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Telepathology is the practice of pathology at a distance. It uses telecommunications technology to facilitate the transfer of image-rich pathology data between distant locations for the purposes of diagnosis , education , and research . [ 1 ] [ 2 ] Performance of telepathology requires that a pathologist selects the video images for analysis and the rendering of diagnoses. [ 3 ] The use of " television microscopy ", the forerunner of telepathology, did not require that a pathologist have physical or virtual "hands-on" involvement in the selection of microscopic fields-of-view for analysis and diagnosis.
An academic pathologist, Ronald S. Weinstein , M.D., coined the term "telepathology" in 1986. In a medical journal editorial , Weinstein outlined the actions that would be needed to create remote pathology diagnostic services. [ 4 ] He and his collaborators published the first scientific paper on robotic telepathology. [ 5 ] Weinstein was also granted the first U.S. patents for robotic telepathology systems and telepathology diagnostic networks. [ 6 ] Weinstein is known to many as the "father of telepathology". [ 7 ] In Norway , Eide and Nordrum implemented the first sustainable clinical telepathology service in 1989; [ 8 ] this is still in operation decades later. A number of clinical telepathology services have benefited many thousands of patients in North America , Europe , and Asia .
Telepathology has been successfully used for many applications, including the rendering of histopathology tissue diagnoses at a distance. Although digital pathology imaging, including virtual microscopy , is the mode of choice for telepathology services in developed countries, analog telepathology imaging is still used for patient services in some developing countries.
Telepathology systems are divided into three major types: static image-based systems, real-time systems , and virtual slide systems.
Static image systems have the benefit of being the most reasonably priced and usable systems. They have the significant drawback in only being able to capture a selected subset of microscopic fields for off-site evaluation.
Real-time robotic microscopy systems and virtual slides allow a consultant pathologist the opportunity to evaluate histopathology slides in their entirety, from a distance. With real-time systems, the consultant actively operates a robotically controlled motorized microscope located at a distant site—changing focus, illumination, magnification, and field of view—at will. Either an analog video camera or a digital video camera can be used for robotic microscopy. Another form of real-time microscopy involves utilizing a high resolution video camera mounted on a path lab microscope to send live digital video of a slide to a large computer monitor at the pathologist's remote location via encrypted store-and-forward software. An echo-cancelling microphone at each end of the video conference allows the pathologist to communicate with the person moving the slide under the microscope.
Virtual slide systems utilize automated digital slide scanners that create a digital image file of an entire glass slide (whole slide image). This file is stored on a computer server and can be navigated at a distance, over the Internet , using a browser. [ 9 ] Digital imaging is required for virtual microscopy.
While real-time and virtual slide systems offer higher diagnostic accuracy when compared with static-image telepathology, there are drawbacks to each. Real-time systems perform best on local area networks (LANs), but performance may suffer if employed during periods of high network traffic or using the Internet proper as a backbone. Expense is an issue with real-time systems and virtual slide systems as they can be costly. Virtual slide telepathology is emerging as the technology of choice for telepathology services. However, high throughput virtual slide scanners (those producing one virtual slide or more per minute) are currently expensive. Also, virtual slide digital files are relatively large, often exceeding one gigabyte in size. Storing and simultaneously retrieving large numbers of telepathology whole-slide image files can be cumbersome, introducing their own workflow challenges in the clinical laboratory.
Types of Telepathology Platform: Telepathology platforms that have adopted whole slide imaging enables remote viewing to aid pathologist in following ways: By remote sharing and secondly by uploading images for expert consultations. [ 10 ]
Telepathology is currently being used for a wide spectrum of clinical applications including diagnosing of frozen section specimens , [ 11 ] primary histopathology diagnoses, [ 12 ] second opinion diagnoses, [ 13 ] subspecialty pathology expert diagnoses, [ 14 ] investigative and regulated preclinical toxicology studies, [ 15 ] education, [ 16 ] competency assessment, [ 17 ] and research. Benefits of telepathology include providing immediate access to off-site pathologists for rapid frozen section diagnoses. Another benefit can be gaining direct access to subspecialty pathologists such as a renal pathologist , a neuropathologist , or a dermatopathologist , for immediate consultations.
Canada Health Infoway is the organization responsible for the implementation of telepathology in Canada . Canada Health Infoway is a federal non-profit which provides funding for improving digital health infrastructure.
Canada Health Infoway has targeted funding of $1.2 million CAD to the Telepathology Solution for the province of British Columbia . [ 18 ] The system is designed to connect all pathologists within the province. The long-term expectations are improvement to patient care and safety through access to pathology expertise, improved timeliness of results and quality of service.
In Ontario , the University Health Network (UHN) hospitals are the primary drivers of the development of telepathology. The three northern Ontario communities of Timmins , Sault Ste. Marie and Kapuskasing have several community hospitals virtually linked to UHN pathologists via the Internet 24 hours a day. [ 19 ] | https://en.wikipedia.org/wiki/Telepathology |
Telephone density or teledensity is the number of telephone connections for every hundred individuals living within an area. It varies widely across the nations and also between urban and rural areas within a country. Telephone density has significant correlation with the per capita GDP of the area. [ 1 ] It is also used as an indicator of the purchasing power of the middle class of the country or specific region.
In earlier days teledensity was computed as the number of fixed telephone lines per hundred inhabitants. But this method has become less significant with an increasing number of countries register a trend of mobile cellular subscribers outnumbering the fixed line connections. Hence, as an alternative, mobidensity or mobile cellular subscribers per hundred inhabitants was proposed. Since this method caused disadvantage to some countries where the fixed line network is well established, or others where the mobile network is still in its initial stage of development, effective teledensity has been proposed by International Telecommunication Union (ITU) as the solution, which is defined as either fixed line connections or mobile subscribers per hundred inhabitants – whichever is higher. [ 2 ]
Fixed telephone lines per hundred inhabitants is calculated by dividing the number of fixed telephone lines by the total population and then multiplying by 100. Fixed telephone lines include PSTN , WLL , ISDN and DSL . A single ISDN or DSL subscriber connection may cater to multiple voice channels. This leads to a lack of global standard in the computation of fixed line density and hence ITU has recommended that all the countries shall provide the methodology of calculation of this figure in order to enhance comparability. [ 2 ]
Mobidensity or mobile cellular subscribers per hundred inhabitants is obtained by dividing the number of mobile cellular subscribers by the population and multiplying by 100. While computing Mobile cellular subscribers users of both post-paid subscriptions and pre-paid accounts are included. Inactive prepaid connections where a call has not been made or received within the last 3 months, are excluded. [ 3 ]
The correlation between teledensity and per capita GDP could be represented by a straight line in a logarithmic graph. This relation was first mentioned by A.G.W. Jipp. a German engineer, in his book published in 1962. The graph is helpful to compare the telephone infrastructure development of different countries or regions, on the basis of teledensity. [ 4 ] | https://en.wikipedia.org/wiki/Telephone_density |
A telescope is a device used to observe distant objects by their emission, absorption , or reflection of electromagnetic radiation . [ 1 ] Originally, it was an optical instrument using lenses , curved mirrors , or a combination of both to observe distant objects – an optical telescope . Nowadays, the word "telescope" is defined as a wide range of instruments capable of detecting different regions of the electromagnetic spectrum , and in some cases other types of detectors.
The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy .
The reflecting telescope , which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope.
In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s.
The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei 's instruments presented at a banquet at the Accademia dei Lincei . [ 2 ] [ 3 ] In the Starry Messenger , Galileo had used the Latin term perspicillum . The root of the word is from the Ancient Greek τῆλε, tele 'far' and σκοπεῖν, skopein 'to look or see'; τηλεσκόπος, teleskopos 'far-seeing'. [ 4 ]
The earliest existing record of a telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lipperhey for a refracting telescope . [ 6 ] The actual inventor is unknown but word of it spread through Europe. Galileo heard about it and, in 1609, built his own version, and made his telescopic observations of celestial objects. [ 7 ] [ 8 ]
The idea that the objective , or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope. [ 9 ] The potential advantages of using parabolic mirrors —reduction of spherical aberration and no chromatic aberration —led to many proposed designs and several attempts to build reflecting telescopes . [ 10 ] In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name, the Newtonian reflector . [ 11 ]
The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens [ 12 ] and enabled the construction of shorter, more functional refracting telescopes. [ 13 ] Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857, and aluminized mirrors in 1932. [ 14 ] The maximum physical size limit for refracting telescopes is about 1 meter (39 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger than 10 meters (33 feet), and work is underway on several 30–40m designs. [ 15 ]
The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays . The first purpose-built radio telescope went into operation in 1937. Since then, a large variety of complex astronomical instruments have been developed.
Since the atmosphere is opaque for most of the electromagnetic spectrum, only a few bands can be observed from the Earth's surface. These bands are visible – near-infrared and a portion of the radio-wave part of the spectrum. [ 16 ] For this reason there are no X-ray or far-infrared ground-based telescopes as these have to be observed from orbit. Even if a wavelength is observable from the ground, it might still be advantageous to place a telescope on a satellite due to issues such as clouds, astronomical seeing and light pollution . [ 17 ]
The disadvantages of launching a space telescope include cost, size, maintainability and upgradability. [ 18 ]
Some examples of space telescopes from NASA are the Hubble Space Telescope that detects visible light, ultraviolet, and near-infrared wavelengths, the Spitzer Space Telescope that detects infrared radiation, and the Kepler Space Telescope that discovered thousands of exoplanets. [ 19 ] The latest telescope that was launched was the James Webb Space Telescope on December 25, 2021, in Kourou, French Guiana. The Webb telescope detects infrared light. [ 20 ]
The name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation , but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands.
As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it is possible to make very tiny antenna). The near-infrared can be collected much like visible light; however, in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna. [ 21 ] On the other hand, the Spitzer Space Telescope , observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the frequency range from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light). [ 22 ]
With photons of the shorter wavelengths, with the higher frequencies, glancing-incident optics, rather than fully reflecting optics are used. Telescopes such as TRACE and SOHO use special mirrors to reflect extreme ultraviolet , producing higher resolution and brighter images than are otherwise possible. A larger aperture does not just mean that more light is collected, it also enables a finer angular resolution.
Telescopes may also be classified by location: ground telescope, space telescope , or flying telescope . They may also be classified by whether they are operated by professional astronomers or amateur astronomers . A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory .
Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed.
Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains a single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array .
By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and the technique is called aperture synthesis . The 'virtual' apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter of the Earth – using space-based very-long-baseline interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. [ 23 ]
Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes.
Radio telescopes are also used to collect microwave radiation , which has the advantage of being able to pass through the atmosphere and interstellar gas and dust clouds.
Some radio telescopes such as the Allen Telescope Array are used by programs such as SETI [ 24 ] and the Arecibo Observatory to search for extraterrestrial life. [ 25 ] [ 26 ]
An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum. [ 27 ] Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness . For the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements, usually made from glass lenses and/or mirrors , to gather light and other electromagnetic radiation to bring that light or radiation to a focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits ), spotting scopes , monoculars , binoculars , camera lenses , and spyglasses . There are three main optical types:
A Fresnel imager is a proposed ultra-lightweight design for a space telescope that uses a Fresnel lens to focus light. [ 30 ] [ 31 ]
Beyond these basic optical types there are many sub-types of varying optical design classified by the task they perform such as astrographs , [ 32 ] comet seekers [ 33 ] and solar telescopes . [ 34 ]
Most ultraviolet light is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space. [ 35 ] [ 36 ]
X-rays are much harder to collect and focus than electromagnetic radiation of longer wavelengths. X-ray telescopes can use X-ray optics , such as Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect the rays just a few degrees . The mirrors are usually a section of a rotated parabola and a hyperbola , or ellipse . In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. [ 37 ] [ 38 ] Examples of space observatories using this type of telescope are the Einstein Observatory , [ 39 ] ROSAT , [ 40 ] and the Chandra X-ray Observatory . [ 41 ] [ 42 ] In 2012 the NuSTAR X-ray Telescope was launched which uses Wolter telescope design optics at the end of a long deployable mast to enable photon energies of 79 keV. [ 43 ] [ 44 ]
Higher energy X-ray and gamma ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image.
X-ray and Gamma-ray telescopes are usually installed on high-flying balloons [ 45 ] [ 46 ] or Earth-orbiting satellites since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum. An example of this type of telescope is the Fermi Gamma-ray Space Telescope which was launched in June 2008. [ 47 ] [ 48 ]
The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. Such detections can be made either with the Imaging Atmospheric Cherenkov Telescopes (IACTs) or with Water Cherenkov Detectors (WCDs). Examples of IACTs are H.E.S.S. [ 49 ] and VERITAS [ 50 ] [ 51 ] with the next-generation gamma-ray telescope, the Cherenkov Telescope Array ( CTA ), currently under construction. HAWC and LHAASO are examples of gamma-ray detectors based on the Water Cherenkov Detectors.
A discovery in 2012 may allow focusing gamma-ray telescopes. [ 52 ] At photon energies greater than 700 keV, the index of refraction starts to increase again. [ 52 ] | https://en.wikipedia.org/wiki/Telescope |
Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy ( THEIA ) is a NASA -proposed 4-metre optical/ultraviolet space telescope that would succeed the Hubble Space Telescope and complement the infrared- James Webb Space Telescope . THEIA would use a 40-metre occulter to block starlight so as to directly image exoplanets .
It was proposed with three main instruments and an occulter: [ 1 ]
This telescope -related article is a stub . You can help Wikipedia by expanding it .
This article about one or more spacecraft of the United States is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telescope_for_Habitable_Exoplanets_and_Interstellar/Intergalactic_Astronomy |
A telescopic handler , also called a telehandler , teleporter , reach forklift , or zoom boom , is a machine widely used in agriculture and industry . It is somewhat like a forklift but has a boom ( telescopic cylinder ), making it more a crane than a forklift, with the increased versatility of a single telescopic boom that can extend forwards and upwards from the vehicle. The boom can be fitted with different attachments, such as a bucket, pallet forks, muck grab, or winch .
The first telescopic handler was believed to have been manufactured by French company Sambron in 1957.
In 1971, Liner Construction Equipment of Hull launched the Giraffe 4WD, 4WS telehandler based on a design by Matbro who created a similar machine based on their articulated forestry machines.
JCB launched their 2WD, rear steer Loadall in October 1977. The JCB 520 was originally aimed at construction sites, the potential for agricultural uses soon followed. [ 1 ] JCB sold 100,000 units by
In industry, the most common attachment for a telehandler is pallet forks and the most common application is to move loads to and from places unreachable for a conventional forklift. For example, telehandlers have the ability to remove palletised cargo from within a trailer and to place loads on rooftops and other high places. The latter application would otherwise require a crane, which is not always practical or time-efficient. [ citation needed ]
In agriculture the most common attachment for a telehandler are buckets or bucket grabs; again the most common application is to move loads to and from places unreachable for a 'conventional machine' which in this case is a wheeled loader or backhoe loader. [ citation needed ] For example, telehandlers have the ability to reach directly into a high-sided trailer or hopper. The latter application would otherwise require a loading ramp, conveyor, or something similar.
The telehandler can also work with a crane jib for lifting loads. Attachments on the market include dirt buckets, grain buckets, rotators, and power booms. Agricultural models can also be fitted with three-point linkage and power take-off.
The advantage of the telehandler is also its biggest limitation: as the boom extends or raises while bearing a load, it acts as a lever and causes the vehicle to become increasingly unstable, despite counterweights in the rear. That means the lifting capacity quickly decreases as the working radius (distance between the front of the wheels and the centre of the load) increases. When used as a loader the single boom (rather than twin arms) is very highly loaded and is a weakness, even with careful design. A vehicle which has a 5,000 lb (2,300 kg) lift capacity with the boom retracted may be able to safely lift as little as 400 lb (180 kg) with the boom fully extended at a low angle. The same machine, with the boom retracted, may be able to support as much as 10,000 lb (4,500 kg) with the boom raised to 70°.
The operator is equipped with a load chart which helps determine whether a given task is possible, taking into account weight, boom angle and height. Failing that, most telehandlers now utilize a computer, which uses sensors to monitor the vehicle, and will warn the operator and/or cut off further control input if the limits of the vehicle are exceeded. The latter is a legal requirement in Europe, controlled by EN15000. Machines can also be equipped with front stabilizers which extend the lifting capability of the equipment while stationary. Machines that are fully stabilised with a rotary joint between upper and lower frames can be called mobile cranes . They can typically still use a bucket, and are also often referred to as 'Roto' machines, and may be considered a hybrid between a telehandler and small crane.
Under the laws or regulations of some national or other jurisdictional authorities, a license is required in order to operate a telehandler.
For example, in Australia , a Gold Card, issued by the Telescopic Handler Association of Australia (TSHA), can be obtained to allow the operation of telehandlers with a capacity of three tonnes or less with standard attachments, when the machine is operated from below. [ 2 ] The Gold Card is not a legally required qualification, but verbal instruction is not considered an appropriate training method [ according to whom? ] because of a lack of evidence of competency training. Competency training with evidence of learning and written assessment is legally required in Australia.
In Victoria, Australia , a WorkSafe CN licence is a legally required licence for machines with a capacity of over three tonnes with standard attachments, when the machine is operated from below. Telehandlers fitted with elevated work platform attachments, and are operated from the basket, are classified as elevated work platforms and require elevated work platform licences, such as the EWPA Yellow Card or Worksafe WP Licence. A WorkSafe C2 licence or higher may apply when using slewing-type telehandlers. [ 3 ]
Media related to Telescopic handlers at Wikimedia Commons | https://en.wikipedia.org/wiki/Telescopic_handler |
Telescoping in mechanics describes the movement of one part sliding out from another, lengthening an object (such as a telescope or the lift arm of an aerial work platform ) from its rest state. [ 1 ] In modern equipment this can be achieved by a hydraulics , but pulleys are generally used for simpler designs such as extendable ladders and amateur radio antennas.
This classical mechanics –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telescoping_(mechanics) |
In a railway accident , telescoping occurs when the underframe of one vehicle overrides that of another, and smashes through the second vehicle's body. The term is derived from the resulting appearance of the two vehicle bodies: the body of one vehicle may appear to be slid inside the other like the tubes of a collapsible telescope – the body sides, roof and underframe of the latter vehicle being forced apart from each other. [ 1 ]
Telescoping often results in heavy fatalities if the cars telescoped are fully occupied. The car riding on top will often destroy the structure of the car below, crushing those on board (although the physics of the incident may reverse the cars' roles). The chances of telescoping can be reduced by use of anticlimbers and other structural systems which direct crash energy and debris away from the passenger and crew areas. [ 2 ] One such energy absorbing system is the Green Buffer, winners of the 2023 Swedish Steel Prize, [ 3 ] where a collapsing steel structure in the buffers dissipate energy similarly to the crumple zones used in the automotive industry.
Accidents where telescoping occurred are numerous and include:
To reduce the chance of telescoping, rail and tramway vehicles are often provided with an anticlimber: a horizontally ridged plate at the end of the chassis, which in a collision will engage with the anticlimber on the next car. | https://en.wikipedia.org/wiki/Telescoping_(rail_cars) |
Telescoping generations can occur in parthenogenetic species, such as aphids or other life forms that have the ability to reproduce without ovum fertilization. [ 1 ] This occurrence is characterized by a viviparous female having a daughter growing inside her that is also parthenogenetically pregnant with a daughter cell.
This pattern of reproduction can also occur in certain mites that are not parthenogenetic, e.g. Adactylidium , in which the young hatch and mate within the mother, eating her from the inside and then escaping; in some species the males never escape, and in others they die shortly afterwards. However, the resulting inbreeding has consequences much like those of parthenogenesis, and the females are not actually pregnant on hatching but become pregnant before emerging into free living.
This biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telescoping_generations |
The teletransportation paradox or teletransport paradox (also known in alternative forms as the duplicates paradox ) is a thought experiment on the philosophy of identity that challenges common intuitions on the nature of self and consciousness , formulated by Derek Parfit in his 1984 book Reasons and Persons . [ 1 ] If a person is somehow re-created, say by teletransportation, is the re-creation the same person?
The Polish science-fiction writer Stanisław Lem described the same problem in the mid-twentieth century. [ 2 ] He put it in writing in his philosophical text Dialogs in 1957. Similarly, in Lem's Star Diaries ("Fourteenth Voyage") of 1957, the hero visits a planet and finds himself recreated from a backup record, after his death from a meteorite strike, which on this planet is a very commonplace procedure. In chapter 6 of his later discursive book " Summa Technologiae ", first published in 1964, he discussed in detail the identity paradoxes associated with teleportation and hibernation of human beings.
Similar questions of identity have been raised as early as 1775.
I would be glad to know your Lordship's opinion whether when my brain has lost its original structure, and when some hundred years after the same materials are fabricated so curiously as to become an intelligent being, whether, I say that being will be me; or, if, two or three such beings should be formed out of my brain; whether they will all be me, and consequently one and the same intelligent being.
Derek Parfit and others consider a hypothetical "teletransporter", a machine that puts a person to sleep, records their molecular composition, breaking it down into atoms, and relaying its recording to Mars at the speed of light. On Mars, another machine re-creates the person (from local stores of carbon, hydrogen, and so on), each atom in exactly the same relative position. Parfit poses the question of whether or not the teletransporter is actually a method of travel, or if it simply kills and makes an exact replica of the user. [ 4 ]
Then the teleporter is upgraded. The teletransporter on Earth is modified to not destroy the person who enters it, but instead it can simply make infinite replicas, all of whom would claim to remember entering the teletransporter on Earth in the first place.
Using thought experiments such as these, Parfit argues that any criteria we attempt to use to determine sameness of person will be lacking, because there is no further fact. What matters, to Parfit, is simply "Relation R", psychological connectedness, including memory, personality, and so on. [ 5 ]
Parfit continues this logic to establish a new context for morality and social control. He cites that it is morally wrong for one person to harm or interfere with another person and it is incumbent on society to protect individuals from such transgressions. That accepted, it is a short extrapolation to conclude that it is also incumbent on society to protect an individual's "Future Self" from such transgressions; tobacco use could be classified as an abuse of a Future Self's right to a healthy existence. Parfit resolves the logic to reach this conclusion, which appears to justify incursion into personal freedoms, but he does not explicitly endorse such invasive control. [ citation needed ] | https://en.wikipedia.org/wiki/Teletransportation_paradox |
A television antenna , also called a television aerial (in British English ), is an antenna specifically designed for use with a television receiver (TV) to receive terrestrial over-the-air (OTA) broadcast television signals from a television station . Terrestrial television is broadcast on frequencies from about 47 to 250 MHz in the very high frequency (VHF) band, and 470 to 960 MHz in the ultra high frequency (UHF) band in different countries .
Television antennas are manufactured in two different types: indoor and outdoor antennas. Indoor antennas are designed to be located on top of or next to the television set , but are ideally placed near a window in a room and as high up as possible for the best reception. [ 1 ] The most common types of indoor antennas are the dipole [ 2 ] ("rabbit ears"), which work best for VHF channels, and loop antennas , which work best for UHF. [ 3 ] Outdoor antennas on the other hand are designed to be mounted on a mast on top of the owner's house, [ 4 ] or in a loft or attic where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install but are necessary for adequate reception in fringe areas far from television stations; the most common types of these are the Yagi , [ 2 ] log periodic , [ 2 ] and (for UHF) the multi-bay reflective array antenna .
The purpose of the antenna is to intercept radio waves from the desired television stations and convert them to tiny radio frequency alternating currents which are applied to the television's tuner , which extracts the television signal. [ 5 ] The antenna is connected to the television with a specialized cable designed to carry radio current, called transmission line . Earlier antennas used a flat cable called 300 ohm twin-lead . The standard today is 75 ohm coaxial cable , which is less susceptible to interference which plugs into an F connector or Belling-Lee connector (depending on region) on the back of the TV. [ 6 ] To convert the signal from antennas that use a twin-lead line to the modern coaxial cable input, a small transformer called a balun is used in the line.
In most countries, television broadcasting is allowed in the very high frequency (VHF) band from 47 to 68 MHz, called VHF low band or band I in Europe; 174 to 216 MHz, called VHF high band or band III in Europe, and in the ultra high frequency (UHF) band from 470 to 698 MHz, called band IV and V in Europe. [ 7 ] The boundaries of each band vary somewhat in different countries. Radio waves in these bands travel by line-of-sight ; they are blocked by hills and the visual horizon , limiting a television station's reception area to 65–95 km (40–60 miles), depending on terrain.
In the previous standard analog television , used before 2006, the VHF and UHF bands required separate tuners in the television receiver, which had separate antenna inputs. The wavelength of a radio wave equals the speed of light (c), divided by the frequency. The above frequency bands cover a 15:1 wavelength ratio, or almost 4 octaves . It is difficult to design a single antenna to receive such a wide wavelength range, and there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies. So traditionally, separate antennas (outdoor antennas with separate sets of elements on a single support boom) have been used to receive the VHF and UHF channels. [ 6 ]
Starting in 2006, many countries in the world switched from broadcasting using an older analog television standard to newer digital television [ 8 ] (DTV). However, the same broadcast frequencies are generally used, so the antennas used for the older analog television will also receive the new DTV broadcasts. Sellers often claim to supply a special digital or high-definition television (HDTV) antenna advised as a replacement for an existing analog television antenna; at best this is misinformation to generate sales of unneeded equipment, [ 9 ] [ 10 ] At worst, it may leave the viewer with a UHF-only antenna in a local market (particularly in North America) where some digital stations remain on their original high VHF or low VHF frequencies.
Places unable to be reached by television broadcast transmitters are known as black spots in Australia . [ 11 ] In East Germany , the areas that could not receive western TV signals were referred to as the Tal der Ahnungslosen , or Valley of the Clueless .
Indoor antennas may be mounted on the television itself or stand on a table next to it, connected to the television by a short feed line . Due to space constraints, indoor antennas cannot be as large and elaborate as outdoor antennas, they are not mounted at as high an elevation, and the building walls block some of the radio waves; for these reasons, indoor antennas generally do not give as good reception as outdoor antennas. [ 6 ] They are often perfectly adequate in urban and suburban areas, which are usually within the strong radiation footprint of local television stations. Still, in rural fringe reception areas, only an outdoor antenna may give adequate reception. A few of the simplest indoor antennas are described below, but a great variety of designs and types exist. Many have a dial on the antenna with a number of different settings to alter the antenna's reception pattern. This should be rotated with the set on while looking at the screen until the best picture is obtained.
The oldest and most widely used (at least in the United States) indoor antenna is the rabbit ears or bunny ears , which are often provided with new television sets. [ 6 ] It is a simple half-wave dipole antenna used to receive the VHF television bands, consisting in the US of 54 to 88 MHz ( band I ) and 174 to 216 MHz ( band III ), with wavelengths of 5.5 to 1.4 m (18 to 5 feet). It is constructed of two telescoping rods attached to a base, which extend out to about 1 m (3.3 feet) length (approximately one-quarter wavelength at 54 MHz) and can be collapsed when not in use. For best reception, the rods should be adjusted to be a little less than 1 / 4 wavelength at the frequency of the television channel being received. However, the dipole has a wide bandwidth , so often adequate reception is achieved without adjusting the length.
The measured gain of rabbit ears is low, about ―2 dBi, or ―4 dB with respect to a half wave dipole. [ 6 ] This means it is not as directional and sensitive to distant stations as a large rooftop antenna. Still, its wide-angle reception pattern may allow it to receive several stations located in different directions without requiring readjustment when the channel is changed. Dipole antennas are bi-directional; that is, they have two main lobes in opposite directions, 180° apart. Instead of being fixed in position like other antennas, the elements are mounted on ball-and-socket joints. They can be adjusted to various angles in a V shape, allowing them to be moved out of the way in crowded quarters. Another reason for the V shape is that when receiving channels at the top of the band with the rods fully extended, the antenna elements will typically resonate at their 3rd harmonic . In this mode, the direction of maximum gain (the main lobe ) is no longer perpendicular to the rods. Still, the radiation pattern will have lobes at an angle to the rods, making it advantageous to be able to adjust them to various angles.
Some portable televisions use a whip antenna . [ 6 ] This consists of a single telescoping rod about a meter (3.3 feet) long attached to the television, which can be retracted when not in use. It functions as a quarter-wave monopole antenna . The other side of the feedline is connected to the ground plane on the TV's circuit board, which acts as ground . The whip antenna generally has an omnidirectional reception pattern, with maximum sensitivity in directions perpendicular to the antenna axis and gain similar to rabbit ears.
