Sample records for imf clock angle

  1. The effects of a rapid IMF cone-angle change on Earth's magnetopause and boundary fluctuations

    NASA Astrophysics Data System (ADS)

    Hwang, K.; Goldstein, M. L.; Sibeck, D. G.

    2010-12-01

    One of the most important questions in magnetospheric physics is that of understanding how plasma, momentum, and energy are transferred across the magnetopause due to the interaction of the solar wind with Earth’s magnetic field. The generation of magnetopause waves, often identified as resulting from a Kelvin-Helmholtz instability, has long been considered as playing a significant role in the dynamics of Earth’s boundary layer that separates fast magnetosheath plasma from the relatively stagnant magnetosphere. Although the properties of such waves have been related to certain solar wind parameters, such as the IMF clock angle and the solar wind dynamic pressure, the effect of IMF cone angle has not been studied. In this paper we present Cluster observations of the magnetopause motion and boundary waves in the northern hemisphere on January 12, 2003 during which the IMF cone angle changes from ~90° to ~14°. During this interval changes in the IMF clock angle and in other solar wind parameters are less significant. Cluster and GOES 8 and 10 observations, together with ground magnetometer data, indicate that the magnetopause moves outward following an initial transient inward motion. This motion probably results from the pressure perturbation that is associated with the formation and expansion of the foreshock region upstream of Earth’s bow shock. There exist two superposed magnetopause waves with a frequency of 8 mHz, and 0.6 mHz, respectively, near the arrival of the IMF discontinuity. After the magnetopause moves outward, the surface wave is significantly enhanced and its frequency, amplitude, and propagation direction have all changed. These changes are closely correlated with a change in shear-layer thickness associated with the rarefaction and compression of density and magnetic fields at the boundary that arises due to foreshock dynamics.

  2. Ionospheric flow during extended intervals of northward but By -dominated IMF

    Microsoft Academic Search

    A. Grocott; S. W. H. Cowley; J. B. Sigwarth

    2003-01-01

    We present SuperDARN radar observations of the nightside high-latitude ionospheric flow during two 6-hour intervals of quasi-steady northward interplanetary magnetic field (IMF). During both intervals (01:30 07:30 UT on 2 December and 21:00 03:00 UT on 14\\/15 December 1999), the solar wind and IMF remained relatively steady with Bz positive and By negative, such that the IMF clock angle was

  3. Effects of dipole tilt angle on geomagnetic activity

    NASA Astrophysics Data System (ADS)

    Nowada, M.; Shue, J.-H.; Russell, C. T.

    2009-09-01

    The relationship between the orientation of the interplanetary magnetic field (IMF), represented by the clock angle which is the angle defined by IMF-By and -Bz components, and the AL and AU indices is examined at various dipole tilt angles for the period of 1978-1988. We use the IMF data obtained from the IMP 8 satellite, AL and AU indices with corrected seasonal variations, and the dipole tilt angle, which is the dipole magnetic latitude of the subsolar point calculated as a function of the day of year and universal time. For both positive (dipole tilted to the Sun) and negative dipole tilt angles, the values of |AL| and AU decrease as the IMF clock angle moves away from 180?, becoming more northward. The indices also tend to become smaller for larger dipole tilt angle, either toward or away from the Sun. This dependence on dipole tilt angle enhances the semiannual variation of geomagnetic activity.

  4. The dipole tilt angle dependence of the bow shock for southward IMF: MHD results

    NASA Astrophysics Data System (ADS)

    Wang, M.; Lu, J. Y.; Yuan, H. Z.; Kabin, K.; Liu, Z.-Q.; Zhao, M. X.; Li, G.

    2015-02-01

    The location and shape of the Earth's bow shock depend on the properties of the upstream solar wind, as well as the size and shape of the downstream magnetopause. Many studies have suggested that the influence of the dipole tilt angle on the magnetopause is significant, especially at the high-latitude region, however, to date there is no bow shock model which depends on the dipole tilt angle. Using a physics-based global magnetohydrodynamic (MHD) model, the Space Weather Modeling Framework (SWMF), we investigate the effect of the dipole tilt angle on the location and shape of the bow shock, and our results show that (1) the subsolar standoff distance and the north-south asymmetry of bow shock increase with the increasing dipole tilt angle; (2) with the dipole tilt angle positively increasing, the flaring angle of the bow shock increases in the northern hemisphere but keeps almost unchanged in the southern hemisphere, and the rotational asymmetry slightly decreases in the northern hemisphere and rapidly decreases in the southern hemisphere; and (3) the influence of dipole tilt angle on the shape of the bow shock is north-south symmetric.

  5. Effects of Dipole Tilt Angle on Geomagnetic Activities

    NASA Astrophysics Data System (ADS)

    Nowada, M.; Shue, J.; Russell, C. T.

    2007-12-01

    Relationships between the clock angle of the interplanetary magnetic field (IMF) and each of the AL and AU indices are examined under various Earth's dipole tilt angles using the observational data for a period of 1978 to 1988. This study is performed by correlating the interplanetary magnetic field data obtained from the IMP 8 satellite, the AL and AU indices with the corrected seasonal variations, and the dipole tilt angle. It is found that for any value of the IMF clock angle, the values of AL and AU decrease when the dipole tilt angle becomes larger. It suggests that the geomagnetic activities strongly depend on the dipole tilt angle. Furthermore, our results are consistent with the semiannual variation of the geomagnetic activity and the predicted relationships between the geomagnetic activity, the IMF clock angle, and the dipole tilt angle, derived from the MHD simulation.

  6. Dynamics of Solar Wind Flows and Characteristics of Geomagnetic Activity at Different Angles of IMF Spiral for Period of Space Measurements at Near-Earth Orbit

    NASA Astrophysics Data System (ADS)

    Kuznetsova, Tamara

    Solar wind streams form a spiral with a different longitude angle U: fast-moving streams moving more directly and slow-moving streams wrapping more around Sun. The azimuth component of spiral corresponds to east-west component By (GSE) which plays important role in reconnection on magnetopause and in progress of geomagnetic activity (GA). We take as our aim to find connection between solar wind parameters (IMF B, solar wind velocity V, concentration N, electric field ? =[V?B], Poyting vector of electromagnetic flux density P =[ExB]) and angle U during period of SC 20-24. Such approach allows not only to identify power quasi-stationary flows on basis of the solar wind parameters for each solar cycle, but to see evolution of the flows during period of 4 SC. Dependence of parameters of flows for odd-even SC and their effects in GA from U allows to find influence of the 22-yr magnetic cycle on interaction efficiency. We use data base of B, V, N, temperature T measured at 1 a.u. near ecliptic plane for period of 1963-2013. In particular, it was shown that E and P for By>0 have its maxima in each solar cycle at mean U=80 deg, herewith the maxima for odd SC 21, 23 are considerably larger than ones for even SC 20, 22. Besides, the value of P for 23 cycle has absolute maximum among SC 20-23! These peaks of P and E for By>0 belongs to slow flow of dense cold plasma. The fact that Bx changes its sign at its external boundary points to internal edge of HCS. We have obtained not only new characteristic of SC23, but and its influence on GA. Really, Dst(U) shows absolute maximum of depression for SC 23 at near the same U=80 (By>0). Polar cap index Pc obtained at Thule shows also absolute maximum for SC23 at the same U for By>0. Our analysis confirms that odd SC with low maximal sunspot numbers Wm will have high P and E for similar flows with By>0 and consequently high GA. So, low value of Wm=121 of SC 23 is a parameter, which does not determine power of solar wind electromagnetic flux (that is proportional to rate of e/m energy transfer to magnetopause) and consequently high GA. Our results also allowed us to explain annual distribution of appearance frequency of large geomagnetic disturbances, when additional peaks (under IMF with By>0 in solar wind) appear on classical profile of semiannual variation of GA (with peaks near equinoxes). We discuss too the other results of our study: quasi-stationary flows with the other sign of azimuth component By<0, connection of their parameters with different phases of the 22-yr magnetic cycle and sunspot number Wm of the SC.

  7. Measuring the IMF

    NSDL National Science Digital Library

    This is an activity about measuring the interplanetary magnetic field, or IMF. Learners will utilize cardboard boxes with a magnet inside to design a spacecraft, and experiment with ways to attach a magnetometer that will measure the IMF rather than the magnetic field of the spacecraft. This is Activity 2 in Session 3 of the Exploring Magnetism in the Solar Wind teachers guide.

  8. Angles

    NSDL National Science Digital Library

    Jo Edkins

    2007-01-01

    This set of eight interactive activities lets the user explore angles from many different perspectives. Activities include (1) visualizing the size of an angle; (2) examining objects that will stand or fall with right and non-right angles; (3) identifying obtuse, right, acute and straight angles; (4) guessing angle measures with different levels of precision; (5) exploring regular shapes and their angle measures; (6) studying angles in a fractal tree that is drawn with user inputs of the same angle measure between the branches at each stage; (7) exploring angle measures through firing a cannon (8) drawing with a Logo activity.

  9. Angles

    NSDL National Science Digital Library

    Practice your knowledge of acute, obtuse, and alternate angles. Also, practice relationships between angles - vertical, adjacent, alternate, same-side, and corresponding. Angles is one of the Interactivate assessment explorers.

  10. Clocks, Angles and Functions

    ERIC Educational Resources Information Center

    Kemp, Andy

    2006-01-01

    In this article, the author describes a week of "timely" open-ended lessons with a high ability Y9 group of boys. He gives lessons that would give the students some sense of purpose, as they try to generate a mathematical entity to represent something they used regularly. He states that understanding metric time is something his students really…

  11. Angles

    NSDL National Science Digital Library

    Shodor Education Foundation

    2004-01-01

    This Java applet enables students to investigate acute, obtuse, and right angles. The student decides to work with one or two transversals and a pair of parallel lines. Angle measure is given for one angle. The student answers a short series of questions about the size of other angles, identifying relationships such as vertical and adjacent angles and alternate interior and alternate exterior angles. In addition to automatically checking the student's answers, the applet can keep score of correct answers. From the activity page, What, How, and Why buttons open pages that explain the activity's purpose, function, and how the mathematics fits into the curriculum. Supplemental resources include lesson plans and a handout with a grid for showing the relationship between all possible angles that occur when parallel lines are cut by a transversal. Copyright 2005 Eisenhower National Clearinghouse

  12. Clock Counting

    NSDL National Science Digital Library

    Ms. McDuffee

    2008-11-12

    Students will practice telling time. Review clock counting with the interactive clock. Now match the clocks. Move over the hour clock to see if you chose correctly. Click the arrows to match the dragon clock to the written time. ...

  13. Localized polar cap flow enhancement tracing using airglow patches: Statistical properties, IMF dependence, and contribution to polar cap convection

    NASA Astrophysics Data System (ADS)

    Zou, Ying; Nishimura, Yukitoshi; Lyons, Larry R.; Shiokawa, Kazuo; Donovan, Eric F.; Ruohoniemi, J. Michael; McWilliams, Kathryn A.; Nishitani, Nozomu

    2015-05-01

    Recent radar observations have suggested that polar cap flows are highly structured and that localized flow enhancements can lead to nightside auroral disturbances. However, knowledge of these flows is limited to available echo regions. Utilizing wide spatial coverage by an all-sky imager at Resolute Bay and simultaneous Super Dual Auroral Radar Network measurements, we statistically determined properties of such flows and their interplanetary magnetic field (IMF) dependence. We found that narrow flow enhancements are well collocated with airglow patches with substantially larger velocities (?200 m/s) than the weak large-scale background flows. The flow azimuthal widths are similar to the patch widths. During the evolution across the polar cap, the flow directions and speeds are consistent with the patch propagation directions and speeds. These correspondences indicate that patches can optically trace localized flow enhancements reflecting the flow width, speed, and direction. Such associations were found common (~67%) in statistics, and the typical flow speed, propagation time, and width within our observation areas are 600 m/s, tens of minutes, and 200-300 km, respectively. By examining IMF dependence of the occurrence and properties of these flows, we found that they tend to be observed under By-dominated IMF. Flow speeds are large under oscillating IMF clock angles. Localized flow enhancements are usually observed as a channel elongated in the noon-midnight meridian and directed toward premidnight (postmidnight) for +By (-By). The potential drops across localized flow enhancements account for ~10-40% of the cross polar cap potential, indicating that they significantly contribute to polar cap plasma transport.

  14. Recent Advances on IMF Research

    NASA Astrophysics Data System (ADS)

    Kroupa, Pavel

    Here I discuss recent work on brown dwarfs, massive stars and the IMF in general, which are areas of research to which Anthony Whitworth has been contributing major work. The stellar IMF can be well described by an invariant two-part power law in present-day star-formation events (SFevs) within the Local Group of galaxies. It is nearly identical in shape to the pre-stellar core mass function (André, A&A 518:L102, 2010). The majority of brown dwarfs follow a separate IMF. Evidence from globular clusters and ultra-compact dwarf galaxies has emerged that IMFs may have been top heavy depending on the star-formation rate density (Marks et al., MNRAS 422:2246, 2012). The IGIMF then ranges from bottom heavy at low galaxy-wide star formation rates to being top-heavy in galaxy-scale star bursts.

  15. Embedded Clusters and the IMF

    E-print Network

    Charles J. Lada

    2004-11-19

    Despite valiant efforts over nearly five decades, attempts to determine the IMF over a complete mass range for galactic field stars and in open clusters have proved difficult. Infrared imaging observations of extremely young embedded clusters coupled with Monte Carlo modeling of their luminosity functions are improving this situation and providing important new contributions to our fundamental knowledge of the IMF and its universality in both space and time.

  16. IMF Financial Transactions Plan Quarterly Report

    NSDL National Science Digital Library

    On August 31, 2000, the International Monetary Fund (IMF) announced that, for the first time, it will start regular publication of "information on the sources of financing for IMF lending." After each quarterly financial transaction plan is completed, the IMF will post on their Website the data on the amount of money donated by each member country used to finance lending operations as well as other transactions. This first report covers member lending from March 1, 2000 to May 31, 2000. Along with the data, it also explains the significance of each column in the report and the criteria for selecting members to finance IMF transactions. On the left side of the screen, users will find a short menu which links to other sources of information about the IMF, including a lengthy explanation on the financial operations and organization of the IMF, lending information, and a helpful glossary of terms.

  17. IMF Length Scales and Predictability: The Two Length Scale Medium

    NASA Technical Reports Server (NTRS)

    Collier, Michael R.; Szabo, Adam; Slavin, James A.; Lepping, R. P.; Kokubun, S.

    1999-01-01

    We present preliminary results from a systematic study using simultaneous data from three spacecraft, Wind, IMP 8 (Interplanetary Monitoring Platform) and Geotail to examine interplanetary length scales and their implications on predictability for magnetic field parcels in the typical solar wind. Time periods were selected when the plane formed by the three spacecraft included the GSE (Ground Support Equipment) x-direction so that if the parcel fronts were strictly planar, the two adjacent spacecraft pairs would determine the same phase front angles. After correcting for the motion of the Earth relative to the interplanetary medium and deviations in the solar wind flow from radial, we used differences in the measured front angle between the two spacecraft pairs to determine structure radius of curvature. Results indicate that the typical radius of curvature for these IMF parcels is of the order of 100 R (Sub E). This implies that there are two important IMF (Interplanetary Magnetic Field) scale lengths relevant to predictability: (1) the well-established scale length over which correlations observed by two spacecraft decay along a given IMF parcel, of the order of a few tens of Earth radii and (2) the scale length over which two spacecraft are unlikely to even observe the same parcel because of its curvature, of the order of a hundred Earth radii.

  18. Clock Arithmetic

    NSDL National Science Digital Library

    2010-01-01

    In this activity, students set the starting time and elapsed time on an analog clock to see what time it will be after the elapsed time. Students can also adjust the number of hours on the clock so that it's not just the standard twelve-hour clock. This activity allows students to explore elapsed time as an introduction to clock arithmetic, also referred to as modular arithmetic. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

  19. IMF control of the Earth's magnetosphere

    Microsoft Academic Search

    A. Nishida

    1983-01-01

    We review recent progress in the understanding of the IMF control on the Earth's magnetosphere through the reconnection process. Major points include, (1) the identification of the magnetopause structure under the southward IMF polarity to be the rotational discontinuity and the resulting inference that the reconnection line is formed in the equatorial region, and (2) the confirmation from several observational

  20. Primary Clock

    NSDL National Science Digital Library

    2012-01-01

    This Flash applet includes a working analog clock face displaying the current time, and stating the time in text, which optionally may be spoken. Clicking on the right or left sides of the face displays the number of minutes "past" or "to" the hour, respectively. A smaller clock on the right can be set to any time specified by the user.

  1. Laser clock

    SciTech Connect

    Facklam, R.L.

    1983-05-26

    A laser clock includes a linear laser in one embodiment of the clock and a ring laser gyro in the other embodiment. The linear laser is frequency stabilized and utilizes a single active medium in the form of a low pressure gas, such as He-Ne, with a Doppler broadened gain curve. The ring laser gyro is a four frequency laser with a Faraday rotor. Detector and electronic circuitry associated with the laser of each embodiment detects a beat frequency and convert it to a clock signal.

  2. Latitudinal electron precipitation patterns during large and small IMF magnitudes for northward IMF conditions

    NASA Technical Reports Server (NTRS)

    Makita, K.; Meng, C.-I.; Akasofu, S.-I.

    1988-01-01

    It is demonstrated that there are distinct differences in the electron precipitation patterns (or the polar cap size), geomagnetic activity, and field-aligned currents in the highest-latitude region for small and large IMF B(z) values when the IMF B(z) component is positive. First, during periods of weakly northward IMF, there is a distinct area in the highest-latitude region in which the electron precipitation is absent except for the polar rain. By contrast, during strongly northward IMF, the entire polar region is often filled with burst-type soft electron precipitations. Second, geomagnetic disturbances and field-aligned-current intensities in the highest-latitude region are less during a weak IMF B(z) condition than those during a strongly northward IMF B(z) condition. Geomagnetic activity in the auroral zone for both conditions is absent or very weak.

  3. The Square Light Clock and Special Relativity

    ERIC Educational Resources Information Center

    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…

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

    NASA Technical Reports Server (NTRS)

    Suess, Matthias; Matsakis, Demetrios; Greenhall, Charles A.

    2010-01-01

    Using the GPS Toolkit, the GPS constellation is simulated using 31 satellites (SV) and a ground network of 17 monitor stations (MS). At every 15-minutes measurement epoch, the monitor stations measure the time signals of all satellites above a parameterized elevation angle. Once a day, the satellite clock estimates the station and satellite clocks. The first composite clock (B) is based on the Brown algorithm, and is now used by GPS. The second one (G) is based on the Greenhall algorithm. The composite clock of G and B performance are investigated using three ground-clock models. Model C simulates the current GPS configuration, in which all stations are equipped with cesium clocks, except for masers at USNO and Alternate Master Clock (AMC) sites. Model M is an improved situation in which every station is equipped with active hydrogen masers. Finally, Models F and O are future scenarios in which the USNO and AMC stations are equipped with fountain clocks instead of masers. Model F is a rubidium fountain, while Model O is more precise but futuristic Optical Fountain. Each model is evaluated using three performance metrics. The timing-related user range error having all satellites available is the first performance index (PI1). The second performance index (PI2) relates to the stability of the broadcast GPS system time itself. The third performance index (PI3) evaluates the stability of the time scales computed by the two composite clocks. A distinction is made between the "Signal-in-Space" accuracy and that available through a GNSS receiver.

  5. Living Clocks

    NSDL National Science Digital Library

    Nancy P. Moreno

    2009-01-01

    In this activity about daily rhythms (on page 17 of the PDF), learners will explore circadian patterns in humans, animals and plants. They will observe that some behaviors and functions of living organisms vary predictably every 24 hours and many regular functions are governed by internal "clocks," which run independently but are cued or reset by the environment. Groups of learners can conduct one of four (or more) body clock investigations: body temperature, animal behavior, bean leaf, and alertness/heart rate. Materials required for each group will vary, depending on the investigation(s) being conducted. This lesson guide includes background information, setup and management tips, extensions and a handout.

  6. Atomic Clocks Ultimate Clocks, W. Wayt Gibbs

    E-print Network

    Safronova, Marianna

    Atomic Clocks Ultimate Clocks, W. Wayt Gibbs Scientific American Time 306, 60-67 (19 January 2012-75 (22 January 2014) An Atomic Clock with 10­18 Instability N. Hinkley, J. A. Sherman, N. B. Phillips, M. Rosenband, and D. J. Wineland Science 24 September 2010: 1630-1633. Two Atomic Clocks Ticking as One Bruce

  7. Wolf-Rayet Stars as IMF Probes

    E-print Network

    Claus Leitherer

    2004-08-25

    Wolf-Rayet stars are the evolved descendents of massive stars. Their extraordinary properties make them useful tracers of the stellar initial mass function (IMF) in a young stellar population. I discuss how the interpretation of spectral diagnostics are complicated by the interplay of stellar, nebular, and dust properties. There is mounting observational evidence for spatial inhomogeneities in the gas and dust distribution. The interplay of these inhomogeneities can significantly alter frequently used star-formation and IMF indicators. Specific examples presented in this contribution are the starburst galaxies NGC 1614, NGC 2798, and NGC 3125.

  8. Clocking the melting transition of charge and lattice order in 1T-TaS2 with ultrafast extreme-ultraviolet angle-resolved photoemission spectroscopy.

    PubMed

    Petersen, J C; Kaiser, S; Dean, N; Simoncig, A; Liu, H Y; Cavalieri, A L; Cacho, C; Turcu, I C E; Springate, E; Frassetto, F; Poletto, L; Dhesi, S S; Berger, H; Cavalleri, A

    2011-10-21

    We use time- and angle-resolved photoemission spectroscopy with sub-30-fs extreme-ultraviolet pulses to map the time- and momentum-dependent electronic structure of photoexcited 1T-TaS(2). This compound is a two-dimensional Mott insulator with charge-density wave ordering. Charge order, evidenced by splitting between occupied subbands at the Brillouin zone boundary, melts well before the lattice responds. This challenges the view of a charge-density wave caused by electron-phonon coupling and Fermi-surface nesting alone, and suggests that electronic correlations play a key role in driving charge order. PMID:22107580

  9. The IMF image analysis in Bidimensional EMD

    Microsoft Academic Search

    Guangtao Ge

    2011-01-01

    As bridge technology in the study of the Bidimensional Empirical Mode Decomposition (BEMD) application, this paper gives an integrated anlysis of the Intrinsic Mode Function (IMF) image characters including energy characters, amplitude&frequency characters and phase&frequency characters . Some important conclusions are drawned that the main part energy of the original image's frequency amplitude remains in the residue and most part

  10. Fifty Years of IMF Theory and Observations

    E-print Network

    : uncertain, inhomogeneous, and incomplete LFs, M-L relation, sensitivity to SFR history, scale height diagram Hernandez et al. (2000, SFR history), Binney et al. (2000, age of disk), Bertelli & Nasi (2001, IMF, SFR history) Schroder & Pagel 2003: All thin disk stars out to 100 pc with MV

  11. Time Clocks

    NSDL National Science Digital Library

    Stephen Greb

    This exercise can be used to demonstrate changes in the Earth through time, and the length of time it took for those changes to take place. A list of Important Dates in Earth History is provided that contains the dates of the events shown on a time clock. The teacher can pick events from the list of key events and calculate (or have students calculate) the time for the key events they wish to use. A page-size image of the clock can be printed and turned into an overhead transparency. To better demonstrate the changes since the beginning of the Paleozoic Era, the same exercise could be done the second day of class, using only the last 570 million years of time.

  12. A reexamination of long-duration radial IMF events

    NASA Astrophysics Data System (ADS)

    Pi, G.; Shue, J. H.; Chao, C. K.; Nemecek, Z.; Safrankova, J.; Lin, C. H.

    2014-12-01

    The radial interplanetary magnetic field (IMF) is one of the special solar wind conditions when the orientation of the IMF is aligned with the solar wind velocity. In this study, we reexamine the solar wind condition during the long-duration radial IMF (>4hrs) using the OMNI solar wind data. During the events, the IMF magnitude, solar wind speed and density, and especially its temperature are depressed in comparison with their yearly averages. In contrast to previous studies, we have found that the total time of the radial IMF per year does not change with solar activity. MHD simulation models failed to predict the location of the magnetopause under the radial IMF condition. A part of the inaccuracy is due to a use of assumed solar wind parameters in the simulations. Here we provide MHD modelers with the real solar wind parameters for simulations of the radial IMF.

  13. IMF Center: EconEd Online

    NSDL National Science Digital Library

    "If ignorance paid dividends, most Americans could make a fortune out of what they don't know about economics." So says the U.S. Secretary of Commerce, Luther H. Hodges. This site from the International Monetary Fund (IMF) seeks to transform that ignorance into understanding. Features include Student Interactives, Lessons, and Online Exhibitions & Facts. The Student Interactives and Lesson Plans sections are segmented for specific age groups, from the fifth grade through the end of college. Educators will want to start with the Teacher Guide accompanying each feature. For instance, the guide to the Money Mania interactive provides a background and teaching tips for social studies teachers working with students from grades nine through twelve. Links reach out into nearly limitless resources available on the IMF web page.

  14. Optical Atomic Clocks

    E-print Network

    Ludlow, Andrew D; Ye, Jun; Peik, Ekkehard; Schmidt, Piet O

    2014-01-01

    Optical atomic clocks represent the state-of-the-art in the frontier of modern measurement science. In this article we provide a detailed review on the development of optical atomic clocks that are based on trapped single ions and many neutral atoms. We discuss important technical ingredients for optical clocks, and we present measurement precision and systematic uncertainty associated with some of the best clocks to date. We conclude with an outlook on the exciting prospect for clock applications.

  15. Beat the Clock

    NSDL National Science Digital Library

    Mrs. Wells

    2008-06-23

    Students: use these interactive sites to solve linear equations. The faster you solve the equations the better your score. Pick a link below, play the game solving the equations as fast as you can then show me your score. Beat the clock: solving addition equations Beat the clock: subtracting equations Beat the clock: Solving Multiplication equations Beat the clock: Solving Division Equations Beat the clock: Solving two-step equations ...

  16. Thermal photon-IMF anticorrelation: a signal of prompt multifragmentation?

    E-print Network

    R. Alba

    2005-07-22

    The mechanism responsible for IMF emission in central $^{58}$Ni + $^{197}$Au reactions at 30 and 45 MeV/nucleon is investigated by looking at the thermal bremsstrahlung photon production. An IMF - photon anticorrelation signal is observed, for central collisions, at 45 MeV/nucleon with IMF velocity around the center of mass value. This observation is proposed as an evidence for prompt nuclear fragmentation events.

  17. Does the IMF contain information about how massive stars form

    NASA Astrophysics Data System (ADS)

    Melnick, J.; Selman, F.

    2013-06-01

    The remarkable similarity between the mass distribution of pre-stellar cores and the IMF of stars can be interpreted as implying that the stellar IMF was actually imprinted on the ISM, such that the stellar IMF is the cause rather than the consequence of star formation. We will discuss the latest observations of both distributions and show how one follows from the other without imposing any conditions on the actual physics of massive star formation.

  18. Massive Star Feedback on the IMF

    E-print Network

    M. Robberto; J. Song; G. Mora Carrillo; S. V. W. Beckwith; R. B. Makidon; N. Panagia

    2004-10-14

    We have obtained the first measures of the mass accretion rates on stars of the Trapezium Cluster. They appear systematically lower than those of similar stars in the Taurus-Auriga association. Together with premature disk evaporation, dramatically revealed by the HST images of the Orion proplyds, this result suggests that low mass stars in a rich cluster may be ``dwarfed'' by the influence of nearby OB stars. This feedback mechanism affects the IMF, producing an excess of low mass stars and brown dwarfs. The observed frequency of low mass objects in Orion vs. Taurus seems to confirm this scenario.

  19. Population III Star Formation and IMF

    E-print Network

    Michael L. Norman

    2008-01-31

    We review recent 3D cosmological hydrodynamic simulations of primordial star formation from cosmological initial conditions (Pop III.1) and from initial conditions that have been altered by radiative feedback from stellar sources (Pop III.2). We concentrate on simulations that resolve the formation of the gravitationally unstable cloud cores in mini-halos over the mass range $10^5 < M/\\Msun < 10^7 $ and follow their evolution to densities of at least $10^{10} \\cmm3$ and length scales of $<10^{-2}$ pc such that accretion rates can be estimated. The advent of ensembles of such simulations exploring a variety of conditions permits us to assess the robustness of the standard model for Pop III.1 star formation and investigate scatter in their formation redshifts and accretion rates, thereby providing much needed information about the Pop III IMF. The simulations confirm the prediction that Pop III.1 stars were massive ($\\sim 100 \\Msun$), and form in isolation in primordial mini-halos. Simulations of Pop III.2 star forming in relic HII regions suggest somewhat lower masses ($\\sim 30 \\Msun$) which may help explain the chemical abundances of extremely metal poor stars. We note that no 3D simulation at present has achieved stellar density let alone followed the entire accretion history of the star in any scenario, and thus the IMF of Pop III stars remains poorly determined theoretically.

  20. Hanle Detection for Optical Clocks

    PubMed Central

    Zhang, Xiaogang; Zhang, Shengnan; Pan, Duo; Chen, Peipei; Xue, Xiaobo; Zhuang, Wei; Chen, Jingbiao

    2015-01-01

    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. PMID:25734183

  1. High-latitude Joule heating response to IMF inputs

    Microsoft Academic Search

    M. McHarg; F. Chun; D. Knipp; G. Lu; B. Emery; A. Ridley

    2005-01-01

    We evaluate the response of the high-latitude Joule heating to orientation and magnitude of the interplanetary magnetic field (IMF). Approximately 9000 individual Joule heating patterns derived from data assimilation for the northern hemisphere were used to develop averaged and hemispherically integrated Joule power maps for the northern hemisphere north of 40° magnetic latitude. Hemispherically integrated Joule heating increases with IMF

  2. The IMF/World Bank Structural Adjustment Program and its

    E-print Network

    support but the 1988 SAP (ERP) was the first full fledged program · The 1998 SAP as in other countries Bank/IMF imposed its SAP as a pre-condition for debt rescheduling and new loans · Economic conditions in the Caribbean forced Guyana, Jamaica and others to accept the SAP · Guyana had a number of IMF/World Bank

  3. Atomic fountain clocks

    Microsoft Academic Search

    R. Wynands; S. Weyers

    2005-01-01

    We describe and review the current state of the art in atomic fountain clocks. These clocks provide the best realization of the SI second possible today, with relative uncertainties of a few parts in 1016.

  4. Connection between dynamically derived IMF normalisation and stellar populations

    E-print Network

    McDermid, Richard M

    2015-01-01

    In this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the Atlas3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that `heavy' IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future w...

  5. Connection between dynamically derived IMF normalisation and stellar populations

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.

    2015-04-01

    In this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the ATLAS3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that `heavy' IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future work.

  6. Atomic clocks for astrophysical measurements

    NASA Technical Reports Server (NTRS)

    Vessot, R. F. C.; Mattison, E. M.

    1982-01-01

    It is noted that recently developed atomic hydrogen masers have achieved stability well into the 10 to the -16th domain for averaging time intervals beyond 1000 sec and that further improvements are in prospect. These devices are highly adaptable for space use in very high precision measurements of angle through Very Long Baseline Interferometry (VLBI) and of range and range-rate through Doppler techniques. Space missions that will use these clocks for measuring the sun's gravity field distribution and for testing gravitation and relativity (a project that will include a search for pulsed low-frequency gravitational waves) are discussed. Estimates are made of system performance capability, and the accuracy capability of relativistic measurements is evaluated in terms of the results from the 1976 NASA/SAO spaceborne clock test of the Einstein Equivalence Principle.

  7. VLBI clock synchronization. [for atomic clock rate

    NASA Technical Reports Server (NTRS)

    Counselman, C. C., III; Shapiro, I. I.; Rogers, A. E. E.; Hinteregger, H. F.; Knight, C. A.; Whitney, A. R.; Clark, T. A.

    1977-01-01

    The potential accuracy of VLBI (very long baseline interferometry) for clock epoch and rate comparisons was demonstrated by results from long- and short-baseline experiments. It was found that atomic clocks at widely separated sites (several thousand kilometers apart) can be synchronized to within several nanoseconds from a few minutes of VLBI observations and to within one nanosecond from several hours of observations.

  8. Radioactive Counting Clocks

    Microsoft Academic Search

    Shankar Radhakrishnan; Amit Lal

    2006-01-01

    We report on a radioactive counting clock (RCC) based on radioactive beta emissions from nickel-63 thin films. We present a theoretical analysis of the clock that uses the radioactive source (physics package) to lock and stabilize the frequency of a voltage-to-frequency converter (local oscillator). We present frequency stability measurements of the RCC over 10 days of clock operation. We analyze

  9. Magnetic fields in the Venus ionosphere: Dependence on the IMF direction—Venus express observations

    NASA Astrophysics Data System (ADS)

    Dubinin, E.; Fraenz, M.; Zhang, T. L.; Woch, J.; Wei, Y.

    2014-09-01

    The structure of the magnetized ionosphere of Venus is investigated using the magnetometer and plasma (Analyzer of Space Plasmas and Energetic Atoms 4) data from the Venus Express spacecraft. Observations surveying the low-altitude (h ? 250 km) ionosphere were made at solar zenith angles ? 75°. The magnetic field permeating the Venus ionosphere at solar minimum conditions increases at low altitudes and reaches a maximum at an altitude of ˜200 km. The orientation of the magnetic field in the peak is almost insensible to the magnetic field direction in the solar wind. For both sector polarities of the IMF, the magnetic field vector has a dominant dawn-dusk component. The topology of the magnetic field also occurs different for different signs of the cross-flow component of the IMF revealing either a sudden straightening with liberation of the magnetic field stresses or a closing into a loop. We discuss different mechanisms of the peak formation including local magnetization, a weak intrinsic planetary field, a dipole field induced by eddy currents, a remnant origin, or giant flux ropes. All of them fail to explain most of the observed features. We suggest that a decoupling of ion and electron motion at low altitudes due to ion-neutral collisions results in currents which produce different field configurations depending on the IMF orientation.

  10. Optimizing passive quantum clocks

    NASA Astrophysics Data System (ADS)

    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. Equatorial Magnetic Reconnection Lines during Northward IMF Conditions

    NASA Astrophysics Data System (ADS)

    Trattner, Karlheinz; Thresher, Summer; Trenchi, Lorenzo; Fuselier, Stephen; Petrinec, Steven; Peterson, William

    2015-04-01

    Reconnection at the Earth's magnetopause is the mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. The location of the reconnection line at the magnetopause depends on the conditions of the solar wind, especially the direction of the interplanetary magnetic field (IMF). Dayside equatorial region locations of reconnection during southward IMF have been inferred from global ionospheric images and studies based on incident ion beams in the cusp and boundary layer of the magnetopause. For such conditions the most likely location is along the line of Maximum Magnetic Shear crossing the magnetopause (for large IMF By cases) or along the high latitude antiparallel reconnection region (for large IMF Bx or Bz cases). The same studies have also revealed a poleward of the cusp reconnection line for northward IMF conditions. In this study we discuss several cusp crossings by the Polar satellite during conditions with a weak northward IMF component for which cusp ion-energy dispersion profiles typical for a equatorial dayside reconnection line have been observed. This dayside reconnection location during northward IMF conditions is also inferred from magnetopause crossings of the Double-Star satellites.

  12. Equatorial Magnetic Reconnection Lines during Northward IMF Conditions

    NASA Astrophysics Data System (ADS)

    Trattner, K. J.; Thresher, S.; Trenchi, L.; Fuselier, S.; Petrinec, S. M.; Peterson, W. K.; Marcucci, M. F.

    2014-12-01

    Reconnection at the Earth's magnetopause is the mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. The location of the reconnection line at the magnetopause depends on the conditions of the solar wind, especially the direction of the interplanetary magnetic field (IMF). Dayside equatorial region locations of reconnection during southward IMF have been inferred from global ionospheric images and studies based on incident ion beams in the cusp and boundary layer of the magnetopause. For such conditions the most likely location is along the line of Maximum Magnetic Shear crossing the magnetopause (for large IMF BY cases) or along the high latitude antiparallel reconnection region (for large IMF BX or BZ cases). The same studies have also revealed a poleward of the cusp reconnection line for northward IMF conditions. In this study we discuss several cusp crossings by the Polar satellite during conditions with a weak northward IMF component for which cusp ion-energy dispersion profiles typical for a equatorial dayside reconnection line have been observed. This dayside reconnection location during northward IMF conditions is also inferred from magnetopause crossings of the Double-Star satellites.

  13. Space weather predictions based on the Universal Time variations of geoeffeciency of solar wind and IMF

    NASA Astrophysics Data System (ADS)

    Kuznetsova, T.; Laptukhov, A.; Oraevsky, V.; Kuznetsov, V.

