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Encyclopedia > Atomic clock
Chip-scale atomic clock unveiled by NIST
Chip-scale atomic clock unveiled by NIST

An atomic clock is a type of yellow inflateable clock that uses an atomic resonance frequency standard as its timekeeping element. They are the most accurate time and frequency standards known, and are used as primary standards for international time distribution services, and to control the frequency of television broadcasts and GPS satellite signals. Minutes to Midnight redirects here, along with other titles incorporating that term. ... Download high resolution version (1465x1449, 1419 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1465x1449, 1419 KB) Wikipedia does not have an article with this exact name. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... For other uses, see Atom (disambiguation). ... In telecommunication, a frequency standard is a stable oscillator used for frequency calibration or reference. ... For other uses, see Frequency (disambiguation). ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...


Atomic clocks do not use radioactivity, but rather the precise microwave signal that electrons in atoms emit when they change energy levels. Early atomic clocks were masers with attached equipment. Today's best atomic frequency standards (or clocks) are based on absorption spectroscopy of cold atoms in atomic fountains. Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... This article is about the type of Electromagnetic radiation. ... For other uses, see Electron (disambiguation). ... A quantum mechanical system can only be in certain states, so that only certain energy levels are possible. ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ... Absorption spectroscopy refers to a wide range of techniques where one measures how much light of a particular wavelength (color) is absorbed by a sample. ...


National standards agencies maintain an accuracy of 10-9 seconds per day (approximately 1 part in 1014), and a precision set by the radio transmitter pumping the maser. The clocks maintain a continuous and stable time scale, International Atomic Time (TAI). For civil time, another time scale is disseminated, Coordinated Universal Time (UTC). UTC is derived from TAI, but synchronized using leap seconds to UT1, which is based on actual rotations of the earth with respect to the mean sun. International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ... UTC redirects here. ... A leap second is a one-second adjustment to civil time in order to keep it close to the mean solar time. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ... Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ...

Contents

History

The first atomic clock was built in 1949 at the U.S. National Bureau of Standards (NBS). The first accurate atomic clock, a caesium standard based on a certain transition of the caesium-133 atom, was built by Louis Essen in 1955 at the National Physical Laboratory in the UK. This led to the internationally agreed definition of the second being based on atomic time. As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... A caesium standard is a primary frequency standard in which electronic transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Standard atomic weight 132. ... Louis Essen (September 6, 1908 – August 24, 1997) was an English physicist whose most notable achievements were in the precise measurement of time and the determination of the speed of light. ... The National Physical Laboratory (NPL) is the national measurement standards laboratory for the United Kingdom, based at Bushy Park in Teddington in the London Borough of Richmond upon Thames. ... This article is about the unit of time. ...


Since the beginning of development in the 1950s, atomic clocks have been made based on the hyperfine (microwave) transitions in hydrogen-1, caesium-133, and rubidium-87. For decades, scientific-instrument companies such as Hewlett-Packard have been making caesium-beam clocks and hydrogen masers for entities like NIST and USNO, at prices rivalling those of cars. This article is about the chemistry of hydrogen. ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Standard atomic weight 85. ... The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ...


In August 2004, NIST scientists demonstrated a chip-scaled atomic clock.[1] According to the researchers, the clock was believed to be one-hundredth the size of any other. It was also claimed that it requires just 75 mW, making it suitable for battery-driven applications. This device could conceivably become a consumer product. It will presumably be much smaller, consume less power, and be much cheaper to produce than the traditional caesium-fountain clocks used by NIST and USNO as reference clocks. NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... Milliwatt (SI symbol: mW) is a unit for measuring electrical power, equal to one-thousandth (10-3) of a watt. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... Aerial view of USNO. The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States. ...


In February 2008, physicists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, demonstrated a new clock based on strontium atoms trapped in a laser grid. The new clock is more than twice as accurate as the best clock up to now, the NIST-F1, and has an inaccuracy of less than one second in 200 million years (compared to 1 second per 80 million years for the F1). [2] JILA, formerly known as the Joint Institute for Laboratory Astrophysics, is one of the leading physical science research institutes in the United States. ... The University of Colorado at Boulder (CU-Boulder, UCB officially[3]; Colorado and CU colloquially) is the flagship university of the University of Colorado System in Boulder, Colorado. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... For other uses, see Laser (disambiguation). ... NIST-F1, source of the official time of the United States NIST-F1 is a cesium fountain atomic clock that serves as the United States primary time and frequency standard. ...


