is only subject to the owner of the vehicle, who operates the vehicle themselves. For public transport and freight transport, operations are done through private enterprise or by governments. The infrastructure and vehicles may be owned and operated by the same company, or they may be operated by different entities. Traditionally, many countries have had a national airline and national railway. Since the 1980s, many of these have been privatized. International shipping remains a highly competitive industry with little regulation, but ports can be public-owned.
Policy
As the population of the world increases, cities grow in size and population—according to the United Nations, 55% of the world's population live in cities, and by 2050 this number is expected to rise to 68%. Public transport policy must evolve to meet the changing priorities of the urban world. The institution of policy enforces order in transport, which is by nature chaotic as people attempt to travel from one place to another as fast as possible. This policy helps to reduce accidents and save lives.
Functions
Relocation of travelers and cargo are the most common uses of transport. However, other uses exist, such as the strategic and tactical relocation of armed forces during warfare, or the civilian mobility construction or emergency equipment.
Passenger
Passenger transport, or travel, is divided into public and private transport. Public transport is scheduled services on fixed routes, while private is vehicles that provide ad hoc services at the riders desire. The latter offers better flexibility, but has lower capacity and a higher environmental impact. Travel may be as part of daily commuting or for business, leisure, or migration.
Short-haul transport is dominated by the automobile and mass transit. The latter consists of buses in rural and small cities, supplemented with commuter rail, trams, and rapid transit in larger cities. Long-haul transport involves the use of the automobile, trains, coaches, and aircraft, the last of which have become predominantly used for the longest, including intercontinental, travel. Intermodal passenger transport is where a journey is performed through the use of several modes of transport; since all human transport normally starts and ends with walking, all passenger transport can be considered intermodal. Public transport may also involve the intermediate change of vehicle, within or across modes, at a transport hub, such as a bus or railway station.
Taxis and buses can be found on both ends of the public transport spectrum. Buses are the cheapest mode of transport but are not necessarily flexible, and taxis are very flexible but more expensive. In the middle is demand-responsive transport, offering flexibility whilst remaining affordable.
International travel may be restricted for some individuals due to legislation and visa requirements.
Medical
An ambulance is a vehicle used to transport people from or between places of treatment, and in some instances will also provide out-of-hospital medical care to the patient. The word is often associated with road-going "emergency ambulances", which form part of emergency medical services, administering emergency care to those with acute medical problems.
Air medical services is a comprehensive term covering the use of air transport to move patients to and from healthcare facilities and accident scenes. Personnel provide comprehensive prehospital and emergency and critical care to all types of patients during aeromedical evacuation or rescue operations, aboard helicopters, propeller aircraft, or jet aircraft.
Freight
Freight transport, or shipping, is a key in the value chain in manufacturing. With increased specialization and globalization, production is being located further away from consumption, rapidly increasing the demand for transport. Transport creates place utility by moving the goods from the place of production to the place of consumption. While all modes of transport are used for cargo transport, there is high differentiation between the nature of the cargo transport, in which mode is chosen. Logistics refers to the entire process of transferring products from producer to consumer, including storage, transport, transshipment, warehousing, material-handling, and packaging, with associated exchange of information. Incoterm deals with the handling of payment and responsibility of risk during transport.
Containerization, with the standardization of ISO containers on all vehicles and at all ports, has revolutionized international and domestic trade, offering a huge reduction in transshipment costs. Traditionally, all cargo had to be manually loaded and unloaded into the haul of any ship or car; containerization allows for automated handling and transfer between modes, and the standardized sizes allow for gains in economy of scale in vehicle operation. This has been one of the key driving factors in international trade and globalization since the 1950s.
Bulk transport is common with cargo that can be handled roughly without deterioration; typical examples are ore, coal, cereals, and petroleum. Because of the uniformity of the product, mechanical handling can allow enormous quantities to be handled quickly and efficiently. The low value of the cargo combined with high volume also means that economies of scale become essential in transport, and gigantic ships and whole trains are commonly used to transport bulk. Liquid products with sufficient volume may also be transported by pipeline.
Air freight has become more common for products of high value; while less than one percent of world transport by volume is by airline, it amounts to forty percent of the value. Time has become especially important in regards to principles such as postponement and just-in-time within the value chain, resulting in a high willingness to pay for quick delivery of key components or items of high value-to-weight ratio. In addition to mail, common items sent by air include electronics and fashion clothing.
Industry
Impact
Economic
Transport is a key necessity for specialization—allowing production and consumption of products to occur at different locations. Throughout history, transport has been a spur to expansion; better transport allows more trade and a greater spread of people. Economic growth has always been dependent on increasing the capacity and rationality of transport. But the infrastructure and operation of transport have a great impact on the land, and transport is the largest drainer of energy, making transport sustainability a major issue.
Due to the way modern cities and communities are planned and operated, a physical distinction between home and work is usually created, forcing people to transport themselves to places of work, study, or leisure, as well as to temporarily relocate for other daily activities. Passenger transport is also the essence of tourism, a major part of recreational transport. Commerce requires the transport of people to conduct business, either to allow face-to-face communication for important decisions or to move specialists from their regular place of work to sites where they are needed.
In lean thinking, transporting materials or work in process from one location to another is seen as one of the seven wastes (Japanese term: muda) which do not add value to a product.
Planning
Transport planning allows for high use and less impact regarding new infrastructure. Using models of transport forecasting, planners are able to predict future transport patterns. On the operative level, logistics allows owners of cargo to plan transport as part of the supply chain. Transport as a field is also studied through transport economics, a component for the creation of regulation policy by authorities. Transport engineering, a sub-discipline of civil engineering, must take into account trip generation, trip distribution, mode choice, and route assignment, while the operative level is handled through traffic engineering.
Because of the negative impacts incurred, transport often becomes the subject of controversy related to choice of mode, as well as increased capacity. Automotive transport can be seen as a tragedy of the commons, where the flexibility and comfort for the individual deteriorate the natural and urban environment for all. Density of development depends on mode of transport, with public transport allowing for better spatial use. Good land use keeps common activities close to people's homes and places higher-density development closer to transport lines and hubs, to minimize the need for transport. There are economies of agglomeration. Beyond transport, some land uses are more efficient when clustered. Transport facilities consume land, and in cities pavement (devoted to streets and parking) can easily exceed 20 percent of the total land use. An efficient transport system can reduce land waste.
Too much infrastructure and too much smoothing for maximum vehicle throughput mean that in many cities there is too much traffic and many—if not all—of the negative impacts that come with it. It is only in recent years that traditional practices have started to be questioned in many places; as a result of new types of analysis which bring in a much broader range of skills than those traditionally relied on—spanning such areas as environmental impact analysis, public health, sociology, and economics—the viability of the old mobility solutions is increasingly being questioned.
Environment
Transport is a major use of energy and burns most of the world's petroleum. This creates air pollution, including nitrous oxides and particulates, and is a significant contributor to global warming through emission of carbon dioxide, for which transport is the fastest-growing emission sector. By sub-sector, road transport is the largest contributor to global warming. Environmental regulations in developed countries have reduced individual vehicles' emissions; however, this has been offset by increases in the numbers of vehicles and in the use of each vehicle. Some pathways to reduce the carbon emissions of road vehicles considerably have been studied. Energy use and emissions vary largely between modes, causing environmentalists to call for a transition from air and road to rail and human-powered transport, as well as increased transport electrification and energy efficiency.
Other environmental impacts of transport systems include traffic congestion and automobile-oriented urban sprawl, which can consume natural habitat and agricultural lands. By reducing transport emissions globally, it is predicted that there will be significant positive effects on Earth's air quality, acid rain, smog, and climate change.
While electric cars are being built to cut down CO2 emission at the point of use, an approach that is becoming popular among cities worldwide is to prioritize public transport, bicycles, and pedestrian movement. Redirecting vehicle movement to create 20-minute neighbourhoods that promotes exercise while greatly reducing vehicle dependency and pollution. Some policies are levying a congestion charge to cars for travelling within congested areas during peak time.
Airplane emissions change depending on the flight distance. It takes a lot of energy to take off and land, so longer flights are more efficient per mile traveled. However, longer flights naturally use more fuel in total. Short flights produce the most per passenger mile, while long flights produce slightly less. Things get worse when planes fly high in the atmosphere. Their emissions trap much more heat than those released at ground level. This isn't just because of , but a mix of other greenhouse gases in the exhaust. City buses produce about 0.3 kg of for every mile traveled per passenger. For long-distance bus trips (over 20 miles), that pollution drops to about 0.08 kg of per passenger mile. On average, commuter trains produce around 0.17 kg of for each mile traveled per passenger. Long-distance trains are slightly higher at about 0.19 kg of per passenger mile. The fleet emission average for delivery vans, trucks and big rigs is per gallon of diesel consumed. Delivery vans and trucks average about 7.8 mpg (or 1.3 kg of per mile) while big rigs average about 5.3 mpg (or 1.92 kg of per mile).
Sustainable development
The United Nations first formally recognized the role of transport in sustainable development in the 1992 United Nations Earth summit. In the 2012 United Nations World Conference, global leaders unanimously recognized that transport and mobility are central to achieving the sustainability targets. In recent years, data has been collected to show that the transport sector contributes to a quarter of the global greenhouse gas emissions, and therefore sustainable transport has been mainstreamed across several of the 2030 Sustainable Development Goals, especially those related to food, security, health, energy, economic growth, infrastructure, and cities and human settlements. Meeting sustainable transport targets is said to be particularly important to achieving the Paris Agreement.
There are various Sustainable Development Goals (SDGs) that are promoting sustainable transport to meet the defined goals. These include SDG 3 on health (increased road safety), SDG 7 on energy, SDG 8 on decent work and economic growth, SDG 9 on resilient infrastructure, SDG 11 on sustainable cities (access to transport and expanded public transport), SDG 12 on sustainable consumption and production (ending fossil fuel subsidies), and SDG 14 on oceans, seas, and marine resources.
History
Natural
Humans' first ways to move included walking, running, and swimming. The domestication of animals introduced a new way to lay the burden of transport on more powerful creatures, allowing the hauling of heavier loads, or humans riding animals for greater speed and duration. Inventions such as the wheel and the sled (U.K. sledge) helped make animal transport more efficient through the introduction of vehicles.
The first forms of road transport involved animals, such as horses (domesticated in the 4th or the 3rd millennium BCE), oxen (from about 8000 BCE), or humans carrying goods over dirt tracks that often followed game trails.
Water transport
Water transport, including rowed and sailed vessels, dates back to time immemorial and was the only efficient way to transport large quantities or over large distances prior to the Industrial Revolution. The first watercraft were canoes cut out from tree trunks. Early water transport was accomplished with ships that were either rowed or used the wind for propulsion, or a combination of the two. The importance of water has led to most cities that grew up as sites for trading being located on rivers or on the sea-shore, often at the intersection of two bodies of water.
Mechanical
Until the Industrial Revolution, transport remained slow and costly, and production and consumption gravitated as close to each other as feasible. The Industrial Revolution in the 19th century saw several inventions fundamentally change transport. With telegraphy, communication became instant and independent of the transport of physical objects. The invention of the steam engine, closely followed by its application in rail transport, made land transport independent of human or animal muscles. Both speed and capacity increased, allowing specialization through manufacturing being located independently of natural resources. The 19th century also saw the development of the steam ship, which sped up global transport.
With the development of the combustion engine and the automobile around 1900, road transport became more competitive again, and mechanical private transport originated. The first "modern" highways were constructed during the 19th century with macadam. Later, tarmac and concrete became the dominant paving materials.
In 1903 the Wright brothers demonstrated the first successful controllable airplane, and after World War I (1914–1918) aircraft became a fast way to transport people and express goods over long distances.
After World War II (1939–1945) the automobile and airlines took higher shares of transport, reducing rail and water to freight and short-haul passenger services. Scientific spaceflight began in the 1950s, with rapid growth until the 1970s, when interest dwindled. In the 1950s the introduction of containerization gave massive efficiency gains in freight transport, fostering globalization. International air travel became much more accessible in the 1960s with the commercialization of the jet engine. Along with the growth in automobiles and motorways, rail and water transport declined in relative importance. After the introduction of the Shinkansen in Japan in 1964, high-speed rail in Asia and Europe started attracting passengers on long-haul routes away from the airlines.
Early in U.S. history, private joint-stock corporations owned most aqueducts, bridges, canals, railroads, roads, and tunnels. Most such transport infrastructure came under government control in the late 19th and early 20th centuries, culminating in the nationalization of inter-city passenger rail-service with the establishment of Amtrak. Recently, however, a movement to privatize roads and other infrastructure has gained some ground and adherents.
See also
Car-free movement
Energy efficiency in transport
Environmental impact of aviation
Free public transport
Green transport hierarchy
Health and environmental impact of transport
Health impact of light rail systems
IEEE Intelligent Transportation Systems Society
Journal of Transport and Land Use
List of emerging transportation technologies
Outline of transport
Personal rapid transit
Public transport
Public transport accessibility level
Rail transport by country
Speed record
Taxicabs by country
Transport divide
Transportation engineering
References
Bibliography
Further reading
McKibben, Bill, "Toward a Land of Buses and Bikes" (review of Ben Goldfarb, Crossings: How Road Ecology Is Shaping the Future of Our Planet, Norton, 2023, 370 pp.; and Henry Grabar, Paved Paradise: How Parking Explains the World, Penguin Press, 2023, 346 pp.), The New York Review of Books, vol. LXX, no. 15 (5 October 2023), pp. 30–32. "Someday in the not impossibly distant future, if we manage to prevent a global warming catastrophe, you could imagine a post-auto world where bikes and buses and trains are ever more important, as seems to be happening in Europe at the moment." (p. 32.)
External links
Transportation from UCB Libraries GovPubs
America On the Move An online transportation exhibition from the National Museum of American History, Smithsonian Institution
Economics of transport and utility industries
Logistics | Transport | Physics | 6,168 |
48,987,289 | https://en.wikipedia.org/wiki/Free%20stationing | In surveying, free stationing (also known as resection) is a method of determining a location of one unknown point in relation to known points. There is a zero point of reference called a total station. The instrument can be freely positioned so that all survey points are at a suitable sight from the instrument. When setting up the total station on a known point, it is often not possible to see all survey points of interest. When performing a resection (free stationing) with the total station, bearings and distances are measured to at least two known points of a control network. With use of a handheld computer, recorded data can be related to local polar coordinates, defined by the horizontal circle of the total station. By a geometric transformation, these polar coordinates are transformed to the coordinate system of the control network. Error can be distributed by least squares adjustment. Upon completion of observations and calculations, a coordinate is produced, and the position and orientation of the total station in relation to where the control network is established.
Comparison of methods
Angular resection and triangulation: only bearings are measured to the known points.
Trilateration: only distances are measured to the known points.
Free stationing and triangulateration: both bearings and distances are measured to the known points.
Naming
Because bearings and distances are measured in a full resection (free stationing), the result may have a different mathematical solution. This method has different names in other languages, e.g. in German: Freie Standpunktwahl (free stationing).
Naming is also regulated by the German Institute for Standardization DIN 18 709.
Different mathematical solution
By measuring bearings and distances, local polar coordinates are recorded. The orientation of this local polar coordinate system is defined by the 0° horizontal circle of the total station (polar axis L). The pole of this local polar coordinate system is the vertical axis (pole O) of the total stations. The polar coordinates (r,f) with the pole are transformed using surveying software on a data collector to the Cartesian coordinates (x,y) of the known points. The coordinates for the position of the total station are then calculated.
In a resection (triangulation) measuring bearings only, there can be a problem with an infinite number of solutions known as a "danger circle", or "inscribed angle theorem".
Back-sight points
The back-sight points of the control network should cover and surround the stationing site. The position of the total station is not part of the area. This is the area where you want to measure with this station setup. Topographic points or stakeout points should not be measured outside this area. If measured outside this area, the errors in orientation will be extrapolated instead of being interpolated.
While it is possible to use only two known control points in a resection (free stationing), it is recommended to use three control points. There is no redundancy for orientation, using two points only.
When performing a resection (free-stationing) on more than 4 points, diminishing returns are achieved in the returned results.
Advantages
The surveyor may freely set a station point:
Where there is best visibility to all points that must be staked out or recorded
Where there are no obstructions or traffic
Where there is the highest safety for the operator and the instrument
Because of the range and accuracy of total stations, the method of a resection (free stationing) permits a great freedom of positioning the total station. For this reason, this method is one of the most used station set ups.
Application
With the calculated coordinates and orientation of the total station, it can be used to set out points in construction surveying, machine guidance, site plan or other types of surveys.
References
External links
Topcon Magnet Field 1.0 Help
Leica SmartWorx Viva Field Software Datasheet
CarlsonSurvCE Reference Manual
12d Field – Helmert Resection
Trimble: Advantages and Disadvantages of the Stationing Programs
Trimble: Design of the Backsight Point Configuration
Trimble: Problems in Resection Without Redundancy
Trimble: The Influence of Weights in Resection
Trimble: Neighborhood Adjustment
Surveying
Surveying instruments
Geodesy
Civil engineering | Free stationing | Mathematics,Engineering | 858 |
38,320,611 | https://en.wikipedia.org/wiki/Deborah%20Temkin | Deborah A. Temkin (aka Deborah Temkin Cahill; born 1985) is an American child development and prevention research scientist, specializing in bullying prevention, school climate, and connecting education policy to healthy youth development. She was the Research and Policy Coordinator for Bullying Prevention Initiatives at the U.S. Department of Education from 2010 to 2012, where she was charged with coordinating the Obama administration's bullying prevention efforts, including launching StopBullying.gov. She was a finalist for the 2012 "Call to Service Medal" for the Samuel J. Heyman Service to America Medals for her work at the Department. Temkin is currently the vice president for youth development and education research at Child Trends.
Early life and education
Temkin grew up in Tucson, Arizona, where she was reportedly a victim of bullying while she was in middle school. Temkin describes the bullying she faced as having started over a feud over her middle school newspaper, which quickly escalated into relational, verbal, and physical bullying including social exclusion by a majority of her school-mates. In newspaper and radio interviews, Temkin reported that her personal experiences with bullying, and particularly her school's lack of response inspired her to understand bullying and what could be done to prevent it. Temkin graduated from Vassar College in 2007, where she majored in Psychology and Education Policy, and then went to The Pennsylvania State University where she received an M.A. in Education Theory and Policy and both her M.S. and Ph.D. in Human Development and Family Studies. Temkin was a Prevention and Methodology Pre-Doctoral Fellow through the Pennsylvania State University's Prevention and Methodology Centers, and her research focused on bullying, adolescent friendship networks, and education policy.
U.S. Department of Education and StopBullying.gov
In November 2009, Temkin attended the International Bullying Prevention Association Conference in Pittsburgh, Pennsylvania, where Kevin Jennings, then Assistant Deputy Secretary for the Office of Safe and Drug-Free Schools, was the keynote speaker. Temkin reportedly went up to Jennings following his speech and asked to work for him. Jennings offered Temkin an unpaid internship, which she began in January, 2010. During the Summer of 2010, Jennings charged Temkin with planning the first annual Federal Partners in Bullying Prevention Summit. After the successful event, Temkin was hired on into the first federal position dedicated to bullying prevention.
As attention to bullying grew in the fall of 2010, after a string of bullying related suicides, Jennings and Temkin began working closely with the White House to plan the first ever White House Conference on Bullying Prevention and to design and launch the government's central repository on bullying prevention, StopBullying.gov. Temkin also began work on several other initiatives, including closely managing the Federal Partners in Bullying Prevention, a coalition of 9 Federal departments, and launching research projects with the CDC and internally at the Department of Education to understand the definition of bullying and to understand the scope and impact of anti-bullying laws.
After Jennings left the Department of Education in July, 2011, Temkin continued to lead the bullying prevention initiatives, organizing the second and third annual Federal Partners in Bullying Prevention Summits in 2011 and 2012 and overseeing the relaunch of StopBullying.gov in April, 2012. During this time she also helped coordinate a partnership between the Department of Education and the Ad Council to launch a public service campaign targeted towards parents on the need to become "more than a bystander.". She also worked to support the release of a teacher training module on bullying. Temkin was also a featured speaker at several events, including the White House Conference on LGBT Families and a Townhall for Senator Frank Lautenberg as well as a trusted media source, quoted in several articles in major publications and appearing on radio and television programming.
In March, 2012 Temkin was named a finalist for the "Call to Service" medal of the Samuel J. Heyman Service to America Medals, recognizing the outstanding federal service of those under 35 years old.
Current position
Following her departure from the Department of Education, Temkin worked from 2012 to 2014 at the Robert F. Kennedy Center for Justice and Human Rights where she launched a new bullying prevention initiative, Project SEATBELT (Safe Environments Achieved Through Bullying prevention, Engagement, Leadership, & Teaching respect). Temkin is now the vice president for youth development and education research at Child Trends.
References
1985 births
Living people
Harassment and bullying | Deborah Temkin | Biology | 915 |
24,399,529 | https://en.wikipedia.org/wiki/C15H19NO3 | {{DISPLAYTITLE:C15H19NO3}}
The molecular formula C15H19NO3 may refer to:
Hydroxytropacocaine
3',4'-Methylenedioxy-α-pyrrolidinobutiophenone
Molecular formulas | C15H19NO3 | Physics,Chemistry | 59 |
54,157,502 | https://en.wikipedia.org/wiki/Reinforced%20Concrete%20Association | The Reinforced Concrete Association was a British engineering organisation. Many important British buildings in the twentieth century were made from reinforced concrete.
Function
It produced the journal Structural Concrete.
Presidents
1956–57, Sir Frederick Snow
Structure
In the 1930s it has headquartered on Dartmouth Street in London, then moved to Petty France, London in the 1950s.
References
Construction organizations
Organisations based in the City of Westminster
Reinforced concrete | Reinforced Concrete Association | Engineering | 78 |
32,164,037 | https://en.wikipedia.org/wiki/Hubert%20%C3%96sterle | Hubert Österle (born 24 June 1949, Dornbirn) is an Austrian academic, and Professor Emeritus of Business and Information Systems, and former director of the Institute of Information Management at the University of St. Gallen.
Career
Hubert Österle studied business administration at the University of Innsbruck and the Johannes Kepler Universität Linz. He obtained his PhD at the University of Erlangen-Nuremberg in 1973 with his dissertation “Computerunterstütztes Entscheidungstraining” (computer assisted decision training). After working as a consultant at IBM Germany, Österle completed his postdoctoral work (habilitation) on the "Design of information systems" at the Technical University of Dortmund in 1980.
In 1980 Österle became full professor of business and information systems engineering at the University of St. Gallen. In 1989, he founded the Institute of Information Management. In 1997 he initiated the executive MBA program "Business Engineering" at the University of St. Gallen. Österle was editor-in-chief of Electronic Markets and a member of the editorial boards of other journals. In March 2015 Österle received an honorary doctorate from the Wroclaw University of Economics.
Besides his academic achievements, Österle founded in 1989 the consultancy company "The Information Management Group" and the Business Engineering Institute St. Gallen AG in 2003. In addition, Österle is founder and president of the board of directors of the Amiona AG and a member of the supervisory board of the CDQ AG.
Research areas
Research areas of Österle are business engineering, consumerization, independent living, sourcing in the financial industry, corporate data quality and life engineering.
Selected publications
Books
Life Engineering: Machine Intelligence and Quality of Life, Springer, Wiesbaden 2020.
Corporate Data Quality: Prerequisite for Successful Business Models. (with Boris Otto), epubli, Berlin 2015.
IT-Driven Business Models (with Henning Kagermann and John M. Jordan), Wiley, Hoboken/NJ 2010.
Geschäftsmodelle 2010: Wie CEOs Unternehmen transformieren (with Henning Kagermann), FAZ, Frankfurt, 2006.
Real-Time Business: Lösungen, Bausteine und Potentiale des Business Networking (with Rainer Alt), Springer, Berlin 2004.
Customer Knowledge Management: Kundenwissen erfolgreich einsetzen (with Lutz M. Kolbe and Walter Brenner), Springer, Berlin 2003.
Business Engineering: Auf dem Weg zum Unternehmen im Informationszeitalter. (with Robert Winter), Springer, Berlin 2000 (2nd edition, 2003).
Business Networking: Shaping Collaboration between Enterprises (with Elgar Fleisch and Rainer Alt), Springer, Heidelberg 2000 (2nd edition, 2001).
Customer Relationship Management in der Praxis. (with Volker Bach), Springer, Berlin 2000.
Enabling Systematic Business Change: Integrated Methods and Software Tools for Business Process Redesign. (with Leo Brecht and Thomas Hess), Vieweg, Wiesbaden 1996.
Business in the Information Age: Heading for new Processes. Springer, Heidelberg, 1995.
Total Information Systems Management: A European Approach (with Walter Brenner and Konrad Hilbers), Wiley, Hoboken, New Jersey, 1994.
Unternehmensführung und Informationssystem: Der Ansatz des St. Galler Informationssystem-Managements. (with Walter Brenner and Konrad Hilbers), Teubner, Stuttgart, 1991 (2nd edition, 1992).
Entwurf betrieblicher Informationssysteme, Hanser, München 1980.
Selected articles
Towards an electronic marketplace for bricks-and-mortar services (with Peter Schenkel and Philipp Osl), Acis 2013 Proceedings (2013)
Toward a functional reference model for master data quality management (with Boris Otto and Kai Hüner), Information Systems and e-Business Management (2012)
Product data quality in supply chains: the case of Beiersdorf (with Kai Hüner, Andreas Schierning, and Boris Otto), Electronic Markets (2011)
Collaborative management of business metadata (with Kai Hüner and Boris Otto), International Journal of Information Management (2011)
Memorandum on design-oriented information system research (with Jörg Becker, Ulrich Frank, Thomas Hess, Dimitris Karagiannis, Helmut Krcmar, Peter Loos, Peter Mertens, Andreas Oberweis, and Elmar J. Sinz), European Journal of Information Systems (2010)
Management of the Master Data Lifecycle: A Framework for Analysis (with Martin Ofner, Kevin Straub, and Boris Otto), Journal of Enterprise Information Management (2004)
References
External links
Abschiedsvorlesung Prof. Dr. Hubert Österle, May 14, 2014 at iwi.unisg.ch (in German)
1949 births
Living people
Information systems researchers
Austrian business theorists
Austrian computer scientists
Academic staff of the University of St. Gallen
University of Erlangen-Nuremberg alumni
Academic journal editors | Hubert Österle | Technology | 1,058 |
47,840,549 | https://en.wikipedia.org/wiki/Fluopyram | Fluopyram is a fungicide and nematicide used in agriculture. It is used to control fungal diseases such as gray mold (Botrytis cinerea), powdery mildew, apple scab, Alternaria, Sclerotinia, and Monilinia. It is an inhibitor of succinate dehydrogenase (SDHI fungicide).
Developed and produced by Bayer, it was approved in 2012 by the U.S. Environmental Protection Agency and in 2013 it was approved in the EU for use as an active ingredient in pesticides.
References
Fungicides
Nematicides
Trifluoromethyl compounds
Benzamides
Chloropyridines | Fluopyram | Biology | 142 |
2,916,590 | https://en.wikipedia.org/wiki/Omega2%20Cancri | {{DISPLAYTITLE:Omega2 Cancri}}
ω2 Cancri is a star in the zodiac constellation Cancer, located around 810 light years away from the Sun. It has the Flamsteed designation 4 Cancri; ω2 Cancri is the Bayer designation, which is Latinised to omega2 Cancri and abbreviated to ω2 Cnc or omega2 Cnc. The star is near the lower limit of visibility to the naked eye, having an apparent visual magnitude of 6.32. It is moving closer to the Earth with a heliocentric radial velocity of −8 km/s. The position of this star near the ecliptic means it is subject to lunar occultations.
This is an ordinary A-type main-sequence star with a stellar classification of A1 V, which indicates it is generating energy through hydrogen fusion at its core. It has 2.6 times the mass of the Sun and about 2.5 times the Sun's radius. The star is radiating 68 times the Sun's luminosity from its photosphere at an effective temperature of 9354 K.
References
A-type main-sequence stars
Cancer (constellation)
Cancri, Omega2
BD+25 1816
Cancri, 04
065856
039263
3132 | Omega2 Cancri | Astronomy | 269 |
49,234,192 | https://en.wikipedia.org/wiki/Frank%20Garvan | Francis G. Garvan (born March 9, 1955) is an Australian-born mathematician who specializes in number theory and combinatorics. He holds the position Professor of Mathematics at the University of Florida. He received his Ph.D. from Pennsylvania State University (January, 1986) with George E. Andrews as his thesis advisor. Garvan's thesis, Generalizations of Dyson's rank, concerned the rank of a partition and formed the groundwork for several of his later papers.
Garvan is well-known for his work in the fields of q-series and integer partitions. Most famously, in 1988, Garvan and Andrews discovered a definition of the crank of a partition. The crank of a partition is an elusive combinatorial statistic similar to the rank of a partition which provides a key to the study of Ramanujan congruences in partition theory. It was first described by Freeman Dyson in a paper on ranks for the journal Eureka in 1944. Andrews and Garvan's definition was the first definition of a crank to satisfy the properties hypothesized for it in Dyson's paper.
References
External links
http://people.clas.ufl.edu/fgarvan/
1955 births
Living people
20th-century American mathematicians
21st-century American mathematicians
Australian mathematicians
Number theorists
University of Florida faculty | Frank Garvan | Mathematics | 283 |
34,956,689 | https://en.wikipedia.org/wiki/Holospondyli | Holospondyli is a proposed clade of lepospondyls from the Early Carboniferous to the Late Permian that includes the aistopods, the paraphyletic nectrideans, and possibly also Adelospondyli. However, aistopods have since been recovered as stem-tetrapods more primitive than temnospondyls or other groups of lepospondyls.
References
Stegocephalians
Polyphyletic groups | Holospondyli | Biology | 102 |
28,341,819 | https://en.wikipedia.org/wiki/Redundant%20Array%20of%20Inexpensive%20Servers | A Redundant Array of Inexpensive Servers (RAIS) or Redundant Array of Independent Nodes (RAIN) is the use of multiple servers to maintain service if one server fails. This is similar in concept to how RAID turns a cluster of ordinary disks into a single block device. RAIS was designed to provide the benefits of a symmetric multiprocessor system (SMP) at the entry cost of computer clusters.
The term may imply some kind of load balancing between the servers.
Technology
RAIS is a simple, high performance, mainframe-grade alternative to more expensive enterprise computing infrastructure solutions. It turns an array of ordinary servers into a single virtual machine, similar in concept to how RAID turns a cluster of ordinary disks into a single block device. Every RAIS node is a stateless computing unit. RAIS stripes and mirrors application code and memory across an array of ordinary servers using the standard RAID schemata of level 0, level 1, level 5, level 1+0. This is possible through a memory management system called Versioned Memory.
Data blocks of each stream are striped across the array servers. A fast packet switch is used to connect server and client stations. Each server has a dedicated network segment, and each client contacts the server one by one. Each server has its own storage, CPU, and network segment. The server capacity increases with the number of servers.
In a manner more usually associated with high cost SMP architectures, RAIS achieves this by turning a cluster of independent servers into a single large server running applications across a virtualised network of nodes. The concept is similar to how RAID stripes and mirrors data across multiple independent disks and code of an application program across multiple independent nodes of a cluster. The applications see only a single logical shared memory which functions as a binary compatible SMP system.
If the data is split into segments and distributed between multiple storage providers, the technology has applications for improving confidentiality in cloud computing.
See also
Disk array controller
Disk Data Format (DDF)
Vinum volume manager
References
Servers (computing) | Redundant Array of Inexpensive Servers | Technology | 413 |
2,909,281 | https://en.wikipedia.org/wiki/Upjohn | The Upjohn Company was an American pharmaceutical manufacturing firm (est. 1886) in Hastings, Michigan, by Dr. William E. Upjohn, a 1875 graduate of the University of Michigan medical school. The company was originally formed to make friable pills, specifically designed to crush easily, and thus be easier for patients to digest. Upjohn initially marketed the pills to doctors by sending them a wooden plank along with a rival’s pill and one of Upjohn’s, with instructions to try to hammer the pills into the plank.
History
Upjohn developed a process for the large scale production of cortisone. The oxygen atom group must be in position 11 for this steroid to function. There are, however, no known natural starting materials with an oxo-group in position 11. The only method for preparing cortisone prior to 1952 was a lengthy synthesis, starting from cholic acid isolated from bile. In 1952, two Upjohn biochemists, Dury Peterson and Herb Murray, announced that they had invented a new method by fermenting the steroid progesterone with a common mold of the genus Rhizopus. Over the next several years, a group of chemists headed by John Hogg developed a process for preparing cortisone from the soybean sterol stigmasterol. The microbiological oxygenation invented by Peterson and Murry is a key step in this process.
Subsequently, Upjohn (together with Schering) biochemically converted cortisone into the more potent steroid prednisone via bacterial fermentation. In chemical research, the company is known for the development of the Upjohn dihydroxylation by V. VanRheenen, R. C. Kelly, and D. Y. Cha in 1976. Upjohn's best known drugs before its acquisition by Pfizer were Xanax, Halcion, Motrin, Lincocin, and Rogaine.
In 1995, Upjohn merged with Pharmacia AB to form Pharmacia & Upjohn. The company was owned by Pfizer from 2002 until 2020.
In 2015, Pfizer resurrected the Upjohn brand name for a division which manufactures and licenses drugs with patents that have expired. Pfizer planned to divest itself of this business in 2020.
In July 2019, Pfizer announced plans to merge Upjohn with Mylan. The merger was expected to close in the first half of 2020, was delayed due to the COVID-19 pandemic, and finally completed in November 2020. The resultant entity was named Viatris.
See also
W. E. Upjohn Institute for Employment Research
Upjohn Co. v. United States (449 U.S. 383) (1981)
References
External links
Memories of The Upjohn Company
1886 establishments in Michigan
1995 disestablishments in Michigan
1995 mergers and acquisitions
Companies based in Kalamazoo, Michigan
Pharmaceutical companies established in 1886
Pharmaceutical companies disestablished in 1995
Defunct pharmaceutical companies of the United States
Pfizer
Life sciences industry | Upjohn | Biology | 646 |
16,311,904 | https://en.wikipedia.org/wiki/17%20Leporis | 17 Leporis is a binary star system in the southern constellation of Lepus. It has an overall apparent visual magnitude which varies between 4.82 and 5.06, making it luminous enough to be visible to the naked eye as a faint star. The variable star designation for this system is SS Leporis, while 17 Leporis is the Flamsteed designation. Parallax measurements yield a distance estimate of around 910 light years from the Sun. The system is moving further away from the Earth with a heliocentric radial velocity of +18.7 km/s.
This is a double-lined spectroscopic binary system with an orbital period of 260 days and an eccentricity of 0.005. The spectrum reveals the pair to consist of an A-type main-sequence star with a stellar classification of A1 V, and a red giant with a class of M6III. The close pair form a symbiotic binary with ongoing mass transfer from the giant to the hotter component. The giant does not appear to be filling its Roche lobe, so the mass transfer is coming from stellar wind off the giant. The pair are surrounded by a shell and a dusty circumbinary disk, with the former obliterating the lines from the A-type star.
Gallery
References
A-type main-sequence stars
M-type giants
Emission-line stars
Circumstellar disks
Lepus (constellation)
BD-16 1349
Leporis, 17
041511
028816
2148
Leporis, SS
Articles containing video clips
Spectroscopic binaries | 17 Leporis | Astronomy | 326 |
744,569 | https://en.wikipedia.org/wiki/Stone%E2%80%93von%20Neumann%20theorem | In mathematics and in theoretical physics, the Stone–von Neumann theorem refers to any one of a number of different formulations of the uniqueness of the canonical commutation relations between position and momentum operators. It is named after Marshall Stone and John von Neumann.
Representation issues of the commutation relations
In quantum mechanics, physical observables are represented mathematically by linear operators on Hilbert spaces.
For a single particle moving on the real line , there are two important observables: position and momentum. In the Schrödinger representation quantum description of such a particle, the position operator and momentum operator are respectively given by
on the domain of infinitely differentiable functions of compact support on . Assume to be a fixed non-zero real number—in quantum theory is the reduced Planck constant, which carries units of action (energy times time).
The operators , satisfy the canonical commutation relation Lie algebra,
Already in his classic book, Hermann Weyl observed that this commutation law was impossible to satisfy for linear operators , acting on finite-dimensional spaces unless vanishes. This is apparent from taking the trace over both sides of the latter equation and using the relation ; the left-hand side is zero, the right-hand side is non-zero. Further analysis shows that any two self-adjoint operators satisfying the above commutation relation cannot be both bounded (in fact, a theorem of Wielandt shows the relation cannot be satisfied by elements of any normed algebra). For notational convenience, the nonvanishing square root of may be absorbed into the normalization of and , so that, effectively, it is replaced by 1. We assume this normalization in what follows.
The idea of the Stone–von Neumann theorem is that any two irreducible representations of the canonical commutation relations are unitarily equivalent. Since, however, the operators involved are necessarily unbounded (as noted above), there are tricky domain issues that allow for counter-examples. To obtain a rigorous result, one must require that the operators satisfy the exponentiated form of the canonical commutation relations, known as the Weyl relations. The exponentiated operators are bounded and unitary. Although, as noted below, these relations are formally equivalent to the standard canonical commutation relations, this equivalence is not rigorous, because (again) of the unbounded nature of the operators. (There is also a discrete analog of the Weyl relations, which can hold in a finite-dimensional space, namely Sylvester's clock and shift matrices in the finite Heisenberg group, discussed below.)
Uniqueness of representation
One would like to classify representations of the canonical commutation relation by two self-adjoint operators acting on separable Hilbert spaces, up to unitary equivalence. By Stone's theorem, there is a one-to-one correspondence between self-adjoint operators and (strongly continuous) one-parameter unitary groups.
Let and be two self-adjoint operators satisfying the canonical commutation relation, , and and two real parameters. Introduce and , the corresponding unitary groups given by functional calculus. (For the explicit operators and defined above, these are multiplication by and pullback by translation .) A formal computation (using a special case of the Baker–Campbell–Hausdorff formula) readily yields
Conversely, given two one-parameter unitary groups and satisfying the braiding relation
formally differentiating at 0 shows that the two infinitesimal generators satisfy the above canonical commutation relation. This braiding formulation of the canonical commutation relations (CCR) for one-parameter unitary groups is called the Weyl form of the CCR.
It is important to note that the preceding derivation is purely formal. Since the operators involved are unbounded, technical issues prevent application of the Baker–Campbell–Hausdorff formula without additional domain assumptions. Indeed, there exist operators satisfying the canonical commutation relation but not the Weyl relations (). Nevertheless, in "good" cases, we expect that operators satisfying the canonical commutation relation will also satisfy the Weyl relations.
The problem thus becomes classifying two jointly irreducible one-parameter unitary groups and which satisfy the Weyl relation on separable Hilbert spaces. The answer is the content of the Stone–von Neumann theorem: all such pairs of one-parameter unitary groups are unitarily equivalent. In other words, for any two such and acting jointly irreducibly on a Hilbert space , there is a unitary operator so that
where and are the explicit position and momentum operators from earlier. When is in this equation, so, then, in the -representation, it is evident that is unitarily equivalent to , and the spectrum of must range along the entire real line. The analog argument holds for .
There is also a straightforward extension of the Stone–von Neumann theorem to degrees of freedom.
Historically, this result was significant, because it was a key step in proving that Heisenberg's matrix mechanics, which presents quantum mechanical observables and dynamics in terms of infinite matrices, is unitarily equivalent to Schrödinger's wave mechanical formulation (see Schrödinger picture),
Representation theory formulation
In terms of representation theory, the Stone–von Neumann theorem classifies certain unitary representations of the Heisenberg group. This is discussed in more detail in the Heisenberg group section, below.
Informally stated, with certain technical assumptions, every representation of the Heisenberg group is equivalent to the position operators and momentum operators on . Alternatively, that they are all equivalent to the Weyl algebra (or CCR algebra) on a symplectic space of dimension .
More formally, there is a unique (up to scale) non-trivial central strongly continuous unitary representation.
This was later generalized by Mackey theory – and was the motivation for the introduction of the Heisenberg group in quantum physics.
In detail:
The continuous Heisenberg group is a central extension of the abelian Lie group by a copy of ,
the corresponding Heisenberg algebra is a central extension of the abelian Lie algebra (with trivial bracket) by a copy of ,
the discrete Heisenberg group is a central extension of the free abelian group by a copy of , and
the discrete Heisenberg group modulo is a central extension of the free abelian -group by a copy of .
In all cases, if one has a representation , where is an algebra and the center maps to zero, then one simply has a representation of the corresponding abelian group or algebra, which is Fourier theory.
If the center does not map to zero, one has a more interesting theory, particularly if one restricts oneself to central representations.
Concretely, by a central representation one means a representation such that the center of the Heisenberg group maps into the center of the algebra: for example, if one is studying matrix representations or representations by operators on a Hilbert space, then the center of the matrix algebra or the operator algebra is the scalar matrices. Thus the representation of the center of the Heisenberg group is determined by a scale value, called the quantization value (in physics terms, the Planck constant), and if this goes to zero, one gets a representation of the abelian group (in physics terms, this is the classical limit).
More formally, the group algebra of the Heisenberg group over its field of scalars K, written , has center , so rather than simply thinking of the group algebra as an algebra over the field , one may think of it as an algebra over the commutative algebra . As the center of a matrix algebra or operator algebra is the scalar matrices, a -structure on the matrix algebra is a choice of scalar matrix – a choice of scale. Given such a choice of scale, a central representation of the Heisenberg group is a map of -algebras , which is the formal way of saying that it sends the center to a chosen scale.
Then the Stone–von Neumann theorem is that, given the standard quantum mechanical scale (effectively, the value of ħ), every strongly continuous unitary representation is unitarily equivalent to the standard representation with position and momentum.
Reformulation via Fourier transform
Let be a locally compact abelian group and be the Pontryagin dual of . The Fourier–Plancherel transform defined by
extends to a C*-isomorphism from the group C*-algebra of and , i.e. the spectrum of is precisely . When is the real line , this is Stone's theorem characterizing one-parameter unitary groups. The theorem of Stone–von Neumann can also be restated using similar language.
The group acts on the *-algebra by right translation : for in and in ,
Under the isomorphism given above, this action becomes the natural action of on :
So a covariant representation corresponding to the *-crossed product
is a unitary representation of and of such that
It is a general fact that covariant representations are in one-to-one correspondence with *-representation of the corresponding crossed product. On the other hand, all irreducible representations of
are unitarily equivalent to the , the compact operators on . Therefore, all pairs are unitarily equivalent. Specializing to the case where yields the Stone–von Neumann theorem.
Heisenberg group
The above canonical commutation relations for , are identical to the commutation relations that specify the Lie algebra of the general Heisenberg group for a positive integer. This is the Lie group of square matrices of the form
In fact, using the Heisenberg group, one can reformulate the Stone von Neumann theorem in the language of representation theory.
Note that the center of consists of matrices . However, this center is not the identity operator in Heisenberg's original CCRs. The Heisenberg group Lie algebra generators, e.g. for , are
and the central generator is not the identity.
All these representations are unitarily inequivalent; and any irreducible representation which is not trivial on the center of is unitarily equivalent to exactly one of these.
Note that is a unitary operator because it is the composition of two operators which are easily seen to be unitary: the translation to the left by and multiplication by a function of absolute value 1. To show is multiplicative is a straightforward calculation. The hard part of the theorem is showing the uniqueness; this claim, nevertheless, follows easily from the Stone–von Neumann theorem as stated above. We will sketch below a proof of the corresponding Stone–von Neumann theorem for certain finite Heisenberg groups.
In particular, irreducible representations , of the Heisenberg group which are non-trivial on the center of are unitarily equivalent if and only if for any in the center of .
One representation of the Heisenberg group which is important in number theory and the theory of modular forms is the theta representation, so named because the Jacobi theta function is invariant under the action of the discrete subgroup of the Heisenberg group.
Relation to the Fourier transform
For any non-zero , the mapping
is an automorphism of which is the identity on the center of . In particular, the representations and are unitarily equivalent. This means that there is a unitary operator on such that, for any in ,
Moreover, by irreducibility of the representations , it follows that up to a scalar, such an operator is unique (cf. Schur's lemma). Since is unitary, this scalar multiple is uniquely determined and hence such an operator is unique.
This means that, ignoring the factor of in the definition of the Fourier transform,
This theorem has the immediate implication that the Fourier transform is unitary, also known as the Plancherel theorem. Moreover,
From this fact the Fourier inversion formula easily follows.
Example: Segal–Bargmann space
The Segal–Bargmann space is the space of holomorphic functions on that are square-integrable with respect to a Gaussian measure. Fock observed in 1920s that the operators
acting on holomorphic functions, satisfy the same commutation relations as the usual annihilation and creation operators, namely,
In 1961, Bargmann showed that is actually the adjoint of with respect to the inner product coming from the Gaussian measure. By taking appropriate linear combinations of and , one can then obtain "position" and "momentum" operators satisfying the canonical commutation relations. It is not hard to show that the exponentials of these operators satisfy the Weyl relations and that the exponentiated operators act irreducibly. The Stone–von Neumann theorem therefore applies and implies the existence of a unitary map from to the Segal–Bargmann space that intertwines the usual annihilation and creation operators with the operators and . This unitary map is the Segal–Bargmann transform.
Representations of finite Heisenberg groups
The Heisenberg group is defined for any commutative ring . In this section let us specialize to the field for a prime. This field has the property that there is an embedding of as an additive group into the circle group . Note that is finite with cardinality . For finite Heisenberg group one can give a simple proof of the Stone–von Neumann theorem using simple properties of character functions of representations. These properties follow from the orthogonality relations for characters of representations of finite groups.
For any non-zero in define the representation on the finite-dimensional inner product space by
It follows that
By the orthogonality relations for characters of representations of finite groups this fact implies the corresponding Stone–von Neumann theorem for Heisenberg groups , particularly:
Irreducibility of
Pairwise inequivalence of all the representations .
Actually, all irreducible representations of on which the center acts nontrivially arise in this way.
Generalizations
The Stone–von Neumann theorem admits numerous generalizations. Much of the early work of George Mackey was directed at obtaining a formulation of the theory of induced representations developed originally by Frobenius for finite groups to the context of unitary representations of locally compact topological groups.
See also
Oscillator representation
Wigner–Weyl transform
CCR and CAR algebras (for bosons and fermions respectively)
Segal–Bargmann space
Moyal product
Weyl algebra
Stone's theorem on one-parameter unitary groups
Hille–Yosida theorem
C0-semigroup
Notes
References
Rosenberg, Jonathan (2004) "A Selective History of the Stone–von Neumann Theorem" Contemporary Mathematics 365. American Mathematical Society.
Summers, Stephen J. (2001). "On the Stone–von Neumann Uniqueness Theorem and Its Ramifications." In John von Neumann and the foundations of quantum physics, pp. 135-152. Springer, Dordrecht, 2001, online.
Functional analysis
Mathematical quantization
Theorems in functional analysis
Theorems in mathematical physics
John von Neumann | Stone–von Neumann theorem | Physics,Mathematics | 3,054 |
9,302,182 | https://en.wikipedia.org/wiki/Watson%20interferometer | The Watson interferometer is a vintage microscope accessory (for use only in reflected light microscopy) which was manufactured by the Watson Company in Great Britain. It is a variant of Michelson interferometer that can be installed on a conventional microscope. It consists of a beam splitter and varying the distance between the specimen surface and the image of the reference mirror creates interference fringes. For transmitted light investigations in biology, the C. Watson company produced the Smith/Baker system in the 1950s.
References
Interferometers | Watson interferometer | Technology,Engineering | 105 |
16,548,097 | https://en.wikipedia.org/wiki/Walkman%20effect | The Walkman effect is the way music listened to via headphones grants the listener more control over their environment. The term was coined by Shuhei Hosokawa, a professor at the International Research Center for Japanese Studies, in an article published in Popular Music in 1984. While the term was named after the dominant portable music technology of the time, the Sony Walkman, it generically applies to all such devices and has been cited numerous times to refer to similar products released later, such as the Apple iPod.
History
When Sony released the first Walkmans, they featured two headphone jacks and a "hotline" switch. When pressed, this button activated a microphone and lowered the volume to enable those listening to have a conversation without removing their headphones. Sony Chairman Akio Morita added these features to the design for fear the technology would be isolating. Although Morita "thought it would be considered rude for one person to be listening to his music in isolation", people bought their own units rather than share and these features were removed for later models.
Autonomy
The initial Walkman marketing campaign showcased the freedom it brought. The first presentation to the press involved young people riding bikes and skateboarding while listening to Walkmans. Hosokawa points to this ability to listen to music do something else as making those experiences more pleasurable. The Walkman, he says, the "autonomy-of-the-walking-self."
Sony's vice president in charge of audio products said that Walkman's achievement was that it "provided listeners with a personal soundtrack to their lives", allowing its users "to make even the most boring daily activities interesting, adding a bit of personal style to everything they do."
University of Sussex Professor Michael Bull (aka "Professor iPod") argues that a personal stereo changes the way its user processes the world, allowing for greater confidence and control over personal experiences in space and time. From an interview in Wired: "People like to control their environment, and the iPod is the perfect way to manage your experience. Music is the most powerful medium for thought, mood and movement control." Basically, Bull describes how music empowers the listener because of what one is now enabled to do, which is to "inhabit" the space in which they move. Controlling one's own space is the power of the Walkman effect, which then causes no dead air, giving the user more power through their music.