    The Earth's magnetosphere is the most studied object of space physics, yet the establishment of a predictive model of its behavior remains an elusive goal. The dependence of the transfer processes (and associated geomagnetic state of the magnetosphere and its dynamics) from the parameters of solar wind plasma and the IMF are not well understood. Sometimes the power space weather events initiate great geomagnetic storms. The risks connected with such space weather events could be avoided if reliable space weather forecasts were possible and available. The paper presents those results of our analysis of the UT variations in Kp and Dst indexes for the period from 1964-1996 of space measurements of the solar wind and the IMF at 1 a.u. at ecliptic plane that can be used for effective predictions of geomagnetic activity, especially great geomagnetic storms. At first stage we analyze annual regularities in behavior of solar wind parameters and IMF for the 33 yrs. We show that such parameters as mean tilt angles of vectors of the IMF B and electric field of the solar wind E to the ecliptic plane have clear annual course, mean correlation coefficient Cc=0.85 between the data from different years. In first approximation Dst and Kp follow by the changes of these angles and have maximal values at equinoxes, when both E and B lie at ecliptic plane. We attract for the studies a reconnection model that describes a reconnection between the Earth's magnetic field and an IMF of arbitrary orientation taking into account annual and daily rotations of the Earth (Kuznetsova and Laptukhov, 2001). We use the data to study the model parameters that determine geoefficiency of the reconnection. 1)cos(BM), where (BM) is angle between vectors of the IMF B and geomagnetic moment M; 2)vector of electric field of the solar wind E presented by its projections along and across the M vector (Em and Emv). Calculated model parameters (on basis of data for the studied 33 yr.) allowed to receive the following results. Loss of geoefficiency at the summer solstice is explained by the fact that mean Emv and of Em fields are close to zero (ones change their signs in all sectors of the IMF directions). This result explains absence of great magnetic storms at this period. Loss of efficiency at the winter solstice is caused by two factors: minimal values of cos(BM) and values of Em and Emv. Derived from experimental data functions Kp=F(Emv) and Kp=f(Em) (Kp changes from 0 to 9) show essentially different behavior and differs from the suggested earlier. An interesting feature of this functions is that the dispersion of values is small and the same both for small values of Kp and large one (up to 9). Our results allow forecasting the geomagnetic activity with reliable probability, if a monitoring the discussed parameters will be used.

  14. What does the IMF really tell us about star formation?

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, M. B. N.; Goodwin, S. P.

    2010-04-01

    Obtaining accurate measurements of the initial mass function (IMF) is often considered to be the key to understanding star formation, and a universal IMF is often assumed to imply a universal star formation process. Here, we illustrate that different modes of star formation can result in the same IMF, and that, in order to truly understand star formation, a deeper understanding of the primordial binary population is necessary. Detailed knowledge on the binary fraction, mass ratio distribution, and other binary parameters, as a function of mass, is a requirement for recovering the star formation process from stellar population measurements.

  15. Elevated ion density at geosynchronous orbit during sustained northwards IMF.

    NASA Astrophysics Data System (ADS)

    Denton, M. H.; Thomsen, M. F.; Lavraud, B.; Borovsky, J. E.; Weygand, J. M.

    2006-12-01

    Data from seven magnetospheric plasma analyser (MPA) instruments on-board satellites in geosynchronous orbit, used in conjunction with interplanetary magnetic field (IMF) data taken upstream of the Earth, provide evidence of magnetospheric preconditioning during events of sustained northwards IMF. Previous reports have found little evidence of enhanced densities of medium energy ions (0.1-45 keV) close to local noon regardless of the strength of convection. We present evidence of a clear factor of two difference between ion densities on the dayside during sustained periods of northwards IMF and similar periods of southwards IMF. This effect is likely to be a contributary factor in the preconditioning of the magnetosphere which can occur prior to some of the largest geomagnetic storms.

  16. IMF polarity effects on the equatorial ionospheric F-region

    SciTech Connect

    Sastri, J.H.

    1985-01-01

    An exploratory study is made of the influence, during the equinoxes, of the interplanetary magnetic field (IMF) sector structure on the ionospheric F-region using ionosonde data from several equatorial stations for a 3-yr period around the 19th sunspot cycle maximum. It is found that, compared with days having positive IMF polarity, the post-sunset increase of h'F near the dip equator and the depth of the equatorial ionization anomaly (EIA) are reduced during the vernal equinox and enhanced during the autumnal equinox on days with negative IMF polarity. Similar trends are also noted in the data for the 20th sunspot cycle maximum, but with reduced amplitude. The systematic changes in the F-region characteristics suggest a modification of the equatorial zonal electric fields in association with the IMF polarity-related changes in the semi-annual variation of geomagnetic activity. 24 references.

  17. IMF polarity effects on the equatorial ionospheric F-region

    Microsoft Academic Search

    J. H. Sastri

    1985-01-01

    An exploratory study is made of the influence, during the equinoxes, of the interplanetary magnetic field (IMF) sector structure on the ionospheric F-region using ionosonde data from several equatorial stations for a 3-yr period around the 19th sunspot cycle maximum. It is found that, compared with days having positive IMF polarity, the post-sunset increase of h'F near the dip equator

  18. Clock genes and sleep.

    PubMed

    Landgraf, Dominic; Shostak, Anton; Oster, Henrik

    2012-01-01

    In most species--from cyanobacteria to humans--endogenous clocks have evolved that drive 24-h rhythms of behavior and physiology. In mammals, these circadian rhythms are regulated by a hierarchical network of cellular oscillators controlled by a set of clock genes organized in a system of interlocked transcriptional feedback loops. One of the most prominent outputs of the circadian system is the synchronization of the sleep-wake cycle with external (day-) time. Clock genes also have a strong impact on many other biological functions, such as memory formation, energy metabolism, and immunity. Remarkably, large overlaps exist between clock gene and sleep (loss) mediated effects on these processes. This review summarizes sleep clock gene interactions for these three phenomena, highlighting potential mediators linking sleep and/or clock function to physiological output in an attempt to better understand the complexity of diurnal adaptation and its consequences for health and disease. PMID:21833490

  19. Science Nation: Biological Clocks

    NSDL National Science Digital Library

    From bacteria to humans, the biological clocks in living things help them determine when to eat, when to sleep, even how to avoid becoming some other creature's lunch. With the help of the National Science Foundation (NSF), University of Georgia geneticist Jonathan Arnold is examining the molecular basis of the biological clock. Understanding specific clock functions may have applications in medicine, from sleep disorders, to heart and lung disease, to aging and reproduction.

  20. Clock Arithmetic and Cryptography

    NSDL National Science Digital Library

    2011-01-14

    This lesson is designed to hone students' arithmetic skills by introducing them to clock arithmetic and its applications in cryptography. The lesson provides links to discussions and activities related to arithmetic, clock arithmetic, and cryptography as well as suggested ways to integrate them into the lesson. Finally, this lesson provides links to follow-up lessons designed for use in succession with an introduction to clock arithmetic.

  1. Cryogenic optical lattice clocks

    NASA Astrophysics Data System (ADS)

    Ushijima, Ichiro; Takamoto, Masao; Das, Manoj; Ohkubo, Takuya; Katori, Hidetoshi

    2015-03-01

    The accuracy of atomic clocks relies on the superb reproducibility of atomic spectroscopy, which is accomplished by careful control and the elimination of environmental perturbations on atoms. To date, individual atomic clocks have achieved a 10?18 level of total uncertainties, but a two-clock comparison at the 10?18 level has yet to be demonstrated. Here, we demonstrate optical lattice clocks with 87Sr atoms interrogated in a cryogenic environment to address the blackbody radiation-induced frequency shift, which remains the primary source of systematic uncertainty and has initiated vigorous theoretical and experimental investigations. The systematic uncertainty for the cryogenic clock is evaluated to be 7.2?×?10?18, which is expedited by operating two such cryo-clocks synchronously. After 11 measurements performed over a month, statistical agreement between the two cryo-clocks reached 2.0?×?10?18. Such clocks' reproducibility is a major step towards developing accurate clocks at the low 10?18 level, and is directly applicable as a means for relativistic geodesy.

  2. World Population Clock

    NSDL National Science Digital Library

    David Levine

    This world population clock is an applet that uses a logarithmic equation obtained through a statistical analysis of data from the U.S. Bureau of the Census. The clock takes into account both births and deaths. You can compare the current world population to any date since 1970.

  3. Number Base Clocks

    NSDL National Science Digital Library

    Visually explore counting and place value with different number bases, from base 2 to base 16, and up to the hundreds place using a clock like interface. The activity also allows you to look at the numbers on the clock in base 10 or in your other chosen base to explore the relationship between those values.

  4. GPS Composite Clock Analysis

    Microsoft Academic Search

    James R Wright; Allan Variance

    2007-01-01

    The GPS Composite Clock defines GPS Time, the timescale used today in GPS operations. GPS Time is illuminated by examination of its role in the complete estimation and control problem relative to UTC\\/TAI. Simulated GPS clock phase and frequency deviations, and simulated GPS pseudo-range measurements, are used to understand GPS Time in terms of Kalman filter estimation errors.

  5. Radio Controlled Clocks

    Microsoft Academic Search

    Michael A. Lombardi

    Radio controlled clocks have existed for decades, but have become far more common in the United States in recent years, due mainly to the explosion of new products that receive time signals from NIST radio station WWVB. This paper explores the history of radio controlled clocks, how they work, and the types of radio signals that control them.

  6. Biological Clocks & Circadian Rhythms

    ERIC Educational Resources Information Center

    Robertson, Laura; Jones, M. Gail

    2009-01-01

    The study of biological clocks and circadian rhythms is an excellent way to address the inquiry strand in the National Science Education Standards (NSES) (NRC 1996). Students can study these everyday phenomena by designing experiments, gathering and analyzing data, and generating new experiments. As students explore biological clocks and circadian…

  7. Strongly Southward IMF Substorms, Dynamic Pressure Disturbances, and Null Events

    NASA Astrophysics Data System (ADS)

    Lyons, L. R.; Lee, D.; Wang, C.; Mende, S. B.; Frey, H. U.

    2004-12-01

    Solar wind discontinuities can lead to important large-scale disturbances that significantly affect the space environment, including energetic particle fluxes, the aurora, and magnetospheric and ionospheric current systems. Understanding what discontinuity characteristics lead to what kind of disturbance is thus critical for disturbance prediction and understanding. Global auroral images from the wideband imaging camera (WIC) on the IMAGE spacecraft show striking new information on this relationship. Two well-studied types of discontinuity driven disturbance are: substorms resulting from northward interplanetary magnetic field (IMF) turnings and dynamic pressure (P) disturbances that result from enhancements of solar wind dynamic pressure. During typical substorms, auroral activity initiates near the equatorward boundary of the auroral oval within a ~1-2 hr MLT sector within the Harang electric-field reversal region and then expands to cover a few hours in MLT. Typical P disturbances show rapid global enhancement of auroral emissions as well as a significant poleward motion of the poleward boundary of the aurora, but enhancement related to the Harang reversal is not evident. The WIC images show that, during periods of strongly southward IMF, substorms expand to a significantly broader MLT range than do typical substorms, and that, in addition to a global auroral enhancement, P disturbances exhibit a substorm-like auroral enhancement within the Harang reversal that extends over a broad MLT range. These observations show that, for strongly southward IMF, both IMF and P changes cause Harang region activation. Because of this, it is reasonable to expect that IMF and P interplay effects may be important for solar wind discontinuities having both a significant IMF change and a significant P change. The WIC images show that such interplay effects can indeed be important. In particularly, discontinuities having a significant IMF northward turning and a significant decrease in P or having a significant increase in P and a significant southward turning of the IMF are found to not lead to a substorm-like aurora disturbance within the Harang reversal region. We refer to such events as "null events," since the IMF northward turning or P increase for each would, by themselves, be expected to cause a large substorm disturbance, but the effects of these appear to be nullified by the simultaneous change in the other quantity.

  8. ULF foreshock under radial IMF: THEMIS observations and global kinetic simulation Vlasiator results compared

    NASA Astrophysics Data System (ADS)

    Palmroth, Minna; Rami, Vainio; Archer, Martin; Hietala, Heli; Afanasiev, Alexandr; Kempf, Yann; Hoilijoki, Sanni; von Alfthan, Sebastian

    2015-04-01

    For decades, a certain type of ultra low frequency waves with a period of about 30 seconds have been observed in the Earth's quasi-parallel foreshock. These waves, with a wavelength of about an Earth radius, are compressive and propagate with an average angle of 20 degrees with respect of the interplanetary magnetic field (IMF). The latter property has caused trouble to scientists as the growth rate for the instability causing the waves is maximized along the magnetic field. So far, these waves have been characterized by single or multi-spacecraft methods and 2-dimensional hybrid-PIC simulations, which have not fully reproduced the wave properties. Vlasiator is a newly developed, global hybrid-Vlasov simulation, which solves the six-dimensional phase space utilising the Vlasov equation for protons, while electrons are a charge-neutralising fluid. The outcome of the simulation is a global reproduction of ion-scale physics in a holistic manner where the generation of physical features can be followed in time and their consequences can be quantitatively characterised. Vlasiator produces the ion distribution functions and the related kinetic physics in unprecedented detail, in the global scale magnetospheric scale with a resolution of a couple of hundred kilometres in the ordinary space and 20 km/s in the velocity space. We run Vlasiator under a radial IMF in five dimensions consisting of the three-dimensional velocity space embedded in the ecliptic plane. We observe the generation of the 30-second ULF waves, and characterize their evolution and physical properties in time. We compare the results both to THEMIS observations and to the quasi-linear theory. We find that Vlasiator reproduces the foreshock ULF waves in all reported observational aspects, i.e., they are of the observed size in wavelength and period, they are compressive and propagate obliquely to the IMF. In particular, we discuss the issues related to the long-standing question of oblique propagation.

  9. The IntraCluster Medium: An Invariant Stellar IMF

    E-print Network

    Rosemary F. G. Wyse

    1997-10-17

    Evidence supporting the hypothesis of an invariant stellar Initial Mass Function is strong and varied. The intra-cluster medium in rich clusters of galaxies is one of the few contrary locations where recent interpretations of the chemical abundances have favoured an IMF that is biased towards massive stars, compared to the `normal' IMF. This interpretation hinges upon the neglect of Type Ia supernovae to the ICM enrichment, and a particular choice of the nucleosynthesis yields of Type II supernovae. We demonstrate here that when one adopts yields determined empirically from observations of Galactic stars, rather than the uncertain model yields, a self-consistent picture may be obtained with an invariant stellar IMF, and about half of the iron in the ICM being produced by Type Ia supernovae.

  10. Optical clocks and relativity.

    PubMed

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

    2010-09-24

    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. PMID:20929843

  11. Optical Clocks and Relativity

    NASA Astrophysics Data System (ADS)

    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.

  12. IMF sector boundary and cosmic ray intensity variations

    NASA Astrophysics Data System (ADS)

    Fujimoto, K.; Murakami, K.; Nagashima, K.; Kojima, H.

    It is shown, by an analysis of cosmic ray intensity variations around IMF sector boundaries using the Chree epoch method, that cosmic ray density is high near the sector boundary irrespective of the sense of IMF polarity change. The decrease of neutron intensities after the boundary passage appears to be due to Forbush decreases which occur often after boundary passages. The increment per change of the solar wind velocity is found to be consistent with the 0.5 percent per 100 km/sec change rate of decrease derived by Iucci et al. (1979) and Munakata et al. (1979).

  13. Accessories Around the Clock

    E-print Network

    Boyles, Rheba Merle; Hard, Graham; Roberson, Nena; Eaton, Fannie Brown

    1958-01-01

    Accessories Around the Clock RHEBA MERLE BOYLES GRAHAM HARD NENA ROBERSON FANNIE BROWN EATON Extension Clothing Specialists k. The Texas A. a M. College System 2? well-dressed woman of today believes a wardrobe of fewer q, well chosen...

  14. Iodine Clock Reaction.

    ERIC Educational Resources Information Center

    Mitchell, Richard S.

    1996-01-01

    Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)

  15. Atomic and gravitational clocks

    NASA Technical Reports Server (NTRS)

    Canuto, V. M.; Goldman, I.

    1982-01-01

    Atomic and gravitational clocks are governed by the laws of electrodynamics and gravity, respectively. While the strong equivalence principle (SEP) assumes that the two clocks have been synchronous at all times, recent planetary data seem to suggest a possible violation of the SEP. Past analysis of the implications of an SEP violation on different physical phenomena revealed no disagreement. However, these studies assumed that the two different clocks can be consistently constructed within the framework. The concept of scale invariance, and the physical meaning of different systems of units, are now reviewed and the construction of two clocks that do not remain synchronous - whose rates are related by a non-constant function beta sub a - is demonstrated. The cosmological character of beta sub a is also discussed.

  16. Clock Time and Entropy

    E-print Network

    Don N. Page

    1993-03-12

    Testable conditional probabilities appear to be restricted to single hypersurfaces (marvelous moments) and depend only on stationary observables. Observable evolution, such as a change of entropy, should be expressed as a dependence upon clock time, not upon inaccessible coordinate time.

  17. Mammalian molecular clocks.

    PubMed

    Kwon, Ilmin; Choe, Han Kyoung; Son, Gi Hoon; Kim, Kyungjin

    2011-03-01

    As a consequence of the Earth's rotation, almost all organisms experience day and night cycles within a 24-hr period. To adapt and synchronize biological rhythms to external daily cycles, organisms have evolved an internal time-keeping system. In mammals, the master circadian pacemaker residing in the suprachiasmatic nucleus (SCN) of the anterior hypothalamus generates circadian rhythmicity and orchestrates numerous subsidiary local clocks in other regions of the brain and peripheral tissues. Regardless of their locations, these circadian clocks are cell-autonomous and self-sustainable, implicating rhythmic oscillations in a variety of biochemical and metabolic processes. A group of core clock genes provides interlocking molecular feedback loops that drive the circadian rhythm even at the single-cell level. In addition to the core transcription/translation feedback loops, post-translational modifications also contribute to the fine regulation of molecular circadian clocks. In this article, we briefly review the molecular mechanisms and post-translational modifications of mammalian circadian clock regulation. We also discuss the organization of and communication between central and peripheral circadian oscillators of the mammalian circadian clock. PMID:22110358

  18. The Impact of the Integrated Galaxy IMF on Supernovae Rate

    NASA Astrophysics Data System (ADS)

    Molina, F.; Weidner, C.; Zoccali, M.

    2009-05-01

    Recent research regarding the star formation in star clusters on galaxy wide scales indicates that, in the hypothesis that all stars are born within clusters, the supposedly universal initial stellar mass function (IMF) within young star clusters, does not necessarily yield the same IMF for whole galaxies. As star clusters also follow an embedded cluster mass function (ECMF), the whole integrated galaxy initial stellar mass function (IGIMF) has to be steeper than the individual IMFs of star clusters -- depending on the steepness of the ECMF (Kroupa & Weidner 2003, ApJ, 598, 1076; Weidner & Kroupa 2005, ApJ, 625, 754). This result has found to be able to explain the mass-metallicity relation of galaxies (Köppen et al. 2007, MNRAS, 375, 673). Investigating the effects of the IGIMF further, this project concentrates on the expected temporal evolution of the supernova rate in comparison with a rate for a single-slope Salpeter-like IMF, for a wide range of galaxies with different masses and star-formation histories. Type II and type Ia supernovae are included at a later stage, as well as the influence of massive starbursts.

  19. On the IMF in a Triggered Star Formation Context

    NASA Astrophysics Data System (ADS)

    Zhou, Tingtao; Huang, Chelsea X.; Lin, D. N. C.; Gritschneder, Matthias; Lau, Herbert

    2015-07-01

    The origin of the stellar initial mass function (IMF) is a fundamental issue in the theory of star formation. It is generally fit with a composite power law. Some clues on the progenitors can be found in dense starless cores that have a core mass function (CMF) with a similar shape. In the low-mass end, these mass functions increase with mass, albeit the sample may be somewhat incomplete; in the high-mass end, the mass functions decrease with mass. There is an offset in the turn-over mass between the two mass distributions. The stellar mass for the IMF peak is lower than the corresponding core mass for the CMF peak in the Pipe Nebula by about a factor of three. Smaller offsets are found between the IMF and the CMFs in other nebulae. We suggest that the offset is likely induced during a starburst episode of global star formation which is triggered by the formation of a few O/B stars in the multi-phase media, which naturally emerged through the onset of thermal instability in the cloud-core formation process. We consider the scenario that the ignition of a few massive stars photoionizes the warm medium between the cores, increases the external pressure, reduces their Bonnor–Ebert mass, and triggers the collapse of some previously stable cores. We quantitatively reproduce the IMF in the low-mass end with the assumption of additional rotational fragmentation.

  20. The IMF in a World of Private Capital Markets

    Microsoft Academic Search

    Barry Eichengreen; Kenneth Kletzer; Ashoka Mody

    2005-01-01

    The IMF attempts to stabilize private capital flows to emerging markets by providing public monitoring and emergency finance. In analyzing its role we contrast cases where banks and bondholders do the lending. Banks have a natural advantage in monitoring and creditor coordination, while bonds have superior risk sharing characteristics. Consistent with this assumption, banks reduce spreads as they obtain more

  1. The IMF in a World of Private Capital Markets

    Microsoft Academic Search

    Barry Eichengreen; Kenneth Kletzer; Ashoka Mody

    2005-01-01

    The IMF attempts to catalyze and stabilize private capital flows to emerging markets by providing public monitoring and emergency finance. In analyzing its role we contrast cases where banks and bondholders do the lending. Banks have a natural advantage in monitoring and creditor coordination, while bonds have superior risk sharing characteristics. Consistent with this assumption, banks reduce spreads as they

  2. IMF Direction Derived from Cycloid-Like Ion Distributions Observed by Mars Express

    Microsoft Academic Search

    M. Yamauchi; Y. Futaana; A. Fedorov; E. Dubinin; R. Lundin; J.-A. Sauvaud; D. Winningham; R. Frahm; S. Barabash; M. Holmstrom; J. Woch; M. Fraenz; E. Budnik; H. Borg; J. R. Sharber; A. J. Coates; Y. Soobiah; H. Koskinen; E. Kallio; K. Asamura; H. Hayakawa; C. Curtis; K. C. Hsieh; B. R. Sandel; M. Grande; A. Grigoriev; P. Wurz; S. Orsini; P. Brandt; S. McKenna-Lawler; J. Kozyra; J. Luhmann

    2007-01-01

    Although the Mars Express (MEX) does not carry a magnetometer, it is in principle possible to derive the interplanetary magnetic field (IMF) orientation from the three dimensional velocity distribution of pick-up ions measured by the Ion Mass Analyser (IMA) on board MEX because pick-up ions' orbits, in velocity phase space, are expected to gyrate around the IMF when the IMF

  3. Does the IMF vary with galaxy velocity dispersion?

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter; Conroy, Charlie

    2011-08-01

    Using LRIS on Keck we recently found that very massive elliptical galaxies (with velocity dispersions ?>250 km/s) have enhanced Na I 8190 Aand FeH 9916 Aabsorption compared to population synthesis models and globular clusters. These absorption features are strong in dwarf stars and weak or absent in other types of stars, and the most straightforward interpretation is that the IMF in massive ellipticals had a much higher proportion of dwarf stars than the IMF in the disk of the Milky Way. A key test of this result is to measure these same absorption features in elliptical galaxies with lower velocity dispersions. Dynamical and lensing studies have shown that the mass-to-light ratios (M/L) of these ellipticals are much lower than the M/L implied by dwarf-rich IMFs, which means that their IMFs must be closer to the Milky Way IMF. Here we propose to observe a carefully selected sample of 12 well-studied elliptical galaxies with velocity dispersions in the range 100-250 km/s. The galaxies were selected to have similar ages, metal abundances, and (alpha)-enhancements as the ?>250 km/s galaxies we studied previously. If Na I and FeH behave like the other metal lines and do not increase with velocity dispersion, we can rule out the interpretation of van Dokkum & Conroy (2010, 2011). If, instead, Na I and FeH are decoupled from the other metals and scale with velocity dispersion, they likely reflect a systematically varying dwarf contribution with velocity dispersion.

  4. Subtleties of the clock retardation

    E-print Network

    Redzic, D V

    2015-01-01

    For a simple electromagnetic model of a clock introduced by Jefimenko (clock $\\#$ 1 in 1996 {\\it Am. J. Phys.} {\\bf 64} 812), a change of the rate of the clock when it is set in uniform motion is calculated exactly, employing the correct equation of motion of a charged particle in the electromagnetic field and the universal boostability assumption. Thus, for the clock under consideration, a dynamical content of the clock retardation is demonstrated. Somewhat surprisingly, the analysis presented discloses that some familiar relativistic generalisations concerning the retardation of clocks have to be amended.

  5. Molecular Clocks in Pharmacology

    PubMed Central

    Musiek, Erik S.; FitzGerald, Garret A.

    2013-01-01

    Circadian rhythms regulate a vast array of biological processes and play a fundamental role in mammalian physiology. As a result, considerable diurnal variation in the pharmacokinetics, efficacy, and side effect profiles of many therapeutics has been described. This variation has subsequently been tied to diurnal rhythms in absorption, distribution, metabolism, and excretion, as well as in pharmacodynamic variables, such as target expression. More recently, the molecular basis of circadian rhythmicity has been elucidated with the identification of clock genes, which oscillate in a circadian manner in most cells and tissues and regulate transcription of large sets of genes. Ongoing research efforts are beginning to reveal the critical role of circadian clock genes in the regulation of pharmacologic parameters, as well as the reciprocal impact of drugs on circadian clock function. This chapter will review the role of circadian clocks in the pharmacokinetics and pharmacodynamics of drug response, and provide several examples of the complex regulation of pharmacologic systems by components of the molecular circadian clock. PMID:23604482

  6. Zero skew clock routing in multiple-clock synchronous systems

    Microsoft Academic Search

    Wasini Khan; M. Hossain; Naveed Sherwani

    1992-01-01

    A clock routing algorithm for two-phase clock systems is presented. The algorithm, which minimizes both intraclock skew and interclock skew, has been implemented on SPARC 1+ in C and has been tested on several industrial benchmarks as well as on randomly generated examples. In particular, the result was tested for a 267 synchronous component circuit at clock rates of 100

  7. Data to Clock Phase Alignment

    Microsoft Academic Search

    Nick Sawyer

    When designing digital systems, there is often a requirement to synchronize incoming data and clock signals with an internal system clock, i. e., the internal and external clock are at exactly the same frequency, but due to variable backplane, board, or application-specific standard product (ASSP) delays, the phase relationship is not known. The circuit described in this application note addresses

  8. Generation of Birkeland Currents during IMF By: Mechanisms and theory

    NASA Astrophysics Data System (ADS)

    Tenfjord, Paul; Østgaard, Nikolai; Snekvik, Kristian; Laundal, Karl; Reistad, Jone; Milan, Steve; Haaland, Stein

    2015-04-01

    We investigate the role of IMF By in the generation of Birkeland Currents (BC), comparing observations from AMPERE and MHD simulations. Observations have shown that the intensity and position of the aurora is not always symmetric between the two hemispheres. Asymmetric BCs arise due to non-uniform penetration of IMF BY in to the closed magnetosphere. We investigate associated BCs, and whether asymmetric currents between the two hemispheres can be observed. We show how asymmetrical footpoints are produced, and how this may lead to asymmetrical BCs at conjugate points. We also present current measurements from AMPERE that are consistent with this picture. We argue that the induced BY produces asymmetrical Birkeland currents as a consequence of asymmetric stress balance between the hemispheres. Such an asymmetry will also lead to asymmetrical footpoints and asymmetries in the azimuthal flow in the ionosphere. These phenomena should therefore be treated in a unified way.

  9. World Bank Group - International Monetary Fund (IMF) Annual Meetings 1997

    NSDL National Science Digital Library

    The World Bank Group and the International Monetary Fund (IMF) held its 1997 Annual Meeting in Hong Kong. The site contains the text of the Annual Meeting Speech titled The Challenge of Inclusion by John D. Wolfenshon, President of the World Bank, and the Per Jacobsson Lecture titled Asian Monetary Cooperation presented by Joseph Yam, chief executive of the Hong Kong Monetary Authority. Speeches by Michael Camdessus, George Soros and Dato Seri Dr Mahathir Bin Mohamad (Prime Minister of Malaysia) are also available. The 1997 Annual Reports of the IMF and World Bank Group can also be viewed at the site. The Focus on Asia section contains various relevant speeches, publications, and other information on Asia produced by the World Bank Group and the International Monetary Fund.

  10. Clocked CMOS calculator circuitry

    Microsoft Academic Search

    Y. Suzuki; K. Odagawa; T. Abe

    1973-01-01

    A novel circuit technique that has been applied to the world's first CMOS-LSI for a desktop calculator is described in detail. The CMOS-LSI includes 3300 elements and has a chip size of about 200 mil square, operates at 6 V supply voltage, and dissipates power of about 1 mW at a clock frequency of 50 kHz.

  11. Iodine Clock Reaction

    NSDL National Science Digital Library

    This site allows the user to vary initial solution concentration and temperature for the iodine clock reaction. A simulation of the reaction lets reaction times be measured. The data can then be used to determine the order of reaction for the various components.

  12. World Food Clock

    NSDL National Science Digital Library

    Twyman, Luke

    The Scout Staff keeps an eye out for sites that are both informative and interactive, and the World Food Clock does not disappoint. A true feat of graphic design, we loved this site for its innovative and effective presentation of information. The World Food Clock succeeds in providing relevant statistics in an easily digestible manner, with clean and informative visual representations. Likewise, the navigation is both fun and functional, allowing the user to have a stimulating learning experience about global consumption and production.How much food is being consumed around the world right now? It's a vast question that can be answered by the World Food Clock. This interesting website draws on information provided by the Food and Agricultural Organization (FAO) of the United Nations and presents a streaming set of data on global food consumption, global food waste, and other informative topics. It's visually arresting and users can scroll down to look through different "clocks" that track statistics such as the land used to grow wasted food and the stages of food waste, which include production, processing, and consumption. This is a wonderful tool for folks with an interest in food security, environmental studies, public health, and international relations. It could also be used in any number of design courses to illustrate a range of techniques and visualization strategies.

  13. The modern molecular clock

    Microsoft Academic Search

    David Penny; Lindell Bromham

    2003-01-01

    The discovery of the molecular clock — a relatively constant rate of molecular evolution — provided an insight into the mechanisms of molecular evolution, and created one of the most useful new tools in biology. The unexpected constancy of rate was explained by assuming that most changes to genes are effectively neutral. Theory predicts several sources of variation in the

  14. The male biological clock

    Microsoft Academic Search

    Sarah M. Lambert; Puneet Masson; Harry Fisch

    2006-01-01

    Do men have biological clocks that affect their hormone levels, fertility, and the genetic quality of their sperm? Women can no longer be viewed as solely responsible for age-related fertility and genetic problems. The effects of andropause and advanced paternal age on fertility and offspring are still under investigation. Further research is needed to fully characterize the associated risks and

  15. Circadian clock, cancer, and chemotherapy.

    PubMed

    Sancar, Aziz; Lindsey-Boltz, Laura A; Gaddameedhi, Shobhan; Selby, Christopher P; Ye, Rui; Chiou, Yi-Ying; Kemp, Michael G; Hu, Jinchuan; Lee, Jin Hyup; Ozturk, Nuri

    2015-01-20

    The circadian clock is a global regulatory system that interfaces with most other regulatory systems and pathways in mammalian organisms. Investigations of the circadian clock-DNA damage response connections have revealed that nucleotide excision repair, DNA damage checkpoints, and apoptosis are appreciably influenced by the clock. Although several epidemiological studies in humans and a limited number of genetic studies in mouse model systems have indicated that clock disruption may predispose mammals to cancer, well-controlled genetic studies in mice have not supported the commonly held view that circadian clock disruption is a cancer risk factor. In fact, in the appropriate genetic background, clock disruption may instead aid in cancer regression by promoting intrinsic and extrinsic apoptosis. Finally, the clock may affect the efficacy of cancer treatment (chronochemotherapy) by modulating the pharmacokinetics and pharmacodynamics of chemotherapeutic drugs as well as the activity of the DNA repair enzymes that repair the DNA damage caused by anticancer drugs. PMID:25302769

  16. Telling Time With Analog Clocks.

    NSDL National Science Digital Library

    Alyssa Nichols

    2012-04-27

    Telling time is an important skill that you will use on a daily basis. It is important to understand and know how to read both analog clocks and digital clocks because they are both still used today. Analog clocks are becoming more out of date, but you don't ever want to be in a situation where you have to say "I can't read that kind of clock! I don't know what time it is." Let's practice your skills of telling time with analog clocks to help you avoid those situations. Move the hands of the clock to show the correct time. Time Clock See if you can match the analog time with the digital time. Match Analog and Digital When you get to this page, click the random button and then practice telling the analog time. If level one is too easy, then try levels ...

  17. Strong IMF By-Related Plasma Convection in the Ionosphere and Cusp Field-Aligned Currents Under Northward IMF Conditions

    NASA Technical Reports Server (NTRS)

    Le, G.; Lu, G.; Strangeway, R. J.; Pfaff, R. F., Jr.; Vondrak, Richard R. (Technical Monitor)

    2001-01-01

    We present in this paper an investigation of IMF-By related plasma convection and cusp field-aligned currents using FAST data and AMIE model during a prolonged interval with large positive IMF By and northward Bz conditions (By/Bz much greater than 1). Using the FAST single trajectory observations to validate the global convection patterns at key times and key locations, we have demonstrated that the AMIE procedure provides a reasonably good description of plasma circulations in the ionosphere during this interval. Our results show that the plasma convection in the ionosphere is consistent with the anti-parallel merging model. When the IMF has a strongly positive By component under northward conditions, we find that the global plasma convection forms two cells oriented nearly along the Sun-earth line in the ionosphere. In the northern hemisphere, the dayside cell has clockwise convection mainly circulating within the polar cap on open field lines. A second cell with counterclockwise convection is located in the nightside circulating across the polar cap boundary, The observed two-cell convection pattern appears to be driven by the reconnection along the anti-parallel merging lines poleward of the cusp extending toward the dusk side when IMF By/Bz much greater than 1. The magnetic tension force on the newly reconnected field lines drives the plasma to move from dusk to dawn in the polar cusp region near the polar cap boundary. The field-aligned currents in the cusp region flow downward into the ionosphere. The return field-aligned currents extend into the polar cap in the center of the dayside convection cell. The field-aligned currents are closed through the Peterson currents in the ionosphere, which flow poleward from the polar cap boundary along the electric field direction.

  18. Microchip-Based Trapped-Atom Clocks

    E-print Network

    Vladan Vuletic; Ian D. Leroux; Monika H. Schleier-Smith

    2011-04-20

    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.

  19. Cold Atom Clocks

    Microsoft Academic Search

    Y. Sortais; S. Bize; M. Abgrall; S Zhang; C Nicolas; C Mandache; P Lemonde; P Laurent; G Santarelli; N Dimarcq; P Petit; A Clairon; A Mann; A Luiten; S Chang; C Salomon

    2001-01-01

    This paper reviews recent progress on microwave clocks using laser cooled neutral atoms. With an ultra-stable cryogenic sapphire oscillator as interrogation oscillator, a cesium fountain operates at the quantum projection noise limit. With 6·105 detected atoms, the relative frequency stability deltanu\\/nu is 4·10-14tau-1\\/2 where tau is the integration time in seconds. This stability is comparable to that of hydrogen masers.

  20. Comparison of plasma sheet ion composition with the IMF and solar wind plasma

    NASA Technical Reports Server (NTRS)

    Lennartsson, W.

    1988-01-01

    Plasma sheet energetic ion data (0.1- to 16 keV/e) obtained by the Plasma Composition Experiment on ISEE-1 between 10 and 23 earth radii are compared with concurrent IMF and solar wind plasma data. The densities of H(+) and He(++) ions in the plasma sheet are found to be the highest, and the most nearly proportional to the solar wind density, when the IMF B(z) is not northward. The density of terrestrial O(+) ions increases strongly with increasing magnitude of the IMF, in apparent agreement with the notion that the IMF plays a fundamental role in the electric coupling between the solar wind and the ionosphere.

  1. The Vitamin C Clock Reaction

    NASA Astrophysics Data System (ADS)

    Wright, Stephen W.

    2002-01-01

    An iodine clock reaction that gives a colorless to black result similar to that of the familiar Landolt iodate-bisulfite clock reaction is described. The vitamin C clock reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, 3% hydrogen peroxide, and laundry starch. Orange juice may be used as the vitamin C source to give an orange to black reaction.

  2. Understanding Neutral Genomic Molecular Clocks

    Microsoft Academic Search

    Soojin V. Yi

    2007-01-01

    The molecular clock hypothesis is a central concept in molecular evolution and has inspired much research into why evolutionary\\u000a rates vary between and within genomes. In the age of modern comparative genomics, understanding the neutral genomic molecular\\u000a clock occupies a critical place. It has been demonstrated that molecular clocks run differently between closely related species,\\u000a and generation time is an

  3. The Mechanism of the Formaldehyde Clock Reaction.

    ERIC Educational Resources Information Center

    Burnett, M. G.

    1982-01-01

    Provides background information and problems with the formaldehyde clock reaction, including comparisons of experimental clock times reported in the literature and conditions for the reliable use of the formaldehyde clock based on a method discussed. (JN)

  4. An alternative derivation of the gravitomagnetic clock effect

    E-print Network

    Lorenzo Iorio; Herbert I. M. Lichtenegger; Bahram Mashhoon

    2001-11-09

    The possibility of detecting the gravitomagnetic clock effect using artificial Earth satellites provides the incentive to develop a more intuitive approach to its derivation. We first consider two test electric charges moving on the same circular orbit but in opposite directions in orthogonal electric and magnetic fields and show that the particles take different times in describing a full orbit. The expression for the time difference is completely analogous to that of the general relativistic gravitomagnetic clock effect in the weak-field and slow-motion approximation. The latter is obtained by considering the gravitomagnetic force as a small classical non-central perturbation of the main central Newtonian monopole force. A general expression for the clock effect is given for a spherical orbit with an arbitrary inclination angle. This formula differs from the result of the general relativistic calculations by terms of order c^{-4}.

  5. Angle Hunting

    NSDL National Science Digital Library

    Exploratorium

    2010-01-01

    In this activity, learners use a hand-made protractor to measure angles they find in playground equipment. Learners will observe that angle measurements do not change with distance, because they are distance invariant, or constant. Note: The "Pocket Protractor" activity should be done ahead as a separate activity (see related resource), but a standard protractor can be used as a substitute.

  6. Intensity asymmetries in the dusk sector of the poleward auroral oval due to IMF Bx

    NASA Astrophysics Data System (ADS)

    Reistad, J. P.; Østgaard, N.; Laundal, K. M.; Haaland, S.; Tenfjord, P.; Snekvik, K.; Oksavik, K.; Milan, S. E.

