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Overuse in some journals
Starting in the 2010s, some journals began questioning whether significance testing, and particularly using a threshold of =5%, was being relied on too heavily as the primary measure of validity of a hypothesis. Some journals encouraged authors to do more detailed analysis than just a statistical significance test. In social psychology, the journal Basic and Applied Social Psychology banned the use of significance testing altogether from papers it published, requiring authors to use other measures to evaluate hypotheses and impact.
Other editors, commenting on this ban have noted: "Banning the reporting of p-values, as Basic and Applied Social Psychology recently did, is not going to solve the problem because it is merely treating a symptom of the problem. There is nothing wrong with hypothesis testing and p-values per se as long as authors, reviewers, and action editors use them correctly." Some statisticians prefer to use alternative measures of evidence, such as likelihood ratios or Bayes factors. Using Bayesian statistics can avoid confidence levels, but also requires making additional assumptions, and may not necessarily improve practice regarding statistical testing.
The widespread abuse of statistical significance represents an important topic of research in metascience.
Redefining significance
In 2016, the American Statistical Association (ASA) published a statement on p-values, saying that "the widespread use of 'statistical significance' (generally interpreted as 'p ≤ 0.05') as a license for making a claim of a scientific finding (or implied truth) leads to considerable distortion of the scientific process". In 2017, a group of 72 authors proposed to enhance reproducibility by changing the p-value threshold for statistical significance from 0.05 to 0.005. Other researchers responded that imposing a more stringent significance threshold would aggravate problems such as data dredging; alternative propositions are thus to select and justify flexible p-value thresholds before collecting data, or to interpret p-values as continuous indices, thereby discarding thresholds and statistical significance. Additionally, the change to 0.005 would increase the likelihood of false negatives, whereby the effect being studied is real, but the test fails to show it.
In 2019, over 800 statisticians and scientists signed a message calling for the abandonment of the term "statistical significance" in science, and the ASA published a further official statement declaring (page 2): | Statistical significance | Wikipedia | 479 | 160995 | https://en.wikipedia.org/wiki/Statistical%20significance | Mathematics | Statistics | null |
In logic, negation, also called the logical not or logical complement, is an operation that takes a proposition to another proposition "not ", written , , or . It is interpreted intuitively as being true when is false, and false when is true. For example, if is "Spot runs", then "not " is "Spot does not run". An operand of a negation is called a negand or negatum.
Negation is a unary logical connective. It may furthermore be applied not only to propositions, but also to notions, truth values, or semantic values more generally. In classical logic, negation is normally identified with the truth function that takes truth to falsity (and vice versa). In intuitionistic logic, according to the Brouwer–Heyting–Kolmogorov interpretation, the negation of a proposition is the proposition whose proofs are the refutations of .
Definition
Classical negation is an operation on one logical value, typically the value of a proposition, that produces a value of true when its operand is false, and a value of false when its operand is true. Thus if statement is true, then (pronounced "not P") would then be false; and conversely, if is true, then would be false.
The truth table of is as follows:
{| class="wikitable" style="text-align:center; background-color: #ddffdd;"
|- bgcolor="#ddeeff"
| ||
|-
| ||
|-
| ||
|}
Negation can be defined in terms of other logical operations. For example, can be defined as (where is logical consequence and is absolute falsehood). Conversely, one can define as for any proposition (where is logical conjunction). The idea here is that any contradiction is false, and while these ideas work in both classical and intuitionistic logic, they do not work in paraconsistent logic, where contradictions are not necessarily false. As a further example, negation can be defined in terms of NAND and can also be defined in terms of NOR.
Algebraically, classical negation corresponds to complementation in a Boolean algebra, and intuitionistic negation to pseudocomplementation in a Heyting algebra. These algebras provide a semantics for classical and intuitionistic logic. | Negation | Wikipedia | 493 | 161019 | https://en.wikipedia.org/wiki/Negation | Mathematics | Specific functions | null |
Notation
The negation of a proposition is notated in different ways, in various contexts of discussion and fields of application. The following table documents some of these variants:
The notation is Polish notation.
In set theory, is also used to indicate 'not in the set of': is the set of all members of that are not members of .
Regardless how it is notated or symbolized, the negation can be read as "it is not the case that ", "not that ", or usually more simply as "not ".
Precedence
As a way of reducing the number of necessary parentheses, one may introduce precedence rules: ¬ has higher precedence than ∧, ∧ higher than ∨, and ∨ higher than →. So for example, is short for
Here is a table that shows a commonly used precedence of logical operators.
Properties
Double negation
Within a system of classical logic, double negation, that is, the negation of the negation of a proposition , is logically equivalent to . Expressed in symbolic terms, . In intuitionistic logic, a proposition implies its double negation, but not conversely. This marks one important difference between classical and intuitionistic negation. Algebraically, classical negation is called an involution of period two.
However, in intuitionistic logic, the weaker equivalence does hold. This is because in intuitionistic logic, is just a shorthand for , and we also have . Composing that last implication with triple negation implies that .
As a result, in the propositional case, a sentence is classically provable if its double negation is intuitionistically provable. This result is known as Glivenko's theorem.
Distributivity
De Morgan's laws provide a way of distributing negation over disjunction and conjunction:
, and
.
Linearity
Let denote the logical xor operation. In Boolean algebra, a linear function is one such that:
If there exists ,
,
for all .
Another way to express this is that each variable always makes a difference in the truth-value of the operation, or it never makes a difference. Negation is a linear logical operator.
Self dual
In Boolean algebra, a self dual function is a function such that:
for all
.
Negation is a self dual logical operator. | Negation | Wikipedia | 466 | 161019 | https://en.wikipedia.org/wiki/Negation | Mathematics | Specific functions | null |
Negations of quantifiers
In first-order logic, there are two quantifiers, one is the universal quantifier (means "for all") and the other is the existential quantifier (means "there exists"). The negation of one quantifier is the other quantifier ( and ). For example, with the predicate P as "x is mortal" and the domain of x as the collection of all humans, means "a person x in all humans is mortal" or "all humans are mortal". The negation of it is , meaning "there exists a person x in all humans who is not mortal", or "there exists someone who lives forever".
Rules of inference
There are a number of equivalent ways to formulate rules for negation. One usual way to formulate classical negation in a natural deduction setting is to take as primitive rules of inference negation introduction (from a derivation of to both and , infer ; this rule also being called reductio ad absurdum), negation elimination (from and infer ; this rule also being called ex falso quodlibet), and double negation elimination (from infer ). One obtains the rules for intuitionistic negation the same way but by excluding double negation elimination.
Negation introduction states that if an absurdity can be drawn as conclusion from then must not be the case (i.e. is false (classically) or refutable (intuitionistically) or etc.). Negation elimination states that anything follows from an absurdity. Sometimes negation elimination is formulated using a primitive absurdity sign . In this case the rule says that from and follows an absurdity. Together with double negation elimination one may infer our originally formulated rule, namely that anything follows from an absurdity.
Typically the intuitionistic negation of is defined as . Then negation introduction and elimination are just special cases of implication introduction (conditional proof) and elimination (modus ponens). In this case one must also add as a primitive rule ex falso quodlibet.
Programming language and ordinary language
As in mathematics, negation is used in computer science to construct logical statements.
if (!(r == t))
{
/*...statements executed when r does NOT equal t...*/
} | Negation | Wikipedia | 497 | 161019 | https://en.wikipedia.org/wiki/Negation | Mathematics | Specific functions | null |
The exclamation mark "!" signifies logical NOT in B, C, and languages with a C-inspired syntax such as C++, Java, JavaScript, Perl, and PHP. "NOT" is the operator used in ALGOL 60, BASIC, and languages with an ALGOL- or BASIC-inspired syntax such as Pascal, Ada, Eiffel and Seed7. Some languages (C++, Perl, etc.) provide more than one operator for negation. A few languages like PL/I and Ratfor use ¬ for negation. Most modern languages allow the above statement to be shortened from if (!(r == t)) to if (r != t), which allows sometimes, when the compiler/interpreter is not able to optimize it, faster programs.
In computer science there is also bitwise negation. This takes the value given and switches all the binary 1s to 0s and 0s to 1s. This is often used to create ones' complement (or "~" in C or C++) and two's complement (just simplified to "-" or the negative sign, as this is equivalent to taking the arithmetic negation of the number).
To get the absolute (positive equivalent) value of a given integer the following would work as the "-" changes it from negative to positive (it is negative because "x < 0" yields true)
unsigned int abs(int x)
{
if (x < 0)
return -x;
else
return x;
}
To demonstrate logical negation:
unsigned int abs(int x)
{
if (!(x < 0))
return x;
else
return -x;
}
Inverting the condition and reversing the outcomes produces code that is logically equivalent to the original code, i.e. will have identical results for any input (depending on the compiler used, the actual instructions performed by the computer may differ). | Negation | Wikipedia | 404 | 161019 | https://en.wikipedia.org/wiki/Negation | Mathematics | Specific functions | null |
In C (and some other languages descended from C), double negation (!!x) is used as an idiom to convert x to a canonical Boolean, ie. an integer with a value of either 0 or 1 and no other. Although any integer other than 0 is logically true in C and 1 is not special in this regard, it is sometimes important to ensure that a canonical value is used, for example for printing or if the number is subsequently used for arithmetic operations.
The convention of using ! to signify negation occasionally surfaces in ordinary written speech, as computer-related slang for not. For example, the phrase !voting means "not voting". Another example is the phrase !clue which is used as a synonym for "no-clue" or "clueless".
Kripke semantics
In Kripke semantics where the semantic values of formulae are sets of possible worlds, negation can be taken to mean set-theoretic complementation (see also possible world semantics for more). | Negation | Wikipedia | 209 | 161019 | https://en.wikipedia.org/wiki/Negation | Mathematics | Specific functions | null |
A document is a written, drawn, presented, or memorialized representation of thought, often the manifestation of non-fictional, as well as fictional, content. The word originates from the Latin , which denotes a "teaching" or "lesson": the verb denotes "to teach". In the past, the word was usually used to denote written proof useful as evidence of a truth or fact. In the Computer Age, "document" usually denotes a primarily textual computer file, including its structure and format, e.g. fonts, colors, and images. Contemporarily, "document" is not defined by its transmission medium, e.g., paper, given the existence of electronic documents. "Documentation" is distinct because it has more denotations than "document". Documents are also distinguished from "realia", which are three-dimensional objects that would otherwise satisfy the definition of "document" because they memorialize or represent thought; documents are considered more as two-dimensional representations. While documents can have large varieties of customization, all documents can be shared freely and have the right to do so, creativity can be represented by documents, also. History, events, examples, opinions, stories etc. all can be expressed in documents.
Abstract definitions
The concept of "document" has been defined by Suzanne Briet as "any concrete or symbolic indication, preserved or recorded, for reconstructing or for proving a phenomenon, whether physical or mental."
An often-cited article concludes that "the evolving notion of document" among Jonathan Priest, Paul Otlet, Briet, Walter Schürmeyer, and the other documentalists increasingly emphasized whatever functioned as a document rather than traditional physical forms of documents. The shift to digital technology would seem to make this distinction even more important. David M. Levy has said that an emphasis on the technology of digital documents has impeded our understanding of digital documents as documents.
A conventional document, such as a mail message or a technical report, exists physically in digital technology as a string of bits, as does everything else in a digital environment. As an object of study, it has been made into a document. It has become physical evidence by those who study it. | Document | Wikipedia | 453 | 161228 | https://en.wikipedia.org/wiki/Document | Technology | Media and communication: Basics | null |
"Document" is defined in library and information science and documentation science as a fundamental, abstract idea: the word denotes everything that may be represented or memorialized to serve as evidence. The classic example provided by Briet is an antelope: "An antelope running wild on the plains of Africa should not be considered a document[;] she rules. But if it were to be captured, taken to a zoo and made an object of study, it has been made into a document. It has become physical evidence being used by those who study it. Indeed, scholarly articles written about the antelope are secondary documents, since the antelope itself is the primary document." This opinion has been interpreted as an early expression of actor–network theory.
Kinds
A document can be structured, like tabular documents, lists, forms, or scientific charts, semi-structured like a book or a newspaper article, or unstructured like a handwritten note. Documents are sometimes classified as secret, private, or public. They may also be described as drafts or proofs. When a document is copied, the source is denominated the "original".
Documents are used in numerous fields, e.g.:
Academia:
manuscript,
thesis,
paper,
journal,
chart,
and technical drawing
Media:
mock-up,
script,
image,
photography,
and newspaper article
Administration, law, and politics:
application,
brief,
certificate,
commission,
constitutional document,
form,
gazette,
identity document,
license,
manifesto,
summons,
census,
and white paper
Business:
invoice,
request for proposal,
proposal,
contract,
packing slip,
manifest,
report (detailed and summary),
spreadsheet,
material safety data sheet,
waybill,
bill of lading,
financial statement,
nondisclosure agreement (NDA),
mutual nondisclosure agreement,
and user guide
Geography and planning:
topographic map,
cadastre,
legend,
and architectural plan
Such standard documents can be drafted based on a template. | Document | Wikipedia | 409 | 161228 | https://en.wikipedia.org/wiki/Document | Technology | Media and communication: Basics | null |
Drafting
The page layout of a document is how information is graphically arranged in the space of the document, e.g., on a page. If the appearance of the document is of concern, the page layout is generally the responsibility of a graphic designer. Typography concerns the design of letter and symbol forms and their physical arrangement in the document (see typesetting). Information design concerns the effective communication of information, especially in industrial documents and public signs. Simple textual documents may not require visual design and may be drafted only by an author, clerk, or transcriber. Forms may require a visual design for their initial fields, but not to complete the forms.
Media
Traditionally, the medium of a document was paper and the information was applied to it in ink, either by handwriting (to make a manuscript) or by a mechanical process (e.g., a printing press or laser printer). Today, some short documents also may consist of sheets of paper stapled together.
Historically, documents were inscribed with ink on papyrus (starting in ancient Egypt) or parchment; scratched as runes or carved on stone using a sharp tool, e.g., the Tablets of Stone described in the Bible; stamped or incised in clay and then baked to make clay tablets, e.g., in the Sumerian and other Mesopotamian civilizations. The papyrus or parchment was often rolled into a scroll or cut into sheets and bound into a codex (book).
Contemporary electronic means of memorializing and displaying documents include:
Monitor of a desktop computer, laptop, tablet; optionally with a printer to produce a hard copy;
Personal digital assistant;
Dedicated e-book device;
Electronic paper, typically, using the Portable Document Format (PDF);
Information appliance;
Digital audio player; and
Radio and television service provider.
Digital documents usually require a specific file format to be presentable in a specific medium.
In law
Documents in all forms frequently serve as material evidence in criminal and civil proceedings. The forensic analysis of such a document is within the scope of questioned document examination. To catalog and manage the large number of documents that may be produced during litigation, Bates numbering is often applied to all documents in the lawsuit so that each document has a unique, arbitrary, identification number. | Document | Wikipedia | 459 | 161228 | https://en.wikipedia.org/wiki/Document | Technology | Media and communication: Basics | null |
In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. They are minute random fluctuations in the values of the fields which represent elementary particles, such as electric and magnetic fields which represent the electromagnetic force carried by photons, W and Z fields which carry the weak force, and gluon fields which carry the strong force.
The uncertainty principle states the uncertainty in energy and time can be related by , where ≈ . This means that pairs of virtual particles with energy and lifetime shorter than are continually created and annihilated in empty space. Although the particles are not directly detectable, the cumulative effects of these particles are measurable. For example, without quantum fluctuations, the "bare" mass and charge of elementary particles would be infinite; from renormalization theory the shielding effect of the cloud of virtual particles is responsible for the finite mass and charge of elementary particles.
Another consequence is the Casimir effect. One of the first observations which was evidence for vacuum fluctuations was the Lamb shift in hydrogen. In July 2020, scientists reported that quantum vacuum fluctuations can influence the motion of macroscopic, human-scale objects by measuring correlations below the standard quantum limit between the position/momentum uncertainty of the mirrors of LIGO and the photon number/phase uncertainty of light that they reflect.
Field fluctuations
In quantum field theory, fields undergo quantum fluctuations. A reasonably clear distinction can be made between quantum fluctuations and thermal fluctuations of a quantum field (at least for a free field; for interacting fields, renormalization substantially complicates matters). An illustration of this distinction can be seen by considering quantum and classical Klein–Gordon fields: For the quantized Klein–Gordon field in the vacuum state, we can calculate the probability density that we would observe a configuration at a time in terms of its Fourier transform to be
In contrast, for the classical Klein–Gordon field at non-zero temperature, the Gibbs probability density that we would observe a configuration at a time is | Quantum fluctuation | Wikipedia | 432 | 161253 | https://en.wikipedia.org/wiki/Quantum%20fluctuation | Physical sciences | Quantum mechanics | Physics |
These probability distributions illustrate that every possible configuration of the field is possible, with the amplitude of quantum fluctuations controlled by the Planck constant , just as the amplitude of thermal fluctuations is controlled by , where is the Boltzmann constant. Note that the following three points are closely related:
the Planck constant has units of action (joule-seconds) instead of units of energy (joules),
the quantum kernel is instead of (the quantum kernel is nonlocal from a classical heat kernel viewpoint, but it is local in the sense that it does not allow signals to be transmitted),
the quantum vacuum state is Lorentz-invariant (although not manifestly in the above), whereas the classical thermal state is not (the classical dynamics is Lorentz-invariant, but the Gibbs probability density is not a Lorentz-invariant initial condition).
A classical continuous random field can be constructed that has the same probability density as the quantum vacuum state, so that the principal difference from quantum field theory is the measurement theory (measurement in quantum theory is different from measurement for a classical continuous random field, in that classical measurements are always mutually compatible – in quantum-mechanical terms they always commute). | Quantum fluctuation | Wikipedia | 238 | 161253 | https://en.wikipedia.org/wiki/Quantum%20fluctuation | Physical sciences | Quantum mechanics | Physics |
A period 5 element is one of the chemical elements in the fifth row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.
Physical properties
This period contains technetium, one of the two elements until lead that has no stable isotopes (along with promethium), as well as molybdenum and iodine, two of the heaviest elements with a known biological role. Niobium has the largest known magnetic penetration depth of all the elements. Zirconium is one of the main components of zircon crystals, currently the oldest known minerals in the Earth's crust. Many later transition metals, such as rhodium, are very commonly used in jewelry as they are very shiny.
This period is known to have a large number of exceptions to the Madelung rule. | Period 5 element | Wikipedia | 275 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Elements and their properties
{| class="wikitable sortable"
! colspan="3" | Chemical element
! Block
! Electron configuration
|-
!
!
!
!