The UHF channels are often received by a single turn loop antenna . [ 6 ] Since a rabbit ears antenna only covers the VHF bands, it is often combined with a UHF loop mounted on the same base to cover all the TV channels. This of course also depends by country and region: for example in the UK and Ireland, terrestrial TV broadcasts are only on the UHF band, meaning that a loop antenna is necessary and the rabbit ears would only be useful for FM radio reception. [ 12 ] [ 13 ]
A more recent phenomenon for indoor antennas are flat antennas, which are lightweight, thin, and usually square-shaped with the claim of having more omnidirectional reception. They are also marketed as being more in line with modern minimalistic home designs. [ 14 ] Flat antennas may have a stand or could be hung on a wall or a window. [ 15 ] Internally, the thin, flat square is a loop antenna with its circular metallic wiring embedded into conductive plastic. [ citation needed ]
When a higher-gain antenna is needed to achieve adequate reception in suburban or fringe reception areas, an outdoor directional antenna is usually used. Although most simple antennas have null directions where they have zero response, the directions of useful gain are very broad. In contrast, directional antennas can have an almost unidirectional radiation pattern , so the correct end of the antenna must be pointed at the TV station. As an antenna design provides higher gain (compared to a dipole), the main lobe of the radiation pattern becomes narrower. Outdoor antennas provide up to a 15 dB gain in signal strength and 15-20 dB greater rejection of ghost signals in analog TV. [ 6 ] Combined with a signal increase of 14 dB due to height and 11 dB due to lack of attenuating building walls, an outdoor antenna can result in a signal strength increase of up to 40 dB at the TV receiver. [ 6 ]
Outdoor antenna designs are often based on the Yagi–Uda antenna [ 16 ] or log-periodic dipole array (LPDA). [ 17 ] These are composed of multiple half-wave dipole elements, consisting of metal rods approximately half of the wavelength of the television signal, mounted in a line on a support boom. These act as resonators ; the electric field of the incoming radio wave pushes the electrons in the rods back and forth, creating standing waves of oscillating voltage in the rods. The antenna can have a smaller or larger number of rod elements; in general, the more elements, the higher the gain and the more directional. Another design used mainly for UHF reception is the reflective array antenna , consisting of a vertical metal screen with multiple dipole elements mounted in front of it.
The television broadcast bands are too wide in frequency to be covered by a single antenna, so the two options are separate antennas used for the VHF and UHF bands or a combination (combo) VHF/UHF antenna. [ 6 ] A VHF/UHF antenna combines two antennas feeding the same feedline mounted on the same support boom. More extended elements that pick up VHF frequencies are located at the back of the boom and often function as a log-periodic antenna . Shorter elements that receive the UHF stations are located at the front of the boom and often function as a Yagi antenna .
Since directional antennas must be pointed at the transmitting antenna, this is a problem when the television stations to be received are located in different directions. In this case, two or more directional rooftop antennas, each pointed at a different transmitter, are often mounted on the same mast and connected to one receiver for best performance filter or matching circuits are used to keep each antenna from degrading the performance of the others connected to the same transmission line. An alternative is to use a single antenna mounted on a rotator , a remote servo system that rotates the antenna to a new direction when a dial next to the television is turned.
Sometimes television transmitters are deliberately located such that receivers in a given region need only receive transmissions in a relatively narrow band of the full UHF television spectrum and from the same direction, hence allowing the use of a higher gain grouped aerial. [ 18 ]
Antennas are commonly placed on rooftops and sometimes in attics. Placing an antenna indoors significantly attenuates the level of the available signal. [ 19 ] [ 20 ] Directional antennas must be pointed at the transmitter they are receiving; in most cases great accuracy is not needed. In a given region, it is sometimes arranged that all television transmitters are located in roughly the same direction and use frequencies spaced closely enough that a single antenna suffices for all. A single transmitter location may transmit signals for several channels. [ 21 ] CABD (communal antenna broadcast distribution) is a system installed inside a building to receive free-to-air TV/FM signals transmitted via radio frequencies and distribute them to the audience. [ 22 ]
Analog television signals are susceptible to ghosting in the image, multiple closely spaced images giving the impression of blurred and repeated images of edges in the picture. This is due to the signal being reflected from nearby objects (buildings, trees, mountains); several copies of the signal, of different strengths and subject to different delays, are picked up. This is different for other transmissions. Careful positioning of the antenna can produce a compromise position, which minimizes the ghosts on different channels. Ghosting is also possible if multiple antennas connected to the same receiver pick up the same station, especially if the lengths of the cables connecting them to the splitter/merger are different lengths or the antennas are too close together. [ 23 ] Analog television is being replaced by digital, which is not subject to ghosting; the same reflected signal that causes ghosting in an analog signal would produce no viewable content at all in digital. However, in this case, interference causes significantly more significant image quality degradation.
Aerials are attached to roofs in various ways, usually on a pole to elevate it above the roof. This is generally sufficient in most areas. In some places, however, such as a deep valley or near taller structures, the antenna may need to be placed significantly higher, using a guyed mast or mast . The wire connecting the antenna indoors is referred to as the downlead or drop , and the longer the downlead is, the greater the signal degradation in the wire. Certain cables may help reduce this tendency.
The higher the antenna is placed, the better it will perform. An antenna of higher gain will be able to receive weaker signals from its preferred direction. Intervening buildings, topographical features (mountains), and dense forests will weaken the signal; in many cases, the signal will be reflected such that a usable signal is still available. There are physical dangers inherent to high or complex antennas, such as the structure falling or being destroyed by weather. There are also varying local ordinances which restrict and limit such things as the height of a structure without obtaining permits . For example, in the United States, the Telecommunications Act of 1996 (Over-the-Air Reception Devices OTARD Rule) allows "any owner or a tenant" [ 24 ] the right, "on property that they own or over which they have exclusive use or control", [ 24 ] to install "An antenna that is designed to receive local television broadcast signals" but that "masts higher than 12 feet [3.5 m] above the roof-line may be subject to local permitting requirements." [ 25 ]
As discussed previously, antennas may be placed indoors where signals are strong enough to overcome antenna shortcomings. The antenna is simply plugged into the television receiver and placed conveniently, often on the top of the receiver ("set-top"). Sometimes, the position needs to be experimented with to get the best picture. Indoor antennas can also benefit from RF amplification, commonly called a TV booster. Reception from indoor antennas can be problematic in weak signal areas. [ citation needed ]
Sometimes, it is desirable not to put an antenna on the roof; in these cases, antennas designed for outdoor use are often mounted in the attic or loft, although antennas designed for attic use are also available. Putting an antenna indoors significantly decreases its performance due to lower elevation above ground level and intervening walls; however, in strong signal areas, reception may be satisfactory. [ 20 ] One layer of asphalt shingles , roof felt , and a plywood roof deck is considered to attenuate the signal to about half. [ 26 ]
It is sometimes desired to receive signals from transmitters which are not in the same direction. This can be achieved, for one station at a time, by using a rotator operated by an electric motor to turn the antenna as desired. Alternatively, two or more antennas, each pointing at a desired transmitter and coupled by appropriate circuitry, can be used. To prevent the antennas from interfering with each other, the vertical spacing between the booms must be at least half the wavelength of the lowest frequency to be received (Distance = λ / 2 ). [ 23 ] The wavelength of 54 MHz (Channel 2) is 5.5 m (18 feet) (λ × f = c ) so the antennas must be a minimum of 2.25 m (90 inches) apart. It is also important that the cables connecting the antennas to the signal splitter/merger be precisely the same length to prevent phasing issues, which cause ghosting with analog reception. That is, the antennas might both pick up the same station; the signal from the one with the shorter cable will reach the receiver slightly sooner, supplying the receiver with two pictures slightly offset. There may be phasing issues even with the same length of down-lead cable. Band-pass filters or signal traps may help to reduce this problem.
For side-by-side placement of multiple antennas, as is common in a space of limited height such as an attic, they should be separated by at least one full wavelength of the lowest frequency to be received at their closest point.
When multiple antennas are often used, one is for a range of co-located stations, and the other is for a single transmitter in a different direction. | https://en.wikipedia.org/wiki/Television_antenna |
Television interference ( TVI ) is a particular case of electromagnetic interference which affects television reception . Many natural and man-made phenomena can disrupt the reception of television signals. These include naturally occurring and artificial spark discharges, and effects due to the operation of radio transmitters.
Analog television broadcasts display different effects due to different kinds of interference. Digital television reception generally gives a good quality picture until the interference is so large that it can no longer be eliminated by the error checking systems in the receiver, at which point the video display becomes pixelated, distorts, or goes blank.
During unusual atmospheric conditions, a distant station normally undectable at a particular location may provide a much stronger signal than usual. The analog television picture may display the sum of the two signals, producing an image from the strong local signal with traces or "ghosts" from the distant, weaker signal. Television broadcast stations are located and assigned to channels so that such events are rare. Readjustment of the receiving antenna may allow more of the distant signal to be rejected, improving image quality.
A local signal may travel by more than one path from the transmitter to receiving antenna. "Multipath" reception is visible as multiple impressions of the same image, slightly shifted along the width of the screen due to the varying transmission path. Some multipath reception is momentary due to road vehicles or aircraft passing; other multipath problems may persist due to reflection off tall buildings or other landscape features. Strong multipath can cause the analog picture to "tear" or momentarily lose synchronization, causing it to roll or flip. [ 1 ]
The sparks generated by static electricity can generate interference.
Many systems where radio frequency interface is caused by sparking can be modeled as the following circuit. The source of energy charges C1 via a resistance, and when the spark gap breaks down, the electricity passes through L and excites the resonant LC circuit. The energy in the LC circuit is then radiated through the aerial.
As an example, when a person walks over a nylon carpet, the rubbing of shoes on carpet performs the role of a battery and resistor, while the person acts as a capacitor (C1 and C2), and the air between a hand and a door knob is a spark gap . Stray inductance acts as L.
Horizontal lines randomly arranged on a television screen may be caused by sparking in a malfunctioning electrical device. Electric railways can also be a strong source of this type of interference.
Other possible sources of such interference include thermostats, fridges, freezers, fish tank heaters, central heating systems. These can create sparks as they turn on or off; as they age they can become worse. In some rare cases they can create non-stop interference through sparking. Electric motors that have a commutator can suffer from sparking at the brushes . Ignition systems on cars and motorbikes.
Power line hardware can generate sparks at either a 100 or 120 Hz rate
Light dimmers and other solid state power control devices can generate interference.
Thyristor and TRIAC regulators without proper chokes are a common source of EMI as well. It is likely that a thyristor (SCR) power controller using the variable phase angle method will generate harmonics of the mains supply, while the spark at a contact will be a very wide band source whose frequency is not related to the power supply frequency. In Thyristor control systems the potential for EMI problems can be minimised by using zero crossing switching where the thyristor is switched on at the moment of time when the AC voltage changes from one direction to the other.
Computers and other digital electronic equipment containing rapidly switching circuits. These devices create and use signals which are switched on/off at great speed, approximately square waves . Any repetitive signal can be reduced down to a Fourier series of sine waves. A perfect square wave with fundamental frequency ω is:
The square wave contains harmonics of the fundamental (that is, sine waves with a frequency that is a multiple of the fundamental frequency ω ) which go on upwards in frequency for ever, although at a decreasing amplitude. These harmonics are responsible for much [ quantify ] of the interference created by computers . A modern PC is a device which is operating in the VHF / UHF frequency range using square waves. As the cases on many computers are not perfect shields, some of this radio-frequency energy can leak out and cause interference to radio (and sometimes TV) reception.
Switched-mode power supplies or packs can be a source of interference. [ quantify ] These are used in consumer electronic products such as phone charges and in some lighting systems.
It is possible to also get a bad picture if the signal strength of the TV transmitter is too high. An attenuator inserted in the antenna lead-in wire may be used if the television receiver displays signs of overload in the RF front end . Strong out-of-band signals may also affect television reception and may require band-pass filters to reduce the level of the undesired signal at the receiver. | https://en.wikipedia.org/wiki/Television_interference |
Telex is a telecommunication system that allows text-based messages to be sent and received by teleprinter over telephone lines. The term "telex" may refer to the service, the network, the devices, or a message sent using these. [ 1 ] Telex emerged in the 1930s and became a major method of sending text messages electronically between businesses in the post– World War II period. Its usage declined as the fax machine grew in popularity in the 1980s.
The technology operates on switched station-to-station basis with teleprinter devices at the receiving and sending locations. [ 2 ] It operates over the circuits of the public switched telephone network or by private lines. Point-to-point teleprinter systems had been in use long before telex exchanges were built in the 1930s. Teleprinters evolved from telegraph systems, and, like the telegraph, use binary signals , with mark and space logic represented by the presence or absence of a certain level of electric current. This differs from the analog telephone system, which used varying voltage to represent sound. For this reason, telex exchanges were entirely separate from the telephone system, with their own signalling standards, exchanges and system of telex numbers (the counterpart of telephone numbers).
Telex provided the first common medium for international record communications using standard signalling techniques and operating criteria as specified by the International Telecommunication Union . Customers on any telex exchange could deliver messages to any other, around the world. To reduce connecting line usage, telex messages were encoded onto paper tape and then read into the line as quickly as possible. The system normally delivered information at 50 baud or approximately 66 words per minute, encoded using the International Telegraph Alphabet No. 2 . In the last days of the traditional telex networks, end-user equipment was often replaced by modems and phone lines , reducing the telex network to what was effectively a directory service running on the telephone network.
Telex began in Germany as a research and development program in 1926 that became an operational teleprinter service in 1933. The service, operated by the German Reichspost [ 3 ] had a speed of 50 baud , which is approximately 66 words per minute.
Soon after, telex services were developed by other nations. Telex spread within Europe and after 1945 around the world. [ 4 ]
By 1978, West Germany , including West Berlin , had 123,298 telex connections. Long before automatic telephony became available, most countries, even in central Africa and Asia , had at least a few high-frequency shortwave telex links. Often, government postal and telegraph services (PTTs) initiated these radio links. The most common radio standard, CCITT R.44 had error-corrected retransmitting time-division multiplexing of radio channels. Most impoverished PTTs operated their telex-on-radio (TOR) channels non-stop, to get the maximum value from them.
The cost of TOR equipment has continued to fall. Although the system initially required specialised equipment, as of 2016 [update] many amateur radio operators operate TOR, also known as radioteletype (RTTY), with special software and inexpensive hardware to connect computer sound cards to short-wave radios. [ 5 ]
Modern cablegrams or telegrams actually operate over dedicated telex networks, using TOR whenever required. [ citation needed ]
Telex served as the forerunner of modern fax , email , and text messaging – both technically and stylistically. Abbreviated English (like "CU L8R" for "see you later") as used in texting originated with telex operators exchanging informal messages in real time [ citation needed ] – they became the first "texters" long before the introduction of mobile phones [ citation needed ] . Telex users could send the same message to several places around the world at the same time, like email today, using the Western Union InfoMaster Computer. This involved transmitting the message via paper tape to the InfoMaster Computer (dial code 6111) and specifying the destination addresses for the single text. In this way, a single message could be sent to multiple distant telex and TWX machines as well as delivering the same message to non-telex and non-TWX subscribers via Western Union Mailgram .
Telex messages are routed by addressing them to a telex address, e.g., "14910 ERIC S", where 14910 is the subscriber number, ERIC is an abbreviation for the subscriber's name (in this case Telefonaktiebolaget L.M. Ericsson in Sweden) and S is the country code or location code. Solutions also exist for the automatic routing of messages to different telex terminals within a subscriber organization, by using different terminal identities, e.g., "+T148". The country codes (formally, network identification codes) for the first countries to adopt telex are single letters, while other countries have two-letter codes. [ 6 ] [ 7 ] Some specialty services and American cities have three-letter network or location codes (such as MAS for Inmarsat or LSA for Los Angeles), and a few towns have four-letter codes (such as ROVE for Rockville, Maryland ). [ 8 ]
A major advantage of telex is that the receipt of the message by the recipient could be confirmed with a high degree of certainty by the "answerback", which is a transmission-control enquiry character . At the beginning of the message, the sender would transmit a WRU ( Who are you? ) code, and the recipient machine would automatically initiate a response which was usually encoded in a rotating drum with pegs, much like a music box . The position of the pegs sent an unambiguous identifying code to the sender, so the sender could verify connection to the correct recipient. The WRU code would also be sent at the end of the message, so a correct response would confirm that the connection had remained unbroken during the message transmission. This gave telex a major advantage over group 2 fax, which had no inherent error-checking capability.
The usual method of operation was that the message would be prepared off-line, using paper tape . All common telex machines incorporated a five-hole paper-tape punch and reader. Once the paper tape had been prepared, the message could be transmitted in minimum time. Telex billing was always by connected duration, so minimizing the connected time saved money. However, it was also possible to connect in "real-time", where the sender and the recipient could both type on the keyboard and these characters would be immediately printed on the distant machine.
Telex could also be used as a rudimentary but functional carrier of information from one IT system to another, in effect a primitive forerunner of electronic data interchange . The sending IT system would create an output (e.g., an inventory list) on paper tape using a mutually agreed format. The tape would be sent by telex and collected on a corresponding paper tape by the receiver and this tape could then be read into the receiving IT system.
One use of telex circuits, in use until the widescale adoption of X.400 and Internet email, was to facilitate a message handling system, allowing local email systems to exchange messages with other email and telex systems via a central routing operation, or switch. One of the largest such switches was operated by Royal Dutch Shell as recently as 1994, permitting the exchange of messages between a number of IBM Officevision, Digital Equipment Corporation ALL-IN-1 and Microsoft Mail systems. In addition to permitting email to be sent to telex, formal coding conventions adopted in the composition of telex messages enabled automatic routing of telexes to email recipients.
The Teletypewriter Exchange Service (TWX) was developed by the American Telephone and Telegraph Company (AT&T) in the United States, commencing service on November 21, 1931. [ 9 ]
From 1942 to 1952, AT&T published progress with the system in the trade magazine TWX . It published articles that touched upon many aspects of the technology.
From inception to 1962, access to the service was provided by operator-assisted, manual switching. By 1962, the network had grown to 100 switchboard locations to handle the traffic, causing considerable delay in the speed of connections of up to 2 1 ⁄ 2 minutes on average. [ 9 ] On August 31, 1962, the service was integrated into the Direct Distance Dialing (DDD) network, which improved connection times to about thirty seconds. [ 9 ] For the new dial technology, each station was assigned a ten-digit telephone number from a reserved set of N10 area codes, designated as Service Access Codes (SAC). Area code 510 was assigned for the United States and Area Code 610 in Canada. Sixteen operating centers were established across the United States.
Later in the decade, the United States was subdivided into three service regions. and assigned codes from the remaining set of SACs (710, 810, and 910). SAC 710 covered the Northeast of the United States (New England, New York, New Jersey, Pennsylvania, Maryland, the District of Columbia, Virginia, and West Virginia). 810 was assigned from Michigan southward and east of the Mississippi River to Ohio, Indiana, and Kentucky, and the entire South and 910 served west of the Mississippi to the Southwest and West Coast. [ 10 ]
TWX lines were configured with a special Class of Service to prevent interconnections with voice services.
Western Union purchased the TWX system from AT&T in January 1969. [ 11 ] The TWX system and the use of the special US area codes continued until 1981, when Western Union completed the conversion to the Western Union Telex II system.
Canada moved its TWX-numbers, as well as Datalink services, to the non-geographic area code 600 , effective October 1, 1993, in exchange for returning 610. [ 12 ]
The network originally transmitted at a speed of 45.45 baud, or approximately 60 words per minute, using five-bit Baudot code , often referred to as 3-row coding with 32 characters arranged in three key rows of the keyboard. [ 13 ] [ 14 ]
In 1963, AT&T implemented a new coding technology for TWX, called 4-row (64 characters in four key rows) based on the new Teletype Model 33 teleprinter using a 110-baud modem and a subset of the seven-bit ASCII code without lower-case letters. [ 15 ] TWX was offered in both 3-row Baudot and 4-row ASCII versions up to the late 1970s.
The modem for the 4-row ASCII service was the Bell 101 dataset, developed by 1958 for military applications. It is the direct ancestor of the Bell 103 modem that launched computer time-sharing . The 101 was revolutionary because it allowed the Bell System to run TWX on its regular voice telephone lines.
The code and speed conversion between 3-row Baudot and 4-row ASCII TWX service was accomplished using a special Bell 10A/B board via a live operator. A TWX customer would place a call to the 10A/B board operator for Baudot–ASCII calls, ASCII–Baudot calls, and also TWX conference calls . The code and speed conversion was facilitated by a special service unit made by Western Electric . Multiple code and speed conversion units were placed at each operator position.
During the conversion to Telex II, the remaining 3-row Baudot customers were converted to the new service during the period 1979 to 1981.
In February 1969, AT&T installed the first electronic switching system (ESS) for TWX service. It was a version of the No. 1ESS switch, arranged for data features (1ESS-AFD) in the Long Lines Department of AT&T. It had a capacity of handling 1,250 4-row teletypewriters. [ 16 ] However, due to the purchase of TWX by Western Union, further installations were canceled.
Western Union's Telex II system was re-acquired by AT&T in 1990 in the purchase of the Western Union assets that became AT&T EasyLink Services . [ 17 ] [ 18 ]
In 1958, Western Union started to build a telex network in the United States. [ 19 ] This telex network started as a satellite exchange located in New York City and expanded to a nationwide network. Western Union chose Siemens & Halske AG, [ 20 ] now Siemens AG, and ITT [ 21 ] to supply the exchange equipment, provisioned the exchange trunks via the Western Union national microwave system and leased the exchange to customer site facilities from the local telephone company. Teleprinter equipment was originally provided by Siemens & Halske AG [ 22 ] and later by Teletype Corporation. [ 23 ] Initial direct international telex service was offered by Western Union, via W.U. International, in the summer of 1960 with limited service to London and Paris. [ 24 ] In 1962, the major exchanges were located in New York City (1), Chicago (2), San Francisco (3), Kansas City (4) and Atlanta (5). [ 25 ] The telex network expanded by adding the final parent exchange cities of Los Angeles (6), Dallas (7), Philadelphia (8) and Boston (9), starting in 1966.
The telex numbering plan, usually a six-digit number in the United States, was based on the major exchange where the customer's telex machine terminated. [ 26 ] For example, all telex customers that terminated in the New York City exchange were assigned a telex number that started with a first digit "1". Further, all Chicago-based customers had telex numbers that started with a first digit of "2". This numbering plan was maintained by Western Union as the telex exchanges proliferated to smaller cities in the United States. The Western Union Telex network was built on three levels of exchanges. [ 27 ] The highest level was made up of the nine exchange cities previously mentioned. Each of these cities had the dual capability of terminating telex customer lines and setting up trunk connections to multiple distant telex exchanges. The second level of exchanges, located in large cities such as Buffalo, Cleveland, Miami, Newark, Pittsburgh and Seattle, were similar to the highest level of exchanges in capability of terminating telex customer lines and setting up trunk connections. However, these second level exchanges had a smaller customer line capacity and only had trunk circuits connected to regional cities. The third level of exchanges, located in small to medium-sized cities, could terminate telex customer lines and had a single trunk group running to its parent exchange.
Loop signaling was offered in two different configurations for Western Union Telex in the United States. The first option, sometimes called local or loop service , provided a 60 milliampere loop circuit from the exchange to the customer teleprinter. The second option, sometimes called long distance or polar was used when a 60 milliampere connection could not be achieved, provided a ground return polar circuit using 35 milliamperes on separate send and receive wires. By the 1970s, under pressure from the Bell operating companies wanting to modernize their cable plant and lower the adjacent circuit noise that these telex circuits sometimes caused, Western Union migrated customers to a third option called F1F2. This F1F2 option replaced the DC voltage of the local and long distance options with Bell 108 modems at the exchange and subscriber ends of the telex circuit. The Bell 108 was operationally compatible with the Bell 103 standard, minus ring detection, as it was designed for use over leased lines. [ 28 ]
Western Union offered connections from telex to the AT&T Teletypewriter Exchange (TWX) system in May 1966 via its New York Information Services Computer Center. [ 29 ] These connections were limited to those TWX machines that were equipped with automatic answerback capability per CCITT standard.
USA-based telex users could send the same message to several places around the world at the same time, like email today, using the Western Union InfoMaster Computer. This involved transmitting the message via paper tape to the InfoMaster Computer (dial code 6111) and specifying the destination addresses for the single text. In this way, a single message could be sent to multiple distant telex and TWX machines as well as delivering the same message to non-telex and non-TWX subscribers via Western Union Mailgram .
International record carrier (IRC) was a term created by the Federal Communications Commission in the United States. Bell's original consent agreement limited it to international dial telephony, and the Western Union Telegraph Company had given up its international telegraphic operation in a 1939 bid to monopolize U.S. telegraphy by taking over ITT's postal, telegraph and telephone service (PTT) business. The result was a de-emphasis on telex in the U.S. and the creation of several international telex and telegraphy companies, collectively called IRCs:
Bell Telex users had to select which IRC to use, and then append the necessary routing digits. The IRCs converted between TWX and Western Union Telegraph Co. standards.
Telex began in the UK as an evolution from the 1930s Telex Printergram service, appearing in 1932 on a limited basis. This used the telephone network in conjunction with a Teleprinter 7B and signalling equipment to send a message to another subscriber with a teleprinter, or to the Central Telegraph Office.
In 1945, as the traffic increased, it was decided to have a separate network for telex traffic, and the first manual exchange opened in London. By 1954, the public inland telex service opened via manually switched exchanges. A number of subscribers were served via automatic sub-centres which used relays and Type 2 uniselectors , acting as concentrators for a manual exchange.
In the late 1950s, the decision was made to convert to automatic switching and this was completed by 1961; there were 21 exchanges spread across the country, with one international exchange in London. The equipment used the Strowger system for switching, as was the case for the telephone network. Conversion to Stored Programme Control (SPC) began in 1984 using exchanges made by Canadian Marconi , with the last Strowger exchange closing in 1992. User numbers increased over the ensuing years into the 1990s.
The dominant supplier of the telex machines was Creed & Company , a division of the ITT Corporation .
A separate service Secure Stream 300 (previously Circuit Switched Data Network) was a variant of telex running at 300 baud, used for telemetry and monitoring purposes by utility companies and banks, among others. This was a high-security virtual private wire system with a high degree of resilience through diversely routed dual-path network configurations.
After privatization of the telecommunications network under Margaret Thatcher's government at the start of the 1980s, Mercury Communications [ 38 ] also provided a telex network, based on T200-series switching equipment [ 39 ] supplied by the Swiss company Hasler in 1986 (after 1987 a member of the Ascom company). In 1996 Mercury was incorporated into Cable & Wireless Communications , which continued telex operation until 2006 when the remaining telex subscribers were transferred to Swiss Telex, which operated a multinational telex network until 2020 (also with T200 equipment).
British Telecom stopped offering the telex service to new customers in 2004 and discontinued the service in 2008, allowing users to transfer to Swiss Telex if they wished to continue to use telex. [ 40 ]
Canada-wide automatic teleprinter exchange service was introduced by the CPR Telegraph Company and CN Telegraph in July 1957 (the two companies, operated by rivals Canadian National Railway and Canadian Pacific Railway , would join to form CNCP Telecommunications in 1967). This service supplemented the existing international telex service that was put in place in November 1956. Canadian telex customers could connect with nineteen European countries in addition to eighteen Latin American, African, and trans-Pacific countries. [ 41 ] The major exchanges were located in Montreal (01), Toronto (02), and Winnipeg (03). [ 42 ]
Telex is still in operation but not in the sense described in the CCITT Blue Book documentation. Telex has been mostly superseded by fax , email , and SWIFT , although radiotelex (telex via HF radio ) is still used in the maritime industry and is a required element of the Global Maritime Distress and Safety System . | https://en.wikipedia.org/wiki/Telex |
Teliospore (sometimes called teleutospore ) is the thick-walled resting spore of some fungi ( rusts and smuts ), from which the basidium arises.
They develop in telia (sing. telium or teliosorus ).
The telial host is the primary host in heteroecious rusts. The aecial host is the alternate host (look for pycnia and aecia ).
These terms apply when two hosts are required by a heteroecious rust fungus to complete its life cycle.
Teliospores consist of one, two or more dikaryote cells.
Teliospores are often dark-coloured and thick-walled, especially in species where they overwinter (acting as chlamydospores ).
Two-celled teliospores formerly defined the genus Puccinia . Here the wall is particularly thick at the tip of the terminal cell which extends into a beak in some species.
Teliospores consist of dikaryote cells. As the teliospore cells germinate, the nuclei undergo karyogamy and thereafter meiosis , giving rise to a four-celled basidium with haploid basidiospores .
