WorldWideScience

Sample records for atomic clocks

  1. Optical atomic clocks

    CERN Document Server

    Poli, N; Gill, P; Tino, G M

    2014-01-01

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femto-second optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in $10^{18}$. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  2. Microchip-Based Trapped-Atom Clocks

    CERN Document Server

    Vuletic, Vladan; Schleier-Smith, Monika H

    2011-01-01

    This is a chapter of a recently published book entitled Atom Chips, edited by Jakob Reichel and Vladan Vuletic. The contents of this chapter include: Basic Principles; Atomic-Fountain versus Trapped-Atom Clocks; Optical-Transition Clocks versus Microwave Clocks; Clocks with Magnetically Trapped Atoms--Fundamental Limits and Experimental Demonstrations; Readout in Trapped-Atom Clocks; and Spin Squeezing.

  3. Stochastic models for atomic clocks

    Science.gov (United States)

    Barnes, J. A.; Jones, R. H.; Tryon, P. V.; Allan, D. W.

    1983-01-01

    For the atomic clocks used in the National Bureau of Standards Time Scales, an adequate model is the superposition of white FM, random walk FM, and linear frequency drift for times longer than about one minute. The model was tested on several clocks using maximum likelihood techniques for parameter estimation and the residuals were acceptably random. Conventional diagnostics indicate that additional model elements contribute no significant improvement to the model even at the expense of the added model complexity.

  4. Collisionally induced atomic clock shifts and correlations

    Energy Technology Data Exchange (ETDEWEB)

    Band, Y. B.; Osherov, I. [Departments of Chemistry and Electro-Optics and the Ilse Katz Center for Nano-Science, Ben-Gurion University, Beer-Sheva 84105 (Israel)

    2011-07-15

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature {sup 87}Sr {sup 1}S{sub 0} (F=9/2) atomic clock in a magic wavelength optical lattice are presented.

  5. Laser controlled atom source for optical clocks

    Science.gov (United States)

    Kock, Ole; He, Wei; Świerad, Dariusz; Smith, Lyndsie; Hughes, Joshua; Bongs, Kai; Singh, Yeshpal

    2016-11-01

    Precision timekeeping has been a driving force in innovation, from defining agricultural seasons to atomic clocks enabling satellite navigation, broadband communication and high-speed trading. We are on the verge of a revolution in atomic timekeeping, where optical clocks promise an over thousand-fold improvement in stability and accuracy. However, complex setups and sensitivity to thermal radiation pose limitations to progress. Here we report on an atom source for a strontium optical lattice clock which circumvents these limitations. We demonstrate fast (sub 100 ms), cold and controlled emission of strontium atomic vapours from bulk strontium oxide irradiated by a simple low power diode laser. Our results demonstrate that millions of strontium atoms from the vapour can be captured in a magneto-optical trap (MOT). Our method enables over an order of magnitude reduction in scale of the apparatus. Future applications range from satellite clocks testing general relativity to portable clocks for inertial navigation systems and relativistic geodesy.

  6. Could Atomic clocks be affected by neutrinos?

    CERN Document Server

    Hanafi, Hanaa

    2016-01-01

    An atomic clock is a clock device that uses an electronic transition frequency of the electromagnetic spectrum of atoms as a frequency standard in order to derive a time standard since time is the reciprocal of frequency. If the electronic transition frequencies are in an "optical region", we are talking in this case about optical atomic clocks. If they are in an "microwave region" these atomic clocks are made of the metallic element cesium so they are called Cesium atomic clocks. Atomic clocks are the most accurate time and frequency standards known despite the different perturbations that can affect them, a lot of researches were made in this domain to show how the transitions can be different for different type of perturbations..Since atomic clocks are very sensitive devices, based on coherent states (A coherent state tends to loose coherence after interacting). One question can arise (from a lot of questions) which is why cosmic neutrinos are not affecting these clocks? The answer to this question requir...

  7. Atomic clocks with suppressed blackbody radiation shift

    CERN Document Server

    Yudin, V I; Okhapkin, M V; Bagayev, S N; Tamm, Chr; Peik, E; Huntemann, N; Mehlstaubler, T E; Riehle, F

    2011-01-01

    We develop a nonstandard concept of atomic clocks where the blackbody radiation shift (BBRS) and its temperature fluctuations can be dramatically suppressed (by one to three orders of magnitude) independent of the environmental temperature. The suppression is based on the fact that in a system with two accessible clock transitions (with frequencies $\

  8. Using Atomic Clocks to Detect Gravitational Waves

    CERN Document Server

    Loeb, Abraham

    2015-01-01

    Atomic clocks have recently reached a fractional timing precision of $<10^{-18}$. We point out that an array of atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

  9. Cesium Atomic Fountain Clocks at NMIJ

    Science.gov (United States)

    2010-11-01

    shift in caesium fountain clocks,” Physical Review Letters, 98, 153002. [10] A. Takamizawa, Y. Shirakawa, S. Yanagimachi et al., 2010, “Proposal of a...beam of laser-cooled cesium atoms,” Physical Review, A 60, R4241-R4244. [13] V. Gerginov, N. Nemitz, S. Weyers, et al., 2010, “Uncertainty evaluation of the caesium fountain clock PTB-CSF2,” Metrologia, 47, 65-79.

  10. Sagnac interferometry with a single atomic clock

    CERN Document Server

    Stevenson, R; Bishop, T; Lesanovsky, I; Fernholz, T

    2015-01-01

    We theoretically discuss an implementation of a Sagnac interferometer with cold atoms. In contrast to currently existing schemes our protocol does not rely on any free propagation of atoms. Instead it is based on superpositions of fully confined atoms and state-dependent transport along a closed path. Using Ramsey sequences for an atomic clock, the accumulated Sagnac phase is encoded in the resulting population imbalance between two internal (clock) states. Using minimal models for the above protocol we analytically quantify limitations arising from atomic dynamics and finite temperature. We discuss an actual implementation of the interferometer with adiabatic radio-frequency potentials that is inherently robust against common mode noise as well as phase noise from the reference oscillator.

  11. Satellite virtual atomic clock with pseudorange difference function

    Institute of Scientific and Technical Information of China (English)

    2009-01-01

    Satellite atomic clocks are the basis of GPS for the control of time and frequency of navigation signals. In the Chinese Area Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed. Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic clocks are used to implement satellite navigation. With the satellite virtual atomic clocks, the time at which the signals are transmitted from the ground can be delayed into the time that the signals are transmitted from the satellites and the pseudorange measuring can be fulfilled as in GPS. Satellite virtual atomic clocks can implement the navigation, make a pseudorange difference, remove the ephemeris error, and improve the accuracy of navigation positioning. They not only provide a navigation system without satellite clocks, but also a navigation system with pseudorange difference.

  12. Miniaturized optical system for atomic fountain clock

    Institute of Scientific and Technical Information of China (English)

    Lü De-Sheng; Qu Qiu-Zhi; Wang Bin; Zhao Jian-Bo; Li Tang; Liu Liang; Wang Yu-Zhu

    2011-01-01

    Using modularized components, we have built a miniaturized optical system for 87Rb atomic fountain clock that is fitted on an 80 cm × 60 cm optical breadboard. Compared with the conventional optical setup on the table, our system is more compact, more robust and miniaturized. Taking advantage of this system, laser beams are transmitted through eight optical fibre patch cords from the optical breadboard to an ultra high vacuum system. This optical setup has operated for five months in our fountain system and required no alignment.

  13. Atomic fountains and optical clocks at SYRTE: status and perspectives

    CERN Document Server

    Abgrall, M; De Sarlo, L; Guéna, J; Laurent, Ph; Coq, Y Le; Targat, R Le; Lodewyck, J; Lours, M; Rosenbusch, P; Rovera, D; Bize, S

    2015-01-01

    In this article, we report on the work done with the LNE-SYRTE atomic clock ensemble during the last 10 years. We cover progress made in atomic fountains and in their application to timekeeping. We also cover the development of optical lattice clocks based on strontium and on mercury. We report on tests of fundamental physical laws made with these highly accurate atomic clocks. We also report on work relevant to a future possible redefinition of the SI second.

  14. Designing Zeeman slower for strontium atoms - towards optical atomic clock

    CERN Document Server

    Bober, Marcin; Gawlik, Wojciech

    2010-01-01

    We report on design and construction of a Zeeman slower for strontium atoms which will be used in an optical atomic clock experiment. The paper describes briefly required specifications of the device, possible solutions, and concentrates on the chosen design. The magnetic field produced by the built Zeeman slower has been measured and compared with the simulations. The system consisting of an oven and Zeeman slower are designed to produce an atomic beam of 10-12 s-1 flux and final velocity of ~30 m/s.

  15. Designing Zeeman slower for strontium atoms - towards optical atomic clock

    OpenAIRE

    Bober, Marcin; Zachorowski, Jerzy; Gawlik, Wojciech

    2010-01-01

    We report on design and construction of a Zeeman slower for strontium atoms which will be used in an optical atomic clock experiment. The paper describes briefly required specifications of the device, possible solutions, and concentrates on the chosen design. The magnetic field produced by the built Zeeman slower has been measured and compared with the simulations. The system consisting of an oven and Zeeman slower are designed to produce an atomic beam of 10-12 s-1 flux and final velocity of...

  16. Miniature Optical Atomic Clock: Stabilization of a Kerr Comb Oscillator

    CERN Document Server

    Savchenkov, A A; Liang, W; Ilchenko, V S; Byrd, J; Matsko, A B; Seidel, D; Maleki, L

    2013-01-01

    Mechanical clocks consist of a pendulum and a clockwork that translates the pendulum period to displayed time. The most advanced clocks utilize optical transitions in atoms in place of the pendulum and an optical frequency comb generated by a femtosecond laser as the clockwork. The comb must be stabilized at two points along its frequency spectrum: one with a laser to lock a comb line to a transition in the atom, and another through self referencing to stabilize the frequency interval between the comb lines. This approach requires advanced techniques, so optical atomic clocks are currently laboratory devices in specialized labs. In this paper we leverage unique properties of Kerr comb oscillators for realization of optical atomic clocks in miniature form factors. In particular, we describe a clock based on D1 transition of 87Rb that fits in the palm of the hand, and can be further miniaturized to chip scale.

  17. Hunting for topological dark matter with atomic clocks

    CERN Document Server

    Derevianko, A

    2013-01-01

    The cosmological applications of atomic clocks so far have been limited to searches of the uniform-in-time drift of fundamental constants. In this paper, we point out that a transient in time change of fundamental constants can be induced by dark matter objects that have large spatial extent, and are built from light non-Standard Model fields. The stability of this type of dark matter can be dictated by the topological reasons. We point out that correlated networks of atomic clocks, some of them already in existence, can be used as a powerful tool to search for the topological defect dark matter, thus providing another important fundamental physics application to the ever-improving accuracy of atomic clocks. During the encounter with a topological defect, as it sweeps through the network, initially synchronized clocks will become desynchronized. Time discrepancies between spatially-separated clocks are expected to exhibit a distinct signature, encoding defect's space structure and its interaction strength wit...

  18. Remote atomic clock synchronization via satellites and optical fibers

    CERN Document Server

    Piester, D; Fujieda, M; Feldmann, T; Bauch, A

    2011-01-01

    In the global network of institutions engaged with the realization of International Atomic Time (TAI), atomic clocks and time scales are compared by means of the Global Positioning System (GPS) and by employing telecommunication satellites for two-way satellite time and frequency transfer (TWSTFT). The frequencies of the state-of-the-art primary caesium fountain clocks can be compared at the level of 10e-15 (relative, 1 day averaging) and time scales can be synchronized with an uncertainty of one nanosecond. Future improvements of worldwide clock comparisons will require also an improvement of the local signal distribution systems. For example, the future ACES (atomic clock ensemble in space) mission shall demonstrate remote time scale comparisons at the uncertainty level of 100 ps. To ensure that the ACES ground instrument will be synchronized to the local time scale at PTB without a significant uncertainty contribution, we have developed a means for calibrated clock comparisons through optical fibers. An un...

  19. The quantum beat principles and applications of atomic clocks

    CERN Document Server

    Major, F

    2007-01-01

    This work attempts to convey a broad understanding of the physical principles underlying the workings of these quantum-based atomic clocks, with introductory chapters placing them in context with the early development of mechanical clocks and the introduction of electronic time-keeping as embodied in the quartz-controlled clocks. While the book makes no pretense at being a history of atomic clocks, it nevertheless takes a historical perspective in its treatment of the subject. Intended for nonspecialists with some knowledge of physics or engineering, The Quantum Beat covers a wide range of salient topics relevant to atomic clocks, treated in a broad intuitive manner with a minimum of mathematical formalism. Detailed descriptions are given of the design principles of the rubidium, cesium, hydrogen maser, and mercury ion standards; the revolutionary changes that the advent of the laser has made possible, such as laser cooling, optical pumping, the formation of "optical molasses," and the cesium "fountain" stand...

  20. Ultrastable optical clock with two cold-atom ensembles

    Science.gov (United States)

    Schioppo, M.; Brown, R. C.; McGrew, W. F.; Hinkley, N.; Fasano, R. J.; Beloy, K.; Yoon, T. H.; Milani, G.; Nicolodi, D.; Sherman, J. A.; Phillips, N. B.; Oates, C. W.; Ludlow, A. D.

    2017-01-01

    Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with the 'dead' time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise from the laser interrogating the atomic transition. Despite recent advances in optical clock stability that have been achieved by improving laser coherence, the Dick effect has continually limited the performance of optical clocks. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock that is based on the interleaved interrogation of two cold-atom ensembles. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability assessed to be for an averaging time τ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the standard quantum limit of clock stability, achieving a spectroscopy line quality factor of Q > 4 × 1015.

  1. Hunting for dark matter with GPS and atomic clocks

    Science.gov (United States)

    Derevianko, Andrei

    2015-05-01

    Atomic clocks are arguably the most accurate scientific instruments ever build. Modern clocks are astonishing timepieces guaranteed to keep time within a second over the age of the Universe. The cosmological applications of atomic clocks so far have been limited to searches of the uniform-in-time drift of fundamental constants. We point out that a transient in time change of fundamental constants (translating into clocks being sped up or slowed down) can be induced by dark matter objects that have large spatial extent, and are built from light non-Standard Model fields. The stability of this type of dark matter can be dictated by the topological reasons. We argue that correlated networks of atomic clocks, such as atomic clocks onboard satellites of the GPS constellation, can be used as a powerful tool to search for the topological defect dark matter. In other words, one could envision using GPS as a 50,000 km-aperture dark-matter detector. Similar arguments apply to terrestrial networks of atomic clocks. Details:

  2. Experimental constraint on dark matter detection with optical atomic clocks

    Science.gov (United States)

    Wcisło, P.; Morzyński, P.; Bober, M.; Cygan, A.; Lisak, D.; Ciuryło, R.; Zawada, M.

    2016-12-01

    The total mass density of the Universe appears to be dominated by dark matter. However, beyond its gravitational interactions at the galactic scale, little is known about its nature1. Several proposals have been advanced in recent years for the detection of dark matter2-4. In particular, a network of atomic clocks could be used to search for transient indicators of hypothetical dark matter5 in the form of stable topological defects; for example, monopoles, strings or domain walls6. The clocks become desynchronized when a dark-matter object sweeps through the network. This pioneering approach5 requires a comparison between at least two distant optical atomic clocks7-9. Here, by exploiting differences in the susceptibilities of the atoms and the cavity to the fine-structure constant10,11, we show that a single optical atomic clock12 is already sensitive to dark-matter events. This implies that existing optical atomic clocks13,14 can serve as a global topological-defect dark-matter observatory, without any further developments in experimental apparatus or the need for long phase-noise-compensated optical-fibre links15. Using optical atomic clocks, we explored a new dimension of astrophysical observations by constraining the strength of atomic coupling to hypothetical dark-matter cosmic objects. Under the conditions of our experiments, the degree of constraint was found to exceed the previously reported limits16 by more than three orders of magnitude.

  3. Improvement of an Atomic Clock using Squeezed Vacuum

    DEFF Research Database (Denmark)

    Kruse, I.; Lange, K; Peise, Jan;

    2016-01-01

    , the vacuum noise restricts the precision of the interferometer to the standard quantum limit (SQL). Here, we propose and experimentally demonstrate a novel clock configuration that surpasses the SQL by squeezing the vacuum in the empty input state. We create a squeezed vacuum state containing an average of 0.......75 atoms to improve the clock sensitivity of 10000 atoms by 2.05+0.34−0.37  dB. The SQL poses a significant limitation for today’s microwave fountain clocks, which serve as the main time reference. We evaluate the major technical limitations and challenges for devising a next generation of fountain clocks......Since the pioneering work of Ramsey, atom interferometers are employed for precision metrology, in particular to measure time and to realize the second. In a classical interferometer, an ensemble of atoms is prepared in one of the two input states, whereas the second one is left empty. In this case...

  4. Geophysical applicability of atomic clocks: direct continental geoid mapping

    CERN Document Server

    Bondarescu, Ruxandra; Hetényi, György; Boschi, Lapo; Jetzer, Philippe; Balakrishna, Jayashree; 10.1111/j.1365-246X.2012.05636.x

    2012-01-01

    The geoid is the true physical figure of the Earth, a particular equipotential surface of the gravity field of the Earth that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General Relativity Theory predicts constant clock rate at sea level, and faster (resp. slower) clock rate above (resp. below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate that is equivalent to 1 cm in determining equipotential surface (including geoid) he...

  5. Atomic Clocks and Variations of the FIne Structure Constant

    Science.gov (United States)

    Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute

    1995-01-01

    We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.

  6. The Rubidium Atomic Clock and Basic Research

    Science.gov (United States)

    2007-12-10

    photodetector . (Chip-scale clock image from ref. 14.) 38 November 2007 Physics Today www.physicstoday.org an all-optical fashion:13 The laser field is...spectroscopy, laser chemistry, atmospheric propagation and beam control, LIDAR /LADAR remote sensing; solar cell and array testing and evaluation, battery

  7. Phase locking a clock oscillator to a coherent atomic ensemble

    CERN Document Server

    Kohlhaas, R; Cantin, E; Aspect, A; Landragin, A; Bouyer, P

    2015-01-01

    The sensitivity of an atomic interferometer increases when the phase evolution of its quantum superposition state is measured over a longer interrogation interval. In practice, a limit is set by the measurement process, which returns not the phase, but its projection in terms of population difference on two energetic levels. The phase interval over which the relation can be inverted is thus limited to the interval $[-\\pi/2,\\pi/2]$; going beyond it introduces an ambiguity in the read out, hence a sensitivity loss. Here, we extend the unambiguous interval to probe the phase evolution of an atomic ensemble using coherence preserving measurements and phase corrections, and demonstrate the phase lock of the clock oscillator to an atomic superposition state. We propose a protocol based on the phase lock to improve atomic clocks under local oscillator noise, and foresee the application to other atomic interferometers such as inertial sensors.

  8. Evaluating and Minimizing Distributed Cavity Phase Errors in Atomic Clocks

    CERN Document Server

    Li, Ruoxin

    2010-01-01

    We perform 3D finite element calculations of the fields in microwave cavities and analyze the distributed cavity phase errors of atomic clocks that they produce. The fields of cylindrical cavities are treated as an azimuthal Fourier series. Each of the lowest components produces clock errors with unique characteristics that must be assessed to establish a clock's accuracy. We describe the errors and how to evaluate them. We prove that sharp structures in the cavity do not produce large frequency errors, even at moderately high powers, provided the atomic density varies slowly. We model the amplitude and phase imbalances of the feeds. For larger couplings, these can lead to increased phase errors. We show that phase imbalances produce a novel distributed cavity phase error that depends on the cavity detuning. We also design improved cavities by optimizing the geometry and tuning the mode spectrum so that there are negligible phase variations, allowing this source of systematic error to be dramatically reduced.

  9. Heisenberg-limited atom clocks based on entangled qubits.

    Science.gov (United States)

    Kessler, E M; Kómár, P; Bishof, M; Jiang, L; Sørensen, A S; Ye, J; Lukin, M D

    2014-05-16

    We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.

  10. Searching for dark matter with optical atomic clocks

    CERN Document Server

    Wcislo, Piotr; Bober, Marcin; Cygan, Agata; Lisak, Daniel; Ciurylo, Roman; Zawada, Michal

    2016-01-01

    One of the most fundamental questions of modern physics is the existence of yet unknown forms of matter and interactions. The total mass density of the Universe appears to be dominated by some hypothetical dark matter (DM). However, beyond its gravitational interaction at galactic scale, little is known about the DM nature and properties. One possibility is that it has a form of stable topological defects built from light scalar fields which, for nonzero DM-SM coupling, would result in transient variations of fundamental constants. Optical atomic clocks, highly sensitive to variations of the fine-structure constant, seem to be natural candidates for such searches. Here we demonstrate the first experimental constraint on the strength of transient DM-SM coupling determined with optical atomic clocks. Instead of measuring the phase difference between two distant clocks we determine a common component of their readouts. We show that our constraint, even for one-day measurement, greatly exceeds previous laboratory...

  11. The fission time scale measured with an atomic clock

    NARCIS (Netherlands)

    Kravchuk, VL; Wilschut, HW; Hunyadi, M; Kopecky, S; Lohner, H; Rogachevskiy, A; Siemssen, RH; Krasznahorkay, A; Hamilton, JH; Ramayya, AV; Carter, HK

    2003-01-01

    We present a new direct method of measuring the fission absolute time scale using an atomic clock based on the lifetime of a vacancy in the atomic K-shell. We studied the reaction Ne-20 + Th-232 -> O-16 + U-236* at 30 MeV/u. The excitation energy of about 115 MeV in such a reaction is in the range w

  12. Atomic clocks as a tool to monitor vertical surface motion

    CERN Document Server

    Bondarescu, Ruxandra; Lundgren, Andrew; Hetényi, György; Houlié, Nicolas; Jetzer, Philippe; Bondarescu, Mihai

    2015-01-01

    Atomic clock technology is advancing rapidly, now reaching stabilities of $\\Delta f/f \\sim 10^{-18}$, which corresponds to resolving $1$ cm in equivalent geoid height over an integration timescale of about 7 hours. At this level of performance, ground-based atomic clock networks emerge as a tool for monitoring a variety of geophysical processes by directly measuring changes in the gravitational potential. Vertical changes of the clock's position due to magmatic, volcanic, post-seismic or tidal deformations can result in measurable variations in the clock tick rate. As an example, we discuss the geopotential change arising due to an inflating point source (Mogi model), and apply it to the Etna volcano. Its effect on an observer on the Earth's surface can be divided into two different terms: one purely due to uplift and one due to the redistribution of matter. Thus, with the centimetre-level precision of current clocks it is already possible to monitor volcanoes. The matter redistribution term is estimated to b...

  13. 2e-18 total uncertainty in an atomic clock

    CERN Document Server

    Nicholson, T L; Hutson, R B; Marti, G E; Bloom, B J; McNally, R L; Zhang, W; Barrett, M D; Safronova, M S; Strouse, G F; Tew, W L; Ye, J

    2014-01-01

    The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, new insights in quantum science, tighter limits on fundamental constant variation, and improved tests of relativity. The record for the best stability and accuracy is currently held by optical lattice clocks. This work takes an important step towards realizing the full potential of a many-particle clock with a state-of-the-art stable laser. Here, we achieve fractional stability of 2.2e-16 at 1 s by using seconds-long coherent interrogations of our clock transition in a low-density system not limited by atomic interactions. With this better stability, we perform a new accuracy evaluation of our clock, improving many systematic uncertainties that limited our previous measurements, such as the lattice ac Stark and blackbody radiation (BBR) shifts. For the lattice ac Stark systematic, we identify the lattice laser frequency where the scalar and tensor components of the shift cancel, allowing for state ind...

  14. Synchronization of Active Atomic Clocks via Quantum and Classical Channels

    CERN Document Server

    Roth, Alexander

    2016-01-01

    Superradiant lasers based on atomic ensembles exhibiting ultra-narrow optical transitions can emit light of unprecedented spectral purity and may serve as active atomic clocks. We consider two frequency-detuned active atomic clocks, which are coupled in a cascaded setup, i.e. as master & slave lasers, and study the synchronization of the slave to the master clock. In a setup where both atomic ensembles are coupled to a common cavity mode such synchronization phenomena have been predicted by Xu et al. [Phys. Rev. Lett. 113, 154101 (2014)] and experimentally observed by Weiner et al. [arXiv:1503.06464 (2015)]. Here we demonstrate that synchronization still occurs in cascaded setups but exhibits distinctly different phase diagrams. We study the characteristics of synchronization in comparison to the case of coupling through a common cavity. We also consider synchronization through a classical channel where light of the master laser is measured phase sensitively and the slave laser is injection locked by feed...

  15. Synchronization of active atomic clocks via quantum and classical channels

    Science.gov (United States)

    Roth, Alexander; Hammerer, Klemens

    2016-10-01

    Superradiant lasers based on atomic ensembles exhibiting ultranarrow optical transitions can emit light of unprecedented spectral purity and may serve as active atomic clocks. We consider two frequency-detuned active atomic clocks, which are coupled in a cascaded setup, i.e., as master and slave lasers, and study the synchronization of the slave to the master clock. In a setup where both atomic ensembles are coupled to a common cavity mode, such synchronization phenomena have been predicted by Xu et al. [M. Xu, D. A. Tieri, E. C. Fine, J. K. Thompson, and M. J. Holland, Phys. Rev. Lett. 113, 154101 (2014)., 10.1103/PhysRevLett.113.154101] and experimentally observed by Weiner et al. (J. M. Weiner et al., arXiv:1503.06464). Here we demonstrate that synchronization still occurs in cascaded setups but exhibits distinctly different phase diagrams. We study the characteristics of synchronization in comparison to the case of coupling through a common cavity. We also consider synchronization through a classical channel where light of the master laser is measured phase sensitively and the slave laser is injection locked by feedback and compare to the results achievable by coupling through quantum channels.

  16. Gravitational wave detection with optical lattice atomic clocks

    CERN Document Server

    Kolkowitz, Shimon; Langellier, Nicholas; Lukin, Mikhail D; Walsworth, Ronald L; Ye, Jun

    2016-01-01

    We propose a space-based gravitational wave detector consisting of two spatially separated, drag-free satellites sharing ultra-stable optical laser light over a single baseline. Each satellite contains an optical lattice atomic clock, which serves as a sensitive, narrowband detector of the local frequency of the shared laser light. A synchronized two-clock comparison between the satellites will be sensitive to the effective Doppler shifts induced by incident gravitational waves (GWs) at a level competitive with other proposed space-based GW detectors, while providing complementary features. The detected signal is a differential frequency shift of the shared laser light due to the relative velocity of the satellites, rather than a phase shift arising from the relative satellite positions, and the detection window can be tuned through the control sequence applied to the atoms' internal states. This scheme enables the detection of GWs from continuous, spectrally narrow sources, such as compact binary inspirals, ...

  17. Optical lattice clock with Strontium atoms; Horloge a reseau optique a atomes de strontium

    Energy Technology Data Exchange (ETDEWEB)

    Baillard, X

    2008-01-15

    This thesis presents the latest achievements regarding the optical lattice clock with Strontium atoms developed at LNE-SYRTE. After a review of the different types of optical clocks that are currently under development, we stress on the concept of optical lattice clock which was first imagined for Sr{sup 87} using the {sup 1}S{sub 0} {yields} {sup 3}P{sub 0} transition. We exhibit the features of this atom, in particular the concept of magic wavelength for the trap, and the achievable performances for this kind of clock. The second part presents the experimental aspects, insisting particularly on the ultra-stable laser used for the interrogation of the atoms which is a central part of the experiment. Among the latest improvements, an optical pumping phase and an interrogation phase using a magnetic field have been added in order to refine the evaluation of the Zeeman effect. Finally, the last part presents the experimental results. The last evaluation of the clock using Sr{sup 87} atoms allowed us to reach a frequency accuracy of 2.6*10{sup -15} and a measurement in agreement with the one made at JILA (Tokyo university) at the 10{sup -15} level. On another hand, thanks to recent theoretical proposals, we made a measurement using the bosonic isotope Sr{sup 88} by adapting the experimental setup. This measurement represents the first evaluation for this type of clock, with a frequency accuracy of 7*10{sup -14}. (author)

  18. Generating and probing entangled states for optical atomic clocks

    Science.gov (United States)

    Braverman, Boris; Kawasaki, Akio; Vuletic, Vladan

    2016-05-01

    The precision of quantum measurements is inherently limited by projection noise caused by the measurement process itself. Spin squeezing and more complex forms of entanglement have been proposed as ways of surpassing this limitation. In our system, a high-finesse asymmetric micromirror-based optical cavity can mediate the atom-atom interaction necessary for generating entanglement in an 171 Yb optical lattice clock. I will discuss approaches for creating, characterizing, and optimally utilizing these nonclassical states for precision measurement, as well as recent progress toward their realization. This research is supported by DARPA QuASAR, NSF, and NSERC.

  19. Development of a compact cold-atom atomic clock based on coherent population trapping

    Science.gov (United States)

    Blanshan, Eric M.

    Field-grade atomic clocks capable of primary standard performance in compact physics packages would be of significant value in a variety of applications ranging from network synchronization and secure communications to GPS hold-over and inertial navigation. A cold-atom coherent population trapping (CACPT) clock featuring laser-cooled atoms and pulsed Ramsey interrogation is a strong candidate for this technology if the principal frequency shifts can be controlled and the performance degradation associated with miniaturization can be overcome. In this thesis, research focused on the development of this type of compact atomic clock is presented. To address the low atom numbers obtained in small cold-atom sources, experiments were performed in which an atomic beam was decelerated with bichromatic stimulated laser forces and loaded into a mm-scale magneto-optical trap, increasing the atom number by a factor of 12.5. A CACPT clock using the high-contrast lin||lin optical interrogation technique was developed and achieved a stability of 7 x 10-13 after one hour of integration. Doppler shifts in the clock are explained using a simple kinematic model and canceled by interrogating the atoms with a counter-propagating CPT configuration. Finally, a thorough characterization of the AC-stark effect in lin||lin CPT was performed. Observed shifts are explained in terms of contributions from coherent CPT-generating couplings and population transfer effects caused by optical pumping from incoherent light. Measurements are compared with existing and new theoretical treatments, and a laser configuration is identified that reduces clock drift from light shifts to less than 10-14 for the current system.

  20. Ultra-stable optical clock with two cold-atom ensembles

    CERN Document Server

    Schioppo, M; McGrew, W F; Hinkley, N; Fasano, R J; Beloy, K; Yoon, T H; Milani, G; Nicolodi, D; Sherman, J A; Phillips, N B; Oates, C W; Ludlow, A D

    2016-01-01

    Atomic clocks based on optical transitions are the most stable, and therefore precise, timekeepers available. These clocks operate by alternating intervals of atomic interrogation with dead time required for quantum state preparation and readout. This non-continuous interrogation of the atom system results in the Dick effect, an aliasing of frequency noise of the laser interrogating the atomic transition. Despite recent advances in optical clock stability achieved by improving laser coherence, the Dick effect has continually limited optical clock performance. Here we implement a robust solution to overcome this limitation: a zero-dead-time optical clock based on the interleaved interrogation of two cold-atom ensembles. This clock exhibits vanishingly small Dick noise, thereby achieving an unprecedented fractional frequency instability of $6 \\times 10^{-17} / \\sqrt{\\tau}$ for an averaging time $\\tau$ in seconds. We also consider alternate dual-atom-ensemble schemes to extend laser coherence and reduce the stan...

  1. Compact atomic clock prototype based on coherent population trapping

    Directory of Open Access Journals (Sweden)

    Danet Jean-Marie

    2014-01-01

    Full Text Available Toward the next generations of compact atomic clocks, clocks based on coherent population trapping (CPT offer a very interesting alternative. Thanks to CPT, a quantum interfering process, this technology has made a decisive step in the miniaturization direction. Fractional frequency stability of 1.5x10-10 at 1 s has been demonstrated in commercial devices of a few cm3. The laboratory prototype presented here intends to explore what could be the ultimate stability of a CPT based device. To do so, an original double-Λ optical scheme and a pulsed interrogation have been implemented in order to get a good compromise between contrast and linewidth. A study of two main sources of noise, the relative intensity and the local oscillator (LO noise, has been performed. By designing simple solutions, it led to a new fractional frequency limitation lower than 4x10-13 at 1 s integration. Such a performance proves that such a technology could rival with classical ones as double resonance clocks.

  2. Atomic clocks: A brief history and current status of research in India

    Indian Academy of Sciences (India)

    Poonam Arora; Amrita Awasthi; Vattikonda Bharath; Aishik Acharya; Suchi Yadav; Aashish Agarwal; Amitava Sen Gupta

    2014-02-01

    Frequency corresponding to the energy difference between designated levels of an atom provides precise reference for making a universally accurate clock. Since the middle of the 20th century till now, there have been tremendous efforts in the field of atomic clocks making time the most accurately measured physical quantity. National Physical Laboratory India (NPLI) is the nation’s timekeeper and is developing an atomic fountain clock which will be a primary frequency standard. The fountain is currently operational and is at the stage of complete frequency evaluation. In this paper, a brief review on atomic time along with some of the recent results from the fountain clock will be discussed.

  3. Making optical atomic clocks more stable with $10^{-16}$ level laser stabilization

    CERN Document Server

    Jiang, Y Y; Lemke, N D; Fox, R W; Sherman, J A; Ma, L -S; Oates, C W

    2011-01-01

    The superb precision of an atomic clock is derived from its stability. Atomic clocks based on optical (rather than microwave) frequencies are attractive because of their potential for high stability, which scales with operational frequency. Nevertheless, optical clocks have not yet realized this vast potential, due in large part to limitations of the laser used to excite the atomic resonance. To address this problem, we demonstrate a cavity-stabilized laser system with a reduced thermal noise floor, exhibiting a fractional frequency instability of $2 \\times 10^{-16}$. We use this laser as a stable optical source in a Yb optical lattice clock to resolve an ultranarrow 1 Hz transition linewidth. With the stable laser source and the signal to noise ratio (S/N) afforded by the Yb optical clock, we dramatically reduce key stability limitations of the clock, and make measurements consistent with a clock instability of $5 \\times 10^{-16} / \\sqrt{\\tau}$.

  4. The dynamic Allan Variance IV: characterization of atomic clock anomalies.

    Science.gov (United States)

    Galleani, Lorenzo; Tavella, Patrizia

    2015-05-01

    The number of applications where precise clocks play a key role is steadily increasing, satellite navigation being the main example. Precise clock anomalies are hence critical events, and their characterization is a fundamental problem. When an anomaly occurs, the clock stability changes with time, and this variation can be characterized with the dynamic Allan variance (DAVAR). We obtain the DAVAR for a series of common clock anomalies, namely, a sinusoidal term, a phase jump, a frequency jump, and a sudden change in the clock noise variance. These anomalies are particularly common in space clocks. Our analytic results clarify how the clock stability changes during these anomalies.

  5. High accuracy measure of atomic polarizability in an optical lattice clock

    OpenAIRE

    Sherman, J. A.; Lemke, N. D.; Hinkley, N.; Pizzocaro, M.; Fox, R. W.; Ludlow, A. D.; Oates, C. W.

    2011-01-01

    Despite being a canonical example of quantum mechanical perturbation theory, as well as one of the earliest observed spectroscopic shifts, the Stark effect contributes the largest source of uncertainty in a modern optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock's sensitivity to electric fields (suc...

  6. Precision Excited State Lifetime Measurements for Atomic Parity Violation and Atomic Clocks

    Science.gov (United States)

    Sell, Jerry; Patterson, Brian; Gearba, Alina; Snell, Jeremy; Knize, Randy

    2016-05-01

    Measurements of excited state atomic lifetimes provide a valuable test of atomic theory, allowing comparisons between experimental and theoretical transition dipole matrix elements. Such tests are important in Rb and Cs, where atomic parity violating experiments have been performed or proposed, and where atomic structure calculations are required to properly interpret the parity violating effect. In optical lattice clocks, precision lifetime measurements can aid in reducing the uncertainty of frequency shifts due to the surrounding blackbody radiation field. We will present our technique for precisely measuring excited state lifetimes which employs mode-locked ultrafast lasers interacting with two counter-propagating atomic beams. This method allows the timing in the experiment to be based on the inherent timing stability of mode-locked lasers, while counter-propagating atomic beams provides cancellation of systematic errors due to atomic motion to first order. Our current progress measuring Rb excited state lifetimes will be presented along with future planned measurements in Yb.

  7. Atomic clock using coherent population trapping in a cesium cell: frequency stability and limitations

    Science.gov (United States)

    Mejri, Sinda; Tricot, Francois; Danet, Jean-Marie; Yun, Peter; De Clercq, Emeric; Guerandel, Stephane

    2016-06-01

    Toward the next generation of compact devices, atomic clocks based on coherent population trapping (CPT) offer a very interesting alternative. We present a review of our studies on the short and mid term stability of a compact high performance atomic clock based on CPT in view of portable applications.

  8. Searching for dilaton dark matter with atomic clocks

    CERN Document Server

    Arvanitaki, Asimina; Van Tilburg, Ken

    2014-01-01

    We propose an experiment to search for ultralight scalar dark matter (DM) with dilatonic interactions. Such couplings can arise for the dilaton as well as for moduli and axion-like particles in the presence of CP violation. Ultralight dilaton DM acts as a background field that can cause tiny but coherent oscillations in Standard Model parameters such as the fine structure constant and the proton-electron mass ratio. These minute variations can be detected through precise frequency comparisons of atomic clocks. Our experiment extends current searches for drifts in fundamental constants to the well-motivated high-frequency regime. Our proposed setups can probe scalars lighter than 10^-15 eV with discovery potential of dilatonic couplings as weak as 10^-11 times the strength of gravity, improving current equivalence principle bounds by up to 8 orders of magnitude. We point out potential 10^4 sensitivity enhancements with future optical and nuclear clocks, as well as possible signatures in gravitational wave dete...

  9. Towards a Re-definition of the Second Based on Optical Atomic Clocks

    CERN Document Server

    Riehle, Fritz

    2015-01-01

    The rapid increase in accuracy and stability of optical atomic clocks compared to the caesium atomic clock as primary standard of time and frequency asks for a future re-definition of the second in the International System of Units (SI). The status of the optical clocks based on either single ions in radio-frequency traps or on neutral atoms stored in an optical lattice is described with special emphasis of the current work at the Physikalisch-Technische Bundesanstalt (PTB). Besides the development and operation of different optical clocks with estimated fractional uncertainties in the 10^-18 range, the supporting work on ultra-stable lasers as core elements and the means to compare remote optical clocks via transportable standards, optical fibers, or transportable clocks is reported. Finally, the conditions, methods and next steps are discussed that are the prerequisites for a future re-definition of the second.

  10. Frequency Stability of Atomic Clocks Based on Coherent Population Trapping Resonance in 85Rb

    Institute of Scientific and Technical Information of China (English)

    LIU Lu; GUO Tao; DENG Ke; LIU Xin-Yuan; CHEN Xu-Zong; WANG Zhong

    2007-01-01

    An atomic clock system based on coherent population trapping (CPT) resonance in 85Rb is reported, while most past works about the CPT clock are in 87Rb. A new modulation method (full-hyperfine-frequency-splitting modulation) is presented to reduce the effect of light shift to improve the frequency stability of the CPT clock in 85Rb. The experimental results show that the short-term frequency stability of the CPT clock in 85Rb is in the order of 10-10/s and the long-term frequency stability can achieve 1.5 × 10-11 /80000s, which performs as well as 87Rb in CPT resonance. This very good frequency stability performance associated with the low-cost and low-power properties of 85Rb indicates that an atomic clock based on CPT in 85 Rb should be a promising candidate for making the chip scale atomic clock.

  11. Decreasing the uncertainty of atomic clocks via real-time noise distinguish

    CERN Document Server

    Dong, Richang; Wei, Rong; Wang, Wenli; Zou, Fan; Du, Yuanbo; Chen, Tingting; Wang, Yuzhu

    2016-01-01

    The environmental perturbation on atoms is the key factor restricting the performance of atomic frequency standards, especially in long term scale. In this letter, we demonstrate a real-time noise distinguish operation of atomic clocks. The operation improves the statistical uncertainty by about an order of magnitude of our fountain clock which is deteriorated previously by extra noises. The frequency offset bring by the extra noise is also corrected. The experiment proves the real-time noise distinguish operation can reduce the contribution of ambient noises and improve the uncertainty limit of atomic clocks.

  12. A Compact Microchip-Based Atomic Clock Based on Ultracold Trapped Rb Atoms

    CERN Document Server

    Farkas, Daniel M; Anderson, Dana Z

    2009-01-01

    We propose a compact atomic clock based on ultracold Rb atoms that are magnetically trapped near the surface of an atom microchip. An interrogation scheme that combines electromagnetically-induced transparency (EIT) with Ramsey's method of separated oscillatory fields can achieve atomic shot-noise level performance of 10^{-13}/sqrt(tau) for 10^6 atoms. The EIT signal can be detected with a heterodyne technique that provides noiseless gain; with this technique the optical phase shift of a 100 pW probe beam can be detected at the photon shot-noise level. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2*10^{-14}. An overview of the apparatus is presented with estimates of duty cycle and power consumption.

  13. Hyperfine-induced quadrupole moments of alkali-metal atom ground states and their implications for atomic clocks

    CERN Document Server

    Derevianko, Andrei

    2016-01-01

    Spherically-symmetric ground states of alkali-metal atoms do not posses electric quadrupole moments. However, the hyperfine interaction between nuclear moments and atomic electrons distorts the spherical symmetry of electronic clouds and leads to non-vanishing atomic quadrupole moments. We evaluate these hyperfine-induced quadrupole moments using techniques of relativistic many-body theory and compile results for Li, Na, K, Rb, and Cs atoms. For heavy atoms we find that the hyperfine-induced quadrupole moments are strongly (two orders of magnitude) enhanced by correlation effects. We further apply the results of the calculation to microwave atomic clocks where the coupling of atomic quadrupole moments to gradients of electric fields leads to clock frequency uncertainties. We show that for $^{133}$Cs atomic clocks, the spatial gradients of electric fields must be smaller than $30 \\, \\mathrm{V}/\\mathrm{cm}^2$ to guarantee fractional inaccuracies below $10^{-16}$.

  14. Enhancing coherence in molecular spin qubits via atomic clock transitions

    Science.gov (United States)

    Shiddiq, Muhandis; Komijani, Dorsa; Duan, Yan; Gaita-Ariño, Alejandro; Coronado, Eugenio; Hill, Stephen

    2016-03-01

    Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest. There are many competing candidates for qubits, including superconducting circuits, quantum optical cavities, ultracold atoms and spin qubits, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction. To minimize it, spins are typically diluted in a diamagnetic matrix. For example, this dilution can be taken to the extreme of a single phosphorus atom in silicon, whereas in molecular matrices a typical ratio is one magnetic molecule per 10,000 matrix molecules. However, there is a fundamental contradiction between reducing decoherence by dilution and allowing quantum operations via the interaction between spin qubits. To resolve this contradiction, the design and engineering of quantum hardware can benefit from a ‘bottom-up’ approach whereby the electronic structure of magnetic molecules is chemically tailored to give the desired physical behaviour. Here we present a way of enhancing coherence in solid-state molecular spin qubits without resorting to extreme dilution. It is based on the design of molecular structures with crystal field ground states possessing large tunnelling gaps that give rise to optimal operating points, or atomic clock transitions, at which the quantum spin dynamics become protected against dipolar decoherence. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. This finding opens new avenues for quantum computing based on molecular spin qubits.

  15. Demonstration of a Dual Alkali Rb/Cs Atomic Fountain Clock

    CERN Document Server

    Guéna, J; Laurent, Ph; Abgrall, M; Rovera, D; Lours, M; Santarelli, G; Tobar, M E; Bize, S; Clairon, A; 10.1109/TUFFC.2010.1461

    2013-01-01

    We report the operation of a dual Rb/Cs atomic fountain clock. 133Cs and 87Rb atoms are cooled, launched, and detected simultaneously in LNE-SYRTE's FO2 double fountain. The dual clock operation occurs with no degradation of either the stability or the accuracy. We describe the key features for achieving such a simultaneous operation. We also report on the results of the first Rb/Cs frequency measurement campaign performed with FO2 in this dual atom clock configuration, including a new determination of the absolute 87Rb hyperfine frequency.

  16. A New Generation of Atomic Clocks: Accuracy and Stability at the 10^{-18} Level

    CERN Document Server

    Bloom, B J; Williams, J R; Campbell, S L; Bishof, M; Zhang, X; Zhang, W; Bromley, S L; Ye, J

    2013-01-01

    The exquisite control exhibited over quantum states of individual particles has revolutionized the field of precision measurement, as exemplified by the most accurate atomic clock realized in single trapped ions. Whereas many-atom lattice clocks have shown advantages in measurement precision over trapped-ion clocks, their accuracy has remained 20 times worse. Here we demonstrate, for the first time, that a many-atom system achieves accuracy (6x10^{-18}) better than a single ion-based clock, with vastly reduced averaging times (3000 s). This is the first time a single clock has achieved the best performance in all three key ingredients necessary for consideration as a primary standard - stability, reproducibility, and accuracy. This work paves the way for future experiments to integrate many-body quantum state engineering into the frontiers of quantum metrology, creating exciting opportunities to advance precision beyond the standard quantum limit. Improved frequency standards will have impact to a wide range ...

  17. A VLBI experiment using a remote atomic clock via a coherent fibre link

    Science.gov (United States)

    Clivati, Cecilia; Ambrosini, Roberto; Artz, Thomas; Bertarini, Alessandra; Bortolotti, Claudio; Frittelli, Matteo; Levi, Filippo; Mura, Alberto; Maccaferri, Giuseppe; Nanni, Mauro; Negusini, Monia; Perini, Federico; Roma, Mauro; Stagni, Matteo; Zucco, Massimo; Calonico, Davide

    2017-02-01

    We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks.

  18. A VLBI experiment using a remote atomic clock via a coherent fibre link

    Science.gov (United States)

    Clivati, Cecilia; Ambrosini, Roberto; Artz, Thomas; Bertarini, Alessandra; Bortolotti, Claudio; Frittelli, Matteo; Levi, Filippo; Mura, Alberto; Maccaferri, Giuseppe; Nanni, Mauro; Negusini, Monia; Perini, Federico; Roma, Mauro; Stagni, Matteo; Zucco, Massimo; Calonico, Davide

    2017-01-01

    We describe a VLBI experiment in which, for the first time, the clock reference is delivered from a National Metrology Institute to a radio telescope using a coherent fibre link 550 km long. The experiment consisted of a 24-hours long geodetic campaign, performed by a network of European telescopes; in one of those (Medicina, Italy) the local clock was alternated with a signal generated from an optical comb slaved to a fibre-disseminated optical signal. The quality of the results obtained with this facility and with the local clock is similar: interferometric fringes were detected throughout the whole 24-hours period and it was possible to obtain a solution whose residuals are comparable to those obtained with the local clock. These results encourage further investigation of the ultimate VLBI performances achievable using fibre dissemination at the highest precision of state-of-the-art atomic clocks. PMID:28145451

  19. An atomic clock with $1\\times 10^{-18}$ room-temperature blackbody Stark uncertainty

    CERN Document Server

    Beloy, K; Phillips, N B; Sherman, J A; Schioppo, M; Lehman, J; Feldman, A; Hanssen, L M; Oates, C W; Ludlow, A D

    2014-01-01

    The Stark shift due to blackbody radiation (BBR) is the key factor limiting the performance of many atomic frequency standards, with the BBR environment inside the clock apparatus being difficult to characterize at a high level of precision. Here we demonstrate an in-vacuum radiation shield that furnishes a uniform, well-characterized BBR environment for the atoms in an ytterbium optical lattice clock. Operated at room temperature, this shield enables specification of the BBR environment to a corresponding fractional clock uncertainty contribution of $5.5 \\times 10^{-19}$. Combined with uncertainty in the atomic response, the total uncertainty of the BBR Stark shift is now $1\\times10^{-18}$. Further operation of the shield at elevated temperatures enables a direct measure of the BBR shift temperature dependence and demonstrates consistency between our evaluated BBR environment and the expected atomic response.

  20. Loading of a fountain clock with an enhanced Low-Velocity Intense Source of atoms

    CERN Document Server

    Dobrev, Georgi; Weyers, Stefan

    2016-01-01

    We present experimental work for improved atom loading in the optical molasses of a caesium fountain clock, employing a low-velocity intense source of atoms (LVIS) [Lu et al., Phys. Rev. Lett. 77, 3331 (1996)], which we modified by adding a "dark" state pump laser. With this modification the atom source has a mean flux of $4 \\times 10^{8}$ atoms/s at a mean atom velocity of $8.6$ m/s. Compared to fountain operation using background gas loading, we achieved a significant increase of the loaded and detected atom number by a factor of 40. Operating the fountain clock with a total number of detected atoms $N_{\\mathrm{at}}=2.9 \\times 10^6$ in the quantum projection noise-limited regime, a frequency instability $\\sigma_y\\left(1\\text{s}\\right)=2.7 \\times 10^{-14}$ was demonstrated.

  1. Testing spatial α-variation with optical atomic clocks based on highly charged ions

    Directory of Open Access Journals (Sweden)

    Berengut J. C.

    2013-08-01

    Full Text Available We review recent works illustrating the potential use of highly charged ions as the basis of optical atomic clocks of exceptional accuracy and very high sensitivity to variation of the fine structure constant, α. The tendency towards large transition energies in highly charged ions can be overcome using level crossings, which allow transitions between different orbitals to be within the range of usual lasers. We present simple scaling laws that demonstrate reduced systematics that could be realised in highly charged ion clocks. Such clocks could allow us to corroborate astronomical studies that suggest a spatial gradient in values of α across the Universe.

  2. Determination of a high spatial resolution geopotential model using atomic clock comparisons

    OpenAIRE

    Lion, Guillaume; Panet, Isabelle; Wolf, Peter; Guerlin, Christine; Bize, Sébastien; Delva, Pacôme

    2016-01-01

    Recent technological advances in optical atomic clocks are opening new perspectives for the direct determination of geopotential differences between any two points at a centimeter-level accuracy in geoid height. However, so far detailed quantitative estimates of the possible improvement in geoid determination when adding such clock measurements to existing data are lacking. We present a first step in that direction with the aim and hope of triggering further work and efforts in this emerging ...

  3. Modeling and Estimation of Stationary and Non-stationary Noises of Rubidium Atomic Clock

    Directory of Open Access Journals (Sweden)

    Deepak Mishra,

    2014-07-01

    Full Text Available Noise estimation of atomic clock is one of the important research areas in the field of atomic clock development and application. Most of the atomic clocks are having random-stochastic noises and periodic noises due to temperature variation. Random-stochastic noises have a well identified signature in time domain but periodic noises are difficult to analyze in time domain. However, in this paper, an effort is made to identify and analyze the deterministic trends of both random-stochastic noises and periodic noises due to variation in temperature using an alternate approach of least-squares normalized-error (LSNE regression algorithm. A MATLAB based application with graphical user interface (GUI is developed to estimate and analyze random-stochastic noises and periodic noises and re-estimate the stability of rubidium atomic clock after removing these noises from the raw phase data. The estimation of stationary noises are done using Allan variance from time domain data and noise profile is calculated using curve fit method. The estimation of periodic noises due to temperature variation is carried in frequency domain through spurious analysis of the frequency data of atomic clock.

  4. NAVEX - A Space Shuttle Experiment with Atomic Clocks

    Science.gov (United States)

    1982-12-01

    for synchronization will be clock transportations. In cooperation with our national time institute ’ Physikalisch -Technische Bundesanstalt’ (FTB...Einwegentfernungsrnessung" Nachrichtentechniskh Zeitschrift 29 (1976) H. 9, S. 673-677. [41 Tschiesche, H, : Experiment zur "Syllchronisation und Ein

  5. The magneto-optical effect of cold atoms in an integrating sphere for atomic clock and optical magnetometer

    CERN Document Server

    Wan, Jinyin; Meng, Yanling; Xiao, Ling; Liu, Peng; Wang, Xiumei; Wang, Yaning; Liu, Liang

    2014-01-01

    We investigate the magneto-optical effect of cold atoms in an integrating sphere both experimentally and theoretically. The dependence of magneto-optical rotation angle on the biased magnetic field, the probe light intensity, and the probe light detuning are investigated. The probe light background is blocked and the shot noise is strongly suppressed. This detection scheme may provide a new approach for high contrast cold atom clock and cold atom optical magnetometer.

  6. Near-Heisenberg-limited atomic clocks in the presence of decoherence.

    Science.gov (United States)

    Borregaard, J; Sørensen, A S

    2013-08-30

    The ultimate stability of atomic clocks is limited by the quantum noise of the atoms. To reduce this noise it has been suggested to use entangled atomic ensembles with reduced atomic noise. Potentially this can push the stability all the way to the limit allowed by the Heisenberg uncertainty relation, which is denoted the Heisenberg limit. In practice, however, entangled states are often more prone to decoherence, which may prevent reaching this performance. Here we present an adaptive measurement protocol that in the presence of a realistic source of decoherence enables us to get near-Heisenberg-limited stability of atomic clocks using entangled atoms. The protocol may thus realize the full potential of entanglement for quantum metrology despite the detrimental influence of decoherence.

  7. The Potential of Continuous, Local Atomic Clock Measurements for Earthquake Prediction and Volcanology

    CERN Document Server

    Bondarescu, Mihai; Jetzer, Philippe; Lundgren, Andrew

    2015-01-01

    Modern optical atomic clocks along with the optical fiber technology currently being developed can measure the geoid, which is the equipotential surface that extends the mean sea level on continents, to a precision that competes with existing technology. In this proceeding, we point out that atomic clocks have the potential to not only map the sea level surface on continents, but also look at variations of the geoid as a function of time with unprecedented timing resolution. The local time series of the geoid has a plethora of applications. These include potential improvement in the predictions of earthquakes and volcanoes, and closer monitoring of ground uplift in areas where hydraulic fracturing is performed.

  8. Hg-201 (+) CO-Magnetometer for HG-199(+) Trapped Ion Space Atomic Clocks

    Science.gov (United States)

    Burt, Eric A. (Inventor); Taghavi, Shervin (Inventor); Tjoelker, Robert L. (Inventor)

    2011-01-01

    Local magnetic field strength in a trapped ion atomic clock is measured in real time, with high accuracy and without degrading clock performance, and the measurement is used to compensate for ambient magnetic field perturbations. First and second isotopes of an element are co-located within the linear ion trap. The first isotope has a resonant microwave transition between two hyperfine energy states, and the second isotope has a resonant Zeeman transition. Optical sources emit ultraviolet light that optically pump both isotopes. A microwave radiation source simultaneously emits microwave fields resonant with the first isotope's clock transition and the second isotope's Zeeman transition, and an optical detector measures the fluorescence from optically pumping both isotopes. The second isotope's Zeeman transition provides the measure of magnetic field strength, and the measurement is used to compensate the first isotope's clock transition or to adjust the applied C-field to reduce the effects of ambient magnetic field perturbations.

  9. Testing General Relativity and Alternative Theories of Gravity with Space-based Atomic Clocks and Atom Interferometers

    CERN Document Server

    Bondarescu, Ruxandra; Jetzer, Philippe; Angélil, Raymond; Saha, Prasenjit; Lundgren, Andrew

    2015-01-01

    The successful miniaturisation of extremely accurate atomic clocks and atom interferometers invites prospects for satellite missions to perform precision experiments. We discuss the effects predicted by general relativity and alternative theories of gravity that can be detected by a clock, which orbits the Earth. Our experiment relies on the precise tracking of the spacecraft using its observed tick-rate. The spacecraft's reconstructed four-dimensional trajectory will reveal the nature of gravitational perturbations in Earth's gravitational field, potentially differentiating between different theories of gravity. This mission can measure multiple relativistic effects all during the course of a single experiment, and constrain the Parametrized Post-Newtonian Parameters around the Earth. A satellite carrying a clock of fractional timing inaccuracy of $\\Delta f/f \\sim 10^{-16}$ in an elliptic orbit around the Earth would constrain the PPN parameters $|\\beta -1|, |\\gamma-1| \\lesssim 10^{-6}$. We also briefly revi...