!
|- bgcolor=""
|| 37 || Rb || Rubidium || s-block || [Kr] 5s1
|- bgcolor=""
|| 38 || Sr || Strontium || s-block || [Kr] 5s2
|- bgcolor=""
|| 39 || Y || Yttrium || d-block || [Kr] 4d1 5s2
|- bgcolor=""
|| 40 || Zr || Zirconium || d-block || [Kr] 4d2 5s2
|- bgcolor=""
|| 41 || Nb || Niobium || d-block || [Kr] 4d4 5s1 (*)
|- bgcolor=""
|| 42 || Mo || Molybdenum || d-block || [Kr] 4d5 5s1 (*)
|- bgcolor=""
|| 43 || Tc || Technetium || d-block || [Kr] 4d5 5s2
|- bgcolor=""
|| 44 || Ru || Ruthenium || d-block || [Kr] 4d7 5s1 (*)
|- bgcolor=""
|| 45 || Rh || Rhodium || d-block|| [Kr] 4d8 5s1 (*)
|- bgcolor=""
|| 46 || Pd || Palladium || d-block || [Kr] 4d10 (*)
|- bgcolor=""
|| 47 || Ag || Silver || d-block || [Kr] 4d10 5s1 (*)
|- bgcolor=""
|| 48 || Cd || Cadmium || d-block || [Kr] 4d10 5s2
|- bgcolor="" | Period 5 element | Wikipedia | 502 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
|| 49 || In || Indium || p-block || [Kr] 4d10 5s2 5p1
|- bgcolor=""
|| 50 || Sn || Tin || p-block || [Kr] 4d10 5s2 5p2
|- bgcolor=""
|| 51 || Sb || Antimony || p-block || [Kr] 4d10 5s2 5p3
|- bgcolor=""
|| 52 || Te || Tellurium || p-block || [Kr] 4d10 5s2 5p4
|- bgcolor=""
|| 53 || I || Iodine || p-block || [Kr] 4d10 5s2 5p5
|- bgcolor=""
|| 54 || Xe || Xenon || p-block || [Kr] 4d10 5s2 5p6
|} | Period 5 element | Wikipedia | 230 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
(*) Exception to the Madelung rule
s-block elements
Rubidium
Rubidium is the first element placed in period 5. It is an alkali metal, the most reactive group in the periodic table, having properties and similarities with both other alkali metals and other period 5 elements. For example, rubidium has 5 electron shells, a property found in all other period 5 elements, whereas its electron configuration's ending is similar to all other alkali metals: s1. Rubidium also follows the trend of increasing reactivity as the atomic number increases in the alkali metals, for it is more reactive than potassium, but less so than caesium. In addition, both potassium and rubidium yield almost the same hue when ignited, so researchers must use different methods to differentiate between these two 1st group elements. Rubidium is very susceptible to oxidation in air, similar to most of the other alkali metals, so it readily transforms into rubidium oxide, a yellow solid with the chemical formula Rb2O.
Strontium
Strontium is the second element placed in the 5th period. It is an alkaline earth metal, a relatively reactive group, although not nearly as reactive as the alkali metals. Like rubidium, it has 5 electron shells or energy levels, and in accordance with the Madelung rule it has two electrons in its 5s subshell. Strontium is a soft metal and is extremely reactive upon contact with water. If it comes in contact with water, it will combine with the atoms of both oxygen and hydrogen to form strontium hydroxide and pure hydrogen gas which quickly diffuses in the air. In addition, strontium, like rubidium, oxidizes in air and turns a yellow color. When ignited, it will burn with a strong red flame.
d-block elements
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is never found in nature as a free element. Its only stable isotope, 89Y, is also its only naturally occurring isotope. | Period 5 element | Wikipedia | 465 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
In 1787, Carl Axel Arrhenius found a new mineral near Ytterby in Sweden and named it ytterbite, after the village. Johan Gadolin discovered yttrium's oxide in Arrhenius' sample in 1789, and Anders Gustaf Ekeberg named the new oxide yttria. Elemental yttrium was first isolated in 1828 by Friedrich Wöhler.
The most important use of yttrium is in making phosphors, such as the red ones used in television set cathode-ray tube (CRT) displays and in LEDs. Other uses include the production of electrodes, electrolytes, electronic filters, lasers and superconductors; various medical applications; and as traces in various materials to enhance their properties. Yttrium has no known biological role, and exposure to yttrium compounds can cause lung disease in humans.
Zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name of zirconium is taken from the mineral zircon. Its atomic mass is 91.224. It is a lustrous, gray-white, strong transition metal that resembles titanium. Zirconium is mainly used as a refractory and opacifier, although minor amounts are used as alloying agent for its strong resistance to corrosion. Zirconium is obtained mainly from the mineral zircon, which is the most important form of zirconium in use.
Zirconium forms a variety of inorganic and organometallic compounds such as zirconium dioxide and zirconocene dichloride, respectively. Five isotopes occur naturally, three of which are stable. Zirconium compounds have no biological role.
Niobium
Niobium, or columbium, is a chemical element with the symbol Nb and atomic number 41. It is a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite. The name comes from Greek mythology: Niobe, daughter of Tantalus. | Period 5 element | Wikipedia | 443 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Niobium has physical and chemical properties similar to those of the element tantalum, and the two are therefore difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical. The German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably. The name of the element was officially adopted as niobium in 1949.
It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although alloys contain only a maximum of 0.1%, that small percentage of niobium improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials. These superconducting alloys, also containing titanium and tin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, numismatics and jewelry. In the last two applications, niobium's low toxicity and ability to be colored by anodization are particular advantages.
Molybdenum | Period 5 element | Wikipedia | 373 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Molybdenum is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores. The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as a free metal on Earth, but rather in various oxidation states in minerals. Industrially, molybdenum compounds are used in high-pressure and high-temperature applications, as pigments and catalysts.
Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 by Peter Jacob Hjelm.
Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42− is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water.
Technetium
Technetium is the chemical element with atomic number 43 and symbol Tc. It is the lowest atomic number element without any stable isotopes; every form of it is radioactive. Nearly all technetium is produced synthetically and only minute amounts are found in nature. Naturally occurring technetium occurs as a spontaneous fission product in uranium ore or by neutron capture in molybdenum ores. The chemical properties of this silvery gray, crystalline transition metal are intermediate between rhenium and manganese.
Many of technetium's properties were predicted by Dmitri Mendeleev before the element was discovered. Mendeleev noted a gap in his periodic table and gave the undiscovered element the provisional name ekamanganese (Em). In 1937 technetium (specifically the technetium-97 isotope) became the first predominantly artificial element to be produced, hence its name (from the Greek , meaning "artificial"). | Period 5 element | Wikipedia | 468 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Its short-lived gamma ray-emitting nuclear isomer—technetium-99m—is used in nuclear medicine for a wide variety of diagnostic tests. Technetium-99 is used as a gamma ray-free source of beta particles. Long-lived technetium isotopes produced commercially are by-products of fission of uranium-235 in nuclear reactors and are extracted from nuclear fuel rods. Because no isotope of technetium has a half-life longer than 4.2 million years (technetium-98), its detection in red giants in 1952, which are billions of years old, helped bolster the theory that stars can produce heavier elements.
Ruthenium
Ruthenium is a chemical element with symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is inert to most chemicals. The Russian scientist Karl Ernst Claus discovered the element in 1844 and named it after Ruthenia, the Latin word for Rus'. Ruthenium usually occurs as a minor component of platinum ores and its annual production is only about 12 tonnes worldwide. Most ruthenium is used for wear-resistant electrical contacts and the production of thick-film resistors. A minor application of ruthenium is its use in some platinum alloys.
Rhodium
Rhodium is a chemical element that is a rare, silvery-white, hard, and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one isotope, 103Rh. Naturally occurring rhodium is found as the free metal, alloyed with similar metals, and never as a chemical compound. It is one of the rarest precious metals and one of the most costly (gold has since taken over the top spot of cost per ounce).
Rhodium is a so-called noble metal, resistant to corrosion, found in platinum or nickel ores together with the other members of the platinum group metals. It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds, produced after it reacted with the powerful acid mixture aqua regia. | Period 5 element | Wikipedia | 466 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
The element's major use (about 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converters of automobiles. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its optical impression while sterling silver is often rhodium plated for tarnish resistance.
Rhodium detectors are used in nuclear reactors to measure the neutron flux level.
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form a group of elements referred to as the platinum group metals (PGMs). These have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.
The unique properties of palladium and other platinum group metals account for their widespread use. A quarter of all goods manufactured today either contain PGMs or have a significant part in their manufacturing process played by PGMs. Over half of the supply of palladium and its congener platinum goes into catalytic converters, which convert up to 90% of harmful gases from auto exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide) into less-harmful substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications, and groundwater treatment. Palladium plays a key role in the technology used for fuel cells, which combine hydrogen and oxygen to produce electricity, heat, and water. | Period 5 element | Wikipedia | 422 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Ore deposits of palladium and other PGMs are rare, and the most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering the Transvaal Basin in South Africa, the Stillwater Complex in Montana, United States, the Thunder Bay District of Ontario, Canada, and the Norilsk Complex in Russia. Recycling is also a source of palladium, mostly from scrapped catalytic converters. The numerous applications and limited supply sources of palladium result in the metal attracting considerable investment interest.
Silver
Silver is a metallic chemical element with the chemical symbol Ag (, from the Indo-European root *arg- for "grey" or "shining") and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining.
Silver has long been valued as a precious metal, and it is used to make ornaments, jewelry, high-value tableware, utensils (hence the term silverware), and currency coins. Today, silver metal is also used in electrical contacts and conductors, in mirrors and in catalysis of chemical reactions. Its compounds are used in photographic film, and dilute silver nitrate solutions and other silver compounds are used as disinfectants and microbiocides. While many medical antimicrobial uses of silver have been supplanted by antibiotics, further research into clinical potential continues.
Cadmium | Period 5 element | Wikipedia | 358 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Cadmium is a chemical element with the symbol Cd and atomic number 48. This soft, bluish-white metal is chemically similar to the two other stable metals in group 12, zinc and mercury. Like zinc, it prefers oxidation state +2 in most of its compounds and like mercury it shows a low melting point compared to transition metals. Cadmium and its congeners are not always considered transition metals, in that they do not have partly filled d or f electron shells in the elemental or common oxidation states. The average concentration of cadmium in the Earth's crust is between 0.1 and 0.5 parts per million (ppm). It was discovered in 1817 simultaneously by Stromeyer and Hermann, both in Germany, as an impurity in zinc carbonate.
Cadmium occurs as a minor component in most zinc ores and therefore is a byproduct of zinc production. It was used for a long time as a pigment and for corrosion resistant plating on steel while cadmium compounds were used to stabilize plastic. With the exception of its use in nickel–cadmium batteries and cadmium telluride solar panels, the use of cadmium is generally decreasing. These declines have been due to competing technologies, cadmium's toxicity in certain forms and concentration and resulting regulations.
p-block elements
Indium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible other metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two. Indium was discovered in 1863 and named for the indigo blue line in its spectrum that was the first indication of its existence in zinc ores, as a new and unknown element. The metal was first isolated in the following year. Zinc ores continue to be the primary source of indium, where it is found in compound form. Very rarely the element can be found as grains of native (free) metal, but these are not of commercial importance.
Indium's current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays and touchscreens, and this use largely determines its global mining production. It is widely used in thin-films to form lubricated layers (during World War II it was widely used to coat bearings in high-performance aircraft). It is also used for making particularly low melting point alloys, and is a component in some lead-free solders. | Period 5 element | Wikipedia | 505 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Indium is not known to be used by any organism. In a similar way to aluminium salts, indium(III) ions can be toxic to the kidney when given by injection, but oral indium compounds do not have the chronic toxicity of salts of heavy metals, probably due to poor absorption in basic conditions. Radioactive indium-111 (in very small amounts on a chemical basis) is used in nuclear medicine tests, as a radiotracer to follow the movement of labeled proteins and white blood cells in the body.
Tin
Tin is a chemical element with the symbol Sn (for ) and atomic number 50. It is a main-group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4. Tin is the 49th most abundant element and has, with 10 stable isotopes, the largest number of stable isotopes in the periodic table. Tin is obtained chiefly from the mineral cassiterite, where it occurs as tin dioxide, SnO2.
This silvery, malleable post-transition metal is not easily oxidized in air and is used to coat other metals to prevent corrosion. The first alloy, used in large scale since 3000 BC, was bronze, an alloy of tin and copper. After 600 BC pure metallic tin was produced. Pewter, which is an alloy of 85–90% tin with the remainder commonly consisting of copper, antimony and lead, was used for tableware from the Bronze Age until the 20th century. In modern times tin is used in many alloys, most notably tin/lead soft solders, typically containing 60% or more of tin. Another large application for tin is corrosion-resistant tin plating of steel. Because of its low toxicity, tin-plated metal is also used for food packaging, giving the name to tin cans, which are made mostly of steel.
Antimony
Antimony () is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient times and were used for cosmetics, metallic antimony was also known but mostly identified as lead. | Period 5 element | Wikipedia | 474 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
For some time China has been the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. Antimony compounds are prominent additives for chlorine and bromine containing fire retardants found in many commercial and domestic products. The largest application for metallic antimony is as alloying material for lead and tin. It improves the properties of the alloys which are used as in solders, bullets and ball bearings. An emerging application is the use of antimony in microelectronics.
Tellurium
Tellurium is a chemical element that has the symbol Te and atomic number 52. A brittle, mildly toxic, rare, silver-white metalloid which looks similar to tin, tellurium is chemically related to selenium and sulfur. It is occasionally found in native form, as elemental crystals. Tellurium is far more common in the universe than on Earth. Its extreme rarity in the Earth's crust, comparable to that of platinum, is partly due to its high atomic number, but also due to its formation of a volatile hydride which caused the element to be lost to space as a gas during the hot nebular formation of the planet.
Tellurium was discovered in Transylvania (today part of Romania) in 1782 by Franz-Joseph Müller von Reichenstein in a mineral containing tellurium and gold. Martin Heinrich Klaproth named the new element in 1798 after the Latin word for "earth", tellus. Gold telluride minerals (responsible for the name of Telluride, Colorado) are the most notable natural gold compounds. However, they are not a commercially significant source of tellurium itself, which is normally extracted as by-product of copper and lead production.
Tellurium is commercially primarily used in alloys, foremost in steel and copper to improve machinability. Applications in solar panels and as a semiconductor material also consume a considerable fraction of tellurium production.
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is from Greek ioeidēs, meaning violet or purple, due to the color of elemental iodine vapor. | Period 5 element | Wikipedia | 443 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Iodine and its compounds are primarily used in nutrition, and industrially in the production of acetic acid and certain polymers. Iodine's relatively high atomic number, low toxicity, and ease of attachment to organic compounds have made it a part of many X-ray contrast materials in modern medicine. Iodine has only one stable isotope. A number of iodine radioisotopes are also used in medical applications.
Iodine is found on Earth mainly as the highly water-soluble iodide I−, which concentrates it in oceans and brine pools. Like the other halogens, free iodine occurs mainly as a diatomic molecule I2, and then only momentarily after being oxidized from iodide by an oxidant like free oxygen. In the universe and on Earth, iodine's high atomic number makes it a relatively rare element. However, its presence in ocean water has given it a role in biology (see below).
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.
Naturally occurring xenon consists of nine stable isotopes. There are also over 40 unstable isotopes that undergo radioactive decay. The isotope ratios of xenon are an important tool for studying the early history of the Solar System. Radioactive xenon-135 is produced from iodine-135 as a result of nuclear fission, and it acts as the most significant neutron absorber in nuclear reactors.
Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe2) as its lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is also being used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft.
Biological role
Rubidium, strontium, yttrium, zirconium, and niobium have no biological role. Yttrium can cause lung disease in humans. | Period 5 element | Wikipedia | 485 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
Molybdenum-containing enzymes are used as catalysts by some bacteria to break the chemical bond in atmospheric molecular nitrogen, allowing biological nitrogen fixation. At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Owing to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms (eukaryotes), though not in all bacteria.
Technetium, ruthenium, rhodium, palladium, and silver have no biological role. Although cadmium has no known biological role in higher organisms, a cadmium-dependent carbonic anhydrase has been found in marine diatoms. Rats fed a tin-free diet exhibited improper growth, but the evidence for essentiality is otherwise limited. Indium has no biological role and can be toxic as well as antimony.
Tellurium has no biological role, although fungi can incorporate it in place of sulfur and selenium into amino acids such as tellurocysteine and telluromethionine. In humans, tellurium is partly metabolized into dimethyl telluride, (CH3)2Te, a gas with a garlic-like odor which is exhaled in the breath of victims of tellurium toxicity or exposure.
Iodine is the heaviest essential element utilized widely by life in biological functions (only tungsten, employed in enzymes by a few species of bacteria, is heavier). Iodine's rarity in many soils, due to initial low abundance as a crust-element, and also leaching of soluble iodide by rainwater, has led to many deficiency problems in land animals and inland human populations. Iodine deficiency affects about two billion people and is the leading preventable cause of intellectual disabilities. Iodine is required by higher animals, which use it to synthesize thyroid hormones, which contain the element. Because of this function, radioisotopes of iodine are concentrated in the thyroid gland along with nonradioactive iodine. The radioisotope iodine-131, which has a high fission product yield, concentrates in the thyroid, and is one of the most carcinogenic of nuclear fission products.
Xenon has no biological role, and is used as a general anaesthetic. | Period 5 element | Wikipedia | 495 | 161278 | https://en.wikipedia.org/wiki/Period%205%20element | Physical sciences | Periods | Chemistry |
A noble metal is ordinarily regarded as a metallic element that is generally resistant to corrosion and is usually found in nature in its raw form. Gold, platinum, and the other platinum group metals (ruthenium, rhodium, palladium, osmium, iridium) are most often so classified. Silver, copper, and mercury are sometimes included as noble metals, but each of these usually occurs in nature combined with sulfur.
In more specialized fields of study and applications the number of elements counted as noble metals can be smaller or larger. It is sometimes used for the three metals copper, silver, and gold which have filled d-bands, while it is often used mainly for silver and gold when discussing surface-enhanced Raman spectroscopy involving metal nanoparticles. It is sometimes applied more broadly to any metallic or semimetallic element that does not react with a weak acid and give off hydrogen gas in the process. This broader set includes copper, mercury, technetium, rhenium, arsenic, antimony, bismuth, polonium, gold, the six platinum group metals, and silver.
Many of the noble metals are used in alloys for jewelry or coinage. In dentistry, silver is not always considered a noble metal because it is subject to corrosion when present in the mouth. All the metals are important heterogeneous catalysts.
Meaning and history
While lists of noble metals can differ, they tend to cluster around gold and the six platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum.
In addition to this term's function as a compound noun, there are circumstances where noble is used as an adjective for the noun metal. A galvanic series is a hierarchy of metals (or other electrically conductive materials, including composites and semimetals) that runs from noble to active, and allows one to predict how materials will interact in the environment used to generate the series. In this sense of the word, graphite is more noble than silver and the relative nobility of many materials is highly dependent upon context, as for aluminium and stainless steel in conditions of varying pH.
The term noble metal can be traced back to at least the late 14th century and has slightly different meanings in different fields of study and application. | Noble metal | Wikipedia | 468 | 161291 | https://en.wikipedia.org/wiki/Noble%20metal | Physical sciences | d-Block | Chemistry |
Prior to Mendeleev's publication in 1869 of the first (eventually) widely accepted periodic table, Odling published a table in 1864, in which the "noble metals" rhodium, ruthenium, palladium; and platinum, iridium, and osmium were grouped together, and adjacent to silver and gold.
Properties
Geochemical
The noble metals are siderophiles (iron-lovers). They tend to sink into the Earth's core because they dissolve readily in iron either as solid solutions or in the molten state. Most siderophile elements have practically no affinity whatsoever for oxygen: indeed, oxides of gold are thermodynamically unstable with respect to the elements.
Copper, silver, gold, and the six platinum group metals are the only native metals that occur naturally in relatively large amounts.
Corrosion resistance
Noble metals tend to be resistant to oxidation and other forms of corrosion, and this corrosion resistance is often considered to be a defining characteristic. Some exceptions are described below.