This Basidiomycota -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Teliospore |
Telisotuzumab vedotin is an antibody drug conjugate developed by AbbVie for non-small cell lung cancer . [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] | https://en.wikipedia.org/wiki/Telisotuzumab_vedotin |
Telit Cinterion (known as Telit prior to January 1, 2023) is an Internet of Things (IoT) Enabler company headquartered in Irvine, California , United States. It is a privately held company with key operations in the US, Brazil, Italy, Israel, and Korea.
Telit Cinterion is an IoT Enabler providing IoT modules, edge-to-cloud services including connectivity plans, IoT SIMs, IoT embedded software and PaaS IoT deployment managed services . On July 29 2022, Telit and Thales (Euronext Paris: HO), a global leader in Aerospace, Defense, Security & Digital Identity, jointly announced they entered into an agreement under which Telit would acquire Thales' cellular IoT products. [ 1 ] The transaction which was concluded on December 31, 2022, included Thales' IoT services platform and portfolio of cellular wireless communication modules, gateways, and data (modem) cards, ranging from 4G LTE, LPWAN to 5G. On August 26 2022, Telit announced the acquisition of group assets from Mobilogix, a California-based startup company specializing in custom IoT solutions worldwide. [ 2 ] The acquisition added device engineering expertise and resources that focus on optimizing specifications for handoff to electronic manufacturing services, original device manufacturing, and the attainment of regulatory approvals and carrier certifications. In 2021, the company launched Telit NeXT, a cloud-native core network to enhance its global IoT connectivity offering. [ 3 ]
The company developed the ball-grid-array (BGA) module; [ 4 ] the “Family” and “Unified-Form-Factor” concepts; [ 5 ] the smallest GPS receiver module; [ 6 ] a Gigabit LTE data card module; [ 7 ] a 5G data card module; [ 8 ] simWISE, integrated SIM technology with data subscription services; [ 9 ] OneEdge, an IoT deployment management tool; [ 10 ] deviceWISE® Industrial IoT Integration and Enablement Platform; [ 11 ] Telit IoT Portal, a Cloud-Based Platform as a Service for IoT; and Telit secureWISE, a Secure IIoT Platform for Industrial Systems. [ 12 ]
The company also provides cellular, short-range, and global navigation satellite system (GNSS) modules. [ 13 ] The products are available in over 80 countries from 20 sales offices, supported regionally from 12 application engineering hubs. [ 14 ]
Its module portfolio includes products in GSM / GPRS , EDGE , UMTS , HSPA , LTE (including NB-IoT, LTE-M, Categories 1, 4, 6, 9, 11, 12, 13 Gigabit LTE Category 18), 5G (3GPP Rel 15 and 16) products as well as Wi-Fi , Bluetooth and GPS /GNSS modules. Its module families feature a single form factor that is interchangeable across regional cellular networks, technologies and standards. [ 15 ]
In 2006, with the acquisition of Bellwave, a regional headquarters was opened in Seoul. [ 16 ] In 2008, it further expanded with regional operations in São Paulo, Brazil; Johannesburg, South Africa and Ankara, Turkey.
In 2009 Telit acquired France-based One RF. [ 17 ] It also launched Infinita Services to simplify M2M solution deployment and maintenance of device software, and a short-range GSM/GPRS module, the GE865-QUAD.
In March 2011, Telit acquired Motorola Solutions' M2M modules business unit [ 18 ] In January 2012 Telit acquired California-based Navman Wireless OEM Solutions. [ 19 ]
In July 2012, Telit formed a new business unit, m2mAIR, [ 20 ] to offer M2M services. m2mAIR offers module and subscription lifecycle management via a Software as a Service (SaaS) platform and global wireless coverage in partnership with Telefónica. [ 21 ] It also includes the Jupiter SL869 multi-constellation GNSS receiver supporting GPS, GLONASS, Galileo and QZSS; followed by the 3D-SiP based SE880.
In 2013, the company acquired Florida-based ILS Technology LLC, a provider of industrial automation and IoT cloud platform. [ 22 ] It also acquired Illinois-based CrossBridge Solutions [ 23 ] and NXP B.V., NXP’s ATOP business and a fully owned subsidiary of NXP Semiconductors N.V. (Nasdaq: NXPI) adding to the company's company’s OEM automotive products unit. [ 24 ] The OEM automotive product business unit was sold in 2019. [ 25 ]
In 2017, Telit acquired GainSpan for US$ 8 million. [ 26 ] [ 27 ]
In 2022, the company announced its acquisition of Thales Cinterion for a 25% stake in Telit. [ 28 ] In 2022, the company also announced the acquisition of California-based Mobilogix Inc. [ 29 ]
The company has R&D centers in Irvine - California, Boca Raton - Florida, Trieste - Italy, Seoul - Korea, and Bangalore - India. The Trieste R&D center is complemented with facilities in Cagliari. This center focuses on the advancement of 4G LTE Categories 4, 1, Mobile IoT standards LTE-M and NB-IoT and hardware design for short range wireless and Wi-Fi products. It is also the R&D base for the Telit simWISE integrated SIM (iUICC) product and Telit OneEdge, software suite and tools for IoT deployment management. The facility also houses the company's advanced RF lab.
The Florida center in Boca Raton, houses software engineering and R&D in charge of advancing cloud and platform technologies. It is the lead software development center for Telit Connectivity, Telit simWISE, Telit OneEdge and deviceWISE IoT/Industrial IoT platform. Boca Raton is also the Global Headquarters for Telit's secureWISE platform—the leading remote connection solution for the semiconductor industry.
The R&D center in Seoul (Korea) is the company’s primary APAC hardware R&D center is located in Seoul, South Korea, and is the development site for the cellular broadband products in 5G, and in 4G LTE Categories 1 and above.
The Bangalore (India) software competence hub is for short-range wireless technologies. The Bangalore center develops system and application software for the company's cellular, Wi-Fi and Bluetooth modules. [ 30 ]
The Irvine center is responsible for turnkey IoT solutions, engineering, and design. | https://en.wikipedia.org/wiki/Telit_Cinterion |
Telium , plural telia , are structures produced by rust fungi as part of the reproductive cycle . [ 1 ] They are typically yellow or orange drying to brown or black and are exclusively a mechanism for the release of teliospores which are released by wind or water to infect the alternate host in the rust life-cycle. The telial stage provides an overwintering strategy in the life cycle of a parasitic heteroecious fungus by producing teliospores; this occurs on cedar trees. A primary aecial stage is spent parasitizing a separate host plant which is a precursor in the life cycle of heteroecious fungi. Teliospores are released from the telia in the spring. The spores can spread many kilometers through the air, however most are spread near the host plant. [ 2 ]
There are a number of plants that can be infected by the telial stage. Therefore, the telial stage is considered a pathogen to those plants. A few specific plant pathogenic species are listed here with their hosts .
The life cycle of rust fungi can have up to five different spore stages and can get quite complex. [ 4 ] These stages are:
This Basidiomycota -related article is a stub . You can help Wikipedia by expanding it .
This plant disease article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telium |
Telluric iron , also called native iron , is iron that originated on Earth , and is found in a metallic form rather than as an ore . Telluric iron is extremely rare, with only one known major deposit in the world, located in Greenland .
With the exception of its molten core, nearly all elemental iron on Earth is found as iron ores . All metallic iron was thought to have been transformed into iron oxides during the Great Oxidation Event , beginning roughly 2 billion years ago, among other theories. Until the late 1800s, iron as a native metal was only a matter of speculation, outside of isolated Greenland. The only known, terrestrial iron in metallic form was found as meteorites , which were deposited onto the Earth from outer space.
Telluric iron is so named after the Latin word Tellus , meaning "Earth" (the planet, as opposed to terra meaning "earth": the land, ground or soil), combined with the suffix -ic meaning "of" or "born from", differentiating it from meteorites . Telluric iron resembles meteoric iron , in that it contains both a significant amount of nickel and Widmanstatten structures . However, telluric iron typically contains only around 3% nickel, which is too low for meteorites, of which none have been found with less than 5%. There are two types of telluric iron: Both type 1 and type 2 contain comparable amounts of nickel and other impurities. The main difference between the two is the carbon content, which greatly affects the hardness, workability, and melting point of the metal.
Telluric iron is metallic iron that formed within the Earth's mantle and crust. Although minor deposits of telluric iron have been found around the world, the west shores of Greenland hold the only known major deposits. However, these deposits may vary drastically in shape and composition, even in the same region, as well as drastic variations between different regions such as Uivfaq, Asuk, Blaafjeld, and Mellemfjord. The common factor is that all Greenlandic deposits tend to be found in dikes (lava-filled fractures in the bedrock) or extrusions where molten rock was able to flow out onto the surface. Another commonality is that all deposits are found in association with graphite -rich feldspar , likely contributing to the high carbon-content and low oxide presence in the metal, although it is unknown if the metal managed to escape being oxidized with the rest of Earth's iron, or if it began as beds of ore and coal that subducted and then were naturally smelted in the lava due to the reducing environment provided by the carbon-rich, graphitic feldspar .
Telluric iron in Greenland is unique, in that it can be found in nearly all phases of iron-carbon alloys , and with drastically varying crystalline structures. In some rock it is found mixed with basalt as very small grains with sharp corners and irregular shapes, whereas in others the small, grain-sized droplets in the molten magma were able to coalesce into larger, pea-sized droplets that crystallized with a mostly spherical or oblong shape. Still in others the dike or extrusion may be made almost entirely out of very high-carbon cast-iron, which could more easily coalesce within the magma and flow into cracks due to its lower viscosity and melting point. This cast iron is often crusted with or contains inclusions of basalt, as it extruded out of the ground as very large, globular masses within the lava, out of which large boulders formed due to natural erosion of the surrounding basalt.
Telluric iron is largely divided into two groups, depending on the carbon content. Type 1 is a cast-iron typically containing over 2.0% carbon, while type 2 ranges somewhere between wrought iron and a eutectoid steel. Both types tend to handle weathering in the elements very well, but tend to decompose and crumble very quickly in the dry, controlled atmosphere of a museum, although type 2 is far more prone to this kind of damage. [ 4 ]
Type 1 telluric iron contains a significant amount of carbon. Type 1 is a white nickel cast-iron, containing 1.7 to 4% carbon and 0.05 to 4% nickel, which is very hard and brittle and does not respond well to cold working . The structure of type 1 consists mainly of pearlite and cementite or cohenite , with inclusions of troilite and silicate . The individual ferrite grains are typically about a millimeter in size. Although the composition of the grains may vary, even within the same grain, they are mostly composed of fairly pure nickel-ferrite. The ferrite grains are connected with cementite laminations; typically 5–25 micrometers thick; forming the pearlite.
Type 1 is found as massive extrusions or very large boulders, typically ranging from a few tons to tens of tons. The metal could not be cold worked by the ancient Inuit , (the local inhabitants of Greenland), and proves extremely difficult to machine even with modern tools. Machining of type 1 is possibly best accomplished with a carborundum wheel and water cooling. However type 1 was possibly used as hammer and anvil stones by the Inuit.
When sawed in half, boulders of type 1 tend to have a thick shell of cast-iron on the outside that can barely be broken with pneumatic jackhammers , but inside a much more brittle construction of iron grains in an almost powdery form, sintered together to form a porous , sponge-iron type of material that pulverizes at the strike of a hammer. [ 4 ]
Type 2 telluric iron also contains around 0.05 to 4% nickel, but typically less than 0.7% carbon. Type 2 is a malleable nickel-iron which responds well to cold working. The carbon and nickel content have a great effect on the final hardness of the cold-worked piece.
Type 2 is found as small grains mixed within basalt rock. The grains are usually 1–5 millimeters in diameter. The grains are usually found individually, separated by the basalt, although they are sometimes sintered together to form larger aggregates. The larger pieces also contain small amounts of cohenite, ilmenite , pearlite, and troilite. Type 2 was used by the Inuit to make items such as knives and ulus . The basalt was usually crushed in order to release the pea-sized grains, which were then hammered into discs about the size of coins. The metal is very soft and can be hammered into very thin plates. These flat discs were usually inserted into long slits carved into bone handles, in rows so that they slightly overlapped each other, forming an edge that resembled a combination of a knife and a saw (an inverted scalloped edge ). [ 5 ] [ 6 ]
Aside from a very small deposit of telluric iron in Kassel, Germany , which has now been depleted, and a few other minor deposits from around the world, the only known major deposits exist in and nearby the area of Disko Bay , in Greenland . The material was found in the volcanic plains of basalt rock, and used by the local Inuit to make cutting edges for tools like knives and ulus . The Inuit were the only people to make practical use of telluric iron. [ 5 ] [ 6 ]
In 1870, Adolf Erik Nordenskiöld discovered large boulders of iron near the Disko Bay area of Greenland. Knowing that the Inuit had made tools from the Cape York meteorite , mainly due to Sir John Ross ' discovery that the natives of Greenland used iron knives, Nordenskiöld landed at Fortune Bay on Disko Island to search for the material. The Inuit had told Ross that they got the iron from high on a mountain, at a site where two large boulders lay. One was very hard and could not be broken, but the other was chipped into smaller pieces from which balls of iron were extracted and hammered into flat discs for the knives. Nordenskiöld searched unsuccessfully for the site, until being led by some of the local Inuit to a place called Uivfaq , where large masses of metallic iron were strewn about the area. He assumed that the metal was of meteoric origin , since both contain significant amounts of nickel and both had Widmanstätten patterns . Most scientists at the time believed that no un- oxidized telluric iron existed, and few questioned Nordenskiöld's finding. [ 5 ] [ 6 ]
Gustav Nauckhoff made an expedition to Greenland in 1871. Armed with dynamite and lifting equipment , his expedition collected three large samples of telluric iron, also believing them to be meteoric, per Nordenskiöld's examination, and brought them back to Europe for further study. These samples can be found currently in Sweden , Finland , and Denmark . A 25-ton block now rests outside of the Riksmuseum in Stockholm, a 6.6 ton block outside the Geological Museum in Copenhagen, and a 3-ton block can be found in the Museum of Natural History in Kumpula, Helsinki. [ 7 ]
Accompanying Nauckhoff in 1871 was K. J. V. Steenstrup . Due to circumstances like the shape of the boulders, which often had sharp corners or jagged edges that are not characteristic of meteorites (which ablate considerably during atmospheric entry ), or the fact that many had areas that were encrusted with basalt , Steenstrup disagreed with Nordenskiöld about the origin of the boulders, and set out on an expedition of his own in 1878. In 1879, Steenstrup first identified the type 2 iron , showing that it also contained Widmanstätten structures . Steenstrup later reported what he found:
In the autumn of 1879, I made a discovery in connection with this matter, for in an old grave at Ekaluit ... I found 9 pieces of basalt containing round balls and irregular pieces of metallic iron. These pieces were lying together with bone knives, similar to those brought home by Ross, as well as with the usual stone tools ... whereas the 9 pieces of basalt with the iron balls were evidently the material for the bone knives. This iron is soft and keeps well in the air, from which reason it is fit for use in the manner described by Ross. The rock in which the iron appears is a typical, large-grained felspar - basalt . The discovery has a double significance, firstly, because it is the first time we have seen the material out of which the Esquimaux made artificial knives , and secondly, because it showed that they have used telluric iron for that purpose .
After the discovery in the grave at Ekaluit , Steenstrup found many large outcrops of basalt containing the type 2 iron . Since the type 2 grains are embedded within volcanic basalt that matches the underlying bedrock, Steenstrup was able to show that the iron was from terrestrial, or telluric, sources. [ 7 ] In his report, Steenstrup added,
This peculiar layer of basalt is filled from top to bottom with iron-grains of all sizes from a fraction of a millimeter to a length of 18 mm with a breadth of 14 mm, which is the greatest I have found. ... When polished, this iron shows beautiful Widmannstätten figures . ... Metallic nickel-iron with Widmannstätten figures has now been proved to be also a telluric mineral , and the presence of nickel together with a certain crystalline structure are consequently not sufficient to give the character of meteorites to loose iron blocks.
Steenstrup's findings were later confirmed by meteorite expert J. Lawrence Smith in 1879, and then by Joh Lorenzen in 1882. The extremely rare telluric iron found in western Greenland has been under study ever since. [ 5 ] [ 6 ] [ 7 ]
In addition to the Disko Island deposit native iron has been reported from Fortune Bay, Mellemfjord, Asuk, and other locations along Greenland's west coast. Other locations include: [ 1 ]
Native nickel-iron alloys with Ni 3 Fe to Ni 2 Fe occur as placer deposits derived from ultramafic rocks . Awaruite was described in 1885 from New Zealand . | https://en.wikipedia.org/wiki/Telluric_iron |
A tellurion (also spelled tellurian , tellurium , and yet another name is loxocosm ), is a clock , typically of French or Swiss origin, surmounted by a mechanism that depicts how day , night , and the seasons are caused by the rotation and orientation of Earth on its axis and its orbit around the Sun . The clock normally also displays the phase of the Moon and the four-year ( perpetual ) calendar. [ 1 ]
It is related to the orrery , which illustrates the relative positions and motions of the planets and moons in the Solar System in a heliocentric model.
The word tellurion derives from the Latin tellus , meaning "earth". [ 2 ]
This astronomy -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tellurion |
The diatomic molecule tellurium monoxide has been found as a transient species. [ 2 ] Previous work that claimed the existence of TeO solid has not been substantiated. [ 3 ] The coating on DVDs called tellurium suboxide may be a mixture of tellurium dioxide and tellurium metal. [ 4 ]
Tellurium monoxide was first reported in 1883 by E. Divers and M. Shimose. [ 5 ] It was supposedly created by the thermal decomposition of tellurium sulfoxide in a vacuum , [ citation needed ] and was shown to react with hydrogen chloride in a 1913 report. [ 6 ] Later work has not substantiated the claim that this was a pure solid compound. [ 2 ] By 1984, the company Panasonic was working on an erasable optical disk drive containing "tellurium monoxide" (really a mixture of Te and TeO 2 ). [ 7 ] | https://en.wikipedia.org/wiki/Tellurium_monoxide |
Tellurium nitride describes chemical compounds of Te containing N 3− . Efforts have been made toward the binary nitrides but the results are inconclusive and it appears that such materials are unstable. Still unconfirmed is Te 4 N 4 , which would be an analogue of tetraselenium tetranitride (Se 4 N 4 ) and tetrasulfur tetranitride (S 4 N 4 ). It has long been known that ammonia reacts with tellurium tetrachloride , which is similar to the method of synthesis of S 4 N 4 . [ 1 ] [ 2 ] The reaction of TeCl 4 with a THF solution of N(SiMe 3 ) 3 gives a well-defined tellurium nitride [Te 6 N 8 (TeCl 2 ) 4 (THF) 4 ]. [ 3 ]
This article about a hypothetical chemical compound is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Tellurium_nitride |
Tellurium tetrachloride is the inorganic compound with the empirical formula TeCl 4 . The compound is volatile, subliming at 200 °C at 0.1 mmHg. [ 2 ] Molten TeCl 4 is ionic, dissociating into TeCl 3 + and Te 2 Cl 10 2− . [ 2 ]
TeCl 4 is monomeric in the gas phase, with a structure similar to that of SF 4 . [ 3 ] In the solid state, it is a tetrameric cubane-type cluster , consisting of a Te 4 Cl 4 core and three terminal chloride ligands for each Te. Alternatively, this tetrameric structure can be considered as a Te 4 tetrahedron with face-capping chlorines and three terminal chlorines per tellurium atom, giving each tellurium atom a distorted octahedral environment
TeCl 4 is prepared by chlorination of tellurium powder:
The reaction is initiated with heat. The product is isolated by distillation. [ 4 ] Crude TeCl 4 can be purified by distillation under an atmosphere of chlorine. [ 1 ]
Alternatively TeCl 4 can be prepared using sulfuryl chloride (SO₂Cl₂) as a chlorine source. [ 1 ] Yet another method involves the reaction of tellurium with sulfur monochloride (S 2 Cl 2 ) at room temperature. This exothermic reaction rapidly forms white needle-like crystals of TeCl 4 . [ 5 ]
Tellurium tetrachloride is the gateway compound for high valent organotellurium compounds . Arylation gives, depending on conditions, Te(C 6 H 4 R) 2 Cl 2 , [Te(C 6 H 4 R) 5 ] − , [Te(C 6 H 4 R) 6 ] 2− . [ 6 ]
TeCl 4 has few applications in organic synthesis. Its equivalent weight is high, and the toxicity of organotellurium compounds is problematic. Possible applications of tellurium tetrachloride to organic synthesis have been reported. [ 7 ] It adds to alkenes to give Cl-C-C-TeCl 3 derivatives, wherein the Te can be subsequently removed with sodium sulfide. Electron-rich arenes react to give aryl Te compounds. Thus, anisole gives TeCl 2 (C 6 H 4 OMe) 2 , which can be reduced to the diaryl telluride. TeCl 4 is a precursor to tellurium-containing heterocycles like tellurophenes . [ 1 ]
Heating a mixture of TeCl 4 and metallic tellurium gives tellurium dichloride (TeCl 2 ). [ 8 ]
In moist air, TeCl 4 forms tellurium oxychloride (TeOCl 2 ), which further decomposes with excess water to form tellurous acid (H 2 TeO 3 ). [ 8 ]
As is the case for other tellurium compounds, TeCl 4 is toxic. It also releases HCl upon hydrolysis. [ 1 ] | https://en.wikipedia.org/wiki/Tellurium_tetrachloride |
A telluroketone is an analog of a ketone in which the oxygen atom has been replaced by a tellurium atom. This change makes the functional group less stable, requiring greater steric and electronic stabilization. [ 1 ]
This organic chemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telluroketone |
Tellurols are analogues of alcohols and phenols where tellurium replaces oxygen. [ 1 ] Tellurols, selenols , and thiols have similar properties, but tellurols are the least stable. [ 2 ] Although they are fundamental representatives of organotellurium compounds , tellurols are lightly studied because of their instability. Tellurol derivatives include telluroesters (RC(O)TeR') and tellurocyanates (RTeCN).
Alkyltellurols are colorless liquids with strong odors. Samples usually appear yellowish owing to the presence of dialkylditelluride impurities. Near room temperature, methanetellurol degrades with loss of elemental tellurium. It is reported to ignite in air. [ 3 ]
Aryltellurols are more robust and have been obtained as colorless crystals. Some of the most stable tellurols are the bulky silylated derivatives of tris(trimethylsilyl)methane and analogues. One series of readily isolable tellurols is (Me 3 Si) 3 CTeH , (Me 3 Si) 3 SiTeH , and (Me 3 Si) 3 GeTeH . [ 1 ]
The acidity of tellurols can be inferred by the acidity and dissociation constant of hydrogen telluride , H 2 Te , which has a (first) pK a of 2.64 corresponding to a dissociation constant of 2.3 × 10 −3 . H 2 Te has a lower pK a and higher dissociation constant than H 2 S and H 2 Se . [ 4 ] The pKa is 9.3 for (Me 3 Si) 3 CTeH vs 10.8 for (Me 3 Si) 3 CSeH . [ 1 ]
The absence of hydrogen-bonding explains the low boiling temperature of tellurols. [ 4 ]
The first tellurol to be synthesized, ethanetellurol, was prepared in 1926 via the Grignard reagent . [ 1 ] The most frequently used method involves reduction of the ditellurides ( R 2 Te 2 ). | https://en.wikipedia.org/wiki/Tellurol |
A telluroxide is a type of organotellurium compound with the formula R 2 TeO. These compounds are analogous to sulfoxides in some respects. Reflecting the decreased tendency of Te to form multiple bonds , telluroxides exist both the monomer and the polymer , which are favored in solution and the solid state, respectively: [ 1 ]
Telluroxides are prepared from the telluroethers by halogenation followed by base hydrolysis: | https://en.wikipedia.org/wiki/Telluroxide |
Tellus Series B: Chemical and Physical Meteorology is an open access scientific journal that is published by Stockholm University Press for the International Meteorological Institute in Stockholm, Sweden since 2022. [ 1 ] Between 2012 and 2022, the issues were published online by Co-action Publishing. [ 2 ] The journal publishes original articles, short contributions, and correspondence on atmospheric chemistry , surface exchange processes, long-range and global transport, aerosol science, and cloud physics including related radiation transfer. Biogeochemical cycles including related aspects of marine chemistry and geochemistry also represent a central theme.
Tellus B is the companion to Tellus Series A: Dynamic Meteorology and Oceanography .
This article about a journal on climatology or meteorology is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page .
This article about a journal on geochemistry is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page . | https://en.wikipedia.org/wiki/Tellus_B |
Telmatology is a branch of physical geography concerned with the study of wetlands , such as marshes or swamps . [ 1 ]
This article about geography terminology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telmatology |
A teloblast is a large cell in the embryos of clitellate annelids which asymmetrically divide to form many smaller cells known as blast cells . These blast cells further proliferate and differentiate to form the segmental tissues of the annelid. Teloblasts are well studied in leeches , though they are also present in the other major class of clitellates: the oligochaetes .
All teloblasts are specified from the D quadrant macromere after the second round of divisions post-fertilization. They are larger than the other cells that result from cleavage of macromere D'. [ 1 ] There are five pairs of teloblasts, one on each side of the embryo. Four of the teloblasts (N, O, P, and Q) give rise to ectodermal tissue and one pair (M) gives rise to mesodermal tissue. The column of blast cells arising out of each teloblast is known as a bandlet. All five bandlets coalesce into one germinal band on each side of the embryo, extending out from the teloblast towards the head (in the rostral direction). There is a ventral plate of blast cells where the lateral columns meet. The teloblasts are located at the rear of the embryo. [ 2 ]
Teloblasts have two separate cytoplasmic domains: the teloplasm and the vitelloplasm. The teloplasm contains the nucleus , ribosomes , mitochondria , and other subcellular organelles . The vitelloplasm contains mostly yolk platelets . Only the teloplasm gets passed onto the daughter stem cells after cell division . [ 3 ] The teloplasm also includes maternal RNA transcripts. [ 1 ]
The O and P teloblasts are specified from two separate but identical precursors, which form an equivalence group . These two precursor cells are termed O/P cells for their ability to become either O or P teloblasts. Signals from the surrounding cells act to specify which fate the teloblasts and their progeny take on. Interactions with the q bandlet, however transient, can induce the p fate in the adjacent o/p bandlet. [ 4 ] In some species (i.e. Helobdella triserialis ), the provisional epithelium covering the cells plays a role in inducing the O fate. [ 5 ] In the absence of cell-cell interactions, the O/P precursors will become O teloblasts. O and P bandlets exhibit very different mitotic patterns (see figure) which are used to identify them in experimental manipulations.
Experimental results in Tubifex hattai suggest that there is not an equivalence group for O and P in these worms, but instead the P lineage is committed at its birth from the O/P proteloblast stage, while the O lineage is induced by the P teloblast. In the absence of the P teloblast, the pluripotent O teloblast becomes P specified. [ 6 ] In Helobdella , the O/P proteloblasts generate four blast cells with segmental progeny by asymmetric division before a symmetric division into O/P teloblasts. [ 1 ] Helobdella austensis appears to have an additional M-lineage-sourced signal that promotes P lineage differentiation [ 7 ] in addition to bone morphogenic protein molecular signaling that is sourced from Q lineage cells and also helps specify P fate. [ 1 ]
The N and Q teloblasts contribute two blast cells per segment, one making up the anterior half of the segment, the second making up the posterior half of the segment. The O, P, and M lineages contribute one blast cell per segment, but the contributions from each blast cell span a segmental boundary. These segmental boundaries were discovered by injecting teloblasts with cell lineage tracers after a few blast cells had already been generated. During development, the N and Q bandlets, which eventually have 64 blast cells each, slide past the O, P, and M bandlets, which only have 32 cells. Thus, the segmental boundaries within each bandlet are already specified before all the bandlets come into complete register. [ 9 ] | https://en.wikipedia.org/wiki/Teloblast |
Telocator Alphanumeric Protocol (TAP) is an industry-standard protocol for sending short messages via a land-line modem to a provider of pager and/or SMS services, for onward transmission to pagers and mobile phones. [ 1 ] [ 2 ]
TAP, initially known as Motorola Page Entry (PET) was adopted in September 1988, by the Personal Communication Industry Association . TAP defines an industry standard for sending alphanumeric messages to pagers.
TAP was also known as IXO protocol. Originally, devices like the IXO Device were used to send Alphanumeric Pages using TAP. Later, Motorola would create a similar device called the AlphaMate .
