Specific activity

Specific activity is the activity per quantity of a radionuclide and is a physical property of that radionuclide.[1][2]

Activity is a quantity related to radioactivity. The SI unit of activity is the becquerel (Bq), equal to one reciprocal second.[3] The becquerel is defined as the number of radioactive transformations per second that occur in a particular radionuclide. Its related non-SI unit equivalent is the Curie (Ci) which is 3.7×1010 transformations per second.

Since the probability of radioactive decay for a given radionuclide is a fixed physical quantity (with some slight exceptions, see changing decay rates), the number of decays that occur in a given time of a specific number of atoms of that radionuclide is also a fixed physical quantity (if there are large enough numbers of atoms to ignore statistical fluctuations).

Thus, specific activity is defined as the activity per quantity of atoms of a particular radionuclide. It is usually given in units of Bq/g, but another commonly used unit of activity is the curie (Ci) allowing the definition of specific activity in Ci/g.

Specific activity
Common symbols
a
SI unitbecquerel
Other units
rutherford, curie
In SI base unitss-1

Formulation

Radioactivity is expressed as the decay rate of a particular radionuclide with decay constant λ and the number of atoms N:

Mass of the radionuclide is given by

where m is mass number of the radionuclide and NA is the Avogadro constant.

Specific radioactivity a is defined as radioactivity per unit mass of the radionuclide:

In addition, decay constant λ is related to the half-life T1/2 by the following equation:

Thus, specific radioactivity can also be described by

This equation is simplified by

When the unit of half-life converts a year

For example, specific radioactivity of radium-226 with a half-life of 1600 years is obtained by

This value derived from radium 226 was defined as unit of radioactivity known as Curie (Ci).

Half-life

Experimentally measured specific activity can be used to calculate the half-life of a radionuclide.

First, radioactivity is expressed as the decay rate of a particular radionuclide with decay constant λ and the number of atoms N:

The integral solution is described by exponential decay

where N0 is the initial quantity of atoms at time t = 0.

Half-life (T1/2) is defined as the length of time for half of a given quantity of radioactive atoms to undergo radioactive decay:

Taking the natural log of both sides, the half-life is given by

Where decay constant λ is related to specific radioactivity a by the following equation:

Therefore, the half-life can also be described by

Example: half-life of Rb-87

One gram of rubidium-87 and a radioactivity count rate that, after taking solid angle effects into account, is consistent with a decay rate of 3200 decays per second corresponds to a specific activity of 3.2×106 Bq/kg. Rubidium's atomic weight is 87, so one gram is one 87th of a mole. Plugging in the numbers:

Applications

The specific activity of radionuclides is particularly relevant when it comes to select them for production for therapeutic pharmaceuticals, as well as for immunoassays or other diagnostic procedures, or assessing radioactivity in certain environments, among several other biomedical applications.[4][5][6][7][8][9]