Copper is dissolved by nitric acid and aqueous potassium cyanide.
Ruthenium can be dissolved in aqua regia, a highly concentrated mixture of hydrochloric acid and nitric acid, only when in the presence of oxygen, while rhodium must be in a fine pulverized form. Palladium and silver are soluble in nitric acid, while silver's solubility in aqua regia is limited by the formation of silver chloride precipitate.
Rhenium reacts with oxidizing acids, and hydrogen peroxide, and is said to be tarnished by moist air. Osmium and iridium are chemically inert in ambient conditions. Platinum and gold can be dissolved in aqua regia. Mercury reacts with oxidising acids.
In 2010, US researchers discovered that an organic "aqua regia" in the form of a mixture of thionyl chloride SOCl2 and the organic solvent pyridine C5H5N achieved "high dissolution rates of noble metals under mild conditions, with the added benefit of being tunable to a specific metal" for example, gold but not palladium or platinum.
However, Gold can be dissolved in Selenic Acid (H2SeO4).
Anion (-ide) formation
The noble elements Gold and Platinum also have a comparatively high electronegativity for a metallic element, thus alowing them to exist as single-metallic anions.
For example: | Noble metal | Wikipedia | 506 | 161291 | https://en.wikipedia.org/wiki/Noble%20metal | Physical sciences | d-Block | Chemistry |
Cs + Au -> CsAu
(Caesium Auride, a yellow crystalline salt with the ion). Platinum also exhibits similar properties with
BaPt, BaPt2, Cs2Pt (Barium and Caesium Platinides, which are reddish salts).
Electronic
The expression noble metal is sometimes confined to copper, silver, and gold since their full d-subshells can contribute to their noble character. There are also known to be significant contributions from how readily there is overlap of the d-electron states with the orbitals of other elements, particularly for gold. Relativistic contributions are also important, playing a role in the catalytic properties of gold.
The elements to the left of gold and silver have incompletely filled d-bands, which is believed to play a role in their catalytic properties. A common explanation is the d-band filling model of Hammer and Jens Nørskov, where the total d-bands are considered, not just the unoccupied states.
The low-energy plasmon properties are also of some importance, particularly those of silver and gold nanoparticles for surface-enhanced Raman spectroscopy, localized surface plasmons and other plasmonic properties.
Electrochemical
Standard reduction potentials in aqueous solution are also a useful way of predicting the non-aqueous chemistry of the metals involved. Thus, metals with high negative potentials, such as sodium, or potassium, will ignite in air, forming the respective oxides. These fires cannot be extinguished with water, which also react with the metals involved to give hydrogen, which is itself explosive. Noble metals, in contrast, are disinclined to react with oxygen and, for that reason (as well as their scarcity) have been valued for millennia, and used in jewellery and coins.
The adjacent table lists standard reduction potential in volts; electronegativity (revised Pauling); and electron affinity values (kJ/mol), for some metals and metalloids.
The simplified entries in the reaction column can be read in detail from the Pourbaix diagrams of the considered element in water. Noble metals have large positive potentials; elements not in this table have a negative standard potential or are not metals.
Electronegativity is included since it is reckoned to be, "a major driver of metal nobleness and reactivity".
The black tarnish commonly seen on silver arises from its sensitivity to sulphur containing gases such as hydrogen sulfide: | Noble metal | Wikipedia | 512 | 161291 | https://en.wikipedia.org/wiki/Noble%20metal | Physical sciences | d-Block | Chemistry |
2 Ag + H2S + O2 → Ag2S + H2O.
Rayner-Canham contends that, "silver is so much more chemically-reactive and has such a different chemistry, that it should not be considered as a 'noble metal'." In dentistry, silver is not regarded as a noble metal due to its tendency to corrode in the oral environment.
The relevance of the entry for water is addressed by Li et al. in the context of galvanic corrosion. Such a process will only occur when:
"(1) two metals which have different electrochemical potentials are...connected, (2) an aqueous phase with electrolyte exists, and (3) one of the two metals has...potential lower than the potential of the reaction ( + 4e + = 4 OH•) which is 0.4 V...The...metal with...a potential less than 0.4 V acts as an anode...loses electrons...and dissolves in the aqueous medium. The noble metal (with higher electrochemical potential) acts as a cathode and, under many conditions, the reaction on this electrode is generally − 4 e• − = 4 OH•)."
The superheavy elements from hassium (element 108) to livermorium (116) inclusive are expected to be "partially very noble metals"; chemical investigations of hassium has established that it behaves like its lighter congener osmium, and preliminary investigations of nihonium and flerovium have suggested but not definitively established noble behavior. Copernicium's behaviour seems to partly resemble both its lighter congener mercury and the noble gas radon.
Oxides
As long ago as 1890, Hiorns observed as follows:
"Noble Metals. Gold, Platinum, Silver, and a few rare metals. The members of this class have little or no tendency to unite with oxygen in the free state, and when placed in water at a red heat do not alter its composition. The oxides are readily decomposed by heat in consequence of the feeble affinity between the metal and oxygen."
Smith, writing in 1946, continued the theme:
"There is no sharp dividing line [between 'noble metals' and 'base metals'] but perhaps the best definition of a noble metal is a metal whose oxide is easily decomposed at a temperature below a red heat." | Noble metal | Wikipedia | 511 | 161291 | https://en.wikipedia.org/wiki/Noble%20metal | Physical sciences | d-Block | Chemistry |
"It follows from this that noble metals...have little attraction for oxygen and are consequently not oxidised or discoloured at moderate temperatures."
Such nobility is mainly associated with the relatively high electronegativity values of the noble metals, resulting in only weakly polar covalent bonding with oxygen. The table lists the melting points of the oxides of the noble metals, and for some of those of the non-noble metals, for the elements in their most stable oxidation states.
Catalytic properties
All the noble metals can act as catalysts. For example, platinum is used in catalytic converters, devices which convert toxic gases produced in car engines, such as the oxides of nitrogen, into non-polluting substances.
Gold has many industrial applications; it is used as a catalyst in hydrogenation and the water gas shift reaction. | Noble metal | Wikipedia | 169 | 161291 | https://en.wikipedia.org/wiki/Noble%20metal | Physical sciences | d-Block | Chemistry |
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
Etymology and terminology
Amphoteric is derived from the Greek word () meaning "both". Related words in acid-base chemistry are amphichromatic and amphichroic, both describing substances such as acid-base indicators which give one colour on reaction with an acid and another colour on reaction with a base.
Amphiprotism
Amphiprotism is exhibited by compounds with both Brønsted acidic and basic properties. A prime example is H2O.
Amphiprotic molecules can either donate or accept a proton (). Amino acids (and proteins) are amphiprotic molecules because of their amine () and carboxylic acid () groups.
Ampholytes
Ampholytes are zwitterions. Molecules or ions that contain both acidic and basic functional groups. Amino acids hav both a basic group and an acidic group . Often such species exists as several structures in chemical equilibrium:
H2N-RCH-CO2H + H2O<=> H2N-RCH-COO- + H3O+<=> H3N+-RCH-COOH + OH-<=> H3N+-RCH-COO- + H2O
In approximately neutral aqueous solution (pH ≅ 7), the basic amino group is mostly protonated and the carboxylic acid is mostly deprotonated, so that the predominant species is the zwitterion . The pH at which the average charge is zero is known as the molecule's isoelectric point. Ampholytes are used to establish a stable pH gradient for use in isoelectric focusing.
Metal oxides which react with both acids as well as bases to produce salts and water are known as amphoteric oxides. Many metals (such as zinc, tin, lead, aluminium, and beryllium) form amphoteric oxides or hydroxides. Aluminium oxide () is an example of an amphoteric oxide. Amphoterism depends on the oxidation states of the oxide. Amphoteric oxides include lead(II) oxide and zinc oxide, among many others. | Amphoterism | Wikipedia | 489 | 161293 | https://en.wikipedia.org/wiki/Amphoterism | Physical sciences | Concepts | Chemistry |
Amphiprotic molecules
According to the Brønsted-Lowry theory of acids and bases, acids are proton donors and bases are proton acceptors. An amphiprotic molecule (or ion) can either donate or accept a proton, thus acting either as an acid or a base. Water, amino acids, hydrogencarbonate ion (or bicarbonate ion) , dihydrogen phosphate ion , and hydrogensulfate ion (or bisulfate ion) are common examples of amphiprotic species. Since they can donate a proton, all amphiprotic substances contain a hydrogen atom. Also, since they can act like an acid or a base, they are amphoteric.
Examples
The water molecule is amphoteric in aqueous solution. It can either gain a proton to form a hydronium ion , or else lose a proton to form a hydroxide ion .
Another possibility is the molecular autoionization reaction between two water molecules, in which one water molecule acts as an acid and another as a base.
H2O + H2O <=> H3O+ + OH-
The bicarbonate ion, , is amphoteric as it can act as either an acid or a base:
As an acid, losing a proton: HCO3- + OH- <=> CO3^2- + H2O
As a base, accepting a proton: HCO3- + H+ <=> H2CO3
Note: in dilute aqueous solution the formation of the hydronium ion, , is effectively complete, so that hydration of the proton can be ignored in relation to the equilibria.
Other examples of inorganic polyprotic acids include anions of sulfuric acid, phosphoric acid and hydrogen sulfide that have lost one or more protons. In organic chemistry and biochemistry, important examples include amino acids and derivatives of citric acid.
Although an amphiprotic species must be amphoteric, the converse is not true. For example, a metal oxide such as zinc oxide, ZnO, contains no hydrogen and so cannot donate a proton. Nevertheless, it can act as an acid by reacting with the hydroxide ion, a base:
Zinc oxide can also act as a base: | Amphoterism | Wikipedia | 464 | 161293 | https://en.wikipedia.org/wiki/Amphoterism | Physical sciences | Concepts | Chemistry |
Oxides
Zinc oxide (ZnO) reacts both with acids and with bases:
ZnO + \overset{acid}{H2SO4} -> ZnSO4 + H2O
ZnO + \overset{base}{2 NaOH} + H2O -> Na2[Zn(OH)4]
This reactivity can be used to separate different cations, for instance zinc(II), which dissolves in base, from manganese(II), which does not dissolve in base.
Lead oxide (PbO):
PbO + \overset{acid}{2 HCl} -> PbCl2 + H2O
PbO + \overset{base}{2 NaOH} + H2O -> Na2[Pb(OH)4]
Lead oxide ():
PbO2 + \overset{acid}{4 HCl} -> PbCl4 + 2H2O
PbO2 + \overset{base}{2 NaOH} + 2H2O -> Na2[Pb(OH)6]
Aluminium oxide ():
Al2O3 + \overset{acid}{6 HCl} -> 2 AlCl3 + 3 H2O
Al2O3 + \overset{base}{2 NaOH} + 3 H2O -> 2 Na[Al(OH)4] (hydrated sodium aluminate)
Stannous oxide (SnO):
SnO + \overset{acid}{2 HCl} <=> SnCl2 + H2O
SnO + \overset{base}{4 NaOH} + H2O <=> Na4[Sn(OH)6]
Stannic oxide ():
SnO2 + \overset{acid}{4 HCl} <=> SnCl4 + 2H2O
SnO2 + \overset{base}{4 NaOH} + 2H2O <=> Na4[Sn(OH)8]
Vanadium dioxide ():
VO2 + \overset{acid}{2 HCl} -> VOCl2 + H2O
4 VO2 + \overset{base}{2 NaOH} -> Na2V4O9 + H2O | Amphoterism | Wikipedia | 493 | 161293 | https://en.wikipedia.org/wiki/Amphoterism | Physical sciences | Concepts | Chemistry |
Some other elements which form amphoteric oxides are gallium, indium, scandium, titanium, zirconium, chromium, iron, cobalt, copper, silver, gold, germanium, antimony, bismuth, beryllium, and tellurium.
Hydroxides
Aluminium hydroxide is also amphoteric:
Al(OH)3 + \overset{acid}{3 HCl} -> AlCl3 + 3 H2O
Al(OH)3 + \overset{base}{NaOH} -> Na[Al(OH)4]
Beryllium hydroxide:
Be(OH)2 + \overset{acid}{2 HCl} -> BeCl2 + 2 H2O
Be(OH)2 + \overset{base}{2 NaOH} -> Na2[Be(OH)4]
Chromium hydroxide:
Cr(OH)3 + \overset{acid}{3 HCl} -> CrCl3 + 3H2O
Cr(OH)3 + \overset{base}{NaOH} -> Na[Cr(OH)4] | Amphoterism | Wikipedia | 245 | 161293 | https://en.wikipedia.org/wiki/Amphoterism | Physical sciences | Concepts | Chemistry |
In biology, a colony is composed of two or more conspecific individuals living in close association with, or connected to, one another. This association is usually for mutual benefit such as stronger defense or the ability to attack bigger prey.
Colonies can form in various shapes and ways depending on the organism involved. For instance, the bacterial colony is a cluster of identical cells (clones). These colonies often form and grow on the surface of (or within) a solid medium, usually derived from a single parent cell.
Colonies, in the context of development, may be composed of two or more unitary (or solitary) organisms or be modular organisms. Unitary organisms have determinate development (set life stages) from zygote to adult form and individuals or groups of individuals (colonies) are visually distinct. Modular organisms have indeterminate growth forms (life stages not set) through repeated iteration of genetically identical modules (or individuals), and it can be difficult to distinguish between the colony as a whole and the modules within. In the latter case, modules may have specific functions within the colony.
In contrast, solitary organisms do not associate with colonies; they are ones in which all individuals live independently and have all of the functions needed to survive and reproduce.
Some organisms are primarily independent and form facultative colonies in reply to environmental conditions while others must live in a colony to survive (obligate). For example, some carpenter bees will form colonies when a dominant hierarchy is formed between two or more nest foundresses (facultative colony), while corals are animals that are physically connected by living tissue (the coenosarc) that contains a shared gastrovascular cavity.
Colony types
Social colonies
Unicellular and multicellular unitary organisms may aggregate to form colonies. For example,
Protists such as slime molds are many unicellular organisms that aggregate to form colonies when food resources are hard to come by, as together they are more reactive to chemical cues released by preferred prey.
Eusocial insects like ants and honey bees are multicellular animals that live in colonies with a highly organized social structure. Colonies of some social insects may be deemed superorganisms.
Animals, such as humans and rodents, form breeding or nesting colonies, potentially for more successful mating and to better protect offspring.
The Bracken Cave is the summer home to a colony of around 20 million Mexican free-tailed bats, making it the largest known concentration of mammals.
Modular organisms | Colony (biology) | Wikipedia | 503 | 161296 | https://en.wikipedia.org/wiki/Colony%20%28biology%29 | Biology and health sciences | Ecology | Biology |
Modular organisms are those in which a genet (or genetic individual formed from a sexually-produced zygote) asexually reproduces to form genetically identical clones called ramets.
A clonal colony is when the ramets of a genet live in close proximity or are physically connected. Ramets may have all of the functions needed to survive on their own or be interdependent on other ramets. For example, some sea anemones go through the process of pedal laceration in which a genetically identical individual is asexually produced from tissue broken off from the anemone's pedal disc. In plants, clonal colonies are created through the propagation of genetically identical individuals by stolons or rhizomes.
Colonial organisms are clonal colonies composed of many physically connected, interdependent individuals. The subunits of colonial organisms can be unicellular, as in the alga Volvox (a coenobium), or multicellular, as in the phylum Bryozoa. Colonial organisms may have been the first step toward multicellular organisms. Individuals within a multicellular colonial organism may be called ramets, modules, or zooids. Structural and functional variation (polymorphism), when present, designates ramet responsibilities such as feeding, reproduction, and defense. To that end, being physically connected allows the colonial organism to distribute nutrients and energy obtained by feeding zooids throughout the colony. The hydrozoan Portuguese man o' war is a classic example of a colonial organism, one of many in the taxonomic class.
Microbial colonies
A microbial colony is defined as a visible cluster of microorganisms growing on the surface of or within a solid medium, presumably cultured from a single cell. Because the colony is clonal, with all organisms in it descending from a single ancestor (assuming no contamination), they are genetically identical, except for any mutations (which occur at low frequencies). Obtaining such genetically identical organisms (or pure strains) can be useful; this is done by spreading organisms on a culture plate and starting a new stock from a single resulting colony.
A biofilm is a colony of microorganisms often comprising several species, with properties and capabilities greater than the aggregate of capabilities of the individual organisms. | Colony (biology) | Wikipedia | 463 | 161296 | https://en.wikipedia.org/wiki/Colony%20%28biology%29 | Biology and health sciences | Ecology | Biology |
Colony ontogeny for eusocial insects
Colony ontogeny refers to the developmental process and progression of a colony. It describes the various stages and changes that occur within a colony from its initial formation to its mature state. The exact duration and dynamics of colony ontogeny can vary greatly depending on the species and environmental conditions. Factors such as resource availability, competition, and environmental cues can influence the progression and outcome of colony development.
During colony ontogeny for eusocial insects such as ants and bees, a colony goes through several distinct phases, each characterised by specific behavioural patterns, division of labor, and structural modifications. While the exact details can vary depending on the species, the general progression typically involves a number of well-defined stages, detailed below.
Founding stage
In this initial stage, a single female individual or small group of female individuals, often called the foundress(es), queen(s) (and kings for termites) or primary reproductive(s), establish a new colony. The foundresses build a basic nest structure and begin to lay eggs. The foundresses can also perform non-reproductive tasks at this early stage, such as nursing these first eggs and leaving the nest to gather resources.
Worker emergence
This is also known as the ergonomic stage. As the eggs laid by the foundresses develop, they give rise to the first generation of workers. These workers can assume various tasks, such as foraging, brood care, and nest maintenance. Initially, the worker population is relatively small, and their tasks are not as specialised. As the colony grows, more workers emerge, and the division of labor becomes more pronounced. Some individuals may specialise in tasks like foraging, defense, or tending to the brood, while others may take on general tasks within the nest. These specialised tasks can change throughout the life of a worker.
Reproductive phase
At a certain point in the colony ontogeny, usually after a period of growth and maturation, the colony produces reproductives, including new virgin queens (princesses) and males. These individuals have the potential to leave the nest and start new colonies, ensuring the transmission of the gene pool of its natal colony. | Colony (biology) | Wikipedia | 435 | 161296 | https://en.wikipedia.org/wiki/Colony%20%28biology%29 | Biology and health sciences | Ecology | Biology |
Colony death
Over time, colonies may go through a senescence phase where the reproductive output declines, and the colony's overall vitality diminishes. Eventually, the colony may die off or be replaced by a new generation of reproductives. After the death of the queen in a monogyne colony, possible fates other than colony death include serial polygyny (when a virgin queen of the colony replaces the dead queen as the primary reproductive) or colony inheritance (when a worker takes over as primary reproductive).
Life history
Individuals in social colonies and modular organisms receive benefit to such a lifestyle. For example, it may be easier to seek out food, defend a nesting site, or increase competitive ability against other species. Modular organisms' ability to reproduce asexually in addition to sexually allows them unique benefits that social colonies do not have.
The energy required for sexual reproduction varies based on the frequency and length of reproductive activity, number and size of offspring, and parental care. While solitary individuals bear all of those energy costs, individuals in some social colonies share a portion of those costs.