The standard protocol is ASCII with XON/XOFF flow control, using a 10-bit code (1 start bit, 7 data bits, even parity, 1 stop bit). No echo shall be employed in full duplex mode. [ 3 ]
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telocator_Alphanumeric_Protocol |
Telogis was a privately-held US-based company that develops location-based software to manage mobile resources. [ 2 ] Telogis sold software as a service (SaaS) which incorporated location information into applications for fleet owners as well as geospatial software development toolkits. [ 3 ]
In 2016, Telogis was acquired by Verizon . [ 4 ]
Telogis was founded in 2001 by Newth Morris, Jason Koch and Ralph Mason, as a trunked radio hardware and software provider. Former Novell Inc. Chairman and CEO Jack Messman was chairman of the board of directors. [ 5 ] [ 6 ] The company was started with investments from its founders, and by 2012 the privately-held company had approximately $69 million in revenue. [ 7 ]
Wall Street Journal reporter Don Clark stated of the company's technology that, "Telogis exploited the evolution of software-as-a-service–placing data from vehicles in the cloud ... so that companies that own vehicle fleets can track their cars and trucks without the need to set up their own servers for the purpose." [ 8 ] In July 2010 Telogis acquired the assets of Remote Dynamics, [ 9 ] then in February, 2011 Telogis acquired the assets of Intergis, a provider of routing, mobile resource and fleet management software for approximately 2,000 small to mid-sized business fleets. [ 10 ] In July 2012 Telogis acquired Navtrak. The acquisition resulted in Telogis Navigation, commercial navigation software that gives professional drivers built-in feedback systems to provide up-to-date road network information. [ 11 ]
The company's first outside venture capital was announced in October 2013, with $93 million from Kleiner Perkins Caufield & Byers . [ 3 ] In February 2011 private investors provided $2.9 million. [ 12 ] Additional funding was received from GM Ventures in 2014. [ 13 ]
On 21 June 2016, it was announced that Telogis will merge with Verizon via an acquisition. [ 14 ]
On 6 March 2018, a press release [ 15 ] announced that Telogis would be rebranded along with sister companies– Fleetmatics and Verizon Telematics–as Verizon Connect .
Telogis software collects location-based data from embedded and installed hardware in vehicles, as well as from mobile devices. It works on over 40 different hardware platforms from 12 different manufacturers and collects an important array of data. [ 16 ] Telogis also provides a software development kit for users to create location-based mobile and desktop applications. [ 17 ] One of the primary functions of Telogis's software is to provide United States Federal Government mandated hours of service commercial driver activity logs.
Telogis provides a built-in telematics option for several OEMs including Ford , GM , [ 18 ] Volvo , Mack , Hino , Isuzu (United States based trucks), and Manitowoc. This allows fleet owners to opt for factory-installed telematics hardware when purchasing selected new cars and trucks. The advantages include immediate over-the-air activation when adding new vehicles to their fleet management system and additional data points such as DEF ( Diesel Exhaust Fluid ) quality, water in the diesel and extra DTCs ( Diagnostic Trouble Codes ) across the body, powertrain and chassis. For off-highway vehicles, Telogis also works with John Deere . [ 19 ]
In addition to the OEM built-in options, selected Freightliner trucks offer a pre-wired option that makes it simpler to add the required hardware for tracking trucks. [ 20 ]
In October 2013 the Wall Street Journal reported that trucking companies were using Telogis to monitor their drivers, using the data they received to either reward or discipline their drivers. [ 21 ] This has led some employees to become concerned about privacy issues. [ 22 ] Councilman Lewis Rotella of Niagara Falls, New York , stated that, "It’s almost like big brother ’s watching you ... You have to put some trust into the employees doing the job," in response to a 2006 contract placing Telogis devices in Niagara city vehicles. He stated further that he believed that such devices can be used to ensure safety, but should not be used for "surreptitiously trailing employees". Rotella also admitted to using the devices himself in his private business to monitor safety. [ 23 ] Stephen Roy, president of Mack Trucks , another Telogis partner, also stated that the software would be used by Mack to help manage workflow and not to track the minute-by-minute decisions of its employees. [ 24 ] | https://en.wikipedia.org/wiki/Telogis |
Telomerase , also called terminal transferase , [ 1 ] is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres . A telomere is a region of repetitive sequences at each end of the chromosomes of most eukaryotes . Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring chromosomes. The fruit fly Drosophila melanogaster lacks telomerase, but instead uses retrotransposons to maintain telomeres. [ 2 ]
Telomerase is a reverse transcriptase enzyme that carries its own RNA molecule (e.g., with the sequence 3′- C CC A A U CCC-5′ in Trypanosoma brucei ) [ 3 ] which is used as a template when it elongates telomeres. Telomerase is active in gametes and most cancer cells, but is normally absent in most somatic cells .
The existence of a compensatory mechanism for telomere shortening was first found by Soviet biologist Alexey Olovnikov in 1973, [ 4 ] who also suggested the telomere hypothesis of aging and the telomere's connections to cancer and perhaps some neurodegenerative diseases. [ 5 ]
Telomerase in the ciliate Tetrahymena was discovered by Carol W. Greider and Elizabeth Blackburn in 1984. [ 6 ] Together with Jack W. Szostak , Greider and Blackburn were awarded the 2009 Nobel Prize in Physiology or Medicine for their discovery. [ 7 ] Later the cryo-EM structure of telomerase was first reported in T. thermophila , to be followed a few years later by the cryo-EM structure of telomerase in humans. [ 8 ]
The role of telomeres and telomerase in cell aging and cancer was established by scientists at biotechnology company Geron with the cloning of the RNA and catalytic components of human telomerase [ 9 ] and the development of a polymerase chain reaction (PCR) based assay for telomerase activity called the TRAP assay, which surveys telomerase activity in multiple types of cancer. [ 10 ]
The negative stain electron microscopy (EM) structures of human and Tetrahymena telomerases were characterized in 2013. [ 11 ] [ 12 ] Two years later, the first cryo-electron microscopy ( cryo-EM ) structure of telomerase holoenzyme ( Tetrahymena ) was determined. [ 13 ] In 2018, the structure of human telomerase was determined through cryo-EM by UC Berkeley scientists. [ 14 ]
The molecular composition of the human telomerase complex was determined by Scott Cohen and his team at the Children's Medical Research Institute (Sydney Australia) and consists of two molecules each of human telomerase reverse transcriptase (TERT), Telomerase RNA Component (TR or TERC), and dyskerin (DKC1). [ 15 ] The genes of telomerase subunits, which include TERT, [ 16 ] TERC, [ 17 ] DKC1 [ 18 ] and TEP1, [ 19 ] are located on different chromosomes. The human TERT gene (hTERT) is translated into a protein of 1132 amino acids . [ 20 ] TERT polypeptide folds with (and carries) TERC, a non-coding RNA (451 nucleotides long). TERT has a 'mitten' structure that allows it to wrap around the chromosome to add single-stranded telomere repeats. [ 21 ]
TERT is a reverse transcriptase , which is a class of enzymes that creates single-stranded DNA using single-stranded RNA as a template. [ 22 ]
The protein consists of four conserved domains (RNA-Binding Domain (TRBD), fingers, palm and thumb), organized into a "right hand" ring configuration that shares common features with retroviral reverse transcriptases, viral RNA replicases and bacteriophage B-family DNA polymerases. [ 23 ] [ 24 ]
TERT proteins from many eukaryotes have been sequenced. [ 25 ]
The shelterin protein TPP1 is both necessary and sufficient to recruit the telomerase enzyme to telomeres, and is the only shelterin protein in direct contact with telomerase. [ 26 ]
By using TERC, TERT can add a six-nucleotide repeating sequence, 5'- T TA G GG (in vertebrates; the sequence differs in other organisms) to the 3' strand of chromosomes. These TTAGGG repeats (with their various protein binding partners) are called telomeres. The template region of TERC is 3'-CAAUCCCAAUC-5'. [ 27 ]
Telomerase can bind the first few nucleotides of the template to the last telomere sequence on the chromosome, add a new telomere repeat (5'-GGTTAG-3') sequence, let go, realign the new 3'-end of telomere to the template, and repeat the process. Telomerase reverses telomere shortening .
Telomerase restores short bits of DNA known as telomeres , which are otherwise shortened after repeated division of a cell via mitosis .
In normal circumstances, where telomerase is absent, if a cell divides recursively, at some point the progeny reach their Hayflick limit , [ 28 ] which is believed to be between 50 and 70 cell divisions. At the limit the cells become senescent and cell division stops. [ 29 ] Telomerase allows each offspring to replace the lost bit of DNA, allowing the cell line to divide without ever reaching the limit. This same unbounded growth is a feature of cancerous growth . [ 30 ]
Embryonic stem cells express telomerase, which allows them to divide repeatedly and form the individual. In adults, telomerase is highly expressed only in cells that need to divide regularly, especially in male sperm cells , [ 31 ] but also in epidermal cells , [ 32 ] in activated T cell [ 33 ] and B cell [ 34 ] lymphocytes , as well as in certain adult stem cells , but in the great majority of cases somatic cells do not express telomerase. [ 35 ]
A comparative biology study of mammalian telomeres indicated that telomere length of some mammalian species correlates inversely, rather than directly, with lifespan, and concluded that the contribution of telomere length to lifespan is unresolved. [ 36 ] Telomere shortening does not occur with age in some postmitotic tissues, such as in the rat brain. [ 37 ] In humans, skeletal muscle telomere lengths remain stable from ages 23 –74. [ 38 ] In baboon skeletal muscle, which consists of fully differentiated postmitotic cells, less than 3% of myonuclei contain damaged telomeres and this percentage does not increase with age. [ 39 ] Thus, telomere shortening does not appear to be a major factor in the aging of the differentiated cells of brain or skeletal muscle. In human liver, cholangiocytes and hepatocytes show no age-related telomere shortening. [ 40 ] Another study found little evidence that, in humans, telomere length is a significant biomarker of normal aging with respect to important cognitive and physical abilities. [ 41 ]
Some experiments have raised questions on whether telomerase can be used as an anti-aging therapy , namely, the fact that mice with elevated levels of telomerase have higher cancer incidence and hence do not live longer. [ 42 ] On the other hand, one study showed that activating telomerase in cancer-resistant mice by overexpressing its catalytic subunit extended lifespan. [ 43 ] A study found that long-lived subjects inherited a hyperactive version of telomerase. [ 44 ]
Premature aging syndromes including Werner syndrome , Progeria , Ataxia telangiectasia , Ataxia-telangiectasia like disorder, Bloom syndrome , Fanconi anemia and Nijmegen breakage syndrome are associated with short telomeres. [ 45 ] However, the genes that have mutated in these diseases all have roles in the repair of DNA damage and the increased DNA damage may, itself, be a factor in the premature aging (see DNA damage theory of aging ). An additional role in maintaining telomere length is an active area of investigation.
In vitro, when cells approach the Hayflick limit , the time to senescence can be extended by inactivating the tumor suppressor proteins p53 and Retinoblastoma protein (pRb). [ 46 ] Cells that have been so-altered eventually undergo an event termed a "crisis" when the majority of the cells in the culture die. Sometimes, a cell does not stop dividing once it reaches a crisis. In a typical situation, the telomeres are shortened [ 47 ] and chromosomal integrity declines with every subsequent cell division. Exposed chromosome ends are interpreted as double-stranded breaks (DSB) in DNA; such damage is usually repaired by reattaching the broken ends together. When the cell does this due to telomere-shortening, the ends of different chromosomes can be attached to each other. This solves the problem of lacking telomeres, but during cell division anaphase , the fused chromosomes are randomly ripped apart, causing many mutations and chromosomal abnormalities. As this process continues, the cell's genome becomes unstable. Eventually, either fatal damage is done to the cell's chromosomes (killing it via apoptosis ), or an additional mutation that activates telomerase occurs. [ 46 ]
With telomerase activation some types of cells and their offspring become immortal (bypass the Hayflick limit ), thus avoiding cell death as long as the conditions for their duplication are met. Many cancer cells are considered 'immortal' because telomerase activity allows them to live much longer than any other somatic cell, which, combined with uncontrollable cell proliferation [ 48 ] is why they can form tumors . A good example of immortal cancer cells is HeLa cells , which have been used in laboratories as a model cell line since 1951.
While this method of modelling human cancer in cell culture is effective and has been used for many years by scientists, it is also very imprecise. The exact changes that allow for the formation of the tumorigenic clones in the above-described experiment are not clear. Scientists addressed this question by the serial introduction of multiple mutations present in a variety of human cancers. This has led to the identification of mutation combinations that form tumorigenic cells in a variety of cell types. While the combination varies by cell type, the following alterations are required in all cases: TERT activation, loss of p53 pathway function, loss of pRb pathway function, activation of the Ras or myc proto-oncogenes , and aberration of the Protein phosphatase 2 (PP2A). [ 49 ] That is to say, the cell has an activated telomerase, eliminating the process of death by chromosome instability or loss, absence of apoptosis-induction pathways, and continued mitosis activation.
This model of cancer in cell culture accurately describes the role of telomerase in actual human tumors. Telomerase activation has been observed in ~90% of all human tumors, [ 50 ] suggesting that the immortality conferred by telomerase plays a key role in cancer development. Of the tumors without TERT activation, [ 51 ] most employ a separate pathway to maintain telomere length termed Alternative Lengthening of Telomeres (ALT). [ 52 ] The presence of this alternative pathway was first described in an SV40 virus-transformed human cell line, and based on the dynamics of the changes in telomere length, was proposed to result through recombination . [ 53 ] However, the exact mechanism remains unclear.
Elizabeth Blackburn et al. , identified the upregulation of 70 genes known or suspected in cancer growth and spread through the body, and the activation of glycolysis , which enables cancer cells to rapidly use sugar to facilitate their programmed growth rate (roughly the growth rate of a fetus). [ 54 ]
Approaches to controlling telomerase and telomeres for cancer therapy include gene therapy , immunotherapy , small-molecule and signal pathway inhibitors. [ 55 ]
The ability to maintain functional telomeres may be one mechanism that allows cancer cells to grow in vitro for decades. [ 56 ] Telomerase activity is necessary to preserve many cancer types and is inactive in somatic cells , creating the possibility that telomerase inhibition could selectively repress cancer cell growth with minimal side effects. [ 57 ] If a drug can inhibit telomerase in cancer cells, the telomeres of successive generations will progressively shorten, limiting tumor growth. [ 58 ]
Telomerase is a good biomarker for cancer detection because most human cancer cells express high levels of it. Telomerase activity can be identified by its catalytic protein domain ( hTERT ). This [ clarify ] is the rate-limiting step in telomerase activity. It is associated with many cancer types. Various cancer cells and fibroblasts transformed with hTERT cDNA have high telomerase activity, while somatic cells do not. Cells testing positive for hTERT have positive nuclear signals. Epithelial stem cell tissue and its early daughter cells are the only noncancerous cells in which hTERT can be detected. Since hTERT expression is dependent only on the number of tumor cells within a sample, the amount of hTERT indicates the severity of cancer. [ 59 ]
The expression of hTERT can also be used to distinguish benign tumors from malignant tumors . Malignant tumors have higher hTERT expression than benign tumors. Real-time reverse transcription polymerase chain reaction (RT-PCR) quantifying hTERT expression in various tumor samples verified this varying expression. [ 60 ]
The lack of telomerase does not affect cell growth until the telomeres are short enough to cause cells to "die or undergo growth arrest". However, inhibiting telomerase alone is not enough to destroy large tumors. It must be combined with surgery, radiation , chemotherapy or immunotherapy. [ 59 ]
Cells may reduce their telomere length by only 50-252 base pairs per cell division, which can lead to a long lag phase . [ 61 ] [ 62 ]
A telomerase activator TA-65 is commercially available and is claimed to delay aging and to provide relief from certain disease conditions. [ 63 ] [ 64 ] [ 65 ] [ 66 ] [ 67 ] This formulation contains a molecule called cycloastragenol derived from a legume Astragalus membranaceus. Several other compounds have been found to increase telomerase activity: Centella asiatica extract 8.8-fold, oleanolic acid 5.9-fold, astragalus extract 4.3-fold, TA-65 2.2-fold, and maslinic acid 2-fold. [ 68 ]
Immunotherapy successfully treats some kinds of cancer, such as melanoma . This treatment involves manipulating a human's immune system to destroy cancerous cells. Humans have two major antigen identifying lymphocytes : CD8 + cytotoxic T-lymphocytes (CTL) and CD4 + helper T-lymphocytes that can destroy cells. Antigen receptors on CTL can bind to a 9-10 amino acid chain that is presented by the major histocompatibility complex (MHC) as in Figure 4. HTERT is a potential target antigen. Immunotargeting should result in relatively few side effects since hTERT expression is associated only with telomerase and is not essential in almost all somatic cells. [ 69 ] GV1001 uses this pathway. [ 55 ] Experimental drug and vaccine therapies targeting active telomerase have been tested in mouse models , and clinical trials have begun. One drug, imetelstat , is being clinically researched as a means of interfering with telomerase in cancer cells. [ 70 ] Most of the harmful cancer-related effects of telomerase are dependent on an intact RNA template. Cancer stem cells that use an alternative method of telomere maintenance are still killed when telomerase's RNA template is blocked or damaged.
Two telomerase vaccines have been developed: GRNVAC1 and GV1001 . GRNVAC1 isolates dendritic cells and the RNA that codes for the telomerase protein and puts them back into the patient to make cytotoxic T cells that kill the telomerase-active cells. GV1001 is a peptide from the active site of hTERT and is recognized by the immune system that reacts by killing the telomerase-active cells. [ 55 ]
Another independent approach is to use oligoadenylated anti-telomerase antisense oligonucleotides and ribozymes to target telomerase RNA, leading to the dissociation of the RNA and to apoptosis (Figure 5). The fast induction of apoptosis through antisense binding may be a good alternative to the slower telomere shortening. [ 61 ]
siRNAs are small RNA molecules that induce the sequence-specific degradation of other RNAs. siRNA treatment can function similar to traditional gene therapy by destroying the mRNA products of particular genes, and therefore preventing the expression of those genes. A 2012 study found that targeting TERC with an siRNA reduced telomerase activity by more than 50% and resulted in decreased viability of immortal cancer cells. [ 71 ] Treatment with both the siRNA and radiation caused a greater reduction in tumor size in mice than treatment with radiation alone, suggesting that targeting telomerase could be a way to increase the efficacy of radiation in treating radiation-resistant tumors.
Blackburn also discovered that mothers caring for very sick children have shorter telomeres when they report that their emotional stress is at a maximum and that telomerase was active at the site of blockages in coronary artery tissue, possibly accelerating heart attacks.
In 2009, it was shown that the amount of telomerase activity significantly increased following psychological stress . Across the sample of patients telomerase activity in peripheral blood mononuclear cells increased by 18% one hour after the end of the stress. [ 72 ]
A study in 2010 found that there was "significantly greater" telomerase activity in participants than controls after a three-month meditation retreat. [ 73 ]
Telomerase deficiency has been linked to diabetes mellitus and impaired insulin secretion in mice, due to loss of pancreatic insulin-producing cells . [ 74 ]
Mutations in TERT have been implicated in predisposing patients to aplastic anemia , a disorder in which the bone marrow fails to produce blood cells, in 2005. [ 75 ]
Cri du chat syndrome (CdCS) is a complex disorder involving the loss of the distal portion of the short arm of chromosome 5 . TERT is located in the deleted region, and loss of one copy of TERT has been suggested as a cause or contributing factor of this disease. [ 76 ]
Dyskeratosis congenita (DC) is a disease of the bone marrow that can be caused by some mutations in the telomerase subunits. [ 77 ] In the DC cases, about 35% cases are X-linked - recessive on the DKC1 locus [ 78 ] and 5% cases are autosomal dominant on the TERT [ 79 ] and TERC [ 80 ] loci.
Patients with DC have severe bone marrow failure manifesting as abnormal skin pigmentation , leucoplakia (a white thickening of the oral mucosa) and nail dystrophy , as well as a variety of other symptoms. Individuals with either TERC or DKC1 mutations have shorter telomeres and defective telomerase activity in vitro versus other individuals of the same age. [ 81 ]
In one family autosomal dominant DC was linked to a heterozygous TERT mutation. [ 5 ] These patients also exhibited an increased rate of telomere-shortening, and genetic anticipation (i.e., the DC phenotype worsened with each generation). | https://en.wikipedia.org/wiki/Telomerase |
A telomere ( / ˈ t ɛ l ə m ɪər , ˈ t iː l ə -/ ; from Ancient Greek τέλος ( télos ) ' end ' and μέρος ( méros ) ' part ' ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences ). Telomeres are a widespread genetic feature most commonly found in eukaryotes . In most, if not all species possessing them, they protect the terminal regions of chromosomal DNA from progressive degradation and ensure the integrity of linear chromosomes by preventing DNA repair systems from mistaking the very ends of the DNA strand for a double-strand break .
The existence of a special structure at the ends of chromosomes was independently proposed in 1938 by Hermann Joseph Muller , studying the fruit fly Drosophila melanogaster , and in 1939 by Barbara McClintock , working with maize. [ 1 ] Muller observed that the ends of irradiated fruit fly chromosomes did not present alterations such as deletions or inversions. He hypothesized the presence of a protective cap, which he coined "telomeres", from the Greek telos (end) and meros (part). [ 2 ]
In the early 1970s, Soviet theorist Alexey Olovnikov first recognized that chromosomes could not completely replicate their ends; this is known as the "end replication problem". Building on this, and accommodating Leonard Hayflick 's idea of limited somatic cell division, Olovnikov suggested that DNA sequences are lost every time a cell replicates until the loss reaches a critical level, at which point cell division ends. [ 3 ] [ 4 ] [ 5 ] According to his theory of marginotomy, DNA sequences at the ends of telomeres are represented by tandem repeats, which create a buffer that determines the number of divisions that a certain cell clone can undergo. Furthermore, it was predicted that a specialized DNA polymerase (originally called a tandem-DNA-polymerase) could extend telomeres in immortal tissues such as germ line, cancer cells and stem cells. It also followed from this hypothesis that organisms with circular genome, such as bacteria, do not have the end replication problem and therefore do not age.
Olovnikov suggested that in germline cells, cells of vegetatively propagated organisms, and immortal cell populations such as most cancer cell lines, an enzyme might be activated to prevent the shortening of DNA termini with each cell division. [ 6 ] [ 7 ]
In 1975–1977, Elizabeth Blackburn , working as a postdoctoral fellow at Yale University with Joseph G. Gall , discovered the unusual nature of telomeres, with their simple repeated DNA sequences composing chromosome ends. [ 8 ] Blackburn, Carol Greider , and Jack Szostak were awarded the 2009 Nobel Prize in Physiology or Medicine for the discovery of how chromosomes are protected by telomeres and the enzyme telomerase . [ 9 ]
During DNA replication, DNA polymerase cannot replicate the sequences present at the 3' ends of the parent strands. This is a consequence of its unidirectional mode of DNA synthesis: it can only attach new nucleotides to an existing 3'-end (that is, synthesis progresses 5'-3') and thus it requires a primer to initiate replication. On the leading strand (oriented 5'-3' within the replication fork), DNA-polymerase continuously replicates from the point of initiation all the way to the strand's end with the primer (made of RNA ) then being excised and substituted by DNA. The lagging strand, however, is oriented 3'-5' with respect to the replication fork so continuous replication by DNA-polymerase is impossible, which necessitates discontinuous replication involving the repeated synthesis of primers further 5' of the site of initiation (see lagging strand replication ). The last primer to be involved in lagging-strand replication sits near the 3'-end of the template (corresponding to the potential 5'-end of the lagging-strand). Originally it was believed that the last primer would sit at the very end of the template, thus, once removed, the DNA-polymerase that substitutes primers with DNA (DNA-Pol δ in eukaryotes) [ note 1 ] would be unable to synthesize the "replacement DNA" from the 5'-end of the lagging strand so that the template nucleotides previously paired to the last primer would not be replicated. [ 10 ] It has since been questioned whether the last lagging strand primer is placed exactly at the 3'-end of the template and it was demonstrated that it is rather synthesized at a distance of about 70–100 nucleotides which is consistent with the finding that DNA in cultured human cell is shortened by 50–100 base pairs per cell division . [ 11 ]
If coding sequences are degraded in this process, potentially vital genetic code would be lost. Telomeres are non-coding, repetitive sequences located at the termini of linear chromosomes to act as buffers for those coding sequences further behind. They "cap" the end-sequences and are progressively degraded in the process of DNA replication.
The "end replication problem" is exclusive to linear chromosomes as circular chromosomes do not have ends lying without reach of DNA-polymerases. Most prokaryotes , relying on circular chromosomes, accordingly do not possess telomeres. [ 12 ] A small fraction of bacterial chromosomes (such as those in Streptomyces , Agrobacterium , and Borrelia ), however, are linear and possess telomeres, which are very different from those of the eukaryotic chromosomes in structure and function. The known structures of bacterial telomeres take the form of proteins bound to the ends of linear chromosomes, or hairpin loops of single-stranded DNA at the ends of the linear chromosomes. [ 13 ]
At the very 3'-end of the telomere there is a 300 base pair overhang which can invade the double-stranded portion of the telomere forming a structure known as a T-loop. This loop is analogous to a knot, which stabilizes the telomere, and prevents the telomere ends from being recognized as breakpoints by the DNA repair machinery. Should non-homologous end joining occur at the telomeric ends, chromosomal fusion would result. The T-loop is maintained by several proteins, collectively referred to as the shelterin complex. In humans, the shelterin complex consists of six proteins identified as TRF1 , TRF2 , TIN2 , POT1 , TPP1 , and RAP1 . [ 14 ] In many species, the sequence repeats are enriched in guanine , e.g. TTAGGG in vertebrates , [ 15 ] which allows the formation of G-quadruplexes , a special conformation of DNA involving non-Watson-Crick base pairing. There are different subtypes depending on the involvement of single- or double-stranded DNA, among other things. There is evidence for the 3'-overhang in ciliates (that possess telomere repeats similar to those found in vertebrates ) to form such G-quadruplexes that accommodate it, rather than a T-loop. G-quadruplexes present an obstacle for enzymes such as DNA-polymerases and are thus thought to be involved in the regulation of replication and transcription. [ 16 ]
Many organisms have a ribonucleoprotein enzyme called telomerase, which carries out the task of adding repetitive nucleotide sequences to the ends of the DNA. Telomerase "replenishes" the telomere "cap" and requires no ATP. [ 17 ] In most multicellular eukaryotic organisms, telomerase is active only in germ cells , some types of stem cells such as embryonic stem cells , and certain white blood cells . Telomerase can be reactivated and telomeres reset back to an embryonic state by somatic cell nuclear transfer . [ 18 ] The steady shortening of telomeres with each replication in somatic (body) cells may have a role in senescence [ 19 ] and in the prevention of cancer . [ 20 ] [ 21 ] This is because the telomeres act as a sort of time-delay "fuse", eventually running out after a certain number of cell divisions and resulting in the eventual loss of vital genetic information from the cell's chromosome with future divisions. [ 22 ] [ 23 ]
Telomere length varies greatly between species, from approximately 300 base pairs in yeast [ 24 ] to many kilobases in humans, and usually is composed of arrays of guanine -rich, six- to eight-base-pair-long repeats. Eukaryotic telomeres normally terminate with 3′ single-stranded-DNA overhang ranging from 75 to 300 bases, which is essential for telomere maintenance and capping. Multiple proteins binding single- and double-stranded telomere DNA have been identified. [ 25 ] These function in both telomere maintenance and capping. Telomeres form large loop structures called telomere loops, or T-loops. Here, the single-stranded DNA curls around in a long circle, stabilized by telomere-binding proteins . [ 26 ] At the very end of the T-loop, the single-stranded telomere DNA is held onto a region of double-stranded DNA by the telomere strand disrupting the double-helical DNA, and base pairing to one of the two strands. This triple-stranded structure is called a displacement loop or D-loop. [ 27 ]
Apart from the end replication problem, in vitro studies have shown that telomeres accumulate damage due to oxidative stress and that oxidative stress-mediated DNA damage has a major influence on telomere shortening in vivo . There is a multitude of ways in which oxidative stress, mediated by reactive oxygen species (ROS), can lead to DNA damage; however, it is yet unclear whether the elevated rate in telomeres is brought about by their inherent susceptibility or a diminished activity of DNA repair systems in these regions. [ 28 ] Despite widespread agreement of the findings, widespread flaws regarding measurement and sampling have been pointed out; for example, a suspected species and tissue dependency of oxidative damage to telomeres is said to be insufficiently accounted for. [ 29 ] Population-based studies have indicated an interaction between anti-oxidant intake and telomere length. In the Long Island Breast Cancer Study Project (LIBCSP), authors found a moderate increase in breast cancer risk among women with the shortest telomeres and lower dietary intake of beta carotene, vitamin C or E. [ 30 ] These results [ 31 ] suggest that cancer risk due to telomere shortening may interact with other mechanisms of DNA damage, specifically oxidative stress.