  10. Double-resonance spectroscopy in Rubidium vapour-cells for high performance and miniature atomic clocks

    Science.gov (United States)

    Gharavipour, M.; Affolderbach, C.; Kang, S.; Mileti, G.

    2017-01-01

    We report our studies on using microwave-optical double-resonance (DR) spectroscopy for a high-performance Rb vapour-cell atomic clock in view of future industrial applications. The clock physics package is very compact with a total volume of only 0.8 dm3. It contains a recently in-house developed magnetron-type cavity and a Rb vapour cell. A homed-made frequency-stabilized laser system with an integrated acousto-optical-modulator (AOM) – for switching and controlling the light output power– is used as an optical source in a laser head (LH). The LH has the overall volume of 2.5 dm3 including the laser diode, optical elements, AOM and electronics. In our Rb atomic clock two schemes of continuous-wave DR and Ramsey-DR schemes are used, where the latter one strongly reduces the light-shift effect by separation of the interaction of light and microwave. Applications of the DR clock approach to more radically miniaturized atomic clocks are discussed.

  11. Atomic clock with nuclear transition: current status in TU Wien

    OpenAIRE

    Kazakov, G. A.; Schreitl, M.; Winkler, G.; Sterba, J. H.; Steinhauser, G; Schumm, T.

    2011-01-01

    The nucleus of 229Thorium presents a unique isomer state of very low energy and long lifetime, current estimates are around 7.8 eV and seconds to hours respectively. This nuclear transitions therefore is a promising candidate for a novel type of frequency standard and several groups worldwide have set out to investigate this system. Our aim is to construct a "solid state nuclear clock", i.e. a frequency standard where Thorium ions are implanted into Calciumfluoride crystals transparent in vac...

  12. Hyperfine-induced electric dipole contributions to the electric octupole and magnetic quadrupole atomic clock transitions

    CERN Document Server

    Dzuba, V A

    2016-01-01

    Hyperfine-induced electric dipole contributions may significantly increase probabilities of otherwise very weak electric octupole and magnetic quadrupole atomic clock transitions (e.g. transitions between $s$ and $f$ electron orbitals). These transitions can be used for exceptionally accurate atomic clocks, quantum information processing and search for dark matter. They are very sensitive to new physics beyond the Standard Model, such as temporal variation of the fine structure constant, the Lorentz invariance and Einstein equivalence principle violation. We formulate conditions under which the hyperfine-induced electric dipole contribution dominates. Due to the hyperfine quenching the electric octupole clock transition in $^{173}$Yb$^+$ is two orders of magnitude stronger than that in currently used $^{171}$Yb$^+$. Some enhancement is found in $^{143}$Nd$^{13+}$, $^{149}$Pm$^{14+}$, $^{147}$Sm$^{14+}$, and $^{147}$Sm$^{15+}$ ions.

  13. DFB-ridge laser diodes at 894 nm for Cesium atomic clocks

    Science.gov (United States)

    von Bandel, N.; Garcia, M.; Lecomte, M.; Larrue, A.; Robert, Y.; Vinet, E.; Driss, O.; Parrilaud, O.; Krakowski, M.; Gruet, F.; Matthey, R.; Mileti, G.

    2016-02-01

    Time and frequency applications are in need of high accuracy and high stability clocks. Optically pumped compact industrial Cesium atomic clocks are a promising approach that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of the laser diodes that are used. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for ground applications. This work will provide key experience for further space technology qualification. III-V Lab is in charge of the design, fabrication and reliability of Distributed-Feedback diodes (DFB) at 894 nm (D1 line of Cesium) and 852 nm (D2 line). LTF-Unine is in charge of their spectral characterisation. The use of D1 line for pumping will provide simplified clock architecture compared to the D2 line pumping thanks to simpler atomic transitions and a larger spectral separation between lines in the 894 nm case. Also, D1 line pumping overcomes the issue of unpumped "idle states" that occur with D2 line. The modules should provide narrow linewidth (= 10 Hz and 109 Hz2/Hz @ f >= 10 Hz.

  14. Atomic fountain clock with very high frequency stability employing a pulse-tube-cryocooled sapphire oscillator.

    Science.gov (United States)

    Takamizawa, Akifumi; Yanagimachi, Shinya; Tanabe, Takehiko; Hagimoto, Ken; Hirano, Iku; Watabe, Ken-ichi; Ikegami, Takeshi; Hartnett, John G

    2014-09-01

    The frequency stability of an atomic fountain clock was significantly improved by employing an ultra-stable local oscillator and increasing the number of atoms detected after the Ramsey interrogation, resulting in a measured Allan deviation of 8.3 × 10(-14)τ(-1/2)). A cryogenic sapphire oscillator using an ultra-low-vibration pulse-tube cryocooler and cryostat, without the need for refilling with liquid helium, was applied as a local oscillator and a frequency reference. High atom number was achieved by the high power of the cooling laser beams and optical pumping to the Zeeman sublevel m(F) = 0 employed for a frequency measurement, although vapor-loaded optical molasses with the simple (001) configuration was used for the atomic fountain clock. The resulting stability is not limited by the Dick effect as it is when a BVA quartz oscillator is used as the local oscillator. The stability reached the quantum projection noise limit to within 11%. Using a combination of a cryocooled sapphire oscillator and techniques to enhance the atom number, the frequency stability of any atomic fountain clock, already established as primary frequency standard, may be improved without opening its vacuum chamber.

  15. The Physics of Miniature Atomic Clocks: 0-0 Versus "End" Transitions

    Science.gov (United States)

    Post, Amber; Jau, Yuan-Yu; Kuzma, Nicholas; Happer, William

    2003-05-01

    The majority of traditional atomic-clock designs are based on the 0-0 hyperfine transition of a Cs 133 atom. We are currently investigating the advantages of operating a miniature optical atomic clock using the "end" transitions, e.g. connecting states |f=1, mf =+/-1> and |f=2, mf=+/-2> in 87Rb. In our paper we present extensive new measurements of relevant relaxation rates, such as those due to spin-exchange collisions, buffer-gas pressure shifts, Carver Rates and others, which ultimately determine the choices of an operating regime for the miniature optical atomic clock. The relationship between these rates is non-trivial: for example, using higher laser power will increase polarization and reduce the spin-exchange rate [1], but it can simultaneously increase the linewidth due to the optical pumping rate. The dependence of these and other relaxation rates on the cell size, temperature, pressure, a choice of buffer gas, and other parameters will be reported. Based on these measured rates, our modeling can be used to predict the transition linewidths, signal-to-noise ratios and thus the stability of the clock in different operating regimes. The trade-off between the stability of the clock and the desired small cell size and low power consumption needs to be carefully considered in order to optimize our design. In our experiments we used optical, microwave, and radio-frequency excitation to study hyperfine and Zeeman resonance lines in heated glass cells containing pure-isotope alkali-metal vapor and buffer gasses (N2, Ar, He, etc.) at low (0 - 10 G) magnetic fields. Simultaneous use of light, microwave and radio-frequency fields allowed us to calibrate surrounding magnetic fields by observing the corresponding shifts of the resonance, thus leading us to a quantitative understanding of our system. [1] S. Appelt, A. B. Baranga, A. R. Young, W. Happer, Phys. Rev. A 59, 2078 (1999).

  16. Improved spacecraft radio science using an on-board atomic clock: application to gravitational wave searches

    CERN Document Server

    Tinto, Massimo; Prestage, John D; Armstrong, J W

    2008-01-01

    Recent advances in space-qualified atomic clocks (low-mass, low power-consumption, frequency stability comparable to that of ground-based clocks) can enable interplanetary spacecraft radio science experiments at unprecedented Doppler sensitivities. The addition of an on-board digital receiver would allow the up- and down-link Doppler frequencies to be measured separately. Such separate, high-quality measurements allow optimal data combinations that suppress the currently-leading noise sources: phase scintillation noise from the Earth's atmosphere and Doppler noise caused by mechanical vibrations of the ground antenna. Here we provide a general expression for the optimal combination of ground and on-board Doppler data and compute the sensitivity such a system would have to low-frequency gravitational waves (GWs). Assuming a plasma scintillation noise calibration comparable to that already demonstrated with the multi-link CASSINI radio system, the space-clock/digital-receiver instrumentation enhancements would ...

  17. Cold Atom Clocks, Precision Oscillators and Fundamental Tests

    CERN Document Server

    Bize, S; Abgrall, M; Cacciapuoti, L; Clairon, A; Gruenert, J; Laurent, P; Lemonde, P; Maksimovic, I; Mandache, C; Marion, H; Dos Santos, F P; Rosenbusch, P; Santarelli, G; Sortais, Y; Vian, C; Zhang, S; Salomon, C; Luiten, A N; Tobar, M E; Laurent, Ph.

    2003-01-01

    We describe two experimental tests of the Equivalence Principle that are based on frequency measurements between precision oscillators and/or highly accurate atomic frequency standards. Based on comparisons between the hyperfine frequencies of 87Rb and 133Cs in atomic fountains, the first experiment constrains the stability of fundamental constants. The second experiment is based on a comparison between a cryogenic sapphire oscillator and a hydrogen maser. It tests Local Lorentz Invariance. In both cases, we report recent results which improve significantly over previous experiments.

  18. Magnetic field-induced spectroscopy of forbidden optical transitions with application to lattice-based optical atomic clocks.

    Science.gov (United States)

    Taichenachev, A V; Yudin, V I; Oates, C W; Hoyt, C W; Barber, Z W; Hollberg, L

    2006-03-01

    We develop a method of spectroscopy that uses a weak static magnetic field to enable direct optical excitation of forbidden electric-dipole transitions that are otherwise prohibitively weak. The power of this scheme is demonstrated using the important application of optical atomic clocks based on neutral atoms confined to an optical lattice. The simple experimental implementation of this method--a single clock laser combined with a dc magnetic field--relaxes stringent requirements in current lattice-based clocks (e.g., magnetic field shielding and light polarization), and could therefore expedite the realization of the extraordinary performance level predicted for these clocks. We estimate that a clock using alkaline-earth-like atoms such as Yb could achieve a fractional frequency uncertainty of well below 10(-17) for the metrologically preferred even isotopes.

  19. Al-free active region laser diodes at 894 nm for compact Cesium atomic clocks

    Science.gov (United States)

    Von Bandel, N.; Bébé Manga Lobé, J.; Garcia, M.; Larrue, A.; Robert, Y.; Vinet, E.; Lecomte, M.; Drisse, O.; Parillaud, O.; Krakowski, M.

    2015-03-01

    Time-frequency applications are in need of high accuracy and high stability clocks. Compact industrial Cesium atomic clocks optically pumped is a promising area that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of laser diodes that are used for atomic pumping. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for earth applications. This work will provide key experience for further space technology qualification. We are in charge of the design, fabrication and reliability of Distributed-Feedback diodes (DFB) at 894nm (D1 line of Cesium) and 852nm (D2 line). The use of D1 line for pumping will provide simplified clock architecture compared to D2 line pumping thanks to simpler atomic transitions and larger spectral separation between lines in the 894nm case. Also, D1 line pumping overcomes the issue of unpumped "dark states" that occur with D2 line. The modules should provide narrow linewidth (<1MHz), very good reliability in time and, crucially, be insensitive to optical feedback. The development of the 894nm wavelength is grounded on our previous results for 852nm DFB. Thus, we show our first results from Al-free active region with InGaAsP quantum well broad-area lasers (100μm width, with lengths ranging from 2mm to 4mm), for further DFB operation at 894nm. We obtained low internal losses below 2cm-1, the external differential efficiency is 0.49W/A with uncoated facets and a low threshold current density of 190A/cm², for 2mm lasers at 20°C.

  20. Collective non-equilibrium spin exchange in cold alkaline-earth atomic clocks

    Science.gov (United States)

    Acevedo, Oscar Leonardo; Rey, Ana Maria

    2016-05-01

    Alkaline-earth atomic (AEA) clocks have recently been shown to be reliable simulators of two-orbital SU(N) quantum magnetism. In this work, we study the non-equilibrium spin exchange dynamics during the clock interrogation of AEAs confined in a deep one-dimensional optical lattice and prepared in two nuclear levels. The two clock states act as an orbital degree of freedom. Every site in the lattice can be thought as populated by a frozen set of vibrational modes collectively interacting via predominantly p-wave collisions. Due to the exchange coupling, orbital state transfer between atoms with different nuclear states is expected to happen. At the mean field level, we observe that in addition to the expected suppression of population transfer in the presence of a large magnetic field, that makes the single particle levels off-resonance, there is also an interaction induced suppression for initial orbital population imbalance. This suppression resembles the macroscopic self-trapping mechanism seen in bosonic systems. However, by performing exact numerical solutions and also by using the so-called Truncated Wigner Approximation, we show that quantum correlations can significantly modify the mean field suppression. Our predictions should be testable in optical clock experiments. Project supported by NSF-PHY-1521080, JILA-NSF-PFC-1125844, ARO, AFOSR, and MURI-AFOSR.

  1. A compact microchip atomic clock based on all-optical interrogation of ultra-cold trapped Rb atoms

    Science.gov (United States)

    Farkas, D. M.; Zozulya, A.; Anderson, D. Z.

    2010-12-01

    We propose a compact atomic clock that uses all-optical interrogation of ultra-cold Rb atoms that are magnetically trapped near the surface of an atom microchip. The interrogation scheme, which combines electromagnetically induced transparency with Ramsey's method of separated oscillatory fields, can achieve an atomic shot-noise-level performance better than 10^{-13}/sqrt{tau} for 106 atoms. A two-color Mach-Zehnder interferometer can detect a 100-pW probe beam at the optical shot-noise level using conventional photodetectors. This measurement scheme is nondestructive and therefore can be used to increase the operational duty cycle by reusing the trapped atoms for multiple clock cycles. Numerical calculations of the density matrix equations are used to identify realistic operating parameters at which AC Stark shifts are eliminated. By considering fluctuations in these parameters, we estimate that AC Stark shifts can be canceled to a level better than 2×10-14. An overview of the apparatus is presented with estimates of cycle time and power consumption.

  2. Testing general relativity and alternative theories of gravity with space-based atomic clocks and atom interferometers

    Directory of Open Access Journals (Sweden)

    Bondarescu Ruxandra

    2015-01-01

    Full Text Available The successful miniaturisation of extremely accurate atomic clocks and atom interferometers invites prospects for satellite missions to perform precision experiments. We discuss the effects predicted by general relativity and alternative theories of gravity that can be detected by a clock, which orbits the Earth. Our experiment relies on the precise tracking of the spacecraft using its observed tick-rate. The spacecraft’s reconstructed four-dimensional trajectory will reveal the nature of gravitational perturbations in Earth’s gravitational field, potentially differentiating between different theories of gravity. This mission can measure multiple relativistic effects all during the course of a single experiment, and constrain the Parametrized Post-Newtonian Parameters around the Earth. A satellite carrying a clock of fractional timing inaccuracy of Δ f / f ∼ 10−16 in an elliptic orbit around the Earth would constrain the PPN parameters |β − 1|, |γ − 1| ≲ 10−6. We also briefly review potential constraints by atom interferometers on scalar tensor theories and in particular on Chameleon and dilaton models.

  3. Microwave lensing frequency shift of the PHARAO laser-cooled microgravity atomic clock

    Science.gov (United States)

    Peterman, Phillip; Gibble, Kurt; Laurent, Phillipe; Salomon, Christophe

    2016-04-01

    We evaluate the microwave lensing frequency shift of the microgravity laser-cooled caesium clock PHARAO. We find microwave lensing frequency shifts of δν/ν  =  11  ×  10-17 to 13  ×  10-17, larger than the shift of typical fountain clocks. The shift has a weak dependence on PHARAO parameters, including the atomic temperature, size of the atomic cloud, detection laser intensities, and the launch velocity. We also find the lensing frequency shift to be insensitive to selection and detection spatial inhomogeneities and the expected low-frequency vibrations. We conservatively assign a nominal microwave lensing frequency uncertainty of  ±4  ×  10-17.

  4. Limits on gravitational Einstein equivalence principle violation from monitoring atomic clock frequencies during a year

    Science.gov (United States)

    Dzuba, V. A.; Flambaum, V. V.

    2017-01-01

    The Sun's gravitational potential at Earth varies during a year due to varying Earth-Sun distance. Comparing the results of very accurate measurements of atomic clock transitions performed at different times in the year allows us to study the dependence of the atomic frequencies on the gravitational potential. We examine the measurement data for the ratio of the frequencies in Hg+ and Al+ clock transitions and absolute frequency measurements (with respect to the caesium frequency standard) for Dy, Sr, H, hyperfine transitions in Rb and H and obtain significantly improved limits on the values of the gravity-related parameter of the Einstein equivalence principle violating term in the electron sector of the Standard Model extension Hamiltonian c00=(-3.0 ±5.7 )×10-7 and the parameter for the gravity-related variation of the fine structure constant κα=(-5.3 ±10 )×10-8.

  5. Limits on gravitational Einstein Equivalence Principle violation from monitoring atomic clock frequencies during a year

    CERN Document Server

    Dzuba, V A

    2016-01-01

    Sun's gravitation potential at earth varies during a year due to varying Earth-Sun distance. Comparing the results of very accurate measurements of atomic clock transitions performed at different time in the year allows us to study the dependence of the atomic frequencies on the gravitational potential. We examine the measurement data for the ratio of the frequencies in Hg$^+$ and Al$^+$ clock transitions and absolute frequency measurements (with respect to caesium frequency standard) for Dy, Sr, H, hyperfine transitions in Rb and H, and obtain significantly improved limits on the values of the gravity related parameter of the Einstein Equivalence Principle violating term in the Standard Model Extension Hamiltonian $c_{00} = (3.0 \\pm 5.7) \\times 10^{-7}$ and the parameter for the gravity-related variation of the fine structure constant $\\kappa_{\\alpha} = (-5.3 \\pm 10) \\times 10^{-8}$.

  6. Highly charged ions for atomic clocks, quantum information, and search for α variation.

    Science.gov (United States)

    Safronova, M S; Dzuba, V A; Flambaum, V V; Safronova, U I; Porsev, S G; Kozlov, M G

    2014-07-18

    We propose 10 highly charged ions as candidates for the development of next generation atomic clocks, quantum information, and search for α variation. They have long-lived metastable states with transition wavelengths to the ground state between 170-3000 nm, relatively simple electronic structure, stable isotopes, and high sensitivity to α variation (e.g., Sm(14+), Pr(10+), Sm(13+), Nd(10+)). We predict their properties crucial for the experimental exploration and highlight particularly attractive systems for these applications.

  7. Controlling the magnetic field sensitivity of atomic clock states by microwave dressing

    CERN Document Server

    Sárkány, L; Hattermann, H; Fortágh, J

    2014-01-01

    We demonstrate control of the differential Zeeman shift between clock states of ultracold rubidium atoms by means of non-resonant microwave dressing. Using the dc-field dependence of the microwave detuning, we suppress the first and second order differential Zeeman shift in magnetically trapped $^{87}$Rb atoms. By dressing the state pair 5S$_{1/2} F= 1, m_F = -1$ and $F= 2, m_F = 1$, a residual frequency spread of <0.1 Hz in a range of 100 mG around a chosen magnetic offset field can be achieved. This is one order of magnitude smaller than the shift of the bare states at the magic field of the Breit-Rabi parabola. We further identify double magic points, around which the clock frequency is insensitive to fluctuations both in the magnetic field and the dressing Rabi frequency. The technique is compatible with chip-based cold atom systems and allows the creation of clock and qubit states with reduced sensitivity to magnetic field noise.

  8. Optical lattice clock with strontium atoms: a second generation of cold atom clocks; Horloge a reseau optique au strontium: une 2. generation d'horloges a atomes froids

    Energy Technology Data Exchange (ETDEWEB)

    Le Targat, R

    2007-07-15

    Atomic fountains, based on a microwave transition of Cesium or Rubidium, constitute the state of the art atomic clocks, with a relative accuracy close to 10{sup -16}. It nevertheless appears today that it will be difficult to go significantly beyond this level with this kind of device. The use of an optical transition, the other parameters being unchanged, gives hope for a 4 or 5 orders of magnitude improvement of the stability and of the relative uncertainty on most systematic effects. As for motional effects on the atoms, they can be controlled on a very different manner if they are trapped in an optical lattice instead of experiencing a free ballistic flight stage, characteristic of fountains. The key point of this approach lies in the fact that the trap can be operated in such a way that a well chosen, weakly allowed, J=0 {yields} J=0 clock transition can be free from light shift effects. In this respect, the strontium atom is one of the most promising candidate, the 1S{sub 0} {yields} 3P{sub 0} transition has a natural width of 1 mHz, and several other easily accessible transitions can be used to efficiently laser cool atoms down to 10 {mu}K. This thesis demonstrates the experimental feasibility of an optical lattice clock based on the strontium atom, and reports on a preliminary evaluation of the relative accuracy with the fermionic isotope {sup 87}Sr, at a level of a few 10{sup -15}. (author)

  9. Inner-shell magnetic dipole transition in Tm atom as a candidate for optical lattice clocks

    CERN Document Server

    Sukachev, D; Tolstikhina, I; Kalganova, E; Vishnyakova, G; Khabarova, K; Tregubov, D; Golovizin, A; Sorokin, V; Kolachevsky, N

    2016-01-01

    We consider a narrow magneto-dipole transition in the $^{169}$Tm atom at the wavelength of $1.14\\,\\mu$m as a candidate for a 2D optical lattice clock. Calculating dynamic polarizabilities of the two clock levels $[\\text{Xe}]4f^{13}6s^2 (J=7/2)$ and $[\\text{Xe}]4f^{13}6s^2 (J=5/2)$ in the spectral range from $250\\,$nm to $1200\\,$nm, we suggest the "magic" wavelength for the optical lattice at $807\\,$nm. Frequency shifts due to black-body radiation (BBR), the van der Waals interaction, the magnetic dipole-dipole interaction and other effects which can perturb the transition frequency are calculated. The transition at $1.14\\,\\mu$m demonstrates low sensitivity to the BBR shift corresponding to $8\\times10^{-17}$ in fractional units at room temperature which makes it an interesting candidate for high-performance optical clocks. The total estimated frequency uncertainty is less than $5 \\times 10^{-18}$ in fractional units. By direct excitation of the $1.14\\,\\mu$m transition in Tm atoms loaded into an optical dipole ...

  10. Status of the atomic fountain clock at the National Research Council of Canada

    Science.gov (United States)

    Beattie, S.; Alcock, J.; Jian, B.; Gertsvolf, M.; Bernard, J.

    2016-06-01

    Despite the rapid advances in optical frequency standards, caesium fountain clocks retain a critical role as the most accurate primary frequency standards available. At the National Research Council Canada, we are working to develop a second generation caesium fountain clock. Work is currently underway to improve several systems of FCs1, such as the laser system and microwave local oscillator, which will be incorporated into its refurbished version, FCs2. In addition, we have added an optical pumping stage which has increased the detected atom number by over a factor of six. In collaboration with the National Physical Laboratory (NPL), we are planning on replacing the physics package of FCs1. We will report on several recent improvements to FCs1, along with our progress in the development of FCs2.

  11. Quantum noise limited interferometric measurement of atomic noise: towards spin squeezing on the Cs clock transition

    CERN Document Server

    Oblak, D; Tittel, W; Vershovski, A K; Sørensen, J L; Petrov, P G; Alzar, C L G; Polzik, E S; Oblak, Daniel; Mikkelsen, Jens K.; Tittel, Wolfgang; Vershovski, Anton K.; Sorensen, Jens L.; Petrov, Plamen G.; Alzar, Carlos L. Garrido; Polzik, Eugene S.

    2003-01-01

    We investigate theoretically and experimentally a nondestructive interferometric measurement of the state population of an ensemble of laser cooled and trapped atoms. This study is a step towards generation of (quasi-) spin squeezing of cold atoms targeted at the improvement of the Caesium clock performance beyond the limit set by the quantum projection noise of atoms. We propose a protocol for the sequence of operations required to generate and utilize spin squeezing for the improved microwave clock performance via a quantum nondemolition measurement (qnd) on the probe light. We calculate the phase shift and the quantum noise of a near resonant optical probe pulse propagating through a cloud of cold 133Cs atoms. We analyze the figure of merit for a qnd measurement of the collective quasi-spin and show that it can be expressed simply as a product of the ensemble optical depth and the probability of the spontaneous emission caused by the off-resonant probe light. In the experimental part we report on the preli...

  12. Composite pulses in Hyper-Ramsey spectroscopy for the next generation of atomic clocks

    Science.gov (United States)

    Zanon-Willette, T.; Minissale, M.; Yudin, V. I.; Taichenachev, A. V.

    2016-06-01

    The next generation of atomic frequency standards based on an ensemble of neutral atoms or a single-ion will provide very stringent tests in metrology, applied and fundamental physics requiring a new step in very precise control of external systematic corrections. In the proceedings of the 8th Symposium on Frequency Standards and Metrology, we present a generalization of the recent Hyper-Ramsey spectroscopy with separated oscillating fields using composites pulses in order to suppress field frequency shifts induced by the interrogation laser itself. Sequences of laser pulses including specific selection of phases, frequency detunings and durations are elaborated to generate spectroscopic signals with a strong reduction of the light-shift perturbation by off resonant states. New optical clocks based on weakly allowed or completely forbidden transitions in atoms, ions, molecules and nuclei will benefit from these generalized Ramsey schemes to reach relative accuracies well below the 10-18 level.

  13. Composite pulses in Hyper-Ramsey spectroscopy for the next generation of atomic clocks

    CERN Document Server

    Zanon-Willette, T; Yudin, V I; Taichenachev, A V

    2016-01-01

    The next generation of atomic frequency standards based on an ensemble of neutral atoms or a single-ion will provide very stringent tests in metrology, applied and fundamental physics requiring a new step in very precise control of external systematic corrections. In the proceedings of the 8th Symposium on Frequency Standards and Metrology, we present a generalization of the recent Hyper-Ramsey spectroscopy with separated oscillating fields using composites pulses in order to suppress field frequency shifts induced by the interrogation laser itself. Sequences of laser pulses including specific selection of phases, frequency detunings and durations are elaborated to generate spectroscopic signals with a strong reduction of the light-shift perturbation by off resonant states. New optical clocks based on weakly allowed or completely forbidden transitions in atoms, ions, molecules and nuclei will benefit from these generalized Ramsey schemes to reach relative accuracies well below the 10$^{-18}$ level.

  14. Automatic compensation of magnetic field for a rubidium space cold atom clock

    Science.gov (United States)

    Lin, Li; Jingwei, Ji; Wei, Ren; Xin, Zhao; Xiangkai, Peng; Jingfeng, Xiang; Desheng, Lü; Liang, Liu

    2016-07-01

    When the cold atom clock operates in microgravity around the near-earth orbit, its performance will be affected by the fluctuation of magnetic field. A strategy is proposed to suppress the fluctuation of magnetic field by additional coils, whose current is changed accordingly to compensate the magnetic fluctuation by the linear and incremental compensation. The flight model of the cold atom clock is tested in a simulated orbital magnetic environment and the magnetic field fluctuation in the Ramsey cavity is reduced from 17 nT to 2 nT, which implied the uncertainty due to the second order Zeeman shift is reduced to be less than 2×10-16. In addition, utilizing the compensation, the magnetic field in the trapping zone can be suppressed from 7.5 μT to less than 0.3 μT to meet the magnetic field requirement of polarization gradients cooling of atoms. Project supported by the Ministry of Science and Technology of China (Grant No. 2013YQ09094304), the Youth Innovation Promotion Association, Chinese Academy of Sciences, and the National Natural Science Foundation of China (Grant Nos. 11034008 and 11274324).

  15. Role of the multipolar black-body radiation shifts in the atomic clocks at the 10-18 uncertainty level

    Indian Academy of Sciences (India)

    B K Sahoo

    2014-08-01

    We present here an overview of the role of the multipolar black-body radiation (BBR) shifts in the single ion atomic clocks to appraise the anticipated 10-18 uncertainty level. With an attempt to use the advanced technologies for reducing the instrumental uncertainties at the unprecedented low, it is essential to investigate contributions from the higher-order systematics to achieve the ambitious goal of securing the most precise clock frequency standard. In this context, we have analysed contributions to the BBR shifts from the multipolar polarizabilities in a few ion clocks.

  16. Determination of a high spatial resolution geopotential model using atomic clock comparisons

    Science.gov (United States)

    Lion, G.; Panet, I.; Wolf, P.; Guerlin, C.; Bize, S.; Delva, P.

    2017-01-01

    Recent technological advances in optical atomic clocks are opening new perspectives for the direct determination of geopotential differences between any two points at a centimeter-level accuracy in geoid height. However, so far detailed quantitative estimates of the possible improvement in geoid determination when adding such clock measurements to existing data are lacking. We present a first step in that direction with the aim and hope of triggering further work and efforts in this emerging field of chronometric geodesy and geophysics. We specifically focus on evaluating the contribution of this new kind of direct measurements in determining the geopotential at high spatial resolution (≈ 10 km). We studied two test areas, both located in France and corresponding to a middle (Massif Central) and high (Alps) mountainous terrain. These regions are interesting because the gravitational field strength varies greatly from place to place at high spatial resolution due to the complex topography. Our method consists in first generating a synthetic high-resolution geopotential map, then drawing synthetic measurement data (gravimetry and clock data) from it, and finally reconstructing the geopotential map from that data using least squares collocation. The quality of the reconstructed map is then assessed by comparing it to the original one used to generate the data. We show that adding only a few clock data points (less than 1% of the gravimetry data) reduces the bias significantly and improves the standard deviation by a factor 3. The effect of the data coverage and data quality on the results is investigated, and the trade-off between the measurement noise level and the number of data points is discussed.

  17. Microfabricated cells for chip-scale atomic clock based on coherent population trapping: Fabrication and investigation

    Directory of Open Access Journals (Sweden)

    S.V. Ermak

    2015-03-01

    Full Text Available A universal method for fabrication of miniature cells for frequency standards and quantum magnetometers containing 87Rb atoms in the atmosphere of inert gas neon based on integrated technologies is considered. The results of experimental studies of coherent population trapping signals observed for a series of cells which provided recovery of vapors of an alkali metal from the rubidium dichromate salt with the help of laser radiation are presented. The coherent population trapping signals with a typical linewidth of 2–3 kHz and a signal-to-noise ratio of 1500 in the 1-Hz bandwidth were observed, which allows one to provide a relative frequency stability of atomic clock of 10−11 at 100 s.

  18. Improved limits on interactions of low-mass spin-0 dark matter from atomic clock spectroscopy

    CERN Document Server

    Stadnik, Y V

    2016-01-01

    Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently oscillating classical field $\\phi = \\phi_0 \\cos(m_\\phi t)$, can induce oscillating variations in the fundamental constants through their interactions with the Standard Model sector. We calculate the effects of such possible interactions, which may include the linear interaction of $\\phi$ with the Higgs boson, on atomic and molecular transitions. Using recent atomic clock spectroscopy measurements, we derive new limits on the linear interaction of $\\phi$ with the Higgs boson, as well as its quadratic interactions with the photon and light quarks. For the linear interaction of $\\phi$ with the Higgs boson, our derived limits improve on existing constraints by up to $2-3$ orders of magnitude.

  19. Improved limits on interactions of low-mass spin-0 dark matter from atomic clock spectroscopy

    Science.gov (United States)

    Stadnik, Y. V.; Flambaum, V. V.

    2016-08-01

    Low-mass (sub-eV) spin-0 dark matter particles, which form a coherently oscillating classical field ϕ =ϕ0cos(mϕt ) , can induce oscillating variations in the fundamental constants through their interactions with the standard model sector. We calculate the effects of such possible interactions, which may include the linear interaction of ϕ with the Higgs boson, on atomic and molecular transitions. Using recent atomic clock spectroscopy measurements, we derive limits on the linear interaction of ϕ with the Higgs boson, as well as its quadratic interactions with the photon and light quarks. For the linear interaction of ϕ with the Higgs boson, our derived limits improve on existing constraints by up to 2-3 orders of magnitude.

  20. Effects of variation of fundamental constants from Big Bang to atomic clocks

    Science.gov (United States)

    Flambaum, Victor

    2004-05-01

    Theories unifying gravity with other interactions suggest temporal and spatial variation of the fundamental "constants" in expanding Universe. I discuss effects of variation of the fine structure constant, strong interaction, quark mass and gravitational constant. The measurements of these variations cover the lifespan of the Universe from few minutes after Big Bang to the present time and give controversial results. There are some hints for the variations in Big Bang nucleosynthesis, quasar absorption spectra and Oklo natural nuclear reactor data. A very promising method to search for the variation of the fundamental constants consists in comparison of different atomic clocks. A billion times enhancement of the variation effects happens in transitions between accidentally degenerate atomic energy levels.

  1. Dependence of microwave-excitation signal parameters on frequency stability of caesium atomic clock

    Science.gov (United States)

    Petrov, A. A.; Davydov, V. V.; Vologdin, V. A.; Zalyotov, D. V.

    2015-11-01

    New scheme of the microwave - excitation signal for the caesium atomic clock is based on method of direct digital synthesis. The theoretical calculations and experimental research showed decrease step frequency tuning by several orders and improvement the spectral characteristics of the output signal of frequency synthesizer. A range of generated output frequencies is expanded, and the possibility of detuning the frequency of the neighboring resonance of spectral line that makes it possible to adjust the C-field in quantum frequency standard is implemented. Experimental research of the metrological characteristics of the quantum frequency standard on the atoms of caesium - 133 with new design scheme of the microwave - excitation signal showed improvement in daily frequency stability on 1.2*10-14.

  2. Generalized Collective States and Their Role in a Collective State Atomic Interferometer and Atomic Clock

    CERN Document Server

    Sarkar, Resham; Fang, Renpeng; Tu, Yanfei; Shahriar, Selim M

    2014-01-01

    We investigate the behavior of an ensemble of N non-interacting, identical atoms, excited by a laser with a wavelength of $\\lambda$. In general, the i-th atom sees a Rabi frequency $\\Omega_i$, an initial position dependent laser phase $\\phi_i$, and a motion induced Doppler shift of $\\delta_i$. When $\\Omega_i=\\Omega$ and $\\delta_i=\\delta$ for all atoms, the system evolves into a superposition of (N+1) symmetric collective states (SCS), independent of the values of $\\phi_i$. If $\\phi_i=\\phi$ for all atoms, these states simplify to the well-known Dicke collective states. When $\\Omega_i$ or $\\delta_i$ is distinct for each atom, the system evolves into a superposition of SCS as well as asymmetric collective states (ACS). For large N, the number of ACS's $(2^N-N-1)$ is far greater than that of the SCS. We show how to formulate the properties of all the collective states under various non-idealities, and use this formulation to understand the dynamics thereof. For the case where $\\Omega_i=\\Omega$ and $\\delta_i=\\delt...

  3. Explaining atomic clock behavior in a gravitational field with only 1905 Relativity

    CERN Document Server

    Hidalgo-Gato, Rafael A Valls

    2010-01-01

    Supported only in the two 1905 Einstein's papers on Relativity and a very rigid respect for the historical context, an analysis is done of the derivation of the universal mass-energy relationship. It is found, contrary to the today accepted Physics knowledge, that a body's Rest Mass measures its Potential Energy in the 1905 context. After emphasizing the difference between 1905 Relativity (1905R) and Special Relativity (SR), the developing of a 1905R relativistic gravity is started for a small mass m material point moving in the central gravitational field of a great mass M one. A formula for the rest mass m_0 as a function of its distance r from M is obtained. Finally, those results are applied to an atomic clock in a gravitational field, reaching a factor to obtain the clock time rate change very close to the GR one. The factors from 1905R and GR are compared, emphasizing the absent of a singularity in 1905R. In the conclusions, a new road for the development of a 1905R relativistic mechanics is declared, r...

  4. The Long-term Performance Analysis for On-board Atomic Clocks of BDS

    OpenAIRE

    WANG Yupu; LÜ Zhiping; Wang, Ning

    2017-01-01

    BeiDou Navigation Satellite System (BDS) has begun to provide regional services since the end of 2012. It plays an important role in analyzing the long-term performance of BDS satellite clocks in evaluating the performance of the whole system, determining and predicting satellite clock bias (SCB) etc. Precise satellite clock data products derived from multi-satellite orbit determination are used to conduct the performance analysis of BDS satellite clocks. Specifically, the characteristics of ...

  5. Measurement of the magnetic field profile in the atomic fountain clock FoCS-2 using Zeeman spectroscopy

    CERN Document Server

    Laurent, Devenoges; André, Stefanov; Antoine, Jallageas; Jacques, Morel; Thomas, Südmeyer; Pierre, Thomann

    2016-01-01

    We report the evaluation of the second order Zeeman shift in the continuous atomic fountain clock FoCS-2. Because of the continuous operation and its geometrical constraints, the methods used in pulsed fountain are not applicable. We use here time-resolved Zeeman spectroscopy to probe the magnetic field profile in the clock. The pulses of ac magnetic excitation allow us to measure the Zeeman frequency with spatial resolution and to evaluate the Zeeman shift with an uncertainty smaller than 10E-16 in relative units.

  6. The Long-term Performance Analysis for On-board Atomic Clocks of BDS

    Directory of Open Access Journals (Sweden)

    WANG Yupu

    2017-02-01

    Full Text Available BeiDou Navigation Satellite System (BDS has begun to provide regional services since the end of 2012. It plays an important role in analyzing the long-term performance of BDS satellite clocks in evaluating the performance of the whole system, determining and predicting satellite clock bias (SCB etc. Precise satellite clock data products derived from multi-satellite orbit determination are used to conduct the performance analysis of BDS satellite clocks. Specifically, the characteristics of SCB data are discussed by using a proposed modified median absolute deviation (MAD to preprocess original SCB data. Long-term variations of satellite clocks' phase, frequency, frequency drift and model noise level are analyzed based on the quadratic polynomial SCB model. Frequency stability of BDS satellite clocks is calculated and discussed based on Overlapping Hadamard Variance. Periodicity of BDS SCB is analyzed by using spectral analysis method. Integrating the above mentioned discussions and corresponding experiment results, the long-term performance of BDS satellite clocks is relatively comprehensively evaluated and analyzed. In addition, some valuable conclusions are obtained. For example, in the aspects of noise characteristics and clock drift, the performance of MEO satellite clocks is the best, followed by the IGSO satellite clocks, and the GEO satellite clocks' performance is the worst. The average values of noise level and frequency drift of BDS satellite clocks are respectively 0.677 ns and 1.922×10-18. There are also obvious periodic terms in BDS SCB data derived from multi-satellite orbit determination and their primary periods are approximate equal or one-half to the corresponding satellite orbit periods. The average value of frequency stability of BDS satellite clocks is 1.484×10-13.

  7. How ticks an atomic clock? Realization of the second from 1955 until today; Wie tickt eine Atomuhr? Realisierung der Sekunde von 1955 bis heute

    Energy Technology Data Exchange (ETDEWEB)

    Bauch, Andreas [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany). Arbeitsgruppe ' Zeituebertragung' ; Weyers, Stefan [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany). Arbeitsgruppe ' Zeitnormale' ; Peik, Ekkehard [Physikalisch-Technische Bundesanstalt (PTB), Braunschweig (Germany). Fachbereich ' Zeit und Frequenz'

    2016-06-15

    In this paper the principle of the atomic clock on the base of the hyperfine-structure transition in {sup 133}Cs is described. Additional further developments in the definition of the second on the base of optical clocks are considered. (HSI)

  8. A low phase noise microwave frequency synthesis for a high-performance cesium vapor cell atomic clock.

    Science.gov (United States)

    François, B; Calosso, C E; Danet, J M; Boudot, R

    2014-09-01

    We report the development, absolute phase noise, and residual phase noise characterization of a 9.192 GHz microwave frequency synthesis chain devoted to be used as a local oscillator in a high-performance cesium vapor cell atomic clock based on coherent population trapping (CPT). It is based on frequency multiplication of an ultra-low phase noise 100 MHz oven-controlled quartz crystal oscillator using a nonlinear transmission line-based chain. Absolute phase noise performances of the 9.192 GHz output signal are measured to be -42, -100, -117 dB rad(2)/Hz and -129 dB rad(2)/Hz at 1 Hz, 100 Hz, 1 kHz, and 10 kHz offset frequencies, respectively. Compared to current results obtained in a state-of-the-art CPT-based frequency standard developed at LNE-SYRTE, this represents an improvement of 8 dB and 10 dB at f = 166 Hz and f = 10 kHz, respectively. With such performances, the expected Dick effect contribution to the atomic clock short term frequency stability is reported at a level of 6.2 × 10(-14) at 1 s integration time, that is a factor 3 higher than the atomic clock shot noise limit. Main limitations are pointed out.

  9. Atomic clocks based on extened-cavity diode laser in multimode operation

    Science.gov (United States)

    Yim, Sin; Cho, D.

    2011-05-01

    We demonstrated the possibilities to develope an atomic clock based on coherent population trapping (CPT) without using a local oscillator and a modulator. Instead of using a modulator, we use two modes from a single extended-cavity diode laser in multimode operation. Two different types of feedback system are applied to stabilize a difference frequency between the two modes and eliminate the need for an extra frequency modulation. In the first type, we employ an electronic feedback using dispersion of the CPT resonance as an error signal. The two modes are phase locked with reference to a dispersion signal from a CPT resonance of 85Rb at 3.036 GHz ground hyperfine splitting. We use D1 transition at 794.8 nm with lin ⊥lin polarizations to obtain large-contrast CPT signal. Allan deviation of the beat frequency between the two modes is 1 ×10-10 at 200-s integration time. In the second type, we employ optoelectronic feedback to construct an opto-electronic oscillator (OEO). In an OEO, the beating signal between two modes is recovered by a fast photodiode, and its output is amplified and fed back to the laser diode by using a direct modulation of an injection current. When the OEO loop is closed, oscillation frequency depends on variations of the loop length. In order to stabilize an OEO loop length and thereby its oscillation frequency, CPT cell is inserted to play a role of microwave band pass filter. Allan deviation of the CPT-stabilized OEO is 2 ×10-10 at 100-s integration time.

  10. Optimizing passive quantum clocks

    Science.gov (United States)

    Mullan, Michael; Knill, Emanuel

    2014-10-01

    We describe protocols for passive atomic clocks based on quantum interrogation of the atoms. Unlike previous techniques, our protocols are adaptive and take advantage of prior information about the clock's state. To reduce deviations from an ideal clock, each interrogation is optimized by means of a semidefinite program for atomic state preparation and measurement whose objective function depends on the prior information. Our knowledge of the clock's state is maintained according to a Bayesian model that accounts for noise and measurement results. We implement a full simulation of a running clock with power-law noise models and find significant improvements by applying our techniques.

  11. Precision Clock Evaluation Facility

    Data.gov (United States)

    Federal Laboratory Consortium — FUNCTION: Tests and evaluates high-precision atomic clocks for spacecraft, ground, and mobile applications. Supports performance evaluation, environmental testing,...

  12. One single trapped and laser cooled radium ion: Towards an all-optical atomic clock

    Energy Technology Data Exchange (ETDEWEB)

    Versolato, Oscar; Wansbeek, Lotje; Willmann, Lorenz; Timmermans, Rob; Jungmann, Klaus [KVI, University of Groningen (Netherlands)

    2008-07-01

    One single trapped radium ion is an ideal candidate for an all-optical frequency standard (*clock*). This system provides a long coherence time and tractable systematics. If the ion is laser cooled to the Lamb-Dicke regime, first order Doppler shifts are eliminated. Ultra-narrow transitions in radium ions provide an excellent basis for such a high stability clock, using commercially available semiconductor lasers in the visible regime. In certain odd isotopes of radium, the nuclear electric quadrupole shift is absent. Further, the radium ion is an excellent candidate for a high sensitivity experiment to search for a time variation of the finestructure constant.

  13. Dynamic polarizabilities and related properties of clock states of ytterbium atom

    CERN Document Server

    Dzuba, V A

    2009-01-01

    We carry out relativistic many-body calculations of the static and dynamic dipole polarizabilities of the ground $6s^2 ^1S_0$ and the first excited $6s6p ^3P^o_0$ states of Yb. With these polarizabilities, we compute several properties of Yb relevant to optical lattice clocks operating on the $6s^2 ^1S_0 - 6s6p ^3P^o_0$ transition. We determine (i) the first four {\\em magic} wavelengths of the laser field for which the frequency of the clock transition is insensitive to the laser intensity. While the first magic wavelength is known, we predict the second, the third and the forth magic wavelengths to be 551 nm, 465 nm, and 413 nm. (ii) We reevaluate the effect of black-body radiation on the frequency of the clock transition, the resulting clock shift at $T=300 \\mathrm{K}$ being $-1.41(17)$ Hz. (iii) We compute long-range interatomic van der Waals coefficients (in a.u.) $C_6(6s^2 ^1S_0 +6s^2 ^1S_0) = 1909(160)$, $C_6(6s^2 ^1S_0 + 6s6p ^3P_0) =2709(338) $, and $C_6(6s6p ^3P_0 + 6s6p ^3P_0) =3886(360) $. Finally,...

  14. Accuracy budget of the 88Sr optical atomic clocks at KL FAMO

    Science.gov (United States)

    Radzewicz, Czesław; Bober, Marcin; Morzyński, Piotr; Cygan, Agata; Lisak, Daniel; Bartoszek-Bober, Dobrosława; Masłowski, Piotr; Ablewski, Piotr; Zachorowski, Jerzy; Gawlik, Wojciech; Ciuryło, Roman; Zawada, Michał

    2016-08-01

    This paper presents a detailed accuracy budget of two independent strontium optical lattice clocks at the National Laboratory FAMO (KL FAMO) probed with a single shared ultra-narrow laser. The combined instability of the two frequency standards was 7× {10}-17 after 105s of averaging.

  15. Optical clock networks

    Science.gov (United States)

    Riehle, Fritz

    2017-01-01

    Within the last decade, optical atomic clocks have surpassed the best cesium clocks, which are used to realize the unit of time and frequency, in terms of accuracy and stability by about two orders of magnitude. When remote optical atomic clocks are connected by links without degradation in the clock signals, an optical clock network is formed, with distinct advantages for the dissemination of time, geodesy, astronomy and basic and applied research. Different approaches for time and frequency transfer in the microwave and optical regime, via satellites and free-space links, optical fibre links, or transportable optical atomic clocks, can be used to form a hybrid clock network that may allow a future redefinition of the unit of time based on an optical reference transition.

  16. A New Rb Lamp Exciter Circuit for Rb atomic clocks and Studies on Transition from Ring to Red mode

    CERN Document Server

    Singh, Savita; Saxena, G M

    2010-01-01

    In this paper we describe the development of novel RF exciter circuit for electrode less Rb lamp. The lamp exciter circuit is a RF oscillator with a a new configuration operating at 60 to 65 MHz frequency with 3 to 4 watt power. The Rb lamp is used in exciting the ground state hyperfine transitions in Rb atom in a glass cell placed inside a tuned microwave cavity, As the frequency of these hyperfine transitions is very stable it is used in the development of Rb atomic clock by phase locking the oven controlled crystal oscillator (OCXO) to this atomic transition frequency. The details of the Rb lamp exciter are presented in the paper.The Lamp is ideally operated in ring mode as in this mode the linewidth is narrow and there is no self reversal. However, high temperature and RF excitation power may drive the Rb lamp to red mode which gives rise to line broadening and self reversal. It is the experience that mode change from ring to red deteriorates the atomic signal strength and S/N. In this paper the reasons o...

  17. Formulation of geopotential difference determination using optical-atomic clocks onboard satellites and on ground based on Doppler cancellation system

    Science.gov (United States)

    Shen, Ziyu; Shen, Wen-Bin; Zhang, Shuangxi

    2016-08-01

    In this study, we propose an approach for determining the geopotential difference using high-frequency-stability microwave links between satellite and ground station based on Doppler cancellation system. Suppose a satellite and a ground station are equipped with precise optical-atomic clocks (OACs) and oscillators. The ground oscillator emits a signal with frequency fa towards the satellite and the satellite receiver (connected with the satellite oscillator) receives this signal with frequency fb which contains the gravitational frequency shift effect and other signals and noises. After receiving this signal, the satellite oscillator transmits and emits, respectively, two signals with frequencies fb and fc towards the ground station. Via Doppler cancellation technique, the geopotential difference between the satellite and the ground station can be determined based on gravitational frequency shift equation by a combination of these three frequencies. For arbitrary two stations on ground, based on similar procedures as described above, we may determine the geopotential difference between these two stations via a satellite. Our analysis shows that the accuracy can reach 1 m2 s- 2 based on the clocks' inaccuracy of about 10-17 (s s-1) level. Since OACs with instability around 10-18 in several hours and inaccuracy around 10-18 level have been generated in laboratory, the proposed approach may have prospective applications in geoscience, and especially, based on this approach a unified world height system could be realized with one-centimetre level accuracy in the near future.

  18. Stable clocks and general relativity

    CERN Document Server

    Will, C M

    1995-01-01

    We survey the role of stable clocks in general relativity. Clock comparisons have provided important tests of the Einstein Equivalence Principle, which underlies metric gravity. These include tests of the isotropy of clock comparisons (verification of local Lorentz invariance) and tests of the homogeneity of clock comparisons (verification of local position invariance). Comparisons of atomic clocks with gravitational clocks test the Strong Equivalence Principle by bounding cosmological variations in Newton's constant. Stable clocks also play a role in the search for gravitational radiation: comparision of atomic clocks with the binary pulsar's orbital clock has verified gravitational-wave damping, and phase-sensitive detection of waves from inspiralling compact binaries using laser interferometric gravitational observatories will facilitate extraction of useful source information from the data. Stable clocks together with general relativity have found important practical applications in navigational systems s...

  19. Light-Shifts of an Integrated Filter-Cell Rubidium Atomic Clock

    Science.gov (United States)

    2015-05-25

    of the upper atmosphere, remote sensing using atmospheric radiation; solar physics, infrared astronomy , infrared signature analysis; infrared... Introduction Overview The rubidium (Rb) atomic frequency standard is the workhorse of precise atomic timekeeping in space due to its low weight, small volume

  20. Active optical clock

    Institute of Scientific and Technical Information of China (English)

    CHEN JingBiao

    2009-01-01

    This article presents the principles and techniques of active optical clock, a special laser combining the laser physics of one-atom laser, bad-cavity gas laser, super-cavity stabilized laser and optical atomic clock together. As a simple example, an active optical clock based on thermal strontium atomic beam shows a quantum-limited linewidth of 0.51 Hz, which is insensitive to laser cavity-length noise, and may surpass the recorded narrowest 6.7 Hz of Hg ion optical clock and 1.5 Hz of very recent optical lattice clock. The estimated 0.1 Hz one-second instability and 0.27 Hz uncertainty are limited only by the rela-tivistic Doppler effect, and can be improved by cold atoms.

  1. Compact Yb$^+$ optical atomic clock project: design principle and current status

    CERN Document Server

    Lacroûte, Clément; Bourgeois, Pierre-Yves; Millo, Jacques; Saleh, Khaldoun; Bigler, Emmanuel; Boudot, Rodolphe; Giordano, Vincent; Kersalé, Yann

    2016-01-01

    We present the design of a compact optical clock based on the $^2S_{1/2} \\rightarrow ^2D_{3/2}$ 435.5 nm transition in $^{171}$Yb$^+$. The ion trap will be based on a micro-fabricated circuit, with surface electrodes generating a trapping potential to localize a single Yb ion a few hundred $\\mu$m from the electrodes. We present our trap design as well as simulations of the resulting trapping pseudo-potential. We also present a compact, multi-channel wavelength meter that will permit the frequency stabilization of the cooling, repumping and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion. We use this wavelength meter to characterize and stabilize the frequency of extended cavity diode lasers at 369.5 nm and 638.6 nm.

  2. Quantum theory of atomic clocks and gravito-inertial sensors: an update

    Energy Technology Data Exchange (ETDEWEB)

    Antoine, Ch [Equipe de Relativite Gravitation et Astrophysique, LERMA, UMR 8112, CNRS-Observatoire de Paris, Universite Pierre et Marie Curie, 4 place Jussieu, 75005 Paris (France); Borde, Ch J [Equipe de Relativite Gravitation et Astrophysique, LERMA, UMR 8112, CNRS-Observatoire de Paris, Universite Pierre et Marie Curie, 4 place Jussieu, 75005 Paris (France)

    2003-04-01

    In the framework of the ABCD{xi} formulation of atom optics and with an adequate modelization of the beam splitters, we establish an exact analytical phase shift expression for atom interferometers. This result is valid for a time-dependent external Hamiltonian at most quadratic in position and momentum operators and is expressed in terms of coordinates and momenta of the wave packet centres at the interaction vertices only. As a specific application, the case of atom gyrometers and accelerometers is presented in detail.

  3. Single-Ion Atomic Clock with 3×10(-18) Systematic Uncertainty.

    Science.gov (United States)

    Huntemann, N; Sanner, C; Lipphardt, B; Tamm, Chr; Peik, E

    2016-02-12

    We experimentally investigate an optical frequency standard based on the (2)S1/2(F=0)→(2)F7/2(F=3) electric octupole (E3) transition of a single trapped (171)Yb+ ion. For the spectroscopy of this strongly forbidden transition, we utilize a Ramsey-type excitation scheme that provides immunity to probe-induced frequency shifts. The cancellation of these shifts is controlled by interleaved single-pulse Rabi spectroscopy, which reduces the related relative frequency uncertainty to 1.1×10(-18). To determine the frequency shift due to thermal radiation emitted by the ion's environment, we measure the static scalar differential polarizability of the E3 transition as 0.888(16)×10(-40)  J m(2)/V(2) and a dynamic correction η(300  K)=-0.0015(7). This reduces the uncertainty due to thermal radiation to 1.8×10(-18). The residual motion of the ion yields the largest contribution (2.1×10(-18)) to the total systematic relative uncertainty of the clock of 3.2×10(-18).

  4. Ra{sup +} ion trapping - atomic parity violation measurement and an optical clock

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Amita; Dijck, Elwin A.; Nunez Portela, Mayerlin; Valappol, Nivedya; Boell, Oliver; Jungmann, Klaus; Onderwater, Cornelis G. G.; Schlesser, Sophie; Timmermans, Rob G.E.; Willmann, Lorenz; Wilschut, Hans W. [University of Groningen, FWN, Groningen (Netherlands)

    2014-07-01

    A single trapped Ra{sup +} ion has an excellent potential for a precision measurement of the Weinberg mixing angle at low momentum transfer and testing thereby the electroweak running. The absolute frequencies of the transition 7s {sup 2}S{sub 1/2}-7d{sup 2}D{sub 3/2} at wavelength 828 nm have been determined in {sup 212*214}Ra{sup +} to better than 19 MHz with laser spectroscopy on small samples of ions trapped in a linear Paul trap at the online facility TRIμP of KVI. The measurement of the Weinberg angle requires the localization of the ion within a fraction of an optical wavelength. The current experiments are focused on trapping and laser spectroscopy on a single Ba{sup +} as a precursor for Ra{sup +}. Work towards single ion trapping of Ra{sup +}, including the preparation of an offline {sup 223}Ra source is in progress. Most elements of the setup for single Ra+ ion parity measurement are also well suited for realizing a most stable optical clock.

  5. Optical Lattice Clocks

    Science.gov (United States)

    Oates, Chris

    2012-06-01

    Since they were first proposed in 2003 [1], optical lattice clocks have become one of the leading technologies for the next generation of atomic clocks, which will be used for advanced timing applications and in tests of fundamental physics [2]. These clocks are based on stabilized lasers whose frequency is ultimately referenced to an ultra-narrow neutral atom transition (natural linewidths magic'' value so as to yield a vanishing net AC Stark shift for the clock transition. As a result lattice clocks have demonstrated the capability of generating high stability clock signals with small absolute uncertainties (˜ 1 part in 10^16). In this presentation I will first give an overview of the field, which now includes three different atomic species. I will then use experiments with Yb performed in our laboratory to illustrate the key features of a lattice clock. Our research has included the development of state-of-the-art optical cavities enabling ultra-high-resolution optical spectroscopy (1 Hz linewidth). Together with the large atom number in the optical lattice, we are able to achieve very low clock instability (< 0.3 Hz in 1 s) [3]. Furthermore, I will show results from some of our recent investigations of key shifts for the Yb lattice clock, including high precision measurements of ultracold atom-atom interactions in the lattice and the dc Stark effect for the Yb clock transition (necessary for the evaluation of blackbody radiation shifts). [4pt] [1] H. Katori, M. Takamoto, V. G. Pal'chikov, and V. D. Ovsiannikov, Phys. Rev. Lett. 91, 173005 (2003). [0pt] [2] Andrei Derevianko and Hidetoshi Katori, Rev. Mod. Phys. 83, 331 (2011). [0pt] [3] Y. Y. Jiang, A. D. Ludlow, N. D. Lemke, R. W. Fox, J. A. Sherman, L.-S. Ma, and C. W. Oates, Nature Photonics 5, 158 (2011).

