Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routine precisions in the 0.1–1 percent range. The dating method is performed on the mineral zircon; the mineral incorporates uranium and thorium atoms into its crystal structure, but rejects lead. Therefore, one can assume that the entire lead content of the zircon is radiogenic, i.e. it is produced by a process of radioactive decay after the formation of the mineral. Thus the current ratio of lead to uranium in the mineral can be used to determine its age; the method relies on two separate decay chains, the uranium series from 238U to 206Pb, with a half-life of 4.47 billion years and the actinium series from 235U to 207Pb, with a half-life of 710 million years. The above uranium to lead decay routes occur via a series of alpha decays, in which 238U with daughter nuclides undergo total eight alpha and six beta decays whereas 235U with daughters only experience seven alpha and four beta decays.
The existence of two'parallel' uranium–lead decay routes leads to multiple dating techniques within the overall U–Pb system. The term U–Pb dating implies the coupled use of both decay schemes in the'concordia diagram'. However, use of a single decay scheme leads to the U–Pb isochron dating method, analogous to the rubidium–strontium dating method. Ages can be determined from the U–Pb system by analysis of Pb isotope ratios alone; this is termed the lead–lead dating method. Clair Cameron Patterson, an American geochemist who pioneered studies of uranium–lead radiometric dating methods, is famous for having used it to obtain one of the earliest estimates of the age of the Earth. Although zircon is most used, other minerals such as monazite and baddeleyite can be used. Where crystals such as zircon with uranium and thorium inclusions do not occur, a better, more inclusive, model of the data must be applied. Uranium-lead dating techniques have been applied to other minerals such as calcite/aragonite and other carbonate minerals.
These types of minerals produce lower precision ages than igneous and metamorphic minerals traditionally used for age dating, but are more common in the geologic record. During the alpha decay steps, the zircon crystal experiences radiation damage, associated with each alpha decay; this damage is most concentrated around the parent isotope, expelling the daughter isotope from its original position in the zircon lattice. In areas with a high concentration of the parent isotope, damage to the crystal lattice is quite extensive, will interconnect to form a network of radiation damaged areas. Fission tracks and micro-cracks within the crystal will further extend this radiation damage network; these fission tracks act as conduits deep within the crystal, thereby providing a method of transport to facilitate the leaching of lead isotopes from the zircon crystal. Under conditions where no lead loss or gain from the outside environment has occurred, the age of the zircon can be calculated by assuming exponential decay of Uranium.
That is N N o w = N. N O r i g is the number of uranium atoms - equal to the sum of uranium and lead atoms U + P b measured now. Λ = λ U is the decay rate of Uranium. T is the age of the zircon; this gives U = e − λ U t, which can be written as P b U = e λ U t − 1. The more used decay chains of Uranium and Lead gives the following equations: These are said to yield concordant ages, it is these concordant ages, plotted over a series of time intervals, that result in the concordant line. Loss of lead from the sample will result in a discrepancy in the ages determined by each decay scheme; this effect is referred to as discordance and is demonstrated in Figure 1. If a series of zircon samples has lost different amounts of lead, the samples generate a discordant line; the upper intercept of the concordia and the discordia line will reflect the original age of formation, while the lower intercept will reflect the age of the event that led to open system behavior and therefore the lead loss. Undamaged zircon retains the lead generated by radioactive decay of uranium and thorium until ver
Speleothems known as cave formations, are secondary mineral deposits formed in a cave. Speleothems form in limestone or dolostone solutional caves; the term "speleothem" as first introduced by Moore, is derived from the Greek words spēlaion "cave" + théma "deposit". The definition of "speleothem" in most publications excludes secondary mineral deposits in mines, tunnels and on man-made structures. Hill and Forti more concisely defined "secondary minerals". 319 variations of cave mineral deposits have been identified. The vast majority of speleothems are calcareous, composed of calcium carbonate in the form of calcite or aragonite, or calcium sulfate in the form of gypsum. Calcareous speleothems form via carbonate dissolution reactions. Rainwater in the soil zone reacts with soil CO2 to create weakly acidic water via the reaction: H2O + CO2 → H2CO3As the lower pH water travels through the calcium carbonate bedrock from the surface to the cave ceiling, it dissolves the bedrock via the reaction: CaCO3 + H2CO3 → Ca2+ + 2 HCO3−When the solution reaches a cave, degassing due to lower cave pCO2 drives precipitation of CaCO3: Ca2+ + 2 HCO3− → CaCO3 + H2O + CO2Over time the accumulation of these precipitates form stalagmites and flowstones, which compose the major categories of speleothems.