Although telomeres shorten during the lifetime of an individual, it is telomere shortening-rate rather than telomere length that is associated with the human lifespan. [ 32 ] Critically short telomeres trigger a DNA damage response and cellular senescence . [ 32 ] Mice have much longer telomeres, but a greatly accelerated telomere shortening-rate and greatly reduced lifespan compared to humans and elephants. [ 33 ]
Telomere shortening is associated with aging, mortality, and aging-related diseases in experimental animals. [ 8 ] [ 34 ] Although many factors can affect human lifespan, such as smoking, diet, and exercise, as persons approach the upper limit of human life expectancy , longer telomeres may be associated with lifespan. [ 35 ]
Meta-analyses found that increased perceived psychological stress was associated with a small decrease in telomere length—but that these associations attenuate to no significant association when accounting for publication bias . The literature concerning telomeres as integrative biomarkers of exposure to stress and adversity is dominated by cross-sectional and correlational studies, which makes causal interpretation problematic. [ 31 ] [ 36 ] A 2020 review argued that the relationship between psychosocial stress and telomere length appears strongest for stress experienced in utero or early life. [ 37 ]
The phenomenon of limited cellular division was first observed by Leonard Hayflick , and is now referred to as the Hayflick limit . [ 38 ] [ 39 ] Significant discoveries were subsequently made by a group of scientists organized at Geron Corporation by Geron's founder Michael D. West , that tied telomere shortening with the Hayflick limit. [ 40 ] The cloning of the catalytic component of telomerase enabled experiments to test whether the expression of telomerase at levels sufficient to prevent telomere shortening was capable of immortalizing human cells. Telomerase was demonstrated in a 1998 publication in Science to be capable of extending cell lifespan, and now is well-recognized as capable of immortalizing human somatic cells. [ 41 ]
Two studies on long-lived seabirds demonstrate that the role of telomeres is far from being understood. In 2003, scientists observed that the telomeres of Leach's storm-petrel ( Oceanodroma leucorhoa ) seem to lengthen with chronological age, the first observed instance of such behaviour of telomeres. [ 42 ]
A study reported that telomere length of different mammalian species correlates inversely rather than directly with lifespan, and concluded that the contribution of telomere length to lifespan remains controversial. [ 43 ] There is little evidence that, in humans, telomere length is a significant biomarker of normal aging with respect to important cognitive and physical abilities. [ 44 ]
Experimentally verified and predicted telomere sequence motifs from more than 9000 species are collected in research community curated database TeloBase . [ 45 ] Some of the experimentally verified telomere nucleotide sequences are also listed in Telomerase Database website (see nucleic acid notation for letter representations).
Preliminary research indicates that disease risk in aging may be associated with telomere shortening, senescent cells , or SASP ( senescence-associated secretory phenotype ). [ 32 ]
Several techniques are currently employed to assess average telomere length in eukaryotic cells. One method is the Terminal Restriction Fragment (TRF) southern blot. [ 49 ] [ 50 ] There is a Web-based Analyser of the Length of Telomeres ( WALTER ), software processing the TRF pictures. [ 51 ] A Real-Time PCR assay for telomere length involves determining the Telomere-to-Single Copy Gene (T/S) ratio, which is demonstrated to be proportional to the average telomere length in a cell. [ 52 ]
Tools have also been developed to estimate the length of telomere from whole genome sequencing (WGS) experiments. Amongst these are TelSeq, [ 53 ] Telomerecat [ 54 ] and telomereHunter. [ 55 ] Length estimation from WGS typically works by differentiating telomere sequencing reads and then inferring the length of telomere that produced that number of reads. These methods have been shown to correlate with preexisting methods of estimation such as PCR and TRF. Flow-FISH is used to quantify the length of telomeres in human white blood cells. A semi-automated method for measuring the average length of telomeres with Flow FISH was published in Nature Protocols in 2006. [ 56 ]
While multiple companies offer telomere length measurement services, the utility of these measurements for widespread clinical or personal use has been questioned. [ 57 ] [ 58 ] Nobel Prize winner Elizabeth Blackburn , who was co-founder of one company, promoted the clinical utility of telomere length measures. [ 59 ]
During the last two decades, eco-evolutionary studies have investigated the relevance of life-history traits and environmental conditions on telomeres of wildlife. Most of these studies have been conducted in endotherms , i.e. birds and mammals. They have provided evidence for the inheritance of telomere length; however, heritability estimates vary greatly within and among species. [ 60 ] Age and telomere length often negatively correlate in vertebrates, but this decline is variable among taxa and linked to the method used for estimating telomere length. [ 61 ] In contrast, the available information shows no sex differences in telomere length across vertebrates. [ 62 ] Phylogeny and life history traits such as body size or the pace of life can also affect telomere dynamics. For example, it has been described across species of birds and mammals. [ 63 ] In 2019, a meta-analysis confirmed that the exposure to stressors (e.g. pathogen infection, competition, reproductive effort and high activity level) was associated with shorter telomeres across different animal taxa. [ 64 ]
Studies on ectotherms , and other non-mammalian organisms, show that there is no single universal model of telomere erosion; rather, there is wide variation in relevant dynamics across Metazoa , and even within smaller taxonomic groups these patterns appear diverse. [ 65 ] | https://en.wikipedia.org/wiki/Telomere |
Telomerization is a reaction that produces a particular kind of oligomer with two distinct end groups. The oligomer is called a telomer . [ 1 ] Some telomerizations proceed by radical pathways, many do not. A generic equation is:
where M is the monomer, and A and B are the end groups, and n is the degree of polymerization .
One example is the coupled dimerization and hydroesterification of buta-1,3-diene . This step produces a doubly unsaturated C9-ester: [ 2 ]
The monomer in this reaction is butadiene, the degree of polymerization is 2, and the end groups are vinyl and the carboxy methyl (CO 2 CH 3 ). This and several related reactions proceed with palladium catalysts. [ 3 ] Many telomerizations are used in industrial chemistry. [ 4 ]
According to the jargon in polymer chemistry, telomerization requires a telogen to react with at least one unsaturated taxogen molecule. [ 4 ] Fluorotelomers are an example.
This chemical reaction article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Telomerization |
The telomerization is the linear dimerization of 1,3-dienes with simultaneous addition of a nucleophile in a catalytic reaction.
The reaction was independently discovered by E. J. Smutny at Shell and Takahashi at the Osaka University in the late sixties. The general reaction equation is as follows: [ 1 ] [ 2 ]
The formation of several isomers are possible. In addition to 1,3-butadiene also substituted dienes such as isoprene or cyclic dienes such as cyclopentadiene can be used. A variety of substances such as water , ammonia , alcohols , or C-H-acidic compounds can be used as nucleophiles . When water is used, for example di-unsaturated alcohols are obtained.
The catalysts used are mainly metal-organic palladium and nickel compounds. In 1991, Kuraray implemented the
production of 1-octanol on an industrial scale (5000 t a(-1)).
The commercial route to produce 1-octene based on butadiene as developed by Dow Chemical came on stream in Tarragona in 2008. The telomerization of butadiene with methanol in the presence of a palladium catalyst yields 1-methoxy-2,7-octadiene, which is fully hydrogenated to 1-methoxyoctane in the next step. Subsequent cracking of 1-methoxyoctane gives 1-octene and methanol for recycle.
While the reaction is catalyzed by Pd(0) complexes, the pre-catalyst can also be a Pd(II) compound that is reduced in situ. Once the Pd(0) catalyst is formed it can coordinate two butadienes which by oxidative coupling give the intermediate B . Even though the oxidative coupling is facile it is nonetheless reversible; the latter is illustrated by the fact that B is only stable at high butadiene concentration. Subsequent protonation of this intermediate by NuH at the 6-position of the η 3 -,η 1 -octadienyl ligand leads to intermediate C . Nw direct attack of the nucleophile can take place at either the 1- or 3-position of the η 3 -octadienyl chain, which leads to the linear or branched product complexes D n and D iso respectively. Upon displacement by new 1,3-butadiene the product telomer is liberated while the catalyst is regenerated and can continue the cycle. [ 3 ]
While from purely steric reasons nucleophilic attack at the less substituted side of the allyl is favored, the regioselectivity of nucleophilic attack can heavily depend on the exact nature of ligands positioned trans to the allyl group. [ 4 ] | https://en.wikipedia.org/wiki/Telomerization_(dimerization) |
TelstraClear Limited was New Zealand's second-largest telecommunications company before being acquired by Vodafone New Zealand in October 2012, [ 1 ] previous to which it was a subsidiary of Australian company Telstra .
It provided residential line rental services, internet services, IT services, security services, cable TV/cable modem and mobile telephone services to 70,000 subscribers on its network in Wellington, Christchurch and Kapiti. Overall the company had around 200,000 customers. [ 2 ]
In 2004, TelstraClear began offering residential line HomePlan services including broadband outside those areas where it has its own network, reselling the ADSL wholesale product from Telecom New Zealand, and investing millions in local loop unbundling, which entailed TelstraClear installing its own equipment in Telecom exchanges (the Telecom infrastructure business later became Chorus Limited ).
TelstraClear had its beginnings in New Zealand with Kiwi Cable in the Kāpiti Coast district, Clear Communications in 1990, and Telstra New Zealand in 1996.
Telstra NZ slowly expanded its operations in the business market, bundling Telecom New Zealand services distributed as a reseller with its own network services. It installed switches in Auckland and Wellington to manage incoming and outgoing international traffic and maintained an interconnect agreement with Telecom New Zealand and is likely to have had others with companies such as Clear Communications.
In 1999 Saturn Communications was sold by its parent company, Austar United Communications, to a new joint venture with Telstra that became known as TelstraSaturn .
TelstraClear was then created by the merger of Telstra 's TelstraSaturn and Clear Communications in December 2001. Austar United Communications held an initial investment of 42% in TelstraClear before selling it back to Telstra. [ citation needed ] In March 2003, TelstraClear unveiled a new advertising campaign highlighting what the company saw as the increased competition and benefits the merger would create for New Zealand. [ 3 ]
TelstraClear had plans to expand its cable network into Auckland, but cancelled the plan in 2004 due to community opposition and questions about the business case. [ 4 ]
In 2004 TelstraClear made its first acquisition in the IT market with the purchase of Sytec, [ 5 ] mainly for its IP telephony and security skills, in particular the specialist managed security subsidiary DMZGlobal . In 2007 Sytec was formally introduced into the TelstraClear's enterprise and government division and the brand retired, but the DMZGlobal brand was retained and invested in.
In July 2012, Vodafone New Zealand announced plans to acquire TelstraClear. [ 6 ] Vodafone approached Telstra to purchase TelstraClear for a payment of $840 million, and $450 million that TelstraClear had in its accounts. The Commerce Commission approved the bid on 30 October, and the sale was completed on 31 October. TelstraClear's final trading day was 31 March 2013. [ 1 ] By May 2013, Vodafone said it had made good progress merging the two businesses, and that the TelstraClear branding would completely disappear by April or May 2013. [ 7 ]
Services are available from the "on-net" areas, where TelstraClear has its own network technology based on copper wires or fibre. These areas include parts of Central Auckland, Hamilton, Rotorua, Napier, Palmerston North, Wanganui, Kapiti, Wellington, and Christchurch, with actual technology varying based on reach and type.
'InHome' residential telephone service with vertical service code products were available in one of the following ways depending on location:
Single fixed line business telephone services were offered in 'on-net' ADSL and 'off-net' POTS Chorus fixed line areas.
Business telephone services are available in 'on-net' ISDN inner city suburbs with basic and primary rate lines. In other areas, services are available using Chorus owned ISDN/ADSL lines and exchanges (primary lite, basic and (in special cases) legacy primary rates).
With 'IP Connect' SIP trunking became available in inner city suburbs.
'Private IP', was a non-VPN leased line WAN service for business and wholesale customers is essentially an 'Ethernet Anywhere' service delivered over a combination of the TelstraClear fixed line network, networks leased from Chorus HSNS, Araneo Wireless and Network Tasman Fibre. The service provided interconnection into Australia via either Telstra GWAN or TelstraClear operated TransTasman lines.
TelstraClear provided mobile data service through Vodafone, on their 3G GSM network since early 2010.
ADSL TelstraClear owned two ISPs, Paradise.net and Clearnet, with Clearnet becoming the umbrella brand. Both offered nationwide dialup and DSL service, resold over Telecom's DSL lines and also over unbundled exchanges. A number of their dial-up IP numbers were blacklisted as abusers by sites such as DSBL .
VDSL2 Only available to business customers in the 'on-net' areas, this technology was used to deliver the product BizBroadband and BizNet, as well as the IP Voice products (IP FeatureLine, IP Connect, IP Gateway, IP Clarity).
DOCSIS (cable) TelstraClear also offered DOCSIS cable modem internet access within TelstraClear's own (built) network. [ 10 ] TelstraClear offered standard speeds of up to 15 Mbit/s, and TelstraClear have also released 100 Mbit/s plans with 10 Mbit/s upload.
Since late 2009, new connections were only available on Clearnet.
With the acquisition of Sytec and the formation of Enterprise and Government division, TelstraClear provided managed network solutions, ICT services (such as desktop and device management and co-location), enterprise comms and contact center solutions. In addition under the DMZGlobal brand TelstraClear provided Internet security, managed security, and security consulting services.
TelstraClear operated the Hybrid Fibre Cable pay television network under the brand "InHomeTV". It was developed by Saturn Communications in Wellington , Kāpiti and Christchurch , prior to the sale to Telstra, and formerly known as Saturn TV. The network infrastructure includes twisted pair cabling used for residential and business local telephone service.
Programming is sourced from SKY Network Television following an agreement in 2002 and also locally received and sourced channels. The agreement allowed TelstraClear to distribute and bill for services provided by SKY Network Television on its own InHome digital TV network.
In September 2010, TelstraClear released their own PVR called the T-BOX. The launch followed the release by parent company Telstra (AU) of a similar product.
As of June 2011 TelstraClear ceased all analogue transmission on its cable network.
In May 2012 TelstraClear started sourcing its own Pay Per View movies and changes its branding to InHome Movies.
InHomeTV was available on TelstraClear's HFC Cable network in Wellington, Christchurch and Kapiti. The service was only available if bundled with TelstraClear's telephony service or internet products.
TelstraClear issued remote memory phonecards. The cards started in March 2002 after Net Tel was taken over TelstraClear. The TalkPlus card, issued by Clear Communications since 1998 had similar cards issued under the TelstraClear branding.
The cards include Talk Talk, E-Phone, Pacific Talk, TalkPlus Global and Cheap Chat.
In 2003, the Holiday Parks Association phonecard introduced as a E-Phone card. Later the card changed to a TalkPlus Global card. In 2010, TelstraClear introduced the Prepaid Max card, which is only available online. In 2014 Vodafone issued the SuperGold phonecard.
1 More than 400,000 television service subscribers. | https://en.wikipedia.org/wiki/TelstraClear |
Temocapril (also known as temocaprilum [Latin]; brand name Acecol) is an ACE inhibitor . It was not approved for use in the US .
It is administered as inactive prodrug , then converted to its active metabolite, temocaprilat. [ 1 ]
It was patented in 1984 and approved for medical use in 1994. [ 2 ]
This drug article relating to the cardiovascular system is a stub . You can help Wikipedia by expanding it .
This stereochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Temocapril |
Temozolomide , sold under the brand name Temodar among others, is an anticancer medication used to treat brain tumors such as glioblastoma and anaplastic astrocytoma . [ 3 ] [ 4 ] It is taken by mouth or via intravenous infusion. [ 3 ] [ 4 ]
The most common side effects with temozolomide are nausea , vomiting , constipation , loss of appetite , alopecia (hair loss), headache , fatigue , convulsions (seizures), rash , neutropenia or lymphopenia (low white-blood-cell counts), and thrombocytopenia (low blood platelet counts). [ 4 ] People receiving the solution for infusion may also have injection-site reactions, such as pain, irritation, itching, warmth, swelling and redness, as well as bruising. [ 4 ]
Temozolomide is an alkylating agent used to treat serious brain cancers; most commonly as second-line treatments for astrocytoma and as the first-line treatment for glioblastoma. [ 3 ] [ 5 ] [ 6 ] Olaparib in combination with temozolomide demonstrated substantial clinical activity in relapsed small cell lung cancer . [ 7 ] It is available as a generic medication .
In the United States, temozolomide is indicated for the treatment of adults with newly diagnosed glioblastoma concomitantly with radiotherapy and subsequently as monotherapy treatment; [ 3 ] [ 8 ] or adults with newly diagnosed or refractory anaplastic astrocytoma. [ 3 ] [ 8 ]
In the European Union, temozolomide is indicated for adults with newly diagnosed glioblastoma multiforme concomitantly with radiotherapy and subsequently as monotherapy treatment; [ 4 ] [ 5 ] or children from the age of three years, adolescents and adults with malignant glioma, such as glioblastoma multiforme or anaplastic astrocytoma, showing recurrence or progression after standard therapy. [ 4 ] [ 5 ]
Temozolomide is also used to treat aggressive pituitary tumors and pituitary cancer. [ 9 ]
Temozolomide is contraindicated in people with hypersensitivity to it or to the similar drug dacarbazine . [ 10 ]
The most common side effects include nausea (feeling sick), vomiting, constipation, loss of appetite, alopecia (hair loss), headache, fatigue (tiredness), convulsions (fits), rash, neutropenia or lymphopenia (low white-blood-cell counts), and thrombocytopenia (low blood platelet counts). [ 4 ] People receiving the solution for infusion may also have injection-site reactions, such as pain, irritation, itching, warmth, swelling and redness, as well as bruising. [ 4 ]
Combining temozolomide with other myelosuppressants may increase the risk of myelosuppression. [ 10 ]
The therapeutic benefit of temozolomide depends on its ability to alkylate / methylate DNA, which most often occurs at the N-7 or O-6 positions of guanine residues. [ 11 ] [ medical citation needed ] This methylation damages the DNA and triggers the death of tumor cells. [ 12 ] [ medical citation needed ] However, some tumor cells are able to repair this type of DNA damage, and therefore diminish the therapeutic efficacy of temozolomide, by expressing a protein O 6 -alkylguanine DNA alkyltransferase (AGT) encoded in humans by the O -6-methylguanine-DNA methyltransferase ( MGMT ) gene. [ 13 ] In some tumors, epigenetic silencing of the MGMT gene prevents the synthesis of this enzyme, and as a consequence such tumors are more sensitive to killing by temozolomide. [ 14 ] Conversely, the presence of AGT protein in brain tumors predicts poor response to temozolomide and these patients receive little benefit from chemotherapy with temozolomide. [ 15 ]
Temozolomide is quickly and almost completely absorbed from the gut, and readily penetrates the blood–brain barrier ; the concentration in the cerebrospinal fluid is 30% of the concentration in the blood plasma . [ medical citation needed ] Intake with food decreases maximal plasma concentrations by 33% and the area under the curve by 9%. [ medical citation needed ] Only 15% (10–20%) of the substance are bound to blood plasma proteins. [ medical citation needed ] Temozolomide is a prodrug ; it is spontaneously hydrolyzed at physiological pH to 3-methyl-(triazen-1-yl)imidazole-4-carboxamide (MTIC), which further splits into monomethylhydrazine , likely the active methylating agent, and 5-aminoimidazole-4-carboxamide (AIC). [ medical citation needed ] Other metabolites include temozolomide acid and unidentified hydrophilic substances. [ 10 ]
Plasma half-life is 1.8 hours. [ medical citation needed ] The substance and its metabolites are mainly excreted via the urine. [ 10 ]
Temozolomide is an imidazotetrazine derivative. [ 16 ] It is slightly soluble in water and aqueous acids, [ 17 ] and decomposes at 212 °C (414 °F). [ 18 ] It was recently discovered that temozolomide is an explosive, tentatively assigned as UN Class 1 . [ 19 ] [ 20 ]
Temozolomide has also been reported to be a comparatively safe and stable in situ source of diazomethane in organic synthesis. [ citation needed ] In particular, use as a methylating and cyclopropanating reagent has been demonstrated. [ 21 ]
The agent was discovered at Aston University in Birmingham, England . Its preclinical activity was reported in 1987. [ 16 ] [ 22 ] [ 23 ]
It was approved for medical use in the European Union in January 1999, [ 4 ] and in the United States in August 1999. [ 24 ] The intravenous formulation was approved in the United States in February 2009. [ 25 ]
Laboratory studies and clinical trials have started investigating the possibility of increasing the anticancer potency of temozolomide by combining it with other pharmacologic agents. For example, clinical trials have indicated that the addition of chloroquine might be beneficial for the treatment of glioma patients. [ 26 ] Laboratory studies found that temozolomide killed brain tumor cells more efficiently when epigallocatechin gallate ( EGCG ), a component of green tea , was added; however, the efficacy of this effect has not yet been confirmed in brain-tumor patients. [ 27 ] Preclinical studies reported in 2010 on investigations into the use of the novel oxygen diffusion-enhancing compound trans sodium crocetinate (TSC) when combined with temozolomide and radiation therapy [ 28 ] and a clinical trial was underway as of August 2015 [update] . [ 29 ]
While the above-mentioned approaches have investigated whether the combination of temozolomide with other agents might improve therapeutic outcome, efforts have also started to study whether altering the temozolomide molecule itself can increase its activity. One such approach permanently fused perillyl alcohol , a natural compound with demonstrated therapeutic activity in brain cancer patients, [ 30 ] to the temozolomide molecule. The resultant novel compound, called NEO212 or TMZ-POH, revealed anticancer activity that was significantly greater than that of either of its two parent molecules, temozolomide and perillyl alcohol. Although as of 2016 [update] , NEO212 has not been tested in humans, it has shown superior cancer therapeutic activity in animal models of glioma , [ 31 ] melanoma , [ 32 ] and brain metastasis of triple-negative breast cancer . [ 33 ]
Because tumor cells that express the O-6-methylguanine-DNA methyltransferase (MGMT) gene are more resistant to the effects of temozolomide, researchers investigated whether the inclusion of O 6 -benzylguanine ( O 6 -BG), an AGT inhibitor, could overcome this resistance and improve the drug's therapeutic effectiveness. In the laboratory, this combination indeed showed increased temozolomide activity in tumor-cell culture in vitro and in animal models in vivo . [ 34 ] However, a recently [ timeframe? ] completed phase-II clinical trial with brain-tumor patients yielded mixed outcomes; while there was some improved therapeutic activity when O 6 -BG and temozolomide were given to patients with temozolomide-resistant anaplastic glioma, there seemed to be no significant restoration of temozolomide sensitivity in patients with temozolomide-resistant glioblastoma multiforme . [ 35 ]
Some efforts focus on engineering hematopoietic stem cells expressing the MGMT gene prior to transplanting them into brain-tumor patients. This would allow for the patients to receive stronger doses of temozolomide, since the patient's hematopoietic cells would be resistant to the drug. [ 36 ]
High doses of temozolomide in high-grade gliomas have low toxicity, but the results are comparable to the standard doses. [ 37 ]
Two mechanisms of resistance to temozolomide effects have now been described: 1) intrinsic resistance conferred by MGMT deficiency (MGMTd) and 2) intrinsic or acquired resistance through MMR deficiency (MMRd). The MGMT enzyme is the first line of repair of mismatched bases created by temozolomide. Cells are normally MGMT proficient (MGMTp) as they have an unmethylated MGMT promoter allowing the gene to be expressed normally. In this state, temozolomide induced DNA damage is able to be efficiently repaired in tumor cells (and normal cells) by the active MGMT enzyme. Cells may grow and pass through the cell cycle normally without arrest or death. However, some tumors cells are MGMT deficient (MGMTd). This is most commonly due to abnormal methylation of the MGMT gene promoter and suppression of gene expression. MGMTd has also been described to occur by promoter rearrangement. In cells with MGMTd, DNA damage by temozolomide activates the next stage of repair in cells with a proficient Mismatch Repair enzyme complex (MMRp). In MMRp the MMR protein complex identifies the damage and causes cells to arrest and undergo death which inhibits tumor growth. However, if cells have combined MGMTd and MMR deficiency (MGMTd + MMRd) then cells retain the induced mutations and continue to cycle and are resistant to effects of temozolomide. [ medical citation needed ]
In gliomas and other cancers MMRd has now been reported to occur as primary MMRd (intrinsic or germline Lynch bMMRd) or as secondary MMRd (acquired - not present in the original untreated tumor). The latter occurs after effective treatment and cytoreduction of tumors with temozolomide and then selection or induction of mutant MSH6, MSH2, MLH1, or PMS2 proteins and cells which are MMRd and temozolomide resistant. The latter is described as an acquired resistance pathway with hotspot mutations in glioma patients (MSH6 p.T1219I). [ 38 ] | https://en.wikipedia.org/wiki/Temozolomide |
The World Geographical Scheme for Recording Plant Distributions ( WGSRPD ) is a biogeographical system developed by the international Biodiversity Information Standards (TDWG) organization, formerly the International Working Group on Taxonomic Databases. [ 1 ] The WGSRPD standards, like other standards for data fields in botanical databases, were developed to promote "the wider and more effective dissemination of information about the world's heritage of biological organisms for the benefit of the world at large". The system provides clear definitions and codes for recording plant distributions at four scales or levels, from "botanical continents" down to parts of large countries. The codes may be referred to as TDWG geographical codes . Current users of the system include the International Union for Conservation of Nature (IUCN), the Germplasm Resources Information Network (GRIN), and Plants of the World Online (POWO).
The scheme is one of a number developed by Biodiversity Information Standards particularly aimed at taxonomic databases . [ 2 ] The starting point was the "need for an agreed system of geographical units at approximately 'country' level and upwards for use in recording plant distributions". [ 1 ] The scheme represents a compromise between political and botanical divisions. [ 3 ] All boundaries either follow a political boundary (country boundary, province boundary, etc.), or coastlines. [ 1 ] The scheme also aims to follow botanical tradition, in terms of the distribution categories used in works like the Flora Europaea , Flora Malesiana , or Med-Checklist. [ 4 ] This approach occasionally leads to departures from political boundaries. Thus the scheme follows Flora Europaea [ 5 ] in placing the eastern Aegean islands (such as Lesbos , Samos and Rhodes ) in the West Asia region, [ 6 ] rather than in Europe where they belong politically as part of Greece.
The scheme defines geographic places at four scales or levels, from "botanical continents" down to parts of large countries: [ 7 ]
Standardized codes are used to represent the units at each level. Numerical codes are used for Levels 1 and 2, alphabetic codes for Levels 3 and 4.
For more botanically oriented classifications using phytogeography, the scheme's documentation endorses the use of floristic kingdoms , floristic regions , and floristic provinces , as classified by Armen Takhtajan . [ 10 ]
The WGSRPD defines nine botanical continents (Level 1), each assigned a single digit code from 1 (Europe) to 9 (Antarctica). Although it is said that "popular concepts of the continents of the world have been maintained, but with one or two slight modifications", [ 3 ] some of the botanical continents are notably different from the traditional geographical continents . In particular, Asia is divided into two botanical continents; 5 Australasia consists only of Australia and New Zealand and small outlying islands; most of the islands in the Pacific Ocean are allocated to 6 Pacific; and the division of the Americas into 7 Northern America and 8 Southern America differs from the traditional North America and South America . [ 3 ]
The botanical continent of Europe is defined broadly in line with Flora Europaea [ 5 ] and with the traditional geographical definition . To the north-west it includes Iceland and Svalbard (Spitsbergen). The southern boundary with Africa encloses most of the Mediterranean islands. The eastern boundary places Crimea and European Russia in Europe, with the border defined by the administrative units. Novaya Zemlya is excluded from Europe. The south-eastern boundary excludes the Caucasus and Turkey east of the Bosporus , as well as the Eastern Aegean Islands and Cyprus , which although geopolitically part of Europe are considered floristically part of Western Asia. [ 11 ]
The botanical continent of Africa corresponds closely to the usual geographical definition. It excludes the Sinai Peninsula , politically a part of Egypt , which is placed in region 34 Western Asia. To the west, it includes islands grouped as Macaronesia , comprising the Azores , Madeira , the Canary Islands , the Savage Islands and the Cape Verde islands. To the east, it includes Madagascar and other Indian Ocean islands out as far as the island of Rodrigues . [ 12 ]
The geographical continent of Asia is divided into two botanical continents, 3 Asia-Temperate and 4 Asia-Tropical. The reason for the division was described as largely for convenience. [ 3 ] Asia-Temperate borders Europe and Africa; the boundaries are described above. To the south-east, the Indian Subcontinent and the rest of Asia from region 41 Indo-China southwards are placed in Asia-Tropical. [ 13 ]
Asia-Tropical forms the second part of the traditional geographical continent of Asia. Its western and northern boundaries are formed by the two regions 40 Indian Subcontinent and 41 Indo-China. The southern boundary separates Asia-Tropical from Australia . The south-eastern boundary was changed between the first edition of 1992 and the second edition of 2001. In the first edition, Asia-Tropical was divided into three regions: 40 Indian Subcontinent, 41 Indo-China and 42 Malesia. The eastern boundary of Malesia was placed between the Bismarck Archipelago and the Solomon Islands Archipelago , which were put into region 60 Southwest Pacific. It was subsequently argued that it made more "floristic sense" to link the Solomon Islands with the Bismarck Archipelago and the island of New Guinea . Accordingly, in the second edition, a new region 43 Papuasia was created within Asia-Tropical, comprising New Guinea, Near Oceania (the Bismarck Archipelago and the Solomon Islands Archipelago), so that Asia-Tropical consists of four regions. [ 14 ]
The botanical continent of Australasia, as defined by the WGSRPD, consists only of Australia and New Zealand , plus outlying islands. The name was described as having been "controversial", since it has been used to describe larger areas. [ 15 ] Other definitions may include Indonesia , New Guinea and many Pacific islands, which the WGSRPD divides between 4 Asia-Tropical and 6 Pacific.