Urban strategy
The appeal of personal experience management seems to be strongest in cities. As Hosokawa puts it, "To think about [the Walkman effect] is to reflect on the urban itself: [W]alkman as urban strategy, as urban sonic/musical device." The very nature of an urban environment is such that the potential for chance encounters and unpredictable human interactions is omnipresent. Whereas someone's attention is fair game while simply walking down the street, riding on the subway, or sitting on a bench to rest, one can appear busy and engaged when doing these activities while listening to music, making any attempt at communication effectively an interruption. Those who might otherwise be willing to interrupt may be further deterred by the fact that there is a good chance they won't even be heard, rendering their effort futile or embarrassing. Even if the interrupter is heard, it is easy for the listener to act as if they weren't. Headphones enable listeners to float through public areas in a protective bubble, actively tuning in or out who or what they want.
One specific effect noted by both Patton and Bull is what Bull calls "auditized looking", the ability of those listening to a personal stereo to make or escape eye contact with others in ways they would not otherwise. Traditional messages carried by eye contact are, to some extent, dissolved by the music's protective bubble, with the listener seen as unavailable.
Criticism
The Walkman was the first of a long line of mobile devices to attract criticism for isolating its users, promoting narcissism, detachment, and rude behavior, while at the same time preventing interactions that are the basis for traditional place-based communities.
In his phenomenological analysis of this effect, Rainer Schönhammer argues that wearing headphones interrupts a form of contact between people in a shared situation, even if there is no explicit communication, thereby violating "an unwritten law of interpersonal reciprocity: the certainty of common sensual presence in shared situations." He goes on to draw a similarity with the wearing of dark sunglasses, which irritates because there is an inequality in the balance of looking at and being looked at. Similarly, according to Hosokawa, Walkman users blatantly "confess" that they have a secret (something that you can not hear), which can cause negative feelings in observers.
Both men, however, make an effort to counter negative accusations of detachment, isolation, and narcissism. Perhaps most importantly, Walkman listeners are generally happier, more confident, and calmer. The users are "unified in the autonomous and singular moment—neither as persons nor as individuals—with the real," when "absence does not mean that the world is no longer worth attention. On the contrary, the subject's disengagement sets him free to enjoy the world attentively as a colorful and rich spectacle."
See also
Networked individualism
Space of flows
References
Computing and society
1984 neologisms | Walkman effect | Technology | 1,105 |
8,140,632 | https://en.wikipedia.org/wiki/Midkine | Midkine (MK or MDK), also known as neurite growth-promoting factor 2 (NEGF2), is a protein that in humans is encoded by the MDK gene.
Midkine is a basic heparin-binding growth factor of low molecular weight, and forms a family with pleiotrophin (NEGF1, 46% homologous with MK). It is a nonglycosylated protein, composed of two domains held by disulfide bridges. It is a developmentally important retinoic acid-responsive gene product strongly induced during mid-gestation, hence the name midkine. Restricted mainly to certain tissues in the normal adult, it is strongly induced during oncogenesis, inflammation and tissue repair.
MK is pleiotropic, capable of exerting activities such as cell proliferation, cell migration, angiogenesis and fibrinolysis. A molecular complex containing receptor-type tyrosine phosphatase zeta (PTPζ), low density lipoprotein receptor-related protein (LRP1), anaplastic leukemia kinase (ALK) and syndecans is considered to be its receptor.
Role in cancer
MK appears to enhance the angiogenic and proliferative activities of cancer cells. The expression of MK (mRNA and protein expression) has been found to be elevated in multiple cancer types, such as neuroblastoma, glioblastoma, Wilms' tumors, thyroid papillary carcinomas, colorectal, liver, ovary, bladder, breast, lung, esophageal, stomach, and prostate cancers. Serum MK in normal individuals is usually less than 0.5-0.6 ng/ml, whereas patients with these malignancies have much higher levels than this. In some cases, these elevated levels of MK also indicate a poorer prognosis of the disease, such as in neuroblastoma, glioblastoma, and bladder carcinomas. In neuroblastoma, for example, the levels of MK are elevated about three times the level in Stage 4 of the cancer (one of the final stages) than they are in Stage 1.
In neuroblastoma, MK has been found to be over expressed in the cancer cells that are resistant to chemotherapeutic drugs. The resistance to chemotherapy seems to be reversible by administering chemo-resensitization drugs, such as verapamil, which acts not via MK alteration, but by inhibiting the P-glycoprotein pump that exports cytotoxins out of cells. Since chemotherapeutic drugs are cytotoxic, the drugs administered are also exported by this pump, rendering the chemotherapy ineffective. It has been found that when the neuroblastoma cells that are resistant to chemotherapy are grown in co-culture with the wild type (WT), or chemotherapy-sensitive cells, the resistance to chemotherapy is conferred to the wild type cells, and thus no cell death or senescence occurs in either cell type, despite the chemotherapeutic treatment. MK has been identified as one of the factors that "transfers" this chemoresistance from the resistant cells to the WT cells.
MK is a secreted protein, and is therefore found in the microenvironment (media) of the resistant neuroblastoma cells. Following co-culture experiments and the determination that MK was one of the factors that was conferring chemo-resistance to the wild, non-resistant cell type, the gene for MK was transfected into WT cells to determine if MK was overexpressed in the WT cells themselves, would the cells become resistant to chemotherapy independent of resistant cell influence. The tests further confirmed that MK specifically increased chemotherapeutic resistance in the transfected WT-MK cells versus regular WT cells, confirming the specific chemoresistant properties of MK.
In addition, the mechanism for such anti-apoptotic (anti-cell death) activity was studied, specifically using the chemotherapeutic Doxorubicin (Adriamycin) on osteosarcoma (Saos2) cells. Doxorubicin works by putting rampant cancer cells into a senescent state. MK, in WT-MK transfected cells versus WT cells, seemed to activate PKB (Akt), mTOR, and Bad protein, while it inactivated caspase-3. PKB, mTOR, and Bad are all elements associated with the cell cycle survival pathway, whereas caspase-3 is important in the apoptotic pathway (cell death). This indicates that MK caused the cells to initiate the survival pathway (via PKB, mTOR, and Bad activation) and inhibit the senescent or apoptotic pathway (via inhibiting caspase-3) encouraging the chemoresistance seen in resistant cells and in the co-culture experiments. The activation and inhibition of these particular factors clearly is maintaining the immortal quality inherent in cancer cells and specifically in the resistant cell types. Stat-3, however, which is another survival pathway factor, does not appear to have any change in activation between the wild type cells and the MK-transfected WT cells, as was initially believed from a previous study.
MK may potentially be indirectly targeted as a cancer treatment as a result of its cancerous proliferation properties. Drugs by the name of anti-cancer aptamers have been created to inhibit to proteins involved in MK's cancer cell "activation". Specifically, the extra-cellular matrix (ECM) protein nucleolin has been targeted with an aptamer that would bind nucleolin and prevent MK from being transported into cancerous cell nuclei, preventing the protein from enhancing the cancerous properties of the cell. Miyakawa et al. have successfully established the method to prepare the MDK specific RNA aptamers by the use of the recombinant midkine and pleiotrophin.
Mdk is also a tumor antigen able to induce CD8 and CD4 T cell responses (Kerzerho et al. 2010 Journal of Immunology).
HIV infection
Midkine binds to cell-surface nucleolin as a low affinity receptor. This binding can inhibit HIV infection.
Trivia
In the Japanese film "L: Change the World", Midkine is used as a major plot element, as it is used in a vaccine to treat the ebola virus combined with influenza, from spreading.
References
Further reading
External links
Proteins
Human proteins | Midkine | Chemistry | 1,382 |
34,961,349 | https://en.wikipedia.org/wiki/Buchsbaum%20ring | In mathematics, Buchsbaum rings are Noetherian local rings such that every system of parameters is a weak sequence.
A sequence of the maximal ideal is called a weak sequence if for all .
They were introduced by and are named after David Buchsbaum.
Every Cohen–Macaulay local ring is a Buchsbaum ring. Every Buchsbaum ring is a generalized Cohen–Macaulay ring.
References
Commutative algebra
Ring theory | Buchsbaum ring | Mathematics | 89 |
30,109,600 | https://en.wikipedia.org/wiki/Parataxonomy | Parataxonomy is a system of labor division for use in biodiversity research, in which the rough sorting tasks of specimen collection, field identification, documentation and preservation are conducted by primarily local, less specialized individuals, thereby alleviating the workload for the "alpha" or "master" taxonomist. Parataxonomy may be used to improve taxonomic efficiency by enabling more expert taxonomists to restrict their activity to the tasks that require their specialist knowledge and skills, which has the potential to expedite the rate at which new taxa may be described and existing taxa may be sorted and discussed. Parataxonomists generally work in the field, sorting collected samples into recognizable taxonomic units (RTUs) based on easily recognized features. The process can be used alone for rapid assessment of biodiversity.
Some researchers consider reliance on parataxonomist-generated data to be prone to error depending on the sample, the sorter and the group of organisms in question. Therefore, quantitative studies based on parataxonomic processes may be unreliable and is therefore controversial. Today, the concepts of citizen science and parataxonomy are somewhat overlapping, with unclear distinctions between those employed to provide supplemental services to taxonomists and those who do so voluntarily, whether for personal enrichment or the altruistic desire to make substantive scientific contributions. These terms are occasionally used interchangeably, but some taxonomists maintain that each possess unique differences.
History of concept
A "parataxonomist" is a term coined by Dr. Daniel Janzen and Dr. Winnie Hallwachs in the late 1980s who used it to describe the role of assistants working at INBio in Costa Rica. It describes a person who collects specimens for ecological studies as well as the basic information for a specimen as it is being collected in the field. Information they collect includes date, location (lat/long), collector's name, the species of plant and caterpillar if known, and each specimen is assigned a unique voucher code. The term was a play on the word "paramedic", someone who can operate independently, may not have a specialized university degree, but has some taxonomic training.
Hallwachs and Janzen created and implemented an intensive six-month course that taught everything from taxonomy to how to operate a chainsaw. Dr. Janzen trained the first cohort in January 1989, additional cohorts receiving training up until 1992. From 1992 onward, all other training was conducted by parataxonomists. As of 2017, some 10,000 new species in the Area de Conservacion Guanacaste have been identified thanks to the efforts of parataxonomists.
During the time period that Janzen's parataxonomic model was in place, INBio became the second largest biological collection in Latin America with over 3.5 million collections, all of which were digitized. As of 2015, the institute had produced over 2,500 scientific articles, 250 books and 316 conventions. Its website logged an average of 25,000 unique visitors daily from 125 countries, and its park had received upwards of 15 million visitors.
See also
Folk taxonomy
Citizen science
References
External links
Biological nomenclature
Taxonomy (biology)
Research methods | Parataxonomy | Biology | 653 |
21,402,632 | https://en.wikipedia.org/wiki/Electroencephalography | Electroencephalography (EEG)
is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex. It is typically non-invasive, with the EEG electrodes placed along the scalp (commonly called "scalp EEG") using the International 10–20 system, or variations of it. Electrocorticography, involving surgical placement of electrodes, is sometimes called "intracranial EEG". Clinical interpretation of EEG recordings is most often performed by visual inspection of the tracing or quantitative EEG analysis.
Voltage fluctuations measured by the EEG bioamplifier and electrodes allow the evaluation of normal brain activity. As the electrical activity monitored by EEG originates in neurons in the underlying brain tissue, the recordings made by the electrodes on the surface of the scalp vary in accordance with their orientation and distance to the source of the activity. Furthermore, the value recorded is distorted by intermediary tissues and bones, which act in a manner akin to resistors and capacitors in an electrical circuit. This means that not all neurons will contribute equally to an EEG signal, with an EEG predominately reflecting the activity of cortical neurons near the electrodes on the scalp. Deep structures within the brain further away from the electrodes will not contribute directly to an EEG; these include the base of the cortical gyrus, mesial walls of the major lobes, hippocampus, thalamus, and brain stem.
A healthy human EEG will show certain patterns of activity that correlate with how awake a person is. The range of frequencies one observes are between 1 and 30 Hz, and amplitudes will vary between 20 and 100 μV. The observed frequencies are subdivided into various groups: alpha (8–13 Hz), beta (13–30 Hz), delta (0.5–4 Hz), and theta (4–7 Hz). Alpha waves are observed when a person is in a state of relaxed wakefulness and are mostly prominent over the parietal and occipital sites. During intense mental activity, beta waves are more prominent in frontal areas as well as other regions. If a relaxed person is told to open their eyes, one observes alpha activity decreasing and an increase in beta activity. Theta and delta waves are not generally seen in wakefulness - if they are, it is a sign of brain dysfunction.
EEG can detect abnormal electrical discharges such as sharp waves, spikes, or spike-and-wave complexes, as observable in people with epilepsy; thus, it is often used to inform medical diagnosis. EEG can detect the onset and spatio-temporal (location and time) evolution of seizures and the presence of status epilepticus. It is also used to help diagnose sleep disorders, depth of anesthesia, coma, encephalopathies, cerebral hypoxia after cardiac arrest, and brain death. EEG used to be a first-line method of diagnosis for tumors, stroke, and other focal brain disorders, but this use has decreased with the advent of high-resolution anatomical imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT). Despite its limited spatial resolution, EEG continues to be a valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with CT, PET, or MRI.
Derivatives of the EEG technique include evoked potentials (EP), which involves averaging the EEG activity time-locked to the presentation of a stimulus of some sort (visual, somatosensory, or auditory). Event-related potentials (ERPs) refer to averaged EEG responses that are time-locked to more complex processing of stimuli; this technique is used in cognitive science, cognitive psychology, and psychophysiological research.
Uses
Epilepsy
EEG is the gold standard diagnostic procedure to confirm epilepsy. The sensitivity of a routine EEG to detect interictal epileptiform discharges at epilepsy centers has been reported to be in the range of 29–55%. Given the low to moderate sensitivity, a routine EEG (typically with a duration of 20–30 minutes) can be normal in people that have epilepsy. When an EEG shows interictal epileptiform discharges (e.g. sharp waves, spikes, spike-and-wave, etc.) it is confirmatory of epilepsy in nearly all cases (high specificity), however up to 3.5% of the general population may have epileptiform abnormalities in an EEG without ever having had a seizure (low false positive rate) or with a very low risk of developing epilepsy in the future.
When a routine EEG is normal and there is a high suspicion or need to confirm epilepsy, it may be repeated or performed with a longer duration in the epilepsy monitoring unit (EMU) or at home with an ambulatory EEG. In addition, there are activating maneuvers such as photic stimulation, hyperventilation and sleep deprivation that can increase the diagnostic yield of the EEG.
Epilepsy Monitoring Unit (EMU)
At times, a routine EEG is not sufficient to establish the diagnosis or determine the best course of action in terms of treatment. In this case, attempts may be made to record an EEG while a seizure is occurring. This is known as an ictal recording, as opposed to an interictal recording, which refers to the EEG recording between seizures. To obtain an ictal recording, a prolonged EEG is typically performed accompanied by a time-synchronized video and audio recording. This can be done either as an outpatient (at home) or during a hospital admission, preferably to an Epilepsy Monitoring Unit (EMU) with nurses and other personnel trained in the care of patients with seizures. Outpatient ambulatory video EEGs typically last one to three days. An admission to an Epilepsy Monitoring Unit typically lasts several days but may last for a week or longer. While in the hospital, seizure medications are usually withdrawn to increase the odds that a seizure will occur during admission. For reasons of safety, medications are not withdrawn during an EEG outside of the hospital. Ambulatory video EEGs, therefore, have the advantage of convenience and are less expensive than a hospital admission, but they also have the disadvantage of a decreased probability of recording a clinical event.
Epilepsy monitoring is often considered when patients continue having events despite being on anti-seizure medications or if there is concern that the patient's events have an alternate diagnosis, e.g., psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders, migraine variants, stroke, etc. In cases of epileptic seizures, continuous EEG monitoring helps to characterize seizures and localize/lateralize the region of the brain from which a seizure originates. This can help identify appropriate non-medication treatment options. In clinical use, EEG traces are visually analyzed by neurologists to look at various features. Increasingly, quantitative analysis of EEG is being used in conjunction with visual analysis. Quantitative analysis displays like power spectrum analysis, alpha-delta ratio, amplitude integrated EEG, and spike detection can help quickly identify segments of EEG that need close visual analysis or, in some cases, be used as surrogates for quick identification of seizures in long-term recordings.
Other brain disorders
An EEG might also be helpful for diagnosing or treating the following disorders:
Brain tumor
Brain damage from head injury
Brain dysfunction that can have a variety of causes (encephalopathy)
Inflammation of the brain (encephalitis)
Stroke
Sleep disorders
It can also:
distinguish epileptic seizures from other types of spells, such as psychogenic non-epileptic seizures, syncope (fainting), sub-cortical movement disorders and migraine variants
differentiate "organic" encephalopathy or delirium from primary psychiatric syndromes such as catatonia
serve as an adjunct test of brain death in comatose patients
prognosticate in comatose patients (in certain instances) or in newborns with brain injury from various causes around the time of birth
determine whether to wean anti-epileptic medications.
Intensive Care Unit (ICU)
EEG can also be used in intensive care units for brain function monitoring to monitor for non-convulsive seizures/non-convulsive status epilepticus, to monitor the effect of sedative/anesthesia in patients in medically induced coma (for treatment of refractory seizures or increased intracranial pressure), and to monitor for secondary brain damage in conditions such as subarachnoid hemorrhage (currently a research method).
In cases where significant brain injury is suspected, e.g., after cardiac arrest, EEG can provide some prognostic information.
If a patient with epilepsy is being considered for resective surgery to treat epilepsy, it is often necessary to localize the focus (source) of the epileptic brain activity with a resolution greater than what is provided by scalp EEG. In these cases, neurosurgeons typically implant strips and grids of electrodes or penetrating depth electrodes under the dura mater, through either a craniotomy or a burr hole. The recording of these signals is referred to as electrocorticography (ECoG), subdural EEG (sdEEG), intracranial EEG (icEEG), or stereotactic EEG (sEEG). The signal recorded from ECoG is on a different scale of activity than the brain activity recorded from scalp EEG. Low-voltage, high-frequency components that cannot be seen easily (or at all) in scalp EEG can be seen clearly in ECoG. Further, smaller electrodes (which cover a smaller parcel of brain surface) allow for better spatial resolution to narrow down the areas critical for seizure onset and propagation. Some clinical sites record data from penetrating microelectrodes.
Home ambulatory EEG
Sometimes it is more convenient or clinically necessary to perform ambulatory EEG recordings in the home of the person being tested. These studies typically have a duration of 24–72 hours.
Research use
EEG and the related study of ERPs are used extensively in neuroscience, cognitive science, cognitive psychology, neurolinguistics, and psychophysiological research, as well as to study human functions such as swallowing. Any EEG techniques used in research are not sufficiently standardised for clinical use, and many ERP studies fail to report all of the necessary processing steps for data collection and reduction, limiting the reproducibility and replicability of many studies. Based on a 2024 systematic literature review and meta analysis commissioned by the Patient-Centered Outcomes Research Institute (PCORI), EEG scans cannot be used reliably to assist in making a clinical diagnosis of ADHD. However, EEG continues to be used in research on mental disabilities, such as auditory processing disorder (APD), ADD, and ADHD. EEGs have also been studied for their utility in detecting neurophysiological changes in the brain after concussion, however, at this time there are no advanced imaging techniques that can be used clinically to diagnose or monitor recovery from concussion.
Advantages
Several other methods to study brain function exist, including functional magnetic resonance imaging (fMRI), positron emission tomography (PET), magnetoencephalography (MEG), nuclear magnetic resonance spectroscopy (NMR or MRS), electrocorticography (ECoG), single-photon emission computed tomography (SPECT), near-infrared spectroscopy (NIRS), and event-related optical signal (EROS). Despite the relatively poor spatial sensitivity of EEG, the "one-dimensional signals from localised peripheral regions on the head make it attractive for its simplistic fidelity and has allowed high clinical and basic research throughput". Thus, EEG possesses some advantages over some of those other techniques:
Hardware costs are significantly lower than those of most other techniques
EEG prevents limited availability of technologists to provide immediate care in high traffic hospitals.
EEG only requires a quiet room and briefcase-size equipment, whereas fMRI, SPECT, PET, MRS, or MEG require bulky and immobile equipment. For example, MEG requires equipment consisting of liquid helium-cooled detectors that can be used only in magnetically shielded rooms, altogether costing upwards of several million dollars; and fMRI requires the use of a 1-ton magnet in, again, a shielded room.
EEG can readily have a high temporal resolution, (although sub-millisecond resolution generates less meaningful data), because the two to 32 data streams generated by that number of electrodes is easily stored and processed, whereas 3D spatial technologies provide thousands or millions times as many input data streams, and are thus limited by hardware and software. EEG is commonly recorded at sampling rates between 250 and 2000 Hz in clinical and research settings.
EEG is relatively tolerant of subject movement, unlike most other neuroimaging techniques. There even exist methods for minimizing, and even eliminating movement artifacts in EEG data
EEG is silent, which allows for better study of the responses to auditory stimuli.
EEG does not aggravate claustrophobia, unlike fMRI, PET, MRS, SPECT, and sometimes MEG
EEG does not involve exposure to high-intensity (>1 Tesla) magnetic fields, as in some of the other techniques, especially MRI and MRS. These can cause a variety of undesirable issues with the data, and also prohibit use of these techniques with participants that have metal implants in their body, such as metal-containing pacemakers
EEG does not involve exposure to radioligands, unlike positron emission tomography.
ERP studies can be conducted with relatively simple paradigms, compared with IE block-design fMRI studies
Relatively non-invasive, in contrast to electrocorticography, which requires electrodes to be placed on the actual surface of the brain.
EEG also has some characteristics that compare favorably with behavioral testing:
EEG can detect covert processing (i.e., processing that does not require a response)
EEG can be used in subjects who are incapable of making a motor response
EEG is a method widely used in the study of sport performance, valued for its portability and lightweight design
Some ERP components can be detected even when the subject is not attending to the stimuli
Unlike other means of studying reaction time, ERPs can elucidate stages of processing (rather than just the result)
the simplicity of EEG readily provides for tracking of brain changes during different phases of life. EEG sleep analysis can indicate significant aspects of the timing of brain development, including evaluating adolescent brain maturation.
In EEG there is a better understanding of what signal is measured as compared to other research techniques, e.g. the BOLD response in MRI.
Disadvantages
Low spatial resolution on the scalp. fMRI, for example, can directly display areas of the brain that are active, while EEG requires intense interpretation just to hypothesize what areas are activated by a particular response.
Depending on the orientation and location of the dipole causing an EEG change, there may be a false localization due to the inverse problem.
EEG poorly measures neural activity that occurs below the upper layers of the brain (the cortex).
Unlike PET and MRS, EEG cannot identify specific locations in the brain at which various neurotransmitters, drugs, etc. can be found.
Often takes a long time to connect a subject to EEG, as it requires precise placement of dozens of electrodes around the head and the use of various gels, saline solutions, and/or pastes to maintain good conductivity, and a cap is used to keep them in place. While the length of time differs dependent on the specific EEG device used, as a general rule it takes considerably less time to prepare a subject for MEG, fMRI, MRS, and SPECT.
Signal-to-noise ratio is poor, so sophisticated data analysis and relatively large numbers of subjects are needed to extract useful information from EEG.
EEGs are not currently very compatible with individuals who have coarser and/or textured hair. Even protective styles can pose issues during testing. Researchers are currently trying to build better options for patients and technicians alike Furthermore, researchers are starting to implement more culturally-informed data collection practices to help reduce racial biases in EEG research.
With other neuroimaging techniques
Simultaneous EEG recordings and fMRI scans have been obtained successfully, though recording both at the same time effectively requires that several technical difficulties be overcome, such as the presence of ballistocardiographic artifact, MRI pulse artifact and the induction of electrical currents in EEG wires that move within the strong magnetic fields of the MRI. While challenging, these have been successfully overcome in a number of studies.
MRI's produce detailed images created by generating strong magnetic fields that may induce potentially harmful displacement force and torque. These fields produce potentially harmful radio frequency heating and create image artifacts rendering images useless. Due to these potential risks, only certain medical devices can be used in an MR environment.
Similarly, simultaneous recordings with MEG and EEG have also been conducted, which has several advantages over using either technique alone:
EEG requires accurate information about certain aspects of the skull that can only be estimated, such as skull radius, and conductivities of various skull locations. MEG does not have this issue, and a simultaneous analysis allows this to be corrected for.
MEG and EEG both detect activity below the surface of the cortex very poorly, and like EEG, the level of error increases with the depth below the surface of the cortex one attempts to examine. However, the errors are very different between the techniques, and combining them thus allows for correction of some of this noise.
MEG has access to virtually no sources of brain activity below a few centimetres under the cortex. EEG, on the other hand, can receive signals from greater depth, albeit with a high degree of noise. Combining the two makes it easier to determine what in the EEG signal comes from the surface (since MEG is very accurate in examining signals from the surface of the brain), and what comes from deeper in the brain, thus allowing for analysis of deeper brain signals than either EEG or MEG on its own.
Recently, a combined EEG/MEG (EMEG) approach has been investigated for the purpose of source reconstruction in epilepsy diagnosis.
EEG has also been combined with positron emission tomography. This provides the advantage of allowing researchers to see what EEG signals are associated with different drug actions in the brain.
Recent studies using machine learning techniques such as neural networks with statistical temporal features extracted from frontal lobe EEG brainwave data has shown high levels of success in classifying mental states (Relaxed, Neutral, Concentrating), mental emotional states (Negative, Neutral, Positive) and thalamocortical dysrhythmia.
Mechanisms
The brain's electrical charge is maintained by billions of neurons. Neurons are electrically charged (or "polarized") by membrane transport proteins that pump ions across their membranes. Neurons are constantly exchanging ions with the extracellular milieu, for example to maintain resting potential and to propagate action potentials. Ions of similar charge repel each other, and when many ions are pushed out of many neurons at the same time, they can push their neighbours, who push their neighbours, and so on, in a wave. This process is known as volume conduction. When the wave of ions reaches the electrodes on the scalp, they can push or pull electrons on the metal in the electrodes. Since metal conducts the push and pull of electrons easily, the difference in push or pull voltages between any two electrodes can be measured by a voltmeter. Recording these voltages over time gives us the EEG.
The electric potential generated by an individual neuron is far too small to be picked up by EEG or MEG. EEG activity therefore always reflects the summation of the synchronous activity of thousands or millions of neurons that have similar spatial orientation. If the cells do not have similar spatial orientation, their ions do not line up and create waves to be detected. Pyramidal neurons of the cortex are thought to produce the most EEG signal because they are well-aligned and fire together. Because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull.
Scalp EEG activity shows oscillations at a variety of frequencies. Several of these oscillations have characteristic frequency ranges, spatial distributions and are associated with different states of brain functioning (e.g., waking and the various sleep stages). These oscillations represent synchronized activity over a network of neurons. The neuronal networks underlying some of these oscillations are understood (e.g., the thalamocortical resonance underlying sleep spindles), while many others are not (e.g., the system that generates the posterior basic rhythm). Research that measures both EEG and neuron spiking finds the relationship between the two is complex, with a combination of EEG power in the gamma band and phase in the delta band relating most strongly to neuron spike activity.
Method
In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste, usually after preparing the scalp area by light abrasion to reduce impedance due to dead skin cells. Many systems typically use electrodes, each of which is attached to an individual wire. Some systems use caps or nets into which electrodes are embedded; this is particularly common when high-density arrays of electrodes are needed.
Electrode locations and names are specified by the International 10–20 system for most clinical and research applications (except when high-density arrays are used). This system ensures that the naming of electrodes is consistent across laboratories. In most clinical applications, 19 recording electrodes (plus ground and system reference) are used. A smaller number of electrodes are typically used when recording EEG from neonates. Additional electrodes can be added to the standard set-up when a clinical or research application demands increased spatial resolution for a particular area of the brain. High-density arrays (typically via cap or net) can contain up to 256 electrodes more-or-less evenly spaced around the scalp.
Each electrode is connected to one input of a differential amplifier (one amplifier per pair of electrodes); a common system reference electrode is connected to the other input of each differential amplifier. These amplifiers amplify the voltage between the active electrode and the reference (typically 1,000–100,000 times, or 60–100 dB of power gain). In analog EEG, the signal is then filtered (next paragraph), and the EEG signal is output as the deflection of pens as paper passes underneath. Most EEG systems these days, however, are digital, and the amplified signal is digitized via an analog-to-digital converter, after being passed through an anti-aliasing filter. Analog-to-digital sampling typically occurs at 256–512 Hz in clinical scalp EEG; sampling rates of up to 20 kHz are used in some research applications.
During the recording, a series of activation procedures may be used. These procedures may induce normal or abnormal EEG activity that might not otherwise be seen. These procedures include hyperventilation, photic stimulation (with a strobe light), eye closure, mental activity, sleep and sleep deprivation. During (inpatient) epilepsy monitoring, a patient's typical seizure medications may be withdrawn.
The digital EEG signal is stored electronically and can be filtered for display. Typical settings for the high-pass filter and a low-pass filter are 0.5–1 Hz and 35–70 Hz respectively. The high-pass filter typically filters out slow artifact, such as electrogalvanic signals and movement artifact, whereas the low-pass filter filters out high-frequency artifacts, such as electromyographic signals. An additional notch filter is typically used to remove artifact caused by electrical power lines (60 Hz in the United States and 50 Hz in many other countries).
The EEG signals can be captured with opensource hardware such as OpenBCI and the signal can be processed by freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox.
As part of an evaluation for epilepsy surgery, it may be necessary to insert electrodes near the surface of the brain, under the surface of the dura mater. This is accomplished via burr hole or craniotomy. This is referred to variously as "electrocorticography (ECoG)", "intracranial EEG (I-EEG)" or "subdural EEG (SD-EEG)". Depth electrodes may also be placed into brain structures, such as the amygdala or hippocampus, structures, which are common epileptic foci and may not be "seen" clearly by scalp EEG. The electrocorticographic signal is processed in the same manner as digital scalp EEG (above), with a couple of caveats. ECoG is typically recorded at higher sampling rates than scalp EEG because of the requirements of Nyquist theorem – the subdural signal is composed of a higher predominance of higher frequency components. Also, many of the artifacts that affect scalp EEG do not impact ECoG, and therefore display filtering is often not needed.
A typical adult human EEG signal is about 10 μV to 100 μV in amplitude when measured from the scalp.
Since an EEG voltage signal represents a difference between the voltages at two electrodes, the display of the EEG for the reading encephalographer may be set up in one of several ways. The representation of the EEG channels is referred to as a montage.
Sequential montage Each channel (i.e., waveform) represents the difference between two adjacent electrodes. The entire montage consists of a series of these channels. For example, the channel "Fp1-F3" represents the difference in voltage between the Fp1 electrode and the F3 electrode. The next channel in the montage, "F3-C3", represents the voltage difference between F3 and C3, and so on through the entire array of electrodes.
Referential montage Each channel represents the difference between a certain electrode and a designated reference electrode. There is no standard position for this reference; it is, however, at a different position than the "recording" electrodes. Midline positions are often used because they do not amplify the signal in one hemisphere vs. the other, such as Cz, Oz, Pz etc. as online reference. The other popular offline references are:
REST reference: which is an offline computational reference at infinity where the potential is zero. REST (reference electrode standardization technique) takes the equivalent sources inside the brain of any a set of scalp recordings as springboard to link the actual recordings with any an online or offline( average, linked ears etc.) non-zero reference to the new recordings with infinity zero as the standardized reference.
"linked ears": which is a physical or mathematical average of electrodes attached to both earlobes or mastoids.
Average reference montage The outputs of all of the amplifiers are summed and averaged, and this averaged signal is used as the common reference for each channel.
Laplacian montage Each channel represents the difference between an electrode and a weighted average of the surrounding electrodes.
When analog (paper) EEGs are used, the technologist switches between montages during the recording in order to highlight or better characterize certain features of the EEG. With digital EEG, all signals are typically digitized and stored in a particular (usually referential) montage; since any montage can be constructed mathematically from any other, the EEG can be viewed by the electroencephalographer in any display montage that is desired.
The EEG is read by a clinical neurophysiologist or neurologist (depending on local custom and law regarding medical specialities), optimally one who has specific training in the interpretation of EEGs for clinical purposes. This is done by visual inspection of the waveforms, called graphoelements. The use of computer signal processing of the EEG – so-called quantitative electroencephalography – is somewhat controversial when used for clinical purposes (although there are many research uses).
Dry EEG electrodes
In the early 1990s Babak Taheri, at University of California, Davis demonstrated the first single and also multichannel dry active electrode arrays using micro-machining. The single channel dry EEG electrode construction and results were published in 1994. The arrayed electrode was also demonstrated to perform well compared to silver/silver chloride electrodes. The device consisted of four sites of sensors with integrated electronics to reduce noise by impedance matching. The advantages of such electrodes are: (1) no electrolyte used, (2) no skin preparation, (3) significantly reduced sensor size, and (4) compatibility with EEG monitoring systems. The active electrode array is an integrated system made of an array of capacitive sensors with local integrated circuitry housed in a package with batteries to power the circuitry. This level of integration was required to achieve the functional performance obtained by the electrode. The electrode was tested on an electrical test bench and on human subjects in four modalities of EEG activity, namely: (1) spontaneous EEG, (2) sensory event-related potentials, (3) brain stem potentials, and (4) cognitive event-related potentials. The performance of the dry electrode compared favorably with that of the standard wet electrodes in terms of skin preparation, no gel requirements (dry), and higher signal-to-noise ratio.
In 1999 researchers at Case Western Reserve University, in Cleveland, Ohio, led by Hunter Peckham, used 64-electrode EEG skullcap to return limited hand movements to quadriplegic Jim Jatich. As Jatich concentrated on simple but opposite concepts like up and down, his beta-rhythm EEG output was analysed using software to identify patterns in the noise. A basic pattern was identified and used to control a switch: Above average activity was set to on, below average off. As well as enabling Jatich to control a computer cursor the signals were also used to drive the nerve controllers embedded in his hands, restoring some movement.
In 2018, a functional dry electrode composed of a polydimethylsiloxane elastomer filled with conductive carbon nanofibers was reported. This research was conducted at the U.S. Army Research Laboratory. EEG technology often involves applying a gel to the scalp which facilitates strong signal-to-noise ratio. This results in more reproducible and reliable experimental results. Since patients dislike having their hair filled with gel, and the lengthy setup requires trained staff on hand, utilizing EEG outside the laboratory setting can be difficult. Additionally, it has been observed that wet electrode sensors' performance reduces after a span of hours. Therefore, research has been directed to developing dry and semi-dry EEG bioelectronic interfaces.
Dry electrode signals depend upon mechanical contact. Therefore, it can be difficult getting a usable signal because of impedance between the skin and the electrode. Some EEG systems attempt to circumvent this issue by applying a saline solution. Others have a semi dry nature and release small amounts of the gel upon contact with the scalp. Another solution uses spring loaded pin setups. These may be uncomfortable. They may also be dangerous if they were used in a situation where a patient could bump their head since they could become lodged after an impact trauma incident.
Currently, headsets are available incorporating dry electrodes with up to 30 channels. Such designs are able to compensate for some of the signal quality degradation related to high impedances by optimizing pre-amplification, shielding and supporting mechanics.
Limitations
EEG has several limitations. Most important is its poor spatial resolution. EEG is most sensitive to a particular set of post-synaptic potentials: those generated in superficial layers of the cortex, on the crests of gyri directly abutting the skull and radial to the skull. Dendrites which are deeper in the cortex, inside sulci, in midline or deep structures (such as the cingulate gyrus or hippocampus), or producing currents that are tangential to the skull, make far less contribution to the EEG signal.
EEG recordings do not directly capture axonal action potentials. An action potential can be accurately represented as a current quadrupole, meaning that the resulting field decreases more rapidly than the ones produced by the current dipole of post-synaptic potentials. In addition, since EEGs represent averages of thousands of neurons, a large population of cells in synchronous activity is necessary to cause a significant deflection on the recordings. Action potentials are very fast and, as a consequence, the chances of field summation are slim. However, neural backpropagation, as a typically longer dendritic current dipole, can be picked up by EEG electrodes and is a reliable indication of the occurrence of neural output.
Not only do EEGs capture dendritic currents almost exclusively as opposed to axonal currents, they also show a preference for activity on populations of parallel dendrites and transmitting current in the same direction at the same time. Pyramidal neurons of cortical layers II/III and V extend apical dendrites to layer I. Currents moving up or down these processes underlie most of the signals produced by electroencephalography.
EEG thus provides information with a large bias in favor of particular neuron types, locations and orientations. So it generally should not be used to make claims about global brain activity. The meninges, cerebrospinal fluid and skull "smear" the EEG signal, obscuring its intracranial source.
It is mathematically impossible to reconstruct a unique intracranial current source for a given EEG signal, as some currents produce potentials that cancel each other out. This is referred to as the inverse problem. However, much work has been done to produce remarkably good estimates of, at least, a localized electric dipole that represents the recorded currents.
EEG vis-à-vis fMRI, fNIRS, fUS and PET
EEG has several strong points as a tool for exploring brain activity. EEGs can detect changes over milliseconds, which is excellent considering an action potential takes approximately 0.5–130 milliseconds to propagate across a single neuron, depending on the type of neuron. Other methods of looking at brain activity, such as PET, fMRI or fUS have time resolution between seconds and minutes. EEG measures the brain's electrical activity directly, while other methods record changes in blood flow (e.g., SPECT, fMRI, fUS) or metabolic activity (e.g., PET, NIRS), which are indirect markers of brain electrical activity.
EEG can be used simultaneously with fMRI or fUS so that high-temporal-resolution data can be recorded at the same time as high-spatial-resolution data, however, since the data derived from each occurs over a different time course, the data sets do not necessarily represent exactly the same brain activity.
There are technical difficulties associated with combining EEG and fMRI including the need to remove the MRI gradient artifact present during MRI acquisition. Furthermore, currents can be induced in moving EEG electrode wires due to the magnetic field of the MRI.
EEG can be used simultaneously with NIRS or fUS without major technical difficulties. There is no influence of these modalities on each other and a combined measurement can give useful information about electrical activity as well as hemodynamics at medium spatial resolution.
EEG vis-à-vis MEG
EEG reflects correlated synaptic activity caused by post-synaptic potentials of cortical neurons. The ionic currents involved in the generation of fast action potentials may not contribute greatly to the averaged field potentials representing the EEG. More specifically, the scalp electrical potentials that produce EEG are generally thought to be caused by the extracellular ionic currents caused by dendritic electrical activity, whereas the fields producing magnetoencephalographic signals are associated with intracellular ionic currents.
Normal activity
The EEG is typically described in terms of (1) rhythmic activity and (2) transients. The rhythmic activity is divided into bands by frequency. To some degree, these frequency bands are a matter of nomenclature (i.e., any rhythmic activity between 8–12 Hz can be described as "alpha"), but these designations arose because rhythmic activity within a certain frequency range was noted to have a certain distribution over the scalp or a certain biological significance. Frequency bands are usually extracted using spectral methods (for instance Welch) as implemented for instance in freely available EEG software such as EEGLAB or the Neurophysiological Biomarker Toolbox.
Computational processing of the EEG is often named quantitative electroencephalography (qEEG).
Most of the cerebral signal observed in the scalp EEG falls in the range of 1–20 Hz (activity below or above this range is likely to be artifactual, under standard clinical recording techniques). Waveforms are subdivided into bandwidths known as alpha, beta, theta, and delta to signify the majority of the EEG used in clinical practice.
Comparison of EEG bands
The practice of using only whole numbers in the definitions comes from practical considerations in the days when only whole cycles could be counted on paper records. This leads to gaps in the definitions, as seen elsewhere on this page. The theoretical definitions have always been more carefully defined to include all frequencies. Unfortunately there is no agreement in standard reference works on what these ranges should be – values for the upper end of alpha and lower end of beta include 12, 13, 14 and 15. If the threshold is taken as 14 Hz, then the slowest beta wave has about the same duration as the longest spike (70 ms), which makes this the most useful value.
Wave patterns
Delta waves is the frequency range up to 4 Hz. It tends to be the highest in amplitude and the slowest waves. It is seen normally in adults in slow-wave sleep. It is also seen normally in babies. It may occur focally with subcortical lesions and in general distribution with diffuse lesions, metabolic encephalopathy hydrocephalus or deep midline lesions. It is usually most prominent frontally in adults (e.g. FIRDA – frontal intermittent rhythmic delta) and posteriorly in children (e.g. OIRDA – occipital intermittent rhythmic delta).
Theta is the frequency range from 4 Hz to 7 Hz. Theta is seen normally in young children. It may be seen in drowsiness or arousal in older children and adults; it can also be seen in meditation. Excess theta for age represents abnormal activity. It can be seen as a focal disturbance in focal subcortical lesions; it can be seen in generalized distribution in diffuse disorder or metabolic encephalopathy or deep midline disorders or some instances of hydrocephalus. On the contrary this range has been associated with reports of relaxed, meditative, and creative states.
Alpha is the frequency range from 8 Hz to 12 Hz. Hans Berger named the first rhythmic EEG activity he observed the "alpha wave". This was the "posterior basic rhythm" (also called the "posterior dominant rhythm" or the "posterior alpha rhythm"), seen in the posterior regions of the head on both sides, higher in amplitude on the dominant side. It emerges with closing of the eyes and with relaxation, and attenuates with eye opening or mental exertion. The posterior basic rhythm is actually slower than 8 Hz in young children (therefore technically in the theta range).
In addition to the posterior basic rhythm, there are other normal alpha rhythms such as the mu rhythm (alpha activity in the contralateral sensory and motor cortical areas) that emerges when the hands and arms are idle; and the "third rhythm" (alpha activity in the temporal or frontal lobes). Alpha can be abnormal; for example, an EEG that has diffuse alpha occurring in coma and is not responsive to external stimuli is referred to as "alpha coma".
Beta is the frequency range from 13 Hz to about 30 Hz. It is seen usually on both sides in symmetrical distribution and is most evident frontally. Beta activity is closely linked to motor behavior and is generally attenuated during active movements. Low-amplitude beta with multiple and varying frequencies is often associated with active, busy or anxious thinking and active concentration. Rhythmic beta with a dominant set of frequencies is associated with various pathologies, such as Dup15q syndrome, and drug effects, especially benzodiazepines. It may be absent or reduced in areas of cortical damage. It is the dominant rhythm in patients who are alert or anxious or who have their eyes open.
Gamma is the frequency range approximately 30–100 Hz. Gamma rhythms are thought to represent binding of different populations of neurons together into a network for the purpose of carrying out a certain cognitive or motor function.
Mu range is 8–13 Hz and partly overlaps with other frequencies. It reflects the synchronous firing of motor neurons in rest state. Mu suppression is thought to reflect motor mirror neuron systems, because when an action is observed, the pattern extinguishes, possibly because the normal and mirror neuronal systems "go out of sync" and interfere with one other.
"Ultra-slow" or "near-DC" activity is recorded using DC amplifiers in some research contexts. It is not typically recorded in a clinical context because the signal at these frequencies is susceptible to a number of artifacts.
Some features of the EEG are transient rather than rhythmic. Spikes and sharp waves may represent seizure activity or interictal activity in individuals with epilepsy or a predisposition toward epilepsy. Other transient features are normal: vertex waves and sleep spindles are seen in normal sleep.
There are types of activity that are statistically uncommon, but not associated with dysfunction or disease. These are often referred to as "normal variants". The mu rhythm is an example of a normal variant.
The normal electroencephalogram (EEG) varies by age. The prenatal EEG and neonatal EEG is quite different from the adult EEG. Fetuses in the third trimester and newborns display two common brain activity patterns: "discontinuous" and "trace alternant." "Discontinuous" electrical activity refers to sharp bursts of electrical activity followed by low frequency waves. "Trace alternant" electrical activity describes sharp bursts followed by short high amplitude intervals and usually indicates quiet sleep in newborns. The EEG in childhood generally has slower frequency oscillations than the adult EEG.
The normal EEG also varies depending on state. The EEG is used along with other measurements (EOG, EMG) to define sleep stages in polysomnography. Stage I sleep (equivalent to drowsiness in some systems) appears on the EEG as drop-out of the posterior basic rhythm. There can be an increase in theta frequencies. Santamaria and Chiappa cataloged a number of the variety of patterns associated with drowsiness. Stage II sleep is characterized by sleep spindles – transient runs of rhythmic activity in the 12–14 Hz range (sometimes referred to as the "sigma" band) that have a frontal-central maximum. Most of the activity in Stage II is in the 3–6 Hz range. Stage III and IV sleep are defined by the presence of delta frequencies and are often referred to collectively as "slow-wave sleep". Stages I–IV comprise non-REM (or "NREM") sleep. The EEG in REM (rapid eye movement) sleep appears somewhat similar to the awake EEG.
EEG under general anesthesia depends on the type of anesthetic employed. With halogenated anesthetics, such as halothane or intravenous agents, such as propofol, a rapid (alpha or low beta), nonreactive EEG pattern is seen over most of the scalp, especially anteriorly; in some older terminology this was known as a WAR (widespread anterior rapid) pattern, contrasted with a WAIS (widespread slow) pattern associated with high doses of opiates. Anesthetic effects on EEG signals are beginning to be understood at the level of drug actions on different kinds of synapses and the circuits that allow synchronized neuronal activity.
Artifacts
EEG is an extremely useful technique for studying brain activity, but the signal measured is always contaminated by artifacts which can impact the analysis of the data. An artifact is any measured signal that does not originate within the brain. Although multiple algorithms exist for the removal of artifacts, the problem of how to deal with them remains an open question. The source of artifacts can be from issues relating to the instrument, such as faulty electrodes, line noise or high electrode impedance, or they may be from the physiology of the subject being recorded. This can include, eye blinks and movement, cardiac activity and muscle activity and these types of artifacts are more complicated to remove. Artifacts may bias the visual interpretation of EEG data as some may mimic cognitive activity that could affect diagnoses of problems such as Alzheimer's disease or sleep disorders. As such the removal of such artifacts in EEG data used for practical applications is of the utmost importance.
Artifact removal
It is important to be able to distinguish artifacts from genuine brain activity in order to prevent incorrect interpretations of EEG data. General approaches for the removal of artifacts from the data are, prevention, rejection and cancellation. The goal of any approach is to develop methodology capable of identifying and removing artifacts without affecting the quality of the EEG signal. As artifact sources are quite different the majority of researchers focus on developing algorithms that will identify and remove a single type of noise in the signal. Simple filtering using a notch filter is commonly employed to reject components with a 50/60 Hz frequency. However such simple filters are not an appropriate choice for dealing with all artifacts, as for some, their frequencies will overlap with the EEG frequencies.
Regression algorithms have a moderate computation cost and are simple. They represented the most popular correction method up until the mid-1990s when they were replaced by "blind source separation" type methods. Regression algorithms work on the premise that all artifacts are comprised by one or more reference channels. Subtracting these reference channels from the other contaminated channels, in either the time or frequency domain, by estimating the impact of the reference channels on the other channels, would correct the channels for the artifact. Although the requirement of reference channels ultimately lead to this class of algorithm being replaced, they still represent the benchmark against which modern algorithms are evaluated.
Blind source separation (BSS) algorithms employed to remove artifacts include principal component analysis (PCA) and independent component analysis (ICA) and several algorithms in this class have been successful at tackling most physiological artifacts.
Physiological artifacts
Ocular artifacts
Ocular artifacts affect the EEG signal significantly. This is due to eye movements involving a change in electric fields surrounding the eyes, distorting the electric field over the scalp, and as EEG is recorded on the scalp, it therefore distorts the recorded signal. A difference of opinion exists among researchers, with some arguing ocular artifacts are, or may be reasonably described as a single generator, whilst others argue it is important to understand the potentially complicated mechanisms. Three potential mechanisms have been proposed to explain the ocular artifact.
The first is corneal retinal dipole movement which argues that an electric dipole is formed between the cornea and retina, as the former is positively and the latter negatively charged. When the eye moves, so does this dipole which impacts the electrical field over the scalp, this is the most standard view. The second mechanism is retinal dipole movement, which is similar to the first but differing in that it argues there is a potential difference, hence dipole across the retina with the cornea having little effect. The third mechanism is eyelid movement. It is known that there is a change in voltage around the eyes when the eyelid moves, even if the eyeball does not. It is thought that the eyelid can be described as a sliding potential source and that the impacting of blinking is different to eye movement on the recorded EEG.
Eyelid fluttering artifacts of a characteristic type were previously called Kappa rhythm (or Kappa waves). It is usually seen in the prefrontal leads, that is, just over the eyes. Sometimes they are seen with mental activity. They are usually in the Theta (4–7 Hz) or Alpha (7–14 Hz) range. They were named because they were believed to originate from the brain. Later study revealed they were generated by rapid fluttering of the eyelids, sometimes so minute that it was difficult to see. They are in fact noise in the EEG reading, and should not technically be called a rhythm or wave. Therefore, current usage in electroencephalography refers to the phenomenon as an eyelid fluttering artifact, rather than a Kappa rhythm (or wave).
The propagation of the ocular artifact is impacted by multiple factors including the properties of the subject's skull, neuronal tissues and skin but the signal may be approximated as being inversely proportional to the distance from the eyes squared. The electrooculogram (EOG) consists of a series of electrodes measuring voltage changes close to the eye and is the most common tool for dealing with the eye movement artifact in the EEG signal.
Muscular artifacts
Another source of artifacts are various muscle movements across the body. This particular class of artifact is usually recorded by all electrodes on the scalp due to myogenic activity (increase or decrease of blood pressure). The origin of these artifacts have no single location and arises from functionally independent muscle groups, meaning the characteristics of the artifact are not constant. The observed patterns due to muscular artifacts will change depending on subject sex, the particular muscle tissue, and its degree of contraction. The frequency range for muscular artifacts is wide and overlaps with every classic EEG rhythm. However most of the power is concentrated in the lower range of the observed frequencies of 20 to 300 Hz making the gamma band particularly susceptible to muscular artifacts. Some muscle artifacts may have activity with a frequency as low as 2 Hz, so delta and theta bands may also be affected by muscle activity. Muscular artifacts may impact sleep studies, as unconscious bruxism (grinding of teeth) movements or snoring can seriously impact the quality of the recorded EEG. In addition the recordings made of epilepsy patients may be significantly impacted by the existence of muscular artifacts.
