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| [[File:The Southern Milky Way Above ALMA.jpg|thumb|Some of the [[Atacama Large Millimeter Array]] radio telescopes.]]
| | Additionally, whenever you're initially starting, we have a limited budget, and beginning with ppc campaigns can not even be an option for we at this point inside time. Free traffic exchanges will be a amazing method to get traffic to your url. We should furthermore recognize there's absolutely no such thing because free because we must invest your time surfing from additional websites to make credits.<br><br><br><br>The BMI scale is employed to help identify a healthy fat. The calculator additionally advises when a person is obese or obese. A person may use supplements for as lengthy as one has an unhealthy BMI.<br><br>If you're a athlete that will function with the [http://safedietplans.com/calories-burned-walking calories burned] to determine whether or not or not you are fit, wholesome, or getting achievements together with your jogging or fitness system, we would like to be aware of some shortcomings from the BMI calculation. To start with, Quetelet lived in the 1800s. People looked and lived in a different method back then. People today had been commonly very a bit less.<br><br>A lot of people are effortlessly simply less apt to place about bodyweight as others, however they are not harmful by any means. Asian people commonly drop into this class more usually than many other races. So for anyone that is Asian, or whenever you learn which you are an "ectomorph" body design, the calories burned walking calculator may say you're in the 20 to 25 array whenever you're really obese (you've additionally considerably extra fat tissue, not enough lean muscle). Similarly, it will allow you know that you simply are "scrawny" whenever actually, pound for pound, you are quite sturdy.<br><br>Calculating a BMI will be performed manually using a formula or it can be conducted conveniently by using a handy online calories burned walking calculator that is present about most health/diet connected websites. If you wish To do it manually, you are able to come up with a body mass index by using the imperial formula. Your BMI is equal to a fat in lbs x 703, then we take this amount plus separate it by your height inside inches. However, with the advantageous calories burned walking calculators online, it is really simpler to login a favorite site plus connect in the numbers plus hit calculate.<br><br>Would we switch to foods for motives aside from hunger? Are you currently obsessive about thoughts of food - whether we propose to consume it or are focusing on restricting a self from eating it?<br><br>Website traffic is exactly what it sounds like - traffic coming into a url. That is, folks selecting to visit your website. Without constant traffic along with a lot of it, you are losing out about a lot of business. You will moreover not be getting the many from your website investment itself. Consider it, when you create a site that converts 2. 5% of its visitors into visitors, why wouldn't we try to get more visitors? The website may handle it. The question is, are you able to handle the additional load? If it was profitable, plus it could be, why wouldn't we try to get more traffic? |
| [[File:Smithsonian Submillimeter Array.jpg|thumb|The eight radio telescopes of the Smithsonian [[Submillimeter Array]], located at the [[Mauna Kea Observatory]] in Hawai'i.]]
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| '''Very-long-baseline interferometry''' ('''VLBI''') is a type of [[astronomical interferometer|astronomical interferometry]] used in [[radio astronomy]]. In VLBI a signal from an [[astronomical radio source]], such as a [[quasar]], is collected at multiple radio telescopes on Earth. The distance between the radio telescopes is then calculated using the time difference between the arrivals of the radio signal at different telescopes. This allows observations of an object that are made simultaneously by many radio telescopes to be combined, emulating a telescope with a size equal to the maximum separation between the telescopes.
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| Data received at each antenna in the array include arrival times from a local [[atomic clock]], such as a [[hydrogen maser]]. At a later time, the data are correlated with data from other antennas that recorded the same radio signal, to produce the resulting image. The resolution achievable using interferometry is proportional to the observing frequency. The VLBI technique enables the distance between telescopes to be much greater than that possible with conventional [[interferometry]], which requires antennas to be physically connected by [[coaxial cable]], [[waveguide]], [[optical fiber]], or other type of [[transmission line]]. The greater telescope separations are possible in VLBI due to the development of the [[closure phase]] imaging technique by [[Roger Clifton Jennison|Roger Jennison]] in the 1950s, allowing VLBI to produce images with superior resolution.