  6. Simple-design ultra-low phase noise microwave frequency synthesizers for high-performing Cs and Rb vapor-cell atomic clocks

    Energy Technology Data Exchange (ETDEWEB)

    François, B. [FEMTO-ST, CNRS, Université de Franche-Comté, 26 chemin de l’Epitaphe, 25030 Besançon (France); INRIM, Strada delle Cacce 91, 10135 Torino (Italy); Calosso, C. E.; Micalizio, S. [INRIM, Strada delle Cacce 91, 10135 Torino (Italy); Abdel Hafiz, M.; Boudot, R. [FEMTO-ST, CNRS, Université de Franche-Comté, 26 chemin de l’Epitaphe, 25030 Besançon (France)

    2015-09-15

    We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwave frequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a high spectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHz with minor excess noise. Frequency multiplication, division, and mixing stages are then implemented to generate the exact output atomic resonance frequencies. Absolute phase noise performances of the output 4.596 GHz signal are measured to be −109 and −141 dB rad{sup 2}/Hz at 100 Hz and 10 kHz Fourier frequencies, respectively. The phase noise of the 6.834 GHz signal is −105 and −138 dB rad{sup 2}/Hz at 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chains contribute to the atomic clock short term fractional frequency stability at a level of 3.1 × 10{sup −14} for the Cs cell clock and 2 × 10{sup −14} for the Rb clock at 1 s averaging time. This value is comparable with the clock shot noise limit. We describe the residual phase noise measurements of key components and stages to identify the main limitations of the synthesis chains. The residual frequency stability of synthesis chains is measured to be at the 10{sup −15} level for 1 s integration time. Relevant advantages of the synthesis design, using only commercially available components, are to combine excellent phase noise performances, simple-architecture, low-cost, and to be easily customized for signal output generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequency standards.

  7. Simple-design ultra-low phase noise microwave frequency synthesizers for high-performing Cs and Rb vapor-cell atomic clocks.

    Science.gov (United States)

    François, B; Calosso, C E; Abdel Hafiz, M; Micalizio, S; Boudot, R

    2015-09-01

    We report on the development and characterization of novel 4.596 GHz and 6.834 GHz microwave frequency synthesizers devoted to be used as local oscillators in high-performance Cs and Rb vapor-cell atomic clocks. The key element of the synthesizers is a custom module that integrates a high spectral purity 100 MHz oven controlled quartz crystal oscillator frequency-multiplied to 1.6 GHz with minor excess noise. Frequency multiplication, division, and mixing stages are then implemented to generate the exact output atomic resonance frequencies. Absolute phase noise performances of the output 4.596 GHz signal are measured to be -109 and -141 dB rad(2)/Hz at 100 Hz and 10 kHz Fourier frequencies, respectively. The phase noise of the 6.834 GHz signal is -105 and -138 dB rad(2)/Hz at 100 Hz and 10 kHz offset frequencies, respectively. The performances of the synthesis chains contribute to the atomic clock short term fractional frequency stability at a level of 3.1 × 10(-14) for the Cs cell clock and 2 × 10(-14) for the Rb clock at 1 s averaging time. This value is comparable with the clock shot noise limit. We describe the residual phase noise measurements of key components and stages to identify the main limitations of the synthesis chains. The residual frequency stability of synthesis chains is measured to be at the 10(-15) level for 1 s integration time. Relevant advantages of the synthesis design, using only commercially available components, are to combine excellent phase noise performances, simple-architecture, low-cost, and to be easily customized for signal output generation at 4.596 GHz or 6.834 GHz for applications to Cs or Rb vapor-cell frequency standards.

  8. Improved limit on a temporal variation of mp/me from comparisons of Yb+ and Cs atomic clocks.

    Science.gov (United States)

    Huntemann, N; Lipphardt, B; Tamm, Chr; Gerginov, V; Weyers, S; Peik, E

    2014-11-21

    Accurate measurements of different transition frequencies between atomic levels of the electronic and hyperfine structure over time are used to investigate temporal variations of the fine structure constant α and the proton-to-electron mass ratio μ. We measure the frequency of the (2)S1/2→(2)F7/2 electric octupole (E3) transition in (171)Yb(+) against two caesium fountain clocks as f(E3)=642,121,496,772,645.36  Hz with an improved fractional uncertainty of 3.9×10(-16). This transition frequency shows a strong sensitivity to changes of α. Together with a number of previous and recent measurements of the (2)S1/2→(2)D3/2 electric quadrupole transition in (171)Yb(+) and with data from other elements, a least-squares analysis yields (1/α)(dα/dt)=-0.20(20)×10(-16)/yr and (1/μ)(dμ/dt)=-0.5(1.6)×10(-16)/yr, confirming a previous limit on dα/dt and providing the most stringent limit on dμ/dt from laboratory experiments.

  9. An analytic technique for statistically modeling random atomic clock errors in estimation

    Science.gov (United States)

    Fell, P. J.

    1981-01-01

    Minimum variance estimation requires that the statistics of random observation errors be modeled properly. If measurements are derived through the use of atomic frequency standards, then one source of error affecting the observable is random fluctuation in frequency. This is the case, for example, with range and integrated Doppler measurements from satellites of the Global Positioning and baseline determination for geodynamic applications. An analytic method is presented which approximates the statistics of this random process. The procedure starts with a model of the Allan variance for a particular oscillator and develops the statistics of range and integrated Doppler measurements. A series of five first order Markov processes is used to approximate the power spectral density obtained from the Allan variance.

  10. Optical Clocks and Relativity

    Science.gov (United States)

    Chou, C. W.; Hume, D. B.; Rosenband, T.; Wineland, D. J.

    2010-09-01

    Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation. We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth’s surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics.

  11. The ac stark shift and space-borne rubidium atomic clocks

    Science.gov (United States)

    Formichella, V.; Camparo, J.; Sesia, I.; Signorile, G.; Galleani, L.; Huang, M.; Tavella, P.

    2016-11-01

    Due to its small size, low weight, and low power consumption, the Rb atomic frequency standard (RAFS) is routinely the first choice for atomic timekeeping in space. Consequently, though the device has very good frequency stability (rivaling passive hydrogen masers), there is interest in uncovering the fundamental processes limiting its long-term performance, with the goal of improving the device for future space systems and missions. The ac Stark shift (i.e., light shift) is one of the more likely processes limiting the RAFS' long-term timekeeping ability, yet its manifestation in the RAFS remains poorly understood. In part, this comes from the fact that light-shift induced frequency fluctuations must be quantified in terms of the RAFS' light-shift coefficient and the output variations in the RAFS' rf-discharge lamp, which is a nonlinear inductively-couple plasma (ICP). Here, we analyze the light-shift effect for a family of 10 on-orbit Block-IIR GPS RAFS, examining decade-long records of their on-orbit frequency and rf-discharge lamp fluctuations. We find that the ICP's light intensity variations can take several forms: deterministic aging, jumps, ramps, and non-stationary noise, each of which affects the RAFS' frequency via the light shift. Correlating these light intensity changes with RAFS frequency changes, we estimate the light-shift coefficient, κLS, for the family of RAFS: κLS = -(1.9 ± 0.3) × 10-12/%. The 16% family-wide variation in κLS indicates that while each RAFS may have its own individual κLS, the variance of κLS among similarly designed RAFS can be relatively small. Combining κLS with our estimate of the ICP light intensity's non-stationary noise, we find evidence that random-walk frequency noise in high-quality space-borne RAFS is strongly influenced by the RAFS' rf-discharge lamp via the light shift effect.

  12. 星载原子钟数据预处理的方法研究%Research on the Methods of Preprocessing the Satellite-Borne Atomic Clocks Data

    Institute of Scientific and Technical Information of China (English)

    李斌; 杨富春; 江峻毅

    2015-01-01

    Satellite-borne atomic clocks data preprocessing is the basis of atomic clocks performance analysis and clock forecasting,phase and frequency of data conversion and abnormal data analysis and processing methods are used to preprocess the clocks data, these methods can effectively guarantee the re-liability of the clocks data.%星载原子钟的数据预处理是进行原子钟性能分析和钟差预报的前提,本文主要利用相位数据和频率数据的转换和异常数据的分析处理方法对原子钟数据进行了预处理,有效的保证了数据的可靠性。

  13. First Results of the GPS.DM Observatory: Search for Dark Matter and Exotic Physics with Atomic Clocks and GPS Constellation

    Science.gov (United States)

    Roberts, Benjamin; Blewitt, Geoff; Dailey, Conner; Pospelov, Maxim; Rollings, Alex; Sherman, Jeff; Williams, Wyatt; Derevianko, Andrei; GPS. DM Collaboration

    2017-01-01

    Despite the overwhelming cosmological evidence for the existence of dark matter, and the considerable effort of the scientific community over decades, there is no evidence for dark matter in terrestrial experiments. The GPS.DM observatory uses the existing GPS constellation as a 50,000 km-aperture sensor array, analysing the satellite and terrestrial atomic clock data for exotic physics signatures. In particular, the collaboration searches for evidence of transient variations of fundamental constants correlated with the Earth's galactic motion through the dark matter halo. There already exists more than 10 years of good clock timing data that can be used in the search. This type of search is particularly sensitive to exotic forms of dark matter, such as topological defects. Supported by the NSF.

  14. A HBAR-oscillator-based 4.596~GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock

    CERN Document Server

    Daugey, Thomas; Martin, Gilles; Boudot, Rodolphe

    2015-01-01

    This article reports on the design and characterization of a high-overtone bulk acoustic wave resonator (HBAR)-oscillator-based 4.596~GHz frequency source. A 2.298~GHz signal, generated by an oscillator constructed around a thermally-controlled two-port AlN-sapphire HBAR resonator with a Q-factor of 24000 at 68$^{\\circ}$C, is frequency multiplied by 2 to 4.596~GHz, half of the Cs atom clock frequency. The temperature coefficient of frequency (TCF) of the HBAR is measured to be $-23$~ppm/$^{\\circ}$C at 2.298~GHz. The measured phase noise of the 4.596~GHz source is $-105$~dBrad$^2$/Hz at 1~kHz offset and $-150$~dBrad$^2$/Hz at 100~kHz offset. The 4.596~GHz output signal is used as a local oscillator (LO) in a laboratory-prototype Cs microcell-based coherent population trapping (CPT) atomic clock. The signal is stabilized onto the atomic transition frequency by tuning finely a voltage-controlled phase shifter (VCPS) implemented in the 2.298~GHz HBAR-oscillator loop, preventing the need for a high-power-consuming...

  15. Stability Analysis of the In-Orbit Satellite Atomic Clocks%GPS在轨卫星原子钟的稳定性分析

    Institute of Scientific and Technical Information of China (English)

    李长会; 闫国锋

    2012-01-01

    导航卫星星载原子钟的相位或频率数据,作为导航系统应用研究的基础,将直接影响导航系统时间尺度建立以及定位的精度和准确性.本文针对由IGS官网提供的四种GPS卫星钟的钟差数据,采用修正阿伦方差进行了稳定性分析,得到了一些有益的结论.%As the application research basis of navigation system, the phase or frequency data of in - orbit satellite atomic clocks directly affect the precision and accuracy of navigation system. This paper analyzes the stability of four types of data of GPS satellite a-tomic clocks which is provided by the official website of IGS using Allan variance method and reaches some beneficial conclusions.

  16. A high-overtone bulk acoustic wave resonator-oscillator-based 4.596 GHz frequency source: Application to a coherent population trapping Cs vapor cell atomic clock

    Energy Technology Data Exchange (ETDEWEB)

    Daugey, Thomas; Friedt, Jean-Michel; Martin, Gilles; Boudot, Rodolphe [FEMTO-ST, CNRS, UFC, 26 chemin de l’Epitaphe 25030 Besançon Cedex (France)

    2015-11-15

    This article reports on the design and characterization of a high-overtone bulk acoustic wave resonator (HBAR)-oscillator-based 4.596 GHz frequency source. A 2.298 GHz signal, generated by an oscillator constructed around a thermally controlled two-port aluminum nitride-sapphire HBAR resonator with a Q-factor of 24 000 at 68 °C, is frequency multiplied by 2–4.596 GHz, half of the Cs atom clock frequency. The temperature coefficient of frequency of the HBAR is measured to be −23 ppm/ °C at 2.298 GHz. The measured phase noise of the 4.596 GHz source is −105 dB rad{sup 2}/Hz at 1 kHz offset and −150 dB rad{sup 2}/Hz at 100 kHz offset. The 4.596 GHz output signal is used as a local oscillator in a laboratory-prototype Cs microcell-based coherent population trapping atomic clock. The signal is stabilized onto the atomic transition frequency by tuning finely a voltage-controlled phase shifter implemented in the 2.298 GHz HBAR-oscillator loop, preventing the need for a high-power-consuming direct digital synthesis. The short-term fractional frequency stability of the free-running oscillator is 1.8 × 10{sup −9} at one second integration time. In locked regime, the latter is improved in a preliminary proof-of-concept experiment at the level of 6.6 × 10{sup −11} τ{sup −1/2} up to a few seconds and found to be limited by the signal-to-noise ratio of the detected CPT resonance.

  17. Progress of the ~(87)Rb Fountain Clock

    Institute of Scientific and Technical Information of China (English)

    ZHOU Zi-Chao; WEI Rong; SHI Chun-Yan; LV De-Sheng; LI Tang; WANG Yu-Zhu

    2009-01-01

    A fountain atomic clock based on cold ~(87)Rb atoms has been in operation in our laboratory for several months.We therefore report the design of the rubidium fountain clock including its physical package,optical system and daily operation.Ramsey fringes have been attained with the signal to noise ratio of about 100.

  18. 航天器铷钟的一种精密控温系统%A Precise Temperature Control System for Spacecraft Rubidium Atomic Clock

    Institute of Scientific and Technical Information of China (English)

    李国强; 耿利寅; 童叶龙

    2011-01-01

    研究了一种应用于航天器的高精度、高稳定度的温度控制系统:使用热敏电阻作为温度传感器;采用多级控温策略,核心级采用基于径向基函数(Radial Basis Function,RBF)神经网络比例、积分、微分(PID)控制算法,非核心级采用积分分离式PID算法;采用脉宽调制(PWM)控制作为控制方式。以航天器铷钟作为控制对象,通过铷钟模拟件的热平衡试验,验证了高精度控温系统的控制效果。试验结果表明:核心级施加RBF神经网络PID控制时,稳态控温精度优于±0.08℃;内热源阶跃冲击或外热流正弦扰动下,其温度波动%The paper shows a high-precision and high-stability temperature control system for spacecraft,which uses thermistor as sensor.The system control strategy is step-by-step,using RBF-based nenral network PID control for core stage,using integral separation PID control for others;and using pulse width modulation(PWM) as control mode.The system's performance is verified through thermal balance test of rubidium atomic clock simulator.Test results are shown as follows.When the core stage is controlled by nerval network PID control,its temperature change can be within ±0.08℃ in steady case;when it is disturbed by internal heat source or orbit heat flux,the core stage's temperature change can be within ±0.1℃ and the temperature stability is ±0.1℃/day.The temperature control system can be applied in precision temperature control for spacecraft atomic clock and high-resolution camera.

  19. A quantum network of clocks

    Science.gov (United States)

    Kómár, P.; Kessler, E. M.; Bishof, M.; Jiang, L.; Sørensen, A. S.; Ye, J.; Lukin, M. D.

    2014-08-01

    The development of precise atomic clocks plays an increasingly important role in modern society. Shared timing information constitutes a key resource for navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System. By combining precision metrology and quantum networks, we propose a quantum, cooperative protocol for operating a network of geographically remote optical atomic clocks. Using nonlocal entangled states, we demonstrate an optimal utilization of global resources, and show that such a network can be operated near the fundamental precision limit set by quantum theory. Furthermore, the internal structure of the network, combined with quantum communication techniques, guarantees security both from internal and external threats. Realization of such a global quantum network of clocks may allow construction of a real-time single international time scale (world clock) with unprecedented stability and accuracy.

  20. Entangling the lattice clock: Towards Heisenberg-limited timekeeping

    CERN Document Server

    Weinstein, Jonathan D; Derevianko, Andrei

    2009-01-01

    We present a scheme for entangling the atoms of an optical lattice to reduce the quantum projection noise of a clock measurement. The divalent clock atoms are held in a lattice at a ``magic'' wavelength that does not perturb the clock frequency -- to maintain clock accuracy -- while an open-shell J=1/2 ``head'' atom is coherently transported between lattice sites via the lattice polarization. This polarization-dependent ``Archimedes' screw'' transport at magic wavelength takes advantage of the vanishing vector polarizability of the scalar, J=0, clock states of bosonic isotopes of divalent atoms. The on-site interactions between the clock atoms and the head atom are used to engineer entanglement and for clock readout.

  1. 铯原子喷泉钟均匀C场的实现%A realization of uniform C field in caesium atomic fountain clock

    Institute of Scientific and Technical Information of China (English)

    吴长江; 管勇; 陈江; 张辉; 阮军; 张首刚

    2011-01-01

    C场均匀度是影响铯原子喷泉钟性能的重要因素。为了消除漏磁等对磁场均匀度的影响,加入补偿线圈,通过用最小二乘法计算,逐次得出补偿线圈的个数、位置与电流。实验表明:计算数据与实验结果吻合,得到c场不均匀性小于2nT、长度达48cm的均匀区。%The performance of the caesium atomic fountain clock is affected by the uniformity of the C field. In order to compensate the uneven magnetic field caused by the leakage in magnetic shielding region, compensation coils are introduced and the number, position and current of the coils are calculated by the least square methgd. The experimental results agree with the theoretical prediction and an uniform magnetic-field of 48 cm with a fluctuation of less than 2 nT is obtained.

  2. 欧洲空间原子钟组ACES 与超高精度时频传递技术新进展%Advances in Atomic Clock Ensemble in Space of Europe and Ultraprecise Time and Frequency Transfer

    Institute of Scientific and Technical Information of China (English)

    杨文可; 孟文东; 韩文标; 谢勇辉; 任晓乾; 胡小工; 董文丽

    2016-01-01

    高精度时间频率的产生和超高精度时频信号的传递是现代物理学、天文学和计量科学的基础。空间原子钟组计划(Atomic Clock Ensemble in Space, ACES)是由欧洲空间局实施的基于国际空间站(International Space Station, ISS)微重力环境下的新型空间微波原子钟实验验证项目。概要介绍ACES项目基本情况,重点介绍ACES项目的主要科学和技术目标,围绕科学目标而形成的ACES 组成结构,并梳理涉及的关键技术,特别介绍了ACES 将应用的超高精度时频传递技术,为我国自主研究并实现相关空间时间频率系统及其应用提供参考。最后简述了我国正在建设的空间站时频系统主要情况和实施计划。%One of the foundations for the development of modern physics, astronomy and metrology is the generation, transfer and measurement of high precision time frequency signals. As a space mission for the study of high precision time frequency signals, Atomic Clock Ensemble in Space, or ACES, sponsored by European Space Agency to launch in 2017 or later, will take advantage of the excellent stability performance of microwave atomic clocks in a microgravity environment. One clock using laser-cooled Cs atoms working together with one hydrogen maser clock are planned to be placed onboard the International Space Station in hope to produce a frequency standard with both accuracy and stability reaching the level of 10−16. A microwave link along with a laser link will be set up between ACES and ground atomic clocks distributed around the world for high precision comparison and transfer. Various basic researches will benefit from a high precision space atomic clock such as the verification of Einstein’s general relativity, detection of possible time variability of certain fundamental constants in physics, as well as brand new applications such as relativistic gravity and GNSS remote sensing. This paper reviews and summarizes the

  3. First observation of the strongly forbidden transition {sup 1}S{sub 0} - {sup 3}P{sub 0} in Strontium, for an atomic clock with trapped atoms; Premiere observation de la transition fortement interdite {sup 1}S{sub 0} - {sup 3}P{sub 0} du strontium, pour une horloge optique a atomes pieges

    Energy Technology Data Exchange (ETDEWEB)

    Courtillot, I

    2003-11-01

    This thesis reports the first results towards the realization of an optical clock using trapped strontium atoms. This set up would combine advantages of the different approaches commonly used to develop an atomic frequency standard. The first part describes the cold atoms source which is implemented. A magneto-optical trap operating on the {sup 1}S{sub 0}-{sup 1}P{sub 1} transition at 461 nm is loaded from an atomic beam decelerated by a Zeeman slower. The 461 nm laser is obtained by sum-frequency mixing in a potassium titanyl phosphate (KTP) crystal. The second part is devoted to the different stages developed to achieve the direct excitation of the {sup 1}S{sub 0}-{sup 3}P{sub 0} clock transition in {sup 87}Sr. This line has a theoretical natural width of 10{sup -3} Hz. Before this detection, we obtained an estimate of the resonance frequency by measuring absolute frequencies of several allowed optical transitions. (author)

  4. Body Clock

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2000-01-01

    “Body clocks” are biological methods of controling body activities.Every living thing has one. In humans, a body clock controls normal periods of sleeping and waking. It controls the time swhen you are most likely to feel pain.Eating, sleeping and exercising at about the same time each day will help keep body activities normal. But changes in your life, a new job, for example, destroy the balance and thus cause health problems.

  5. Performances evaluation of the PHARAO atomic fountain: participation to the study of the PHARAO space clock; Evaluation des performances de la fontaine atomique PHARAO, participation a l'etude de l'horloge spatiale PHARAO

    Energy Technology Data Exchange (ETDEWEB)

    Abgrall, M

    2003-01-01

    The performances of an atomic frequency standard depend drastically on the observation time of the atoms. The interrogation of laser cooled atoms allows to obtain about half a second interaction time in a fountain geometry. This duration could be much more varied in absence of gravity, and would allow a better trade-off between stability and accuracy. The application of this principle is the aim of the PHARAO project, that should attend to the ACES mission planned in 2006 onboard the International Space Station. The first part of this thesis deals with the cold Cs{sup 133} PHARAO fountain. This clock stems from the transformation of a space clock prototype previously tested in microgravity. A detailed evaluation of the whole frequency shifts has been carried out, reaching a 7.7 10{sup -16} accuracy and a 1.7 10{sup -13}{tau}{sup -1/2} short term stability. These values are obtained for 4 10{sup 5} detected atoms, that provides a good stability-accuracy trade-off. This transportable fountain, built at BNM-SYRTE, has been operating at MPQ in Munich (Germany). The collaboration between the 2 laboratories gave a {approx} 10 improvement factor on the measurement accuracy (1.8 10{sup -14}) for the 1S - 2S two photons hydrogen transition. In a second part of this thesis, we present the characterisation of 2 elements of the PHARAO space clock: the construction of a standard extended cavity laser and the test of the phase symmetry between the two interrogating areas of the space cavity. (author)

  6. Distinction between Clock and Time, and a Suggested Experiment with Different Types of Clocks in GPS

    Science.gov (United States)

    Smarandache, Florentin

    2013-03-01

    The clock is an instrument for measuring the time, instrument that may not run perfectly (accurately) under certain conditions (like, say, in strong electromagnetic field, in strong gravitational field, in extremely high or low temperature, pressure, etc.), but this does not mean that time itself runs slower or faster as Einstein's Theory of Relativity asserts. We are referring to an absolute time, i.e. time measured not with respect to ether or non-ether, but with respect to an absolute mathematical reference frame. Several types of clocks could run at a more slowly rate in a moving frame of reference than other types of clocks; it depends on the construction material and functioning principle of each type of clock. Relativists say that ``gravity slows time''. This is incorrect, since actually gravity slows today's types of clocks. And one type of clock is slowed more or less than another type of clock. Not only gravity but other (electric, magnetic, etc.) fields or various medium composition elements or structures may slow or accelerate clocks that are in that medium. The clocks used today in the satellites for the GPS necessitate a correction with respect to the Earth clocks. But in the future, when new types of clocks will be built based on different construction material and functioning principle, the correction of the GPS clocks would be different. In order to make the distinction between ``clock'' and ``time'', we suggest a Experiment # 1 with different types of clocks for the GPS clocks, in order to prove that the resulted dilation and contraction factors are different from those obtained with today's cesium atomic clock.

  7. Synthetic Spin-Orbit Coupling in an Optical Lattice Clock

    Science.gov (United States)

    Wall, Michael L.; Koller, Andrew P.; Li, Shuming; Zhang, Xibo; Cooper, Nigel R.; Ye, Jun; Rey, Ana Maria

    2016-01-01

    We propose the use of optical lattice clocks operated with fermionic alkaline-earth atoms to study spin-orbit coupling (SOC) in interacting many-body systems. The SOC emerges naturally during the clock interrogation, when atoms are allowed to tunnel and accumulate a phase set by the ratio of the "magic" lattice wavelength to the clock transition wavelength. We demonstrate how standard protocols such as Rabi and Ramsey spectroscopy that take advantage of the sub-Hertz resolution of state-of-the-art clock lasers can perform momentum-resolved band tomography and determine SOC-induced s -wave collisions in nuclear-spin-polarized fermions. With the use of a second counterpropagating clock beam, we propose a method for engineering controlled atomic transport and study how it is modified by p - and s -wave interactions. The proposed spectroscopic probes provide clean and well-resolved signatures at current clock operating temperatures.

  8. Noise in state of the art clocks and their impact for fundamental physics

    Science.gov (United States)

    Maleki, L.

    2001-01-01

    In this paper a review of the use of advanced atomic clocks in testing the fundamental physical laws will be presented. Noise sources of clocks will be discussed, together with an outline their characterization based on current models. The paper will conclude with a discussion of recent attempts to reduce the fundamental, as well as technical noise in atomic clocks.

  9. Internal Clock Drift Estimation in Computer Clusters

    Directory of Open Access Journals (Sweden)

    Hicham Marouani

    2008-01-01

    Full Text Available Most computers have several high-resolution timing sources, from the programmable interrupt timer to the cycle counter. Yet, even at a precision of one cycle in ten millions, clocks may drift significantly in a single second at a clock frequency of several GHz. When tracing the low-level system events in computer clusters, such as packet sending or reception, each computer system records its own events using an internal clock. In order to properly understand the global system behavior and performance, as reported by the events recorded on each computer, it is important to estimate precisely the clock differences and drift between the different computers in the system. This article studies the clock precision and stability of several computer systems, with different architectures. It also studies the typical network delay characteristics, since time synchronization algorithms rely on the exchange of network packets and are dependent on the symmetry of the delays. A very precise clock, based on the atomic time provided by the GPS satellite network, was used as a reference to measure clock drifts and network delays. The results obtained are of immediate use to all applications which depend on computer clocks or network time synchronization accuracy.

  10. Magic Wavelengths for Terahertz Clock Transitions

    OpenAIRE

    Zhou, Xiaoji; Xu, Xia; Chen, Xuzong; Chen, Jingbiao

    2010-01-01

    Magic wavelengths for laser trapping of boson isotopes of alkaline-earth Sr, Ca and Mg atoms are investigated while considering terahertz clock transitions between the $^{3}P_{0}, ^{3}P_{1}, ^{3}P_{2}$ metastable triplet states. Our calculation shows that magic wavelengths of trapping laser do exist. This result is important because those metastable states have already been used to realize accurate clocks in the terahertz frequency domain. Detailed discussions for magic wavelength for teraher...

  11. Atoms

    Institute of Scientific and Technical Information of China (English)

    刘洪毓

    2007-01-01

    Atoms(原子)are all around us.They are something like the bricks (砖块)of which everything is made. The size of an atom is very,very small.In just one grain of salt are held millions of atoms. Atoms are very important.The way one object acts depends on what

  12. Lego clocks: building a clock from parts.

    Science.gov (United States)

    Brunner, Michael; Simons, Mirre J P; Merrow, Martha

    2008-06-01

    A new finding opens up speculation that the molecular mechanism of circadian clocks in Synechococcus elongatus is composed of multiple oscillator systems (Kitayama and colleagues, this issue, pp. 1513-1521), as has been described in many eukaryotic clock model systems. However, an alternative intepretation is that the pacemaker mechanism-as previously suggested-lies primarily in the rate of ATP hydrolysis by the clock protein KaiC.

  13. Optical Clocks in Space

    CERN Document Server

    Schiller, S; Nevsky, A; Koelemeij, J C J; Wicht, A; Gill, P; Klein, H A; Margolis, H S; Mileti, G; Sterr, U; Riehle, F; Peik, E; Tamm, C; Ertmer, W; Rasel, E; Klein, V; Salomon, C; Tino, G M; Lemonde, P; Holzwarth, R; Hänsch, T W; Tamm, Chr.

    2007-01-01

    The performance of optical clocks has strongly progressed in recent years, and accuracies and instabilities of 1 part in 10^18 are expected in the near future. The operation of optical clocks in space provides new scientific and technological opportunities. In particular, an earth-orbiting satellite containing an ensemble of optical clocks would allow a precision measurement of the gravitational redshift, navigation with improved precision, mapping of the earth's gravitational potential by relativistic geodesy, and comparisons between ground clocks.

  14. Frequency comparison of optical lattice clocks beyond the Dick limit

    Science.gov (United States)

    Takamoto, Masao; Takano, Tetsushi; Katori, Hidetoshi

    2011-05-01

    The supreme accuracy of atomic clocks relies on the universality of atomic transition frequencies. The stability of a clock, meanwhile, measures how quickly the clock's statistical uncertainties are reduced. The ultimate measure of stability is provided by the quantum projection noise, which improves as 1/√N by measuring N uncorrelated atoms. Quantum projection noise limited stabilities have been demonstrated in caesium clocks and in single-ion optical clocks, where the quantum noise overwhelms the Dick effect attributed to local oscillator noise. Here, we demonstrate a synchronous frequency comparison of two optical lattice clocks using 87Sr and 88Sr atoms, respectively, for which the Allan standard deviation reached 1 × 10-17 in an averaging time of 1,600 s by cancelling out the Dick effect to approach the quantum projection noise limit. The scheme demonstrates the advantage of using a large number (N ~ 1,000) of atoms in optical clocks and paves the way to investigating the inherent uncertainties of clocks and relativistic geodesy on a timescale of tens of minutes.

  15. Hanle Detection for Optical Clocks

    Directory of Open Access Journals (Sweden)

    Xiaogang Zhang

    2015-01-01

    Full Text Available Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423 nm fluorescence, the improved 657 nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard.

  16. Frequency Ratio of ${}^{199}$Hg and ${}^{87}$Sr Optical Lattice Clocks beyond the SI Limit

    CERN Document Server

    Yamanaka, Kazuhiro; Ushijima, Ichiro; Takamoto, Masao; Katori, Hidetoshi

    2015-01-01

    We report on a frequency ratio measurement of a ${}^{199}$Hg-based optical lattice clock referencing a ${}^{87}$Sr-based clock. Evaluations of lattice light shift, including atomic-motion-dependent shift, enable us to achieve a total systematic uncertainty of $7.2 \\times 10^{-17}$ for the Hg clock. The frequency ratio is measured to be $\

  17. Stability Transfer between Two Clock Lasers Operating at Different Wavelengths for Absolute Frequency Measurement of Clock Transition in 87Sr

    CERN Document Server

    Yamaguchi, A; Nagano, S; Li, Y; Ishijima, H; Hachisu, H; Kumagai, M; Ido, T; 10.1143/APEX.5.022701

    2012-01-01

    We demonstrated transferring the stability of one highly stable clock laser operating at 729 nm to another less stable laser operating at 698 nm. The two different wavelengths were bridged using an optical frequency comb. The improved stability of the clock laser at 698 nm enabled us to evaluate the systematic frequency shifts of the Sr optical lattice clock with shorter averaging time. We determined the absolute frequency of the clock transition 1S0 - 3P0 in 87Sr to be 429 228 004 229 873.9 (1.4) Hz referenced to the SI second on the geoid via International Atomic Time (TAI).

  18. Realization of a time-scale with an optical clock

    CERN Document Server

    Grebing, C; Dörscher, S; Häfner, S; Gerginov, V; Weyers, S; Lipphardt, B; Riehle, F; Sterr, U; Lisdat, C

    2015-01-01

    Optical clocks are not only powerful tools for prime fundamental research, but are also deemed for the re-definition of the SI base unit second as they surpass the performance of caesium atomic clocks in both accuracy and stability by more than an order of magnitude. However, an important obstacle in this transition has so far been the limited reliability of the optical clocks that made a continuous realization of a time-scale impractical. In this paper, we demonstrate how this dilemma can be resolved and that a time-scale based on an optical clock can be established that is superior to one based on even the best caesium fountain clocks. The paper also gives further proof of the international consistency of strontium lattice clocks on the $10^{-16}$ accuracy level, which is another prerequisite for a change in the definition of the second.

  19. Orbitography for next generation space clocks

    CERN Document Server

    Duchayne, Loïc; Wolf, Peter

    2007-01-01

    Over the last decade of the 20th century and the first few years of the 21st, the uncertainty of atomic clocks has decreased by about two orders of magnitude, passing from the low 10^-14 to below 10^-16, in relative frequency . Space applications in fundamental physics, geodesy, time/frequency metrology, navigation etc... are among the most promising for this new generation of clocks. Onboard terrestrial or solar system satellites, their exceptional frequency stability and accuracy makes them a prime tool to test the fundamental laws of nature, and to study gravitational potentials and their evolution. In this paper, we study in more detail the requirements on orbitography compatible with operation of next generation space clocks at the required uncertainty based on a completely relativistic model. Using the ACES (Atomic Clock Ensemble in Space) mission as an example, we show that the required accuracy goal can be reached with relatively modest constraints on the orbitography of the space clock, much less str...

  20. Clocked combustor can array

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Won-Wook; McMahan, Kevin Weston; Srinivasan, Shiva Kumar

    2017-01-17

    The present application provides a clocked combustor can array for coherence reduction in a gas turbine engine. The clocked combustor can array may include a number of combustor cans positioned in a circumferential array. A first set of the combustor cans may have a first orientation and a second set of the combustor cans may have a second orientation.

  1. Prototype of the DLR Operational Composite Clock: Methods and Test Cases

    Science.gov (United States)

    2009-11-01

    Study of Time Scale Algorithms,” Metrologia , 28, 57-63. [2] R. Jones and P. Tryon, 1983, “Estimating Time From Atomic Clocks,” Journal of Research of...L. Galleani and P. Tavella, 2008, “Detection and identification of atomic clock anomalies,” Metrologia , 45, 127-133. [16] C. Zucca and P

  2. Resetting Biological Clocks

    Science.gov (United States)

    Winfree, Arthur T.

    1975-01-01

    Reports on experiments conducted on two biological clocks, in organisms in the plant and animal kingdoms, which indicate that biological oscillation can be arrested by a single stimulus of a definite strength delivered at the proper time. (GS)

  3. High-Performance Coherent Population Trapping Clock with Polarization Modulation

    Science.gov (United States)

    Yun, Peter; Tricot, François; Calosso, Claudio Eligio; Micalizio, Salvatore; François, Bruno; Boudot, Rodolphe; Guérandel, Stéphane; de Clercq, Emeric

    2017-01-01

    We demonstrate a vapor-cell atomic-clock prototype based on a continuous-wave interrogation and double-modulation coherent population trapping (DM-CPT) technique. The DM-CPT technique uses a synchronous modulation of polarization and the relative phase of a bichromatic laser beam in order to increase the number of atoms trapped in a dark state, i.e., a nonabsorbing state. The narrow resonance, observed in the transmission of a Cs vapor cell, is used as a narrow frequency discriminator in an atomic clock. A detailed characterization of the CPT resonance versus numerous parameters is reported. A short-term fractional-frequency stability of 3.2 ×10-13τ-1 /2 up to a 100-s averaging time is measured. These performances are more than one order of magnitude better than industrial Rb clocks and are comparable to those of the best laboratory-prototype vapor-cell clocks. The noise-budget analysis shows that the short- and midterm frequency stability is mainly limited by the power fluctuations of the microwave used to generate the bichromatic laser. These preliminary results demonstrate that the DM-CPT technique is well suited for the development of a high-performance atomic clock, with the potential compact and robust setup due to its linear architecture. This clock could find future applications in industry, telecommunications, instrumentation, or global navigation satellite systems.

  4. Detection of weak frequency jumps for GNSS onboard clocks.

    Science.gov (United States)

    Huang, Xinming; Gong, Hang; Ou, Gang

    2014-05-01

    In this paper, a weak frequency jump detection method is developed for onboard clocks in global navigation satellite systems (GNSS). A Kalman filter is employed to facilitate the onboard real-time processing of atomic clock measurements, whose N-step prediction residuals are used to construct the weak frequency jump detector. Numerical simulations show that the method can successfully detect weak frequency jumps. The detection method proposed in this paper is helpful for autonomous integrity monitoring of GNSS satellite clocks, and can also be applied to other frequency anomalies with an appropriately modified detector.

  5. General relativistic effects in quantum interference of "clocks"

    CERN Document Server

    Zych, Magdalena; Costa, Fabio; Brukner, Časlav

    2016-01-01

    Quantum mechanics and general relativity have been each successfully tested in numerous experiments. However, the regime where both theories are jointly required to explain physical phenomena remains untested by laboratory experiments, and is also not fully understood by theory. This contribution reviews recent ideas for a new type of experiments: quantum interference of "clocks", which aim to test novel quantum effects that arise from time dilation. "Clock" interference experiments could be realised with atoms or photons in near future laboratory experiments.

  6. Frequency ratios of Sr, Yb and Hg based optical lattice clocks and their applications

    CERN Document Server

    Takamoto, Masao; Das, Manoj; Nemitz, Nils; Ohkubo, Takuya; Yamanaka, Kazuhiro; Ohmae, Noriaki; Takano, Tetsushi; Akatsuka, Tomoya; Yamaguchi, Atsushi; Katori, Hidetoshi

    2015-01-01

    This article describes the recent progress of optical lattice clocks with neutral strontium ($^{87}$Sr), ytterbium ($^{171}$Yb) and mercury ($^{199}$Hg) atoms. In particular, we present frequency comparison between the clocks locally via an optical frequency comb and between two Sr clocks at remote sites using a phase-stabilized fibre link. We first review cryogenic Sr optical lattice clocks that reduce the room-temperature blackbody radiation shift by two orders of magnitude and serve as a reference in the following clock comparisons. Similar physical properties of Sr and Yb atoms, such as transition wavelengths and vapour pressure, have allowed our development of a compatible clock for both species. A cryogenic Yb clock is evaluated by referencing a Sr clock. We also report on a Hg clock, which shows one order of magnitude less sensitivity to blackbody radiation, while its large nuclear charge makes the clock sensitive to the variation of fine-structure constant. Connecting all three types of clocks by an o...

  7. On clocks and clouds

    Directory of Open Access Journals (Sweden)

    M. K. Witte

    2013-09-01

    Full Text Available Cumulus clouds exhibit a life cycle that consists of: (a the growth phase (increasing size, most notably in the vertical direction; (b the mature phase (growth ceases; any precipitation that develops is strongest during this period; and (c the dissipation phase (cloud dissipates because of precipitation and/or entrainment; no more dynamical support. Although radar can track clouds over time and give some sense of the age of a cloud, most aircraft in situ measurements lack temporal context. We use large eddy simulations of trade wind cumulus cloud fields from cases during the Barbados Oceanographic and Meteorological Experiment (BOMEX and Rain In Cumulus over the Ocean (RICO campaigns to demonstrate a potential cumulus cloud "clock". We find that the volume-averaged total water mixing ratio rt is a useful cloud clock for the 12 clouds studied. A cloud's initial rt is set by the subcloud mixed-layer mean rt and decreases monotonically from the initial value due primarily to entrainment. The clock is insensitive to aerosol loading, environmental sounding and extrinsic cloud properties such as lifetime and volume. In some cases (more commonly for larger clouds, multiple pulses of buoyancy occur, which complicate the cumulus clock by replenishing rt. The clock is most effectively used to classify clouds by life phase.

  8. Relativistic quantum clocks

    CERN Document Server

    Lock, Maximilian P E

    2016-01-01

    The conflict between quantum theory and the theory of relativity is exemplified in their treatment of time. We examine the ways in which their conceptions differ, and describe a semiclassical clock model combining elements of both theories. The results obtained with this clock model in flat spacetime are reviewed, and the problem of generalizing the model to curved spacetime is discussed, before briefly describing an experimental setup which could be used to test of the model. Taking an operationalist view, where time is that which is measured by a clock, we discuss the conclusions that can be drawn from these results, and what clues they contain for a full quantum relativistic theory of time.

  9. Analysis of Atom-Interferometer Clocks

    Science.gov (United States)

    2014-01-21

    particle has been mostly ignored [3]. But in recent years it has appeared in the literature with claims that the redshift of the Compton oscillation... literature it has been claimed that ω0 does not correspond to a physical oscillation, with the points being made that it is not Doppler shifted to an...Peters, and S. Chu, Nature (London) 463, 926 (2010). [5] P. Catillon, N. Cue, M. J. Gaillard, R. Genre , M. Gouanère, R. G. Kirsch, J. C. Poizat, J

  10. SRC: Smart Reminder Clock

    Science.gov (United States)

    Kasim, Shahreen; Hafit, Hanayanti; Leong, Tan Hua; Hashim, Rathiah; Ruslai, Husni; Jahidin, Kamaruzzaman; Syafwan Arshad, Mohammad

    2016-11-01

    Nowadays, some people facing the problem to wake up in the morning. This was result to absence of the classes, meetings, and even exams. The aim of this project is to develop an android application that can force the user to wake up. The method used in this application are pedometer and Short Message Service (SMS) function. This application need the user to take their smartphone and walk about 10 steps to disable it, when the alarm clock is activated. After that, when the alarm clock was rang, this alarm application has automatically send a message to the users’ friends or parents phone to wake them up.

  11. Evaluation of Long Term Performance of Continuously Running Atomic Fountains

    Science.gov (United States)

    2014-05-28

    Observatory (USNO). These fountains are used as continuous clocks in the manner of commercial caesium beams and hydrogen masers for the purpose of improved...clock, rubidium fountain, operational atomic fountain (Some figures may appear in colour only in the online journal) 1. Introduction: beyond caesiums ...and masers The performance of atomic clocks has improved more than seven orders of magnitude since the first caesium clock was demonstrated by Essen

  12. Decamp Clock Board Firmware

    Energy Technology Data Exchange (ETDEWEB)

    Vicente, J. de; Castilla, J.; Martinez, G.

    2007-09-27

    Decamp (Dark Energy Survey Camera) is a new instrument designed to explore the universe aiming to reveal the nature of Dark Energy. The camera consists of 72 CCDs and 520 Mpixels. The readout electronics of DECam is based on the Monsoon system. Monsoon is a new image acquisition system developed by the NOAO (National Optical Astronomical Observatory) for the new generation of astronomical cameras. The Monsoon system uses three types of boards inserted in a Eurocard format based crate: master control board, acquisition board and clock board. The direct use of the Monsoon system for DECam readout electronics requires nine crates mainly due to the high number of clock boards needed. Unfortunately, the available space for DECam electronics is constrained to four crates at maximum. The major drawback to achieve such desired compaction degree resides in the clock board signal density. This document describes the changes performed at CIEMAT on the programmable logic of the Monsoon clock board aiming to meet such restricted space constraints. (Author) 5 refs.

  13. Cyclotomic quantum clock

    CERN Document Server

    Rosu, H C

    2003-01-01

    In the wake of our recent work on cyclotomic effects in quantum phase locking [M. Planat and H. C. Rosu, Phys. Lett. A 315, 1 (2003)], we briefly discuss here a cyclotomic extension of the Salecker and Wigner quantum clock. We also hint on a possible cyclotomic structure of time at the Planck scales

  14. The absolute frequency of the 87Sr optical clock transition

    DEFF Research Database (Denmark)

    Campbell, Gretchen K.; Ludlow, Andrew D.; Blatt, Sebastian;

    2008-01-01

    The absolute frequency of the 1S0–3P0 clock transition of 87Sr has been measured to be 429 228 004 229 873.65 (37) Hz using lattice-confined atoms, where the fractional uncertainty of 8.6 × 10-16 represents one of the most accurate measurements of an atomic transition frequency to date. After a d...... is made possible using a femtosecond laser based optical frequency comb to phase coherently connect the optical and microwave spectral regions and by a 3.5 km fibre transfer scheme to compare the remotely located clock signals....

  15. Relativity and Al^+ Optical Clocks

    Science.gov (United States)

    Chou, Chin-Wen; Hume, David B.; Wineland, David J.; Rosenband, Till

    2010-03-01

    We have constructed an optical clock based on quantum logic spectroscopy of an Al+ ion that has a fractional frequency inaccuracy of 8.6x10-18. The frequency of the ^1S0^3P0 clock transition is compared to that of a previously constructed Al^+ optical clock with a statistical measurement uncertainty of 7.0x10-18. The two clocks exhibit a relative stability of 2.8x10-15&-1/2circ;, and a fractional frequency difference of -1.8x10-17, consistent with the accuracy limit of the older clock. By comparing the frequencies of the clocks, we have observed relativistic effects, such as time dilation due to velocities less than 10 m/s and the gravitational red shift from a 0.33 m height change of one of the clocks.

  16. Round the clock librarianship

    OpenAIRE

    1995-01-01

    The concept of Round the Clock Librarianship (ROCLOLIB) is one such opportunity of terminal and critical importance to librarians, which helps people (clients) in general and reassures them about the professional commitment and devotedness of librarians. Although the concept is old, it is an exercise here to analyse its importance for the overall image and status of the practice/occupation. The chapter discusses the proposal of opening Libraries for 24 Hours. It also points out the reasons fo...

  17. Circadian clocks and breast cancer

    OpenAIRE

    Blakeman, Victoria; Jack L. Williams; Meng, Qing-Jun; Streuli, Charles H

    2016-01-01

    Circadian clocks respond to environmental time cues to coordinate 24-hour oscillations in almost every tissue of the body. In the breast, circadian clocks regulate the rhythmic expression of numerous genes. Disrupted expression of circadian genes can alter breast biology and may promote cancer. Here we overview circadian mechanisms, and the connection between the molecular clock and breast biology. We describe how disruption of circadian genes contributes to cancer via multiple mechanisms, an...

  18. Radium single-ion optical clock

    CERN Document Server

    Versolato, O O; Jungmann, K; Timmermans, R G E; Willmann, L; Wilschut, H W

    2011-01-01

    We explore the potential of the electric quadrupole transitions $7s\\,^2S_{1/2}$ - $6d\\,^2D_{3/2}$, $6d\\,^2D_{5/2}$ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition $7s\\,^2S_{1/2}\\,(F=2,m_F=0)$ - $6d\\,^2D_{3/2}\\,(F=0,m_F=0)$ at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.

  19. A Light Clock Satisfying the Clock Hypothesis of Special Relativity

    Science.gov (United States)

    West, Joseph

    2007-01-01

    The design of the FMEL, a floor-mirrored Einstein-Langevin "light clock", is introduced. The clock provides a physically intuitive manner to calculate and visualize the time dilation effects for a spatially extended set of observers (an accelerated "frame") undergoing unidirectional acceleration or observers on a rotating cylinder of constant…

  20. Frequency shift due to blackbody radiation in a cesium atomic fountain and improvement of the clock performances; Deplacement de frequence du au rayonnement du corps noir dans une fontaine atomique a cesium et amelioration des performances de l'horloge

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, S

    2004-07-01

    FO1 was the first caesium fountain primary frequency standard in the world. The most recent evaluation in 2002 before improvement reached an accuracy of 1*10{sup -15} when operated with optical molasses. Working as an extremely precise and stable instrument, FO1 has contributed to fundamental physics and technical measurements: - Frequency comparison between Cs and Rb fountains over an interval of 5 years sets an upper limit for a possible variation of the fine structure constant as |alpha/alpha| < 2*10{sup -15}/y. The resolution is about 5 times better than the previous test in our laboratory. The projected accuracy of the space clock PHARAO is 1*10{sup -16}. We confirmed its Ramsey cavity performance by testing the phase difference between the two interaction zones in FO1. The measured temperature T dependent frequency shift of the Cs clock induced by the blackbody radiation field is given as nu(T)=154(6)*10{sup -6}*(T/300){sup 4}[1+{epsilon}(T/300){sup 2}] Hz with the theoretical value {epsilon} = 0,014. The obtained accuracy represents a 3 times improvement over the previous measurement by the PTB group. Some improvements have been carried out on FO1. The new FO1 version works directly with optical molasses loaded by a laser slowed atomic beam. The application of the adiabatic passage method to perform the state selection allows us to determine the atom number dependent frequency shifts due to the cold collision and cavity pulling effects at a level of of 10{sup -16}. Recently, the obtained frequency stability is 2,8*10{sup -14}*{tau}{sup -1/2} for about 4*10{sup 6} detected atoms. The accuracy is currently under evaluation, the expected value is a few times 10{sup -16}. (author)

  1. Clocks and cardiovascular function

    Science.gov (United States)

    McLoughlin, Sarah C.; Haines, Philip; FitzGerald, Garret A.

    2016-01-01

    Circadian clocks in central and peripheral tissues enable the temporal synchronization and organization of molecular and physiological processes of rhythmic animals, allowing optimum functioning of cells and organisms at the most appropriate time of day. Disruption of circadian rhythms, from external or internal forces, leads to widespread biological disruption and is postulated to underlie many human conditions, such as the incidence and timing of cardiovascular disease. Here, we describe in vivo and in vitro methodology relevant to studying the role of circadian rhythms in cardiovascular function and dysfunction PMID:25707279

  2. CSAC Characterization and Its Impact on GNSS Clock Augmentation Performance

    Directory of Open Access Journals (Sweden)

    Enric Fernández

    2017-02-01

    Full Text Available Chip Scale Atomic Clocks (CSAC are recently-developed electronic instruments that, when used together with a Global Navigation Satellite Systems (GNSS receiver, help improve the performance of GNSS navigation solutions in certain conditions (i.e., low satellite visibility. Current GNSS receivers include a Temperature Compensated Cristal Oscillator (TCXO clock characterized by a short-term stability (τ = 1 s of 10−9 s that leads to an error of 0.3 m in pseudorange measurements. The CSAC can achieve a short-term stability of 2.5 × 10−12 s, which implies a range error of 0.075 m, making for an 87.5% improvement over TCXO. Replacing the internal TCXO clock of GNSS receivers with a higher frequency stability clock such as a CSAC oscillator improves the navigation solution in terms of low satellite visibility positioning accuracy, solution availability, signal recovery (holdover, multipath and jamming mitigation and spoofing attack detection. However, CSAC suffers from internal systematic instabilities and errors that should be minimized if optimal performance is desired. Hence, for operating CSAC at its best, the deterministic errors from the CSAC need to be properly modelled. Currently, this modelling is done by determining and predicting the clock frequency stability (i.e., clock bias and bias rate within the positioning estimation process. The research presented in this paper aims to go a step further, analysing the correlation between temperature and clock stability noise and the impact of its proper modelling in the holdover recovery time and in the positioning performance. Moreover, it shows the potential of fine clock coasting modelling. With the proposed model, an improvement in vertical positioning precision of around 50% with only three satellites can be achieved. Moreover, an increase in the navigation solution availability is also observed, a reduction of holdover recovery time from dozens of seconds to only a few can be achieved.

  3. CSAC Characterization and Its Impact on GNSS Clock Augmentation Performance

    Science.gov (United States)

    Fernández, Enric; Calero, David; Parés, M. Eulàlia

    2017-01-01

    Chip Scale Atomic Clocks (CSAC) are recently-developed electronic instruments that, when used together with a Global Navigation Satellite Systems (GNSS) receiver, help improve the performance of GNSS navigation solutions in certain conditions (i.e., low satellite visibility). Current GNSS receivers include a Temperature Compensated Cristal Oscillator (TCXO) clock characterized by a short-term stability (τ = 1 s) of 10−9 s that leads to an error of 0.3 m in pseudorange measurements. The CSAC can achieve a short-term stability of 2.5 × 10−12 s, which implies a range error of 0.075 m, making for an 87.5% improvement over TCXO. Replacing the internal TCXO clock of GNSS receivers with a higher frequency stability clock such as a CSAC oscillator improves the navigation solution in terms of low satellite visibility positioning accuracy, solution availability, signal recovery (holdover), multipath and jamming mitigation and spoofing attack detection. However, CSAC suffers from internal systematic instabilities and errors that should be minimized if optimal performance is desired. Hence, for operating CSAC at its best, the deterministic errors from the CSAC need to be properly modelled. Currently, this modelling is done by determining and predicting the clock frequency stability (i.e., clock bias and bias rate) within the positioning estimation process. The research presented in this paper aims to go a step further, analysing the correlation between temperature and clock stability noise and the impact of its proper modelling in the holdover recovery time and in the positioning performance. Moreover, it shows the potential of fine clock coasting modelling. With the proposed model, an improvement in vertical positioning precision of around 50% with only three satellites can be achieved. Moreover, an increase in the navigation solution availability is also observed, a reduction of holdover recovery time from dozens of seconds to only a few can be achieved. PMID:28216600

  4. Highly charged ions as a basis of optical atomic clockwork of exceptional accuracy.

    Science.gov (United States)

    Derevianko, Andrei; Dzuba, V A; Flambaum, V V

    2012-11-02

    We propose a novel class of atomic clocks based on highly charged ions. We consider highly forbidden laser-accessible transitions within the 4f(12) ground-state configurations of highly charged ions. Our evaluation of systematic effects demonstrates that these transitions may be used for building exceptionally accurate atomic clocks which may compete in accuracy with recently proposed nuclear clocks.

  5. A mixed relaxed clock model

    Science.gov (United States)

    2016-01-01

    Over recent years, several alternative relaxed clock models have been proposed in the context of Bayesian dating. These models fall in two distinct categories: uncorrelated and autocorrelated across branches. The choice between these two classes of relaxed clocks is still an open question. More fundamentally, the true process of rate variation may have both long-term trends and short-term fluctuations, suggesting that more sophisticated clock models unfolding over multiple time scales should ultimately be developed. Here, a mixed relaxed clock model is introduced, which can be mechanistically interpreted as a rate variation process undergoing short-term fluctuations on the top of Brownian long-term trends. Statistically, this mixed clock represents an alternative solution to the problem of choosing between autocorrelated and uncorrelated relaxed clocks, by proposing instead to combine their respective merits. Fitting this model on a dataset of 105 placental mammals, using both node-dating and tip-dating approaches, suggests that the two pure clocks, Brownian and white noise, are rejected in favour of a mixed model with approximately equal contributions for its uncorrelated and autocorrelated components. The tip-dating analysis is particularly sensitive to the choice of the relaxed clock model. In this context, the classical pure Brownian relaxed clock appears to be overly rigid, leading to biases in divergence time estimation. By contrast, the use of a mixed clock leads to more recent and more reasonable estimates for the crown ages of placental orders and superorders. Altogether, the mixed clock introduced here represents a first step towards empirically more adequate models of the patterns of rate variation across phylogenetic trees. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325829

  6. Development of a strontium optical lattice clock for space applications

    Science.gov (United States)

    Singh, Yeshpal

    2016-07-01

    With timekeeping being of paramount importance for modern life, much research and major scientific advances have been undertaken in the field of frequency metrology, particularly over the last few years. New Nobel-prize winning technologies have enabled a new era of atomic clocks; namely the optical clock. These have been shown to perform significantly better than the best microwave clocks reaching an inaccuracy of 1.6x10-18 [1]. With such results being found in large lab based apparatus, the focus now has shifted to portability - to enable the accuracy of various ground based clocks to be measured, and compact autonomous performance - to enable such technologies to be tested in space. This could lead to a master clock in space, improving not only the accuracy of technologies on which modern life has come to require such as GPS and communication networks. But also more fundamentally, this could lead to the redefinition of the second and tests of fundamental physics including applications in the fields of ground based and satellite geodesy, metrology, positioning, navigation, transport and logistics etc. Within the European collaboration, Space Optical Clocks (SOC2) [2-3] consisting of various institutes and industry partners across Europe we have tried to tackle this problem of miniaturisation whilst maintaining stability, accuracy (5x10-17) and robustness whilst keeping power consumption to a minimum - necessary for space applications. We will present the most recent results of the Sr optical clock in SOC2 and also the novel compact design features, new methods employed and outlook. References [1] B. J. Bloom, T. L. Nicholson, J. R. Williams, S. L. Campbell, M. Bishof, X. Zhang, W. Zhang, S. L. Bromley, and J. Ye, "An optical lattice clock with accuracy and stability at the 10-18 level," Nature 506, 71-75 (2014). [2] S. Schiller et al. "Towards Neutral-atom Space Optical Clocks (SOC2): Development of high-performance transportable and breadboard optical clocks and

  7. High-performance coherent population trapping clock with polarization modulation

    CERN Document Server

    Yun, Peter; Calosso, Claudio Eligio; Micalizio, Salvatore; François, Bruno; Boudot, Rodolphe; Guérandel, Stéphane; de Clercq, Emeric

    2016-01-01

    We demonstrate a vapor cell atomic clock prototype based on continuous-wave (CW) interrogation and double-modulation coherent population trapping (DM-CPT) technique. The DM-CPT technique uses a synchronous modulation of polarization and relative phase of a bi-chromatic laser beam in order to increase the number of atoms trapped in a dark state, i.e. a non-absorbing state. The narrow resonance, observed in transmission of a Cs vapor cell, is used as a narrow frequency discriminator in an atomic clock. A detailed characterization of the CPT resonance versus numerous parameters is reported. A short-term frequency stability of $3.2 \\times 10^{-13} \\tau^{-1/2}$ up to 100 s averaging time is measured. These performances are more than one order of magnitude better than industrial Rb clocks and comparable to those of best laboratory-prototype vapor cell clocks. The noise budget analysis shows that the short and mid-term frequency stability is mainly limited by the power fluctuations of the microwave used to generate ...