    2014-12-01

    In the exploration of global-scale features of the Earth's aurora, little attention has been given to the radial component of the Interplanetary Magnetic Field (IMF). This study investigates the global auroral response in both hemispheres when the IMF is southward and lies in the xz plane. We present a statistical study of the average auroral response in the 12-24 magnetic local time (MLT) sector to an x component in the IMF. Maps of auroral intensity in both hemispheres for two IMF Bx dominated conditions (± IMF Bx) are shown during periods of negative IMF Bz, small IMF By, and local winter. This is obtained by using global imaging from the Wideband Imaging Camera on the IMAGE satellite. The analysis indicates a significant asymmetry between the two IMF Bx dominated conditions in both hemispheres. In the Northern Hemisphere the aurora is brighter in the 15-19 MLT region during negative IMF Bx. In the Southern Hemisphere the aurora is brighter in the 16-20 MLT sector during positive IMF Bx. We interpret the results in the context of a more efficient solar wind dynamo in one hemisphere. Both the intensity asymmetry and its location are consistent with this idea. This has earlier been suggested from case studies of simultaneous observations of the aurora in both hemispheres, but hitherto never been observed to have a general impact on global auroral brightness in both hemispheres from a statistical study. The observed asymmetries between the two IMF Bx cases are not large; however, the difference is significant with a 95% confidence level. As the solar wind conditions examined in the study are rather common (37% of the time) the accumulative effect of this small influence may be important for the total energy budget.

  7. The IMF of open star clusters with Tycho-2

    E-print Network

    J. Sanner; M. Geffert

    2001-02-12

    We studied the fields of nine nearby open star clusters based on the Tycho-2 catalogue. The clusters are: Blanco 1, Stock 2, the alpha Per cluster, the Pleiades, NGC 2451, IC 2391, Praesepe, IC 2602, and NGC 7092. We determined membership probabilities for the stars in the cluster fields from the stellar proper motions and used the Tycho-2 photometry to compute the initial mass function (IMF) of the clusters from the main sequence turn-off point down to approx. 1 M_sun. We found IMF slopes ranging from Gamma=-0.69 down to Gamma=-2.27 (when the Salpeter (1955) value would be Gamma=-1.35). We also studied the membership of individual stars of special astrophysical interest. In some cases previous results had to be revised. As a by-product, we investigated some general properties of the Tycho-2 catalogue; we confirmed that the Tycho-2 proper motions show only marginal deviations from the Hipparcos catalogue. On the other hand, in some regions the completeness of the catalogue seems to decrease at magnitudes brighter than claimed by Hog et al. (2000).

  8. Master/slave clock arrangement for providing reliable clock signal

    NASA Technical Reports Server (NTRS)

    Abbey, Duane L. (Inventor)

    1977-01-01

    The outputs of two like frequency oscillators are combined to form a single reliable clock signal, with one oscillator functioning as a slave under the control of the other to achieve phase coincidence when the master is operative and in a free-running mode when the master is inoperative so that failure of either oscillator produces no effect on the clock signal.

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

    ERIC Educational Resources Information Center

    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…

  10. Digital processing clock

    NASA Technical Reports Server (NTRS)

    Phillips, D. H.

    1982-01-01

    Tthe digital processing clock SG 1157/U is described. It is compatible with the PTTI world where it can be driven by an external cesium source. Built-in test equipment shows synchronization with cesium through 1 pulse per second. It is built to be expandable to accommodate future time-keeping needs of the Navy as well as any other time ordered functions. Examples of this expandibility are the inclusion of an unmodulated XR3 time code and the 2137 modulate time code (XR3 with 1 kHz carrier).

  11. Latin American debt, the IMF, and Adam Smith: A proposal for ethical reform

    Microsoft Academic Search

    Gary M. Woller; David Kirkwood Hart

    1995-01-01

    We examine the role of the IMF orthodox paradigm, and the value system upon which it rests, in the Latin American debt crisis. We conclude that the IMF orthodoxy is an inappropriate basis for international transactions because of the a priori utilitarian value assumptions on which it is based. Furthermore, those value premises have hardened into a narrow and inflexible

  12. Faults Diagnostics of Railway Axle Bearings Based on IMF’s Confidence Index Algorithm for Ensemble EMD

    PubMed Central

    Yi, Cai; Lin, Jianhui; Zhang, Weihua; Ding, Jianming

    2015-01-01

    As train loads and travel speeds have increased over time, railway axle bearings have become critical elements which require more efficient non-destructive inspection and fault diagnostics methods. This paper presents a novel and adaptive procedure based on ensemble empirical mode decomposition (EEMD) and Hilbert marginal spectrum for multi-fault diagnostics of axle bearings. EEMD overcomes the limitations that often hypothesize about data and computational efforts that restrict the application of signal processing techniques. The outputs of this adaptive approach are the intrinsic mode functions that are treated with the Hilbert transform in order to obtain the Hilbert instantaneous frequency spectrum and marginal spectrum. Anyhow, not all the IMFs obtained by the decomposition should be considered into Hilbert marginal spectrum. The IMFs’ confidence index arithmetic proposed in this paper is fully autonomous, overcoming the major limit of selection by user with experience, and allows the development of on-line tools. The effectiveness of the improvement is proven by the successful diagnosis of an axle bearing with a single fault or multiple composite faults, e.g., outer ring fault, cage fault and pin roller fault. PMID:25970256

  13. Design of a nuclear clock

    NASA Astrophysics Data System (ADS)

    Notea, A.

    Fixing dates, assigning periods of time and determining age are essential subjects in archeology and geology. Reliable results permit the construction of an absolute time scale and hence a sequence of historical events. A nuclear clock based on radioactive sources produced at present may serve as a time message for future cultures. The characteristic functions of the clock are presented, and a clock, designed for implantation at the corner stone of the Canada Nuclear Engineering Institute at the Technion, is discussed. The clock provides time with a lowest relative uncertainty at 2.95 times the half-life for a single step decay. For the multi-step decay chain the optimal time is shorter. The measuring time range obtained by an acceptable relative resolving power is used as a criterion in the choice of the radionuclides for the clock.

  14. Directly Measuring the Low Mass IMF Outside the Milky Way with JWST

    NASA Astrophysics Data System (ADS)

    Geha, Marla C.

    2014-01-01

    The stellar initial mass function (IMF) parameterizes the relative number of stars formed in a single age population as a function of stellar mass. The IMF is fundamental to all calculations of star formation rates and galaxy stellar masses. Recent indirect estimates of the IMF, based on integrated galaxy light, suggest that the low mass IMF is not 'universal' and instead depends on galaxy properties. The majority of direct IMF studies, via counting stars, are limited to the nearby Galactic field and star clusters, which do not reflect the wide range of environments over which the IMF is routinely applied. We have recently demonstrated via optical HST/ACS photometry that the Milky Way ultra-faint dwarf galaxies have shallower IMF slopes as compared to the Milky Way over the mass range 0.5 - 0.75 M_sun. Infrared imaging is far more efficient in detecting a given low mass star, requiring a factor two less observing time as compared to the optical. However, even deep HST infrared imaging can measure the low mass IMF for only the innermost dwarf galaxies around the Milky Way. JWST provides a unique opportunity to probe the low mass IMF down to 0.3 Msun for all Milky Way dwarf galaxies and down to the hydrogen burning limit for the nearest dwarfs. JWST offers the promise of unambiguously measuring the functional form and slope of the low mass IMF in significantly different environments than the Milky Way and will directly test theories of low mass star formation.

  15. Analysis of inhomogeneous-excitation frequency shifts of ytterbium optical lattice clocks

    NASA Astrophysics Data System (ADS)

    Chen, Ning; Xu, Xinye

    2015-01-01

    We have investigated the frequency shifts caused by inhomogeneous excitation in a 171Yb optical lattice clock. The dependences of the inhomogeneity on the temperature of the cold ytterbium atoms and the misaligning angle between the lattice laser and the clock laser are analyzed by numerical calculations. The dependence of the fractional collisional frequency shift on the ground state fraction under different cold atom temperatures, atom numbers, lattice trap depths and unequal transverse and longitudinal temperatures are also shown. The results show that the uncertainty of the ytterbium clocks, contributed by the inhomogeneous excitation, can be reduced to be 10?19 or even lower with certain conditions.

  16. IMF-By effect on the mid-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Maruyama, Takashi; Jin, Hidekatsu

    The primary factor that controls ionospheric total electron content (TEC) variations is solar UV/EUV radiations through the ionization of the thermospheric neutral particles and through the modification of the thermosphere. Changes in temperature and composition of the neutral atmosphere and the atmospheric circulation greatly affect the ionospheric electron density. Because such a relationship between the solar spectral irradiance and the ionospheric TEC is highly complex, we applied an artificial neural network (ANN) technique that has a great capability of function approximation of complex systems to model solar irradiance effects on TEC. Three solar proxies, F_{10.7}, SOHO_SEM_{26-34} EUV emission index, and MgII_c-w-r were chosen as input parameters to the ANN-TEC model. Another channel of energy flow from the sun to the earth’s ionosphere is the solar wind. The am index and several solar wind magnetosphere coupling functions were chosen as additional inputs to the ANN to model the effects of magnetic disturbances. Somewhat minor but interesting effects on TEC variations emerged when the major effects of solar irradiance and magnetic disturbances were removed. We analyzed the time series of the residual error in TEC prediction by using a wavelet transformation, which revealed a periodic increase in error approximately every 27 days in the summer. Possible origins of the error are (1) insufficient modeling of the solar activity effect, (2) lunar tidal forcing, (3) coupling with planetary waves in the lower atmosphere, and (4) solar wind effects. Examinations refused the first three possibilities. We investigated solar wind parameters that are not concerned in geomagnetic disturbances. The 27-day periodic error during the summer disappeared when the IMF-By component and the solar wind velocity were included in the input space of the ANN. Possible explanation of the IMF-By effect is discussed in terms of changes in the thermospheric general circulation pattern.

  17. GPS clock calibration using an atomic clock Shuei YAMADA,Hans Gerd BERNS

    E-print Network

    Berns, Hans-Gerd

    GPS clock calibration using an atomic clock Shuei YAMADA,Hans Gerd BERNS Abstract Time di#11;ernece of GPS at SK and KEK was measured by making reference to an atomic clock. Following value was obtained and atomic clock at MIZU- SAWA (1999 Oct 19th), 2. measured time di#11;erence of GPS and atomic clock at KEK

  18. Flip-Flop Energy\\/Performance Versus Clock Slope and Impact on the Clock Network Design

    Microsoft Academic Search

    Massimo Alioto; Elio Consoli; Gaetano Palumbo

    2010-01-01

    In this paper, the influence of the clock slope on the speed of various classes of flip-flops (FFs) and on the overall energy dissipation of both FFs and clock domain buffers is analyzed. Analysis shows that an optimum clock slope exists, which minimizes the energy spent in a clock domain. Results show that the clock slope requirement can be relaxed

  19. BMAL1 and CLOCK, Two Essential Components of the Circadian Clock, Are Involved in Glucose Homeostasis

    Microsoft Academic Search

    R. Daniel Rudic; Peter McNamara; Anne-Maria Curtis; Raymond C. Boston; Satchidananda Panda; John B. Hogenesch; Garret A. FitzGerald

    2004-01-01

    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

  20. Trapped ion optical clocks for space applications

    Microsoft Academic Search

    Patrick Gill

    2010-01-01

    The last two decades have seen Cs fountain microwave clocks reach a level of better than 10-15 uncertainty per day, and the Pharao Cs space clock due for launch on the ISS in 2013 should provide improvement to the ground-based fountain clocks. However, the rapid pace of development of optical atomic clocks has reached a stage where they now challenge

  1. Synchronizing clocks in the presence of faults

    Microsoft Academic Search

    Leslie Lamport; P. M. Melliar-Smith

    1985-01-01

    Algorithms are described for maintaining clock synchrony in a distributed multiprocess system where each process has its own clock. These algorithms work in the presence of arbitrary clock or process failures, including “two-faced clocks” that present different values to different processes. Two of the algorithms require that fewer than one-third of the processes be faulty. A third algorithm works if

  2. Serial reconfigurable mismatch-tolerant clock distribution

    Microsoft Academic Search

    Atanu Chattopadhyay; Zeljko Zilic

    2009-01-01

    We present an unconventional clock distribution that emphasizes flexibility and layout independence. It suits a variety of applications, clock domain shapes and sizes using a modular standard cell approach that compensates intra-die temperature and process variances. Our clock distribution provides control over regional clock skew, permits use in beneficial skew applications and facilitates silicon-debug. By adding routing to the serial

  3. A microfabricated atomic clock

    SciTech Connect

    Knappe, Svenja; Shah, Vishal; Schwindt, Peter D.D.; Hollberg, Leo; Kitching, John; Liew, Li-Anne; Moreland, John [Time and Frequency Division, National Institute of Standards and Technology, Boulder, Colorado 80305-3328 (United States); Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305-3328 (United States)

    2004-08-30

    Fabrication techniques usually applied to microelectromechanical systems (MEMS) are used to reduce the size and operating power of the core physics assembly of an atomic clock. With a volume of 9.5 mm{sup 3}, a fractional frequency instability of 2.5x10{sup -10} at 1 s of integration, and dissipating less than 75 mW of power, the device has the potential to bring atomically precise timing to hand-held, battery-operated devices. In addition, the design and fabrication process allows for wafer-level assembly of the structures, enabling low-cost mass-production of thousands of identical units with the same process sequence, and easy integration with other electronics.

  4. A Superfluid Clock

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin

    2004-01-01

    The performance of clocks is limited by the characteristics of the underlying oscillator. Both the quality factor of the oscillator and the signal-to-noise ratio for the resonator state measurement are important. A superfluid helium Helmholtz resonator operating at approx.100mK temperatures has the potential of maintaining frequency stability of 5x10(exp -15)/t(exp 1/2) on the time scale of a few months. The high dynamic range of lossless SQUID position displacement measurement, and low losses associated with the superfluid flow, combined with high mechanical stability of cryogenic assemblies, contribute to the projected stability. Low overall mass of the assembly allows for multiple stages of vibration isolation.

  5. Acceleration effects on atomic clocks

    E-print Network

    F. Dahia; P. J. Felix de Araujo

    2014-12-16

    We consider a free massive particle inside a box which is dragged by Rindler observers. Admitting that the particle obeys the Klein-Gordon equation, we find the frequencies of the stationary states of this system. Transitions between the stationary states are employed to set a standard frequency for a toy atomic clock. Comparing the energy spectrum of the accelerated system with the energy spectrum of an identical system in an inertial frame, we determine the influence of the instantaneous acceleration on the rate of atomic clocks. We argue that our result does not violate the clock hypothesis.

  6. Acceleration effects on atomic clocks

    E-print Network

    Dahia, F

    2014-01-01

    We consider a free massive particle inside a box which is dragged by Rindler observers. Admitting that the particle obeys the Klein-Gordon equation, we find the frequencies of the stationary states of this system. Transitions between the stationary states are employed to set a standard frequency for a toy atomic clock. Comparing the energy spectrum of the accelerated system with the energy spectrum of an identical system in an inertial frame, we determine the influence of the instantaneous acceleration on the rate of atomic clocks. We argue that our result does not violate the clock hypothesis.

  7. Biological Clocks and Circadian Rhythms

    NSDL National Science Digital Library

    Laura Robertson

    2009-02-01

    The study of biological clocks and circadian rhythms is an excellent way to address the inquiry strand in the National Science Education Standards (NSES) (NRC 1996). Students can study these everyday phenomena by designing experiments, gathering and analyzing data, and generating new experiments. As students explore biological clocks and circadian rhythms, they are provided with opportunities to connect learning to experiences and observations from their own lives. This article describes how to reset the biological clock of a shamrock plant while shedding light on its circadian rhythms.

  8. North-south asymmetry of the high-latitude thermospheric density: IMF BY effect

    NASA Astrophysics Data System (ADS)

    Yamazaki, Yosuke; Kosch, Michael J.; Sutton, Eric K.

    2015-01-01

    Previous studies have established that the y component of the interplanetary magnetic field (IMF By) plays a role in the north-south asymmetry of the high-latitude plasma convection and wind. The effect of the positive/negative IMF By in the Northern Hemisphere resembles the effect that the negative/positive IMF By would have in the Southern Hemisphere. In this study, we demonstrate that the IMF By effect can also contribute to the hemispheric asymmetry of the thermospheric density. We use high-accuracy air drag measurements from the CHAllenging Minisatellite Payload (CHAMP) satellite and SuperMAG AE index during the period 2001-2006 to examine the response of the high-latitude thermospheric density to geomagnetic activity. Our statistical analysis reveals that the density response at 400 km is greater in the Southern Hemisphere under positive IMF By conditions, and greater in the Northern Hemisphere under negative IMF By conditions. The results suggest that the IMF By effect needs to be taken into account in upper atmospheric modeling for an accurate description of high-latitude densities during periods of enhanced geomagnetic activity.

  9. Gravitomagnetism and Relative Observer Clock Effects

    E-print Network

    Donato Bini; Robert T. Jantzen; Bahram Mashhoon

    2001-01-18

    The gravitomagnetic clock effect and the Sagnac effect for circularly rotating orbits in stationary axisymmetric spacetimes are studied from a relative observer point of view, clarifying their relationships and the roles played by special observer families. In particular Semer\\'ak's recent characterization of extremely accelerated observers in terms of the two-clock clock effect is shown to be complemented by a similarly special property of the single-clock clock effect.

  10. Empirical Model of Ionospheric Potential for IMF Variations and Substorm Development

    NASA Astrophysics Data System (ADS)

    Taguchi, S.; Nishimura, H.

    2002-05-01

    High-latitude ionospheric potentials are dramatically changed by IMF variations and with substorm development. In this study, potential maps have been derived which cover their change. These have been calculated as functions of IMF and solar wind speed, by statistical analysis of electric potential data for more than 2600 passes of DE 2, using a data interpolation technique with spline. Our model for substorm conditions shows that early in the expansion phase, the positive potential that usually occurs in the postmidnight sector, starts to enter the poleward side of the negative premidnight potential, leading to the development of a distorted pattern. At the substorm maximum, the negative premidnight potential occurs at higher latitudes than in earlier stages, leading to a pronounced Harang discontinuity. Following the substorm maximum, the positive potential gradually retreats from the premidnight potential, and the negative premidnight potential also begins to return to lower latitudes. In the final stage of the recovery phase, the negative premidnight potential extends to the equatorward side of the positive potential, which returns to its initial position. For nonsubstorm conditions, our model shows some features that are not identified in previous empirical models. A reverse convection pattern exists on the dayside even for small ( ~2 nT) northward IMF, and the potential becomes large with the increase of the IMF. When IMF |By| becomes equal to or larger than Bz during northward IMF, a potential structure appears near midnight, which is enhanced with the increase of the IMF magnitude. Details of relations of the potential variations with IMF, which are used in the model construction, will be presented, and possibility of the prediction of potential maps for extremely large IMF with the extrapolation of these relations will be also discussed.

  11. Testing the universality of the IMF with Bayesian statistics: young clusters

    NASA Astrophysics Data System (ADS)

    Dib, Sami

    2014-10-01

    The universality of the stellar initial mass function (IMF) is tested using Bayesian statistics with a sample of eight young Galactic stellar clusters (IC 348, ONC, NGC 2024, NGC 6611, NGC 2264, ? Ophiuchi, Chameleon I, and Taurus). We infer the posterior probability distribution function (pPDF) of the IMF parameters when the likelihood function is described by a tapered power-law function, a lognormal distribution at low masses coupled to a power law at higher masses, and a multicomponent power-law function. The intercluster comparison of the pPDFs of the IMF parameters for each likelihood function shows that these distributions do not overlap within the 1? uncertainty level. Furthermore, the most probable values of the IMF parameters for most of the clusters deviate substantially from their values for the Galactic field stellar IMF. We also quantify the effects of taking into account the completeness correction as well as the uncertainties on the measured masses. The inclusion of the former affects the inferred pPDFs of the slope of the IMF at the low-mass end while considering the latter affects the pPDFs of the slope of the IMF in the intermediate- to high-mass regime. As variations are observed in all of the IMF parameters at once and for each of the considered likelihood functions, even for completeness corrected samples, we argue that the observed variations are real and significant, at least for the sample of eight clusters considered in this work. The results presented here clearly show that the IMF is not universal.

  12. IMF&ndashMetallicity: A Tight Local Relation Revealed by the CALIFA Survey

    NASA Astrophysics Data System (ADS)

    Martín-Navarro, Ignacio; Vazdekis, Alexandre; La Barbera, Francesco; Falcón-Barroso, Jesús; Lyubenova, Mariya; van de Ven, Glenn; Ferreras, Ignacio; Sánchez, S. F.; Trager, S. C.; García-Benito, R.; Mast, D.; Mendoza, M. A.; Sánchez-Blázquez, P.; González Delgado, R.; Walcher, C. J.; The CALIFA Team

    2015-06-01

    Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies (ETGs). However, no observations have yet been able to disentangle the physical driver. We analyze here a sample of 24 ETGs drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy toward metal-rich populations. Our result, combined with the galaxy mass–metallicity relation, naturally explains previous claims of a galaxy mass–IMF relation, derived from non-IFU spectra. If we assume that—within the star formation environment of ETGs—metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.

  13. IMF - metallicity: a tight local relation revealed by the CALIFA survey

    E-print Network

    Martín-Navarro, Ignacio; La Barbera, Francesco; Falcón-Barroso, Jesús; Lyubenova, Mariya; van de Ven, Glenn; Ferreras, Ignacio; Sánchez, S F; Trager, S C; García-Benito, R; Mast, D; Mendoza, M A; Sánchez-Blázquez, P; Delgado, R González; Walcher, C J

    2015-01-01

    Variations in the stellar initial mass function (IMF) have been invoked to explain the spectroscopic and dynamical properties of early-type galaxies. However, no observations have yet been able to disentangle the physical driver. We analyse here a sample of 24 early-type galaxies drawn from the CALIFA survey, deriving in a homogeneous way their stellar population and kinematic properties. We find that the local IMF is tightly related to the local metallicity, becoming more bottom-heavy towards metal-rich populations. Our result, combined with the galaxy mass-metallicity relation, naturally explains previous claims of a galaxy mass-IMF relation, derived from non-IFU spectra. If we assume that - within the star formation environment of early-type galaxies - metallicity is the main driver of IMF variations, a significant revision of the interpretation of galaxy evolution observables is necessary.

  14. Oxygen ion escape from Venus: The acceleration mechanisms and the escape rate under different IMF configurations

    NASA Astrophysics Data System (ADS)

    Masunaga, K.; Futaana, Y.; Yamauchi, M.; Barabash, S.; Zhang, T.; Fedorov, A.; Okano, S.; Terada, N.

    2012-12-01

    Using data obtained from ASPERA-4 (Analyser of Space Plasma and Energetic Atoms) and MAG (magnetometer) experiments onboard Venus Express, we investigate the acceleration mechanisms, the escape rate of the oxygen ions from the Venus upper atmosphere, and the contribution of the upstream condition to them. We first produce spatial distribution maps of O+ fluxes (>100 eV) around Venus for two different convection electric fields, namely the solar wind electric field (SWEF; Esw = -Vsw x Bsw) and the local convection electric field (LCEF; EL = -VL x BL where VL and BL are the local proton velocity and the local magnetic field that obtained over one-scan (192 s)). Comparison between the two distributions, we find that the O+ fluxes are frequently observed in the hemisphere where LCEF orients. Moreover, such structure can be identified regardless of the upstream interplanetary magnetic field (IMF) direction. Thus we conclude that the O+ ions are accelerated more effectively by LCEF rather than SWEF in the Venusian upper atmosphere. In the induced magnetosphere, O+ fluxes are frequently associated with Bx reversals where the IMF curvature is strong. It indicates that a magnetic tension force also contributes to O+ acceleration. We also investigate the dependency of the O+ escape rates on the upstream IMF directions. Here, the IMF condition is classified into two cases: the perpendicular IMF case and the parallel IMF case, where IMF directs nearly perpendicular to the Venus-Sun line (60° < ? < 120°) and nearly parallel to it (0° < ? < 30° or 150° < ? < 180°). During the data period between 20 Jun 2006 and 20 Dec 2009 we have obtained 141 perpendicular IMF cases and 71 parallel IMF cases. Using these data, total O+ escape rates are estimated by integrating the anti-sunward fluxes in the nightside region. We find that the total escape rates between the two IMF cases are of the same order, and thus we conclude that the upstream IMF direction does not significantly affect to the total amount of O+ outflow from the Venusian upper atmosphere.

  15. Main results of the development of dispersion type IMF at A.A. Bochvar Institute

    Microsoft Academic Search

    A. M. Savchenko; A. V. Vatulin; E. M. Glagovsky; I. I. Konovalov; A. V. Morozov; A. V. Kozlov; S. A. Ershov; V. A. Mishunin; G. V. Kulakov; V. I. Sorokin; A. P. Simonov; Z. N. Petrova; V. V. Fedotov

    2010-01-01

    At A.A. Bochvar Institute a novel conception of IMF to burn civil and weapon’s grade Pu is currently accepted. It consists in the fact, that instead of using pelletized IMF, that features low serviceability and dust forming route of fuel element fabrication, the usage is made of dispersion type fuel element with aluminium or zirconium matrices.Dispersion fuels feature a high

  16. A Floor in the Open Flux IMF Strength Constant in Time (Centuries) and Space (Latitude)

    NASA Astrophysics Data System (ADS)

    Svalgaard, L.

    2006-12-01

    The Interplanetary Magnetic Field (IMF) is with some success often modeled by assuming a spherical "source surface" near the sun where the magnetic potential is constant giving rise to the "open flux" of a radial IMF (eventually turning into a coned helix by solar rotation). 150 years of geomagnetic activity measurements suggest that the solar cycle variation of the IMF strength can be expressed as a constant component (Br ~ 3 nT at 1 AU near the Earth) plus a component that varies with the square root of the sunspot number (a proxy for the frequency of CMEs). There is growing evidence that CMEs represent "closed flux" with both footpoints in close proximity at the sun. If so, the remaining IMF (subtracting flux added by CMEs) varies little over the solar cycle. We suggest (and present evidence for) that the exists a "floor" in the IMF that is nearly constant over time (centuries) and space (latitude) reviving an old idea of Schulz et al. (1978) that the source surface might be thought of as a (prolate) surface of constant field strength. A consequence of this view is that the IMF strength does not depend on the solar polar fields.

  17. Detecting the bonding state of explosive welding structures based on EEMD and sensitive IMF time entropy

    NASA Astrophysics Data System (ADS)

    Si, Yue; Zhang, Zhousuo; Liu, Qiang; Cheng, Wei; Yuan, Feichen

    2014-07-01

    With the increasing application of explosive welding structures in many engineering fields, interface bonding state detection has become more and more significant to avoid catastrophic accidents. However, the complexity of the interface bonding state makes this task challenging. In this paper, a new method based on ensemble empirical mode decomposition (EEMD) and sensitive intrinsic mode function (IMF) time entropy is proposed for this task. As a self-adaptive non-stationary signal analysis method, EEMD can decompose a complicated signal into a set of IMFs with truly physical meaning, which is beneficial to allocate the structural vibration response signal containing a wealth of bonding state information to certain IMFs. Then, the time entropies of these IMFs are calculated to quantitatively assess the bonding state of the explosive welding structure. However, the IMF time entropies have different sensitivities to the bonding state. Therefore, the most sensitive IMF time entropy is selected based on a distance evaluation technique to detect the bonding state of explosive welding structures. The proposed method is applied to bonding state detection of explosive welding pipes in three cases, and the results demonstrate its effectiveness.

  18. Atomic clock ensemble in space

    NASA Astrophysics Data System (ADS)

    Cacciapuoti, L.; Salomon, C.

    2011-12-01

    Atomic Clock Ensemble in Space (ACES) is a mission using high-performance clocks and links to test fundamental laws of physics in space. Operated in the microgravity environment of the International Space Station, the ACES clocks, PHARAO and SHM, will generate a frequency reference reaching instability and inaccuracy at the 1 · 10-16 level. A link in the microwave domain (MWL) and an optical link (ELT) will make the ACES clock signal available to ground laboratories equipped with atomic clocks. Space-to-ground and ground-to-ground comparisons of atomic frequency standards will be used to test Einstein's theory of general relativity including a precision measurement of the gravitational red-shift, a search for time variations of fundamental constants, and Lorentz Invariance tests. Applications in geodesy, optical time transfer, and ranging will also be supported. ACES has now reached an advanced technology maturity, with engineering models completed and successfully tested and flight hardware under development. This paper presents the ACES mission concept and the status of its main instruments.

  19. Proposal of atomic clock in motion: Time in moving clock

    E-print Network

    Masanori Sato

    2004-11-22

    The time in an atomic clock in motion is discussed using the analogy of a sing around sound source. Sing around frequency is modified according to the motion of the sing around sound source, using the Lorentz transformation equation. Thus, if we use the sing around frequency as a reference, we can define the reference time. We propose that the time delay of an atomic clock in motion be derived using the sing around method. In this letter, we show that time is defined by a combination of light speed and motion.

  20. The US Naval Observatory Clock Time Reference and the Performance of a Sample of Atomic Clocks

    Microsoft Academic Search

    G M R Winkler; R G Hall; D B Percival

    1970-01-01

    The US Naval Observatory (USNO) uses clock averaging of about 16 selected cesium beam clocks for the derivation of an extremely uniform clock time scale. Frequency stabilities of better than 2 × 10-14 for very long intervals are being achieved together with utmost reliability of the time scale. Individual clocks differ widely in their performance and are carefully selected for

  1. Half-swing clocking scheme for 75% power saving in clocking circuitry

    Microsoft Academic Search

    Hirotsugu Kojima; Satoshi Tanaka; Katsuro Sasaki

    1995-01-01

    We propose a half-swing clocking scheme that allows us to reduce power consumption of clocking circuitry by as much as 75%, because all the clock signal swings are reduced to half of the LSI supply voltage. The new clocking scheme causes quite small speed degradation, because the random logic circuits in the critical path are still supplied by the full

  2. A monolithic digital clock-generator for on-chip clocking of custom DSP's

    Microsoft Academic Search

    Peter Nilsson; Mats Torkelson

    1996-01-01

    This paper shows a robust and easily implemented clock generator for custom designs. It is a fully digital design suitable for both high-speed clocking and low-voltage applications. This clocking method is digital, and it avoids analog methods like phase locked loops or delay line loops. Instead, the clock generator is based on a ring counter which stops a ring oscillator

  3. Colloquium: Physics of optical lattice clocks

    SciTech Connect

    Derevianko, Andrei; Katori, Hidetoshi [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States); Department of Applied Physics, Graduate School of Engineering, University of Tokyo, Bunkyo-ku, 113-8656 Tokyo (Japan) and CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama (Japan)

    2011-04-01

    Recently invented and demonstrated optical lattice clocks hold great promise for improving the precision of modern time keeping. These clocks aim at the 10{sup -18} fractional accuracy, which translates into a clock that would neither lose nor gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here the principles of operation of these clocks are discussed and, in particular, a novel concept of magic trapping of atoms in optical lattices. Recently proposed microwave lattice clocks are also highlights and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.

  4. Multiwavelength all-optical clock recovery

    E-print Network

    Johnson, C.; Demarest, Kenneth; Allen, Christopher Thomas; Hui, Rongqing; Peddanarappagari, K. V.; Zhu, B.

    1999-07-01

    Multiwavelength clock recovery is especially desirable in systems that use wavelength-division-multipleged technology. A multiwavelength clock-recovery device can greatly simplify costs by eliminating the need to have a ...

  5. Colloquium: Physics of optical lattice clocks

    NASA Astrophysics Data System (ADS)

    Derevianko, Andrei; Katori, Hidetoshi

    2011-04-01

    Recently invented and demonstrated optical lattice clocks hold great promise for improving the precision of modern time keeping. These clocks aim at the 10-18 fractional accuracy, which translates into a clock that would neither lose nor gain a fraction of a second over an estimated age of the Universe. In these clocks, millions of atoms are trapped and interrogated simultaneously, dramatically improving clock stability. Here the principles of operation of these clocks are discussed and, in particular, a novel concept of magic trapping of atoms in optical lattices. Recently proposed microwave lattice clocks are also highlights and several applications that employ the optical lattice clocks as a platform for precision measurements and quantum information processing.

  6. What's my angle? : do people with big hands have larger angles between their fingers?

    NSDL National Science Digital Library

    National Action Council for Minorities in Engineering

    2002-01-01

    This activity challenges students to think about angles as geometric shapes and to find the sizes of the angles between their fingers. It is part of the Figure This! collection of 80 online mathematical challenges emphasizing real world uses of mathematics. For this challenge, the students trace a hand stretched to form an L-shape with the thumb and sketches angles of 90 degrees and 45 degrees between the thumb and index finger. They use the sketches to estimate the angles between their other fingers. Questions extend the challenge to finding the distance a bike wheel travels in one rotation, the headings of compass directions, and the number of degrees between the hands of a clock. Also included are directions for making a protractor by folding a circle of paper and a question about the meaning of negative angles. Copyright 2005 Eisenhower National Clearinghouse

  7. Synchronous clock stopper for microprocessor

    NASA Technical Reports Server (NTRS)

    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.

  8. Single-transistor-clocked flip-flop

    DOEpatents

    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.

  9. On the gravitomagnetic clock effect

    E-print Network

    Bahram Mashhoon; Lorenzo Iorio; Herbert Lichtenegger

    2001-10-10

    General relativity predicts that two freely counter-revolving test particles in the exterior field of a central rotating mass take different periods of time to complete the same full orbit; this time difference leads to the gravitomagnetic clock effect. The effect has been derived for circular equatorial orbits; moreover, it has been extended via azimuthal closure to spherical orbits around a slowly rotating mass. In this work, a general formula is derived for the main gravitomagnetic clock effect in the case of slow motion along an arbitrary {\\it elliptical} orbit in the exterior field of a slowly rotating mass. Some of the implications of this result are briefly discussed.

  10. Investigation of the Effects of IMF Orientation Upon Delivery of Plasma Sheet Material to the Inner Magnetosphere

    NASA Astrophysics Data System (ADS)

    Denton, M. H.; Thomsen, M. F.; Skoug, R. M.; Henderson, M. G.; Pollock, C. J.

    2004-12-01

    The orientation of the interplanetary magnetic field (IMF) is known to strongly control the entry of solar wind material into the Earth's magnetosphere. Within the magnetosphere various plasma properties and parameters are known to be IMF dependent. In this study we use Magnetospheric Plasma Analyser (MPA) data from the LANL constellation of satellites located in geosynchronous orbit, in conjunction with the imaging capabilities of the Medium Energy Neutral Atom (MENA) imager on-board the IMAGE satellite, to determine the effects of IMF orientation on the transport of plasma from the plasma sheet into the inner magnetosphere. A statistical study of MPA data is performed to determine bulk plasma properties at geosynchronous orbit in relation to IMF-By and IMF-Bz. In a parallel statistical study we use MENA data to determine the location of the peak nightside energetic neutral atom (ENA) emissons and to investigate whether this peak, which may indicate substorm injection regions, is IMF-dependent.

  11. Variations in the directions of north-south component of IMF in the GSE System near Earth and Parker's Model

    NASA Astrophysics Data System (ADS)

    Pereira, B. Felix; Girish, T. E.

    The monthly probability of occurence of southward IMF events in the GSE system in association with IMF sectors of away and toward polarity is shown to exhibit an annual variation following the heliographic latitude of earth if the IMF orientations are inferred to be in agreement with the Parker's model. Using this new idea we can infer deviations of IMF north-south (Bz components) orientations observed near eath from that predicted by Parker's model of the solar wind. Analysis of relevant earth-orbiting satellite observations of the interplanetary medium during the period 1973-80 does not reveal any systematic sunspot cycle and solar wind speed dependence for the inferred deviaitons of IMF from the Paker's model. However IMF north-south orientations for the year 1974, a period of recurrent high speed solar wind stream activity, show a significant departure from the Parker's model.

  12. Collisionally Induced Atomic Clock Shifts and Correlations

    E-print Network

    Y. B. Band; I. Osherov

    2011-06-23

    We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts and blackbody radiation effects for atomic clock transitions using a density matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Results for a finite temperature ${}^{87}$Sr ${}^1S_0$ ($F = 9/2$) atomic clock in a magic wavelength optical lattice are presented.

  13. A Predictive Synchronizer for Periodic Clock Domains

    Microsoft Academic Search

    Uri Frank; Ran Ginosar

    2004-01-01

    An adaptive predictive clock synchronizer is presented. The synchro- nizer takes advantage of the periodic nature of clocks in order to predict poten- tial conflicts in advance, and to conditionally employ an input sampling delay to avoid such conflicts. The result is conflict-free synchronization with minimal latency. The adaptive predictive synchronizer adjusts automatically to a wide range of clock frequencies,

  14. Spin squeezing in a Rydberg lattice clock.

    PubMed

    Gil, L I R; Mukherjee, R; Bridge, E M; Jones, M P A; Pohl, T

    2014-03-14

    We theoretically demonstrate a viable approach to spin squeezing in optical lattice clocks via optical dressing of one clock state to a highly excited Rydberg state, generating switchable atomic interactions. For realistic experimental parameters, these interactions are shown to generate over 10 dB of squeezing in large ensembles within a few microseconds and without degrading the subsequent clock interrogation. PMID:24679291

  15. Quasars as very-accurate clock synchronizers

    NASA Technical Reports Server (NTRS)

    Hurd, W. J.; Goldstein, R. M.

    1975-01-01

    Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks.

  16. Microwave Cavity Clocks On Space Station

    NASA Technical Reports Server (NTRS)

    Lipa, J. a.; Nissen, J. A.; Wang, S.; Stricker, D. A.; Avaloff, D.