How they work

Since 1967, the International System of Units (SI) has defined the second as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the ground state of the caesium-133 atom. This definition makes the caesium oscillator (often called an atomic clock) the primary standard for time and frequency measurements (see caesium standard). Other physical quantities, like the volt and metre, rely on the definition of the second as part of their own definitions.[3] Look up si, Si, SI in Wiktionary, the free dictionary. ... A caesium standard is a primary frequency standard in which electronic transitions between the two hyperfine ground states of caesium-133 atoms is used to control the output frequency. ... Josephson junction array chip developed by NIST as a standard volt. ... This article is about the unit of length. ...


The core of the atomic clock is a tunable microwave cavity containing the gas. In a hydrogen maser clock the gas emits microwaves (mases) on a hyperfine transition, the field in the cavity oscillates, and the cavity is tuned for maximum microwave amplitude. Alternatively, in a caesium or rubidium clock, the beam or gas absorbs microwaves and the cavity contains an electronic amplifier to make it oscillate. For both types the atoms in the gas are prepared in one electronic state prior to filling them into the cavity. For the second type the number of atoms which change electronic state is detected and the cavity is tuned for a maximum of detected state changes. Microwave Slang for small waves, like at a beach, often used by surfers. ... A hydrogen radio frequency discharge, the first element inside a hydrogen maser (see description below) A maser is a device that produces coherent electromagnetic waves through amplification due to stimulated emission. ... Hyperfine structure is a small perturbation in the energy levels (or spectral) of atoms due to the proton-electron dipole moment interaction. ...


This adjustment process is where most of the work and complexity of the clock lies. The adjustment tries to correct for unwanted side-effects, such as frequencies from other electron transitions, temperature changes, and the "spreading" in frequencies caused by ensemble effects. One way of doing this is to sweep the microwave oscillator's frequency across a narrow range to generate a modulated signal at the detector. The detector's signal can then be demodulated to apply feedback to control long-term drift in the radio frequency. In this way, the quantum-mechanical properties of the atomic transition frequency of the caesium can be used to tune the microwave oscillator to the same frequency, except for a small amount of experimental error. When a clock is first turned on, it takes a while for the oscillator to stabilize. A Lock-in Amplifier (also known as a Phase Sensitive Detector) is a type of amplifier that can extract a signal with a known carrier wave from a noisy environment. ...


In practice, the feedback and monitoring mechanism is much more complex than described above.

Historical accuracy of atomic clocks from NIST.
Historical accuracy of atomic clocks from NIST.

A number of other atomic clock schemes are in use for other purposes. Rubidium standard clocks are prized for their low cost, small size (commercial standards are as small as 400 cm³) and short-term stability. They are used in many commercial, portable and aerospace applications. Hydrogen masers (often manufactured in Russia) have superior short-term stability compared to other standards, but lower long-term accuracy. Image File history File links Chart of stomic clock accuracy history from NIST. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Chart of stomic clock accuracy history from NIST. File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... As a non-regulatory agency of the United States Department of Commerce’s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... A rubidium standard is a frequency standard in which a specified hyperfine transition of electrons in rubidium-87 atoms is used to control the output frequency. ...


Often, one standard is used to fix another. For example, some commercial applications use a Rubidium standard periodically corrected by a GPS receiver. This achieves excellent short-term accuracy, with long-term accuracy equal to (and traceable to) the U.S. national time standards. GPS redirects here. ...


The lifetime of a standard is an important practical issue. Modern rubidium standard tubes last more than ten years, and can cost as little as US$50. Caesium reference tubes suitable for national standards currently last about seven years and cost about US$35,000. The long-term stability of hydrogen maser standards decreases because of changes in the cavity's properties over time.


Modern clocks use magneto-optical traps to cool the atoms for improved precision. experimental setup of the MOT A magneto-optical trap (abbreviated MOT) is a device that cools down atoms to temperatures near absolute zero and traps them at a certain place using magnetic fields and circularly polarised laser light. ...