  8. Clocks around Sgr A*

    CERN Document Server

    Angélil, Raymond

    2014-01-01

    The S stars near the Galactic centre and any pulsars that may be on similar orbits, can be modelled in a unified way as clocks orbiting a black hole, and hence are potential probes of relativistic effects, including block-hole spin. The high eccentricities of many S stars mean that relativistic effects peak strongly around pericentre; for example, orbit precession is not a smooth effect but almost a kick at pericentre. We argue that concentration around pericentre will be an advantage when analysing redshift or pulse-arrival data to measure relativistic effects, because cumulative precession will be drowned out by Newtonian perturbations from other mass in the Galactic-centre region. Wavelet decomposition may be a way to disentangle relativistic effects from Newton perturbations. Assuming a plausible model for Newtonian perturbations on S2, relativity appears to be strongest in a two-year interval around pericentre, in wavelet modes of timescale approximately 6 months.

  9. Clock Genes in Glia Cells

    Science.gov (United States)

    Chi-Castañeda, Donají

    2016-01-01

    Circadian rhythms are periodic patterns in biological processes that allow the organisms to anticipate changes in the environment. These rhythms are driven by the suprachiasmatic nucleus (SCN), the master circadian clock in vertebrates. At a molecular level, circadian rhythms are regulated by the so-called clock genes, which oscillate in a periodic manner. The protein products of clock genes are transcription factors that control their own and other genes’ transcription, collectively known as “clock-controlled genes.” Several brain regions other than the SCN express circadian rhythms of clock genes, including the amygdala, the olfactory bulb, the retina, and the cerebellum. Glia cells in these structures are expected to participate in rhythmicity. However, only certain types of glia cells may be called “glial clocks,” since they express PER-based circadian oscillators, which depend of the SCN for their synchronization. This contribution summarizes the current information about clock genes in glia cells, their plausible role as oscillators and their medical implications. PMID:27666286

  10. Simulating Future GPS Clock Scenarios with Two Composite Clock Algorithms

    Science.gov (United States)

    2010-11-01

    Alexandria, Virginia), pp. 223-242. [8] C. A. Greenhall, 2007, “A Kalman filter clock ensemble algorithm that admits measurement noise,” Metrologia ...43, S311-S321. [9] J. A. Davis, C. A. Greenhall, and P. W. Stacey, 2005, “A Kalman filter clock algorithm for use in the presence of flicker frequency modulation noise,” Metrologia , 42, 1-10.

  11. Circadian clock components in the rat neocortex

    DEFF Research Database (Denmark)

    Rath, Martin Fredensborg; Rohde, Kristian; Fahrenkrug, Jan

    2013-01-01

    The circadian master clock of the mammalian brain resides in the suprachiasmatic nucleus (SCN) of the hypothalamus. At the molecular level, the clock of the SCN is driven by a transcriptional/posttranslational autoregulatory network with clock gene products as core elements. Recent investigations...... have shown the presence of peripheral clocks in extra-hypothalamic areas of the central nervous system. However, knowledge on the clock gene network in the cerebral cortex is limited. We here show that the mammalian clock genes Per1, Per2, Per3, Cry1, Cry2, Bmal1, Clock, Nr1d1 and Dbp are expressed...

  12. Einstein's Clocks and Langevin's Twins

    CERN Document Server

    Weinstein, Galina

    2012-01-01

    In 1905 Einstein presented the Clock Paradox and in 1911 Paul Langevin expanded Einstein's result to human observers, the "Twin Paradox." I will explain the crucial difference between Einstein and Langevin. Einstein did not present the so-called "Twin Paradox." Later Einstein continued to speak about the clock paradox. Einstein might not have been interested in the question: what happens to the observers themselves. The reason for this could be the following; Einstein dealt with measurement procedures, clocks and measuring rods. Einstein's observers were measuring time with these clocks and measuring rods. Einstein might not have been interested in so-called biology of the observers, whether these observers were getting older, younger, or whether they have gone any other changes; these changes appeared to be out of the scope of his "Principle of relativity" or kinematics. The processes and changes occurring within observers seemed to be good for philosophical discussions. Later writers criticized Einstein's c...

  13. Quantum Repeaters and Atomic Ensembles

    DEFF Research Database (Denmark)

    Borregaard, Johannes

    a previous protocol, thereby enabling fast local processing, which greatly enhances the distribution rate. We then move on to describe our work on improving the stability of atomic clocks using entanglement. Entanglement can potentially push the stability of atomic clocks to the so-called Heisenberg limit......, which is the absolute upper limit of the stability allowed by the Heisenberg uncertainty relation. It has, however, been unclear whether entangled state’s enhanced sensitivity to noise would prevent reaching this limit. We have developed an adaptive measurement protocol, which circumvents this problem...... based on atomic ensembles....

  14. Testing the Gravitational Redshift with Atomic Gravimeters?

    CERN Document Server

    Wolf, Peter; Bordé, Christian J; Reynaud, Serge; Salomon, Christophe; Cohen-Tannoudji, Claude

    2011-01-01

    Atom interferometers allow the measurement of the acceleration of freely falling atoms with respect to an experimental platform at rest on Earth's surface. Such experiments have been used to test the universality of free fall by comparing the acceleration of the atoms to that of a classical freely falling object. In a recent paper, M\\"uller, Peters and Chu [Nature {\\bf 463}, 926-929 (2010)] argued that atom interferometers also provide a very accurate test of the gravitational redshift (or universality of clock rates). Considering the atom as a clock operating at the Compton frequency associated with the rest mass, they claimed that the interferometer measures the gravitational redshift between the atom-clocks in the two paths of the interferometer at different values of gravitational potentials. In the present paper we analyze this claim in the frame of general relativity and of different alternative theories, and conclude that the interpretation of atom interferometers as testing the gravitational redshift ...

  15. Cooling of rubidium atoms in pulsed diffuse laser light

    Institute of Scientific and Technical Information of China (English)

    Cheng Hua-Dong; Wang Xu-Cheng; Xiao Ling; Zhang Wen-Zhuo; Liu Liang; Wang Yu-Zhu

    2011-01-01

    This paper reports an experiment on laser cooling of 87Rb atoms in pulsed diffuse light, which is the key step towards a compact cold atom clock. It deduces an empirical formula to simulate the pulse cooling process based on the loading of cold atoms in cooling time and the loss in the dead time, which is in agreement with the experimental data. The formula gives a reference to select the parameters for the cold atom clock.

  16. A scheme for implementing quantum clock synchronization algorithm in cavity QED

    Institute of Scientific and Technical Information of China (English)

    Wu Qin-Qin; Kuang Le-Man

    2006-01-01

    In this paper, we propose a scheme for implementing the quantum clock synchronization (QCS) algorithm in cavity quantum electrodynamic (QED) formalism. Our method is based on three-level ladder-type atoms interacting with classical and quantized cavity fields. Atom-qubit realizations of three-qubit and four-qubit QCS algorithms are explicitly presented.

  17. Spin-orbit coupled fermions in an optical lattice clock

    CERN Document Server

    Kolkowitz, S; Bothwell, T; Wall, M L; Marti, G E; Koller, A P; Zhang, X; Rey, A M; Ye, J

    2016-01-01

    Engineered spin-orbit coupling (SOC) in cold atom systems can aid in the study of novel synthetic materials and complex condensed matter phenomena. Despite great advances, alkali atom SOC systems are hindered by heating from spontaneous emission, which limits the observation of many-body effects. Here we demonstrate the use of optical lattice clocks (OLCs) to engineer and study SOC with metrological precision and negligible heating. We show that clock spectroscopy of the ultra-narrow transition in fermionic 87Sr represents a momentum- and spin-resolved in situ probe of the SOC band structure and eigenstates, providing direct access to the SOC dynamics and control over lattice band populations, internal electronic states, and quasimomenta. We utilize these capabilities to study Bloch oscillations, spin-momentum locking, and van Hove singularities in the transition density of states. Our results lay the groundwork for the use of OLCs to probe novel SOC phases including magnetic crystals, helical liquids, and to...

  18. Simulation of the clock framework of Gaia

    CERN Document Server

    Castaneda, J; Portell, J; García-Berro, E; Luri, X; Castaneda, Javier; Gordo, Jose P.; Portell, Jordi; Garcia-Berro, Enrique; Luri, Xavier

    2005-01-01

    Gaia will perform astrometric measurements with an unprecedented resolution. Consequently, the electronics of the Astro instrument must time tag every measurement with a precision of a few nanoseconds. Hence, it requires a high stability clock signal, for which a Rb-type spacecraft master clock has been baselined. The distribution of its signal and the generation of clock subproducts must maintain these high accuracy requirements. We have developed a software application to simulate generic clock frameworks. The most critical clock structures for Gaia have also been identified, and its master clock has been parameterised.

  19. Circadian clocks, epigenetics, and cancer

    KAUST Repository

    Masri, Selma

    2015-01-01

    The interplay between circadian rhythm and cancer has been suggested for more than a decade based on the observations that shift work and cancer incidence are linked. Accumulating evidence implicates the circadian clock in cancer survival and proliferation pathways. At the molecular level, multiple control mechanisms have been proposed to link circadian transcription and cell-cycle control to tumorigenesis.The circadian gating of the cell cycle and subsequent control of cell proliferation is an area of active investigation. Moreover, the circadian clock is a transcriptional system that is intricately regulated at the epigenetic level. Interestingly, the epigenetic landscape at the level of histone modifications, DNA methylation, and small regulatory RNAs are differentially controlled in cancer cells. This concept raises the possibility that epigenetic control is a common thread linking the clock with cancer, though little scientific evidence is known to date.This review focuses on the link between circadian clock and cancer, and speculates on the possible connections at the epigenetic level that could further link the circadian clock to tumor initiation or progression.

  20. Types for X10 Clocks

    Directory of Open Access Journals (Sweden)

    Francisco Martins

    2011-10-01

    Full Text Available X10 is a modern language built from the ground up to handle future parallel systems, from multicore machines to cluster configurations. We take a closer look at a pair of synchronisation mechanisms: finish and clocks. The former waits for the termination of parallel computations, the latter allow multiple concurrent activities to wait for each other at certain points in time. In order to better understand these concepts we study a type system for a stripped down version of X10. The main result assures that well typed programs do not run into the errors identified in the X10 language reference, namely the ClockUseException. The study will open, we hope, doors to a more flexible utilisation of clocks in the X10 language.

  1. Metabolic regulation of circadian clocks.

    Science.gov (United States)

    Haydon, Michael J; Hearn, Timothy J; Bell, Laura J; Hannah, Matthew A; Webb, Alex A R

    2013-05-01

    Circadian clocks are 24-h timekeeping mechanisms, which have evolved in plants, animals, fungi and bacteria to anticipate changes in light and temperature associated with the rotation of the Earth. The current paradigm to explain how biological clocks provide timing information is based on multiple interlocking transcription-translation negative feedback loops (TTFL), which drive rhythmic gene expression and circadian behaviour of growth and physiology. Metabolism is an important circadian output, which in plants includes photosynthesis, starch metabolism, nutrient assimilation and redox homeostasis. There is increasing evidence in a range of organisms that these metabolic outputs can also contribute to circadian timing and might also comprise independent circadian oscillators. In this review, we summarise the mechanisms of circadian regulation of metabolism by TTFL and consider increasing evidence that rhythmic metabolism contributes to the circadian network. We highlight how this might be relevant to plant circadian clock function.

  2. Synchronous clock stopper for microprocessor

    Science.gov (United States)

    Kitchin, David A. (Inventor)

    1985-01-01

    A synchronous clock stopper circuit for inhibiting clock pulses to a microprocessor in response to a stop request signal, and for reinstating the clock pulses in response to a start request signal thereby to conserve power consumption of the microprocessor when used in an environment of limited power. The stopping and starting of the microprocessor is synchronized, by a phase tracker, with the occurrences of a predetermined phase in the instruction cycle of the microprocessor in which the I/O data and address lines of the microprocessor are of high impedance so that a shared memory connected to the I/O lines may be accessed by other peripheral devices. The starting and stopping occur when the microprocessor initiates and completes, respectively, an instruction, as well as before and after transferring data with a memory. Also, the phase tracker transmits phase information signals over a bus to other peripheral devices which signals identify the current operational phase of the microprocessor.

  3. The NIST 27 Al+ quantum-logic clock

    Science.gov (United States)

    Leibrandt, David; Brewer, Samuel; Chen, Jwo-Sy; Hume, David; Hankin, Aaron; Huang, Yao; Chou, Chin-Wen; Rosenband, Till; Wineland, David

    2016-05-01

    Optical atomic clocks based on quantum-logic spectroscopy of the 1 S0 3 P0 transition in 27 Al+ have reached a systematic fractional frequency uncertainty of 8 . 0 ×10-18 , enabling table-top tests of fundamental physics as well as measurements of gravitational potential differences. Currently, the largest limitations to the accuracy are second order time dilation shifts due to the driven motion (i.e., micromotion) and thermal motion of the trapped ions. In order to suppress these shifts, we have designed and built new ion traps based on gold-plated, laser-machined diamond wafers with differential RF drive, and we have operated one of our clocks with the ions laser cooled to near the six mode motional ground state. We present a characterization of the time dilation shifts in the new traps with uncertainties near 1 ×10-18 . Furthermore, we describe a new protocol for clock comparison measurements based on synchronous probing of the two clocks using phase-locked local oscillators, which allows for probe times longer than the laser coherence time and avoids the Dick effect. This work is supported by ARO, DARPA, and ONR.

  4. Single-transistor-clocked flip-flop

    Science.gov (United States)

    Zhao, Peiyi; Darwish, Tarek; Bayoumi, Magdy

    2005-08-30

    The invention provides a low power, high performance flip-flop. The flip-flop uses only one clocked transistor. The single clocked transistor is shared by the first and second branches of the device. A pulse generator produces a clock pulse to trigger the flip-flop. In one preferred embodiment the device can be made as a static explicit pulsed flip-flop which employs only two clocked transistors.

  5. BMAL1 and CLOCK, two essential components of the circadian clock, are involved in glucose homeostasis.

    Directory of Open Access Journals (Sweden)

    R Daniel Rudic

    2004-11-01

    Full Text Available Circadian timing is generated through a unique series of autoregulatory interactions termed the molecular clock. Behavioral rhythms subject to the molecular clock are well characterized. We demonstrate a role for Bmal1 and Clock in the regulation of glucose homeostasis. Inactivation of the known clock components Bmal1 (Mop3 and Clock suppress the diurnal variation in glucose and triglycerides. Gluconeogenesis is abolished by deletion of Bmal1 and is depressed in Clock mutants, but the counterregulatory response of corticosterone and glucagon to insulin-induced hypoglycaemia is retained. Furthermore, a high-fat diet modulates carbohydrate metabolism by amplifying circadian variation in glucose tolerance and insulin sensitivity, and mutation of Clock restores the chow-fed phenotype. Bmal1 and Clock, genes that function in the core molecular clock, exert profound control over recovery from insulin-induced hypoglycaemia. Furthermore, asynchronous dietary cues may modify glucose homeostasis via their interactions with peripheral molecular clocks.

  6. Light and the human circadian clock

    NARCIS (Netherlands)

    Roenneberg, Till; Kantermann, Thomas; Juda, Myriam; Vetter, Céline; Allebrandt, Karla V

    2013-01-01

    The circadian clock can only reliably fulfil its function if it is stably entrained. Most clocks use the light-dark cycle as environmental signal (zeitgeber) for this active synchronisation. How we think about clock function and entrainment has been strongly influenced by the early concepts of the f

  7. Biological clocks: riding the tides.

    Science.gov (United States)

    de la Iglesia, Horacio O; Johnson, Carl Hirschie

    2013-10-21

    Animals with habitats in the intertidal zone often display biological rhythms that coordinate with both the tidal and the daily environmental cycles. Two recent studies show that the molecular components of the biological clocks mediating tidal rhythms are likely different from the phylogenetically conserved components that mediate circadian (daily) rhythms.

  8. A generalized gravitomagnetic clock effect

    CERN Document Server

    Hackmann, Eva

    2014-01-01

    In General Relativity the rotation of a gravitating body like the Earth influences the motion of orbiting test particles or satellites in a non-Newtonian way. This causes e.g. a precession of the orbital plane, known as the Lense-Thirring effect, and a precession of the spin of a gyroscope, known as the Schiff effect. Here we discuss a third effect, first introduced by Cohen and Mashhoon, called the gravitomagnetic clock effect. It describes the difference in proper time of counter revolving clocks after a revolution of $2\\pi$. For two clocks on counter rotating equatorial circular orbits around the Earth the effect is about $10^{-7}$ seconds per revolution, which is quite large. We introduce a general relativistic definition of the gravitomagnetic clock effect which is valid for arbitrary pairs of orbits. This includes rotations in the same direction and different initial conditions, which is crucial if the effect can be detected with existing satellites or with payloads on non-dedicated missions. We also de...

  9. Mercury Atomic Frequency Standards for Space Based Navigation and Timekeeping

    Science.gov (United States)

    Tjoelker, R. L.; Burt, E. A.; Chung, S.; Hamell, R. L.; Prestage, J. D.; Tucker, B.; Cash, P.; Lutwak, R.

    2012-01-01

    A low power Mercury Atomic Frequency Standard (MAFS) has been developed and demonstrated on the path towards future space clock applications. A self contained mercury ion breadboard clock: emulating flight clock interfaces, steering a USO local oscillator, and consuming approx 40 Watts has been operating at JPL for more than a year. This complete, modular ion clock instrument demonstrates that key GNSS size, weight, and power (SWaP) requirements can be achieved while still maintaining short and long term performance demonstrated in previous ground ion clocks. The MAFS breadboard serves as a flexible platform for optimizing further space clock development and guides engineering model design trades towards fabrication of an ion clock for space flight.

  10. Synthetic dimensions and spin-orbit coupling with an optical clock transition

    CERN Document Server

    Livi, L F; Diem, M; Franchi, L; Clivati, C; Frittelli, M; Levi, F; Calonico, D; Catani, J; Inguscio, M; Fallani, L

    2016-01-01

    We demonstrate a novel way of synthesizing spin-orbit interactions in ultracold quantum gases, based on a single-photon optical clock transition coupling two long-lived electronic states of two-electron $^{173}$Yb atoms. By mapping the electronic states onto effective sites along a synthetic "electronic" dimension, we have engineered synthetic fermionic ladders with tunable magnetic fluxes. We have detected the spin-orbit coupling with fiber-link-enhanced clock spectroscopy and directly measured the emergence of chiral edge currents, probing them as a function of the magnetic field flux. These results open new directions for the investigation of topological states of matter with ultracold atomic gases.

  11. Circadian clock, cell cycle and cancer

    Directory of Open Access Journals (Sweden)

    Cansu Özbayer

    2011-12-01

    Full Text Available There are a few rhythms of our daily lives that we are under the influence. One of them is characterized by predictable changes over a 24-hour timescale called circadian clock. This cellular clock is coordinated by the suprachiasmatic nucleus in the anterior hypothalamus. The clock consist of an autoregulatory transcription-translation feedback loop compose of four genes/proteins; BMAL1, Clock, Cyrptochrome, and Period. BMAL 1 and Clock are transcriptional factors and Period and Cyrptochrome are their targets. Period and Cyrptochrome dimerize in the cytoplasm to enter the nucleus where they inhibit Clock/BMAL activity.It has been demonstrate that circadian clock plays an important role cellular proliferation, DNA damage and repair mechanisms, checkpoints, apoptosis and cancer.

  12. Ultra-stable clock laser system development towards space applications

    Science.gov (United States)

    Świerad, Dariusz; Häfner, Sebastian; Vogt, Stefan; Venon, Bertrand; Holleville, David; Bize, Sébastien; Kulosa, André; Bode, Sebastian; Singh, Yeshpal; Bongs, Kai; Rasel, Ernst Maria; Lodewyck, Jérôme; Le Targat, Rodolphe; Lisdat, Christian; Sterr, Uwe

    2016-09-01

    The increasing performance of optical lattice clocks has made them attractive for scientific applications in space and thus has pushed the development of their components including the interrogation lasers of the clock transitions towards being suitable for space, which amongst others requires making them more power efficient, radiation hardened, smaller, lighter as well as more mechanically stable. Here we present the development towards a space-compatible interrogation laser system for a strontium lattice clock constructed within the Space Optical Clock (SOC2) project where we have concentrated on mechanical rigidity and size. The laser reaches a fractional frequency instability of 7.9 × 10-16 at 300 ms averaging time. The laser system uses a single extended cavity diode laser that gives enough power for interrogating the atoms, frequency comparison by a frequency comb and diagnostics. It includes fibre link stabilisation to the atomic package and to the comb. The optics module containing the laser has dimensions 60 × 45 × 8 cm3 and the ultra-stable reference cavity used for frequency stabilisation with its vacuum system takes 30 × 30 × 30 cm3. The acceleration sensitivities in three orthogonal directions of the cavity are 3.6 × 10-10/g, 5.8 × 10-10/g and 3.1 × 10-10/g, where g ≈ 9.8 m/s2 is the standard gravitational acceleration.

  13. Researchers Discover Plants Biological Clock

    Institute of Scientific and Technical Information of China (English)

    王全良

    1996-01-01

    Scientists who created glow-in-the-dark plants by shooting up seedlingswith firefly DNA have identified the first biological clock gene in plants. Discovery of the timepiece gene, which controls such biological rhythmsas daily leaf movements and proe openings, flower-blooming schedules andphotosynthesis cycles, could lead to a host of applications in ornamental horti-culture, agriculture and even human health. Many researchers believe that

  14. Physical Layer Ethernet Clock Synchronization

    Science.gov (United States)

    2010-11-01

    42 nd Annual Precise Time and Time Interval (PTTI) Meeting 77 PHYSICAL LAYER ETHERNET CLOCK SYNCHRONIZATION Reinhard Exel , Georg...5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES...Austrian Academy of Sciences Viktor Kaplan StraÃe 2, A-2700 Wiener Neustadt, Austria 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING

  15. Entanglement of quantum clocks through gravity.

    Science.gov (United States)

    Castro Ruiz, Esteban; Giacomini, Flaminia; Brukner, Časlav

    2017-03-21

    In general relativity, the picture of space-time assigns an ideal clock to each world line. Being ideal, gravitational effects due to these clocks are ignored and the flow of time according to one clock is not affected by the presence of clocks along nearby world lines. However, if time is defined operationally, as a pointer position of a physical clock that obeys the principles of general relativity and quantum mechanics, such a picture is, at most, a convenient fiction. Specifically, we show that the general relativistic mass-energy equivalence implies gravitational interaction between the clocks, whereas the quantum mechanical superposition of energy eigenstates leads to a nonfixed metric background. Based only on the assumption that both principles hold in this situation, we show that the clocks necessarily get entangled through time dilation effect, which eventually leads to a loss of coherence of a single clock. Hence, the time as measured by a single clock is not well defined. However, the general relativistic notion of time is recovered in the classical limit of clocks.

  16. Cellular circadian clocks in mood disorders.

    Science.gov (United States)

    McCarthy, Michael J; Welsh, David K

    2012-10-01

    Bipolar disorder (BD) and major depressive disorder (MDD) are heritable neuropsychiatric disorders associated with disrupted circadian rhythms. The hypothesis that circadian clock dysfunction plays a causal role in these disorders has endured for decades but has been difficult to test and remains controversial. In the meantime, the discovery of clock genes and cellular clocks has revolutionized our understanding of circadian timing. Cellular circadian clocks are located in the suprachiasmatic nucleus (SCN), the brain's primary circadian pacemaker, but also throughout the brain and peripheral tissues. In BD and MDD patients, defects have been found in SCN-dependent rhythms of body temperature and melatonin release. However, these are imperfect and indirect indicators of SCN function. Moreover, the SCN may not be particularly relevant to mood regulation, whereas the lateral habenula, ventral tegmentum, and hippocampus, which also contain cellular clocks, have established roles in this regard. Dysfunction in these non-SCN clocks could contribute directly to the pathophysiology of BD/MDD. We hypothesize that circadian clock dysfunction in non-SCN clocks is a trait marker of mood disorders, encoded by pathological genetic variants. Because network features of the SCN render it uniquely resistant to perturbation, previous studies of SCN outputs in mood disorders patients may have failed to detect genetic defects affecting non-SCN clocks, which include not only mood-regulating neurons in the brain but also peripheral cells accessible in human subjects. Therefore, reporters of rhythmic clock gene expression in cells from patients or mouse models could provide a direct assay of the molecular gears of the clock, in cellular clocks that are likely to be more representative than the SCN of mood-regulating neurons in patients. This approach, informed by the new insights and tools of modern chronobiology, will allow a more definitive test of the role of cellular circadian clocks

  17. Improved frequency measurement of the $^1S_{0}$-$^3P_{0}$ clock transition in $^{87}$Sr using the Cs fountain clock at NMIJ as a transfer oscillator

    CERN Document Server

    Tanabe, Takehiko; Kobayashi, Takumi; Takamizawa, Akifumi; Yanagimachi, Shinya; Ikegami, Takeshi; Suzuyama, Tomonari; Inaba, Hajime; Okubo, Sho; Yasuda, Masami; Hong, Feng-Lei; Onae, Atsushi; Hosaka, Kazumoto

    2015-01-01

    We performed an absolute frequency measurement of the $^1S_{0}$-$^3P_{0}$ transition in $^{87}$Sr with a fractional uncertainty of $1.2 \\times 10^{-15}$, which is less than one third that of our previous measurement. A caesium fountain atomic clock was used as a transfer oscillator to reduce the uncertainty of the link between a strontium optical lattice clock and the SI second. The absolute value of the transition frequency is 429 228 004 229 873.56(49) Hz.

  18. Magnetic-dipole transitions in highly charged ions as a basis of ultraprecise optical clocks.

    Science.gov (United States)

    Yudin, V I; Taichenachev, A V; Derevianko, A

    2014-12-05

    We evaluate the feasibility of using magnetic-dipole (M1) transitions in highly charged ions as a basis of an optical atomic clockwork of exceptional accuracy. We consider a range of possibilities, including M1 transitions between clock levels of the same fine-structure and hyperfine-structure manifolds. In highly charged ions these transitions lie in the optical part of the spectra and can be probed with lasers. The most direct advantage of our proposal comes from the low degeneracy of clock levels and the simplicity of atomic structure in combination with negligible quadrupolar shift. We demonstrate that such clocks can have projected fractional accuracies below the 10^{-20}-10^{-21} level for all common systematic effects, such as blackbody radiation, Zeeman, ac-Stark, and quadrupolar shifts.

  19. The circadian clock coordinates ribosome biogenesis.

    Directory of Open Access Journals (Sweden)

    Céline Jouffe

    Full Text Available Biological rhythms play a fundamental role in the physiology and behavior of most living organisms. Rhythmic circadian expression of clock-controlled genes is orchestrated by a molecular clock that relies on interconnected negative feedback loops of transcription regulators. Here we show that the circadian clock exerts its function also through the regulation of mRNA translation. Namely, the circadian clock influences the temporal translation of a subset of mRNAs involved in ribosome biogenesis by controlling the transcription of translation initiation factors as well as the clock-dependent rhythmic activation of signaling pathways involved in their regulation. Moreover, the circadian oscillator directly regulates the transcription of ribosomal protein mRNAs and ribosomal RNAs. Thus the circadian clock exerts a major role in coordinating transcription and translation steps underlying ribosome biogenesis.

  20. Atom gravimeters and gravitational redshift

    CERN Document Server

    Wolf, Peter; Borde, Christian J; Reynaud, Serge; Salomon, Christophe; Cohen-Tannoudji, Claude; 10.1038/nature09340

    2010-01-01

    In a recent paper, H. Mueller, A. Peters and S. Chu [A precision measurement of the gravitational redshift by the interference of matter waves, Nature 463, 926-929 (2010)] argued that atom interferometry experiments published a decade ago did in fact measure the gravitational redshift on the quantum clock operating at the very high Compton frequency associated with the rest mass of the Caesium atom. In the present Communication we show that this interpretation is incorrect.

  1. Optical to microwave clock frequency ratios with a nearly continuous strontium optical lattice clock

    CERN Document Server

    Lodewyck, Jérôme; Bookjans, Eva; Robyr, Jean-Luc; Shi, Chunyan; Vallet, Grégoire; Targat, Rodolphe Le; Nicolodi, Daniele; Coq, Yann Le; Guéna, Jocelyne; Abgrall, Michel; Rosenbusch, Peter; Bize, Sébastien

    2016-01-01

    Optical lattice clocks are at the forefront of frequency metrology. Both the instability and systematic uncertainty of these clocks have been reported to be two orders of magnitude smaller than the best microwave clocks. For this reason, a redefinition of the SI second based on optical clocks seems possible in the near future. However, the operation of optical lattice clocks has not yet reached the reliability that microwave clocks have achieved so far. In this paper, we report on the operation of a strontium optical lattice clock that spans several weeks, with more than 80% uptime. We make use of this long integration time to demonstrate a reproducible measurement of frequency ratios between the strontium clock transition and microwave Cs primary and Rb secondary frequency standards.

  2. The Square Light Clock and Special Relativity

    Science.gov (United States)

    Galli, J. Ronald; Amiri, Farhang

    2012-01-01

    A thought experiment that includes a square light clock is similar to the traditional vertical light beam and mirror clock, except it is made up of four mirrors placed at a 45[degree] angle at each corner of a square of length L[subscript 0], shown in Fig. 1. Here we have shown the events as measured in the rest frame of the square light clock. By…

  3. A Mathematical Model of the Liver Circadian Clock Linking Feeding and Fasting Cycles to Clock Function

    OpenAIRE

    Aurore Woller; Hélène Duez; Bart Staels; Marc Lefranc

    2016-01-01

    To maintain energy homeostasis despite variable energy supply and consumption along the diurnal cycle, the liver relies on a circadian clock synchronized to food timing. Perturbed feeding and fasting cycles have been associated with clock disruption and metabolic diseases; however, the mechanisms are unclear. To address this question, we have constructed a mathematical model of the mammalian circadian clock, incorporating the metabolic sensors SIRT1 and AMPK. The clock response to various tem...

  4. Comparing a mercury optical lattice clock with microwave and optical frequency standards

    CERN Document Server

    Tyumenev, R; Bilicki, S; Bookjans, E; Targat, R Le; Lodewyck, J; Nicolodi, D; Coq, Y Le; Abgrall, M; Guéna, J; De Sarlo, L; Bize, S

    2016-01-01

    In this paper we report the evaluation of an optical lattice clock based on neutral mercury down to a relative uncertainty of $1.7\\times 10^{-16}$. Comparing this characterized frequency standard to a Cs atomic fountain we determine the absolute frequency of the $^1S_0 \\rightarrow \\phantom{}^3P_0$ transition of $^{199}$Hg as $\

  5. A quantum many-body spin system in an optical lattice clock

    CERN Document Server

    Martin, M J; Swallows, M D; Zhang, X; Benko, C; von-Stecher, J; Gorshkov, A V; Rey, A M; Ye, Jun

    2013-01-01

    Strongly interacting quantum many-body systems are fundamentally compelling and ubiquitous in science. However, their complexity generally prevents exact solutions of their dynamics. Precisely engineered ultracold atomic gases are emerging as a powerful tool to unravel these challenging physical problems. Here we present a new laboratory for the study of many-body effects: strongly interacting two-level systems formed by the clock states in ${}^{87}$Sr, which are used to realize a neutral atom optical clock that performs at the highest level of optical-atomic coherence and with precision near the limit set by quantum fluctuations. Our measurements of the collective spin evolution reveal signatures of many-body dynamics, including beyond-mean-field effects. We derive a many-body Hamiltonian that describes the experimental observation of severely distorted lineshapes, atomic spin coherence decay, density-dependent frequency shifts, and correlated quantum spin noise. These investigations open the door to explori...

  6. Clock genes, pancreatic function, and diabetes.

    Science.gov (United States)

    Vieira, Elaine; Burris, Thomas P; Quesada, Ivan

    2014-12-01

    Circadian physiology is responsible for the temporal regulation of metabolism to optimize energy homeostasis throughout the day. Disturbances in the light/dark cycle, sleep/wake schedule, or feeding/activity behavior can affect the circadian function of the clocks located in the brain and peripheral tissues. These alterations have been associated with impaired glucose tolerance and type 2 diabetes. Animal models with molecular manipulation of clock genes and genetic studies in humans also support these links. It has been demonstrated that the endocrine pancreas has an intrinsic self-sustained clock, and recent studies have revealed an important role of clock genes in pancreatic β cells, glucose homeostasis, and diabetes.

  7. Experimenting an optical second with strontium lattice clocks

    CERN Document Server

    Targat, R Le; Coq, Y Le; Zawada, M; Guéna, J; Abgrall, M; Gurov, M; Rosenbusch, P; Rovera, D G; Nagórny, B; Gartman, R; Westergaard, P G; Tobar, M E; Lours, M; Santarelli, G; Clairon, A; Bize, S; Laurent, P; Lemonde, P; Lodewyck, J

    2013-01-01

    Progress in realizing the SI second had multiple technological impacts and enabled to further constraint theoretical models in fundamental physics. Caesium microwave fountains, realizing best the second according to its current definition with a relative uncertainty of 2-4x10^(-16), have already been superseded by atomic clocks referenced to an optical transition, both more stable and more accurate. Are we ready for a new definition of the second? Here we present an important step in this direction: our system of five clocks connects with an unprecedented consistency the optical and the microwave worlds. For the first time, two state-of-the-art strontium optical lattice clocks are proven to agree within their accuracy budget, with a total uncertainty of 1.6x10^(-16). Their comparison with three independent caesium fountains shows a degree of reproducibility henceforth solely limited at the level of 3.1x10^(-16) by the best realizations of the microwave-defined second.

  8. Superradiance on the mHz linewidth clock transition in 87Sr

    Science.gov (United States)

    Norcia, Matthew; Winchester, Matthew; Cline, Julia; Thompson, James

    2016-05-01

    In this talk, I will discuss our recent experimental explorations of superradiant emission from the mHz linewidth clock transition in an ensemble of cold 87 Sr atoms confined within a high-finesse optical cavity. Recent proposals suggest that superradiant lasers based on such dipole-forbidden transitions in alkaline earth atoms could achieve linewidths below the current state of the art, with reduced sensitivity to environmental perturbations.

  9. Probing Many-Body Interactions in an Optical Lattice Clock (Preprint)

    Science.gov (United States)

    2013-10-23

    9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine energy levels of a caesium atom. Since then, the accuracy...as meter, volt and ampere. Thanks to the development of laser trapping and cooling techniques [1, 2], the best caesium standards have reached an...accuracy of one part in 1016. However, caesium clocks are limited by the fact that they are based on atomic transitions in the microwave domain. Because

  10. An atomic clockwork using phase dependent energy shifts

    CERN Document Server

    De Munshi, D; Mukherjee, M

    2011-01-01

    A frequency stabilized laser referenced to an unperturbed atomic two level system acts as the most accurate clock with femtosecond clock ticks. For any meaningful use, a Femtosecond Laser Frequency Comb (FLFC) is used to transfer the atomic clock accuracy to electronically countable nanosecond clock ticks. Here we propose an alternative clockwork based on the phenomenon that when an atomic system is slowly evolved in a cyclic path, the atomic energy levels gather some phase called the geometric phase. This geometric phase dependent energy shift has been used here to couple the two frequency regimes in a phase coherent manner. It has also been shown that such a technique can be implemented experimentally, bypassing the highly involved setup of a FLFC.

  11. Uncertainty principle in larmor clock

    Institute of Scientific and Technical Information of China (English)

    QIAO Chuan; REN Zhong-Zhou

    2011-01-01

    It is well known that the spin operators of a quantum particle must obey uncertainty relations.We use the uncertainty principle to study the Larmor clock.To avoid breaking the uncertainty principle,Larmor time can be defined as the ratio of the phase difference between a spin-up particle and a spin-down particle to the corresponding Larmor frequency.The connection between the dwell time and the Larmor time has also been confirmed.Moreover,the results show that the behavior of the Larmor time depends on the height and width of the barrier.

  12. Clock genes, chronotypes and diseases

    Directory of Open Access Journals (Sweden)

    Bogdan I. Voinescu

    2009-08-01

    Full Text Available Many common diseases in humans (such as cancer, heart disease, diabetes mellitus orpsychiatric disorders, such as depression seem to be linked to disruptions of circadian cycles and toclock genes variation. It is unlikely that such diseases to be caused by a genetic variation within a singlegene. They must be influenced by complex interactions among multiple genes, as well as environmentaland lifestyle factors. Therefore, it is important to understand how the resulting perturbations in ourcircadian biology could affect our physiological processes and susceptibility to disease. Associationsbetween the polymorphisms of the main components of the circadian molecular clock, circadian type(also known as diurnal preference or chronotype and diseases are presented.

  13. Circadian molecular clock in lung pathophysiology.

    Science.gov (United States)

    Sundar, Isaac K; Yao, Hongwei; Sellix, Michael T; Rahman, Irfan

    2015-11-15

    Disrupted daily or circadian rhythms of lung function and inflammatory responses are common features of chronic airway diseases. At the molecular level these circadian rhythms depend on the activity of an autoregulatory feedback loop oscillator of clock gene transcription factors, including the BMAL1:CLOCK activator complex and the repressors PERIOD and CRYPTOCHROME. The key nuclear receptors and transcription factors REV-ERBα and RORα regulate Bmal1 expression and provide stability to the oscillator. Circadian clock dysfunction is implicated in both immune and inflammatory responses to environmental, inflammatory, and infectious agents. Molecular clock function is altered by exposomes, tobacco smoke, lipopolysaccharide, hyperoxia, allergens, bleomycin, as well as bacterial and viral infections. The deacetylase Sirtuin 1 (SIRT1) regulates the timing of the clock through acetylation of BMAL1 and PER2 and controls the clock-dependent functions, which can also be affected by environmental stressors. Environmental agents and redox modulation may alter the levels of REV-ERBα and RORα in lung tissue in association with a heightened DNA damage response, cellular senescence, and inflammation. A reciprocal relationship exists between the molecular clock and immune/inflammatory responses in the lungs. Molecular clock function in lung cells may be used as a biomarker of disease severity and exacerbations or for assessing the efficacy of chronotherapy for disease management. Here, we provide a comprehensive overview of clock-controlled cellular and molecular functions in the lungs and highlight the repercussions of clock disruption on the pathophysiology of chronic airway diseases and their exacerbations. Furthermore, we highlight the potential for the molecular clock as a novel chronopharmacological target for the management of lung pathophysiology.

  14. Tectonic blocks and molecular clocks

    Science.gov (United States)

    2016-01-01

    Evolutionary timescales have mainly used fossils for calibrating molecular clocks, though fossils only really provide minimum clade age constraints. In their place, phylogenetic trees can be calibrated by precisely dated geological events that have shaped biogeography. However, tectonic episodes are protracted, their role in vicariance is rarely justified, the biogeography of living clades and their antecedents may differ, and the impact of such events is contingent on ecology. Biogeographic calibrations are no panacea for the shortcomings of fossil calibrations, but their associated uncertainties can be accommodated. We provide examples of how biogeographic calibrations based on geological data can be established for the fragmentation of the Pangaean supercontinent: (i) for the uplift of the Isthmus of Panama, (ii) the separation of New Zealand from Gondwana, and (iii) for the opening of the Atlantic Ocean. Biogeographic and fossil calibrations are complementary, not competing, approaches to constraining molecular clock analyses, providing alternative constraints on the age of clades that are vital to avoiding circularity in investigating the role of biogeographic mechanisms in shaping modern biodiversity. This article is part of the themed issue ‘Dating species divergences using rocks and clocks’. PMID:27325840

  15. Single electron relativistic clock interferometer

    Science.gov (United States)

    Bushev, P. A.; Cole, J. H.; Sholokhov, D.; Kukharchyk, N.; Zych, M.

    2016-09-01

    Although time is one of the fundamental notions in physics, it does not have a unique description. In quantum theory time is a parameter ordering the succession of the probability amplitudes of a quantum system, while according to relativity theory each system experiences in general a different proper time, depending on the system's world line, due to time dilation. It is therefore of fundamental interest to test the notion of time in the regime where both quantum and relativistic effects play a role, for example, when different amplitudes of a single quantum clock experience different magnitudes of time dilation. Here we propose a realization of such an experiment with a single electron in a Penning trap. The clock can be implemented in the electronic spin precession and its time dilation then depends on the radial (cyclotron) state of the electron. We show that coherent manipulation and detection of the electron can be achieved already with present day technology. A single electron in a Penning trap is a technologically ready platform where the notion of time can be probed in a hitherto untested regime, where it requires a relativistic as well as quantum description.

  16. Fast Clock Recovery for Digital Communications

    Science.gov (United States)

    Tell, R. G.

    1985-01-01

    Circuit extracts clock signal from random non-return-to-zero data stream, locking onto clock within one bit period at 1-gigabitper-second data rate. Circuit used for synchronization in opticalfiber communications. Derives speed from very short response time of gallium arsenide metal/semiconductor field-effect transistors (MESFET's).

  17. A circadian clock in Saccharomyces cerevisiae

    NARCIS (Netherlands)

    Eelderink-Chen, Zheng; Mazzotta, Gabriella; Sturre, Marcel; Bosman, Jasper; Roenneberg, Till; Merrow, Martha

    2010-01-01

    Circadian timing is a fundamental biological process, underlying cellular physiology in animals, plants, fungi, and cyanobacteria. Circadian clocks organize gene expression, metabolism, and behavior such that they occur at specific times of day. The biological clocks that orchestrate these daily cha

  18. Temperature influences in receiver clock modelling

    Science.gov (United States)

    Wang, Kan; Meindl, Michael; Rothacher, Markus; Schoenemann, Erik; Enderle, Werner

    2016-04-01

    In Precise Point Positioning (PPP), hardware delays at the receiver site (receiver, cables, antenna, …) are always difficult to be separated from the estimated receiver clock parameters. As a result, they are partially or fully contained in the estimated "apparent" clocks and will influence the deterministic and stochastic modelling of the receiver clock behaviour. In this contribution, using three years of data, the receiver clock corrections of a set of high-precision Hydrogen Masers (H-Masers) connected to stations of the ESA/ESOC network and the International GNSS Service (IGS) are firstly characterized concerning clock offsets, drifts, modified Allan deviations and stochastic parameters. In a second step, the apparent behaviour of the clocks is modelled with the help of a low-order polynomial and a known temperature coefficient (Weinbach, 2013). The correlations between the temperature and the hardware delays generated by different types of antennae are then analysed looking at daily, 3-day and weekly time intervals. The outcome of these analyses is crucial, if we intend to model the receiver clocks in the ground station network to improve the estimation of station-related parameters like coordinates, troposphere zenith delays and ambiguities. References: Weinbach, U. (2013) Feasibility and impact of receiver clock modeling in precise GPS data analysis. Dissertation, Leibniz Universität Hannover, Germany.

  19. "Molecular Clock" Analogs: A Relative Rates Exercise

    Science.gov (United States)

    Wares, John P.

    2008-01-01

    Although molecular clock theory is a commonly discussed facet of evolutionary biology, undergraduates are rarely presented with the underlying information of how this theory is examined relative to empirical data. Here a simple contextual exercise is presented that not only provides insight into molecular clocks, but is also a useful exercise for…

  20. Global synchronization of parallel processors using clock pulse width modulation

    Science.gov (United States)

    Chen, Dong; Ellavsky, Matthew R.; Franke, Ross L.; Gara, Alan; Gooding, Thomas M.; Haring, Rudolf A.; Jeanson, Mark J.; Kopcsay, Gerard V.; Liebsch, Thomas A.; Littrell, Daniel; Ohmacht, Martin; Reed, Don D.; Schenck, Brandon E.; Swetz, Richard A.

    2013-04-02

    A circuit generates a global clock signal with a pulse width modification to synchronize processors in a parallel computing system. The circuit may include a hardware module and a clock splitter. The hardware module may generate a clock signal and performs a pulse width modification on the clock signal. The pulse width modification changes a pulse width within a clock period in the clock signal. The clock splitter may distribute the pulse width modified clock signal to a plurality of processors in the parallel computing system.

  1. A Mathematical Model of the Liver Circadian Clock Linking Feeding and Fasting Cycles to Clock Function

    Directory of Open Access Journals (Sweden)

    Aurore Woller

    2016-10-01

    Full Text Available To maintain energy homeostasis despite variable energy supply and consumption along the diurnal cycle, the liver relies on a circadian clock synchronized to food timing. Perturbed feeding and fasting cycles have been associated with clock disruption and metabolic diseases; however, the mechanisms are unclear. To address this question, we have constructed a mathematical model of the mammalian circadian clock, incorporating the metabolic sensors SIRT1 and AMPK. The clock response to various temporal patterns of AMPK activation was simulated numerically, mimicking the effects of a normal diet, fasting, and a high-fat diet. The model reproduces the dampened clock gene expression and NAD+ rhythms reported for mice on a high-fat diet and predicts that this effect may be pharmacologically rescued by timed REV-ERB agonist administration. Our model thus identifies altered AMPK signaling as a mechanism leading to clock disruption and its associated metabolic effects and suggests a pharmacological approach to resetting the clock in obesity.

  2. A Mathematical Model of the Liver Circadian Clock Linking Feeding and Fasting Cycles to Clock Function.

    Science.gov (United States)

    Woller, Aurore; Duez, Hélène; Staels, Bart; Lefranc, Marc

    2016-10-18

    To maintain energy homeostasis despite variable energy supply and consumption along the diurnal cycle, the liver relies on a circadian clock synchronized to food timing. Perturbed feeding and fasting cycles have been associated with clock disruption and metabolic diseases; however, the mechanisms are unclear. To address this question, we have constructed a mathematical model of the mammalian circadian clock, incorporating the metabolic sensors SIRT1 and AMPK. The clock response to various temporal patterns of AMPK activation was simulated numerically, mimicking the effects of a normal diet, fasting, and a high-fat diet. The model reproduces the dampened clock gene expression and NAD(+) rhythms reported for mice on a high-fat diet and predicts that this effect may be pharmacologically rescued by timed REV-ERB agonist administration. Our model thus identifies altered AMPK signaling as a mechanism leading to clock disruption and its associated metabolic effects and suggests a pharmacological approach to resetting the clock in obesity.

  3. Cost and Precision of Brownian Clocks

    CERN Document Server

    Barato, Andre C

    2016-01-01

    Brownian clocks are biomolecular networks that can count time. A paradigmatic example are proteins that go through a cycle thus regulating some oscillatory behaviour in a living system. Typically, such a cycle requires free energy often provided by ATP hydrolysis. We investigate the relation between the precision of such a clock and its thermodynamic costs. For clocks driven by a constant thermodynamic force, a given precision requires a minimal cost that diverges as the uncertainty of the clock vanishes. In marked contrast, we show that a clock driven by a periodic variation of an external protocol can achieve arbitrary precision at arbitrarily low cost. This result constitutes a fundamental difference between processes driven by a fixed thermodynamic force and those driven periodically. As a main technical tool, we map a periodically driven system with a deterministic protocol to one subject to an external protocol that changes in stochastic time intervals, which simplifies calculations significantly. In th...

  4. Frequency shifts in an optical lattice clock due to magnetic-dipole and electric-quadrupole transitions.

    Science.gov (United States)

    Taichenachev, A V; Yudin, V I; Ovsiannikov, V D; Pal'chikov, V G; Oates, C W

    2008-11-01

    We report a hitherto undiscovered frequency shift for forbidden J = 0-->J = 0 clock transitions excited in atoms confined to an optical lattice. These shifts result from magnetic-dipole and electric-quadrupole transitions, which have a spatial dependence in an optical lattice that differs from that of the stronger electric-dipole transitions. In combination with the residual translational motion of atoms in an optical lattice, this spatial mismatch leads to a frequency shift via differential energy level spacing in the lattice wells for ground state and excited state atoms. We estimate that this effect could lead to fractional frequency shifts as large as 10(-16), which might prevent lattice-based optical clocks from reaching their predicted performance levels. Moreover, these effects could shift the magic wavelength in lattice clocks in three dimensions by as much as 100 MHz, depending on the lattice configuration.

  5. Atomic frequency standard relativistic Doppler shift experiment

    Science.gov (United States)

    Peters, H. E.; Reinhardt, V. S.

    1974-01-01

    An experiment has been performed to measure possible space anisotropy as it would effect the frequency of a cesium atomic beam standard clock in a laboratory on earth due to motion relative to external coordinate frames. The cesium frequency was measured as a function of orientation with respect to an atomic hydrogen maser standard. Over a period of 34 days 101 measurements were made. The results are consistent with a conclusion that no general orientation dependance attributable to spacial anisotropy was observed. It is shown that both the airplane clock results, and the null results for the atomic beam clock, are consistent with Einstein general or special relativity, or with the Lorentz transformations alone.

  6. Three errors in the article:" The OPERA neutrino velocity result and the synchronisation of clocks, "

    CERN Document Server

    Besida, Olivier

    2011-01-01

    We found three mistakes in the article " The OPERA neutrino velocity result and the synchronisation of clocks" by Contaldi \\cite{Contaldi}. First, the definition of the angle of the latitude in the geoid description leads to a prolate spheroid (rugby ball shape) instead of an oblate spheroid with the usual equatorial flattening. Second, Contaldi forgot a cosine of the latitude in the centripetal contribution term. And last but not least, a profound conceptual mistake was done in believing that an atomic clock or any timekeeper apparatus was carried in a journey by car or plane between CERN and Gran Sasso; instead of that atomic clocks are continuously resynchronized through a GPS device, and the variation of the potential term applies only for the neutrino travel itself. Thus instead of a $\\Delta t \\approx 30ns $ correction claimed by the author in a travel of 12 hours plus 4 days at rest for an atomic clock, we have found a time correction only for the neutrino itself $\\Delta t=3.88 \\, 10^{-16} s$! That mean...

  7. Horloge à réseau optique à atomes de Strontium

    OpenAIRE

    2008-01-01

    This thesis presents the latest achievements regarding the optical lattice clock with Strontium atoms developed at LNE-SYRTE. After a review of the different types of optical clocks that are currently under development, we stress on the concept of optical lattice clock which was first imagined for 87Sr using the 1S0 - 3P0 transition. We exhibit the features of this atom, in particular the concept of magic wavelength for the trap, and the achievable performances for this kind of clock. The sec...

  8. Gravitational Wave Detection with Single-Laser Atom Interferometers

    Science.gov (United States)

    Yu, Nan; Tinto, Massimo

    2011-01-01

    A new design for a broadband detector of gravitational radiation relies on two atom interferometers separated by a distance L. In this scheme, only one arm and one laser are used for operating the two atom interferometers. The innovation here involves the fact that the atoms in the atom interferometers are not only considered as perfect test masses, but also as highly stable clocks. Atomic coherence is intrinsically stable, and can be many orders of magnitude more stable than a laser.

  9. Imaging the Mott Insulator Shells using Atomic Clock Shifts

    OpenAIRE

    Campbell, Gretchen K.; Mun, Jongchul; Boyd, Micah; Medley, Patrick; Leanhardt, Aaron E.; Marcassa, Luis; Pritchard, David E.; Ketterle, Wolfgang

    2006-01-01

    Microwave spectroscopy was used to probe the superfluid-Mott Insulator transition of a Bose-Einstein condensate in a 3D optical lattice. Using density dependent transition frequency shifts we were able to spectroscopically distinguish sites with different occupation numbers, and to directly image sites with occupation number n=1 to n=5 revealing the shell structure of the Mott Insulator phase. We use this spectroscopy to determine the onsite interaction and lifetime for individual shells.

  10. An Atomic Clock with 10 (exp -18) Instability

    Science.gov (United States)

    2013-09-13

    Parker, Metrologia 47, 1 10 (2010). 6. T. Rosenband et al., Science 319, 1808 1812 (2008). 7. C. W. Chou, D. B. Hume , J. C. J. Koelemeij, D. J. Wineland...W. Chou, D. B. Hume , T. Rosenband, D. J. Wineland, Science 329, 1630 1633 (2010). 27. D. Kleppner, Phys. Today 59, 10 (2006). 28. S. Schiller et al...for financial support; D. Hume for experimental assistance; and T. Fortier and S. Diddams for femtosecond optical frequency comb measurements

  11. Developing an "atomic clock" for fission lifetime measurements

    NARCIS (Netherlands)

    Wilschut, H.W.E.M.; Kravchuk, V.

    2004-01-01

    The relevance of measuring fission lifetimes of hot nuclei is briefly discussed. It is shown that K X-ray emission prior to fission can be used to measure fission lifetimes. The preparation of the K-shell hole, the simultaneous nuclear excitation, and the analysis of the X-ray spectra is described.

  12. PHARAO: A Space Clock with Cold Cesium Atoms

    Science.gov (United States)

    1996-12-01

    Fundamental Tests. [z] R. Vessot et al. 1980, Physical Review Letters , 45, 2081. IS] R. Vessot 1993, Proceedings of the 28th Moriond Conference. [4...World Scientific, Singapore), pp. 49-59. [6] M. Kasevich, E. Riis, S. Chu, and R. de Voe 1989, Physical Review Letters , 63, 612. 171 A. Clairon, C...Salomon, S. Guellati, and W. Phillips 1991, Europhysical Letters, 16, 165. [a] K Gibble, and S. Chu 1993, Physical Review Letters , 70, 177. [g] B

  13. Raman transitions between hyperfine clock states in a magnetic trap

    CERN Document Server

    Naber, J B; Hubert, T; Spreeuw, R J C

    2016-01-01

    We present our experimental investigation of an optical Raman transition between the magnetic clock states of $^{87}$Rb in an atom chip magnetic trap. The transfer of atomic population is induced by a pair of diode lasers which couple the two clock states off-resonantly to an intermediate state manifold. This transition is subject to destructive interference of two excitation paths, which leads to a reduction of the effective two-photon Rabi-frequency. Furthermore, we find that the transition frequency is highly sensitive to the intensity ratio of the diode lasers. Our results are well described in terms of light shifts in the multi-level structure of $^{87}$Rb. The differential light shifts vanish at an optimal intensity ratio, which we observe as a narrowing of the transition linewidth. We also observe the temporal dynamics of the population transfer and find good agreement with a model based on the system's master equation and a Gaussian laser beam profile. Finally, we identify several sources of decoheren...