Cardiac artifacts
The potential due to cardiac activity introduces electrocardiograph (ECG) errors in the EEG. Artifacts arising due to cardiac activity may be removed with the help of an ECG reference signal.
Other physiological artifacts
Glossokinetic artifacts are caused by the potential difference between the base and the tip of the tongue. Minor tongue movements can contaminate the EEG, especially in parkinsonian and tremor disorders.
Environmental artifacts
In addition to artifacts generated by the body, many artifacts originate from outside the body. Movement by the patient, or even just settling of the electrodes, may cause electrode pops, spikes originating from a momentary change in the impedance of a given electrode. Poor grounding of the EEG electrodes can cause significant 50 or 60 Hz artifact, depending on the local power system's frequency. A third source of possible interference can be the presence of an IV drip; such devices can cause rhythmic, fast, low-voltage bursts, which may be confused for spikes.
Abnormal activity
Abnormal activity can broadly be separated into epileptiform and non-epileptiform activity. It can also be separated into focal or diffuse.
Focal epileptiform discharges represent fast, synchronous potentials in a large number of neurons in a somewhat discrete area of the brain. These can occur as interictal activity, between seizures, and represent an area of cortical irritability that may be predisposed to producing epileptic seizures. Interictal discharges are not wholly reliable for determining whether a patient has epilepsy nor where his/her seizure might originate. (See focal epilepsy.)
Generalized epileptiform discharges often have an anterior maximum, but these are seen synchronously throughout the entire brain. They are strongly suggestive of a generalized epilepsy.
Focal non-epileptiform abnormal activity may occur over areas of the brain where there is focal damage of the cortex or white matter. It often consists of an increase in slow frequency rhythms and/or a loss of normal higher frequency rhythms. It may also appear as focal or unilateral decrease in amplitude of the EEG signal.
Diffuse non-epileptiform abnormal activity may manifest as diffuse abnormally slow rhythms or bilateral slowing of normal rhythms, such as the PBR.
Intracortical Encephalogram electrodes and sub-dural electrodes can be used in tandem to discriminate and discretize artifact from epileptiform and other severe neurological events.
More advanced measures of abnormal EEG signals have also recently received attention as possible biomarkers for different disorders such as Alzheimer's disease.
Remote communication
Systems for decoding imagined speech from EEG have applications such as in brain–computer interfaces.
EEG diagnostics
The Department of Defense (DoD) and Veteran's Affairs (VA), and U.S Army Research Laboratory (ARL), collaborated on EEG diagnostics in order to detect mild to moderate Traumatic Brain Injury (mTBI) in combat soldiers. Between 2000 and 2012, 75 percent of U.S. military operations brain injuries were classified mTBI. In response, the DoD pursued new technologies capable of rapid, accurate, non-invasive, and field-capable detection of mTBI to address this injury.
Combat personnel often develop PTSD and mTBI in correlation. Both conditions present with altered low-frequency brain wave oscillations. Altered brain waves from PTSD patients present with decreases in low-frequency oscillations, whereas, mTBI injuries are linked to increased low-frequency wave oscillations. Effective EEG diagnostics can help doctors accurately identify conditions and appropriately treat injuries in order to mitigate long-term effects.
Traditionally, clinical evaluation of EEGs involved visual inspection. Instead of a visual assessment of brain wave oscillation topography, quantitative electroencephalography (qEEG), computerized algorithmic methodologies, analyzes a specific region of the brain and transforms the data into a meaningful "power spectrum" of the area. Accurately differentiating between mTBI and PTSD can significantly increase positive recovery outcomes for patients especially since long-term changes in neural communication can persist after an initial mTBI incident.
Another common measurement made from EEG data is that of complexity measures such as Lempel-Ziv complexity, fractal dimension, and spectral flatness, which are associated with particular pathologies or pathology stages.
Economics
Inexpensive EEG devices exist for the low-cost research and consumer markets. Recently, a few companies have miniaturized medical grade EEG technology to create versions accessible to the general public. Some of these companies have built commercial EEG devices retailing for less than US$100.
In 2004 OpenEEG released its ModularEEG as open source hardware. Compatible open source software includes a game for balancing a ball.
In 2007 NeuroSky released the first affordable consumer based EEG along with the game NeuroBoy. This was also the first large scale EEG device to use dry sensor technology.
In 2008 OCZ Technology developed device for use in video games relying primarily on electromyography.
In 2008 the Final Fantasy developer Square Enix announced that it was partnering with NeuroSky to create a game, Judecca.
In 2009 Mattel partnered with NeuroSky to release the Mindflex, a game that used an EEG to steer a ball through an obstacle course. By far the best-selling consumer based EEG to date.
In 2009 Uncle Milton Industries partnered with NeuroSky to release the Star Wars Force Trainer, a game designed to create the illusion of possessing the Force.
In 2010, NeuroSky added a blink and electromyography function to the MindSet.
In 2011, NeuroSky released the MindWave, an EEG device designed for educational purposes and games. The MindWave won the Guinness Book of World Records award for "Heaviest machine moved using a brain control interface".
In 2012, a Japanese gadget project, neurowear, released Necomimi: a headset with motorized cat ears. The headset is a NeuroSky MindWave unit with two motors on the headband where a cat's ears might be. Slipcovers shaped like cat ears sit over the motors so that as the device registers emotional states the ears move to relate. For example, when relaxed, the ears fall to the sides and perk up when excited again.
In 2014, OpenBCI released an eponymous open source brain-computer interface after a successful kickstarter campaign in 2013. The board, later renamed "Cyton", has 8 channels, expandable to 16 with the Daisy module. It supports EEG, EKG, and EMG. The Cyton Board is based on the Texas Instruments ADS1299 IC and the Arduino or PIC microcontroller, and initially costed $399 before increasing in price to $999. It uses standard metal cup electrodes and conductive paste.
In 2015, Mind Solutions Inc released the smallest consumer BCI to date, the NeuroSync. This device functions as a dry sensor at a size no larger than a Bluetooth ear piece.
In 2015, A Chinese-based company Macrotellect released BrainLink Pro and BrainLink Lite, a consumer grade EEG wearable product providing 20 brain fitness enhancement Apps on Apple and Android App Stores.
In 2021, BioSerenity release the Neuronaute and Icecap a single-use disposable EEG headset that allows recording with equivalent quality to traditional cup electrodes.
Future research
The EEG has been used for many purposes besides the conventional uses of clinical diagnosis and conventional cognitive neuroscience. An early use was during World War II by the U.S. Army Air Corps to screen out pilots in danger of having seizures; long-term EEG recordings in epilepsy patients are still used today for seizure prediction. Neurofeedback remains an important extension, and in its most advanced form is also attempted as the basis of brain computer interfaces. The EEG is also used quite extensively in the field of neuromarketing.
The EEG is altered by drugs that affect brain functions, the chemicals that are the basis for psychopharmacology. Berger's early experiments recorded the effects of drugs on EEG. The science of pharmaco-electroencephalography has developed methods to identify substances that systematically alter brain functions for therapeutic and recreational use.
Honda is attempting to develop a system to enable an operator to control its Asimo robot using EEG, a technology it eventually hopes to incorporate into its automobiles.
EEGs have been used as evidence in criminal trials in the Indian state of Maharashtra. Brain Electrical Oscillation Signature Profiling (BEOS), an EEG technique, was used in the trial of State of Maharashtra v. Sharma to show Sharma remembered using arsenic to poison her ex-fiancé, although the reliability and scientific basis of BEOS is disputed.
A lot of research is currently being carried out in order to make EEG devices smaller, more portable and easier to use. So called "Wearable EEG" is based upon creating low power wireless collection electronics and 'dry' electrodes which do not require a conductive gel to be used. Wearable EEG aims to provide small EEG devices which are present only on the head and which can record EEG for days, weeks, or months at a time, as ear-EEG. Such prolonged and easy-to-use monitoring could make a step change in the diagnosis of chronic conditions such as epilepsy, and greatly improve the end-user acceptance of BCI systems. Research is also being carried out on identifying specific solutions to increase the battery lifetime of Wearable EEG devices through the use of the data reduction approach.
In research, currently EEG is often used in combination with machine learning. EEG data are pre-processed then passed on to machine learning algorithms. These algorithms are then trained to recognize different diseases like schizophrenia, epilepsy or dementia. Furthermore, they are increasingly used to study seizure detection. By using machine learning, the data can be analyzed automatically. In the long run this research is intended to build algorithms that support physicians in their clinical practice and to provide further insights into diseases. In this vein, complexity measures of EEG data are often calculated, such as Lempel-Ziv complexity, fractal dimension, and spectral flatness. It has been shown that combining or multiplying such measures can reveal previously hidden information in EEG data.
EEG signals from musical performers were used to create instant compositions and one CD by the Brainwave Music Project, run at the Computer Music Center at Columbia University by Brad Garton and Dave Soldier. Similarly, an hour-long recording of the brainwaves of Ann Druyan was included on the Voyager Golden Record, launched on the Voyager probes in 1977, in case any extraterrestrial intelligence could decode her thoughts, which included what it was like to fall in love.
History
In 1875, Richard Caton (1842–1926), a physician practicing in Liverpool, presented his findings about electrical phenomena of the exposed cerebral hemispheres of rabbits and monkeys in the British Medical Journal. In 1890, Polish physiologist Adolf Beck published an investigation of spontaneous electrical activity of the brain of rabbits and dogs that included rhythmic oscillations altered by light. Beck started experiments on the electrical brain activity of animals. Beck placed electrodes directly on the surface of the brain to test for sensory stimulation. His observation of fluctuating brain activity led to the conclusion of brain waves.
In 1912, Ukrainian physiologist Vladimir Vladimirovich Pravdich-Neminsky published the first animal EEG and the evoked potential of the mammalian (dog). In 1914, Napoleon Cybulski and Jelenska-Macieszyna photographed EEG recordings of experimentally induced seizures.
German physiologist and psychiatrist Hans Berger (1873–1941) recorded the first human EEG in 1924. Expanding on work previously conducted on animals by Richard Caton and others, Berger also invented the electroencephalograph (giving the device its name), an invention described "as one of the most surprising, remarkable, and momentous developments in the history of clinical neurology". His discoveries were first confirmed by British scientists Edgar Douglas Adrian and B. H. C. Matthews in 1934 and developed by them.
In 1934, Fisher and Lowenbach first demonstrated epileptiform spikes. In 1935, Gibbs, Davis and Lennox described interictal spike waves and the three cycles/s pattern of clinical absence seizures, which began the field of clinical electroencephalography. Subsequently, in 1936 Gibbs and Jasper reported the interictal spike as the focal signature of epilepsy. The same year, the first EEG laboratory opened at Massachusetts General Hospital.
Franklin Offner (1911–1999), professor of biophysics at Northwestern University developed a prototype of the EEG that incorporated a piezoelectric inkwriter called a Crystograph (the whole device was typically known as the Offner Dynograph).
In 1947, The American EEG Society was founded and the first International EEG congress was held. In 1953 Aserinsky and Kleitman described REM sleep.
In the 1950s, William Grey Walter developed an adjunct to EEG called EEG topography, which allowed for the mapping of electrical activity across the surface of the brain. This enjoyed a brief period of popularity in the 1980s and seemed especially promising for psychiatry. It was never accepted by neurologists and remains primarily a research tool.
An electroencephalograph system manufactured by Beckman Instruments was used on at least one of the Project Gemini manned spaceflights (1965–1966) to monitor the brain waves of astronauts on the flight. It was one of many Beckman Instruments specialized for and used by NASA.
The first instance of the use of EEG to control a physical object, a robot, was in 1988. The robot would follow a line or stop depending on the alpha activity of the subject. If the subject relaxed and closed their eyes therefore increasing alpha activity, the bot would move. Opening their eyes thus decreasing alpha activity would cause the robot to stop on the trajectory.
See also
References
Further reading
External links
Diagnostic neurology
Electrophysiology
Neurophysiology
Neurotechnology
Electrodiagnosis
Brain–computer interface
Mathematics in medicine | Electroencephalography | Mathematics | 13,592 |
18,646,738 | https://en.wikipedia.org/wiki/International%20Journal%20of%20Biometeorology | The International Journal of Biometeorology is a peer-reviewed scientific journal which publishes original research papers, review articles, and short communications on studies examining the interactions between living organisms and factors of the natural and artificial physical environment. The journal is published by Springer Science+Business Media on behalf of the International Society of Biometeorology, its scope includes the fields of Earth and environmental science, life sciences, animal physiology, plant physiology and environmental medicine/environmental psychology.
See also
List of scientific journals in earth and atmospheric sciences
List of scientific journals in biology
External links
Meteorology journals
Biology journals
Springer Science+Business Media academic journals
English-language journals
Bimonthly journals
Biometeorology | International Journal of Biometeorology | Environmental_science | 141 |
100,643 | https://en.wikipedia.org/wiki/List%20of%20people%20in%20systems%20and%20control | This is an alphabetical list of people who have made significant contributions in the fields of system analysis and control theory.
Eminent researchers
The eminent researchers (born after 1920) include the winners of at least one award of the IEEE Control Systems Award, the Giorgio Quazza Medal, the Hendrik W. Bode Lecture Prize, the Richard E. Bellman Control Heritage Award, the Rufus Oldenburger Medal, or higher awards such as the IEEE Medal of Honor and the National Medal of Science. The earlier pioneers such as Nicolas Minorsky (1885–1970), Harry Nyquist (1889–1976), Harold Locke Hazen (1901–1980), Charles Stark Draper (1901–1987), Hendrik Wade Bode (1905–1982), Gordon S. Brown (1907–1996), John F. Coales (1907–1999), Rufus Oldenburger (1908–1969), John R. Ragazzini (1912–1988), Nathaniel B. Nichols (1914–1997), John Zaborszky (1914–2008) and Harold Chestnut (1917–2001) are not included.
Eminent researchers of USSR (including Russian SFSR, Ukrainian SSR, Byelorussian SSR, etc. from 1922 to 1991)
Other active researchers
Historical figures in systems and control
These people have made outstanding historical contributions to systems and control.
See also
List of engineers
List of systems engineers
List of systems scientists
References
External links
People in control, in: IEEE Control Systems Magazine, Volume 24, Issue 5, Oct. 2004 pp 12–15.
ISA, the International Society for Measurement and Control, homepage.
Systems And Control | List of people in systems and control | Engineering | 334 |
97,830 | https://en.wikipedia.org/wiki/Nuclear%20technology | Nuclear technology is technology that involves the nuclear reactions of atomic nuclei. Among the notable nuclear technologies are nuclear reactors, nuclear medicine and nuclear weapons. It is also used, among other things, in smoke detectors and gun sights.
History and scientific background
Discovery
The vast majority of common, natural phenomena on Earth only involve gravity and electromagnetism, and not nuclear reactions. This is because atomic nuclei are generally kept apart because they contain positive electrical charges and therefore repel each other.
In 1896, Henri Becquerel was investigating phosphorescence in uranium salts when he discovered a new phenomenon which came to be called radioactivity. He, Pierre Curie and Marie Curie began investigating the phenomenon. In the process, they isolated the element radium, which is highly radioactive. They discovered that radioactive materials produce intense, penetrating rays of three distinct sorts, which they labeled alpha, beta, and gamma after the first three Greek letters. Some of these kinds of radiation could pass through ordinary matter, and all of them could be harmful in large amounts. All of the early researchers received various radiation burns, much like sunburn, and thought little of it.
The new phenomenon of radioactivity was seized upon by the manufacturers of quack medicine (as had the discoveries of electricity and magnetism, earlier), and a number of patent medicines and treatments involving radioactivity were put forward.
Gradually it was realized that the radiation produced by radioactive decay was ionizing radiation, and that even quantities too small to burn could pose a severe long-term hazard. Many of the scientists working on radioactivity died of cancer as a result of their exposure. Radioactive patent medicines mostly disappeared, but other applications of radioactive materials persisted, such as the use of radium salts to produce glowing dials on meters.
As the atom came to be better understood, the nature of radioactivity became clearer. Some larger atomic nuclei are unstable, and so decay (release matter or energy) after a random interval. The three forms of radiation that Becquerel and the Curies discovered are also more fully understood. Alpha decay is when a nucleus releases an alpha particle, which is two protons and two neutrons, equivalent to a helium nucleus. Beta decay is the release of a beta particle, a high-energy electron. Gamma decay releases gamma rays, which unlike alpha and beta radiation are not matter but electromagnetic radiation of very high frequency, and therefore energy. This type of radiation is the most dangerous and most difficult to block. All three types of radiation occur naturally in certain elements.
It has also become clear that the ultimate source of most terrestrial energy is nuclear, either through radiation from the Sun caused by stellar thermonuclear reactions or by radioactive decay of uranium within the Earth, the principal source of geothermal energy.
Nuclear fission
In natural nuclear radiation, the byproducts are very small compared to the nuclei from which they originate. Nuclear fission is the process of splitting a nucleus into roughly equal parts, and releasing energy and neutrons in the process. If these neutrons are captured by another unstable nucleus, they can fission as well, leading to a chain reaction. The average number of neutrons released per nucleus that go on to fission another nucleus is referred to as k. Values of k larger than 1 mean that the fission reaction is releasing more neutrons than it absorbs, and therefore is referred to as a self-sustaining chain reaction. A mass of fissile material large enough (and in a suitable configuration) to induce a self-sustaining chain reaction is called a critical mass.
When a neutron is captured by a suitable nucleus, fission may occur immediately, or the nucleus may persist in an unstable state for a short time. If there are enough immediate decays to carry on the chain reaction, the mass is said to be prompt critical, and the energy release will grow rapidly and uncontrollably, usually leading to an explosion.
When discovered on the eve of World War II, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives. The Manhattan Project, run by the United States with the help of the United Kingdom and Canada, developed multiple fission weapons which were used against Japan in 1945 at Hiroshima and Nagasaki. During the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity.
In 1951, the first nuclear fission power plant was the first to produce electricity at the Experimental Breeder Reactor No. 1 (EBR-1), in Arco, Idaho, ushering in the "Atomic Age" of more intensive human energy use.
However, if the mass is critical only when the delayed neutrons are included, then the reaction can be controlled, for example by the introduction or removal of neutron absorbers. This is what allows nuclear reactors to be built. Fast neutrons are not easily captured by nuclei; they must be slowed (slow neutrons), generally by collision with the nuclei of a neutron moderator, before they can be easily captured. Today, this type of fission is commonly used to generate electricity.
Nuclear fusion
If nuclei are forced to collide, they can undergo nuclear fusion. This process may release or absorb energy. When the resulting nucleus is lighter than that of iron, energy is normally released; when the nucleus is heavier than that of iron, energy is generally absorbed. This process of fusion occurs in stars, which derive their energy from hydrogen and helium. They form, through stellar nucleosynthesis, the light elements (lithium to calcium) as well as some of the heavy elements (beyond iron and nickel, via the S-process). The remaining abundance of heavy elements, from nickel to uranium and beyond, is due to supernova nucleosynthesis, the R-process.
Of course, these natural processes of astrophysics are not examples of nuclear "technology". Because of the very strong repulsion of nuclei, fusion is difficult to achieve in a controlled fashion. Hydrogen bombs obtain their enormous destructive power from fusion, but their energy cannot be controlled. Controlled fusion is achieved in particle accelerators; this is how many synthetic elements are produced. A fusor can also produce controlled fusion and is a useful neutron source. However, both of these devices operate at a net energy loss. Controlled, viable fusion power has proven elusive, despite the occasional hoax. Technical and theoretical difficulties have hindered the development of working civilian fusion technology, though research continues to this day around the world.
Nuclear fusion was initially pursued only in theoretical stages during World War II, when scientists on the Manhattan Project (led by Edward Teller) investigated it as a method to build a bomb. The project abandoned fusion after concluding that it would require a fission reaction to detonate. It took until 1952 for the first full hydrogen bomb to be detonated, so-called because it used reactions between deuterium and tritium. Fusion reactions are much more energetic per unit mass of fuel than fission reactions, but starting the fusion chain reaction is much more difficult.
Nuclear weapons
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. Even small nuclear devices can devastate a city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major aspect of international policy since their debut.
The design of a nuclear weapon is more complicated than it might seem. Such a weapon must hold one or more subcritical fissile masses stable for deployment, then induce criticality (create a critical mass) for detonation. It also is quite difficult to ensure that such a chain reaction consumes a significant fraction of the fuel before the device flies apart. The procurement of a nuclear fuel is also more difficult than it might seem, since sufficiently unstable substances for this process do not currently occur naturally on Earth in suitable amounts.
One isotope of uranium, namely uranium-235, is naturally occurring and sufficiently unstable, but it is always found mixed with the more stable isotope uranium-238. The latter accounts for more than 99% of the weight of natural uranium. Therefore, some method of isotope separation based on the weight of three neutrons must be performed to enrich (isolate) uranium-235.
Alternatively, the element plutonium possesses an isotope that is sufficiently unstable for this process to be usable. Terrestrial plutonium does not currently occur naturally in sufficient quantities for such use, so it must be manufactured in a nuclear reactor.
Ultimately, the Manhattan Project manufactured nuclear weapons based on each of these elements. They detonated the first nuclear weapon in a test code-named "Trinity", near Alamogordo, New Mexico, on July 16, 1945. The test was conducted to ensure that the implosion method of detonation would work, which it did. A uranium bomb, Little Boy, was dropped on the Japanese city Hiroshima on August 6, 1945, followed three days later by the plutonium-based Fat Man on Nagasaki. In the wake of unprecedented devastation and casualties from a single weapon, the Japanese government soon surrendered, ending World War II.
Since these bombings, no nuclear weapons have been deployed offensively. Nevertheless, they prompted an arms race to develop increasingly destructive bombs to provide a nuclear deterrent. Just over four years later, on August 29, 1949, the Soviet Union detonated its first fission weapon. The United Kingdom followed on October 2, 1952; France, on February 13, 1960; and China component to a nuclear weapon. Approximately half of the deaths from Hiroshima and Nagasaki died two to five years afterward from radiation exposure. A radiological weapon is a type of nuclear weapon designed to distribute hazardous nuclear material in enemy areas. Such a weapon would not have the explosive capability of a fission or fusion bomb, but would kill many people and contaminate a large area. A radiological weapon has never been deployed. While considered useless by a conventional military, such a weapon raises concerns over nuclear terrorism.
There have been over 2,000 nuclear tests conducted since 1945. In 1963, all nuclear and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground nuclear testing. France continued atmospheric testing until 1974, while China continued up until 1980. The last underground test by the United States was in 1992, the Soviet Union in 1990, the United Kingdom in 1991, and both France and China continued testing until 1996. After signing the Comprehensive Test Ban Treaty in 1996 (which had as of 2011 not entered into force), all of these states have pledged to discontinue all nuclear testing. Non-signatories India and Pakistan last tested nuclear weapons in 1998.
Nuclear weapons are the most destructive weapons known - the archetypal weapons of mass destruction. Throughout the Cold War, the opposing powers had huge nuclear arsenals, sufficient to kill hundreds of millions of people. Generations of people grew up under the shadow of nuclear devastation, portrayed in films such as Dr. Strangelove and The Atomic Cafe.
However, the tremendous energy release in the detonation of a nuclear weapon also suggested the possibility of a new energy source.
Civilian uses
Nuclear power
Nuclear power is a type of nuclear technology involving the controlled use of nuclear fission to release energy for work including propulsion, heat, and the generation of electricity. Nuclear energy is produced by a controlled nuclear chain reaction which creates heat—and which is used to boil water, produce steam, and drive a steam turbine. The turbine is used to generate electricity and/or to do mechanical work.
Currently nuclear power provides approximately 15.7% of the world's electricity (in 2004) and is used to propel aircraft carriers, icebreakers and submarines (so far economics and fears in some ports have prevented the use of nuclear power in transport ships). All nuclear power plants use fission. No man-made fusion reaction has resulted in a viable source of electricity.
Medical applications
The medical applications of nuclear technology are divided into diagnostics and radiation treatment.
Imaging - The largest use of ionizing radiation in medicine is in medical radiography to make images of the inside of the human body using x-rays. This is the largest artificial source of radiation exposure for humans. Medical and dental x-ray imagers use of cobalt-60 or other x-ray sources. A number of radiopharmaceuticals are used, sometimes attached to organic molecules, to act as radioactive tracers or contrast agents in the human body. Positron emitting nucleotides are used for high resolution, short time span imaging in applications known as Positron emission tomography.
Radiation is also used to treat diseases in radiation therapy.
Industrial applications
Since some ionizing radiation can penetrate matter, they are used for a variety of measuring methods. X-rays and gamma rays are used in industrial radiography to make images of the inside of solid products, as a means of nondestructive testing and inspection. The piece to be radiographed is placed between the source and a photographic film in a cassette. After a certain exposure time, the film is developed and it shows any internal defects of the material.
Gauges - Gauges use the exponential absorption law of gamma rays
Level indicators: Source and detector are placed at opposite sides of a container, indicating the presence or absence of material in the horizontal radiation path. Beta or gamma sources are used, depending on the thickness and the density of the material to be measured. The method is used for containers of liquids or of grainy substances
Thickness gauges: if the material is of constant density, the signal measured by the radiation detector depends on the thickness of the material. This is useful for continuous production, like of paper, rubber, etc.
Electrostatic control - To avoid the build-up of static electricity in production of paper, plastics, synthetic textiles, etc., a ribbon-shaped source of the alpha emitter 241Am can be placed close to the material at the end of the production line. The source ionizes the air to remove electric charges on the material.
Radioactive tracers - Since radioactive isotopes behave, chemically, mostly like the inactive element, the behavior of a certain chemical substance can be followed by tracing the radioactivity. Examples:
Adding a gamma tracer to a gas or liquid in a closed system makes it possible to find a hole in a tube.
Adding a tracer to the surface of the component of a motor makes it possible to measure wear by measuring the activity of the lubricating oil.
Oil and Gas Exploration- Nuclear well logging is used to help predict the commercial viability of new or existing wells. The technology involves the use of a neutron or gamma-ray source and a radiation detector which are lowered into boreholes to determine the properties of the surrounding rock such as porosity and lithography.
Road Construction - Nuclear moisture/density gauges are used to determine the density of soils, asphalt, and concrete. Typically a cesium-137 source is used.
Commercial applications
radioluminescence
tritium illumination: Tritium is used with phosphor in rifle sights to increase nighttime firing accuracy. Some runway markers and building exit signs use the same technology, to remain illuminated during blackouts.
Betavoltaics.
Smoke detector: An ionization smoke detector includes a tiny mass of radioactive americium-241, which is a source of alpha radiation. Two ionisation chambers are placed next to each other. Both contain a small source of 241Am that gives rise to a small constant current. One is closed and serves for comparison, the other is open to ambient air; it has a gridded electrode. When smoke enters the open chamber, the current is disrupted as the smoke particles attach to the charged ions and restore them to a neutral electrical state. This reduces the current in the open chamber. When the current drops below a certain threshold, the alarm is triggered.
Food processing and agriculture
In biology and agriculture, radiation is used to induce mutations to produce new or improved species, such as in atomic gardening. Another use in insect control is the sterile insect technique, where male insects are sterilized by radiation and released, so they have no offspring, to reduce the population.
In industrial and food applications, radiation is used for sterilization of tools and equipment. An advantage is that the object may be sealed in plastic before sterilization. An emerging use in food production is the sterilization of food using food irradiation.
Food irradiation is the process of exposing food to ionizing radiation in order to destroy microorganisms, bacteria, viruses, or insects that might be present in the food. The radiation sources used include radioisotope gamma ray sources, X-ray generators and electron accelerators. Further applications include sprout inhibition, delay of ripening, increase of juice yield, and improvement of re-hydration. Irradiation is a more general term of deliberate exposure of materials to radiation to achieve a technical goal (in this context 'ionizing radiation' is implied). As such it is also used on non-food items, such as medical hardware, plastics, tubes for gas-pipelines, hoses for floor-heating, shrink-foils for food packaging, automobile parts, wires and cables (isolation), tires, and even gemstones. Compared to the amount of food irradiated, the volume of those every-day applications is huge but not noticed by the consumer.
The genuine effect of processing food by ionizing radiation relates to damages to the DNA, the basic genetic information for life. Microorganisms can no longer proliferate and continue their malignant or pathogenic activities. Spoilage causing micro-organisms cannot continue their activities. Insects do not survive or become incapable of procreation. Plants cannot continue the natural ripening or aging process. All these effects are beneficial to the consumer and the food industry, likewise.
The amount of energy imparted for effective food irradiation is low compared to cooking the same; even at a typical dose of 10 kGy most food, which is (with regard to warming) physically equivalent to water, would warm by only about 2.5 °C (4.5 °F).
The specialty of processing food by ionizing radiation is the fact, that the energy density per atomic transition is very high, it can cleave molecules and induce ionization (hence the name) which cannot be achieved by mere heating. This is the reason for new beneficial effects, however at the same time, for new concerns. The treatment of solid food by ionizing radiation can provide an effect similar to heat pasteurization of liquids, such as milk. However, the use of the term, cold pasteurization, to describe irradiated foods is controversial, because pasteurization and irradiation are fundamentally different processes, although the intended end results can in some cases be similar.
Detractors of food irradiation have concerns about the health hazards of induced radioactivity. A report for the industry advocacy group American Council on Science and Health entitled "Irradiated Foods" states: "The types of radiation sources approved for the treatment of foods have specific energy levels well below that which would cause any element in food to become radioactive. Food undergoing irradiation does not become any more radioactive than luggage passing through an airport X-ray scanner or teeth that have been X-rayed."
Food irradiation is currently permitted by over 40 countries and volumes are estimated to exceed annually worldwide.
Food irradiation is essentially a non-nuclear technology; it relies on the use of ionizing radiation which may be generated by accelerators for electrons and conversion into bremsstrahlung, but which may use also gamma-rays from nuclear decay. There is a worldwide industry for processing by ionizing radiation, the majority by number and by processing power using accelerators. Food irradiation is only a niche application compared to medical supplies, plastic materials, raw materials, gemstones, cables and wires, etc.
Accidents
Nuclear accidents, because of the powerful forces involved, are often very dangerous. Historically, the first incidents involved fatal radiation exposure. Marie Curie died from aplastic anemia which resulted from her high levels of exposure. Two scientists, an American and Canadian respectively, Harry Daghlian and Louis Slotin, died after mishandling the same plutonium mass. Unlike conventional weapons, the intense light, heat, and explosive force is not the only deadly component to a nuclear weapon. Approximately half of the deaths from Hiroshima and Nagasaki died two to five years afterward from radiation exposure.
Civilian nuclear and radiological accidents primarily involve nuclear power plants. Most common are nuclear leaks that expose workers to hazardous material. A nuclear meltdown refers to the more serious hazard of releasing nuclear material into the surrounding environment. The most significant meltdowns occurred at Three Mile Island in Pennsylvania and Chernobyl in the Soviet Ukraine. The earthquake and tsunami on March 11, 2011 caused serious damage to three nuclear reactors and a spent fuel storage pond at the Fukushima Daiichi nuclear power plant in Japan. Military reactors that experienced similar accidents were Windscale in the United Kingdom and SL-1 in the United States.
Military accidents usually involve the loss or unexpected detonation of nuclear weapons. The Castle Bravo test in 1954 produced a larger yield than expected, which contaminated nearby islands, a Japanese fishing boat (with one fatality), and raised concerns about contaminated fish in Japan. In the 1950s through 1970s, several nuclear bombs were lost from submarines and aircraft, some of which have never been recovered. The last twenty years have seen a marked decline in such accidents.
Examples of environmental benefits
Proponents of nuclear energy note that annually, nuclear-generated electricity reduces 470 million metric tons of carbon dioxide emissions that would otherwise come from fossil fuels. Additionally, the amount of comparatively low waste that nuclear energy does create is safely disposed of by the large scale nuclear energy production facilities or it is repurposed/recycled for other energy uses. Proponents of nuclear energy also bring to attention the opportunity cost of utilizing other forms of electricity. For example, the Environmental Protection Agency estimates that coal kills 30,000 people a year, as a result of its environmental impact, while 60 people died in the Chernobyl disaster. A real world example of impact provided by proponents of nuclear energy is the 650,000 ton increase in carbon emissions in the two months following the closure of the Vermont Yankee nuclear plant.
See also
Atomic age
Lists of nuclear disasters and radioactive incidents
Nuclear power debate
Outline of nuclear technology
Radiology
References
External links
Nuclear Energy Institute – Beneficial Uses of Radiation
Nuclear Technology
National Isotope Development Center – U.S. Government source of isotopes for basic and applied nuclear science and nuclear technology – production, research, development, distribution, and information | Nuclear technology | Physics | 4,663 |
18,933,176 | https://en.wikipedia.org/wiki/Abandonware | Abandonware is a product, typically software, ignored by its owner and manufacturer, which can no longer be found for sale, and for which no official support is available and cannot be bought.
Within an intellectual rights contextual background, abandonware is a software (or hardware) sub-case of the general concept of orphan works. Museums and various organizations dedicated to preserving this software continue to provide legal access.
The term "abandonware" is broad and encompasses many types of old software. Definitions of "abandoned" vary, but in general it is like any item that is abandoned it is ignored by the owner, and as such, product support and possibly copyright enforcement are also "abandoned".
Only 13 percent of all classic games released between 1960 and 2009 are currently commercially available, according to the "Survey of the Video Game Reissue Market in the United States," published in 2023 by Phil Salvador for the Video Game History Foundation and the Software Preservation Network.
Examples of abandonware include The Simpsons: Hit & Run, Lemmings, the first two Civilization games, and all Need for Speed titles released prior to Need for Speed: Hot Pursuit in 2010 (except for 2011's Need for Speed: The Run and Shift 2: Unleashed which are also abandonware.) According to PC Gamer: The Lord of the Rings: The Battle For Middle-earth II, The Neverhood, Black & White, Midtown Madness.
Types
Commercial software unsupported but still owned by a viable company The availability of the software depends on the company's attitude toward the software. In many cases, the company which owns the software rights may not be that which originated it, or may not recognize their ownership. Some companies, such as Borland, make some software available online, in the form of freeware. Others, such as Microsoft and Ubisoft, do not make old versions available for free use and do not permit people to copy the software.
Commercial software owned by a company no longer in business When no owning entity of a software exists, all activities (support, distribution, IP activities etc.) in relationship to this software have ceased. If the rights to a software are non-recoverable in legal limbo ("orphaned work"), the software's rights cannot be bought by another company, and there is no company to enforce the copyright. An example of this is Digital Research's original PL/I compiler for DOS, which was considered for many years as without an owner. Micro Focus, which acquired Novell, which had bought Digital Research's assets, owns this old PL/I compiler, but has a more up-to-date PL/I offering.
Shareware whose author still makes it available Finding historical versions, however, can be difficult since most shareware archives remove past versions with the release of new versions. Authors may or may not make older releases available. Some websites collect and offer for download old versions of shareware, freeware, and (in some cases) commercial applications. In some cases these sites had to remove past versions of software, particularly if the company producing that software still maintains it, or if later software releases introduce digital rights management, whereby old versions could be viewed as DRM circumvention.
Unsupported or unmaintained shareware Occasionally the author of said software will detach from their creation (due to their death in some cases); in the case of trialware, access to the full license could become unavailable after all commercial (rented) links expire, rendering the program impossible to access after the trial ends. This is the case of programs such as ClickRepair.
Open-source and freeware programs that have been abandoned
In some cases, source code remains available, which can prove a historical artifact. One such case is PC-LISP, still found online, which implements the Franz Lisp dialect. The DOS-based PC-LISP still runs well within emulators and on Microsoft Windows.
Orphaned code
The source code or executable might still be available, but the author is unknown or only identified by a dead email or equivalent, and there is no realistic prospect of finding the owner of the IP.
Implications
If a software product reaches end-of-life and becomes abandonware, users are confronted with several potential problems: missing purchase availability (besides used software) and missing technical support, e.g. compatibility fixes for newer hardware and operating systems. These problems are exacerbated if software is bound to physical media with a limited life-expectancy (floppy disks, optical media etc.) and backups are impossible because of copy protection or copyright law. If a software is distributed only in a digital, DRM-locked form or as SaaS, the shutdown of the servers will lead to a public loss of the software. If the software product is without alternatives, the missing replacement availability becomes a challenge for continued software usage.
Once a software product becomes abandonware, there is a high risk that the source code becomes lost or irrecoverable even for its original developers, as multiple cases have shown.
One of many examples is the closure of Atari in Sunnyvale, California in 1996, when the original source codes of several milestones of video game history (such as Asteroids and Centipede) were thrown out as trash, some of which were later recovered.
Unavailability of software and the associated source code can also be a hindrance for software archaeology and research.
Response to abandonware
Early abandonware websites
As response to the missing availability of abandonware, people have distributed old software since shortly after the beginning of personal computing, but the activity remained low-key until the advent of the Internet. While trading old games has taken many names and forms, the term "abandonware" was coined by Peter Ringering in late 1996. Ringering found classic game websites similar to his own, contacted their webmasters, and formed the original Abandonware Ring in February 1997. This original webring was little more than a collection of sites linking to adventureclassicgaming.com. Another was a site indexing them all to provide a rudimentary search facility. In October 1997, the Interactive Digital Software Association sent cease and desist letters to all sites within the Abandonware Ring, which led to most shutting down. An unintended consequence was that it spurred others to create new abandonware sites and organizations that came to outnumber the original Ring members. Sites formed after the demise of the original Abandonware Ring include Abandonia, Bunny Abandonware and Home of the Underdogs. In later years abandonware websites actively acquired and received permissions from developers and copyright holders (e.g. Jeff Minter, Magnetic Fields or Gremlin Interactive) for legal redistribution of abandoned works; an example is World of Spectrum who acquired the permission from many developers and successfully retracted a DMCA case.
Archives
Several websites archive abandonware for download, including old versions of applications that are difficult to find by any other means. Much of this software fits the definition of "software that is no longer current, but is still of interest", but the line separating the use and distribution of abandonware from copyright infringement is blurry, and the term abandonware could be used to distribute software without proper notification of the owner.
The Internet Archive has created an archive of what it describes as "vintage software", as a way to preserve them. The project advocated for an exemption from the United States Digital Millennium Copyright Act to permit them to bypass copy protection, which was approved in 2003 for a period of three years. The exemption was renewed in 2006, and , has been indefinitely extended pending further rulemakings. The Archive does not offer this software for download, as the exemption is solely "for the purpose of preservation or archival reproduction of published digital works by a library or archive." Nevertheless, in 2013 the Internet Archive began to provide antique games as browser-playable emulation via MESS, for instance the Atari 2600 game E.T. the Extra-Terrestrial. Since 23 December 2014 the Internet Archive presents via a browser based DOSBox emulation thousands of archived DOS/PC games for "scholarship and research purposes only".
Starting around 2006, The Library of Congress began the long-time preservation of video games with the Game canon list. In September 2012 the collection had nearly 3,000 games from many platforms and also around 1,500 strategy guides. For instance, the source code of the unreleased PlayStation Portable game Duke Nukem: Critical Mass was discovered in August 2014 to be preserved at the Library of Congress.
Since around 2009 the International Center for the History of Electronic Games (ICHEG) has taken a five-pronged approach to video game preservation: original software and hardware, marketing materials and publications, production records, play capture, and finally the source code. In December 2013 the ICHEG received a donation of several SSI video games, for instance Computer Bismarck, including the source code for preservation. In 2014 a collection of Brøderbund games and a "virtually complete" Atari arcade machine source code and asset collection was added.
In 2010 Computer History Museum began with the preservation of source code of important software, beginning with Apple's MacPaint 1.3. In 2012 the APL programming language followed. Adobe Systems, Inc. donated the Photoshop 1.0.1 source code to the collection in February 2013. The source code is made available to the public under an own non-commercial license. On March 25, 2014, Microsoft followed with the donation of MS-DOS variants as well as Word for Windows 1.1a under their own license. On October 21, 2014, Xerox Alto's source code and other resources followed.
In 2012 a group of European museums and organizations started the European Federation of Game Archives, Museums and Preservation Projects (EFGAMP) to join forces to "Preserve Gaming Legacy". Also in Japan video game software archival happens since several years.
In 2012 the MOMA started with archiving video games and explicitly tries to get the source code of them.
There are also some cases in which the source code of games was given to a fan community for long-time preservation, e.g. several titles of the Wing Commander video game series or Ultima 9 of the Ultima series.
Community support
In response to the missing software support, sometimes the software's user community begins to provide support (bug fixes, compatibility adaptions etc.) even without available source code, internal software documentation and original developer tools. Methods are debugging, reverse engineering of file and data formats, and hacking the binary executables. Often the results are distributed as unofficial patches. Notable examples are Fallout 2, Vampire: The Masquerade – Bloodlines or even Windows 98. Windows XP would also get a community support via unofficial service pack, with POSReady registry hack, as well as Windows 2000 receiving a fanmade extended kernel For instance, in 2012, when the multiplayer game Supreme Commander: Forged Alliance became unsupported abandonware as the official multiplayer server and support was shut down, the game community itself took over with a self-developed multiplayer server and client.
Re-releases by digital distribution
With the new possibility of digital distribution arising in mid-2000, the commercial distribution for many old titles became feasible again as deployment and storage costs dropped significantly. A digital distributor specialized in bringing old games out of abandonware is GOG.com (formerly called Good Old Games) who started in 2008 to search for copyright holders of classic games to release them legally and DRM-free again. For instance, on December 9, 2013 the real-time strategy video game Conquest: Frontier Wars was, after ten years of non-availability, re-released by gog.com, also including the source code.
Arguments for and against distribution
From proponents
Proponents of abandonware preservation argue that it is more ethical to make copies of such software than new software that still sells. Some have incorrectly taken this to mean that abandonware is legal to distribute, although no software written since 1964 is old enough for copyright to have expired in the US. Even in cases where the original company no longer exists, the rights usually belong to someone else, though no one may be able to trace actual ownership, including the owners themselves.
Abandonware advocates also frequently cite historical preservation as a reason for trading abandoned software. Older computer media are fragile and prone to rapid deterioration, necessitating transfer of these materials to more modern, stable media and generation of many copies to ensure the software will not simply disappear. Users of still-functional older computer systems argue for the need of abandonware because re-release of software by copyright holders will most likely target modern systems or incompatible media instead, preventing legal purchase of compatible software.
From game developers with sympathy with abandonware
Some game developers showed sympathy for abandonware websites as they preserve their classical game titles.
Law
In most cases, software classed as abandonware is not in the public domain, as it has never had its original copyright officially revoked and some company or individual may still own rights. While sharing of such software is usually considered copyright infringement, in practice copyright holders rarely enforce their abandonware copyrights for a number of reasons – chiefly among which the software is technologically obsolete and therefore has no commercial value, therefore rendering copyright enforcement a pointless enterprise. By default, this may allow the product to de facto lapse into the public domain to such an extent that enforcement becomes impractical.
Rarely has any abandonware case gone to court, but it is still unlawful to distribute copies of old copyrighted software and games, with or without compensation, in any Berne Convention signatory country.
Enforcement of copyright
Old copyrights are usually left undefended. This can be due to intentional non-enforcement by owners due to software age or obsolescence, but sometimes results from a corporate copyright holder going out of business without explicitly transferring ownership, leaving no one aware of the right to defend the copyright.
Even if the copyright is not defended, copying of such software is still unlawful in most jurisdictions when a copyright is still in effect. Abandonware changes hands on the assumption that the resources required to enforce copyrights outweigh benefits a copyright holder might realize from selling software licenses. Additionally, abandonware proponents argue that distributing software for which there is no one to defend the copyright is morally acceptable, even where unsupported by current law. Companies that have gone out of business without transferring their copyrights are an example of this; many hardware and software companies that developed older systems are long since out of business and precise documentation of the copyrights may not be readily available.
Often the availability of abandonware on the Internet is related to the willingness of copyright holders to defend their copyrights. For example, unencumbered games for Colecovision are markedly easier to find on the Internet than unencumbered games for Mattel Intellivision in large part because there is still a company that sells Intellivision games while no such company exists for the Colecovision.
DMCA
The Digital Millennium Copyright Act (DMCA) can be a problem for the preservation of old software as it prohibits required techniques. In October 2003, the US Congress passed 4 clauses to the DMCA which allow for reverse engineering software in case of preservation.
In November 2006 the Library of Congress approved an exemption to the DMCA that permits the cracking of copy protection on software no longer being sold or supported by its copyright holder so that they can be archived and preserved without fear of retribution.
US copyright law
Currently, US copyright law does not recognize the term or concept of "abandonware" while the general concept "orphan works" is recognized (see Orphan works in the United States). There is a long-held concept of abandonment in trademark law as a direct result of the infinite term of trademark protection. Currently, a copyright can be released into the public domain if the owner clearly does so in writing; however this formal process is not considered abandoning, but rather releasing. Those who do not own a copyright cannot merely claim the copyright abandoned and start using protected works without permission of the copyright holder, who could then seek legal remedy.
Hosting and distributing copyrighted software without permission is illegal. Copyright holders, sometimes through the Entertainment Software Association, send cease and desist letters, and some sites have shut down or removed infringing software as a result. However, most of the Association's efforts are devoted to new games, due to those titles possessing the greatest value.
EU law
In the EU in 2012, an "Orphan Works Directive" (Directive 2012/28/EU) was constituted and is transferred into the members' laws. While the terminology has ambiguities regarding software and especially video games, some scholars argue that abandonware software video games fall under the definition of audiovisual works mentioned there.
Copyright expiration
Once the copyright on a piece of software has expired, it automatically falls into public domain. Such software can be legally distributed without restrictions. However, due to the length of copyright terms in most countries, this has yet to happen for most software. All countries that observe the Berne Convention enforce copyright ownership for at least 50 years after publication or the author's death. However, individual countries may choose to enforce copyrights for longer periods. In the United States, copyright durations are determined based on authorship. For most published works, the duration is 70 years after the author's death. However, for anonymous works, works published under a pseudonym or works made for hire, the duration is 120 years after creation, or 95 years after publication, whichever comes first. In France, copyright durations are 70 years after the relevant date (date of author's death or publication) for either class.
However, because of the length of copyright enforcement in most countries, it is likely that by the time a piece of software defaults to public domain, it will have long become obsolete, irrelevant, or incompatible with any existing hardware. Additionally, due to the relatively short commercial, as well as physical, lifespans of most digital media, it is entirely possible that by the time the copyright expires for a piece of software, it will no longer exist in any form. However, since the largest risk in dealing with abandonware is that of distribution, this may be mitigated somewhat by private users (or organizations such as the Internet Archive) making private copies of such software, which would then be legally redistributable at the time of copyright expiry.
Alternatives to software abandoning
There are alternatives for companies with a software product which faces the end-of-life instead of abandoning the software in an unsupported state.
Availability as freeware
Some user-communities convince companies to voluntarily relinquish copyright on software, putting it into the public domain, or re-license it as freeware. Unlike so-called abandonware, it is perfectly legal to transfer public domain or freely licensed software.
Amstrad is an example which supports emulation and free distribution of CPC and ZX Spectrum hardware ROMs and software. Borland released "antique software" as freeware. Smith Engineering permits not-for-profit reproduction and distribution of Vectrex games and documentation.
Groups that lobby companies to release their software as freeware have met with mixed results. One example is the library of educational titles released by MECC. MECC was sold to Brøderbund, which was sold to The Learning Company. When TLC was contacted about releasing classic MECC titles as freeware, the documentation proving that TLC held the rights to these titles could not be located, and therefore the rights for these titles are "in limbo" and may never be legally released. Lost or unclear copyrights to vintage out-of-print software is not uncommon, as rights to the No One Lives Forever series illustrates.
Support by source code release
The problem of missing technical support for a software can be most effectively solved when the source code becomes available. Therefore, several companies decided to release the source code specifically to allow the user communities to provide further technical software support (bug fixes, compatibility adaptions etc.) themselves, e.g. by community patches or source ports to new computing platforms. For instance, in December 2015 Microsoft released the Windows Live Writer source code to allow the community to continue the support.
Id Software and 3D Realms are early proponents in this practice, releasing the source code for the game engines of some older titles under a free software license (but not the actual game content, such as levels or textures). Also Falcon 4.0's lead designer Kevin Klemmick argued in 2011 that availability of the source code of his software for the community was a good thing:
The chilling effect of drawing a possible lawsuit can discourage release of source code. Efforts to persuade IBM to release OS/2 as open source software were ignored since some of the code was co-developed by Microsoft.
Nevertheless, several notable examples of successfully opened commercial software exist, for instance, the web browser Netscape Communicator, which was released by Netscape Communications on March 31, 1998. The development was continued under the umbrella of the Mozilla Foundation and Netscape Communicator became the basis of several browsers, such as Mozilla Firefox.
Another important example for open sourced general software is the office suite StarOffice which was released by Sun Microsystems in October 2000 as OpenOffice.org and is in continued development as Collabora Online, LibreOffice and Apache OpenOffice, a broad range of enterprise level support options are available.
There are also many examples in the video game domain: Revolution Software released their game Beneath a Steel Sky as freeware and gave the engine's source code to the authors of ScummVM to add support for the game. Other examples are Myth II, Call to Power II and Microsoft's Allegiance which were released to allow the community to continue the support.