References

  1. ^ Breeman, Wouter A. P.; Jong, Marion; Visser, Theo J.; Erion, Jack L.; Krenning, Eric P. (2003). "Optimising conditions for radiolabelling of DOTA-peptides with 90Y, 111In and 177Lu at high specific activities". European Journal of Nuclear Medicine and Molecular Imaging. 30 (6): 917–920. doi:10.1007/s00259-003-1142-0. ISSN 1619-7070. PMID 12677301.
  2. ^ de Goeij, J. J. M.; Bonardi, M. L. (2005). "How do we define the concepts specific activity, radioactive concentration, carrier, carrier-free and no-carrier-added?". Journal of Radioanalytical and Nuclear Chemistry. 263 (1): 13–18. doi:10.1007/s10967-005-0004-6. ISSN 0236-5731.
  3. ^ "SI units for ionizing radiation: becquerel". Resolutions of the 15th CGPM (Resolution 8). 1975. Retrieved 3 July 2015.
  4. ^ Duursma, E. K. "Specific activity of radionuclides sorbed by marine sediments in relation to the stable element composition." Radioactive contamination of the marine environment (1973): 57-71.
  5. ^ Wessels, Barry W. (1984). "Radionuclide selection and model absorbed dose calculations for radiolabeled tumor associated antibodies". Medical Physics. 11 (5): 638–645. Bibcode:1984MedPh..11..638W. doi:10.1118/1.595559. ISSN 0094-2405. PMID 6503879.
  6. ^ I. Weeks, I. Beheshti, F. McCapra, A. K. Campbell & J. S. Woodhead (August 1983). "Acridinium esters as high-specific-activity labels in immunoassay". Clinical Chemistry. 29 (8): 1474–1479. PMID 6191885.CS1 maint: Multiple names: authors list (link)
  7. ^ Neves, M; Kling, A; Lambrecht, R.M (2002). "Radionuclide production for therapeutic radiopharmaceuticals". Applied Radiation and Isotopes. 57 (5): 657–664. doi:10.1016/S0969-8043(02)00180-X. ISSN 0969-8043.
  8. ^ Mausner, Leonard F. (1993). "Selection of radionuclides for radioimmunotherapy". Medical Physics. 20 (2): 503–509. Bibcode:1993MedPh..20..503M. doi:10.1118/1.597045. ISSN 0094-2405. PMID 8492758.
  9. ^ Murray, A. S.; Marten, R.; Johnston, A.; Martin, P. (1987). "Analysis for naturally occuring [sic] radionuclides at environmental concentrations by gamma spectrometry". Journal of Radioanalytical and Nuclear Chemistry Articles. 115 (2): 263–288. doi:10.1007/BF02037443. ISSN 0236-5731.

Further reading

Advanced Test Reactor

The Advanced Test Reactor (ATR) is a research reactor at the Idaho National Laboratory, located east of Arco, Idaho. This reactor was designed and is used to test nuclear fuels and materials to be used in power plants, naval propulsion, research and advanced reactors. It can operate at a maximum power of 250 MW thermal power and has a "Four Leaf Clover" core design (similar to the Camunian rose) that allows for a variety of testing locations. The unique design allows for different neutron flux (number of neutrons impacting one square centimeter every second) conditions in various locations. Six of the test locations allow an experiment to be isolated from the primary cooling system, providing its own environment for temperature, pressure, flow and chemistry, replicating the physical environment while accelerating the nuclear conditions.

The ATR is a pressurized light water reactor (LWR), using water as both coolant and moderator. The core is surrounded by a beryllium neutron reflector to concentrate neutrons on experiments, and houses multiple experiment positions as well. It operates at low temperature and pressure 71°C (160°F) and up to 2.69 MPa water pressure. The ATR reactor vessel is solid stainless steel, 35 feet tall by 12 feet across. The core is approximately 4 feet tall by 4 feet across.

In addition to its role in nuclear fuels and materials irradiation, the ATR is the United States' only domestic source of high specific activity (HSA) cobalt-60 (60Co) for medical applications. HSA 60Co is used primarily in gamma knife treatment of brain cancer. Other medical and industrial isotopes have also been produced, and could be again, including plutonium-238 (238Pu), which is useful for powering spacecraft.

Anti-apolipoprotein antibodies

In autoimmune disease, anti-apolipoprotein H (AAHA) antibodies, also called anti-β2 glycoprotein I antibodies, comprise a subset of anti-cardiolipin antibodies and lupus anticoagulant. These antibodies are involved in sclerosis and are strongly associated with thrombotic forms of lupus. As a result AAHA are strongly implicated in autoimmune deep vein thrombosis.

Also, it was proposed that AAHA is responsible for lupus anticoagulant. However, antiphospholipid antibodies bind phospholipids at sites similar to sites bound by anti-coagulants such as PAP1 sites and augment anti-coagulation activity.

This contrasts with the major, specific, activity of AAHA, defining a subset of anti-cardiolipin antibodies that specifically interacts with Apo-H. AHAA only inhibits the anti-coagulation activity in the presence of Apo-H and the AAHA component of ACLA correlates with a history of frequent thrombosis. This can be contrasted with lupus anticoagulant which inhibits agglutination in the presence of thrombin. A subset of AHAA appear to mimic the activity of lupus anticoagulant and increase Apo-H binding to phospholipids. These two activities can be differentiated by the binding to Apo-H domains, whereas binding to the 5th domain promotes that anti-coagulant activity binding to the more N-terminal domains promotes lupus anticoagulant-like activities.