Calthemites which occur on concrete structures, are created by different chemistry to speleothems. Speleothems take various forms, depending on whether the water drips, condenses, flows, or ponds. Many speleothems are named for their resemblance to natural objects. Types of speleothems include: Dripstone is calcium carbonate in the form of stalactites or stalagmites Stalactites are pointed pendants hanging from the cave ceiling, from which they grow Soda straws are thin but long stalactites having an elongated cylindrical shape rather than the usual more conical shape of stalactites Helictites are stalactites that have a central canal with twig-like or spiral projections that appear to defy gravity Include forms known as ribbon helictites, rods, hands, curly-fries, "clumps of worms" Chandeliers are complex clusters of ceiling decorations Ribbon stalactites, or "ribbons", are shaped accordingly Stalagmites are the "ground-up" counterparts of stalactites blunt mounds Broomstick stalagmites are tall and spindly Totem pole stalagmites are tall and shaped like their namesakes Fried egg stalagmites are small wider than they are tall Columns result when stalactites and stalagmites meet or when stalactites reach the floor of the cave Flowstone is sheet like and found on cave floors and walls Draperies or curtains are thin, wavy sheets of calcite hanging downward Bacon is a drapery with variously colored bands within the sheet Rimstone dams, or gours, occur at stream ripples and form barriers that may contain water Stone waterfall formations simulate frozen cascades Cave crystals Dogtooth spar are large calcite crystals found near seasonal pools Frostwork is needle-like growths of calcite or aragonite Moonmilk is white and cheese-like Anthodites are flower-like clusters of aragonite crystals Cryogenic calcite crystals are loose grains of calcite found on the floors of caves, are formed by segregation of solutes during the freezing of water.
Speleogens are formations within caves that are created by the removal of bedrock, rather than as secondary deposits. These include: Pillars Scallops Boneyard Boxwork Others Cave popcorn known as "coralloids" or "cave coral", are small, knobby clusters of calcite Cave pearls are the result of water dripping from high above, causing small "seed" crystals to turn over so that they form into near-perfect spheres of calcium carbonate Snottites are colonies of predominantly sulfur oxidizing bacteria and have the consistency of "snot", or mucus Calcite rafts are thin accumulations of calcite that appear on the surface of cave poolsSpeleothems made of sulfates, mirabilite or opal occur in some lava tubes. Although sometimes similar in appearance to speleothems in caves formed by dissolution, lava stalactites are formed by the cooling of residual lava within the lava tube. Speleothems formed from salt and other minerals are known. Speleothems made of pure calcium carbonate are a translucent white color, but speleothems are colored by chemicals such as iron oxide, copper or manganese oxide, or may be brown because of mud and silt particulate inclusions.
Many factors impact the shape and color of speleothem formations including the rate and direction of water seepage, the amount of acid in the water, the temperature and humidity content of a cave, air currents, the above ground climate, the amount of annual rainfall and the density of the plant cover. Most cave chemistry revolves around calcium carbonate, the primary mineral in limestone and dolomite, it is a soluble mineral whose solubility increases with the introduction of carbon dioxide. It is paradoxical in that its solubility decreases as the temperature increases, unlike the vast majority of dissolved solids; this decrease is due to interactions with the carbon dioxide, whose solubility is diminished by elevated temperatures. Most other solution caves that are not composed of limestone or dolostone are composed of gypsum, the solubility of, positively c
Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the'precipitate'; the chemical that causes the solid to form is called the'precipitant'. Without sufficient force of gravity to bring the solid particles together, the precipitate remains in suspension. After sedimentation when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a'pellet'. Precipitation can be used as a medium; the precipitate-free liquid remaining above the solid is called the'supernate' or'supernatant'. Powders derived from precipitation have historically been known as'flowers'; when the solid appears in the form of cellulose fibers which have been through chemical processing, the process is referred to as regeneration. Sometimes the formation of a precipitate indicates the occurrence of a chemical reaction. If silver nitrate solution is poured into a solution of sodium chloride, a chemical reaction occurs forming a white precipitate of silver chloride.
When potassium iodide solution reacts with lead nitrate solution, a yellow precipitate of lead iodide is formed. Precipitation may occur. Precipitation may occur from a supersaturated solution. In solids, precipitation occurs if the concentration of one solid is above the solubility limit in the host solid, due to e.g. rapid quenching or ion implantation, the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is used to synthesize nanoclusters. An important stage of the precipitation process is the onset of nucleation; the creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative surface energy of the solid and the solution. If this energy is not available, no suitable nucleation surface is available, supersaturation occurs. Precipitation reactions can be used for making pigments, removing salts from water in water treatment, in classical qualitative inorganic analysis.