See also
List of commercial games released as freeware
List of commercial software with available source code
List of commercial video games with available source code
Orphaned technology
Out of print
Software archaeology
Software release life cycle
Notes
References
Nostalgia
Orphan works
Software distribution
Software maintenance | Abandonware | Engineering | 4,515 |
53,000,969 | https://en.wikipedia.org/wiki/Acetryptine | Acetryptine (INN) (developmental code name W-2965-A), also known as 5-acetyltryptamine (5-AT), is a drug described as an antihypertensive agent which was never marketed. Structurally, acetryptine is a substituted tryptamine, and is closely related to other substituted tryptamines like serotonin (5-hydroxytryptamine). It was developed in the early 1960s. The binding of acetryptine to serotonin receptors does not seem to have been well-investigated, although it was assessed at the 5-HT1A and 5-HT1D receptors and found to bind to them with high affinity. The drug may also act as a monoamine oxidase inhibitor (MAOI); specifically, as an inhibitor of MAO-A.
See also
5-Benzyloxytryptamine
5-Carboxamidotryptamine
5-Ethoxy-DMT
5-Methoxytryptamine
5-Methyltryptamine
5-(Nonyloxy)tryptamine
Azepindole
Indorenate
Metralindole
Pargyline
Pirlindole
Sumatriptan
Tetrindole
References
Antihypertensive agents
Serotonin receptor agonists
Tryptamines
Ketones | Acetryptine | Chemistry | 280 |
195,802 | https://en.wikipedia.org/wiki/Eurasian%20magpie | The Eurasian magpie or common magpie (Pica pica) is a resident breeding bird throughout the northern part of the Eurasian continent. It is one of several birds in the crow family (corvids) designated magpies, and belongs to the Holarctic radiation of "monochrome" magpies. In Europe, "magpie" is used by English speakers as a synonym for the Eurasian magpie: the only other magpie in Europe is the Iberian magpie (Cyanopica cooki), which is limited to the Iberian Peninsula. Despite having a shared name and similar colouration, it is not closely related to the Australian magpie.
The Eurasian magpie is one of the most intelligent birds. The expansion of its nidopallium is approximately the same in its relative size as the brain of chimpanzees, gorillas, orangutans and humans. It is the only non-mamalian species known to pass the mirror test.
Taxonomy and systematics
The magpie was described and illustrated by Swiss naturalist Conrad Gessner in his Historiae animalium of 1555. In 1758, Linnaeus included the species in the 10th edition of his Systema Naturae under the binomial name Corvus pica. The magpie was moved to a separate genus Pica by the French zoologist Mathurin Jacques Brisson in 1760. Pica is the Classical Latin word for this magpie.
The Eurasian magpie is almost identical in appearance to the North American black-billed magpie (Pica hudsonia) and at one time the two species were considered to be conspecific. The English name used was "black-billed magpie" and the scientific name used was Pica pica. In 2000, the American Ornithologists' Union decided to treat the black-billed magpie as a separate species based on studies of the vocalization and behaviour that indicated that the black-billed magpie was closer to the yellow-billed magpie (Pica nuttalli) than to the Eurasian magpie.
The gradual clinal variation over the large geographic range and the intergradation of the different subspecies means that the geographical limits, and acceptance of the various subspecies, vary between authorities. The International Ornithological Congress recognises six subspecies (a seventh, P. p. hemileucoptera, is included in P. p. bactriana):
P. p. fennorum – Lönnberg, 1927: northern Scandinavia and northwest Russia
P. p. pica – (Linnaeus, 1758): British Isles and southern Scandinavia east to Russia, south to Mediterranean, including most islands
P. p. melanotos – A.E. Brehm, 1857: Iberian Peninsula
P. p. bactriana – Bonaparte, 1850: Siberia east to Lake Baikal, south to Caucasus, Iraq, Iran, Central Asia and Pakistan
P. p. leucoptera – Gould, 1862: southeast Russia and northeast China
P. p. camtschatica – Stejneger, 1884: northern Sea of Okhotsk, and Kamchatka Peninsula in Russian Far East
Others now considered as distinct species:
P. mauritanica – Malherbe, 1845: North Africa (Morocco, northern Algeria and Tunisia) (now considered a separate species, the Maghreb magpie)
P. asirensis – Bates, 1936: southwest Saudi Arabia (now considered a separate species, the Asir magpie)
P. serica – Gould, 1845: east and south China, Taiwan, north Myanmar, north Laos and north Vietnam (now considered a separate species, the Oriental magpie)
P. bottanensis – Delessert, 1840: west central China (now considered a separate species, the black-rumped magpie)
A study using both mitochondrial and nuclear DNA found that magpies in eastern and northeastern China are genetically very similar to each other, but differ from those in northwestern China and Spain.
Etymology
Magpies were originally known as simply "pies". This is hypothesized to derive from a Proto-Indo-European root *(s)peyk- meaning "pointed", in reference to the beak or perhaps the tail (cf. woodpecker). The prefix "mag" dates from the 16th century and comes from the short form of the given name Margaret, which was once used to mean women in general (as Joe or Jack is used for men today); the pie's call was considered to sound like the idle chattering of a woman, and so it came to be called the "Mag pie". "Pie" as a term for the bird dates to the 13th century, and the word "pied", first recorded in 1552, became applied to other birds that resembled the magpie in having black-and-white plumage.
Description
The adult male of the nominate subspecies, P. p. pica, is in length, of which more than half is the tail. The wingspan is . The head, neck, breast and vent are glossy black with a metallic green and violet sheen; the belly and scapulars (shoulder feathers) are pure white; the wings are black glossed with green or purple, and the primaries have white inner webs, conspicuous when the wing is open. The graduated tail is black, glossed with green and reddish purple. The legs and bill are black; the iris is dark brown. The rump is black with white stripe above which varies in thickness between subspecies. The plumage of the sexes is similar but females are slightly smaller. The tail feathers of both sexes are quite long, about 12–28 cm long. Males of the nominate subspecies weigh while females weigh . The young resemble the adults, but are at first without much of the gloss on the sooty plumage. The young have the malar region pink, and somewhat clear eyes. The tail is much shorter than the adults.
The subspecies differ in their size, the amount of white on their plumage and the colour of the gloss on their black feathers. The Asian subspecies P. p. bactriana has more extensive white on the primaries and a prominent white rump.
Adults undergo an annual complete moult after breeding. Moult begins in June or July and ends in September or October. The primary flight feathers are replaced over a period of three months. Juvenile birds undergo a partial moult beginning about one month later than the adult birds in which their body feathers are replaced but not those of the wings or the tail.
Eurasian magpies have a well-known call. It is a choking chatter "chac-chac" or a repetitive "chac-chac-chac-chac". The young also emit the previous call, although they also emit an acute call similar to a "Uik Uik", which may resemble the barking of a small dog. Both adults and young can emit a kind of hiss barely noticeable from afar.
Distribution and habitat
The range of the magpie extends across temperate Eurasia from Portugal, Spain and Ireland in the west to the Kamchatka Peninsula.
The preferred habit is open countryside with scattered trees and magpies are normally absent from treeless areas and dense forests. They sometimes breed at high densities in suburban settings such as parks and gardens. They can often be found close to the centre of cities.
Magpies are normally sedentary and spend winters close to their nesting territories but birds living near the northern limit of their range in Sweden, Finland and Russia can move south in harsh weather.
Behaviour and ecology
Breeding
Some magpies breed after their first year, while others remain in the non-breeding flocks and first breed in their second year. They are monogamous, and the pairs often remain together from one breeding season to the next. They generally occupy the same territory on successive years.
Mating takes place in spring. In the courtship display, males rapidly raise and depress their head feathers, uplift, open and close their tails like fans, and call in soft tones quite distinct from their usual chatter. The loose feathers of the flanks are brought over the primaries, and the shoulder patch is spread so the white is conspicuous, presumably to attract females. Short buoyant flights and chases follow.
Magpies prefer tall trees for their bulky nest, firmly attaching them to a central fork in the upper branches. A framework of the sticks is cemented with earth and clay, and a lining of the same is covered with fine roots. Above is a stout though loosely built dome of prickly branches with a single well-concealed entrance. These huge nests are conspicuous when the leaves fall. Where trees are scarce, though even in well-wooded country, nests are at times built in bushes and hedgerows.
In Europe, clutches are typically laid in April, and usually contain five or six eggs, but clutches with as few as three and as many as ten have been recorded. The eggs are laid in early morning, usually at daily intervals. On average, the eggs of the nominate species measure and weigh . Small for the size of the bird, they are typically pale blue-green, with close specks and spots of olive brown, but show much variation in ground and marking.
The eggs are incubated for 21–22 days by the female, who is fed on the nest by the male. The chicks are altricial, hatching nearly naked with closed eyes. They are brooded by the female for the first 5–10 days and fed by both parents. Initially the parents eat the faecal sacs of the nestlings, but as the chicks grow larger, they defecate on the edge of the nest. The nestlings open their eyes 7 to 8 days after hatching. Their body feathers start to appear after around 8 days and the primary wing feathers after 10 days. For several days before they are ready to leave the nest, the chicks clamber around the nearby branches. They fledge at around 27 days. The parents then continue to feed the chicks for several more weeks. They also protect the chicks from predators, as their ability to fly is poor, making them vulnerable. On average, only 3 or 4 chicks survive to fledge successfully. Some nests are lost to predators, but an important factor causing nestling mortality is starvation. Magpie eggs hatch asynchronously, and if the parents have difficulty finding sufficient food, the last chicks to hatch are unlikely to survive. Only a single brood is reared, unless disaster overtakes the first clutch.
A study conducted near Sheffield in Britain, using birds with coloured rings on their legs, found that only 22% of fledglings survived their first year. For subsequent years, the survival rate for the adult birds was 69%, implying that for those birds that survive the first year, the average total lifespan was 3.7 years. The maximum age recorded for a magpie is 21 years and 8 months for a bird from near Coventry in England that was ringed in 1925 and shot in 1947.
Feeding
The magpie is omnivorous, eating young birds and eggs, small mammals, insects, scraps and carrion, acorns, grain, and other vegetable substances.
Intelligence
Along with other corvids such as ravens, western jackdaws and crows, the Eurasian magpie is believed to be not only among the most intelligent of birds, but also among the most intelligent of all animals. The Eurasian magpie's nidopallium is approximately the same relative size as those in chimpanzees and humans, and significantly larger than those of the gibbons. Their total brain-to-body mass ratio is equal to most great apes and cetaceans. A 2004 review suggests that the intelligence of the corvid family to which the Eurasian magpie belongs is equivalent to that of the great apes (bonobos, gorillas and orangutans) in terms of social cognition, causal reasoning, flexibility, imagination and prospection.
Magpies have been observed engaging in elaborate social rituals, possibly including the expression of grief. Mirror self-recognition has been demonstrated in European magpies, making them one of only a few species known to possess this capability. The cognitive abilities of the Eurasian magpie are regarded as evidence that intelligence evolved independently in both corvids and primates. This is indicated by tool use, an ability to hide and store food across seasons, episodic memory, and using their own experience to predict the behavior of conspecifics. Another behaviour exhibiting intelligence is cutting their food in correctly sized proportions for the size of their young. In captivity, magpies have been observed counting up to get food, imitating human voices, and regularly using tools to clean their own cages. In the wild, they organise themselves into gangs and use complex strategies hunting other birds and when confronted by predators.
Status
The Eurasian magpie has an extremely large range. The European population is estimated to be between 7.5 and 19 million breeding pairs. Allowing for the birds breeding in other continents, the total population is estimated to be between 46 and 228 million individuals. The population trend in Europe has been stable since 1980. There is no evidence of any serious overall decline in numbers, so the species is classified by the International Union for Conservation of Nature as being of Least Concern.
Relationship with humans
Traditions, symbolism, and reputation
Europe
In Europe, magpies have been historically demonized by humans, mainly as a result of superstition and myth. The bird has found itself in this situation mainly by association, says Steve Roud: "Large black birds, like crows and ravens, are viewed as evil in British folklore and white birds are viewed as good". In European folklore, the magpie is associated with a number of superstitions surrounding its reputation as an omen of ill fortune. In the 19th century book, A Guide to the Scientific Knowledge of Things Familiar, a proverb concerning magpies is recited: "A single magpie in spring, foul weather will bring". The book further explains that this superstition arises from the habits of pairs of magpies to forage together only when the weather is fine. In Scotland, a magpie near the window of the house is said to foretell death. An English tradition holds that a single magpie be greeted with a salutation in order to ward off the bad luck it may bring. A greeting might be something like "Good morning, Mr Magpie, how are Mrs Magpie and all the other little magpies?", and a 19th century version recorded in Shropshire is to say "Devil, Devil, I defy thee! Magpie, magpie, I go by thee!" and to spit on the ground three times.
In Britain and Ireland, a widespread traditional rhyme, "One for Sorrow", records the myth (it is not clear whether it has been seriously believed) that seeing magpies predicts the future, depending on how many are seen. There are many regional variations on the rhyme, which means that it is impossible to give a definitive version.
In Italian, British and French folklore, magpies are believed to have a penchant for picking up shiny items, particularly precious stones or metal objects. Rossini's opera La gazza ladra and The Adventures of Tintin comic The Castafiore Emerald are based on this theme. However, one recent research study has cast doubt on the veracity of this belief. In Bulgarian, Czech, German, Hungarian, Polish, Russian, Slovak and Swedish folklore the magpie is seen as a thief. In Hungary there is an old saying which said when you heard a magpie singing it meant guests would be coming to your house. Perhaps because the magpie loved to sit on the trees in front of the village houses and signaled when a man was approaching.
In Sweden, it is further associated with witchcraft. In Norway, a magpie is considered cunning and thievish, but also the bird of hulder, the underground people.
Magpies have been attacked for their role as predators, which includes eating other birds' eggs and their young, mostly smaller songbirds. However, one study has disputed the view that they affect total song-bird populations, finding "no evidence of any effects of [magpie] predator species on songbird population growth rates. We therefore had no indication that predators had a general effect on songbird population growth rates". Another study has claimed that smaller songbird populations increased in places where magpie populations were high and that they do not have a negative impact on the total songbird population.
Citations
Cited sources
Further reading
External links
Ageing and sexing (PDF; 2.9 MB) by Javier Blasco-Zumeta & Gerd-Michael Heinze
Feathers of Eurasian magpie
Pica (genus)
Tool-using animals
Birds of Eurasia
Birds described in 1758
Taxa named by Carl Linnaeus | Eurasian magpie | Biology | 3,451 |
43,009,564 | https://en.wikipedia.org/wiki/Candida%20zemplinina | Candida zemplinina is a yeast species that is osmotolerant, psychrotolerant and ferments sweet botrytized wines. Its type strain is 10-372T (=CBS 9494T =NCAIM Y016667T).
References
Further reading
Fungi described in 2003
zemplinina
Yeasts
Fungus species | Candida zemplinina | Biology | 77 |
73,390 | https://en.wikipedia.org/wiki/Residue%20theorem | In complex analysis, the residue theorem, sometimes called Cauchy's residue theorem, is a powerful tool to evaluate line integrals of analytic functions over closed curves; it can often be used to compute real integrals and infinite series as well. It generalizes the Cauchy integral theorem and Cauchy's integral formula. The residue theorem should not be confused with special cases of the generalized Stokes' theorem; however, the latter can be used as an ingredient of its proof.
Statement of Cauchy's residue theorem
The statement is as follows:
Residue theorem: Let be a simply connected open subset of the complex plane containing a finite list of points and a function holomorphic on Letting be a closed rectifiable curve in and denoting the residue of at each point by and the winding number of around by the line integral of around is equal to times the sum of residues, each counted as many times as winds around the respective point:
If is a positively oriented simple closed curve, is if is in the interior of and if not, therefore
with the sum over those inside
The relationship of the residue theorem to Stokes' theorem is given by the Jordan curve theorem. The general plane curve must first be reduced to a set of simple closed curves whose total is equivalent to for integration purposes; this reduces the problem to finding the integral of along a Jordan curve with interior The requirement that be holomorphic on is equivalent to the statement that the exterior derivative on Thus if two planar regions and of enclose the same subset of the regions and lie entirely in hence
is well-defined and equal to zero. Consequently, the contour integral of along is equal to the sum of a set of integrals along paths each enclosing an arbitrarily small region around a single — the residues of (up to the conventional factor at Summing over we recover the final expression of the contour integral in terms of the winding numbers
In order to evaluate real integrals, the residue theorem is used in the following manner: the integrand is extended to the complex plane and its residues are computed (which is usually easy), and a part of the real axis is extended to a closed curve by attaching a half-circle in the upper or lower half-plane, forming a semicircle. The integral over this curve can then be computed using the residue theorem. Often, the half-circle part of the integral will tend towards zero as the radius of the half-circle grows, leaving only the real-axis part of the integral, the one we were originally interested in.
Calculation of residues
Examples
An integral along the real axis
The integral
arises in probability theory when calculating the characteristic function of the Cauchy distribution. It resists the techniques of elementary calculus but can be evaluated by expressing it as a limit of contour integrals.
Suppose and define the contour that goes along the real line from to and then counterclockwise along a semicircle centered at 0 from to . Take to be greater than 1, so that the imaginary unit is enclosed within the curve. Now consider the contour integral
Since is an entire function (having no singularities at any point in the complex plane), this function has singularities only where the denominator is zero. Since , that happens only where or . Only one of those points is in the region bounded by this contour. Because is
the residue of at is
According to the residue theorem, then, we have
The contour may be split into a straight part and a curved arc, so that
and thus
Using some estimations, we have
and
The estimate on the numerator follows since , and for complex numbers along the arc (which lies in the upper half-plane), the argument of lies between 0 and . So,
Therefore,
If then a similar argument with an arc that winds around rather than shows that
and finally we have
(If then the integral yields immediately to elementary calculus methods and its value is .)
Evaluating zeta functions
The fact that has simple poles with residue 1 at each integer can be used to compute the sum
Consider, for example, . Let be the rectangle that is the boundary of with positive orientation, with an integer . By the residue formula,
The left-hand side goes to zero as since is uniformly bounded on the contour, thanks to using on the left and right side of the contour, and so the integrand has order over the entire contour. On the other hand,
where the Bernoulli number
(In fact, .) Thus, the residue is . We conclude:
which is a proof of the Basel problem.
The same argument works for all where is a positive integer, giving usThe trick does not work when , since in this case, the residue at zero vanishes, and we obtain the useless identity .
Evaluating Eisenstein series
The same trick can be used to establish the sum of the Eisenstein series:
See also
Residue (complex analysis)
Cauchy's integral formula
Glasser's master theorem
Jordan's lemma
Methods of contour integration
Morera's theorem
Nachbin's theorem
Residue at infinity
Logarithmic form
Notes
References
External links
Residue theorem in MathWorld
Theorems in complex analysis
Analytic functions | Residue theorem | Mathematics | 1,070 |
33,869,124 | https://en.wikipedia.org/wiki/P-adic%20gamma%20function | In mathematics, the p-adic gamma function Γp is a function of a p-adic variable analogous to the gamma function. It was first explicitly defined by , though pointed out that implicitly used the same function. defined a p-adic analog Gp of log Γ. had previously given a definition of a different p-adic analogue of the gamma function, but his function does not have satisfactory properties and is not used much.
Definition
The p-adic gamma function is the unique continuous function of a p-adic integer x (with values in ) such that
for positive integers x, where the product is restricted to integers i not divisible by p. As the positive integers are dense with respect to the p-adic topology in , can be extended uniquely to the whole of . Here is the ring of p-adic integers. It follows from the definition that the values of are invertible in ; this is because these values are products of integers not divisible by p, and this property holds after the continuous extension to . Thus . Here is the set of invertible p-adic integers.
Basic properties of the p-adic gamma function
The classical gamma function satisfies the functional equation for any . This has an analogue with respect to the Morita gamma function:
The Euler's reflection formula has its following simple counterpart in the p-adic case:
where is the first digit in the p-adic expansion of x, unless , in which case rather than 0.
Special values
and, in general,
At the Morita gamma function is related to the Legendre symbol :
It can also be seen, that hence as .
Other interesting special values come from the Gross–Koblitz formula, which was first proved by cohomological tools, and later was proved using more elementary methods. For example,
where denotes the square root with first digit 3, and denotes the square root with first digit 2. (Such specifications must always be done if we talk about roots.)
Another example is
where is the square root of in congruent to 1 modulo 3.
p-adic Raabe formula
The Raabe-formula for the classical Gamma function says that
This has an analogue for the Iwasawa logarithm of the Morita gamma function:
The ceiling function to be understood as the p-adic limit such that through rational integers.
Mahler expansion
The Mahler expansion is similarly important for p-adic functions as the Taylor expansion in classical analysis. The Mahler expansion of the p-adic gamma function is the following:
where the sequence is defined by the following identity:
See also
Gross–Koblitz formula
References
Number theory
P-adic numbers | P-adic gamma function | Mathematics | 558 |
8,624,952 | https://en.wikipedia.org/wiki/Current%20differencing%20transconductance%20amplifier | Current differencing transconductance amplifier (CDTA) is a new active circuit element.
Properties
The CDTA is not free from parasitic input capacitances and it can operate in a wide frequency range due to current-mode operation. Some voltage and current mode applications using this element have already been reported in literature, particularly from the area of frequency filtering: general higher-order filters, biquad circuits, all-pass sections, gyrators, simulation of grounded and floating inductances and LCR ladder structures. Other studies propose CDTA-based high-frequency oscillators. Nonlinear CDTA applications are also expected, particularly precise rectifiers, current-mode Schmitt triggers for measuring purposes and signal generation, current-mode multipliers, etc.
Basic operation
The CDTA element with its schematic symbol in Fig 1 has a pair of low-impedance current inputs and p, n and an auxiliary terminal z, whose outgoing current is the difference of input currents. Here, output terminal currents are equal in magnitude, but flow in opposite directions, and the product of transconductance () and the voltage at the z terminal gives their magnitudes. Therefore, this active element can be characterized with the following equations:
,
,
,
.
where and is the external impedance connected to z terminal of the CDTA. CDTA can be thought as a combination of a current differencing unit followed by a dual-output operational transconductance amplifier, DO-OTA. Ideally, the OTA is assumed as an ideal voltage-controlled current source and can be described by , where Ix is output current, and denote non-inverting and inverting input voltage of the OTA, respectively. Note that gm is a function of the bias current. When this element is used in CDTA, one of its input terminals is grounded (e.g., ). With dual output availability, condition is assumed.
References
Biolek, D.: CDTA – Building Block for Current- Mode Analog Signal Processing. In: Proceedings of the ECCTD’03, Kraków, Poland, Vol. III, (2003), 397-400
Keskin A.Ü., Biolek, D., Hancioglu, E., Biolková, V: Current-mode KHN filter employing current differencing transconductance amplifiers, AEU — International Journal of Electronics and Communications, 60, (2006), 443-446
Chen, H. Tsao, C. Chen,: Operational transresistance amplifier using CMOS technology. Electronic Letters., 28, 22 (1992), 2087–2088.
Electronic amplifiers | Current differencing transconductance amplifier | Technology | 564 |
216,792 | https://en.wikipedia.org/wiki/Vampire%20tap | A vampire tap (also called a piercing tap) is a device for physically connecting a station, typically a computer, to a network that used 10BASE5 cabling. This device clamped onto and "bit" into the cable (hence the name "vampire"), inserting a probe through a hole drilled using a special tool through the outer shielding to contact the inner conductor, while other spikes bit into the outer conductor.
The vampire tap usually had an integrated AUI (Attachment Unit Interface) in the form of a DA-15 connector, from which a short multicore cable connected to the network card in the station (host computer).
Vampire taps allowed new connections to be made on a given physical cable while the cable was in use. This allowed administrators to expand bus topology network sections without interrupting communications. Without a vampire tap, the cable had to be cut and connectors had to be attached to both ends.
See also
Network tap
Insulation-displacement connector
References
Ethernet cables
Networking hardware | Vampire tap | Technology,Engineering | 199 |
52,286,500 | https://en.wikipedia.org/wiki/Dewan%20Singh%20Bhakuni | Dewan Singh Bhakuni (30 December 1930 – 22 April 2021) was an Indian natural product chemist, stereochemist who was a director general-grade scientist of the Central Drug Research Institute. He is known for his researches on the biogenesis of alkaloids and is an elected fellow of the Indian Academy of Sciences, the National Academy of Sciences, India and the Indian National Science Academy. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 1975, for his contributions to chemical sciences.
Biography
D. S. Bhakuni, born on 30 December 1930 in the Indian state of Uttar Pradesh, graduated in chemistry from Allahabad University and completed his master's degree at the same institution. He started his career in 1958 as a teaching faculty but a year later, joined Central Drug Research Institute (CDRI), Lucknow and worked there for three years. His next move was to National Botanical Research Institute in 1962 but later went to the UK to pursue his doctoral studies. He secured a Phd in 1965 from the University of London under the guidance of Sir Derek Barton of Imperial College London, a renowned organic chemist and 1969 Nobel laureate; his thesis being Studies in alkaloid biosynthesis. He would also receive the degree of Doctor of Science from London University in 1978. Returning to India, he joined CDRI in 1965 where he spent the rest of his official career till his superannuation in 1990 as a director general-grade scientist. In between, he had a stint at University of Concepción, Chile as a visiting professor. Post-retirement, he was selected as an emeritus scientist by the Council of Scientific and Industrial Research. Bhakuni died on 22 April 2021, at the age of 90.
Legacy
Bhakuni, during the course of his active researches, studied the structure and stereochemistry of several indigenous plants and synthesized them for finding out the biologically active compounds; his work on the biogenesis of alkaloids was based on these examinations. These studies are known to be pioneering studies on alkaloid biosynthesis and he developed a new methodology for determining the absolute configuration of alkaloids. Thus, he was able to identify the anti-cancer, anti-leishmanial, anti-viral and anti-allergic properties of a number of plants through mass spectrometric and Nuclear magnetic resonance spectroscopy techniques.
Bhakuni documented his researches in a book, Bioactive Marine Natural Products and over 300 articles published in peer-reviewed journals. His writings have been cited by several authors and he has mentored 40 doctoral scholars in their studies. A multidisciplinary program, under the title, Bioactive Substances from Indian Ocean was initiated by him during his days at the Central Drug Research Institute which is still active. He is a former president of the Indian Chemical Society (1996–97) and the Sectional Committee of Indian Science Congress Association (1994) and sat in the council of the Indian National Sciences Academy from 1982 to 1984.
Awards and honors
The Council of Scientific and Industrial Research awarded Bhakuni the Shanti Swarup Bhatnagar Prize, one of the highest Indian science awards, in 1975. A University Grants Commission National Lecturer (1982), he received the Ranbaxy Research Award in 1988 and Sir C. V. Raman Award in 1989. He is also a recipient of Acharya P. C. Ray Memorial Award which he received in 2000. He has delivered a number of award orations; Platinum Jubilee Lecture of Indian Science Congress Association (1993) and Dr R. C. Shah Memorial Lecture of Bombay University (1993) are some of the notable ones among them. He is an elected fellow of all the three major Indian science academies, Indian National Science Academy, Indian Academy of Sciences and the National Academy of Sciences, India.
Citations
Selected bibliography
Books
Articles
See also
Sir Derek Barton
Notes
References
External links
1930 births
2021 deaths
Recipients of the Shanti Swarup Bhatnagar Award in Chemical Science
Scientists from Uttar Pradesh
Indian organic chemists
Alumni of the University of London
Academics of Imperial College London
Academic staff of the University of Concepción
Council of Scientific and Industrial Research
Fellows of the Indian Academy of Sciences
Fellows of the Indian National Science Academy
Fellows of the National Academy of Sciences, India
University of Allahabad alumni
20th-century Indian chemists | Dewan Singh Bhakuni | Chemistry | 901 |
3,159,833 | https://en.wikipedia.org/wiki/Infiltration%20%28hydrology%29 | Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meters per day but can also be measured in other units of distance over time if necessary. The infiltration capacity decreases as the soil moisture content of soils surface layers increases. If the precipitation rate exceeds the infiltration rate, runoff will usually occur unless there is some physical barrier.
Infiltrometers, parameters and rainfall simulators are all devices that can be used to measure infiltration rates.
Infiltration is caused by multiple factors including; gravity, capillary forces, adsorption, and osmosis. Many soil characteristics can also play a role in determining the rate at which infiltration occurs.
Factors that affect infiltration
Precipitation
Precipitation can impact infiltration in many ways. The amount, type, and duration of precipitation all have an impact. Rainfall leads to faster infiltration rates than any other precipitation event, such as snow or sleet. In terms of amount, the more precipitation that occurs, the more infiltration will occur until the ground reaches saturation, at which point the infiltration capacity is reached. The duration of rainfall impacts the infiltration capacity as well. Initially when the precipitation event first starts the infiltration is occurring rapidly as the soil is unsaturated, but as time continues the infiltration rate slows as the soil becomes more saturated. This relationship between rainfall and infiltration capacity also determines how much runoff will occur. If rainfall occurs at a rate faster than the infiltration capacity runoff will occur.
Soil characteristics
The porosity of soils is critical in determining the infiltration capacity. Soils that have smaller pore sizes, such as clay, have lower infiltration capacity and slower infiltration rates than soils that have large pore sizes, such as sands. One exception to this rule is when the clay is present in dry conditions. In this case, the soil can develop large cracks which lead to higher infiltration capacity.
Soil compaction also impacts infiltration capacity. Compaction of soils results in decreased porosity within the soils, which decreases infiltration capacity.
Hydrophobic soils can develop after wildfires have happened, which can greatly diminish or completely prevent infiltration from occurring.
Soil moisture content
Soil that is already saturated has no more capacity to hold more water, therefore infiltration capacity has been reached and the rate cannot increase past this point. This leads to much more surface runoff. When soil is partially saturated then infiltration can occur at a moderate rate and fully unsaturated soils have the highest infiltration capacity.
Organic materials in soils
Organic materials in the soil (including plants and animals) all increase the infiltration capacity. Vegetation contains roots that extend into the soil which create cracks and fissures in the soil, allowing for more rapid infiltration and increased capacity. Vegetation can also reduce the surface compaction of the soil which again allows for increased infiltration. When no vegetation is present infiltration rates can be very low, which can lead to excessive runoff and increased erosion levels. Similarly to vegetation, animals that burrow in the soil also create cracks in the soil structure.
Land cover
If the land is covered by impermeable surfaces, such as pavement, infiltration cannot occur as the water cannot infiltrate through an impermeable surface. This relationship also leads to increased runoff. Areas that are impermeable often have storm drains that drain directly into water bodies, which means no infiltration occurs.
Vegetative cover of the land also impacts the infiltration capacity. Vegetative cover can lead to more interception of precipitation, which can decrease intensity leading to less runoff, and more interception. Increased abundance of vegetation also leads to higher levels of evapotranspiration which can decrease the amount of infiltration rate. Debris from vegetation such as leaf cover can also increase the infiltration rate by protecting the soils from intense precipitation events.
In semi-arid savannas and grasslands, the infiltration rate of a particular soil depends on the percentage of the ground covered by litter, and the basal cover of perennial grass tufts. On sandy loam soils, the infiltration rate under a litter cover can be nine times higher than on bare surfaces. The low rate of infiltration in bare areas is due mostly to the presence of a soil crust or surface seal. Infiltration through the base of a tuft is rapid and the tufts funnel water toward their own roots.
Slope
When the slope of the land is higher runoff occurs more readily which leads to lower infiltration rates.
Process
The process of infiltration can continue only if there is room available for additional water at the soil surface. The available volume for additional water in the soil depends on the porosity of the soil and the rate at which previously infiltrated water can move away from the surface through the soil. The maximum rate at that water can enter soil in a given condition is the infiltration capacity. If the arrival of the water at the soil surface is less than the infiltration capacity, it is sometimes analyzed using hydrology transport models, mathematical models that consider infiltration, runoff, and channel flow to predict river flow rates and stream water quality.
Research findings
Robert E. Horton suggested that infiltration capacity rapidly declines during the early part of a storm and then tends towards an approximately constant value after a couple of hours for the remainder of the event. Previously infiltrated water fills the available storage spaces and reduces the capillary forces drawing water into the pores. Clay particles in the soil may swell as they become wet and thereby reduce the size of the pores. In areas where the ground is not protected by a layer of forest litter, raindrops can detach soil particles from the surface and wash fine particles into surface pores where they can impede the infiltration process.
Infiltration in wastewater collection
Wastewater collection systems consist of a set of lines, junctions, and lift stations to convey sewage to a wastewater treatment plant. When these lines are compromised by rupture, cracking, or tree root invasion, infiltration/inflow of stormwater often occurs. This circumstance can lead to a sanitary sewer overflow, or discharge of untreated sewage into the environment.
Infiltration calculation methods
Infiltration is a component of the general mass balance hydrologic budget. There are several ways to estimate the volume and water infiltration rate into the soil. The rigorous standard that fully couples groundwater to surface water through a non-homogeneous soil is the numerical solution of Richards' equation. A newer method that allows 1-D groundwater and surface water coupling in homogeneous soil layers and that is related to the Richards equation is the Finite water-content vadose zone flow method solution of the Soil Moisture Velocity Equation. In the case of uniform initial soil water content and deep, well-drained soil, some excellent approximate methods exist to solve the infiltration flux for a single rainfall event. Among these are the Green and Ampt (1911) method, Parlange et al. (1982). Beyond these methods, there are a host of empirical methods such as SCS method, Horton's method, etc., that are little more than curve fitting exercises.
General hydrologic budget
The general hydrologic budget, with all the components, with respect to infiltration F. Given all the other variables and infiltration is the only unknown, simple algebra solves the infiltration question.
where
F is infiltration, which can be measured as a volume or length;
is the boundary input, which is essentially the output watershed from adjacent, directly connected impervious areas;
is the boundary output, which is also related to surface runoff, R, depending on where one chooses to define the exit point or points for the boundary output;
P is precipitation;
E is evaporation;
T is transpiration;
ET is evapotranspiration;
S is the storage through either retention or detention areas;
is the initial abstraction, which is the short-term surface storage such as puddles or even possibly detention ponds depending on size;
R is surface runoff.
The only note on this method is one must be wise about which variables to use and which to omit, for doubles can easily be encountered. An easy example of double counting variables is when the evaporation, E, and the transpiration, T, are placed in the equation as well as the evapotranspiration, ET. ET has included in it T as well as a portion of E. Interception also needs to be accounted for, not just raw precipitation.
Richards' equation (1931)
The standard rigorous approach for calculating infiltration into soils is Richards' equation, which is a partial differential equation with very nonlinear coefficients. The Richards equation is computationally expensive, not guaranteed to converge, and sometimes has difficulty with mass conservation.
Finite water-content vadose zone flow method
This method approximates Richards' (1931) partial differential equation that de-emphasizes soil water diffusion. This was established by comparing the solution of the advection-like term of the Soil Moisture Velocity Equation and comparing against exact analytical solutions of infiltration using special forms of the soil constitutive relations. Results showed that this approximation does not affect the calculated infiltration flux because the diffusive flux is small and that the finite water-content vadose zone flow method is a valid solution of the equation is a set of three ordinary differential equations, is guaranteed to converge and to conserve mass. It requires the assumption that the flow occurs in the vertical direction only (1-dimensional) and that the soil is uniform within layers.
Green and Ampt
The name was derived from two men: Green and Ampt. The Green-Ampt method of infiltration estimation accounts for many variables that other methods, such as Darcy's law, do not. It is a function of the soil suction head, porosity, hydraulic conductivity, and time.
where
is wetting front soil suction head (L);
is water content (-);
is hydraulic conductivity (L/T);
is the cumulative depth of infiltration (L).
Once integrated, one can easily choose to solve for either volume of infiltration or instantaneous infiltration rate:
Using this model one can find the volume easily by solving for . However, the variable being solved for is in the equation itself so when solving for this one must set the variable in question to converge on zero, or another appropriate constant. A good first guess for is the larger value of either or . These values can be obtained by solving the model with a log replaced with its Taylor-Expansion around one, of the zeroth and second order respectively. The only note on using this formula is that one must assume that , the water head or the depth of ponded water above the surface, is negligible. Using the infiltration volume from this equation one may then substitute into the corresponding infiltration rate equation below to find the instantaneous infiltration rate at the time, , was measured.
Horton's equation
Named after the same Robert E. Horton mentioned above, Horton's equation is another viable option when measuring ground infiltration rates or volumes. It is an empirical formula that says that infiltration starts at a constant rate, , and is decreasing exponentially with time, . After some time when the soil saturation level reaches a certain value, the rate of infiltration will level off to the rate .
Where
is the infiltration rate at time t;
is the initial infiltration rate or maximum infiltration rate;
is the constant or equilibrium infiltration rate after the soil has been saturated or the minimum infiltration rate;
is the decay constant specific to the soil.
The other method of using Horton's equation is as below. It can be used to find the total volume of infiltration, F, after time t.
Kostiakov equation
Named after its founder Kostiakov is an empirical equation that assumes that the intake rate declines over time according to a power function.
Where and are empirical parameters.
The major limitation of this expression is its reliance on the zero final intake rate. In most cases, the infiltration rate instead approaches a finite steady value, which in some cases may occur after short periods of time. The Kostiakov-Lewis variant, also known as the "Modified Kostiakov" equation corrects this by adding a steady intake term to the original equation.
in integrated form, the cumulative volume is expressed as:
Where
approximates but does not necessarily equate to the final infiltration rate of the soil.
Darcy's law
This method used for infiltration is using a simplified version of Darcy's law. Many would argue that this method is too simple and should not be used. Compare it with the Green and Ampt (1911) solution mentioned previously. This method is similar to Green and Ampt, but missing the cumulative infiltration depth and is therefore incomplete because it assumes that the infiltration gradient occurs over some arbitrary length . In this model the ponded water is assumed to be equal to and the head of dry soil that exists below the depth of the wetting front soil suction head is assumed to be equal to .
where
is wetting front soil suction head
is the depth of ponded water above the ground surface;
is the hydraulic conductivity;
is the vague total depth of subsurface ground in question. This vague definition explains why this method should be avoided.
or
Infiltration rate f (mm hour−1))
is the hydraulic conductivity (mm hour−1));
is the vague total depth of subsurface ground in question (mm). This vague definition explains why this method should be avoided.
is wetting front soil suction head () = () (mm)
is the depth of ponded water above the ground surface (mm);
See also
Blue roof
Contour trenching
Discharge (hydrology)
Drainage basin
Drainage system (agriculture)
Evapotranspiration
Groundwater recharge
Hydrophobic soil
Interception (water)
Natural Resources Conservation Service
Permeability (fluid)
Runoff curve number
Storm Water Management Model
Sustainable urban drainage systems
References
External links
The Experimental Hydrology Wiki Infiltration – Hood Infiltrometer
Hydrology
Soil physics
Aquifers | Infiltration (hydrology) | Physics,Chemistry,Engineering,Environmental_science | 2,902 |
42,533,047 | https://en.wikipedia.org/wiki/Shivar%20Springs%20Bottling%20Company%20Cisterns | Shivar Springs Bottling Company Cisterns is a set of six historic cisterns located near Winnsboro, Fairfield County, South Carolina. They were built about 1900, and are a group of six cylindrical, stuccoed stone cisterns with concrete domes. The Shivar Springs Bottling Company was in operation from about 1900 to about 1950. At first the company produced only mineral water which was sold for medicinal purposes. Later both mineral water and soft drinks were produced from the spring water and shipped throughout the state.
It was added to the National Register of Historic Places in 1984.
References
Industrial buildings and structures on the National Register of Historic Places in South Carolina
Industrial buildings completed in 1900
Buildings and structures in Fairfield County, South Carolina
National Register of Historic Places in Fairfield County, South Carolina
Reservoirs in South Carolina
Bottled water brands
Mineral water | Shivar Springs Bottling Company Cisterns | Chemistry | 169 |
3,541,802 | https://en.wikipedia.org/wiki/Pilot%20experiment | A pilot experiment, pilot study, pilot test or pilot project is a small-scale preliminary study conducted to evaluate feasibility, duration, cost, adverse events, and improve upon the study design prior to performance of a full-scale research project.
Implementation
Pilot experiments are frequently carried out before large-scale quantitative research, in an attempt to avoid time and money being used on an inadequately designed project. A pilot study is usually carried out on members of the relevant population. A pilot study is used to formulate the design of the full-scale experiment which then can be adjusted. The pilot study is potentially a critical insight to clinical trial design,
recruitment and sample size of participants, treatment testing, and statistical analysis to improve the power of testing the hypothesis of the study. Analysis from the pilot experiment can be added to the full-scale (and more expensive) experiment to improve the chances of a clear outcome.
Applications
In sociology, pilot studies can be referred to as small-scale studies that will help identify design issues before the main research is done. Although pilot experiments have a well-established tradition, their usefulness as a strategy for change has been questioned, at least in the domain of environmental management. Extrapolation from a pilot study to large scale strategy may not be assumed as possible, partly due to the exceptional resources and favorable conditions that accompany a pilot study.
In clinical research, studies conducted in preparation for a future randomized controlled trial are known as "pilot" and "feasibility" studies, where pilot studies are a subset of feasibility studies. A feasibility study asks whether the study should proceed, and if so, how. A pilot study asks the same questions, but also has a specific design feature: in a pilot study, a future study is conducted on a smaller scale, which, if having produced positive results, may lead to a Phase I clinical trial. The use of pilot and feasibility studies to estimate treatment effect is controversial, with ongoing methodologic discussion about appropriateness.
A checklist was published in 2016 to provide guidance on how to report pilot trials.
In engineering, a pilot trial may be conducted to understand the design problems, learn the correct technique’s or to capture unknown requirements prior to building a prototype. It may use prototype parts or simply samples to see which are successful and which are not, prior to more significant development effort. A pilot can typically be differentiated from a prototype by being significantly different in build, if not in function i.e. it is not intended to be developed into the end product, but to learn how to design and build the end product successfully.
See also
Dry run (testing)
Mass production
Mock-up
Pilot plant
Proof of concept
Prototype
References
Industrial design
Evaluation methods
Scientific method | Pilot experiment | Engineering | 548 |
29,450,015 | https://en.wikipedia.org/wiki/Gajski%E2%80%93Kuhn%20chart | The Gajski–Kuhn chart (or Y diagram) depicts the different perspectives in VLSI hardware design. Mostly, it is used for the development of integrated circuits. Daniel Gajski and Robert Kuhn developed it in 1983. In 1985, Robert Walker and Donald Thomas refined it.
According to this model, the development of hardware is perceived within three domains that are depicted as three axis and produce a Y. Along these axis, the abstraction levels that describe the degree of abstraction. The outer shells are generalisations, the inner ones refinements of the same subject.
The issue in hardware development is most often a top-down design problem. This is perceived by the three domains of behaviour, structure, and the layout that goes top-down to more detailed abstraction levels. The designer can select one of the perspectives and then switch from one view to another. Generally, the design process is not following a specific sequence in this diagram.
On the system level, basic properties of an electronic system are determined. For the behavioural description, block diagrams are used by making abstractions of signals and their time response. Blocks used in the structure domain are CPUs, memory chip, etc.
The algorithmic level is defined by the definition of concurrent algorithms (signals, loops, variables, assignments). In the structural domain, blocks like ALUs are in use.
The register-transfer level (RTL) is a more detailed abstraction level on which the behaviour between communicating registers and logic units is described. Here, data structures and data flows are defined. In the geometric view, the design step of the floorplan is located.
The logical level is described in the behaviour perspective by boolean equations. In the structural view, this is displayed with gates and flip-flops. In the geometric domain, the logical level is described by standard cells.
The behaviour of the circuit level is described by mathematics using differential equations or logical equations. This corresponds to transistors and capacitors up to crystal lattices.
References
External links
Gajski–Kuhn chart
Computer engineering
Electronic design automation
Diagrams | Gajski–Kuhn chart | Technology,Engineering | 425 |
48,485,384 | https://en.wikipedia.org/wiki/Sophie%20Germain%20Prize | The Sophie Germain Prize (in French: Prix Sophie Germain) is an annual mathematics prize awarded by the French Academy of Sciences to researchers who have carried out fundamental research in mathematics. The award has been conferred every year since 2003 and comes with a €8000 cash prize. It is named after the French mathematician Sophie Germain.
Recipients
See also
List of mathematics awards
References
Awards of the French Academy of Sciences
Mathematics awards | Sophie Germain Prize | Technology | 83 |
320,997 | https://en.wikipedia.org/wiki/Symmedian | In geometry, symmedians are three particular lines associated with every triangle. They are constructed by taking a median of the triangle (a line connecting a vertex with the midpoint of the opposite side), and reflecting the line over the corresponding angle bisector (the line through the same vertex that divides the angle there in half). The angle formed by the symmedian and the angle bisector has the same measure as the angle between the median and the angle bisector, but it is on the other side of the angle bisector.
The three symmedians meet at a triangle center called the Lemoine point. Ross Honsberger has called its existence "one of the crown jewels of modern geometry".
Isogonality
Many times in geometry, if we take three special lines through the vertices of a triangle, or cevians, then their reflections about the corresponding angle bisectors, called isogonal lines, will also have interesting properties. For instance, if three cevians of a triangle intersect at a point , then their isogonal lines also intersect at a point, called the isogonal conjugate of .
The symmedians illustrate this fact.
In the diagram, the medians (in black) intersect at the centroid .
Because the symmedians (in red) are isogonal to the medians, the symmedians also intersect at a single point, .
This point is called the triangle's symmedian point, or alternatively the Lemoine point or Grebe point.
The dotted lines are the angle bisectors; the symmedians and medians are symmetric about the angle bisectors (hence the name "symmedian.")
Construction of the symmedian
Let be a triangle. Construct a point by intersecting the tangents from and to the circumcircle. Then is the symmedian of .
first proof. Let the reflection of across the angle bisector of meet at . Then:
second proof. Define as the isogonal conjugate of . It is easy to see that the reflection of about the bisector is the line through parallel to . The same is true for , and so, is a parallelogram. is clearly the median, because a parallelogram's diagonals bisect each other, and is its reflection about the bisector.
third proof. Let be the circle with center passing through and , and let be the circumcenter of . Say lines intersect at , respectively. Since , triangles and are similar. Since
we see that is a diameter of and hence passes through . Let be the midpoint of . Since is the midpoint of , the similarity implies that , from which the result follows.
fourth proof. Let be the midpoint of the arc . , so is the angle bisector of . Let be the midpoint of , and It follows that is the Inverse of with respect to the circumcircle. From that, we know that the circumcircle is an Apollonian circle with foci . So is the bisector of angle , and we have achieved our wanted result.
Tetrahedra
The concept of a symmedian point extends to (irregular) tetrahedra. Given a tetrahedron two planes through are isogonal conjugates if they form equal angles with the planes and . Let be the midpoint of the side . The plane containing the side that is isogonal to the plane is called a symmedian plane of the tetrahedron. The symmedian planes can be shown to intersect at a point, the symmedian point. This is also the point that minimizes the squared distance from the faces of the tetrahedron.
References
External links
Symmedian and Antiparallel at cut-the-knot
Symmedian and 2 Antiparallels at cut-the-knot
Symmedian and the Tangents at cut-the-knot
An interactive Java applet for the symmedian point
Straight lines defined for a triangle | Symmedian | Mathematics | 836 |
49,635,656 | https://en.wikipedia.org/wiki/Retropubic%20paravaginal%20repair | A retropubic paravaginal repair is the surgical procedure to reattach the anterior lateral vaginal wall and its connective tissue to its normal position in the pelvis to correct pelvic organ prolapse. It may be necessary to preserve normal function of pelvic organs after the vagina has detached from its normal position and has moved along with underlying tissues away from the pelvic sidewall. A common finding in repairing this condition is that the arcus tendineus fasciae has become detached. The procedure is usually performed by a gynecological surgeon using pelvic surgery techniques.
Women who experience stress incontinence and who need a paravaginal repair often receive a Burch colposuspension to correct the problem.
References
Gynecological surgery
Reproductive system
Vagina
Women's health | Retropubic paravaginal repair | Biology | 172 |
46,177,274 | https://en.wikipedia.org/wiki/R%20Microscopii | R Microscopii is a star in the constellation Microscopium. It is a red giant star of spectral type M4e that is also a Mira variable, with an apparent magnitude ranging between 8.3 and 13.8 over 138 days. Located around 1000 light-years distant, it shines with a luminosity 444 times that of the Sun and has a surface temperature of 3141 K. The Astronomical Society of Southern Africa in 2003 reported that observations of R Microscopii were urgently needed as data on its light curve was incomplete.
References
Microscopium
M-type giants
Mira variables
Microscopii, R
Emission-line stars
196717
101985
CD-29 17235 | R Microscopii | Astronomy | 147 |
455,570 | https://en.wikipedia.org/wiki/Henry%20Gilman | Henry Gilman (May 9, 1893 – November 7, 1986) was an American organic chemist known as the father of organometallic chemistry. He discovered the Gilman reagent, which bears his name.
Early life and education
Henry Gilman was born in Boston, Massachusetts, as the son of a tailor. He was the third of eight children. Gilman graduated from a Boston high school and later attended Harvard University, where he graduated summa cum laude with a Bachelor of Science degree in 1915. During his final year as an undergraduate at Harvard, Gilman researched with Roger Adams. During this time, the two worked on the synthesis of substituted phenyl esters of oxalic acids. Gilman worked hard on his research describing it as 'a sheer delight' and often worked until midnight 'without any compulsion-just for the joy of it' and claimed this was an important step toward his interest in research. After undergraduate work Gilman was invited to stay for graduate work with the head of the Harvard department of chemistry, E.P. Kohler. Based on his work, he received a Master of Arts degree in 1917 (a year late) and a PhD in 1918.