AAHA interferes with factor Xa inhibition by Apo-H increasing factor Xa generation. However, like Apo-H the Lupus anticoagulant inhibits factor Xa generation.AAHA also inhibited the autoactivation of factor XII while at high AAHA concentrations, factor XIIa activation increases at levels comparable to Apo-H that cause inhibition of factor XIIa activation. A synchronized inhibition of factor XII autoactivation by Apo-H and AHAA has been suggested.

Colloquialism

In linguistics, colloquialism is a term referring to the style of language used for casual communication. It is the most used functional style of speech, the idiom normally applied in conversation and other informal contexts.

A specific instance of such language is termed a colloquialism. The most common term used in dictionaries to label such an expression is colloquial.

Copper-64

Copper-64 (64Cu) is a positron emitting isotope of copper, with applications for molecular radiotherapy and positron emission tomography.

Curie

The curie (symbol Ci) is a non-SI unit of radioactivity originally defined in 1910. According to a notice in Nature at the time, it was named in honour of Pierre Curie, but was considered at least by some to be in honour of Marie Curie as well.It was originally defined as "the quantity or mass of radium emanation in equilibrium with one gram of radium (element)" but is currently defined as 1 Ci = 3.7×1010 decays per second after more accurate measurements of the activity of 226Ra (which has a specific activity of 3.66×1010 Bq/g).

In 1975 the General Conference on Weights and Measures gave the becquerel (Bq), defined as one nuclear decay per second, official status as the SI unit of activity.

Therefore:

1 Ci = 3.7×1010 Bq = 37 GBqand

1 Bq ≅ 2.703×10−11 Ci ≅ 27 pCiWhile its continued use is discouraged by National Institute of Standards and Technology (NIST) and other bodies, the curie is still widely used throughout the government, industry and medicine in the United States and in other countries.

At the 1910 meeting which originally defined the curie, it was proposed to make it equivalent to 10 nanograms of radium (a practical amount). But Marie Curie, after initially accepting this, changed her mind and insisted on one gram of radium. According to Bertram Boltwood, Marie Curie thought that 'the use of the name "curie" for so infinitesimally small [a] quantity of anything was altogether inappropriate.'The power in milliwatts emitted by one curie of radiation can be calculated by taking the number of MeV for the radiation times approximately 5.93.

A radiotherapy machine may have roughly 1000 Ci of a radioisotope such as caesium-137 or cobalt-60. This quantity of radioactivity can produce serious health effects with only a few minutes of close-range, unshielded exposure.

Ingesting even a millicurie is usually fatal (unless it is a very short-lived isotope). For example, the LD-50 for ingested polonium-210 is 240 μCi, about 53.5 nanograms.

The typical human body contains roughly 0.1 μCi (14 mg) of naturally occurring potassium-40. A human body containing 16 kg of carbon (see Composition of the human body) would also have about 24 nanograms or 0.1 μCi of carbon-14. Together, these would result in a total of approximately 0.2 μCi or 7400 decays per second inside the person's body (mostly from beta decay but some from gamma decay).

Enzyme assay

Enzyme assays are laboratory methods for measuring enzymatic activity. They are vital for the study of enzyme kinetics and enzyme inhibition.

Ferruginol

Ferruginol is a natural phenol and a meroterpene (a chemical compound containing a terpenoid substructure) that has been isolated from the needles of the redwood Sequoia sempervirens. The terpenoid part is a diterpene of the abietane chemical class.

Research published in 2005 found that this and other compound of the class from Sequoia have anti-tumor properties, and showed in vitro human colon, breast, and lung tumor reduction and reduction in oncogene transformed cells as well. Specific activity of tumor growth inhibition (GI) is 2-5 micrograms/milliliter.Ferruginol has also been found to have antibacterial activity. Gastroprotective effects of ferruginol have also been noted.

Financial intelligence

Financial intelligence (FININT) is the gathering of information about the financial affairs of entities of interest, to understand their nature and capabilities, and predict their intentions. Generally the term applies in the context of law enforcement and related activities.

One of the main purposes of financial intelligence is to identify financial transactions that may involve tax evasion, money laundering or some other criminal activity. FININT may also be involved in identifying financing of criminal and terrorist organisations.