  14. Circadian clocks are designed optimally

    CERN Document Server

    Hasegawa, Yoshihiko

    2014-01-01

    Circadian rhythms are acquired through evolution to increase the chances for survival by synchronizing to the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. Since both properties have been tuned through natural selection, their adaptation can be formalized in the framework of mathematical optimization. By using a succinct model, we found that simultaneous optimization of regularity and entrainability entails inherent features of the circadian mechanism irrespective of model details. At the behavioral level we discovered the existence of a dead zone, a time during which light pulses neither advance nor delay the clock. At the molecular level we demonstrate the role-sharing of two light inputs, phase advance and delay, as is well observed in mammals. We also reproduce the results of phase-controlling experiments and predict molecular elements responsible for the clockwork...

  15. The molecular clock as a metabolic rheostat.

    Science.gov (United States)

    Perelis, M; Ramsey, K M; Bass, J

    2015-09-01

    Circadian clocks are biologic oscillators present in all photosensitive species that produce 24-h cycles in the transcription of rate-limiting metabolic enzymes in anticipation of the light-dark cycle. In mammals, the clock drives energetic cycles to maintain physiologic constancy during the daily switch in behavioural (sleep/wake) and nutritional (fasting/feeding) states. A molecular connection between circadian clocks and tissue metabolism was first established with the discovery that 24-h transcriptional rhythms are cell-autonomous and self-sustained in most tissues and comprise a robust temporal network throughout the body. A major window in understanding how the clock is coupled to metabolism was opened with discovery of metabolic syndrome pathologies in multi-tissue circadian mutant mice including susceptibility to diet-induced obesity and diabetes. Using conditional transgenesis and dynamic metabolic testing, we have pinpointed tissue-specific roles of the clock in energy and glucose homeostasis, with our most detailed understanding of this process in endocrine pancreas. Here, we review evidence for dynamic regulation of insulin secretion and oxidative metabolic functions by the clock transcription pathway to regulate homeostatic responses to feeding and fasting. These studies indicate that clock transcription is a determinant of tissue function and provide a reference for understanding molecular pathologies linking circadian desynchrony to metabolic disease.

  16. Limitations of long term stability in a coherent population trapping Cs clock

    CERN Document Server

    Kozlova, Olga; Guérandel, Stéphane; de Clercq, Emeric

    2013-01-01

    Vapor cell atomic clocks exhibit reduced frequency stability for averaging time between about one hundred and a few thousand seconds. Here we report a study on the impact of the main parameters on the mid-to-long term instability of a buffer-gas vapor cell Cs clock, based on coherent population trapping (CPT). The CPT signal is observed on the Cs D1 line transmission, using a double $\\Lambda$ scheme and a Ramsey interrogation technique. The effects on the clock frequency of the magnetic field, the cell temperature, and the laser intensities are reported. We show in particular that the laser intensity shift is temperature dependent. Along with the laser intensity ratio and laser polarization properties, this is one of the most important parameters.

  17. Iterative quantum algorithm for distributed clock synchronization

    Institute of Scientific and Technical Information of China (English)

    Wang Hong-Fu; Zhang Shou

    2012-01-01

    Clock synchronization is a well-studied problem with many practical and scientific applications.We propose an arbitrary accuracy iterative quantum algorithm for distributed clock synchronization using only three qubits.The n bits of the time difference △ between two spatially separated clocks can be deterministically extracted by communicating only O(n) messages and executing the quantum iteration process n times based on the classical feedback and measurement operations.Finally,we also give the algorithm using only two qubits and discuss the success probability of the algorithm.

  18. CMOS Law-jitter Clock Driver Design

    OpenAIRE

    2012-01-01

    [ANGLÈS] Design of a low-jitter, low-phase noise clock driver in 40 nm CMOS technology. The work is in the field of analog integrated circuit (IC) design in nanometer CMOS technologies. [CASTELLÀ] Diseño de un circuito integrado "clock driver" de bajo jitter y bajo ruido de fase en tecnología CMOS 40 nm. El trabajo se contextualiza en el campo del diseño de circuitos integrados analógicos en tecnologías CMOS nanométricas. [CATALÀ] Disseny d'un circuit "clock driver" de baix jitter i bai...

  19. Light clocks in strong gravitational fields

    CERN Document Server

    Punzi, Raffaele; Wohlfarth, Mattias N R

    2009-01-01

    We argue that the time measured by a light clock operating with photons rather than classical light requires a refinement of the standard clock postulate in general relativity. In the presence of a gravitational field, already the one-loop quantum corrections to classical Maxwell theory affect light propagation and the construction of observers' frames of reference. Carefully taking into account these kinematic effects, a concise geometric expression for the time shown by a light clock is obtained. This result has far-reaching implications for physics in strong gravitational fields.

  20. Transcripts from the Circadian Clock: Telling Time and Season

    NARCIS (Netherlands)

    K. Brand (Karl)

    2011-01-01

    textabstractWe all know it when we wake mere moments before an alarm clock is scheduled to wake us: our body clock made the alarm clock redundant. This phenomenon is driven by an endogenous timer known as the biological, or circadian clock. Each revolution of the Earth about its own axis produces pe

  1. Circadian and Circalunar Clock Interactions in a Marine Annelid

    Directory of Open Access Journals (Sweden)

    Juliane Zantke

    2013-10-01

    Full Text Available Life is controlled by multiple rhythms. Although the interaction of the daily (circadian clock with environmental stimuli, such as light, is well documented, its relationship to endogenous clocks with other periods is little understood. We establish that the marine worm Platynereis dumerilii possesses endogenous circadian and circalunar (monthly clocks and characterize their interactions. The RNAs of likely core circadian oscillator genes localize to a distinct nucleus of the worm’s forebrain. The worm’s forebrain also harbors a circalunar clock entrained by nocturnal light. This monthly clock regulates maturation and persists even when circadian clock oscillations are disrupted by the inhibition of casein kinase 1δ/ε. Both circadian and circalunar clocks converge on the regulation of transcript levels. Furthermore, the circalunar clock changes the period and power of circadian behavior, although the period length of the daily transcriptional oscillations remains unaltered. We conclude that a second endogenous noncircadian clock can influence circadian clock function.

  2. Deregulated expression of circadian clock and clock-controlled cell cycle genes in chronic lymphocytic leukemia.

    Science.gov (United States)

    Rana, Sobia; Munawar, Mustafa; Shahid, Adeela; Malik, Meera; Ullah, Hafeez; Fatima, Warda; Mohsin, Shahida; Mahmood, Saqib

    2014-01-01

    Circadian rhythms are endogenous and self-sustained oscillations of multiple biological processes with approximately 24-h rhythmicity. Circadian genes and their protein products constitute the molecular components of the circadian oscillator that form positive/negative feedback loops and generate circadian rhythms. The circadian regulation extends from core clock genes to various clock-controlled genes that include various cell cycle genes. Aberrant expression of circadian clock genes, therefore, may lead to genomic instability and accelerated cellular proliferation potentially promoting carcinogenesis. The current study encompasses the investigation of simultaneous expression of four circadian clock genes (Bmal1, Clock, Per1 and Per2) and three clock-controlled cell cycle genes (Myc, Cyclin D1 and Wee1) at mRNA level and determination of serum melatonin levels in peripheral blood samples of 37 CLL (chronic lymphocytic leukemia) patients and equal number of age- and sex-matched healthy controls in order to indicate association between deregulated circadian clock and manifestation of CLL. Results showed significantly down-regulated expression of Bmal1, Per1, Per2 and Wee1 and significantly up-regulated expression of Myc and Cyclin D1 (P circadian clock genes can lead to aberrant expression of their downstream targets that are involved in cell proliferation and apoptosis and hence may result in manifestation of CLL. Moreover, shift-work and low melatonin levels may also contribute in etiology of CLL by further perturbing of circadian clock.

  3. The Mechanics of Mechanical Watches and Clocks

    CERN Document Server

    Du, Ruxu

    2013-01-01

    "The Mechanics of Mechanical Watches and Clocks" presents historical views and mathematical models of mechanical watches and clocks. Although now over six hundred years old, mechanical watches and clocks are still popular luxury items that fascinate many people around the world. However few have examined the theory of how they work as presented in this book. The illustrations and computer animations are unique and have never been published before. It will be of significant interest to researchers in mechanical engineering, watchmakers and clockmakers, as well as people who have an engineering background and are interested in mechanical watches and clocks. It will also inspire people in other fields of science and technology, such as mechanical engineering and electronics engineering, to advance their designs. Professor Ruxu Du works at the Chinese University of Hong Kong, China. Assistant Professor Longhan Xie works at the South China University of Technology, China.

  4. Circadian clock circuitry in colorectal cancer.

    Science.gov (United States)

    Mazzoccoli, Gianluigi; Vinciguerra, Manlio; Papa, Gennaro; Piepoli, Ada

    2014-04-21

    Colorectal cancer is the most prevalent among digestive system cancers. Carcinogenesis relies on disrupted control of cellular processes, such as metabolism, proliferation, DNA damage recognition and repair, and apoptosis. Cell, tissue, organ and body physiology is characterized by periodic fluctuations driven by biological clocks operating through the clock gene machinery. Dysfunction of molecular clockworks and cellular oscillators is involved in tumorigenesis, and altered expression of clock genes has been found in cancer patients. Epidemiological studies have shown that circadian disruption, that is, alteration of bodily temporal organization, is a cancer risk factor, and an increased incidence of colorectal neoplastic disease is reported in shift workers. In this review we describe the involvement of the circadian clock circuitry in colorectal carcinogenesis and the therapeutic strategies addressing temporal deregulation in colorectal cancer.

  5. A New Design of Clock Synchronization Algorithm

    Directory of Open Access Journals (Sweden)

    Jingmeng Liu

    2014-05-01

    Full Text Available The introduction of Ethernet makes the distributed network system more flexible and efficient, but it also makes nodes which are far apart from each other unable to work in the same time basis due to the long distance. This is not allowed for the high performance requirements of the system synchronization, such as high-precision multiaxis machining system. This paper presents a high-precision network clock synchronization algorithm, namely, optimal PI clock servo, which imposes a PI controller in order to compensate for the clock drift of each network node. Then a simulation platform established by the toolbox TrueTime is used to verify the stability of the algorithm and compare it with the clock synchronization algorithm of EtherCAT. The results show that the new synchronization algorithm has higher synchronization precision and faster convergence rate.

  6. Programmable Clock Waveform Generation for CCD Readout

    Energy Technology Data Exchange (ETDEWEB)

    Vicente, J. de; Castilla, J.; Martinez, G.; Marin, J.

    2006-07-01

    Charge transfer efficiency in CCDs is closely related to the clock waveform. In this paper, an experimental framework to explore different FPGA based clock waveform generator designs is described. Two alternative design approaches for controlling the rise/fall edge times and pulse width of the CCD clock signal have been implemented: level-control and time-control. Both approaches provide similar characteristics regarding the edge linearity and noise. Nevertheless, dissimilarities have been found with respect to the area and frequency range of application. Thus, while the time-control approach consumes less area, the level control approach provides a wider range of clock frequencies since it does not suffer capacitor discharge effect. (Author) 8 refs.

  7. Turning Back the Aging Clock -- in Mice

    Science.gov (United States)

    ... 164250.html Turning Back the Aging Clock -- in Mice Elderly rodents treated with cellular therapy regained lost fur, became ... 2017 THURSDAY, March 23, 2017 (HealthDay News) -- Aging mice became more youthful following a new cellular therapy ...

  8. Draper Clock-Synchronization Protocol in SAL

    Data.gov (United States)

    National Aeronautics and Space Administration — In 1973, Daly, Hpokins, and McKenna (from Draper Lab.) presented a fault-tolerant digital clocking system at the FTCS conference. This is probably one of the first...

  9. Micro Mercury Ion Clock (MMIC) Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Demonstrate micro clock based on trapped Hg ions with more than 10x size reduction and power; Fractional frequency stability at parts per 1014 level, adequate for...

  10. Reduced Kalman Filters for Clock Ensembles

    Science.gov (United States)

    Greenhall, Charles A.

    2011-01-01

    This paper summarizes the author's work ontimescales based on Kalman filters that act upon the clock comparisons. The natural Kalman timescale algorithm tends to optimize long-term timescale stability at the expense of short-term stability. By subjecting each post-measurement error covariance matrix to a non-transparent reduction operation, one obtains corrected clocks with improved short-term stability and little sacrifice of long-term stability.

  11. Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

    Science.gov (United States)

    Xu, Yi-Lin; Xu, Xin-Ye

    2016-10-01

    We accurately evaluate the blackbody-radiation shift in a 171Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289(7) Hz with an uncertainty of 1.25 × 10-17 for our 171Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber. Project supported by the National Key Basic Research and Development Program of China (Grant No. 2012CB821302), the National Natural Science Foundation of China (Grant No. 11134003), the National High Technology Research and Development Program of China (Grant No. 2014AA123401), and the Shanghai Excellent Academic Leaders Program of China (Grant No. 12XD1402400).

  12. Zebrafish circadian clocks: cells that see light.

    Science.gov (United States)

    Tamai, T K; Carr, A J; Whitmore, D

    2005-11-01

    In the classical view of circadian clock organization, the daily rhythms of most organisms were thought to be regulated by a central, 'master' pacemaker, usually located within neural structures of the animal. However, with the results of experiments performed in zebrafish, mammalian cell lines and, more recently, mammalian tissues, this view has changed to one where clock organization is now seen as being highly decentralized. It is clear that clocks exist in the peripheral tissues of animals as diverse as Drosophila, zebrafish and mammals. In the case of Drosophila and zebrafish, these tissues are also directly light-responsive. This light sensitivity and direct clock entrainability is also true for zebrafish cell lines and early-stage embryos. Using luminescent reporter cell lines containing clock gene promoters driving the expression of luciferase and single-cell imaging techniques, we have been able to show how each cell responds rapidly to a single light pulse by being shifted to a common phase, equivalent to the early day. This direct light sensitivity might be related to the requirement for light in these cells to activate the transcription of genes involved in DNA repair. It is also clear that the circadian clock in zebrafish regulates the timing of the cell cycle, demonstrating the wide impact that this light sensitivity and daily rhythmicity has on the biology of zebrafish.

  13. Adipose Clocks: Burning the Midnight Oil.

    Science.gov (United States)

    Henriksson, Emma; Lamia, Katja A

    2015-10-01

    Circadian clocks optimize the timing of physiological processes in synchrony with daily recurring and therefore predictable changes in the environment. Until the late 1990s, circadian clocks were thought to exist only in the central nervous systems of animals; elegant studies in cultured fibroblasts and using genetically encoded reporters in Drosophila melanogaster and in mice showed that clocks are ubiquitous and cell autonomous. These findings inspired investigations of the advantages construed by enabling each organ to independently adjust its function to the time of day. Studies of rhythmic gene expression in several organs suggested that peripheral organ clocks might play an important role in optimizing metabolic physiology by synchronizing tissue-intrinsic metabolic processes to cycles of nutrient availability and energy requirements. The effects of clock disruption in liver, pancreas, muscle, and adipose tissues support that hypothesis. Adipose tissues coordinate energy storage and utilization and modulate behavior and the physiology of other organs by secreting hormones known as "adipokines." Due to behavior- and environment-driven diurnal variations in supply and demand for chemical and thermal energy, adipose tissues might represent an important peripheral location for coordinating circadian energy balance (intake, storage, and utilization) over the whole organism. Given the complexity of adipose cell types and depots, the sensitivity of adipose tissue biology to age and diet composition, and the plethora of known and yet-to-be-discovered adipokines and lipokines, we have just begun to scratch the surface of understanding the role of circadian clocks in adipose tissues.

  14. Short-term GNSS satellite clock stability

    Science.gov (United States)

    Griggs, E.; Kursinski, E. R.; Akos, D.

    2015-08-01

    Global Navigation Satellite System (GNSS) clock stability is characterized via the modified Allan deviation using active hydrogen masers as the receiver frequency reference. The high stability of the maser reference allows the GNSS clock contribution to the GNSS carrier phase variance to be determined quite accurately. Satellite clock stability for four different GNSS constellations are presented, highlighting the similarities and differences between the constellations as well as satellite blocks and clock types. Impact on high-rate applications, such as GNSS radio occultation (RO), is assessed through the calculation of the maximum carrier phase error due to clock instability. White phase noise appears to dominate at subsecond time scales. However, while we derived the theoretical contribution of white phase modulation to the modified Allan deviation, our analysis of the GNSS satellite clocks was limited to 1-200 s time scales because of inconsistencies between the subsecond results from the commercial and software-defined receivers. The rubidium frequency standards on board the Global Positioning System (GPS) Block IIF, BeiDou, and Galileo satellites show improved stability results in comparison to previous GPS blocks for time scales relevant to RO. The Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) satellites are the least stable of the GNSS constellations in the short term and will need high-rate corrections to produce RO results comparable to those from the other GNSS constellations.

  15. The Chemical and Educational Appeal of the Orange Juice Clock

    Science.gov (United States)

    Kelter, Paul B.; Carr, James D.; Johnson, Tanya; Mauricio Castro-Acuña, Carlos

    1996-12-01

    characterized by seeing educational possibilities in so many things, created a modified version of the clock, with the atomic numbers of the elements representing the hours in the day (see Fig. 2) in his internationally popular workshops. Due largely to Talesnick's efforts, the orange juice clock is a standard demonstration in many chemistry programs and presentations. Figure 2.Irwin Talesnick represents the hours of the day by the corresponding elements in his clock. The Procedure This can be done as a demonstration or as an activity, although at about 10 per clock, expense does become an issue. There are no unusual safety precautions with this demonstration. We know of no accidents that have occurred with the orange juice clock. The demonstration requires: a single AA-cell battery-operated wall clock with a sweep-second hand a medium-sized beaker (600 mL is fine) enough orange juice or other electrolyte mixture or solution to fill the beaker about 2/3 full (tap water often works fine!) a 20-30-cm magnesium strip, coiled at one end or wrapped around a popsicle stick a 20-30-cm copper strip, coiled at one end alligator clips to connect the strips to the battery terminals on the clock a stand against which to lean the setup The demonstration is put together as shown in Figure 3. Connect the magnesium to the "-" contact of the clock and the copper to the "+" contact. Immerse the other ends of the strips into the solution. The clock will start to tick within a few seconds. If it does not work within a short period of time, check that the strips are well connected to the battery terminals, are hooked to the proper poles, and are not touching each other. The clock should keep reasonably close time (in orange juice) for a couple of days, or until the magnesium is nearly completely oxidized. Figure 3.A schematic of the orange juice clock seup. Video of orange juice clock. In video, the copper electrode is on the left and the magnesium electrode is on the right. Video was filmed and

  16. Gated Clock Implementation of Arithmetic Logic Unit (ALU

    Directory of Open Access Journals (Sweden)

    Dr. Neelam R. Prakash

    2013-05-01

    Full Text Available Low power design has emerged as one of the challenging area in today’s ASIC (Application specific integrated circuit design. With continuous decrease in transistor size, power density is increasing and there is an urgent need for reduction in total power consumption. Clock gating is one most effective technique for low power synchronous circuit design. Clock gating technique in low power design is used to reduce the dynamic power consumption. Clock signal in a synchronous circuit is used for synchronization only and hence does not carry any important information. Since clock is applied to each block of a synchronous circuit, and clock switches for every cycle, clock power is the major part of dynamic power consumption in synchronous circuits. Clock gating is a well known technique to reduce clock power. In clock gating clock to an idle block is disabled. Thus significant amount of power consumption is reduced by employing clock gating. In this paper an ALU design is proposed employing Gated clock for its operation. Design simulation has been performed on Xilinx ISE design suite, and power calculation is done by Xilinx Xpower analyzer. Results show that approximately 17% of total clock power consumption is reduced by gated clock implementation.

  17. DESIGN OF TWO-PHASE SINUSOIDAL POWER CLOCK AND CLOCKED TRANSMISSION GATE ADIABATIC LOGIC CIRCUIT

    Institute of Scientific and Technical Information of China (English)

    Wang Pengjun; Yu Junjun

    2007-01-01

    First the research is conducted on the design of the two-phase sinusoidal power clock generator in this paper. Then the design of the new adiabatic logic circuit adopting the two-phase sinusoidal power clocks-Clocked Transmission Gate Adiabatic Logic (CTGAL) circuit is presented. This circuit makes use of the clocked transmission gates to sample the input signals, then the output loads are charged and discharged in a fully adiabatic manner by using bootstrapped N-Channel Metal Oxide Semiconductor (NMOS) and Complementary Metal Oxide Semiconductor (CMOS) latch structure.Finally, with the parameters of Taiwan Semiconductor Manufacturing Company (TSMC) 0.25 μm CMOS device, the transient energy consumption of CTGAL, Bootstrap Charge-Recovery Logic (BCRL)and Pass-transistor Adiabatic Logic (PAL) including their clock generators is simulated. The simulation result indicates that CTGAL circuit has the characteristic of remarkably low energy consumption.

  18. Circadian clock feedback cycle through NAMPT-mediated NAD+ biosynthesis.

    Science.gov (United States)

    Ramsey, Kathryn Moynihan; Yoshino, Jun; Brace, Cynthia S; Abrassart, Dana; Kobayashi, Yumiko; Marcheva, Biliana; Hong, Hee-Kyung; Chong, Jason L; Buhr, Ethan D; Lee, Choogon; Takahashi, Joseph S; Imai, Shin-Ichiro; Bass, Joseph

    2009-05-01

    The circadian clock is encoded by a transcription-translation feedback loop that synchronizes behavior and metabolism with the light-dark cycle. Here we report that both the rate-limiting enzyme in mammalian nicotinamide adenine dinucleotide (NAD+) biosynthesis, nicotinamide phosphoribosyltransferase (NAMPT), and levels of NAD+ display circadian oscillations that are regulated by the core clock machinery in mice. Inhibition of NAMPT promotes oscillation of the clock gene Per2 by releasing CLOCK:BMAL1 from suppression by SIRT1. In turn, the circadian transcription factor CLOCK binds to and up-regulates Nampt, thus completing a feedback loop involving NAMPT/NAD+ and SIRT1/CLOCK:BMAL1.

  19. Direct laser cooling Al+ ions optical clocks

    CERN Document Server

    Zhang, J; Luo, J; Lu, Z H

    2016-01-01

    Al$^+$ ions optical clock is a very promising optical frequency standard candidate due to its extremely small blackbody radiation shift. It has been successfully demonstrated with indirect cooled, quantum-logic-based spectroscopy technique. Its accuracy is limited by second-order Doppler shift, and its stability is limited by the number of ions that can be probed in quantum logic processing. We propose a direct laser cooling scheme of Al$^+$ ions optical clocks where both the stability and accuracy of the clocks are greatly improved. In the proposed scheme, two Al$^+$ ions traps are utilized. The first trap is used to trap a large number of Al$^+$ ions to improve the stability of the clock laser, while the second trap is used to trap a single Al$^+$ ions to provide the ultimate accuracy. Both traps are cooled with a continuous wave 167 nm laser. The expected clock laser stability can reach $9.0\\times10^{-17}/\\sqrt{\\tau}$. For the second trap, in addition to 167 nm laser Doppler cooling, a second stage pulsed ...

  20. Optimized geometries for future generation optical lattice clocks

    CERN Document Server

    Krämer, Sebastian; Ritsch, Helmut

    2015-01-01

    Atoms trapped in magic wavelength optical lattices provide a Doppler- and collision-free dense ensemble of quantum emitters ideal for fast high precision spectroscopy and thus they are the basis of the best optical clock setups to date. Despite the minute optical dipole moments the inherent long range dipole-dipole interactions in such lattices at high densities generate measurable line shifts, increased dephasing and modified decay rates. We show that these effects can be resonantly enhanced or suppressed depending on lattice constant, geometry and excitation procedure. While these interactions generally limit the accuracy and precision of Ramsey spectroscopy, under optimal conditions collective effects can be exploited to yield zero effective shifts and long dipole lifetimes for a measurement precision beyond a noninteracting ensemble. In particular, 2D lattices with a lattice constant below the optical wavelength feature an almost ideal performance.

  1. A Miniature Wide Band Atomic Magnetometer

    Science.gov (United States)

    2011-12-01

    atomic magnetometer CSAC – Chip scale atomic clock DAC – Digital to Analog Converter DARPA – Defense Advanced Research Projects Agency DBR...Finally, the heater frequencies must not beat with the Laser servo’s modulation. Heater amplifiers This circuit is essentially an audio power...amplifier for the heater waveforms. The heater waveforms are made on the DAC board and then amplified in this circuit. The heater PCB consists of 4

  2. Evolutionary links between circadian clocks and photoperiodic diapause in insects.

    Science.gov (United States)

    Meuti, Megan E; Denlinger, David L

    2013-07-01

    In this article, we explore links between circadian clocks and the clock involved in photoperiodic regulation of diapause in insects. Classical resonance (Nanda-Hamner) and night interruption (Bünsow) experiments suggest a circadian basis for the diapause response in nearly all insects that have been studied. Neuroanatomical studies reveal physical connections between circadian clock cells and centers controlling the photoperiodic diapause response, and both mutations and knockdown of clock genes with RNA interference (RNAi) point to a connection between the clock genes and photoperiodic induction of diapause. We discuss the challenges of determining whether the clock, as a functioning module, or individual clock genes acting pleiotropically are responsible for the photoperiodic regulation of diapause, and how a stable, central circadian clock could be linked to plastic photoperiodic responses without compromising the clock's essential functions. Although we still lack an understanding of the exact mechanisms whereby insects measure day/night length, continued classical and neuroanatomical approaches, as well as forward and reverse genetic experiments, are highly complementary and should enable us to decipher the diverse ways in which circadian clocks have been involved in the evolution of photoperiodic induction of diapause in insects. The components of circadian clocks vary among insect species, and diapause appears to have evolved independently numerous times, thus, we anticipate that not all photoperiodic clocks of insects will interact with circadian clocks in the same fashion.

  3. Models of the Primordial Standard Clock

    CERN Document Server

    Chen, Xingang; Wang, Yi

    2014-01-01

    Oscillating massive fields in the primordial universe can be used as Standard Clocks. The ticks of these oscillations induce features in the density perturbations, which directly record the time evolution of the scale factor of the primordial universe, thus if detected, provide a direct evidence for the inflation scenario or the alternatives. In this paper, we construct a full inflationary model of primordial Standard Clock and study its predictions on the density perturbations. This model provides a full realization of several key features proposed previously. We compare the theoretical predictions from inflation and alternative scenarios with the Planck 2013 temperature data on Cosmic Microwave Background (CMB), and identify a statistically marginal but interesting candidate. We discuss how future CMB temperature and polarization data, non-Gaussianity analysis and Large Scale Structure data may be used to further test or constrain the Standard Clock signals.

  4. Quantum clock: A critical discussion on spacetime

    CERN Document Server

    Burderi, Luciano; Iaria, Rosario

    2016-01-01

    We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval $\\Delta t$ that this clock can measure scales as the inverse of its size $\\Delta r$. This implies an uncertainty relation between space and time: $\\Delta r$ $\\Delta t$ $> G \\hbar / c^4$; where G, $\\hbar$ and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.

  5. Sugars, the clock and transition to flowering

    Directory of Open Access Journals (Sweden)

    Mohammad Reza eBolouri Moghaddam

    2013-02-01

    Full Text Available Sugars do not only act as source of energy, but they also act as signals in plants. This mini review summarizes the emerging links between sucrose-mediated signaling and the cellular networks involved in flowering time control and defense. Cross-talks with gibberellin (GA and jasmonate (JA signaling pathways are highlighted. The circadian clock fulfills a crucial role at the heart of cellular networks and the bilateral relation between sugar signaling and the clock is discussed. It is proposed that important factors controlling plant growth (DELLAs, PIFs, invertases and trehalose- 6-phosphate or T6P might fulfill central roles in the transition to flowering as well. The emerging concept of ‘sweet immunity’, modulated by the clock, might at least partly rely on a sucrose-specific signaling pathway that needs further exploration.

  6. Biogeographic calibrations for the molecular clock.

    Science.gov (United States)

    Ho, Simon Y W; Tong, K Jun; Foster, Charles S P; Ritchie, Andrew M; Lo, Nathan; Crisp, Michael D

    2015-09-01

    Molecular estimates of evolutionary timescales have an important role in a range of biological studies. Such estimates can be made using methods based on molecular clocks, including models that are able to account for rate variation across lineages. All clock models share a dependence on calibrations, which enable estimates to be given in absolute time units. There are many available methods for incorporating fossil calibrations, but geological and climatic data can also provide useful calibrations for molecular clocks. However, a number of strong assumptions need to be made when using these biogeographic calibrations, leading to wide variation in their reliability and precision. In this review, we describe the nature of biogeographic calibrations and the assumptions that they involve. We present an overview of the different geological and climatic events that can provide informative calibrations, and explain how such temporal information can be incorporated into dating analyses.

  7. Susceptibility of Redundant Versus Singular Clock Domains Implemented in SRAM-Based FPGA TMR Designs

    Science.gov (United States)

    Berg, Melanie D.; LaBel, Kenneth A.; Pellish, Jonathan

    2016-01-01

    We present the challenges that arise when using redundant clock domains due to their clock-skew. Radiation data show that a singular clock domain (DTMR) provides an improved TMR methodology for SRAM-based FPGAs over redundant clocks.

  8. Sample-Clock Phase-Control Feedback

    Science.gov (United States)

    Quirk, Kevin J.; Gin, Jonathan W.; Nguyen, Danh H.; Nguyen, Huy

    2012-01-01

    To demodulate a communication signal, a receiver must recover and synchronize to the symbol timing of a received waveform. In a system that utilizes digital sampling, the fidelity of synchronization is limited by the time between the symbol boundary and closest sample time location. To reduce this error, one typically uses a sample clock in excess of the symbol rate in order to provide multiple samples per symbol, thereby lowering the error limit to a fraction of a symbol time. For systems with a large modulation bandwidth, the required sample clock rate is prohibitive due to current technological barriers and processing complexity. With precise control of the phase of the sample clock, one can sample the received signal at times arbitrarily close to the symbol boundary, thus obviating the need, from a synchronization perspective, for multiple samples per symbol. Sample-clock phase-control feedback was developed for use in the demodulation of an optical communication signal, where multi-GHz modulation bandwidths would require prohibitively large sample clock frequencies for rates in excess of the symbol rate. A custom mixedsignal (RF/digital) offset phase-locked loop circuit was developed to control the phase of the 6.4-GHz clock that samples the photon-counting detector output. The offset phase-locked loop is driven by a feedback mechanism that continuously corrects for variation in the symbol time due to motion between the transmitter and receiver as well as oscillator instability. This innovation will allow significant improvements in receiver throughput; for example, the throughput of a pulse-position modulation (PPM) with 16 slots can increase from 188 Mb/s to 1.5 Gb/s.

  9. Clocking Scheme for Switched-Capacitor Circuits

    DEFF Research Database (Denmark)

    Steensgaard-Madsen, Jesper

    1998-01-01

    A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed.......A novel clocking scheme for switched-capacitor (SC) circuits is presented. It can enhance the understanding of SC circuits and the errors caused by MOSFET (MOS) switches. Charge errors, and techniques to make SC circuits less sensitive to them are discussed....

  10. The Large Water-Clock of Amphiaraeion

    Science.gov (United States)

    Theodossiou, E.; Manimanis, V. N.; Katsiotis, M.; Mantarakis, P.

    2010-07-01

    A very well preserved ancient water-clock exists at the Amphiaraeion, in Oropos, Greece. The Amphiaraeion, sanctuary of the mythical oracle and deified healer Amphiaraus, was active from the pre-classic period until the 5th Century A.D. In such a place the measurement of time, both day and night, was a necessity. Therefore, time was kept with both a conical sundial and a water-clock in the shape of a fountain, which, according to the archaeologists, dates to the 4th Century B.C.

  11. Secure and self-stabilizing clock synchronization in sensor networks

    NARCIS (Netherlands)

    Hoepman, J.H.; Larsson, A.; Schiller, E.M.; Tsigas, P.

    2007-01-01

    In sensor networks, correct clocks have arbitrary starting offsets and nondeterministic fluctuating skews. We consider an adversary that aims at tampering with the clock synchronization by intercepting messages, replaying intercepted messages (after the adversary's choice of delay), and capturing no

  12. Ultracold photodissociation and progress towards a molecular lattice clock with 88 Sr

    Science.gov (United States)

    Lee, Chih-Hsi; McGuyer, Bart; McDonald, Mickey; Apfelback, Florian; Grier, Andrew; Zelevinsky, Tanya

    2016-05-01

    Techniques originally developed for the construction of atomic clocks can be adapted to the study of ultracold molecules, with applications ranging from studies of ultracold chemistry to searches for new physics. We present recent experimental results involving studies of fully quantum state-resolved photodissociation of 88 Sr2 molecules, as well as progress toward building a molecular clock. First, our system has allowed for precise, quantum state-resolved photodissociation studies, revealing not only excellent control over quantum states but also a more accurate way to describe the photodissociation of diatomic molecules and access ultracold chemistry. Second, the molecular clock will allow us to search for a possible time variation of the proton-electron mass ratio. The ``oscillator'' of such a molecular clock would consist of the frequency difference between two lasers driving a two-photon Raman transition between deeply and intermediately-bound rovibrational levels in the electronic ground state. Accomplishing this task requires exploring several research directions, including the precision spectroscopy of bound states and developing tools for the control and minimization of differential lattice light shifts.

  13. Immunometabolism: Is it under the eye of the clock?

    OpenAIRE

    Early, James O.; Curtis, Anne M.

    2016-01-01

    Molecular clocks allow an organism to track time of day, providing the means to anticipate and respond to the daily changes within the environment. In mammals the molecular clock consists of a network of proteins that form auto-regulatory feedback loops that drive rhythms in physiology and behavior. In recent times the extent to which the molecular clock controls key metabolic and immune pathways has begun to emerge. For example, the main clock protein BMAL1 has been linked to mitochondrial m...

  14. Determination of the thermal radiation effect on an optical strontium lattice clock; Bestimmung des Einflusses thermischer Strahlung auf eine optische Strontium-Gitteruhr

    Energy Technology Data Exchange (ETDEWEB)

    Middelmann, Thomas

    2013-05-31

    Optical clocks have the potential to be 100 times more accurate than current best cesium atomic clocks within a fraction of the averaging time. This corresponds to a fractional uncertainty of the clock frequency on the level of 10{sup -18} and requires highaccuracy knowledge of systematic frequency shifts, such that they can be avoided or corrected for. In strontium optical lattice clocks an ensemble of ultracold strontium atoms is confined in an optical lattice, to allow for spectroscopy of the reference transition 5s{sup 2} {sup 1}S{sub 0}-5s5p {sup 3}P{sub 0} in the Lamb-Dicke regime. The by far largest systematic frequency shift of the strontium clock transition is caused by its high sensitivity to blackbody radiation (BBR). The knowledge of the resulting frequency shift limited the achievable clock uncertainty to about 1 x 10{sup -16}. In this thesis for the first time an experimental approach was followed, to determine the sensitivity of the strontium clock transition to blackbody radiation. At an environmental temperature of 300 K the resulting frequency shift corresponds to 2.277 8(23) Hz. The achieved uncertainty contributes with 5 x 10{sup -18} to the fractional systematic uncertainty of the clock frequency. The determination is based on a precision measurement of the difference of static polarizabilities of the two clock states {Delta}{alpha}{sub dc} = {alpha}(5s5p {sup 3}P{sub 0})-{alpha}(5s{sup 2} {sup 1}S{sub 0}) = 4.078 73(11) x 10{sup -39} Cm{sup 2} /V. For this the de Stark shift of the clock transition has been measured in the accurately known electric field of a precision plate capacitor, which has been developed in this work. The attained static polarizability difference {Delta}{alpha}{sub dc} corresponds to the first term of a power series of the sensitivity to BBR. Higher orders are accumulated as dynamic part of the BBR shift. Which has been modelled using {Delta}{alpha}{sub dc} and experimental data for other atomic properties. To

  15. Circadian clocks - the fall and rise of physiology

    NARCIS (Netherlands)

    Roenneberg, Till; Merrow, Martha

    2005-01-01

    Circadian clocks control the daily life of most light-sensitive organisms- from cyanobacteria to humans. Molecular processes generate cellular rhythmicity, and cellular clocks in animals coordinate rhythms through interaction ( known as coupling). This hierarchy of clocks generates a complex, simila

  16. The mammalian retina as a clock

    Science.gov (United States)

    Tosini, Gianluca; Fukuhara, Chiaki

    2002-01-01

    Many physiological, cellular, and biochemical parameters in the retina of vertebrates show daily rhythms that, in many cases, also persist under constant conditions. This demonstrates that they are driven by a circadian pacemaker. The presence of an autonomous circadian clock in the retina of vertebrates was first demonstrated in Xenopus laevis and then, several years later, in mammals. In X. laevis and in chicken, the retinal circadian pacemaker has been localized in the photoreceptor layer, whereas in mammals, such information is not yet available. Recent advances in molecular techniques have led to the identification of a group of genes that are believed to constitute the molecular core of the circadian clock. These genes are expressed in the retina, although with a slightly different 24-h profile from that observed in the central circadian pacemaker. This result suggests that some difference (at the molecular level) may exist between the retinal clock and the clock located in the suprachiasmatic nuclei of hypothalamus. The present review will focus on the current knowledge of the retinal rhythmicity and the mechanisms responsible for its control.

  17. Circadian clocks - from genes to complex behaviour

    NARCIS (Netherlands)

    Roenneberg, Till; Merrow, Martha

    1999-01-01

    Circadian clocks control temporal structure in practically all organisms and on all levels of biology, from gene expression to complex behaviour and cognition. Over the last decades, research has begun to unravel the physiological and, more recently, molecular mechanisms that underlie this endogenou

  18. Circadian clock proteins in prokaryotes: hidden rhythms?

    Directory of Open Access Journals (Sweden)

    Maria eLoza-Correa

    2010-12-01

    Full Text Available Circadian clock genes are vital features of eukaryotes that have evolved such that organisms can adapt to our planet’s rotation in order to anticipate the coming day or night as well as unfavorable seasons. This circadian clock uses oscillation as a timekeeping element. However, circadian clock mechanisms exist also in prokaryotes. The circadian clock of Cyanobacteria is well studied. It is regulated by a cluster of three genes: kaiA, kaiB and kaiC. In this review, we will discuss the circadian system in cyanobacteria, and provide an overview and up-dated phylogenetic analysis of prokaryotic organisms that contain the main circadian genes. It is evident that the evolution of the kai genes has been influenced by lateral transfers but further and deeper studies are needed to get an in depth understanding of the exact evolutionary history of these genes. Interestingly, Legionella pneumophila an environmental bacterium and opportunistic human pathogen that parasitizes protozoa in fresh water environments also contains kaiB and kaiC, but their functions are not known. All of the residues described for the biochemical functions of the main pacemaker KaiC in Synechoccous elongates are also conserved in the L. pneumophila KaiC protein.

  19. Circadian clocks: Omnes viae Romam ducunt.

    Science.gov (United States)

    Roenneberg, T; Merrow, M

    2000-10-19

    The circadian clock in all organisms is so intimately linked to light reception that it appears as if evolution has simply wired a timer into the mechanism that processes photic information. Several recent studies have provided new insights into the role of light input pathways in the circadian system of Arabidopsis.

  20. Using circadian entrainment to find cryptic clocks

    NARCIS (Netherlands)

    Eelderink-Chen, Zheng; Olmedo, Maria; Bosman, Jasper; Merrow, Martha

    2015-01-01

    Three properties are most often attributed to the circadian clock: a ca. 24-h free-running rhythm, temperature compensation of the circadian rhythm, and its entrainment to zeitgeber cycles. Relatively few experiments, however, are performed under entrainment conditions. Rather, most chronobiology pr

  1. Current Status of the Molecular Clock Hypothesis

    Science.gov (United States)

    Hermann, Gilbert

    2003-01-01

    Molecular genetics is a rapidly changing field with new developments almost from day to day. One interesting hypothesis that has come from everyone's ability to sequence proteins and/or genes is that of the molecular clock. This hypothesis postulates that homologous sequences of DNA and thus macro molecules evolve at a constant and invariable rate…

  2. Circadian Clocks in the Immune System.

    Science.gov (United States)

    Labrecque, Nathalie; Cermakian, Nicolas

    2015-08-01

    The immune system is a complex set of physiological mechanisms whose general aim is to defend the organism against non-self-bodies, such as pathogens (bacteria, viruses, parasites), as well as cancer cells. Circadian rhythms are endogenous 24-h variations found in virtually all physiological processes. These circadian rhythms are generated by circadian clocks, located in most cell types, including cells of the immune system. This review presents an overview of the clocks in the immune system and of the circadian regulation of the function of immune cells. Most immune cells express circadian clock genes and present a wide array of genes expressed with a 24-h rhythm. This has profound impacts on cellular functions, including a daily rhythm in the synthesis and release of cytokines, chemokines and cytolytic factors, the daily gating of the response occurring through pattern recognition receptors, circadian rhythms of cellular functions such as phagocytosis, migration to inflamed or infected tissue, cytolytic activity, and proliferative response to antigens. Consequently, alterations of circadian rhythms (e.g., clock gene mutation in mice or environmental disruption similar to shift work) lead to disturbed immune responses. We discuss the implications of these data for human health and the areas that future research should aim to address.

  3. Clock Synchronization for Multihop Wireless Sensor Networks

    Science.gov (United States)

    Solis Robles, Roberto

    2009-01-01

    In wireless sensor networks, more so generally than in other types of distributed systems, clock synchronization is crucial since by having this service available, several applications such as media access protocols, object tracking, or data fusion, would improve their performance. In this dissertation, we propose a set of algorithms to achieve…

  4. Pineal clock gene oscillation is disturbed in Alzheimer's disease, due to functional disconnection from the "master clock".

    NARCIS (Netherlands)

    Wu, Y.-H.; Fischer, D.F.; Kalsbeek, A.; Garidou-Boof, M.-L.; Vliet, J. van der; Heijningen, C. van; Liu, R.-Y.; Zhou, J.-N.; Swaab, D.F.

    2006-01-01

    The suprachiasmatic nucleus (SCN) is the "master clock" of the mammalian brain. It coordinates the peripheral clocks in the body, including the pineal clock that receives SCN input via a multisynaptic noradrenergic pathway. Rhythmic pineal melatonin production is disrupted in Alzheimer's disease (AD

  5. Maximum likelihood molecular clock comb: analytic solutions.

    Science.gov (United States)

    Chor, Benny; Khetan, Amit; Snir, Sagi

    2006-04-01

    Maximum likelihood (ML) is increasingly used as an optimality criterion for selecting evolutionary trees, but finding the global optimum is a hard computational task. Because no general analytic solution is known, numeric techniques such as hill climbing or expectation maximization (EM), are used in order to find optimal parameters for a given tree. So far, analytic solutions were derived only for the simplest model--three taxa, two state characters, under a molecular clock. Four taxa rooted trees have two topologies--the fork (two subtrees with two leaves each) and the comb (one subtree with three leaves, the other with a single leaf). In a previous work, we devised a closed form analytic solution for the ML molecular clock fork. In this work, we extend the state of the art in the area of analytic solutions ML trees to the family of all four taxa trees under the molecular clock assumption. The change from the fork topology to the comb incurs a major increase in the complexity of the underlying algebraic system and requires novel techniques and approaches. We combine the ultrametric properties of molecular clock trees with the Hadamard conjugation to derive a number of topology dependent identities. Employing these identities, we substantially simplify the system of polynomial equations. We finally use tools from algebraic geometry (e.g., Gröbner bases, ideal saturation, resultants) and employ symbolic algebra software to obtain analytic solutions for the comb. We show that in contrast to the fork, the comb has no closed form solutions (expressed by radicals in the input data). In general, four taxa trees can have multiple ML points. In contrast, we can now prove that under the molecular clock assumption, the comb has a unique (local and global) ML point. (Such uniqueness was previously shown for the fork.).

  6. Suppression of Clock Shifts at Magnetic-Field-Insensitive Transitions

    Science.gov (United States)

    Arnold, K. J.; Barrett, M. D.

    2016-10-01

    We show that it is possible to significantly reduce rank 2 tensor shifts of a clock transition by operating at a judiciously chosen magnetic-field-insensitive point. In some cases shifts are almost completely eliminated making the transition an effective J =0 to J =0 candidate. This significantly improves the feasibility of a recent proposal for clock operation with large ion crystals. For such multi-ion clocks, geometric constraints and selection rules naturally divide clock operation into two categories based on the orientation of the magnetic field. We discuss the limitations imposed on each type and how calibrations might be carried out for clock operation.

  7. Suppression of clock shifts at field-insensitive transitions

    CERN Document Server

    Arnold, Kyle J

    2016-01-01

    We show that it is possible to significantly reduce quadrupole and tensor polarizability shifts of a clock transition by operating at a judiciously chosen field-insensitive point. In some cases shifts are almost completely eliminated making the transition an effective J = 0 to J = 0 candidate. This significantly improves the feasibility of a recent proposal for clock operation with large ion crystals. For such multi-ion clocks, geometric constraints and selection rules naturally divide clock operation into two categories based on the orientation of the magnetic field. We discuss the limitations imposed on each type and how calibrations might be carried out for clock operation.

  8. Comparing a mercury optical lattice clock with microwave and optical frequency standards

    Science.gov (United States)

    Tyumenev, R.; Favier, M.; Bilicki, S.; Bookjans, E.; Le Targat, R.; Lodewyck, J.; Nicolodi, D.; Le Coq, Y.; Abgrall, M.; Guéna, J.; De Sarlo, L.; Bize, S.

    2016-11-01

    In this paper we report the evaluation of an optical lattice clock based on neutral mercury with a relative uncertainty of 1.7× {10}-16. Comparing this characterized frequency standard to a 133Cs atomic fountain we determine the absolute frequency of the {}1{{{S}}}0\\to {}3{{{P}}}0 transition of 199Hg as {ν }{Hg}=1128 575 290 808 154.62 {Hz}+/- 0.19 {Hz}({statistical})+/- 0.38 {Hz} (systematic), limited solely by the realization of the SI second. Furthermore, by comparing the mercury optical lattice clock to a 87Rb atomic fountain, we determine for the first time to our knowledge the ratio between the 199Hg clock transition and the 87Rb ground state hyperfine transition. Finally we present a direct optical to optical measurement of the 199Hg/87Sr frequency ratio. The obtained value of {ν }{Hg}/{ν }{Sr} = 2.629 314 209 898 909 15 with a fractional uncertainty of 1.8× {10}-16 is in excellent agreement with a similar measurement obtained by Yamanaka et al (2015 Phys. Rev. Lett. 114 230801). This makes this frequency ratio one of the few physical quantities agreed upon by different laboratories to this level of uncertainty. Frequency ratio measurements of the kind reported in this paper have a strong impact for frequency metrology and fundamental physics as they can be used to monitor putative variations of fundamental constants.

  9. Molecular-clock methods for estimating evolutionary rates and timescales.

    Science.gov (United States)

    Ho, Simon Y W; Duchêne, Sebastián

    2014-12-01

    The molecular clock presents a means of estimating evolutionary rates and timescales using genetic data. These estimates can lead to important insights into evolutionary processes and mechanisms, as well as providing a framework for further biological analyses. To deal with rate variation among genes and among lineages, a diverse range of molecular-clock methods have been developed. These methods have been implemented in various software packages and differ in their statistical properties, ability to handle different models of rate variation, capacity to incorporate various forms of calibrating information and tractability for analysing large data sets. Choosing a suitable molecular-clock model can be a challenging exercise, but a number of model-selection techniques are available. In this review, we describe the different forms of evolutionary rate heterogeneity and explain how they can be accommodated in molecular-clock analyses. We provide an outline of the various clock methods and models that are available, including the strict clock, local clocks, discrete clocks and relaxed clocks. Techniques for calibration and clock-model selection are also described, along with methods for handling multilocus data sets. We conclude our review with some comments about the future of molecular clocks.

  10. Probe light-shift elimination in generalized hyper-Ramsey quantum clocks

    Science.gov (United States)

    Zanon-Willette, T.; de Clercq, E.; Arimondo, E.

    2016-04-01

    We present an interrogation scheme for the next generation of quantum clocks to suppress frequency shifts induced by laser probing fields that are themselves based on generalized hyper-Ramsey resonances. Sequences of composite laser pulses with a specific selection of phases, frequency detunings, and durations are combined to generate a very efficient and robust frequency locking signal with an almost perfect elimination of the light shift from off-resonant states and to decouple the unperturbed frequency measurement from the laser's intensity. The frequency lock point generated from synthesized error signals using either π /4 or 3 π /4 laser phase steps during the intermediate pulse is tightly protected against large laser-pulse area variations and errors in potentially applied frequency shift compensations. Quantum clocks based on weakly allowed or completely forbidden optical transitions in atoms, ions, molecules, and nuclei will benefit from these hyperstable laser frequency stabilization schemes to reach relative accuracies below the 10-18 level.

  11. Light-shift elimination in Generalized Hyper-Ramsey quantum clocks

    CERN Document Server

    Zanon-Willette, Thomas; Arimondo, Ennio

    2015-01-01

    We present a new generation of quantum clocks absolutely free from ac Stark-shift based on generalized hyper-Ramsey resonances with separated oscillating fields. Sequences of composite laser pulses with specific selection of phases, frequency detunings and durations are combined to generate a very efficient and robust frequency locking signal with a perfect elimination of the light-shift from off resonant states. Laser phase-step modulations during interactions with electromagnetic fields are applied in order to decouple the unperturbed frequency measurement from the laser's intensity. The frequency lock point is protected against laser pulse area fluctuations and errors in potentially applied frequency shift compensations. Quantum clocks based on weakly allowed or completely forbidden optical transitions in atoms, ions, molecules and nuclei will benefit from these hyper-stable laser frequency stabilization schemes to reach relative accuracies well below the 10$^{-18}$ level.

  12. Comparison of Two Independent Sr Optical Clocks with 1*10^-17 Stability at 10^3 s

    CERN Document Server

    Nicholson, T L; Williams, J R; Bloom, B J; Bishof, M; Swallows, M D; Campbell, S L; Ye, J

    2012-01-01

    Many-particle optical lattice clocks have the potential for unprecedented measurement precision and stability due to their low quantum projection noise (QPN). However, this potential has so far never been realized because clock stability has been limited by frequency noise of optical local oscillators. By synchronously probing two 87Sr lattice systems using a laser with a thermal noise floor of 1*10^-15, we remove classically correlated laser noise from the inter-comparison, but this approach does not improve the stability of an independent clock. With an improved optical oscillator that has a 1*10^-16 thermal noise floor, we demonstrate an order of magnitude improvement over the best reported independent clock stability, achieving a record fractional instability of 1*10^-17 in 1000 s of averaging time for synchronous or asynchronous comparisons. This result is within a factor of 2 of the combined QPN limit for a 160 ms probe time with ~10^3 atoms in each clock. We further demonstrate that even at this high p...

  13. Atom interferometry and the Einstein equivalence principle

    CERN Document Server

    Wolf, Peter; Bordé, Christian J; Reynaud, Serge; Salomon, Christophe; Cohen-Tannoudji, Clande

    2011-01-01

    The computation of the phase shift in a symmetric atom interferometer in the presence of a gravitational field is reviewed. The difference of action-phase integrals between the two paths of the interferometer is zero for any Lagrangian which is at most quadratic in position and velocity. We emphasize that in a large class of theories of gravity the atom interferometer permits a test of the weak version of the equivalence principle (or universality of free fall) by comparing the acceleration of atoms with that of ordinary bodies, but is insensitive to that aspect of the equivalence principle known as the gravitational redshift or universality of clock rates.

  14. The mammalian circadian clock protein period counteracts cryptochrome in phosphorylation dynamics of circadian locomotor output cycles kaput (CLOCK).

    Science.gov (United States)

    Matsumura, Ritsuko; Tsuchiya, Yoshiki; Tokuda, Isao; Matsuo, Takahiro; Sato, Miho; Node, Koichi; Nishida, Eisuke; Akashi, Makoto

    2014-11-14

    The circadian transcription factor CLOCK exhibits a circadian oscillation in its phosphorylation levels. Although it remains unclear whether this phosphorylation contributes to circadian rhythm generation, it has been suggested to be involved in transcriptional activity, intracellular localization, and degradative turnover of CLOCK. Here, we obtained direct evidence that CLOCK phosphorylation may be essential for autonomous circadian oscillation in clock gene expression. Importantly, we found that the circadian transcriptional repressors Cryptochrome (CRY) and Period (PER) showed an opposite effect on CLOCK phosphorylation; CRY impaired BMAL1-dependent CLOCK phosphorylation, whereas PER protected the phosphorylation against CRY. Interestingly, unlike PER1 and PER2, PER3 did not exert a protective action, which correlates with the phenotypic differences among mice lacking the Per genes. Further studies on the regulatory mechanism of CLOCK phosphorylation would thus lead to elucidation of the mechanism of CRY-mediated transcriptional repression and an understanding of the true role of PER in the negative feedback system.

  15. The Atomic and Nuclear Physics of Atomic EDMs

    Science.gov (United States)

    Chupp, Timothy

    2016-09-01

    Atomic Electric-Dipole-Moment (EDM) measurements employ low-energy atomic and precision-measurement techniques to measure the effects of elementary particle forces that affect the distribution of charge and mass in the nucleus, which is probed by the atomic electrons. Experiments and their interpretation strongly overlap atomic and nuclear physics in the experimental and theoretical problems presented. On the experimental side, the atomic EDM couples to electric fields while the magnetic dipole moment couples to magnetic fields requiring exquisite control and characerization of the magnetic fields. Measuring the tiny frequency shifts requires clock-comparisons and a large signal-to-noise ratio for frequency resolution much smaller than the linewidths, which are lmitied by observation times. To address the experimental challenges, I will discuss systematic effects related to magnetic fields and techniques of magnetometry and co-magntometery as well as optical pumping and related techniques that enhance signal-to-noise. I will also address the interpretation of atomic EDMs in terms of a set of low-energy parameters that relate to effective-field-theory coefficients, and I will empshaize the need for improved calculations from both atomic-theory and nuclear theory.

  16. Epigenetic drift, epigenetic clocks and cancer risk.

    Science.gov (United States)

    Zheng, Shijie C; Widschwendter, Martin; Teschendorff, Andrew E

    2016-05-01

    It is well-established that the DNA methylation landscape of normal cells undergoes a gradual modification with age, termed as 'epigenetic drift'. Here, we review the current state of knowledge of epigenetic drift and its potential role in cancer etiology. We propose a new terminology to help distinguish the different components of epigenetic drift, with the aim of clarifying the role of the epigenetic clock, mitotic clocks and active changes, which accumulate in response to environmental disease risk factors. We further highlight the growing evidence that epigenetic changes associated with cancer risk factors may play an important causal role in cancer development, and that monitoring these molecular changes in normal cells may offer novel risk prediction and disease prevention strategies.

  17. Optimal Implementations for Reliable Circadian Clocks

    Science.gov (United States)

    Hasegawa, Yoshihiko; Arita, Masanori

    2014-09-01

    Circadian rhythms are acquired through evolution to increase the chances for survival through synchronizing with the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. We find by using a phase model with multiple inputs that achieving the maximal limit of regularity and entrainability entails many inherent features of the circadian mechanism. At the molecular level, we demonstrate the role sharing of two light inputs, phase advance and delay, as is well observed in mammals. At the behavioral level, the optimal phase-response curve inevitably contains a dead zone, a time during which light pulses neither advance nor delay the clock. We reproduce the results of phase-controlling experiments entrained by two types of periodic light pulses. Our results indicate that circadian clocks are designed optimally for reliable clockwork through evolution.

  18. The Large Built Water Clock Of Amphiaraeion.

    Science.gov (United States)

    Theodossiou, E.; Katsiotis, M.; Manimanis, V. N.; Mantarakis, P.