While attending graduate school, Gilman had an opportunity to travel in Europe as a recipient of the Sheldon Fellowship. He spent time at both the Polytechnicum in Zurich and at Oxford in England. During his time in Europe, Gilman met Madame Curie at the Sorbonne, the historic University of Paris. While staying in Paris, Gilman met Victor Grignard and was intrigued by the advances in organic chemistry in France made possible by Grignard reagents. Once he was able to research independently, Gilman was determined to explore the chemistry of these organometallic reagents.
Career
For a short time after receiving his PhD, Henry Gilman worked an associate professor at the University of Illinois after being invited by his former instructor Roger Adams. In 1919, Gilman moved on to become an assistant professor in charge of organic chemistry at Iowa State College of Agriculture and Mechanic Arts (now Iowa State University). At the age of 30, Gilman was given the title of full professor. While at Iowa State College, Gilman met Ruth V. Shaw, a student of his first-year organic chemistry class, and the two were married in 1929. Gilman switched to the Episcopal church from the Jewish faith upon marriage.
Gilman had high expectations for his graduate students, and it often took them more than twice as long as the norm to earn their degrees. They were expected to work in the research lab well into the night and on weekends. Gilman was known for frequently visiting the lab during the day and questioning each student as to what they had accomplished since his last visit. He would also go on business trips and not inform his secretary or students on when he would come back in an effort to discourage skipping. Gilman had another common practice for his graduate students. He would not assign a research project for his graduate students, but he would push students to produce a series of preparations. Students would write short publications that would spark ideas about additional experiments to perform, drawing all the material together to form a central thesis.
During his career, Gilman consulted for many companies such as Quaker Oats and DuPont, although he continued as a professor at Iowa State University, as it came to be known. At the usual retirement age of 70, at that time, Gilman chose not to retire from Iowa State University and remained active in research until 1975 when he was 82 years old.
World War II brought new opportunities for Gilman to do research for the government. He took part in the Manhattan Project, which was the code name for the government's work on the atom bomb. Gilman concentrated on preparing volatile uranium derivatives, mainly dealing with alkoxides, and the syntheses of species with potential anti-malarial activities.
Later years (1947–1986)
In 1947, due to a combination of glaucoma and detachment of a retina Henry Gilman became blind in one eye and lost most of his vision in the other. He was forced to rely on his wife and students to act as his eyes, to read and write for him. His wife was almost always at his side to guide him in unfamiliar places and inform him of the people around him. Remarkably, he continued much of his work and never let his loss of sight hinder his skills. It could be argued that the majority of Gilman's work was done after 1947. In 1973, the current chemistry building at Iowa State University was renamed Henry Gilman Hall.
Gilman had heart problems late in his life and was fitted with a pace-maker at the age of 88. He died in Ames, IA at the age of 93 and was followed by his wife less than two months later and she was followed by their daughter Jane six months later. They are survived by a son and four grandchildren.
Works
During his lifetime, Gilman completed 1020 papers, 584 of which were published after he became blind in 1947. In 1936, the Journal of Organic Chemistry was created by Gilman with the help of M.S. Kharasch. In 1938, he published a two-volume textbook titled Organic Chemistry: An Advanced Treatise, the first major organic chemistry textbook, with each chapter being contributed by leading leaders in the U.S. Subsequent additions were published in 1943 and another two editions in 1953. Gilman reagents are named after him.
Honors and awards
Elected to National Academy of Sciences, 1945
Iowa Award and Midwest Award of American Chemical Society, 1951
Honorary Fellow of the British Chemical Society, 1961
First American Chemical Society Frederic Stanley Kipping Award in Organosilicon Chemistry, 1962
Distinguished Fellowship Awards, Iowa Academy of Sciences, 1975
Priestley Medal of the American Chemical Society, 1977
Iowa Governor's Science Medal, 1982
Along with his numerous state, national, and international awards and honors, Gilman has had many tributes in his memory at Iowa State University. In 1962, Gilman became a distinguished professor at ISU. The chemistry building on Iowa State University's campus was renamed Gilman Hall in 1974. That same year, the annual series of Gilman Lectures was established. In his memory, the Gilman Graduate Fellowship Fund was established in 1987.
References
Further reading
National Academy of Sciences Biography of Henry Gilman
Iowa State University Visions, Fall 2006
John McMurry, Organic Chemistry, 6th edition (Brooks/Cole-Thomson, 2004, )
Eaborn, C. (1990). Biographical Memoirs: Gilman. Biographical Memoirs of Professor Henry Gilman . England.
External links
National Academy of Sciences Biography of Henry Gilman
1893 births
1986 deaths
Iowa State University faculty
American organic chemists
20th-century American chemists
Jewish American scientists
American blind people
Foreign members of the Royal Society
Harvard University alumni
20th-century American Jews
American scientists with disabilities
Blind scholars and academics | Henry Gilman | Chemistry | 1,403 |
77,602,159 | https://en.wikipedia.org/wiki/Embaphias | Embaphias is a dubious genus of plesiosaur from the Late Cretaceous of North America. It was named by Edward Drinker Cope on the basis of three cervical vertebrae. The type species is E. circulosus.
See also
List of plesiosaur genera
References
Late Cretaceous plesiosaurs of North America
Fossil taxa described in 1894
Taxa named by Edward Drinker Cope
Plesiosaurs
Nomina dubia | Embaphias | Biology | 91 |
26,451,850 | https://en.wikipedia.org/wiki/MALAT1-associated%20small%20cytoplasmic%20RNA | MALAT1-associated small cytoplasmic RNA, also known as mascRNA, is a non-coding RNA found in the cytosol. This is a small RNA, roughly 53–61 nucleotides in length, that is processed from a much longer ncRNA called MALAT1 by an enzyme called RNase P. This RNA is expressed in many different human tissues, is highly conserved by evolution and shares a remarkable similarity to tRNA which is also produced by RNase P, yet this RNA is not aminoacylated in HeLa cells. The primary transcript, MALAT1 (metastasis associated lung adenocarcinoma transcript 1), appears to be upregulated in several malignant cancers.
Another small RNA that is homologous to mascRNA, called menRNA, is processed from another long ncRNA called MEN beta.
MALAT1 appears to be involved in the regulation of alternative splicing. MALAT1 interacts with SR proteins, influencing the distribution of these in nuclear speckle domains.
See also
Long noncoding RNA
MALAT1
NEAT1
References
Further reading
External links
OMIM page for MALAT1
HGNC page for MALAT1
Entrez Gene: MALAT1-associated small cytoplasmic RNA
Non-coding RNA | MALAT1-associated small cytoplasmic RNA | Chemistry | 268 |
32,805,335 | https://en.wikipedia.org/wiki/Wintec%20Industries | Wintec Industries, founded in 1988, is headquartered in Newark, California. Wintec provides original equipment manufacturer (OEM), specialized services in product design, manufacturing, and supply chain services related to memory and storage components, featuring: flash modules (CF, SD, USB, CFast, embedded flash, SSD, etc.), DRAM modules (RDIMM, SODIMM, UDIMM, FBDIMM), wireless products, modem products (embedded and USB), and digital display products (ADD2 DVI, HDMI, and digital signage).
On May 31, 2011, Wintec announced a "strategic alliance" with software developer NTI Corporation.
References
Manufacturing companies based in California
Science and technology in the San Francisco Bay Area
Computer hardware companies
Computer companies of the United States | Wintec Industries | Technology | 168 |
19,667,315 | https://en.wikipedia.org/wiki/Tendril%20perversion | Tendril perversion is a geometric phenomenon sometimes observed in helical structures in which the direction of the helix transitions between left-handed and right-handed. Such a reversal of chirality is commonly seen in helical plant tendrils and telephone handset cords.
The phenomenon was known to Charles Darwin, who wrote in 1865,
The term "tendril perversion" was coined by Alain Goriely and Michael Tabor in 1998 based on the word perversion found in 19th-century science literature. "Perversion" is a transition from one chirality to another and was known to James Clerk Maxwell, who attributed it to topologist J. B. Listing.
Tendril perversion can be viewed as an example of spontaneous symmetry breaking, in which the strained structure of the tendril adopts a configuration of minimum energy while preserving zero overall twist.
Tendril perversion has been studied both experimentally and theoretically. Gerbode et al. have made experimental studies of the coiling of cucumber tendrils. A detailed study of a simple model of the physics of tendril perversion was made by McMillen and Goriely in the early 2000s. Liu et al. showed in 2014 that "the transition from a helical to a hemihelical shape, as well as the number of perversions, depends on the height to width ratio of the strip's cross-section."
Generalized tendril perversions were put forward by Silva et al., to include perversions that can be intrinsically produced in elastic filaments, leading to a multiplicity of geometries and dynamical properties.
See also
Helical growth
Hemihelix
References
External links
A close-up image of a tendril perversion in a tendril of Bryonia dioica by Michael Becker
Helices
Curves
Chirality
Symmetry | Tendril perversion | Physics,Chemistry,Mathematics,Biology | 384 |
47,169,068 | https://en.wikipedia.org/wiki/Penicillium%20proteolyticum | Penicillium proteolyticum is an anamorph species of fungus in the genus Penicillium which produces wortmannin.
References
proteolyticum
Fungi described in 1961
Fungus species | Penicillium proteolyticum | Biology | 46 |
54,804,319 | https://en.wikipedia.org/wiki/Stilbonematinae | Stilbonematinae is a subfamily of the nematode worm family Desmodoridae that is notable for its symbiosis with sulfur-oxidizing bacteria.
Systematics
Stilbonematinae Chitwood, 1936 belongs to the family Desmodoridae in the order Desmodorida. Nine genera have been described.
Adelphos Ott, 1997
Catanema Cobb, 1920
Centonema Leduc, 2013
Eubostrichus Greeff, 1869
Laxus Cobb, 1894
Leptonemella Cobb, 1920
Parabostrichus Tchesunov et al. 2012
Robbea Gerlach, 1956
Squanema Gerlach, 1963
Stilbonema Cobb, 1920
Description
Stilbonematines can be up to 10 mm long, with a club-like head. The worms are completely covered in a coat of ectosymbiotic sulfur-oxidizing bacteria except for the anterior region. The presence of the bacteria, which often contain intracellular inclusions of elemental sulfur, gives the worms a bright white appearance under incident light. They have small mouths and buccal cavities, and short pharynges. Many species have multicellular sensory-glandular organs in longitudinal rows along the length of the body, which secrete mucus that the bacterial symbionts are embedded in.
Stilbonematines are found in the meiofaunal habitat in marine environments. Another group of meiofaunal nematodes with sulfur-oxidizing symbionts is the genus Astomonema, although in Astomonema the bacteria are endo- rather than ectosymbionts.
Symbiosis with sulfur-oxidizing bacteria
The bacterial symbionts of stilbonematines are of different shapes and sizes, ranging from small coccoid cells to elongate crescent-like cells, but each host species has only a single morphological type associated with it. The bacterial symbionts of stilbonematines are closely related to the sulfur-oxidizing symbionts of gutless phallodriline oligochaete worms: these bacteria were all descended from a single ancestor, and each host species has its own specific bacterial species.
The bacterial symbionts are chemosynthetic, gaining energy by oxidizing sulfide from the environment, and producing biomass by fixing carbon dioxide through the Calvin-Benson-Bassham cycle. The bacteria benefit from the symbiosis because the host animal can migrate between sulfide- and oxygen-rich regions of the sediment habitat, and the bacteria require both these chemical substances to produce energy. The hosts are believed to consume the bacteria as a food source, based on evidence from their stable carbon isotope ratios.
The specificity of the bacterial symbionts to their respective host species is controlled by a lectin called Mermaid that is produced by the worms. Mermaid occurs in different isoforms, which have differing affinities for the sugar compositions of the lipopolysaccharide coat in different bacterial species.
See also
Olavius algarvensis - A species of gutless phallodriline oligochaete worms whose sulfur-oxidizing bacterial symbionts are related to those of the stilbonematine nematodes.
Astomonema - A genus of nematodes (from a different family) that also has symbiotic sulfur-oxidizing bacteria.
References
Chromadorea
Chemosynthetic symbiosis | Stilbonematinae | Biology | 721 |
7,044,296 | https://en.wikipedia.org/wiki/Cold%20water%20pitting%20of%20copper%20tube | Cold water pitting of copper tube occurs in only a minority of installations. Copper water tubes are usually guaranteed by the manufacturer against manufacturing defects for a period of 50 years. The vast majority of copper systems far exceed this time period but a small minority may fail after a comparatively short time.
The majority of failures seen are the result of poor installation or operation of the water system. The most common failure seen in the last 20 years is pitting corrosion in cold water tubes, also known as Type 1 pitting. These failures are usually the result of poor commissioning practice although a significant number are initiated by flux left in the bore after assembly of soldered joints. Prior to about 1970 the most common cause of Type 1 pitting was carbon films left in the bore by the manufacturing process.
Research and manufacturing improvements in the 1960s virtually eliminated carbon as a cause of pitting with the introduction of a clause in the 1971 edition of BS 2871 requiring tube bores to be free of deleterious films. Despite this, carbon is still regularly blamed for tube failures without proper investigation.
Copper water tubes
Copper tubes have been used to distribute potable water within building for many years and hundreds of miles are installed throughout Europe every year. The long life of copper when exposed to natural waters is a result of its thermodynamic stability, its high resistance to reacting with the environment, and the formation of insoluble corrosion products that insulate the metal from the environment. The corrosion rate of copper in most potable waters is less than 2.5 μm/year, at this rate a 15 mm tube with a wall thickness of 0.7 mm would last for about 280 years. In some soft waters the general corrosion rate may increase to 12.5 μm/year, but even at this rate it would take over 50 years to perforate the same tube. Despite the reliability of copper and copper alloys, in some cold hard waters pits may form in the bore of a tube. If these pits form, failure times can be expected between 6 months and 2 years from initiation. The mechanism that leads to the pitting of copper in cold hard waters is complex, it requires a water with a specific chemistry that is capable of supporting pit growth and a mechanism for the initiation of the pits.
Pitting
The pits that penetrate the bore are usually covered in a hard pale green nodule of copper sulfate and copper hydroxide salts. If the nodule is removed a hemispherical pit is revealed filled with coarse crystals of red cuprous oxide and green cuprous chloride. The pits are often referred to as Type 1 pits and the form of attack as Type 1 pitting.
Water
The characteristics capable of supporting Type 1 pits were determined empirically by Lucey after examining the compositions of waters in which the pitting behaviour was known. They should be cold, less than 30 °C, hard or moderately hard, 170 to 300 mg/L carbonate hardness, and organically pure. Organically pure waters usually originate from deep wells, or boreholes. Surface waters from rivers or lakes contain naturally occurring organic compounds that inhibit the formation of Type 1 pits, unless a deflocculation treatment has been carried out that removes organic material. Type 1 pitting is relatively uncommon in North America and this may be a result of the lower population density allowing a significant proportion of the potable water to be obtained from surface derived sources. In addition to being cold hard and organically pure, the water needs a specific chemistry. The effect of the water chemistry can be empirically determined though use of the Pitting Propensity Rating (PPR) a number that takes into account the sulfate, chloride, nitrate and sodium ion concentrations of the water as well as its acidity or pH. A water with a positive PPR has been shown to be capable of propagating Type 1 pits.
Initiation
Many waters in both the UK and Europe are capable of supporting Type 1 pitting but no problems will be experienced unless a pit is initiated in the wall of the tube. When a copper tube is initially filled with a hard water salts deposit on the wall and the copper slowly reacts with the water producing a thin protective layer of mixed corrosion products and hardness scale. If any pitting of the tube is to occur then this film must be locally disrupted. Three mechanisms allow the disruption of the protective deposits. The most well known, although now the least common, is the presence of carbon films on the bore. Stagnation and flux residues are the most common initiation mechanisms that have led to Type 1 pitting failures in the last ten years.
Carbon films
Copper tubes are made from the large billets of copper that are gradually worked and drawn down to the required size. As the tubes are drawn they are heat treated to produce the correct mechanical properties. The organic oils and greases used to lubricate the tubes during the drawing processes are broken down during the heat treatment and gradually coat the tube with a film of carbon. If the carbon is left in the bore of the tube then it disrupts the formation of the protective scale and allows the initiation of pits in the wall. The presence of deleterious films, such as carbon, has been prohibited by the British Standards in copper tubes since 1969. All copper tubes for water service are treated, usually by sand (or other nonferrous medium) blasting or acid pickling, to remove any films produced during manufacture with the result that Type 1 pitting initiated by carbon films is now rare.
Stagnation
If water is left to stand in a tube for an extended period, the chemical characteristics of the water change as the mixed scale and corrosion products are deposited. In addition any loose scale that is not well adhered to the wall will not be flushed away and air dissolved in the water will form bubbles, producing air pockets. These processes can lead to a number of problems mainly on horizontal tube runs. Particles of scale that do not adhere to the walls and are not washed away tend to fall into the bottom of the tube producing a coarse porous deposit. Air pockets that develop in horizontal runs disrupt the formation of protective scales in two areas: the water lines at the sides, and the air space at the top of the tube.
In each of the areas that the scale has been disrupted, Type 1 pitting can be initiated. Then, even after the tube has been put back into service, the pit will continue to develop until the wall has perforated. This form of attack is often associated with the commissioning of a system. Once a system has been commissioned it should be either put immediately into service or drained down and dried by flushing with compressed air otherwise pitting may initiate. If either of these options is not possible then the system should be flushed through regularly until it is put into use.
Flux
In plumbing systems fluxes are used to keep the mating surfaces clean during soldering operations. The fluxes often consist of corrosive chemicals such as ammonium chloride and zinc chloride in a binder such as petroleum jelly. If too much is applied to the joint, then the excess flux will melt and run down the bore of a vertical tube or pool in the bottom of a horizontal tube. Where the bore of the tube is covered in a layer of flux it may be locally protected from corrosion but at the edges of the flux pits often initiate. If the tube is put into service in a water that supports Type 1 pitting then these pits will develop and eventually perforate the sides of the tube.
Good working practice
In most cases Type 1 pitting can be avoided by good working practices. Always use tubes that have been manufactured to BS EN 1057. Tubes greater than 10 mm in diameter made to this standard will always be marked the number of the standard, the nominal size, wall thickness and temper of the tube, the manufacturer's identification mark and the date of production at least every 600 mm. Tubes less than 10 mm in diameter will be similarly marked at each end.
Once a system has been commissioned it should be either put immediately into service or drained down and dried. If either of these options is not possible then the system should be flushed though regularly until it is put into use. It should not be left to stand for more than a week. At present stagnation is the most common cause of Type 1 pitting.
Flux should be used sparingly. A small quantity should be painted over the areas to be joined and any excess removed after the joint has been made. Some fluxes are marked as water-soluble but under some circumstances they are not removed before pitting has initiated.
See also
Erosion corrosion of copper water tubes
References
External links
NACE International -Professional society for corrosion engineers ( NACE )
Copper Pipe Corrosion Theory and information on Corrosion of Copper Pipe
Corrosion
Copper
Water | Cold water pitting of copper tube | Chemistry,Materials_science,Environmental_science | 1,773 |
26,132 | https://en.wikipedia.org/wiki/Rankine%20scale | The Rankine scale ( ) is an absolute scale of thermodynamic temperature named after the University of Glasgow engineer and physicist Macquorn Rankine, who proposed it in 1859.
History
Similar to the Kelvin scale, which was first proposed in 1848, zero on the Rankine scale is absolute zero, but a temperature difference of one Rankine degree (°R or °Ra) is defined as equal to one Fahrenheit degree, rather than the Celsius degree used on the Kelvin scale. In converting from kelvin to degrees Rankine, 1 K = °R or 1 K = 1.8 °R. A temperature of 0 K (−273.15 °C; −459.67 °F) is equal to 0 °R.
Usage
The Rankine scale is used in engineering systems where heat computations are done using degrees Fahrenheit.
The symbol for degrees Rankine is °R (or °Ra if necessary to distinguish it from the Rømer and Réaumur scales). By analogy with the SI unit kelvin, some authors term the unit Rankine, omitting the degree symbol.
Some temperatures relating the Rankine scale to other temperature scales are shown in the table below.
See also
Outline of metrology and measurement
Comparison of temperature scales
Notes
References
Bibliography
External links
Scales of temperature
1859 introductions | Rankine scale | Physics,Mathematics | 272 |
28,602,711 | https://en.wikipedia.org/wiki/Rapha%C3%ABl%20Dubois | Raphaël Horace Dubois (20 June 1849, Le Mans – 21 January 1929) was a French pharmacologist known for his work on bioluminescence and anesthesia. He coined the terms proteon and bioproteon, from the Greek "proteon" for matter and "bios" for life. Bioproteon means "living matter". He concluded that there was no difference between matter and living matter.
Dubois' bioluminescence work began when he became a research assistant to Paul Bert in 1882. While initially planning to study the effects of anesthesia on mollusks, witnessing the bioluminescence of Pyrophorus noctilucus inspired him to study the beetle more in depth. Dubois discovered that not only do the adults glow, but so do the unfertilized eggs, embryo, and larvae. Dubois later conducted studies on Scolioplanes crassipes, wherein Dubois discovered the source of its luminescence is in cells of the wall of the gut. Dubois published a paper studying the light production of Pholas dactylus in 1887, in which he coined the terms luciferin and luciferase.
References
1849 births
1929 deaths
Bioluminescence
French pharmacologists
People from Le Mans | Raphaël Dubois | Chemistry,Biology | 258 |
2,281,512 | https://en.wikipedia.org/wiki/Delta%20Eridani | Delta Eridani, which is Latinized from δ Eridani, is the fifth-brightest star in the constellation of Eridanus.
The star is visible to the naked eye and has been observed to vary slightly in brightness between magnitudes 3.51 and 3.56, although subsequent observations did not bear this out. It is relatively near to the Sun, with a distance of about 29.5 light years as determined from parallax. The star is drifting closer with a radial velocity of −6 km/s.
Delta Eridani is sometimes called Rana: Rana means "the frog" in Latin, but derivation of this name is uncertain. The name was approved by the International Astronomic Union on 4 April 2022.
Characteristics
The stellar classification of this star is K0 IV, matching a subgiant star that has exhausted its core hydrogen. This has caused the star to expand and become cooler than a comparable main sequence star. Stellar modelling indicates it is near the end of the subgiant stage and about to transition into a giant. It is an estimated six billion years old with 33% more mass than the Sun. The star has 2.35 times the size of the Sun and is radiating three times the Sun's luminosity from its photosphere at an effective temperature of 5,022 K.
Delta Eridani is catalogued as a suspected RS Canum Venaticorum variable in 1983, but the activity level for the star is very low that this is considered a mistake. A low projected rotational velocity of under 1 km/s and the lack of radial velocity variation suggests that this star is being viewed from nearly pole-on. However, an examination of the star using interferometry does not detect the presence of a companion at the expected distance.
Chinese name
In Chinese, (), meaning Celestial Meadows, refers to an asterism consisting of δ Eridani, γ Eridani, π Eridani, ε Eridani, ζ Eridani, η Eridani, π Ceti, τ1 Eridani, τ2 Eridani, τ3 Eridani, τ4 Eridani, τ5 Eridani, τ6 Eridani, τ7 Eridani, τ8 Eridani and τ9 Eridani. Consequently, the Chinese name for δ Eridani itself is (, .)
See also
List of star systems within 25–30 light-years
References
External links
nStars entry
K-type subgiants
Eridani, Delta
Suspected variables
Eridanus (constellation)
Eridani, Delta
BD-10 0728
Eridani, 23
0150
023249
017378
1136
Rana | Delta Eridani | Astronomy | 558 |
5,838,565 | https://en.wikipedia.org/wiki/Urine-indicator%20dye | Urine-indicator dye is a mythical substance that is supposed to be able to react with urine to form a colored cloud in a swimming pool or hot tub, thus indicating the location of people who are urinating while they are in the water. A 2015 report from the National Swimming Pool Foundation called this "the most common pool myth of all time", with nearly half of Americans surveyed by researchers believing that the dye existed.
Urine is difficult to detect, as many of the naturally occurring compounds within urine are unstable and react freely with common disinfectants, such as chlorine, creating a large number of disinfection by-product (DBP) compounds from the original organic chemicals in urine.
Rumours of the origin of urine indicator-dye go back at least as far as 1958, and the story is commonly told to children by parents who do not want them to urinate in the pool. A 1985 biography of Orson Welles describes him using such a dye as part of a prank in 1937.
References
Fictional materials
Swimming pools
Urban legends
Urine | Urine-indicator dye | Physics,Biology | 212 |
3,728,666 | https://en.wikipedia.org/wiki/Central%20Bureau%20for%20Astronomical%20Telegrams | The Central Bureau for Astronomical Telegrams (CBAT) is an official international clearing house for information relating to transient astronomical events.
The CBAT collects and distributes information on comets, natural satellites, novae, meteors, and other transient astronomical events. The CBAT has historically established priority of discovery (who gets credit for it) and announced initial designations and names of new objects.
On behalf of the International Astronomical Union (IAU) from 1920 to 2015, the CBAT distributed IAU Circulars. From the 1920s to 1992, CBAT sent telegrams in urgent cases, although most circulars were sent via regular mail; when telegrams were dropped, the name "telegram" was kept for historical reasons, and the Central Bureau Electronic Telegrams (CBETs) were begun a decade later as a digital-only expanded version of the IAUCs, still issued by e-mail to subscribers and posted at the CBAT website. Since the mid-1980s the IAU Circulars and the related Minor Planet Circulars have been available electronically.
The CBAT is a non-profit organization, but charges for its IAU Circulars and electronic telegrams to finance its continued operation.
History
The Central Bureau was founded by Astronomische Gesellschaft in 1882 at Kiel, Germany. During World War I it was moved to the Østervold Observatory at Copenhagen, Denmark, to be operated there by the Copenhagen University Observatory.
In 1922, the IAU made the Central Bureau its official Bureau Central des Télégrammes Astronomiques (French for Central Bureau for Astronomical Telegrams), and it remained in Copenhagen until 1965, when it moved to the Harvard College Observatory, to be operated there by the Smithsonian Astrophysical Observatory on the Harvard University campus. In 2010, the CBAT moved from SAO to the Department of Earth and Planetary Sciences at Harvard University.
It has remained in Cambridge, Massachusetts to this day. The HCO had maintained a western-hemisphere Central Bureau from 1883 until the IAU's CBAT moved there at the end of 1964, so logically the HCO staff took over the IAU's Bureau.
See also
List of astronomical societies
Minor Planet Center
References
External links
IAU: Central Bureau for Astronomical Telegrams homepage
The Central Bureau for Astronomical Telegrams: A Case Study in Astronomical Internationalism
Astronomy organizations
Organizations established in 1882
1882 establishments in Germany | Central Bureau for Astronomical Telegrams | Astronomy | 479 |
54,870,250 | https://en.wikipedia.org/wiki/Brando%20Huang | Brando Huang (; born 22 March 1981) is a Taiwanese actor and television host.
Early life and education
Born in Huwei, Yunlin, Huang attended Chien Hsin University of Science and Technology and graduated with a bachelor's degree in electronic engineering. After graduating, he became an engineer at Hsinchu Science and Industrial Park.
Career
Huang had an interest in performing since young. Discovered by comedian Hsu Hsiao-shun, Huang started out by making numerous appearances in television shows where he is known for impersonating famous personalities such as the comedian Kang Kang and musician Wu Bai.
Huang's first acting role was in the series Your Home is My Home, and he has appeared in several films and television series since, including Monga, Monga Yao Hui, Partners in Crime and At Cafe 6. In 2015, he earned a Golden Bell Award nomination for his role in the television film Let the Sunshine In.
Filmography
Television series
Film
Variety show
Music video appearances
Awards and nominations
References
External links
1981 births
Living people
People from Yunlin County
21st-century Taiwanese male actors
Taiwanese male film actors
Taiwanese male television actors
Taiwanese television presenters
Taiwanese engineers
Electronics engineers | Brando Huang | Engineering | 237 |
21,632,953 | https://en.wikipedia.org/wiki/Ribosome-inactivating%20protein | A ribosome-inactivating protein (RIP) is a protein synthesis inhibitor that acts at the eukaryotic ribosome. This protein family describes a large family of such proteins that work by acting as rRNA N-glycosylase (EC 3.2.2.22). They inactivate 60S ribosomal subunits by an N-glycosidic cleavage, which releases a specific adenine base from the sugar-phosphate backbone of 28S rRNA. RIPs exist in bacteria and plants.
Members of the family include shiga toxins, and type I (e.g. trichosanthin and luffin) and type II (e.g. ricin, agglutinin, and abrin) ribosome inactivating proteins (RIPs). All these toxins are structurally related. RIPs have been of considerable interest because of their potential use, conjugated with monoclonal antibodies, as immunotoxins to treat cancers. Further, trichosanthin has been shown to have potent activity against HIV-1-infected T cells and macrophages. Elucidation of the structure-function relationships of RIPs has therefore become a major research effort. It is now known that RIPs are structurally related. A conserved glutamic residue has been implicated in the catalytic mechanism; this lies near a conserved arginine residue, which also plays a role in catalysis.
Only a minority of RIPs are toxic to humans when consumed, and proteins of this family are found in the vast majority of plants used for human consumption, such as Rice, Maize, and Barley. In plants, they are thought to defend against pathogens and insects.
Classification
Ribosome-inactivating proteins (RIPs) are separated into the following types based on protein domain composition:
Type I (A): RIPs-I are polypeptides composed of an A domain. This is the site of N-glycosidase activity.
Type II (AB): RIPs-II are composed of an A domain with similar catalytic activity to Type I RIPs, and a B domain with carbohydrate-binding (lectin) properties. The B domain is able to bind galactosyl moieties on the cell surface which facilitates entry into the cell, thus making Type II particularly cytotoxic. The A and B domains are fused together by disulfide bonds. This group excludes bacterial AB5 toxins such as Shiga toxin, as the carbohydrate-binding ability evolved separately and these toxins are more similar to type I RIPs.
Type III: RIPs-III are separated into two subgroups. One subgroup (AC) contains the same original RIP domain (A), and a C-terminal with unknown functionality. The other subgroup (AD) is similar to Type I, but contains a site for inactivation.
Examples
Examples include:
Abrin
Beetin
Ricin
Saporin
Shiga toxin
A Spiroplasma toxin
Trichosanthin
Viscumin (European mistletoe)
Pokeweed antiviral protein (Phytolacca americana)
References
Protein domains | Ribosome-inactivating protein | Biology | 663 |
3,453,654 | https://en.wikipedia.org/wiki/Ribbon%20controller | A ribbon controller is a tactile sensor used to control synthesizers. It generally consists of a resistive strip that acts as a potentiometer. Because of its continuous control, ribbon controllers are often used to produce glissando effects.
Early examples of the use of ribbon controllers in a musical instrument are in the Ondes Martenot and Trautonium. In some early instruments, the slider of the potentiometer was worn as a ring by the player. In later ribbon controllers, the ring was replaced by a conductive layer that covered the resistive element.
Ribbon controllers are found in early Moog synthesizers, but were omitted from most later synthesizers. The Yamaha CS-80 synthesizer is well-known for its inclusion of a ribbon controller, used by Vangelis to create many of the characteristic sounds in the Blade Runner soundtrack.
Although ribbon controllers are less common in analog later synthesizers, they were used in the Moog Liberation and Micromoog.
There was a resurgence of ribbon controllers on synthesizers in the mid-1990s, beginning with Korg's physical and analog modeling performance synthesizer Prophecy (1995), incorporating a unique pressure/position ribbon mounted on a modulation wheel ("log"), and their Trinity (1995) workstation (which could accommodate a Prophecy counterpart SOLO-TRI option board), as well as Kurzweil's K2500-series workstations (keyboard versions, 1996), which incorporated both a 4-inch pressure/position ribbon and a separate 600mm-long position ribbon programmable into multiple zones. Roland incorporated a ribbon controller in their JP-8000 (1996) synthesizer.
, ribbon controllers are available as control voltage and MIDI peripherals. An example of a modern synthesizer that uses a ribbon controller is the Swarmatron.
Later in 2010/2011, Korg released a series of minisynths called Monotron using the ribbon controller, it became so popular that it still in production in 2023.
References
Sensors
Electronic musical instruments | Ribbon controller | Technology,Engineering | 408 |
50,138,236 | https://en.wikipedia.org/wiki/Nitrososphaera%20gargensis | Nitrososphaera gargensis is a non-pathogenic, small coccus measuring 0.9 ± 0.3 μm in diameter. N. gargensis is observed in small abnormal cocci groupings and uses its archaella to move via chemotaxis. Being an Archaeon, Nitrososphaera gargensis has a cell membrane composed of crenarchaeol, its isomer, and a distinct glycerol dialkyl glycerol tetraether (GDGT), which is significant in identifying ammonia-oxidizing archaea (AOA). The organism plays a role in influencing ocean communities and food production.
Discovery
Nitrososphaera gargensis was discovered in a Garga hot spring in Siberia by Hatzenpichler and associates in 2008. The organism was isolated from a sample taken from the Siberian hot springs that was actually located in a microbial mat. Hatzenpichler et al. later grew the culture aerobically at 46°C with ammonium and bicarbonate. In 2007, the first indications of Nitrososphaera gargensis were found through testing a hot spring sample for ammonia oxidizers. The researchers found ammonia-oxidizing archaea instead of the expected bacteria with this capability since no previous archaea had been found to be able to complete this process. Through analyzing 16S rRNA gene sequences and performing the scientific methods of catalyzed reporter deposition (CARD)-FISH (fluorescence in situ hybridization) and microautoradiography, the researchers determined that the organism in the sample was an ammonia-oxidizing archaea and classified this organism as Candidatus Nitrososphaera gargensis.
Genomics
Nitrososphaera gargensis''' genome is 2.83 Mb in size with a GC content of 48%, which is much larger than most other ammonia-oxidizing archaea. The organism encodes for 3565 protein genes and 37 RNA genes.KEGG GENOME: Candidatus Nitrososphaera Gargensis. KEGG GENOME: Candidatus Nitrososphaera Gargensis. KEGG, 2012. http://www.genome.jp/kegg-bin/show_organism?org=nga N. gargensis also contains a CRISPR-Cas type I system able to target viral DNA, gene duplications in its chaperones, and numerous transposase genes.
Taxonomy and phylogenyN. gargensis neighbors Nitrosopumilus maritimus and Nitrososphaera viennensis on the phylogenetic tree. Like Nitrososphaera gargensis, both of these organisms are chemolithoautotrophic ammonia-oxidizers that thrive in hot and humid habitats. Spang et al. elucidated, in 2012, the notable similarities between N. gargensis and N. viennensis through their nitrification ability and PHA (putatively polyhydroxybutyrate) production along with other elements.
Nitrification and metabolism
As a chemolithoautotroph, Nitrososphaera gargensis performs aerobic oxidation of ammonia to nitrite and breaks down cyanate for energy. N. gargensis also encompasses a flexible carbon metabolism, allowing for the uptake of organic material. Nitrification, the process of oxidizing ammonia to nitrate, is a significant step in the nitrogen cycle. Since nitrogen is limited in marine environments, the recent discovery of ammonia-oxidizing archaea proves to be an active source of study for researchers. N. gargensis possesses ammonia monooxygenase, which is the enzyme that enables the organism the ability to oxidize ammonia, or urea and potentially cyanate as other sources of ammonia.
HabitatNitrososphaera gargensis was discovered in a Garga hot spring and most commonly resides in similar heavy metal-containing thermal springs or can be isolated from microbial mats near hot springs. Besides hot springs, other ammonia-oxidizing archaea are commonly found in soil, freshwater, and the sediments in freshwater. N. gargensis grows best at 46°C and thrives on the presence of ammonia or other nitrogen sources, and it utilizes flagella to move via chemotaxis.
Current research
Crenarchaeol isomer
The membrane composition of ammonia-oxidizing archaea, specifically through a crenarchaeol isomer, can be used to identify them as an AOA. N. gargensis was the first cultivated organism with the ability to produce a significant quantity of the crenarchaeol isomer. With its ability to synthesize crenarchaeol, N. gargensis allows scientists to expand this synthesis also to the Group I.1b Crenarchaeota. These discoveries indicate that these organisms are significant sources of crenarchaeol in their habitats of thermophilic and terrestrial environments and corroborate the association between AOA and crenarchaeol.
Marine nitrogen cycles
Furthermore, Nitrososphaera gargensis influence as an ammonia-oxidizing archaea expands from land to water since its nitrification ability plays a role in the nitrogen cycles that are present in the ocean. The nitrogen cycle determines the interplay of organisms in marine ecosystems and the activity of the ocean.
Food production and fertilizers
Along with influencing the structure of soils and ocean communities, Nitrososphaera gargensis also plays a role in food production. Since nitrogen is required for food production, fertilizers containing nitrogen are used. This leads to pollution that can harm the environment and end up in wastewater. Therefore, researchers are trying to develop ways to remove the nitrogen from the affected areas. Organisms similar to Nitrososphaera gargensis'' were found to oxidize ammonia in this study, and with this knowledge, the researchers plan on coupling this ability with other processes in the nitrogen cycle in order to remove the form of nitrogen that is polluting the area. Such couplings could occur due to the fact that AOA are not affected by nitrous acid concentrations whereas nitrite-oxidizing bacteria are inhibited by this chemical. In this difference, techniques could be developed to foster deammonification, which is more cost-effective. Overall, in these studies, researchers are trying to find the correct balance in a thermophilic bioreactor in order to eliminate nitrogen.
References
Further reading
Archaea taxa
Archaea described in 2014
Candidatus taxa | Nitrososphaera gargensis | Biology | 1,368 |
31,360,061 | https://en.wikipedia.org/wiki/Alazopeptin | Alazopeptin is an antibiotic, with moderate anti-trypanosomal and antitumor activity. It was originally isolated from Streptacidiphilus griseoplanus, sourced from soil near Williamsburg, Iowa. It is also isolated from Kitasatospora azatica It is still largely produced via fermentation broths of that organism. Structurally, alazopeptin is a tripeptide and contains 2 molecules of 6-diazo-5-oxo-L-norleucine and one molecule of L-alanine. In 2021 the biosynthetic pathway of alazopeptin was elucidated.
References
Antibiotics
Allylamines
Diazo compounds
Tripeptides | Alazopeptin | Biology | 152 |
75,880,928 | https://en.wikipedia.org/wiki/Trimethylsulfoxonium | Trimethylsulfoxonium (abbreviated TMSO) is a cation with a formula (CH3)3SO+ consisting of a sulfur atom attached to three methyl groups and one oxygen atom. It has a net charge of +1.
Production
Refluxing dimethyl sulfoxide with methyl iodide can yield trimethylsulfoxonium iodide.
Reactions
Treated with sodium hydride, trimethylsulfoxonium forms dimethylsulfoxonium methylide.
Trimethylsulfoxonium can polymerise to yield polyethylene.
Copper, zinc and palladium ions in water react with trimethylsulfoxonium and sodium hydroxide to form sulfur ylide complexes.
Properties
In the chloride, the sulfur-oxygen bond length is 1.436 Å, sulfur-carbon bond is 1.742. OSC angles are 112.6°, and CSC angles are 106.2°.
List of compounds
References
Organosulfur compounds
Cations
Sulfur ions | Trimethylsulfoxonium | Physics,Chemistry | 214 |
450,555 | https://en.wikipedia.org/wiki/Field%20norm | In mathematics, the (field) norm is a particular mapping defined in field theory, which maps elements of a larger field into a subfield.
Formal definition
Let K be a field and L a finite extension (and hence an algebraic extension) of K.
The field L is then a finite-dimensional vector space over K.
Multiplication by α, an element of L,
,
is a K-linear transformation of this vector space into itself.
The norm, NL/K(α), is defined as the determinant of this linear transformation.
If L/K is a Galois extension, one may compute the norm of α ∈ L as the product of all the Galois conjugates of α:
where Gal(L/K) denotes the Galois group of L/K. (Note that there may be a repetition in the terms of the product.)
For a general field extension L/K, and nonzero α in L, let σ(α), ..., σ(α) be the roots of the minimal polynomial of α over K (roots listed with multiplicity and lying in some extension field of L); then
.
If L/K is separable, then each root appears only once in the product (though the exponent, the degree [L:K(α)], may still be greater than 1).
Examples
Quadratic field extensions
One of the basic examples of norms comes from quadratic field extensions where is a square-free integer.
Then, the multiplication map by on an element is
The element can be represented by the vector
since there is a direct sum decomposition as a -vector space.
The matrix of is then
and the norm is , since it is the determinant of this matrix.
Norm of Q(√2)
Consider the number field .
The Galois group of over has order and is generated by the element which sends to . So the norm of is:
The field norm can also be obtained without the Galois group.
Fix a -basis of , say:
.
Then multiplication by the number sends
1 to and
to .
So the determinant of "multiplying by " is the determinant of the matrix which sends the vector
(corresponding to the first basis element, i.e., 1) to ,
(corresponding to the second basis element, i.e., ) to ,
viz.:
The determinant of this matrix is −1.
p-th root field extensions
Another easy class of examples comes from field extensions of the form where the prime factorization of contains no -th powers, for a fixed odd prime.
The multiplication map by of an element isgiving the matrixThe determinant gives the norm
Complex numbers over the reals
The field norm from the complex numbers to the real numbers sends
to
,
because the Galois group of over has two elements,
the identity element and
complex conjugation,
and taking the product yields .
Finite fields
Let L = GF(qn) be a finite extension of a finite field K = GF(q).
Since L/K is a Galois extension, if α is in L, then the norm of α is the product of all the Galois conjugates of α, i.e.
In this setting we have the additional properties,
Properties of the norm
Several properties of the norm function hold for any finite extension.
Group homomorphism
The norm N : L* → K* is a group homomorphism from the multiplicative group of L to the multiplicative group of K, that is
Furthermore, if a in K:
If a ∈ K then
Composition with field extensions
Additionally, the norm behaves well in towers of fields:
if M is a finite extension of L, then the norm from M to K is just the composition of the norm from M to L with the norm from L to K, i.e.
Reduction of the norm
The norm of an element in an arbitrary field extension can be reduced to an easier computation if the degree of the field extension is already known. This isFor example, for in the field extension , the norm of issince the degree of the field extension is .
Detection of units
For the ring of integers of an algebraic number field , an element is a unit if and only if .
For instance
where
.
Thus, any number field whose ring of integers contains has it as a unit.
Further properties
The norm of an algebraic integer is again an integer, because it is equal (up to sign) to the constant term of the characteristic polynomial.
In algebraic number theory one defines also norms for ideals. This is done in such a way that if I is a nonzero ideal of OK, the ring of integers of the number field K, N(I) is the number of residue classes in – i.e. the cardinality of this finite ring. Hence this ideal norm is always a positive integer.
When I is a principal ideal αOK then N(I) is equal to the absolute value of the norm to Q of α, for α an algebraic integer.
See also
Field trace
Ideal norm
Norm form
Notes
References
Algebraic number theory | Field norm | Mathematics | 1,046 |
648,614 | https://en.wikipedia.org/wiki/Exponential%20integral | In mathematics, the exponential integral Ei is a special function on the complex plane.
It is defined as one particular definite integral of the ratio between an exponential function and its argument.
Definitions
For real non-zero values of x, the exponential integral Ei(x) is defined as
Properties
Several properties of the exponential integral below, in certain cases, allow one to avoid its explicit evaluation through the definition above.
Convergent series
For real or complex arguments off the negative real axis, can be expressed as
where is the Euler–Mascheroni constant. The sum converges for all complex , and we take the usual value of the complex logarithm having a branch cut along the negative real axis.
This formula can be used to compute with floating point operations for real between 0 and 2.5. For , the result is inaccurate due to cancellation.
A faster converging series was found by Ramanujan:
Asymptotic (divergent) series
Unfortunately, the convergence of the series above is slow for arguments of larger modulus. For example, more than 40 terms are required to get an answer correct to three significant figures for . However, for positive values of x, there is a divergent series approximation that can be obtained by integrating by parts:
The relative error of the approximation above is plotted on the figure to the right for various values of , the number of terms in the truncated sum ( in red, in pink).
Asymptotics beyond all orders
Using integration by parts, we can obtain an explicit formulaFor any fixed , the absolute value of the error term decreases, then increases. The minimum occurs at , at which point . This bound is said to be "asymptotics beyond all orders".
Exponential and logarithmic behavior: bracketing
From the two series suggested in previous subsections, it follows that behaves like a negative exponential for large values of the argument and like a logarithm for small values. For positive real values of the argument, can be bracketed by elementary functions as follows:
The left-hand side of this inequality is shown in the graph to the left in blue; the central part is shown in black and the right-hand side is shown in red.
Definition by Ein
Both and can be written more simply using the entire function defined as
(note that this is just the alternating series in the above definition of ). Then we have
The function is related to the exponential generating function of the harmonic numbers:
Relation with other functions
Kummer's equation
is usually solved by the confluent hypergeometric functions and But when and that is,
we have
for all z. A second solution is then given by E1(−z). In fact,
with the derivative evaluated at Another connexion with the confluent hypergeometric functions is that E1 is an exponential times the function U(1,1,z):
The exponential integral is closely related to the logarithmic integral function li(x) by the formula
for non-zero real values of .
Generalization
The exponential integral may also be generalized to
which can be written as a special case of the upper incomplete gamma function:
The generalized form is sometimes called the Misra function , defined as
Many properties of this generalized form can be found in the NIST Digital Library of Mathematical Functions.
Including a logarithm defines the generalized integro-exponential function
Derivatives
The derivatives of the generalised functions can be calculated by means of the formula
Note that the function is easy to evaluate (making this recursion useful), since it is just .
Exponential integral of imaginary argument
If is imaginary, it has a nonnegative real part, so we can use the formula
to get a relation with the trigonometric integrals and :
The real and imaginary parts of are plotted in the figure to the right with black and red curves.
Approximations
There have been a number of approximations for the exponential integral function. These include:
The Swamee and Ohija approximation where
The Allen and Hastings approximation where
The continued fraction expansion
The approximation of Barry et al. where: with being the Euler–Mascheroni constant.
Inverse function of the Exponential Integral
We can express the Inverse function of the exponential integral in power series form:
where is the Ramanujan–Soldner constant and is polynomial sequence defined by the following recurrence relation:
For , and we have the formula :
Applications
Time-dependent heat transfer
Nonequilibrium groundwater flow in the Theis solution (called a well function)
Radiative transfer in stellar and planetary atmospheres
Radial diffusivity equation for transient or unsteady state flow with line sources and sinks
Solutions to the neutron transport equation in simplified 1-D geometries
See also
Goodwin–Staton integral
Bickley–Naylor functions
Notes
References
, Chapter 5.
External links
NIST documentation on the Generalized Exponential Integral
Exponential, Logarithmic, Sine, and Cosine Integrals in DLMF.
Exponentials
Special functions
Special hypergeometric functions
Integrals | Exponential integral | Mathematics | 1,029 |
82,859 | https://en.wikipedia.org/wiki/Hamal | Hamal , designated Alpha Arietis (α Arietis, abbreviated Alpha Ari, α Ari), is the brightest star in the northern zodiacal constellation of Aries.
With an apparent visual magnitude of 2.0, it is the mean 50th-brightest star in the night sky. Based upon parallax measurements made with the Hipparcos astrometry satellite, Hamal is about from Earth. It is a giant star that may host an orbiting planet with a mass greater than Jupiter.
Nomenclature
Alpha Arietis is the star's Bayer designation. It also bears the Flamsteed designation of 13 Arietis.
The traditional name Hamal (also written Hemal, Hamul, Ras Hammel) derives from the Arabic rās al-ħamal "head of the ram", in turn from the name for the constellation as a whole, Al Ħamal "the ram". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Hamal for this star.
In Chinese, (), meaning Bond (asterism), refers to an asterism consisting of Hamal, β Arietis and γ Arietis. Consequently, the Chinese name for Hamal itself is (, ).
Properties
The spectrum of this star matches a stellar classification of , with the luminosity class of III indicating that it is an evolved giant star that has exhausted the supply of hydrogen at its core and is now on the red-giant branch. The 'Ca-1' portion of the classification indicates that it shows weaker than normal lines of calcium in its spectrum. Since 1943, the spectrum of this star has served as one of the stable anchor points by which other stars are classified. It is estimated to have 65% more mass than the Sun, while interferometric measurements using the Navy Precision Optical Interferometer show it to be 15 times larger in diameter. Despite its enlarged girth, this star is still spinning with a slightly faster equatorial azimuthal velocity than the Sun, having a projected rotational velocity of 3.44 km s−1.
Hamal is radiating about 91 times the Sun's luminosity from its outer envelope at an effective temperature of . This is cooler than the surface of the Sun, giving it the orange-hued glow of a K-type star. It is suspected to be slightly variable, with an amplitude of 0.06 magnitude. The abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is only around 60% that in the Sun.
Planetary system
In 2011, the likely presence of a planet in orbit around this star was reported by Byeong-Cheol Lee, et al. It was detected using the radial velocity method, based upon measurements made between 2003 and 2010 at the Bohyunsan Optical Astronomy Observatory in Korea. The object has an orbital period of 381 days and an eccentricity of 0.25. The lower bound on this object's mass is about 1.8 times the mass of Jupiter. The estimated semi-major axis of the planet's orbit is 1.2 astronomical units (AU), which would give it a periapsis distance of 0.9 AU and an apoapsis distance of 1.5 AU. By comparison, the star has a radius of 0.07 AU.
In culture
Hamal's orientation with relation to the Earth's orbit around the Sun gives it a certain importance not apparent from its modest brightness. Between 2000 and 100 BCE, the apparent path of the Sun through the Earth's sky placed it in Aries at the northern vernal equinox, the point in time marking the start of spring in the Northern Hemisphere. This is why most astrology columns in modern newspapers begin with Aries. While the vernal equinox has moved to Pisces since then due to precession of the equinoxes, Hamal has remained in mind as a bright star near what was apparently an important place when people first studied the night sky. Currently (epoch J2000) its declination is almost exactly equal to the latitude of the Tropic of Cancer, meaning it can be used to find the position of that imaginary line when the Sun is not nearby.