Modular organisms save energy by using asexual reproduction during their life. Energy reserved in this way allows them to put more energy towards colony growth, regenerating lost modules (due to predation or other cause of death), or response to environmental conditions. | Colony (biology) | Wikipedia | 271 | 161296 | https://en.wikipedia.org/wiki/Colony%20%28biology%29 | Biology and health sciences | Ecology | Biology |
Stripping is a physical separation process where one or more components are removed from a liquid stream by a vapor stream. In industrial applications the liquid and vapor streams can have co-current or countercurrent flows. Stripping is usually carried out in either a packed or trayed column.
Theory
Stripping works on the basis of mass transfer. The idea is to make the conditions favorable for the component, A, in the liquid phase to transfer to the vapor phase. This involves a gas–liquid interface that A must cross. The total amount of A that has moved across this boundary can be defined as the flux of A, NA.
Equipment
Stripping is mainly conducted in trayed towers (plate columns) and packed columns, and less often in spray towers, bubble columns, and centrifugal contactors.
Trayed towers consist of a vertical column with liquid flowing in the top and out the bottom. The vapor phase enters in the bottom of the column and exits out of the top. Inside of the column are trays or plates. These trays force the liquid to flow back and forth horizontally while the vapor bubbles up through holes in the trays. The purpose of these trays is to increase the amount of contact area between the liquid and vapor phases.
Packed columns are similar to trayed columns in that the liquid and vapor flows enter and exit in the same manner. The difference is that in packed towers there are no trays. Instead, packing is used to increase the contact area between the liquid and vapor phases. There are many different types of packing used and each one has advantages and disadvantages.
Variables
The variables and design considerations for strippers are many. Among them are the entering conditions, the degree of recovery of the solute needed, the choice of the stripping agent and its flow, the operating conditions, the number of stages, the heat effects, and the type and size of the equipment.
The degree of recovery is often determined by environmental regulations, such as for volatile organic compounds like chloroform.
Frequently, steam, air, inert gases, and hydrocarbon gases are used as stripping agents. This is based on solubility, stability, degree of corrosiveness, cost, and availability. As stripping agents are gases, operation at nearly the highest temperature and lowest pressure that will maintain the components and not vaporize the liquid feed stream is desired. This allows for the minimization of flow. As with all other variables, minimizing cost while achieving efficient separation is the ultimate goal. | Stripping (chemistry) | Wikipedia | 508 | 15988913 | https://en.wikipedia.org/wiki/Stripping%20%28chemistry%29 | Physical sciences | Other separations | Chemistry |
The size of the equipment, and particularly the height and diameter, is important in determining the possibility of flow channeling that would reduce the contact area between the liquid and vapor streams. If flow channeling is suspected to be occurring, a redistribution plate is often necessary to, as the name indicates, redistribute the liquid flow evenly to reestablish a higher contact area.
As mentioned previously, strippers can be trayed or packed. Packed columns, and particularly when random packing is used, are usually favored for smaller columns with a diameter less than 2 feet and a packed height of not more than 20 feet. Packed columns can also be advantageous for corrosive fluids, high foaming fluids, when fluid velocity is high, and when particularly low pressure drop is desired. Trayed strippers are advantageous because of ease of design and scale up. Structured packing can be used similar to trays despite possibly being the same material as dumped (random) packing. Using structured packing is a common method to increase the capacity for separation or to replace damaged trays.
Trayed strippers can have sieve, valve, or bubble cap trays while packed strippers can have either structured packing or random packing. Trays and packing are used to increase the contact area over which mass transfer can occur as mass transfer theory dictates. Packing can have varying material, surface area, flow area, and associated pressure drop. Older generation packing include ceramic Raschig rings and Berl saddles. More common packing materials are metal and plastic Pall rings, metal and plastic Zbigniew Białecki rings, and ceramic Intalox saddles. Each packing material of this newer generation improves the surface area, the flow area, and/or the associated pressure drop across the packing. Also important, is the ability of the packing material to not stack on top of itself. If such stacking occurs, it drastically reduces the surface area of the material. Lattice design work has been increasing of late that will further improve these characteristics.
During operation, monitoring the pressure drop across the column can help to determine the performance of the stripper. A changed pressure drop over a significant range of time can be an indication that the packing may need to be replaced or cleaned.
Typical applications | Stripping (chemistry) | Wikipedia | 461 | 15988913 | https://en.wikipedia.org/wiki/Stripping%20%28chemistry%29 | Physical sciences | Other separations | Chemistry |
Stripping is commonly used in industrial applications to remove harmful contaminants from waste streams. One example would be the removal of TBT and PAH contaminants from harbor soils. The soils are dredged from the bottom of contaminated harbors, mixed with water to make a slurry and then stripped with steam. The cleaned soil and contaminant rich steam mixture are then separated. This process is able to decontaminate soils almost completely.
Steam is also frequently used as a stripping agent for water treatment. Volatile organic compounds are partially soluble in water and because of environmental considerations and regulations, must be removed from groundwater, surface water, and wastewater. These compounds can be present because of industrial, agricultural, and commercial activity. | Stripping (chemistry) | Wikipedia | 150 | 15988913 | https://en.wikipedia.org/wiki/Stripping%20%28chemistry%29 | Physical sciences | Other separations | Chemistry |
Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, plastics, waste materials, and more. The process is considered an excellent option for the storage and transport of said materials. The technology is widely used in the powder metallurgy engineering and medicine industries.
Pelletizing of iron ore
Edward W Davis of the University of Minnesota is credited for devising the process of pelletizing iron ore.
Pelletizing iron ore is undertaken due to the excellent physical and metallurgical properties of iron ore pellets. Iron ore pellets are spheres of typically to be used as raw material for blast furnaces. They typically contain 64–72% Fe and various additional material adjusting the chemical composition and the metallurgic properties of the pellets. Typically limestone, dolomite and olivine is added and Bentonite is used as binder.
The process of pelletizing combines mixing of the raw material, forming the pellet and a thermal treatment baking the soft raw pellet to hard spheres. The raw material is rolled into a ball, then fired in a kiln or in travelling grate to sinter the particles into a hard sphere.
The configuration of iron ore pellets as packed spheres in the blast furnace allows air to flow between the pellets, decreasing the resistance to the air that flows up through the layers of material during the smelting. The configuration of iron ore powder in a blast furnace is more tightly-packed and restricts the air flow. This is the reason that iron ore is preferred in the form of pellets rather than in the form of finer particles. The quality of the iron ore pellets depends on different factors, which include feed particle size, amount of water used, disc rotating speed, inclination angle of the disc bottom, residence time in the disc as well as the quality and quantity of the binder(s) used. | Pelletizing | Wikipedia | 415 | 7167911 | https://en.wikipedia.org/wiki/Pelletizing | Technology | Industry: General | null |
Preparation of raw materials
Additional materials are added to the iron ore (pellet feed) to meet the requirements of the final pellets. This is done by placing the mixture in the pelletizer, which can hold different types of ores and additives, and mixing to adjust the chemical composition and the metallurgic properties of the pellets. In general, the following stages are included in this period of processing: concentration / separation, homogenization of the substance ratios, milling, classification, increasing thickness, homogenization of the pulp and filtering.
Formation of the raw Pellets
The formation of raw iron ore pellets, also known as pelletizing, has the objective of producing pellets in an appropriate band of sizes and with mechanical properties high usefulness during the stresses of transference, transport, and use. For example, waste materials are ground before being heated and introduced into a press for compression. Both mechanical force and thermal processes are used to produce the correct pellet properties. From an equipment point of view there are two alternatives for industrial production of iron ore pellets: the drum and the pelletizing disk.
Thermal processing
In order to confer to the pellets high resistance metallurgic mechanics and appropriate characteristics, the pellets are subjected to thermal processing, which involves stages of drying, preheating, firing, after-firing and cooling. The duration of each stage and the temperature that the pellets are subjected to have a strong influence on the final product quality.
Pharmaceutical industry
In the field of medicine, pelletization is referred to as the agglomeration process that converts fine powders or granules into more or less spherical pellets. The use of the technology increased because it allows for the controlled release of dosage form, which also lead to a uniform absorption with less mucosal irritation within the gastrointestinal tract. There are different pelletization processes applied in the pharmaceutical industry and these typically vary according to the bonding forces. Some examples of the processes include balling, compression, and spray congealing. Balling is similar to the wet (or green) pelletization used in the iron ore industry.
Pelletizing of animal feeds
Pelletizing of animal feeds can result in pellets from (shrimp feeds), through to (poultry feeds) up to (stock feeds). The pelletizing of stock feed is done with the pellet mill machinery, which is done in a feed mill. | Pelletizing | Wikipedia | 510 | 7167911 | https://en.wikipedia.org/wiki/Pelletizing | Technology | Industry: General | null |
Preparation of raw ingredients
Feed ingredients are normally first hammered to reduce the particle size of the ingredients. Ingredients are then batched, and then combined and mixed thoroughly by a feed mixer. Once the feed has been prepared to this stage the feed is ready to be pelletized.
Formation of the feed pellets
Pelletizing is done in a pellet mill, where feed is normally conditioned and thermal-treated in the fitted conditioners of a pellet mill. The feed is then pushed through the holes and exit the pellet mill as pelleted feed.
Pelletizing of wood
Wood pellets made by compressing sawdust or other ground woody materials are used in a variety of energy and non-energy applications. In the energy sector, wood pellets are often used to replace coal with power plants such as Drax, in England, replacing most of their coal use with woody pellet. As sustainably harvested wood does not lead to a long-term increase in atmospheric carbon dioxide levels, wood fuels are considered to be a low-carbon form of energy. Wood pellets are also used for domestic and commercial heating either in the form of automated boilers or pellet stoves. Compared to other fuels made from wood, pellets have the advantage of higher energy density, simpler handling as it flows similar to grain, and low moisture.
Concerns have been raised about the short-term carbon balance of wood pellet production, particularly if it is driving the harvesting of old or mature harvests that would otherwise not be logged. Areas of concern include the inland rainforests of British Columbia These claims are contested by the pellet and forest industries.
After pelleting processes
After pelleting, the pellets are cooled with a cooler to bring the temperature of the feed down. Other post pelleting applications include post-pelleting conditioning, sorting via a screen, and maybe coating if required.
Gallery | Pelletizing | Wikipedia | 388 | 7167911 | https://en.wikipedia.org/wiki/Pelletizing | Technology | Industry: General | null |
Portlandite is a hydroxide-bearing mineral typically included in the oxide mineral class. It is the naturally occurring form of calcium hydroxide (Ca(OH)2) and the calcium analogue of brucite (Mg(OH)2).
Occurrence
Portlandite occurs in a variety of environments. At the type location in Northern Ireland it occurs as an alteration of calc–silicate rocks by contact metamorphism of larnite–spurrite. It occurs as fumarole deposits in the Vesuvius area. In Jebel Awq, Oman, it occurs as precipitates from an alkaline spring emanating from ultramafic bedrock. In the Chelyabinsk coal basin of Russia it is produced by combustion of coal seams and similarly by spontaneous combustion of bitumen in the Hatrurim Formation of the Negev desert in Israel and the Maqarin area, Jordan. It also occurs in the manganese mining area of Kuruman, Cape Province, South Africa in the Kalahari Desert where it occurs as large crystals and masses.
It occurs in association with afwillite, calcite, larnite, spurrite, halite, brownmillerite, hydrocalumite, mayenite and ettringite.
It was first described in 1933 for an occurrence at Scawt Hill, Larne, County Antrim, Northern Ireland. It was named portlandite because the chemical calcium hydroxide is a common hydrolysis product of Portland cement. | Portlandite | Wikipedia | 306 | 9320833 | https://en.wikipedia.org/wiki/Portlandite | Physical sciences | Minerals | Earth science |
A shingle beach, also known as either a cobble beach or gravel beach, is a commonly narrow beach that is composed of coarse, loose, well-rounded, and waterworn gravel, called shingle. The gravel (shingle) typically consists of smooth, spheroidal to flattened, pebbles, cobbles, and sometimes small boulders, generally in the size range. Shingle beaches typically have a steep slope on both their landward and seaward sides. Shingle beaches form in wave-dominated locations where resistant bedrock cliffs provide gravel-sized rock debris. They are also found in high latitudes and temperate shores where the erosion of Quaternary glacial deposits provide gravel-size rock fragments. This term is most widely used in Great Britain.
While this type of beach is most commonly found in Europe, examples are also found in Bahrain, North America, and a number of other world regions, such as the west coast of New Zealand's South Island, where they are associated with the shingle fans of braided rivers. Though created at shorelines, post-glacial rebound can raise shingle beaches as high as above sea level, as on the High Coast in Sweden.
The ecosystems formed by this association of rock and sand allow colonization by a variety of rare and endangered species.
Formation
Shingle beaches are typically steep, because the waves easily flow through the coarse, porous surface of the beach, decreasing the effect of backwash erosion and increasing the formation of sediment into a steeply sloping beach.
Tourism
Shingle beaches are rare, made up of thousands of smooth rocks with varying geological qualities. The ocean naturally smooths the various rocks over time with crashing waves. Shingle beaches are popular for the varying rock types that can be found. | Shingle beach | Wikipedia | 353 | 11811193 | https://en.wikipedia.org/wiki/Shingle%20beach | Physical sciences | Oceanic and coastal landforms | Earth science |
Working set is a concept in computer science which defines the amount of memory that a process requires in a given time interval.
Definition
Peter Denning (1968) defines "the working set of information of a process at time to be the collection of information referenced by the process during the process time interval ".
Typically the units of information in question are considered to be memory pages. This is suggested to be an approximation of the set of pages that the process will access in the future (say during the next time units), and more specifically is suggested to be an indication of what pages ought to be kept in main memory to allow most progress to be made in the execution of that process.
Rationale
The effect of the choice of what pages to be kept in main memory (as distinct from being paged out to auxiliary storage) is important: if too many pages of a process are kept in main memory, then fewer other processes can be ready at any one time. If too few pages of a process are kept in main memory, then its page fault frequency is greatly increased and the number of active (non-suspended) processes currently executing in the system approaches zero.
The working set model states that a process can be in RAM if and only if all of the pages that it is currently using (often approximated by the most recently used pages) can be in RAM. The model is an all or nothing model, meaning if the pages it needs to use increases, and there is no room in RAM, the process is swapped out of memory to free the memory for other processes to use.
Often a heavily loaded computer has so many processes queued up that, if all the processes were allowed to run for one scheduling time slice, they would refer to more pages than there is RAM, causing the computer to "thrash".
By swapping some processes from memory, the result is that processes—even processes that were temporarily removed from memory—finish much sooner than they would if the computer attempted to run them all at once. The processes also finish much sooner than they would if the computer only ran one process at a time to completion since it allows other processes to run and make progress during times that one process is waiting on the hard drive or some other global resource.
In other words, the working set strategy prevents thrashing while keeping the degree of multiprogramming as high as possible. Thus it optimizes CPU utilization and throughput. | Working set | Wikipedia | 488 | 3007794 | https://en.wikipedia.org/wiki/Working%20set | Technology | Operating systems | null |
Implementation
The main hurdle in implementing the working set model is keeping track of the working set. The working set window is a moving window. At each memory reference a new reference appears at one end and the oldest reference drops off the other end. A page is in the working set if it is referenced in the working set window.
To avoid the overhead of keeping a list of the last k referenced pages, the working set is often implemented by keeping track of the time t of the last reference, and considering the working set to be all pages referenced within a certain period of time.
The working set isn't a page replacement algorithm, but page-replacement algorithms can be designed to only remove pages that aren't in the working set for a particular process. One example is a modified version of the clock algorithm called WSClock.
Variants
Working set can be divided into code working set and data working set. This distinction is important when code and data are separate at the relevant level of the memory hierarchy, as if either working set does not fit in that level of the hierarchy, thrashing will occur. In addition to the code and data themselves, on systems with virtual memory, the memory map (of virtual memory to physical memory) entries of the pages of the working set must be cached in the translation lookaside buffer (TLB) for the process to progress efficiently. This distinction exists because code and data are cached in small blocks (cache lines), not entire pages, but address lookup is done at the page level. Thus even if the code and data working sets fit into cache, if the working sets are split across many pages, the virtual address working set may not fit into TLB, causing TLB thrashing.
Analogs of working set exist for other limited resources, most significantly processes. If a set of processes requires frequent interaction between multiple processes, then it has a that must be coscheduled in order to progress:
If the processes are not scheduled simultaneously – for example, if there are two processes but only one core on which to execute them – then the processes can only advance at the rate of one interaction per time slice. | Working set | Wikipedia | 435 | 3007794 | https://en.wikipedia.org/wiki/Working%20set | Technology | Operating systems | null |
Other resources include file handles or network sockets – for example, copying one file to another is most simply done with two file handles: one for input, one for output, and thus has a "file handle working set" size of two. If only one file handle is available, copying can still be done, but requires acquiring a file handle for the input, reading from it (say into a buffer), releasing it, then acquiring a file handle for the output, writing to it, releasing it, then acquiring the input file handle again and repeating. Similarly a server may require many sockets, and if it is limited would need to repeatedly release and re-acquire sockets. Rather than thrashing, these resources are typically required for the program, and if it cannot acquire enough resources, it simply fails. | Working set | Wikipedia | 161 | 3007794 | https://en.wikipedia.org/wiki/Working%20set | Technology | Operating systems | null |
A radio-quiet neutron star is a neutron star that does not seem to emit radio emissions, but is still visible to Earth through electromagnetic radiation at other parts of the spectrum, particularly X-rays and gamma rays.
Background
Most detected neutron stars are pulsars, and emit radio-frequency electromagnetic radiation. About 700 radio pulsars are listed in the Princeton catalog, and all but one emit radio waves at the 400 MHz and 1400 MHz frequencies. That exception is Geminga, which is radio quiet at frequencies above 100 MHz, but is a strong emitter of X-rays and gamma rays.
In all, ten bodies have been proposed as rotation-powered neutron stars that are not visible as radio sources, but are visible as X-ray and gamma ray sources. Indicators that they are indeed neutron stars include them having a high X-ray to lower frequencies emission ratio, a constant X-ray emission profile, and coincidence with a gamma ray source.
Hypotheses
Quark stars, hypothetical neutron star-like objects composed of quark matter, have been proposed to be radio-quiet.
More plausibly, however, radio-quiet neutron stars may simply be pulsars which do not pulse in our direction. As pulsars spin, it is hypothesized that they emit radiation from their magnetic poles. When the magnetic poles do not lie on the axis of rotation, and cross the line of sight of the observer, one can detect radio emission emitted near the star's magnetic poles. Due to the star's rotation this radiation appears to pulse, colloquially called the "lighthouse effect". Radio-quiet neutron stars may be neutron stars whose magnetic poles do not point towards the Earth during their rotation.
The group of radio-quiet neutrons stars informally known as the Magnificent Seven are thought to emit mainly thermal radiation.
Possibly some powerful neutron star radio emissions are caused by a positron-electron jet emanating from the star blasting through outer material such as a cloud or accretion material. Note some radio quiet neutron stars listed in this article do not have accretion material.
Magnetars
Magnetars, the most widely accepted explanation for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs), are often characterized as being radio-quiet. However, magnetars can produce radio emissions, but the radio spectrums tend to be flat, with only intermittent broad pulses of variable length.