    2003-01-01

    We describe the status of a microwave cavity clock experiment to perform improved tests of Local Position Invariance and Lorentz Invariance on the International Space Station in conjunction with atomic clocks. Significant improvements over present bounds are expected in both cases. The oscillators can also be used to enhance the performance of atomic clocks at short time scales for other experiments.

  17. Phase clocks for transient fault repair

    Microsoft Academic Search

    Ted Herman

    2000-01-01

    Phase clocks are synchronization tools that implement a form of logical time in distributed systems. For systems tolerating transient faults by self-repair of damaged data, phase clocks can enable reasoning about the progress of distributed repair procedures. This paper presents a phase clock algorithm suited to the model of transient memory faults in asynchronous systems with read\\/write registers. The algorithm

  18. Molecular clocks: four decades of evolution

    Microsoft Academic Search

    Sudhir Kumar

    2005-01-01

    During the past four decades, the molecular-clock hypothesis has provided an invaluable tool for building evolutionary timescales, and has served as a null model for testing evolutionary and mutation rates in different species. Molecular clocks have also influenced the development of theories of molecular evolution. As DNA-sequencing technologies have progressed, the use of molecular clocks has increased, with a profound

  19. Ultra Low-Power Clocking Scheme Using Energy Recovery and Clock Gating

    Microsoft Academic Search

    Hamid Mahmoodi; Vishy Tirumalashetty; Matthew Cooke; Kaushik Roy

    2009-01-01

    A significant fraction of the total power in highly synchronous systems is dissipated over clock networks. Hence, low-power clocking schemes are promising approaches for low-power design. We propose four novel energy recovery clocked flip-flops that enable energy recovery from the clock network, resulting in significant energy savings. The proposed flip-flops operate with a single-phase sinusoidal clock, which can be generated

  20. Optical lattice clocks near the QPN limit: a tenfold improvement in optical clock stability

    NASA Astrophysics Data System (ADS)

    Nicholson, Travis

    2013-05-01

    Two classes of optical atomic clocks have surpassed microwave frequency standards: single-ion clocks and optical lattice clocks. Single-ion clocks hold the record for the lowest systematic uncertainty; however, many-atom lattice clocks have the potential to outperform single-ion clocks because the standard quantum limit to atomic clock instability (known as quantum projection noise or QPN) scales as 1 /?{Natoms}. For realistic atom numbers and coherence times, QPN-limited lattice clocks could average down to a given stability hundreds of times faster than the best ion clocks. Up to now lattice clocks with 1000 atoms have not shown improvement over the stability of single-ion clocks. Lattice clock stability has been limited by laser noise (via the optical Dick effect). To address this problem, we constructed a new clock laser with a thermal noise floor of 1 ×10-16 -an order of magnitude improvement over our previous clock laser. With this laser, we compare two lattice clocks, reaching instability of 1 ×10-17 in 2000 s for a single clock. This instability is within a factor of 2 of the theoretical QPN limit for 1000 atoms, representing the lowest reported instability for an independent clock. The high stability of many-particle clocks can come at the price of larger systematic uncertainty due to a frequency shift from atomic interactions. To minimize this shift, we use a cavity-enhanced lattice for our second clock. The high circulating power inside the cavity allows for a large trap volume, yielding a density at 2000 atoms that is 27 times smaller (than in our first clock) and permitting us to trap as many as 5 ×104 atoms. For 2000 atoms in our lattice, we measure a value for this shift (which is linear in density) of - 3 . 11 ×10-17 with an uncertainty of 8 . 2 ×10-19.

  1. Proposal of atomic clock in motion: Time in moving clock

    Microsoft Academic Search

    Masanori Sato

    2004-01-01

    The time in an atomic clock in motion is discussed using the analogy of a sing around sound source. Sing around frequency is modified according to the motion of the sing around sound source, using the Lorentz transformation equation. Thus, if we use the sing around frequency as a reference, we can define the reference time. We propose that the

  2. High-Altitude Cusp Overall Properties and Flows Dependence on IMF Orientation : A Three-Year Cluster Statistical Study

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Fedorov, A.; Budnik, E.; Thomsen, M. F.; Grigoriev, A.; Cargill, P. J.; Dunlop, M. W.; Reme, H.; Dandouras, I.; Balogh, A.

    2004-05-01

    We analyze spatial distributions of the Cluster magnetic field and plasma parameters in the high-altitude cusp region. The technique uses a magnetic field model, taking into account the actual solar wind conditions and level of geomagnetic activity, in order to model the cusp displacement as a function of the IMF conditions. In the present paper we briefly show spatial distributions that use all IMF conditions and then more particularly report on the statistical properties of the flows observed in this region as a function of the IMF orientation. The main conclusions arising from the present study are: (1) The relatively important anti-sunward component of the convection velocity in the exterior cusp region suggests that the region is statistically largely convective under southward IMF conditions, while for northward IMF the region appears more stagnant, (2) The presence of large parallel (downward) flows at the dayside edge of the exterior cusp proves that plasma penetration preferentially occurs near the dayside magnetopause for southward IMF conditions; on the contrary, under northward IMF the results are suggestive of plasma penetration from the poleward edge of the cusp combined with a substantial sunward convection, but no flows are observed at all at the dayside boundary with the plasma sheet, and (3) There is a clear dependence of the transverse plasma convection in the exterior cusp on the IMF By component; for dawnward (duskward) IMF orientations, the convection is clearly directed towards dusk (dawn). These results are interpreted as strong arguments in favor of the occurrence of magnetic reconnection at the high-latitude magnetopause in the lobes for northward IMF and at the low-latitude magnetopause for southward IMF. We will discuss these results in the context of plasma penetration and transport into the inner magnetosphere, which appears to be substantially different between the northward and southward IMF cases.

  3. Analysis of a Magnetically Trapped Atom Clock

    E-print Network

    D. Kadio; Y. B. Band

    2006-12-12

    We consider optimization of a rubidium atom clock that uses magnetically trapped Bose condensed atoms in a highly elongated trap, and determine the optimal conditions for minimum Allan variance of the clock using microwave Ramsey fringe spectroscopy. Elimination of magnetic field shifts and collisional shifts are considered. The effects of spin-dipolar relaxation are addressed in the optimization of the clock. We find that for the interstate interaction strength equal to or larger than the intrastate interaction strengths, a modulational instability results in phase separation and symmetry breaking of the two-component condensate composed of the ground and excited hyperfine clock levels, and this mechanism limits the clock accuracy.

  4. Analysis of a magnetically trapped atom clock

    SciTech Connect

    Kadio, D. [Departments of Chemistry and Electro-Optics, and Ilse Katz Center for Nano-Science, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Band, Y. B. [Departments of Chemistry and Electro-Optics, and Ilse Katz Center for Nano-Science, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Atomic Physics Division, A267 Physics, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

    2006-11-15

    We consider optimization of a rubidium atom clock that uses magnetically trapped Bose condensed atoms in a highly elongated trap, and determine the optimal conditions for minimum Allan variance of the clock using microwave Ramsey fringe spectroscopy. Elimination of magnetic field shifts and collisional shifts are considered. The effects of spin-dipolar relaxation are addressed in the optimization of the clock. We find that for the interstate interaction strength equal to or larger than the intrastate interaction strengths, a modulational instability results in phase separation and symmetry breaking of the two-component condensate composed of the ground and excited hyperfine clock levels, and this mechanism limits the clock accuracy.

  5. Superposed epoch analysis of the ionospheric convection evolution during substorms: IMF BY dependence

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Milan, S. E.; Yeoman, T. K.; Sato, N.; Yukimatu, A. S.; Wild, J. A.

    2010-10-01

    We present superposed epoch analyses of the average ionospheric convection response in the northern and southern hemispheres to magnetospheric substorms occurring under different orientations of the interplanetary magnetic field (IMF). Observations of the ionospheric convection were provided by the Super Dual Auroral Radar Network (SuperDARN) and substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft. We find that during the substorm growth phase the expected IMF BY-dependent dawn-dusk asymmetry is observed over the entire convection pattern, but that during the expansion phase this asymmetry is retained only in the polar cap and dayside auroral zone. In the nightside auroral zone the convection is reordered according to the local substorm electrodynamics with any remaining dusk-dawn asymmetry being more closely related to the magnetic local time of substorm onset, itself only weakly governed by IMF BY. Owing to the preponderance of substorms occurring just prior to magnetic midnight, the substorm-asymmetry tends to be an azimuthal extension of the dusk convection cell across the midnight sector, a manifestation of the so-called “Harang discontinuity.” This results in the northern (southern) hemisphere nightside auroral convection during substorms generally resembling the expected pattern for negative (positive) IMF BY. When the preexisting convection pattern in the northern (southern) hemisphere is driven by positive (negative) IMF BY, the nightside auroral convection changes markedly over the course of the substorm to establish this same “Harang” configuration.

  6. The (galaxy-wide) IMF in giant elliptical galaxies: from top to bottom

    NASA Astrophysics Data System (ADS)

    Weidner, Carsten; Ferreras, Ignacio; Vazdekis, Alexandre; La Barbera, Francesco

    2013-11-01

    Recent evidence based independently on spectral line strengths and dynamical modelling point towards a non-universal stellar initial mass function (IMF), probably implying an excess of low-mass stars in elliptical galaxies with a high velocity dispersion. Here, we show that a time-independent bottom-heavy IMF is compatible neither with the observed metal-rich populations found in giant ellipticals nor with the number of stellar remnants observed within these systems. We suggest a two-stage formation scenario involving a time-dependent IMF to reconcile these observational constraints. In this model, an early strong starbursting stage with a top-heavy IMF is followed by a more prolonged stage with a bottom-heavy IMF. Such model is physically motivated by the fact that a sustained high star formation will bring the interstellar medium to a state of pressure, temperature and turbulence that can drastically alter the fragmentation of the gaseous component into small clumps, promoting the formation of low-mass stars. This toy model is in good agreement with the different observational constrains on massive elliptical galaxies, such as age, metallicity, ?-enhancement, mass-to-light ratio or the mass fraction of the stellar component in low-mass stars.

  7. Atomic clocks and inertial sensors

    Microsoft Academic Search

    Ch J Bordé

    2002-01-01

    We show that the language of atom interferometry provides a unified picture for microwave and optical atomic clocks as well as for gravito-inertial sensors. The sensitivity and accuracy of these devices is now such that a new theoretical framework common to all these interferometers is required that includes: (a) a fully quantum mechanical treatment of the atomic motion in free

  8. Stochastic Models for Atomic Clocks

    Microsoft Academic Search

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

    Most workers in the field of atomic clocks encounter frequency and time instabilities which can be character- ized ( or model led) as random fluctuations. These random f 1 uctuations typical ly display a power spectral density which varies as a power-law over some signisicant range of (Fourier) frequencies (e. q. , 5 (f) = h f , where Y

  9. A generalized gravitomagnetic clock effect

    E-print Network

    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...

  10. Optical frequency standards and clocks

    Microsoft Academic Search

    H. S. Margolis

    2010-01-01

    Optical frequency standards based on single trapped ions or ensembles of neutral atoms have recently demonstrated stability and accuracy superior to that of the current generation of microwave primary frequency standards, with significant potential for further improvements. When combined with femtosecond optical frequency combs, these standards can be operated as optical clocks generating a direct microwave output signal, raising the

  11. GPS composite clock software performance

    NASA Technical Reports Server (NTRS)

    Satin, Arthur L.; Feess, W. A.; Fliegel, Henry F.; Yinger, C. H.

    1990-01-01

    Computer software for ensembling all the space vehicle (SV) and ground clocks of the Global Positioning Systems (GPS) was implemented at the Master Control Station (MCS) on 17 June 1990. Improved GPS time stability and steering control are predicted. The perceptions of both Air Force and outside users are assessed. Current performance is compared with theoretical predictions.

  12. Zero skew clock net routing

    Microsoft Academic Search

    Ting-Hai Chao; J.-M. Ho; Y.-C. Hsu

    1992-01-01

    The authors present an algorithm, called the zero skew segment tree method (ZSTM), for the clock net routing problem. To eliminate the lock skew and minimize the total wire length, ZSTM recursively partitions the sink nodes into two subsets which have equal loadings and minimum sum of diameters, and then constructs a zero skew segment tree according to the partitioning

  13. Biological Clocks: Riding the Tides

    PubMed Central

    de la Iglesia, Horacio O.; Johnson, Carl Hirschie

    2015-01-01

    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. PMID:24156810

  14. IMF Approves SDR 15.5 Billion Stand-by Credit for Korea

    NSDL National Science Digital Library

    1997-01-01

    The "IMF Approves SDR 15.5 Billion Stand-by Credit for Korea" details the aid package put together for Korea and provides a background of the events and the objectives of the aid package. The beginning of the financial crisis in South Korea can be traced to the collapse of Hanbo Steel Corp., the first in a string of large corporate failures in South Korea. This was followed by the decline in the value of the Korean won against the dollar in October 1997, which persisted until November when the Central Bank of Korea stopped intervening to support the won. The continued decline in won forced the Korean government to seek financial assistance from the International Monetary Fund (IMF). On December 3, the IMF announced a $55 billion aid package for South Korea.

  15. Clock Laser System for a Strontium Lattice Clock

    NASA Astrophysics Data System (ADS)

    Legero, T.; Lisdat, Ch.; Vellore Winfred, J. S. R.; Schnatz, H.; Grosche, G.; Riehle, F.; Sterr, U.

    2009-04-01

    We describe the setup and the characterization of a 698 nm master-slave diode laser system to probe the 1S0-3P0 clock transition of strontium atoms confined in a 1D optical lattice. The frequency noise and the linewidth of the laser system have been measured with respect to an ultrastable 657 nm diode laser with 1 Hz linewidth. The large frequency difference of more than 25 THz was bridged using a femtosecond fiber comb as transfer oscillator. In a second step the virtual beat was used to establish a phase lock between the narrow line 657 nm laser and the strontium clock laser. This technique allowed to transfer the stability from the 657 nm to the 698 nm laser.

  16. Integrated Placement and Skew Optimization for Rotary Clocking

    E-print Network

    Hu, Jiang

    issues. Ro- tary clocking is a novel technique which employs untermi- nated rings formed by differential clocking requires latch locations to match pre-designed clock skew on rotary clock rings. This require] is a promising approach. The basic component of a rotary clock is a pair of cross-connected differential trans

  17. Conveyor-belt clock synchronization

    SciTech Connect

    Giovannetti, Vittorio; Maccone, Lorenzo; Shapiro, Jeffrey H.; Wong, Franco N.C. [Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Lloyd, Seth [Research Laboratory of Electronics, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States); Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139 (United States)

    2004-10-01

    A protocol for synchronizing distant clocks is proposed that does not rely on the arrival times of the signals which are exchanged, and an optical implementation based on coherent-state pulses is described. This protocol is not limited by any dispersion that may be present in the propagation medium through which the light signals are exchanged. Possible improvements deriving from the use of quantum-mechanical effects are also addressed.

  18. How does a low-mass cut-off in the stellar IMF affect the evolution of young star clusters?

    NASA Astrophysics Data System (ADS)

    Kouwenhoven, M. B. N.; Goodwin, S. P.; de Grijs, R.; Rose, M.; Kim, Sungsoo S.

    2014-12-01

    We investigate how different stellar initial mass functions (IMFs) can affect the mass-loss and survival of star clusters. We find that IMFs with radically different low-mass cut-offs (between 0.1 and 2 M?) do not change cluster destruction time-scales as much as might be expected. Unsurprisingly, we find that clusters with more high-mass stars lose relatively more mass through stellar evolution, but the response to this mass-loss is to expand and hence significantly slow their dynamical evolution. We also argue that it is very difficult, if not impossible, to have clusters with different IMFs that are initially `the same', since the mass, radius and relaxation times depend on each other and on the IMF in a complex way. We conclude that changing the IMF to be biased towards more massive stars does speed up mass-loss and dissolution, but that it is not as dramatic as might be thought.

  19. Precise time dissemination via portable atomic clocks

    NASA Technical Reports Server (NTRS)

    Putkovich, K.

    1982-01-01

    The most precise operational method of time dissemination over long distances presently available to the Precise Time and Time Interval (PTTI) community of users is by means of portable atomic clocks. The Global Positioning System (GPS), the latest system showing promise of replacing portable clocks for global PTTI dissemination, was evaluated. Although GPS has the technical capability of providing superior world-wide dissemination, the question of present cost and future accessibility may require a continued reliance on portable clocks for a number of years. For these reasons a study of portable clock operations as they are carried out today was made. The portable clock system that was utilized by the U.S. Naval Observatory (NAVOBSY) in the global synchronization of clocks over the past 17 years is described and the concepts on which it is based are explained. Some of its capabilities and limitations are also discussed.

  20. Future Laser-Cooled Microwave Clock Performance

    NASA Technical Reports Server (NTRS)

    Gibble, Kurt

    1997-01-01

    Limitations to the performance of laser-cooled earth and space-based Cs clocks will be critically discussed. The most significant limitation to the stability and accuracy of laser-cooled atomic clocks is the frequency shift due to cold collisions. Because of it, laser-cooled Cs clocks must be operated at low density and this implies that space based Cs clock performance will not be significantly better than earth based. To regain some of the high accuracy and stability lost to the low density, clocks can be designed to multiply launch (or juggle) atoms. Clocks based on other atoms, in particular Rb-87 or possibly Rb-85, may have much smaller cold collision frequency shifts and therefore be capable of higher stability and accuracy, especially in a space environment.

  1. The Circadian Clock Coordinates Ribosome Biogenesis

    PubMed Central

    Symul, Laura; Martin, Eva; Atger, Florian; Naef, Felix; Gachon, Frédéric

    2013-01-01

    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. PMID:23300384

  2. Mechanism of the circadian clock in physiology

    PubMed Central

    Richards, Jacob

    2013-01-01

    It has been well established that the circadian clock plays a crucial role in the regulation of almost every physiological process. It also plays a critical role in pathophysiological states including those of obesity and diabetes. Recent evidence has highlighted the potential for targeting the circadian clock as a potential drug target. New studies have also demonstrated the existence of “clock-independent effects” of the circadian proteins, leading to exciting new avenues of research in the circadian clock field in physiology. The goal of this review is to provide an introduction to and overview of the circadian clock in physiology, including mechanisms, targets, and role in disease states. The role of the circadian clocks in the regulation of the cardiovascular system, renal function, metabolism, the endocrine system, immune, and reproductive systems will be discussed. PMID:23576606

  3. Molecular components of the mammalian circadian clock

    PubMed Central

    Buhr, Ethan D.; Takahashi, Joseph S.

    2013-01-01

    Mammals synchronize their circadian activity primarily to the cycles of light and darkness in the environment. This is achieved by ocular photoreception relaying signals to the suprachiasmatic nucleus (SCN) in the hypothalamus. Signals from the SCN cause the synchronization of independent circadian clocks throughout the body to appropriate phases. Signals that can entrain these peripheral clocks include humoral signals, metabolic factors, and body temperature. At the level of individual tissues, thousands of genes are brought to unique phases through the actions of a local transcription/translation-based feedback oscillator and systemic cues. In this molecular clock, the proteins CLOCK and BMAL1 cause the transcription of genes which ultimately feedback and inhibit CLOCK and BMAL1 transcriptional activity. Finally, there are also other molecular circadian oscillators which can act independently of the transcription-based clock in all species which have been tested. PMID:23604473

  4. A Scalable Dual-Clock FIFO for Data Transfers Between Arbitrary and Haltable Clock Domains

    Microsoft Academic Search

    Ryan W. Apperson; Zhiyi Yu; Michael J. Meeuwsen; Tinoosh Mohsenin; Bevan M. Baas

    2007-01-01

    A robust, scalable, and power efficient dual-clock first-input first-out (FIFO) architecture which is useful for transferring data between modules operating in different clock domains is presented. The architecture supports correct opera- tion in applications where multiple clock cycles of latency exist between the data producer, FIFO, and the data consumer; and with arbitrary clock frequency changes, halting, and restarting in

  5. Collisionally induced atomic clock shifts and correlations

    SciTech Connect

    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.

  6. A predictive synchronizer for periodic clock domains

    Microsoft Academic Search

    Uri Frank; Tsachy Kapschitz; Ran Ginosar

    2006-01-01

    An adaptive predictive clock synchronizer for systems on chip incorporating multiple clock domains is presented. The synchronizer\\u000a takes advantage of the periodic nature of clocks in order to predict potential conflicts in advance, and to conditionally\\u000a employ an input sampling delay to avoid such conflicts. The result is conflict-free synchronization with maximal throughput\\u000a and minimal latency. The adaptive predictive synchronizer

  7. Molecular origin of the kidney clock.

    PubMed

    Gumz, Michelle L

    2014-11-01

    Increasing evidence suggests that a functional circadian clock in the kidney contributes to the regulation of renal function including blood pressure and sodium balance. When does this kidney clock begin ticking? Mészáros et al. provide the first evidence that the endogenous molecular machinery of the circadian clock begins oscillating in the late fetal kidney. These findings have important implications for our understanding of how homeostasis is maintained in early life. PMID:25360489

  8. Clock Routing for High-Performance ICs

    Microsoft Academic Search

    Michael A. B. Jackson; Arvind Srinivasan; Ernest S. Kuh

    1990-01-01

    In this paper we focus on routing techniques for optimizing clock signals in small-cell (e.g., standard-cell, sea-of gate, etc.…) ASICs. In previously reported work, the routing of the clock net has been performed using ordinary global routing techniques based on a minimum spanning or minimal Steiner tree that have little understanding of clock routing problems. We present a novel approach

  9. Associative skew clock routing for difficult instances 

    E-print Network

    Kim, Min-seok

    2006-08-16

    by: Chair of Committee, Jiang Hu Committee Members, Weiping Shi Eun J. Kim Head of Department, Costas N. Georghiades May 2006 Major Subject: Electrical Engineering iii ABSTRACT Associative Skew Clock Routing for Difficult Instances. (May 2006) Min...-seok Kim, B.S., Texas A&M University Chair of Advisory Committee: Dr. Jiang Hu This thesis studies the associative skew clock routing problem, which seeks a clock routing tree such that zero skew is preserved only within identified groups of sinks. Al...

  10. Clock power reduction for virtex-5 FPGAs

    Microsoft Academic Search

    Qiang Wang; Subodh Gupta; Jason Helge Anderson

    2009-01-01

    Clock network power in field-programmable gate arrays (FP- GAs) is considered and two complementary approaches for clock power reduction in the Xilinx R VirtexTM-5 FPGA are presented. The approaches are unique in that they lever- age specific architectural aspects of Virtex-5 to achieve re- ductions in dynamic power consumed by the clock network. The first approach comprises a placement-based technique

  11. Csac - the Chip-Scale Atomic Clock

    Microsoft Academic Search

    R. Lutwak; A. Rashed; M. Varghese; G. Tepolt; J. Leblanc; M. Mescher; D. K. Serkland; K. M. Geib; G. M. Peake

    2009-01-01

    The authors have developed a Chip-Scale Atomic Clock (CSAC) of sufficiently low power and small size to enable atomic timing in portable battery-powered devices. The collaboration of diverse research teams in clock technology, micro-electromechanical systems (MEMS), and optoelectronic devices has resulted in size and power reduction of atomic clock technology by more than two orders of magnitude. In 2007, we

  12. Huygens synchronization of two pendulum clocks

    E-print Network

    Henrique M. Oliveira; Luís V. Melo

    2014-10-29

    The synchronization of two pendulum clocks hanging from a wall was first observed by Huygens during the XVII century. This type of synchronization is observed in other areas, and is fundamentally different from the problem of two clocks hanging from a moveable base. We present a model explaining the phase opposition synchronization of two pendulum clocks in those conditions. The predicted behavior is observed experimentally, validating the model.

  13. Circadian Clock, Cell Cycle and Cancer

    Microsoft Academic Search

    Zhaoyang Zhao; Cheng Chi Lee

    \\u000a The circadian clock is a fundamental biological process that is pervasive in living organisms. Over the past decade, much\\u000a has been learned about the molecular mechanism of the mammalian circadian clock. Studies have also led to the revelation of\\u000a various connections between the circadian clock function and other basic biological processes, including the cell cycle and\\u000a the DNA damage response.

  14. Low-power clock trees for CPUs

    Microsoft Academic Search

    Dong-Jin Lee; Myung-Chul Kim; Igor L. Markov

    2010-01-01

    Clock networks contribute a significant fraction of dynamic power and can be a limiting factor in high-performance CPUs and SoCs. The need for multi-objective optimization over a large parameter space and the increasing impact of process variation make clock network synthesis particularly challenging. In this work, we develop new modeling techniques and algorithms, as well as a methodology, for clock

  15. Phase Clocks for Transient Fault Repair

    Microsoft Academic Search

    Ted Herman

    2000-01-01

    Abstract Phase clocks are synchronization tools that implement,a form of logical time in distributed systems. For systems tolerating transient faults by self-repair of damaged data, phase clocks can enable reasoning about the progress of distributed repair procedures. This paper presents a phase clock algorithm suited to the model of transient memory,faults in asynchronous systems with read\\/write registers. The algorithm is

  16. Enhanced solar wind geoeffectiveness after a sudden increase in dynamic pressure during southward IMF orientation

    E-print Network

    Lummerzheim, Dirk

    Enhanced solar wind geoeffectiveness after a sudden increase in dynamic pressure during southward increase in solar wind pressure results in poleward expansion of the auroral oval and closing of the polar show that southward IMF conditions combined with high solar wind dynamic pressure immediately after

  17. IMF-sense-dependent cosmic ray anisotropy produced from diffusion-convection in heliosphere

    NASA Astrophysics Data System (ADS)

    Nagashima, K.; Munakata, K.; Tatsuoka, R.

    1985-08-01

    The authors discuss the characteristics of the daily variations caused by the IMF-sense-dependent 2nd order anisotropy obtained on the same condition as adopted by Munakata and Nagashima (1984). A brief comparison of these variations with observations will also be made in order to demonstrate their existence.

  18. Proton aurora dynamics in response to the IMF and solar wind variations

    E-print Network

    California at Berkeley, University of

    Proton aurora dynamics in response to the IMF and solar wind variations S.-W. Chang,1,2 S. B. Mende; accepted 24 April 2002; published 13 July 2002. [1] On May 23, 2000, proton auroras observed by IMAGE FUV wind parameters. A proton aurora brightened at high latitude poleward from the dayside oval after solar

  19. The mass function of dense molecular cores and the origin of the IMF

    Microsoft Academic Search

    J. Alves; M. Lombardi; C. J. Lada

    2007-01-01

    Context: Stars form in the cold dense cores of interstellar molecular clouds and the detailed knowledge of the spectrum of masses of such cores is clearly a key for the understanding of the origin of the IMF. To date, observations have presented somewhat contradictory evidence relating to this issue. Aims: In this paper we propose to derive the mass function

  20. Do IMF and World Bank programs induce government crises? An empirical analysis

    E-print Network

    Krivobokova, Tatyana

    Do IMF and World Bank programs induce government crises? An empirical analysis Axel Drehera Martin of the German Economic Association for helpful comments, Richard Jong-A-Pin for valuable input to an earlier, and CESifo. E-mail: mail@axel-dreher.de. b ETH Zurich, KOF Swiss Economic Institute, Weinbergstrasse 35, CH

  1. The Response of Heavy Planetary Ions at Mars to Reversals of the IMF

    NASA Astrophysics Data System (ADS)

    Curry, S.; Dong, C.; Luhmann, J. G.; Ma, Y.; Bougher, S. W.; Modolo, R.; Leblanc, F.

    2014-12-01

    We present a kinetic study to quantify the response of Mars' atmosphere to changes in the interplanetary magnetic field (IMF) configuration, specifically with respect to the escape rate of the atmosphere. Because Mars lacks a dipole magnetic field, the solar wind directly interacts with the upper neutral atmosphere to create 'pick-up' ions. We will present global maps of escaping O+ pick up ions during different solar cycle phases for multiple IMF conditions using a magnetohydrodynamic (MHD) and test particle simulation. This study also examines the role of the crustal fields for the different IMF configurations; the remanent crustal magnetic fields, especially in extreme conditions, influence the magnetic topology at Mars and subsequently drive changes in heavy ion atmospheric escape. The results indicate that the escape rate from Mars' atmosphere can change over an order of magnitude due to the IMF, solar cycle, and crustal field orientation, directly impacting Mars' climate and our understanding of the processes that influence atmospheric evolution. These results directly support MAVEN, the next Mars Scout, whose primary objective is to understand the evolution of Mars' atmosphere.

  2. Magnetospheric Magnetic Reconnection with Southward IMF by a 3D EMPM Simulation

    NASA Technical Reports Server (NTRS)

    Nishikawa, K.-I.; Yan, X. Y.; Cai, D. S.; Lembege, B.

    2004-01-01

    We report our new simulation results on magnetospheric magnetic reconnection with southward IMF using a 3D EMPM model, with greater resolution and more particles using the parallelized 3D HPF TRISTAN code on VPP5000 supercomputer. Main parameters used in the new simulation are: domain size is 215 x 145 x 145, grid size = 0.5 Earth radius, initial particle number is 16 per cell, the IMF is southward. Arrival of southward IMF will cause reconnection in the magnetopause, thus allowing particles to enter into the inner magnetosphere. Sunward and tailward high particle flow are observed by satellites, and these phenomena are also observed in the simulation near the neutral line (X line) of the near-Earth magnetotail. This high particle flow goes along with the reconnected island. The magnetic reconnection process contributes to direct plasma entry between the magnetosheath to the inner magnetosphere and plasma sheet, in which the entry process eats the magnetosheath plasma to plasma sheet temperatures. We investigate magnetic, electric fields, density, and current during this magnetic reconnection with southward IMF. Further investigation with this simulation will provide insight into unsolved problems, such as the triggering of storms and substorms, and the storm-substorm relationship. New results will be presented at the meeting.

  3. Cold dense magnetopause boundary layer under northward IMF: Results from THEMIS and MHD simulations

    E-print Network

    California at Berkeley, University of

    Cold dense magnetopause boundary layer under northward IMF: Results from THEMIS and MHD simulations 2008; accepted 8 December 2008; published 3 February 2009. [1] A layer of nearly stagnant cold dense numerical model, we successfully reproduce this observed cold dense plasma layer in the simulation

  4. Appropriate IMFs associated with cepstrum and envelope analysis for ball-bearing fault diagnosis

    NASA Astrophysics Data System (ADS)

    Tsao, Wen-Chang; Pan, Min-Chun

    2014-03-01

    The traditional envelope analysis is an effective method for the fault detection of rolling bearings. However, all the resonant frequency bands must be examined during the bearing-fault detection process. To handle the above deficiency, this paper proposes using the empirical mode decomposition (EMD) to select a proper intrinsic mode function (IMF) for the subsequent detection tools; here both envelope analysis and cepstrum analysis are employed and compared. By virtue of the band-pass filtering nature of EMD, the resonant frequency bands of structure to be measured are captured in the IMFs. As impulses arising from rolling elements striking bearing faults modulate with structure resonance, proper IMFs potentially enable to characterize fault signatures. In the study, faulty ball bearings are used to justify the proposed method, and comparisons with the traditional envelope analysis are made. Post the use of IMFs highlighting faultybearing features, the performance of using envelope analysis and cepstrum analysis to single out bearing faults is objectively compared and addressed; it is noted that generally envelope analysis offers better performance.

  5. Injection-Locked Clocking: A Low-Power Clock Distribution Scheme for High-End Microprocessors

    E-print Network

    Wu, Hui

    Injection-Locked Clocking: A Low-Power Clock Distribution Scheme for High-End Microprocessors Hui-performance microprocessors. Clocking circuitry accounts for an overwhelming amount of total power consumption in multi is a crucial aspect of modern multi- GHz microprocessor design. Conventional distribution schemes are more

  6. Low velocity limits of cold atom clocks

    E-print Network

    J. Muñoz; I. Lizuain; J. G. Muga

    2009-09-08

    Fundamental low-energy limits to the accuracy of quantum clock and stopwatch models in which the clock hand motion is activated by the presence of a particle in a region of space have been studied in the past, but their relevance for actual atomic clocks had not been assessed. In this work we address the effect of slow atomic quantum motion on Rabi and Ramsey resonance fringe patterns, as a perturbation of the results based on classical atomic motion. We find the dependence of the fractional error of the corresponding atomic clocks on the atomic velocity and interaction parameters.

  7. A transportable strontium optical lattice clock

    NASA Astrophysics Data System (ADS)

    Poli, N.; Schioppo, M.; Vogt, S.; Falke, St.; Sterr, U.; Lisdat, Ch.; Tino, G. M.

    2014-12-01

    We report on a transportable optical clock, based on laser-cooled strontium atoms trapped in an optical lattice. The experimental apparatus is composed of a compact source of ultra-cold strontium atoms including a compact cooling laser setup and a transportable ultra-stable laser for interrogating the optical clock transition. The whole setup (excluding electronics) fits within a volume of <2 m3. The high degree of operation reliability of both systems allowed the spectroscopy of the clock transition to be performed with 10 Hz resolution. We estimate a relative uncertainty of the clock of 7 × 10-15.

  8. Peripheral circadian clocks--a conserved phenotype?

    PubMed

    Weigl, Yuval; Harbour, Valerie L; Robinson, Barry; Dufresne, Line; Amir, Shimon

    2013-05-01

    The circadian system of mammals regulates the timing of occurrence of behavioral and physiological events, thereby optimizing adaptation to their surroundings. This system is composed of a single master pacemaker located in the suprachiasmatic nucleus (SCN) and a population of peripheral clocks. The SCN integrates time information from exogenous sources and, in turn, synchronizes the downstream peripheral clocks. It is assumed that under normal conditions, the circadian phenotype of different peripheral clocks would be conserved with respect to its period and robustness. To study this idea, we measured the daily wheel-running activity (WRA; a marker of the SCN output) in 84 male inbred LEW/Crl rats housed under a 12 h:12 h light-dark cycle. In addition, we assessed the mRNA expression of two clock genes, rPer2 and rBmal1, and one clock-controlled gene, rDbp, in four tissues that have the access to time cues other than those emanating from the SCN: olfactory bulbs (OBs), liver, tail skin, and white blood cells (WBCs). In contrast with the assumption stated above, we found that circadian clocks in peripheral tissues differ in the temporal pattern of the expression of circadian clock genes, in the robustness of the rhythms, and possibly in the number of functional ~24-h-clock cells. Based on the tissue diversity in the robustness of the clock output, the hepatic clock is likely to house the highest number of functional ~24-h-clock cells, and the OBs, the fewest number. Thus, the phenotype of the circadian clock in the periphery is tissue specific and may depend not only on the SCN but also on the sensitivity of the tissue to non-SCN-derived time cues. In the OBs and liver, the circadian clock phenotypes seem to be dominantly shaped by the SCN output. However, in the tail skin and WBC, other time cues participate in the phenotype design. Finally, our study suggests that the basic phenotype of the circadian clock is constructed at the transcript level of the core clock genes. Yet, additional posttranscriptional and translational events can contribute to the robustness and periodicity of the clock output. PMID:23425359

  9. Song I-Yeong's Armillary Clock

    NASA Astrophysics Data System (ADS)

    Kim, Sang Hyuk; Lee, Yong Sam

    In 1669 (the 10th year of the reign of King Hyeonjong), Song I-Yeong (???, 1619-1692), who was a professor of astronomy at Gwansanggam (Bureau of Astronomy), developed the armillary clock which uses the weight power system of an alarm clock. The armillary clock is a unique astronomical clock that combines the traditional armillary sphere of Joseon and the principle of a Western alarm clock. Song I-Yeong's armillary clock was repaired in 1687-1688 according to the records, and since then not much is known about the history of the armillary clock. After many years, in the early 1930s which was the Japanese colonial era, Inchon (??) Kim Seong-Su (???, 1891-1955) purchased the armillary clock at the Insa-dong antique street and donated to the Korea University Museum of the present time (designated as National Treasure No. 230 in 1985). Currently, the armillary clock is not in operation because some of the parts are damaged or lost.

  10. Reconfigurable Clock Distribution Circuitry Atanu Chattopadhyay, Zeljko Zilic

    E-print Network

    Zilic, Zeljko

    Reconfigurable Clock Distribution Circuitry Atanu Chattopadhyay, Zeljko Zilic Department the circuitry required for implementing a multi-clock reconfigurable, reprogrammable clock distribution network-defined switchpoints, making the distribution reconfigurable. The circuitry can be used to create fully programmable

  11. Synchronization: from pendulum clocks to chaotic lasers and chemical oscillators

    E-print Network

    Potsdam, Universität

    Synchronization: from pendulum clocks to chaotic lasers and chemical oscillators MICHAEL ROSENBLUM Christiaan Huygens reported on his observation of synchronization of two pendulum clocks which he had briefly described in his memoirs Horologium Oscillatorium (The Pendulum Clock, or Geome- trical

  12. Clock Distribution Network Optimization by Sequential Quadratic Programing 

    E-print Network

    Mekala, Venkata

    2010-07-14

    delay models which are computationally expensive. Existing methods on clock network optimization are either restricted to clock trees, which are easy to be separated into smaller problems, or naive heuristics based on crude delay models. A clock mesh...

  13. Gigabit Ethernet Asynchronous Clock Compensation FIFO

    NASA Technical Reports Server (NTRS)

    Duhachek, Jeff

    2012-01-01

    Clock compensation for Gigabit Ethernet is necessary because the clock recovered from the 1.25 Gb/s serial data stream has the potential to be 200 ppm slower or faster than the system clock. The serial data is converted to 10-bit parallel data at a 125 MHz rate on a clock recovered from the serial data stream. This recovered data needs to be processed by a system clock that is also running at a nominal rate of 125 MHz, but not synchronous to the recovered clock. To cross clock domains, an asynchronous FIFO (first-in-first-out) is used, with the write pointer (wprt) in the recovered clock domain and the read pointer (rptr) in the system clock domain. Because the clocks are generated from separate sources, there is potential for FIFO overflow or underflow. Clock compensation in Gigabit Ethernet is possible by taking advantage of the protocol data stream features. There are two distinct data streams that occur in Gigabit Ethernet where identical data is transmitted for a period of time. The first is configuration, which happens during auto-negotiation. The second is idle, which occurs at the end of auto-negotiation and between every packet. The identical data in the FIFO can be repeated by decrementing the read pointer, thus compensating for a FIFO that is draining too fast. The identical data in the FIFO can also be skipped by incrementing the read pointer, which compensates for a FIFO draining too slowly. The unique and novel features of this FIFO are that it works in both the idle stream and the configuration streams. The increment or decrement of the read pointer is different in the idle and compensation streams to preserve disparity. Another unique feature is that the read pointer to write pointer difference range changes between compensation and idle to minimize FIFO latency during packet transmission.