The other name of Hamal, Hamul, was used for the name of a U.S. Navy ship, .
In 1953, fictional planet orbiting Alpha Arietis, named Lithia, appeared in A Case of Conscience, a classic science fiction novel by James Blish. The planet serves as the arena of the major part of the story, being a homeworld to a fictional sentient race, being studied by humans. Real-life equivalent of Lithia was unknown at the time of the novel's creation.
Notes
References
External links
GJ 84.3, entry in the Gliese–Jahreiß catalogue (Preliminary Version of the Third Catalogue of Nearby Stars, W. Gliese and H. Jahreiss, 1991, CDS ID V/70A.)
Image of Hamal from Aladin.
The Constellations and Named Stars, Purple Hell.
Aries (constellation)
K-type giants
Stars with proper names
Arietis, Alpha
Arietis, 13
012929
009884
BD+22 0306
0617
Gliese and GJ objects
Planetary systems with one confirmed planet | Hamal | Astronomy | 1,148 |
23,475,732 | https://en.wikipedia.org/wiki/Local%20oxidation%20nanolithography | Local oxidation nanolithography (LON) is a tip-based nanofabrication method. It is based on the spatial confinement on an oxidation reaction under the sharp tip of an atomic force microscope.
The first materials on which LON was demonstrated were Si(111) and polycrystalline tantalum. Subsequently, the technique has been extended to III–V semiconductors, silicon carbide, metals such as titanium, tantalum, aluminium, molybdenum, nickel and niobium; thin films of manganite in the perovskite form; dielectrics like silicon nitride, organosilane self-assembled monolayers, dendritic macromolecules and carbonaceous films.
History
The local oxidation of a surface by means of a scanning probe technique was first observed by Dagata and co-workers in 1990 who locally modified a hydrogen-terminated silicon surface into silicon dioxide by applying a bias voltage between the tip of a scanning tunneling microscope and the surface itself. In 1993 Day and Allee demonstrated the possibility of performing local oxidation experiments with an atomic force microscope, which opened the way to applying the technique to a large variety of materials.
Basic principle
Currently, local oxidation experiments are performed with an atomic force microscope operated in contact or noncontact mode with additional circuits to apply voltage pulses between tip and sample. The local oxidation process is mediated by the formation of a water meniscus.
In order to perform local oxidation nanolithography, the relative humidity in the AFM chamber is kept between 30% and 60%. A voltage pulse is applied between a conductive AFM tip and the sample. The applied voltage induces the formation of a water bridge between tip and sample whenever the amplitude of the voltage pulse is above a certain threshold voltage. When the liquid meniscus is created the applied voltage pulse causes an oxidation reaction by breaking the covalent bonds in the water molecules. The liquid bridge provides the oxyanions (OH−,O−) needed to form the oxide and confines the lateral extension of the region to be oxidized.
The chemical reactions that govern the local oxidation in a metallic substrate (M) are the following:
while hydrogen gas is liberated at the AFM tip through the reduction reaction:
2H+ + 2e- -> H2
When the voltage pulse is off the AFM feedback forces the cantilever to recover its original oscillation amplitude withdrawing the tip from the sample and breaking the liquid meniscus. Finally the AFM continues to scan the sample thus allowing to image MOn nanostructure fabricated during the Local Oxidation process with the very same tip used for its fabrication.
The method to form liquid bridges is so precise that water meniscus diameters of 20 nm or below are easily obtained. This has led to the reproducible fabrication of sub-10 nm structures in silicon and other metallic surfaces.
Experimental setup
Local oxidation experiments can be performed with almost any kind of atomic force microscope. The key requirement is the possibility to apply voltage pulses between the tip and the sample. It is recommendable to enclose the microscope in a chamber where the atmosphere is controlled. In the simplest case, the oxidant is water vapor, which is naturally present in the air. Controlling the relative humidity generally helps to obtain more reproducible results. The size of the fabricated features depends on a number of parameters, such as the distance between the sample and the tip, the amplitude and the duration of the voltage pulse, and the relative humidity of the atmosphere.
Applications
The development of nanometer-scale lithographies is the focus of an intense research activity because progress on nanotechnology depends on the capability to fabricate, position and interconnect nanometer-scale structures.
Patterning
Local Oxidation Nanolithography allows to create a large variety of motives like dots, lines and letters with nanometer accuracy. In 2005, researchers at the Spanish National Research Council in Madrid wrote the first ten lines of Cervantes' Don Quixote on a few square micrometres of silicon. This pattern versatility can be used for information storage or to design etch-resistant nanomasks in order to fabricate nanodevices as well as many other applications.
Data storage
It is possible to store information using dot-like nanostructures created by the local oxidation of a surface. This storage uses the binary code considering the presence of a nanostructure as a 1 and its lack as a 0. In this way information can be stored in a small surface with a single SiO2 dot constituting a bit. In 1999 Cooper et al. demonstrated that this methods allows to obtain an information density of 1.6 Tbit/in2. However, only read-only memories can be fabricated with this technique.
Molecular template growth and preferential deposition
Local oxidation of silicon surfaces by noncontact atomic-force microscopy is an emerging and promising method for patterning surfaces at the nanometer scale due to its very precise control of the feature size. The features created with this technique can be used for the template growth and preferential deposition of different molecules like single-molecule magnets, biomolecules and conjugated organic molecules.
This method of nanopositioning is an important tool for the fabrication of new nanodevices based on the novel properties exhibited by some nanoparticles and molecules. Potential applications of single-molecule magnets (SMMs) such as Mn12 as bits for information storage or qubits for quantum computation require methods for nanoscale-controlled positioning and/or manipulation of those molecules. The patterning of the Mn12 molecules on a silicon surface is achieved by first derivatizing this surface with a self-assembled monolayer of APTES, which leaves it terminated by amino groups (-NH2). Such termination electrostatically repels the Mn12 molecules. Subsequently, a pattern of silicon dioxide is defined by LON. The SMM molecules are predominantly deposited on the oxide motives because of electrostatic attraction. The electrostatic attraction between the silicon oxide fabricated by LON and the Mn12 molecules achieves the preferential deposition of this molecules with a nanoscale accuracy.
Fabrication of nanodevices
By using local oxidation nanolithography as tool for the fabrication of etch-resistant nanomasks, it is possible to fabricate nanoscale electronic devices, such as field-effect transistors, single-electron transistors, Josephson junctions, quantum rings or SQUIDs. LON also allows to fabricate silicon nanowires (SiNWs) in a top-down fashion starting from silicon on insulator (SOI) wafers. Local oxidation nanolithography contributes to the nanometric precision of the device fabrication. This top-down fabrication technique allows the fabrication of a large variety of SiNWs with different shapes, from angular to circular. It also allows the precise positioning of the silicon nanowires in any desired position, making easier its integration; indeed, this technique is compatible with the standard silicon CMOS processing technology. Single crystalline silicon nanowires have already shown a great potential as ultrasensitive sensors by detecting changes in the nanowire conductivity when a specific analyte is present. Local oxidation nanolithography, therefore, is a promising technique to allow the realisation of array of biosensors.
References
External links
Local oxidation nanolithography page in García's research group at CSIC
Miles' research group at the University of Bristol
Quate's group at Stanford University
Scanning probe microscopy
Lithography (microfabrication) | Local oxidation nanolithography | Chemistry,Materials_science | 1,557 |
24,604,906 | https://en.wikipedia.org/wiki/C40H80NO8P | {{DISPLAYTITLE:C40H80NO8P}}
The molecular formula C40H80NO8P (molar mass: 734.03 g/mol) may refer to:
Colfosceril palmitate
Dipalmitoylphosphatidylcholine (DPPC)
Molecular formulas | C40H80NO8P | Physics,Chemistry | 71 |
2,990,507 | https://en.wikipedia.org/wiki/Telent | Telent Technology Services Limited is a British radio, telecommunications, and digital infrastructure systems installation and services provision company. The name is used from 2006 for those parts of the United Kingdom and German services businesses of Marconi Corporation (formerly General Electric Company, GEC) which had not been acquired by Ericsson. Companies with Marconi in their name can trace their ultimate origins, through mergers and takeovers, to The Marconi Company Ltd., founded by Guglielmo Marconi in 1897 as The Wireless Telegraph & Signal Company.
History
The company's predecessor was formed in September 1961 as GEC Telecommunications Limited, a division of the GEC conglomerate. In 1988 the division became part of the GEC Plessey Telecommunications joint venture, and following the breakup of GPT during the 1990s it was renamed Marconi Communications Limited in 1998, when GEC decided to switch to use the better known Marconi brand name which it had owned for some time.
In January 2006, following Ericsson's acquisition of most Marconi assets, including the rights to the Marconi name, the remaining UK and German services business of Marconi Corporation which was not acquired and no longer had the rights to use the Marconi name was renamed Telent. In May 2007, Telent announced its move from Coventry to Warwick's Opus 40 business park.
In November 2007 Telent, which had inherited GEC's £2.5 billion pension scheme with several tens of thousands of members, was purchased by Pension Corporation for £400 million; the following month its shares were delisted and Telent became a private company.
In 2008 Telent made various acquisitions, including intelligent traffic systems group TSEU in March, leading communications infrastructure provider, the Alan Campbell Group, in July and telecoms service provider Premises Networks in September.
In September 2019 the pension scheme, described by Telent as a "disproportionately large liability", was bought out by Rothesay Life.
In September 2020, it was announced that Telent were awarded a contract with Openreach to support a £12 billion project for the UK's largest ultrafast broadband build, which would bring 'Full Fibre' broadband to thousands of homes and businesses.
Operations
The company provides a range of network and communications services to industries including Rail, Traffic, Public Safety, Defence, Service Providers, Enterprise and Public Sector. Products include enterprise software systems, emergency services communications and logistics, integrated warehouse logistics systems and rail and metro systems. Customers include BAE Systems, BT, National Highways, HM Coastguard, Interoute, London Ambulance Service, Merseyside Fire & Rescue, Metropolitan Police, Network Rail, RNLI, Sky, Transport for London, Virgin Media and Vodafone.
The company has many operational sites within the UK and Ireland, including at Chorley in Lancashire, Warwick, Camberley in Surrey, Harbour Exchange in London, and Dublin. A team of telecommunications technicians and engineers provide support and new features development for the TDM System X network used by BT, Virgin Media, Kingston Communications, Vodafone, and Gibtelecom.
People
From its formation in 2006, Telent's CEO was Mark Plato. He died in a motorcycle accident in September 2019. Non-executive director Frank McKay, former CEO of Travis Perkins and Brakes Group, was appointed as his temporary replacement and was succeeded in July 2020 by Jo Gretton, a Telent executive since 2006.
See also
Marconi Electronic Systems
References
Engineering companies of the United Kingdom
Computer companies of the United Kingdom
Computer hardware companies
Telecommunications companies of the United Kingdom
Guglielmo Marconi
Companies formerly listed on the London Stock Exchange
Telecommunications companies established in 2006 | Telent | Technology | 743 |
46,181,068 | https://en.wikipedia.org/wiki/Crisaborole | Crisaborole, sold under the brand name Eucrisa among others, is a nonsteroidal topical medication used for the treatment of mild-to-moderate atopic dermatitis (eczema) in adults and children.
The most common side effects are reactions at the application site (including burning or stinging).
Crisaborole is a phosphodiesterase 4 (PDE-4) inhibitor, although its specific mechanism of action in atopic dermatitis is not known.
Side effects
At the site of application, crisaborole may cause burning or stinging. Rarely, there may be an allergic reaction.
Medical uses
In the US, crisaborole is indicated for topical treatment of mild to moderate atopic dermatitis in people three months of age and older.
In the EU, crisaborole was authorized for treatment of mild to moderate atopic dermatitis in people two years of age and older with ≤ 40% body surface area (BSA) affected.
Pharmacology
Pharmacodynamics
Crisaborole is a phosphodiesterase-4 inhibitor, mainly acting on phosphodiesterase 4B (PDE4B), which causes inflammation. Chemically, crisaborole is a phenoxybenzoxaborole. Inhibition of PDE4B appears to suppress the release of tumor necrosis factor alpha (TNFα), interleukin-12 (IL-12), IL-23 and other cytokines, proteins believed to be involved in the immune response and inflammation.
People with atopic dermatitis produce high levels of cytokines, which can cause the inflammation of the skin seen in dermatitis. Crisaborole blocks the release of certain cytokines involved in the inflammation process such as tumor necrosis factor alpha, interleukins (IL‑2, IL-4, IL-5), and interferon gamma. By blocking their release, crisaborole is expected to ease the inflammation and therefore relieve symptoms of the disease.
Chemistry
Crisaborole (chemical name: 4-[(1-hydroxy-1,3-dihydro-2,1-benzoxaborol-5-yl)oxy]benzonitrile) is a member of the class of benzoxaboroles characterized by the presence of a boronic acid hemiester with a phenolic ether and a nitrile. Crisaborole crystallizes into two polymorphs that differ in the conformation of the oxaborole ring. A cocrystal with 4,4'-bipyridine has been prepared and studied by X-ray crystallography.
History
Crisaborole was developed by Anacor Pharmaceuticals for the topical treatment of psoriasis. During preclinical and clinical development, crisaborole was called AN2728 and PF-06930164. The drug was assumed to be potential $2bn-a-year blockbuster, when Pfizer acquired Anacor Pharmaceuticals. However, the drug was commercially not successful, reaching only in sales in 2018, and in sales in 2019.
Crisaborole was approved for use in the United States in December 2016 and for use in Canada in June 2018.
The safety and efficacy of crisaborole were established in two placebo-controlled trials with a total of 1,522 participants ranging in age from two years of age to 79 years of age, with mild to moderate atopic dermatitis. In both trials participants received treatment with either crisaborole or placebo twice daily for 28 days. Neither the participants nor the health care providers knew which treatment was being given until after the trials were completed. Overall, participants receiving crisaborole achieved greater response with clear or almost clear skin after 28 days of treatment. The trials were conducted in the US.
Crisaborole, approved for the treatment of mild to moderate atopic dermatitis in the European Union, has been rapidly withdrawn from the European market (March 2020 - February 2022).
See also
Tavaborole – a structurally related topical antifungal developed by Anacor
References
Ethers
Nitriles
Boronate esters
PDE4 inhibitors
Drugs developed by Pfizer
Phosphodiesterase inhibitors
Oxaboroles | Crisaborole | Chemistry | 906 |
21,347,660 | https://en.wikipedia.org/wiki/Generating%20Availability%20Data%20System | The Generating Availability Data System (GADS) is a database produced by the North American Electric Reliability Corporation (NERC). It includes annual summary reports comprising the statistics for power stations in the United States and Canada.
GADS is the main source of power station outage data in North America. This reporting system, initiated by the electric utility industry in 1982, expands and extends the data collection procedures begun by the industry in 1963. NERC GADS is recognized today as a valuable source of reliability, availability, and maintainability (RAM) information.
This information, collected for both total unit and major equipment groups, is used by analysts industry-wide in numerous applications. GADS maintains complete operating histories on more than 5,800 generating units representing 71% of the installed generating capacity of the United States and Canada. GADS is a mandatory industry program for conventional generating units 50 MW and larger starting January 1, 2012 and 20 MW and larger starting January 1, 2013. GADS remains open to all non-required participants in the Regional Entities (shown in Figure I-2 of the NERC GADS DRI) and any other organization (domestic or international) that operate electric generating facilities who is willing to follow the GADS mandatory requirements as presented in the document Final GADSTF Recommendations Report dated July 20, 2011.
GADS data consists of three data types:
Design – equipment descriptions such as manufacturers, number of boiler feedwater pumps, steam turbine MW rating, etc.
Performance – summaries of generation produced, fuels units, start ups, etc.
Event – description of equipment failures such as when the event started/ended, type of outage (forced, maintenance, planned), etc.
One example of such detail is that in its data pertaining to forced outages and unplanned unit failures, it makes the fine distinction between immediate, delayed, and postponed outages.
An important statistic calculated from the raw GADS data is the Equivalent Forced Outage Rate (EFOR), which is the hours of unit failure (unplanned outage hours and equivalent unplanned derated hours) given as a percentage of the total hours of the availability of that unit (unplanned outage, unplanned derated, and service hours).
Recently, in response to the deregulated energy markets, the Equivalent Forced Outage Rate – Demand (EFORd) has taken on greater importance:
The probability that a unit will not meet its demand periods for generating requirements.
Best measure of reliability for all loading types (base, cycling, peaking, etc.)
Best measure of reliability for all unit types (fossil, nuclear, gas turbines, diesels, etc.)
For demand period measures and not for the full 24-hour clock.
Industry Development of GADS
Before any data element was included in GADS, an industry committee to determine its applicability to utility operation and RAM analyses scrutinized it. A series of industry meetings were held to discuss the analytical usefulness of each element and to determine if utilities could reasonably provide that data to GADS. Consequently, the only data requested in the GADS Data Reporting Instructions (DRI) meet industry-prescribed needs.
The industry also realized a need to include standardized terminology in the GADS program if it were to function on an international scale. As a result, the definitions promulgated by The Institute of Electrical and Electronics Engineers' (IEEE) Standard 762, "Definitions for Reporting Electric Generating Unit Reliability, Availability and Productivity" were incorporated.
Utilities started their reporting using the GADS guidelines on January 1, 1982.
GADS superseded the earlier data collection procedures begun by the Edison Electric Institute (EEI), a program started in the mid-1960s. GADS contains many of the same elements previously collected by EEI in addition to the many new data items. This seeming duplication of data was done intentionally: the EEI information can be derived from GADS so analyses that include data from earlier than 1982 can be completed.
See also
Availability
References
Electric power | Generating Availability Data System | Physics,Engineering | 822 |
62,289,299 | https://en.wikipedia.org/wiki/Pavel%20Winternitz | Pavel Winternitz (July 25, 1936 – February 13, 2021) was a Canadian Czech-born mathematical physicist. He completed undergraduate studies at Prague University
and received a doctorate from Leningrad University (Ph.D. 1962) under the supervision of J. A. Smorodinsky.
His research is on integrable systems and symmetries.
He was a member of the Mathematical Physics group at the Centre de recherches mathématiques (CRM), a national research centre in mathematics at the Université de Montréal and Professor in the Department of Mathematics and Statistics at Université de Montréal.
His work has had a strong impact in several domains of mathematical physics, and his publications are very widely cited.
In 2001, he was recipient of the CAP-CRM Prize in Theoretical and Mathematical Physics
.
In 2018, he was recipient of the Wigner medal.
He died on 13 February 2021.
References
External links
Centre de recherches mathématiques
P Winternitz publications in Google Scholar
Canadian physicists
Mathematical physicists
Theoretical physicists
Canadian mathematicians
Scientists from Prague
20th-century Canadian physicists
21st-century Canadian scientists
1936 births
20th-century Canadian mathematicians
2021 deaths | Pavel Winternitz | Physics | 235 |
14,816,679 | https://en.wikipedia.org/wiki/Minlos%27s%20theorem | In the mathematics of topological vector spaces, Minlos's theorem states that a cylindrical measure on the dual of a nuclear space is a Radon measure if its Fourier transform is continuous. It is named after Robert Adol'fovich Minlos and can be proved using Sazonov's theorem.
References
Theorems in functional analysis
Theorems regarding stochastic processes | Minlos's theorem | Mathematics | 76 |
4,724,840 | https://en.wikipedia.org/wiki/Space%20physics | Space physics, also known as space plasma physics, is the study of naturally occurring plasmas within Earth's upper atmosphere and the rest of the Solar System. It includes the topics of aeronomy, aurorae, planetary ionospheres and magnetospheres, radiation belts, and space weather (collectively known as solar-terrestrial physics). It also encompasses the discipline of heliophysics, which studies the solar physics of the Sun, its solar wind, the coronal heating problem, solar energetic particles, and the heliosphere.
Space physics is both a pure science and an applied science, with applications in radio transmission, spacecraft operations (particularly communications and weather satellites), and in meteorology. Important physical processes in space physics include magnetic reconnection, synchrotron radiation, ring currents, Alfvén waves and plasma instabilities. It is studied using direct in situ measurements by sounding rockets and spacecraft, indirect remote sensing of electromagnetic radiation produced by the plasmas, and theoretical magnetohydrodynamics.
Closely related fields include plasma physics, which studies more fundamental physics and artificial plasmas; atmospheric physics, which investigates lower levels of Earth's atmosphere; and astrophysical plasmas, which are natural plasmas beyond the Solar System.
History
Space physics can be traced to the Chinese who discovered the principle of the compass, but did not understand how it worked. During the 16th century, in De Magnete, William Gilbert gave the first description of the Earth's magnetic field, showing that the Earth itself is a great magnet, which explained why a compass needle points north. Deviations of the compass needle magnetic declination were recorded on navigation charts, and a detailed study of the declination near London by watchmaker George Graham resulted in the discovery of irregular magnetic fluctuations that we now call magnetic storms, so named by Alexander Von Humboldt. Gauss and William Weber made very careful measurements of Earth's magnetic field which showed systematic variations and random fluctuations. This suggested that the Earth was not an isolated body, but was influenced by external forces – especially from the Sun and the appearance of sunspots. A relationship between individual aurora and accompanying geomagnetic disturbances was noticed by Anders Celsius and Olof Peter Hiorter in 1747. In 1860, Elias Loomis (1811–1889) showed that the highest incidence of aurora is seen inside an oval of 20 - 25 degrees around the magnetic pole. In 1881, Hermann Fritz published a map of the "isochasms" or lines of constant magnetic field.
In the late 1870s, Henri Becquerel offered the first physical explanation for the statistical correlations that had been recorded: sunspots must be a source of fast protons. They are guided to the poles by the Earth's magnetic field. In the early twentieth century, these ideas led Kristian Birkeland to build a terrella, or laboratory device which simulates the Earth's magnetic field in a vacuum chamber, and which uses a cathode ray tube to simulate the energetic particles which compose the solar wind. A theory began to be formulated about the interaction between the Earth's magnetic field and the solar wind.
Space physics began in earnest with the first in situ measurements in the early 1950s, when a team led by Van Allen launched the first rockets to a height around 110 km. Geiger counters on board the second Soviet satellite, Sputnik 2, and the first US satellite, Explorer 1, detected the Earth's radiation belts, later named the Van Allen belts. The boundary between the Earth's magnetic field and interplanetary space was studied by Explorer 10. Future space craft would travel outside Earth orbit and study the composition and structure of the solar wind in much greater detail. These include WIND (spacecraft), (1994), Advanced Composition Explorer (ACE), Ulysses, the Interstellar Boundary Explorer (IBEX) in 2008, and Parker Solar Probe. Other spacecraft would study the sun, such as STEREO and Solar and Heliospheric Observatory (SOHO).
See also
Effects of spaceflight on the human body
Space environment
Space science
Weightlessness
References
Further reading
External links
Atmospheric sciences | Space physics | Astronomy | 842 |
3,982,513 | https://en.wikipedia.org/wiki/Turret%20lathe | A turret lathe is a form of metalworking lathe that is used for repetitive production of duplicate parts, which by the nature of their cutting process are usually interchangeable. It evolved from earlier lathes with the addition of the turret, which is an indexable toolholder that allows multiple cutting operations to be performed, each with a different cutting tool, in easy, rapid succession, with no need for the operator to perform set-up tasks in between (such as installing or uninstalling tools) or to control the toolpath. The latter is due to the toolpath's being controlled by the machine, either in jig-like fashion, via the mechanical limits placed on it by the turret's slide and stops, or via digitally-directed servomechanisms for computer numerical control lathes.
The name derives from the way early turrets took the general form of a flattened cylindrical block mounted to the lathe's cross-slide, capable of rotating about the vertical axis and with toolholders projecting out to all sides, and thus vaguely resembled a swiveling gun turret.
Capstan lathe is the usual name in the UK and Commonwealth, though the two terms are also used in contrast: see below, Capstan versus turret.
History
Turret lathes became indispensable to the production of interchangeable parts and for mass production.
The first turret lathe was built by Stephen Fitch in 1845 to manufacture screws for pistol percussion parts. In the mid-nineteenth century, the need for interchangeable parts for Colt revolvers enhanced the role of turret lathes in achieving this goal as part of the "American system" of manufacturing arms. Clock-making and bicycle manufacturing had similar requirements. Christopher Spencer invented the first fully automated turret lathe in 1873, which led to designs using cam action or hydraulic mechanisms.
From the late-19th through mid-20th centuries, turret lathes, both manual and automatic (i.e., screw machines and chuckers), were one of the most important classes of machine tools for mass production. They were used extensively in the mass production for the war effort in World War II.
Types
There are many variants of the turret lathe. They can be most generally classified by size (small, medium, or large); method of control (manual, automated mechanically, or automated via computer (numerical control (NC) or computer numerical control (CNC)); and bed orientation (horizontal or vertical).
Archetypical: horizontal, manual
In the late 1830s a "capstan lathe" with a turret was patented in Britain. The first American turret lathe was invented by Stephen Fitch in 1845. The archetypical turret lathe, and the first in order of historical appearance, is the horizontal-bed, manual turret lathe. The term "turret lathe" without further qualification is still understood to refer to this type. The formative decades for this class of machine were the 1840s through 1860s, when the basic idea of mounting an indexable turret on a bench lathe or engine lathe was born, developed, and disseminated from the originating shops to many other factories. Some important tool-builders in this development were Stephen Fitch; Gay, Silver & Co.; Elisha K. Root of Colt; J.D. Alvord of the Sharps Armory; Frederick W. Howe, Richard S. Lawrence, and Henry D. Stone of Robbins & Lawrence; J.R. Brown of Brown & Sharpe; and Francis A. Pratt of Pratt & Whitney. Various designers at these and other firms later made further refinements.
Semi-automatic
Sometimes machines similar to those above, but with power feeds and automatic turret-indexing at the end of the return stroke, are called "semi-automatic turret lathes". This nomenclature distinction is blurry and not consistently observed. The term "turret lathe" encompasses them all. During the 1860s, when semi-automatic turret lathes were developed, they were sometimes called "automatic". What we today would call "automatics", that is, fully automatic machines, had not been developed yet. During that era both manual and semi-automatic turret lathes were sometimes called "screw machines", although we today reserve that term for fully automatic machines.
Automatic
During the 1870s through 1890s, the mechanically automated "automatic" turret lathe was developed and disseminated. These machines can execute many part-cutting cycles without human intervention. Thus the duties of the operator, which were already greatly reduced by the manual turret lathe, were even further reduced, and productivity increased. These machines use cams to automate the sliding and indexing of the turret and the opening and closing of the chuck. Thus, they execute the part-cutting cycle somewhat analogously to the way in which an elaborate cuckoo clock performs an automated theater show. Small- to medium-sized automatic turret lathes are usually called "screw machines" or "automatic screw machines", while larger ones are usually called "automatic chucking lathes", "automatic chuckers", or "chuckers".
Machine tools of the "automatic" variety, which in the pre-computer era meant mechanically automated, had already reached a highly advanced state by World War I.
Computer numerical control
When World War II ended, the digital computer was poised to develop from a colossal laboratory curiosity into a practical technology that could begin to disseminate into business and industry. The advent of computer-based automation in machine tools via numerical control (NC) and then computer numerical control (CNC) displaced to a large extent, but not at all completely, the previously existing manual and mechanically automated machines.
Numerically controlled turrets allow automated selection of tools on a turret. CNC lathes may be horizontal or vertical in orientation and mount six separate tools on one or more turrets. Such machine tools can work in two axes per turret, with up to six axes being feasible for complex work.
Vertical
Vertical turret lathes have the workpiece held vertically, which allows the headstock to sit on the floor and the faceplate to become a horizontal rotating table, analogous to a huge potter's wheel. This is useful for the handling of very large, heavy, short workpieces. Vertical lathes in general are also called "vertical boring mills" or often simply "boring mills"; therefore a vertical turret lathe is a vertical boring mill equipped with a turret.
Other variations
Capstan versus turret
The term "capstan lathe" overlaps in sense with the term "turret lathe" to a large extent. In many times and places, it has been understood to be synonymous with "turret lathe". In other times and places it has been held in technical contradistinction to "turret lathe", with the difference being in whether the turret's slide is fixed to the bed (ram-type turret) or slides on the bed's ways (saddle-type turret). The difference in terminology is mostly a matter of United Kingdom and Commonwealth usage versus United States usage.
Flat
A subtype of horizontal turret lathe is the flat-turret lathe. Its turret is flat (and analogous to a rotary table), allowing the turret to pass beneath the part. Patented by James Hartness of Jones & Lamson, and first disseminated in the 1890s, it was developed to provide more rigidity via requiring less overhang in the tool setup, especially when the part is relatively long.
Hollow-hexagon
Hollow-hexagon turret lathes competed with flat-turret lathes by taking the conventional hexagon turret and making it hollow, allowing the part to pass into it during the cut, analogously to how the part would pass over the flat turret. In both cases, the main idea is to increase rigidity by allowing a relatively long part to be turned without the tool overhang that would be needed with a conventional turret, which is not flat or hollow.
Monitor lathe
The term "monitor lathe" formerly (1860s–1940s) referred to the class of small- to medium-sized manual turret lathes used on relatively small work. The name was inspired by the monitor-class warships, which the monitor lathe's turret resembled. Today, lathes of such appearance, such as the Hardinge DSM-59 and its many clones, are still common, but the name "monitor lathe" is no longer current in the industry.
Toolpost turrets and tailstock turrets
Turrets can be added to non-turret lathes (bench lathes, engine lathes, toolroom lathes, etc.) by mounting them on the toolpost, tailstock, or both. Often these turrets are not as large as a turret lathe's, and they usually do not offer the sliding and stopping that a turret lathe's turret does; but they do offer the ability to index through successive tool settings.
References
Bibliography
.
.
External links
Example cycle on a manual turret lathe, narrated by operator from YouTube
Movement of the turrets and the taking of various cuts on a CNC vertical turret lathe from YouTube
Movement of the turret and the taking of various cuts on a manual engine lathe retrofitted with a CNC turret from YouTube
Industrial history
Lathes
Industrial equipment | Turret lathe | Engineering | 1,888 |
2,527,008 | https://en.wikipedia.org/wiki/Isotopes%20of%20rubidium | Rubidium (37Rb) has 36 isotopes, with naturally occurring rubidium being composed of just two isotopes; 85Rb (72.2%) and the radioactive 87Rb (27.8%).
87Rb has a half-life of . It readily substitutes for potassium in minerals, and is therefore fairly widespread. 87Rb has been used extensively in dating rocks; 87Rb decays to stable strontium-87 by emission of a beta particle (an electron ejected from the nucleus). During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. The highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the 87Sr/86Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See rubidium–strontium dating for a more detailed discussion.
Other than 87Rb, the longest-lived radioisotopes are 83Rb with a half-life of 86.2 days, 84Rb with a half-life of 33.1 days, and 86Rb with a half-life of 18.642 days. All other radioisotopes have half-lives less than a day.
82Rb is used in some cardiac positron emission tomography scans to assess myocardial perfusion. It has a half-life of 1.273 minutes. It does not exist naturally, but can be made from the decay of 82Sr.
List of isotopes
|-id=Rubidium-72
| 72Rb
| style="text-align:right" | 37
| style="text-align:right" | 35
| 71.95885(54)#
| 103(22) ns
| p
| 71Kr
| 1+#
|
|
|-id=Rubidium-73
| 73Rb
| style="text-align:right" | 37
| style="text-align:right" | 36
| 72.950605(44)
| <81 ns
| p
| 72Kr
| 3/2−#
|
|
|-id=Rubidium-74
| 74Rb
| style="text-align:right" | 37
| style="text-align:right" | 37
| 73.9442659(32)
| 64.78(3) ms
| β+
| 74Kr
| 0+
|
|
|-id=Rubidium-75
| 75Rb
| style="text-align:right" | 37
| style="text-align:right" | 38
| 74.9385732(13)
| 19.0(12) s
| β+
| 75Kr
| 3/2−
|
|
|-id=Rubidium-76
| rowspan=2|76Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 39
| rowspan=2|75.9350730(10)
| rowspan=2|36.5(6) s
| β+
| 76Kr
| rowspan=2|1−
| rowspan=2|
| rowspan=2|
|-
| β+, α (3.8×10−7%)
| 72Se
|-id=Rubidium-76m
| style="text-indent:1em" | 76mRb
| colspan="3" style="text-indent:2em" | 316.93(8) keV
| 3.050(7) μs
| IT
| 76Rb
| (4+)
|
|
|-id=Rubidium-77
| 77Rb
| style="text-align:right" | 37
| style="text-align:right" | 40
| 76.9304016(14)
| 3.78(4) min
| β+
| 77Kr
| 3/2−
|
|
|-id=Rubidium-78
| 78Rb
| style="text-align:right" | 37
| style="text-align:right" | 41
| 77.9281419(35)
| 17.66(3) min
| β+
| 78Kr
| 0+
|
|
|-id=Rubidium-78m1
| style="text-indent:1em" | 78m1Rb
| colspan="3" style="text-indent:2em" | 46.84(14) keV
| 910(40) ns
| IT
| 78Rb
| (1−)
|
|
|-id=Rubidium-78m2
| rowspan=2 style="text-indent:1em" | 78m2Rb
| rowspan=2 colspan="3" style="text-indent:2em" | 111.19(22) keV
| rowspan=2|5.74(3) min
| β+ (91%)
| 78Kr
| rowspan=2|4−
| rowspan=2|
| rowspan=2|
|-
| IT (9%)
| 78Rb
|-id=Rubidium-79
| 79Rb
| style="text-align:right" | 37
| style="text-align:right" | 42
| 78.9239901(21)
| 22.9(5) min
| β+
| 79Kr
| 5/2+
|
|
|-id=Rubidium-80
| 80Rb
| style="text-align:right" | 37
| style="text-align:right" | 43
| 79.9225164(20)
| 33.4(7) s
| β+
| 80Kr
| 1+
|
|
|-id=Rubidium-80m
| style="text-indent:1em" | 80mRb
| colspan="3" style="text-indent:2em" | 493.9(5) keV
| 1.63(4) μs
| IT
| 80Rb
| (6+)
|
|
|-id=Rubidium-81
| 81Rb
| style="text-align:right" | 37
| style="text-align:right" | 44
| 80.9189939(53)
| 4.572(4) h
| β+
| 81Kr
| 3/2−
|
|
|-id=Rubidium-81m
| rowspan=2 style="text-indent:1em" | 81mRb
| rowspan=2 colspan="3" style="text-indent:2em" | 86.31(7) keV
| rowspan=2|30.5(3) min
| IT (97.6%)
| 81Rb
| rowspan=2|9/2+
| rowspan=2|
| rowspan=2|
|-
| β+ (2.4%)
| 81Kr
|-
| 82Rb
| style="text-align:right" | 37
| style="text-align:right" | 45
| 81.9182090(32)
| 1.2575(2) min
| β+
| 82Kr
| 1+
|
|
|-id=Rubidium-82m
| rowspan=2 style="text-indent:1em" | 82mRb
| rowspan=2 colspan="3" style="text-indent:2em" | 69.0(15) keV
| rowspan=2|6.472(6) h
| β+ (>99.67%)
| 82Kr
| rowspan=2|5−
| rowspan=2|
| rowspan=2|
|-
| IT (<0.33%)
| 82Rb
|-id=Rubidium-83
| 83Rb
| style="text-align:right" | 37
| style="text-align:right" | 46
| 82.9151142(25)
| 86.2(1) d
| EC
| 83Kr
| 5/2−
|
|
|-id=Rubidium-83m
| style="text-indent:1em" | 83mRb
| colspan="3" style="text-indent:2em" | 42.0780(20) keV
| 7.8(7) ms
| IT
| 83Rb
| 9/2+
|
|
|-id=Rubidium-84
| rowspan=2|84Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 47
| rowspan=2|83.9143752(24)
| rowspan=2|32.8(07) d
| β+ (96.1%)
| 84Kr
| rowspan=2|2−
| rowspan=2|
| rowspan=2|
|-
| β− (3.9%)
| 84Sr
|-id=Rubidium-84m
| rowspan=2 style="text-indent:1em" | 84mRb
| rowspan=2 colspan="3" style="text-indent:2em" | 463.59(8) keV
| rowspan=2|20.26(4) min
| IT
| 84Rb
| rowspan=2|6−
| rowspan=2|
| rowspan=2|
|-
| β+ (<0.0012%)
| 84Kr
|-id=Rubidium-85
| 85Rb
| style="text-align:right" | 37
| style="text-align:right" | 48
| 84.9117897360(54)
| colspan=3 align=center|Stable
| 5/2−
| 0.7217(2)
|
|-id=Rubidium-85m
| style="text-indent:1em" | 85mRb
| colspan="3" style="text-indent:2em" | 514.0065(22) keV
| 1.015(1) μs
| IT
| 85Rb
| 9/2+
|
|
|-id=Rubidium-86
| rowspan=2|86Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 49
| rowspan=2|85.91116744(21)
| rowspan=2|18.645(8) d
| β− (99.99%)
| 86Sr
| rowspan=2|2−
| rowspan=2|
| rowspan=2|
|-
| EC (.0052%)
| 86Kr
|-id=Rubidium-86m
| rowspan=2 style="text-indent:1em" | 86mRb
| rowspan=2 colspan="3" style="text-indent:2em" | 556.05(18) keV
| rowspan=2|1.017(3) min
| IT (>99.7%)
| 86Rb
| rowspan=2|6−
| rowspan=2|
| rowspan=2|
|-
| β− (<0.3%)
| 86Sr
|-
| 87Rb
| style="text-align:right" | 37
| style="text-align:right" | 50
| 86.909180529(6)
| 4.97(3)×1010 y
| β−
| 87Sr
| 3/2−
| 0.2783(2)
|
|-id=Rubidium-88
| 88Rb
| style="text-align:right" | 37
| style="text-align:right" | 51
| 87.91131559(17)
| 17.78(3) min
| β−
| 88Sr
| 2−
|
|
|-id=Rubidium-88m
| style="text-indent:1em" | 88mRb
| colspan="3" style="text-indent:2em" | 1373.8(3) keV
| 123(13) ns
| IT
| 88Rb
| (7+)
|
|
|-id=Rubidium-89
| 89Rb
| style="text-align:right" | 37
| style="text-align:right" | 52
| 88.9122781(58)
| 15.32(10) min
| β−
| 89Sr
| 3/2−
|
|
|-id=Rubidium-90
| 90Rb
| style="text-align:right" | 37
| style="text-align:right" | 53
| 89.9147976(69)
| 158(5) s
| β−
| 90Sr
| 0−
|
|
|-id=Rubidium-90m
| rowspan=2 style="text-indent:1em" | 90mRb
| rowspan=2 colspan="3" style="text-indent:2em" | 106.90(3) keV
| rowspan=2|258(4) s
| β− (97.4%)
| 90Sr
| rowspan=2|3−
| rowspan=2|
| rowspan=2|
|-
| IT (2.6%)
| 90 Rb
|-id=Rubidium-91
| 91Rb
| style="text-align:right" | 37
| style="text-align:right" | 54
| 90.9165373(84)
| 58.2(3) s
| β−
| 91Sr
| 3/2−
|
|
|-id=Rubidium-92
| rowspan=2|92Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 55
| rowspan=2|91.9197285(66)
| rowspan=2|4.48(3) s
| β− (99.99%)
| 92Sr
| rowspan=2|0−
| rowspan=2|
| rowspan=2|
|-
| β−, n (0.0107%)
| 91Sr
|-id=Rubidium-93
| rowspan=2|93Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 56
| rowspan=2|92.9220393(84)
| rowspan=2|5.84(2) s
| β− (98.61%)
| 93Sr
| rowspan=2|5/2−
| rowspan=2|
| rowspan=2|
|-
| β−, n (1.39%)
| 92Sr
|-id=Rubidium-93m
| style="text-indent:1em" | 93mRb
| colspan="3" style="text-indent:2em" | 4423.1(15) keV
| 111(11) ns
| IT
| 93Rb
| (27/2−)
|
|
|-id=Rubidium-94
| rowspan=2|94Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 57
| rowspan=2|93.9263948(22)
| rowspan=2|2.702(5) s
| β− (89.7%)
| 94Sr
| rowspan=2|3−
| rowspan=2|
| rowspan=2|
|-
| β−, n (10.3%)
| 93Sr
|-id=Rubidium-94m1
| style="text-indent:1em" | 94m1Rb
| colspan="3" style="text-indent:2em" | 104.2(2) keV
| 130(15) ns
| IT
| 94Rb
| (0−)
|
|
|-id=Rubidium-94m2
| style="text-indent:1em" | 94m2Rb
| colspan="3" style="text-indent:2em" | 2074.9(14) keV
| 107(16) ns
| IT
| 94Rb
| (10−)
|
|
|-id=Rubidium-95
| rowspan=2|95Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 58
| rowspan=2|94.929264(22)
| rowspan=2|377.7(8) ms
| β− (91.3%)
| 95Sr
| rowspan=2|5/2−
| rowspan=2|
| rowspan=2|
|-
| β−, n (8.7%)
| 94Sr
|-id=Rubidium-95m
| style="text-indent:1em" | 95mRb
| colspan="3" style="text-indent:2em" | 835.0(6) keV
| <500 ns
| IT
| 95Rb
| 9/2+#
|
|
|-id=Rubidium-96
| rowspan=2|96Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 59
| rowspan=2|95.9341334(36)
| rowspan=2|201.5(9) ms
| β− (86.3%)
| 96Sr
| rowspan=2|2−
| rowspan=2|
| rowspan=2|
|-
| β−, n (13.7%)
| 95Sr
|-id=Rubidium-96m1
| style="text-indent:1em" | 96m1Rb
| colspan="3" style="text-indent:2em" | 0(200)# keV
| 200# ms[>1 ms]
|
|
| 1(+#)
|
|
|-id=Rubidium-96m2
| style="text-indent:1em" | 96m2Rb
| colspan="3" style="text-indent:2em" | 1134.6(11) keV
| 1.80(4) μs
| IT
| 96Rb
| (10−)
|
|
|-id=Rubidium-97
| rowspan=2|97Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 60
| rowspan=2|96.9371771(21)
| rowspan=2|169.1(6) ms
| β− (74.5%)
| 97Sr
| rowspan=2|3/2+
| rowspan=2|
| rowspan=2|
|-
| β−, n (25.5%)
| 96Sr
|-id=Rubidium-97m
| style="text-indent:1em" | 97mRb
| colspan="3" style="text-indent:2em" | 76.6(2) keV
| 5.7(6) μs
| IT
| 97Rb
| (1/2,3/2)−
|
|
|-id=Rubidium-98
| rowspan=3|98Rb
| rowspan=3 style="text-align:right" | 37
| rowspan=3 style="text-align:right" | 61
| rowspan=3|97.941632(17)
| rowspan=3|115(6) ms
| β−(85.65%)
| 98Sr
| rowspan=3|(0−)
| rowspan=3|
| rowspan=3|
|-
| β−, n (14.3%)
| 97Sr
|-
| β−, 2n (0.054%)
| 96Sr
|-id=Rubidium-98m1
| style="text-indent:1em" | 98m1Rb
| colspan="3" style="text-indent:2em" | 73(26) keV
| 96(3) ms
| β−
| 98Sr
| (3+)
|
|
|-id=Rubidium-98m2
| style="text-indent:1em" | 98m2Rb
| colspan="3" style="text-indent:2em" | 178.5(4) keV
| 358(7) ns
| IT
| 98Rb
| (2−)
|
|
|-id=Rubidium-99
| rowspan=2|99Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 62
| rowspan=2|98.9451192(43)
| rowspan=2|54(4) ms
| β− (82.7%)
| 99Sr
| rowspan=2|(3/2+)
| rowspan=2|
| rowspan=2|
|-
| β−, n (17.3%)
| 98Sr
|-id=Rubidium-100
| rowspan=3|100Rb
| rowspan=3 style="text-align:right" | 37
| rowspan=3 style="text-align:right" | 63
| rowspan=3|99.950332(14)
| rowspan=3|51.3(16) ms
| β− (94.3%)
| 100Sr
| rowspan=3|4−#
| rowspan=3|
| rowspan=3|
|-
| β−, n (5.6%)
| 99Sr
|-
| β−, 2n (0.15%)
| 98Sr
|-id=Rubidium-101
| rowspan=2|101Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 64
| rowspan=2|100.954302(22)
| rowspan=2|31.8(33) ms
| β− (72%)
| 101Sr
| rowspan=2|3/2+#
| rowspan=2|
| rowspan=2|
|-
| β−, n (28%)
| 100Sr
|-id=Rubidium-102
| rowspan=2|102Rb
| rowspan=2 style="text-align:right" | 37
| rowspan=2 style="text-align:right" | 65
| rowspan=2|101.960008(89)
| rowspan=2|37(4) ms
| β−, n (65%)
| 101Sr
| rowspan=2| (4+)
| rowspan=2|
| rowspan=2|
|-
| β− (35%)
| 102Sr
|-id=Rubidium-103
| 103Rb
| style="text-align:right" | 37
| style="text-align:right" | 66
| 102.96440(43)#
| 26(11) ms
| β−
| 103Sr
| 3/2+#
|
|
|-id=Rubidium-104
| 104Rb
| style="text-align:right" | 37
| style="text-align:right" | 67
| 103.97053(54)#
| 35# ms[>550 ns]
|
|
|
|
|
|-id=Rubidium-105
| 105Rb
| style="text-align:right" | 37
| style="text-align:right" | 68
|
|
|
|
|
|
|
|-id=Rubidium-106
| 106Rb
| style="text-align:right" | 37
| style="text-align:right" | 69
|
|
|
|
|
|
|
Rubidium-87
Rubidium-87 was the first and the most popular atom for making Bose–Einstein condensates in dilute atomic gases. Even though rubidium-85 is more abundant, rubidium-87 has a positive scattering length, which means it is mutually repulsive, at low temperatures. This prevents a collapse of all but the smallest condensates. It is also easy to evaporatively cool, with a consistent strong mutual scattering. There is also a strong supply of cheap uncoated diode lasers typically used in CD writers, which can operate at the correct wavelength.
Rubidium-87 has an atomic mass of 86.9091835 u, and a binding energy of 757,853 keV. Its atomic percent abundance is 27.835%, and has a half-life of .
References
Isotope masses from:
Isotopic compositions and standard atomic masses from:
Half-life, spin, and isomer data selected from the following sources.
Rubidium
Rubidium | Isotopes of rubidium | Chemistry | 5,489 |
3,195,612 | https://en.wikipedia.org/wiki/Longifolene | Longifolene is a common sesquiterpene. It is an oily liquid hydrocarbon found primarily in the high-boiling fraction of certain pine resins. The name is derived from that of a pine species from which the compound was isolated. It is a tricyclic chiral molecule. The enantiomer commonly found in pines and other higher plants exhibits a positive optical rotation of +42.73°. The other enantiomer (optical rotation −42.73°) is found in small amounts in certain fungi and liverworts.
Occurrence
Terpentine obtained from Pinus longifolia (obsolete name for Pinus roxburghii Sarg.) contains as much as 20% of longifolene.
Longifolene is also one of two most abundant aroma constituents of lapsang souchong tea, because the tea is smoked over pinewood fires.
Biosynthesis
The biosynthesis of longifolene begins with farnesyl diphosphate (1) (also called farnesyl pyrophosphate) by means of a cationic polycyclization cascade. Loss of the pyrophosphate group and cyclization by the distal alkene gives intermediate 3, which by means of a 1,3-hydride shift gives intermediate 4. After two additional cyclizations, intermediate 6 produces longifolene by a 1,2-alkyl migration.
Synthesis and related chemistry
The laboratory characterization and synthesis of longifolene has long attracted attention.
It reacts with borane to give the derivative dilongifolylborane, which is a chiral hydroborating agent.
References
External links
Longifolene Total Syntheses @ SynArchive.com
Polycyclic nonaromatic hydrocarbons
Sesquiterpenes
Total synthesis | Longifolene | Chemistry | 382 |
65,906,611 | https://en.wikipedia.org/wiki/Near%20future%20%28grammar%29 | Some languages have grammatical categories to represent near future, a subcategory of the future tense.
Going-to future in English may express near future.
Similarly to English, the French verb (to go) can be used as an auxiliary verb to create a near-future tense (le futur proche). Whereas English uses the continuous aspect (to be going), French uses the simple present tense; for example, the English sentence "I am going to do it tomorrow" would in French be « Je vais le faire demain ». As in English, this form can generally be replaced by the present or future tense: "I am doing it tomorrow", "I shall do it tomorrow", « Je le fais demain », « Je le ferai demain ».
Chichewa tenses can be divided into present, recent past, remote past, near future, and remote future. The dividing line between near and remote tenses is not exact, however. Remote tenses cannot be used of events of today, but near tenses can be used of events earlier or later than today.
Mizo language uses conjugational suffixes dáwn mék for forming near future.
See also
Crastinal tense
References
Time in linguistics
Grammatical tenses
Grammatical aspects | Near future (grammar) | Physics | 264 |
32,463,332 | https://en.wikipedia.org/wiki/C18H28N2O3S | The molecular formula C18H28N2O3S (molar mass: 352.49 g/mol, exact mass: 352.1821 u) may refer to:
Almokalant, a potassium channel blocker used to treat arrhythmia
SB-269,970 | C18H28N2O3S | Chemistry | 63 |
477,287 | https://en.wikipedia.org/wiki/Zenith%20number | A Zenith number was a telephone service in the United States that allowed a calling party to call the service subscriber at no charge by requesting the name Zenith and the number from a switchboard operator. The service preceded the system of toll-free telephone numbers with area code 800 in the United States. Some areas used the names "Enterprise" or "WX" number.