The WGSRPD groups most islands with a nearby continental landmass, usually the closest but may also make a decision influenced by the floristic similarity (hence the placement of the Azores with Africa and not Europe). The exception is the islands of the central part of the Pacific Ocean , which are placed in a separate botanical continent. The largest of these islands include New Caledonia , Fiji and Hawaii . [ 16 ]
The WGSRPD divides the Americas into 7 Northern America and 8 Southern America rather than into the traditional continents of North America and South America . The boundary between Northern America and Southern America was changed from the first edition to the second edition. In the first edition, a south-eastern part of Mexico was included in Southern America, the rest of Mexico being placed in Northern America. This followed the boundary of Mesoamerica in Flora Mesoamericana . However, it proved unpopular, especially with Mexican botanists, so in the second edition, all of Mexico is placed in Northern America, which thus consists of Mexico, the contiguous United States plus Alaska, Canada, and Greenland , together with associated offshore islands. [ 17 ]
As noted above , the Americas are divided into 7 Northern America and 8 Southern America rather than into the traditional continents of North America and South America, with the precise boundary between the two having changed between the first and second editions of the WGSRPD. Southern America consists of the Caribbean , the WGSRPD definition of Central America (those countries south of Mexico and north of Colombia ), and the traditional geographical continent of South America, together with some offshore islands, such as the Galapagos . [ 18 ]
The Antarctic botanical continent consists of continental Antarctica , plus a number of Subantarctic Islands, including the Falkland Islands , South Georgia and Tristan da Cunha . [ 19 ]
The nine botanical continents (Level 1) are each divided into between two and ten Level 2 regions; see the table above. Each region is given a two digit code, the first digit being that of the Level 1 continent to which it belongs. Altogether, there are 52 regions. [ 9 ]
Many of the regions are geographical divisions of the continents, e.g. 12 Southwestern Europe, 34 Western Asia or 77 South-Central U.S.A. Others are whole countries within the continents, e.g. 36 China, 79 Mexico or 84 Brazil. [ 9 ] Some less well-known regions include:
Levels 3 and 4 are identified by letter codes. Three letter codes are used for Level 3; [ 4 ] e.g. "NWG" stands for New Guinea . [ 24 ] Where the Level 3 area is subdivided into Level 4 "basic recording units", a two letter code is appended; [ 25 ] thus "NWG-IJ" represents Irian Jaya , [ 26 ] the Indonesian part of New Guinea. Where the Level 3 area is not subdivided, "OO" may be added to create a five letter code to show that the Level 4 unit is identical to the Level 3 area. [ 25 ] Thus "BIS" represents the Bismarck Archipelago at Level 3. This area is not subdivided, so "BIS-OO" can be used to represent it at Level 4. [ 23 ] As an example, the complete division of the Level 2 Papuasia region is shown below.
43 Papuasia
Organizations and works using the scheme include the International Union for Conservation of Nature (IUCN), [ 27 ] the Germplasm Resources Information Network (GRIN), and the World Checklist of Vascular Plants, which supports Plants of the World Online , published by Kew . [ 28 ]
Thus in the GRIN Taxonomy for Plants database, the distribution of Magnolia grandiflora is given in terms of WGSRPD botanical continents and regions as: [ 29 ]
Below the Level 2 regions, the Level 3 areas in this case are US states, which are then listed. | https://en.wikipedia.org/wiki/Temperate_Asia |
A temperate forest is a forest found between the tropical and boreal regions, located in the temperate zone . It is the second largest terrestrial biome, covering 25% [ 1 ] of the world's forest area, only behind the boreal forest , which covers about 33%. These forests cover both hemispheres at latitudes ranging from 25 to 50 degrees, [ 2 ] wrapping the planet in a belt similar to that of the boreal forest. Due to its large size spanning several continents, there are several main types: deciduous , coniferous , mixed forest , and rainforest .
The climate of a temperate forest is highly variable depending on the location of the forest. For example, Los Angeles and Vancouver , Canada are both considered to be located in a temperate zone, however, Vancouver is located in a temperate rainforest, while Los Angeles is a relatively dry subtropical climate . [ 3 ]
They are found in Europe, East Asia, North America, and in some parts of South America.
Deciduous forests are composed mainly of broadleaf trees , such as maple and oak, that shed all their leaves during one season. [ 4 ] They are typically found in three middle-latitude regions with temperate climates characterized by a winter season and year-round precipitation: eastern North America, western Eurasia and northeastern Asia. [ 5 ]
Coniferous forests are composed of needle-leaved evergreen trees, such as pine or fir. Evergreen forests are typically found in regions with moderate climates. Boreal forests , however, are an exception as they are found in subarctic regions. [ 6 ] Coniferous trees often have an advantage over broadleaf trees in harsher environments. Their leaves are typically hardier and longer lived but require more energy to grow.
As the name implies, conifers and broadleaf trees grow in the same area. The main trees found in these forests in North America and Eurasia include fir, oak, ash, maple, birch, beech, poplar, elm and pine. Other plant species may include magnolia, prunus, holly, and rhododendron. In South America, conifer and oak species predominate. In Australia, eucalypts are the predominant trees. Hardwood evergreen trees which are widely spaced and are found in the Mediterranean region are olive, cork, oak and stone pine.
Temperate rainforests are the wettest of all the types, and are found only in very wet coastal areas. Adding to its rarity is that most of the temperate rainforests outside protected areas have been cut down and no longer exist. [ 7 ] Temperate rainforests can, however, still be found in some areas, including the Pacific Northwest , southern Chile , northern Turkey (along with some regions of Bulgaria and Georgia ), most of Japan , and others.
Temperate forests are located in the middle latitudes where much of the planet's population is. Not only were these forests cut down to build cities (i.e. New York City, Seattle , London, Tokyo, Paris), they have also been "cut down long ago to make way for cultivation." [ 8 ] This biome has been subject to mining, logging, hunting , pollution, deforestation and habitat loss . [ 9 ] | https://en.wikipedia.org/wiki/Temperate_forest |
Temperature-programmed reduction is a technique for the characterization of solid materials and is often used in the field of heterogeneous catalysis to find the most efficient reduction conditions, [ 1 ] an oxidized catalyst precursor is submitted to a programmed temperature rise while a reducing gas mixture is flowed over it. It was developed by John Ward Jenkins whilst developing heterogeneous catalysts for Shell Oil company , but was never patented. [ 2 ]
A simple container (U-tube) is filled with a solid or catalyst. This sample vessel is positioned in a furnace with temperature control equipment. A thermocouple is placed in the solid for temperature measurement. The air originally present in the container is flushed out with an inert gas ( nitrogen , argon ). Flow controllers are used to add hydrogen (for example, 10% hydrogen in nitrogen). The composition of the gaseous mixture is measured at the exit of the sample container with appropriate detectors ( thermal conductivity detector , mass spectrometer ). Now, the sample in the oven is heated up on predefined values. Heating rates are usually between 1 K/min and 20 K/min. If a reduction takes place at a certain temperature, hydrogen is consumed, which is recorded by the detector. In practice the production of water is a more accurate way of measuring the reduction. This is due to the potential for varying hydrogen concentrations at the inlet, so the decrease in this number may not be precise, however as the starting concentration of water will be zero, any increase can be measured more accurately. | https://en.wikipedia.org/wiki/Temperature-programmed_reduction |
Temperature-responsive polymers or thermoresponsive polymers are polymers that exhibit drastic and discontinuous changes in their physical properties with temperature. [ 1 ] The term is commonly used when the property concerned is solubility in a given solvent , but it may also be used when other properties are affected. Thermoresponsive polymers belong to the class of stimuli-responsive materials , in contrast to temperature-sensitive (for short, thermosensitive) materials, which change their properties continuously with environmental conditions.
In a stricter sense, thermoresponsive polymers display a miscibility gap in their temperature-composition diagram. Depending on whether the miscibility gap is found at high or low temperatures, either an upper critical solution temperature (UCST) or a lower critical solution temperature (LCST) exists.
Research mainly focuses on polymers that show thermoresponsivity in aqueous solution. Promising areas of application are tissue engineering , [ 2 ] liquid chromatography , [ 3 ] [ 4 ] drug delivery [ 2 ] [ 5 ] and bioseparation. [ 6 ] Only a few commercial applications exist, for example, cell culture plates coated with an LCST-polymer.
The theory of thermoresponsive polymer (similarly, microgels) begins in the 1940s with work from Flory and Huggins who both independently produced similar theoretical expectations for polymer in solution with varying temperature.
The effects of external stimuli on particular polymers were investigated in the 1960s by Heskins and Guillet. [ 7 ] They established 32°C as the lower critical solution temperature (LCST) for poly(N-isopropylacrylamide) .
Thermoresponsive polymer chains in solution adopt an expanded coil conformation. At the phase separation temperature they collapse to form compact globuli. This process can be observed directly by methods of static and dynamic light scattering. [ 8 ] [ 9 ] The drop in viscosity can be indirectly observed. When mechanisms which reduce surface tension are absent, the globules aggregate, subsequently causing turbidity and the formation of visible particles.
The phase separation temperature (and hence, the cloud point) is dependent on polymer concentration. Therefore, temperature-composition diagrams are used to display thermoresponsive behavior over a wide range of concentrations. [ 10 ] Phases separate into a polymer-poor and a polymer-rich phase. In strictly binary mixtures the composition of the coexisting phases can be determined by drawing tie-lines. However, since polymers display a molar mass distribution this straightforward approach may be insufficient.
During the process of phase separation the polymer-rich phase can vitrify before equilibrium is reached. This depends on the glass transition temperature for each individual composition. It is convenient to add the glass transition curve to the phase diagram, although it is no real equilibrium. The intersection of the glass transition curve with the cloud point curve is called Berghmans point. [ 11 ] In the case of UCST polymers, above the Berghmans point the phases separate into two liquid phases, below this point into a liquid polymer-poor phase and a vitrified polymer-rich phase. For LCST polymers the inverse behavior is observed.
Polymers dissolve in a solvent when the Gibbs energy of the system decreases, i.e., the change of Gibbs energy (ΔG) is negative. From the known Legendre transformation of the Gibbs–Helmholtz equation it follows that ΔG is determined by the enthalpy of mixing (ΔH) and entropy of mixing (ΔS).
Δ G m i x = Δ H m i x − T ⋅ Δ S m i x {\displaystyle \Delta G_{mix}=\Delta H_{mix}-T\cdot \Delta S_{mix}}
Without interactions between the compounds there would be no enthalpy of mixing and the entropy of mixing would be ideal. The ideal entropy of mixing of multiple pure compounds is always positive (the term -T∙ΔS is negative) and ΔG would be negative for all compositions, causing complete miscibility. Therefore, the fact that miscibility gaps are observed can only be explained by interaction. In the case of polymer solutions, polymer-polymer, solvent-solvent and polymer-solvent interactions have to be taken into account. A model for the phenomenological description of polymer phase diagrams was developed by Flory and Huggins (see Flory–Huggins solution theory ). The resulting equation for the change of Gibbs energy consists of a term for the entropy of mixing for polymers and an interaction parameter that describes the sum of all interactions. [ 11 ]
Δ G m i x R T = ϕ 1 m 1 l n ϕ 1 + ϕ 2 m 2 l n ϕ 2 + χ ϕ 1 ϕ 2 {\displaystyle {\frac {\Delta G_{mix}}{RT}}={\frac {\phi _{1}}{m}}_{1}ln\phi _{1}+{\frac {\phi _{2}}{m}}_{2}ln\phi _{2}+\chi \phi _{1}\phi _{2}}
where
A consequence of the Flory-Huggins theory is, for instance, that the UCST (if it exists) increases and shifts into the solvent-rich region when the molar mass of the polymer increases. Whether a polymer shows LCST and/or UCST behavior can be derived from the temperature-dependence of the interaction parameter (see figure). The interaction parameter not only comprises enthalpic contributions but also the non-ideal entropy of mixing, which again consists of many individual contributions (e.g., the strong hydrophobic effect in aqueous solutions). For these reasons, classical Flory-Huggins theory cannot provide much insight into the molecular origin of miscibility gaps.
Thermoresponsive polymers can be functionalized with moieties that bind to specific biomolecules. The polymer-biomolecule conjugate can be precipitated from solution by a small change of temperature. [ 6 ] [ 12 ] Isolation may be achieved by filtration or centrifugation.
For some polymers it was demonstrated that thermoresponsive behavior can be transferred to surfaces. The surface is either coated with a polymer film or the polymer chains are bound covalently to the surface.
This provides a way to control the wetting properties of a surface by small temperature changes. The described behavior can be exploited in tissue engineering since the adhesion of cells is strongly dependent on the hydrophilicity / hydrophobicity . [ 2 ] [ 13 ] This way, it is possible to detach cells from a cell culture dish by only small changes in temperature, without the need to additionally use enzymes (see figure). Respective commercial products are already available.
Thermoresponsive polymers can be used as the stationary phase in liquid chromatography . [ 3 ] Here, the polarity of the stationary phase can be varied by temperature changes, altering the power of separation without changing the column or solvent composition. Thermally related benefits of gas chromatography can now be applied to classes of compounds that are restricted to liquid chromatography due to their thermolability. In place of solvent gradient elution, thermoresponsive polymers allow the use of temperature gradients under purely aqueous isocratic conditions. [ 14 ] The versatility of the system is controlled not only by changing temperature, but also by adding modifying moieties that allow for a choice of enhanced hydrophobic interaction, or by introducing the prospect of electrostatic interaction. [ 15 ] These developments have already brought major improvements to the fields of hydrophobic interaction chromatography, size exclusion chromatography, ion exchange chromatography, and affinity chromatography separations, as well as pseudo-solid phase extractions ("pseudo" because of phase transitions ).
Three-dimensional covalently linked polymer networks are insoluble in all solvents, they merely swell in good solvents. [ 16 ] [ 17 ] Thermoresponsive polymer gels show a discontinuous change of the degree of swelling with temperature. At the volume phase transition temperature (VPTT) the degree of swelling changes drastically. Researchers try to exploit this behavior for temperature-induced drug delivery. In the swollen state, previously incorporated drugs are released easily by diffusion. [ 18 ] More sophisticated "catch and release" techniques have been elaborated in combination with lithography [ 19 ] and molecular imprinting . [ 20 ]
In physical gels unlike covalently linked gels the polymers chains are not covalently linked together. That means that the gel could re-dissolve in a good solvent under some conditions. Thermoresponsive physical gels, also sometimes called thermoresponsive injectable gels have been used in Tissue Engineering. [ 21 ] [ 22 ] [ 23 ] [ 2 ] [ 24 ] This involves mixing at room temperature the thermoresponsive polymer in solution with the cells and then inject the solution to the body. Due to the temperature increase (to body temperature) the polymer creates a physical gel. Within this physical gel the cells are encapsulated. Tailoring the temperature that the polymer solution gels can be challenging because this depend by many factors like the polymer composition, [ 25 ] [ 26 ] [ 27 ] [ 28 ] architecture [ 25 ] [ 26 ] as well as the molar mass. [ 27 ]
Some thermoreversible gels are used in biomedicine . For instance, hydrogels made of proteins are used as scaffolds in knee replacement . [ 29 ] In baking, thermoreversible glazes such as pectin are prized for their ability to set and then reset after melting, [ 30 ] and are used in nappage and other processes to ensure a smooth final surface for a presented dish. [ 31 ] [ 32 ] In manufacturing, thermoplastic elastomers can be set into a shape and then reset to their original shape through thermal reversibility, unlike one-way thermoset elastomers. [ 33 ]
Experimentally, the phase separation can be followed by turbidimetry . There is no universal approach for determining the cloud point suitable for all systems. It is often defined as the temperature at the onset of cloudiness, the temperature at the inflection point of the transmittance curve, or the temperature at a defined transmittance (e.g., 50%). [ 11 ] The cloud point can be affected by many structural parameters of the polymer like the hydrophobic content, [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 34 ] architecture [ 25 ] [ 26 ] and even the molar mass. [ 27 ] [ 35 ]
The cloud points upon cooling and heating of a thermoresponsive polymer solution do not coincide because the process of equilibration takes time. The temperature interval between the cloud points upon cooling and heating is called hysteresis. The cloud points are dependent on the cooling and heating rates, and hysteresis decreases with lower rates. There are indications that hysteresis is influenced by the temperature, viscosity , glass transition temperature and the ability to form additional intra- and inter-molecular hydrogen bonds in the phase separated state. [ 36 ]
Another important property for potential applications is the extent of phase separation, represented by the difference in polymer content in the two phases after phase separation. For most applications, phase separation in pure polymer and pure solvent would be desirable although it is practically impossible. The extent of phase separation in a given temperature interval depends on the particular polymer-solvent phase diagram.
Example : From the phase diagram of polystyrene (molar mass 43,600 g/mol) in the solvent cyclohexane it follows that at a total polymer concentration of 10%, cooling from 25 to 20 °C causes phase separation into a polymer-poor phase with 1% polymer and a polymer-rich phase with 30% polymer content. [ 37 ]
Also desirable for many applications is a sharp phase transition, which is reflected by a sudden drop in transmittance. The sharpness of the phase transition is related to the extent of phase separation but additionally relies on whether all present polymer chains exhibit the same cloud point. This depends on the polymer endgroups, dispersity, or—in the case of copolymers —varying copolymer compositions. [ 36 ] As a result of phase separation, thermoresponsive polymer systems can form well-defined self-assembled nanostructures with a number of different practical application such as in drug and gene delivery, tissue engineering, etc. In order to establish the required properties for applications, a rigorous characterization of the phase separation phenomenon can be carried out by different spectroscopic and calorimetric methods, including nuclear magnetic resonance (NMR) , dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), infrared spectroscopy (IR), Raman spectroscopy , and Differential scanning calorimetry (DSC). [ 38 ]
Due to the low entropy of mixing, miscibility gaps are often observed for polymer solutions. [ 11 ] Many polymers are known that show UCST or LCST behavior in organic solvents. [ 39 ] Examples for organic polymer solutions with UCST are polystyrene in cyclohexane, [ 37 ] [ 40 ] polyethylene in diphenylether [ 41 ] [ 42 ] or polymethylmethacrylate in acetonitrile. [ 43 ] An LCST is observed for, e.g., polypropylene in n-hexane, [ 44 ] polystyrene in butylacetate [ 45 ] or polymethylmethacrylate in 2-propanone. [ 46 ]
Polymer solutions that show thermoresponsivity in water are especially important since water as a solvent is cheap, safe and biologically relevant. Current research efforts focus on water-based applications like drug delivery systems, tissue engineering, bioseparation (see the section Applications ). Numerous polymers with LCST in water are known. [ 11 ] The most studied polymer is poly(N-isopropylacrylamide) . [ 47 ] [ 48 ] [ 49 ] Further examples are poly[2-(dimethylamino)ethyl methacrylate] (pDMAEMA) [ 25 ] [ 26 ] [ 27 ] [ 28 ] [ 35 ] hydroxypropylcellulose , [ 50 ] poly(vinylcaprolactam) , [ 51 ] poly-2-isopropyl-2-oxazoline [ 52 ] and polyvinyl methyl ether . [ 53 ]
Some industrially relevant polymers show LCST as well as UCST behavior whereas the UCST is found outside the 0-to-100 °C region and can only be observed under extreme experimental conditions. [ 36 ] Examples are polyethylene oxide , [ 54 ] [ 55 ] [ 56 ] polyvinylmethylether [ 57 ] and polyhydroxyethylmethacrylate . [ 58 ] There are also polymers that exhibit UCST behavior between 0 and 100 °C. However, there are large differences concerning the ionic strength at which UCST behavior is detected. Some zwitterionic polymers show UCST behavior in pure water and also in salt-containing water or even at higher salt concentration. [ 59 ] [ 60 ] [ 61 ] [ 62 ] By contrast, polyacrylic acid displays UCST behavior solely at high ionic strength. [ 63 ] Examples for polymer that show UCST behavior in pure water as well as under physiological conditions are poly( N -acryloylglycinamide), [ 64 ] [ 65 ] [ 66 ] [ 67 ] ureido-functionalized polymers, [ 68 ] copolymers from N -vinylimidazole and 1-vinyl-2-(hydroxylmethyl)imidazole [ 69 ] or copolymers from acrylamide and acrylonitrile . [ 70 ] Polymers for which UCST relies on non-ionic interactions are very sensitive to ionic contamination. Small amounts of ionic groups may suppress phase separation in pure water.
The UCST is dependent on the molecular mass of the polymer. For the LCST this is not necessarily the case, as shown for poly( N -isopropylacrylamide). [ 71 ] [ 72 ] [ 73 ]
A more complex scenario can be found in the case of diblock copolymers that feature two orthogonally thermo-responsive blocks, i.e., an UCST and an LCST-type block. By applying a temperature stimulus, the individual polymer blocks show different phase transitions, e.g. by increasing the temperature, the UCST-type block features an insoluble-soluble transition, while the LCST-type block undergoes a soluble-insoluble transition. [ 74 ] [ 75 ] [ 76 ] The order of the individual phase transitions depends on the relative positions of the UCST and LCST. Thus, upon temperature change the roles of the soluble and insoluble polymer blocks are reversed and this structural inversion is typically called ‘schizophrenic’ in the literature. [ 77 ] [ 78 ] [ 79 ] Besides the fundamental interest in the mechanism of this behavior, such block copolymers have been proposed for application in smart emulsification, drug delivery, and rheology control. [ 80 ] [ 81 ] [ 82 ] Schizophrenic diblock copolymer have also been applied as thin films for potential use as sensors, smart coatings or nanoswitches, and soft robotics. [ 83 ] [ 84 ] [ 85 ] [ 86 ] [ 59 ] | https://en.wikipedia.org/wiki/Temperature-responsive_polymer |
Temperature-sensitive mutations are variants of genes that allow the organism to function normally at low temperatures but alter its function at higher temperatures. Cold-sensitive mutants are variants of genes that allow normal function of the organism at higher temperatures but altered function at low temperatures.
Most temperature-sensitive mutations affect proteins , and cause loss of protein function at the non-permissive temperature. The permissive temperature is one at which the protein typically can fold properly or remain properly folded. At higher temperatures, the protein is unstable and ceases to function properly. These mutations are usually recessive in diploid organisms. Temperature -sensitive mutations arrange a reversible mechanism and can reduce particular gene products at varying stages of growth, which is asily done by changing the temperature of growth.
[edit] The permissive temperature is the temperature at which a temperature-sensitive mutation gene product takes on a normal, functional phenotype . When a temperature-sensitive mutant is grown in a permissive condition, the mutant gene product behaves normally (meaning that the phenotype is not observed), even if there is a mutant allele present. This results in the survival of the cell or organism,as if it were a wild type strain. In contrast, the nonpermissive temperature or restrictive temperature is the temperature at which the mutant phenotype is observed.
Temperature-sensitive mutations are usually missense mutations, which slightly modify the energy landscape of the protein folding. The mutant protein will function at the standard, permissive, low temperature. It will alternatively lack the function at a rather high, non-permissive temperature and display a hypomorphic (partial loss of gene function) and a middle, semi-permissive temperature.
Temperature-sensitive mutations can significantly impact an organism's development by altering gene function at specific temperatures. These mutations affect proteins that may function normally at a lower, "permissive" temperature but become dysfunctional or degrade at a higher, "restrictive" temperature. This characteristic allows researchers to study gene function by controlling temperature conditions.
One example is a mutation in the virilizer ( vir ) gene in Drosophila melanogaster , which prevents the proper development of female traits at elevated temperatures. [ 1 ] This demonstrates the crucial role temperature-sensitive mutations play in regulating developmental pathways.
Temperature-sensitive mutations have also been observed in human diseases. For instance, in spinal muscular atrophy (SMA), mutations affecting the Survival of Motor Neuron ( SMN ) protein can render it unstable at higher temperatures, leading to impaired nerve function. [ 2 ]
Researchers have developed methods to introduce temperature-sensitive mutations artificially. One approach utilizes intein -mediated protein splicing, where protein segments remove themselves under specific temperature conditions. A study by Tan et al. (2009) demonstrated how engineered inteins can regulate protein function by allowing the intein to splice at lower temperatures while remaining intact at higher temperatures, thereby disrupting protein activity. [ 3 ]
By leveraging temperature-sensitive mutations, scientists can study the functional roles of genes and proteins in both normal development and disease processes.
At a base level, all organisms respond to their environment. Specifically, the temperature in an organism's environment can greatly impact many different aspects of its life. Understanding how temperature affects different species is difficult to study due to the fact that each one reacts differently to temperatures. Some may be more susceptible to higher temperatures due to not having the correct machinery to deal with it. Additionally, it is difficult to predict how a species would respond due to the fact that the fitness of the organism is closely intertwined with others inside of a single ecosystem [14].
Temperature is an environmental factor that influences the evolution of organisms by shaping their genetic variation , physiological traits, adaptations , and survivability. As global temperatures increase due to climate change, species have to adapt to these changes through mutations that affect protein function, such as temperature sensitive mutations. Specifically, higher temperatures can increase mutation rates, alter the stability of proteins, and influence natural selection . These factors can lead to evolutionary changes in populations over time. However, when adapting to these higher temperatures, organisms often experience trade-offs, which are compromises where gaining an advantage in one trait leads to a disadvantage in another. [ 4 ]
Higher temperatures can directly influence mutation rates by increasing the rate of spontaneous mutations leading to more errors during DNA replication or increased exposure to mutagens . Studies have shown that these effects are potentially due to enhanced metabolic rates. More specifically, a study involving Daphnia pulex found that spontaneous mutations had varied fitness effects under different thermal conditions, which suggests that temperature plays a role in shaping mutational impacts. [ 5 ] In addition, this heightened mutation rate provides a broader range of genetic diversity for natural selection to act upon, allowing populations to adapt more rapidly. However, too many mutations can result in higher rates of genetic disorders or maladaptive traits which reduce the overall fitness .
Since proteins rely on precise folding to function correctly, higher temperatures can destabilize their structure, leading to loss of function. This instability creates challenges for evolution, as living organisms have to find a way to maintain protein function while dealing with temperature changes. As a result, organisms evolving in hotter environments may develop compensatory mutations that enhance protein stability or adopt proteins that assist in proper folding. However, studies have shown that these mutations, which could help restore the function of destabilized proteins, are rare, emphasizing how crucial it is to keep proteins stable. [ 5 ] One study by researchers demonstrated how genome-wide CRISPR screens using temperature-sensitive mutations can map critical pathways involved in protein homeostasis and disease regulation. [ 6 ] These evolutionary shifts ensure that essential cellular functions remain unharmed despite thermal conditions.
Populations exposed to persistent high temperatures face selective pressures that favor individuals with heat-resistant traits, leading to the spread of beneficial alleles related to thermal tolerance—such as changes in membrane lipids, heat shock proteins, and thermostable enzymes. As global temperatures rise, organisms with temperature-sensitive mutations may experience shifting fitness landscapes , where previously neutral or deleterious mutations become advantageous. This dynamic drives natural selection and rapid adaptation, as seen in experimental evolution studies showing changes in mutation rates and variations in response to elevated temperatures. [ 7 ]
Adaptation to higher temperatures is not without costs. Proteins optimized for stability at higher temperatures may show reduced flexibility or functionality at lower temperatures, leading to trade-offs in the performance of organisms across different environments. Another possible trade-off would be the energy required to maintain protein stability can take away resources from other vital processes, such as reproduction and growth. These trade-offs can shape evolutionary trajectories, as organisms must balance between thermal tolerance and overall fitness.
Climate change is a huge topic in today's science world. Scientists have been asking many questions about how climate change will affect different ecosystems, organisms, and the human race. This question also arises from the standpoint of temperature-sensitive mutations.