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| VLBI is most well known for imaging distant cosmic radio sources, spacecraft tracking, and for applications in [[astrometry]]. However, since the VLBI technique measures the time differences between the arrival of radio waves at separate antennas, it can also be used "in reverse" to perform earth rotation studies, map movements of [[tectonic plate]]s very precisely (within millimetres), and perform other types of [[geodesy]]. Using VLBI in this manner requires large numbers of time difference measurements from distant sources (such as [[quasar]]s) observed with a global network of antennas over a period of time.
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| == Scientific results ==
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| {{prose|section|date=October 2012}}
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| [[File:Very Long Baseline Interferometry.ogv|thumb|350px|Geodesist Chopo Ma explains some of the geodetic uses of VLBI.]]
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| Some of the scientific results derived from VLBI include:
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| *High resolution radio imaging of cosmic radio sources.
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| *Imaging the surfaces of nearby stars at radio wavelengths (see also [[astronomical interferometer|interferometry]]) – similar techniques have also been used to make infrared and optical images of stellar surfaces
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| *Definition of the [[International Celestial Reference Frame|celestial reference frame]]
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| *Motion of the Earth's tectonic plates
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| *Regional deformation and local uplift or subsidence.
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| *Variations in the Earth's orientation and length of day.
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| *Maintenance of the terrestrial reference frame
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| *Measurement of [[gravitational force]]s of the [[Sun]] and [[Moon]] on the Earth and the deep structure of the Earth
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| *Improvement of atmospheric models
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| *Measurement of the fundamental [[speed of gravity]]
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| *The tracking of the [[Huygens probe]] as it passed through [[Titan (moon)|Titan's]] atmosphere, allowing wind velocity measurements
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| == VLBI arrays ==
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| There are several VLBI arrays located in Europe, Canada, the United States, Russia, Japan and Australia. The most sensitive VLBI array in the world is the [[European VLBI Network]] (EVN). This is a part-time array with the data being processed at the [[Joint Institute for VLBI in Europe]] (JIVE). The [[Very Long Baseline Array]] (VLBA) uses ten dedicated, 25-meter telescopes spanning 5351 miles across the United States, and is the largest VLBI array that operates all year round as both an astronomical and [[geodesy]] instrument.<ref>http://www.nrao.edu/index.php/about/facilities/vlba</ref> The combination of the EVN and VLBA is known as Global VLBI. When one or both of these arrays are combined with one or more space-based VLBI antennas such as [[HALCA]] (previously) and now with RadioAstron ([[Spektr-R]]), the resolution obtained is higher than any other astronomical instrument, capable of imaging the sky with a level of detail measured in microarcseconds. A notable early example of international cooperation was in 1976, when radio telescopes in the United States, USSR and Australia were linked to observe hydroxyl-maser sources.<ref>First Global Radio Telescope, Sov. Astron., Oct 1976</ref>
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| == e-VLBI == <!-- NOTE: [[e-VLBI]] and [[eVLBI]] redirect to this section. Please fix the redirects if you change the section name. -->
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| [[Image:E-vlbi science.jpg|thumb|400px|Image of the source IRC+10420. The lower resolution image on the left image was taken with the UK's MERLIN array and shows the shell of [[maser]] emission produced by an expanding shell of gas with a diameter about 200 times that of our own Solar System. The shell of gas was ejected from a supergiant star (10 times the mass of our sun) at the centre of the emission about 900 years ago. The corresponding EVN e-VLBI image (right) shows the much finer structure of the masers because of the higher resolution of the VLBI array.]]
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| Recently it has become possible to connect VLBI radio telescopes in real-time, while still employing the local time references of the VLBI technique, in a technique known as '''e-VLBI'''. In Europe, six [[radio telescopes]] of the [[European VLBI Network| European VLBI Network (EVN)]] are now connected with Gigabit per second links via their National Research Networks and the Pan-European research network [[GEANT2]], and the first astronomical experiments using this new technique have been successfully conducted.<ref>{{cite web | url=http://www.jive.nl/astronomers-demonstrate-global-internet-telescope | title=Astronomers Demonstrate a Global Internet Telescope | accessdate=2011-05-06}}</ref>
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| The image to the right shows the first science produced by the European VLBI Network using e-VLBI. The data from 6 telescopes were processed in real time at the European Data Processing centre at [[Joint Institute for VLBI in Europe|JIVE]]. The Netherlands Academic Research Network SURFnet provides 6 x 1 Gbit/s connectivity between JIVE and the GEANT2 network.