List of radio-quiet neutron stars | Radio-quiet neutron star | Wikipedia | 509 | 5501614 | https://en.wikipedia.org/wiki/Radio-quiet%20neutron%20star | Physical sciences | Stellar astronomy | Astronomy |
X-ray Dim Isolated Neutron Stars
Can be classified as XDINS (X-ray Dim Isolated Neutron Stars), XTINS (X-ray Thermal Isolated Neutron Stars), XINS (X-ray Isolated Neutron Stars), TEINS (Thermally Emitting Neutron Star), INS (Isolated Neutron Stars).
Defined as thermally emitting neutron stars of high magnetic fields, although lower than that of magnetars. Identified in thermal X-rays, and thought to be radio-quiet.
A group of seven individual, physically similar and relatively nearby neutron stars nicknamed The Magnificent Seven, consisting of:
RX J185635-3754
RX J0720.4-3125
RBS1556
RBS1223
RX J0806.4-4132
RX J0420.0-5022
MS 0317.7-6647
1RXS J214303.7+065419/RBS 1774
Compact Central Objects in Supernova remnants
Compact Central Objects in Supernova remnants (CCOs in SNRs) are identified as being radio-quiet compact X-ray sources surrounded by supernova remnants. They have thermal emission spectra, and lower magnetic fields than XDINSs and magnetars.
RX J0822-4300 (1E 0820–4247) in the Puppis A supernova remnant (SNR G260.4-3.4).
1E 1207.4-5209 in the PKS 1209-51/52 supernova remnant (SNR G296.5+10).
RXJ0007.0+7302 (in SNR G119.5+10.2, CTA1)
RXJ0201.8+6435 (in SNR G130.7+3.1, 3C58)
1E 161348–5055 (in SNR G332.4-0.4, RCW103)
RXJ2020.2+4026 (in SNR G078.2+2.1, γ–Cyg)
Other neutron stars
IGR J11014-6103: a runaway pulsar ejected from a supernova remnant. | Radio-quiet neutron star | Wikipedia | 471 | 5501614 | https://en.wikipedia.org/wiki/Radio-quiet%20neutron%20star | Physical sciences | Stellar astronomy | Astronomy |
The Antilocapridae are a family of ruminant artiodactyls endemic to North America. Their closest extant relatives are the giraffids. Only one species, the pronghorn (Antilocapra americana), is living today; all other members of the family are extinct. The living pronghorn is a small ruminant mammal resembling an antelope.
Description
In most respects, antilocaprids resemble other ruminants. They have a complex, four-chambered stomach for digesting tough plant matter, cloven hooves, and small, forked horns. Their horns resemble those of the bovids, in that they have a true horny sheath, but, uniquely, they are shed outside the breeding season, and subsequently regrown. Their lateral toes are even further diminished than in bovids, with the digits themselves being entirely lost, and only the cannon bones remaining. Antilocaprids have the same dental formula as most other ruminants: .
Classification
The antilocaprids are ruminants of the clade Pecora. Other extant pecorans are the families Giraffidae (giraffes), Cervidae (deer), Moschidae (musk deer), and Bovidae (cattle, goats and sheep, wildebeests and allies, and antelopes). The exact interrelationships among the pecorans have been debated, mainly focusing on the placement of Giraffidae, but a large-scale ruminant genome sequencing study in 2019 suggested that Antilocapridae are the sister taxon to Giraffidae, as shown in the cladogram below.
Evolution
The ancestors of pronghorn diverged from the giraffids in the Early Miocene. This was in part of a relatively late mammal diversification following a climate change that transformed subtropical woodlands into open savannah grasslands.
The antilocaprids evolved in North America, where they filled a niche similar to that of the bovids that evolved in the Old World. During the Miocene and Pliocene, they were a diverse and successful group, with many different species. Some had horns with bizarre shapes, or had four, or even six, horns. Examples include Osbornoceros, with smooth, slightly curved horns, Paracosoryx, with flattened horns that widened to forked tips, Ramoceros, with fan-shaped horns, and Hayoceros, with four horns. | Antilocapridae | Wikipedia | 512 | 5504707 | https://en.wikipedia.org/wiki/Antilocapridae | Biology and health sciences | Other artiodactyla | Animals |
Species
Subfamily Antilocaprinae
Tribe Antilocaprini
Genus Antilocapra
Antilocapra americana - pronghorn
A. a. americana - Common pronghorn
A. a. mexicana - Mexican pronghorn
A. a. peninsularis - Baja California pronghorn
A. a. sonoriensis - Sonoran pronghorn
A. a. oregona - Oregon pronghorn
†Antilocapra pacifica
Genus †Texoceros
Texoceros altidens
Texoceros edensis
Texoceros guymonensis
Texoceros minorei
Texoceros texanus
Texoceros vaughani
Tribe †Ilingoceratini
Genus †Ilingoceros
Ilingoceros alexandrae
Ilingoceros schizoceros
Genus †Ottoceros
Ottoceros peacevalleyensis
Genus †Plioceros
Plioceros blicki
Plioceros dehlini
Plioceros floblairi
Genus †Sphenophalos
Sphenophalos garciae
Sphenophalos middleswarti
Sphenophalos nevadanus
Tribe †Proantilocaprini
Genus †Proantilocapra
Proantilocapra platycornea
Genus †Osbornoceros
Osbornoceros osborni
Tribe Stockoceratini
Genus †Capromeryx - (junior synonym Breameryx)
Capromeryx arizonensis - (junior synonym B. arizonensis)
Capromeryx furcifer - (junior synonyms B. minimus, C. minimus)Capromeryx gidleyi - (junior synonym B. gidleyi)Capromeryx mexicana - (junior synonym B. mexicana)Capromeryx minor - (junior synonym B. minor)Capromeryx tauntonensisGenus †CeratomeryxCeratomeryx prenticeiGenus †HayocerosHayoceros barbouriHayoceros falkenbachiGenus †HexameryxHexameryx simpsoniGenus †HexobelomeryxHexobelomeryx frickiHexobelomeryx simpsoniGenus †StockocerosStockoceros conklingi (junior synonym S. onusrosagris)
Genus †TetrameryxTetrameryx irvingtonensisTetrameryx knoxensisTetrameryx mooseriTetrameryx shuleriTetrameryx tacubayensisSubfamily †Merycodontinae | Antilocapridae | Wikipedia | 511 | 5504707 | https://en.wikipedia.org/wiki/Antilocapridae | Biology and health sciences | Other artiodactyla | Animals |
Genus †CosoryxCosoryx cerroensisCosoryx furcatusCosoryx ilfonensisGenus †MerriamocerosMerriamoceros coronatusGenus †Merycodus (syn. Meryceros and Submeryceros)Merycodus crucensisMerycodus hookwayiMerycodus jorakiMerycodus majorMerycodus minimusMerycodus minorMerycodus necatusMerycodus nenzelensisMerycodus prodromusMerycodus sabulonisMerycodus warreniGenus †ParacosoryxParacosoryx alticornisParacosoryx burgensisParacosoryx dawesensisParacosoryx furlongiParacosoryx loxocerosParacosoryx nevadensisParacosoryx wilsoniGenus †RamocerosRamoceros brevicornisRamoceros marthaeRamoceros merriamiRamoceros osborniRamoceros palmatusRamoceros ramosus'' | Antilocapridae | Wikipedia | 221 | 5504707 | https://en.wikipedia.org/wiki/Antilocapridae | Biology and health sciences | Other artiodactyla | Animals |
A substellar object, sometimes called a substar, is an astronomical object, the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and former stars similar to EF Eridani B, and can also include objects of planetary mass, regardless of their formation mechanism and whether or not they are associated with a primary star.
Assuming that a substellar object has a composition similar to the Sun's and at least the mass of Jupiter (approximately 0.001 solar masses), its radius will be comparable to that of Jupiter (approximately 0.1 solar radii) regardless of the mass of the substellar object (brown dwarfs are less than 75 Jupiter masses). This is because the center of such a substellar object at the top range of the mass (just below the hydrogen-burning limit) is quite degenerate, with a density of ≈103 g/cm3, but this degeneracy lessens with decreasing mass until, at the mass of Jupiter, a substellar object has a central density less than 10 g/cm3. The density decrease balances the mass decrease, keeping the radius approximately constant.
Substellar objects like brown dwarfs do not have enough mass to fuse hydrogen and helium, hence do not undergo the usual stellar evolution that limits the lifetime of stars.
A substellar object with a mass just below the hydrogen-fusing limit may ignite hydrogen fusion temporarily at its center. Although this will provide some energy, it will not be enough to overcome the object's ongoing gravitational contraction. Likewise, although an object with mass above approximately 0.013 solar masses will be able to fuse deuterium for a time, this source of energy will be exhausted in approximately 1100million years. Apart from these sources, the radiation of an isolated substellar object comes only from the release of its gravitational potential energy, which causes it to gradually cool and shrink. A substellar object in orbit around a star will shrink more slowly as it is kept warm by the star, evolving towards an equilibrium state where it emits as much energy as it receives from the star.
Substellar objects are cool enough to have water vapor in their atmosphere. Infrared spectroscopy can detect the distinctive color of water in gas giant size substellar objects, even if they are not in orbit around a star. | Substellar object | Wikipedia | 486 | 13313000 | https://en.wikipedia.org/wiki/Substellar%20object | Physical sciences | Astronomy basics | Astronomy |
Classification
William Duncan MacMillan proposed in 1918 the classification of substellar objects into three categories based on their density and phase state: solid, transitional and dark (non-stellar) gaseous. Solid objects include Earth, smaller terrestrial planets and moons; with Uranus and Neptune (as well as later mini-Neptune and Super Earth planets) as transitional objects between solid and gaseous. Saturn, Jupiter and large gas giant planets are in a fully "gaseous" state.
Substellar companion
A substellar object may be a companion of a star, such as an exoplanet or brown dwarf that is orbiting a star. Objects as low as 823 Jupiter masses have been called substellar companions.
Objects orbiting a star are often called planets below 13 Jupiter masses and brown dwarves above that. Companions at that planet-brown dwarf borderline have been called Super-Jupiters, such as that around the star Kappa Andromedae. Nevertheless, objects as small as 8 Jupiter masses have been called brown dwarfs. | Substellar object | Wikipedia | 201 | 13313000 | https://en.wikipedia.org/wiki/Substellar%20object | Physical sciences | Astronomy basics | Astronomy |
In chemical engineering, a vapor–liquid separator is a device used to separate a vapor–liquid mixture into its constituent phases. It can be a vertical or horizontal vessel, and can act as a 2-phase or 3-phase separator.
A vapor–liquid separator may also be referred to as a flash drum, breakpot, knock-out drum or knock-out pot, compressor suction drum, suction scrubber or compressor inlet drum, or vent scrubber. When used to remove suspended water droplets from streams of air, it is often called a demister.
Method of operation
In vapor-liquid separators gravity is utilized to cause the denser fluid (liquid) to settle to the bottom of the vessel where it is withdrawn, less dense fluid (vapor) is withdrawn from the top of the vessel.
In low gravity environments such as a space station, a common liquid separator will not function because gravity is not usable as a separation mechanism. In this case, centrifugal force needs to be utilised in a spinning centrifugal separator to drive liquid towards the outer edge of the chamber for removal. Gaseous components migrate towards the center.
An inlet diffuser reduces the velocity and spreads the incoming mixture across the full cross-section of the vessel. A mesh pad in the upper part of the vessel aids separation and prevents liquid from being carried over with the vapor. The pad or mist mat traps entrained liquid droplets and allows them to coalesce until they are large enough to fall through the up-flowing vapor to the bottom of the vessel. Vane packs and cyclonic separators are also used to remove liquid from the outlet vapor.
The gas outlet may itself be surrounded by a spinning mesh screen or grating, so that any liquid that does approach the outlet strikes the grating, is accelerated, and thrown away from the outlet.
The vapor travels through the gas outlet at a design velocity which minimises the entrainment of any liquid droplets in the vapor as it exits the vessel.
A vortex breaker on the liquid outlet prevents the formation of vortices and of vapor being drawn into the liquid outlet. | Vapor–liquid separator | Wikipedia | 444 | 13320206 | https://en.wikipedia.org/wiki/Vapor%E2%80%93liquid%20separator | Physical sciences | Phase separations | Chemistry |
Liquid level monitoring
The separator is only effective as long as there is a vapor space inside the chamber. The separator can fail if either the mixed inlet is overwhelmed with supply material, or the liquid drain is unable to handle the volume of liquid being collected. The separator may therefore be combined with some other liquid level sensing mechanism such as a sight glass or float sensor. In this manner, both the supply and drain flow can be regulated to prevent the separator from becoming overloaded.
Applications
Vertical separators are generally used when the gas-liquid ratio is high or gas volumes are high. Horizontal separators are used where large volumes of liquid are involved.
A vapor-liquid separator may operate as a 3-phase separator, with two immiscible liquid phases of different densities. For example natural gas (vapor), water and oil/condensate. The two liquids settle at the bottom of the vessel with oil floating on the water. Separate liquid outlets are provided.
The feed to a vapor–liquid separator may also be a liquid that is being partially or totally flashed into a vapor and liquid as it enters the separator.
A slug catcher is a type of vapor–liquid separator that is able to receive a large inflow of liquid at random times. It is usually found at the end of gas pipelines where condensate may be present as slugs of liquid. It is usually a horizontal vessel or array of large diameter pipes.
The liquid capacity of a separator is usually defined by the residence time of the liquid in the vessel. Some typical residence times are as shown.
Where vapor–liquid separators are used
Vapor–liquid separators are very widely used in a great many industries and applications, such as:
Oil refineries
Offshore platforms
Natural-gas processing plants (NGL)
Petrochemical and chemical plants
Refrigeration systems
Air conditioning
Compressor systems
Gas pipelines
Steam condensate flash drums
Geothermal power plants
Combined cycle power plants
Flare stacks
Soil vapor extraction
Paper mills
Liquid ring pumps
Preventing pump damage
In refrigeration systems, it is common for the system to contain a mixture of liquid and gas, but for the mechanical gas compressor to be intolerant of liquid. | Vapor–liquid separator | Wikipedia | 464 | 13320206 | https://en.wikipedia.org/wiki/Vapor%E2%80%93liquid%20separator | Physical sciences | Phase separations | Chemistry |
Some compressor types such as the scroll compressor use a continuously shrinking compression volume. Once liquid completely fills this volume the pump may either stall and overload, or the pump chamber may be warped or otherwise damaged by the fluid that can not fit into a smaller space. | Vapor–liquid separator | Wikipedia | 52 | 13320206 | https://en.wikipedia.org/wiki/Vapor%E2%80%93liquid%20separator | Physical sciences | Phase separations | Chemistry |
Praya dubia, the giant siphonophore, lives in the mesopelagic zone to bathypelagic zone at to below sea level. It has been found off the coasts around the world, from Iceland in the North Atlantic to Chile in the South Pacific.
Praya dubia is a member of the order Siphonophorae within the class Hydrozoa. With a body length of up to , it is the second-longest sea organism after the bootlace worm. Its length also rivals the blue whale, the sea's largest mammal, although Praya dubia is as thin as a broomstick.
A siphonophore is not a single, multi-cellular organism, but a colony of tiny biological components called zooids, each having evolved with a specific function. Zooids cannot survive on their own, relying on symbiosis in order for a complete Praya dubia specimen to survive.
Description
Praya dubia zooids arrange themselves in a long stalk—usually whitish and transparent (though other colours have been seen)—known as a physonect colony. The larger end features a transparent, dome-like float known as a pneumatophore, filled with gas which provides buoyancy, allowing the organism to remain at its preferred ocean depth. Next to it are the nectophores, powerful medusae which pulsate in rhythmic coordination which propel Praya dubia through ocean waters. Together, the array is known as the nectosome.
Beneath the nectosome is the siphosome which extends to the far end of Praya dubia, containing several types of specialized zooids in repeating patterns. Some have a long tentacle used for catching and immobilizing food and distributing their digested nutrients to the rest of the colony. Other zooids known as palpons, or dactylozooids, appear to contain an excretory system that may also assist in defense, though little is known about their precise function in Praya dubia. Transparent bracts (also called hydrophyllia), are leaf-shaped organs generally thought to be another type of zooid which covers and forces other zooids to contract in times of danger. | Praya dubia | Wikipedia | 455 | 14485893 | https://en.wikipedia.org/wiki/Praya%20dubia | Biology and health sciences | Cnidarians | Animals |
Due to their hydrostatic skeleton being held together by water pressure above , these animals burst when brought to the surface. The remains of Praya dubia dredged up in fishing nets resemble a blob of gelatin, which prevented their identification as a unique creature until the 19th century. In 1987, Monterey Bay Aquarium Research Institute observed living Praya dubia during a systematic study of a water column, the animal's natural habitat, in Monterey Bay.
Behavior
Praya dubia is an active swimmer that attracts its prey with bright blue bioluminescent light. When it finds itself in a region abundant with food, it holds its position and deploys a curtain of tentacles covered with nematocysts which produce a powerful, toxic sting that can paralyze or kill prey that happen to bump into it. Praya dubia's diet includes gelatinous sea life, small crustaceans, and possibly small fish and fish larvae. It has no known predators.
A Praya dubia specimen, filmed in its native habitat, was featured in Episode 2 of the David Attenborough television series Blue Planet II, produced for the BBC. | Praya dubia | Wikipedia | 234 | 14485893 | https://en.wikipedia.org/wiki/Praya%20dubia | Biology and health sciences | Cnidarians | Animals |
In chemistry, rotamers are chemical species that differ from one another primarily due to rotations about one or more single bonds. Various arrangements of atoms in a molecule that differ by rotation about single bonds can also be referred to as different conformations. Conformers/rotamers differ little in their energies, so they are almost never separable in a practical sense. Rotations about single bonds are subject to small energy barriers. When the time scale for interconversion is long enough for isolation of individual rotamers (usually arbitrarily defined as a half-life of interconversion of 1000 seconds or longer), the species are termed atropisomers (see: atropisomerism). The ring-flip of substituted cyclohexanes constitutes a common form of conformers.
The study of the energetics of bond rotation is referred to as conformational analysis. In some cases, conformational analysis can be used to predict and explain product selectivity, mechanisms, and rates of reactions. Conformational analysis also plays an important role in rational, structure-based drug design.
Types
Rotating their carbon–carbon bonds, the molecules ethane and propane have three local energy minima. They are structurally and energetically equivalent, and are called the staggered conformers. For each molecule, the three substituents emanating from each carbon–carbon bond are staggered, with each H–C–C–H dihedral angle (and H–C–C–CH3 dihedral angle in the case of propane) equal to 60° (or approximately equal to 60° in the case of propane). The three eclipsed conformations, in which the dihedral angles are zero, are transition states (energy maxima) connecting two equivalent energy minima, the staggered conformers.
The butane molecule is the simplest molecule for which single bond rotations result in two types of nonequivalent structures, known as the anti- and gauche-conformers (see figure). | Rotamer | Wikipedia | 414 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
For example, butane has three conformers relating to its two methyl (CH3) groups: two gauche conformers, which have the methyls ±60° apart and are enantiomeric, and an anti conformer, where the four carbon centres are coplanar and the substituents are 180° apart (refer to free energy diagram of butane). The energy difference between gauche and anti is 0.9 kcal/mol associated with the strain energy of the gauche conformer. The anti conformer is, therefore, the most stable (≈ 0 kcal/mol). The three eclipsed conformations with dihedral angles of 0°, 120°, and 240° are transition states between conformers. Note that the two eclipsed conformations have different energies: at 0° the two methyl groups are eclipsed, resulting in higher energy (≈ 5 kcal/mol) than at 120°, where the methyl groups are eclipsed with hydrogens (≈ 3.5 kcal/mol).