Financial intelligence can be broken down into two main areas, collection and analysis. Collection is normally done by a government agency, known as a financial intelligence organisation or Financial Intelligence Unit (FIU). The agency will collect raw transactional information and Suspicious activity reports (SAR) usually provided by banks and other entities as part of regulatory requirements. Data may be shared with other countries through intergovernmental networks.

Analysis, may consist of scrutinizing a large volume of transactional data using data mining or data-matching techniques to identify persons potentially engaged in a particular activity. SARs can also be scrutinized and linked with other data to try and identify specific activity.

Imiglucerase

Imiglucerase is a medication used in the treatment of Gaucher's disease.It is a recombinant DNA-produced analogue of the human enzyme β-glucocerebrosidase.

Cerezyme is a freeze-dried medicine containing imiglucerase, manufactured by Genzyme Corporation. It is given

intravenously after reconstitution as a treatment for Type 1 and Type 3 Gaucher's disease. It is available in formulations containing 200 or 400 units per vial. The specific activity of highly purified human enzyme is 890,000 units/mg. A typical dose is 2.5U/kg every two weeks, up to a maximum of 60 U/kg once every two weeks, and safety has been established from ages 2 and up. It is one of the most expensive drugs sold, with an annual cost to U.S. patients of $200,000. Imiglucerase has been granted orphan drug status in the United States, Australia, and Japan.Cerezyme was one of the drugs manufactured at Genzyme's Allston, Massachusetts plant, for which production was disrupted in 2009 after contamination with Vesivirus 2117.

Mycoplasma pneumonia

Mycoplasma pneumonia (also known as "walking pneumonia" because it can spread bilaterally (“walk”) from one lung to the other) is a form of bacterial pneumonia caused by the bacterial species Mycoplasma pneumoniae.

Ontario Arts Council

The Ontario Arts Council (OAC) is a publicly funded Canadian organization in the province of Ontario whose purpose is to promote and assist the development of the arts for the enjoyment and benefit of all Ontarians. Based in Toronto, OAC was founded in 1963 by Ontario's Premier at the time, John Robarts.OAC plays a vital role in fostering the stability and growth of Ontario's arts community. An arm's-length agency of the Ministry of Culture, OAC offers more than fifty funding programs for Ontario-based artists and arts organizations. Grants provide assistance for a specific activity, support for a period of time, or for ongoing operations. OAC administers the Premier's Awards for Excellence in the Arts, offers additional prizes as well as scholarships from private funds, and further supports Ontario's arts community by conducting research and statistical analyses of the arts and culture. OAC staff manage granting programs, while a 12-member volunteer board of directors oversees the fulfilment of the organization's mandate. The board of directors is appointed by the Government of Ontario for a three-year term (and may be re-appointed for one additional term).

OAC provides grants in three ways:

Artistic discipline: crafts, dance, theatre, literature; music; visual and media arts.

Artistic or other activity: arts education; community arts; touring; residencies; and capacity building/professional development.

Cultural practice: Aboriginal Arts and Franco-Ontarian Arts.

PZM21

PZM21 is an experimental opioid analgesic drug that is being researched for the treatment of pain.

It is claimed to be a functionally selective μ-opioid receptor agonist which produces μ-opioid receptor mediated G protein signaling, with potency and efficacy similar to morphine, but with less β-arrestin 2 recruitment. In tests on mice, PZM21 was slightly less potent than morphine or TRV130 as an analgesic, but also had significantly reduced adverse effects, with less constipation than morphine, and very little respiratory depression, even at high doses. This research was described as a compelling example of how modern high-throughput screening techniques can be used to discover new chemotypes with specific activity profiles, even at targets such as the μ-opioid receptor which have already been thoroughly investigated. More recent research has suggested however that at higher doses, PZM21 is capable of producing classic opioid side effects such as respiratory depression and development of tolerance and may have only limited functional selectivity.