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| == Space VLBI ==
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| In the quest for even greater angular resolution, dedicated VLBI satellites have been placed in Earth orbit to provide greatly extended baselines. Experiments incorporating such space-borne array elements are termed Space Very Long Baseline Interferometry (SVLBI).
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| The first such dedicated VLBI mission was [[HALCA]], an 8 meter [[radio telescope]], which was launched in February 1997 and made observations until October 2003, but due to the small size of the dish only very strong radio sources could be observed with SVLBI arrays incorporating it.
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| Another space VLBI mission, [[RadioAstron|Spektr-R (or RadioAstron)]], was launched in July 2011.
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| == How VLBI Works ==
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| [[Image:Vlbi data record.gif|thumb|350px|Recording data at each of the telescopes in a VLBI array. Extremely accurate high-frequency clocks are recorded alongside the astronomical data in order to help get the synchronization correct]]
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| In VLBI interferometry, the digitized antenna data are usually recorded at each of the telescopes (in the past this was done on large magnetic tapes, but nowadays it is usually done on large [[redundant array of independent disks|RAID]] arrays of computer disk drives). The antenna signal is sampled with an extremely precise and stable atomic clock (usually a hydrogen [[maser]]) that is additionally locked onto a GPS time standard. Alongside the astronomical data samples, the output of this clock is recorded on the tape/disk media. The recorded media are then transported to a central location. More recently experiments have been conducted with "electronic" VLBI (e-VLBI) where the data are sent by fibre-optics (e.g., 10 Gbit/s fiber-optic paths in the European [[GEANT2]] research network) and not recorded at the telescopes, speeding up and simplifying the observing process significantly.
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| Even though the data rates are very high, the data can be sent over normal Internet connections taking advantage of the fact that many of the international high speed networks have significant spare capacity at present.
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| At the location of the '''correlator''' the data are played back. The timing of the playback is adjusted according to the atomic clock signals on the (tapes/disk drives/fibre optic signal), and the estimated times of arrival of the radio signal at each of the telescopes. A range of playback timings over a range of nanoseconds are usually tested until the correct timing is found.
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| [[Image:Vlbi data playback.gif|thumb|350px|Playing back the data from each of the telescopes in a VLBI array. Great care must be taken to synchronize the play back of the data from different telescopes. [[Atomic clock]] signals recorded with the data help in getting the timing correct.]]
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| Each antenna will be a different distance from the radio source, and as with the short baseline radio [[interferometer]] the delays incurred by the extra distance to one antenna must be added artificially to the signals received at each of the other antennas. The approximate delay required can be calculated from the geometry of the problem. The tape playback is synchronized using the recorded signals from the atomic clocks as time references, as shown in the drawing on the right. If the position of the antennas is not known to sufficient accuracy or atmospheric effects are significant, fine adjustments to the delays must be made until interference fringes are detected. If the signal from antenna A is taken as the reference, inaccuracies in the delay will lead to errors <math>\epsilon_{B}</math> and <math>\epsilon_{C}</math> in the phases of the signals from tapes B and C respectively (see drawing on right). As a result of these errors the phase of the complex visibility cannot be measured with a very-long-baseline interferometer.
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| The phase of the complex visibility depends on the symmetry of the source brightness distribution. Any brightness distribution can be written as the sum of a [[symmetric component]] and an [[anti-symmetric component]]. The symmetric component of the brightness distribution only contributes to the real part of the complex visibility, while the anti-symmetric component only contributes to the imaginary part. As the phase of each complex visibility measurement cannot be determined with a very-long-baseline interferometer the symmetry of the corresponding contribution to the source brightness distributions is not known.