While simple molecules can be described by these types of conformations, more complex molecules require the use of the Klyne–Prelog system to describe the different conformers.
More specific examples of conformations are detailed elsewhere:
Ring conformation
Cyclohexane conformations, including with chair and boat conformations among others.
Cycloalkane conformations, including medium rings and macrocycles
Carbohydrate conformation, which includes cyclohexane conformations as well as other details.
Allylic strain – energetics related to rotation about the single bond between an sp2 carbon and an sp3 carbon.
Atropisomerism – due to restricted rotation about a bond.
Folding, including the secondary and tertiary structure of biopolymers (nucleic acids and proteins).
Akamptisomerism – due to restricted inversion of a bond angle.
Equilibrium of conformers
Conformers generally exist in a dynamic equilibrium | Rotamer | Wikipedia | 408 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
Three isotherms are given in the diagram depicting the equilibrium distribution of two conformers at different temperatures. At a free energy difference of 0 kcal/mol, this gives an equilibrium constant of 1, meaning that two conformers exist in a 1:1 ratio. The two have equal free energy; neither is more stable, so neither predominates compared to the other. A negative difference in free energy means that a conformer interconverts to a thermodynamically more stable conformation, thus the equilibrium constant will always be greater than 1. For example, the ΔG° for the transformation of butane from the gauche conformer to the anti conformer is −0.47 kcal/mol at 298 K. This gives an equilibrium constant is about 2.2 in favor of the anti conformer, or a 31:69 mixture of gauche:anti conformers at equilibrium. Conversely, a positive difference in free energy means the conformer already is the more stable one, so the interconversion is an unfavorable equilibrium (K < 1). Even for highly unfavorable changes (large positive ΔG°), the equilibrium constant between two conformers can be increased by increasing the temperature, so that the amount of the less stable conformer present at equilibrium increases (although it always remains the minor conformer).
Population distribution of conformers
The fractional population distribution of different conformers follows a Boltzmann distribution:
The left hand side is the proportion of conformer i in an equilibrating mixture of M conformers in thermodynamic equilibrium. On the right side, Ek (k = 1, 2, ..., M) is the energy of conformer k, R is the molar ideal gas constant (approximately equal to 8.314 J/(mol·K) or 1.987 cal/(mol·K)), and T is the absolute temperature. The denominator of the right side is the partition function. | Rotamer | Wikipedia | 417 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
Factors contributing to the free energy of conformers
The effects of electrostatic and steric interactions of the substituents as well as orbital interactions such as hyperconjugation are responsible for the relative stability of conformers and their transition states. The contributions of these factors vary depending on the nature of the substituents and may either contribute positively or negatively to the energy barrier. Computational studies of small molecules such as ethane suggest that electrostatic effects make the greatest contribution to the energy barrier; however, the barrier is traditionally attributed primarily to steric interactions.
In the case of cyclic systems, the steric effect and contribution to the free energy can be approximated by A values, which measure the energy difference when a substituent on cyclohexane in the axial as compared to the equatorial position. In large (>14 atom) rings, there are many accessible low-energy conformations which correspond to the strain-free diamond lattice.
Observation of conformers
The short timescale of interconversion precludes the separation of conformer in most cases. Atropisomers are conformational isomers which can be separated due to restricted rotation. The equilibrium between conformational isomers can be observed using a variety of spectroscopic techniques.
Protein folding also generates conformers which can be observed. The Karplus equation relates the dihedral angle of vicinal protons to their J-coupling constants as measured by NMR. The equation aids in the elucidation of protein folding as well as the conformations of other rigid aliphatic molecules. Protein side chains exhibit rotamers, whose distribution is determined by their steric interaction with different conformations of the backbone. This is evident from statistical analysis of the conformations of protein side chains in the Backbone-dependent rotamer library. | Rotamer | Wikipedia | 371 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
Spectroscopy
Conformational dynamics can be monitored by variable temperature NMR spectroscopy. The technique applies to barriers of 8–14 kcal/mol, and species exhibiting such dynamics are often called "fluxional". For example, in cyclohexane derivatives, the two chair conformers interconvert rapidly at room temperature. The ring-flip proceeds at a rates of approximately 105 ring-flips/sec, with an overall energy barrier of 10 kcal/mol (42 kJ/mol). This barrier precludes separation at ambient temperatures. However, at low temperatures below the coalescence point one can directly monitor the equilibrium by NMR spectroscopy and by dynamic, temperature dependent NMR spectroscopy the barrier interconversion.
Besides NMR spectroscopy, IR spectroscopy is used to measure conformer ratios. For the axial and equatorial conformer of bromocyclohexane, νCBr differs by almost 50 cm−1.
Conformation-dependent reactions
Reaction rates are highly dependent on the conformation of the reactants. In many cases the dominant product arises from the reaction of the less prevalent conformer, by virtue of the Curtin-Hammett principle. This is typical for situations where the conformational equilibration is much faster than reaction to form the product. The dependence of a reaction on the stereochemical orientation is therefore usually only visible in Configurational analysis, in which a particular conformation is locked by substituents. Prediction of rates of many reactions involving the transition between sp2 and sp3 states, such as ketone reduction, alcohol oxidation or nucleophilic substitution is possible if all conformers and their relative stability ruled by their strain is taken into account.
One example where the rotamers become significant is elimination reactions, which involve the simultaneous removal of a proton and a leaving group from vicinal or antiperiplanar positions under the influence of a base. | Rotamer | Wikipedia | 391 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
The mechanism requires that the departing atoms or groups follow antiparallel trajectories. For open chain substrates this geometric prerequisite is met by at least one of the three staggered conformers. For some cyclic substrates such as cyclohexane, however, an antiparallel arrangement may not be attainable depending on the substituents which might set a conformational lock. Adjacent substituents on a cyclohexane ring can achieve antiperiplanarity only when they occupy trans diaxial positions (that is, both are in axial position, one going up and one going down).
One consequence of this analysis is that trans-4-tert-butylcyclohexyl chloride cannot easily eliminate but instead undergoes substitution (see diagram below) because the most stable conformation has the bulky t-Bu group in the equatorial position, therefore the chloride group is not antiperiplanar with any vicinal hydrogen (it is gauche to all four). The thermodynamically unfavored conformation has the t-Bu group in the axial position, which is higher in energy by more than 5 kcal/mol (see A value). As a result, the t-Bu group "locks" the ring in the conformation where it is in the equatorial position and substitution reaction is observed. On the other hand, cis-4-tert-butylcyclohexyl chloride undergoes elimination because antiperiplanarity of Cl and H can be achieved when the t-Bu group is in the favorable equatorial position.
The repulsion between an axial t-butyl group and hydrogen atoms in the 1,3-diaxial position is so strong that the cyclohexane ring will revert to a twisted boat conformation. The strain in cyclic structures is usually characterized by deviations from ideal bond angles (Baeyer strain), ideal torsional angles (Pitzer strain) or transannular (Prelog) interactions.
Alkane stereochemistry | Rotamer | Wikipedia | 423 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
Alkane conformers arise from rotation around sp3 hybridised carbon–carbon sigma bonds. The smallest alkane with such a chemical bond, ethane, exists as an infinite number of conformations with respect to rotation around the C–C bond. Two of these are recognised as energy minimum (staggered conformation) and energy maximum (eclipsed conformation) forms. The existence of specific conformations is due to hindered rotation around sigma bonds, although a role for hyperconjugation is proposed by a competing theory.
The importance of energy minima and energy maxima is seen by extension of these concepts to more complex molecules for which stable conformations may be predicted as minimum-energy forms. The determination of stable conformations has also played a large role in the establishment of the concept of asymmetric induction and the ability to predict the stereochemistry of reactions controlled by steric effects.
In the example of staggered ethane in Newman projection, a hydrogen atom on one carbon atom has a 60° torsional angle or torsion angle with respect to the nearest hydrogen atom on the other carbon so that steric hindrance is minimised. The staggered conformation is more stable by 12.5 kJ/mol than the eclipsed conformation, which is the energy maximum for ethane. In the eclipsed conformation the torsional angle is minimised.
In butane, the two staggered conformations are no longer equivalent and represent two distinct conformers:the anti-conformation (left-most, below) and the gauche conformation (right-most, below).
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Both conformations are free of torsional strain, but, in the gauche conformation, the two methyl groups are in closer proximity than the sum of their van der Waals radii. The interaction between the two methyl groups is repulsive (van der Waals strain), and an energy barrier results.
A measure of the potential energy stored in butane conformers with greater steric hindrance than the 'anti'-conformer ground state is given by these values:
Gauche, conformer – 3.8 kJ/mol
Eclipsed H and CH3 – 16 kJ/mol
Eclipsed CH3 and CH3 – 19 kJ/mol.
The eclipsed methyl groups exert a greater steric strain because of their greater electron density compared to lone hydrogen atoms. | Rotamer | Wikipedia | 496 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
The textbook explanation for the existence of the energy maximum for an eclipsed conformation in ethane is steric hindrance, but, with a C-C bond length of 154 pm and a Van der Waals radius for hydrogen of 120 pm, the hydrogen atoms in ethane are never in each other's way. The question of whether steric hindrance is responsible for the eclipsed energy maximum is a topic of debate to this day. One alternative to the steric hindrance explanation is based on hyperconjugation as analyzed within the Natural Bond Orbital framework. In the staggered conformation, one C-H sigma bonding orbital donates electron density to the antibonding orbital of the other C-H bond. The energetic stabilization of this effect is maximized when the two orbitals have maximal overlap, occurring in the staggered conformation. There is no overlap in the eclipsed conformation, leading to a disfavored energy maximum. On the other hand, an analysis within quantitative molecular orbital theory shows that 2-orbital-4-electron (steric) repulsions are dominant over hyperconjugation. A valence bond theory study also emphasizes the importance of steric effects.
Nomenclature
Naming alkanes per standards listed in the IUPAC Gold Book is done according to the Klyne–Prelog system for specifying angles (called either torsional or dihedral angles) between substituents around a single bond: | Rotamer | Wikipedia | 295 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
a torsion angle between 0° and ±90° is called syn (s)
a torsion angle between ±90° and 180° is called anti (a)
a torsion angle between 30° and 150° or between −30° and −150° is called clinal (c)
a torsion angle between 0° and ±30° or ±150° and 180° is called periplanar (p)
a torsion angle between 0° and ±30° is called synperiplanar (sp), also called syn- or cis- conformation
a torsion angle between 30° to 90° and −30° to −90° is called synclinal (sc), also called gauche or skew
a torsion angle between 90° and 150° or −90° and −150° is called anticlinal (ac)
a torsion angle between ±150° and 180° is called antiperiplanar (ap), also called anti- or trans- conformation
Torsional strain or "Pitzer strain" refers to resistance to twisting about a bond.
Special cases
In n-pentane, the terminal methyl groups experience additional pentane interference.
Replacing hydrogen by fluorine in polytetrafluoroethylene changes the stereochemistry from the zigzag geometry to that of a helix due to electrostatic repulsion of the fluorine atoms in the 1,3 positions. Evidence for the helix structure in the crystalline state is derived from X-ray crystallography and from NMR spectroscopy and circular dichroism in solution. | Rotamer | Wikipedia | 335 | 1527574 | https://en.wikipedia.org/wiki/Rotamer | Physical sciences | Stereochemistry | Chemistry |
A trip hammer, also known as a tilt hammer or helve hammer, is a massive powered hammer. Traditional uses of trip hammers include pounding, decorticating and polishing of grain in agriculture. In mining, trip hammers were used for crushing metal ores into small pieces, although a stamp mill was more usual for this. In finery forges they were used for drawing out blooms made from wrought iron into more workable bar iron. They were also used for fabricating various articles of wrought iron, latten (an early form of brass), steel and other metals.
One or more trip hammers were set up in a forge, also known variously as a hammer mill, hammer forge or hammer works. The hammers were usually raised by a cam and then released to fall under the force of gravity. Historically, trip hammers were often powered hydraulically by a water wheel.
Trip hammers are known to have been used in Imperial China since the Western Han dynasty. They also existed in the contemporary Greco-Roman world, with more evidence of their use in medieval Europe during the 12th century. During the Industrial Revolution the trip hammer fell out of favor and was replaced with the power hammer. Often multiple hammers were powered via a set of line shafts, pulleys and belts from a centrally located power supply.
Early history
China
In ancient China, the trip hammer evolved out of the use of the mortar and pestle, which in turn gave rise to the treadle-operated tilt-hammer (Chinese: 碓 Pinyin: dui; Wade-Giles: tui). The latter was a simple device employing a lever and fulcrum (operated by pressure applied by the weight of one's foot to one end), which featured a series of catches or lugs on the main revolving shaft as well. This device enabled the labor of pounding, often in the decorticating and polishing of grain, and avoided manual use of pounding with hand and arm. | Trip hammer | Wikipedia | 401 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
Although Chinese historians assert that its origins may span as far back as the Zhou dynasty (1050 BC–221 BC), the British sinologist Joseph Needham regards the earliest texts to describe the device are the Jijiupian dictionary of 40 BC, Yang Xiong's text known as the Fangyan of 15 BC, as well as the "best statement" the Xin Lun written by Huan Tan about 20 AD (during the usurpation of Wang Mang). The latter book states that the legendary mythological king known as Fu Xi was the one responsible for the pestle and mortar (which evolved into the tilt-hammer and then trip hammer device). Although the author speaks of the mythological Fu Xi, a passage of his writing gives hint that the waterwheel and trip-hammer were in widespread use by the 1st century AD in China (for water-powered Chinese metallurgy, see Du Shi):
Fu Hsi invented the pestle and mortar, which is so useful, and later on it was cleverly improved in such a way that the whole weight of the body could be used for treading on the tilt-hammer (tui), thus increasing the efficiency ten times. Afterwards the power of animals—donkeys, mules, oxen, and horses—was applied by means of machinery, and water-power too used for pounding, so that the benefit was increased a hundredfold.
However, this passage as well as other early references from the Han era may rather refer to a water lever, not a trip hammer. Later research, pointing to two contemporary Han era funeral wares depicting hydraulic hammers, proved that vertical waterwheels were used to power batteries of trip hammers during the Han dynasty. | Trip hammer | Wikipedia | 354 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
With his description, it is seen that the out-of-date Chinese term for pestle and mortar (dui, tui) would soon be replaced with the Chinese term for the water-powered trip-hammer (. The Han dynasty scholar and poet Ma Rong (79–166 AD) mentioned in one of his poems of hammers 'pounding in the water-echoing caves'. As described in the Hou Han Shu, in 129 AD the official Yu Xu gave a report to Emperor Shun of Han that trip hammers were being exported from Han China to the Western Qiang people by way of canals through the Qilian Mountains. In his Rou Xing Lun, the government official Kong Rong (153–208 AD) remarked that the invention of the trip hammer was an excellent example of a product created by intelligent men during his own age (comparing the relative achievements of the sages of old). During the 3rd century AD, the high government official and engineer Du Yu established the use of combined trip hammer batteries (lian zhi dui), which employed several shafts that were arranged to work off one large waterwheel. In Chinese texts of the 4th century, there are written accounts of men possessing and operating hundreds of trip hammer machines, such as the venerable mathematician Wang Rong (died 306 AD), Deng Yu (died 326 AD), and Shi Chong (died 300 AD), responsible for the operation of hundreds of trip hammers in over thirty governmental districts throughout China. There are numerous references to trip hammers during the Tang dynasty (618–907 AD) and Song dynasty (960–1279), and there are Ming dynasty (1368–1644) references that report the use of trip hammers in papermills of Fujian Province.
Although Chinese trip hammers in China were sometimes powered by the more efficient vertical-set waterwheel, the Chinese often employed the horizontal-set waterwheel in operating trip hammers, along with recumbent hammers. The recumbent hammer was found in Chinese illustrations by 1313 AD, with the publishing of Wang Zhen's Nong Shu book on ancient and contemporary (medieval) metallurgy in China. There were also illustrations of trip hammers in an encyclopedia of 1637, written by Song Yingxing (1587–1666). | Trip hammer | Wikipedia | 476 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
The Chinese use of the cam remained confined to the horizontal type and was limited to a "small variety of machines" that included only rice hulling and much later mica-pounders, paper mills and saw mills, while fulling stocks, ore stamps or forge hammers were unknown.
Classical antiquity
The main components for water-powered trip hammers – water wheels, cams, and hammers – were known in the Hellenistic world. Early cams are in evidence in water-powered automata from the 3rd century BC. According to M.J.T. Lewis, a flute player whose mechanism was described by the Persian Banū Mūsā brothers in the 9th century AD and can be "reasonably" attributed to Apollonius of Perge, functions on the principle of water-powered trip hammers.
The Roman scholar Pliny (Natural History XVIII, 23.97) indicates that water-driven pestles had become fairly widespread in Italy by the first century AD:
While some scholars have viewed this passage to mean a watermill, later scholarship argued that mola must refer to water-powered trip hammers which were used for the pounding and hulling of grain. Their mechanical character is also suggested by an earlier reference of Lucius Pomponius (fl. 100–85 BC) to a fuller's mill, a type of mill that has been operated at all times with falling stocks. However, it has been pointed out that the translation of Pomponius' fragmentary text could be faulty, and relies on translating mola, which is often thought to mean either a mill or millstone, to instead refer to a water powered trip hammer. Grain-pounders with pestles, as well as ordinary watermills, are attested as late as the middle of the 5th century AD in a monastery founded by Romanus of Condat in the remote Jura region, indicating that the knowledge of trip hammers continued into the early Middle Ages.
At the Italian site of Saepinum excavators have recently unearthed a late antique water mill that may have employed trip hammers for tanning, the earliest evidence of its kind in a classical context. | Trip hammer | Wikipedia | 438 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
The widest application of trip hammers seems to have occurred in Roman mining, where ore from deep veins was first crushed into small pieces for further processing. Here, the regularity and spacing of large indentations on stone anvils indicate the use of cam-operated ore stamps, much like the devices of later medieval mining. Such mechanically deformed anvils have been found at numerous Roman silver and gold mining sites in Western Europe, including at Dolaucothi (Wales), and on the Iberian peninsula,<ref>Sánchez-Palencia Ramos, Francisco-Javier (1984/1985): "Los «Morteros» de Fresnedo ( Allande) y Cecos (Ibias) y los lavaderos de oro romanos en el noroeste de la Península Ibérica, "Zephyrus", Vol. 37/38, pp. 349–359 (356f.)</ref> where the datable examples are from the 1st and 2nd century AD. At Dolaucothi, these trip-hammers were hydraulic-driven and possibly also at other Roman mining sites, where the large-scale use of the hushing and ground sluicing technique meant that large amounts of water were directly available for powering the machines. However, none of the Spanish and Portuguese anvils can be convincingly associated with mill sites, though most mines had water sources and leat systems which could easily be harnessed. Likewise, the dating of the Pumsaint stone to the Roman era did not address that the stone could have been moved, and relies on a series of interlinked probabilities which would jeopardize the conclusion of a Roman dating should any of them unravel.