  14. Multi-fault detection of rolling element bearings under harsh working condition using IMF-based adaptive envelope order analysis.

    PubMed

    Zhao, Ming; Lin, Jing; Xu, Xiaoqiang; Li, Xuejun

    2014-01-01

    When operating under harsh condition (e.g., time-varying speed and load, large shocks), the vibration signals of rolling element bearings are always manifested as low signal noise ratio, non-stationary statistical parameters, which cause difficulties for current diagnostic methods. As such, an IMF-based adaptive envelope order analysis (IMF-AEOA) is proposed for bearing fault detection under such conditions. This approach is established through combining the ensemble empirical mode decomposition (EEMD), envelope order tracking and fault sensitive analysis. In this scheme, EEMD provides an effective way to adaptively decompose the raw vibration signal into IMFs with different frequency bands. The envelope order tracking is further employed to transform the envelope of each IMF to angular domain to eliminate the spectral smearing induced by speed variation, which makes the bearing characteristic frequencies more clear and discernible in the envelope order spectrum. Finally, a fault sensitive matrix is established to select the optimal IMF containing the richest diagnostic information for final decision making. The effectiveness of IMF-AEOA is validated by simulated signal and experimental data from locomotive bearings. The result shows that IMF-AEOA could accurately identify both single and multiple faults of bearing even under time-varying rotating speed and large extraneous shocks. PMID:25353982

  15. EVIDENCE FOR A CONSTANT IMF IN EARLY-TYPE GALAXIES BASED ON THEIR X-RAY BINARY POPULATIONS

    NASA Astrophysics Data System (ADS)

    Zepf, Stephen E.; Maccarone, T. J.; Kundu, A.; Gonzalez, A. H.; Lehmer, B.; Maraston, C.

    2014-01-01

    A number of recent studies have proposed that the stellar initial mass function (IMF) of early type galaxies varies systematically as a function of galaxy mass, with higher mass galaxies having steeper IMFs. These steeper IMFs have more low-mass stars relative to the number of high mass stars, and therefore naturally result in proportionally fewer neutron stars and black holes. In this paper, we specifically predict the variation in the number of black holes and neutron stars in early type galaxies based on the IMF variation required to reproduce the observed mass-to-light ratio trends with galaxy mass. We then test whether such variations are observed by studying the field low-mass X-ray binary populations (LMXBs) of nearby early-type galaxies. These binaries are field neutron stars or black holes accreting from a low-mass donor star. We specifically compare the number of field LMXBs per K-band light in a well-studied sample of elliptical galaxies, and use this result to distinguish between an invariant IMF and one that is Kroupa/Chabrier-like at low masses and steeper at high masses. We discuss how these observations constrain the possible forms of the IMF variations and how future Chandra observations can enable sharper tests of the IMF.

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

    ERIC Educational Resources Information Center

    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…

  17. GPS SIGNAL INTEGRITY DEPENDENCIES ON ATOMIC CLOCKS

    Microsoft Academic Search

    Marc Weiss; Pradipta Shome; Ron Beard

    The problem of signal integrity for GPS satellites and the primary dependency upon inherent characteristics of onboard atomic frequency standards are discussed. In particular, there is a need for characterizing peak deviation of GPS clocks from prediction. Results from a preliminary study of two GPS clocks tested on the ground show that the distribution of peak deviations from prediction cannot

  18. Development of a compact cold atom clock

    Microsoft Academic Search

    S. Tremine; S. Guerandel; D. Holleville; A. Clairon; N. Dimarcq

    2004-01-01

    HORACE is a compact cold atom clock where the atoms are cooled inside the microwave interrogation cavity. About 108 atoms can be cooled at kinetic temperatures as low as 2.5 ?K. We report, for the first time, a Ramsey pattern observed with a 14 Hz linewidth and fringe contrast better than 80%. Since this clock is designed for space applications,

  19. Globally Integrated Power and Clock Distribution Network

    E-print Network

    Friedman, Eby G.

    Globally Integrated Power and Clock Distribution Network Renatas Jakushokas and Eby G. Friedman [jakushok, friedman]@ece.rochester.edu Abstract-- The global networks within a conventional inte- grated circuits (IC) consists of three major types: power, ground, and clock networks. These three networks

  20. Connecting the Circadian Clock with Chemosensation 

    E-print Network

    Chatterjee, Abhishek

    2012-07-16

    Molecular underpinnings of chemosensory rhythms......................... 73 Neurobiological correlates of chemosensory rhythms ...................... 79 Regulation of feeding and metabolism by GRN clock... in organisms ranging from bacteria and fungi to humans. Clock deficiencies are associated with abnormal sleep wake cycles (e.g. Familial Advanced Sleep Phase Syndrome), epilepsy, cerebrovascular disease, mood disorders, diabetes, cancer, etc. Disorders...

  1. Fast Clock Recovery for Digital Communications

    NASA Technical Reports Server (NTRS)

    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).

  2. Gradient Clock Synchronization in Wireless Sensor Networks

    E-print Network

    Gradient Clock Synchronization in Wireless Sensor Networks Philipp Sommer Computer Engineering clocks are crucial for many ap- plications in sensor networks. Existing time synchro- nization algorithms Francisco, California, USA. Copyright 2009 ACM 978-1-60558-371-6/09/04 ...$5.00. 1. INTRODUCTION A wireless

  3. Quality monitoring in clock synchronized distributed systems

    Microsoft Academic Search

    Georg Gaderer; Patrick Loschmidt; Thilo Sauter

    2006-01-01

    Clock synchronization in distributed computer systems is an enabler for the introduction of real-time. So far, many approaches are published which implement clock synchronization on a protocol basis over state of the art packet oriented networks. One very recent example is the introduction of real-time into industrial Ethernet net- works, like in Profinet or Powerlink. In addition to this usually

  4. Metabolism and cancer: the circadian clock connection

    Microsoft Academic Search

    Saurabh Sahar; Paolo Sassone-Corsi

    2009-01-01

    Circadian rhythms govern a remarkable variety of metabolic and physiological functions. Accumulating epidemiological and genetic evidence indicates that the disruption of circadian rhythms might be directly linked to cancer. Intriguingly, several molecular gears constituting the clock machinery have been found to establish functional interplays with regulators of the cell cycle, and alterations in clock function could lead to aberrant cellular

  5. Does clock-watching make you clockwise?

    PubMed

    Richards, A; French, C C; Harris, P

    1996-01-01

    French and Richards (1993) found that subjects asked to draw from memory a clock that had Roman numerals on its face typically represented the number four on the clock face as "IV" rather than the correct "IIII", whereas those merely asked to copy it typically drew "IIII". The current experiments followed the methodology of French and Richards, but then went on to examine the subsequent memorial representation of the number four. Subjects drew a clock with Roman numerals on its face, either from memory (with or without forewarning) or while the clock remained in full view. Subsequently, subjects were asked to recall the exact form in which the numbers were represented on the clock (Experiment 1) or were asked to recognise which of two clocks had been presented earlier (Experiment 2). Findings supported the idea that subjects in the copy condition were more likely than subjects in other conditions to draw the clock without invoking schematic knowledge of Roman numerals. The basic effect reported by French and Richards was replicated in both experiments. Furthermore, in both experiments, subjects who correctly drew the clock with the number four represented as "IIII" were more likely to misrepresent it as "IV" in the subsequent memory task if they were in the copy condition rather than the two memory conditions. The results are interpreted in terms of schema theory. PMID:8821085

  6. Designing the best clock distribution network

    Microsoft Academic Search

    Phillip J. Restle; Alina Deutsch

    1998-01-01

    Clock distribution has become an increasingly challenging problem for VLSI designs, consuming an increasing fraction of resources such as wiring, power, and design time. Unwanted differences or uncertainties in clock network delays degrade performance or cause functional errors. Three dramatically different strategies being used in the VLSI industry to address these challenges are compared. Novel modeling and measurement techniques are

  7. Hypothalamic clocks and rhythms in feeding behaviour.

    PubMed

    Bechtold, David A; Loudon, Andrew S I

    2013-02-01

    Daily rhythms are evident across our physiology, ranging from overt behavioural patterns like sleep to intricate molecular rhythms in epigenetic coding. Driving these rhythms at an anatomical and cellular level are circadian clock networks comprising core clock genes and an ever-expanding list of clock-controlled genes. Research over the past decade has revealed an intimate relationship between the clockwork and metabolic processes. In line with this, feeding behaviour in many species exhibits a strong circadian rhythm and, when restricted, food becomes the most potent entraining stimulus for clocks of the body. Critically, there are several indications that disturbance of our daily rhythms contributes to the development of obesity and diabetes. Given our 24-h society, it is important that we understand how the circadian clock influences what and when we eat. PMID:23333345

  8. Orbit determination for next generation space clocks

    NASA Astrophysics Data System (ADS)

    Duchayne, L.; Mercier, F.; Wolf, P.

    2009-09-01

    We study the requirements on orbit determination compatible with operation of next generation space clocks at their expected uncertainty. Using the ACES (Atomic Clock Ensemble in Space) mission as an example, we develop a relativistic model for time and frequency transfer to investigate the effects of orbit determination errors. For the orbit error models considered we show that the required uncertainty goal can be reached with relatively modest constraints on the orbit determination of the space clock, which are significantly less stringent than expected from “naive” estimates. Our results are generic to all space clocks and represent a significant step towards the generalized use of next generation space clocks in fundamental physics, geodesy, and time/frequency metrology.

  9. [The roles of clock genes in obesity].

    PubMed

    Shimba, Shigeki

    2013-02-01

    Several epidemiological studies have suggested that the perturbation of circadian rhythm has adverse metabolic consequences (e.g., obesity) in humans. At the molecular level, circadian rhythms are encoded by an autoregulatory loop composed of a set of transcription activators (BMAL1/CLOCK) that induce expression of repressors (PER/CRY). The mammalian molecular clock is not only expressed within the master suprachiasmatic nucleus pacemaker neurons, but also within nearly all cells. In addition to this core loop, BMAL1/CLOCK also induce expression of the orphan nuclear hormone receptor, which modulates Bmal1 transcription. Disruption of clock genes results in metabolic dysregulation in mice. In this article, the roles of clock genes in the regulation of metabolism were summarized based on the phenotypes of the knockout mice. PMID:23631200

  10. Initial ionospheric observations made by the new Resolute incoherent scatter radar and comparison to solar wind IMF

    NASA Astrophysics Data System (ADS)

    Bahcivan, Hasan; Tsunoda, Roland; Nicolls, Michael; Heinselman, Craig

    2010-08-01

    The first Resolute incoherent scatter radar observations of the polar ionospheric F region show the fine control of the ionospheric plasma density and flow (electric field) by the solar wind interplanetary magnetic field (IMF). A summary of 8 days of observations is presented and 10 IMF Bz southward turning events during this period are analyzed in terms of the time delay of plasma density enhancements and ionospheric convection intensification with respect to the timing of Bz southward turning. We find that Ne enhancements are strongly tied to strong ($\\gtrsim$5 nT) IMF Bz southward turnings; arrive 25-75 mins (depending on MLT) after the IMF pulse arrives at the bowshock nose; last as long as Bz stays southward; contain as small as ˜25 km horizontal substructures; are altitudinally smooth, a characteristic of a solar produced plasma. The most predictable response of ionospheric convection is anti-sunward flow intensification on average ˜25 mins after Bz southward change.

  11. IMF and Ejecta Coherence Lengths During the Events of October-November 2003

    Microsoft Academic Search

    C. J. Farrugia; H. Matsui; H. Kucharek; C. W. Smith; K. W. Ogilvie; J. Kaspar; R. B. Torbert; R. P. Lepping; R. Skoug; T. Terasawa; T. Nagai; T. Mukai; Y. Saito

    2004-01-01

    A three-spacecraft study is presented on coherence\\/correlation lengths of the IMF and interplanetary ejecta during the violent events of October-November 2003. The data come from ACE, orbiting around the L1 point, Geotail, following a trajectory in the dayside magnetosheath\\/ solar wind, and WIND, nominally located near midtail at ~150 Earth radii downstream. The rapid flapping of the geomagnetic tail yielded

  12. Stellar populations in the CFHTLS. I. New constraints on the IMF at low mass

    NASA Astrophysics Data System (ADS)

    Schultheis, M.; Robin, A. C.; Reylé, C.; McCracken, H. J.; Bertin, E.; Mellier, Y.; Le Fèvre, O.

    2006-02-01

    We present a stellar populations analysis of the first release of the CFHTLS (Canada-France-Hawai Telescope Legacy Survey) data. A detailed comparison between the Besançon model of the Galaxy and the first data release of the CFHTLS-Deep survey is performed by implementing the MEGACAM photometric system in this model using stellar atmosphere model libraries. The reliability of the theoretical libraries to reproduce the observed colours in the MEGACAM system is investigated. The locations of various stellar species like subdwarfs, white dwarfs, late-type and brown dwarfs, binary systems are identified. The contamination of the stellar sample by quasars and compact galaxies is quantified using spectroscopic data from the VIMOS-VLT Deep Survey (VVDS) as a function of i' magnitude and r'-i' colour. A comparison between simulated counts using the standard IMF at low masses show that the number of very low mass dwarfs may have been underestimated in previous studies. These observations favour a power law IMF following d(n)/dm propto m-? with ?=2.5 for m < 0.25 M? or ?=3.0 for m < 0.2 M? for single stars. The resulting LF is in agreement with the local LF as measured from the 5 or 25 pc samples. It is in strong disagreement with the Zheng et al. (2001) LF measured from deep HST data. We show that this discrepancy can be understood as an indication of a different IMF at low masses at early epochs of the Galaxy compared to the local thin disc IMF.

  13. Relationship between four-cell and distorted two-cell convection patterns during northward IMF

    Microsoft Academic Search

    L. Zhu; J. R. Kan

    1990-01-01

    Four-cell convection pattern in the ionosphere during a northward IMF (interplanetary magnetic field) was widely accepted until it was challenged by the distorted two-cell convection pattern proposed by Heppner and Maynard [1987]. We propose that a four-cell convection pattern, imposed on the magnetosphere by the solar wind, can be distorted into a wrapped two-cell pattern by the nonuniform and anisotropic

  14. Relationship between four-cell and distorted two-cell convection patterns during northward IMF

    Microsoft Academic Search

    L. Zhu; J. R. Kan

    1990-01-01

    Four-cell convection pattern in the ionosphere during a northward IMF was widely accepted until it was challenged by the distorted two-cell convection pattern proposed by Heppner and Maynard (1987). It is proposed here that a four-cell convection pattern, imposed on the magnetosphere by the solar wind, can be distorted into a wrapped two-cell pattern by the nonuniform and anisotropic conductance

  15. Zero-dead-time operation of interleaved atomic clocks.

    PubMed

    Biedermann, G W; Takase, K; Wu, X; Deslauriers, L; Roy, S; Kasevich, M A

    2013-10-25

    We demonstrate a zero-dead-time operation of atomic clocks. This clock reduces sensitivity to local oscillator noise, integrating as nearly 1/? whereas a clock with dead time integrates as 1/?(1/2) under identical conditions. We contend that a similar scheme may be applied to improve the stability of optical clocks. PMID:24206471

  16. Receiver clock-based integrity monitoring for GPS precision approaches

    Microsoft Academic Search

    SEAN BEDNARZ; PRATAP MISRA

    2006-01-01

    The errors in the vertical position and clock bias estimates obtained from GPS pseudo-range measurements are highly correlated. Therefore, the error in a vertical position estimate can be predicted if we know the clock bias estimation error. The latter can be estimated if the clock bias changes smoothly and, therefore, predictably. The current technology appears capable of manufacturing clocks which

  17. PulseSync: An Efficient and Scalable Clock Synchronization Protocol

    E-print Network

    Lynch, Nancy

    information based on their atomic clocks, which are synchronized from ground-based stations. GPS receivers employ data packets from the GPS satellites to provide an accurate clock signal. NTP uses a GPS clock for in-situ monitoring of physical phenomena. Access to a GPS clock is often not feasible due

  18. Jitter model of direct digital synthesis clock generators

    Microsoft Academic Search

    Dorin Emil Calbaza; Yvon Savaria

    1999-01-01

    Direct Digital Synthesis (DDS) has become a popular technique for synthesis of very accurate clocks. For example, in Digital Television (DTV) an audio data stream must be inserted into a video data stream, which implies that we must synchronize the audio clock with the video clock. According to the digital audio standard, the audio clock frequency is 5,6448 MHz and

  19. Direct digital frequency synthesis of low-jitter clocks

    Microsoft Academic Search

    Dorin Emil Calbaza; Yvon Savaria

    2000-01-01

    The development of communication systems in the past years has increased the necessity to synthesize very accurate clocks. For example, in Digital Television (DTV) an audio data stream must be inserted into a video data stream, which implies that we must synchronize the audio clock with the video clock. According to one digital audio standard, the audio clock frequency is

  20. Decentralized Fault-Tolerant Clock Pulse Generation in VLSI Chips

    E-print Network

    Szmolyan, Peter

    Decentralized Fault-Tolerant Clock Pulse Generation in VLSI Chips The invention offers a solution for various problems associated with the steady increase of clock rates of chips. It offers a fault of faults; · self generation of clock pulses. Instead of globally distributing the clock produced

  1. Flexible and Reconfigurable Mismatch-Tolerant Serial Clock Distribution Networks

    Microsoft Academic Search

    Atanu Chattopadhyay; Zeljko Zilic

    2012-01-01

    We present a clock distribution network that emphasizes flexibility and layout independence. It suits a variety of applications, clock domain shapes and sizes using a modular, standard cell-based design approach that mitigates the effect of intra-die temperature and process variances. We route the clock line serially, using an averaging technique to eliminate skew between clock regions in a domain. Routing

  2. The Interaction of Kelvin-Helmholtz Modes and Magnetic Reconnection for Southward IMF

    NASA Astrophysics Data System (ADS)

    Ma, X.; Otto, A.; Nykyri, K.

    2012-12-01

    Magnetic reconnection and Kelvin Helmholtz (KH) instability are the two most important mechanisms for plasma transport across the Earth's magnetospheric boundary layer. Magnetic reconnection is considered as a dominated mechanism for southward interplanetary magnetic field (IMF), and the KH instability is suggested to play an important role for northward IMF. Nonlinear KH waves have been observed at the flank boundaries of the magnetosphere and models show that these waves can force reconnection and the transport of magnetosheath plasma onto closed geomagnetic field. Nevertheless, recently THEMIS data has shown that KH modes also operate for southward (largely anti-parallel) IMF orientation. This presentation provides a systematic study on this interaction between magnetic reconnection and KH modes by means of three-dimensional MHD and Hall MHD numerical simulation. It is demonstrated that the onset of magnetic reconnection changes the width of the shear flow, and thereby the KH instability onset condition. Vice versa the nonlinear KH waves change the width of the current layer, thus modifying the onset condition for magnetic reconnection. It is shown that dynamics of the system can be strongly modified by a guide field or Hall physics. Mass, momentum and energy transport rates and their dependence on the solar wind parameters will also be discussed in this presentation.

  3. Magnetosphere preconditioning by the formation of a cold-dense plasma sheet under northward IMF

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Thomsen, M. F.; Jordanova, V. K.; Borovsky, J. E.; Denton, M. H.; Pulkkinen, T. I.

    2009-04-01

    Motivated by recent observations and simulations of the formation of a cold and dense plasma sheet in the tail of the magnetosphere under northward interplanetary magnetic field (IMF) and of the direct influence of the plasma sheet density on the ring current strength, this study aims at (1) highlighting how the coupling of these effects may lead to a preconditioning of the magnetosphere under northward IMF and (2) performing first tests of the validity of this hypothesis. We performed both parametric kinetic ring current simulation studies to investigate how the density and temperature of the plasma sheet affect the ring current strength during geomagnetic storms, and superposed epoch analysis of various parameters to investigate the response of the magnetosphere (as indicated by the Dst index) to the passage of Coronal Mass Ejections (CMEs) and Corotating Interaction Regions (CIRs). The results all suggest that solar wind structures may be more geoeffective if preceded by a northward IMF interval, and they are consistent with the hypothesis of a preconditioning by a cold, dense plasma sheet. A colder and denser plasma sheet may lead to a stronger ring current when that plasma is convected inward during the main phase of an ensuing storm.

  4. Cusp and LLBL as Sources of the Isolated Dayside Auroral Feature During Northward IMF

    NASA Technical Reports Server (NTRS)

    Chang, S.; Gallagher, D. L.; Spann, J. F., Jr.; Mende, S.; Greenwald, R.; Newell, P. T.

    2004-01-01

    An intense dayside proton aurora was observed by IMAGE FUV for an extensive period of northward interplanetary magnetic field (IMF) on 17 and 18 September, 2000. This aurora partially coincided with the auroral oval and intruded farther poleward into the polar cap, and it showed longitudinal motions in response to IMF $B-y$ variation. Intense magnetosheath-like electron and ion precipitations have been simultaneously detected by DMSP above the poleward portion of the high-latitude dayside aurora. They resemble the typical plasmas observed in the low-altitude cusp. However, less intense electrons and more intense energetic ions were detected over the equatorward part of the aurora. These plasmas are closer to the low-latitude boundary layer (LLBL) plasmas. Under strongly northward IMF, global ionospheric convection derived from SuperDARN radar measurements showed a 4-cell pattern with sunward convection in the middle of the dayside polar cap and the dayside aurora corresponded to two different convection cells. This result further supports two source regions for the aurora. The cusp proton aurora is on open magnetic field lines convecting sunward whereas the LLBL proton aurora is on closed field lines convecting antisunward. These IMAGE, DMSP and SuperDARN observations reveal the structure and dynamics of the aurora and provide strong evidence for magnetic merging occurring at the high-latitude magnetopause poleward from the cusp. This merging process was very likely quasi-stationary.

  5. Simulated orbits of heavy planetary ions at Mars for different IMF configurations

    NASA Astrophysics Data System (ADS)

    Curry, Shannon; Luhmann, Janet; Livi, Roberto; Hara, Takuya; Dong, Chuanfei; Ma, Yingjuan; McFadden, James; Bougher, Stephen

    2014-11-01

    We present simulated detections of O+, O2+ and CO2+ ions at Mars along a virtual orbit in the Mars space environment. Planetary pick-up ions are formed through the direct interaction of the solar wind with the neutral upper atmosphere, causing the newly created ions to be picked up and accelerated by the background convective electric field. Because previous missions such as Mars Global Surveyor (MGS) and Mars Express (MEX) have not been able to measure the interplanetary magnetic field (IMF) components simultaneously with plasma measurements, the response of heavy planetary pick-up ions to changes in the IMF has not been well characterized. Using a steady-state multi-species MHD model to provide the background electric and magnetic fields, the Mars Test Particle (MTP) simulation can trace each of these particles along field lines in near-Mars space and construct virtual ion detections from a spacecraft orbit. Specifically, we will present energy-time spectrograms and velocity space distributions (VSDs) for a selection of orbits during different IMF configurations and solar cycle conditions. These simulated orbits have broader implications for how to measure ion escape. Using individual particle traces, the origin and trajectories of different ion populations can be analyzed in order to assess how and where they contribute to the total atmospheric escape rate, which is a major objective of the upcoming MAVEN mission.

  6. [Circadian clocks and energy metabolism in rodents].

    PubMed

    Challet, Etienne

    2014-01-01

    Circadian rhythmicity is an important component of physiological processes which provides them with a 24-hour temporal organization and adjustment to cyclical changes in the environment. Circadian rhythms are controlled by a network of endogenous clocks, comprising the main clock in the suprachiasmatic nuclei of the hypothalamus and many secondary clocks in the brain and peripheral tissues. All aspects of energy metabolism, from food intake to intracellular signaling pathways, are strongly influenced by circadian rhythmicity. In turn, meal timing is an efficient synchronizer (time-giver) to set the phase of the peripheral clocks, while the suprachiasmatic clock is synchronized by ambient light. In certain nutritional conditions (i.e., low- or high-calory diets), metabolic factors remaining to be identified modulate the functioning of the suprachiasmatic clock. Animal models of obesity and diabetes show circadian alterations. Conversely, when circadian rhythmicity is disturbed, either due to genetically defective circadian clocks, or to circadian desynchronization (chronic light exposure or repeated meals at odd times of the cycle), lipid and glucose metabolism is deregulated. The metabolic impact of circadian desynchronization justifies the development of preventive or therapeutic strategies that could rely, among others, on dietary interventions combining timed meals and specific composition. PMID:25840453

  7. Highly precise clocks to test fundamental physics

    NASA Astrophysics Data System (ADS)

    Bize, S.; Wolf, P.

    2012-12-01

    Highly precise atomic clocks and precision oscillators are excellent tools to test founding principles, such as the Equivalence Principle, which are the basis of modern physics. A large variety of tests are possible, including tests of Local Lorentz Invariance, of Local Position Invariance like, for example, tests of the variability of natural constants with time and with gravitation potential, tests of isotropy of space, etc. Over several decades, SYRTE has developed an ensemble of highly accurate atomic clocks and oscillators using a large diversity of atomic species and methods. The SYRTE clock ensemble comprises hydrogen masers, Cs and Rb atomic fountain clocks, Sr and Hg optical lattice clocks, as well as ultra stable oscillators both in the microwave domain (cryogenic sapphire oscillator) and in the optical domain (Fabry-Perot cavity stabilized ultra stable lasers) and means to compare these clocks locally or remotely (fiber links in the RF and the optical domain, femtosecond optical frequency combs, satellite time and frequency transfer methods). In this paper, we list the fundamental physics tests that have been performed over the years with the SYRTE clock ensemble. Several of these tests are done thanks to the collaboration with partner institutes including the University of Western Australia, the Max Planck Institut für Quantenoptik in Germany, and others.

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

    PubMed

    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. PMID:25965674

  9. Comparison of features of all-sky imager identified substorms associated with, and not associated with, IMF northward turnings

    NASA Astrophysics Data System (ADS)

    Gallardo-Lacourt, B. I.; Lyons, L. R.; Nishimura, T.

    2010-12-01

    Knowledge of the period before the auroral onset of a substorm is crucial for understanding the sequence of events leading to a substorm. It is accepted that substorm onsets are preceded by a growth-phase period of predominantly southward IMF. Such prolonged periods of southward IMF have enhanced magnetospheric convection, leading to enhanced inward motion and energization of plasma sheet particles. In a previous analysis [Hsu and McPherron, 2003] of substorm onsets identified using sudden changes in the slope of the AL index and the start of a Pi 2 pulsation burst, 60% of events were found to be associated with a partial northward recovery of the IMF Bz, indicating that an substantial number of substorms are apparently triggered by such IMF changes. Now we have the capability to study substorm onsets with the high-resolution all-sky images of the THEMIS program, obtaining onsets unambiguously, including for very weak substorms which are difficult to identify with the AL index. We identify the percentage of cases associated, and not associated, with northward turnings. Differences in optical and convection features between substorms associated, and not associated, with northward turnings are addressed. Also differences in solar wind speed are considered, because it has been found that the large IMF fluctuating during high speed streams can lead to substorms independent of the IMF direction.

  10. Circadian and Circalunar Clock Interactions in a Marine Annelid

    PubMed Central

    Zantke, Juliane; Ishikawa-Fujiwara, Tomoko; Arboleda, Enrique; Lohs, Claudia; Schipany, Katharina; Hallay, Natalia; Straw, Andrew D.; Todo, Takeshi; Tessmar-Raible, Kristin

    2013-01-01

    Summary 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 1?/?. 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. PMID:24075994

  11. Molecular Architecture of the Mammalian Circadian Clock

    PubMed Central

    Partch, Carrie L.; Green, Carla B.; Takahashi, Joseph S.

    2013-01-01

    Circadian clocks coordinate physiology and behavior with the 24-hour solar day to provide temporal homeostasis with the external environment. The molecular clocks that drive these intrinsic rhythmic changes are based on interlocked transcription/translation feedback loops that integrate with diverse environmental and metabolic stimuli to generate internal 24-hour timing. In this review we highlight recent advances in our understanding of the core molecular clock and how it utilizes diverse transcriptional and post-transcriptional mechanisms to impart temporal control onto mammalian physiology. Understanding the way in which biological rhythms are generated throughout the body may provide avenues for temporally-directed therapeutics to improve health and prevent disease. PMID:23916625

  12. Magic wavelengths for terahertz clock transitions

    SciTech Connect

    Zhou Xiaoji; Xu Xia; Chen Xuzong; Chen Jingbiao [School of Electronics Engineering and Computer Science, Peking University, Beijing 100871 (China)

    2010-01-15

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

  13. Using Atomic Clocks to Detect Gravitational Waves

    E-print Network

    Abraham Loeb; Dan Maoz

    2015-01-28

    Atomic clocks have recently reached a fractional timing precision 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.

  14. Using Atomic Clocks to Detect Gravitational Waves

    E-print Network

    Loeb, Abraham

    2015-01-01

    Atomic clocks have recently reached a fractional timing precision 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.

  15. Atomic Clock Based On Linear Ion Trap

    NASA Technical Reports Server (NTRS)

    Prestage, John D.; Dick, G. John

    1992-01-01

    Highly stable atomic clock based on excitation and measurement of hyperfine transition in 199Hg+ ions confined in linear quadrupole trap by radio-frequency and static electric fields. Configuration increases stability of clock by enabling use of enough ions to obtain adequate signal while reducing non-thermal component of motion of ions in trapping field, reducing second-order Doppler shift of hyperfine transition. Features described in NPO-17758 "Linear Ion Trap for Atomic Clock." Frequency standard based on hyperfine transition described in NPO-17456, "Trapped-Mercury-Ion Frequency Standard."

  16. Clock Drawing in Spatial Neglect: A Comprehensive Analysis of Clock Perimeter, Placement, and Accuracy

    PubMed Central

    Chen, Peii; Goedert, Kelly M.

    2012-01-01

    Clock drawings produced by right-brain-damaged (RBD) individuals with spatial neglect often contain an abundance of empty space on the left while numbers and hands are placed on the right. However, the clock perimeter is rarely compromised in neglect patients’ drawings. By analyzing clock drawings produced by 71 RBD and 40 healthy adults, this study investigated whether the geometric characteristics of the clock perimeter reveal novel insights to understanding spatial neglect. Neglect participants drew smaller clocks than either healthy or non-neglect RBD participants. While healthy participants’ clock perimeter was close to circular, RBD participants drew radially extended ellipses. The mechanisms for these phenomena were investigated by examining the relation between clock-drawing characteristics and performance on six subtests of the Behavioral Inattention Test (BIT). The findings indicated that the clock shape was independent of any BIT subtest or the drawing placement on the test sheet and that the clock size was significantly predicted by one BIT subtest: the poorer the figure and shape copying, the smaller the clock perimeter. Further analyses revealed that in all participants, clocks decreased in size as they were placed farther from the center of the paper. However, even when neglect participants placed their clocks towards the center of the page, they were smaller than those produced by healthy or non-neglect RBD participants. These results suggest a neglect-specific reduction in the subjectively available workspace for graphic production from memory, consistent with the hypothesis that neglect patients are impaired in the ability to enlarge the attentional aperture. PMID:22390278

  17. Optical atomic clocks with suppressed black body radiation shift

    E-print Network

    Kozlov, Alexander; Flambaum, Victor

    2014-01-01

    We study a wide range of neutral atoms and ions suitable for ultra-precise atomic optical clocks with naturally suppressed black body radiation shift of clock transition frequency. Calculations show that scalar polarizabilities of clock states cancel each other for at least one order of magnitude for considered systems. Results for calculations of frequencies, quadrupole moments of the states, clock transition amplitudes and natural widths of upper clock states are presented.

  18. Optical atomic clocks with suppressed blackbody-radiation shift

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    We study a wide range of neutral atoms and ions suitable for ultraprecise atomic optical clocks with naturally suppressed blackbody-radiation shift of clock transition frequency. Calculations show that scalar polarizabilities of clock states cancel each other for at least one order of magnitude for the considered systems. Results for calculations of frequencies, quadrupole moments of the states, clock transition amplitudes, and natural widths of upper clock states are presented.

  19. Sensitivity Based Link Insertion for Variation Tolerant Clock Network Synthesis

    Microsoft Academic Search

    Joon-sung Yang; Anand Rajaram; Ninghy Shi; Jian Chen; David Z. Pan

    2007-01-01

    Clock distribution is one of the key limiting factors in any high speed, sub-100nm VLSI design. Unwanted clock skews, caused by variation effects like manufacturing varia- tions, power-ground noise etc., consume increasing propor- tion of the clock cycle. Thus, reducing the clock skew varia- tions is one of the most important objectives of any high-speed clock distribution methodology. Inserting cross-links

  20. Clock tree synthesis for prescribed skew specifications 

    E-print Network

    Chaturvedi, Rishi

    2005-08-29

    In ultra-deep submicron VLSI designs, clock network layout plays an increasingly important role in determining circuit performance including timing, power consumption, cost, power supply noise and tolerance to process ...

  1. Avian Circadian Organization: A Chorus of Clocks

    PubMed Central

    Cassone, Vincent M

    2013-01-01

    In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents. PMID:24157655

  2. Connecting the Circadian Clock with Chemosensation

    E-print Network

    Chatterjee, Abhishek

    2012-07-16

    , high level of G proteincoupled receptor kinase 2 (GPRK2), a clock controlled signaling molecule present in chemosensory neurons, suppresses tastant-evoked responses and promotes olfactory responses. G-protein mediated signaling was shown to be involved...

  3. Circadian clock circuitry in colorectal cancer.

    PubMed

    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. PMID:24764658

  4. Satellite-based quantum clock synchronization

    E-print Network

    Wang, Jieci; Jing, Jiliang; Fan, Heng

    2015-01-01

    We propose a practical satellite-based quantum clock synchronization scheme with dispersion cancellation and by taking into account effects of gravitational frequency shift of the Earth. Two frequency entangled pulses are employed to synchronize two clocks, one at a ground station and the other at a satellite. The time discrepancy of the two clocks is introduced into the pulses by moving mirrors and is extracted by measuring the coincidence rate of the pulses in the interferometer. We find that the pulses are distorted due to effects of the gravitational frequency shift when they propagate between the Earth and the satellite. It is shown that the coincidence rate as well as precision of the time discrepancy are remarkably affected by gravitational frequency shift effects both for the low earth orbits satellite and geostationary earth orbits satellite cases. We also find that the precision of the clock synchronization are sensitive to the source parameters and the altitude of the satellite. Our proposal can be...

  5. Clock synchronization for mobile ad hoc networks 

    E-print Network

    Chandra, Rajan

    2013-02-22

    As mobile networking advances, there is a need for services such as clock synchronization that improve performance and support the development of higher-level applications. This can be achieved by adapting existing algorithms ...