    A very well preserved ancient water clock was discovered during excavations at the Amphiaraeion, in Oropos, Greece. The Amphiaraeion, a famous religious and oracle center of the deified healer Amphiaraus, was active from the pre-classic period until the replacement of the ancient religion by Christianity in the 5th Century A.D.. The foretelling was supposedly done through dreams sent by the god to the believers sleeping in a special gallery. In these dreams the god suggesting to them the therapy for their illness or the solution to their problems. The patients, then threw coins into a spring of the sanctuary. In such a place, the measurement of time was a necessity. Therefore, time was kept with both a conical sundial and a water clock in the form of a fountain. According to archeologists, the large built structure that measured the time for the sanctuary dates from the 4th Century B.C.

  19. Molecular clock on a neutral network.

    Science.gov (United States)

    Raval, Alpan

    2007-09-28

    The number of fixed mutations accumulated in an evolving population often displays a variance that is significantly larger than the mean (the overdispersed molecular clock). By examining a generic evolutionary process on a neutral network of high-fitness genotypes, we establish a formalism for computing all cumulants of the full probability distribution of accumulated mutations in terms of graph properties of the neutral network, and use the formalism to prove overdispersion of the molecular clock. We further show that significant overdispersion arises naturally in evolution when the neutral network is highly sparse, exhibits large global fluctuations in neutrality, and small local fluctuations in neutrality. The results are also relevant for elucidating aspects of neutral network topology from empirical measurements of the substitution process.

  20. The Circadian Clock, Reward, and Memory

    OpenAIRE

    Urs eAlbrecht

    2011-01-01

    During our daily activities, we experience variations in our cognitive performance, which is often accompanied by cravings for small rewards, such as consuming coffee or chocolate. This indicates that the time of day, cognitive performance, and reward may be related to one another. This review will summarize data that describe the influence of the circadian clock on addiction and mood-related behavior and put the data into perspective in relation to memory processes.

  1. The circadian clock, reward and memory

    Directory of Open Access Journals (Sweden)

    Urs eAlbrecht

    2011-11-01

    Full Text Available During our daily activities, we experience variations in our cognitive performance, which is often accompanied by cravings for small rewards, such as consuming coffee or chocolate. This indicates that the time of day, cognitive performance and reward may be related to one another. This review will summarize data that describes the influence of the circadian clock on addiction and mood-related behavior and put the data into perspective in relation to memory processes.

  2. Molecular clock in neutral protein evolution

    Directory of Open Access Journals (Sweden)

    Wilke Claus O

    2004-08-01

    Full Text Available Abstract Background A frequent observation in molecular evolution is that amino-acid substitution rates show an index of dispersion (that is, ratio of variance to mean substantially larger than one. This observation has been termed the overdispersed molecular clock. On the basis of in silico protein-evolution experiments, Bastolla and coworkers recently proposed an explanation for this observation: Proteins drift in neutral space, and can temporarily get trapped in regions of substantially reduced neutrality. In these regions, substitution rates are suppressed, which results in an overall substitution process that is not Poissonian. However, the simulation method of Bastolla et al. is representative only for cases in which the product of mutation rate μ and population size Ne is small. How the substitution process behaves when μNe is large is not known. Results Here, I study the behavior of the molecular clock in in silico protein evolution as a function of mutation rate and population size. I find that the index of dispersion decays with increasing μNe, and approaches 1 for large μNe . This observation can be explained with the selective pressure for mutational robustness, which is effective when μNe is large. This pressure keeps the population out of low-neutrality traps, and thus steadies the ticking of the molecular clock. Conclusions The molecular clock in neutral protein evolution can fall into two distinct regimes, a strongly overdispersed one for small μNe, and a mostly Poissonian one for large μNe. The former is relevant for the majority of organisms in the plant and animal kingdom, and the latter may be relevant for RNA viruses.

  3. Regulated DNA Methylation and the Circadian Clock: Implications in Cancer

    Directory of Open Access Journals (Sweden)

    Tammy M. Joska

    2014-09-01

    Full Text Available Since the cloning and discovery of DNA methyltransferases (DNMT, there has been a growing interest in DNA methylation, its role as an epigenetic modification, how it is established and removed, along with the implications in development and disease. In recent years, it has become evident that dynamic DNA methylation accompanies the circadian clock and is found at clock genes in Neurospora, mice and cancer cells. The relationship among the circadian clock, cancer and DNA methylation at clock genes suggests a correlative indication that improper DNA methylation may influence clock gene expression, contributing to the etiology of cancer. The molecular mechanism underlying DNA methylation at clock loci is best studied in the filamentous fungi, Neurospora crassa, and recent data indicate a mechanism analogous to the RNA-dependent DNA methylation (RdDM or RNAi-mediated facultative heterochromatin. Although it is still unclear, DNA methylation at clock genes may function as a terminal modification that serves to prevent the regulated removal of histone modifications. In this capacity, aberrant DNA methylation may serve as a readout of misregulated clock genes and not as the causative agent. This review explores the implications of DNA methylation at clock loci and describes what is currently known regarding the molecular mechanism underlying DNA methylation at circadian clock genes.

  4. Geopotential measurements with synchronously linked optical lattice clocks

    Science.gov (United States)

    Takano, Tetsushi; Takamoto, Masao; Ushijima, Ichiro; Ohmae, Noriaki; Akatsuka, Tomoya; Yamaguchi, Atsushi; Kuroishi, Yuki; Munekane, Hiroshi; Miyahara, Basara; Katori, Hidetoshi

    2016-10-01

    According to Einstein's theory of relativity, the passage of time changes in a gravitational field. On Earth, raising a clock by 1 cm increases its apparent tick rate by 1.1 parts in 1018, allowing chronometric levelling through comparison of optical clocks. Here, we demonstrate such geopotential measurements by determining the height difference of master and slave clocks separated by 15 km with an uncertainty of 5 cm. A subharmonic of the master clock laser is delivered through a telecom fibre to synchronously operate the distant clocks. Clocks operated under such phase coherence reject clock laser noise and facilitate proposals for linking clocks and interferometers. Taken over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be 1,652.9(5.9) × 10-18, consistent with an independent measurement by levelling and gravimetry. Our system demonstrates a building block for an internet of clocks, which may constitute ‘quantum benchmarks’, serving as height references with dynamic responses.

  5. Photoperiodic plasticity in circadian clock neurons in insects

    Directory of Open Access Journals (Sweden)

    Sakiko eShiga

    2013-08-01

    Full Text Available Since Bünning’s observation of circadian rhythms and photoperiodism in the runner bean Phaseolus multiflorus in 1936, many studies have shown that photoperiodism is based on the circadian clock system. In insects, involvement of circadian clock genes or neurons has been recently shown in the photoperiodic control of developmental arrests, diapause. Based on molecular and neuronal studies in Drosophila melanogaster, photoperiodic changes have been reported for expression patterns of the circadian clock genes, subcellular distribution of clock proteins, fiber distribution, or the number of plausible clock neurons in different species. Photoperiod sets peaks of per or tim mRNA abundance at lights-off in Sarcophaga crassipalpis, Chymomyza costata and Protophormia terraenovae. Abundance of per and Clock mRNA changes by photoperiod in Pyrrhocoris apterus. Subcellular Per distribution in circadian clock neurons changes with photoperiod in P. terraenovae. Although photoperiodism is not known in Leucophaea maderae, under longer day length, more stomata and longer commissural fibers of circadian clock neurons have been found. These plastic changes in the circadian clock neurons could be an important constituent for photoperiodic clock mechanisms to integrate repetitive photoperiodic information and produce different outputs based on day length.

  6. Incremental Placement-Based Clock Network Minimization Methodology

    Institute of Scientific and Technical Information of China (English)

    ZHOU Oiang; CAI Yici; HUANG Liang; HONG Xianlong

    2008-01-01

    Power is the major challenge threatening the progress of very large scale integration (VLSI) tech-nology development. In ultra-deep submicron VLSI designs, clock network size must be minimized to re-duce power consumption, power supply noise, and the number of clock buffers which are vulnerable to process variations. Traditional design methodologies usually let the clock router independently undertake the clock network minimization. Since clock routing is based on register locations, register placement actu-ally strongly influences the clock network size. This paper describes a clock network design methodology that optimizes register placement. For a given cell placement result, incremental modifications are per-formed based on the clock skew specifications by moving registers toward preferred locations that may re-duce the clock network size. At the same time, the side-effects to logic cell placement, such as signal net wirelength and critical path delay, are controlled. Test results on benchmark circuits show that the methodol-ogy can considerably reduce clock network size with limited impact on signal net wirelength and critical path delay.

  7. A compact model for the complex plant circadian clock

    Directory of Open Access Journals (Sweden)

    Didier eGonze

    2016-02-01

    Full Text Available The circadian clock is an endogenous timekeeper that allows organisms to anticipate and adapt to the daily variations of their environment. The plant clock is an intricate network of interlocked feedback loops, in which transcription factors regulate each other to generate oscillations with expression peaks at specific times of the day. Over the last decade, mathematical modeling approaches have been used to understand the inner workings of the clock in the model plant Arabidopsis thaliana. Those efforts have produced a number of models of ever increasing complexity. Here, we present an alternative model that combines a low number of equations and parameters, similar to the very earliest models, with the complex network structure found in more recent ones. This simple model describes the temporal evolution of the abundance of eight clock genes and captures key features of the clock on a qualitative level, namely the entrained and free-running behaviors of the wild type clock, as well as the defects found in knockout mutants (such as altered free-running periods, lack of entrainment, or changes in the expression of other clock genes. Additionally, our model produces complex responses to various light cues, such as extreme photoperiods and non-24h environmental cycles, and can describe the control of hypocotyl growth by the clock. Our model constitutes a useful tool to probe dynamical properties of the clock as well as model more clock-dependent processes.

  8. A microresonator frequency comb optical clock

    CERN Document Server

    Papp, Scott B; DelHaye, Pascal; Quinlan, Franklyn; Lee, Hansuek; Vahala, Kerry J; Diddams, Scott A

    2013-01-01

    Optical-frequency combs enable measurement precision at the 20th digit, and accuracy entirely commensurate with their reference oscillator. A new direction in experiments is the creation of ultracompact frequency combs by way of nonlinear parametric optics in microresonators. We refer to these as microcombs, and here we report a silicon-chip-based microcomb optical clock that phase-coherently converts an optical-frequency reference to a microwave signal. A low-noise comb spectrum with 25 THz span is generated with a 2 mm diameter silica disk and broadening in nonlinear fiber. This spectrum is stabilized to rubidium frequency references separated by 3.5 THz by controlling two teeth 108 modes apart. The optical clocks output is the electronically countable 33 GHz microcomb line spacing, which features an absolute stability better than the rubidium transitions by the expected factor of 108. Our work demonstrates the comprehensive set of tools needed for interfacing microcombs to state-of-the-art optical clocks.

  9. Clock drawing performance in cognitively normal elderly.

    Science.gov (United States)

    Hubbard, Emily J; Santini, Veronica; Blankevoort, Christiaan G; Volkers, Karin M; Barrup, Melissa S; Byerly, Laura; Chaisson, Christine; Jefferson, Angela L; Kaplan, Edith; Green, Robert C; Stern, Robert A

    2008-05-01

    The Clock Drawing Test (CDT) is a common neuropsychological measure sensitive to cognitive changes and functional skills (e.g., driving test performance) among older adults. However, normative data have not been adequately developed. We report the distribution of CDT scores using three common scoring systems [Mendez, M. F., Ala, T., & Underwood, K. L. (1992). Development of scoring criteria for the Clock Drawing Task in Alzheimer's Disease. Journal of the American Geriatrics Society, 40, 1095-1099; Cahn, D. A., Salmon, D. P., Monsch, A. U., Butters, N., Wiederholt, W. C., & Corey-Bloom, J. (1996). Screening for dementia of the Alzheimer type in the community: The utility of the Clock Drawing Test. Archives of Clinical Neuropsychology, 11(6), 529-539], among 207 cognitively normal elderly. The systems were well correlated, took little time to use, and had high inter-rater reliability. We found statistically significant differences in CDT scores based on age and WRAT-3 Reading score, a marker of education quality. We present means, standard deviations, and t- and z-scores based on these subgroups. We found that "normal" CDT performance includes a wider distribution of scores than previously reported. Our results may serve as useful comparisons for clinicians wishing to know whether their patients perform in the general range of cognitively normal elderly.

  10. Cold Atom Source Containing Multiple Magneto-Optical Traps

    Science.gov (United States)

    Ramirez-Serrano, Jaime; Kohel, James; Kellogg, James; Lim, Lawrence; Yu, Nan; Maleki, Lute

    2007-01-01

    An apparatus that serves as a source of a cold beam of atoms contains multiple two-dimensional (2D) magneto-optical traps (MOTs). (Cold beams of atoms are used in atomic clocks and in diverse scientific experiments and applications.) The multiple-2D-MOT design of this cold atom source stands in contrast to single-2D-MOT designs of prior cold atom sources of the same type. The advantages afforded by the present design are that this apparatus is smaller than prior designs.

  11. Clock genes in hypertension: novel insights from rodent models.

    Science.gov (United States)

    Richards, Jacob; Diaz, Alexander N; Gumz, Michelle L

    2014-10-01

    The circadian clock plays an integral role in the regulation of physiological processes, including the regulation of blood pressure. However, deregulation of the clock can lead to pathophysiological states including hypertension. Recent work has implicated the circadian clock genes in the regulation of processes in the heart, kidney, vasculature, and the metabolic organs, which are all critical in the regulation of the blood pressure. The goal of this review is to provide an introduction and general overview into the role of circadian clock genes in the regulation of blood pressure with a focus on their deregulation in the etiology of hypertension. This review will focus on the core circadian clock genes CLOCK, BMAL1, Per, and Cry.

  12. A clock network for geodesy and fundamental science

    CERN Document Server

    Lisdat, C; Quintin, N; Shi, C; Raupach, S M F; Grebing, C; Nicolodi, D; Stefani, F; Al-Masoudi, A; Dörscher, S; Häfner, S; Robyr, J -L; Chiodo, N; Bilicki, S; Bookjans, E; Koczwara, A; Koke, S; Kuhl, A; Wiotte, F; Meynadier, F; Camisard, E; Abgrall, M; Lours, M; Legero, T; Schnatz, H; Sterr, U; Denker, H; Chardonnet, C; Coq, Y Le; Santarelli, G; Amy-Klein, A; Targat, R Le; Lodewyck, J; Lopez, O; Pottie, P -E

    2015-01-01

    Leveraging the unrivaled performance of optical clocks in applications in fundamental physics beyond the standard model, in geo-sciences, and in astronomy requires comparing the frequency of distant optical clocks truthfully. Meeting this requirement, we report on the first comparison and agreement of fully independent optical clocks separated by 700 km being only limited by the uncertainties of the clocks themselves. This is achieved by a phase-coherent optical frequency transfer via a 1415 km long telecom fiber link that enables substantially better precision than classical means of frequency transfer. The fractional precision in comparing the optical clocks of three parts in $10^{17}$ was reached after only 1000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than with any other existing frequency transfer method. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optic...

  13. Self-Adaptive Clock Synchronization for Computational Grid

    Institute of Scientific and Technical Information of China (English)

    ZHAO Ying(赵英); ZHOU WanLei(周万雷); HUANG JiuMei(黄九梅); YU Shui(余水); E.J.Lanham

    2003-01-01

    This paper presents an innovative method to synchronize physical clocks for a computational grid, in particular for a computational grid linked through the asynchronous Intranet or Internet environments. The method discussed is an asynchronous self-adaptive clock synchronization mechanism. Two strategies for clock synchronisation are introduced. (1) Use continuous time intervals to calculate the precision of clocks, which can reduce the effect of network delay efficiently. (2) Every node synchronizes its clock with its leader actively. In addition, a node self-adaptive model is presented, and the relationship between the clock precision and synchronization time is induced, hence a node can predict when it should begin the synchronization process.Detailed simulation and extension of this issue are provided at the end of the paper. The presented model is both practical and feasible.

  14. Immunometabolism: Is it under the eye of the clock?

    Science.gov (United States)

    Early, James O; Curtis, Anne M

    2016-10-01

    Molecular clocks allow an organism to track time of day, providing the means to anticipate and respond to the daily changes within the environment. In mammals the molecular clock consists of a network of proteins that form auto-regulatory feedback loops that drive rhythms in physiology and behavior. In recent times the extent to which the molecular clock controls key metabolic and immune pathways has begun to emerge. For example, the main clock protein BMAL1 has been linked to mitochondrial metabolism, mitochondrial dynamics and various host defense pathways. The molecular clock may function to integrate daily metabolic changes driven by feeding-fasting to immune function and output. Understanding how the clock intersects with metabolic pathways within immune cells to affect immune phenotypes will have broad implications for the management of metabolic, inflammatory and infectious diseases.

  15. Transcriptional repressor PRR5 directly regulates clock-output pathways

    OpenAIRE

    Nakamichi, Norihito; Kiba, Takatoshi; Kamioka, Mari; Suzuki, Takamasa; Yamashino, Takafumi; Higashiyama, Tetsuya; Sakakibara, Hitoshi; Mizuno, Takeshi

    2012-01-01

    The circadian clock is an endogenous time-keeping mechanism that enables organisms to adapt to external daily cycles. The clock coordinates biological activities with these cycles, mainly through genome-wide gene expression. However, the exact mechanism underlying regulation of circadian gene expression is poorly understood. Here we demonstrated that an Arabidopsis PSEUDO-RESPONSE REGULATOR 5 (PRR5), which acts in the clock genetic circuit, directly regulates expression timing of key transcri...

  16. The Rock Island Clock Tower, From Ordnance to Engineers

    Science.gov (United States)

    1977-05-01

    11.) The Clock Tower shows no influence of two other architectural styles which were rapidly becoming popular in 1863: the Victor ian and gothic ...the hoist and to the clock on the fifth and sixth floors. The outside of the building, however, shows more attention to architectural design than...called for on the original plans. A comparison of the Columbus plans with the Rock Island Clock Tower shows an interesting architectural shift

  17. System-wide power management control via clock distribution network

    Energy Technology Data Exchange (ETDEWEB)

    Coteus, Paul W.; Gara, Alan; Gooding, Thomas M.; Haring, Rudolf A.; Kopcsay, Gerard V.; Liebsch, Thomas A.; Reed, Don D.

    2015-05-19

    An apparatus, method and computer program product for automatically controlling power dissipation of a parallel computing system that includes a plurality of processors. A computing device issues a command to the parallel computing system. A clock pulse-width modulator encodes the command in a system clock signal to be distributed to the plurality of processors. The plurality of processors in the parallel computing system receive the system clock signal including the encoded command, and adjusts power dissipation according to the encoded command.

  18. Circadian clocks and cell division: What's the pacemaker?

    OpenAIRE

    Johnson, Carl Hirschie

    2010-01-01

    Evolution has selected a system of two intertwined cell cycles: the cell division cycle (CDC) and the daily (circadian) biological clock. The circadian clock keeps track of solar time and programs biological processes to occur at environmentally appropriate times. One of these processes is the CDC, which is often gated by the circadian clock. The intermeshing of these two cell cycles is probably responsible for the observation that disruption of the circadian system enhances susceptibility to...

  19. Chronobiology of micturition: putative role of the circadian clock.

    OpenAIRE

    Negoro, Hiromitsu; Kanematsu, Akihiro; Yoshimura, Koji; Ogawa, Osamu

    2013-01-01

    [Purpose]Mammals urinate less frequently during the sleep period than the awake period. This is modulated by a triad of factors, including decreased arousal in the brain, a decreased urine production rate in the kidneys and increased functional bladder capacity during sleep. The circadian clock is genetic transcription-translation feedback machinery. It exists in most organs and cells, termed the peripheral clock, which is orchestrated by the central clock in the suprachiasmatic nucleus of th...

  20. Study on Short-Term Prediction for Satellite Clock Bias Based on ARIMA Model%基于 ARIMA 模型的卫星钟差短期预报研究

    Institute of Scientific and Technical Information of China (English)

    范旭亮; 王晓红; 张显云; 王阳; 潘绍林; 冯富寿

    2015-01-01

    The precision of satellite clock bias has a significant impact on the capacity of navigation and positioning system .Based on the space atomic clocks from different types , this paper used the ARIMA time series model to predict the short -term (6h and one day) satellite clock error by adopting IGS 5min and 30s -interval precise satellite clock products on one day .Results show that, the prediction accuracy of rubidium clock can reach sub nanosecond level ;caesium clock is at the nanosecond level .Moreover, the sam-ple interval of original satellite clock products has effect on the precision of satellite clock error prediction .%卫星钟差的精度直接影响导航定位的性能。本文针对不同类型的星载原子钟,采用ARIMA时间序列模型分别对1 d的IGS 5 min、30 s采样间隔的精密卫星钟差产品进行建模,并作6 h、一天的短期预报。结果表明,铷钟的预报精度达到了亚纳秒级,铯钟的预报精度处于纳秒级,并且原始钟差产品的采样间隔对卫星钟差预报精度有一定的影响。

  1. Experiments with a New 201Hg+ Ion Clock

    Science.gov (United States)

    Burt, E. A.; Taghavi-Larigani, S.; Lea, S. N.; Prestage, J. D.; Tjoelker, R. L.

    2009-04-01

    In this paper we describe a new clock based on 201Hg+. All previous mercury ion clocks have been based on 199Hg+. We have recently completed construction of the 201Hg+ clock and will describe modifications to the design of our existing 199Hg+ clocks to accommodate the new isotope. We will also describe initial spectroscopic measurements of the hyperfine manifold, and possible future experiments. One experiment could place a limit on variations in the strong interaction fundamental constant ratio mq/ΛQCD.REFID="9789812838223_0043FN001">

  2. A Simple Loop for Simultaneous OTDM Demultiplexing and Clock Recovery

    Institute of Scientific and Technical Information of China (English)

    CHEN Ming; LU Dan; GONG Tao-Rong; LV Bo; WANG Mu-Guang; LI Tang-Jun; JIAN Shui-Sheng

    2009-01-01

    A simple and stable loop consisting of a pair of concatenated electroabsorption modulators (EAMs) and 10 GHz clock recovery module is presented and demonstrated experimentally for simultaneous demultiplexing and clock recovery for OTDM networks. The 1OGb/s demultiplexed signai and IOGHz recovered clock are successfully implemented from 80 Gbit/s and 160 Gbit/s OTDM signals utilizing the loop. The loop based on EAM-PLL can provide excellent tolerance range (> 5 dB) of the OSCR of the source laser, and the recovered clock signa J exhibits low rms jitter over a dynamic input optical power range of 15 dB.

  3. Real-time geopotentiometry with synchronously linked optical lattice clocks

    CERN Document Server

    Takano, Tetsushi; Ushijima, Ichiro; Ohmae, Noriaki; Akatsuka, Tomoya; Yamaguchi, Atsushi; Kuroishi, Yuki; Munekane, Hiroshi; Miyahara, Basara; Katori, Hidetoshi

    2016-01-01

    According to the Einstein's theory of relativity, the passage of time changes in a gravitational field. On earth, raising a clock by one centimetre increases its tick rate by 1.1 parts in 10$^{18}$, enabling optical clocks to perform precision geodesy. Here, we demonstrate geopotentiometry by determining the height difference of master and slave clocks separated by 15 km with uncertainty of 5 cm. The subharmonic of the master clock is delivered through a telecom fibre to phase-lock and synchronously interrogate the slave clock. This protocol rejects laser noise in the comparison of two clocks, which improves the stability of measuring the gravitational red shift. Such phase-coherently operated clocks facilitate proposals for linking clocks and interferometers. Over half a year, 11 measurements determine the fractional frequency difference between the two clocks to be $1,652.9(5.9)\\times 10^{-18}$, or a height difference of 1,516(5) cm, consistent with an independent measurement by levelling and gravimetry. Ou...

  4. Temperature regulates transcription in the zebrafish circadian clock.

    Directory of Open Access Journals (Sweden)

    Kajori Lahiri

    2005-11-01

    Full Text Available It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation. In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic model, we demonstrate first that in the absence of light, exposure of embryos and primary cell lines to temperature cycles entrains circadian rhythms of clock gene expression. Temperature steps drive changes in the basal expression of certain clock genes in a gene-specific manner, a mechanism potentially contributing to entrainment. In the case of the per4 gene, while E-box promoter elements mediate circadian clock regulation, they do not direct the temperature-driven changes in transcription. Second, by studying E-box-regulated transcription as a reporter of the core clock mechanism, we reveal that the zebrafish clock is temperature-compensated. In addition, temperature strongly influences the amplitude of circadian transcriptional rhythms during and following entrainment by light-dark cycles, a property that could confer temperature compensation. Finally, we show temperature-dependent changes in the expression levels, phosphorylation, and function of the clock protein, CLK. This suggests a mechanism that could account for changes in the amplitude of the E-box-directed rhythm. Together, our results imply that several key transcriptional regulatory elements at the core of the zebrafish clock respond to temperature.

  5. Glucocorticoids entrain molecular clock components in human peripheral cells.

    Science.gov (United States)

    Cuesta, Marc; Cermakian, Nicolas; Boivin, Diane B

    2015-04-01

    In humans, shift work induces a desynchronization between the circadian system and the outside world, which contributes to shift work-associated medical disorders. Using a simulated night shift experiment, we previously showed that 3 d of bright light at night fully synchronize the central clock to the inverted sleep schedule, whereas the peripheral clocks located in peripheral blood mononuclear cells (PBMCs) took longer to reset. This underlines the need for testing the effects of synchronizers on both the central and peripheral clocks. Glucocorticoids display circadian rhythms controlled by the central clock and are thought to act as synchronizers of rodent peripheral clocks. In the present study, we tested whether the human central and peripheral clocks were sensitive to exogenous glucocorticoids (Cortef) administered in the late afternoon. We showed that 20 mg Cortef taken orally acutely increased PER1 expression in PBMC peripheral clocks. After 6 d of Cortef administration, the phases of central markers were not affected, whereas those of PER2-3 and BMAL1 expression in PBMCs were shifted by ∼ 9.5-11.5 h. These results demonstrate, for the first time, that human peripheral clocks are entrained by glucocorticoids. Importantly, they suggest innovative interventions for shift workers and jet-lag travelers, combining synchronizing agents for the central and peripheral clocks.

  6. The molecular clock regulates circadian transcription of tissue factor gene.

    Science.gov (United States)

    Oishi, Katsutaka; Koyanagi, Satoru; Ohkura, Naoki

    2013-02-01

    Tissue factor (TF) is involved in endotoxin-induced inflammation and mortality. We found that the circadian expression of TF mRNA, which peaked at the day to night transition (activity onset), was damped in the liver of Clock mutant mice. Luciferase reporter and chromatin immunoprecipitation analyses using embryonic fibroblasts derived from wild-type or Clock mutant mice showed that CLOCK is involved in transcription of the TF gene. Furthermore, the results of real-time luciferase reporter experiments revealed that the circadian expression of TF mRNA is regulated by clock molecules through a cell-autonomous mechanism via an E-box element located in the promoter region.

  7. The ac Stark shifts of the terahertz clock transitions of barium

    Institute of Scientific and Technical Information of China (English)

    余庚华; 耿鹰鸽; 李隆; 周超; 段丞博; 柴瑞鹏; 杨永明

    2015-01-01

    Wavelength-dependent AC Stark shifts and magic wavelengths of the terahertz clock transitions between the metastable triplet states 6s5d 3D1 and 6s5d 3D2 are investigated with considering the optical lattice trapping of barium atoms with the linearly polarized laser. The trap depths and the slopes of light shift difference with distinct magic wave-lengths of the optical lattices are also discussed in detail. Several potentially suitable working points for the optical lattice trapping laser are recommended and selected from these magic wavelengths.

  8. Clocks underneath: the role of peripheral clocks in the timing of female reproductive physiology

    Directory of Open Access Journals (Sweden)

    Michael T Sellix

    2013-07-01

    Full Text Available The central circadian pacemaker in the suprachiasmatic nucleus (SCN is a critical component of the neuroendocrine circuit controlling gonadotropin secretion from the pituitary gland. The SCN conveys photic information to hypothalamic targets including the gonadotropin releasing hormone (GnRH neurons. Many of these target cells are also cell autonomous clocks. It has been suggested that, rather then being singularly driven by the SCN, the timing of gonadotropin secretion depends on the activity of multiple hypothalamic oscillators. While this view provides a novel twist to an old story, it does little to diminish the central role of rhythmic hypothalamic output in this system. It is now clear that the pituitary, ovary, uterus and oviduct have functional molecular clocks. Evidence supports the notion that the clocks in these tissues contribute to the timing of events in reproductive physiology. The goal of this review is to highlight the current evidence for molecular clock function in the peripheral components of the female hypothalamo-pituitary-gonadal (HPG axis as it relates to the timing of gonadotropin secretion, ovulation and parturition.

  9. Strontium Optical Lattice Clock: In Quest of the Ultimate Performance; Horloge a reseau optique au strontium: en quete de la performance ultime

    Energy Technology Data Exchange (ETDEWEB)

    Westergaard, Ph.G.

    2010-10-15

    This thesis presents the latest achievements regarding the Sr optical lattice clock experiment at LNESYRTE, Observatoire de Paris. After having described the general principles for optical lattice clocks and the operation of the clock in question, the emphasis is put on the features that have been added to the experiment since 2007. The most important new elements are an ultra-stable reference cavity for the clock laser, the development of a non-destructive detection technique, and the construction of a second Sr lattice clock. The ultra-stable cavity is constructed from a ULE spacer and fused silica mirrors and has shown a thermal noise floor at 6.5 * 10{sup -16}, placing it among the best in the world. The non-destructive detection is effectuated by a phase measurement of a weak probe beam that traverses the atoms placed in one arm of a Mach-Zender interferometer. The non-destructive aspect enables a recycling of the atoms from cycle to cycle which consequently increases the duty cycle, allowing for an increase of the stability of the clock. With these new tools the frequency stability is expected to be 2.2 * 10{sup -16}/{radical}{tau} for an optimized sequence. The most recent comparisons between the two Sr clocks reach an accuracy level of 10{sup -16} after about 1000 s, and this way we have been able to characterize lattice related frequency shifts with an unprecedented accuracy. The measurements ensure a control of lattice related effects at the 10{sup -18} level even for trap depths as large as 50E{sub r}. (authors)

  10. Laser-Free Cold-Atom Gymnastics

    Science.gov (United States)

    Gould, Harvey; Feinberg, Benedict; Munger, Charles T., Jr.; Nishimura, Hiroshi

    2017-01-01

    We have performed beam transport simulations on ultra cold (2 μK) and cold (130 μK) neutral Cs atoms in the F = M = + 4 (magnetic weak-field seeking) ground state. We use inhomogeneous magnetic fields to focus and accelerate the atoms. Acceleration of neutral atoms by an inhomogeneous magnetic field was demonstrated by Stern and Gerlach in 1922. In the simulations, a two mm diameter cloud of atoms is released to fall under gravity. A magnetic coil focuses the falling atoms. After falling 41 cm, the atoms are reflected in the magnetic fringe field of a solenoid. They return to their starting height, about 0.7 s later, having passed a second time through the focusing coil. The simulations show that > 98 % of ultra cold Cs atoms and > 70 % of cold Cs atoms will survive at least 15 round trips (assuming perfect vacuum). More than 100 simulations were run to optimize coil currents and focusing coil diameter and height. Simulations also show that atoms can be launched into a fountain. An experimental apparatus to test the simulations, is being constructed. This technique may find application in atomic fountain clocks, interferometers, and gravitometers, and may be adaptable for use in microgravity. It may also work with Bose-Einstein condensates of paramagnetic atoms.

  11. Improved master clock reference system at USNO

    Science.gov (United States)

    Winkler, G. M. R.

    1985-04-01

    The first phase of the NAVELEX/NRL/USNO Master Clock (MC) upgrade program has been completed with the delivery of two VLG11B hydrogen Masers to the U.S. Naval Observatory (USNO). After installation in a specially prepaid Maser Laboratory with redundant environmental control, and a ten-day burn-in operation, the masers were independently tuned. Their subsequent performance caused a review of our plans for their operational use as part of the USNO MC complex. A revised concept is the basis for system integration presently in progress.

  12. A precise clock distribution network for MRPC-based experiments

    Science.gov (United States)

    Wang, S.; Cao, P.; Shang, L.; An, Q.

    2016-06-01

    In high energy physics experiments, the MRPC (Multi-Gap Resistive Plate Chamber) detectors are widely used recently which can provide higher-resolution measurement for particle identification. However, the application of MRPC detectors leads to a series of challenges in electronics design with large number of front-end electronic channels, especially for distributing clock precisely. To deal with these challenges, this paper presents a universal scheme of clock transmission network for MRPC-based experiments with advantages of both precise clock distribution and global command synchronization. For precise clock distributing, the clock network is designed into a tree architecture with two stages: the first one has a point-to-multipoint long range bidirectional distribution with optical channels and the second one has a fan-out structure with copper link inside readout crates. To guarantee the precision of clock frequency or phase, the r-PTP (reduced Precision Time Protocol) and the DDMTD (digital Dual Mixer Time Difference) methods are used for frequency synthesis, phase measurement and adjustment, which is implemented by FPGA (Field Programmable Gate Array) in real-time. In addition, to synchronize global command execution, based upon this clock distribution network, synchronous signals are coded with clock for transmission. With technique of encoding/decoding and clock data recovery, signals such as global triggers or system control commands, can be distributed to all front-end channels synchronously, which greatly simplifies the system design. The experimental results show that both the clock jitter (RMS) and the clock skew can be less than 100 ps.

  13. Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

    Science.gov (United States)

    Okaba, Shoichi; Takano, Tetsushi; Benabid, Fetah; Bradley, Tom; Vincetti, Luca; Maizelis, Zakhar; Yampol'Skii, Valery; Nori, Franco; Katori, Hidetoshi

    2014-06-01

    Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom-atom and atom-wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom-atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0-3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time.

  14. Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

    CERN Document Server

    Okaba, Shoichi; Benabid, Fetah; Bradley, Tom; Vincetti, Luca; Maizelis, Zakhar; Yampol'skii, Valery; Nori, Franco; Katori, Hidetoshi

    2014-01-01

    Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom-atom and atom-wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturisation. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kKagome-lattice hollow-core photonic crystal fibre (HC-PCF) are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom-atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the $^1 S_0-{}^3P_1$ (m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibresHC-PCFs improve the optical depth while preserving atomic coherence time.

  15. Reexamining the roles of gravitational and inertial masses in gravimetry with atom interferometers

    Energy Technology Data Exchange (ETDEWEB)

    Unnikrishnan, C.S., E-mail: unni@tifr.res.in [Gravitation Group, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005 (India); Gillies, G.T., E-mail: gtg@virginia.edu [School of Engineering and Applied Science, University of Virginia, Charlottesville, VA 22904-4746 (United States)

    2012-12-03

    We reassess the true roles of the gravitational charge (mass) and the inertial mass in quantum phases acquired in matter-wave interferometry in a gravitational field. The insights gained allow us to address the question of whether gravimetry with atom interferometers is equivalent to a high precision measurement of the relative gravitational time dilation of two clocks separated in space. In particular we show that the gravitational phase is inversely related to the Compton frequency, invalidating the suggested equivalence to a Compton clock. Clarity of arguments is achieved by comparison to a charged matter-wave interferometer. Though quantum states have a similarity to oscillator clocks through the Planck–Einstein–de Broglie relations, it is shown clearly that the claim of greatly enhanced precision over real atomic clock comparison cannot be maintained.

  16. The Renaissance or the cuckoo clock.

    Science.gov (United States)

    Pines, Jonathon; Hagan, Iain

    2011-12-27

    '…in Italy, for thirty years under the Borgias, they had warfare, terror, murder and bloodshed, but they produced Michelangelo, Leonardo da Vinci and the Renaissance. In Switzerland, they had brotherly love, they had five hundred years of democracy and peace-and what did that produce? The cuckoo clock'. Orson Welles as Harry Lime: The Third Man. Orson Welles might have been a little unfair on the Swiss, after all cuckoo clocks were developed in the Schwartzwald, but, more importantly, Swiss democracy gives remarkably stable government with considerable decision-making at the local level. The alternative is the battling city-states of Renaissance Italy: culturally rich but chaotic at a higher level of organization. As our understanding of the cell cycle improves, it appears that the cell is organized more along the lines of Switzerland than Renaissance Italy, and one major challenge is to determine how local decisions are made and coordinated to produce the robust cell cycle mechanisms that we observe in the cell as a whole.

  17. The circadian clock regulates auxin signaling and responses in Arabidopsis.

    Directory of Open Access Journals (Sweden)

    Michael F Covington

    2007-08-01

    Full Text Available The circadian clock plays a pervasive role in the temporal regulation of plant physiology, environmental responsiveness, and development. In contrast, the phytohormone auxin plays a similarly far-reaching role in the spatial regulation of plant growth and development. Went and Thimann noted 70 years ago that plant sensitivity to auxin varied according to the time of day, an observation that they could not explain. Here we present work that explains this puzzle, demonstrating that the circadian clock regulates auxin signal transduction. Using genome-wide transcriptional profiling, we found many auxin-induced genes are under clock regulation. We verified that endogenous auxin signaling is clock regulated with a luciferase-based assay. Exogenous auxin has only modest effects on the plant clock, but the clock controls plant sensitivity to applied auxin. Notably, we found both transcriptional and growth responses to exogenous auxin are gated by the clock. Thus the circadian clock regulates some, and perhaps all, auxin responses. Consequently, many aspects of plant physiology not previously thought to be under circadian control may show time-of-day-specific sensitivity, with likely important consequences for plant growth and environmental responses.

  18. Secure and self-stabilizing clock synchronization in sensor networks

    NARCIS (Netherlands)

    Hoepman, J.H.; Larsson, A.; Schiller, E.M.; Tsigas, P.

    2011-01-01

    In sensor networks, correct clocks have arbitrary starting offsets and nondeterministic fluctuating skews. We consider an adversary that aims at tampering with the clock synchronization by intercepting messages, replaying intercepted messages (after the adversary’s choice of delay), and capturing no

  19. Clock accuracy analysis for a coherent IR-UWB system

    NARCIS (Netherlands)

    Wang, X.; Young, A.; Philips, K.; Groot, H. de

    2011-01-01

    The performance of a duty-cycled coherent impulse radio UWB system is typically dominated by the accuracy of its timing references. In this paper, a timing analysis is presented for an IR-UWB system to specify the accuracy requirements for the internal clocks of the transceiver. A possible clock gen

  20. Verge and Foliot Clock Escapement: A Simple Dynamical System

    Science.gov (United States)

    Denny, Mark

    2010-01-01

    The earliest mechanical clocks appeared in Europe in the 13th century. From about 1250 CE to 1670 CE, these simple clocks consisted of a weight suspended from a rope or chain that was wrapped around a horizontal axle. To tell time, the weight must fall with a slow uniform speed, but, under the action of gravity alone, such a suspended weight would…

  1. Assignment of circadian function for the Neurospora clock gene frequency

    NARCIS (Netherlands)

    Merrow, Martha; Brunner, Michael; Roenneberg, Till

    1999-01-01

    Circadian clocks consist of three elements: entrainment pathways (inputs), the mechanism generating the rhythmicity (oscillator), and the output pathways that control the circadian rhythms. It is difficult to assign molecular clock components to any one of these elements. Experiments show that input

  2. Molecular clock integration of brown adipose tissue formation and function.

    Science.gov (United States)

    Nam, Deokhwa; Yechoor, Vijay K; Ma, Ke

    2016-01-01

    The circadian clock is an essential time-keeping mechanism that entrains internal physiology to environmental cues. Despite the well-established link between the molecular clock and metabolic homeostasis, an intimate interplay between the clock machinery and the metabolically active brown adipose tissue (BAT) is only emerging. Recently, we came to appreciate that the formation and metabolic functions of BAT, a key organ for body temperature maintenance, are under an orchestrated circadian clock regulation. Two complementary studies from our group uncover that the cell-intrinsic clock machinery exerts concerted control of brown adipogenesis with consequent impacts on adaptive thermogenesis, which adds a previously unappreciated temporal dimension to the regulatory mechanisms governing BAT development and function. The essential clock transcriptional activator, Bmal1, suppresses adipocyte lineage commitment and differentiation, whereas the clock repressor, Rev-erbα, promotes these processes. This newly discovered temporal mechanism in fine-tuning BAT thermogenic capacity may enable energy utilization and body temperature regulation in accordance with external timing signals during development and functional recruitment. Given the important role of BAT in whole-body metabolic homeostasis, pharmacological interventions targeting the BAT-modulatory activities of the clock circuit may offer new avenues for the prevention and treatment of metabolic disorders, particularly those associated with circadian dysregulation.

  3. The role of biological clock in glucose homeostasis 

    Directory of Open Access Journals (Sweden)

    Piotr Chrościcki

    2013-06-01

    Full Text Available The mechanism of the biological clock is based on a rhythmic expression of clock genes and clock-controlled genes. As a result of their transcripto-translational associations, endogenous rhythms in the synthesis of key proteins of various physiological and metabolic processes are created. The major timekeeping mechanism for these rhythms exists in the central nervous system. The master circadian clock, localized in suprachiasmatic nucleus (SCN, regulates multiple metabolic pathways, while feeding behavior and metabolite availability can in turn regulate the circadian clock. It is also suggested that in the brain there is a food entrainable oscillator (FEO or oscillators, resulting in activation of both food anticipatory activity and hormone secretion that control digestion processes. Moreover, most cells and tissues express autonomous clocks. Maintenance of the glucose homeostasis is particularly important for the proper function of the body, as this sugar is the main source of energy for the brain, retina, erythrocytes and skeletal muscles. Thus, glucose production and utilization are synchronized in time. The hypothalamic excited orexin neurons control energy balance of organism and modulate the glucose production and utilization. Deficiency of orexin action results in narcolepsy and weight gain, whereas glucose and amino acids can affect activity of the orexin cells. Large-scale genetic studies in rodents and humans provide evidence for the involvement of disrupted clock gene expression rhythms in the pathogenesis of obesity and type 2 diabetes. In general, the current lifestyle of the developed modern societies disturbs the action of biological clock

  4. Atom chip based generation of entanglement for quantum metrology

    CERN Document Server

    Riedel, Max F; Li, Yun; Hänsch, Theodor W; Sinatra, Alice; Treutlein, Philipp

    2010-01-01

    Atom chips provide a versatile `quantum laboratory on a microchip' for experiments with ultracold atomic gases. They have been used in experiments on diverse topics such as low-dimensional quantum gases, cavity quantum electrodynamics, atom-surface interactions, and chip-based atomic clocks and interferometers. A severe limitation of atom chips, however, is that techniques to control atomic interactions and to generate entanglement have not been experimentally available so far. Such techniques enable chip-based studies of entangled many-body systems and are a key prerequisite for atom chip applications in quantum simulations, quantum information processing, and quantum metrology. Here we report experiments where we generate multi-particle entanglement on an atom chip by controlling elastic collisional interactions with a state-dependent potential. We employ this technique to generate spin-squeezed states of a two-component Bose-Einstein condensate and show that they are useful for quantum metrology. The obser...

  5. Frequency Comparison of Two High-Accuracy Al+ Optical Clocks

    CERN Document Server

    Chou, C -W; Koelemeij, J C J; Wineland, D J; Rosenband, T

    2009-01-01

    We have constructed an optical clock with a fractional frequency inaccuracy of 8.6e-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser-cool the Al+ ion and detect its quantum state. The frequency of the 1S0->3P0 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0e-18. The two clocks exhibit a relative stability of 2.8e-15/ sqrt(tau), and a fractional frequency difference of -1.8e-17, consistent with the accuracy limit of the older clock.

  6. The circadian clock and cell cycle: interconnected biological circuits.

    Science.gov (United States)

    Masri, Selma; Cervantes, Marlene; Sassone-Corsi, Paolo

    2013-12-01

    The circadian clock governs biological timekeeping on a systemic level, helping to regulate and maintain physiological processes, including endocrine and metabolic pathways with a periodicity of 24-hours. Disruption within the circadian clock machinery has been linked to numerous pathological conditions, including cancer, suggesting that clock-dependent regulation of the cell cycle is an essential control mechanism. This review will highlight recent advances on the 'gating' controls of the circadian clock at various checkpoints of the cell cycle and also how the cell cycle can influence biological rhythms. The reciprocal influence that the circadian clock and cell cycle exert on each other suggests that these intertwined biological circuits are essential and multiple regulatory/control steps have been instated to ensure proper timekeeping.

  7. Cell "circadian" cycle: new role for mammalian core clock genes.

    Science.gov (United States)

    Borgs, Laurence; Beukelaers, Pierre; Vandenbosch, Renaud; Belachew, Shibeshih; Nguyen, Laurent; Malgrange, Brigitte

    2009-03-15

    In mammals, 24 hours rhythms are organized as a biochemical network of molecular clocks that are operative in all tissues, with the master clock residing in the hypothalamic suprachiasmatic nucleus (SCN). The core pacemakers of these clocks consist of auto-regulatory transcriptional/post-transcriptional feedback loops. Several lines of evidence suggest the existence of a crosstalk between molecules that are responsible for the generation of circadian rhythms and molecules that control the cell cycle progression. In addition, highly specialized cell cycle checkpoints involved in DNA repair after damage seem also, at least in part, mediated by clock proteins. Recent studies have also highlighted a putative connection between clock protein dysfunction and cancer progression. This review discusses the intimate relation that exists between cell cycle progression and components of the circadian machinery.

  8. Frequency Comparison of Two High-Accuracy Al+ Optical Clocks

    Science.gov (United States)

    Chou, C. W.; Hume, D. B.; Koelemeij, J. C. J.; Wineland, D. J.; Rosenband, T.

    2010-02-01

    We have constructed an optical clock with a fractional frequency inaccuracy of 8.6×10-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the S01↔P03 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0×10-18. The two clocks exhibit a relative stability of 2.8×10-15τ-1/2, and a fractional frequency difference of -1.8×10-17, consistent with the accuracy limit of the older clock.

  9. The molecular clock mediates leptin-regulated bone formation.

    Science.gov (United States)

    Fu, Loning; Patel, Millan S; Bradley, Allan; Wagner, Erwin F; Karsenty, Gerard

    2005-09-01

    The hormone leptin is a regulator of bone remodeling, a homeostatic function maintaining bone mass constant. Mice lacking molecular-clock components (Per and Cry), or lacking Per genes in osteoblasts, display high bone mass, suggesting that bone remodeling may also be subject to circadian regulation. Moreover, Per-deficient mice experience a paradoxical increase in bone mass following leptin intracerebroventricular infusion. Thus, clock genes may mediate the leptin-dependent sympathetic regulation of bone formation. We show that expression of clock genes in osteoblasts is regulated by the sympathetic nervous system and leptin. Clock genes mediate the antiproliferative function of sympathetic signaling by inhibiting G1 cyclin expression. Partially antagonizing this inhibitory loop, leptin also upregulates AP-1 gene expression, which promotes cyclin D1 expression, osteoblast proliferation, and bone formation. Thus, leptin determines the extent of bone formation by modulating, via sympathetic signaling, osteoblast proliferation through two antagonistic pathways, one of which involves the molecular clock.

  10. Clock-turning gait synthesis for humanoid robots

    Institute of Scientific and Technical Information of China (English)

    Zhe TANG; Zengqi SUN; Hongbo LIU; Meng Joo ER

    2007-01-01

    Turning gait is a basic motion for humanoid robots.This paper presents a method for humanoid turning.i.e.clock-turning.The objective of clock-turning is to change robot direction at a stationary spot.The clock-turning planning consists of four steps:ankle trajectory generation,hip trajectory generation,knee trajectory generation,and inverse kinematics calculation.Our proposed method is based on a typical humanoid structure with 12 DOFs(degrees of freedom).The final output of clock-turning planning is 12 reference trajectories.which are used to control a humanoid robot wim 12 DOFs.ZMP(zero moment point)is used as stability criterion for the planning.Simulation experiments are conducted to verify the effectiveness of our proposed clock-turning method.

  11. Atom chips

    CERN Document Server

    Reichel, Jakob

    2010-01-01

    This book provides a stimulating and multifaceted picture of a rapidly developing field. The first part reviews fundamentals of atom chip research in tutorial style, while subsequent parts focus on the topics of atom-surface interaction, coherence on atom chips, and possible future directions of atom chip research. The articles are written by leading researchers in the field in their characteristic and individual styles.

  12. Atomic energy

    CERN Multimedia

    1996-01-01

    Interviews following the 1991 co-operation Agreement between the Department of Atomic Energy (DAE) of the Government of India and the European Organization for Nuclear Research (CERN) concerning the participation in the Large Hadron Collider Project (LHC) . With Chidambaram, R, Chairman, Atomic Energy Commission and Secretary, Department of Atomic Energy, Department of Atomic Energy (DAE) of the Government of India and Professor Llewellyn-Smith, Christopher H, Director-General, CERN.

  13. Rigorous Comparison of Gravimetry Employing Atom Interferometers and the Measurement of Gravitational Time Dilation

    CERN Document Server

    Unnikrishnan, C S

    2011-01-01

    We present a gravitationally rigorous and clear answer, in the negative, to the question whether gravimetry with atom interferometers is equivalent to the the measurement of the relative gravitational time dilation of two clocks separated in space. Though matter and light waves, quantum states and oscillator clocks are quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle, there are crucial differences in the context of tests of gravitation theories.

  14. Math Clock: Perangkat Penunjuk Waktu Kreatif untuk Olahraga Otak

    Directory of Open Access Journals (Sweden)

    Galuh Boy Hertantyo

    2014-11-01

    Full Text Available Brain is one of the most vital parts for humans, with the number of brain function that is needed for the body, the brain becomes a very important part of the human body. If there is damage to the brain will certainly cause the performance of the human body will not run properly. Because of that, it’s very important to maintain brain health. There is a way to maintain brain health, for example is by doing brain exercise. Examples of brain exercise is to do simple math calculations or doing brain games like sudoku. Because of that, created a tool that can help the brain to maintain brain exercise. The tool is called math clock. Making math clock tool consists of hardware and software. The hardware consists of RTC as real time data input, ATmega328 as microcontroller and dot matrix 32x16 as a tool to display the output that has been processed by the microcontroller. The software is built using C with Arduino IDE. Math clock will process the data from RTC then processed it, in microcontroller so when output displayed on dot matrix, output will be simple mathematical operation with real time clock data on it. Test results show that, math clock is capable of displaying a simple mathematical calculation operations such as addition, subtraction, multiplication and division. The mathematical operation that display on math clock, appears to be random, so it’s not triggered by same mathematical operation. In math clock the display will change every 20 second, so in 1 minute there are 3 different kinds of mathematical operations. The results of questionnaires of 10 different students, showed 9 out of 10 students said math clock is a tool that easy to use as a clock. Math clock will be alternative for doing brain exercise every day.

  15. Postnatal ontogenesis of molecular clock in mouse striatum.

    Science.gov (United States)

    Cai, Yanning; Liu, Shu; Li, Ning; Xu, Shengli; Zhang, Yanli; Chan, Piu

    2009-04-01

    Striatum is an important brain area whose function is related to motor, emotion and motivation. Interestingly, biological and physiological circadian rhythms have been found in the striatum extensively, suggesting molecular clock machinery works efficiently therein. However, the striatal expression profiles of clock genes have not been characterized systematically. In addition, little is known about when the expression rhythms start during postnatal ontogenesis. In the present study, 24 h mRNA oscillations of 6 principle clock genes (Bmal1, Clock, Npas2, Cry1, Per1 and Rev-erb alpha) were examined in mouse striatum, at early postnatal stage (postnatal day 3), pre-weaning stage (postnatal day 14) and in adult (postnatal day 60). At P3, no daily oscillation was found for all clock genes. At P14, a significant time effect was identified only for Rev-erb alpha and Npas2. At P60, the daily oscillations of these clock genes were at least borderline significant, with peak time at Circadian time (CT) 01 for Bmal1, Clock, Npas2 and Cry1; at CT 13 for Per1; and at CT 07 for Rev-erb alpha. In addition, the overall mean mRNA levels of these clock genes also underwent a dynamic change postnatally. For Bmal1, Clock, Npas2, Per1 and Rev-erb alpha, the expression level increased throughout the postnatal ontogenesis from P3, P14 to P60. For Cry1, however, the abundance at P3 and P60 were similar while that at P14 was much lower. In conclusion, the striatal molecular clock machinery, although works efficiently in adult, develops gradually after birth in mice.

  16. The genetic basis of the circadian clock : identification of frq and FRQ as clock components in Neurospora

    NARCIS (Netherlands)

    Dunlap, Jay C.; Loros, Jennifer J.; Aronson, Benjamin D.; Merrow, Martha; Crosthwaite, Susan; Bell-Pedersen, Deborah; Johnson, Keith; Lindgren, Kristin; Garceau, Norman Y.

    1995-01-01

    Genetic approaches to the identification of clock components have succeeded in two model systems, Neurospora and Drosophila. In each organism, genes identified through screens for clock-affecting mutations (frq in Neurospora, per in Drosophila) have subsequently been shown to have characteristics of

  17. Atomic polarizabilities

    Energy Technology Data Exchange (ETDEWEB)

    Safronova, M. S. [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Mitroy, J. [School of Engineering, Charles Darwin University, Darwin NT 0909 (Australia); Clark, Charles W. [Joint Quantum Institute, National Institute of Standards and Technology and the University of Maryland, Gaithersburg, Maryland 20899-8410 (United States); Kozlov, M. G. [Petersburg Nuclear Physics Institute, Gatchina 188300 (Russian Federation)

    2015-01-22

    The atomic dipole polarizability governs the first-order response of an atom to an applied electric field. Atomic polarization phenomena impinge upon a number of areas and processes in physics and have been the subject of considerable interest and heightened importance in recent years. In this paper, we will summarize some of the recent applications of atomic polarizability studies. A summary of results for polarizabilities of noble gases, monovalent, and divalent atoms is given. The development of the CI+all-order method that combines configuration interaction and linearized coupled-cluster approaches is discussed.