As mentioned before, certain species' characteristics or behaviors rely on temperature. With the global climate becoming warmer, the question is what will happen with organisms that are sensitive to temperature change, and it affects their characteristics or ability to obtain nutrients. [ 8 ] Though climate change is not necessarily a good thing, some research has shown that some organisms have benefited from the increasing climate temperature. It showed that the rising temperature can increase the fitness of an organism. [ 9 ]
Climate change can also begin to effect the outcome of the ratio of male and females in the wild. Some animals mainly reptiles sex is determined by the temperature of the outside world when developing in an egg. Example of this happen in most species of turtles, which the increasing tempurute this could lead to more of one sex which would result in less mates being coulped to repopulate. Though this is not a mutation it does show that many processes in certain species are sesntive to temperature. [ 10 ]
[edit]Temperature-sensitive mutantations are useful in biological research. They allow the study of essential processes required for the survival of the cell or organism. Mutations to essential genes are generally lethal, and hence, temperature-sensitive mutations enable researchers to induce the phenotype at restrictive temperatures and study the effects. The temperature-sensitive phenotype could be expressed during a specific developmental stage to study the effects. This is also done to determine what can happen to certain living organisms with the effects of climate change. Temperature senstive mutations are imortant for many different kinds of research especially for genetic reseach which can help us determine many aspect of life from a molecular level. [ 11 ]
[edit] In the late 1970s, the Saccharomyces cerevisiae secretory pathway , essential for viability of the cell and for growth of new buds, was dissected using temperature-sensitive mutants, resulting in the identification of twenty-three essential genes.
In the 1970s, several temperature-sensitive mutant genes were identified in Drosophila melanogaster , such as shibire ts , which led to the first genetic dissection of synaptic function.< In the 1990s, the heat shock promoter hsp70 was used in temperature-modulated gene expression in the fruit fly.
[edit] An infection of an Escherichia coli host cell by a bacteriophage (phage) T4 temperature -ensitive (TS) conditionally lethal mutant at a high restrictive temperature generally leads to no phage growth. However, a co-infection under restrictive conditions with two TS mutants defective in different genes generally leads to robust growth because of intergenic complementation . The discovery of TS mutants of phage T4 and the employment of such mutants in complementation tests contributed to the identification of many of the genes in this organism. Because multiple copies of a polypeptide specified by a gene often form multimers, mixed infections with two different TS mutants defective in the same gene often lead to mixed multimers and partial restoration of function, a phenomenon referred to as intragenic complementation. Intragenic complementation of TS mutants defective in the same gene can provide information on the structural organization of the multimer. The growth of phage TS mutants under partially restrictive conditions has been used to identify the functions of genes. Thus, genes employed in the repair of DNA damages were identified, as well as genes affecting genetic recombination . For example, growing a TS DNA repair mutant at an intermediate temperature will allow some progeny phage to be produced. However, if that TS mutant is irradiated with UV light, its survival will be more strongly reduced compared to the reduction of survival of irradiated wild-type phage T4.
Conditional lethal mutants able to grow at high temperatures but unable to grow at low temperatures were also isolated in phage T4. These cold-sensitive mutants defined a discrete set of genes, some of which had been previously identified by other types of conditional lethal mutants. | https://en.wikipedia.org/wiki/Temperature-sensitive_mutant |
The temperature-size rule denotes the plastic response (i.e. phenotypic plasticity ) of organismal body size to environmental temperature variation. [ 1 ] [ 2 ] Organisms exhibiting a plastic response are capable of allowing their body size to fluctuate with environmental temperature. First coined by David Atkinson in 1996, [ 3 ] it is considered to be a unique case of Bergmann's rule [ 1 ] that has been observed in plants, animals, birds, and a wide variety of ectotherms . [ 2 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] Although exceptions to the temperature-size rule exist, recognition of this widespread "rule" has amassed efforts to understand the physiological mechanisms (via possible tradeoffs) underlying growth and body size variation in differing environmental temperatures. [ 2 ] [ 8 ]
In 1847, Carl Bergmann published his observations that endothermic body size (i.e. mammals ) increased with increasing latitude, commonly known as Bergmann's rule . [ 9 ] His rule postulated that selection favored within species individuals with larger body sizes in cooler temperatures because the total heat loss would be diminished through lower surface area to volume ratios. [ 8 ] However, ectothermic individuals thermoregulate and allow their internal body temperature to fluctuate with environmental temperature whereas endotherms maintain a constant internal body temperature. This creates an inaccurate description of observed body size variation in ectotherms since they routinely allow evaporative heat loss and do not maintain constant internal temperatures. [ 8 ] [ 10 ] Despite this, ectotherms have largely been observed to still exhibit larger body sizes in colder environments.
Ray (1960) originally examined body sizes in several species of ectotherms and discovered that around 80% of them exhibited larger body sizes in lower temperatures. [ 11 ] A few decades later, Atkinson (1994) performed a similar review of temperature effects on body size in ectotherms. His study, which included 92 species of ectotherms ranging from animals and plants to protists and bacteria, concluded that a reduction in temperature resulted in an increase in organism size in 83.5% of cases. [ 11 ] [ 12 ] [ 13 ] Atkinson's findings provided support for Ray's published works that ectotherms have an observable trend in body size when temperature is the primary environmental variable. The results of his study prompted him to name the increase in ectothermic body size in colder environments as the temperature-size rule.
Life history models highlighting optimal growth patterns suggest that individuals assess the environment for potential resources and other proximate factors and mature at a body size that yields the greatest reproductive success, or highest percentage of offspring surviving to reach reproductive maturity. [ 14 ]
Environmental temperature is one of the most important proximate factors affecting ectotherm body size because of their need to thermoregulate. Individuals that have been observed to follow the temperature-size rule have slower growth rates in colder environments, yet they enter a period of prolonged growth that yields larger adult body sizes. [ 3 ] [ 15 ] [ 16 ] One proposed explanation for this involves a trade-off in life history traits. Ectotherms experience longer daily and seasonal activity times in warmer climates versus cooler climates, however, the increase in daily activity time is accompanied by higher infant and adult mortality rates due to predation. [ 16 ] [ 17 ] Under these environmental conditions, some individuals occupying these warmer climate environments will mature at smaller body sizes and undergo a shift in energy allocation of all acquired energy resources to reproduction. [ 18 ] [ 19 ] [ 20 ] In doing so, these individuals sacrifice growth to larger adult body sizes to ensure reproductive success, even if the trade-off results in smaller offspring that have increased mortality rates. [ 20 ]
Ectotherms occupying colder environments, such as mountain ranges or other areas of higher elevation, have been observed to invest in reproduction at larger adult body sizes due to a prolonged growth period. These populations of ectotherms are characterized as having smaller clutches of larger eggs, favoring a greater reproductive investment per egg and enhances offspring survival rates. [ 21 ] Individuals occupying warmer environments experience a trade-off between body size and overall reproductive success that many individuals occupying colder environments do not, hence, prolonging growth to yield greater reproductive success in colder environments could potentially be an underlying mechanism for why a large percentage of ectotherms exhibit greater body sizes in colder environments. However, a sufficient explanation for this observable pattern has yet to be produced. [ 14 ]
The supporting evidence and the exceptions to the temperature-size rule listed above are only a few of the potential supporting/opposing evidence available for the temperature-size rule. Each was provided to support the claim that patterns of body size observed in variable environments are not 100% predictable and more research is required to identify and understand all of the mechanisms responsible. | https://en.wikipedia.org/wiki/Temperature-size_rule |
A temperature coefficient describes the relative change of a physical property that is associated with a given change in temperature . For a property R that changes when the temperature changes by dT , the temperature coefficient α is defined by the following equation:
Here α has the dimension of an inverse temperature and can be expressed e.g. in 1/K or K −1 .
If the temperature coefficient itself does not vary too much with temperature and α Δ T ≪ 1 {\displaystyle \alpha \Delta T\ll 1} , a linear approximation will be useful in estimating the value R of a property at a temperature T , given its value R 0 at a reference temperature T 0 :
where Δ T is the difference between T and T 0 .
For strongly temperature-dependent α, this approximation is only useful for small temperature differences Δ T .
Temperature coefficients are specified for various applications, including electric and magnetic properties of materials as well as reactivity. The temperature coefficient of most of the reactions lies between 2 and 3.
Most ceramics exhibit negative temperature dependence of resistance behaviour. This effect is governed by an Arrhenius equation over a wide range of temperatures:
where R is resistance, A and B are constants, and T is absolute temperature (K).
The constant B is related to the energies required to form and move the charge carriers responsible for electrical conduction – hence, as the value of B increases, the material becomes insulating. Practical and commercial NTC resistors aim to combine modest resistance with a value of B that provides good sensitivity to temperature. Such is the importance of the B constant value, that it is possible to characterize NTC thermistors using the B parameter equation:
where R 0 {\displaystyle R_{0}} is resistance at temperature T 0 {\displaystyle T_{0}} .
Therefore, many materials that produce acceptable values of R 0 {\displaystyle R_{0}} include materials that have been alloyed or possess variable negative temperature coefficient (NTC), which occurs when a physical property (such as thermal conductivity or electrical resistivity ) of a material lowers with increasing temperature, typically in a defined temperature range. For most materials, electrical resistivity will decrease with increasing temperature.
Materials with a negative temperature coefficient have been used in floor heating since 1971. The negative temperature coefficient avoids excessive local heating beneath carpets, bean bag chairs, mattresses , etc., which can damage wooden floors , and may infrequently cause fires.
Residual magnetic flux density or B r changes with temperature and it is one of the important characteristics of magnet performance. Some applications, such as inertial gyroscopes and traveling-wave tubes (TWTs), need to have constant field over a wide temperature range. The reversible temperature coefficient (RTC) of B r is defined as:
To address these requirements, temperature compensated magnets were developed in the late 1970s. [ 1 ] For conventional SmCo magnets , B r decreases as temperature increases. Conversely, for GdCo magnets, B r increases as temperature increases within certain temperature ranges. By combining samarium and gadolinium in the alloy, the temperature coefficient can be reduced to nearly zero.
The temperature dependence of electrical resistance and thus of electronic devices ( wires , resistors) has to be taken into account when constructing devices and circuits . The temperature dependence of conductors is to a great degree linear and can be described by the approximation below.
where
ρ 0 {\displaystyle \rho _{0}} just corresponds to the specific resistance temperature coefficient at a specified reference value (normally T = 0 °C) [ 2 ]
That of a semiconductor is however exponential:
where S {\displaystyle S} is defined as the cross sectional area and α {\displaystyle \alpha } and B {\displaystyle B} are coefficients determining the shape of the function and the value of resistivity at a given temperature.
For both, α {\displaystyle \alpha } is referred to as the temperature coefficient of resistance (TCR). [ 3 ]
This property is used in devices such as thermistors.
A positive temperature coefficient (PTC) refers to materials that experience an increase in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, i.e. a higher coefficient. The higher the coefficient, the greater an increase in electrical resistance for a given temperature increase. A PTC material can be designed to reach a maximum temperature for a given input voltage, since at some point any further increase in temperature would be met with greater electrical resistance. Unlike linear resistance heating or NTC materials, PTC materials are inherently self-limiting. On the other hand, NTC material may also be inherently self-limiting if constant current power source is used.
Some materials even have exponentially increasing temperature coefficient. Example of such a material is PTC rubber .
A negative temperature coefficient (NTC) refers to materials that experience a decrease in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show a relatively rapid decrease with temperature, i.e. a lower coefficient. The lower the coefficient, the greater a decrease in electrical resistance for a given temperature increase. NTC materials are used to create inrush current limiters (because they present higher initial resistance until the current limiter reaches quiescent temperature), temperature sensors and thermistors .
An increase in the temperature of a semiconducting material results in an increase in charge-carrier concentration. This results in a higher number of charge carriers available for recombination, increasing the conductivity of the semiconductor. The increasing conductivity causes the resistivity of the semiconductor material to decrease with the rise in temperature, resulting in a negative temperature coefficient of resistance.
The elastic modulus of elastic materials varies with temperature, typically decreasing with higher temperature.
In nuclear engineering , the temperature coefficient of reactivity is a measure of the change in reactivity (resulting in a change in power), brought about by a change in temperature of the reactor components or the reactor coolant. This may be defined as
Where ρ {\displaystyle \rho } is reactivity and T is temperature. The relationship shows that α T {\displaystyle \alpha _{T}} is the value of the partial differential of reactivity with respect to temperature and is referred to as the "temperature coefficient of reactivity". As a result, the temperature feedback provided by α T {\displaystyle \alpha _{T}} has an intuitive application to passive nuclear safety . A negative α T {\displaystyle \alpha _{T}} is broadly cited as important for reactor safety, but wide temperature variations across real reactors (as opposed to a theoretical homogeneous reactor) limit the usability of a single metric as a marker of reactor safety. [ 4 ]
In water moderated nuclear reactors, the bulk of reactivity changes with respect to temperature are brought about by changes in the temperature of the water. However each element of the core has a specific temperature coefficient of reactivity (e.g. the fuel or cladding). The mechanisms which drive fuel temperature coefficients of reactivity are different from water temperature coefficients. While water expands as temperature increases , causing longer neutron travel times during moderation , fuel material will not expand appreciably. Changes in reactivity in fuel due to temperature stem from a phenomenon known as doppler broadening , where resonance absorption of fast neutrons in fuel filler material prevents those neutrons from thermalizing (slowing down). [ 5 ]
In its more general form, the temperature coefficient differential law is:
Where is defined:
And α {\displaystyle \alpha } is independent of T {\displaystyle T} .
Integrating the temperature coefficient differential law:
Applying the Taylor series approximation at the first order, in the proximity of T 0 {\displaystyle T_{0}} , leads to:
The thermal coefficient of electrical circuit parts is sometimes specified as ppm /° C , or ppm / K . This specifies the fraction (expressed in parts per million) that its electrical characteristics will deviate when taken to a temperature above or below the operating temperature . | https://en.wikipedia.org/wiki/Temperature_coefficient |
A temperature data logger , also called temperature monitor , is a portable measurement instrument that is capable of autonomously recording temperature over a defined period of time. The digital data can be retrieved, viewed and evaluated after it has been recorded. A data logger is commonly used to monitor shipments in a cold chain and to gather temperature data from diverse field conditions.
A variety of constructions are available. Most have an internal thermistor or thermocouple or can be connected to external sources. Sampling and measurement are periodically taken and digitally stored. Some have a built in display of data or out-of- tolerance warnings. Data retrieval can be by cable, RFID , wireless systems, etc. They generally are small, battery powered, portable, and equipped with a microprocessor, internal memory for data storage, and sensors. Some data loggers interface with personal computers or smart phones for set-up, control, and analysis.
Some include other sensors such as relative humidity, wind, light, etc. Others may record input from GPS devices.
Depending on the use, governing quality management systems sometimes require calibration to national standards and compliance with formal verification and validation protocols [ 1 ]
Choices of temperature data loggers can be based on many factors, such as:
Autonomous data loggers can be taken to diverse locations that cannot easily support fixed temperature monitoring equipment. [ 3 ] These might include: mountains, deserts, jungles, mines, ice flows, caves, etc. Portable data loggers are also used in industry and laboratory situations where stand-alone recording is desired.
Temperature sensitive products such as foods, [ 4 ] pharmaceuticals, [ 5 ] and some chemicals are often monitored during shipment and logistics operations. Exposure to temperatures outside of an acceptable range, for a critical time period, can degrade the product or shorten shelf life. Regulations and contracts make temperature monitoring mandatory for some products.
Battery-powered, formerly mechanical, the data logger is today an electronic device that can be programmed to record individual values over periods of a few hours to several months. Most are used to monitor temperature conditions, and some versions can also measure the relative humidity.
Data loggers are often small enough to be placed inside an insulated shipping container or directly attached to a product inside a refrigerator truck or a refrigerated container . These monitor the temperature of the product being shipped. Some data loggers are placed on the outside of the package or in the truck or intermodal container to monitor the air temperature. Placement of data loggers and sensors is critical: Studies have shown that temperatures inside a truck or intermodal container are strongly affected by proximity to exterior walls and roof and to locations on the lading. [ 6 ] [ 7 ]
Modern digital data loggers are very portable and record the actual times and temperatures. This information can be used to model product degradation and to pinpoint the location and cause of excessive exposure.
The measured data reveals whether the goods in transit have been subjected to potentially damaging temperature extremes or an excessive Mean kinetic temperature . Based on this data, the options may be:
Multiple replicate shipments of data loggers are also used to compare modes of shipment (routes, vendors) and to develop composite data to be used in package testing protocols. [ 9 ]
There are many brands and models of data loggers. Most are a connectable device that must be plugged into a computer to extract the data that the logger has logged. | https://en.wikipedia.org/wiki/Temperature_data_logger |
A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature spatial gradient is a vector quantity with dimension of temperature difference per unit length . The SI unit is kelvin per meter (K/m).
Temperature gradients in the atmosphere are important in the atmospheric sciences ( meteorology , climatology and related fields).
Assuming that the temperature T is an intensive quantity , i.e., a single-valued, continuous and differentiable function of three-dimensional space (often called a scalar field ), i.e., that
where x , y and z are the coordinates of the location of interest, then the temperature gradient is the vector quantity defined as
Differences in air temperature between different locations are critical in weather forecasting and climate. The absorption of solar light at or near the planetary surface increases the temperature gradient and may result in convection (a major process of cloud formation, often associated with precipitation ). Meteorological fronts are regions where the horizontal temperature gradient may reach relatively high values, as these are boundaries between air masses with rather distinct properties.
Clearly, the temperature gradient may change substantially in time, as a result of diurnal or seasonal heating and cooling for instance. This most likely happens during an inversion . For instance, during the day the temperature at ground level may be cold while it's warmer up in the atmosphere. As the day shifts over to night the temperature might drop rapidly while at other places on the land stay warmer or cooler at the same elevation . This happens on the West Coast of the United States sometimes due to geography.
Expansion and contraction of rock, caused by temperature changes during a wildfire , through thermal stress weathering , may result in thermal shock and subsequent structure failure. | https://en.wikipedia.org/wiki/Temperature_gradient |
Temperature gradient gel electrophoresis ( TGGE ) and denaturing gradient gel electrophoresis ( DGGE ) are forms of electrophoresis which use either a temperature or chemical gradient to denature the sample as it moves across an acrylamide gel. TGGE and DGGE can be applied to nucleic acids such as DNA and RNA , and (less commonly) proteins. TGGE relies on temperature dependent changes in structure to separate nucleic acids . DGGE separates genes of the same size based on their different denaturing ability which is determined by their base pair sequence. DGGE was the original technique, and TGGE a refinement of it.
DGGE was invented by Leonard Lerman , while he was a professor at SUNY Albany. [ 1 ] [ 2 ] [ 3 ]
The same equipment can be used for analysis of protein , which was first done by Thomas E. Creighton of the MRC Laboratory of Molecular Biology , Cambridge, England. [ 4 ] Similar looking patterns are produced by proteins and nucleic acids, but the fundamental principles are quite different.
TGGE was first described by Thatcher and Hodson [ 5 ] and by Roger Wartell of Georgia Tech. Extensive work was done by the group of Riesner in Germany. Commercial equipment for DGGE is available from Bio-Rad, INGENY and CBS Scientific; a system for TGGE is available from Biometra.
DNA has a negative charge and so will move to the positive electrode in an electric field. A gel is a molecular mesh, with holes roughly the same size as the diameter of the DNA string. When an electric field is applied, the DNA will begin to move through the gel, at a speed roughly inversely proportional to the length of the DNA molecule (shorter lengths of DNA travel faster) — this is the basis for size dependent separation in standard electrophoresis .
In TGGE there is also a temperature gradient across the gel. At room temperature, the DNA will exist stably in a double-stranded form. As the temperature is increased, the strands begin to separate ( melting ), and the speed at which they move through the gel decreases drastically. Critically, the temperature at which melting occurs depends on the sequence (GC basepairs are more stable than AT due to stacking interactions, not due to the difference in hydrogen bonds [ citation needed ] (there are three hydrogen bonds between a cytosine and guanine base pair, but only two between adenine and thymine ), so TGGE provides a "sequence dependent, size independent method" for separating DNA molecules. TGGE separates molecules and gives additional information about melting behavior and stability (Biometra, 2000).
Denaturing gradient gel electrophoresis (DGGE) works by applying a small sample of DNA (or RNA) to an electrophoresis gel that contains a denaturing agent. Researchers have found that certain denaturing gels are capable of inducing DNA to melt at various stages. As a result of this melting, the DNA spreads through the gel and can be analyzed for single components, even those as small as 200-700 base pairs .
What is unique about the DGGE technique is that as the DNA is subjected to increasingly extreme denaturing conditions, the melted strands fragment completely into single strands. The process of denaturation on a denaturing gel is very sharp: "Rather than partially melting in a continuous zipper-like manner, most fragments melt in a step-wise process. Discrete portions or domains of the fragment suddenly become single-stranded within a very narrow range of denaturing conditions" (Helms, 1990). This makes it possible to discern differences in DNA sequences or mutations of various genes: sequence differences in fragments of the same length often cause them to partially melt at different positions in the gradient and therefore "stop" at different positions in the gel. By comparing the melting behavior of the polymorphic DNA fragments side by side on denaturing gradient gels, it is possible to detect fragments that have mutations in the first melting domain (Helms, 1990). Placing two samples side by side on the gel and allowing them to denature together, researchers can easily see even the smallest differences in two samples or fragments of DNA.
There are a number of disadvantages to this technique: "Chemical gradients such as those used in DGGE are not as reproducible, are difficult to establish and often do not completely resolve heteroduplexes " (Westburg, 2001). These problems are addressed by TGGE, which uses a temperature, rather than chemical, gradient to denature the sample.
To separate nucleic acids by TGGE, the following steps must be performed: preparing and pouring the gels, electrophoresis, staining, and elution of DNA. Because a buffered system must be chosen, it is important that the system remain stable within the context of increasing temperature. Thus, urea is typically utilized for gel preparation; however, researchers need to be aware that the amount of urea used will affect the overall temperature required to separate the DNA. [ 6 ] The gel is loaded, the sample is placed on the gel according to the type of gel that is being run—i.e. parallel or perpendicular—the voltage is adjusted and the sample can be left to run. [ 6 ] Depending on which type of TGGE is to be run, either perpendicular or parallel , varying amounts of sample need to be prepared and loaded. A larger amount of one sample is used with perpendicular, while a smaller amount of many samples are used with parallel TGGE. Once the gel has been run, the gel must be stained to visualize the results. While there are a number of stains that can be used for this purpose, silver staining has proven to be the most effective tool. [ 6 ] The DNA can be eluted from the silver stain for further analysis through PCR amplification. [ 6 ]
TGGE and DGGE are broadly useful in biomedical and ecological research; selected applications are described below.
According to a recent investigation by Wong, Liang, Kwon, Bai, Alper and Gropman, [ 7 ] TGGE can be utilized to examine the mitochondrial DNA of an individual. According to these authors, TGGE was utilized to determine two novel mutations in the mitochondrial genome : "A 21-year-old woman who has been suspected of mitochondrial cytopathy, but negative for common mitochondrial DNA (mtDNA) point mutations and deletions, was screened for unknown mutations in the entire mitochondrial genome by temperature gradient gel electrophoresis". [ 8 ]
Lohr and coworkers (2001) report [ citation needed ] that in a comprehensive study of pancreatic secretions of individuals without pancreatic carcinoma , p53 mutations could be found in the pancreatic juices of a small percentage of participants. Because mutations of p53 has been extensively found in pancreatic carcinomas, the researchers for this investigation were attempting to determine if the mutation itself can be linked to the development of pancreatic cancer. While Lohr was able to find p53 mutations via TGGE in a few subjects, none subsequently developed pancreatic carcinoma. Thus, the researchers conclude by noting that the p53 mutation may not be the sole indicator of pancreatic carcinoma oncogenesis.
DGGE of small ribosomal subunit coding genes was first described by Gerard Muyzer , [ 9 ] while he was Post-doc at Leiden University , and has become a widely used technique in microbial ecology.
PCR amplification of DNA extracted from mixed microbial communities with PCR primers specific for 16S rRNA gene fragments of bacteria and archaea , and 18S rRNA gene fragments of eukaryotes results in mixtures of PCR products.
Because these amplicons all have the same length, they cannot be separated from each other by agarose gel electrophoresis. However, sequence variations (i.e. differences in GC content and distribution) between different microbial rRNAs result in different denaturation properties of these DNA molecules.
Hence, DGGE banding patterns can be used to visualize variations in microbial genetic diversity and provide a rough estimate of the richness of abundance of predominant microbial community members. This method is often referred to as community fingerprinting . Recently, several studies have shown that DGGE of functional genes (e.g. genes involved in sulfur reduction, nitrogen fixation, and ammonium oxidation) can provide information about microbial function and phylogeny simultaneously. For instance, Tabatabaei et al. (2009) applied DGGE and managed to reveal the microbial pattern during the anaerobic fermentation of palm oil mill effluent (POME) for the first time. [ 10 ] | https://en.wikipedia.org/wiki/Temperature_gradient_gel_electrophoresis |
The temperature jump method is a technique used in chemical kinetics for the measurement of very rapid reaction rates . It is one of a class of chemical relaxation methods pioneered by the German physical chemist Manfred Eigen in the 1950s. In these methods, a reacting system initially at equilibrium is perturbed rapidly and then observed as it relaxes back to equilibrium. [ 1 ] [ 2 ] [ 3 ] In the case of temperature jump, the perturbation involves rapid heating which changes the value of the equilibrium constant , followed by relaxation to equilibrium at the new temperature.
The heating usually involves discharging of a capacitor (in the kV range) through a small volume (< 1 mL) of a conducting solution containing the molecule/reaction to be studied. In some versions of the apparatus used, the solution is heated instead by the output of a pulsed laser which emits in the near infra-red. When laser heating is employed, the solution need not be conducting. In both cases, the temperature of the solution is caused to rise by a small amount in microseconds (or less in the case of laser heating). This allows the study of the shift in equilibrium of reactions that equilibrate in milliseconds (or microseconds with laser temperature jump), these changes most commonly being observed using absorption spectroscopy or fluorescence spectroscopy . Due to the small volumes involved the temperature of the solution returns to that of its surroundings in minutes. [ 4 ]
The fractional extent of the reaction ( i.e. the percentage change in concentration of a measurable species) depends on the molar enthalpy change (Δ H °) between the reactants and products and the equilibrium position. If K is the equilibrium constant and dT is the change in temperature then the enthalpy change is given by the Van 't Hoff equation :
where R is the universal gas constant and T is the absolute temperature . When a single step in a reaction is perturbed in a temperature jump experiment, the reaction follows a single exponential decay function with time constant ( τ ) {\displaystyle (\tau )} equal to a function of the forward (k a ) and reverse (k b ) rate constants. For the perturbation of a simple equilibrium A ↽ − − ⇀ B {\displaystyle {\ce {A <=> B}}} which is first order in both directions, the reciprocal of the time constant equals the sum of the two rate constants [ 2 ]
The two rate constants can be determined from the values of ( τ ) {\displaystyle (\tau )} and the equilibrium constant : K = k a / k b {\displaystyle K=k_{a}/k_{b}} , yielding two equations for two unknowns.
In more complex reaction networks, when multiple reaction steps are perturbed, then the reciprocal time constants are given by the eigenvalues of the characteristic rate equations. The ability to observe intermediate steps in a reaction pathway is one of the attractive features of this technology. [ 5 ]
Related chemical relaxation methods include pressure jump , [ 6 ] [ 3 ] electric field jump [ 6 ] and pH jump. [ 3 ] [ 7 ] | https://en.wikipedia.org/wiki/Temperature_jump |
Temperature measurement (also known as thermometry ) describes the process of measuring a current temperature for immediate or later evaluation. Datasets consisting of repeated standardized measurements can be used to assess temperature trends.
Attempts at standardized temperature measurement prior to the 17th century were crude at best. For instance in 170 AD, physician Claudius Galenus [ 1 ] : 18 mixed equal portions of ice and boiling water to create a "neutral" temperature standard. The modern scientific field has its origins in the works by Florentine scientists in the 1600s including Galileo constructing devices able to measure relative change in temperature, but subject also to confounding with atmospheric pressure changes. These early devices were called thermoscopes . The first sealed thermometer was constructed in 1654 by the Grand Duke of Tuscany, Ferdinand II . [ 1 ] : 19 The development of today's thermometers and temperature scales began in the early 18th century, when Daniel Gabriel Fahrenheit produced a mercury thermometer and scale, both developed by Ole Christensen Rømer . Fahrenheit's scale is still in use, alongside the Celsius and Kelvin scales.