  6. The MAC - a miniature atomic clock

    Microsoft Academic Search

    R. Lutwak; P. Vlitas; M. Varghese; M. Mescher; D. K. Serkland; G. M. Peake

    2005-01-01

    The authors are developing a chip-scale atomic clock (CSAC), more than two orders of magnitude smaller and lower power than any existing technology. As an intermediate milestone, en route to the ultimate CSAC objectives, we have developed a miniature atomic clock (MAC), combining the low-power CSAC physics package with a low-parts count, low-power digital control and microwave system. The MAC

  7. Clock gene variation in Tachycineta swallows.

    PubMed

    Dor, Roi; Cooper, Caren B; Lovette, Irby J; Massoni, Viviana; Bulit, Flor; Liljesthrom, Marcela; Winkler, David W

    2012-01-01

    Many animals use photoperiod cues to synchronize reproduction with environmental conditions and thereby improve their reproductive success. The circadian clock, which creates endogenous behavioral and physiological rhythms typically entrained to photoperiod, is well characterized at the molecular level. Recent work provided evidence for an association between Clock poly-Q length polymorphism and latitude and, within a population, an association with the date of laying and the length of the incubation period. Despite relatively high overall breeding synchrony, the timing of clutch initiation has a large impact on the fitness of swallows in the genus Tachycineta. We compared length polymorphism in the Clock poly-Q region among five populations from five different Tachycineta species that breed across a hemisphere-wide latitudinal gradient (Fig. 1). Clock poly-Q variation was not associated with latitude; however, there was an association between Clock poly-Q allele diversity and the degree of clutch size decline within breeding seasons. We did not find evidence for an association between Clock poly-Q variation and date of clutch initiation in for any of the five Tachycineta species, nor did we found a relationship between incubation duration and Clock genotype. Thus, there is no general association between latitude, breeding phenology, and Clock polymorphism in this clade of closely related birds.Figure 1Photos of Tachycineta swallows that were used in this study: A) T. bicolor from Ithaca, New York, B) T. leucorrhoa from Chascomús, Argentina, C) T. albilinea from Hill Bank, Belize, D) T. meyeni from Puerto Varas, Chile, and E) T. thalassina from Mono Lake, California, Photographers: B: Valentina Ferretti; A, C-E: David Winkler. PMID:22408729

  8. Clock gene variation in Tachycineta swallows

    PubMed Central

    Dor, Roi; Cooper, Caren B; Lovette, Irby J; Massoni, Viviana; Bulit, Flor; Liljesthrom, Marcela; Winkler, David W

    2012-01-01

    Many animals use photoperiod cues to synchronize reproduction with environmental conditions and thereby improve their reproductive success. The circadian clock, which creates endogenous behavioral and physiological rhythms typically entrained to photoperiod, is well characterized at the molecular level. Recent work provided evidence for an association between Clock poly-Q length polymorphism and latitude and, within a population, an association with the date of laying and the length of the incubation period. Despite relatively high overall breeding synchrony, the timing of clutch initiation has a large impact on the fitness of swallows in the genus Tachycineta. We compared length polymorphism in the Clock poly-Q region among five populations from five different Tachycineta species that breed across a hemisphere-wide latitudinal gradient (Fig. 1). Clock poly-Q variation was not associated with latitude; however, there was an association between Clock poly-Q allele diversity and the degree of clutch size decline within breeding seasons. We did not find evidence for an association between Clock poly-Q variation and date of clutch initiation in for any of the five Tachycineta species, nor did we found a relationship between incubation duration and Clock genotype. Thus, there is no general association between latitude, breeding phenology, and Clock polymorphism in this clade of closely related birds. Figure 1 Photos of Tachycineta swallows that were used in this study: A) T. bicolor from Ithaca, New York, B) T. leucorrhoa from Chascomús, Argentina, C) T. albilinea from Hill Bank, Belize, D) T. meyeni from Puerto Varas, Chile, and E) T. thalassina from Mono Lake, California, Photographers: B: Valentina Ferretti; A, C-E: David Winkler. PMID:22408729

  9. Circadian clock, cancer and lipid metabolism

    Microsoft Academic Search

    Norio Ishida

    2007-01-01

    Genetic analysis has revealed that mammalian circadian oscillator is driven by a cell autonomous transcription\\/translation-based negative feedback loop, wherein positive elements (CLOCK and BMAL1) induce the expression of negative regulators (Periods, CRY1 and CRY2) that inhibit the transactivation of positive regulators. Recent research reveals that this clock feedback loop affects many aspects of our physiology, such as cell cycle and

  10. Narrowing the margins with elastic clocks

    Microsoft Academic Search

    Jordi Cortadella; Luciano Lavagno; Djavad Amiri; J. Casanova; C. Macian; F. Martorell; J. A. Moya; L. Necchi; D. Sokolov; E. Tuncer

    2010-01-01

    The continuous shrinking of process geometries increases variability and demands for conservative margins that have a negative impact on performance. With conventional clocks, the cycle period has to be defined to accommodate the worst-case variations during the lifetime of the circuit. Elastic Clocks arise as a new paradigm to reduce the margins without sacrificing robustness. Their cycle-by-cycle adaptation to static

  11. A test of precision GPS clock synchronization

    Microsoft Academic Search

    D. C. Jefferson; S. M. Lichten; L. E. Young

    1996-01-01

    This paper describes tests of precision GPS time transfer using geodetic-quality TurboRogue receivers. The GPS data are processed with the GIPSY-OASIS II software, which simultaneously estimates the GPS satellite orbits and clocks, receiver locations and clock offsets, as well as other parameters such as Earth orientation. This GPS solution technique, which emphasizes high accuracy GPS orbit determination and observable modeling,

  12. Opto-chemical micro-capillary clocks

    Microsoft Academic Search

    Stefan Wilhelm; Otto S. Wolfbeis

    2010-01-01

    Opto-chemical capillary clocks are presented that are based on the measurement of a colored segment in a microchannel (a capillary).\\u000a Color is created by a chromogenic chemistry involving the oxidation of a (virtually colorless) leuco-dye. Poly(ethylene glycol)\\u000a (PEG) is used as a solvent, and indigo and thioindigo (in their reduced leuco forms) act as oxygen-sensitive dyes. The clock\\u000a is started

  13. NRC CsV Primary Clock Performance

    Microsoft Academic Search

    A. G. Mungall; C. C. Costain

    1977-01-01

    Performance of the new 2.1 metre NRC cesium standard during its first year of operation as a continuously running primary clock is described. Comparisons with the best NRC secondary HP high performance cesium clock and with UTC(USNO) and TAI indicate that, after compensation for Loran C discontinuities, the best relative value of sigma(2, 60 days) is about 2 × 10-14.

  14. What's Your Angle?

    NSDL National Science Digital Library

    2010-01-01

    In this activity, students devise procedures for using a protractor to measure the number of degrees in an angle, and use inductive reasoning to develop "angle sense." Then they describe circumstances and careers that require a working knowledge of angles and their measurements.

  15. Angles All Around

    NSDL National Science Digital Library

    Mrs. Bennett

    2011-12-14

    Standard: Identify and measure right, obtuse, and acute angles. This is a two day activity. OBJECTIVE: We have learned about five different types of angles: right, acute, obtuse, straight, and reflex. We have also learned how to use a protractor to measure angles. With this lesson, you will practice what ...

  16. Nuclear spin effects in optical lattice clocks

    SciTech Connect

    Boyd, Martin M.; Zelevinsky, Tanya; Ludlow, Andrew D.; Blatt, Sebastian; Zanon-Willette, Thomas; Foreman, Seth M.; Ye Jun [JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

    2007-08-15

    We present a detailed experimental and theoretical study of the effect of nuclear spin on the performance of optical lattice clocks. With a state-mixing theory including spin-orbit and hyperfine interactions, we describe the origin of the {sup 1}S{sub 0}-{sup 3}P{sub 0} clock transition and the differential g factor between the two clock states for alkaline-earth-metal(-like) atoms, using {sup 87}Sr as an example. Clock frequency shifts due to magnetic and optical fields are discussed with an emphasis on those relating to nuclear structure. An experimental determination of the differential g factor in {sup 87}Sr is performed and is in good agreement with theory. The magnitude of the tensor light shift on the clock states is also explored experimentally. State specific measurements with controlled nuclear spin polarization are discussed as a method to reduce the nuclear spin-related systematic effects to below 10{sup -17} in lattice clocks.

  17. The aging biological clock in Neurospora crassa.

    PubMed

    Case, Mary E; Griffith, James; Dong, Wubei; Tigner, Ira L; Gaines, Kimberly; Jiang, James C; Jazwinski, S Michal; Arnold, Jonathan

    2014-09-01

    The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response. PMID:25535564

  18. The aging biological clock in Neurospora crassa

    PubMed Central

    Case, Mary E; Griffith, James; Dong, Wubei; Tigner, Ira L; Gaines, Kimberly; Jiang, James C; Jazwinski, S Michal; Arnold, Jonathan

    2014-01-01

    The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response PMID:25535564

  19. Towards a strontium optical lattice clock

    NASA Astrophysics Data System (ADS)

    Bridge, Elizabeth Michelle

    This thesis describes the design and build of the strontium optical lattice clock (Sr OLC) at the National Physical Laboratory (NPL), discussing the considerations behind the design. Details of the first cooling stage are given, which includes the characterisation of a novel permanent-magnet Zeeman slower by measurements of the longitudinal velocity distributions and loading of the MOT at 461 nm. Development of a narrow linewidth laser system at 689 nm is described, which is used for initial spectroscopy of the second-stage cooling transition. In particular, this work describes progress towards two independent ultra-narrow linewidth clock lasers. The new generation of strontium lattice clock experiments have focused on characterising the systematic frequency shifts and reducing their associated fractional frequency uncertainties, as well as reducing the fractional frequency instability of the measurement. One focus of the Sr OLC at NPL is to help characterise the frequency shift of the clock transition due to black-body radiation (BBR), which is currently the largest contributor to the uncertainty budget of the measured clock frequency. Our approach, discussed here, is to make a direct, differential measurement of the shift with the atoms housed alternately in environments of differing temperatures. Better characterisation and control of the BBR frequency shift of the strontium clock transition is crucial for the future of the Sr OLC as a leading frequency standard.

  20. The Circadian Clock Modulates Renal Sodium Handling

    PubMed Central

    Nikolaeva, Svetlana; Pradervand, Sylvain; Centeno, Gabriel; Zavadova, Vlasta; Tokonami, Natsuko; Maillard, Marc; Bonny, Olivier

    2012-01-01

    The circadian clock contributes to the control of BP, but the underlying mechanisms remain unclear. We analyzed circadian rhythms in kidneys of wild-type mice and mice lacking the circadian transcriptional activator clock gene. Mice deficient in clock exhibited dramatic changes in the circadian rhythm of renal sodium excretion. In parallel, these mice lost the normal circadian rhythm of plasma aldosterone levels. Analysis of renal circadian transcriptomes demonstrated changes in multiple mechanisms involved in maintaining sodium balance. Pathway analysis revealed the strongest effect on the enzymatic system involved in the formation of 20-HETE, a powerful regulator of renal sodium excretion, renal vascular tone, and BP. This correlated with a significant decrease in the renal and urinary content of 20-HETE in clock-deficient mice. In summary, this study demonstrates that the circadian clock modulates renal function and identifies the 20-HETE synthesis pathway as one of its principal renal targets. It also suggests that the circadian clock affects BP, at least in part, by exerting dynamic control over renal sodium handling. PMID:22440902

  1. Maser and secondary clock in telecommunications networks

    NASA Technical Reports Server (NTRS)

    Risley, A.

    1984-01-01

    Telecommunication networks of time division switches, interconnected by digital transmission are being put into place. At each switch, each incoming bit stream is brought into its own buffer. Then the clock in the switch reads each buffer to re-establish phase. Care must be taken to keep frequency differences between various clocks from becoming too large. Based on empirically defined data transmission requirements, one major network has determined that fractional frequency inequality between switches should be no worse than 1.7 X 10 to the minus 9 power. A network needs near frequency equality between its own switches, and also between its switches and other networks with which it interfaces. As a practical matter, the best way to achieve needed frequency equality is for each network to have master clock with an accuracy which is at least as good as 1 X 10 to the minus 10 power. The relationship between the master and the secondary clock is discussed. The questions of master clock accuracy and precision and the free-running capability of the secondary clocks are examined.

  2. Evolutionary Links Between Circadian Clocks and Photoperiodic Diapause in Insects

    PubMed Central

    Meuti, Megan E.; Denlinger, David L.

    2013-01-01

    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. PMID:23615363

  3. UCAIR Quarterly News Report STROKE: FROM TIME CLOCK TO TISSUE CLOCK

    E-print Network

    Tipple, Brett

    UCAIR Quarterly News Report STROKE: FROM TIME CLOCK TO TISSUE CLOCK A unique real-time imaging tool on the state of the brain tissue that can be used as a surrogate for time. In addition, we hope to develop sequences that will help us to better differentiate brain tissue that is irreversibly dead (the core) from

  4. Injection-Locked Clocking: A Low-Power Clock Distribution Scheme for High-Performance Microprocessors

    E-print Network

    Wu, Hui

    -Performance Microprocessors Lin Zhang, Aaron Carpenter, Berkehan Ciftcioglu, Alok Garg, Michael Huang, and Hui Wu Department consumption in high- performance microprocessors. In the new clocking scheme, injection-locked oscillators to each other. I. INTRODUCTION CLOCK distribution is a crucial aspect of modern multi- GHz microprocessor

  5. N+CPT clock resonance

    SciTech Connect

    Crescimanno, M. [Department of Physics and Astronomy, Youngstown State University, Youngstown, Ohio 44555 (United States); Hohensee, M. [MS-59, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts 02138 (United States)

    2008-12-15

    In a typical compact atomic time standard a current modulated semiconductor laser is used to create the optical fields that interrogate the atomic hyperfine transition. A pair of optical sidebands created by modulating the diode laser become the coherent population trapping (CPT) fields. At the same time, other pairs of optical sidebands may contribute to other multiphoton resonances, such as three-photon N-resonance [Phys. Rev. A 65, 043817 (2002)]. We analyze the resulting joint CPT and N-resonance (hereafter N+CPT) analytically and numerically. Analytically we solve a four-level quantum optics model for this joint resonance and perturbatively include the leading ac Stark effects from the five largest optical fields in the laser's modulation comb. Numerically we use a truncated Floquet solving routine that first symbolically develops the optical Bloch equations to a prescribed order of perturbation theory before evaluating. This numerical approach has, as input, the complete physical details of the first two excited-state manifolds of {sup 87}Rb. We test these theoretical approaches with experiments by characterizing the optimal clock operating regimes.

  6. Cusp and LLBL as Sources of the Isolated Dayside Auroral Feature During Northward IMF

    NASA Technical Reports Server (NTRS)

    Chang, S.-W.; Gallagher, D. L.; Spann, J. F.; Mende, S. B.; Greenwald, R. A.; Newell, P. T.

    2004-01-01

    An intense dayside proton aurora was observed by Imager for Magnetopause-to- Aurora Global Exploration Far Ultra-Violet imager (IMAGE FUV) for an extensive period of northward interplanetary magnetic field (IMF) on 17 and 18 September 2000. This aurora partially coincided with the auroral oval and intruded farther poleward into the polar cap, and it showed longitudinal motions in response to IMF By variation. Intense magnetosheath-like electron and ion precipitations have been simultaneously detected by Defense Meteorological Satellite Program (DMSP) above the poleward portion of the high-latitude dayside aurora. They resemble the typical plasmas observed in the low-altitude cusp. However, less intense electrons and more energetic ions were detected over the equatonvard part of the aurora. These plasmas are closer to the low-latitude boundary layer (LLBL) plasmas. Under strongly northward IMF, global ionospheric convection derived from Super Dual Auroral Radar Network (SuperDARN) radar measurements showed a four-cell pattern with sunward convection in the middle of the dayside polar cap and the dayside aurora corresponded to two different convection cells. This result further supports two source regions for the aurora. The cusp proton aurora is on open magnetic field lines convecting sunward whereas the LLBL proton aurora is on closed field lines convecting antisunward. These IMAGE, DMSP, and SuperDARN observations reveal the structure and dynamics of the aurora and provide strong evidence for magnetic merging occurring at the high-latitude magnetopause poleward from the cusp. This merging process was very likely quasi-stationary.

  7. Orientation of Birkeland current sheets in the dayside polar region and its relationship to the IMF

    SciTech Connect

    Saflekos, N.A.; Potemra, T.A.

    1980-05-01

    Vector magnetic field observations made with the three-axes magnetometer on the Triad satellite have been used to study the orientation of magnetic disturbances in the dayside polar region. These measurements were all made over the southern polar region and recorded at McMurdo, Antarctica. Thesa distwrbafces are transverse to the main geomagnetic field and may be interpreted as being caused by field-aligned Birkeland current sheets consistent with Maxwell's equatioNs. The current sheets in the regions usuallq associated with the morning and afternoon auroral regions are most often aligned in the geomagnetic east-west direction. The amplitudes of these 'south auroral' currents are larger in the morning than in the afternoon when the interplanetary magnetic field (IMF) is directed toward the sun (B/sub y/<0, B/sub x/>0) and larger in the afternoon when the IMF is directed away (B/sub y/>0, B/sub x/<0). This is the systematically reversed relationship between Birkeland current intensities and IMF found in the northern auroral zone by McDiarmid et at. (1977). The Birkeland current sheets in the region associated with the southern cusp are also aligned in the geomagnetic east-west direction during periods of negative B/sub z/. During the periods of B/sub y/<0 and B/sub x/>0 the Birkeland current flow in the region of the southern cusp is predominantly away from the ionosphere in contrast to the downward flow into the northern cusp as determined earlier (e.g., McDiarmid et al., 1978b; Iijima et al., 1978). The cusp Birkeland current flow directions appear to reverse for B/sub y/>0 and B/sub x/<0. From a search of the Triad data set, some rare examples of magnetic disturbances with a large north-south (noon-midnight) component have been discovered in the polar cap near noon.

  8. The Stellar Initial Mass Function of Ultra-faint Dwarf Galaxies: Evidence for IMF Variations with Galactic Environment

    NASA Astrophysics Data System (ADS)

    Geha, Marla; Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.; Simon, Joshua D.; Kirby, Evan N.; VandenBerg, Don A.; Muñoz, Ricardo R.; Avila, Roberto J.; Guhathakurta, Puragra; Ferguson, Henry C.

    2013-07-01

    We present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. The Hercules and Leo IV galaxies are extremely low luminosity (MV = -6.2, -5.5), metal-poor (lang[Fe/H]rang = -2.4, -2.5) systems that have old stellar populations (>11 Gyr). Because they have long relaxation times, we can directly measure the low-mass stellar IMF by counting stars below the main-sequence turnoff without correcting for dynamical evolution. Over the stellar mass range probed by our data, 0.52-0.77 M ?, the IMF is best fit by a power-law slope of \\alpha = 1.2_{-0.5}^{+0.4} for Hercules and ? = 1.3 ± 0.8 for Leo IV. For Hercules, the IMF slope is more shallow than a Salpeter (? = 2.35) IMF at the 5.8? level, and a Kroupa (? = 2.3 above 0.5 M ?) IMF slope at 5.4? level. We simultaneously fit for the binary fraction, f binary, finding f_binary = 0.47^{+0.16}_{-0.14} for Hercules, and 0.47^{+0.37}_{-0.17} for Leo IV. The UFD binary fractions are consistent with that inferred for Milky Way stars in the same mass range, despite very different metallicities. In contrast, the IMF slopes in the UFDs are shallower than other galactic environments. In the mass range 0.5-0.8 M ?, we see a trend across the handful of galaxies with directly measured IMFs such that the power-law slopes become shallower (more bottom-light) with decreasing galactic velocity dispersion and metallicity. This trend is qualitatively consistent with results in elliptical galaxies inferred via indirect methods and is direct evidence for IMF variations with galactic environment. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  9. THE STELLAR INITIAL MASS FUNCTION OF ULTRA-FAINT DWARF GALAXIES: EVIDENCE FOR IMF VARIATIONS WITH GALACTIC ENVIRONMENT

    SciTech Connect

    Geha, Marla [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.; Avila, Roberto J.; Ferguson, Henry C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Simon, Joshua D. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Kirby, Evan N. [Department of Physics and Astronomy, University of California Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); VandenBerg, Don A. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6 (Canada); Munoz, Ricardo R. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Guhathakurta, Puragra, E-mail: marla.geha@yale.edu, E-mail: tbrown@stsci.edu, E-mail: tumlinson@stsci.edu [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-07-01

    We present constraints on the stellar initial mass function (IMF) in two ultra-faint dwarf (UFD) galaxies, Hercules and Leo IV, based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. The Hercules and Leo IV galaxies are extremely low luminosity (M{sub V} = -6.2, -5.5), metal-poor (([Fe/H]) = -2.4, -2.5) systems that have old stellar populations (>11 Gyr). Because they have long relaxation times, we can directly measure the low-mass stellar IMF by counting stars below the main-sequence turnoff without correcting for dynamical evolution. Over the stellar mass range probed by our data, 0.52-0.77 M{sub Sun }, the IMF is best fit by a power-law slope of {alpha}= 1.2{sub -0.5}{sup +0.4} for Hercules and {alpha} = 1.3 {+-} 0.8 for Leo IV. For Hercules, the IMF slope is more shallow than a Salpeter ({alpha} = 2.35) IMF at the 5.8{sigma} level, and a Kroupa ({alpha} = 2.3 above 0.5 M{sub Sun }) IMF slope at 5.4{sigma} level. We simultaneously fit for the binary fraction, f{sub binary}, finding f{sub binary}= 0.47{sup +0.16}{sub -0.14} for Hercules, and 0.47{sup +0.37}{sub -0.17} for Leo IV. The UFD binary fractions are consistent with that inferred for Milky Way stars in the same mass range, despite very different metallicities. In contrast, the IMF slopes in the UFDs are shallower than other galactic environments. In the mass range 0.5-0.8 M{sub Sun }, we see a trend across the handful of galaxies with directly measured IMFs such that the power-law slopes become shallower (more bottom-light) with decreasing galactic velocity dispersion and metallicity. This trend is qualitatively consistent with results in elliptical galaxies inferred via indirect methods and is direct evidence for IMF variations with galactic environment.

  10. A high-speed photonic clock and carrier regenerator

    NASA Technical Reports Server (NTRS)

    Yao, X. S.; Lutes, G.

    1995-01-01

    As data communications rates climb toward 10 Gbits/s, clock recovery and synchronization become more difficult, if not impossible, using conventional electronic circuits. The high-speed photonic clock regenerator described in this article may be more suitable for such use. This photonic regenerator is based on a previously reported photonic oscillator capable of fast acquisition and synchronization. With both electrical and optical clock inputs and outputs, the device is easily interfaced with fiber-optic systems. The recovered electrical clock can be used locally and the optical clock can be used anywhere within a several kilometer radius of the clock/carrier regenerator.

  11. Relationship between the IMF magnitude and Pc 3 magnetic pulsations in the magnetosphere

    NASA Technical Reports Server (NTRS)

    Yumoto, K.; Saito, T.; Tsurutani, B. T.; Smith, E. J.; Akasofu, S.-I.

    1984-01-01

    The relationships between the IMF magnitude and pulsation frequencies in the Pc 3-4 range simultaneously observed both at synchronous orbit and at low latitudes on the ground are statistically described. A theoretical discussion is given on how these observations can be interpreted in terms of the characteristic frequency of compressional Pc 3-4 magnetic pulsations in the magnetosphere, based on the well-established ion cyclotron resonance mechanism between magnetosonic mode of low-frequency upstream waves and narrowly reflected ion beams in the earth's foreshock.

  12. The social clock of the honeybee.

    PubMed

    Bloch, Guy

    2010-10-01

    The honeybee has long been an important model for studying the interplay between the circadian clock and complex behaviors. This article reviews studies further implicating the circadian clock in complex social behaviors in bees. The article starts by introducing honeybee social behavior and sociality and then briefly summarizes current findings on the molecular biology and neuroanatomy of the circadian system of honeybees that point to molecular similarities to the mammalian clockwork rather than to that of Drosophila. Foraging is a social behavior in honeybees that relies on the circadian clock for timing visits to flowers, time-compensated sun-compass navigation, and dance communication used by foragers to recruit nestmates to rewarding flower patches. The circadian clock is also important for the social organization of honeybee societies. Social factors influence the ontogeny of circadian rhythms and are important for social synchronization of worker activities. Both queen and worker bees switch between activities with and without circadian rhythms. In workers this remarkable plasticity is associated with the division of labor; nurse bees care for the brood around the clock with similar levels of clock gene expression throughout the day, whereas foragers have strong behavioral circadian rhythms with oscillating brain clock gene levels. This plasticity in circadian rhythms is regulated by direct contact with the brood and is context-specific in that nurse bees that are removed from the hive exhibit activity with strong behavioral and molecular rhythms. These studies on the sociochronobiology of honeybees and comparative studies with other social insects suggest that the evolution of sociality has influenced the characteristics of the circadian system in honeybees. PMID:20876811

  13. predicting the initial IMF Bz polarity's change at 1 AU caused by shocks that precede coronal mass ejections

    NASA Astrophysics Data System (ADS)

    Wu, Chin-Chun; Dryer, Murray

    There are important geomagnetic implications whenever the interplanetary magnetic field (IMF) turns northward or southward. This paper addresses only the initial turning when the solar events' shock signals first reach 1 AU. A three-dimensional (3D), time-dependent, MHD model [Han et al., 1988] of disturbances' propagation through the solar wind and interplanetary magnetic field (IMF) has been used by Wu (1993) to develop a “recipe” for the initial north- or south-turning of the IMF's polarity. Its temporal behavior thereafter is not addressed in this paper. Four independent data sets have been used [Wu et al., 1996a, b, c] in a study currently underway to test this idea. A fifth data set [Gosling et al., 1990] is used in this paper to examine, via this idea, the initial Bz polarity's change at 1 AU caused by shocks associated with interplanetary/coronal mass ejection events and large geomagnetic storms during the period of August 1978 to October 1982. Twenty-five events from this fifth data set are studied; the prediction model is in agreement with twenty-one of them. Our results suggest that the initial IMF Bz polarity's change at 1 AU may be associated with a simple relationship between the location of the solar disturbance, the relative position of the heliospheric current sheet, and the initial toward or away polarity of the IMF at Earth.

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

    PubMed

    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. PMID:23615363

  15. Compact, Highly Stable Ion Atomic Clock

    NASA Technical Reports Server (NTRS)

    Prestage, John

    2008-01-01

    A mercury-ion clock now at the breadboard stage of development (see figure) has a stability comparable to that of a hydrogen-maser clock: In tests, the clock exhibited an Allan deviation of between 2 x 10(exp -13) and 3 x 10(exp -13) at a measurement time of 1 second, averaging to about 10(exp -15) at 1 day. However, the clock occupies a volume of only about 2 liters . about a hundredth of the volume of a hydrogen-maser clock. The ion-handling parts of the apparatus are housed in a sealed vacuum tube, wherein only a getter pump is used to maintain the vacuum. Hence, this apparatus is a prototype of a generation of small, potentially portable high-precision clocks for diverse ground- and space-based navigation and radio science applications. Furthermore, this new ion-clock technology is about 100 times more stable and precise than the rubidium atomic clocks currently in use in the NAV STAR GPS Earth-orbiting satellites. In this clock, mercury ions are shuttled between a quadrupole and a 16-pole linear radio-frequency trap. In the quadrupole trap, the ions are tightly confined and optical state selection from a Hg-202 radio-frequency-discharge ultraviolet lamp is carried out. In the 16-pole trap, the ions are more loosely confined and atomic transitions resonant at frequency of about 40.507 GHz are interrogated by use of a microwave beam at that frequency. The trapping of ions effectively eliminates the frequency pulling caused by wall collisions inherent to gas-cell clocks. The shuttling of the ions between the two traps enables separation of the state-selection process from the clock microwave- resonance process, so that each of these processes can be optimized independently of the other. The basic ion-shuttling, two-trap scheme as described thus far is not new: it has been the basis of designs of prior larger clocks. The novelty of the present development lies in major redesigns of its physics package (the ion traps and the vacuum and optical subsystems) to effect the desired reduction of size to a volume of no more than a couple of liters. The redesign effort has included selection of materials for the vacuum tube, ion trap, and ultraviolet windows that withstand bakeout at a temperature of approx.450 C in preparation for sealing the tube to contain the vacuum. This part of the redesign effort follows the approach taken in the development of such other vacuum-tube electronic components as flight traveling- wave-tube amplifiers having operational and shelf lives as long as 15 years. The redesign effort has also included a thorough study of residual-gas-induced shifts of the ion-clock frequency and a study of alternative gases as candidates for use as a buffer gas within the sealed tube. It has been found that neon is more suitable than is helium, which has been traditionally used for this purpose, in that the pressure-induced frequency pulling by neon is between a third and a half of that of helium. In addition, because neon diffuses through solids much more slowly than does helium, the loss of neon by diffusion over the operational lifetime is expected to be negligible.

  16. Dating Phylogenies with Hybrid Local Molecular Clocks

    PubMed Central

    Aris-Brosou, Stéphane

    2007-01-01

    Background Because rates of evolution and species divergence times cannot be estimated directly from molecular data, all current dating methods require that specific assumptions be made before inferring any divergence time. These assumptions typically bear either on rates of molecular evolution (molecular clock hypothesis, local clocks models) or on both rates and times (penalized likelihood, Bayesian methods). However, most of these assumptions can affect estimated dates, oftentimes because they underestimate large amounts of rate change. Principal Findings A significant modification to a recently proposed ad hoc rate-smoothing algorithm is described, in which local molecular clocks are automatically placed on a phylogeny. This modification makes use of hybrid approaches that borrow from recent theoretical developments in microarray data analysis. An ad hoc integration of phylogenetic uncertainty under these local clock models is also described. The performance and accuracy of the new methods are evaluated by reanalyzing three published data sets. Conclusions It is shown that the new maximum likelihood hybrid methods can perform better than penalized likelihood and almost as well as uncorrelated Bayesian models. However, the new methods still tend to underestimate the actual amount of rate change. This work demonstrates the difficulty of estimating divergence times using local molecular clocks. PMID:17849008

  17. The Slope of the Upper End of the IMF and the Upper Mass Limit: An Observer's Perspective

    NASA Astrophysics Data System (ADS)

    Massey, P.

    2011-06-01

    There are various ways of measuring the slope of the upper end of the initial mass function (IMF). Arguably the most direct of these is to place stars on the H-R diagram and compare their positions with stellar evolutionary models. Even so, the masses one infers from this depend upon the exact methodology used. I briefly discuss some of the caveats and go through a brief error analysis. I conclude that the current data suggest that the IMF slopes are the same to within the errors. Similarly the determination of the upper mass "limit" is dependent upon how well one can determine the masses of the most massive stars within a cluster. The recent finding by Crowther et al. (2010) invalidates the claim that there is a 150 M? upper limit to the IMF, but this is really not surprising given the weakness of the previous evidence.

  18. The stellar IMF in early-type galaxies from a non-degenerate set of optical line indices

    NASA Astrophysics Data System (ADS)

    Spiniello, Chiara; Trager, Scott; Koopmans, Léon V. E.; Conroy, Charlie

    2014-02-01

    We investigate the optical spectral region of spectra of ˜1000 stars searching for initial mass function (IMF)-sensitive features to constrain the low-mass end of the IMF slope in elliptical galaxies. The use of indicators bluer than near-infrared features (NaI, CaT, Wing-Ford FeH) is crucial if we want to compare our observations to optical simple stellar population (SSP) models. We use the MILES stellar library (Sánchez-Blázquez et al.) in the wavelength range 3500-7500 Å to select indices that are sensitive to cool dwarf stars and that do not or only weakly depend on age and metallicity. We find several promising indices of molecular TiO and CaH lines. In this wavelength range, the response of a change in the effective temperature of the cool red giant (RGB) population is similar to the response of a change in the number of dwarf stars in the galaxy. We therefore investigate the degeneracy between IMF variation and ?Teff, RGB, and show that it is possible to break this degeneracy with the new IMF indicators defined here. In particular, we define a CaH1 index around ?6380 Å that arises purely from cool dwarfs, does not strongly depend on age and is anticorrelated with [?/Fe]. This index allows the determination of the low-mass end of the IMF slope from integrated-light measurements when combined with different TiO lines and age- and metallicity-dependent features such as H?, Mgb, Fe5270 and Fe5335. The use of several indicators is crucial to break degeneracies between IMF variations, age, abundance pattern and effective temperature of the cool red giant (RGB) population. We measure line-index strengths of our new optical IMF indicators in the Conroy & van Dokkum SSP models and compare these with index strengths of the same spectral features in a sample of stacked Sloan Digital Sky Survey early-type galaxy spectra with varying velocity dispersions. Using different indicators, we find a clear trend of a steepening IMF with increasing velocity dispersion from 150 to 310 km s-1 described by the linear equation x = (2.3 ± 0.1) log ?200 + (2.13 ± 0.15), where x is the IMF slope and ?200 is the central stellar velocity dispersion measured in units of 200 km s-1. We test the robustness of this relation by repeating the analysis with 10 different sets of indicators. We found that the NaD feature has the largest impact on the IMF slope, if we assume solar [Na/Fe] abundance. By including NaD, the slope of the linear relation increases by 0.3 (2.6 ± 0.2). We compute the `IMF mismatch' parameter as the ratio of stellar mass-to-light ratio predicted from the x-?200 relation to that inferred from SSP models assuming a Salpeter IMF and find good agreement with independent published results.

  19. The effect of the Interplanetary Magnetic Field (IMF) on HF radar scattering volume electron densities

    NASA Astrophysics Data System (ADS)

    Gillies, R.; Yau, A. W.; Hussey, G. C.; Sofko, G. J.

    2012-12-01

    The Cascade Small-Sat and Ionospheric Polar Explorer (CASSIOPE) satellite will be launched in late 2012 with a suite of eight scientific instruments comprising the enhanced Polar Outflow Probe (ePOP). The Radio Receiver Instrument (RRI) will be used in conjunction with Super Dual Auroral Radar Network (SuperDARN) radars for detailed studies of the radar scattering volume. The Doppler velocities that are measured by the SuperDARN radars tend to be underestimated because the refractive index in the scattering volume is not known and, therefore, not taken into account when the velocities are calculated. A technique using frequency shifts made by the SuperDARN radars to study the electron density of the radar scattering volume has been developed. These scattering volume electron density values have been calculated for various parameters from SuperDARN frequency shifting data. This study focuses on the dependence of the Interplanetary Magnetic Field (IMF) on the scattering volume electron density results. The dependence of the average scattering volume electron density at different times and locations for various IMF orientations has been determined. This study allows improvements to be made to SuperDARN velocity measurements for various conditions and provides insight into the physics of the coherent scattering process. Finally, the upcoming launch of the ePOP satellite is anticipated to further confirm these results. The instruments on ePOP satellite will provide in situ high resolution measurements of the scattering volumes of the HF radars.

  20. IMF-based chaotic characterization of AP and ML visually-driven postural responses

    NASA Astrophysics Data System (ADS)

    Azhar, Hanif; Giraudet, Guillaume; Faubert, Jocelyn

    2013-03-01

    The objective was to analyze visually driven postural responses and characterize any non-linear behaviour. We recorded physiological responses for two adults, 260 trials each. The subjects maintained quite stance while fixating for four seconds within an immersive room, EON Icube, where the reference to the visual stimuli, i.e., the virtual platform, randomly oscillated in Gaussian orientation 90° and 270° for antero-posterior (AP), and, 0° and 180° for medio-lateral (ML) at three different frequencies (0.125, 0.25, and 0.5 Hz). We accomplished stationary derivatives of posture time series by taking the intrinsic mode functions (IMFs). The phase space plot of IMF shows evidence of the existence of non-linear attractors in both ML and AP. Correlation integral slope with increasing embedding dimension is similar to random white noise for ML, and similar to non-linear chaotic series for AP. Next, recurrence plots indicate the existence of more non-linearity for AP than that for ML. The patterns of the dots after 200th time stamp (near onset) appears to be aperodic in AP. At higher temporal windows, AP entropy tends more toward chaotic series, than that of ML. There are stronger non-linear components in AP than that in ML regardless of the speed conditions.

  1. On the importance of IMF |BY| on polar cap patch formation

    NASA Astrophysics Data System (ADS)

    Zhang, Q.-H.; Zhang, B.-C.; Liu, R.-Y.; Dunlop, M. W.; Lockwood, M.; Moen, J.; Yang, H.-G.; Hu, H.-Q.; Hu, Z.-J.; Liu, S.-L.; McCrea, I.; Lester, M.

    2012-04-01

    A number of poleward-moving events were observed between 1130-1300 UT on 11 Feb 2004, during periods of southward interplanetary magnetic field (IMF), while the steerable antenna of the EISCAT Svalbard Radar (ESR) and the Tromsø VHF Radar pointed nearly northward at low elevation. In this interval, simultaneous SuperDARN CUTLASS Finland radar measurements showed poleward-moving radar aurora forms (PMRAFs) which appeared very similar to the density enhancements observed by the ESR northward-pointing antenna. These events appeared quasi-periodically with a period of about 10 minutes. Comparing the observations from the above three radars, it is inferred that there is an almost one-to-one correspondence between the Poleward-Moving Plasma Concentration Enhancements (PMPCEs) observed by the ESR and the VHF radar, and the PMRAFs measured by the CUTLASS Finland radar. These observations are consistent with the interpretation that the polar cap patch material was generated by photo-ionisation at sub-auroral latitudes, and that the plasma was structured by bursts of magnetopause reconnection giving access to the polar cap. There is clear evidence that plasma structuring into patches was dependent on the variability in IMF |BY|. The duration of these events implies that the average evolution time of the newly opened flux tubes from the sub-auroral region to the polar cap was about 33 minutes.

  2. Corotating and transient structures of IMF at Venus and Earth orbits

    NASA Technical Reports Server (NTRS)

    Marubashi, K.

    1995-01-01

    Magnetometer data obtained from the Pioneer Venus orbiter (PVO) provide a unique data base for studying interplanetary magnetic field (IMF) structures at 0.7 AU. Comparison of the same structure observed at 0.7 and 1 AU provides information about the effects of stream interactions between these two distances. Besides, the PVO observations provide solar wind conditions at various longitude separations from the Sun-Earth line, because the orbital motion of Venus is about 0.6 deg/day faster than that of Earth. Thus, it is possible to examine the effects of time variations in the coronal conditions on the solar wind conditions by comparing corotating structures observed at Earth and those from the PVO at different longitude separations. Some results obtained so far are as follows. We have found several transient structures observed at both 0.7 and 1 AU, when the Sun, Venus, and Earth are closely aligned. Each event exhibits magnetic field variations very similar to each other between Venus and Earth, implying that the effects of stream interactions are small. The IMF sector boundaries were compared between the Venus and Earth orbits as typical examples of corotating structures. We have found both well-correlated and poorly-correlated structures depending on the longitude separation between the Earth and Venus, and on the persistence of the sector structures.

  3. Faults Diagnostics of Railway Axle Bearings Based on IMF's Confidence Index Algorithm for Ensemble EMD.

    PubMed

    Yi, Cai; Lin, Jianhui; Zhang, Weihua; Ding, Jianming

    2015-01-01

    As train loads and travel speeds have increased over time, railway axle bearings have become critical elements which require more efficient non-destructive inspection and fault diagnostics methods. This paper presents a novel and adaptive procedure based on ensemble empirical mode decomposition (EEMD) and Hilbert marginal spectrum for multi-fault diagnostics of axle bearings. EEMD overcomes the limitations that often hypothesize about data and computational efforts that restrict the application of signal processing techniques. The outputs of this adaptive approach are the intrinsic mode functions that are treated with the Hilbert transform in order to obtain the Hilbert instantaneous frequency spectrum and marginal spectrum. Anyhow, not all the IMFs obtained by the decomposition should be considered into Hilbert marginal spectrum. The IMFs' confidence index arithmetic proposed in this paper is fully autonomous, overcoming the major limit of selection by user with experience, and allows the development of on-line tools. The effectiveness of the improvement is proven by the successful diagnosis of an axle bearing with a single fault or multiple composite faults, e.g., outer ring fault, cage fault and pin roller fault. PMID:25970256

  4. Solar flare and IMF sector structure effects in the lower ionosphere

    SciTech Connect

    Lastovicka, J.