  18. Cryptochrome mediates light-dependent magnetosensitivity of Drosophila's circadian clock.

    Directory of Open Access Journals (Sweden)

    Taishi Yoshii

    2009-04-01

    Full Text Available Since 1960, magnetic fields have been discussed as Zeitgebers for circadian clocks, but the mechanism by which clocks perceive and process magnetic information has remained unknown. Recently, the radical-pair model involving light-activated photoreceptors as magnetic field sensors has gained considerable support, and the blue-light photoreceptor cryptochrome (CRY has been proposed as a suitable molecule to mediate such magnetosensitivity. Since CRY is expressed in the circadian clock neurons and acts as a critical photoreceptor of Drosophila's clock, we aimed to test the role of CRY in magnetosensitivity of the circadian clock. In response to light, CRY causes slowing of the clock, ultimately leading to arrhythmic behavior. We expected that in the presence of applied magnetic fields, the impact of CRY on clock rhythmicity should be altered. Furthermore, according to the radical-pair hypothesis this response should be dependent on wavelength and on the field strength applied. We tested the effect of applied static magnetic fields on the circadian clock and found that flies exposed to these fields indeed showed enhanced slowing of clock rhythms. This effect was maximal at 300 muT, and reduced at both higher and lower field strengths. Clock response to magnetic fields was present in blue light, but absent under red-light illumination, which does not activate CRY. Furthermore, cry(b and cry(OUT mutants did not show any response, and flies overexpressing CRY in the clock neurons exhibited an enhanced response to the field. We conclude that Drosophila's circadian clock is sensitive to magnetic fields and that this sensitivity depends on light activation of CRY and on the applied field strength, consistent with the radical pair mechanism. CRY is widespread throughout biological systems and has been suggested as receptor for magnetic compass orientation in migratory birds. The present data establish the circadian clock of Drosophila as a model system

  19. Transcriptional oscillation of canonical clock genes in mouse peripheral tissues

    Directory of Open Access Journals (Sweden)

    Nakahata Yasukazu

    2004-10-01

    Full Text Available Abstract Background The circadian rhythm of about 24 hours is a fundamental physiological function observed in almost all organisms from prokaryotes to humans. Identification of clock genes has allowed us to study the molecular bases for circadian behaviors and temporal physiological processes such as hormonal secretion, and has prompted the idea that molecular clocks reside not only in a central pacemaker, the suprachiasmatic nuclei (SCN of hypothalamus in mammals, but also in peripheral tissues, even in immortalized cells. Furthermore, previous molecular dissection revealed that the mechanism of circadian oscillation at a molecular level is based on transcriptional regulation of clock and clock-controlled genes. Results We systematically analyzed the mRNA expression of clock and clock-controlled genes in mouse peripheral tissues. Eight genes (mBmal1, mNpas2, mRev-erbα, mDbp, mRev-erbβ, mPer3, mPer1 and mPer2; given in the temporal order of the rhythm peak showed robust circadian expressions of mRNAs in all tissues except testis, suggesting that these genes are core molecules of the molecular biological clock. The bioinformatics analysis revealed that these genes have one or a combination of 3 transcriptional elements (RORE, DBPE, and E-box, which are conserved among human, mouse, and rat genome sequences, and indicated that these 3 elements may be responsible for the biological timing of expression of canonical clock genes. Conclusions The observation of oscillatory profiles of canonical clock genes is not only useful for physiological and pathological examination of the circadian clock in various organs but also important for systematic understanding of transcriptional regulation on a genome-wide basis. Our finding of the oscillatory expression of canonical clock genes with a temporal order provides us an interesting hypothesis, that cyclic timing of all clock and clock-controlled genes may be dependent on several transcriptional elements

  20. Clock and light regulation of the CREB coactivator CRTC1 in the suprachiasmatic circadian clock.

    Science.gov (United States)

    Sakamoto, Kensuke; Norona, Frances E; Alzate-Correa, Diego; Scarberry, Daniel; Hoyt, Kari R; Obrietan, Karl

    2013-05-22

    The CREB/CRE transcriptional pathway has been implicated in circadian clock timing and light-evoked clock resetting. To date, much of the work on CREB in circadian physiology has focused on how changes in the phosphorylation state of CREB regulate the timing processes. However, beyond changes in phosphorylation, CREB-dependent transcription can also be regulated by the CREB coactivator CRTC (CREB-regulated transcription coactivator), also known as TORC (transducer of regulated CREB). Here we profiled both the rhythmic and light-evoked regulation of CRTC1 and CRTC2 in the murine suprachiasmatic nucleus (SCN), the locus of the master mammalian clock. Immunohistochemical analysis revealed rhythmic expression of CRTC1 in the SCN. CRTC1 expression was detected throughout the dorsoventral extent of the SCN in the middle of the subjective day, with limited expression during early night, and late night expression levels intermediate between mid-day and early night levels. In contrast to CRTC1, robust expression of CRTC2 was detected during both the subjective day and night. During early and late subjective night, a brief light pulse induced strong nuclear accumulation of CRTC1 in the SCN. In contrast with CRTC1, photic stimulation did not affect the subcellular localization of CRTC2 in the SCN. Additionally, reporter gene profiling and chromatin immunoprecipitation analysis indicated that CRTC1 was associated with CREB in the 5' regulatory region of the period1 gene, and that overexpression of CRTC1 leads to a marked upregulation in period1 transcription. Together, these data raise the prospect that CRTC1 plays a role in fundamental aspects of SCN clock timing and entrainment.

  1. Atom Interferometers and the Gravitational Redshift

    CERN Document Server

    Sinha, Supurna

    2011-01-01

    Muller, Peters and Chu (MPC) claim that a reinterpretation of decade old experiments with atom interferometers leads to a sensitive test of the gravitational redshift effect. This claim has been disputed by Wolf et al (WBBRSC), who adduce arguments to show that MPC's claim is incorrect. In this Letter, we distill the arguments offered by WBBRSC to a single fundamental objection: an atom is not a clock ticking at the Compton frequency. We show that atom interferometric experiments conducted to date do not test the gravitational redshift effect. Our analysis is general and focuses on points of principle rather thanon the present state of technology. We then observe that it is in principle possible to use atom lasers to produce sensitive tests of the red shift effect at the Compton frequency. Such tests may become technologically realisable in the future.

  2. Laser cooling and trapping of ytterbium atoms

    Institute of Scientific and Technical Information of China (English)

    Xin-ye XU; Wen-li WANG; Qing-hong ZHOU; Guo-hui LI; Hai-ling JIANG; Lin-fang CHEN; Jie YE; Zhi-hong ZHOU; Yin CAI; Hai-yao TANG; Min ZHOU

    2009-01-01

    The experiments on the laser cooling and trapping of ytterbium atoms are reported, including the two-dimensional transversal cooling, longitudinal velocity Zeeman deceleration, and a magneto-optical trap with a broadband transition at a wavelength of 399 nm. The magnetic field distributions along the axis of a Zeeman slower were measured and in a good agreement with the calculated results. Cold ytterbium atoms were produced with a number of about 107 and a temperature of a few milli-Kelvin.In addition, using a 556-nm laser, the excitations of cold tterbium atoms at 1S0-3p1 transition were observed. The ytterbium atoms will be further cooled in a 556-nm magneto-optical trap and loaded into a three-dimensional optical lattice to make an ytterbium optical clock.

  3. Cold atom quantum sensors for space

    Science.gov (United States)

    Singh, Yeshpal

    2016-07-01

    Quantum sensors based on cold atoms offer the opportunity to perform highly accurate measurements of physical phenomena related to time, gravity and rotation. The deployment of such technologies in the microgravity environment of space may enable further enhancement of their performance, whilst permitting the detection of these physical phenomena over much larger scales than is possible with a ground-based instrument. In this talk, I will present an overview of the activities of the UK National Quantum Hub in Sensors and Metrology in developing cold atoms technology for space. Our activities are focused in two main areas: optical clocks and atom interferometers. I will also discuss our contributions to recent initiatives including STE-QUEST and AI-GOAT, the ESA/NASA initiative aiming at an atom interferometer gravitational wave detector in space.

  4. Modes Of The Spiral Clock Gong

    Science.gov (United States)

    Perrin, R.; Charnley, T.; Swallowe, G. M.; Banu, H.

    1993-03-01

    The modal frequencies of a spiral clock gong have been measured. The mode numbers and forms of vibrations have been identified by finite element modelling and photographic techniques; very good agreement between modelling and experiment was achieved. All modes were found to be either purely in-plane or out-of-plane. In both cases plots of log (2 n - 1) vs. log ƒ yielded curves with two distinct regions, the transition occurring where the wavelength corresponded to one turn of the spiral. Both sets of lower modes were very complex but the modal frequencies above n = 11 were found to fit a modified form of Chladni's law. It is suggested that the modified Chladni law may form the basis of many musical sounds.

  5. Clock comparison based on laser ranging technologies

    Science.gov (United States)

    Samain, Etienne

    2015-06-01

    Recent progress in the domain of time and frequency standards has required some important improvements of existing time transfer links. Several time transfer by laser link (T2L2) projects have been carried out since 1972 with numerous scientific or technological objectives. There are two projects currently under exploitation: T2L2 and Lunar Reconnaissance Orbiter (LRO). The former is a dedicated two-way time transfer experiment embedded on the satellite Jason-2 allowing for the synchronization of remote clocks with an uncertainty of 100 ps and the latter is a one-way link devoted for ranging a spacecraft orbiting around the Moon. There is also the Laser Time Transfer (LTT) project, exploited until 2012 and designed in the frame of the Chinese navigation constellation. In the context of future space missions for fundamental physics, solar system science or navigation, laser links are of prime importance and many missions based on that technology have been proposed for these purposes.

  6. Automatic minimisation of micromotion in a 88Sr+ optical clock

    Science.gov (United States)

    Barwood, G. P.; Huang, G.; Klein, H. A.; Gill, P.

    2015-07-01

    Optical clocks based on narrow linewidth transitions in single cold ions confined in RF traps are being developed at a number of laboratories worldwide. For these ion clock systems, excess micromotion can cause both Stark and Doppler frequency shifts and also a degradation of frequency stability as a result of a reduced excitation rate to the clock transition. At NPL, we detect micromotion in our 88Sr+ optical clocks by observing the correlation between photon arrival times and the zero crossing of the RF trap drive signal. Recently, two nominally identical 88Sr+ optical clocks have been operated over several days and their frequencies compared against one another. During this time the dc voltages on the endcap and compensation voltage electrodes required to minimise the micromotion can change significantly, particularly following the loading of an ion. This paper describes an automatic method to monitor and minimise micromotion applicable to single ion clocks and which we demonstrate using our two NPL 88Sr+ ion clocks.

  7. Diurnal oscillations of soybean circadian clock and drought responsive genes.

    Directory of Open Access Journals (Sweden)

    Juliana Marcolino-Gomes

    Full Text Available Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicate that some connection between the drought response and the circadian clock may exist in soybean since (i drought stress affects gene expression of circadian clock components and (ii several stress responsive genes display diurnal oscillation in soybeans.

  8. CREB influences timing and entrainment of the SCN circadian clock.

    Science.gov (United States)

    Lee, Boyoung; Li, Aiqing; Hansen, Katelin F; Cao, Ruifeng; Yoon, Jae Hwa; Obrietan, Karl

    2010-12-01

    The transcriptional feedback circuit, which is at the core of the suprachiasmatic nucleus (SCN) circadian (i.e., 24 h) clock, is tightly coupled to both external entrainment cues, such as light, as well as rhythmic cues that arise on a system-wide level within the SCN. One potential signaling pathway by which these cues are conveyed to the molecular clock is the CREB/CRE transcriptional cascade. In this study, we employed a tetracycline-inducible CREB repressor mouse strain, in which approximately 60% of the SCN neurons express the transgene, to test CREB functionality in the clock and its effects on overt rhythmicity. We show that attenuated CREB signaling in the SCN led to a significant reduction in light-evoked clock entrainment. An examination of circadian timing revealed that CREB repressor mice exhibited normal free-running rhythms in the absence of external lighting cues. However, under conditions of constant light, which typically leads to a lengthening of the circadian period, CREB repressor mice exhibited a dramatic arrhythmic phenotype, which could be reversed with doxycycline. At a cellular level, the repression of CREB led to a significant reduction in both the expression of the circadian clock proteins PERIOD1 and PERIOD2 and the clock output hormones AVP and VIP. Together, these data support the idea that the CRE transcriptional pathway orchestrates transcriptional events that are essential for both the maintenance of SCN timing and light entrainment of the circadian clock.

  9. Crosstalk of clock gene expression and autophagy in aging

    Science.gov (United States)

    Kalfalah, Faiza; Janke, Linda; Schiavi, Alfonso; Tigges, Julia; Ix, Alexander; Ventura, Natascia; Boege, Fritz; Reinke, Hans

    2016-01-01

    Autophagy and the circadian clock counteract tissue degeneration and support longevity in many organisms. Accumulating evidence indicates that aging compromises both the circadian clock and autophagy but the mechanisms involved are unknown. Here we show that the expression levels of transcriptional repressor components of the circadian oscillator, most prominently the human Period homologue PER2, are strongly reduced in primary dermal fibroblasts from aged humans, while raising the expression of PER2 in the same cells partially restores diminished autophagy levels. The link between clock gene expression and autophagy is corroborated by the finding that the circadian clock drives cell-autonomous, rhythmic autophagy levels in immortalized murine fibroblasts, and that siRNA-mediated downregulation of PER2 decreases autophagy levels while leaving core clock oscillations intact. Moreover, the Period homologue lin-42 regulates autophagy and life span in the nematode Caenorhabditis elegans, suggesting an evolutionarily conserved role for Period proteins in autophagy control and aging. Taken together, this study identifies circadian clock proteins as set-point regulators of autophagy and puts forward a model, in which age-related changes of clock gene expression promote declining autophagy levels. PMID:27574892

  10. Use of Very Stable Clocks in Satellite Geodesy

    Science.gov (United States)

    Hugentobler, Urs; Romanyuk, Tetyana

    2016-07-01

    Time and frequency play an essential role in satellite geodesy and navigation. Global Navigation Satellite Systems (GNSS) rely on precise measurements of signal travel times. The satellite and receiver clocks involved in measuring this time interval need to be synchronized at the picosecond level. The concept of GNSS allows for an epoch-wise synchronization of space and ground clocks, a feature which is consequently used in satellite geodesy by estimating epoch-wise clock corrections for all clocks in the system, either explicitly or implicitly by forming double differences. Ultra-stable clocks allow to estimate only few parameters for each clock, e.g., offset and drift. The much reduced number of parameters should stabilize GNSS solutions, e.g., tracking network station coordinates. On the other hand systematic errors, e.g., from troposphere or orbit modeling deficiencies or temperature induced hardware delay variations may systematically affect the solutions. The presentation shows trade-offs of modelling higly stable clocks and negative impact of error sources based on simulations.

  11. A molecular clock regulates angiopoietin-like protein 2 expression.

    Science.gov (United States)

    Kadomatsu, Tsuyoshi; Uragami, Shota; Akashi, Makoto; Tsuchiya, Yoshiki; Nakajima, Hiroo; Nakashima, Yukiko; Endo, Motoyoshi; Miyata, Keishi; Terada, Kazutoyo; Todo, Takeshi; Node, Koichi; Oike, Yuichi

    2013-01-01

    Various physiological and behavioral processes exhibit circadian rhythmicity. These rhythms are usually maintained by negative feedback loops of core clock genes, namely, CLOCK, BMAL, PER, and CRY. Recently, dysfunction in the circadian clock has been recognized as an important foundation for the pathophysiology of lifestyle-related diseases, such as obesity, cardiovascular disease, and some cancers. We have reported that angiopoietin-like protein 2 (ANGPTL2) contributes to the pathogenesis of these lifestyle-related diseases by inducing chronic inflammation. However, molecular mechanisms underlying regulation of ANGPTL2 expression are poorly understood. Here, we assess circadian rhythmicity of ANGPTL2 expression in various mouse tissues. We observed that ANGPTL2 rhythmicity was similar to that of the PER2 gene, which is regulated by the CLOCK/BMAL1 complex. Promoter activity of the human ANGPTL2 gene was significantly induced by CLOCK and BMAL1, an induction markedly attenuated by CRY co-expression. We also identified functional E-boxes in the ANGPTL2 promoter and observed occupancy of these sites by endogenous CLOCK in human osteosarcoma cells. Furthermore, Cry-deficient mice exhibited arrhythmic Angptl2 expression. Taken together, these data suggest that periodic expression of ANGPTL2 is regulated by a molecular clock.

  12. A molecular clock regulates angiopoietin-like protein 2 expression.

    Directory of Open Access Journals (Sweden)

    Tsuyoshi Kadomatsu

    Full Text Available Various physiological and behavioral processes exhibit circadian rhythmicity. These rhythms are usually maintained by negative feedback loops of core clock genes, namely, CLOCK, BMAL, PER, and CRY. Recently, dysfunction in the circadian clock has been recognized as an important foundation for the pathophysiology of lifestyle-related diseases, such as obesity, cardiovascular disease, and some cancers. We have reported that angiopoietin-like protein 2 (ANGPTL2 contributes to the pathogenesis of these lifestyle-related diseases by inducing chronic inflammation. However, molecular mechanisms underlying regulation of ANGPTL2 expression are poorly understood. Here, we assess circadian rhythmicity of ANGPTL2 expression in various mouse tissues. We observed that ANGPTL2 rhythmicity was similar to that of the PER2 gene, which is regulated by the CLOCK/BMAL1 complex. Promoter activity of the human ANGPTL2 gene was significantly induced by CLOCK and BMAL1, an induction markedly attenuated by CRY co-expression. We also identified functional E-boxes in the ANGPTL2 promoter and observed occupancy of these sites by endogenous CLOCK in human osteosarcoma cells. Furthermore, Cry-deficient mice exhibited arrhythmic Angptl2 expression. Taken together, these data suggest that periodic expression of ANGPTL2 is regulated by a molecular clock.

  13. Machine learning helps identify CHRONO as a circadian clock component.

    Directory of Open Access Journals (Sweden)

    Ron C Anafi

    2014-04-01

    Full Text Available Over the last decades, researchers have characterized a set of "clock genes" that drive daily rhythms in physiology and behavior. This arduous work has yielded results with far-reaching consequences in metabolic, psychiatric, and neoplastic disorders. Recent attempts to expand our understanding of circadian regulation have moved beyond the mutagenesis screens that identified the first clock components, employing higher throughput genomic and proteomic techniques. In order to further accelerate clock gene discovery, we utilized a computer-assisted approach to identify and prioritize candidate clock components. We used a simple form of probabilistic machine learning to integrate biologically relevant, genome-scale data and ranked genes on their similarity to known clock components. We then used a secondary experimental screen to characterize the top candidates. We found that several physically interact with known clock components in a mammalian two-hybrid screen and modulate in vitro cellular rhythms in an immortalized mouse fibroblast line (NIH 3T3. One candidate, Gene Model 129, interacts with BMAL1 and functionally represses the key driver of molecular rhythms, the BMAL1/CLOCK transcriptional complex. Given these results, we have renamed the gene CHRONO (computationally highlighted repressor of the network oscillator. Bi-molecular fluorescence complementation and co-immunoprecipitation demonstrate that CHRONO represses by abrogating the binding of BMAL1 to its transcriptional co-activator CBP. Most importantly, CHRONO knockout mice display a prolonged free-running circadian period similar to, or more drastic than, six other clock components. We conclude that CHRONO is a functional clock component providing a new layer of control on circadian molecular dynamics.

  14. Using a transportable optical clock for chronometric levelling

    Science.gov (United States)

    Lisdat, Christian; Sterr, Uwe; Koller, Silvio; Grotti, Jacopo; Vogt, Stefan; Häfner, Sebastian; Herbers, Sofia; Al-Masoudi, Ali

    2016-07-01

    With their supreme accuracy and precision, optical clocks in combination with new methods of long-distance frequency transfer can be used to determine height differences by measuring the gravitational red shift between two clocks without accumulation of measurement errors, as in classical levelling. We are developing transportable optical clocks for this purpose that will also serve for the technology development regarding optical clocks in Space and for international comparisons between optical clocks that cannot be linked with sufficient accuracy otherwise. In this talk we will focus on the transportable strontium lattice clock that we are developing and its first evaluation. Presently, we achieve a fractional frequency instability of 3 × 10^{-17} after 1000 s averaging time, which is equivalent to a height resolution of 30 cm. The first uncertainty evaluation of the system yielded 7 × 10^{-17}. We expect rapid improvements to an uncertainty of a few parts in 10^{17}. The clock is now located within a car trailer, which requires compact and rugged lasers systems and physics package. Special care has been taken in the design of the ultra-frequency stable interrogation laser that has to achieve fractional frequency instabilities of considerably below 10^{-15}. Typical laboratory constructions of the reference resonator system used to pre-stabilize the laser frequency are not compatible with the requirement of transportability. In an actual levelling campaign, this clock will be connected via a stabilized optical fibre link with another, stationary frequency standard. The measured gravitational red shift will be compared with the ones calculated from potential differences derived with state of the art geodetic data and models. We will discuss the status of measurements of geodetic relevance with optical clocks and give an outlook on our next steps. This work is supported by QUEST, DFG (RTG 1729, CRC 1128), EU-FP7 (FACT) and EMRP (ITOC). The EMRP is jointly funded

  15. Circadian rhythms, the molecular clock, and skeletal muscle.

    Science.gov (United States)

    Lefta, Mellani; Wolff, Gretchen; Esser, Karyn A

    2011-01-01

    Almost all organisms ranging from single cell bacteria to humans exhibit a variety of behavioral, physiological, and biochemical rhythms. In mammals, circadian rhythms control the timing of many physiological processes over a 24-h period, including sleep-wake cycles, body temperature, feeding, and hormone production. This body of research has led to defined characteristics of circadian rhythms based on period length, phase, and amplitude. Underlying circadian behaviors is a molecular clock mechanism found in most, if not all, cell types including skeletal muscle. The mammalian molecular clock is a complex of multiple oscillating networks that are regulated through transcriptional mechanisms, timed protein turnover, and input from small molecules. At this time, very little is known about circadian aspects of skeletal muscle function/metabolism but some progress has been made on understanding the molecular clock in skeletal muscle. The goal of this chapter is to provide the basic terminology and concepts of circadian rhythms with a more detailed review of the current state of knowledge of the molecular clock, with reference to what is known in skeletal muscle. Research has demonstrated that the molecular clock is active in skeletal muscles and that the muscle-specific transcription factor, MyoD, is a direct target of the molecular clock. Skeletal muscle of clock-compromised mice, Bmal1(-/-) and Clock(Δ19) mice, are weak and exhibit significant disruptions in expression of many genes required for adult muscle structure and metabolism. We suggest that the interaction between the molecular clock, MyoD, and metabolic factors, such as PGC-1, provide a potential system of feedback loops that may be critical for both maintenance and adaptation of skeletal muscle.

  16. Differential clock comparisons with phase-locked local oscillators

    CERN Document Server

    Hume, David B

    2015-01-01

    We develop protocols that circumvent the laser noise limit in the stability of optical clock comparisons by synchronous probing of two clocks using phase-locked local oscillators. This allows for probe times longer than the laser coherence time, avoids the Dick effect, and supports Heisenberg-limited scaling of measurement precision. We present a model for such frequency comparisons and develop numerical simulations of the protocol with realistic noise sources. This provides a route to reduce frequency ratio measurement durations by more than an order of magnitude as clock inaccuracies reach 1x10^-18.

  17. Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders.

    Science.gov (United States)

    Barandas, Rita; Landgraf, Dominic; McCarthy, Michael J; Welsh, David K

    2015-12-01

    Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms.

  18. Standard Clock in Primordial Density Perturbations and Cosmic Microwave Background

    CERN Document Server

    Chen, Xingang

    2014-01-01

    Standard Clocks in the primordial epoch leave a special type of features in the primordial perturbations, which can be used to directly measure the scale factor of the primordial universe as a function of time a(t), thus discriminating between inflation and alternatives. We have started to search for such signals in the Planck 2013 data using the key predictions of the Standard Clock. In this Letter, we present an interesting candidate with the inflation fingerprint. Motivated by this candidate, we construct and compute full Standard Clock models and use the more complete prediction to make more extensive comparison with data.

  19. Regulation of behavioral circadian rhythms and clock protein PER1 by the deubiquitinating enzyme USP2

    DEFF Research Database (Denmark)

    Yang, Yaoming; Duguay, David; Bédard, Nathalie

    2012-01-01

    Endogenous 24-hour rhythms are generated by circadian clocks located in most tissues. The molecular clock mechanism is based on feedback loops involving clock genes and their protein products. Post-translational modifications, including ubiquitination, are important for regulating the clock...

  20. Magneto-Optical Trapping of Ytterbium Atoms with a 398.9 nm Laser

    Institute of Scientific and Technical Information of China (English)

    ZHAO Peng-Yi; XIONG Zhuan-Xian; LIANG Jie; HE Ling-Xiang; LU Bao-Long

    2008-01-01

    We report the realization of ytterbium magneto-optical trap (MOT) operating on the dipole-allowed 1S0 - 1P1 transition at 398.9nm. The MOT is loaded by a slowed atomic beam produced by a Zeeman slower. All seven stable isotopes of Yb atoms could be trapped separately at different laser detuning values. Over 107 174Yb atoms are collected in the MOT, whereas the atom number of fermionic isotope 171Yb is roughly 2.3 × 106 due to a lower abundance. Without the Zeeman slower, the trapped atom numbers are one order of magnitude lower.Both the even and odd isotopes are recognized as excellent candidates of optical clock transition, so the cooling and trapping of ytterbium atoms by the blue MOT is an important step for building an optical clock.

  1. Daily oscillation and photoresponses of clock gene, Clock, and clock-associated gene, arylalkylamine N-acetyltransferase gene transcriptions in the rat pineal gland.

    Science.gov (United States)

    Wang, Guo-Qing; Du, Yu-Zhen; Tong, Jian

    2007-01-01

    This study was conducted to investigate the circadian rhythms and light responses of Clock and arylalkylamine N-acetyltransferase (NAT) gene expressions in the rat pineal gland under the environmental conditions of a 12 h light (05:00-17:00 h): 12 h-dark (17:00-05:00 h) cycle (LD) and constant darkness (DD). The pineal gland of Sprague-Dawley rats housed under a LD regime (n=42) for four weeks and of a regime (n=42) for eight weeks were sampled at six different times, every 4 h (n=7 animals per time point), during a 24 h period. Total RNA was extracted from each sample, and the semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was used to determine temporal changes in mRNA levels of Clock and NAT genes during different circadian or zeitgeber times. The data and parameters were analyzed by the cosine function software, Clock Lab software, and the amplitude F test was used to reveal the circadian rhythm. In the DD or LD condition, both the Clock and NAT mRNA levels in the pineal gland showed robust circadian oscillation (ppineal gland were significantly reduced (ppineal gland (p>0.05). These findings indicate that the transcriptions of Clock and NAT genes in the pineal gland not only show remarkably synchronous endogenous circadian rhythmic changes, but also respond to the ambient light signal in a reduced manner.

  2. The manipulation of atoms and bio-molecules by laser light

    CERN Document Server

    Chu, S

    1998-01-01

    A brief history of the laser cooling and trapping of atoms developed over the past 15 years will be presented. The cooling and trapping technology is already being applied in numerous areas of science and engineering. Applications to be discussed include atomic clocks, atom interferometers, as well as studies in polymer dynamics and protein motion. The talk also includes a video tape of DNA molecules being moved with optical tweezers.

  3. Two-photon assisted clock comparison to picosecond precision

    CERN Document Server

    Zhang, Shi-Wei; Yao, Yin-Ping; Wan, Ren-Gang; Zhang, Tong-Yi

    2015-01-01

    We have experimentally demonstrated a clock comparison scheme utilizing time-correlated photon pairs generated from the spontaneous parametric down conversion process of a laser pumped beta-barium borate crystal. The coincidence of two-photon events are analyzed by the cross correlation of the two time stamp sequences. Combining the coarse and fine part of the time differences at different resolutions, a 64 ps precision for clock synchronization has been realized. We also investigate the effects of hardware devices used in the system on the precision of clock comparison. The results indicate that the detector's time jitter and the background noise will degrade the system performance. With this method, comparison and synchronization of two remote clocks could be implemented with a precision at the level of a few tens of picoseconds.

  4. Clocked, fast electronics trigger for high energy physics

    Energy Technology Data Exchange (ETDEWEB)

    Gray, R.; Rutherfoord, J.P.

    1986-04-01

    For a Fermilab experiment we have designed and built gated-pulse-stretcher modules which allow us to clock all of the fast electronics with the accelerator rf, thus simplifying the trigger design. (orig.).

  5. Speed of light as measured by two terrestrial stable clocks

    Science.gov (United States)

    Hsu, J. P.; Sherry, T. N.; Chiu, C. B.

    1977-01-01

    Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.

  6. Novel putative mechanisms to link circadian clocks to healthy aging.

    Science.gov (United States)

    Popa-Wagner, Aurel; Catalin, Bogdan; Buga, Ana-Maria

    2015-08-01

    The circadian clock coordinates the internal physiology to increase the homeostatic capacity thereby providing both a survival advantage to the system and an optimization of energy budgeting. Multiple-oscillator circadian mechanisms are likely to play a role in regulating human health and may contribute to the aging process. Our aim is to give an overview of how the central clock in the hypothalamus and peripheral clocks relate to aging and metabolic disorders, including hyperlipidemia and hyperglycemia. In particular, we unravel novel putative mechanisms to link circadian clocks to healthy aging. This review may lead to the design of large-scale interventions to help people stay healthy as they age by adjusting daily activities, such as feeding behavior, and or adaptation to age-related changes in individual circadian rhythms.

  7. Open Core Protocol (OCP) Clock Domain Crossing Interfaces

    DEFF Research Database (Denmark)

    Herlev, Mathias; Poulsen, Christian Keis; Sparsø, Jens

    2014-01-01

    The open core protocol (OCP) is an openly licensed configurable and scalable interface protocol for on-chip subsystem communications. The protocol defines read and write transactions from a master towards a slave across a point-to-point connection and the protocol assumes a single common clock....... This paper presents the design of two OCP clock domain crossing interface modules that can be used to construct systems with multiple clock domains. An OCP interface typically has control signals related to both the master issuing a read or write request and the slave producing a response. If all...... these control signals are passed across the clock-domain boundary and synchronized it may add significant latency to the duration of a transaction. Our interface designs avoid this and synchronize only a single signal transition in each direction during a read or a write transaction. While the problem...

  8. Complementary approaches to understanding the plant circadian clock

    CERN Document Server

    Akman, Ozgur E; Loewe, Laurence; Troein, Carl; 10.4204/EPTCS.19.1

    2010-01-01

    Circadian clocks are oscillatory genetic networks that help organisms adapt to the 24-hour day/night cycle. The clock of the green alga Ostreococcus tauri is the simplest plant clock discovered so far. Its many advantages as an experimental system facilitate the testing of computational predictions. We present a model of the Ostreococcus clock in the stochastic process algebra Bio-PEPA and exploit its mapping to different analysis techniques, such as ordinary differential equations, stochastic simulation algorithms and model-checking. The small number of molecules reported for this system tests the limits of the continuous approximation underlying differential equations. We investigate the difference between continuous-deterministic and discrete-stochastic approaches. Stochastic simulation and model-checking allow us to formulate new hypotheses on the system behaviour, such as the presence of self-sustained oscillations in single cells under constant light conditions. We investigate how to model the timing of...

  9. Cellular Clocks : Coupled Circadian Dispatch and Cell Division Cycles

    NARCIS (Netherlands)

    Merrow, Martha; Roenneberg, Till

    2004-01-01

    Gating of cell division by the circadian clock is well known, yet its mechanism is little understood. Genetically tractable model systems have led to new hypotheses and questions concerning the coupling of these two cellular cycles.

  10. Time in motion: the molecular clock meets the microbiome.

    Science.gov (United States)

    Liang, Xue; Bushman, Frederic D; FitzGerald, Garret A

    2014-10-23

    Thaiss et al. report that the intestinal microbiota undergoes diurnal oscillation, which is controlled by host feeding time. Disruption of the host circadian clock induces dysbiosis, which is associated with host metabolic disorders.

  11. Atomic physics

    CERN Document Server

    Born, Max

    1989-01-01

    The Nobel Laureate's brilliant exposition of the kinetic theory of gases, elementary particles, the nuclear atom, wave-corpuscles, atomic structure and spectral lines, electron spin and Pauli's principle, quantum statistics, molecular structure and nuclear physics. Over 40 appendices, a bibliography, numerous figures and graphs.

  12. Tissue-intrinsic dysfunction of circadian clock confers transplant arteriosclerosis.

    Science.gov (United States)

    Cheng, Bo; Anea, Ciprian B; Yao, Lin; Chen, Feng; Patel, Vijay; Merloiu, Ana; Pati, Paramita; Caldwell, R William; Fulton, David J; Rudic, R Daniel

    2011-10-11

    The suprachiasmatic nucleus of the brain is the circadian center, relaying rhythmic environmental and behavioral information to peripheral tissues to control circadian physiology. As such, central clock dysfunction can alter systemic homeostasis to consequently impair peripheral physiology in a manner that is secondary to circadian malfunction. To determine the impact of circadian clock function in organ transplantation and dissect the influence of intrinsic tissue clocks versus extrinsic clocks, we implemented a blood vessel grafting approach to surgically assemble a chimeric mouse that was part wild-type (WT) and part circadian clock mutant. Arterial isografts from donor WT mice that had been anastamosed to common carotid arteries of recipient WT mice (WT:WT) exhibited no pathology in this syngeneic transplant strategy. Similarly, when WT grafts were anastamosed to mice with disrupted circadian clocks, the structural features of the WT grafts immersed in the milieu of circadian malfunction were normal and absent of lesions, comparable to WT:WT grafts. In contrast, aortic grafts from Bmal1 knockout (KO) or Period-2,3 double-KO mice transplanted into littermate control WT mice developed robust arteriosclerotic disease. These lesions observed in donor grafts of Bmal1-KO were associated with up-regulation in T-cell receptors, macrophages, and infiltrating cells in the vascular grafts, but were independent of hemodynamics and B and T cell-mediated immunity. These data demonstrate the significance of intrinsic tissue clocks as an autonomous influence in experimental models of arteriosclerotic disease, which may have implications with regard to the influence of circadian clock function in organ transplantation.

  13. Quantum Clock Synchronization a Multi-Party Protocol

    CERN Document Server

    Krco, M; Krco, Marko; Paul, Prabasaj

    2001-01-01

    We present a multi-party quantum clock synchronization protocol that utilizes shared prior entanglement and broadcast of classical information to synchronize spatially separated clocks. Notably, it is necessary only for any one party to publish classical information. Consequently, the efficacy of the method is independent of the relative location of the parties. The suggested protocol is robust and does not require precise sequencing of procedural steps.

  14. Clock reading: an underestimated topic in children with mathematics difficulties

    OpenAIRE

    2012-01-01

    Recent studies have shown that children with mathematics difficulties (MD) have weaknesses in multiple areas of mathematics. Andersson (2008), for example, recently found that children with MD perform significantly worse than other children on clock reading tasks. The present study builds on this recent finding and aims at a more profound understanding of the difficulties that children with MD experience with telling time. Therefore, clock reading abilities of 154 children with MD were compar...

  15. Rethinking transcriptional activation in the Arabidopsis circadian clock.

    Directory of Open Access Journals (Sweden)

    Karl Fogelmark

    2014-07-01

    Full Text Available Circadian clocks are biological timekeepers that allow living cells to time their activity in anticipation of predictable daily changes in light and other environmental factors. The complexity of the circadian clock in higher plants makes it difficult to understand the role of individual genes or molecular interactions, and mathematical modelling has been useful in guiding clock research in model organisms such as Arabidopsis thaliana. We present a model of the circadian clock in Arabidopsis, based on a large corpus of published time course data. It appears from experimental evidence in the literature that most interactions in the clock are repressive. Hence, we remove all transcriptional activation found in previous models of this system, and instead extend the system by including two new components, the morning-expressed activator RVE8 and the nightly repressor/activator NOX. Our modelling results demonstrate that the clock does not need a large number of activators in order to reproduce the observed gene expression patterns. For example, the sequential expression of the PRR genes does not require the genes to be connected as a series of activators. In the presented model, transcriptional activation is exclusively the task of RVE8. Predictions of how strongly RVE8 affects its targets are found to agree with earlier interpretations of the experimental data, but generally we find that the many negative feedbacks in the system should discourage intuitive interpretations of mutant phenotypes. The dynamics of the clock are difficult to predict without mathematical modelling, and the clock is better viewed as a tangled web than as a series of loops.

  16. A control theory approach to clock steering techniques.

    Science.gov (United States)

    Farina, Marcello; Galleani, Lorenzo; Tavella, Patrizia; Bittanti, Sergio

    2010-10-01

    Several clock and time scale steering methods have been developed according to different viewpoints by various time laboratories. By resorting to control theory ideas, we propose a common theoretical framework encompassing these methods. A comparison of the most common steering methodologies, namely, the classical steering approach, the GPS bang-bang method, and the linear quadratic Gaussian technique, is carried out. We believe that the use of control theory methods can potentially lead to a better understanding of clock steering algorithms.

  17. A model of guarded recursion with clock synchronisation

    DEFF Research Database (Denmark)

    Bizjak, Aleš; Møgelberg, Rasmus Ejlers

    2015-01-01

    productivity to be captured in types. The calculus uses clocks representing time streams and clock quantifiers which allow limited and controlled elimination of modalities. The calculus has since been extended to dependent types by Møgelberg. Both works give denotational semantics but no rewrite semantics...... by removing freshness restrictions from typing rules, and is a necessary step towards defining rewrite semantics, and ultimately implementing the calculus....

  18. Rethinking transcriptional activation in the Arabidopsis circadian clock.

    Science.gov (United States)

    Fogelmark, Karl; Troein, Carl

    2014-07-01

    Circadian clocks are biological timekeepers that allow living cells to time their activity in anticipation of predictable daily changes in light and other environmental factors. The complexity of the circadian clock in higher plants makes it difficult to understand the role of individual genes or molecular interactions, and mathematical modelling has been useful in guiding clock research in model organisms such as Arabidopsis thaliana. We present a model of the circadian clock in Arabidopsis, based on a large corpus of published time course data. It appears from experimental evidence in the literature that most interactions in the clock are repressive. Hence, we remove all transcriptional activation found in previous models of this system, and instead extend the system by including two new components, the morning-expressed activator RVE8 and the nightly repressor/activator NOX. Our modelling results demonstrate that the clock does not need a large number of activators in order to reproduce the observed gene expression patterns. For example, the sequential expression of the PRR genes does not require the genes to be connected as a series of activators. In the presented model, transcriptional activation is exclusively the task of RVE8. Predictions of how strongly RVE8 affects its targets are found to agree with earlier interpretations of the experimental data, but generally we find that the many negative feedbacks in the system should discourage intuitive interpretations of mutant phenotypes. The dynamics of the clock are difficult to predict without mathematical modelling, and the clock is better viewed as a tangled web than as a series of loops.

  19. The Molecular Circadian Clock and Alcohol-Induced Liver Injury

    OpenAIRE

    2015-01-01

    Emerging evidence from both experimental animal studies and clinical human investigations demonstrates strong connections among circadian processes, alcohol use, and alcohol-induced tissue injury. Components of the circadian clock have been shown to influence the pathophysiological effects of alcohol. Conversely, alcohol may alter the expression of circadian clock genes and the rhythmic behavioral and metabolic processes they regulate. Therefore, we propose that alcohol-mediated disruption in...

  20. Clocking In Turbines: Remarks On Physical Nature And Geometric Requirements

    Directory of Open Access Journals (Sweden)

    Swirydczuk Jerzy

    2015-04-01

    Full Text Available The article discusses two issues relating to the clocking phenomenon in turbines, which are the physical course of stator wake deformation in rotor passages and its further interaction with downstream stator blades, and turbine geometry parameters which are believed to be most favourable for clocking. In both cases, the results presented in the article have made it possible to verify and reformulate the previously accepted opinions.

  1. Expanding circadian input, output, and the clock through genomic screens

    OpenAIRE

    2011-01-01

    Many aspects of mammalian physiology display circadian--or once daily--rhythms, such as heart rate, blood pressure, activity levels, metabolism, and liver regeneration. These rhythms are regulated by an entrainable, self-sustaining, cell-autonomous mechanism found in nearly every cell of the body: the circadian clock. The circadian clock itself represents a regulatory network, composed of interlocking negative feedback loops, that in turn is influenced by two other types of regulatory network...

  2. Low-cost on-chip clock jitter measurement scheme

    OpenAIRE

    Omana, Martin; Rossi, Daniele; Giaffreda, Daniele; Metra, Cecilia; Mak, T.M.; Raman, Asifur; Tam, Simon

    2014-01-01

    In this paper, we present a low-cost, on-chip clock jitter digital measurement scheme for high performance microprocessors. It enables in situ jitter measurement during the test or debug phase. It provides very high measurement resolution and accuracy, despite the possible presence of power supply noise (representing a major source of clock jitter), at low area and power costs. The achieved resolution is scalable with technology node and can in principle be increased as much as desired, at lo...

  3. A Clock Enhanced Loop for Simultaneous Error-Free Demultiplexing and Clock Recovery of 160 Gb/s OTDM Signal Single-Channel Transmission over 100 km

    Institute of Scientific and Technical Information of China (English)

    JIA Nan; LI Tang-Jun; ZHONG Kang-Ping; WANG Mu-Guang; CHEN Ming; LI Jing; CHI Jian-Feng

    2010-01-01

    @@ A simple clock enhanced loop of cascaded electro-absorption modulators(EAMs)and 10GHz clock recovery modules is presented.The intensity of harmonic of clock-frequency component is analyzed theoretically and verified experimentally in a 160Gb/s OTDM 100km transmission system.The 10GHz clock component is enhanced obviously before launching into the clock recovery module and the recovered clock signal exhibits low rms jitter of < 400 fs.Moreover,completely error-free(10-12)transmission is observed for more than two hours without using forward error correction technology.The power penalty is about 3.6dB.The proposed loop has merits of enhancing base clock component,simultaneously de-multiplexing and clock recovery,which make the performance of this loop more stable and high suppression of non-target channels.

  4. Register Clustering Methodology for Low Power Clock Tree Synthesis

    Institute of Scientific and Technical Information of China (English)

    邓超; 蔡懿慈; 周强

    2015-01-01

    Clock networks dissipate a significant fraction of the entire chip power budget. Therefore, the optimization for power consumption of clock networks has become one of the most important objectives in high performance IC designs. In contrast to most of the traditional studies that handle this problem with clock routing or buffer insertion strategy, this paper proposes a novel register clustering methodology in generating the leaf level topology of the clock tree to reduce the power consumption. Three register clustering algorithms called KMR, KSR and GSR are developed and a comprehensive study of them is discussed in this paper. Meanwhile, a buffer allocation algorithm is proposed to satisfy the slew constraint within the clusters at a minimum cost of power consumption. We integrate our algorithms into a classical clock tree synthesis (CTS) flow to test the register clustering methodology on ISPD 2010 benchmark circuits. Experimental results show that all the three register clustering algorithms achieve more than 20% reduction in power consumption without affecting the skew and the maximum latency of the clock tree. As the most effective method among the three algorithms, GSR algorithm achieves a 31%reduction in power consumption as well as a 4%reduction in skew and a 5%reduction in maximum latency. Moreover, the total runtime of the CTS flow with our register clustering algorithms is significantly reduced by almost an order of magnitude.

  5. A clock network for geodesy and fundamental science

    Science.gov (United States)

    Lisdat, C.; Grosche, G.; Quintin, N.; Shi, C.; Raupach, S. M. F.; Grebing, C.; Nicolodi, D.; Stefani, F.; Al-Masoudi, A.; Dörscher, S.; Häfner, S.; Robyr, J.-L.; Chiodo, N.; Bilicki, S.; Bookjans, E.; Koczwara, A.; Koke, S.; Kuhl, A.; Wiotte, F.; Meynadier, F.; Camisard, E.; Abgrall, M.; Lours, M.; Legero, T.; Schnatz, H.; Sterr, U.; Denker, H.; Chardonnet, C.; Le Coq, Y.; Santarelli, G.; Amy-Klein, A.; Le Targat, R.; Lodewyck, J.; Lopez, O.; Pottie, P.-E.

    2016-08-01

    Leveraging the unrivalled performance of optical clocks as key tools for geo-science, for astronomy and for fundamental physics beyond the standard model requires comparing the frequency of distant optical clocks faithfully. Here, we report on the comparison and agreement of two strontium optical clocks at an uncertainty of 5 × 10-17 via a newly established phase-coherent frequency link connecting Paris and Braunschweig using 1,415 km of telecom fibre. The remote comparison is limited only by the instability and uncertainty of the strontium lattice clocks themselves, with negligible contributions from the optical frequency transfer. A fractional precision of 3 × 10-17 is reached after only 1,000 s averaging time, which is already 10 times better and more than four orders of magnitude faster than any previous long-distance clock comparison. The capability of performing high resolution international clock comparisons paves the way for a redefinition of the unit of time and an all-optical dissemination of the SI-second.

  6. Time in the 10,000-Year Clock

    CERN Document Server

    Hillis, Danny; Allen, Steve; Giorgini, Jon

    2011-01-01

    The Long Now Foundation is building a mechanical clock that is designed to keep time for the next 10,000 years. The clock maintains its long-term accuracy by synchronizing to the Sun. The 10,000-Year Clock keeps track of five different types of time: Pendulum Time, Uncorrected Solar Time, Corrected Solar Time, Displayed Solar Time and Orrery Time. Pendulum Time is generated from the mechanical pendulum and adjusted according to the equation of time to produce Uncorrected Solar Time, which is in turn mechanically corrected by the Sun to create Corrected Solar Time. Displayed Solar Time advances each time the clock is wound, at which point it catches up with Corrected Solar Time. The clock uses Displayed Solar Time to compute various time indicators to be displayed, including the positions of the Sun, and Gregorian calendar date. Orrery Time is a better approximation of Dynamical Time, used to compute positions of the Moon, planets and stars and the phase of the Moon. This paper describes how the clock reckons ...

  7. The Molecular Circadian Clock and Alcohol-Induced Liver Injury.

    Science.gov (United States)

    Udoh, Uduak S; Valcin, Jennifer A; Gamble, Karen L; Bailey, Shannon M

    2015-10-14

    Emerging evidence from both experimental animal studies and clinical human investigations demonstrates strong connections among circadian processes, alcohol use, and alcohol-induced tissue injury. Components of the circadian clock have been shown to influence the pathophysiological effects of alcohol. Conversely, alcohol may alter the expression of circadian clock genes and the rhythmic behavioral and metabolic processes they regulate. Therefore, we propose that alcohol-mediated disruption in circadian rhythms likely underpins many adverse health effects of alcohol that cut across multiple organ systems. In this review, we provide an overview of the circadian clock mechanism and showcase results from new studies in the alcohol field implicating the circadian clock as a key target of alcohol action and toxicity in the liver. We discuss various molecular events through which alcohol may work to negatively impact circadian clock-mediated processes in the liver, and contribute to tissue pathology. Illuminating the mechanistic connections between the circadian clock and alcohol will be critical to the development of new preventative and pharmacological treatments for alcohol use disorders and alcohol-mediated organ diseases.

  8. Electronics for the pulsed rubidium clock: design and characterization.

    Science.gov (United States)

    Calosso, Claudio E; Micalizio, Salvatore; Godone, Aldo; Bertacco, Elio K; Levi, Filippo

    2007-09-01

    Pulsing the different operation phases of a vapor-cell clock (optical pumping, interrogation, and detection) has been recognized as one of the most effective techniques to reduce light shift and then to improve the stability perspectives of vapor cell clocks. However, in order to take full advantage of the pulsed scheme, a fast-gated electronics is required, the times involved being of the order of milliseconds. In this paper we describe the design and the implementation of the electronics that synchronizes the different phases of the clock operation, as well as of the electronics that is mainly devoted to the thermal stabilization of the clock physics package. We also report some characterization measurements, including a measurement of the clock frequency stability. In particular, in terms of Allan deviation, we measured a frequency stability of 1.2 x 10(-12) tao(-1/2) for averaging times up to tao = 10(5) s, a very interesting result by itself and also for a possible space application of such a clock.

  9. The Molecular Circadian Clock and Alcohol-Induced Liver Injury

    Directory of Open Access Journals (Sweden)

    Uduak S. Udoh

    2015-10-01

    Full Text Available Emerging evidence from both experimental animal studies and clinical human investigations demonstrates strong connections among circadian processes, alcohol use, and alcohol-induced tissue injury. Components of the circadian clock have been shown to influence the pathophysiological effects of alcohol. Conversely, alcohol may alter the expression of circadian clock genes and the rhythmic behavioral and metabolic processes they regulate. Therefore, we propose that alcohol-mediated disruption in circadian rhythms likely underpins many adverse health effects of alcohol that cut across multiple organ systems. In this review, we provide an overview of the circadian clock mechanism and showcase results from new studies in the alcohol field implicating the circadian clock as a key target of alcohol action and toxicity in the liver. We discuss various molecular events through which alcohol may work to negatively impact circadian clock-mediated processes in the liver, and contribute to tissue pathology. Illuminating the mechanistic connections between the circadian clock and alcohol will be critical to the development of new preventative and pharmacological treatments for alcohol use disorders and alcohol-mediated organ diseases.

  10. Measurement of an atomic quadrupole moment using dynamic decoupling

    Science.gov (United States)

    Akerman, Nitzan; Shaniv, Ravid; Ozeri, Roee

    2016-05-01

    Some of the best clocks today are ion-based optical clocks. These clocks are referenced to a narrow optical transition in a trapped ion. An example for such a narrow transition is the electric quadrupole E 2 transition between states with identical parity. An important systematic shift of such a transition is the quadrupole shift resulting from the electric field gradient inherent to the ion trap. We present a new dynamic decoupling method that rejects magnetic field noise while measuring the small quadrupole shift of the optical clock transition. Using our sequence we measured the quadrupole moment of the 4D5/2 level in a trapped 88 Sr+ ion to be 2 .973-0 . 033 + 0 . 026 ea02 , where e is the electron charge and a0 is the Bohr radius. Our measurement improves the uncertainty of this value by an order of magnitude and thus helps mitigate an important systematic uncertainty in 88 Sr+ based optical atomic clocks and verifies complicated many-body quantum calculations.

  11. Feasibility of Extreme Ultraviolet Active Optical Clock

    Institute of Scientific and Technical Information of China (English)

    ZHUANG Wei; CHEN Jing-Biao

    2011-01-01

    @@ We propose an experimental scheme of vacuum ultraviolet(VUV)and extreme ultraviolet(XUV)optical fre-quency standards with noble gas atoms.Considering metastable state 3P2 noble atoms pumped by a conventional discharging method,the atomic beam is collimated with transverse laser cooling at the metastable state and en-ters into the laser cavity in the proposed setup.Due to stimulated emission from the metasable state to the ground state inside the laser cavity consisting of VUV reflection coating mirrors,our calculations show that with enough population inversion to compensate for the cavity loss,an active optical frequency standard at VUV and XUV is feasible.

  12. Reduced Voltage Scaling in Clock Distribution Networks

    Directory of Open Access Journals (Sweden)

    Khader Mohammad

    2009-01-01

    Full Text Available We propose a novel circuit technique to generate a reduced voltage swing (RVS signals for active power reduction on main buses and clocks. This is achieved without performance degradation, without extra power supply requirement, and with minimum area overhead. The technique stops the discharge path on the net that is swinging low at a certain voltage value. It reduces active power on the target net by as much as 33% compared to traditional full swing signaling. The logic 0 voltage value is programmable through control bits. If desired, the reduced-swing mode can also be disabled. The approach assumes that the logic 0 voltage value is always less than the threshold voltage of the nMOS receivers, which eliminate the need of the low to high voltage translation. The reduced noise margin and the increased leakage on the receiver transistors using this approach have been addressed through the selective usage of multithreshold voltage (MTV devices and the programmability of the low voltage value.

  13. Chemical clocks for early-type galaxies

    CERN Document Server

    Carretero, C; Beckman, J E

    2007-01-01

    We present a detailed stellar population analysis of 27 massive elliptical galaxies within 4 very rich clusters at redshift z~0.2. We obtained accurate estimates of the mean luminosity-weighted ages and relative abundances of CN, Mg and Fe as functions of the galaxy velocity dispersion, sigma. Our results are compatible with a scenario in which the stellar populations of massive elliptical galaxies, independently of their environment and mass, had formation timescales shorter than ~1 Gyr. This result implies that massive elliptical galaxies have evolved passively since, at least, as long ago as z~2. For a given galaxy mass the duration of star formation is shorter in those galaxies belonging to more dense environments. Finally, we show that the abundance ratios [CN/Fe] and [Mg/Fe] are the key "chemical clocks" to infer the star formation history timescales in ellipticals. In particular, [Mg/Fe] provides an upper limit for those formation timescales, while [CN/Fe] apperars to be the most suitable parameter to ...

  14. Maternal feeding controls fetal biological clock.

    Directory of Open Access Journals (Sweden)

    Hidenobu Ohta

    Full Text Available BACKGROUND: It is widely accepted that circadian physiological rhythms of the fetus are affected by oscillators in the maternal brain that are coupled to the environmental light-dark (LD cycle. METHODOLOGY/PRINCIPAL FINDINGS: To study the link between fetal and maternal biological clocks, we investigated the effects of cycles of maternal food availability on the rhythms of Per1 gene expression in the fetal suprachiasmatic nucleus (SCN and liver using a transgenic rat model whose tissues express luciferase in vitro. Although the maternal SCN remained phase-locked to the LD cycle, maternal restricted feeding phase-advanced the fetal SCN and liver by 5 and 7 hours respectively within the 22-day pregnancy. CONCLUSIONS/SIGNIFICANCE: Our results demonstrate that maternal feeding entrains the fetal SCN and liver independently of both the maternal SCN and the LD cycle. This indicates that maternal-feeding signals can be more influential for the fetal SCN and particular organ oscillators than hormonal signals controlled by the maternal SCN, suggesting the importance of a regular maternal feeding schedule for appropriate fetal molecular clockwork during pregnancy.

  15. Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre

    Science.gov (United States)

    Okaba, Shoichi; Takano, Tetsushi; Benabid, Fetah; Bradley, Tom; Vincetti, Luca; Maizelis, Zakhar; Yampol'skii, Valery; Nori, Franco; Katori, Hidetoshi

    2014-01-01

    Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom–atom and atom–wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom–atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0−3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time. PMID:24934478

  16. Resetting chemical clocks of hot cores based on S-bearing molecules

    CERN Document Server

    Caselli, P; Wakelam, V; Herbst, E; Castets, A; Caselli, Paola; Ceccarelli, Cecilia; Wakelam, Valentine; Herbst, Eric; Castets, Alain

    2004-01-01

    We report a theoretical study of sulphur chemistry, as applied to hot cores, where S-bearing molecular ratios have been previously proposed and used as chemical clocks. As in previous models, we follow the S-bearing molecular composition after the injection of grain mantle components into the gas phase. For this study, we developed a time-dependent chemical model with up-to-date reaction rate coefficients. We ran several cases, using different realistic chemical compositions for the grain mantles and for the gas prior to mantle evaporation. The modeling shows that S-bearing molecular ratios depend very critically on the gas temperature and density, the abundance of atomic oxygen, and, most importantly, on the form of sulphur injected in the gas phase, which is very poorly known. Consequently, ratios of S-bearing molecules cannot be easily used as chemical clocks. However, detailed observations and careful modeling of both physical and chemical structure can give hints on the source age and constrain the mantl...

  17. British domestic synchronous clocks 1930-1980 the rise and fall of a technology

    CERN Document Server

    Pook, Leslie Philip

    2015-01-01

    This book complements available one-make books on domestic synchronous clocks. It is also a history of science book that sets British domestic synchronous clocks, their manufacturers and technology in their social context. Part I covers the historical background, British domestic synchronous clock manufacturers and brands, how synchronous clocks work, domestic synchronous clock cases, practical advice on the servicing of domestic synchronous clocks, and analysis of the marketing and reliability of British domestic synchronous clocks. This analysis provides an explanation of the rise and eventual fall of their technology. Part II contains galleries of a selection of British domestic synchronous clocks, and of the movements with which they are fitted. There is a front and back view of each clock, together with a brief description. Views of each movement include views with the movement partly dismantled, together with a brief technical description of the movement. This profusely illustrated book is primarily fo...

  18. Synergism of coupled subsarcolemmal Ca2+ clocks and sarcolemmal voltage clocks confers robust and flexible pacemaker function in a novel pacemaker cell model.

    Science.gov (United States)

    Maltsev, Victor A; Lakatta, Edward G

    2009-03-01

    Recent experimental studies have demonstrated that sinoatrial node cells (SANC) generate spontaneous, rhythmic, local subsarcolemmal Ca(2+) releases (Ca(2+) clock), which occur during late diastolic depolarization (DD) and interact with the classic sarcolemmal voltage oscillator (membrane clock) by activating Na(+)-Ca(2+) exchanger current (I(NCX)). This and other interactions between clocks, however, are not captured by existing essentially membrane-delimited cardiac pacemaker cell numerical models. Using wide-scale parametric analysis of classic formulations of membrane clock and Ca(2+) cycling, we have constructed and initially explored a prototype rabbit SANC model featuring both clocks. Our coupled oscillator system exhibits greater robustness and flexibility than membrane clock operating alone. Rhythmic spontaneous Ca(2+) releases of sarcoplasmic reticulum (SR)-based Ca(2+) clock ignite rhythmic action potentials via late DD I(NCX) over much broader ranges of membrane clock parameters [e.g., L-type Ca(2+) current (I(CaL)) and/or hyperpolarization-activated ("funny") current (I(f)) conductances]. The system Ca(2+) clock includes SR and sarcolemmal Ca(2+) fluxes, which optimize cell Ca(2+) balance to increase amplitudes of both SR Ca(2+) release and late DD I(NCX) as SR Ca(2+) pumping rate increases, resulting in a broad pacemaker rate modulation (1.8-4.6 Hz). In contrast, the rate modulation range via membrane clock parameters is substantially smaller when Ca(2+) clock is unchanged or lacking. When Ca(2+) clock is disabled, the system parametric space for fail-safe SANC operation considerably shrinks: without rhythmic late DD I(NCX) ignition signals membrane clock substantially slows, becomes dysrhythmic, or halts. In conclusion, the Ca(2+) clock is a new critical dimension in SANC function. A synergism of the coupled function of Ca(2+) and membrane clocks confers fail-safe SANC operation at greatly varying rates.