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| [[Roger Clifton Jennison|R. C. Jennison]] developed a novel technique for obtaining information about visibility phases when delay errors are present, using an observable called the [[closure phase]]. Although his initial laboratory measurements of closure phase had been done at optical wavelengths, he foresaw greater potential for his technique in radio interferometry. In 1958 he demonstrated its effectiveness with a radio interferometer, but it only became widely used for long-baseline radio interferometry in 1974. At least three antennas are required. This method was used for the first VLBI measurements, and a modified form of this approach ("Self-Calibration") is still used today.
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| == References ==
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| {{Refimprove|date=January 2009}}
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| {{reflist}}
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| ==External links==
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| *[http://www.merlin.ac.uk/e-merlin/ E-MERLIN] fibre-linked radio telescope array used in VLBI observations
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| *[http://www.expres-eu.org EXPReS] Express Production Real-time e-VLBI Service: a three-year project (est. March 2006) funded by the European Commission to develop an intercontinental e-VLBI instrument available to the scientific community
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| *[http://www.jive.nl JIVE] Joint Institute for VLBI in Europe
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| *[http://ivscc.gsfc.nasa.gov/ The International VLBI Service for Geodesy and Astrometry (IVS)]
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| *[http://ivsopar.obspm.fr/ IVSOPAR: the VLBI analysis center at the Paris Observatory]
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| *[http://www.geod.nrcan.gc.ca/edu/geod/vlbi/vlbi05_e.php "VLBI - Canada's Role"]
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| {{Radio-telescope}}
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| [[Category:Astronomical imaging]]
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| [[Category:Interferometry]]
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| [[Category:Radio astronomy]]
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| [[Category:Geodesy]]
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| [[Category:Radio telescopes|*]]
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Additionally, whenever you're initially starting, we have a limited budget, and beginning with ppc campaigns can not even be an option for we at this point inside time. Free traffic exchanges will be a amazing method to get traffic to your url. We should furthermore recognize there's absolutely no such thing because free because we must invest your time surfing from additional websites to make credits.
The BMI scale is employed to help identify a healthy fat. The calculator additionally advises when a person is obese or obese. A person may use supplements for as lengthy as one has an unhealthy BMI.
If you're a athlete that will function with the calories burned to determine whether or not or not you are fit, wholesome, or getting achievements together with your jogging or fitness system, we would like to be aware of some shortcomings from the BMI calculation. To start with, Quetelet lived in the 1800s. People looked and lived in a different method back then. People today had been commonly very a bit less.
A lot of people are effortlessly simply less apt to place about bodyweight as others, however they are not harmful by any means. Asian people commonly drop into this class more usually than many other races. So for anyone that is Asian, or whenever you learn which you are an "ectomorph" body design, the calories burned walking calculator may say you're in the 20 to 25 array whenever you're really obese (you've additionally considerably extra fat tissue, not enough lean muscle). Similarly, it will allow you know that you simply are "scrawny" whenever actually, pound for pound, you are quite sturdy.
Calculating a BMI will be performed manually using a formula or it can be conducted conveniently by using a handy online calories burned walking calculator that is present about most health/diet connected websites. If you wish To do it manually, you are able to come up with a body mass index by using the imperial formula. Your BMI is equal to a fat in lbs x 703, then we take this amount plus separate it by your height inside inches. However, with the advantageous calories burned walking calculators online, it is really simpler to login a favorite site plus connect in the numbers plus hit calculate.
Would we switch to foods for motives aside from hunger? Are you currently obsessive about thoughts of food - whether we propose to consume it or are focusing on restricting a self from eating it?
Website traffic is exactly what it sounds like - traffic coming into a url. That is, folks selecting to visit your website. Without constant traffic along with a lot of it, you are losing out about a lot of business. You will moreover not be getting the many from your website investment itself. Consider it, when you create a site that converts 2. 5% of its visitors into visitors, why wouldn't we try to get more visitors? The website may handle it. The question is, are you able to handle the additional load? If it was profitable, plus it could be, why wouldn't we try to get more traffic?