Precipitation is useful to isolate the products of a reaction during workup. Ideally, the product of the reaction is insoluble in the reaction solvent. Thus, it precipitates. An example of this would be the synthesis of porphyrins in refluxing propionic acid. By cooling the reaction mixture to room temperature, crystals of the porphyrin precipitate, are collected by filtration: Precipitation may occur when an antisolvent is added, drastically reducing the solubility of the desired product. Thereafter, the precipitate may be separated by filtration, decanting, or centrifugation. An example would be the synthesis of chromic tetraphenylporphyrin chloride: water is added to the DMF reaction solution, the product precipitates. Precipitation is useful in purifying products: crude bmim-Cl is taken up in acetonitrile, dropped into ethyl acetate, where it precipitates. Another important application of an antisolvent is in ethanol precipitation of DNA. In metallurgy, precipitation from a solid solution is a useful way to strengthen alloys.
An example of a precipitation reaction: Aqueous silver nitrate is added to a solution containing potassium chloride, the precipitation of a white solid, silver chloride, is observed. AgNO 3 + KCl ⟶ AgCl ↓ + KNO 3 The silver chloride has formed a solid, observed as a precipitate; this reaction can be written emphasizing the dissociated ions in a combined solution. This is known as the ionic equation. Ag + + NO 3 − + K + + Cl − ⟶ AgCl ↓ + K + + NO 3 − A final way to represent a precipitate reaction is known as a net ionic reaction. Many compounds containing metal ions produce precipitates with distinctive colors; the following are typical colors for various metals. However, many of these compounds can produce colors different from those listed. Other compounds form white precipitates. Precipitate formation is useful in the detection of the type of cation in a salt. To do this, an alkali first reacts with the unknown salt to produce a precipitate, the hydroxide of the unknown salt. To identify the cation, the color of the precipitate and its solubility in excess are noted.
Similar processes are used in sequence – for example, a barium nitrate solution will react with sulfate ions to form a solid barium sulfate precipitate, indicating that it is that sulfate ions are present. Digestion, or precipitate ageing, happens when a freshly formed precipitate is left at a higher temperature, in the solution from which it precipitates, it results in bigger particles. The physico-chemical process underlying digestion is called Ostwald ripening. Coprecipitation Salting in Salting out Effervescence Zumdahl, Steven S.. Chemical Principles. New York: Houghton Mifflin. ISBN 0-618-37206-7. Precipitation reactions of certain cations Digestion Instruments A Thesis on pattern formation in precipitation reactions
Digital object identifier
In computing, a Digital Object Identifier or DOI is a persistent identifier or handle used to identify objects uniquely, standardized by the International Organization for Standardization. An implementation of the Handle System, DOIs are in wide use to identify academic and government information, such as journal articles, research reports and data sets, official publications though they have been used to identify other types of information resources, such as commercial videos. A DOI aims to be "resolvable" to some form of access to the information object to which the DOI refers; this is achieved by binding the DOI to metadata about the object, such as a URL, indicating where the object can be found. Thus, by being actionable and interoperable, a DOI differs from identifiers such as ISBNs and ISRCs which aim only to identify their referents uniquely; the DOI system uses the indecs Content Model for representing metadata. The DOI for a document remains fixed over the lifetime of the document, whereas its location and other metadata may change.
Referring to an online document by its DOI is supposed to provide a more stable link than using its URL. But every time a URL changes, the publisher has to update the metadata for the DOI to link to the new URL, it is the publisher's responsibility to update the DOI database. If they fail to do so, the DOI resolves to a dead link leaving the DOI useless; the developer and administrator of the DOI system is the International DOI Foundation, which introduced it in 2000. Organizations that meet the contractual obligations of the DOI system and are willing to pay to become a member of the system can assign DOIs; the DOI system is implemented through a federation of registration agencies coordinated by the IDF. By late April 2011 more than 50 million DOI names had been assigned by some 4,000 organizations, by April 2013 this number had grown to 85 million DOI names assigned through 9,500 organizations. A DOI is a type of Handle System handle, which takes the form of a character string divided into two parts, a prefix and a suffix, separated by a slash.