  19. Progress on a Miniature Cold-Atom Frequency Standard

    CERN Document Server

    Scherer, David R; Mescher, Mark; Stoner, Richard; Timmons, Brian; Rogomentich, Fran; Tepolt, Gary; Mahnkopf, Sven; Noble, Jay; Chang, Sheng; Taylor, Dwayne

    2014-01-01

    Atomic clocks play a crucial role in timekeeping, communications, and navigation systems. Recent efforts enabled by heterogeneous MEMS integration have led to the commercial introduction of Chip-Scale Atomic Clocks (CSAC) with a volume of 16 cm3, power consumption of 120 mW, and instability (Allan Deviation) of {\\sigma}({\\tau} = 1 sec) < 2e-10. In order to reduce the temperature sensitivity of next-generation CSACs for timing applications, the interaction of atoms with the environment must be minimized, which can be accomplished in an architecture based on trapped, laser-cooled atoms. In this paper, we present results describing the development of a miniature cold-atom apparatus for operation as a frequency standard. Our architecture is based on laser-cooling a sample of neutral atoms in a Magneto-Optical Trap (MOT) using a conical retro-reflector in a miniature vacuum chamber. Trapping the atoms in vacuum and performing microwave interrogation in the dark reduces the temperature sensitivity compared to va...

  20. Differentially timed extracellular signals synchronize pacemaker neuron clocks.

    Directory of Open Access Journals (Sweden)

    Ben Collins

    2014-09-01

    Full Text Available Synchronized neuronal activity is vital for complex processes like behavior. Circadian pacemaker neurons offer an unusual opportunity to study synchrony as their molecular clocks oscillate in phase over an extended timeframe (24 h. To identify where, when, and how synchronizing signals are perceived, we first studied the minimal clock neural circuit in Drosophila larvae, manipulating either the four master pacemaker neurons (LNvs or two dorsal clock neurons (DN1s. Unexpectedly, we found that the PDF Receptor (PdfR is required in both LNvs and DN1s to maintain synchronized LNv clocks. We also found that glutamate is a second synchronizing signal that is released from DN1s and perceived in LNvs via the metabotropic glutamate receptor (mGluRA. Because simultaneously reducing Pdfr and mGluRA expression in LNvs severely dampened Timeless clock protein oscillations, we conclude that the master pacemaker LNvs require extracellular signals to function normally. These two synchronizing signals are released at opposite times of day and drive cAMP oscillations in LNvs. Finally we found that PdfR and mGluRA also help synchronize Timeless oscillations in adult s-LNvs. We propose that differentially timed signals that drive cAMP oscillations and synchronize pacemaker neurons in circadian neural circuits will be conserved across species.

  1. Buffer Gas Experiments in Mercury (Hg+) Ion Clock

    Science.gov (United States)

    Chung, Sang K.; Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute

    2004-01-01

    We describe the results of the frequency shifts measured from various buffer gases that might be used as a buffer gas to increase the loading efficiency and cooling of ions trapped in a small mercury ion clock. The small mass, volume and power requirement of space clock precludes the use of turbo pumps. Hence, a hermetically sealed vacuum system, incorporating a suitable getter material with a fixed amount of inert buffer gas may be a practical alternative to the groundbased system. The collision shifts of 40,507,347.996xx Hz clock transition for helium, neon and argon buffer gases were measured in the ambient earth magnetic field. In addition to the above non-getterable inert gases we also measured the frequency shifts due to getterable, molecular hydrogen and nitrogen gases which may be used as buffer gases when incorporated with a miniature ion pump. We also examined the frequency shift due to the low methane gas partial pressure in a fixed higher pressure neon buffer gas environment. Methane gas interacted with mercury ions in a peculiar way as to preserve the ion number but to relax the population difference in the two hyperfine clock states and thereby reducing the clock resonance signal. The same population relaxation was also observed for other molecular buffer gases (N H,) but at much reduced rate.

  2. Energy Efficient Global Clock Synchronization for Wireless Sensor Networks

    Directory of Open Access Journals (Sweden)

    Vinod Namboodiri

    2010-05-01

    Full Text Available Clock synchronization is critical to many sensor networks for the success of the application as well as energyefficiency. Achieving a global time frame through localized averaging of clock values for multiple rounds till convergenceis a promising approach to clock synchronization due to the decentralized nature of computation coupled withscalability. However, it is not clear what power levels for all nodes would make the synchronization process energyefficient.Large power levels lead to faster convergence but consume a lot of energy per round of synchronization.On the other hand, smaller powers consume little energy per round, but convergence is very slow requiring a lotof rounds to achieve synchronization. In this paper we look at the problem of finding a power assignment thatachieves global clock synchronization in the most energy-efficient manner possible. We look at the problem throughtwo dimensions; rate of convergence and energy consumed per round of synchronization. A centralized algorithm ispresented that uses the path congestion of the induced communication graph to estimate which power assignmentshave good convergence properties and find one that minimizes the total energy to achieve clock synchronization.Our evaluation demonstrates that the power assignment derived from this algorithm is very energy-efficient and isapplicable for wireless communication environments with various distance-power gradients. Further, we present asimple distributed algorithm which nodes can execute locally to derive energy-efficient power levels for global clocksynchronization, and is especially useful in large-scale deployments.

  3. Synchronization of the Drosophila circadian clock by temperature cycles.

    Science.gov (United States)

    Glaser, F T; Stanewsky, R

    2007-01-01

    The natural light/dark and temperature cycles are considered to be the most prominent factors that synchronize circadian clocks with the environment. Understanding the principles of temperature entrainment significantly lags behind our current knowledge of light entrainment in any organism subject to circadian research. Nevertheless, several effects of temperature on circadian clocks are well understood, and similarities as well as differences to the light-entrainment pathways start to emerge. This chapter provides an overview of the temperature effects on the Drosophila circadian clock with special emphasis on synchronization by temperature cycles. As in other organisms, such temperature cycles can serve as powerful time cues to synchronize the clock. Mutants that specifically interfere with aspects of temperature entrainment have been isolated and will likely help to reveal the underlying mechanisms. These mechanisms involve transcriptional and posttranscriptional regulation of clock genes. For synchronization of fly behavior by temperature cycles, the generation of a whole organism or systemic signal seems to be required, even though individual fly tissues can be synchronized under isolated culture conditions. If true, the requirement for such a signal would reveal a fundamental difference to the light-entrainment mechanism.

  4. The circadian molecular clock creates epidermal stem cell heterogeneity.

    Science.gov (United States)

    Janich, Peggy; Pascual, Gloria; Merlos-Suárez, Anna; Batlle, Eduard; Ripperger, Jürgen; Albrecht, Urs; Cheng, Hai-Ying M; Obrietan, Karl; Di Croce, Luciano; Benitah, Salvador Aznar

    2011-11-09

    Murine epidermal stem cells undergo alternate cycles of dormancy and activation, fuelling tissue renewal. However, only a subset of stem cells becomes active during each round of morphogenesis, indicating that stem cells coexist in heterogeneous responsive states. Using a circadian-clock reporter-mouse model, here we show that the dormant hair-follicle stem cell niche contains coexisting populations of cells at opposite phases of the clock, which are differentially predisposed to respond to homeostatic cues. The core clock protein Bmal1 modulates the expression of stem cell regulatory genes in an oscillatory manner, to create populations that are either predisposed, or less prone, to activation. Disrupting this clock equilibrium, through deletion of Bmal1 (also known as Arntl) or Per1/2, resulted in a progressive accumulation or depletion of dormant stem cells, respectively. Stem cell arrhythmia also led to premature epidermal ageing, and a reduction in the development of squamous tumours. Our results indicate that the circadian clock fine-tunes the temporal behaviour of epidermal stem cells, and that its perturbation affects homeostasis and the predisposition to tumorigenesis.

  5. Autonomous Rubidium Clock Weak Frequency Jump Detector for Onboard Navigation Satellite System.

    Science.gov (United States)

    Khare, Akshay; Arora, Rajat; Banik, Alak; Mehta, Sanjay D

    2016-02-01

    Frequency jumps are common in rubidium frequency sources. They affect the estimation of user position in navigational satellite systems. These jumps must be detected and corrected immediately as they have direct impact on the navigation system integrity. A novel weak frequency jump detector is proposed based on a Kalman filter with a multi-interval approach. This detector can be applied for both "sudden" and "slow" frequency transitions. In this detection method, noises of clock data are reduced by Kalman filtering, for accurate estimation of jump size with less latency. Analysis on in-orbit rubidium atomic frequency standard (RAFS) phase telemetry data shows that the detector can be used for fast detection and correction of weak frequency jumps. Furthermore, performance comparison of different existing frequency jump detection techniques with the proposed detector is discussed. A multialgorithm-based strategy is proposed depending on the jump size and latency for onboard navigation satellites having RAFS as the primary frequency source.

  6. Precision spectroscopy on atomic hydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Parthey, Christian Godehard

    2011-12-15

    This Thesis reports on three measurements involving the 1S-2S transition in atomic hydrogen and deuterium conducted on a 5.8 K atomic beam. The transition is excited Doppler-free via two counter-propagating photons near 243 nm. The H/D isotope shift has been determined as {delta}{integral}{sub exp}=670 994 334 606(15) Hz. Comparing with the theoretical value for the isotope shift, excluding the leading nuclear size effect, {delta}{integral}{sub th}=670 999 566.90(66)(60) kHz we confirm, twice more accurate, the rms charge radius difference of the deuteron and the proton as left angle r{sup 2} right angle {sub d}- left angle r{sup 2} right angle {sub p}=3.82007(65) fm{sup 2} and the deuteron structure radius r{sub str}=1.97507(78) fm. The frequency ratio of the 1S-2S transition in atomic hydrogen to the cesium ground state hyperfine transition provided by the mobile cesium fountain clock FOM is measured to be {integral}{sub 1S-2S}=2 466 061 413 187 035 (10) Hz which presents a fractional frequency uncertainty of 4.2 x 10{sup -15}. The second absolute frequency measurement of the 1S-2S transition in atomic hydrogen presents the first application of a 900 km fiber link between MPQ and Physikalisch- Technische Bundesanstalt (PTB) in Braunschweig which we have used to calibrate the MPQ hydrogen maser with the stationary cesium fountain clock CSF1 at PTB. With the result of {integral}{sub 1S-2S}=2 466 061 413 187 017 (11) Hz we can put a constraint on the electron Lorentz boost violating coefficients 0.95c{sub (TX)}-0.29c{sub (TY)}-0.08 c{sub (TZ)}=(2.2{+-}1.8) x 10{sup -11} within the framework of minimal standard model extensions. We limit a possible drift of the strong coupling constant through the ratio of magnetic moments at a competitive level ({partial_derivative})/({partial_derivative}t)ln ({mu}{sub Cs})/({mu}{sub B})=-(3.0{+-}1.2) x 10{sup -15} yr{sup -1}.

  7. Simultaneous Faraday filtering of the Mollow triplet sidebands with the Cs-D1 clock transition

    Science.gov (United States)

    Portalupi, Simone Luca; Widmann, Matthias; Nawrath, Cornelius; Jetter, Michael; Michler, Peter; Wrachtrup, Jörg; Gerhardt, Ilja

    2016-11-01

    Hybrid quantum systems integrating semiconductor quantum dots (QDs) and atomic vapours become important building blocks for scalable quantum networks due to the complementary strengths of individual parts. QDs provide on-demand single-photon emission with near-unity indistinguishability comprising unprecedented brightness--while atomic vapour systems provide ultra-precise frequency standards and promise long coherence times for the storage of qubits. Spectral filtering is one of the key components for the successful link between QD photons and atoms. Here we present a tailored Faraday anomalous dispersion optical filter based on the caesium-D1 transition for interfacing it with a resonantly pumped QD. The presented Faraday filter enables a narrow-bandwidth (Δω=2π × 1 GHz) simultaneous filtering of both Mollow triplet sidebands. This result opens the way to use QDs as sources of single as well as cascaded photons in photonic quantum networks aligned to the primary frequency standard of the caesium clock transition.

  8. Simultaneous Faraday filtering of the Mollow triplet sidebands with the Cs-D1 clock transition.

    Science.gov (United States)

    Portalupi, Simone Luca; Widmann, Matthias; Nawrath, Cornelius; Jetter, Michael; Michler, Peter; Wrachtrup, Jörg; Gerhardt, Ilja

    2016-11-25

    Hybrid quantum systems integrating semiconductor quantum dots (QDs) and atomic vapours become important building blocks for scalable quantum networks due to the complementary strengths of individual parts. QDs provide on-demand single-photon emission with near-unity indistinguishability comprising unprecedented brightness-while atomic vapour systems provide ultra-precise frequency standards and promise long coherence times for the storage of qubits. Spectral filtering is one of the key components for the successful link between QD photons and atoms. Here we present a tailored Faraday anomalous dispersion optical filter based on the caesium-D1 transition for interfacing it with a resonantly pumped QD. The presented Faraday filter enables a narrow-bandwidth (Δω=2π × 1 GHz) simultaneous filtering of both Mollow triplet sidebands. This result opens the way to use QDs as sources of single as well as cascaded photons in photonic quantum networks aligned to the primary frequency standard of the caesium clock transition.

  9. Time-variable gravity potential components for optical clock comparisons and the definition of international time scales

    Science.gov (United States)

    Voigt, C.; Denker, H.; Timmen, L.

    2016-12-01

    The latest generation of optical atomic clocks is approaching the level of one part in 1018 in terms of frequency stability and uncertainty. For clock comparisons and the definition of international time scales, a relativistic redshift effect of the clock frequencies has to be taken into account at a corresponding uncertainty level of about 0.1 m2 s-2 and 0.01 m in terms of gravity potential and height, respectively. Besides the predominant static part of the gravity potential, temporal variations must be considered in order to avoid systematic frequency shifts. Time-variable gravity potential components induced by tides and non-tidal mass redistributions are investigated with regard to the level of one part in 1018. The magnitudes and dominant time periods of the individual gravity potential contributions are investigated globally and for specific laboratory sites together with the related uncertainty estimates. The basics of the computation methods are presented along with the applied models, data sets and software. Solid Earth tides contribute by far the most dominant signal with a global maximum amplitude of 4.2 m2 s-2 for the potential and a range (maximum-to-minimum) of up to 1.3 and 10.0 m2 s-2 in terms of potential differences between specific laboratories over continental and intercontinental scales, respectively. Amplitudes of the ocean tidal loading potential can amount up to 1.25 m2 s-2, while the range of the potential between specific laboratories is 0.3 and 1.1 m2 s-2 over continental and intercontinental scales, respectively. These are the only two contributors being relevant at a 10-17 level. However, several other time-variable potential effects can particularly affect clock comparisons at the 10-18 level. Besides solid Earth pole tides, these are non-tidal mass redistributions in the atmosphere, the oceans and the continental water storage.

  10. The Brazilian time and frequency atomic standards program

    Directory of Open Access Journals (Sweden)

    Mushtaq Ahmed

    2008-06-01

    Full Text Available Cesium atomic beam clocks have been the workhorse for many demanding applications in science and technology for the past four decades. Tests of the fundamental laws of physics and the search for minute changes in fundamental constants, the synchronization of telecommunication networks, and realization of the satellite-based global positioning system would not be possible without atomic clocks. The adoption of optical cooling and trapping techniques, has produced a major advance in atomic clock precision. Cold-atom fountain and compact cold-atom clocks have also been developed. Measurement precision of a few parts in 10(15 has been demonstrated for a cold-atom fountain clock. We present here an overview of the time and frequency metrology program based on cesium atoms under development at USP São Carlos. This activity consists of construction and characterization of atomic-beam, and several variations of cold-atom clocks. We discuss the basic working principles, construction, evaluation, and important applications of atomic clocks in the Brazilian program.Relógios atômicos de feixe de Césio têm sido a base para diversas aplicações em ciência e tecnologia nas últimas quatro décadas. Testes de leis fundamentais de física, buscas por mínimas variações em constantes fundamentais, sincronização de redes de telecomunicações e o funcionamento do sistema de posicionamento global, baseado em satélites de navegação, não seriam possíveis sem os relógios atômicos. A adoção de técnicas de aprisionamento e resfriamento ópticos tem permitido um grande avanço na precisão dos relógios atômicos. Chafarizes de átomos frios e relógios compactos de átomos frios também têm sido desenvolvidos. Precisões de medida de algumas partes em 1015 foram demonstradas para relógios do tipo chafariz de átomos frios. Apresentamos uma visão geral do programa de metrologia de tempo e freqüência baseado em átomos de césio, em

  11. Revisiting a Classic Study of the Molecular Clock.

    Science.gov (United States)

    Robinson, Lauren M; Boland, Joseph R; Braverman, John M

    2016-03-01

    A constant rate of molecular evolution among homologous proteins and across lineages is known as the molecular clock. This concept has been useful for estimating divergence times. Here, we revisit a study by Richard Dickerson (J Mol Evol 1:26-45, 1971), wherein he provided striking visual evidence for a constant rate of amino acid changes among various evolutionary branch points. Dickerson's study is commonly cited as support of the molecular clock and a figure from it is often reproduced in textbooks. Since its publication, however, there have been updates made to dates of common ancestors based on the fossil record that should be considered. Additionally, collecting the accession numbers and carefully outlining Dickerson's methods serves as a resource to students of the molecular clock hypothesis.

  12. Clock Synchronization and Navigation in the Vicinity of the Earth

    CERN Document Server

    Bahder, T B

    2004-01-01

    Clock synchronization is the backbone of applications such as high-accuracy satellite navigation, geolocation, space-based interferometry, and cryptographic communication systems. The high accuracy of synchronization needed over satellite-to-ground and satellite-to-satellite distances requires the use of general relativistic concepts. The role of geometrical optics and antenna phase center approximations are discussed in high accuracy work. The clock synchronization problem is explored from a general relativistic point of view, with emphasis on the local measurement process and the use of the tetrad formalism as the correct model of relativistic measurements. The treatment makes use of J. L. Synge's world function of space-time as a basic coordinate independent geometric concept. A metric is used for space-time in the vicinity of the Earth, where coordinate time is proper time on the geoid. The problem of satellite clock syntonization is analyzed by numerically integrating the geodesic equations of motion for...

  13. Fault-tolerant clock synchronization validation methodology. [in computer systems

    Science.gov (United States)

    Butler, Ricky W.; Palumbo, Daniel L.; Johnson, Sally C.

    1987-01-01

    A validation method for the synchronization subsystem of a fault-tolerant computer system is presented. The high reliability requirement of flight-crucial systems precludes the use of most traditional validation methods. The method presented utilizes formal design proof to uncover design and coding errors and experimentation to validate the assumptions of the design proof. The experimental method is described and illustrated by validating the clock synchronization system of the Software Implemented Fault Tolerance computer. The design proof of the algorithm includes a theorem that defines the maximum skew between any two nonfaulty clocks in the system in terms of specific system parameters. Most of these parameters are deterministic. One crucial parameter is the upper bound on the clock read error, which is stochastic. The probability that this upper bound is exceeded is calculated from data obtained by the measurement of system parameters. This probability is then included in a detailed reliability analysis of the system.

  14. The twin paradox with macroscopic clocks in superconducting circuits

    CERN Document Server

    Lindkvist, Joel; Fuentes, Ivette; Dragan, Andrzej; Svensson, Ida-Maria; Delsing, Per; Johansson, Göran

    2014-01-01

    Time dilation, a striking prediction of Einstein's relativity, plays an important role in applications such as the Global Positioning System. One of the most compelling consequences of time dilation is known as the twin paradox, where a twin at rest ages more than her sibling travelling at relativistic speeds. In this paper, we propose an implementation of the twin paradox in superconducting circuits with velocities as large as a few percent of the speed of light. Ultrafast modulation of the boundary conditions for the electromagnetic field in a microwave cavity simulates a clock moving at relativistic speeds. While previous demonstrations of this effect involve point-like clocks, our superconducting cavity has a finite length, allowing us to investigate the role of clock size as well as interesting quantum effects on time dilation. In particular, our theoretical results show that the travelling twin ages slower for larger cavity lengths and that quantum particle creation, known in this context as the dynamic...

  15. Circadian clocks optimally adapt to sunlight for reliable synchronization

    CERN Document Server

    Hasegawa, Yoshihiko

    2014-01-01

    Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to properly respond to external stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist because better entrainability favors higher sensitivity, which may sacrifice the regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase-response curve with a variational method. Our result indicates an existence of a dead zone, i.e., a time during which external stimuli neither advance nor delay the clock. This result is independent of model details and a dead zone appears only when the input stimuli obey the time course of actual insolation. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle. Our result also explains the lack of a dead zone in osc...

  16. Multi-GNSS Orbit and Clock Combination: Preliminary Results

    Science.gov (United States)

    Fritsche, Mathias

    2016-04-01

    In the framework of the Multi-GNSS Experiment (MGEX) a number of Analysis Centers (ACs) extended their software capabilities to process signals from the BeiDou, Galileo, and QZSS systems in addition to the well established systems GPS and GLONASS. Currently, the MGEX product portfolio covers precise satellite orbits and clocks, receiver clocks, signal biases, and Earth rotation parameters generated by the individual ACs. This presentation will provide an overview on the available AC-specific MGEX products. In addition, an introduction to a multi-GNSS orbit and clock combination procedure will be given. Finally, preliminary results from that multi-GNSS combination including a comparison with corresponding operational IGS products will be reported along with a discussion of the results.

  17. Atomic theories

    CERN Document Server

    Loring, FH

    2014-01-01

    Summarising the most novel facts and theories which were coming into prominence at the time, particularly those which had not yet been incorporated into standard textbooks, this important work was first published in 1921. The subjects treated cover a wide range of research that was being conducted into the atom, and include Quantum Theory, the Bohr Theory, the Sommerfield extension of Bohr's work, the Octet Theory and Isotopes, as well as Ionisation Potentials and Solar Phenomena. Because much of the material of Atomic Theories lies on the boundary between experimentally verified fact and spec

  18. Gravitational wave detection using atom interferometry

    Science.gov (United States)

    Hogan, Jason

    2016-05-01

    The advent of gravitational wave astronomy promises to provide a new window into the universe. Low frequency gravitational waves below 10 Hz are expected to offer rich science opportunities both in astrophysics and cosmology, complementary to signals in LIGO's band. Detector designs based on atom interferometry have a number of advantages over traditional approaches in this band, including the possibility of substantially reduced antenna baseline length in space and high isolation from seismic noise for a terrestrial detector. In particular, atom interferometry based on the clock transition in group II atoms offers tantalizing new possibilities. Such a design is expected to be highly immune to laser frequency noise because the signal arises strictly from the light propagation time between two ensembles of atoms. This would allow for a gravitational wave detector with a single linear baseline, potentially offering advantages in cost and design flexibility. In support of these proposals, recent progress in long baseline atom interferometry in a 10-meter drop tower has enabled observation of matter wave interference with atomic wavepacket separations exceeding 50 cm and interferometer durations of more than 2 seconds. This approach can provide ground-based proof-of-concept demonstrations of many of the technical requirements of both terrestrial and satellite gravitational wave detectors.

  19. Reference clock parameters for digital communications systems applications

    Science.gov (United States)

    Kartaschoff, P.

    1981-01-01

    The basic parameters relevant to the design of network timing systems describe the random and systematic time departures of the system elements, i.e., master (or reference) clocks, transmission links, and other clocks controlled over the links. The quantitative relations between these parameters were established and illustrated by means of numerical examples based on available measured data. The examples were limited to a simple PLL control system but the analysis can eventually be applied to more sophisticated systems at the cost of increased computational effort.

  20. Methods to study the mechanism of the Neurospora Circadian Clock

    Science.gov (United States)

    Cha, Joonseok; Zhou, Mian; Liu, Yi

    2015-01-01

    Eukaryotic circadian clocks are comprised of interlocked auto-regulatory feedback loops that control gene expression at the levels of transcription and translation. The filamentous fungus Neurospora crassa is an excellent model for the complex molecular network of regulatory mechanisms that are common to all eukaryotes. In the heart of the network, post-translational regulations and functions of the core clock elements are of major interest. This chapter will discuss the methods that were recently used to study the Neurospora circadian oscillator mechanisms at the molecular level. PMID:25662455

  1. General flat four-dimensional world pictures and clock systems

    Science.gov (United States)

    Hsu, J. P.; Underwood, J. A.

    1978-01-01

    We explore the mathematical structure and the physical implications of a general four-dimensional symmetry framework which is consistent with the Poincare-Einstein principle of relativity for physical laws and with experiments. In particular, we discuss a four-dimensional framework in which all observers in different frames use one and the same grid of clocks. The general framework includes special relativity and a recently proposed new four-dimensional symmetry with a nonuniversal light speed as two special simple cases. The connection between the properties of light propagation and the convention concerning clock systems is also discussed, and is seen to be nonunique within the four-dimensional framework.

  2. Probing beyond the laser coherence time in optical clock comparisons

    Science.gov (United States)

    Hume, David B.; Leibrandt, David R.

    2016-03-01

    We develop differential measurement protocols that circumvent the laser noise limit in the stability of optical clock comparisons by synchronous probing of two clocks using phase-locked local oscillators. This allows for probe times longer than the laser coherence time, avoids the Dick effect, and supports Heisenberg-limited measurement precision. We present protocols for such frequency comparisons and develop numerical simulations of the protocols with realistic noise sources. These methods provide a route to reduce frequency ratio measurement durations by more than an order of magnitude.

  3. THE STOCHASTIC ESTIMATION OF SATELLITE CLOCK CORRECTION INFORMATION IN WADGPS

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Using autocorrelation information of the pseudorange errors generated by se lective availability (SA) frequency dithering, we have constructed a simple first order stochas tic model for SA effects. This model has been used in a Kalman filter to account for the stochastic behavior of SA dithering in estimating satellite clock information in wide area dif ferential GPS. We have obtained fifteen percent improvement in the user positioning using the correlation information on the satellite clock information in a Kalman filter, when comparing the results obtained using a regular least square estimation.

  4. Nuclear clocks based on resonant excitation of gamma-transitions

    CERN Document Server

    Peik, Ekkehard

    2015-01-01

    We review the ideas and concepts for a clock that is based on a radiative transition in the nucleus rather than in the electron shell. This type of clock offers advantages like an insensitivity against field-induced systematic frequency shifts and the opportunity to obtain high stability from interrogating many nuclei in the solid state. Experimental work concentrates on the low-energy (about 8 eV) isomeric transition in Th-229. We review the status of the experiments that aim at a direct optical observation of this transition and outline the plans for high-resolution laser spectroscopy experiments.

  5. Stability improvements for the NIST Yb optical lattice clock

    Science.gov (United States)

    Fasano, R. J.; Schioppo, M.; McGrew, W. F.; Brown, R. C.; Hinkley, N.; Yoon, T. H.; Beloy, K.; Oates, C. W.; Ludlow, A. D.

    2016-05-01

    To reach the fundamental limit given by quantum projection noise, optical lattice clocks require advanced laser stabilization techniques. The NIST ytterbium clock has benefited from several generations of extremely high finesse optical cavities, with cavity linewidths below 1 kHz. Characterization of the cavity drift rate has allowed compensation to the mHz/s level, improving the medium-term stability of the cavity. Based on recent measurements using Ramsey spectroscopy with synchronous interrogation, we report a fractional instability σy(1s) thermal noise floor, which will improve our Dick-limited fractional instability at 1 s to below 10-16. Also at University of Colorado.

  6. Clocks, computers, black holes, spacetime foam, and holographic principle

    CERN Document Server

    Ng, Y J

    2000-01-01

    What do simple clocks, simple computers, black holes, space-time foam, and holographic principle have in common? I will show that the physics behind them is inter-related, linking together our concepts of information, gravity, and quantum uncertainty. Thus, the physics that sets the limits to computation and clock precision also yields Hawking radiation of black holes and the holographic principle. Moreover, the latter two strongly imply that space-time undergoes much larger quantum fluctuations than what the folklore suggests --- large enough to be detected with modern gravitational-wave interferometers through future refinements.

  7. Nobel Prize in Physics 1997 "for development of methods to cool and trap atoms with laser light" : Steven Chu, Claude Cohen-Tannoudji and William D. Phillips

    CERN Multimedia

    1998-01-01

    Prof.S. Chu presents "the manipulation of atoms and bio-molecules by laser light" : a brief history of the laser cooling and trapping of atoms developed over the past 15 years will be presented. The cooling and trapping technology is already being applied in numerous areas of science and engineering. Applications to be discussed include atomic clocks, atom interferometers, as well as studies in polymer dynamics and protein motion.

  8. Altered expression pattern of clock genes in a rat model of depression

    DEFF Research Database (Denmark)

    Christiansen, Sofie; Bouzinova, Elena; Fahrenkrug, Jan;

    2016-01-01

    quantified expression of clock genes on brain sections in the prefrontal cortex, nucleus accumbens, pineal gland, suprachiasmatic nucleus, substantia nigra, amygdala, ventral tegmental area, subfields of the hippocampus, and the lateral habenula using in situ hybridization histochemistry. Expression of clock...

  9. The E3 ubiquitin ligase CTRIP controls CLOCK levels and PERIOD oscillations in Drosophila.

    Science.gov (United States)

    Lamaze, Angélique; Lamouroux, Annie; Vias, Carine; Hung, Hsiu-Cheng; Weber, Frank; Rouyer, François

    2011-06-01

    In the Drosophila circadian clock, the CLOCK/CYCLE complex activates the period and timeless genes that negatively feedback on CLOCK/CYCLE activity. The 24-h pace of this cycle depends on the stability of the clock proteins. RING-domain E3 ubiquitin ligases have been shown to destabilize PERIOD or TIMELESS. Here we identify a clock function for the circadian trip (ctrip) gene, which encodes a HECT-domain E3 ubiquitin ligase. ctrip expression in the brain is mostly restricted to clock neurons and its downregulation leads to long-period activity rhythms in constant darkness. This altered behaviour is associated with high CLOCK levels and persistence of phosphorylated PERIOD during the subjective day. The control of CLOCK protein levels does not require PERIOD. Thus, CTRIP seems to regulate the pace of the oscillator by controlling the stability of both the activator and the repressor of the feedback loop.

  10. Generating clock signals for a cycle accurate, cycle reproducible FPGA based hardware accelerator

    Science.gov (United States)

    Asaad, Sameth W.; Kapur, Mohit

    2016-01-05

    A method, system and computer program product are disclosed for generating clock signals for a cycle accurate FPGA based hardware accelerator used to simulate operations of a device-under-test (DUT). In one embodiment, the DUT includes multiple device clocks generating multiple device clock signals at multiple frequencies and at a defined frequency ratio; and the FPG hardware accelerator includes multiple accelerator clocks generating multiple accelerator clock signals to operate the FPGA hardware accelerator to simulate the operations of the DUT. In one embodiment, operations of the DUT are mapped to the FPGA hardware accelerator, and the accelerator clock signals are generated at multiple frequencies and at the defined frequency ratio of the frequencies of the multiple device clocks, to maintain cycle accuracy between the DUT and the FPGA hardware accelerator. In an embodiment, the FPGA hardware accelerator may be used to control the frequencies of the multiple device clocks.

  11. Circadian Clock genes Per2 and clock regulate steroid production, cell proliferation, and luteinizing hormone receptor transcription in ovarian granulosa cells

    Energy Technology Data Exchange (ETDEWEB)

    Shimizu, Takashi, E-mail: shimizut@obihiro.ac.jp [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan); Hirai, Yuko; Murayama, Chiaki; Miyamoto, Akio [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan); Miyazaki, Hitoshi [Gene Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8572 (Japan); Miyazaki, Koyomi [Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) Central 6, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566 (Japan)

    2011-08-19

    Highlights: {yields} Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression. {yields}Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom. {yields} Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. {yields}Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. {yields} The expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. -- Abstract: Circadian Clock genes are associated with the estrous cycle in female animals. Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression in follicle-stimulating hormone FSH-treated granulosa cells. Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom, whereas Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. Similarly, expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. Our data provide a new insight that Per2 and Clock have different action on ovarian granulosa cell functions.

  12. Timing Jitter Analysis for Clock recovery Circuits Based on an Optoelectronic Phase-Locked Loop (OPLL)

    DEFF Research Database (Denmark)

    Zibar, Darko; Mørk, Jesper; Oxenløwe, Leif Katsuo;

    2005-01-01

    Timing jitter of an OPLL based clock recovery is investigated. We demonstrate how loop gain, input and VCO signal jitter, loop filter bandwidth and a loop time delay influence jitter of the extracted clock signal......Timing jitter of an OPLL based clock recovery is investigated. We demonstrate how loop gain, input and VCO signal jitter, loop filter bandwidth and a loop time delay influence jitter of the extracted clock signal...

  13. Oscillating perceptions: the ups and downs of the CLOCK protein in the mouse circadian system

    Indian Academy of Sciences (India)

    Jason P. Debruyne

    2008-12-01

    A functional mouse CLOCK protein has long been thought to be essential for mammalian circadian clockwork function, based mainly on studies of mice bearing a dominant negative, antimorphic mutation in the Clock gene. However, new discoveries using recently developed Clock-null mutant mice have shaken up this view. In this review, I discuss how this recent work impacts and alters the previous view of the role of CLOCK in the mouse circadian clockwork.

  14. Nonvisual Opsins and the Regulation of Peripheral Clocks by Light and Hormones.

    Science.gov (United States)

    Poletini, Maristela O; Ramos, Bruno C; Moraes, Maria Nathalia; Castrucci, Ana Maria L

    2015-01-01

    The molecular clock machinery is conserved throughout evolution. However, how environmental cues are perceived has evolved in such a way that peripheral clocks in mammals require a variety of signals, including hormones. On the other hand, in nonmammalian cells able to directly detect light, light seems to play a major role in the synchronization of the clock. The interaction between perception of circadian light by nonvisual opsins and hormones will be discussed under the perspective of clock synchronization at the molecular level.

  15. All-optical clock recovery of NRZ-DPSK signals using optical resonator-type filters

    DEFF Research Database (Denmark)

    Peucheret, Christophe; Seoane, Jorge; Ji, Hua

    2009-01-01

    It is shown how introducing a limited rise time to the driving signal enables all-optical clock recovery of NRZ-DPSK signals generated using a phase modulator. A Fabry-Perot filter is used to generate the optical clock.......It is shown how introducing a limited rise time to the driving signal enables all-optical clock recovery of NRZ-DPSK signals generated using a phase modulator. A Fabry-Perot filter is used to generate the optical clock....

  16. High-order inertial phase shifts for time-domain atom interferometers

    CERN Document Server

    Bongs, K; Kasevich, M A; Bongs, Kai; Launay, Romain; Kasevich, Mark A.

    2002-01-01

    High-order inertial phase shifts are calculated for time-domain atom interferometers. We obtain closed-form analytic expressions for these shifts in accelerometer, gyroscope, optical clock and photon recoil measurement configurations. Our analysis includes Coriolis, centrifugal, gravitational, and gravity gradient-induced forces. We identify new shifts which arise at levels relevant to current and planned experiments.

  17. A self-sustaining atomic magnetometer with τ(-1) averaging property.

    Science.gov (United States)

    Xu, C; Wang, S G; Feng, Y Y; Zhao, L; Wang, L J

    2016-06-30

    Quantum measurement using coherent superposition of intrinsic atomic states has the advantage of being absolute measurement and can form metrological standards. One example is the absolute measurement of magnetic field by monitoring the Larmor precession of atomic spins whilst another being the Ramsey type atomic clock. Yet, in almost all coherent quantum measurement, the precision is limited by the coherence time beyond which, the uncertainty decreases only as τ(-1/2). Here we show that by non-destructively measuring the phase of the Larmor precession and regenerating the coherence via optical pumping, the self-sustaining Larmor precession signal can persist indefinitely. Consequently, the precision of the magnetometer increases with time following a much faster τ(-1) rule. A mean sensitivity of 240  from 1 Hz to 10 Hz is realized, being close to the shot noise level. This method of coherence regeneration may also find important applications in improving the performance of atomic clocks.

  18. CRY Drives Cyclic CK2-Mediated BMAL1 Phosphorylation to Control the Mammalian Circadian Clock

    NARCIS (Netherlands)

    T. Tamaru (Teruya); M. Hattori (Mitsuru); K. Honda (Kousuke); Y. Nakahata (Yasukazu); P. Sassone-Corsi (Paolo); G.T.J. van der Horst (Gijsbertus); T. Ozawa (Takeaki); K. Takamatsu (Ken)

    2015-01-01

    textabstractIntracellular circadian clocks, composed of clock genes that act in transcription-translation feedback loops, drive global rhythmic expression of the mammalian transcriptome and allow an organism to anticipate to the momentum of the day. Using a novel clock-perturbing peptide, we establi

  19. Using Integer Clocks to Verify the Timing-Sync Sensor Network Protocol

    Science.gov (United States)

    Huang, Xiaowan; Singh, Anu; Smolka, Scott A.

    2010-01-01

    We use the UPPAAL model checker for Timed Automata to verify the Timing-Sync time-synchronization protocol for sensor networks (TPSN). The TPSN protocol seeks to provide network-wide synchronization of the distributed clocks in a sensor network. Clock-synchronization algorithms for sensor networks such as TPSN must be able to perform arithmetic on clock values to calculate clock drift and network propagation delays. They must be able to read the value of a local clock and assign it to another local clock. Such operations are not directly supported by the theory of Timed Automata. To overcome this formal-modeling obstacle, we augment the UPPAAL specification language with the integer clock derived type. Integer clocks, which are essentially integer variables that are periodically incremented by a global pulse generator, greatly facilitate the encoding of the operations required to synchronize clocks as in the TPSN protocol. With this integer-clock-based model of TPSN in hand, we use UPPAAL to verify that the protocol achieves network-wide time synchronization and is devoid of deadlock. We also use the UPPAAL Tracer tool to illustrate how integer clocks can be used to capture clock drift and resynchronization during protocol execution

  20. Curriculum Sequencing and the Acquisition of Clock-Reading Skills among Chinese and Flemish Children

    Science.gov (United States)

    Burny, Elise; Valcke, Martin; Desoete, Annemie; Van Luit, Johannes E. Hans

    2013-01-01

    The present study addresses the impact of the curriculum on primary school children's acquisition of clock-reading knowledge from analog and digital clocks. Focusing on Chinese and Flemish children's clock-reading knowledge, the study is about whether the differences in sequencing of learning and instruction opportunities--as defined by the…

  1. Regulation of behavioral circadian rhythms and clock protein PER1 by the deubiquitinating enzyme USP2

    Directory of Open Access Journals (Sweden)

    Yaoming Yang

    2012-06-01

    Endogenous 24-hour rhythms are generated by circadian clocks located in most tissues. The molecular clock mechanism is based on feedback loops involving clock genes and their protein products. Post-translational modifications, including ubiquitination, are important for regulating the clock feedback mechanism. Previous work has focused on the role of ubiquitin ligases in the clock mechanism. Here we show a role for the rhythmically-expressed deubiquitinating enzyme ubiquitin specific peptidase 2 (USP2 in clock function. Mice with a deletion of the Usp2 gene (Usp2 KO display a longer free-running period of locomotor activity rhythms and altered responses of the clock to light. This was associated with altered expression of clock genes in synchronized Usp2 KO mouse embryonic fibroblasts and increased levels of clock protein PERIOD1 (PER1. USP2 can be coimmunoprecipitated with several clock proteins but directly interacts specifically with PER1 and deubiquitinates it. Interestingly, this deubiquitination does not alter PER1 stability. Taken together, our results identify USP2 as a new core component of the clock machinery and demonstrate a role for deubiquitination in the regulation of the circadian clock, both at the level of the core pacemaker and its response to external cues.

  2. Representing the object of controversy: the case of the molecular clock.

    Science.gov (United States)

    Dietrich, Michael R

    2007-01-01

    Through a case study of the controversies surrounding the molecular clock, this paper examines the role of visual representation in the dynamics of scientific controversies. Representations of the molecular clock themselves became objects of controversy and so were not a means for closure. Instead visual representations of the molecular clock became tools for the further articulation of an ongoing controversy.

  3. FOREWORD: Fifty years of atomic time-keeping: 1955 to 2005

    Science.gov (United States)

    Quinn, Terry

    2005-06-01

    The year 2005 is the centenary of Einstein's four famous papers that were published in 1905. This anniversary is being widely celebrated all over the world and, indeed, 2005 has been dubbed World Year of Physics. The year 2005, however, also marks the fiftieth anniversary of the first operation of Essen and Parry's caesium beam atomic frequency standard at the NPL in May 1955. While Einstein's papers signalled a revolution in physics and in our understanding of the natural world, the first atomic clock signalled a revolution in time-keeping that has become, among other things, one of the most powerful tools in pushing back the frontiers of Einstein's theories of special and general relativity. The atomic clock has also had consequences for navigation comparable to those brought about by Harrison's mechanical clocks almost exactly two hundred years before. Harrison's H3 was completed in 1757 and H4 in 1759. The atomic clock, and the creation of an atomic time scale that quickly followed, led ten years later to the adoption of an atomic definition for the SI second in Resolution 1 of the 13th General Conference on Weights and Measures, 1967/68. This marked the end of time-keeping based on the movements of the heavenly bodies that had beaten the rhythm of the days and the seasons since the dawn of human civilization. Fifty years on is a good occasion to look back, to look forward and at the same time to examine where we are today, in terms of measuring time. While we still arrange for our atomic clocks to show noon when the sun is overhead on the Greenwich meridian, everything else has changed in the fifty years since 1955. In this special issue of Metrologia the reader will find articles on the development of the atomic clock, its theory and practice, how the first atomic time scale was devised and formally introduced and how we maintain atomic time today, as well as articles looking forward to even more accurate clocks and time scales. Included also are articles on

  4. Analysis of Random Jitter in a Clock Multiplying DLL Architecture

    NARCIS (Netherlands)

    Beek, van de R.C.H; Klumperink, E.A.M.; Vaucher, C.S.; Nauta, B.

    2001-01-01

    In this paper, a thorough analysis of the jitter behavior of a Delay Locked Loop (DLL) based clock multiplying architecture is presented. The noise sources that are included in the analysis are the noise of the delay elements, the reference jitter and the noise of the Phase Frequency Detector and Ch

  5. Special Relativity in Week One: 2) All Clocks Run Slow

    Science.gov (United States)

    Huggins, Elisha

    2011-01-01

    In our initial article on teaching special relativity in the first week of an introductory physics course, we used the principle of relativity and Maxwell's theory of light to derive Einstein's second postulate (that the speed of light is the same to all observers). In this paper we study thought experiments involving a light pulse clock moving…

  6. The AGS Ggamma Meter and Calibrating the Gauss Clock

    Energy Technology Data Exchange (ETDEWEB)

    Ahrens, Leif [Brookhaven National Laboratory (BNL), Upton, NY (United States). Collider-Accelerator Dept.

    2014-03-31

    During AGS Polarized Proton acceleration periods, one output from the AGS Ggamma Meter, namely the energy (or Ggamma) calculated from the magnetic field in the AGS main magnets and the beam radius- both measured in particular instant, is used to figure out the times in the AGS magnet acceleration cycle when the beam passes through a particular set of depolarizing resonances. The resonance set occur whenever a particle’s Ggamma (energy*(G/m) becomes nearly equal to n*Qx (i.e. any integer multiplied by the horizontal betatron tune). This deliverable is why the machinery is referred to as the ''Ggamma Meter'' rather than the AGS energy meter. The Ggamma Meter takes as inputs a set of measurements of frequency (F(t)), radius (r(t)), and gauss clock counts (GCC(t)). The other energy (GgammaBr) assumes the field when the gauss clock starts counting is known. The change in field to time t is given by the measured accumulated gauss clock counts multiplied by the gauss clock calibration (gauss/GCC). In order to deal with experimental data, this calibration factor gets an added ad hoc complication, namely a correction dependent on the rate of change the counting rate. The Ggamma meter takes GCC(t) and together with the past history for this cycle calculates B(t).

  7. Enhanced Phenotyping of Complex Traits with a Circadian Clock Model

    NARCIS (Netherlands)

    Merrow, Martha; Roenneberg, Till

    2005-01-01

    Models of biological systems are increasingly used to generate and test predictions in silico. This article explores the basic workings of a multifeedback network model of a circadian clock. In a series of in silico experiments, we investigated the influence of the number of feedbacks by adding and

  8. Clock Reading: An Underestimated Topic in Children with Mathematics Difficulties

    Science.gov (United States)

    Burny, Elise; Valcke, Martin; Desoete, Annemie

    2012-01-01

    Recent studies have shown that children with mathematics difficulties (MD) have weaknesses in multiple areas of mathematics. Andersson, for example, recently found that children with MD perform significantly worse than other children on clock reading tasks. The present study builds on this recent finding and aims at a more profound understanding…

  9. Experimental Progress on the NIST ^27Al^+ Optical Clock

    Science.gov (United States)

    Chou, Chin-Wen; Hume, David B.; Koelemeij, Jeroen C. J.; Rosenband, Till; Bergquist, James C.; Wineland, Dave J.

    2009-05-01

    A recent measurement of the frequency ratio between single-ion optical clocks based on ^27Al^+ and ^199Hg^+ at NIST showed a combined statistical and systematic uncertainty of 5.2 x 10-17[1]. Here we report progress on improving both the accuracy and stability of the ^27Al^+ optical clock. We have developed a new trap and laser systems that enable the use of ^25Mg^+ for sympathetic cooling and clock-state detection of ^27Al^+. These developments should reduce time-dilation shifts caused by harmonic motion of the ions and thus lower the dominant systematic uncertainty below 10-17. In the new clock apparatus we have demonstrated spectroscopy of the ^27Al^+ ^1S0 to ^3P0 transition with a quality factor of Q = 3.5 x 10^14 and simultaneously a contrast approaching unity. In addition, we have developed techniques for the sympathetic laser cooling and quantum logic spectroscopy of multiple aluminum ions with the goal of further improving measurement stability [2]. *supported by ONR and NIST [1] T. Rosenband et al., Science 319, 1808 (2008) [2] D. B. Hume et al., Phys. Rev. Lett. 99, 120502 (2007)

  10. A Medieval Clock Made out of Simple Materials

    Science.gov (United States)

    Danese, B.; Oss, S.

    2008-01-01

    A cheap replica of the verge-and-foliot clock has been built from simple materials. It is a didactic tool of great power for physics teaching at every stage of schooling, in particular at university level. An account is given of its construction and its working principles, together with motivated examples of a few activities. (Contains 3 tables…

  11. Signaling to the circadian clock: plasticity by chromatin remodeling.

    Science.gov (United States)

    Nakahata, Yasukazu; Grimaldi, Benedetto; Sahar, Saurabh; Hirayama, Jun; Sassone-Corsi, Paolo

    2007-04-01

    Circadian rhythms govern several fundamental physiological functions in almost all organisms, from prokaryotes to humans. The circadian clocks are intrinsic time-tracking systems with which organisms can anticipate environmental changes and adapt to the appropriate time of day. In mammals, circadian rhythms are generated in pacemaker neurons within the suprachiasmatic nuclei (SCN), a small area of the hypothalamus, and are entrained by environmental cues, principally light. Disruption of these rhythms can profoundly influence human health, being linked to depression, insomnia, jet lag, coronary heart disease and a variety of neurodegenerative disorders. It is now well established that circadian clocks operate via transcriptional feedback autoregulatory loops that involve the products of circadian clock genes. Furthermore, peripheral tissues also contain independent clocks, whose oscillatory function is orchestrated by the SCN. The complex program of gene expression that characterizes circadian physiology involves dynamic changes in chromatin transitions. These remodeling events are therefore of great importance to ensure the proper timing and extent of circadian regulation. How signaling influences chromatin remodeling through histone modifications is therefore highly relevant in the context of circadian oscillation. Recent advances in the field have revealed unexpected links between circadian regulators, chromatin remodeling and cellular metabolism.

  12. The Chemical and Educational Appeal of the Orange Juice Clock.

    Science.gov (United States)

    Kelter, Paul B.; And Others

    1996-01-01

    Describes the recent history, chemistry, and educational uses of the Orange Juice Clock demonstration in which a galvanic cell is made from the combination of a magnesium strip, a copper strip, and juice in a beaker. Discusses the chemistry basics, extensions for more advanced students, questions for student/teacher workshop participants, and…

  13. The Cell Cycle & Circadian Clock: a tale of two cycles

    NARCIS (Netherlands)

    E. Destici (Eugin)

    2010-01-01

    textabstractMost organisms have evolved an internal timekeeper to anticipate and coordinate internal processes with the external 24-h environment imposed upon all living creatures due to rotation of the Earth around its axis. At the cellular level, the circadian clock is generated by a genetic progr

  14. Living by the clock: the circadian pacemaker in older people.

    NARCIS (Netherlands)

    Hofman, M.A.; Swaab, D.F.

    2006-01-01

    The suprachiasmatic nucleus (SCN) of the hypothalamus is considered to be a critical component of a neural oscillator system implicated in the timing of a wide variety of biological processes. The circadian cycles established by this biological clock occur throughout nature and have a period of appr

  15. The circadian clock mutation alters sleep homeostasis in the mouse.

    Science.gov (United States)

    Naylor, E; Bergmann, B M; Krauski, K; Zee, P C; Takahashi, J S; Vitaterna, M H; Turek, F W

    2000-11-01

    The onset and duration of sleep are thought to be primarily under the control of a homeostatic mechanism affected by previous periods of wake and sleep and a circadian timing mechanism that partitions wake and sleep into different portions of the day and night. The mouse Clock mutation induces pronounced changes in overall circadian organization. We sought to determine whether this genetic disruption of circadian timing would affect sleep homeostasis. The Clock mutation affected a number of sleep parameters during entrainment to a 12 hr light/dark (LD 12:12) cycle, when animals were free-running in constant darkness (DD), and during recovery from 6 hr of sleep deprivation in LD 12:12. In particular, in LD 12:12, heterozygous and homozygous Clock mutants slept, respectively, approximately 1 and approximately 2 hr less than wild-type mice, and they had 25 and 51% smaller increases in rapid eye movement (REM) sleep during 24 hr recovery, respectively, than wild-type mice. The effects of the mutation on sleep are not readily attributable to differential entrainment to LD 12:12 because the baseline sleep differences between genotypes were also present when animals were free-running in DD. These results indicate that genetic alterations of the circadian clock system and/or its regulatory genes are likely to have widespread effects on a variety of sleep and wake parameters, including the homeostatic regulation of sleep.

  16. Disruption of the somitic molecular clock causes abnormal vertebral segmentation.

    Science.gov (United States)

    Sparrow, Duncan B; Chapman, Gavin; Turnpenny, Peter D; Dunwoodie, Sally L

    2007-06-01

    Somites are the precursors of the vertebral column. They segment from the presomitic mesoderm (PSM) that is caudally located and newly generated from the tailbud. Somites form in synchrony on either side of the embryonic midline in a reiterative manner. A molecular clock that operates in the PSM drives this reiterative process. Genetic manipulation in mouse, chick and zebrafish has revealed that the molecular clock controls the activity of the Notch and WNT signaling pathways in the PSM. Disruption of the molecular clock impacts on somite formation causing abnormal vertebral segmentation (AVS). A number of dysmorphic syndromes manifest AVS defects. Interaction between developmental biologists and clinicians has lead to groundbreaking research in this area with the identification that spondylocostal dysostosis (SCD) is caused by mutation in Delta-like 3 (DLL3), Mesoderm posterior 2 (MESP2), and Lunatic fringe (LFNG); three genes that are components of the Notch signaling pathway. This review describes our current understanding of the somitic molecular clock and highlights how key findings in developmental biology can impact on clinical practice.

  17. Nanomagnetic logic with non-uniform states of clocking

    Science.gov (United States)

    Puliafito, Vito; Giordano, Anna; Azzerboni, Bruno; Finocchio, Giovanni

    2016-04-01

    Nanomagnetic logic transmits information along a path of nanomagnets. The basic mechanism to drive such a transmission, known as clocking, can be achieved by exploiting the spin-Hall effect (SHE), as recently observed in experiments on Ta/CoFeB/MgO multilayers (Bhowmik et al 2014 Nat. Nano 9 59). This paper shows the fundamental mechanism of the spin-Hall driven clocking by using a full micromagnetic framework and considering two different devices, Ta/CoFeB/MgO and Pt/CoFeB/MgO. The former is used for a direct comparison of the numerical results with the experiments while the latter permits the effect of the Dzyaloshinskii-Moriya interaction (DMI) in the clocking mechanism to be predicted. Results show that the clocking state is non-uniform and it is characterized by the presence of domains separated by Bloch (Néel) domain walls depending on the absence (presence) of the DMI. Our findings point out that for the design of nanomagnetic logic a full micromagnetic approach is necessary.

  18. Robustness of synthetic circadian clocks to multiple environmental changes.

    Science.gov (United States)

    Gurevich, Lilia; Cohen-Luria, Rivka; Wagner, Nathaniel; Ashkenasy, Gonen

    2015-04-04

    A molecular network that mimics circadian clocks from cyanobacteria is constructed in silico. Simulating its oscillatory behaviour under variable conditions reveals its robustness relative to networks of alternative topologies. The principles for synthetic chemical circadian networks to work properly are consequently highlighted.

  19. Atomic physics

    Energy Technology Data Exchange (ETDEWEB)

    Livingston, A.E.; Kukla, K.; Cheng, S. [Univ. of Toledo, OH (United States)] [and others

    1995-08-01

    In a collaboration with the Atomic Physics group at Argonne and the University of Toledo, the Atomic Physics group at the University of Notre Dame is measuring the fine structure transition energies in highly-charged lithium-like and helium-like ions using beam-foil spectroscopy. Precise measurements of 2s-2p transition energies in simple (few-electron) atomic systems provide stringent tests of several classes of current atomic- structure calculations. Analyses of measurements in helium-like Ar{sup 16+} have been completed, and the results submitted for publication. A current goal is to measure the 1s2s{sup 3}S{sub 1} - 1s2p{sup 3}P{sub 0} transition wavelength in helium-like Ni{sup 26+}. Measurements of the 1s2s{sup 2}S{sub 1/2} - 1s2p{sup 2}P{sub 1/2,3/2} transition wavelengths in lithium-like Kr{sup 33+} is planned. Wavelength and lifetime measurements in copper-like U{sup 63+} are also expected to be initiated. The group is also participating in measurements of forbidden transitions in helium-like ions. A measurement of the lifetime of the 1s2s{sup 3}S{sub 1} state in Kr{sup 34+} was published recently. In a collaboration including P. Mokler of GSI, Darmstadt, measurements have been made of the spectral distribution of the 2E1 decay continuum in helium-like Kr{sup 34+}. Initial results have been reported and further measurements are planned.

  20. CULLIN-3 controls TIMELESS oscillations in the Drosophila circadian clock.

    Directory of Open Access Journals (Sweden)

    Brigitte Grima

    Full Text Available Eukaryotic circadian clocks rely on transcriptional feedback loops. In Drosophila, the PERIOD (PER and TIMELESS (TIM proteins accumulate during the night, inhibit the activity of the CLOCK (CLK/CYCLE (CYC transcriptional complex, and are degraded in the early morning. The control of PER and TIM oscillations largely depends on post-translational mechanisms. They involve both light-dependent and light-independent pathways that rely on the phosphorylation, ubiquitination, and proteasomal degradation of the clock proteins. SLMB, which is part of a CULLIN-1-based E3 ubiquitin ligase complex, is required for the circadian degradation of phosphorylated PER. We show here that CULLIN-3 (CUL-3 is required for the circadian control of PER and TIM oscillations. Expression of either Cul-3 RNAi or dominant negative forms of CUL-3 in the clock neurons alters locomotor behavior and dampens PER and TIM oscillations in light-dark cycles. In constant conditions, CUL-3 deregulation induces behavioral arrhythmicity and rapidly abolishes TIM cycling, with slower effects on PER. CUL-3 affects TIM accumulation more strongly in the absence of PER and forms protein complexes with hypo-phosphorylated TIM. In contrast, SLMB affects TIM more strongly in the presence of PER and preferentially associates with phosphorylated TIM. CUL-3 and SLMB show additive effects on TIM and PER, suggesting different roles for the two ubiquitination complexes on PER and TIM cycling. This work thus shows that CUL-3 is a new component of the Drosophila clock, which plays an important role in the control of TIM oscillations.