Performance metric

A performance metric measures an organization's behavior, activities, and performance. It assesses how well workers are doing their respective tasks and how companies are accomplishing their objectives. It provides hard data and gives off outcomes that appraise clearly defined quantities within a range that facilitates improvement and upgrading. Ideally, good performance metrics form the basis for better achieving a small business' overall goals.It should support a range of stakeholder needs from customers, shareholders to employees. While traditionally, metrics are finance-based and are inwardly focusing on the performance of the organization, metrics may also focus on the performance against customer requirements and value.In project management, performance metrics are used to assess the entire well-being of a project and focus its appraisal based on seven criterions:

safety,

time,

cost,

resources,

scope,

quality, and

actions.In call centres, performance metrics help capture internal performance and can include productivity measurements and the quality of service provided by the customer service advisor. These metrics can include: Calls Answered, Calls Abandoned, Average Handle Time and Average Wait Time.Developing performance metrics usually follows a process of:

Establishing critical processes/customer requirements

Identifying specific, quantifiable outputs of work

Establishing targets against which results can be scoredA criticism of performance metrics is that when the value of information is computed using mathematical methods, it shows that even performance metrics professionals choose measures that have little value. This is referred to as the "measurement inversion". For example, metrics seem to emphasize what organizations find immediately measurable—even if those are low value—and tend to ignore high value measurements simply because they seem harder to measure (whether they are or not).

To correct for the measurement inversion other methods, like applied information economics, introduce the "value of information analysis" step in the process so that metrics focus on high-value measures. Organizations where this has been applied find that they define completely different metrics than they otherwise would have and, often, fewer metrics. For projects, the effort to collect a metric has to be weighed against its value as projects are temporary endeavors performed with finite resources.

There are a variety of ways in which organizations may react to results. This may be to trigger specific activity relating to performance (i.e., an improvement plan) or to use the data merely for statistical information. Often closely tied in with outputs, performance metrics should usually encourage improvement, effectiveness and appropriate levels of control.

Performance metrics are often linked in with corporate strategy and are often derived in order to measure performance against a critical success factor.

Radioactivity in the life sciences

Radioactivity is generally used in life sciences for highly sensitive and direct measurements of biological phenomena, and for visualizing the location of biomolecules radiolabelled with a radioisotope.

All atoms exist as stable or unstable isotopes and the latter decay at a given half-life ranging from attoseconds to billions of years; radioisotopes useful to biological and experimental systems have half-lives ranging from minutes to months. In the case of the hydrogen isotope tritium (half-life = 12.3 years) and carbon-14 (half-life = 5,730 years), these isotopes derive their importance from all organic life containing hydrogen and carbon and therefore can be used to study countless living processes, reactions, and phenomena. Most short lived isotopes are produced in cyclotrons, linear particle accelerators, or nuclear reactors and their relatively short half-lives give them high maximum theoretical specific activities which is useful for detection in biological systems.

Radiolabeling is a technique used to track the passage of a molecule that incorporates a radioisotope through a reaction, metabolic pathway, cell, tissue, organism, or biological system. The reactant is 'labeled' by replacing specific atoms by their isotope. Replacing an atom with its own radioisotope is an intrinsic label that does not alter the structure of the molecule. Alternatively, molecules can be radiolabeled by chemical reactions that introduce an atom, moiety, or functional group that contains a radionuclide. For example, radio-iodination of peptides and proteins with biologically useful iodine isotopes is easily done by an oxidation reaction that replaces the hydroxyl group with iodine on tyrosine and histadine residues. Another example is to use chelators such DOTA that can be chemically coupled to a protein; the chelator in turn traps radiometals thus radiolabeling the protein. This has been used for introducing Yttrium-90 onto a monoclonal antibody for therapeutic purposes and for introducing Gallium-68 onto the peptide Octreotide for diagnostic imaging by PET imaging. (See DOTA uses.)

Radiolabeling is not necessary for some applications. For some purposes, soluble ionic salts can be used directly without further modification (e.g., gallium-67, gallium-68, and radioiodine isotopes). These uses rely on the chemical and biological properties of the radioisotope itself, to localize it within the organism or biological system.

Molecular imaging is the biomedical field that employs radiotracers to visualize and quantify biological processes using positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging. Again, a key feature of using radioactivity in life science applications is that it is a quantitative technique, so PET/SPECT not only reveals where a radiolableled molecule is but how much is there.

Radiobiology (also known as radiation biology) is a field of clinical and basic medical sciences that involves the study of the action of radioactivity on biological systems. The controlled action of deleterious radioactivity on living systems is the basis of radiation therapy.