Prefix/suffixThe prefix identifies the registrant of the identifier, the suffix is chosen by the registrant and identifies the specific object associated with that DOI. Most legal Unicode characters are allowed in these strings, which are interpreted in a case-insensitive manner; the prefix takes the form 10. NNNN, where NNNN is a series of at least 4 numbers greater than or equal to 1000, whose limit depends only on the total number of registrants; the prefix may be further subdivided with periods, like 10. NNNN. N. For example, in the DOI name 10.1000/182, the prefix is 10.1000 and the suffix is 182. The "10." Part of the prefix distinguishes the handle as part of the DOI namespace, as opposed to some other Handle System namespace, the characters 1000 in the prefix identify the registrant. 182 is item ID, identifying a single object. DOI names can identify creative works in both electronic and physical forms and abstract works such as licenses, parties to a transaction, etc; the names can refer to objects at varying levels of detail: thus DOI names can identify a journal, an individual issue of a journal, an individual article in the journal, or a single table in that article.
The choice of level of detail is left to the assigner, but in the DOI system it must be declared as part of the metadata, associated with a DOI name, using a data dictionary based on the indecs Content Model. The official DOI Handbook explicitly states that DOIs should display on screens and in print in the format doi:10.1000/182. Contrary to the DOI Handbook, CrossRef, a major DOI registration agency, recommends displaying a URL instead of the specified format This URL is persistent, so it is a PURL — providing the location of an HTTP proxy server which will redirect web accesses to the correct online location of the linked item; the CrossRef recommendation is based on the assumption that the DOI is being displayed without being hyperlinked to its appropriate URL – the argument being that without the hyperlink it is not as easy to copy-and-paste the full URL to bring up the page for the DOI, thus the entire URL should be displayed, allowing people viewing the page containing the DOI to copy-and-paste the URL, by hand, into a new window/tab in their browser in order to go to the appropriate page for the document the DOI represents.
Major applications of the DOI system include: scholarly materials through CrossRef, a consortium of around 3,000 publishers. Research datasets through DataCite, a consortium of leading research libraries, technical information providers, scientific data centers. Permanent global identifiers for commercial video content through the Entertainment ID Registry known as EIDR. In the Organisation for Economic Co-operation and Development's publication service OECD iLibrary, each table or graph
University of Dublin
The University of Dublin, corporately designated the Chancellor and Masters of the University of Dublin, is a university located in Dublin, Ireland. It is the degree awarding body for Trinity College Dublin, it was founded in 1592 when Queen Elizabeth I issued a charter for Trinity College as "the mother of a university", thereby making it Ireland's oldest operating university. It was modelled after the collegiate universities of Oxford and of Cambridge, but unlike these other ancient universities, only one college was established; the University of Dublin is one of the seven ancient universities of Ireland. It is a member of the Irish Universities Association, Universities Ireland, the Coimbra Group; the University of Dublin was modelled on the University of Oxford and the University of Cambridge as a collegiate university, Trinity College being named by the Queen as the mater universitatis. The founding Charter conferred a general power on the College to make provision for university functions to be carried out.
So, for example, the Charter while naming the first Provost of the College, the first fellows and the first scholars, in addition named William Cecil, 1st Baron Burghley to be the first Chancellor of the University. No other college has been established, Trinity remains the sole constituent college of the university; the project of establishing another college within the University was considered on at least two occasions, but the required finance or endowment was never available. The most recent authoritative statement of the position is in the Universities Act, 1997. In the section relating to interpretation it specifies that:- "3.— In this Act, unless the context otherwise requires— "Trinity College” means the College of the Holy and Undivided Trinity of Queen Elizabeth near Dublin established by charter dated the 3rd day of March, 1592, shall be held to include the University of Dublin save where the context otherwise requires in accordance with the charters and letters patent relating to Trinity College.
Subsequently, in a remarkable High Court case of 1898, the Provost and Scholars of Trinity were the claimants and the Chancellor and Masters of the University of Dublin were among the defendants, the court held that Trinity College and the University of Dublin "are one body". The judge noted pointedly that "he advisers of Queen Victoria knew how to incorporate a University when they meant to do so" and that the letters patent dealt with "not the incorporation of the University of Dublin but of its Senate merely". Notwithstanding, the statutes of the university and the college grant the university separate corporate legal rights to own property, borrow money, employ staff, enable it to sue and be sued as occurred in the case referred to above. To date the other rights have not been exercised. Current Officers of the University are either unpaid and purely honorary, or have duties relating to the college for which they are paid, but by the College; some of the legal definitions and differences between college and university were discussed in the reform of the University and College in The Charters and Letters Patent Amendment Bill, which became law, but many of the College contributions to this were unclear or not comprehensive because it concerned an internal dispute within College as to outside interference and as misconduct by College Authorities in overseeing voting which led to a visitors enquiry which in turn found problems with the voting procedures and ordered a repeat ballot.