    1984-05-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  5. Solar flare and IMF sector structure effects in the lower ionosphere

    NASA Astrophysics Data System (ADS)

    Lastovicka, J.

    1984-05-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  6. Solar Flare and IMF Sector Structure Effects in the Lower Ionosphere

    NASA Technical Reports Server (NTRS)

    Lastovicka, J.

    1984-01-01

    About 1% of all sudden ionospheric disturbances (SIDs) observed at the Panska Ves Observatory (Czechoslovakia), were found to be not of solar-XUV origin. Among them, the very rare SWF events (observed at L = 2.4) of corpuscular origin are the most interesting. The IMF sector structure effects in the midlatitude lower ionosphere are minor in comparison with effects of solar flares, geomagnetic storms, etc. There are two basic types of effects. The first type is a disturbance, best developed in geomagnetic activity, and observed in the night-time ionosphere. It can be interpreted as a response to sector structure related changes of geomagnetic (= magnetospheric) activity. The other type is best developed in the tropospheric vorticity area index and is also observed in the day-time ionosphere in winter. This effect is quietening in the ionosphere as well as troposphere. While the occurrence of the former type is persistent in time, the latter is severely diminished in some periods. All the stratosphere, the 10-mb level temperature and height above Berlin-Tempelhof do not display any observable IMF section structure effect.

  7. Dulling Occam's Razor: ICM Enrichment, the Elliptical Galaxy IMF, and the Diversity of Star Formation

    NASA Astrophysics Data System (ADS)

    Loewenstein, Michael

    2013-04-01

    Stars born in galaxy cluster potential wells must be responsible for the high level of enrichment measured in the intracluster medium (ICM); however, there is increasing tension between this truism and the parsimonious assumption that the stars in the generally old population studied optically in cluster galaxies emerged from the same formation sites at the same epochs. We construct a phenomenological cluster model to demonstrate that ICM enrichment is underestimated by a factor >2 for standard assumptions, and quantify the adjustments to the star formation efficiency and initial mass function (IMF), and SNIa production efficiency, required to rectify this while being consistent with the observed ICM abundance pattern. Given recent evidence of a steep IMF in elliptical galaxies that conflicts with the nucleosynthetic requirements of the ICM, we are led to conclude that the stellar population responsible for enriching the ICM is currently hidden and offer some suggestions as to where. This study proves that the star formation cannot be invariant in space and time.

  8. Variation and power issues in VLSI clock networks

    E-print Network

    Venkataraman, Ganesh

    2009-05-15

    correlated power supply variations, buffer and wire process variations. 3. Methodology and Algorithms for Rotary Clocking In order to solve the power and the variation problem more effectively, several novel clocking technologies have been developed. Among...

  9. Intrachip clock signal distribution via si-based optical interconnect

    E-print Network

    Ahn, Donghwan

    2007-01-01

    The Optical clocking has emerged as an innovative alternative approach to the electrical clocking, in order to overcome the difficulties associated with electrical interconnects in the synchronization of high-performance ...

  10. Tick Tock: New Clues about Biological Clocks and Health

    MedlinePLUS

    ... Articles | Inside Life Science Home Page Tick Tock: New Clues About Biological Clocks and Health By Emily ... be linked to problems with biological clocks, and new scientific findings support this. A few years ago, ...

  11. Oxyntomodulin regulates resetting of the liver circadian clock by food.

    PubMed

    Landgraf, Dominic; Tsang, Anthony H; Leliavski, Alexei; Koch, Christiane E; Barclay, Johanna L; Drucker, Daniel J; Oster, Henrik

    2015-01-01

    Circadian clocks coordinate 24-hr rhythms of behavior and physiology. In mammals, a master clock residing in the suprachiasmatic nucleus (SCN) is reset by the light-dark cycle, while timed food intake is a potent synchronizer of peripheral clocks such as the liver. Alterations in food intake rhythms can uncouple peripheral clocks from the SCN, resulting in internal desynchrony, which promotes obesity and metabolic disorders. Pancreas-derived hormones such as insulin and glucagon have been implicated in signaling mealtime to peripheral clocks. In this study, we identify a novel, more direct pathway of food-driven liver clock resetting involving oxyntomodulin (OXM). In mice, food intake stimulates OXM secretion from the gut, which resets liver transcription rhythms via induction of the core clock genes Per1 and 2. Inhibition of OXM signaling blocks food-mediated resetting of hepatocyte clocks. These data reveal a direct link between gastric filling with food and circadian rhythm phasing in metabolic tissues. PMID:25821984

  12. CIPC is a mammalian circadian clock protein without invertebrate homologues.

    PubMed

    Zhao, Wen-Ning; Malinin, Nikolay; Yang, Fu-Chia; Staknis, David; Gekakis, Nicholas; Maier, Bert; Reischl, Silke; Kramer, Achim; Weitz, Charles J

    2007-03-01

    At the core of the mammalian circadian clock is a feedback loop in which the heterodimeric transcription factor CLOCK-Brain, Muscle Arnt-like-1 (BMAL1) drives expression of its negative regulators, periods (PERs) and cryptochromes (CRYs). Here, we provide evidence that CLOCK-Interacting Protein, Circadian (CIPC) is an additional negative-feedback regulator of the circadian clock. CIPC exhibits circadian regulation in multiple tissues, and it is a potent and specific inhibitor of CLOCK-BMAL1 activity that functions independently of CRYs. CIPC-CLOCK protein complexes are present in vivo, and depletion of endogenous CIPC shortens the circadian period length. CIPC is unrelated to known proteins and has no recognizable homologues outside vertebrates. Our results suggest that negative feedback in the mammalian circadian clock is divided into distinct pathways, and that the addition of new genes has contributed to the complexity of vertebrate clocks. PMID:17310242

  13. Clock mechanisms and their effects, leads into steam engine

    E-print Network

    Dugan, David

    2004-08-17

    In a clock-maker’s shop, Simon Schaffer explains the great precision needed to make clocks, and the development of standardized parts. The feed-back mechanisms or governors are absolutely essential in the first stationary steam engines....

  14. Magnetosphere preconditioning under northward IMF: Evidence from the study of coronal mass ejection and corotating interaction region geoeffectiveness

    NASA Astrophysics Data System (ADS)

    Lavraud, B.; Thomsen, M. F.; Borovsky, J. E.; Denton, M. H.; Pulkkinen, T. I.

    2006-09-01

    Motivated by recent observations and simulations of the formation of a cold and dense plasma sheet in the tail of the magnetosphere under northward interplanetary magnetic field (IMF) and of the direct influence of the plasma sheet density on the ring current strength, this paper aims at (1) highlighting how the coupling of these effects may lead to a preconditioning of the magnetosphere under northward IMF and (2) performing first tests of the validity of this hypothesis. We have analyzed superposed epoch time series of various parameters to investigate the response of the magnetosphere (as indicated by the Dst index) to the passage of coronal mass ejections (CMEs) and corotating interaction regions (CIRs). We first focused on the difference between the measured Dst signature and that predicted by a semiempirical Dst model. For both CME- and CIR-driven storms the superposed epoch results show that the model Dst predictions tend to underestimate the actual storm strength (by up to 10-30%) for events that are preceded by a substantial interval of northward IMF, as opposed to those with no such preceding northward IMF. We also analyzed Los Alamos geosynchronous spacecraft data for these events. The average density and temperature measured at storm onset are substantially higher and slightly lower, respectively, for the cases with preceding northward IMF intervals. These results suggest that solar wind structures may be more geoeffective if preceded by a northward IMF interval and they are consistent with the hypothesis of a preconditioning by a cold, dense plasma sheet. A colder and denser plasma sheet may lead to a stronger ring current when that plasma is convected inward during the main phase of an ensuing storm.

  15. Sugars, the clock and transition to flowering

    PubMed Central

    Moghaddam, Mohammad R. Bolouri; den Ende, Wim Van

    2013-01-01

    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 and jasmonate 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, PHYTOCHROME INTERACTING FACTORS, invertases, and trehalose-6-phosphate) 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. PMID:23420760

  16. Which came first, spacetime or clocks?

    NASA Astrophysics Data System (ADS)

    Ord, G. N.

    2014-04-01

    Emergent quantum mechanics seeks a deeper level theory, anticipating that such a theory will provide a clearer picture of the relation between the quantum and classical worlds. In this work we show that the quantum-classical divide is a manifestation of the transition from Newton's absolute time to relativity's path-dependent time. The prior theory in this case is that particles are intrinsic clocks. The emergence of separate classical and quantum behaviour is seen by considering different continuum limits in a single digital clock model. A continuum limit that constructs a continuous worldline provides a simple basis for Minkowski spacetime. An alternative limit in which the clock itself contains boost information leads to the Dirac equation.

  17. Csac - the Chip-Scale Atomic Clock

    NASA Astrophysics Data System (ADS)

    Lutwak, R.; Rashed, A.; Varghese, M.; Tepolt, G.; Leblanc, J.; Mescher, M.; Serkland, D. K.; Geib, K. M.; Peake, G. M.

    2009-04-01

    The authors have developed a Chip-Scale Atomic Clock (CSAC) of sufficiently low power and small size to enable atomic timing in portable battery-powered devices. The collaboration of diverse research teams in clock technology, micro-electromechanical systems (MEMS), and optoelectronic devices has resulted in size and power reduction of atomic clock technology by more than two orders of magnitude. In 2007, we completed a pre-production build and evaluation of ten identical CSACs, with power <125 mW and short-term stability of ?y(?) < 2 × 10-10 ?-1/2 1. This paper reviews the physics and engineering considerations which underlie CSAC technology, describes in detail our CSAC implementation, and presents the results from the pre-production build.

  18. Circadian clock: linking epigenetics to aging.

    PubMed

    Orozco-Solis, Ricardo; Sassone-Corsi, Paolo

    2014-06-01

    Circadian rhythms are generated by an intrinsic cellular mechanism that controls a large array of physiological and metabolic processes. There is erosion in the robustness of circadian rhythms during aging, and disruption of the clock by genetic ablation of specific genes is associated with aging-related features. Importantly, environmental conditions are thought to modulate the aging process. For example, caloric restriction is a very strong environmental effector capable of delaying aging. Intracellular pathways implicating nutrient sensors, such as SIRTs and mTOR complexes, impinge on cellular and epigenetic mechanisms that control the aging process. Strikingly, accumulating evidences indicate that these pathways are involved in both the modulation of the aging process and the control of the clock. Hence, innovative therapeutic strategies focused at controlling the circadian clock and the nutrient sensing pathways might beneficially influence the negative effects of aging. PMID:25033025

  19. CENTRAL AND PERIPHERAL CIRCADIAN CLOCKS IN MAMMALS

    PubMed Central

    Mohawk, Jennifer A.; Green, Carla B.; Takahashi, Joseph S.

    2013-01-01

    The circadian system of mammals is composed of a hierarchy of oscillators that function at the cellular, tissue and systems levels. A common molecular mechanism underlies the cell autonomous circadian oscillator throughout the body, yet this clock system is adapted to different functional contexts. In the central suprachiasmatic nucleus (SCN) of the hypothalamus, a coupled population of neuronal circadian oscillators acts as a master pacemaker for the organism to drive rhythms in activity and rest, feeding, body temperature and hormones. Coupling within the SCN network confers robustness to the SCN pacemaker which in turn provides stability to the overall temporal architecture of the organism. Throughout the majority of the cells in the body, cell autonomous circadian clocks are intimately enmeshed within metabolic pathways. Thus, an emerging view for the adaptive significance of circadian clocks is their fundamental role in orchestrating metabolism. PMID:22483041

  20. The Deep Space Atomic Clock Mission

    NASA Technical Reports Server (NTRS)

    Ely, Todd A.; Koch, Timothy; Kuang, Da; Lee, Karen; Murphy, David; Prestage, John; Tjoelker, Robert; Seubert, Jill

    2012-01-01

    The Deep Space Atomic Clock (DSAC) mission will demonstrate the space flight performance of a small, low-mass, high-stability mercury-ion atomic clock with long term stability and accuracy on par with that of the Deep Space Network. The timing stability introduced by DSAC allows for a 1-Way radiometric tracking paradigm for deep space navigation, with benefits including increased tracking via utilization of the DSN's Multiple Spacecraft Per Aperture (MSPA) capability and full ground station-spacecraft view periods, more accurate radio occultation signals, decreased single-frequency measurement noise, and the possibility for fully autonomous on-board navigation. Specific examples of navigation and radio science benefits to deep space missions are highlighted through simulations of Mars orbiter and Europa flyby missions. Additionally, this paper provides an overview of the mercury-ion trap technology behind DSAC, details of and options for the upcoming 2015/2016 space demonstration, and expected on-orbit clock performance.

  1. Rat retina shows robust circadian expression of clock and clock output genes in explant culture

    PubMed Central

    Buonfiglio, Daniella C.; Malan, André; Sandu, Cristina; Jaeger, Catherine; Cipolla-Neto, José; Hicks, David

    2014-01-01

    Purpose Circadian rhythms are central to vision and retinal physiology. A circadian clock located within the retina controls various rhythmic processes including melatonin synthesis in photoreceptors. In the present study, we evaluated the rhythmic expression of clock genes and clock output genes in retinal explants maintained for several days in darkness. Methods Retinas were dissected from Wistar rats, either wild-type or from the Per1-luciferase transgenic line housed under a daily 12 h:12 h light-dark cycle (LD12/12), and put in culture at zeitgeber time (ZT) 12 on semipermeable membranes. Explants from wild-type rats were collected every 4 h over 3 days, and total RNA was extracted, quantified, and reverse transcribed. Gene expression was assessed with quantitative PCR, and the periodicity of the relative mRNA amounts was assessed with nonlinear least squares fitting to sine wave functions. Bioluminescence in explants from Per1-luciferase rats was monitored for several days under three different culture protocols. Results Rhythmic expression was found for all studied clock genes and for clock downstream targets such as c-fos and arylalkylamine N-acetyltransferase (Aanat) genes. Clock and output genes cycled with relatively similar periods and acrophases (peaks of expression during subjective night, except c-fos, which peaked around the end of the subjective day). Data for Per1 were confirmed with bioluminescence monitoring, which also permitted culture conditions to be optimized to study the retina clock. Conclusions Our work shows the free-running expression profile of multiple clock genes and potential clock targets in mammalian retinal explants. This research further strengthens the notion that the retina contains a self-sustained oscillator that can be functionally characterized in organotypic culture. PMID:24940028

  2. Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock

    SciTech Connect

    Leroux, Ian D.; Schleier-Smith, Monika H.; Vuletic, Vladan [Department of Physics, MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

    2010-06-25

    We study experimentally the application of a class of entangled states, squeezed spin states, to the improvement of atomic-clock precision. In the presence of anisotropic noise, the entanglement lifetime is strongly dependent on squeezing orientation. We measure the Allan deviation spectrum of a clock operated with a phase-squeezed input state. For averaging times up to 50 s the squeezed clock achieves a given precision 2.8(3) times faster than a clock operating at the standard quantum limit.

  3. Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock

    E-print Network

    Ian D. Leroux; Monika H. Schleier-Smith; Vladan Vuleti?

    2010-04-10

    We study experimentally the lifetime of a special class of entangled states in an atomic clock, squeezed spin states. In the presence of anisotropic noise, their lifetime is strongly dependent on squeezing orientation. We measure the Allan deviation spectrum of a clock operated with a phase-squeezed input state. For integration times up to 50 s the squeezed clock achieves a given precision 2.8(3) times faster than a clock operating at the standard quantum limit.

  4. Satellite virtual atomic clock with pseudorange difference function

    Microsoft Academic Search

    Xiaohui Li; Haitao Wu; Yujing Bian; Danni Wang

    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\\u000a Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed.\\u000a Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic\\u000a clocks are used

  5. Positional Cloning of the Mouse Circadian Clock Gene

    Microsoft Academic Search

    David P King; Yaliang Zhao; Ashvin M Sangoram; Lisa D Wilsbacher; Minoru Tanaka; Marina P Antoch; Thomas D. L Steeves; Martha Hotz Vitaterna; Jon M Kornhauser; Phillip L Lowrey; Fred W Turek; Joseph S Takahashi

    1997-01-01

    We used positional cloning to identify the circadian Clock gene in mice. Clock is a large transcription unit with 24 exons spanning ?100,000 bp of DNA from which transcript classes of 7.5 and ?10 kb arise. Clock encodes a novel member of the bHLH–PAS family of transcription factors. In the Clock mutant allele, an A?T nucleotide transversion in a splice

  6. Timescale algorithms combining cesium clocks and hydrogen masers

    NASA Technical Reports Server (NTRS)

    Breakiron, Lee A.

    1992-01-01

    The United States Naval Observatory (USNO) atomic timescale, formerly based on an ensemble of cesium clocks, is now produced by an ensemble of cesium clocks and hydrogen masers. In order to optimize stability and reliability, equal clock weighting has been replaced by a procedure reflecting the relative, time-varying noise characteristics of the two different types of clocks. Correlation of frequency drift is required, and residual drift is avoided by the eventual complete deweighting of the masers.

  7. Circadian clock control of the cellular response to DNA damage

    Microsoft Academic Search

    Aziz Sancar; Laura A. Lindsey-Boltz; Tae-Hong Kang; Joyce T. Reardon; Jin Hyup Lee; Nuri Ozturk

    2010-01-01

    Mammalian cells possess a cell-autonomous molecular clock which controls the timing of many biochemical reactions and hence the cellular response to environmental stimuli including genotoxic stress. The clock consists of an autoregulatory transcription–translation feedback loop made up of four genes\\/proteins, BMal1, Clock, Cryptochrome, and Period. The circadian clock has an intrinsic period of about 24h, and it dictates the rates

  8. Complementary approaches to understanding the plant circadian clock

    Microsoft Academic Search

    Ozgur E. Akman; Maria Luisa Guerriero; Laurence Loewe; Carl Troein

    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

  9. Complementary approaches to understanding the plant circadian clock

    Microsoft Academic Search

    Ozgur E. Akman; Maria Luisa Guerriero; Laurence Loewe; Carl Troein

    2010-01-01

    Circadian clocks are oscillatory genetic networks that help organisms adapt\\u000ato the 24-hour day\\/night cycle. The clock of the green alga Ostreococcus tauri\\u000ais the simplest plant clock discovered so far. Its many advantages as an\\u000aexperimental system facilitate the testing of computational predictions.\\u000a We present a model of the Ostreococcus clock in the stochastic process\\u000aalgebra Bio-PEPA and exploit

  10. Sample-Clock Phase-Control Feedback

    NASA Technical Reports Server (NTRS)

    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.

  11. Special Angle Pairs Discovery Activity

    NSDL National Science Digital Library

    Barbara Henry

    2012-04-16

    This lesson uses a discovery approach to identify the special angles formed when a set of parallel lines is cut by a transversal. During this lesson students identify the angle pair and the relationship between the angles. Students use this relationship and special angle pairs to make conjectures about which angle pairs are considered special angles.

  12. Real clocks and the Zeno effect

    SciTech Connect

    Egusquiza, Inigo L. [Department of Theoretical Physics, The University of the Basque Country, 644 Posta Kutxa, 48080 Bilbao (Spain); Garay, Luis J. [Institute of Mathematics and Fundamental Physics, CSIC, c/ Serrano 121, 28006 Madrid (Spain)

    2003-08-01

    Real clocks are not perfect. This must have an effect in our predictions for the behavior of a quantum system, an effect for which we present a unified description, encompassing several previous proposals. We study the relevance of clock errors in the Zeno effect and find that generically no Zeno effect can be present (in such a way that there is no contradiction with currently available experimental data). We further observe that, within the class of stochasticities in time addressed here, there is no modification in emission line shapes.

  13. Associative skew clock routing for difficult instances

    E-print Network

    Kim, Min-seok

    2006-08-16

    ASSOCIATIVE SKEW CLOCK ROUTING FOR DIFFICULT INSTANCES A Thesis by MIN-SEOK KIM Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2006 Major Subject...: Electrical Engineering ASSOCIATIVE SKEW CLOCK ROUTING FOR DIFFICULT INSTANCES A Thesis by MIN-SEOK KIM Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved...

  14. The Fermilab D0 Master Clock System

    SciTech Connect

    Rotolo, C.; Fachin, M.; Chappa, S.; Rauch, M.; Needles, C.; Dyer, A.

    1991-11-01

    The Clock System provides bunch crossing related timing signals to various detector subsystems. Accelerator synchronization and monitoring as well as timing signal generation and distribution are discussed. The system is built using three module types implemented in Eurostandard hardware with a VME communications interface. The first two types of modules are used to facilitate synchronization with the accelerator and to generate 23 timing signals that are programmable with one RF bucket (18.8 ns) resolution and 1 ns accuracy. Fifty-four of the third module type are used to distribute the timing signals and two synchronous 53 MHz and 106 MHz clocks to various detector subsystems. 6 refs., 5 figs.

  15. A relativistic analysis of clock synchronization

    NASA Technical Reports Server (NTRS)

    Thomas, J. B.

    1974-01-01

    The relativistic conversion between coordinate time and atomic time is reformulated to allow simpler time calculations relating analysis in solar-system barycentric coordinates (using coordinate time) with earth-fixed observations (measuring earth-bound proper time or atomic time.) After an interpretation of terms, this simplified formulation, which has a rate accuracy of about 10 to the minus 15th power, is used to explain the conventions required in the synchronization of a world wide clock network and to analyze two synchronization techniques-portable clocks and radio interferometry. Finally, pertinent experiment tests of relativity are briefly discussed in terms of the reformulated time conversion.

  16. Weather Alarm Clock 2.1

    NSDL National Science Digital Library

    2007-01-01

    This handy application is fairly self-explanatory: It displays both the weather and tells the time. Now, it does so in a visually pleasing manner, and for that alone it should be praised. It comes with a few customized skins, and users can create alarms which can be accompanied by pop-up messages. Finally, for those who are quite particular about the exact time, the clock feature can be synchronized with various omnipotent atomic clock servers. This version is compatible with computers running Windows 2000, XP, and 2003.

  17. Polygon Angle Applet

    NSDL National Science Digital Library

    Nicholas Exner

    2000-05-31

    This interactive Java applet supports the investigation of the relationship between the number of vertices of a polygon and its interior angle sum. Learners choose and locate the vertices, the angle measures are displayed, and then the student can drag the measures into a circle to see them summed relative to 360 degrees.

  18. Blackbody radiation shifts and magic wavelengths for atomic clock research

    E-print Network

    Safronova, Marianna

    Blackbody radiation shifts and magic wavelengths for atomic clock research M. S. Safronova of interest to atomic clock development are reported. We also calculated the blackbody radiation shift The operation of atomic clocks is generally carried out at room temperature, whereas the definition

  19. PARCS: a Primary Atomic Reference Clock in Space

    Microsoft Academic Search

    S. R. Jefferts; T. P. Heavner; L. W. Hollberg; J. Kitching; D. M. Meekhof; T. E. Parker; W. Phillips; S. Rolston; H. G. Robinson; J. H. Shirley; D. B. Sullivan; F. L. Walls; N. Ashby; W. M. Klipstein; L. Maleki; D. Seidel; R. Thompson; S. Wu; L. Young; R. F. C. Vessot; A. DeMarchi

    1999-01-01

    NIST, in collaboration with the Jet Propulsion Laboratories (JPL), the University of Colorado, Politecnico di Torino and Harvard Smithsonian Center for Astrophysics (SAO) is building a laser-cooled cesium-beam atomic clock for flight on the International Space Station (ISS). The clock, named PARCS (Primary Atomic Reference Clock in Space) is designed to perform certain tests of relativity and fundamental physics and

  20. Microchip-based trapped-atom clocks Vladan Vuletic

    E-print Network

    Vuletic, Vladan

    1 1 Microchip-based trapped-atom clocks Vladan Vuleti´c Ian D. Leroux Monika H. Schleier-Smith 1 , the fractional stability improves with higher transi- tion frequency. #12;2 1 Microchip-based trapped-atom clocks 1.2 Atomic-fountain versus trapped-atom clocks In the absence of other fields, particles fall under

  1. The effect of humidity on commercial cesium beam atomic clocks

    Microsoft Academic Search

    J. E. Gray; H. E. Machlan; D. W. Allan

    1988-01-01

    Control of humidity is studied in one of the environmental chambers for the NBS cesium beam clock ensemble. The relative humidity was changed from a few percent to 48%. All of the clocks underwent a change in frequency. The resulting frequency changes were of different sign and of varying magnitudes among the clocks. In some, the changes were an order

  2. Atomic clocks of the future: using the ultrafast and ultrastable'

    E-print Network

    Atomic clocks of the future: using the ultrafast and ultrastable' Leo Hollberg, Scott Diddanis based on laser cooled and trapped atoms. In contrast to today's atomic clocks that are based on electronic oscillators locked to microwave transitions in atoms, the nest generation of atomic clocks

  3. Byzantine Self-Stabilizing Clock Distribution with HEX

    E-print Network

    Lynch, Nancy

    synchrony (a maximum skew of a few clock cycles) also between different clock domains. This mesochronous enables metastability-free high-speed cross-domain communication via FIFO buffers [6][7]. As mesochronous- ant approaches for distributed mesochronous clock generation [8][9][10][11][12][13] described

  4. Robust Clock Synchronization Methods for Wireless Sensor Networks 

    E-print Network

    Lee, Jae Han

    2011-10-21

    . . . . 73 2. PCRB for Exponential and Gamma Network Delay Models . . . . . . . . . . . . . . . . . . . . . . . . . . 75 3. Comparison between PCRB and CRLB . . . . . . . . 76 C. An Iterative Gaussian Mixture Kalman Particle Filter- ing Approach... with clock offset (?A: clock offset, d: propagation delay, Lk,Mk: random delays) . . . . . . 12 2.2 MSEs of clock offset estimators for asymmetric exponential delays (?1 = 1, ?2 = 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.3 MSEs...

  5. Network classless time protocol based on clock offset optimization

    Microsoft Academic Search

    Omer Gurewitz; Israel Cidon; Moshe Sidi

    2006-01-01

    Time synchronization is critical in distributed environments. A variety of network protocols, middleware and business applications rely on proper time synchronization across the computational infrastructure and depend on the clock accuracy. The Network Time Protocol (NTP) is the current widely accepted standard for synchronizing clocks over the Internet. NTP uses a hierarchical scheme in order to synchronize the clocks in

  6. Atomic clock augmentation for receivers using the Global Positioning System

    Microsoft Academic Search

    Paul Andrew Kline

    1997-01-01

    For receivers using the Global Positioning System (GPS), it is standard procedure to treat the receiver clock bias from GPS time as an unknown. This requires four range measurements to the satellites in order to solve for three dimensional position and clock offset. If the receiver clock could be synchronized with GPS time, the extra range measurement would not be

  7. Molecular genetics of the fruit-fly circadian clock

    Microsoft Academic Search

    Ezio Rosato; Eran Tauber; Charalambos P Kyriacou

    2006-01-01

    The circadian clock percolates through every aspect of behaviour and physiology, and has wide implications for human and animal health. The molecular basis of the Drosophila circadian clock provides a model system that has remarkable similarities to that of mammals. The various cardinal clock molecules in the fly are outlined, and compared to those of their actual and ‘functional’ homologues

  8. Improved Algorithms for Synchronizing Computer Network Clocks 1,23

    E-print Network

    Mills, David L.

    local­area and wide­area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined

  9. Improved Algorithms for Synchronizing Computer Network Clocks1,23

    E-print Network

    Mills, David L.

    local-area and wide-area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined

  10. A unified single-phase clocking scheme for VLSI systems

    Microsoft Academic Search

    MORTEZA AFGHAHI; CHRISTER SVENSSON

    1990-01-01

    Two of the main consequences of advances in VLSI technologies are increased cost of design and wiring. In CMOS synchronous systems, this cost is partly due to tedious synchronization of different clock phases and routing of these clock signals. Here, a single-phase clocking scheme that makes the design very compact and simple is described. It is shown that this scheme

  11. DCS: Distributed Asynchronous Clock Synchronization in Delay Tolerant Networks

    E-print Network

    Shen, Xuemin "Sherman"

    DCS: Distributed Asynchronous Clock Synchronization in Delay Tolerant Networks Bong Jun Choi, Fellow, IEEE Abstract--In this paper, we propose a distributed asynchronous clock synchronization (DCS, the proposed DCS protocol can achieve global clock synchronization among mobile nodes within the network over

  12. Edinburgh Research Explorer Stochastic properties of the plant circadian clock

    E-print Network

    Millar, Andrew J.

    of molecular noise in single cells on the behaviour of the circadian clock in the plant model speciesEdinburgh Research Explorer Stochastic properties of the plant circadian clock Citation, 'Stochastic properties of the plant circadian clock' Journal of the Royal Society Interface., 10.1098/rsif

  13. Sun Watching Lesson 4: Making a Sun Clock

    E-print Network

    Maxwell, Bruce D.

    29 Sun Watching Lesson 4: Making a Sun Clock Lesson 4: Making a Sun Clock A major factor contributing toward our concept of time is based on the apparent motion of the Sun. In this activity, students will construct Pocket Sun Clocks. They are challenged to determine the correct orientation needed for the Sun

  14. Role of biological clocks in cancer processes and chronotherapy

    Microsoft Academic Search

    P. Subramanian; P. Kumaravel; T. Manivasagam

    2010-01-01

    Biological rhythms are considered in the rational use of therapeutic agents to optimize the treatment of several diseases. In cancer, several stages of cell cycle are regulated by the circadian clock. Clock genes play a vital role in cell proliferation and apoptosis. Therefore, mutation\\/abnormal function of circadian clock genes could result in tumor development. Circadian rhythmicity can be used as

  15. A New Fault-Tolerant Algorithm for Clock Synchronization

    E-print Network

    Lynch, Nancy

    a characterization of how far the clocks drift from real time. Reintegration of a repaired process carA New Fault-Tolerant Algorithm for Clock Synchronization Jennifer Lundelius Nancy Lynch Laboratory a new fault-tolerant algorithm for solving a variant of Lamport's clock synchronization problem

  16. Signs of the time: environmental input to the circadian clock

    Microsoft Academic Search

    Paul F. Devlin

    2002-01-01

    The circadian clock forms one of the most fascinat- ing adaptations to life on earth. Organisms can not only anticipate the day\\/night cycle but can make use of an internal clock to measure daylength as an indi- cator of the changing of the seasons. The innate per- iod of the clock is not exactly equal to 24 h, but is

  17. The Ion Composition of the Plasma Sheet at 15-19 Re as a function of the IMF and the Solar Wind conditions

    Microsoft Academic Search

    C. Mouikis; L. M. Kistler; Y. Liu; B. Klecker; A. Korth; I. S. Dandouras

    2010-01-01

    Recent observational and simulation studies have reported a close correlation of the ionospheric outflow and the IMF and Solar Wind conditions. In this study we use the ion composition data from the CIS\\/CODIF instrument on Cluster to determine how the H+, He+ and O+ contributions to the plasma sheet density change as a function of certain IMF and Solar Wind

  18. The Economic Impact of IMF and World Bank Programs in the Middle East and North Africa: A Case Study of Jordan, Egypt, Morocco and Tunisia, 1983 - 2004

    Microsoft Academic Search

    Jane R. Harrigan; Hamed El-Said

    2010-01-01

    This paper examines whether the economic reforms attached to IMF and World Bank policy-based lending in the Middle East and North Africa have stimulated sustained economic growth. In order to investigate this, we chose four countries to study in depth: Jordan, Egypt, Tunisia and Morocco. These were chosen as they have been put forward by both the IMF and the

  19. Clusters Near the Center of the Galaxy - How Weird is Their IMF?

    NASA Astrophysics Data System (ADS)

    Stolte, A.

    2011-06-01

    It has been argued on theoretical grounds that the initial mass function (IMF) in the hot, UV-rich Galactic center environment might be biased to high-mass stars. Over the past decade, several attempts were made to derive the stellar mass function in the young, massive Arches cluster near the Galactic center, as well as in the nuclear cluster itself. While there is indirect evidence for a top-heavy IMF in the young and old population in the nuclear cluster in the immediate vicinity of the supermassive black hole, the direct observations of the MF are subject to large uncertainties, such as field contamination, age and distance estimation, varying extinction along the line of sight towards the center of the Galaxy, and cluster membership. Progressing from the observed present-day stellar mass distribution to conclusions on the initial stellar mass function is particularly difficult in the Galactic center environment, where clusters are rapidly disrupted by the strong tidal field in the inner bulge. Here, the evidence for a top-heavy IMF in the young nuclear cluster is briefly summarised, and the different observational studies of the Arches cluster are compared. The major focus, however, is placed on the discussion of the biases still inherent to present-day MF derivations, both along the Galactic center line of sight and in dense, young clusters in general. The effects of spatially varying extinction, non-radially symmetric incompleteness in high-density environments, and membership selection are addressed. The spatial area within which the present-day MF can reliably be derived in young, massive clusters is frequently restricted by the field star density, and hence does not need to cover even a major fraction of the complete cluster. Biases arising from these selection effects are analysed. Finally, proper motion studies with precision astrometry employing adaptive optics systems from the ground are suggested as a solution to the membership problem, and the Arches cluster is chosen as an example to display the advantages of this approach.

  20. Seasonal and diurnal variation of geomagnetic activity: Russell-McPherron effect during different IMF polarity and/or extreme solar wind conditions

    NASA Astrophysics Data System (ADS)

    Zhao, H.; Zong, Q.-G.

    2012-11-01

    The Russell-McPherron (R-M) effect is one of the most prevailing hypotheses accounting for semiannual variation of geomagnetic activity. To validate the R-M effect and investigate the difference of geomagnetic activity variation under different interplanetary magnetic field (IMF) polarity and during extreme solar wind conditions (interplanetary shock), we have analyzed 42 years interplanetary magnetic field and geomagnetic indices data and 1270 SSC (storm sudden commencement) events from the year 1968 to 2010 by defining the R-M effect with positive/negative IMF polarity (IMF away/toward the Sun). The results obtained in this study have shown that the response of geomagnetic activity to the R-M effect with positive/negative IMF polarity are rather profound: the geomagnetic activity is much more intense around fall equinox when the direction of IMF is away the Sun, while much more intense around spring equinox when the direction of IMF is toward the Sun. The seasonal and diurnal variation of geomagnetic activity after SSCs can be attributed to both R-M effect and the equinoctial hypothesis; the R-M effect explains most part of variance of southward IMF, while the equinoctial hypothesis explains similar variance of ring current injection and geomagnetic indices as the R-M effect. However, the R-M effect with positive/negative IMF polarity explains the difference between SSCs with positive/negative IMF By accurately, while the equinoctial hypothesis cannot explain such difference at the spring and fall equinoxes. Thus, the R-M effect with positive/negative IMF polarity is more reasonable to explain seasonal and diurnal variation of geomagnetic activity under extreme solar wind conditions.

  1. Generalized Latency-Insensitive Systems for Single-Clock and Multi-Clock Architectures

    Microsoft Academic Search

    Montek Singh; Michael Theobald

    2004-01-01

    Latency-insensitive systems were recently proposed by Carloni et al. as a correct-by-construction methodology for single-clock system-on-a-chip (SoC) design using predesigned IP blocks. Their approach overcomes the problem of long latencies of global interconnects in deep-submicron technologies, while still maintaining much of the inherent simplicity of synchronous design. In particular, wires whose latency is greater than a clock cycle are segmented

  2. s-Wave collisional frequency shift of a fermion clock.

    PubMed

    Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M

    2013-04-19

    We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, ?(1). The fermion shift instead depends strongly on the second pulse area ?(2). It allows the shift to be canceled, nominally at ?(2)=?/2, but correlations perturb the null to slightly larger ?(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589

  3. Next Generation JPL Ultra-Stable Trapped Ion Atomic Clocks

    NASA Technical Reports Server (NTRS)

    Burt, Eric; Tucker, Blake; Larsen, Kameron; Hamell, Robert; Tjoelker, Robert

    2013-01-01

    Over the past decade, trapped ion atomic clock development at the Jet Propulsion Laboratory (JPL) has focused on two directions: 1) new atomic clock technology for space flight applications that require strict adherence to size, weight, and power requirements, and 2) ultra-stable atomic clocks, usually for terrestrial applications emphasizing ultimate performance. In this paper we present a new ultra-stable trapped ion clock designed, built, and tested in the second category. The first new standard, L10, will be delivered to the Naval Research Laboratory for use in characterizing DoD space clocks.

  4. Clock distribution and synchronization in large digital systems 

    E-print Network

    Hung, Tzu-Chien

    1991-01-01

    ). After the system is reset, the propagation delay on the path of faster clock is incrementally increased by enabling two PDEs at a time. This process will not stop until DFC (Delayed Fast Clock) is lagging DSC (Delayed Slotv Clock). The number... slow clock (DSC). It has the reset control input, DFC and DSC inputs, and a shift signal output. Whenever the DFC input signal is leading 10 Clock D Fig. 4. Structure of a Positive Edge Triggered D Flip-Flop the DSC input signal, the phase...