Application

Atomic clocks are used to generate standard frequencies.[citation needed] They are installed at sites of time signals, LORAN-C, and Alpha navigation transmitters.[citation needed] They are also installed at some longwave and mediumwave broadcasting stations to deliver a very precise carrier frequency, which can also function as standard frequency.[citation needed] A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ... LORAN (LOng RAnge Navigation) is a terrestrial navigation system using low frequency radio transmitters. ... Alpha (also called RSDN-20 ) is a Russian system for long range radio navigation. ...


Further, atomic clocks are used for long-baseline interferometry in radioastronomy.[citation needed] It has been suggested that Optical interferometry be merged into this article or section. ... Microwave image of 3C353 galaxy at 8. ...


Atomic clocks are the basis of the GPS navigation system. The GPS master clock is a weighted average of atomic clocks at the ground stations and on-board the GPS satellites, each of which has several atomic clocks. Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...


Power consumption

Power consumption varies enormously, but there is a crude scaling with size.[citation needed] Chip scale atomic clocks can use power on the order of 100 mW;[citation needed] NIST F1 uses power orders of magnitude greater.[citation needed] Image File history File links This is a lossless scalable vector image. ... For other uses, see Watt (disambiguation). ...


Research

Most research focuses on ways to make the clocks smaller, cheaper, more accurate, and more reliable. These goals often conflict.


New technologies, such as femtosecond frequency combs, optical lattices and quantum information, have enabled prototypes of next generation atomic clocks. These clocks are based on optical rather than microwave transitions. A major obstacle to developing an optical clock is the difficulty of directly measuring optical frequencies. This problem has been solved with the development of self-referenced mode-locked lasers, commonly referred to as femtosecond frequency combs. Before the demonstration of the frequency comb in 2000, terahertz techniques were needed to bridge the gap between radio and optical frequencies, and the systems for doing so were cumbersome and complicated. With the refinement of the frequency comb these measurements have become much more accessible and numerous optical clock systems are now being developed around the world. An ultrashort pulse of light in the time domain. ... The hertz (symbol: Hz) is the SI unit of frequency. ...


Like in the radio range absorption spectroscopy is used to stabilize an oscillator — in this case a laser. When the optical frequency is divided down into a countable radio frequency using a femtosecond comb, the bandwidth of the phase noise is also divided by that factor. Although the bandwidth of laser phase noise is generally greater than stable microwave sources, after division it is less. An ultrashort pulse of light in the time domain. ...


The two primary systems under consideration for use in optical frequency standards are single ions isolated in an ion trap and neutral atoms trapped in an optical lattice.[4] These two techniques allow the atoms or ions to be highly isolated from external perturbations, thus producing an extremely stable frequency reference.


Optical clocks have already achieved better stability and lower systematic uncertainty than the best microwave clocks.[4] This puts them in a position to replace the current standard for time, the caesium fountain clock.


Atomic systems under consideration include but are not limited to Al+, Hg+,[4] Hg, Sr, Sr+, In+, Ca+, Ca, Yb+ and Yb. Aluminum redirects here. ... This article is about the element. ... This article is about the element. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... General Name, Symbol, Number strontium, Sr, 38 Chemical series alkaline earth metals Group, Period, Block 2, 5, s Appearance silvery white metallic Standard atomic weight 87. ... General Name, Symbol, Number indium, In, 49 Chemical series poor metals Group, Period, Block 13, 5, p Appearance silvery lustrous gray Standard atomic weight 114. ... For other uses, see Calcium (disambiguation). ... For other uses, see Calcium (disambiguation). ... Yb redirects here; for the unit of information see Yottabit General Name, Symbol, Number ytterbium, Yb, 70 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 173. ... Yb redirects here; for the unit of information see Yottabit General Name, Symbol, Number ytterbium, Yb, 70 Chemical series lanthanides Group, Period, Block n/a, 6, f Appearance silvery white Standard atomic weight 173. ...


Radio clocks

Main article: Radio clock

Modern radio clocks can be referenced to atomic clocks, and provide a way of getting high-quality atomic-derived time over a wide area using inexpensive equipment. However, radio clocks are not appropriate for high-precision scientific work. Many retailers market radio clocks as "atomic clocks", but in doing so they are misrepresenting their products. A radio clock A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. ...