Medieval Europe | Trip hammer | Wikipedia | 361 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
Water-powered and mechanised trip hammers reappeared in medieval Europe by the 12th century. Their use was described in medieval written sources of Styria (in modern-day Austria), written in 1135 and another in 1175 AD. Medieval French sources of the years 1116 and 1249 both record the use of mechanised trip hammers used in the forging of wrought iron. Medieval European trip hammers by the 15th century were most often in the shape of the vertical pestle stamp-mill, although they employed more frequent use of the vertical waterwheel than earlier Chinese versions (which often used the horizontal waterwheel). The well-known Renaissance artist and inventor Leonardo da Vinci often sketched trip hammers for use in forges and even file-cutting machinery, those of the vertical pestle stamp-mill type. The oldest depicted European illustration of a forge-hammer is perhaps the A Description of the Northern Peoples of Olaus Magnus, dated to 1565 AD. In this woodcut image, there is the scene of three martinets and a waterwheel working wood and leather bellows of the Osmund Bloomery furnace. The recumbent hammer was first depicted in European artwork in an illustration by Sandrart and Zonca (dated 1621 AD).
Types
A trip hammer has the head mounted at the end of a recumbent helve, hence the alternative name of helve hammer. The choice of which type was used in a particular context may have depended on the strain that its operation imposed on the helve. This was normally of wood, mounted in a cast-iron ring (called the hurst) where it pivoted. However, in the 19th century the heaviest helves were sometimes a single casting, incorporating the hurst. | Trip hammer | Wikipedia | 359 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
The tilt hammer or tail helve hammer has a pivot at the centre of the helve on which it is mounted, and is lifted by pushing the opposite end to the head downwards. In practice, the head on such hammers seems to have been limited to one hundredweight (about 50 kg), but a very rapid stroke rate was possible. This made it suitable for drawing iron down to small sizes suitable for the cutlery trades. There were therefore many such forges known as 'tilts' around Sheffield. They were also used in brass battery works for making brass (or copper) pots and pans. In battery works (at least) it was possible for one power source to operate several hammers. In Germany, tilt hammers of up to 300 kg were used in hammer mills to forge iron. Surviving, working hammers, powered by water wheels, may be seen, for example, at the Frohnauer Hammer in the Ore Mountains.
The belly helve hammer was the kind normally found in a finery forge, used for making pig iron into forgeable bar iron. This was lifted by cams striking the helve between the pivot and the head. The head usually weighed quarter of a ton. This was probably the case because the strain on a wooden helve would have been too great if the head were heavier.
The nose helve hammer seems to have been unusual until the late 18th or early 19th century. This was lifted beyond the head. Surviving nose helves and those in pictures appear to be of cast iron.
Demise
The steam-powered drop hammer replaced the trip hammer (at least for the largest forgings). James Nasmyth invented it in 1839 and patented in 1842. However, by then forging had become less important for the iron industry, following the improvements to the rolling mill that went along with the adoption of puddling from the end of the 18th century. Nevertheless, hammers continued to be needed for shingling. | Trip hammer | Wikipedia | 406 | 1527674 | https://en.wikipedia.org/wiki/Trip%20hammer | Technology | Industrial machinery | null |
Sheet metal is metal formed into thin, flat pieces, usually by an industrial process.
Thicknesses can vary significantly; extremely thin sheets are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate, such as plate steel, a class of structural steel.
Sheet metal is available in flat pieces or coiled strips. The coils are formed by running a continuous sheet of metal through a roll slitter.
In most of the world, sheet metal thickness is consistently specified in millimeters. In the U.S., the thickness of sheet metal is commonly specified by a traditional, non-linear measure known as its gauge. The larger the gauge number, the thinner the metal. Commonly used steel sheet metal ranges from 30 gauge to about 7 gauge. Gauge differs between ferrous (iron-based) metals and nonferrous metals such as aluminum or copper. Copper thickness, for example, is measured in ounces, representing the weight of copper contained in an area of one square foot. Parts manufactured from sheet metal must maintain a uniform thickness for ideal results.
There are many different metals that can be made into sheet metal, such as aluminium, brass, copper, steel, tin, nickel and titanium. For decorative uses, some important sheet metals include silver, gold, and platinum (platinum sheet metal is also utilized as a catalyst). These metal sheets are processed through different processing technologies, mainly including cold rolling and hot rolling. Sometimes hot-dip galvanizing process is adopted as needed to prevent it from rusting due to constant exposure to the outdoors. Sometimes a layer of color coating is applied to the surface of the cold-rolled sheet to obtain a decorative and protective metal sheet, generally called a color-coated metal sheet.
Sheet metal is used in automobile and truck (lorry) bodies, major appliances, airplane fuselages and wings, tinplate for tin cans, roofing for buildings (architecture), and many other applications. Sheet metal of iron and other materials with high magnetic permeability, also known as laminated steel cores, has applications in transformers and electric machines. Historically, an important use of sheet metal was in plate armor worn by cavalry, and sheet metal continues to have many decorative uses, including in horse tack. Sheet metal workers are also known as "tin bashers" (or "tin knockers"), a name derived from the hammering of panel seams when installing tin roofs. | Sheet metal | Wikipedia | 494 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
History
Hand-hammered metal sheets have been used since ancient times for architectural purposes. Water-powered rolling mills replaced the manual process in the late 17th century. The process of flattening metal sheets required large rotating iron cylinders which pressed metal pieces into sheets. The metals suited for this were lead, copper, zinc, iron and later steel. Tin was often used to coat iron and steel sheets to prevent it from rusting. This tin-coated sheet metal was called "tinplate." Sheet metals appeared in the United States in the 1870s, being used for shingle roofing, stamped ornamental ceilings, and exterior façades. Sheet metal ceilings were only popularly known as "tin ceilings" later as manufacturers of the period did not use the term. The popularity of both shingles and ceilings encouraged widespread production. With further advances of steel sheet metal production in the 1890s, the promise of being cheap, durable, easy to install, lightweight and fireproof gave the middle-class a significant appetite for sheet metal products. It was not until the 1930s and WWII that metals became scarce and the sheet metal industry began to collapse. However, some American companies, such as the W.F. Norman Corporation, were able to stay in business by making other products until Historic preservation projects aided the revival of ornamental sheet metal.
Materials
Stainless steel
Grade 304 is the most common of the three grades. It offers good corrosion resistance while maintaining formability and weldability. Available finishes are #2B, #3, and #4. Grade 303 is not available in sheet form.
Grade 316 possesses more corrosion resistance and strength at elevated temperatures than 304. It is commonly used for pumps, valves, chemical equipment, and marine applications. Available finishes are #2B, #3, and #4.
Grade 410 is a heat treatable stainless steel, but it has a lower corrosion resistance than the other grades. It is commonly used in cutlery. The only available finish is dull.
Grade 430 is a popular grade, low-cost alternative to series 300's grades. This is used when high corrosion resistance is not a primary criterion. Common grade for appliance products, often with a brushed finish.
Aluminium
Aluminium is widely used in sheet metal form due to its flexibility, wide range of options, cost effectiveness, and other properties. The four most common aluminium grades available as sheet metal are 1100-H14, 3003-H14, 5052-H32, and 6061-T6. | Sheet metal | Wikipedia | 500 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Grade 1100-H14 is commercially pure aluminium, highly chemical and weather resistant. It is ductile enough for deep drawing and weldable, but has low strength. It is commonly used in chemical processing equipment, light reflectors, and jewelry.
Grade 3003-H14 is stronger than 1100, while maintaining the same formability and low cost. It is corrosion resistant and weldable. It is often used in stampings, spun and drawn parts, mail boxes, cabinets, tanks, and fan blades.
Grade 5052-H32 is much stronger than 3003 while still maintaining good formability. It maintains high corrosion resistance and weldability. Common applications include electronic chassis, tanks, and pressure vessels.
Grade 6061-T6 is a common heat-treated structural aluminium alloy. It is weldable, corrosion resistant, and stronger than 5052, but not as formable. It loses some of its strength when welded. It is used in modern aircraft structures.
Brass
Brass is an alloy of copper, which is widely used as a sheet metal. It has more strength, corrosion resistance and formability when compared to copper while retaining its conductivity.
In sheet hydroforming, variation in incoming sheet coil properties is a common problem for forming process, especially with materials for automotive applications. Even though incoming sheet coil may meet tensile test specifications, high rejection rate is often observed in production due to inconsistent material behavior. Thus there is a strong need for a discriminating method for testing incoming sheet material formability. The hydraulic sheet bulge test emulates biaxial deformation conditions commonly seen in production operations.
For forming limit curves of materials aluminium, mild steel and brass. Theoretical analysis is carried out by deriving governing equations for determining of equivalent stress and equivalent strain based on the bulging to be spherical and Tresca's yield criterion with the associated flow rule. For experimentation circular grid analysis is one of the most effective methods.
Gauge
Use of gauge numbers to designate sheet metal thickness is discouraged by numerous international standards organizations. For example, ASTM states in specification ASTM A480-10a: "The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning." | Sheet metal | Wikipedia | 452 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Manufacturers' Standard Gauge for Sheet Steel is based on an average density of 41.82 lb per square foot per inch thick, equivalent to . The older United States Standard Gauge is based upon 40 lb per square foot per inch thick. Gauge is defined differently for ferrous (iron-based) and non-ferrous metals (e.g. aluminium and brass).
The gauge thicknesses shown in column 2 (U.S. standard sheet and plate iron and steel decimal inch (mm)) seem somewhat arbitrary. The progression of thicknesses is clear in column 3 (U.S. standard for sheet and plate iron and steel 64ths inch (delta)). The thicknesses vary first by inch in higher thicknesses and then step down to increments of inch, then inch, with the final increments at decimal fractions of inch.
Some steel tubes are manufactured by folding a single steel sheet into a square/circle and welding the seam together. Their wall thickness has a similar (but distinct) gauge to the thickness of steel sheets.
Tolerances
During the rolling process the rollers bow slightly, which results in the sheets being thinner on the edges. The tolerances in the table and attachments reflect current manufacturing practices and commercial standards and are not representative of the Manufacturer's Standard Gauge, which has no inherent tolerances.
Forming processes
Bending
The equation for estimating the maximum bending force is,
,
where k is a factor taking into account several parameters including friction. T is the ultimate tensile strength of the metal. L and t are the length and thickness of the sheet metal, respectively. The variable W is the open width of a V-die or wiping die.
Curling
The curling process is used to form an edge on a ring. This process is used to remove sharp edges. It also increases the moment of inertia near the curled end.
The flare/burr should be turned away from the die. It is used to curl a material of specific thickness. Tool steel is generally used due to the amount of wear done by operation.
Decambering
It is a metal working process of removing camber, the horizontal bend, from a strip shaped material. It may be done to a finite length section or coils. It resembles flattening of leveling process, but on a deformed edge.
Deep drawing | Sheet metal | Wikipedia | 476 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Drawing is a forming process in which the metal is stretched over a form or die. In deep drawing the depth of the part being made is more than half its diameter. Deep drawing is used for making automotive fuel tanks, kitchen sinks, two-piece aluminum cans, etc. Deep drawing is generally done in multiple steps called draw reductions. The greater the depth, the more reductions are required. Deep drawing may also be accomplished with fewer reductions by heating the workpiece, for example in sink manufacture.
In many cases, material is rolled at the mill in both directions to aid in deep drawing. This leads to a more uniform grain structure which limits tearing and is referred to as "draw quality" material.
Expanding
Expanding is a process of cutting or stamping slits in alternating pattern much like the stretcher bond in brickwork and then stretching the sheet open in accordion-like fashion. It is used in applications where air and water flow are desired as well as when light weight is desired at cost of a solid flat surface. A similar process is used in other materials such as paper to create a low cost packing paper with better supportive properties than flat paper alone.
Hemming and seaming
Hemming is a process of folding the edge of sheet metal onto itself to reinforce that edge. Seaming is a process of folding two sheets of metal together to form a joint.
Hydroforming
Hydroforming is a process that is analogous to deep drawing, in that the part is formed by stretching the blank over a stationary die. The force required is generated by the direct application of extremely high hydrostatic pressure to the workpiece or to a bladder that is in contact with the workpiece, rather than by the movable part of a die in a mechanical or hydraulic press. Unlike deep drawing, hydroforming usually does not involve draw reductions—the piece is formed in a single step.
Incremental sheet forming
Incremental sheet forming or ISF forming process is basically sheet metal working or sheet metal forming process. In this case, sheet is formed into final shape by a series of processes in which small incremental deformation can be done in each series.
Ironing
Ironing is a sheet metal working or sheet metal forming process. It uniformly thins the workpiece in a specific area. This is a very useful process. It is used to produce a uniform wall thickness part with a high height-to-diameter ratio.
It is used in making aluminium beverage cans.
Laser cutting | Sheet metal | Wikipedia | 494 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Sheet metal can be cut in various ways, from hand tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting. Many sheet metal cutting operations are based on computer numerically controlled (CNC) laser cutting or multi-tool CNC punch press.
CNC laser involves moving a lens assembly carrying a beam of laser light over the surface of the metal. Oxygen, nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth and a precision of around can be obtained. Cutting speeds on thin sheet can be as high as per minute. Most laser cutting systems use a based laser source with a wavelength of around 10 μm; some more recent systems use a YAG based laser with a wavelength of around 1 μm.
Photochemical machining
Photochemical machining, also known as photo etching, is a tightly controlled corrosion process which is used to produce complex metal parts from sheet metal with very fine detail. The photo etching process involves photo sensitive polymer being applied to a raw metal sheet. Using CAD designed photo-tools as stencils, the metal is exposed to UV light to leave a design pattern, which is developed and etched from the metal sheet.
Perforating
Perforating is a cutting process that punches multiple small holes close together in a flat workpiece. Perforated sheet metal is used to make a wide variety of surface cutting tools, such as the surform.
Press brake forming | Sheet metal | Wikipedia | 332 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
This is a form of bending used to produce long, thin sheet metal parts. The machine that bends the metal is called a press brake. The lower part of the press contains a V-shaped groove called the die. The upper part of the press contains a punch that presses the sheet metal down into the v-shaped die, causing it to bend. There are several techniques used, but the most common modern method is "air bending". Here, the die has a sharper angle than the required bend (typically 85 degrees for a 90 degree bend) and the upper tool is precisely controlled in its stroke to push the metal down the required amount to bend it through 90 degrees. Typically, a general purpose machine has an available bending force of around 25 tons per meter of length. The opening width of the lower die is typically 8 to 10 times the thickness of the metal to be bent (for example, 5 mm material could be bent in a 40 mm die). The inner radius of the bend formed in the metal is determined not by the radius of the upper tool, but by the lower die width. Typically, the inner radius is equal to 1/6 of the V-width used in the forming process.
The press usually has some sort of back gauge to position depth of the bend along the workpiece. The backgauge can be computer controlled to allow the operator to make a series of bends in a component to a high degree of accuracy. Simple machines control only the backstop, more advanced machines control the position and angle of the stop, its height and the position of the two reference pegs used to locate the material. The machine can also record the exact position and pressure required for each bending operation to allow the operator to achieve a perfect 90 degree bend across a variety of operations on the part.
Punching | Sheet metal | Wikipedia | 366 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Punching is performed by placing the sheet of metal stock between a punch and a die mounted in a press. The punch and die are made of hardened steel and are the same shape. The punch is sized to be a very close fit in the die. The press pushes the punch against and into the die with enough force to cut a hole in the stock. In some cases the punch and die "nest" together to create a depression in the stock. In progressive stamping, a coil of stock is fed into a long die/punch set with many stages. Multiple simple shaped holes may be produced in one stage, but complex holes are created in multiple stages. In the final stage, the part is punched free from the "web".
A typical CNC turret punch has a choice of up to 60 tools in a "turret" that can be rotated to bring any tool to the punching position. A simple shape (e.g. a square, circle, or hexagon) is cut directly from the sheet. A complex shape can be cut out by making many square or rounded cuts around the perimeter. A punch is less flexible than a laser for cutting compound shapes, but faster for repetitive shapes (for example, the grille of an air-conditioning unit). A CNC punch can achieve 600 strokes per minute.
A typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under 15 seconds by either a press or a laser CNC machine.
Roll forming
A continuous bending operation for producing open profiles or welded tubes with long lengths or in large quantities.
Rolling
Rolling is metal working or metal forming process. In this method, stock passes through one or more pair of rolls to reduce thickness. It is used to make thickness uniform. It is classified according to its temperature of rolling:
Hot rolling: in this temperature is above recrystallisation temperature.
Cold rolling: In this temperature is below recrystallisation temperature.
Warm rolling: In this temperature is used is in between Hot rolling and cold rolling.
Spinning
Spinning is used to make tubular (axis-symmetric) parts by fixing a piece of sheet stock to a rotating form (mandrel). Rollers or rigid tools press the stock against the form, stretching it until the stock takes the shape of the form. Spinning is used to make rocket motor casings, missile nose cones, satellite dishes and metal kitchen funnels.
Stamping | Sheet metal | Wikipedia | 495 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
Stamping includes a variety of operations such as punching, blanking, embossing, bending, flanging, and coining; simple or complex shapes can be formed at high production rates; tooling and equipment costs can be high, but labor costs are low.
Alternatively, the related techniques repoussé and chasing have low tooling and equipment costs, but high labor costs.
Water jet cutting
A water jet cutter, also known as a waterjet, is a tool capable of a controlled erosion into metal or other materials using a jet of water at high velocity and pressure, or a mixture of water and an abrasive substance.
Wheeling
The process of using an English wheel is called wheeling. It is basically a metal working or metal forming process. An English wheel is used by a craftsperson to form compound curves from a flat sheet of metal of aluminium or steel. It is costly, as highly skilled labour is required. It can produce different panels by the same method. A stamping press is used for high numbers in production.
Sheet metal fabrication
The use of sheet metal, through a comprehensive cold working process, including bending, shearing, punching, laser cutting, water jet cutting, riveting, splicing, etc. to make the final product we want (such as computer chassis, washing machine shells, refrigerator door panels, etc.), we generally called sheet metal fabrication. The academic community currently has no uniform definition, but this process has a common feature of the process is that the material is generally a thin sheet, and will not change the thickness of most of the material of the part.
Fasteners
Fasteners that are commonly used on sheet metal include: clecos, rivets, and sheet metal screws. | Sheet metal | Wikipedia | 355 | 1528221 | https://en.wikipedia.org/wiki/Sheet%20metal | Technology | Metallurgy | null |
An aircraft fairing is a structure whose primary function is to produce a smooth outline and reduce drag.
These structures are covers for gaps and spaces between parts of an aircraft to reduce form drag and interference drag, and to improve appearance.
Types
On aircraft, fairings are commonly found on:
Belly fairing
Also called a "ventral fairing", it is located on the underside of the fuselage between the main wings. It can also cover additional cargo storage or fuel tanks.
Cockpit fairing
Also called a "cockpit pod", it protects the crew on ultralight trikes. Commonly made from fiberglass, it may also incorporate a windshield.
Elevator and horizontal stabilizer tips
Elevator and stabilizer tips fairings smooth out airflow at the tips.
Fin and rudder tip fairings Fin and rudder tip fairings reduce drag at low angles of attack, but also reduce the stall angle, so the fairing of control surface tips depends on the application.
Fillets Fillets smooth the airflow at the junction between two components like the fuselage and wing.
Fixed landing gear junctions
Landing gear fairings reduce drag at these junctions.
Flap track fairings
Fairings are needed to enclose the flap operating mechanism when the flap is up. They open up as the flap comes down and may also pivot to allow the necessary sideways movement of the extending mechanism which occurs on swept-wing installations.
Spinner
To protect and streamline the propeller hub.
Strut-to-wing and strut-to-fuselage junctions
Strut end fairings reduce drag at these junctions.