Selenium-79

Selenium-79 is a radioisotope of selenium present in spent nuclear fuel and the wastes resulting from reprocessing this fuel. It is one of only 7 long-lived fission products. Its yield is low (about 0.04%), as it is near the lower end of the mass range for fission products. Its half-life has been variously reported as 650,000 years, 65,000 years, 1.13 million years, 480,000 years, 295,000 years, 377,000 years and most recently with best current precision, 327,000 years.Se-79 decays by emitting a beta particle with no attendant gamma radiation. The low specific activity and relatively low energy of its beta particle have been said to limit the radioactive hazards of this isotope.Performance assessment calculations for the Belgian deep geological repository estimated 79Se may be the major contributor to activity release in terms of becquerels (decays per second), "attributable partly to the uncertainties about its migration behaviour in the Boom Clay and partly to its conversion factor in the biosphere." (p. 169). However, "calculations for the Belgian safety assessments use a half-life of 65 000 years" (p. 177), much less than the currently estimated half-life, and "the migration parameters ... have been estimated very cautiously for 79Se." (p. 179)

Neutron absorption cross sections for 79Se have been estimated at 50 barns for thermal neutrons and 60.9 barns for resonance integral.Se-80 and Se-82 have higher fission yields, about 20 times the yield of Se-79 in the case of U-235, 6 times in the case of Pu-239 or U-233, and 14 times in the case of Pu-241.

Skill

A skill is the ability to carry out a task with determined results often within a given amount of time, energy, or both. Skills can often be divided into domain-general and domain-specific skills. For example, in the domain of work, some general skills would include time management, teamwork and leadership, self-motivation and others, whereas domain-specific skills would be used only for a certain job. Skill usually requires certain environmental stimuli and situations to assess the level of skill being shown and used.

People need a broad range of skills to contribute to a modern economy. A joint ASTD and U.S. Department of Labor study showed that through technology, the workplace is changing, and identified 16 basic skills that employees must have to be able to change with it. Three broad categories of skills are suggested and these are technical, human, and conceptual. The first two can be substituted with hard and soft skills, respectively.

Syncope (medicine)

Syncope, also known as fainting, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. There are sometimes symptoms before the loss of consciousness such as lightheadedness, sweating, pale skin, blurred vision, nausea, vomiting, or feeling warm. Syncope may also be associated with a short episode of muscle twitching. When consciousness and muscle strength are not completely lost, it is called presyncope. It is recommended that presyncope be treated the same as syncope.Causes range from non-serious to potentially fatal. There are three broad categories of causes: heart or blood vessel related, reflex also known as neurally mediated, and orthostatic hypotension. Issues with the heart and blood vessels are the cause in about 10% and typically the most serious while neurally mediated is the most common. Heart related causes may include an abnormal heart rhythm, problems with the heart valves or heart muscle and blockages of blood vessels from a pulmonary embolism or aortic dissection among others. Neurally mediated syncope occurs when blood vessels expand and heart rate decreases inappropriately. This may occur from either a triggering event such as exposure to blood, pain, strong feelings or a specific activity such as urination, vomiting, or coughing. This type of syncope may also occur when an area in the neck known as the carotid sinus is pressed. The third type of syncope is due to a drop in blood pressure from standing up. This is often due to medications that a person is taking but may also be related to dehydration, significant bleeding or infection.A medical history, physical examination, and electrocardiogram (ECG) are the most effective ways to figure out the underlying cause. The ECG is useful to detect an abnormal heart rhythm, poor blood flow to the heart muscle, and other electrical issue such as long QT syndrome and Brugada syndrome. Heart related causes also often have little history of a prodrome. Low blood pressure and a fast heart rate after the event may indicate blood loss or dehydration, while low blood oxygen levels may be seen following the event in those with pulmonary embolism. More specific tests such as implantable loop recorders, tilt table testing or carotid sinus massage may be useful in uncertain cases. Computed tomography (CT) is generally not required unless specific concerns are present. Other causes of similar symptoms that should be considered include seizure, stroke, concussion, low blood oxygen, low blood sugar, drug intoxication and some psychiatric disorders among others. Treatment depends on the underlying cause. Those who are considered at high risk following investigation may be admitted to hospital for further monitoring of the heart.Syncope affects about three to six out of every thousand people each year. It is more common in older people and females. It is the reason for one to three percent of visits to emergency departments and admissions to hospital. Up to half of women over the age of 80 and a third of medical students describe at least one event at some point in their lives. Of those presenting with syncope to an emergency department, about 4% died in the next 30 days. The risk of a poor outcome, however, depends very much on the underlying cause.