Further contributions on the relationship between College and University can be found in submissions to the Oireachtas on reform of Seanad Éireann, the upper house of the Irish Oireachtas, since the University elects members to that body), in particular the verbal submission of the Provost. Traditionally, sport clubs use the name "University", rather than "College"; the university is governed by the university senate, chaired by the chancellor or their pro-chancellor. While the Senate was formally constituted by the Letters Patent of 1857 as a body corporate under the name and title of "The Chancellor and Masters of the University of Dublin", it had existed since soon after the foundation of Trinity College being brought into being by the enabling powers contained in the founding Charter; the Letters Patent had the effect of converting a preexisting non-incorporated body relying on custom and precedent to establish its authority into a corporate body and explicitly established in law. The Letters Patent empowered the university senate by stating:- "It shall be and shall continue to be a body corporate with a common seal, shall have power under the said seal to do all such acts as may be lawful for it to do in conformity with the laws and statutes of the State and with the Charters and Statutes of the College."
The Letters Patent defined the composition of the Senate:- " It shall consist of the Chancellor, the Pro-Chancellors, such Doctors and Masters of the University as s
Isotopes are variants of a particular chemical element which differ in neutron number, in nucleon number. All isotopes of a given element have the same number of protons but different numbers of neutrons in each atom; the term isotope is formed from the Greek roots isos and topos, meaning "the same place". It was coined by a Scottish doctor and writer Margaret Todd in 1913 in a suggestion to chemist Frederick Soddy; the number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral atom. Each atomic number identifies a specific element, but not the isotope; the number of nucleons in the nucleus is the atom's mass number, each isotope of a given element has a different mass number. For example, carbon-12, carbon-13, carbon-14 are three isotopes of the element carbon with mass numbers 12, 13, 14, respectively; the atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7, 8 respectively.
A nuclide is a species of an atom with a specific number of protons and neutrons in the nucleus, for example carbon-13 with 6 protons and 7 neutrons. The nuclide concept emphasizes nuclear properties over chemical properties, whereas the isotope concept emphasizes chemical over nuclear; the neutron number has large effects on nuclear properties, but its effect on chemical properties is negligible for most elements. In the case of the lightest elements where the ratio of neutron number to atomic number varies the most between isotopes it has only a small effect, although it does matter in some circumstances; the term isotopes is intended to imply comparison, for example: the nuclides 126C, 136C, 146C are isotopes, but 4018Ar, 4019K, 4020Ca are isobars. However, because isotope is the older term, it is better known than nuclide, is still sometimes used in contexts where nuclide might be more appropriate, such as nuclear technology and nuclear medicine. An isotope and/or nuclide is specified by the name of the particular element followed by a hyphen and the mass number.
When a chemical symbol is used, e.g. "C" for carbon, standard notation is to indicate the mass number with a superscript at the upper left of the chemical symbol and to indicate the atomic number with a subscript at the lower left. Because the atomic number is given by the element symbol, it is common to state only the mass number in the superscript and leave out the atomic number subscript; the letter m is sometimes appended after the mass number to indicate a nuclear isomer, a metastable or energetically-excited nuclear state, for example 180m73Ta. The common pronunciation of the AZE notation is different from how it is written: 42He is pronounced as helium-four instead of four-two-helium, 23592U as uranium two-thirty-five or uranium-two-three-five instead of 235-92-uranium; some isotopes/nuclides are radioactive, are therefore referred to as radioisotopes or radionuclides, whereas others have never been observed to decay radioactively and are referred to as stable isotopes or stable nuclides.
For example, 14C is a radioactive form of carbon, whereas 12C and 13C are stable isotopes. There are about 339 occurring nuclides on Earth, of which 286 are primordial nuclides, meaning that they have existed since the Solar System's formation. Primordial nuclides include 32 nuclides with long half-lives and 253 that are formally considered as "stable nuclides", because they have not been observed to decay. In most cases, for obvious reasons, if an element has stable isotopes, those isotopes predominate in the elemental abundance found on Earth and in the Solar System. However, in the cases of three elements the most abundant isotope found in nature is one long-lived radioisotope of the element, despite these elements having one or more stable isotopes. Theory predicts that many "stable" isotopes/nuclides are radioactive, with long half-lives; some stable nuclides are in theory energetically susceptible to other known forms of decay, such as alpha decay or double beta decay, but no decay products have yet been observed, so these isotopes are said to be "observationally stable".
The predicted half-lives for these nuclides greatly exceed the estimated age of the universe, in fact there are 27 known radionuclides with half-lives longer than the age of the universe. Adding in the radioactive nuclides that have been created artificially, there are 3,339 known nuclides; these include 905 nuclides that are either stable or have half-lives