Introduced in the 1930s, a Zenith number was listed in local directories in each community from which a business desired to receive calls. In that era, direct-dial numbers were commonly published with telephone exchange names followed by digits, such as in the telephone number "PEnnsylvania 6-5000".
The letter Z appeared on many telephone dials from the early 1930s to the 1950s at the same position as the label Operator with the digit 0, indicating that the caller had to call the operator to place the call. The operator looked up the Zenith number to find the corresponding city and directory telephone number, and completed the call by charging it to the destination number.
For an organization expecting calls from a specific area but not very frequently, a Zenith number could provide savings over using foreign exchange (FX) service. For example, if a bus company had to provide a bus information number for callers in an area distant from its main office, and if a Zenith number cost $6 a month plus about $1.50 per call while an FX number cost $50 a month, then until the Zenith number regularly received at least 30 calls or more a month it would be cheaper than establishing foreign exchange service.
In the United States and Canada, usage of manual Zenith numbers diminished after the 1967 introduction of interstate direct-dial 800 area code InWATS toll-free service, and especially after 1982 when 800 calls no longer had to be placed via special fixed-rate trunks. A similar service in the United Kingdom, in which callers asked operators for "Freephone (name or number)", had no direct-dial counterpart until 1985.
As direct-dial toll-free service declined in cost, Zenith numbers nearly disappeared; telephone companies in most service areas are no longer assigning new Zenith numbers.
A few organizations have continued to keep Zenith numbers. For example, , the California Highway Patrol continued to use its decades-old Zenith 1-2000, On its website it advertises 1-800-TELL-CHP.
Examples
Ontario Provincial Police Detachment Search - Zenith 50000
Ambulance Dispatchers - Ontario Zenith 80000
References
Telephone numbers | Zenith number | Mathematics | 501 |
6,680,683 | https://en.wikipedia.org/wiki/Cubic%20form | In mathematics, a cubic form is a homogeneous polynomial of degree 3, and a cubic hypersurface is the zero set of a cubic form. In the case of a cubic form in three variables, the zero set is a cubic plane curve.
In , Boris Delone and Dmitry Faddeev showed that binary cubic forms with integer coefficients can be used to parametrize orders in cubic fields. Their work was generalized in to include all cubic rings (a is a ring that is isomorphic to Z3 as a Z-module), giving a discriminant-preserving bijection between orbits of a GL(2, Z)-action on the space of integral binary cubic forms and cubic rings up to isomorphism.
The classification of real cubic forms is linked to the classification of umbilical points of surfaces. The equivalence classes of such cubics form a three-dimensional real projective space and the subset of parabolic forms define a surface – the umbilic torus.
Examples
Cubic plane curve
Elliptic curve
Fermat cubic
Cubic 3-fold
Koras–Russell cubic threefold
Klein cubic threefold
Segre cubic
Notes
References
Multilinear algebra
Algebraic geometry
Algebraic varieties | Cubic form | Mathematics | 241 |
1,619,050 | https://en.wikipedia.org/wiki/Game%20of%20the%20Amazons | The Game of the Amazons (in Spanish, El Juego de las Amazonas; often called Amazons for short) is a two-player abstract strategy game invented in 1988 by Walter Zamkauskas of Argentina. The game is played by moving pieces and blocking the opponents from squares, and the last player able to move is the winner. It is a member of the territorial game family, a distant relative of Go and chess.
The Game of the Amazons is played on a 10x10 chessboard (or an international checkerboard). Some players prefer to use a monochromatic board. The two players are White and Black; each player has four amazons (not to be confused with the amazon fairy chess piece), which start on the board in the configuration shown at right. A supply of markers (checkers, poker chips, etc.) is also required.
Rules
White moves first, and the players alternate moves thereafter. Each move consists of two parts. First, one moves one of one's own amazons one or more empty squares in a straight line (orthogonally or diagonally), exactly as a queen moves in chess; it may not cross or enter a square occupied by an amazon of either color or an arrow. Second, after moving, the amazon shoots an arrow from its landing square to another square, using another queenlike move. This arrow may travel in any orthogonal or diagonal direction (even backwards along the same path the amazon just traveled, into or across the starting square if desired). An arrow, like an amazon, cannot cross or enter a square where another arrow has landed or an amazon of either color stands. The square where the arrow lands is marked to show that it can no longer be used. The last player to be able to make a move wins. Draws are impossible.
Territory and scoring
The strategy of the game is based on using arrows (as well as one's four amazons) to block the movement of the opponent's amazons and gradually wall off territory, trying to trap the opponents in smaller regions and gain larger areas for oneself. Each move reduces the available playing area, and eventually each amazon finds itself in a territory blocked off from all other amazons. The amazon can then move about its territory firing arrows until it no longer has any room to move. Since it would be tedious to actually play out all these moves, in practice the game usually ends when all of the amazons are in separate territories. The player with the largest amount of territory will be able to win, as the opponent will have to fill in their own territory more quickly.
Scores are sometimes used for tie-breaking purposes in Amazons tournaments. When scoring, it is important to note that although the number of moves remaining to a player is usually equal to the number of empty squares in the territories occupied by that player's amazons, it is nonetheless possible to have defective territories in which there are fewer moves left than there are empty squares. The simplest such territory is three squares of the same colour, not in a straight line, with the amazon in the middle (for example, a1+b2+c1 with the amazon at b2).
History
El Juego de las Amazonas was first published in Spanish in the Argentine puzzle magazine El Acertijo in December 1992. An approved English translation written by Michael Keller appeared in the magazine World Game Review in January 1994. Other game publications also published the rules, and the game gathered a small but devoted following. The Internet spread the game more widely.
Michael Keller wrote the first known computer version of the game in VAX Fortran in 1994, and an updated version with graphics in Visual Basic in 1995. There are Amazons tournaments at the Computer Olympiad, a series of computer-versus-computer competitions.
El Juego de las Amazonas (The Game of the Amazons) is a trademark of Ediciones de Mente.
Computational complexity
Usually, in the endgame, the board is partitioned into separate "royal chambers", with queens inside each chamber. We define simple Amazons endgames to be endgames where each chamber has at most one queen.
Determining who wins in a simple Amazons endgame is NP-hard. This is proven by reducing it to finding the Hamiltonian path of a cubic subgraph of the square grid graph.
Generalized Amazons (that is, determining the winner of a game of Amazons played on a n x n grid, started from an arbitrary configuration) is PSPACE-complete. This can be proved in two ways.
The first way is by reducing a generalized Hex position, which is known to be PSPACE-complete, into an Amazons position.
The second way is by reducing a certain kind of generalized geography called GEOGRAPHY-BP3, which is PSPACE-complete, to an Amazons position. This Amazons position uses only one black queen and one white queen, thus showing that generalized Amazons is PSPACE-complete even if only one queen on each side is allowed.
References
Further reading
.
.
Board games introduced in 1988
Abstract strategy games
PSPACE-complete problems | Game of the Amazons | Mathematics | 1,040 |
3,528,528 | https://en.wikipedia.org/wiki/Solvent%20Yellow%20124 | Solvent Yellow 124 is a yellow azo dye used in European Union as a fuel dye. It is a marker used since August 2002 to distinguish diesel fuel intended for heating from a higher-taxed motor diesel fuel. It is added to fuels not intended for motor vehicles in amounts of 6 mg/L or 7 mg/kg under the name Euromarker.
Euromarker
Solvent Yellow 124 is a dye with structure similar to Solvent Yellow 56. This dye can be easily hydrolyzed with acids, splitting off the acetal group responsible for its solubility in nonpolar solvents, and yielding a water-soluble form which is easy to extract to water. Like a similar methyl orange dye, it changes color to red in acidic pH. It can be easily detected in the fuel at levels as low as 0.3 ppm by extraction to a diluted hydrochloric acid, allowing detection of the red diesel added into motor diesel in amounts as low as 2-3%.
Solvent Yellow 124 is intended to be difficult to remove from the fuel in an economical way. The Customs, familiar with various tricks including dual fuel systems with hidden fuel tanks, will take samples from the fuel lines to the engine itself if such equipment is suspected in the car.
As the amount of Solvent Yellow 124 added to the fuel is known, by measuring its content in the fuel it is possible to calculate how much of the low-taxed fuel was added to the legal one.
Concerns
The UK government expressed concerns about the possibility of "laundering" the dye out of "illicit" fuel, hampering the detection. Denmark expressed concerns about the dye's toxicity.
Euromarker is intended to be replaced later by newer technology markers, such as biological markers or fuel markers with non-destructive analytical methods. These are all special chemicals tailored for the individual products, and perhaps even for individual refineries, allowing the identification of the source of the material by its content of the molecular markers.
In 2014, a new fuel marker more resistant to removal was announced for the United Kingdom.
References
Azo dyes
Solvent dyes
Vehicle taxes
Fuel dyes
Acetals
Ethanolamines
Tertiary amines | Solvent Yellow 124 | Chemistry | 441 |
37,124,082 | https://en.wikipedia.org/wiki/Boletus%20abruptibulbus | Boletus abruptibulbus is a species of bolete mushroom in the family Boletaceae. Described as new to science in 2009, it is found only in the Gulf Coast of the Florida Panhandle, where it grows on the ground in coastal sand dunes, one of only three North American boletes known to favor this habitat. The fruit bodies have convex brownish caps up to in diameter, supported by solid yellowish to reddish stems measuring long by thick. The pores on the underside of the cap measure about 1–2 mm in diameter and are initially pale yellow before developing a greenish tinge in age. The mushroom's spores, about 20 micrometers long, are unusually long for a member of the Boletaceae. The stem base is bulbous, a diagnostic feature for which the species is named.
Taxonomy
The species was described as new to science in 2009 by Beatriz Ortiz-Santana, William Roody, and Ernst Both in the journal Mycotaxon. The holotype material was collected at St. Joseph Peninsula State Park in Florida in January 2005. In 2007, Roody and Both published a short description and color photograph of the species in their field guide Mushrooms of the Southeastern United States, but this was not a valid name as it lacked a Latin description. The specific epithet abruptibulbus refers to the abruptly (abrupti-) swollen (-bulbus) shape of the bulb at the base of the stem.
Description
The convex cap measures in diameter. Slightly sticky when wet, the cap surface is shiny and smooth. Sometimes, the surface has flattened filaments (formed from aggregated hyphae), and may develop cracks. The thin and easily detached cap cuticle is initially reddish brown to dark brown, later becoming cinnamon brown. The cap margin is curved inward when young, but becomes bent downward when mature. The white to very pale yellow cap flesh does not change color when exposed to air, and has a pleasant odor and mild taste. The tubes comprising the hymenophore on the underside of the cap measure long and are pale yellow initially before developing a greenish tinge in age. The pore surface does not stain when it is bruised. The pores are roughly spherical or polyhedral at first, becoming angular to pentagonal in age, and almost gill-like near the attachment to the stem. Pores are about 1–2 mm in diameter. The stem is solid (i.e., not hollow) long, thick in the upper part, expanding to at the bulbous base. It has pseudorrhiza (cord-like structures resembling a plant root) that are long. The stem surface is dry and smooth except for a powdery region near the apex. The top of the stem is yellow, but it gradually becomes reddish approaching the bulbous base. The stem tissue is pale yellow, although tunnels dug by insect larvae are reddish brown.
A drop of dilute ammonia (as a 12% NH4OH solution) placed on the cap surface immediately turns dark red. If placed on the bulbous part of the stem base of a dried specimen, it will turn dark for roughly 15 seconds before starting to fade.
The spores are smooth, spindle-shaped, and measure 13.5–19.8 by 5.0–7.2 μm—rather large for a member of the Boletaceae. Grayish-yellow or greenish yellow when mounted in a dilute potassium hydroxide, they are dextrinoid (yellowish- or reddish-brown) when stained with Melzer's reagent. The basidia (spore-bearing cells in the hymenium) are club-shaped, hyaline (translucent), four-spored, and measure 28.8–42.3 by 7.2–11.7 μm. The hymenium contains basidioles (immature or aborted basidia), which are club-shaped and measure 20.7–35.1 by 7.2–9.0 μm. Pleurocystidia (cystidia on the surface of the tubes) range in shape from somewhat spindle-shaped to cylindrical, and are hyaline, smooth, and thin-walled, with dimensions of 41.4–61.2 by 7.2–10.8 μm. Cystidia on the edges of the pores (cheilocystidia) are 31.5–49.5 by 7.2–13.5 μm, spindle-shaped to centrally swollen, hyaline, smooth, and thin-walled. Clamp connections are absent from the hyphae.
The bulbous base, large spores, and distinctive habitat are characteristic features that make this species readily distinguishable from other boletes. It has a coloration and cap texture similar to Boletus flaviporus and B. auriporus, but the spores of these species are shorter (11–15 μm and 11–16 μm, respectively).
Habitat and distribution
The fruit bodies of Boletus abruptibulbus grow singly or in groups in sand. The species is known only from the Gulf Coast of the Florida Panhandle, where fruiting occurs on older sand dunes, particularly in areas where the habit changes from coastal scrub to oak-pine woods. This latter habitat is characterized by the presence of the tree species Sand Live Oak (Quercus geminata), Myrtle Oak (Q. myrtifolia), and Sand Pine (Pinus clausa). Fruiting occurs from December to March. Boletus abruptibulbus is one of only three North American Boletaceae species that occur in coastal sand dunes; the others are Leccinum arenicola, found in New Brunswick, Canada, and Phylloporus arenicola, described from Oregon.
See also
List of Boletus species
References
External links
abruptibulbus
Fungi of Florida
Fungi described in 2009
Fungi without expected TNC conservation status
Fungus species | Boletus abruptibulbus | Biology | 1,231 |
25,229,064 | https://en.wikipedia.org/wiki/Evolution%20of%20cells | Evolution of cells refers to the evolutionary origin and subsequent evolutionary development of cells. Cells first emerged at least 3.8 billion years ago approximately 750 million years after Earth was formed.
The first cells
The initial development of the cell marked the passage from prebiotic chemistry to partitioned units resembling modern cells. The final transition to living entities that fulfill all the definitions of modern cells depended on the ability to evolve effectively by natural selection. This transition has been called the Darwinian transition.
If life is viewed from the point of view of replicator molecules, cells satisfy two fundamental conditions: protection from the outside environment and confinement of biochemical activity. The former condition is needed to keep complex molecules stable in a varying and sometimes aggressive environment; the latter is fundamental for the evolution of biocomplexity. If freely floating molecules that code for enzymes are not enclosed in cells, the enzymes will automatically benefit neighboring replicator molecules as well. Thus, the consequences of diffusion in non-partitioned lifeforms would result in "parasitism by default." Therefore, the selection pressure on replicator molecules will be lower, as the 'lucky' molecule that produces the better enzyme does not fully leverage its advantage over its close neighbors. In contrast, if the molecule is enclosed in a cell membrane, the enzymes coded will be available only to itself. That molecule will uniquely benefit from the enzymes it codes for, increasing individuality and thus accelerating natural selection.
Partitioning may have begun from cell-like spheroids formed by proteinoids, which are observed by heating amino acids with phosphoric acid as a catalyst. They bear much of the basic features provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could have been the first cellular life forms on Earth.
Another possibility is that the shores of the ancient coastal waters may have been a suitable environment for the initial development of cells. Waves breaking on the shore create a delicate foam composed of bubbles. Shallow coastal waters also tend to be warmer, further concentrating the molecules through evaporation. While bubbles made mostly of water tend to burst quickly, oily bubbles are much more stable. The phospholipid, the primary material of cell membranes, is an example of a common oily compound prevalent in the prebiotic seas.
Both of these options require the presence of massive amounts of chemicals and organic material in order to form cells. A large gathering of organic molecules most likely came from what scientists now call the prebiotic soup. The prebiotic soup refers to the collection of every organic compound that appeared on Earth after it was formed. This soup would have most likely contained the compounds necessary to form early cells.
Phospholipids are composed of a hydrophilic head on one end and a hydrophobic tail on the other. They can come together to form a bilayer membrane. A lipid monolayer bubble can only contain oil and is not conducive to harboring water-soluble organic molecules. On the other hand, a lipid bilayer bubble can contain water and was a likely precursor to the modern cell membrane. If a protein was introduced that increased the integrity of its parent bubble, then that bubble had an advantage. Primitive reproduction may have occurred when the bubbles burst, releasing the results of the experiment into the surrounding medium. Once enough of the right compounds were released into the medium, the development of the first prokaryotes, eukaryotes, and multi-cellular organisms could be achieved.
However, the first cell membrane could not have been composed of phospholipids due its low permeability, as ions would not able to pass through the membrane. Rather it is suggested they were composed of fatty acids, as they can freely exchange ions, allowing geochemically sustained proton gradients at alkaline hydrothermal vents that might lead to prebiotic chemical reactions via CO2 fixation.
Community metabolism
The common ancestor of the now existing cellular lineages (eukaryotes, bacteria, and archaea) may have been a community of organisms that readily exchanged components and genes. It would have contained:
Autotrophs that produced organic compounds from CO2, either photosynthetically or by inorganic chemical reactions;
Heterotrophs that obtained organics from leakage of other organisms
Saprotrophs that absorbed nutrients from decaying organisms
Phagotrophs that were sufficiently complex to envelop and digest particulate nutrients, including other organisms.
The eukaryotic cell seems to have evolved from a symbiotic community of prokaryotic cells. DNA-bearing organelles like mitochondria and chloroplasts are remnants of ancient symbiotic oxygen-breathing bacteria and cyanobacteria, respectively, where at least part of the rest of the cell may have been derived from an ancestral archaean prokaryote cell. The archean prokaryote cell concept is often termed as the endosymbiotic theory. There is still debate about whether organelles like the hydrogenosome predated the origin of mitochondria, or vice versa: see the hydrogen hypothesis for the origin of eukaryotic cells.
How the current lineages of microbes evolved from this postulated community is currently unsolved, but subject to intense research by biologists, stimulated by the great flow of new discoveries in genome science.
Genetic code and the RNA world
Modern evidence suggests that early cellular evolution occurred in a biological realm radically distinct from modern biology. It is thought that in this ancient realm, the current genetic role of DNA was largely filled by RNA, and catalysis was also largely mediated by RNA (that is, by ribozyme counterparts of enzymes). This concept is known as the RNA world hypothesis.
According to this hypothesis, the ancient RNA world transitioned into the modern cellular world via the evolution of protein synthesis, followed by replacement of many cellular ribozyme catalysts by protein-based enzymes. Proteins are much more flexible in catalysis than RNA due to the existence of diverse amino acid side chains with distinct chemical characteristics. The RNA record in existing cells appears to preserve some 'molecular fossils' from this RNA world. These RNA fossils include the ribosome itself (in which RNA catalyzes peptide-bond formation), the modern ribozyme catalyst RNase P, and RNAs.
The nearly universal genetic code preserves some evidence for the RNA world. For instance, recent studies of transfer RNAs, the enzymes that charge them with amino acids (the first step in protein synthesis) and the way these components recognize and exploit the genetic code, have been used to suggest that the universal genetic code emerged before the evolution of the modern amino acid activation method for protein synthesis. The first RNA polymers probably emerged prior to 4.17 Gya if life originated at freshwater environments similar to Darwin's warm little pond.
Sexual reproduction
The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes, including single cell eukaryotes. Based on a phylogenetic analysis, Dacks and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes. Hofstatter and Lehr reviewed evidence supporting the hypothesis that all eukaryotes can be regarded as sexual, unless proven otherwise.
Sexual reproduction may have arisen in early protocells with RNA genomes (RNA world). Initially, each protocell would likely have contained one RNA genome (rather than multiple) since this maximizes the growth rate. However, the occurrence of damages to the RNA which block RNA replication or interfere with ribozyme function would make it advantageous to fuse periodically with another protocell to restore reproductive ability. This early, simple form of genetic recovery is similar to that occurring in extant segmented single-stranded RNA viruses (see influenza A virus).
As duplex DNA became the predominant form of the genetic material, the mechanism of genetic recovery evolved into the more complex process of meiotic recombination, found today in most species. It thus appears likely that sexual reproduction arose early in the evolution of cells and has had a continuous evolutionary history.
Horizontal gene transfer
Horizontal gene transfer (HGT) is the movement of genetic information between different organisms of the same species mainly being bacteria. This is not the movement of genetic information between a parent and their offspring but by other factors. In contrast to how animals reproduce and evolve from sexual reproduction, bacteria evolve by sharing DNA with other bacteria or their environment.
There are three common mechanisms of transferring genetic material by HGT:
Transformation: The bacteria assimilates DNA from the environment into their own
Conjugation: Bacteria directly transfer genes from one cell to another
Transduction: Bacteriophages (virus) move genes from one bacterial cell to another
Once one of these mechanisms has occurred the bacteria will continue to multiply and grow resistance and evolve by natural selection. HGT is the main cause of the assimilation of certain genetic material and the passing down of antibiotic resistance genes (ARGs).
Canonical patterns
Although the evolutionary origins of the major lineages of modern cells are disputed, the primary distinctions between the three major lineages of cellular life (called domains) are firmly established.
In each of these three domains, DNA replication, transcription, and translation all display distinctive features. There are three versions of ribosomal RNAs, and generally three versions of each ribosomal protein, one for each domain of life. These three versions of the protein synthesis apparatus are called the canonical patterns, and the existence of these canonical patterns provides the basis for a definition of the three domains - Bacteria, Archaea, and Eukarya (or Eukaryota) - of currently existing cells.
Using genomics to infer early lines of evolution
Instead of relying on a single gene such as the small-subunit ribosomal RNA (SSU rRNA) gene to reconstruct early evolution, or a few genes, scientific effort has shifted to analyzing complete genome sequences.
Evolutionary trees based only on SSU rRNA alone do not capture the events of early eukaryote evolution accurately, and the progenitors of the first nucleated cells are still uncertain. For instance, analysis of the complete genome of the eukaryote yeast shows that many of its genes are more closely related to bacterial genes than they are to archaea, and it is now clear that archaea were not the simple progenitors of the eukaryotes, in contradiction to earlier findings based on SSU rRNA and limited samples of other genes.
One hypothesis is that the first nucleated cell arose from two distinctly different ancient prokaryotic (non-nucleated) species that had formed a symbiotic relationship with one another to carry out different aspects of metabolism. One partner of this symbiosis is proposed to be a bacterial cell, and the other an archaeal cell. It is postulated that this symbiotic partnership progressed via the cellular fusion of the partners to generate a chimeric or hybrid cell with a membrane bound internal structure that was the forerunner of the nucleus. The next stage in this scheme was transfer of both partner genomes into the nucleus and their fusion with one another. Several variations of this hypothesis for the origin of nucleated cells have been suggested. Other biologists dispute this conception and emphasize the community metabolism theme, the idea that early living communities would comprise many different entities to extant cells, and would have shared their genetic material more extensively than current microbes.
Quotes
"The First Cell arose in the previously prebiotic world with the coming together of several entities that gave a single vesicle the unique chance to carry out three essential and quite different life processes. These were: (a) to copy informational macromolecules, (b) to carry out specific catalytic functions, and (c) to couple energy from the environment into usable chemical forms. These would foster subsequent cellular evolution and metabolism. Each of these three essential processes probably originated and was lost many times prior to The First Cell, but only when these three occurred together was life jump-started and Darwinian evolution of organisms began." (Koch and Silver, 2005)
"The evolution of modern cells is arguably the most challenging and important problem the field of Biology has ever faced. In Darwin's day the problem could hardly be imagined. For much of the 20th century it was intractable. In any case, the problem lay buried in the catch-all rubric "origin of life"--where, because it is a biological not a (bio)chemical problem, it was effectively ignored. Scientific interest in cellular evolution started to pick up once the universal phylogenetic tree, the framework within which the problem had to be addressed, was determined. But it was not until microbial genomics arrived on the scene that biologists could actually do much about the problem of cellular evolution." (Carl Woese, 2002)
References
Further reading
External links
Life on Earth
The universal nature of biochemistry
Endosymbiosis and The Origin of Eukaryotes
Origins of the Eukarya.
Cell biology
Evolutionary biology | Evolution of cells | Biology | 2,658 |
63,749,890 | https://en.wikipedia.org/wiki/NGC%20544 | NGC 544 (also known as GC 320 or h 2411) is a faint, small, and round elliptical galaxy located in the Sculptor constellation. The galaxy was discovered by John Herschel on 23 October 1835 and its apparent size is 1.5 by 1.1 arc minutes. It is approximately 360 million light years away from Earth, it is similar to those of NGC 534, NGC 546 and NGC 549.
References
External links
Elliptical galaxies
544
Sculptor (constellation)
Astronomical objects discovered in 1835
Discoveries by John Herschel | NGC 544 | Astronomy | 110 |
32,513,367 | https://en.wikipedia.org/wiki/Tris%28dimethylamino%29aluminium%20dimer | Tris(dimethylamino)aluminium dimer, formally bis(μ-dimethylamino)tetrakis(dimethylamino)dialuminium, is an amide complex of aluminium. This compound may be used as a precursor to other aluminium complexes.
Commercially available, this compound may be prepared from lithium dimethylamide and aluminium trichloride.
References
Aluminium complexes
Metal amides
Dimers (chemistry) | Tris(dimethylamino)aluminium dimer | Chemistry,Materials_science | 90 |
73,666,286 | https://en.wikipedia.org/wiki/Boletus%20tylopilopsis | Boletus tylopilopsis is an edible basidiomycete mushroom, of the genus Boletus in the family Boletaceae. Morphologically similar to the members of Tylopilus in the pinkish hymenophore and belonging to the porcini group (Boletus sect. Boletus), it was first described in 2015, and is known to be found only in China, Yunnan.
Morphology
Cap
The cap is 8.5 to 10.5 cm in diameter, hemispherical in shape; The surface is dry and distinctly rugose, dull yellow to yellow with olivacous tinge. The flesh is cream to yellowish in color and does not turn blue when bruised.
Pores
The pores are white-stuffed when young, becoming pinkish like those of Tylopilus spp., unchanged when bruised.
Stipe
From 9 to 12 cm long; 1.5–2.2 cm thick; yellowish with reticulations concolorous to the pileus; shaped clavate to subcylindrical, tapered upwards.
Spores
Subfusiform, 12.5–15 x 4.5–5.5 μm.
Habitat and distribution
Solitary or gregarious in the subtropical Fagaceae forests in Southwest China.
References
External links
Edible fungi
tylopilopsis
Fungi described in 2015
Fungi of China
Fungus species | Boletus tylopilopsis | Biology | 285 |
3,602,968 | https://en.wikipedia.org/wiki/National%20Institute%20for%20Nanotechnology | The National Research Council of Canada Nanotechnology Research Centre (formerly National Institute for Nanotechnology) is a research institution located on the University of Alberta main campus, in Edmonton, Alberta, Canada. Its primary purpose is nanoscience research.
The institute was established in 2001 as a partnership between the National Research Council of Canada, the University of Alberta, and the Government of Alberta. It is administered as an institute of the National Research Council of Canada (NRC), and governed by a board of trustees nominated by the partners. Its core funding comes from the Government of Canada and additional funding and research support comes from the university, Government of Alberta, and various federal and provincial funding agencies.
In June 2006, the institute moved into its present facility, designed to be one of the world's largest buildings for nanotechnological research. There are at most two or three other facilities worldwide matching the new building in scale and capacity.
In 2017, the institute became the Nanotechnology Research Centre, following a recognition of the institute as its own research centre. Although on the premises of the University of Alberta, the research centre is a branch of the National Research Council of Canada.
Research areas
The Nanotechnology Research Centre plans to focus on the following areas of research:
NanoBiology
Antimicrobials
Drug delivery
Gene delivery
Immunity
Biomaterials
Scaffolds
NanoElectronics
Electrochem
Microfluidics
Nano & Micro Fabrication
Optical NEMS
Photonics
Quantum
Next-generation Microscopy
Advanced characterization
Instrument development
Integration & optimization
Microscopy-enabled manufacturing
Achievements
A new approach to nanosensors, revolutionizing the concept, was published in Science magazine in 2018.
The sharpest man-made object, a tungsten needle created by Mohamed Rezeq, was created at NINT in 2006.
See also
Natural scientific research in Canada
Technological and industrial history of Canada
Canadian government scientific research organizations
Canadian university scientific research organizations
Canadian industrial research and development organizations
References
External links
Nanotechnology Research Centre, Government of Canada
University of Alberta Planning and Infrastructure: NINT
2001 establishments in Alberta
Laboratories in Canada
Nanotechnology institutions
National Research Council (Canada)
Research institutes in Canada
Scientific organizations based in Canada
University of Alberta buildings | National Institute for Nanotechnology | Materials_science | 444 |
1,677,109 | https://en.wikipedia.org/wiki/Orthocerida | Orthocerida, also known as the Michelinocerida, is an order of extinct orthoceratoid cephalopods that lived from the Early Ordovician () possibly to the Late Triassic (). A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous (), and the Eocene fossil Antarcticeras is sometimes considered a descendant of the orthocerids although this is disputed. They were most common however from the Ordovician to the Devonian.
Shell form
The shell is usually long, and may be straight ("orthoconic") or gently curved. In life, these animals may have been similar to the modern squid, except for their long shell. The internal structure of the shell consists of concavo-convex chambers linked by a centrally-placed tube called a siphuncle. There is a tendency for the chambers to develop cameral deposits, which were used as ballast to balance the long gas-filled shell. Depending on the family, the siphuncle has orthochoanitic (short and straight) or cyrtochoanitic (outwardly curved) septal necks, which protrude from the septa. The shell surface may be (depending on the species or genus) smooth, transversely ribbed, or ornamented by a network of fine lirae. Fossils are common and have been found on many continents, including the Americas, Africa, Europe, and Asia.
Ecology
Orthocerids may have swum near the sea bed with their buoyant shell resting horizontally in the water, floated more passively among plankton, or rested on the sea floor. Like modern cephalopods they would have used jet-propulsion for locomotion. Their long, bulky shell and relatively weak muscle attachments however make it unlikely that they were as agile as ammonoids or modern cephalopods. They most likely fed on trilobites and small arthropods.
Taxonomy
Orthocerid taxonomy is based primarily on morphological characters found in the shell, principally in the nature of the siphuncle. Parsing these relationships out however can become complicated due to similar characteristics through convergent evolution, making certain taxa appear to have a much longer stratigraphic range than in actuality.
Well preserved embryonic shells of the family Pseudorthoceratidae from the Mississippian (Lower Carboniferous) Imo Formation of Arkansas revealed significant diversity in the shells' morphology, as well as indicating that Pseudorthoceratidae may be in need of revision.
Evolutionary history
Orthocerids likely arose from the Baltoceratidae, a family of the Ellesmerocerida. However, the phylogeny of Orthocerida is heavily debated as it lacks clearly defined characters. Some important characteristics include the diameter and thickness of a calciosiphonate connecting ring and shape of orthocone siphuncles. Orthocerida may thus be a polyphyletic group, having arisen as several lineages from early Ordovician cephalopods. Some workers have split off the Pseudorthocerida and Dissidocerida as separate orders, the latter on the grounds that it arose from a different baltoceratid ancestor. The pseudorthocerids are thought to be distinct because their protoconch and septal necks significantly different than orthocerids.
Orthocerids flourished in the Paleozoic Era, giving rise to multiple orders, most notably ascocerids. The spherical protoconch, or first chamber, of some orthocerids suggests they were ancestors to the Bactritida, small orthoconic forms that gave rise to both the ammonoids and coleoids. Fossilized radulas from orthocerids also suggest a closer affinity with modern coleoids than with Nautilus.
There is some dispute as to when the orthocerids became extinct. Although they are said to have survived into the Triassic Period, the two genera that date from that period may actually be pseudorthocerids. In that case, the last orthocerids may date only to the Permian. However, the discovery in the Caucasus of a possible orthocerid from the Early Cretaceous suggests that they may have endured much longer as a ghost lineage. Even a potential Cenozoic descendant of orthocerids is known in Antarcticeras, an enigmatic cephalopod from the Eocene of Antarctica with an internal shell akin to that of coleoids but with an anatomy closely resembling that of orthocerids, suggesting that it may represent an orthocerid offshoot that diverged as its own subclass during the Paleozoic and survived up to the Eocene, convergently evolving a coleoid-esque internal shell. However, other studies recover it as a primitive oegopsid squid.
References
Sweet, Walter C., (1964), Nautiloidea—Orthocerida, in Treatise on Invertebrate Paleontology. Part K. Mollusca 3. (Geological Society of America, and University of Kansas Press, New York, New York and Lawrence, Kansas)
External links
www.palaeos.com
Orthocerida (Fossil Nautiloidea Page)
Prehistoric cephalopod orders
Mesozoic cephalopods
Paleozoic cephalopods
Early Ordovician first appearances
Triassic extinctions
Paraphyletic groups | Orthocerida | Biology | 1,144 |
1,090,852 | https://en.wikipedia.org/wiki/Software%20prototyping | Software prototyping is the activity of creating prototypes of software applications, i.e., incomplete versions of the software program being developed. It is an activity that can occur in software development and is comparable to prototyping as known from other fields, such as mechanical engineering or manufacturing.
A prototype typically simulates only a few aspects of, and may be completely different from, the final product.
Prototyping has several benefits: the software designer and implementer can get valuable feedback from the users early in the project. The client and the contractor can compare if the software made matches the software specification, according to which the software program is built. It also allows the software engineer some insight into the accuracy of initial project estimates and whether the deadlines and milestones proposed can be successfully met. The degree of completeness and the techniques used in prototyping have been in development and debate since its proposal in the early 1970s.
Overview
The purpose of a prototype is to allow users of the software to evaluate developers' proposals for the design of the eventual product by actually trying them out, rather than having to interpret and evaluate the design based on descriptions. Software prototyping provides an understanding of the software's functions and potential threats or issues. Prototyping can also be used by end users to describe and prove requirements that have not been considered, and that can be a key factor in the commercial relationship between developers and their clients. Interaction design in particular makes heavy use of prototyping with that goal.
This process is in contrast with the 1960s and 1970s monolithic development cycle of building the entire program first and then working out any inconsistencies between design and implementation, which led to higher software costs and poor estimates of time and cost. The monolithic approach has been dubbed the "Slaying the (software) Dragon" technique, since it assumes that the software designer and developer is a single hero who has to slay the entire dragon alone. Prototyping can also avoid the great expense and difficulty of having to change a finished software product.
The practice of prototyping is one of the points Frederick P. Brooks makes in his 1975 book The Mythical Man-Month and his 10-year anniversary article "No Silver Bullet".
An early example of large-scale software prototyping was the implementation of NYU's Ada/ED translator for the Ada programming language. It was implemented in SETL with the intent of producing an executable semantic model for the Ada language, emphasizing clarity of design and user interface over speed and efficiency. The NYU Ada/ED system was the first validated Ada implementation, certified on April 11, 1983.
Outline
The process of prototyping involves the following steps:
Identify basic requirements
Determine basic requirements including the input and output information desired. Details, such as security, can typically be ignored.
Develop initial prototype
The initial prototype is developed that includes only user interfaces. (See Horizontal Prototype, below)
Review
The customers, including end-users, examine the prototype and provide feedback on potential additions or changes.
Revise and enhance the prototype
Using the feedback both the specifications and the prototype can be improved. Negotiation about what is within the scope of the contract/product may be necessary. If changes are introduced then a repeat of steps #3 and #4 may be needed.
Dimensions
Nielsen summarizes the various dimensions of prototypes in his book Usability Engineering:
Horizontal prototype
A common term for a user interface prototype is the horizontal prototype. It provides a broad view of an entire system or subsystem, focusing on user interaction more than low-level system functionality, such as database access. Horizontal prototypes are useful for:
Confirmation of user interface requirements and system scope,
Demonstration version of the system to obtain buy-in from the business,
Develop preliminary estimates of development time, cost and effort.
Vertical prototype
A vertical prototype is an enhanced complete elaboration of a single subsystem or function. It is useful for obtaining detailed requirements for a given function, with the following benefits:
Refinement database design,
Obtain information on data volumes and system interface needs, for network sizing and performance engineering,
Clarify complex requirements by drilling down to actual system functionality.
Types
Software prototyping has many variants. However, all of the methods are in some way based on two major forms of prototyping: throwaway prototyping and evolutionary prototyping.
Throwaway prototyping
Also called close-ended prototyping. Throwaway or rapid prototyping refers to the creation of a model that will eventually be discarded rather than becoming part of the final delivered software. After preliminary requirements gathering is accomplished, a simple working model of the system is constructed to visually show the users what their requirements may look like when they are implemented into a finished system.
It is also a form of rapid prototyping.
Rapid prototyping involves creating a working model of various parts of the system at a very early stage, after a relatively short investigation. The method used in building it is usually quite informal, the most important factor being the speed with which the model is provided. The model then becomes the starting point from which users can re-examine their expectations and clarify their requirements. When this goal has been achieved, the prototype model is 'thrown away', and the system is formally developed based on the identified requirements.
The most obvious reason for using throwaway prototyping is that it can be done quickly. If the users can get quick feedback on their requirements, they may be able to refine them early in the development of the software. Making changes early in the development lifecycle is extremely cost effective since there is nothing at that point to redo. If a project is changed after a considerable amount of work has been done then small changes could require large efforts to implement since software systems have many dependencies. Speed is crucial in implementing a throwaway prototype, since with a limited budget of time and money little can be expended on a prototype that will be discarded.
Another strength of throwaway prototyping is its ability to construct interfaces that the users can test. The user interface is what the user sees as the system, and by seeing it in front of them, it is much easier to grasp how the system will function.
…it is asserted that revolutionary rapid prototyping is a more effective manner in which to deal with user requirements-related issues, and therefore a greater enhancement to software productivity overall. Requirements can be identified, simulated, and tested far more quickly and cheaply when issues of evolvability, maintainability, and software structure are ignored. This, in turn, leads to the accurate specification of requirements, and the subsequent construction of a valid and usable system from the user's perspective, via conventional software development models.
Prototypes can be classified according to the fidelity with which they resemble the actual product in terms of appearance, interaction and timing. One method of creating a low fidelity throwaway prototype is paper prototyping. The prototype is implemented using paper and pencil, and thus mimics the function of the actual product, but does not look at all like it. Another method to easily build high fidelity throwaway prototypes is to use a GUI Builder and create a click dummy, a prototype that looks like the goal system, but does not provide any functionality.
The usage of storyboards, animatics or drawings is not exactly the same as throwaway prototyping, but certainly falls within the same family. These are non-functional implementations but show how the system will look.
Summary: In this approach the prototype is constructed with the idea that it will be discarded and the final system will be built from scratch. The steps in this approach are:
Write preliminary requirements
Design the prototype
User experiences/uses the prototype, specifies new requirements
Repeat if necessary
Write the final requirements
Evolutionary prototyping
Evolutionary prototyping (also known as breadboard prototyping) is quite different from throwaway prototyping. The main goal when using evolutionary prototyping is to build a very robust prototype in a structured manner and constantly refine it. The reason for this approach is that the evolutionary prototype, when built, forms the heart of the new system, and the improvements and further requirements will then be built.
When developing a system using evolutionary prototyping, the system is continually refined and rebuilt.
"…evolutionary prototyping acknowledges that we do not understand all the requirements and builds only those that are well understood."
This technique allows the development team to add features, or make changes that couldn't be conceived during the requirements and design phase.
For a system to be useful, it must evolve through use in its intended operational environment. A product is never "done;" it is always maturing as the usage environment changes…we often try to define a system using our most familiar frame of reference—where we are now. We make assumptions about the way business will be conducted and the technology base on which the business will be implemented. A plan is enacted to develop the capability, and, sooner or later, something resembling the envisioned system is delivered.
Evolutionary prototypes have an advantage over throwaway prototypes in that they are functional systems. Although they may not have all the features the users have planned, they may be used on an interim basis until the final system is delivered.
"It is not unusual within a prototyping environment for the user to put an initial prototype to practical use while waiting for a more developed version…The user may decide that a 'flawed' system is better than no system at all."
In evolutionary prototyping, developers can focus themselves to develop parts of the system that they understand instead of working on developing a whole system.
To minimize risk, the developer does not implement poorly understood features. The partial system is sent to customer sites. As users work with the system, they detect opportunities for new features and give requests for these features to developers. Developers then take these enhancement requests along with their own and use sound configuration-management practices to change the software-requirements specification, update the design, recode and retest.
Incremental prototyping
The final product is built as separate prototypes. At the end, the separate prototypes are merged in an overall design. By the help of incremental prototyping the time gap between user and software developer is reduced.
Extreme prototyping
Extreme prototyping as a development process is used especially for developing web applications. Basically, it breaks down web development into three phases, each one based on the preceding one. The first phase is a static prototype that consists mainly of HTML pages. In the second phase, the screens are programmed and fully functional using a simulated services layer. In the third phase, the services are implemented.
"The process is called Extreme Prototyping to draw attention to the second phase of the process, where a fully functional UI is developed with very little regard to the services other than their contract."
Advantages
There are many advantages to using prototyping in software development – some tangible, some abstract.
Reduced time and costs: Prototyping can improve the quality of requirements and specifications provided to developers. Because changes cost exponentially more to implement as they are detected later in development, the early determination of what the user really wants can result in faster and less expensive software.
Improved and increased user involvement: Prototyping requires user involvement and allows them to see and interact with a prototype allowing them to provide better and more complete feedback and specifications. The presence of the prototype being examined by the user prevents many misunderstandings and miscommunications that occur when each side believe the other understands what they said. Since users know the problem domain better than anyone on the development team does, increased interaction can result in a final product that has greater tangible and intangible quality. The final product is more likely to satisfy the user's desire for look, feel and performance.
Disadvantages
Using, or perhaps misusing, prototyping can also have disadvantages.
Insufficient analysis: The focus on a limited prototype can distract developers from properly analyzing the complete project. This can lead to overlooking better solutions, preparation of incomplete specifications or the conversion of limited prototypes into poorly engineered final projects that are hard to maintain. Further, since a prototype is limited in functionality it may not scale well if the prototype is used as the basis of a final deliverable, which may not be noticed if developers are too focused on building a prototype as a model.
User confusion of prototype and finished system: Users can begin to think that a prototype, intended to be thrown away, is actually a final system that merely needs to be finished or polished. (They are, for example, often unaware of the effort needed to add error-checking and security features which a prototype may not have.) This can lead them to expect the prototype to accurately model the performance of the final system when this is not the intent of the developers. Users can also become attached to features that were included in a prototype for consideration and then removed from the specification for a final system. If users are able to require all proposed features be included in the final system this can lead to conflict.
Developer misunderstanding of user objectives: Developers may assume that users share their objectives (e.g. to deliver core functionality on time and within budget), without understanding wider commercial issues. For example, user representatives attending Enterprise software (e.g. PeopleSoft) events may have seen demonstrations of "transaction auditing" (where changes are logged and displayed in a difference grid view) without being told that this feature demands additional coding and often requires more hardware to handle extra database accesses. Users might believe they can demand auditing on every field, whereas developers might think this is feature creep because they have made assumptions about the extent of user requirements. If the developer has committed delivery before the user requirements were reviewed, developers are between a rock and a hard place, particularly if user management derives some advantage from their failure to implement requirements.
Developer attachment to prototype: Developers can also become attached to prototypes they have spent a great deal of effort producing; this can lead to problems, such as attempting to convert a limited prototype into a final system when it does not have an appropriate underlying architecture. (This may suggest that throwaway prototyping, rather than evolutionary prototyping, should be used.)
Excessive development time of the prototype: A key property to prototyping is the fact that it is supposed to be done quickly. If the developers lose sight of this fact, they very well may try to develop a prototype that is too complex. When the prototype is thrown away the precisely developed requirements that it provides may not yield a sufficient increase in productivity to make up for the time spent developing the prototype. Users can become stuck in debates over details of the prototype, holding up the development team and delaying the final product.
Expense of implementing prototyping: the start up costs for building a development team focused on prototyping may be high. Many companies have development methodologies in place, and changing them can mean retraining, retooling, or both. Many companies tend to just begin prototyping without bothering to retrain their workers as much as they should.
A common problem with adopting prototyping technology is high expectations for productivity with insufficient effort behind the learning curve. In addition to training for the use of a prototyping technique, there is an often overlooked need for developing corporate and project specific underlying structure to support the technology. When this underlying structure is omitted, lower productivity can often result.
Applicability
It has been argued that prototyping, in some form or another, should be used all the time. However, prototyping is most beneficial in systems that will have many interactions with the users.
It has been found that prototyping is very effective in the analysis and design of on-line systems, especially for transaction processing, where the use of screen dialogs is much more in evidence. The greater the interaction between the computer and the user, the greater the benefit is that can be obtained from building a quick system and letting the user play with it.
Systems with little user interaction, such as batch processing or systems that mostly do calculations, benefit little from prototyping. Sometimes, the coding needed to perform the system functions may be too intensive and the potential gains that prototyping could provide are too small.
Prototyping is especially good for designing good human–computer interfaces. "One of the most productive uses of rapid prototyping to date has been as a tool for iterative user requirements engineering and human–computer interface design."
Dynamic systems development method
Dynamic Systems Development Method (DSDM) is a framework for delivering business solutions that relies heavily upon prototyping as a core technique, and is itself ISO 9001 approved. It expands upon most understood definitions of a prototype. According to DSDM the prototype may be a diagram, a business process, or even a system placed into production. DSDM prototypes are intended to be incremental, evolving from simple forms into more comprehensive ones.
DSDM prototypes can sometimes be throwaway or evolutionary. Evolutionary prototypes may be evolved horizontally (breadth then depth) or vertically (each section is built in detail with additional iterations detailing subsequent sections). Evolutionary prototypes can eventually evolve into final systems.
The four categories of prototypes as recommended by DSDM are:
Business prototypes – used to design and demonstrates the business processes being automated.
Usability prototypes – used to define, refine, and demonstrate user interface design usability, accessibility, look and feel.
Performance and capacity prototypes – used to define, demonstrate, and predict how systems will perform under peak loads as well as to demonstrate and evaluate other non-functional aspects of the system (transaction rates, data storage volume, response time, etc.)
Capability/technique prototypes – used to develop, demonstrate, and evaluate a design approach or concept.
The DSDM lifecycle of a prototype is to:
Identify prototype
Agree to a plan
Create the prototype
Review the prototype
Operational prototyping
Operational prototyping was proposed by Alan Davis as a way to integrate throwaway and evolutionary prototyping with conventional system development. "It offers the best of both the quick-and-dirty and conventional-development worlds in a sensible manner. Designers develop only well-understood features in building the evolutionary baseline, while using throwaway prototyping to experiment with the poorly understood features."
Davis' belief is that to try to "retrofit quality onto a rapid prototype" is not the correct method when trying to combine the two approaches. His idea is to engage in an evolutionary prototyping methodology and rapidly prototype the features of the system after each evolution.
The specific methodology follows these steps:
An evolutionary prototype is constructed and made into a baseline using conventional development strategies, specifying and implementing only the requirements that are well understood.
Copies of the baseline are sent to multiple customer sites along with a trained prototyper.
At each site, the prototyper watches the user at the system.
Whenever the user encounters a problem or thinks of a new feature or requirement, the prototyper logs it. This frees the user from having to record the problem, and allows him to continue working.
After the user session is over, the prototyper constructs a throwaway prototype on top of the baseline system.
The user now uses the new system and evaluates. If the new changes aren't effective, the prototyper removes them.
If the user likes the changes, the prototyper writes feature-enhancement requests and forwards them to the development team.
The development team, with the change requests in hand from all the sites, then produce a new evolutionary prototype using conventional methods.
Obviously, a key to this method is to have well trained prototypers available to go to the user sites. The operational prototyping methodology has many benefits in systems that are complex and have few known requirements in advance.
Evolutionary systems development
Evolutionary Systems Development is a class of methodologies that attempt to formally implement evolutionary prototyping. One particular type, called Systemscraft is described by John Crinnion in his book Evolutionary Systems Development.
Systemscraft was designed as a 'prototype' methodology that should be modified and adapted to fit the specific environment in which it was implemented.
Systemscraft was not designed as a rigid 'cookbook' approach to the development process. It is now generally recognised[sic] that a good methodology should be flexible enough to be adjustable to suit all kinds of environment and situation...
The basis of Systemscraft, not unlike evolutionary prototyping, is to create a working system from the initial requirements and build upon it in a series of revisions. Systemscraft places heavy emphasis on traditional analysis being used throughout the development of the system.
Evolutionary rapid development
Evolutionary Rapid Development (ERD) was developed by the Software Productivity Consortium, a technology development and integration agent for the Information Technology Office of the Defense Advanced Research Projects Agency (DARPA).
Fundamental to ERD is the concept of composing software systems based on the reuse of components, the use of software templates and on an architectural template. Continuous evolution of system capabilities in rapid response to changing user needs and technology is highlighted by the evolvable architecture, representing a class of solutions. The process focuses on the use of small artisan-based teams integrating software and systems engineering disciplines working multiple, often parallel short-duration timeboxes with frequent customer interaction.
Key to the success of the ERD-based projects is parallel exploratory analysis and development of features, infrastructures, and components with and adoption of leading edge technologies enabling the quick reaction to changes in technologies, the marketplace, or customer requirements.
To elicit customer/user input, frequent scheduled and ad hoc/impromptu meetings with the stakeholders are held. Demonstrations of system capabilities are held to solicit feedback before design/implementation decisions are solidified. Frequent releases (e.g., betas) are made available for use to provide insight into how the system could better support user and customer needs. This assures that the system evolves to satisfy existing user needs.
The design framework for the system is based on using existing published or de facto standards. The system is organized to allow for evolving a set of capabilities that includes considerations for performance, capacities, and functionality. The architecture is defined in terms of abstract interfaces that encapsulate the services and their implementation (e.g., COTS applications). The architecture serves as a template to be used for guiding development of more than a single instance of the system. It allows for multiple application components to be used to implement the services. A core set of functionality not likely to change is also identified and established.