Taq polymerase

Taq polymerase is a thermostable DNA polymerase I named after the thermophilic bacterium Thermus aquaticus from which it was originally isolated by Chien et al. in 1976. Its name is often abbreviated to Taq Pol or simply Taq. It is frequently used in the polymerase chain reaction (PCR), a method for greatly amplifying the quantity of short segments of DNA.

T. aquaticus is a bacterium that lives in hot springs and hydrothermal vents, and Taq polymerase was identified as an enzyme able to withstand the protein-denaturing conditions (high temperature) required during PCR. Therefore, it replaced the DNA polymerase from E. coli originally used in PCR.Taq's optimum temperature for activity is 75–80 °C, with a half-life of greater than 2 hours at 92.5 °C, 40 minutes at 95 °C and 9 minutes at 97.5 °C, and can replicate a 1000 base pair strand of DNA in less than 10 seconds at 72 °C. At 75-80 °C, Taq reaches its optimal polymerization rate of about 150 nucleotides per second per enzyme molecule, and any deviations from the optimal temperature range inhibit the extension rate of the enzyme. A single Taq synthesizes about 60 nucleotides per second at 70 °C, 24 nucleotides/sec at 55 °C, 1.5 nucleotides/sec at 37 °C, and 0.25 nucleotides/sec at 22 °C. At temperatures above 90 °C, Taq demonstrates very little or no activity at all, but the enzyme itself does not denature and remains intact. Presence of certain ions in the reaction vessel also affects specific activity of the enzyme. Small amounts of potassium chloride (KCl) and magnesium ion (Mg2+) promote Taq's enzymatic activity. Taq polymerase is maximally activated at 50mM KCl and just the right concentration of Mg2+ which is determined by the concentration of nucleoside triphosphates (dNTPs). High concentrations of KCl and Mg2+ inhibit Taq's activity.One of Taq's drawbacks is its lack of 3' to 5' exonuclease proofreading activity resulting in relatively low replication fidelity. Originally its error rate was measured at about 1 in 9,000 nucleotides. Some thermostable DNA polymerases have been isolated from other thermophilic bacteria and archaea, such as Pfu DNA polymerase, possessing a proofreading activity, and are being used instead of (or in combination with) Taq for high-fidelity amplification.Taq makes DNA products that have A (adenine) overhangs at their 3' ends. This may be useful in TA cloning, whereby a cloning vector (such as a plasmid) that has a T (thymine) 3' overhang is used, which complements with the A overhang of the PCR product, thus enabling ligation of the PCR product into the plasmid vector.

Task lighting

Often task lighting refers to increasing illuminance to better accomplish a specific activity. However, the illuminance level is not the only factor governing visibility. Contrast is also important, and a poorly positioned light source may cause contrast reduction, resulting in loss of visibility. The most important purpose of task lighting in the office is not increasing illuminance, but improving contrast. General lighting can be reduced because task lighting provides focused light where needed.Different strategies for task lighting exist. The three main approaches are:

Localized average lighting, where a lamp supplies both ambient light and task light

Freely adjustable task light such as a gooseneck, balanced-arm lamp, or swing-arm light.

Asymmetric task light, where the lamp is placed at the side of the work areaThere are also other approaches to task lighting, for example under-shelf luminaires.

Other instances of task lighting are in machinery, where a specific work area needs illumination, and in workshops, where a task light may illuminate the actual working area. Special instances of task lighting are examination and operation lights for medicine and surgery, as well as the dentist's lamp. Task lamps are also used for many home tasks such as sewing, reading, small repairs, model construction, crafts, writing, and many other activities. The actual task may range from very small up to about as far as you may reach with your hands or available tools. Lighting of larger areas is beyond the scope of task lighting.

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