Tail cones
Tail cones streamline the rear extremity of a fuselage by eliminating any base area which is the source of base drag.
Wing root
Wing roots are often faired to reduce interference drag between the wing and the fuselage. On top and below the wing it consists of small rounded edge to reduce the surface and such friction drag. At the leading and trailing edge it consists of much larger taper and smooths out the pressure differences: high pressure at the leading and trailing edge, low pressure on top of the wing and around the fuselage. | Aircraft fairing | Wikipedia | 421 | 1528883 | https://en.wikipedia.org/wiki/Aircraft%20fairing | Technology | Aircraft components | null |
Wing tips
Wing tips are often formed as complex shapes to reduce vortex generation and so also drag, especially at low speed.
Wheels on fixed gear aircraft
Wheel fairings are often called "wheel pants", "speed fairings" in North America or "wheel spats" or "trousers", in the United Kingdom, the latter enclosing both the wheel and landing gear leg. These fairings are a trade-off in advantages, as they increase the frontal and surface area, but also provide a smooth surface and a faired nose and tail for laminar flow, in an attempt to reduce the turbulence created by the round wheel and its associated gear legs and brakes. They also serve the important function of preventing mud and stones from being thrown upwards against the wings or fuselage, or into the propeller on a pusher craft. | Aircraft fairing | Wikipedia | 167 | 1528883 | https://en.wikipedia.org/wiki/Aircraft%20fairing | Technology | Aircraft components | null |
Betula papyrifera (paper birch, also known as (American) white birch and canoe birch) is a short-lived species of birch native to northern North America. Paper birch is named after the tree's thin white bark, which often peels in paper-like layers from the trunk. Paper birch is often one of the first species to colonize a burned area within the northern latitudes, and is an important species for moose browsing. Primary commercial uses for paper birch wood are as boltwood and sawlogs, while secondary products include firewood and pulpwood. It is the provincial tree of Saskatchewan and the state tree of New Hampshire.
Description
Betula papyrifera is a medium-sized deciduous tree typically reaching tall, and exceptionally to with a trunk up to in diameter. Within forests, it often grows with a single trunk but when grown as a landscape tree it may develop multiple trunks or branch close to the ground.
Paper birch is a typically short-lived species. It handles heat and humidity poorly and may live only 30 years in zones six and up, while trees in colder-climate regions can grow for more than 100 years. B. papyrifera will grow in many soil types, from steep rocky outcrops to flat muskegs of the boreal forest. Best growth occurs in deeper, well drained to dry soils, depending on the location. | Betula papyrifera | Wikipedia | 282 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
In older trees, the bark is white, commonly brightly so, flaking in fine horizontal strips to reveal a pinkish or salmon-colored inner bark. It often has small black marks and scars. In individuals younger than five years, the bark appears a brown red color with white lenticels, making the tree much harder to distinguish from other birches. The bark is highly weather-resistant. It has a high oil content and this gives it its waterproof and weather-resistant characteristics. Often, the wood of a downed paper birch will rot away, leaving the hollow bark intact.
The leaves are dark green and smooth on the upper surface; the lower surface is often pubescent on the veins. They are alternately arranged on the stem, oval to triangular in shape, long and about two-thirds as wide. The leaf is rounded at the base and tapering to an acutely pointed tip. The leaves have a doubly serrated margin with relatively sharp teeth. Each leaf has a petiole about long that connects it to the stems.
The fall color is a bright yellow color that contributes to the bright colors within the northern deciduous forest.
The leaf buds are conical and small and green-colored with brown edges.
The stems are a reddish-brown color and may be somewhat hairy when young.
The flowers are wind-pollinated catkins; the female flowers are greenish and long growing from the tips of twigs. The male (staminate) flowers are long and a brownish color. The tree flowers from mid-April to June depending on location. Paper birch is monoecious, meaning that one plant has both male and female flowers.
The fruit matures in the fall. The mature fruit is composed of numerous tiny winged seeds packed between the catkin bracts. They drop between September and spring. At 15 years of age, the tree will start producing seeds but will be in peak seed production between 40 and 70 years. The seed production is irregular, with a heavy seed crop produced typically every other year and with at least some seeds being produced every year. In average seed years, are produced, but in bumper years may be produced. The seeds are light and blow in the wind to new areas; they also may blow along the surface of snow.
The roots are generally shallow and occupy the upper of the soil and do not form taproots. High winds are more likely to break the trunk than to uproot the tree. | Betula papyrifera | Wikipedia | 495 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
Genetics and taxonomy
B. papyrifera hybridizes with other species within the genus Betula.
Several varieties are recognized:
B. p. var papyrifera the typical paper birch
B. p. var cordifolia the eastern paper birch (now a separate species); see Betula cordifolia
B. p. var kenaica Alaskan paper birch (also treated as a separate species by some authors); see Betula kenaica
B. p. var subcordata Northwestern paper birch
B. p. var. neoalaskana Alaska paper birch (although this is often treated as a separate species); see Betula neoalaskana
Distribution
Betula papyrifera is mostly confined to Canada and the far northern United States. It is found in interior (var. humilus) and south-central (var. kenaica) Alaska and in all provinces and territories of Canada, except Nunavut, as well as the far northern continental United States. Isolated patches are found as far south as the Hudson Valley of New York and Pennsylvania, northern Connecticut, and Washington. High elevation stands are also in mountains to North Carolina, New Mexico, and Colorado. The most southerly stand in the Western United States is located in Long Canyon in the City of Boulder Open Space and Mountain Parks. This is an isolated Pleistocene relict that most likely reflects the southern reach of boreal vegetation into the area during the last Ice Age.
Ecology
In Alaska, paper birch often naturally grows in pure stands by itself or with black or white spruce. In the eastern and central regions of its range, it is often associated with red spruce and balsam fir. It may also be associated with big-toothed aspen, yellow birch, Betula populifolia, and maples.
Shrubs often associated with paper birch in the eastern part of its range include beaked hazel (Corylus cornuta), common bearberry (Arctostaphylos uva-ursi), dwarf bush-honeysuckle (Diervilla lonicera), wintergreen (Gaultheria procumbens), wild sarsaparilla (Aralia nudicaulis), blueberries (Vaccinium spp.), raspberries and blackberries (Rubus spp.), elderberry (Sambucus spp.), and hobblebush (Viburnum alnifolium).
Successional relationships | Betula papyrifera | Wikipedia | 496 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
Betula papyrifera is a pioneer species, meaning it is often one of the first trees to grow in an area after other trees are removed by some sort of disturbance. Typical disturbances colonized by paper birch are wildfire, avalanche, or windthrow areas where the wind has blown down all trees. When it grows in these pioneer, or early successional, woodlands, it often forms stands of trees where it is the only species.
Paper birch is considered well adapted to fires because it recovers quickly by means of reseeding the area or regrowth from the burned tree. The lightweight seeds are easily carried by the wind to burned areas, where they quickly germinate and grow into new trees. Paper birch is adapted to ecosystems where fires occur every 50 to 150 years For example, it is frequently an early invader after fire in black spruce boreal forests. As paper birch is a pioneer species, finding it within mature or climax forests is rare because it will be overcome by trees that are more shade-tolerant as secondary succession progresses.
For example, in Alaskan boreal forests, a paper birch stand 20 years after a fire may have , but after 60 to 90 years, the number of trees will decrease to as spruce replaces the birch. After approximately 75 years, the birch will start dying and by 125 years, most paper birch will have disappeared unless another fire burns the area.
Paper birch trees themselves have varied reactions to wildfire. A group, or stand, of paper birch is not particularly flammable. The canopy often has a high moisture content and the understory is often lush green. As such, conifer crown fires often stop once they reach a stand of paper birch or become slower-moving ground fires. Since these stands are fire-resistant, they may become seed trees to reseed the area around them that was burned. However, in dry periods, paper birch is flammable and will burn rapidly. As the bark is flammable, it often will burn and may girdle the tree. | Betula papyrifera | Wikipedia | 414 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
Wildlife
Birch bark is a winter staple food for moose. The nutritional quality is poor because of the large quantities of lignin, which make digestion difficult, but is important to wintering moose because of its sheer abundance. Moose prefer paper birch over aspen, alder, and balsam poplar, but they prefer willow (Salix spp.) over birch and the other species listed. Although moose consume large amounts of paper birch in the winter, if they were to eat only paper birch, they may starve.
Although white-tailed deer consider birch a "secondary-choice food," it is an important dietary component. In Minnesota, white-tailed deer eat considerable amounts of paper birch leaves in the fall. Snowshoe hares browse paper birch seedlings, and grouse eat the buds. Porcupines and beavers feed on the inner bark. The seeds of paper birch are an important part of the diet of many birds and small mammals, including chickadees, redpolls, voles, and ruffed grouse. Yellow bellied sapsuckers drill holes in the bark of paper birch to get at the sap; this is one of their favorite trees for feeding on.
Conservation
As of 2023, the conservation status of paper birch is considered of least concern according to the International Union for Conservation of Nature (IUCN). However, the species is considered vulnerable in Indiana and Nebraska, imperiled in Illinois, Virginia, and West Virginia, and critically imperiled in Colorado and Tennessee. These areas represent the southerly and southwesterly edge of the paper birch's range.
Uses
Betula papyrifera has a moderately heavy white wood. It makes excellent high-yielding firewood if seasoned properly. The dried wood has a density of and an energy density . Although paper birch does not have a very high overall economic value, it is used in furniture, flooring, popsicle sticks, pulpwood (for paper), plywood, and oriented strand board. The wood can also be made into spears, bows, arrows, snowshoes, sleds, and other items. When used as pulp for paper, the stems and other nontrunk wood are lower in quantity and quality of fibers, and consequently the fibers have less mechanical strength; nonetheless, this wood is still suitable for use in paper. | Betula papyrifera | Wikipedia | 476 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
The sap is boiled down to produce birch syrup. The raw sap contains 0.9% carbohydrates (glucose, fructose, sucrose) as compared to 2 percent to 3 percent within sugar maple sap. The sap flows later in the season than maples. Currently, only a few small-scale operations in Alaska and Yukon produce birch syrup from this species.
Bark
Its bark is an excellent fire starter; it ignites at high temperatures even when wet. The bark has an energy density of and , the highest per unit weight of 24 species tested.
Birch bark is used in a number of crafts by various Native American tribes (e.g. Ojibwe). In the Ashinaabe language birch bark is called wiigwaas. Panels of bark can be fitted or sewn together to make cartons and boxes. The bark is also used to create a durable waterproof layer in the construction of sod-roofed houses. Many indigenous groups (i.e., Wabanaki peoples) use birchbark for making various items, such as canoes, containers, and wigwams. It is also used as a backing for porcupine quillwork and moosehair embroidery. Thin sheets can be employed as a medium for the art of birchbark biting.
Plantings
Paper birch is planted to reclaim old mines and other disturbed sites, often bare-root or small saplings are planted when this is the goal. Since paper birch is an adaptable pioneer species, it is a prime candidate for reforesting drastically disturbed areas.
Paper birch is frequently planted as an ornamental because of its graceful form and attractive bark. The bark changes to the white color at about 3 years of growth. Paper birch grows best in USDA zones 2–6, due to its intolerance of high temperatures. Betula nigra, or river birch, is recommended for warm-climate areas warmer than zone 6, where paper birch is rarely successful. B. papyrifera is more resistant to the bronze birch borer than Betula pendula, which is similarly planted as a landscape tree. | Betula papyrifera | Wikipedia | 432 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
Pests
Bronze birch borer is a major pest among birch species. Under repeated infestation or stress to the tree from other sources, bronze birch borers may kill the tree. The insect bores into the sapwood, beginning at the top of the tree and causing death of the tree crown. The insect has a D-shaped emergence hole where it chews out of the tree. Healthy trees are resistant to the borer, but when grown in less than ideal conditions, the defense mechanisms of the tree may not function properly. Chemical controls exist.
Birch skeletonizers are moths which lay their eggs on the surfaces of birch leaves. Upon hatching, the larvae feed on the undersides of the leaves and cause browning.
Birch leafminer is a species of sawfly and a common pest that feeds from the inside of the leaf and causes the leaf to turn brown. It was introduced to the United States in the 1920s. The first generation appears in May but there will be several generations per year. Severe infestations may stress the tree and make it more vulnerable to the bronze birch borer. | Betula papyrifera | Wikipedia | 223 | 1529114 | https://en.wikipedia.org/wiki/Betula%20papyrifera | Biology and health sciences | Fagales | Plants |
In topology and related areas of mathematics, a neighbourhood (or neighborhood) is one of the basic concepts in a topological space. It is closely related to the concepts of open set and interior. Intuitively speaking, a neighbourhood of a point is a set of points containing that point where one can move some amount in any direction away from that point without leaving the set.
Definitions
Neighbourhood of a point
If is a topological space and is a point in then a neighbourhood of is a subset of that includes an open set containing ,
This is equivalent to the point belonging to the topological interior of in
The neighbourhood need not be an open subset of When is open (resp. closed, compact, etc.) in it is called an (resp. closed neighbourhood, compact neighbourhood, etc.). Some authors require neighbourhoods to be open, so it is important to note their conventions.
A set that is a neighbourhood of each of its points is open since it can be expressed as the union of open sets containing each of its points. A closed rectangle, as illustrated in the figure, is not a neighbourhood of all its points; points on the edges or corners of the rectangle are not contained in any open set that is contained within the rectangle.
The collection of all neighbourhoods of a point is called the neighbourhood system at the point.
Neighbourhood of a set
If is a subset of a topological space , then a neighbourhood of is a set that includes an open set containing ,It follows that a set is a neighbourhood of if and only if it is a neighbourhood of all the points in Furthermore, is a neighbourhood of if and only if is a subset of the interior of
A neighbourhood of that is also an open subset of is called an of
The neighbourhood of a point is just a special case of this definition.
In a metric space
In a metric space a set is a neighbourhood of a point if there exists an open ball with center and radius such that
is contained in
is called a uniform neighbourhood of a set if there exists a positive number such that for all elements of
is contained in
Under the same condition, for the -neighbourhood of a set is the set of all points in that are at distance less than from (or equivalently, is the union of all the open balls of radius that are centered at a point in ):
It directly follows that an -neighbourhood is a uniform neighbourhood, and that a set is a uniform neighbourhood if and only if it contains an -neighbourhood for some value of
Examples | Neighbourhood (mathematics) | Wikipedia | 499 | 1529485 | https://en.wikipedia.org/wiki/Neighbourhood%20%28mathematics%29 | Mathematics | Topology | null |
Given the set of real numbers with the usual Euclidean metric and a subset defined as
then is a neighbourhood for the set of natural numbers, but is a uniform neighbourhood of this set.
Topology from neighbourhoods
The above definition is useful if the notion of open set is already defined. There is an alternative way to define a topology, by first defining the neighbourhood system, and then open sets as those sets containing a neighbourhood of each of their points.
A neighbourhood system on is the assignment of a filter of subsets of to each in such that
the point is an element of each in
each in contains some in such that for each in is in
One can show that both definitions are compatible, that is, the topology obtained from the neighbourhood system defined using open sets is the original one, and vice versa when starting out from a neighbourhood system.
Uniform neighbourhoods
In a uniform space is called a uniform neighbourhood of if there exists an entourage such that contains all points of that are -close to some point of that is, for all
Deleted neighbourhood
A deleted neighbourhood of a point (sometimes called a punctured neighbourhood) is a neighbourhood of without For instance, the interval is a neighbourhood of in the real line, so the set is a deleted neighbourhood of A deleted neighbourhood of a given point is not in fact a neighbourhood of the point. The concept of deleted neighbourhood occurs in the definition of the limit of a function and in the definition of limit points (among other things). | Neighbourhood (mathematics) | Wikipedia | 290 | 1529485 | https://en.wikipedia.org/wiki/Neighbourhood%20%28mathematics%29 | Mathematics | Topology | null |
Aspergillus () is a genus consisting of several hundred mold species found in various climates worldwide.
Aspergillus was first catalogued in 1729 by the Italian priest and biologist Pier Antonio Micheli. Viewing the fungi under a microscope, Micheli was reminded of the shape of an aspergillum (holy water sprinkler), from Latin spargere (to sprinkle), and named the genus accordingly. Aspergillum is an asexual spore-forming structure common to all Aspergillus species; around one-third of species are also known to have a sexual stage. While some species of Aspergillus are known to cause fungal infections, others are of commercial importance.
Taxonomy
Species
In March 2010, Aspergillus covered 837 species of fungi. Notable species placed in Aspergillus include:
Aspergillus flavus is a notable plant pathogen impacting crop yields and a common cause of aspergillosis.
Aspergillus fumigatus is the most common cause of aspergillosis in individuals with an immunodeficiency.
Aspergillus nidulans has seen heavy use as research organism in cell biology.
Aspergillus niger is used in the chemical industry for a variety of applications, while also being a known food contaminant and a possible pathogen to humans.
Aspergillus oryzae and A. sojae are used in East Asian cuisine in the production of sake, soy sauce and other fermented food products.
Aspergillus terreus is used in the production of organic acids but can also cause opportunistic infections in humans.
Inner Taxonomy
The expansive genus Aspergillus is currently divided into six subgenera of which many are further split into a total of 27 sections.
Subgenus Circumdati, divided in 10 sections.
Subgenus Nidulantes, divided in 9 sections.
Subgenus Fumigati, divided in 4 sections.
Subgenus Aspergillus, divided in 2 sections.
Subgenus and section Cremei
Subgenus and section Polypaecilum
Growth and distribution | Aspergillus | Wikipedia | 436 | 1529518 | https://en.wikipedia.org/wiki/Aspergillus | Biology and health sciences | Basics | Plants |
Aspergillus is defined as a group of conidial fungi—that is, fungi in an asexual state. Some of them, however, are known to have a teleomorph (sexual state) in the Ascomycota. With DNA evidence, all members of the genus Aspergillus are members of the phylum Ascomycota.
Members of the genus possess the ability to grow where a high osmotic pressure exists (high concentration of sugar, salt, etc.). Aspergillus species are highly aerobic and are found in almost all oxygen-rich environments, where they commonly grow as molds on the surface of a substrate, as a result of the high oxygen tension. Commonly, fungi grow on carbon-rich substrates like monosaccharides (such as glucose) and polysaccharides (such as amylose). Aspergillus species are common contaminants of starchy foods (such as bread and potatoes), and grow in or on many plants and trees.
In addition to growth on carbon sources, many species of Aspergillus demonstrate oligotrophy where they are capable of growing in nutrient-depleted environments, or environments with a complete lack of key nutrients. Aspergillus niger is a prime example of this; it can be found growing on damp walls, as a major component of mildew.
Several species of Aspergillus, including A. niger and A. fumigatus, will readily colonise buildings, favouring warm and damp or humid areas such as bathrooms and around window frames.
Aspergillus are found in millions of pillows.
Commercial importance
Species of Aspergillus are important medically and commercially. Some species can cause infection in humans and other animals. Some infections found in animals have been studied for years, while other species found in animals have been described as new and specific to the investigated disease, and others have been known as names already in use for organisms such as saprophytes. More than 60 Aspergillus species are medically relevant pathogens. For humans, a range of diseases such as infection to the external ear, skin lesions, and ulcers classed as mycetomas are found. | Aspergillus | Wikipedia | 463 | 1529518 | https://en.wikipedia.org/wiki/Aspergillus | Biology and health sciences | Basics | Plants |
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