The ERD process is structured to use demonstrated functionality rather than paper products as a way for stakeholders to communicate their needs and expectations. Central to this goal of rapid delivery is the use of the "timebox" method. Timeboxes are fixed periods of time in which specific tasks (e.g., developing a set of functionality) must be performed. Rather than allowing time to expand to satisfy some vague set of goals, the time is fixed (both in terms of calendar weeks and person-hours) and a set of goals is defined that realistically can be achieved within these constraints. To keep development from degenerating into a "random walk," long-range plans are defined to guide the iterations. These plans provide a vision for the overall system and set boundaries (e.g., constraints) for the project. Each iteration within the process is conducted in the context of these long-range plans.
Once an architecture is established, software is integrated and tested on a daily basis. This allows the team to assess progress objectively and identify potential problems quickly. Since small amounts of the system are integrated at one time, diagnosing and removing the defect is rapid. User demonstrations can be held at short notice since the system is generally ready to exercise at all times.
Tools
Efficiently using prototyping requires that an organization have the proper tools and a staff trained to use those tools. Tools used in prototyping can vary from individual tools, such as 4th generation programming languages used for rapid prototyping to complex integrated CASE tools. 4th generation visual programming languages like Visual Basic and ColdFusion are frequently used since they are cheap, well known and relatively easy and fast to use. CASE tools, supporting requirements analysis, like the Requirements Engineering Environment (see below) are often developed or selected by the military or large organizations. Object oriented tools are also being developed like LYMB from the GE Research and Development Center. Users may prototype elements of an application themselves in a spreadsheet.
As web-based applications continue to grow in popularity, so too, have the tools for prototyping such applications. Frameworks such as Bootstrap, Foundation, and AngularJS provide the tools necessary to quickly structure a proof of concept. These frameworks typically consist of a set of controls, interactions, and design guidelines that enable developers to quickly prototype web applications.
Screen generators, design tools, and software factories
Screen generating programs are also commonly used and they enable prototypers to show user's systems that do not function, but show what the screens may look like. Developing Human Computer Interfaces can sometimes be the critical part of the development effort, since to the users the interface essentially is the system.
Software factories can generate code by combining ready-to-use modular components. This makes them ideal for prototyping applications, since this approach can quickly deliver programs with the desired behaviour, with a minimal amount of manual coding.
Application definition or simulation software
A new class of software called Application definition or simulation software enables users to rapidly build lightweight, animated simulations of another computer program, without writing code. Application simulation software allows both technical and non-technical users to experience, test, collaborate and validate the simulated program, and provides reports such as annotations, screenshot and schematics. As a solution specification technique, Application Simulation falls between low-risk, but limited, text or drawing-based mock-ups (or wireframes) sometimes called paper-based prototyping, and time-consuming, high-risk code-based prototypes, allowing software professionals to validate requirements and design choices early on, before development begins. In doing so, the risks and costs associated with software implementations can be dramatically reduced.
To simulate applications one can also use software that simulates real-world software programs for computer-based training, demonstration, and customer support, such as screencasting software as those areas are closely related.
Requirements Engineering Environment
"The Requirements Engineering Environment (REE), under development at Rome Laboratory since 1985, provides an integrated toolset for rapidly representing, building, and executing models of critical aspects of complex systems."
Requirements Engineering Environment is currently used by the United States Air Force to develop systems. It is:
an integrated set of tools that allows systems analysts to rapidly build functional, user interface, and performance prototype models of system components. These modeling activities are performed to gain a greater understanding of complex systems and lessen the impact that inaccurate requirement specifications have on cost and scheduling during the system development process. Models can be constructed easily, and at varying levels of abstraction or granularity, depending on the specific behavioral aspects of the model being exercised.
REE is composed of three parts. The first, called proto is a CASE tool specifically designed to support rapid prototyping. The second part is called the Rapid Interface Prototyping System or RIP, which is a collection of tools that facilitate the creation of user interfaces. The third part of REE is a user interface to RIP and proto that is graphical and intended to be easy to use.
Rome Laboratory, the developer of REE, intended that to support their internal requirements gathering methodology. Their method has three main parts:
Elicitation from various sources (users, interfaces to other systems), specification, and consistency checking
Analysis that the needs of diverse users taken together do not conflict and are technically and economically feasible
Validation that requirements so derived are an accurate reflection of user needs.
In 1996, Rome Labs contracted Software Productivity Solutions (SPS) to further enhance REE to create "a commercial quality REE that supports requirements specification, simulation, user interface prototyping, mapping of requirements to hardware architectures, and code generation..." This system is named the Advanced Requirements Engineering Workstation or AREW.
Non-relational environments
Non-relational definition of data (e.g. using Caché or associative models) can help make end-user prototyping more productive by delaying or avoiding the need to normalize data at every iteration of a simulation. This may yield earlier/greater clarity of business requirements, though it does not specifically confirm that requirements are technically and economically feasible in the target production system.
PSDL
PSDL is a prototype description language to describe real-time software.
The associated tool set is CAPS (Computer Aided Prototyping System).
Prototyping software systems with hard real-time requirements is challenging because timing constraints introduce implementation and hardware dependencies.
PSDL addresses these issues by introducing control abstractions that include declarative timing constraints. CAPS uses this information to automatically generate code and associated real-time schedules, monitor timing constraints during prototype execution, and simulate execution in proportional real time relative to a set of parameterized hardware models. It also provides default assumptions that enable execution of incomplete prototype descriptions, integrates prototype construction with a software reuse repository for rapidly realizing efficient implementations, and provides support for rapid evolution of requirements and designs.
References
Software development | Software prototyping | Technology,Engineering | 5,982 |
38,707,323 | https://en.wikipedia.org/wiki/Andexanet%20alfa | Andexanet alfa, sold under the brand name Andexxa among others, is an antidote for the medications rivaroxaban and apixaban, when reversal of anticoagulation is needed due to uncontrolled bleeding. It has not been found to be useful for other factor Xa inhibitors. It is given by injection into a vein.
Common side effects include pneumonia and urinary tract infections. Severe side effects may include blood clots, heart attacks, strokes, or cardiac arrest. It works by binding to rivaroxaban and apixaban.
It was approved for medical use in the United States in May 2018. It was developed by Portola Pharmaceuticals.
Medical uses
Andexanet alfa is used to stop life-threatening or uncontrollable bleeding in people who are taking rivaroxaban or apixaban.
Studies in healthy volunteers show that the molecule binds factor Xa inhibitors and counters their anti-Xa-activity. The first published clinical trial was a prospective, open label, single group study. This study reports results on 352 people and demonstrates a reduction of anti-Xa-activity while also showing an excellent or good hemostatic efficacy in 82%. While people who were expected to die in 30 days were excluded from the study, 14% of participants died. There was no relationship between hemostatic efficacy and reduced anti-Xa-activity. The FDA demanded a randomised clinical trial which resulted in publication in 2024. The ANNEXA-I trial included 530 patients with intracerebral hemorrhage who were receiving factor Xa inhibitors. Andexanet resulted in better control of hematoma expansion than usual care, but was associated with thrombotic events, including ischemic stroke. ANNEXA-I did not have sufficient power or information to draw conclusions about the effect of andexanet on mortality, clinical deterioration, or the need for rescue therapy.
Adverse effects
Common side effects include pneumonia and urinary tract infections. Severe side effects may include blood clots or cardiac arrest.
Andexanet alfa has a boxed warning that it is associated with arterial and venous blood clots, ischemic events, cardiac arrest, and sudden deaths.
Pharmacology
Mechanism of action
Andexanet alfa is a biologic agent, a recombinant modified version of human activated factor X (FXa). Andexanet alfa differs from native FXa due to the removal of a 34 residue fragment that contains the Gla domain. This modification reduces andexanet alfa's anticoagulant potential. Additionally, a serine to alanine (S419A) mutation in the active site eliminates its activity as a prothrombin to thrombin catalyst, but still allows the molecule to bind to FXa inhibitors. FXa inhibitors bind to andexanet alfa with the same affinity as to natural FXa. As a consequence, in the presence of andexanet alfa, natural FXa is partially freed, which can lead to effective hemostasis. In other words, it acts as a decoy receptor. Andexanet alfa reverses effect of all anticoagulants that act directly through FXa or by binding antithrombin III. The drug is not effective against factor IIa inhibitor dabigatran. Its activity is measured using the anti-Xa test, which is utilized to determine the amount of available factor Xa for coagulation
History
It was approved in the United States in 2018 based on data from two phase III studies on reversing the anticoagulant activity of FXa inhibitors rivaroxaban and apixaban in healthy volunteers. As a condition of its accelerated approval, the ANNEXA-I study was conducted comparing it to other currently used reversal agents ("usual care").
Society and culture
Economics
Initial pricing (AWP) is $58,000 per reversal (800 mg bolus + 960 mg infusion, $3,300 per 100 mg vial) which is higher than reversal agents for other DOAC agents (idarucizumab for use in dabigatran reversal is $4,200 per reversal).
References
Further reading
External links
Antidotes
Drugs developed by AstraZeneca
Recombinant proteins | Andexanet alfa | Biology | 891 |
1,688,687 | https://en.wikipedia.org/wiki/Synanthrope | A synanthrope (from ancient Greek σύν sýn "together, with" and ἄνθρωπος ánthrōpos "man") is an organism that evolved to live near humans and benefit from human settlements and their environmental modifications (see also anthropophilia for animals who live close to humans as parasites). The term includes many animals and plants regarded as pests or weeds, but does not include domesticated species. Common synanthrope habitats include houses, sheds and barns, non-building structures, gardens, parks, farms, road verges and rubbish dumps.
Zoology
Examples of synanthropes are various species of insects (ants, lice, bedbugs, silverfish, cockroaches, etc.), myriopods (millipedes and house centipede), arachnids (spiders, dust mite, etc.), common house gecko, birds such as house sparrows, gulls, rock doves (pigeons), crows and magpies, honeyguides, swallows and other passerines, various rodent species (especially rats and house mice), Virginia opossums, raccoons, certain monkey species, coyotes, deer, and other urban wildlife.
The brown rat is counted as one of the most prominent synanthropic animals and can be found in almost every place there are people.
Botany
Synanthropic plants include pineapple weed, dandelion, chicory, and plantain. Plant synanthropes are classified into two main types – apophytes and anthropophytes.
Apophytes are synanthropic species that are native in origin. They can be subdivided into the following:
Cultigen apophytes – spread by cultivation methods
Ruderal apophytes – spread by development of marginal areas
Pyrophyte apophytes – spread by fires
Zoogen apophytes – spread by grazing animals
Substitution apophytes – spread by logging or voluntary extension
Anthropophytes are synanthropic species of foreign origin, whether introduced voluntarily or involuntarily. They can be subdivided into the following:
Archaeophytes – introduced before the end of the 15th century
Kenophytes – introduced after the 15th century
Ephemerophytes – anthropophytic plants that appear episodically
Subspontaneous – voluntarily introduced plants that have escaped cultivation and survived in the wild without further human intervention for a certain period.
Adventive – involuntarily introduced plants that have escaped cultivation and survived in the wild without further human intervention for a certain period.
Naturalized or Neophytes – involuntarily introduced plants that now appear to thrive along with the native flora indefinitely.
See also
Adventive plant
Archaeophyte
Assisted migration
Commensalism
Domestication
Ecosystem management
Environmental impact of agriculture
Escaped plant
Genetic pollution
Hemeroby
Hemerochory
Human impact on the environment
Introduced species
Invasive species
Native American use of fire in ecosystems
Naturalisation
Neophyte
Satoyama
Social forestry in India
Urban wildlife
Literature
Herbert Sukopp & Rüdiger Wittig (eds.): Urban Ecology . 2nd edition G. Fischer; Stuttgart, Jena, Lübeck, Ulm; 1998: p. 276 ff.
References
External links
The Synanthrope Preserve
Plant life-forms
Human ecology
Ecology terminology | Synanthrope | Biology,Environmental_science | 706 |
77,725,324 | https://en.wikipedia.org/wiki/CIA%20fake%20vaccination%20campaign%20in%20Pakistan | During the manhunt for Osama bin Laden, the CIA ran a covert operation utilizing a fake hepatitis vaccine program in Pakistan to illicitly collect blood samples to confirm the presence of bin Laden or his family. The CIA did not administer hepatitis vaccines, and instead planned to compare DNA samples collected from the program with the DNA of bin Laden's sister, who died in Boston in 2010.
The program was ultimately unsuccessful. It led to the arrest of a participating physician, Shakil Afridi, and was widely ridiculed as undermining public health. The program is credited with increasing vaccine hesitancy in Pakistan and a rise in violence against healthcare workers for being perceived as spies. The rise in vaccine hesitancy following the program led to the re-emergence of polio in Pakistan, with Pakistan having by far the largest number of polio cases in the world by 2014.
Aftermath
In September of 2012, after working for 30 years in Pakistan, Save the Children was expelled.
In 2011, the program was condemned by Doctors without Borders. In Feb 2012, the program was condemned by the non-governmental organization InterAction. On January 6, 2013, the deans of twelve American schools of public health sent a letter to Obama condemning the program.
On May 16, 2014, Lisa Monaco responded that vaccine programs would be excluded from espionage:
See also
CIA activities in Pakistan
CIA transnational health and economic activities
References
CIA activities in Pakistan
United States espionage scandals and incidents
Pakistan military scandals
Polio
Vaccine controversies
2011 scandals
Covert operations
Health disasters in Pakistan
2010s in Pakistan
Osama bin Laden
Pakistan–United States relations
Central Intelligence Agency controversies
Vaccine hesitancy | CIA fake vaccination campaign in Pakistan | Chemistry,Biology | 332 |
1,036,259 | https://en.wikipedia.org/wiki/Refrigerator | A refrigerator, commonly shortened to fridge, is a commercial and home appliance consisting of a thermally insulated compartment and a heat pump (mechanical, electronic or chemical) that transfers heat from its inside to its external environment so that its inside is cooled to a temperature below the room temperature. Refrigeration is an essential food storage technique around the world. The low temperature reduces the reproduction rate of bacteria, so the refrigerator lowers the rate of spoilage. A refrigerator maintains a temperature a few degrees above the freezing point of water. The optimal temperature range for perishable food storage is . A freezer is a specialized refrigerator, or portion of a refrigerator, that maintains its contents’ temperature below the freezing point of water. The refrigerator replaced the icebox, which had been a common household appliance for almost a century and a half. The United States Food and Drug Administration recommends that the refrigerator be kept at or below and that the freezer be regulated at .
The first cooling systems for food involved ice. Artificial refrigeration began in the mid-1750s, and developed in the early 1800s. In 1834, the first working vapor-compression refrigeration system, using the same technology seen in air conditioners, was built. The first commercial ice-making machine was invented in 1854. In 1913, refrigerators for home use were invented. In 1923 Frigidaire introduced the first self-contained unit. The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s. Home freezers as separate compartments (larger than necessary just for ice cubes) were introduced in 1940. Frozen foods, previously a luxury item, became commonplace.
Freezer units are used in households as well as in industry and commerce. Commercial refrigerator and freezer units were in use for almost 40 years prior to the common home models. The freezer-over-refrigerator style had been the basic style since the 1940s, until modern, side-by-side refrigerators broke the trend. A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. Newer refrigerators may include automatic defrosting, chilled water, and ice from a dispenser in the door.
Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest are Peltier-type refrigerators designed to chill beverages. A large domestic refrigerator stands as tall as a person and may be about wide with a capacity of . Refrigerators and freezers may be free standing, or built into a kitchen. The refrigerator allows the modern household to keep food fresh for longer than before. Freezers allow people to buy perishable food in bulk and eat it at leisure, and make bulk purchases.
History
Technology development
Ancient origins
Ancient Iranians were among the first to invent a form of cooler utilizing the principles of evaporative cooling and radiative cooling called yakhchāls. These complexes used subterranean storage spaces, a large thickly insulated above-ground domed structure, and outfitted with badgirs (wind-catchers) and series of qanats (aqueducts).
Pre-electric refrigeration
In modern times, before the invention of the modern electric refrigerator, icehouses and iceboxes were used to provide cool storage for most of the year. Placed near freshwater lakes or packed with snow and ice during the winter, they were once very common. Natural means are still used to cool foods today. On mountainsides, runoff from melting snow is a convenient way to cool drinks, and during the winter one can keep milk fresh much longer just by keeping it outdoors. The word "refrigeratory" was used at least as early as the 17th century.
Artificial refrigeration
The history of artificial refrigeration began when Scottish professor William Cullen designed a small refrigerating machine in 1755. Cullen used a pump to create a partial vacuum over a container of diethyl ether, which then boiled, absorbing heat from the surrounding air. The experiment even created a small amount of ice, but had no practical application at that time.
In 1805, American inventor Oliver Evans described a closed vapor-compression refrigeration cycle for the production of ice by ether under vacuum. In 1820, the British scientist Michael Faraday liquefied ammonia and other gases by using high pressures and low temperatures, and in 1834, an American expatriate in Great Britain, Jacob Perkins, built the first working vapor-compression refrigeration system. It was a closed-cycle device that could operate continuously. A similar attempt was made in 1842, by American physician, John Gorrie, who built a working prototype, but it was a commercial failure. American engineer Alexander Twining took out a British patent in 1850 for a vapor compression system that used ether.
The first practical vapor compression refrigeration system was built by James Harrison, a Scottish Australian. His 1856 patent was for a vapor compression system using ether, alcohol or ammonia. He built a mechanical ice-making machine in 1851 on the banks of the Barwon River at Rocky Point in Geelong, Victoria, and his first commercial ice-making machine followed in 1854. Harrison also introduced commercial vapor-compression refrigeration to breweries and meat packing houses, and by 1861, a dozen of his systems were in operation.
The first gas absorption refrigeration system (compressor-less and powered by a heat-source) was developed by Edward Toussaint of France in 1859 and patented in 1860. It used gaseous ammonia dissolved in water ("aqua ammonia").
Carl von Linde, an engineering professor at the Technological University Munich in Germany, patented an improved method of liquefying gases in 1876, creating the first reliable and efficient compressed-ammonia refrigerator. His new process made possible the use of gases such as ammonia (NH3), sulfur dioxide (SO2) and methyl chloride (CH3Cl) as refrigerants, which were widely used for that purpose until the late 1920s despite safety concerns. In 1895 he discovered the refrigeration cycle.
Electric refrigerators
In 1894, Hungarian inventor and industrialist István Röck started to manufacture a large industrial ammonia refrigerator which was powered by electric compressors (together with the Esslingen Machine Works). Its electric compressors were manufactured by the Ganz Works. At the 1896 Millennium Exhibition, Röck and the Esslingen Machine Works presented a 6-tonne capacity artificial ice producing plant. In 1906, the first large Hungarian cold store (with a capacity of 3,000 tonnes, the largest in Europe) opened in Tóth Kálmán Street, Budapest, the machine was manufactured by the Ganz Works. Until nationalisation after the Second World War, large-scale industrial refrigerator production in Hungary was in the hands of Röck and Ganz Works.
Commercial refrigerator and freezer units, which go by many other names, were in use for almost 40 years prior to the common home models. They used gas systems such as ammonia (R-717) or sulfur dioxide (R-764), which occasionally leaked, making them unsafe for home use. Practical household refrigerators were introduced in 1915 and gained wider acceptance in the United States in the 1930s as prices fell and non-toxic, non-flammable synthetic refrigerants such as Freon-12 (R-12) were introduced. However, R-12 proved to be damaging to the ozone layer, causing governments to issue a ban on its use in new refrigerators and air-conditioning systems in 1994. The less harmful replacement for R-12, R-134a (tetrafluoroethane), has been in common use since 1990, but R-12 is still found in many old systems.
Refrigeration, continually operated, typically consumes up to 50% of the energy used by a supermarket. Doors, made of glass to allow inspection of contents, improve efficiency significantly over open display cases, which use 1.3 times the energy.
Residential refrigerators
In 1913, the first electric refrigerators for home and domestic use were invented and produced by Fred W. Wolf of Fort Wayne, Indiana, with models consisting of a unit that was mounted on top of an ice box. His first device, produced over the next few years in several hundred units, was called DOMELRE. In 1914, engineer Nathaniel B. Wales of Detroit, Michigan, introduced an idea for a practical electric refrigeration unit, which later became the basis for the Kelvinator. A self-contained refrigerator, with a compressor on the bottom of the cabinet was invented by Alfred Mellowes in 1916. Mellowes produced this refrigerator commercially but was bought out by William C. Durant in 1918, who started the Frigidaire company to mass-produce refrigerators. In 1918, Kelvinator company introduced the first refrigerator with any type of automatic control. The absorption refrigerator was invented by Baltzar von Platen and Carl Munters from Sweden in 1922, while they were still students at the Royal Institute of Technology in Stockholm. It became a worldwide success and was commercialized by Electrolux. Other pioneers included Charles Tellier, David Boyle, and Raoul Pictet. Carl von Linde was the first to patent and make a practical and compact refrigerator.
These home units usually required the installation of the mechanical parts, motor and compressor, in the basement or an adjacent room while the cold box was located in the kitchen. There was a 1922 model that consisted of a wooden cold box, water-cooled compressor, an ice cube tray and a compartment, and cost $714. (A 1922 Model-T Ford cost about $476.) By 1923, Kelvinator held 80 percent of the market for electric refrigerators. Also in 1923 Frigidaire introduced the first self-contained unit. About this same time porcelain-covered metal cabinets began to appear. Ice cube trays were introduced more and more during the 1920s; up to this time freezing was not an auxiliary function of the modern refrigerator.
The first refrigerator to see widespread use was the General Electric "Monitor-Top" refrigerator introduced in 1927, so-called, by the public, because of its resemblance to the gun turret on the ironclad warship USS Monitor of the 1860s. The compressor assembly, which emitted a great deal of heat, was placed above the cabinet, and enclosed by a decorative ring. Over a million units were produced. As the refrigerating medium, these refrigerators used either sulfur dioxide, which is corrosive to the eyes and may cause loss of vision, painful skin burns and lesions, or methyl formate, which is highly flammable, harmful to the eyes, and toxic if inhaled or ingested.
The introduction of Freon in the 1920s expanded the refrigerator market during the 1930s and provided a safer, low-toxicity alternative to previously used refrigerants. Separate freezers became common during the 1940s; the term for the unit, popular at the time, was deep freeze. These devices, or appliances, did not go into mass production for use in the home until after World War II. The 1950s and 1960s saw technical advances like automatic defrosting and automatic ice making. More efficient refrigerators were developed in the 1970s and 1980s, even though environmental issues led to the banning of very effective (Freon) refrigerants. Early refrigerator models (from 1916) had a cold compartment for ice cube trays. From the late 1920s fresh vegetables were successfully processed through freezing by the Postum Company (the forerunner of General Foods), which had acquired the technology when it bought the rights to Clarence Birdseye's successful fresh freezing methods.
Styles of refrigerators
The majority of refrigerators were white in the early 1950s, but between the mid-1950s and the present, manufacturers and designers have added color. Pastel colors, such as pink and turquoise, gained popularity in the late 1950s and early 1960s. Certain versions also had brushed chrome plating, which is akin to a stainless steel appearance. During the latter part of the 1960s and the early 1970s, earth tone colors were popular, including Harvest Gold, Avocado Green and almond. In the 1980s, black became fashionable. In the late 1990s stainless steel came into vogue. Since 1961 the Color Marketing Group has attempted to coordinate the colors of appliances and other consumer goods.
Freezer
Freezer units are used in households and in industry and commerce. Food stored at or below is safe indefinitely. Most household freezers maintain temperatures from , although some freezer-only units can achieve and lower. Refrigerator freezers generally do not achieve lower than , since the same coolant loop serves both compartments: Lowering the freezer compartment temperature excessively causes difficulties in maintaining above-freezing temperature in the refrigerator compartment. Domestic freezers can be included as a separate compartment in a refrigerator, or can be a separate appliance. Domestic freezers may be either upright, resembling a refrigerator, or chest freezers, wider than tall with the lid or door on top, sacrificing convenience for efficiency and partial immunity to power outages. Many modern upright freezers come with an ice dispenser built into their door. Some upscale models include thermostat displays and controls.
Home freezers as separate compartments (larger than necessary just for ice cubes), or as separate units, were introduced in the United States in 1940. Frozen foods, previously a luxury item, became commonplace.
In 1955 the domestic deep freezer, which was cold enough to allow the owners to freeze fresh food themselves rather than buying food already frozen with Clarence Birdseye's process, went on sale.
Walk-in freezer
There are walk in freezers, as the name implies, they allow for one to walk into the freezer. Safety regulations requires an emergency releases and employers should check to ensure no one will trapped inside when the unit gets locked as hypothermia is possible if one is in freezer for longer periods of time.
Refrigerator technologies
Compressor refrigerators
A vapor compression cycle is used in most household refrigerators, refrigerator–freezers and freezers. In this cycle, a circulating refrigerant such as R134a enters a compressor as low-pressure vapor at or slightly below the temperature of the refrigerator interior. The vapor is compressed and exits the compressor as high-pressure superheated vapor. The superheated vapor travels under pressure through coils or tubes that make up the condenser; the coils or tubes are passively cooled by exposure to air in the room. The condenser cools the vapor, which liquefies. As the refrigerant leaves the condenser, it is still under pressure but is now only slightly above room temperature. This liquid refrigerant is forced through a metering or throttling device, also known as an expansion valve (essentially a pin-hole sized constriction in the tubing) to an area of much lower pressure. The sudden decrease in pressure results in explosive-like flash evaporation of a portion (typically about half) of the liquid. The latent heat absorbed by this flash evaporation is drawn mostly from adjacent still-liquid refrigerant, a phenomenon known as auto-refrigeration. This cold and partially vaporized refrigerant continues through the coils or tubes of the evaporator unit. A fan blows air from the compartment ("box air") across these coils or tubes and the refrigerant completely vaporizes, drawing further latent heat from the box air. This cooled air is returned to the refrigerator or freezer compartment, and so keeps the box air cold. Note that the cool air in the refrigerator or freezer is still warmer than the refrigerant in the evaporator. Refrigerant leaves the evaporator, now fully vaporized and slightly heated, and returns to the compressor inlet to continue the cycle.
Modern domestic refrigerators are extremely reliable because motor and compressor are integrated within a welded container, "sealed unit", with greatly reduced likelihood of leakage or contamination. By comparison, externally-coupled refrigeration compressors, such as those in automobile air conditioning, inevitably leak fluid and lubricant past the shaft seals. This leads to a requirement for periodic recharging and, if ignored, possible compressor failure.
Dual compartment designs
Refrigerators with two compartments need special design to control the cooling of refrigerator or freezer compartments. Typically, the compressors and condenser coils are mounted at the top of the cabinet, with a single fan to cool them both. This arrangement has a few downsides: each compartment cannot be controlled independently and the more humid refrigerator air is mixed with the dry freezer air.
Multiple manufacturers offer dual compressor models. These models have separate freezer and refrigerator compartments that operate independently of each other, sometimes mounted within a single cabinet. Each has its own separate compressor, condenser and evaporator coils, insulation, thermostat, and door.
A hybrid between the two designs is using a separate fan for each compartment, the Dual Fan approach. Doing so allows for separate control and airflow on a single compressor system.
Absorption refrigerators
An absorption refrigerator works differently from a compressor refrigerator, using a source of heat, such as combustion of liquefied petroleum gas, solar thermal energy or an electric heating element. These heat sources are much quieter than the compressor motor in a typical refrigerator. A fan or pump might be the only mechanical moving parts; reliance on convection is considered impractical.
Other uses of an absorption refrigerator (or "chiller") include large systems used in office buildings or complexes such as hospitals and universities. These large systems are used to chill a brine solution that is circulated through the building.
Peltier effect refrigerators
The Peltier effect uses electricity to pump heat directly; refrigerators employing this system are sometimes used for camping, or in situations where noise is not acceptable. They can be totally silent (if a fan for air circulation is not fitted) but are less energy-efficient than other methods.
Ultra-low temperature refrigerators
"Ultra-cold" or "ultra-low temperature (ULT)" (typically ) freezers, as used for storing biological samples, also generally employ two stages of cooling, but in cascade. The lower temperature stage uses methane, or a similar gas, as a refrigerant, with its condenser kept at around −40°C by a second stage which uses a more conventional refrigerant.
For much lower temperatures, laboratories usually purchase liquid nitrogen (), kept in a Dewar flask, into which the samples are suspended. Cryogenic chest freezers can achieve temperatures of down to , and may include a liquid nitrogen backup.
Other refrigerators
Alternatives to the vapor-compression cycle not in current mass production include:
Acoustic cooling
Air cycle
Magnetic cooling
Malone engine
Pulse tube
Stirling cycle
Thermoelectric cooling
Thermionic cooling
Vortex tube
Water cycle systems.
Layout
Many modern refrigerator/freezers have the freezer on top and the refrigerator on the bottom. Most refrigerator-freezers—except for manual defrost models or cheaper units—use what appears to be two thermostats. Only the refrigerator compartment is properly temperature controlled. When the refrigerator gets too warm, the thermostat starts the cooling process and a fan circulates the air around the freezer. During this time, the refrigerator also gets colder. The freezer control knob only controls the amount of air that flows into the refrigerator via a damper system. Changing the refrigerator temperature will inadvertently change the freezer temperature in the opposite direction. Changing the freezer temperature will have no effect on the refrigerator temperature. The freezer control may also be adjusted to compensate for any refrigerator adjustment.
This means the refrigerator may become too warm. However, because only enough air is diverted to the refrigerator compartment, the freezer usually re-acquires the set temperature quickly, unless the door is opened. When a door is opened, either in the refrigerator or the freezer, the fan in some units stops immediately to prevent excessive frost build up on the freezer's evaporator coil, because this coil is cooling two areas. When the freezer reaches temperature, the unit cycles off, no matter what the refrigerator temperature is. Modern computerized refrigerators do not use the damper system. The computer manages fan speed for both compartments, although air is still blown from the freezer.
Features
Newer refrigerators may include:
Automatic defrosting
A power failure warning that alerts the user by flashing a temperature display. It may display the maximum temperature reached during the power failure, and whether frozen food has defrosted or may contain harmful bacteria.
Chilled water and ice from a dispenser in the door. Water and ice dispensing became available in the 1970s. In some refrigerators, the process of making ice is built-in so the user doesn't have to manually use ice trays. Some refrigerators have water chillers and water filtration systems.
Cabinet rollers that lets the refrigerator roll out for easier cleaning
Adjustable shelves and trays
A status indicator that notifies when it is time to change the water filter
An in-door ice caddy, which relocates the ice-maker storage to the freezer door and saves approximately of usable freezer space. It is also removable, and helps to prevent ice-maker clogging.
A cooling zone in the refrigerator door shelves. Air from the freezer section is diverted to the refrigerator door, to cool milk or juice stored in the door shelf.
A drop down door built into the refrigerator main door, giving easy access to frequently used items such as milk, thus saving energy by not having to open the main door.
A Fast Freeze function to rapidly cool foods by running the compressor for a predetermined amount of time and thus temporarily lowering the freezer temperature below normal operating levels. It is recommended to use this feature several hours before adding more than 1 kg of unfrozen food to the freezer. For freezers without this feature, lowering the temperature setting to the coldest will have the same effect.
Freezer Defrost: Early freezer units accumulated ice crystals around the freezing units. This was a result of humidity introduced into the units when the doors to the freezer were opened condensing on the cold parts, then freezing. This frost buildup required periodic thawing ("defrosting") of the units to maintain their efficiency. Manual Defrost (referred to as Cyclic) units are still available. Advances in automatic defrosting eliminating the thawing task were introduced in the 1950s, but are not universal, due to energy performance and cost. These units used a counter that only defrosted the freezer compartment (Freezer Chest) when a specific number of door openings had been made. The units were just a small timer combined with an electrical heater wire that heated the freezer's walls for a short amount of time to remove all traces of frost/frosting. Also, early units featured freezer compartments located within the larger refrigerator, and accessed by opening the refrigerator door, and then the smaller internal freezer door; units featuring an entirely separate freezer compartment were introduced in the early 1960s, becoming the industry standard by the middle of that decade.
These older freezer compartments were the main cooling body of the refrigerator, and only maintained a temperature of around , which is suitable for keeping food for a week.
Butter heater: In the early 1950s, the butter conditioner's patent was filed and published by the inventor Nave Alfred E. This feature was supposed to "provide a new and improved food storage receptacle for storing butter or the like which may quickly and easily be removed from the refrigerator cabinet for the purpose of cleaning." Because of the high interest to the invention, companies in UK, New Zealand, and Australia started to include the feature into the mass refrigerator production and soon it became a symbol of the local culture. However, not long after that it was removed from production as according to the companies this was the only way for them to meet new ecology regulations and they found it inefficient to have a heat generating device inside a refrigerator.
Later advances included automatic ice units and self compartmentalized freezing units.
Types of domestic refrigerators
Domestic refrigerators and freezers for food storage are made in a range of sizes. Among the smallest is a Peltier refrigerator advertised as being able to hold 6 cans of beer. A large domestic refrigerator stands as tall as a person and may be about wide with a capacity of . Some models for small households fit under kitchen work surfaces, usually about high. Refrigerators may be combined with freezers, either stacked with refrigerator or freezer above, below, or side by side. A refrigerator without a frozen food storage compartment may have a small section just to make ice cubes. Freezers may have drawers to store food in, or they may have no divisions (chest freezers).
Refrigerators and freezers may be free-standing, or built into a kitchen's cabinet.
Three distinct classes of refrigerator are common:
Compressor refrigerators
Compressor refrigerators are by far the most common type; they make a noticeable noise, but are most efficient and give greatest cooling effect. Portable compressor refrigerators for recreational vehicle (RV) and camping use are expensive but effective and reliable. Refrigeration units for commercial and industrial applications can be made in various sizes, shapes and styles to fit customer needs. Commercial and industrial refrigerators may have their compressors located away from the cabinet (similar to split system air conditioners) to reduce noise nuisance and reduce the load on air conditioning in hot weather.
Absorption refrigerator
Absorption refrigerators may be used in caravans and trailers, and dwellings lacking electricity, such as farms or rural cabins, where they have a long history. They may be powered by any heat source: gas (natural or propane) or kerosene being common. Models made for camping and RV use often have the option of running (inefficiently) on 12 volt battery power.
Peltier refrigerators
Peltier refrigerators are powered by electricity, usually 12 volt DC, but mains-powered wine coolers are available. Peltier refrigerators are inexpensive but inefficient and become progressively more inefficient with increased cooling effect; much of this inefficiency may be related to the temperature differential across the short distance between the "hot" and "cold" sides of the Peltier cell. Peltier refrigerators generally use heat sinks and fans to lower this differential; the only noise produced comes from the fan. Reversing the polarity of the voltage applied to the Peltier cells results in a heating rather than cooling effect.
Other specialized cooling mechanisms may be used for cooling, but have not been applied to domestic or commercial refrigerators.
Magnetic refrigerator
Magnetic refrigerators are refrigerators that work on the magnetocaloric effect. The cooling effect is triggered by placing a metal alloy in a magnetic field.
Acoustic refrigerators are refrigerators that use resonant linear reciprocating motors/alternators to generate a sound that is converted to heat and cold using compressed helium gas. The heat is discarded and the cold is routed to the refrigerator.
Energy efficiency
In a house without air-conditioning (space heating and/or cooling) refrigerators consume more energy than any other home device. In the early 1990s a competition was held among the major US manufacturers to encourage energy efficiency. Current US models that are Energy Star qualified use 50% less energy than the average 1974 model used. The most energy-efficient unit made in the US consumes about half a kilowatt-hour per day (equivalent to 20 W continuously). But even ordinary units are reasonably efficient; some smaller units use less than 0.2 kWh per day (equivalent to 8 W continuously).
Larger units, especially those with large freezers and icemakers, may use as much as 4 kW·h per day (equivalent to 170 W continuously).
The European Union uses a letter-based mandatory energy efficiency rating label, with A being the most efficient, instead of the Energy Star.
For US refrigerators, the Consortium on Energy Efficiency (CEE) further differentiates between Energy Star qualified refrigerators. Tier 1 refrigerators are those that are 20% to 24.9% more efficient than the Federal minimum standards set by the National Appliance Energy Conservation Act (NAECA). Tier 2 are those that are 25% to 29.9% more efficient. Tier 3 is the highest qualification, for those refrigerators that are at least 30% more efficient than Federal standards. About 82% of the Energy Star qualified refrigerators are Tier 1, with 13% qualifying as Tier 2, and just 5% at Tier 3.
Besides the standard style of compressor refrigeration used in ordinary household refrigerators and freezers, there are technologies such as absorption and magnetic refrigeration. Although these designs generally use a much more energy than compressor refrigeration, other qualities such as silent operation or the ability to use gas can favor their use in small enclosures, a mobile environment or in environments where failure of refrigeration must not be possible.
Many refrigerators made in the 1930s and 1940s were far more efficient than most that were made later. This is partly due to features added later, such as auto-defrost, that reduced efficiency. Additionally, after World War 2, refrigerator style became more important than efficiency. This was especially true in the US in the 1970s, when side-by-side models (known as American fridge-freezers outside of the US) with ice dispensers and water chillers became popular. The amount of insulation used was also often decreased to reduce refrigerator case size and manufacturing costs.
Improvement
Over time standards of refrigerator energy efficiency have been introduced and tightened, which has driven steady improvement; 21st-century refrigerators are typically three times more energy-efficient than in the 1930s.
The efficiency of older refrigerators can be improved by regular defrosting (if the unit is manual defrost) and cleaning, replacing deteriorated door seals with new ones, not setting the thermostat colder than actually required (a refrigerator does not usually need to be colder than ), and replacing insulation, where applicable. Cleaning condenser coils to remove dust impeding heat flow, and ensuring that there is space for air flow around the condenser can improve efficiency.
Auto defrosting
Frost-free refrigerators and freezers use electric fans to cool the appropriate compartment. This could be called a "fan forced" refrigerator, whereas manual defrost units rely on colder air lying at the bottom, versus the warm air at the top to achieve adequate cooling. The air is drawn in through an inlet duct and passed through the evaporator where it is cooled, the air is then circulated throughout the cabinet via a series of ducts and vents. Because the air passing the evaporator is supposedly warm and moist, frost begins to form on the evaporator (especially on a freezer's evaporator). In cheaper and/or older models, a defrost cycle is controlled via a mechanical timer. This timer is set to shut off the compressor and fan and energize a heating element located near or around the evaporator for about 15 to 30 minutes at every 6 to 12 hours. This melts any frost or ice build-up and allows the refrigerator to work normally once more. It is believed that frost free units have a lower tolerance for frost, due to their air-conditioner-like evaporator coils. Therefore, if a door is left open accidentally (especially the freezer), the defrost system may not remove all frost, in this case, the freezer (or refrigerator) must be defrosted.
If the defrosting system melts all the ice before the timed defrosting period ends, then a small device (called a defrost limiter) acts like a thermostat and shuts off the heating element to prevent too large a temperature fluctuation, it also prevents hot blasts of air when the system starts again, should it finish defrosting early. On some early frost-free models, the defrost limiter also sends a signal to the defrost timer to start the compressor and fan as soon as it shuts off the heating element before the timed defrost cycle ends. When the defrost cycle is completed, the compressor and fan are allowed to cycle back on.
Frost-free refrigerators, including some early frost-free refrigerators/freezers that used a cold plate in their refrigerator section instead of airflow from the freezer section, generally don't shut off their refrigerator fans during defrosting. This allows consumers to leave food in the main refrigerator compartment uncovered, and also helps keep vegetables moist. This method also helps reduce energy consumption, because the refrigerator is above freeze point and can pass the warmer-than-freezing air through the evaporator or cold plate to aid the defrosting cycle.
Inverter
With the advent of digital inverter compressors, the energy consumption is even further reduced than a single-speed induction motor compressor, and thus contributes far less in the way of greenhouse gases.
The energy consumption of a refrigerator is also dependent on the type of refrigeration being done. For instance, Inverter Refrigerators consume comparatively less energy than a typical non-inverter refrigerator. In an inverter refrigerator, the compressor is used conditionally on requirement basis. For instance, an inverter refrigerator might use less energy during the winters than it does during the summers. This is because the compressor works for a shorter time than it does during the summers.
Further, newer models of inverter compressor refrigerators take into account various external and internal conditions to adjust the compressor speed and thus optimize cooling and energy consumption. Most of them use at least 4 sensors which help detect variance in external temperature, internal temperature owing to opening of the refrigerator door or keeping new food inside; humidity and usage patterns. Depending on the sensor inputs, the compressor adjusts its speed. For example, if door is opened or new food is kept, the sensor detects an increase in temperature inside the cabin and signals the compressor to increase its speed till a pre-determined temperature is attained. After which, the compressor runs at a minimum speed to just maintain the internal temperature. The compressor typically runs between 1200 and 4500 rpm.
Inverter compressors not only optimizes cooling but is also superior in terms of durability and energy efficiency.
A device consumes maximum energy and undergoes maximum wear and tear when it switches itself on. As an inverter compressor never switches itself off and instead runs on varying speed, it minimizes wear and tear and energy usage.
LG played a significant role in improving inverter compressors as we know it by reducing the friction points in the compressor and thus introducing Linear Inverter Compressors. Conventionally, all domestic refrigerators use a reciprocating drive which is connected to the piston. But in a linear inverter compressor, the piston which is a permanent magnet is suspended between two electromagnets. The AC changes the magnetic poles of the electromagnet, which results in the push and pull that compresses the refrigerant. LG claims that this helps reduce energy consumption by 32% and noise by 25% compared to their conventional compressors.
Form factor
The physical design of refrigerators also plays a large part in its energy efficiency. The most efficient is the chest-style freezer, as its top-opening design minimizes convection when opening the doors, reducing the amount of warm moist air entering the freezer. On the other hand, in-door ice dispensers cause more heat leakage, contributing to an increase in energy consumption.
Impact
Global adoption
The gradual global adoption of refrigerators marks a transformative era in food preservation and domestic convenience. Since the refrigerators introduction in the 20th century, refrigerators have transitioned from being luxurious items to everyday commodities which have altered the understandings of food storage practices. Refrigerators have significantly impacted various aspects of many individual's daily lives by providing food safety to people around the world spanning across a wide variety of cultural and socioeconomic backgrounds.
The global adoption of refrigerators has also changed how societies handle their food supply. The introduction of the refrigerator in different societies has resulted in the monetization and industrialized mass food production systems which are commonly linked to increased food waste, animal wastes, and dangerous chemical wastes being traced back into different ecosystems. In addition, refrigerators have also provided an easier way to access food for many individuals around the world, with many options that commercialization has promoted leaning towards low-nutrient dense foods.
After consumer refrigerators became financially viable for production and sale on a large scale, their prevalence around the globe expanded greatly. In the United States, an estimated 99.5% of households have a refrigerator. Refrigerator ownership is more common in developed Western countries, but has stayed relatively low in Eastern and developing countries despite its growing popularity. Throughout Eastern Europe and the Middle East, only 80% of the population own refrigerators. In addition to this, 65% of the population in China are stated to have refrigerators. The distribution of consumer refrigerators is also skewed as urban areas exhibit larger refrigeration ownership percentages compared to rural areas.
Supplantation of the ice trade
The ice trade was an industry in the 19th and 20th centuries of the harvesting, transportation, and sale of natural and artificial ice for the purposes of refrigeration and consumption. The majority of the ice used for trade was harvested from North America and transported globally with some smaller operations working out of Norway. With the introduction of more affordable large and home scale refrigeration around the 1920s, the need for large scale ice harvest and transportation was no longer needed, and the ice trade subsequently slowed and shrank to smaller scale local services or disappeared altogether.
Effect on diet and lifestyle
The refrigerator allows households to keep food fresh for longer than before. The most notable improvement is for meat and other highly perishable wares, which previously needed to be preserved or otherwise processed for long-term storage and transport. This change in the supply chains of food products led to a marked increase in the quality of food in areas where refrigeration was being used. Additionally, the increased freshness and shelf life of food caused by the advent of refrigeration in addition to growing global communication methods has resulted in an increase in cultural exchange through food products from different regions of the world. There have also been claims that this increase in the quality of food is responsible for an increase in the height of United States citizens around the early 1900s.
Refrigeration has also contributed to a decrease in the quality of food in some regions. By allowing, in part, for the phenomenon of globalization in the food sector, refrigeration has made the creation and transportation of ultra-processed foods and convenience foods inexpensive, leading to their prevalence, especially in lower-income regions. These regions of lessened access to higher quality foods are referred to as food deserts.
Freezers allow people to buy food in bulk and eat it at leisure, and bulk purchases may save money. Ice cream, a popular commodity of the 20th century, could previously only be obtained by traveling to where the product was made and eating it on the spot. Now it is a common food item. Ice on demand not only adds to the enjoyment of cold drinks, but is useful for first-aid, and for cold packs that can be kept frozen for picnics or in case of emergency.
Temperature zones and ratings
Residential units
The capacity of a refrigerator is measured in either liters or cubic feet. Typically the volume of a combined refrigerator-freezer is split with 1/3 to 1/4 of the volume allocated to the freezer although these values are highly variable.
Temperature settings for refrigerator and freezer compartments are often given arbitrary numbers by manufacturers (for example, 1 through 9, warmest to coldest), but generally is ideal for the refrigerator compartment and for the freezer. Some refrigerators must be within certain external temperature parameters to run properly. This can be an issue when placing units in an unfinished area, such as a garage.
Some refrigerators are now divided into four zones to store different types of food:
(freezer)
(meat zone)
(cooling zone)
(crisper)
European freezers, and refrigerators with a freezer compartment, have a four-star rating system to grade freezers.
Although both the three- and four-star ratings specify the same storage times and same minimum temperature of , only a four-star freezer is intended for freezing fresh food, and may include a "fast freeze" function (runs the compressor continually, down to as low as ) to facilitate this. Three (or fewer) stars are used for frozen food compartments that are only suitable for storing frozen food; introducing fresh food into such a compartment is likely to result in unacceptable temperature rises. This difference in categorization is shown in the design of the 4-star logo, where the "standard" three stars are displayed in a box using "positive" colours, denoting the same normal operation as a 3-star freezer, and the fourth star showing the additional fresh food/fast freeze function is prefixed to the box in "negative" colours or with other distinct formatting.
Most European refrigerators include a moist cold refrigerator section (which does require (automatic) defrosting at irregular intervals) and a (rarely frost-free) freezer section.
Commercial refrigeration temperatures
(from warmest to coolest)
Refrigerators , and not greater than maximum refrigerator temperature at
Freezer, Reach-in
Freezer, Walk-in
Freezer, Ice Cream
Cryogenics
Cryocooler: below -153 °C (-243.4 °F)
Dilution refrigerator: down to -273.148 °C (-459.6664 °F)
Disposal
An increasingly important environmental concern is the disposal of old refrigerators—initially because freon coolant damages the ozone layer—but as older generation refrigerators wear out, the destruction of CFC-bearing insulation also causes concern. Modern refrigerators usually use a refrigerant called HFC-134a (1,1,1,2-Tetrafluoroethane), which does not deplete the ozone layer, unlike Freon. R-134a is becoming much rarer in Europe, where newer refrigerants are being used instead. The main refrigerant now used is R-600a (also known as isobutane), which has a smaller effect on the atmosphere if released. There have been reports of refrigerators exploding if the refrigerant leaks isobutane in the presence of a spark. If the coolant leaks into the refrigerator, at times when the door is not being opened (such as overnight) the concentration of coolant in the air within the refrigerator can build up to form an explosive mixture that can be ignited either by a spark from the thermostat or when the light comes on as the door is opened, resulting in documented cases of serious property damage and injury or even death from the resulting explosion.
Disposal of discarded refrigerators is regulated, often mandating the removal of doors for safety reasons. Children have been asphyxiated while playing with discarded refrigerators, particularly older models with latching doors. Since the 1950s regulations in many places have banned the use of refrigerator doors that cannot be opened by pushing from inside. Modern units use a magnetic door gasket that holds the door sealed but allows it to be pushed open from the inside. This gasket was invented, developed and manufactured by Max Baermann (1903–1984) of Bergisch Gladbach/Germany.
Regarding total life-cycle costs, many governments offer incentives to encourage recycling of old refrigerators. One example is the Phoenix refrigerator program launched in Australia. This government incentive picked up old refrigerators, paying their owners for "donating" the refrigerator. The refrigerator was then refurbished, with new door seals, a thorough cleaning, and the removal of items such as the cover that is strapped to the back of many older units. The resulting refrigerators, now over 10% more efficient, were then given to low-income families. The United States also has a program for collecting and replacing older, less-efficient refrigerators and other white goods. These programs seek to replace large appliances that are old and inefficient or faulty by newer, more energy-efficient appliances, to reduce the cost imposed on lower-income families, and reduce pollution caused by the older appliances.
Gallery
See also
Auto-defrost
Cold chain
Continuous freezers
Einstein refrigerator
Home automation
Ice cream maker
Ice famine
Smart refrigerator
Kimchi refrigerator
Home appliance
Pot-in-pot refrigerator
Refrigerator death
Refrigerator magnet
Solar-powered refrigerator
Star rating
Water dispenser
Wine cellar
References
Further reading
Rees, Jonathan. Refrigeration Nation: A History of Ice, Appliances, and Enterprise in America (Johns Hopkins University Press; 2013) 256 pages
External links
Refrigerating apparatus
Refrigerating apparatus
The History of the Refrigerator and Freezers
Refrigerators, Canada Science and Technology Museum
20th-century inventions
Articles containing video clips
Australian inventions
Cooling technology
Food preservation
Food storage
Heat pumps
Home appliances
Home automation
Kitchen | Refrigerator | Physics,Technology | 9,320 |
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