There are a number of longwave radio transmitters around the world, in particular DCF77 (Germany), HPG (Switzerland), JJY (Japan), NPL or MSF (United Kingdom), TDF (France) and WWVB (United States). Many other countries can receive these signals (JJY can sometimes be received even in Western Australia and Tasmania at night), but it depends on time of day and atmospheric conditions. There is also a transit delay of approximately 1 ms for every 300 kilometers (186 mi) the receiver is from the transmitter. When operating properly and when correctly synchronized, better brands of radio clocks are normally accurate to the second. DCF77 is a longwave time signal radio station. ... HBG transmitter in Prangins (emetteurs. ... JJY is the callsign of a longwave time signal radio station similar to WWVB. The station is located in Japan, operated by a branch of the Japanese government known as the National Institute of Information and Communications Technology. ... The Time from NPL is a radio signal broadcast from the Anthorn VLF transmitter near Anthorn, Cumbria which serves as the United Kingdoms national time reference. ... The Time from NPL is a radio signal broadcast from the Anthorn VLF transmitter near Anthorn, Cumbria which serves as the United Kingdoms national time reference. ... Télé Distribution Française, or TDF, is a time signal service, broadcast on shortwave radio by the French Laboratoire primaire du temps et des frequences (LPTF). ... WWVB is a special NIST time signal radio station in Fort Collins, Colorado, co-located with WWV. WWVB is the station that radio-controlled clocks throughout North America use to synchronize themselves. ... One millisecond is one-thousandth of a second. ...


Typical radio "atomic clocks" require placement in a location with a relatively unobstructed atmospheric path to the transmitter, perform synchronization once a day during the night-time, and need fair to good atmospheric conditions to successfully update the time. The device that keeps track of the time between, or without, updates is usually a cheap and relatively inaccurate quartz-crystal clock, since it is thought that an expensive precise time keeper is not necessary with automatic atomic clock updates. The clock may include an indicator to alert users to possible inaccuracy when synchronization has not been successful within the last 24 to 48 hours. A quartz clock A quartz clock is a clock that uses an electronic oscillator which is made up by a quartz crystal to keep precise time. ...


See also

Time Portal
Electronics Portal

Image File history File links Download high resolution version (800x697, 123 KB) fr:: Montre gousset cs:: Kapesní hodinky de: Deutsch: Taschenuhr en: English: Pocket watch it: Italiano: Orologio da taschino (cipolla) es: Español: Reloj de bolsillo Template:ગુજરાતી ગુજરાતી: ખિસ્સામાં રાખવાની ઘડિયાળ ja: 日本語: 懐中時計 pl: Polski: Zegarek kieszonkowy pt: Português: Relógio de bolso... Image File history File links Nuvola_apps_ksim. ... The Network Time Protocol (NTP) is a protocol for synchronizing the clocks of computer systems over packet-switched, variable-latency data networks. ... NIST-F1, source of the official time of the United States NIST-F1 is a cesium fountain atomic clock that serves as the United States primary time and frequency standard. ... A radio clock A radio clock is a clock that is synchronized by a time code bit stream transmitted by a radio transmitter connected to a time standard such as an atomic clock. ... Télé Distribution Française, or TDF, is a time signal service, broadcast on shortwave radio by the French Laboratoire primaire du temps et des frequences (LPTF). ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ... An ultrashort pulse of light in the time domain. ... The Primary Atomic Reference Clock in Space or PARCS is an atomic-clock mission scheduled to fly on the International Space Station (ISS) in 2008. ... experimental setup of the MOT A magneto-optical trap (abbreviated MOT) is a device that cools down atoms to temperatures near absolute zero and traps them at a certain place using magnetic fields and circularly polarised laser light. ... International Atomic Time (TAI, from the French name Temps Atomique International) is a high-precision atomic time standard that tracks proper time on Earths geoid. ...

References

  1. ^ Chip-Scale Atomic Devices at NIST. NIST (May 2007). Retrieved on 2008-01-17.
  2. ^ Collaboration Helps Make JILA Strontium Atomic Clock ‘Best in Class’
  3. ^ FAQs. Franklin Instrument Company (2007). Retrieved on 2008-01-17.
  4. ^ a b c Oskay, WH; Diddams SA, Donley EA, Fortier TM, Heavner TP, Hollberg L, Itano WM, Jefferts SR, Delaney MJ, Kim K, Levi F, Parker TE, Bergquist JC (July 14 2006). "Single-atom optical clock with high accuracy". Physical Review Letters 97 (2): 020801. doi:10.1103/PhysRevLett.97.020801. PMID 16907426. Retrieved on 2007-03-25. 