Many methods have been developed for measuring temperature. Most of these rely on measuring some physical property of a working material that varies with temperature. One of the most common devices for measuring temperature is the glass thermometer . This consists of a glass tube filled with mercury or some other liquid, which acts as the working fluid. Temperature increase causes the fluid to expand, so the temperature can be determined by measuring the volume of the fluid. Such thermometers are usually calibrated so that one can read the temperature simply by observing the level of the fluid in the thermometer. Another type of thermometer that is not really used much in practice, but is important from a theoretical standpoint, is the gas thermometer .
Other important devices for measuring temperature include:
One must be careful when measuring temperature to ensure that the measuring instrument (thermometer, thermocouple, etc.) is really the same temperature as the material that is being measured. Under some conditions heat from the measuring instrument can cause a temperature gradient, so the measured temperature is different from the actual temperature of the system. In such a case the measured temperature will vary not only with the temperature of the system, but also with the heat transfer properties of the system.
What thermal comfort humans, animals and plants experience is related to more than temperature shown on a glass thermometer. Relative humidity levels in ambient air can induce more or less evaporative cooling. Measurement of the wet-bulb temperature normalizes this humidity effect. Mean radiant temperature also can affect thermal comfort. The wind chill factor makes the weather feel colder under windy conditions than calm conditions even though a glass thermometer shows the same temperature. Airflow increases the rate of heat transfer from or to the body, resulting in a larger change in body temperature for the same ambient temperature.
The theoretical basis for thermometers is the zeroth law of thermodynamics which postulates that if you have three bodies, A, B and C, if A and B are at the same temperature, and B and C are at the same temperature then A and C are at the same temperature. B, of course, is the thermometer.
The practical basis of thermometry is the existence of triple point cells. Triple points are conditions of pressure, volume and temperature such that three phases are simultaneously present, for example solid, vapor and liquid. For a single component there are no degrees of freedom at a triple point and any change in the three variables results in one or more of the phases vanishing from the cell. Therefore, triple point cells can be used as universal references for temperature and pressure (see Gibbs phase rule ).
Under some conditions it becomes possible to measure temperature by a direct use of the Planck's law of black-body radiation . For example, the cosmic microwave background temperature has been measured from the spectrum of photons observed by satellite observations such as the WMAP . In the study of the quark–gluon plasma through heavy-ion collisions , single particle spectra sometimes serve as a thermometer.
During recent decades, many thermometric techniques have been developed.
The most promising and widespread non-invasive thermometric techniques in a biotech context are based on the analysis of magnetic resonance images, computerized tomography images and echotomography. These techniques allow monitoring temperature within tissues without introducing a sensing element. [ 2 ] In the field of reactive flows (e.g., combustion, plasmas), laser induced fluorescence (LIF), CARS, and laser absorption spectroscopy have been exploited to measure temperature inside engines, gas-turbines, shock-tubes, synthesis reactors [ 3 ] etc. The capability of such optical-based techniques include rapid measurement (down to nanosecond timescales), notwithstanding the ability to not perturb the subject of measurement (e.g., the flame, shock-heated gases).
The American Society of Mechanical Engineers (ASME) has developed two separate and distinct standards on temperature Measurement, B40.200 and PTC 19.3.
B40.200 provides guidelines for bimetallic-actuated, filled-system, and liquid-in-glass thermometers. It also provides guidelines for thermowells .
PTC 19.3 provides guidelines for temperature measurement related to Performance Test Codes with particular emphasis on basic sources of measurement errors and techniques for coping with them.
Satellite temperature measurements are inferences of the temperature of the atmosphere at various altitudes as well as sea and land surface temperatures obtained from radiometric measurements by satellites . These measurements can be used to locate weather fronts , monitor the El Niño-Southern Oscillation , determine the strength of tropical cyclones , study urban heat islands and monitor the global climate. Wildfires , volcanos , and industrial hot spots can also be found via thermal imaging from weather satellites.
Weather satellites do not measure temperature directly. They measure radiances in various wavelength bands. Since 1978 microwave sounding units (MSUs) on National Oceanic and Atmospheric Administration polar orbiting satellites have measured the intensity of upwelling microwave radiation from atmospheric oxygen , which is related to the temperature of broad vertical layers of the atmosphere. Measurements of infrared radiation pertaining to sea surface temperature have been collected since 1967. | https://en.wikipedia.org/wiki/Temperature_measurement |
The Temperature paradox or Partee's paradox is a classic puzzle in formal semantics and philosophical logic . Formulated by Barbara Partee in the 1970s, it consists of the following argument, which speakers of English judge as wildly invalid .
Despite its obvious invalidity, this argument would be valid in most formalizations based on traditional extensional systems of logic. For instance, the following formalization in first order predicate logic would be valid via Leibniz's law :
To correctly predict the invalidity of the argument without abandoning Leibniz's Law, a formalization must capture the fact that the first premise makes a claim about the temperature at a particular point in time, while the second makes an assertion about how it changes over time. One way of doing so, proposed by Richard Montague , is to adopt an intensional logic for natural language, thus allowing "the temperature" to denote its extension in the first premise and its intension in the second.
Thus, Montague took the paradox as evidence that nominals denote individual concepts , defined as functions from a world -time pair to an individual. Later analyses build on this general idea, but differ in the specifics of the formalization. [ 1 ] [ 2 ] [ 3 ] [ 4 ]
This semantics article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Temperature_paradox |
In thermodynamics , a temperature–entropy ( T–s ) diagram is a thermodynamic diagram used to visualize changes to temperature ( T ) and specific entropy ( s ) during a thermodynamic process or cycle as the graph of a curve . It is a useful and common tool, particularly because it helps to visualize the heat transfer during a process. For reversible (ideal) processes, the area under the T–s curve of a process is the heat transferred to the system during that process. [ 1 ]
Working fluids are often categorized on the basis of the shape of their T–s diagram.
An isentropic process is depicted as a vertical line on a T–s diagram, whereas an isothermal process is a horizontal line. [ 2 ]
This thermodynamics -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Temperature–entropy_diagram |
In oceanography , temperature-salinity diagrams , sometimes called T-S diagrams , are used to identify water masses . In a T-S diagram, rather than plotting each water property as a separate "profile," with pressure or depth as the vertical coordinate, potential temperature (on the vertical axis) is plotted versus salinity (on the horizontal axis).
Temperature and salinity combine to determine the potential density of seawater ; contours of constant potential density are often shown in T-S diagrams. Each contour is known as an isopycnal , or a region of constant density. These isopycnals appear curved because of the nonlinearity of the equation of state of seawater. The thermal expansion coefficient, αT, and the haline contraction coefficient , βS, vary with temperature and salinity because both properties affect the potential density of seawater. [ 1 ]
As long as it remains isolated from the surface, where heat or fresh water can be gained or lost, and in the absence of mixing with other water masses, a water parcel's potential temperature and salinity are conserved. Deep water masses thus retain their T-S characteristics for long periods of time, and can be identified readily on a T-S plot. [ 2 ] [ 3 ] Deep water masses are formed in different locations, and therefore have differing characteristic properties, like ranges of temperature and salinity values. When T-S plots are created by compiling data collected from various locations, it is possible to group the data points based on where the water mass was formed. [ 4 ] This gives an idea of how the properties of different water masses compare to each other, which can give an idea of the way that thermohaline circulation works. In general, the depth of the water increases as you move to the bottom right corner of the graph (high salinity, low temperature), but there is some variation.
This geochemistry article is a stub . You can help Wikipedia by expanding it .
This oceanography article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Temperature–salinity_diagram |
Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tension . Such stresses cause the glass, when broken, to shatter into small granular chunks instead of splintering into large jagged shards as ordinary annealed glass does. These smaller, granular chunks are less likely to cause deep penetration when forced into the surface of an object (e.g. by gravity, by wind, by falling onto them, etc.) compared to larger, jagged shards because the reduction in both the mass and the maximum dimension of a glass fragment corresponds with a reduction in both the momentum and the penetration depth of the glass fragment.
Tempered glass is used for its safety and strength in a variety of applications, including passenger vehicle windows (apart from windshield), shower doors, aquariums, architectural glass doors and tables, refrigerator trays, mobile phone screen protectors, bulletproof glass components, diving masks , and plates and cookware.
Tempered glass is about four times stronger than annealed glass. [ 1 ] [ 2 ] The more rapid contraction of the outer layer during manufacturing induces compressive stresses in the surface of the glass balanced by tensile stresses in the body of the glass. Fully tempered 6-mm thick glass must have either a minimum surface compression of 69 MPa (10 000 psi) or an edge compression of not less than 67 MPa (9 700 psi). [ 3 ] For it to be considered safety glass , the surface compressive stress should exceed 100 megapascals (15,000 psi). As a result of the increased surface stress, when broken the glass breaks into small rounded chunks as opposed to sharp jagged shards.
Compressive surface stresses give tempered glass increased strength. Annealed glass has almost no internal stress and usually forms microscopic cracks on its surface. Tension applied to the glass can drive crack propagation which, once begun, concentrates tension at the tip of the crack driving crack propagation at very high speeds. [ citation needed ] Consequently, annealed glass is fragile and breaks into irregular and sharp pieces. [ 4 ] The compressive stresses on the surface of tempered glass contain flaws, preventing their propagation or expansion.
Any cutting or grinding must be done prior to tempering. Cutting, grinding, and sharp impacts after tempering will cause the glass to fracture.
The strain pattern resulting from tempering can be observed by viewing through an optical polarizer , such as a pair of polarizing sunglasses.
Tempered glass is used when strength, thermal resistance, and safety are important considerations. Passenger vehicles, for example, have all three requirements. Since they are stored outdoors, they are subject to constant heating and cooling as well as dramatic temperature changes throughout the year. Moreover, they must withstand small impacts from road debris such as stones as well as road accidents. Because large, sharp glass shards would present additional and unacceptable danger to passengers, tempered glass is used so that if broken, the pieces are blunt and mostly harmless. The windscreen or windshield is instead made of laminated glass , which will not shatter into pieces when broken while side windows and the rear windshield have historically been made of tempered glass. Some newer luxury vehicles have laminated side windows to meet occupant retention regulations, anti-theft purposes, or sound-deadening purposes.
Other typical applications of tempered glass include:
Tempered glass is also used in buildings for unframed assemblies (such as frameless glass doors), structurally loaded applications, and any other application that would become dangerous in the event of human impact. Building codes in the United States require tempered or laminated glass in several situations including some skylights, glass installed near doorways and stairways, large windows, windows which extend close to floor level, sliding doors, elevators, fire department access panels, and glass installed near swimming pools. [ 5 ]
Tempered glass is also used in the home. Some common household furniture and appliances that use tempered glass are frameless shower doors, glass table tops, glass shelves, cabinet glass and glass for fireplaces.
"Rim-tempered" indicates that a limited area, such as the rim of the glass or plate, is tempered, and is popular in food service. There are also fully tempered variants for strength and thermal shock resistance. Some countries specify requirements regarding this.
Tempered glass has also seen increased usage in bars and pubs, particularly in the United Kingdom and Australia, to prevent broken glass being used as a weapon . [ 6 ] [ 7 ]
Some forms of tempered glass are used for cooking and baking . Manufacturers and brands include Glasslock, Pyrex , Corelle , and Arc International . This is also the type of glass used for oven doors.
Most touchscreen mobile devices use some form of toughened glass (such as Corning 's Gorilla Glass ), but there are also separate tempered screen protectors for touchscreen devices sold as an accessory. [ 8 ]
Tempered glass can be made from annealed glass via a thermal tempering process. The glass is placed onto a roller table, taking it through a furnace that heats it well above its glass transition temperature of 564 °C (1,047 °F) to around 620 °C (1,148 °F). The glass is then rapidly cooled with forced air drafts while the inner portion remains free to flow for a short time.
An alternative chemical toughening process involves forcing a surface layer of glass at least 0.1 mm thick into compression by ion exchange of the sodium ions in the glass surface with potassium ions (which are 30% larger), by immersion of the glass into a bath of molten potassium nitrate . Chemical toughening results in increased toughness compared with thermal tempering and can be applied to glass objects of complex shapes. [ 9 ]
Tempered glass must be cut to size or pressed to shape before tempering, and cannot be re-worked once tempered. Polishing the edges or drilling holes in the glass is carried out before the tempering process starts. Because of the balanced stresses in the glass, damage to any portion will eventually result in the glass shattering into thumbnail-sized pieces. The glass is most susceptible to breakage due to damage at its edge, where the tensile stress is the greatest, but can also shatter in the event of a hard impact in the middle of the glass pane or if the impact is concentrated (for example, the glass is struck with a hardened point).
Using tempered glass can pose a security risk in some situations because of the tendency of the glass to shatter completely upon hard impact rather than leaving shards in the window frame. [ 10 ]
The surface of tempered glass does exhibit surface waves caused by contact with flattening rollers, if it has been formed using this process. This waviness is a significant problem in manufacturing of thin film solar cells. [ 11 ] The float glass process can be used to provide low-distortion sheets with very flat and parallel surfaces as an alternative for different glazing applications. [ 12 ]
Spontaneous glass breakage is a phenomenon by which tempered glass may spontaneously break without any apparent reason. The most common causes are: [ 13 ] [ 14 ]
Any breakage problem has more severe consequences where the glass is installed overhead or in public areas (such as in high-rise buildings). A safety window film can be applied to the tempered panes of glass to protect from its falling. An old-fashioned precaution was to install metal screens below skylights.
François Barthélémy Alfred Royer de la Bastie (1830–1901) of Paris, France is credited with first developing a method of tempering glass [ 16 ] by quenching almost molten glass in a heated bath of oil or grease in 1874, the method patented in England on August 12, 1874, patent number 2783. Tempered glass is sometimes known as Bastie glass after de la Bastie. In 1877 the German Friedrich Siemens developed a different process, sometimes called compressed glass or Siemens glass, producing a tempered glass stronger than the Bastie process by pressing the glass in cool molds. [ 17 ] The first patent on a whole process to make tempered glass was held by chemist Rudolph A. Seiden who was born in 1900 in Austria and emigrated to the United States in 1935. [ 18 ]
Though the underlying mechanism was not known at the time, the effects of "tempering" glass have been known for centuries. In about 1660, Prince Rupert of the Rhine brought the discovery of what are now known as " Prince Rupert's Drops " to the attention of King Charles II . These are teardrop-shaped bits of glass which are produced by allowing a molten drop of glass to fall into a bucket of water, thereby rapidly cooling it. They can withstand a blow from a hammer on the bulbous end without breaking, but the drops will disintegrate explosively into powder if the tail end is even slightly damaged. | https://en.wikipedia.org/wiki/Tempered_glass |
A Temperley transporter is an early form of overhead crane invented by John Ridley Temperley in 1892. [ 1 ] They were manufactured by the Temperley Transporter Company of London . [ 2 ]
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Template-guided self-assembly is a versatile fabrication process that can arrange various micrometer to nanometer sized particles into lithographically created template with defined patterns. The process contain the following four steps. [ 1 ] [ 2 ]
The "template" can be created by either photolithography or e-beam lithography to define binding sites for various building blocks. The binding sites should reflect the footprint of the building blocks or clusters to be bound.
After film development, the created pattern is treated with charged polymers in order to “stick” the particles. Take poly-lysine as an example, the poly-lysine will cover the negatively charged glass surface and turn the charge to be positive; it thus can non-specifically bind negatively charged metallic nanoparticles.
To do particle assembly, treated pattern is submerged in a small amount of aqueous solution of particles. [ 3 ] A few approaches can be used to facilitate the binding efficiency . One of them is to use capillary force at the edge of the aqueous droplet to “push” the particles into the binding sites. [ 4 ] If assembling multiple types of particles, the particles should be assembled in the order of decreasing sizes. [ 2 ] For example, if assembling both 60 nm gold nanoparticles as well as 40 nm silver nanoparticles, 60 nm gold nanoparticles should be applied first because it is too big to enter binding sites tailored for 40 nm particles. Rationally design the binding sequence as well as the binding site sizes can result in minimizing the binding errors from occurring.
After binding of all building blocks, the template can be removed by either dissolving in an organic solvent , or stripped off by a scotch tape. | https://en.wikipedia.org/wiki/Template-guided_self-assembly |
Template-switching polymerase chain reaction ( TS-PCR ) is a method of reverse transcription and polymerase chain reaction (PCR) amplification that relies on a natural PCR primer sequence at the polyadenylation site, also known as the poly(A) tail, and adds a second primer through the activity of murine leukemia virus reverse transcriptase . [ 1 ] This permits reading full cDNA sequences and can deliver high yield from single sources, even single cells that contain 10 to 30 picograms of mRNA , with relatively low levels (3-5%) of contaminating rRNA sequence. This technique is often employed in whole transcriptome shotgun sequencing . It is marketed by Clontech as Switching Mechanism At the 5' end of RNA Template ( SMART ) [ 2 ] [ 3 ] as well as by Diagenode as Capture and Amplification by Tailing and Switching ( CATS ).
By using syringe pumps to transmit a steady rate of isolated cells and uniquely oligonucleotide-barcoded beads, it is possible to isolate individual cells and beads together in droplets of lysis buffer, where the polyadenylation site binds to a primer containing a unique, identifying sequence. [ 4 ] This primer also contains a common sequence upstream of the identifier, so that after it is extended by reverse transcription, subsequent rounds of PCR will incorporate the tag, which permits each isolated cDNA that is sequenced to be tracked back to a specific originating bead. This permits the relative levels of transcripts in many individual cells to be analyzed simultaneously, creating a rational basis for the classification of these cells into particular cell types , [ 5 ] or permitting the logical inference of in situ hybridization data from embryos without actually performing the experiment. [ 6 ]
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A. martiensseni
A. sp. nov.
A. yakusini
P. palmipes
P. sp. nov.
P. perreti
P. juliawurstnerae
P. cameronensis
P. euskircheni
P. aff. euskercheni
P. parkeri
P. vulpiae
P. sp. nov. 2
P. sp. nov. 3
P. johnstoni
Species-level cladogram of the frog family Petropedetidae based on mitochondrial data. [ 1 ]
yields:
A. martiensseni
A. sp. nov.
A. yakusini
P. palmipes
P. sp. nov.
P. perreti
P. juliawurstnerae
P. cameronensis
P. euskircheni
P. aff. euskercheni
P. parkeri
P. vulpiae
P. sp. nov. 2
P. sp. nov. 3
P. johnstoni | https://en.wikipedia.org/wiki/Template:Cladogram_of_Petropedetidae |
Hoplomys gymnurus
Proechimys canicollis (Colombian spiny rat)
Proechimys decumanus (Pacific spiny rat)
Proechimys echinothrix (Stiff-spine spiny rat)
Proechimys simonsi (Simon's spiny rat)
Proechimys kulinae (Kulina spiny rat)
Proechimys gardneri (Gardner's spiny rat)
Proechimys pattoni (Patton's spiny rat)
Proechimys gorgonae
Proechimys oconnelli (O'Connell's spiny rat)
Proechimys semispinosus (Tome's spiny rat)
Proechimys boimensis
Proechimys guyannensis (Guyenne spiny rat)
Proechimys oris
Proechimys roberti (Roberto's spiny rat)
Proechimys cuvieri (Cuvier's spiny rat)
Proechimys brevicauda (Short-tailed spiny rat)
Proechimys gularis
Proechimys longicaudatus (Long-tailed spiny rat)
Proechimys amphichoricus
Proechimys goeldii (Goeldi's spiny rat)
Proechimys hyleae
Proechimys quadruplicatus (Napo spiny rat)
Proechimys steerei (Steere's spiny rat)
Proechimys chrysaeolus (Boyacá spiny rat)
Proechimys guairae (Guaira spiny rat)
Proechimys hoplomyoides (Guyanan spiny rat)
Proechimys magdalenae (Magdalena spiny rat)
Proechimys mincae (Minca spiny rat)
Proechimys poliopus (Gray-footed spiny rat)
Proechimys trinitatus (Trinidad spiny rat)
Proechimys urichi (Sucre spiny rat)
Species-level cladogram of the genus Proechimys , based on morphological and molecular characters. [ 1 ] [ 2 ]
yields:
Hoplomys gymnurus
Proechimys canicollis (Colombian spiny rat)
Proechimys decumanus (Pacific spiny rat)
Proechimys echinothrix (Stiff-spine spiny rat)
Proechimys simonsi (Simon's spiny rat)
Proechimys kulinae (Kulina spiny rat)
Proechimys gardneri (Gardner's spiny rat)
Proechimys pattoni (Patton's spiny rat)
Proechimys gorgonae
Proechimys oconnelli (O'Connell's spiny rat)
Proechimys semispinosus (Tome's spiny rat)
Proechimys boimensis
Proechimys guyannensis (Guyenne spiny rat)
Proechimys oris
Proechimys roberti (Roberto's spiny rat)
Proechimys cuvieri (Cuvier's spiny rat)
Proechimys brevicauda (Short-tailed spiny rat)
Proechimys gularis
Proechimys longicaudatus (Long-tailed spiny rat)
Proechimys amphichoricus
Proechimys goeldii (Goeldi's spiny rat)
Proechimys hyleae
Proechimys quadruplicatus (Napo spiny rat)
Proechimys steerei (Steere's spiny rat)
Proechimys chrysaeolus (Boyacá spiny rat)
Proechimys guairae (Guaira spiny rat)
Proechimys hoplomyoides (Guyanan spiny rat)
Proechimys magdalenae (Magdalena spiny rat)
Proechimys mincae (Minca spiny rat)
Proechimys poliopus (Gray-footed spiny rat)
Proechimys trinitatus (Trinidad spiny rat)
Proechimys urichi (Sucre spiny rat) | https://en.wikipedia.org/wiki/Template:Cladogram_of_Proechimys_species |
Archaeocaris vermiformis
Archaeocaris graffhami
† Bairdops elegans
Perimecturus parki
Perimecturus rapax
† Bairdops beargulchensis
† Daidal pattoni
† Daidal schoellmanni
† Daidal acanthocercus
Gorgonophontes fraiponti
Gorgonophontes peleron
† Chabardella spinosa
† Tyrannophontes theridion
† Tyrannophontes gigantion
† Triassosculda ahyongi
† Tyrannosculda laurae
† Pseudosculda laevis
† Archaeosculda phoenicia
† Sculda pennata
† Sculda syriaca
† Ursquilla yehoachi
† Lysiosquilla nkporoensis
† Nodosculda fisherorum
Squilla mantis
Species-level cladogram of the Paleozoic and Mesozoic mantis shrimp genera, based on morphological characters. [ 1 ]
yields:
Archaeocaris vermiformis
Archaeocaris graffhami
† Bairdops elegans
Perimecturus parki
Perimecturus rapax
† Bairdops beargulchensis
† Daidal pattoni
† Daidal schoellmanni
† Daidal acanthocercus
Gorgonophontes fraiponti
Gorgonophontes peleron
† Chabardella spinosa
† Tyrannophontes theridion
† Tyrannophontes gigantion
† Triassosculda ahyongi
† Tyrannosculda laurae
† Pseudosculda laevis
† Archaeosculda phoenicia
† Sculda pennata
† Sculda syriaca
† Ursquilla yehoachi
† Lysiosquilla nkporoensis
† Nodosculda fisherorum
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New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Geochem-journal-stub |
This geochemistry article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a geochemistry stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Geochem-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Geochem-stub |
This is a navigational template created using {{ navbox }} . It can be transcluded on pages by placing {{Grandi's series}} below the standard article appendices .
This template's initial visibility currently defaults to autocollapse , meaning that if there is another collapsible item on the page (a navbox, sidebar , or table with the collapsible attribute ), it is hidden apart from its title bar; if not, it is fully visible.
To change this template's initial visibility, the |state= parameter may be used:
Templates using the classes class=navbox ( {{ navbox }} ) or class=nomobile ( {{ sidebar }} ) are not displayed in article space on the mobile web site of English Wikipedia. Mobile page views account for approximately 68% of all page views (90-day average as of September 2024 [update] ). Briefly, these templates are not included in articles because 1) they are not well designed for mobile, and 2) they significantly increase page sizes—bad for mobile downloads—in a way that is not useful for the mobile use case. You can review/watch phab:T124168 for further discussion.
A navigational box that can be placed at the bottom of articles.
Template parameters [ Edit template data ]
The initial visibility of the navbox | https://en.wikipedia.org/wiki/Template:Grandi's_series |
The picture and this template share the same colors.
See also: | https://en.wikipedia.org/wiki/Template:Hexadecimal_table |
This article about a hypothetical chemical compound is a stub . You can help Wikipedia by expanding it .
This template is used to identify a stub about a hypothetical chemical compound . It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Hyp-chem-compound-stub}} produces the message shown at the beginning, and adds the article to the following categories:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Hyp-chem-compound-stub |
This template's initial visibility currently defaults to autocollapse , meaning that if there is another collapsible item on the page (a navbox, sidebar , or table with the collapsible attribute ), it is hidden apart from its title bar; if not, it is fully visible.
To change this template's initial visibility, the |state= parameter may be used: | https://en.wikipedia.org/wiki/Template:Immunology_sidebar |
This article about materials science is a stub . You can help Wikipedia by expanding it .
This template is used to identify a stub about materials science . It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Materials-sci-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Materials-sci-stub |
This template's initial visibility currently defaults to autocollapse , meaning that if there is another collapsible item on the page (a navbox, sidebar , or table with the collapsible attribute ), it is hidden apart from its title bar; if not, it is fully visible.
To change this template's initial visibility, the |state= parameter may be used: | https://en.wikipedia.org/wiki/Template:Measuring_and_alignment_tools |
This article about a medicinal chemistry journal is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page .
This template is used to identify a stub about a medicinal chemistry journal. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Medicinal-chem-journal-stub}} produces the message shown at the beginning, and adds the article to the following categories:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Medicinal-chem-journal-stub |
This article about medicinal chemistry is a stub . You can help Wikipedia by expanding it .
This template is used to identify a stub about medicinal chemistry . It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Medicinal-chem-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Medicinal-chem-stub |
This article about metabolism is a stub . You can help Wikipedia by expanding it .
This template is used to identify a stub about metabolism . It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Metabolism-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Metabolism-stub |
This metallurgy -related article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a metallurgy -related stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Metallurgy-stub}} produces the message shown at the beginning, and adds the article to the following categories:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Metallurgy-stub |
This mobile technology related article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a mobile technology related stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Mobile-tech-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Mobile-tech-stub |
This article about molecular modelling software is a stub . You can help Wikipedia by expanding it .
This template is used to identify a stub about molecular modelling software. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Molecular-modelling-software-stub}} produces the message shown at the beginning, and adds the article to the following categories:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Molecular-modelling-software-stub |
This molecular modelling –related article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a molecular modelling –related stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Molecular-modelling-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Molecular-modelling-stub |
This molecular physics –related article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a molecular physics –related stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Molecular-physics-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Molecular-physics-stub |
This nuclear chemistry –related article is a stub . You can help Wikipedia by expanding it .
This template is used to identify a nuclear chemistry –related stub. It uses {{ article stub box }}, which is a meta-template designed to ease the process of creating and maintaining stub templates.
Typing {{Nuclear-chemistry-stub}} produces the message shown at the beginning, and adds the article to the following category:
This is a stub template . A brief explanation of these templates follows; for full details please consult Wikipedia:Stub .
A stub is an article containing only a few sentences of text which is too short to provide encyclopedic coverage of a subject.
Further information can be found at:
New stub templates and categories (collectively "stub types") should not be created without prior proposal at Wikipedia:WikiProject Stub sorting/Proposals . This allows for the proper coordination of all stub types across Wikipedia, and for the checking of any new stub type for possible problems prior to its creation. | https://en.wikipedia.org/wiki/Template:Nuclear-chemistry-stub |
The picture and this template share the same colors.
See also: | https://en.wikipedia.org/wiki/Template:Numeral_systems_for_computation |
This template's initial visibility currently defaults to autocollapse , meaning that if there is another collapsible item on the page (a navbox, sidebar , or table with the collapsible attribute ), it is hidden apart from its title bar; if not, it is fully visible.
To change this template's initial visibility, the |state= parameter may be used:
TemplateData for Overton Prize
This template displays a navigation box containing links to articles about the International Society for Computational Biology ISCB Overton prize winners
Template parameters [ Edit template data ]
This template prefers inline formatting of parameters.
This parameter may be used to set the template's initial visibility: if "collapsed" the content is hidden and only the title bar is visible (with [show] link), if "expanded" the content and title bar are fully visible (with [hide] link), and if "autocollapse" the template is collapsed when the page contains other collapsible items. | https://en.wikipedia.org/wiki/Template:Overton_Prize |
TemplateData for PH indicator
No description.
Template parameters [ Edit template data ]
This template prefers block formatting of parameters.
no description
no description
no description
no description
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no description | https://en.wikipedia.org/wiki/Template:PH_indicator |
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