2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 17th day of the year in the Gregorian calendar. ... 2008 (MMVIII) is the current year, a leap year that started on Tuesday of the Common Era (or Anno Domini), in accordance with the Gregorian calendar. ... is the 17th day of the year in the Gregorian calendar. ... A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 84th day of the year (85th in leap years) in the Gregorian calendar. ...

External links

A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... For other uses, see Equinox (disambiguation). ... For other uses, see Solstice (disambiguation). ... This article is about days of the week. ... This article details various mathematical algorithms to calculate the day of the week for any particular date in the past or future. ... The days of the year are sometimes designated letters A, B, C, D, E, F and G in a cycle of 7 as an aid for finding the day of week of a given calendar date and in calculating Easter. ... The International Commission on Stratigraphy concerns itself with stratigraphy on a global scale. ... Diagram of geological time scale. ... Dating material drawn from the archaeological record can made by a direct study of a artifact or may be deduced by association with materials found in the context the item is drawn from or inferred by its point of discovery in the sequence relative to datable contexts. ... The precession of Earths axis of rotation with respect to inertial space is also called the precession of the equinoxes. ... Sidereal time is time measured by the apparent diurnal motion of the vernal equinox, which is very close to, but not identical with, the motion of stars. ... // Galactic time NGC 4414, a typical spiral galaxy alike our Milky Way Galactic time, not to confuse with siderial time, is the time that is described by our spin relative to the center of the galaxy. ... Look up fortnight in Wiktionary, the free dictionary. ... The term jiffy (or jiffie) is used in different applications for various different short periods of time, usually 1/60 of a second. ... Lustrum was a sacrifice for expiation and purification offered by one of the censors of Rome in name of the Roman people at the close of the taking of the census, and which took place after a period of five years, so that the name came to denote a period... A saeculum is a length of time roughly equal to the lifetime of a person, or about 90 years. ... A shake is an informal unit of time equal to 10 nanoseconds, or 10-8 seconds. ... A tide is an obsolete or archaic term for time, period or season, such as eventide, shrovetide, Eastertide, etc. ... For the novel by Michael Crichton, see Timeline (novel). ... A duration is an amount of time or a particular time interval. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ... Metric time is the measure of time interval using the metric system, which defines the second as the base unit of time, and multiple and submultiple units formed with metric prefixes, such as kiloseconds and milliseconds. ... // Definition and history Psychologists have investigated mental chronometry for over 100 years. ... The time value of money is the premise that an investor prefers to receive a payment of a fixed amount of money today, rather than an equal amount in the future, all else being equal. ... Look up timekeeper in Wiktionary, the free dictionary. ...

  Results from FactBites:
 
NIST Unveils Chip-Scale Atomic Clock (800 words)
Atomic clocks long have provided the most accurate realizations of both of these quantities but also have traditionally been large—up to two meters in height—as well as power-hungry and expensive to build.
The new clock is based on the same general idea as other atomic clocks such as the NIST-F1 fountain clock—measuring time by the natural vibrations of cesium atoms, at 9.2 billion “ticks” per second—but uses a different design.
The "physics package" of the chip-scale atomic clock includes (from the bottom) a laser, a lens, an optical attenuator to reduce the laser power, a waveplate that changes the polarization of the light, a cell containing a vapor of cesium atoms, and (on top) a photodiode to detect the laser light transmitted through the cell.
Atomic clock to sync handhelds TRN 100604 (644 words)
The chip-scale atomic clock consumes 73 thousandths of a watt, which is comparable to common quartz crystal oscillators.
The researchers are working on making the clock accurate to one microsecond per day, or one second in 3,171 years, dropping its power consumption to 30 milliwatts, and putting it in a package that, including an oscillator and control electronics, would measure one cubic centimeter, said Hollberg.
"Compared to the smallest commercial atomic clocks this would be a volume reduction by a factor of about 50 times, and a reduction in power consumption by about 100 times," he said.
  More results at FactBites »

 
 

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