  5. Blackbody radiation shifts in optical atomic clocks.

    PubMed

    Safronova, Marianna; Kozlov, Mikhail; Clark, Charles

    2012-03-01

    A review of recent theoretical calculations of blackbody radiation (BBR) shifts in optical atomic clocks is presented. We summarize previous results for monovalent ions that were obtained by a relativistic all-order single-double method, where all single and double excitations of the Dirac- Fock wave function are included to all orders of perturbation theory. A recently developed method for accurate calculations of BBR shifts in divalent atoms is then presented. This approach combines the relativistic all-order method and the configuration interaction method, which provides for accurate treatment of correlation corrections in atoms with two valence electrons. Calculations of the BBR shifts in B+, Al+, and In+ have enabled us to reduce the present fractional uncertainties in the frequencies of their clock transitions as measured at room temperature: to 4 × 10-19 for Al+ and 10-18 for B+ and In+. These uncertainties approach recent estimates of the limits of precision of currently proposed optical atomic clocks. We discuss directions of future theoretical developments for reducing clock uncertainties resulting from blackbody radiation shifts. PMID:22481777

  6. Caesium atomic clocks: function, performance and applications

    Microsoft Academic Search

    Andreas Bauch

    2003-01-01

    For more than four decades, caesium atomic clocks have been the backbone in a variety of demanding applications in science and technology. Neither satellite based navigation systems, like the US Global Positioning System, nor the syntonization of telecommunication networks at the presently prescribed levels, would function without them. Recent years have brought major breakthroughs in the development, operation and mutual

  7. Testing General Relativity with Atomic Clocks

    E-print Network

    S. Reynaud; C. Salomon; P. Wolf

    2009-03-06

    We discuss perspectives for new tests of general relativity which are based on recent technological developments as well as new ideas. We focus our attention on tests performed with atomic clocks and do not repeat arguments present in the other contributions to the present volume. In particular, we present the scientific motivations of the space projects ACES and SAGAS.

  8. Distant clock synchronization using entangled photon pairs

    SciTech Connect

    Valencia, Alejandra; Scarcelli, Giuliano; Shih, Yanhua [Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250 (United States)

    2004-09-27

    We report a proof-of-principle experiment on distant clock synchronization. Besides the achievement of picosecond resolution at 3 km distance, this experiment demonstrated a concept for high-accuracy nonlocal timing and positioning based on the quantum feature of entangled states.

  9. Cleaning Three Clocks of Communicative Competence.

    ERIC Educational Resources Information Center

    Hopper, Robert

    It is suggested that the literature on communicative competence, replete with various formulations, mirrors the diversity of language outlined by Martin Joos in his essay "The Five Clocks." Three concepts of communicative competence are reviewed, in historical perspective. The first, promoted by Norm Chomsky, distinguished linguistic competence…

  10. Molecular Clocks: Determining the Age of

    E-print Network

    Seaman, Michael I.

    `molecular clock') allows for the estimation of the time of divergence between modern species, dependent acid ­ RNA and protein) of different species could be used to construct phylogenies of primates quantified and collected from numerous species, it was suggested that changes in proteins may be occurring

  11. U. S. and World Population Clocks

    NSDL National Science Digital Library

    These population clocks from the U.S. Census Bureau show population estimates for the United States and world. Estimates are projected to the current date and time; there are also component settings for U. S. population (one birth every X seconds, one death every X seconds), and monthly population figures for the world.

  12. Type I supernovae as cosmological clocks

    Microsoft Academic Search

    G. de Vaucouleurs; W. D. Pence

    1976-01-01

    The use of supernovae as cosmological clocks requires that proper allowance be made for absolute luminosity and color effects. The existence of two luminosity groups of Type I supernovae and, within each group, of a correlation between decay rate and absolute luminosity at maximum has been documented. It is shown that the proper form of the relationship is logarithmic, that

  13. European plans for new clocks in space

    NASA Astrophysics Data System (ADS)

    Leschiutta, Sigfrido M.; Tavella, Patrizia

    1995-05-01

    An outline of the future European space research program where precise clocks are necessary is presented, pointing out how space applications are posing impressive requirements as regards clock mass, power, ruggedness, long life, accuracy and, in some cases, spectral purity. The material presented was gathered in some laboratories; useful information was obtained from the Space Agencies of France (CNES), Germany (DARA) and Italy (ASI), but the bulk is coming from a recent exercise promoted inside ESA (the European Space Agency) and aimed to prefigure space research activities at the beginning of the next millennium. This exercise was called Horizon 2000 plus; the outcomings were summarized in two reports, presented by ESA in may 1994. Precise clocks and time measurements are needed not only for deep-space or out-ward space missions, but are essential tools also for Earth oriented activities. In this latter field, the European views and needs were discussed in October 1994, in a meeting organized by ESA and devoted to Earth Observation problems. By a scrutiny of these reports, an analysis was performed on the missions requiring a precise clock on board and the driving requirements were pointed out, leading to a survey of the necessary PTTI developments that, to some extent, are in the realm of possibility but that pose serious challenges. In this report the use of frequency standards in the satellite navigation systems is not considered.

  14. Compact microwave cavity for hydrogen atomic clock

    NASA Technical Reports Server (NTRS)

    Zhang, Dejun; Zhang, Yan; Fu, Yigen; Zhang, Yanjun

    1992-01-01

    A summary is presented that introduces the compact microwave cavity used in the hydrogen atomic clock. Special emphasis is placed on derivation of theoretical calculating equations of main parameters of the microwave cavity. A brief description is given of several methods for discriminating the oscillating modes. Experimental data and respective calculated values are also presented.

  15. Improved algorithms for synchronizing computer network clocks

    Microsoft Academic Search

    David L. Mills

    1994-01-01

    The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementations. Most of the estimated deployment of 100,000 NTP servers and clients

  16. Improved Algorithms for Synchronizing Computer Network Clocks

    Microsoft Academic Search

    David L. Mills

    1994-01-01

    The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementa- tions. Most of the estimated deployment of 100,000 NTP servers and

  17. Systems Biology of the Mammalian Circadian Clock

    E-print Network

    Spang, Rainer

    . Robust synchronization of 10000 cells in silico ­ an ensemble of driven damped oscillators 4. 2065 clock. The clockwork: running wheel, suprachiasmatic nucleus, molecular oscillations, feedback loops, output 2.g. Period2) positive elements activation nucleus SCN-neuron negative elements inhibition Oscillation

  18. Pleistocene Speciation and the Mitochondrial DNA Clock

    E-print Network

    Arbogast, Brian

    Pleistocene Speciation and the Mitochondrial DNA Clock John Klicka and Robert M. Zink (1) used whether Late Pleistocene ( 250,000 years ago) glaciations may have been an important mechanism in the Late Pliocene or Early Pleistocene, which would suggest that Pleistocene glaciation, in general, did

  19. COMBINATORIAL CLOCK AUCTION OF AIRPORT TIME SLOTS

    E-print Network

    Chen, Yiling

    COMBINATORIAL CLOCK AUCTION OF AIRPORT TIME SLOTS: AN AGENT-BASED ANALYSIS By Rui Dong SUBMITTED . . . . . . . . . . . . . . . . . . . . . . 8 2.2.1 Activity Rule . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.2.2 Monotonic : An Undersell Problem . . . . . . . . . . . . . . . 15 2.4.3 Example 3: Adding Budget Constraints

  20. Reliable Clock Synchronization for Electronic Documents

    Microsoft Academic Search

    S. Dias; Denise B. Demetrio; Ricardo F. Custodio; Carlos R. De Rolt

    Trusted time sources are required to insert time stamps in electronic documents. A signed and time stamped electronic document is equivalent to a traditional paper document and is legally recognized. Clock syn- chronization protocols of the sort provided by Network Time Protocol (NTP) do not satisfy all requirements to assure that a time source is trustworthy. This paper proposes the

  1. Neutralism and selectionism: the molecular clock

    Microsoft Academic Search

    Francisco J. Ayala

    2000-01-01

    The neutrality theory predicts that the rate of molecular evolution will be constant over time, and thus that there is a molecular clock for timing evolutionary events. It has been observed that the variance of the rate of evolution is generally larger than expected according to the neutrality theory. Several modifications of the theory have been proposed to account for

  2. type EMP is [ClockNo: INT;

    E-print Network

    Mannheim, Universität

    type EMP is [Clock­No: INT; Name: STRING; WorksIn: DEPT; Salary: INT; Office: OFFICE; Projects: f; implementation define skill is : : : !! vom Attribut JobHistory abgeleitet end type EMP; type DEPT is [Name MANAGER is supertype EMP is [Backup: EMP; Cars: fCARg;] end type MANAGER; type PROJECT is [Budget: INT; No

  3. Graph algorithms for clock schedule optimization

    Microsoft Academic Search

    Narendra V. Shenoy; Robert K. Brayton; Alberto L. Sangiovanni-Vincentelli

    1992-01-01

    Performance driven synthesis of sequential circuits relies on techniquessuch as optimal clocking, retiming and resynthesis. In this paper we address the optimal clockingproblem and demonstrate that it is reducible to a parametric shortest path problem. We use constraints that take into account both the short and long paths. The main contributions are efjicient graph algorithms to solve the set of

  4. Laser angle sensor development

    NASA Technical Reports Server (NTRS)

    Pond, C. R.; Texeira, P. D.

    1980-01-01

    Electrical and optical parameters were developed for a two axis (pitch/roll) laser angle sensor. The laser source and detector were mounted in the plenum above the model. Two axis optical distortion measurements of flow characteristics in a 0.3 transonic cryogenic tunnel were made with a shearing interferometer. The measurement results provide a basis for estimating the optical parameters of the laser angle sensor. Experimental and analytical information was generated on model windows to cover the reflector. A two axis breadboard was assembled to evaluate different measurement concepts. The measurement results were used to develop a preliminary design of a laser angle sensor. Schematics and expected performance specifications are included.

  5. Evolutionary relationships among barley and Arabidopsis core circadian clock and clock-associated genes.

    PubMed

    Calixto, Cristiane P G; Waugh, Robbie; Brown, John W S

    2015-02-01

    The circadian clock regulates a multitude of plant developmental and metabolic processes. In crop species, it contributes significantly to plant performance and productivity and to the adaptation and geographical range over which crops can be grown. To understand the clock in barley and how it relates to the components in the Arabidopsis thaliana clock, we have performed a systematic analysis of core circadian clock and clock-associated genes in barley, Arabidopsis and another eight species including tomato, potato, a range of monocotyledonous species and the moss, Physcomitrella patens. We have identified orthologues and paralogues of Arabidopsis genes which are conserved in all species, monocot/dicot differences, species-specific differences and variation in gene copy number (e.g. gene duplications among the various species). We propose that the common ancestor of barley and Arabidopsis had two-thirds of the key clock components identified in Arabidopsis prior to the separation of the monocot/dicot groups. After this separation, multiple independent gene duplication events took place in both monocot and dicot ancestors. PMID:25608480

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

    E-print Network

    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.

  7. Propagation of solar wind and IMF disturbances from L1 to Earth's bowshock: Data analysis and MHD modeling

    Microsoft Academic Search

    V. O. Papitashvili; K. Kabin; N. E. Papitashvili; J. H. King

    2007-01-01

    In recent years, significant progress has been achieved in understanding solar wind propagation from the Sun to the Earth's orbit and its interaction with the terrestrial magnetosphere by using global massively parallel MHD models with adaptive grids. However, most global magnetospheric models require knowledge of the solar wind parameters (speed, density, and IMF) at about 35 Re upstream from the

  8. Fluctuation spectroscopy with the ACS ramp filters: a new way to measure the IMF in elliptical galaxies

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter

    2014-10-01

    Images of old stellar populations show pixel-to-pixel fluctuations due to Poisson variations in the number of giant stars. These surface brightness fluctuations can be used to study the spectra of stars as a function of their luminosity, by obtaining differential spectroscopy of pixels with high and low fluctuations. If the average number of stars per pixel is sufficiently low, there will be individual pixels that have almost no light from luminous giants, providing sightlines that are dominated by main sequence stars. In this regime the observed spectral response is strongly dependent on the number of cool, low mass stars, and hence the stellar initial mass function (IMF). We propose to observe the nearest elliptical galaxy, Centaurus A, through four narrowband ACS ramp filters tuned to the 0.8 - 0.9 micron range. From the relation between ACS narrowband indices and the amplitude of the surface brightness fluctuation we will be able to obtain quantitative constraints on the IMF from 0.1-1 Solar masses, and distinguish between a Kroupa-like IMF or a bottom-heavy, Salpeter-like IMF, with ~5 sigma significance. We have demonstrated the feasibility of the technique used in this proposal in a Cycle 19 program, where we used the same observational strategy to measure the properties of luminous giants in the Virgo galaxy NGC 4472.

  9. The Low-Mass Stellar IMF at High Redshift: Faint Stars in the Ursa Minor Dwarf Spheroidal Galaxy

    E-print Network

    Rosemary F. G. Wyse; Gerard Gilmore; Sofia Feltzing; Mark Houdashelt

    1999-11-18

    Low-mass stars, those with main-sequence lifetimes that are of order the age of the Universe, provide unique constraints on the Initial Mass Function (IMF) when they formed. Star counts in systems with simple star-formation histories are particularly straightforward to interpret, and those in old systems allow one to determine the low-mass stellar IMF at large look-back times and thus at high redshift. We present the faint stellar luminosity function (based on optical HST data) in an external galaxy, the Ursa Minor dwarf Spheroidal (dSph). This relatively-nearby (distance 70kpc) companion galaxy to the Milky Way has a stellar population with narrow distributions of age and of metallicity, remarkably similar to that of a classical halo globular cluster such as M92 or M15, i.e. old and metal-poor. Contrasting with globular clusters, the internal velocity dispersion of the Ursa Minor dSph indicates the presence of significant amounts of dark matter. We find that the main sequence stellar luminosity function of the Ursa Minor dSph, and implied IMF, down to 0.4 of a solar mass is indistinguishable from that of the halo globular clusters M92 and M15. Thus the low mass stellar IMF for stars that formed at high redshift is invariant in going from a low-surface-brightness, dark-matter-dominated external galaxy, to a globular cluster within the Milky Way.

  10. Magnetosphere preconditioning under northward IMF: Evidence from the study of coronal mass ejection and corotating interaction region geoeffectiveness

    Microsoft Academic Search

    B. Lavraud; M. F. Thomsen; J. E. Borovsky; M. H. Denton; T. I. Pulkkinen

    2006-01-01

    Motivated by recent observations and simulations of the formation of a cold and dense plasma sheet in the tail of the magnetosphere under northward interplanetary magnetic field (IMF) and of the direct influence of the plasma sheet density on the ring current strength, this paper aims at (1) highlighting how the coupling of these effects may lead to a preconditioning

  11. Magnetosphere preconditioning under northward IMF: Evidence from the study of coronal mass ejection and corotating interaction region geoeffectiveness

    Microsoft Academic Search

    B. Lavraud; M. F. Thomsen; J. E. Borovsky; M. H. Denton; T. I. Pulkkinen

    2006-01-01

    (1) Motivated by recent observations and simulations of the formation of a cold and dense plasma sheet in the tail of the magnetosphere under northward interplanetary magnetic field (IMF) and of the direct influence of the plasma sheet density on the ring current strength, this paper aims at (1) highlighting how the coupling of these effects may lead to a

  12. Are the total mass density and the low-mass end slope of the IMF anti-correlated?

    E-print Network

    Spiniello, C; Koopmans, L V E; Trager, S C

    2015-01-01

    We conduct a detailed lensing, dynamics and stellar population analysis of nine massive lens early-type galaxies (ETGs) from the X-Shooter Lens Survey (XLENS). Combining gravitational lensing constraints from HST imaging with spatially-resolved kinematics and line-indices constraints from VLT X-Shooter (XSH) spectra, we infer the low-mass slope and the low cut-off mass of the stellar Initial Mass Function (IMF): $x_{250}=2.37^{+0.12}_{-0.12}$ and $M_{{\\rm low}, 250}= 0.131^{+0.023}_{-0.026}\\, M_{\\odot}$, respectively, for a reference point with $\\sigma \\equiv 250\\, {{\\rm kms}}^{-1}$ and R$_{{\\rm eff}} \\equiv 10$ kpc. All the XLENS systems are consistent with an IMF slope steeper than Milky Way-like. We find no significant correlations between IMF slope and any other quantity, except for an anti-correlation between total dynamical mass density and low-mass IMF slope at the 87% CL [$dx/d\\log(\\rho)$ = $ -0.19^{+0.15}_{-0.15}$]. This anti-correlation is consistent with the low redshift lenses found by Smith et al...

  13. The stellar IMF determined in early-type galaxies from a non-degenerate set of optical line indices

    E-print Network

    Spiniello, Chiara; Koopmans, Léon V E; Conroy, Charlie

    2013-01-01

    We investigate the optical spectral region of spectra of ~1000 stars searching for IMF-sensitive features to constrain the low-mass end of the initial mass function (IMF) slope in elliptical galaxies. We use the MILES stellar library in the wavelength range [3500-7500] A to select indices that are sensitive to cool dwarf stars and that only weakly depend on age and metallicity. We find several promising indices of molecular TiO and CaH lines. The use of these indicators bluer than NIR features (NaI, CaT, Wing-Ford FeH) is crucial if we want to compare our observations to optical simple stellar population models. In this wavelength range, the response of a change in the effective temperature of the cool red giant (RGB) population is similar to the response of a change in the number of dwarf stars in the galaxy. We show that it is possible to break the degeneracy between IMF variation and Teff,RGB with our new IMF indicators. We conclude that our new CaH1 index (6380A), the only indicator that comes purely from...

  14. Application of immersed MF (IMF) followed by reverse osmosis (RO) membrane for wastewater reclamation: A case study in Malaysia

    Microsoft Academic Search

    Z. Ujang; K. S. Ng; Tg Hazmin Tg Hamzah; P. Roger; M. R. Ismail; S. M. Shahabudin; M. H. Abdul Hamid

    2007-01-01

    A pilot scale membrane plant was constructed and monitored in Shah Alam, Malaysia for municipal wastewater reclamation for industrial application purposes. The aim of this study was to verify its suitability under the local conditions and environmental constraints for secondary wastewater reclamation. Immersed-type crossflow microfiltration (IMF) was selected as the pretreatment step before reverse osmosis filtration. Secondary wastewater after chlorine

  15. Determination of the IMF on the basis of a recently derived SFR history in the solar neighbourhood

    E-print Network

    Maciel, Walter Junqueira

    Determination of the IMF on the basis of a recently derived SFR history in the solar neighbourhood on the basis of a recently derived history of the star formation rate (SFR) which shows the presence of a star) constant SFR, and (ii) variable SFR as derived from the new metallicity distribution of G dwarfs

  16. First In-Situ Observation of Rolled-up Kelvin-Helmholtz Vortices under Southward IMF with Evidence of Reconnection

    NASA Astrophysics Data System (ADS)

    Goldstein, M. L.; Hwang, J.; Sahraoui, F.; Lee, E.; Parks, G. K.

    2009-12-01

    The Kelvin-Helmholtz instability (KHI) has been considered as one of the most dominant mechanisms by which the shocked solar wind enters the almost stagnant magnetosphere at the low-latitude magnetopause. The KHI can grow nonlinearly along the flank of the magnetopause to form large-scale rolled-up vortices. These rolled-up Kelvin-Helmholtz vortices (KHV) have thus far been detected only under northward interplanetary magnetic field (IMF) conditions. In this paper, we present first in-situ observation of rolled-up KHV during southward IMF conditions, using data from a Cluster crossing of the dawn-side flank of the magnetotail. The observation of a mixture of rolled-up and not rolled-up vortices that show inconsistent variations in the scale size, the magnetic perturbation, and the boundary normal direction indicates that KHV under southward IMF might have more temporal or intermittent nature, which might explain the preferential in-situ detection of KHV under northward IMF conditions. As a consequence of the KHV nonlinear growth, plasma transport and mixing are observed within or at the edge of KHV where a variety of magnetic topologies are found, possibly due to either diffusive transport via a turbulent decay of rolled-up KHV, or anti-parallel and/or guide-field reconnection

  17. Modeling the response of the induced magnetosphere of Venus to changing IMF direction using MESSENGER and Venus Express observations

    Microsoft Academic Search

    Mehdi Benna; Mario H. Acuña; Brian J. Anderson; Stanislav Barabash; Scott A. Boardsen; George Gloeckler; Robert E. Gold; George C. Ho; Haje Korth; Stamatios M. Krimigis; Ralph L. McNutt; Jim M. Raines; Menelaos Sarantos; James A. Slavin; Sean C. Solomon; Tielong L. Zhang; Thomas H. Zurbuchen

    2009-01-01

    The second MESSENGER flyby of Venus on 5 June 2007 provided a new opportunity to study the response of the induced magnetosphere of the planet to changes in the direction of the interplanetary magnetic field (IMF). At the time of the MESSENGER flyby, the European Space Agency's Venus Express spacecraft was located outside the magnetosphere and provided a monitor of

  18. Global Auroral Energy Deposition during Substorm Onset Compared with Local Time and Solar Wind IMF Conditions

    NASA Technical Reports Server (NTRS)

    Spann, J. F.; Brittnacher, M.; Fillingim, M. O.; Germany, G. A.; Parks, G. K.

    1998-01-01

    The global images made by the Ultraviolet Imager (UVI) aboard the IASTP/Polar Satellite are used to derive the global auroral energy deposited in the ionosphere resulting from electron precipitation. During a substorm onset, the energy deposited and its location in local time are compared to the solar wind IMF conditions. Previously, insitu measurements of low orbiting satellites have made precipitating particle measurements along the spacecraft track and global images of the auroral zone, without the ability to quantify energy parameters, have been available. However, usage of the high temporal, spatial, and spectral resolution of consecutive UVI images enables quantitative measurement of the energy deposited in the ionosphere not previously available on a global scale. Data over an extended period beginning in January 1997 will be presented.

  19. Around the Tarantula and into the Arches: A Salpeter IMF in the Field and in Clusters

    NASA Astrophysics Data System (ADS)

    Selman, F. J.; Espinoza, P.; Melnick, J.

    2011-06-01

    We propose that NGC 2070, the ionizing cluster of the Tarantula nebula, has the best determined stellar initial mass function (IMF), and that with a power-law slope at 2.17±0.05 it defines what we call Salpeter. The result of a Bayesian analysis of data for the field of the 30 Doradus super-association and for the Arches cluster near the galactic center, previously thought as counter-examples to the universality hypothesis, show that both of them are consitent with a Salpeter slope. We also show that there is no contradiction in principle to have the same stellar mass function in clusters and in the field population independently of what the cluster mass function is.

  20. Photoperiodic plasticity in circadian clock neurons in insects

    PubMed Central

    Shiga, Sakiko

    2013-01-01

    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. Photoperiod sets peaks of period (per) or timeless (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. PMID:23986711

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

    NASA Astrophysics Data System (ADS)

    Weinstein, Jonathan D.; Beloy, Kyle; Derevianko, Andrei

    2010-03-01

    A scheme is presented 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.

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

    NASA Astrophysics Data System (ADS)

    Weinstein, Jonathan D.; Beloy, Kyle; Derevianko, Andrei

    2010-03-01

    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.

  3. The IGIMF and other IMFs in dSphs: the case of Sagittarius

    NASA Astrophysics Data System (ADS)

    Vincenzo, F.; Matteucci, F.; Recchi, S.; Calura, F.; McWilliam, A.; Lanfranchi, G. A.

    2015-05-01

    We have studied the effects of various initial mass functions (IMFs) on the chemical evolution of the Sagittarius dwarf galaxy (Sgr). In particular, we tested the effects of the integrated galactic initial mass function (IGIMF) on various predicted abundance patterns. The IGIMF depends on the star formation rate and metallicity and predicts less massive stars in a regime of low star formation, as it is the case in dwarf spheroidals. We adopted a detailed chemical evolution model following the evolution of ?-elements, Fe and Eu, and assuming the currently best set of stellar yields. We also explored different yield prescriptions for the Eu, including production from neutron star mergers. Although the uncertainties still present in the stellar yields and data prevent us from drawing firm conclusions, our results suggest that the IGIMF applied to Sgr predicts lower [?/Fe] ratios than classical IMFs and lower [hydrostatic/explosive] ?-element ratios, in qualitative agreement with observations. In our model, the observed high [Eu/O] ratios in Sgr is due to reduced O production, resulting from the IGIMF mass cut-off of the massive oxygen-producing stars, as well as to the Eu yield produced in neutron star mergers, a more promising site than core-collapse supernovae, although many uncertainties are still present in the Eu nucleosynthesis. We find that a model, similar to our previous calculations, based on the late addition of iron from the Type Ia supernova time-delay (necessary to reproduce the shape of [X/Fe] versus [Fe/H] relations) but also including the reduction of massive stars due to the IGIMF, better reproduces the observed abundance ratios in Sgr than models without the IGIMF.

  4. Digital System Clocking:Digital System Clocking:Digital System Clocking: HighHigh--Performance and LowPerformance and Low--Power AspectsPower Aspects

    E-print Network

    California at Davis, University of

    ) Clk 3 4 k 2 1 #12;Nov. 14, 2003 Digital System Clocking: Oklobdzija, Stojanovic, Markovic, Nedovic 12 and Supercomputers System Intro Date Technology Class Nominal Clock Period (nS) Nominal Clock Frequency (MHz) Cray-X-MP Cray-1S,-1M CDC Cyber 180/990 IBM 3090 Amdahl 58 IBM 308X Univac 1100/90 MIPS-X HP-900 Motorola 68020

  5. Correlation of core field polarity of magnetotail flux ropes with the IMF By: Reconnection guide field dependency

    NASA Astrophysics Data System (ADS)

    Teh, W.-L.; Nakamura, R.; Karimabadi, H.; Baumjohann, W.; Zhang, T. L.

    2014-04-01

    The relationship between the core field and the interplanetary magnetic field (IMF) By has been addressed by spacecraft observations in the magnetotail, but it is not yet fully clear since observations by Slavin et al. (2003) and Borg et al. (2012) show controversial results. In this study, we examine 13 flux ropes from the Cluster observations to show for the first time that the correlation between the core field Bcore and the IMF By depends on the guide field Bg. For large guide fields (> 20% of the reconnecting field), we show that the Bcore is found to correlate with the IMF By. However, for weak guide fields (< 10% of the reconnecting field) we show that the core fields have either a positive or negative polarity, irrespective of the IMF By. This result indicates that for weak guide field reconnection the core field generation of the magnetotail flux rope is not governed by the external IMF By. We can explain the previous controversy in terms of the guide field dependency. We also confirm earlier suggestions that for weak guide field reconnection the flux ropes can have a significant core field whose polarity agrees with the ambient quadrupole Hall field. In addition, the Grad-Shafranov reconstruction results suggest that the axis of the flux rope may have been kinked. Our findings are crucial and can help advance theoretical simulations of the core field generation for weak guide reconnection. Discussions of the possible core field generation for weak guide field will be given in terms of 3-D reconnection.

  6. 'Magic Angle Precession'

    SciTech Connect

    Binder, Bernd [Quanics.com, Germany, 88679 Salem, P.O. Box 1247 (United States)], E-mail: binder@quanics.com

    2008-01-21

    An advanced and exact geometric description of nonlinear precession dynamics modeling very accurately natural and artificial couplings showing Lorentz symmetry is derived. In the linear description it is usually ignored that the geometric phase of relativistic motion couples back to the orbital motion providing for a non-linear recursive precession dynamics. The high coupling strength in the nonlinear case is found to be a gravitomagnetic charge proportional to the precession angle and angular velocity generated by geometric phases, which are induced by high-speed relativistic rotations and are relevant to propulsion technologies but also to basic interactions. In the quantum range some magic precession angles indicating strong coupling in a phase-locked chaotic system are identified, emerging from a discrete time dynamical system known as the cosine map showing bifurcations at special precession angles relevant to heavy nuclei stability. The 'Magic Angle Precession' (MAP) dynamics can be simulated and visualized by cones rolling in or on each other, where the apex and precession angles are indexed by spin, charge or precession quantum numbers, and corresponding magic angles. The most extreme relativistic warping and twisting effect is given by the Dirac spinor half spin constellation with 'Hyperdiamond' MAP, which resembles quark confinement.

  7. Strong longitudinal difference in ionospheric responses over Fortaleza (Brazil) and Jicamarca (Peru) during the January 2005 magnetic storm, dominated by northward IMF

    NASA Astrophysics Data System (ADS)

    Santos, A. M.; Abdu, M. A.; Sobral, J. H. A.; Koga, D.; Nogueira, P. A. B.; Candido, C. M. N.

    2012-08-01

    In this study we investigate the response of the equatorial F layer to disturbance zonal electric field associated with IMF (interplanetary magnetic field) variations dominated by a strong northward Bz episode during the magnetic storm that occurred on 21 January, 2005. We compared the results obtained from Digisondes operated at Fortaleza, Brazil (Geogr. 3.9°S, 38.45°W; dip angle: -11.7°) and Jicamarca, Peru (Geogr. 12.0°S, 76.8°W; dip angle: 0.64°). A large auroral activity (AE) intensification that occurred at ˜1715 UT produced a large F-layer peak height increase (from 300 km to 600 km) over Jicamarca with no noticeable simultaneous effect over Fortaleza. Then the Bz turning northward at ˜1940 UT with a rapid change in AE that was accompanied by a large decrease of F layer height and total suppression of the PRE over Fortaleza with no simultaneous effect over Jicamarca. Strong increase in the AE index (from ˜400 to 1000 nT) with superimposed oscillations, under Bz North, that soon followed was associated with increases in both the F layer height and the vertical drift velocity over Fortaleza (at 2130 UT), with no corresponding signatures over Jicamarca. These remarkable contrasting responses to prompt penetration electric field (PPEF) as well as to disturbance wind dynamo electric field (DDEF) and other effects observed at the two locations separated only by 2 h in LT in the South American sector are presented and discussed in this paper. Effects onspread-F development and foF2 behavior during this storm event are also addressed in this work.

  8. Tissue-specific clocks in Arabidopsis show asymmetric coupling

    PubMed Central

    Endo, Motomu; Shimizu, Hanako; Nohales, Maria A.; Araki, Takashi; Kay, Steve A.

    2014-01-01

    Many organisms rely on a circadian clock system to adapt to daily and seasonal environmental changes. The mammalian circadian clock consists of a central clock in the suprachiasmatic nucleus that is tightly coupled and synchronizes other clocks in peripheral tissues1, 2. Plants also have a circadian clock, but plant circadian clock function has long been assumed to be uncoupled3. Only a few studies have been able to show a weak, local coupling among cells4, 5, 6, 7. Here, by implementing two novel techniques, we have performed a comprehensive tissue-specific analysis of leaf tissues, and we have discovered that the vasculature and mesophyll clocks asymmetrically regulate each other in Arabidopsis. The circadian clock in the vasculature has characteristics distinct from other tissues, cycles robustly without environmental cues, and affects circadian clock regulation in other tissues. Furthermore, we found that vasculature-enriched genes that are rhythmic are preferentially expressed in the evening, whereas rhythmic mesophyll-enriched genes tend to be expressed in the morning. Our results set the stage for a deeper understanding of how the vasculature circadian clock in plants regulates key physiological responses such as flowering time. PMID:25363766

  9. Transcriptional feedback loops in the ovine circadian clock.

    PubMed

    Dardente, Hugues; Fustin, Jean-Michel; Hazlerigg, David G

    2009-08-01

    In mammals circadian time measurement depends on interlocked feedback loops involving clock genes and their protein products. The model of the mammalian circadian clock mostly rests on findings in the mouse. In comparison, little information is available in diurnal non-rodent species. In this respect, the sheep constitutes an excellent animal model. We cloned ovine clock components and proximal gene promoters and tested in-vitro, in NIH3T3 and COS7 cells, salient molecular characteristics of the circadian clock. We show that transcriptional features of the ovine circadian clock recapitulate those described for the mouse. These include (1) coordinated phasing of expression of Rev-erb alpha, Per1, Cry1 and Bmal1 as assessed by real-time luciferase assays, (2) CLOCK/BMAL1 transactivation at the Per1 and Rev-erb alpha promoters, (3) repression of CLOCK/BMAL1 by CRY1-2 and CIPC, (4) a role for REV-ERB alpha in inhibiting Bmal1 and Rev-erb alpha transcription. DEC1 has bidirectional transcriptional effects, repressor or activator, according to the promoter. We further show that some phosphorylation events affecting clock proteins appear conserved within the ovine clock. Taken together, these data are consistent with a broad conservation of transcriptional and post-translational mechanisms in the circadian clock of diurnal and nocturnal mammals. PMID:19341811

  10. Deterministic and Stochastic Receiver Clock Modeling in Precise Point Positioning

    NASA Astrophysics Data System (ADS)

    Orliac, E.; Dach, R.; Wang, K.; Rothacher, M.; Voithenleitner, D.; Hugentobler, U.; Heinze, M.; Svehla, D.

    2012-04-01

    The traditional GNSS (Global Navigation Satellite System) data analysis assumes an independent set of clock corrections for each epoch. This introduces a huge number of parameters that are highly correlated with station height and troposphere parameters. If the number of clock parameters can be reduced, the GNSS processing procedure may be stabilized. Experiments with kinematic solutions for stations equipped with H-Maser clocks have confirmed this. On the other hand, static coordinates do not significantly benefit from changing the strategy in handling the clock parameter. In the current GNSS constellation only GIOVE-B and the GPS Block IIF satellite clocks seem to be good enough to be modeled instead of freely estimated for each epoch without losing accuracy at the level of phase measurements. With the Galileo constellation this will change in future. In this context, ESA (European Space Agency) funded a project on "Satellite and Station Clock Modelling for GNSS". In the frame of this project, various deterministic and stochastic clock models have been evaluated, implemented and assessed for both, station and satellite clocks. In this paper we focus on the impact of modeling the receiver clock in the processing of GNSS data in static and kinematic precise point positioning (PPP) modes. Initial results show that for stations connected to an H-Maser clock the stability of the vertical position for kinematic PPP could be improved by up to 60%. The impact of clock modeling on the estimation of troposphere parameters is also investigated, along with the role of the tropospheric modeling itself, by testing various sampling rates and relative constraints for the troposphere parameters. Finally, we investigate the convergence time of PPP when deterministic or stochastic clock modeling is applied to the receiver clock.

  11. Cold Atoms and Stable Lasers: The Clocks of the Future Today

    E-print Network

    Van Stryland, Eric

    Cold Atoms and Stable Lasers: The Clocks of the Future Today Leo Hollberg National Institute laser and length metrology Richard Fox #12;Types of Clocks Ruler Clock Decay Stable Oscillator Atomic 158 Counter Generic Atomic Clock Atoms #12;Atomic Beam Clock Ramsey Method Cs Signal # of Atoms d

  12. Circadian Clocks in Antennal Neurons Are Necessary and Sufficient for Olfaction Rhythms in Drosophila

    Microsoft Academic Search

    Shintaro Tanoue; Parthasarathy Krishnan; Balaji Krishnan; Stuart E Dryer; Paul E Hardin

    2004-01-01

    Background: The Drosophila circadian clock is controlled by interlocked transcriptional feedback loops that operate in many neuronal and nonneuronal tissues. These clocks are roughly divided into a central clock, which resides in the brain and is known to control rhythms in locomotor activity, and peripheral clocks, which comprise all other clock tissues and are thought to control other rhythmic outputs.

  13. Dynamic drift compensation for the Distributed clock in EtherCAT

    Microsoft Academic Search

    Jae Chol Lee; Seong Jin Cho; Yong Han Jeon; Jae Wook Jeon

    2009-01-01

    This paper focuses on the synchronization between master clock and slave clock in the Distributed clock of EtherCAT. It supports very accurate synchronization function which let local slaves follow reference time under the degree of few nano second differences. However, there exists the propagation delay between reference clock and slave clock. To remove the delay, EtherCAT uses the static compensation

  14. Sagnac interferometry with a single atomic clock

    E-print Network

    R. Stevenson; M. Hush; T. Bishop; I. Lesanovsky; T. Fernholz

    2015-04-21

    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.

  15. Sagnac interferometry with a single atomic clock

    E-print Network

    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.

  16. Optimal Implementations for Reliable Circadian Clocks

    NASA Astrophysics Data System (ADS)

    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.

  17. Circadian clocks, feeding time, and metabolic homeostasis

    PubMed Central

    Paschos, Georgios K.

    2015-01-01

    Metabolic processes exhibit diurnal variation from cyanobacteria to humans. The circadian clock is thought to have evolved as a time keeping system for the cell to optimize the timing of metabolic events according to physiological needs and environmental conditions. Circadian rhythms temporally separate incompatible cellular processes and optimize cellular and organismal fitness. A modern 24 h lifestyle can run at odds with the circadian rhythm dictated by our molecular clocks and create desynchrony between internal and external timing. It has been suggested that this desynchrony compromises metabolic homeostasis and may promote the development of obesity (Morris et al., 2012). Here we review the evidence supporting the association between circadian misalignment and metabolic homeostasis and discuss the role of feeding time.

  18. Metabolism and the circadian clock converge.

    PubMed

    Eckel-Mahan, Kristin; Sassone-Corsi, Paolo

    2013-01-01

    Circadian rhythms occur in almost all species and control vital aspects of our physiology, from sleeping and waking to neurotransmitter secretion and cellular metabolism. Epidemiological studies from recent decades have supported a unique role for circadian rhythm in metabolism. As evidenced by individuals working night or rotating shifts, but also by rodent models of circadian arrhythmia, disruption of the circadian cycle is strongly associated with metabolic imbalance. Some genetically engineered mouse models of circadian rhythmicity are obese and show hallmark signs of the metabolic syndrome. Whether these phenotypes are due to the loss of distinct circadian clock genes within a specific tissue versus the disruption of rhythmic physiological activities (such as eating and sleeping) remains a cynosure within the fields of chronobiology and metabolism. Becoming more apparent is that from metabolites to transcription factors, the circadian clock interfaces with metabolism in numerous ways that are essential for maintaining metabolic homeostasis. PMID:23303907

  19. An Iodine Fluorescence Quenching Clock Reaction

    NASA Astrophysics Data System (ADS)

    Weinberg, Richard B.

    2007-05-01

    A fluorescent clock reaction is described that is based on the principles of the Landolt iodine reaction but uses the potent fluorescence quenching properties of triiodide to abruptly extinguish the ultraviolet fluorescence of optical brighteners present in liquid laundry detergents. The reaction uses easily obtained household products. One variation illustrates the sequential steps and mechanisms of the reaction; other variations maximize the dramatic impact of the demonstration; and a variation that uses liquid detergent in the Briggs Rauscher reaction yields a striking oscillating luminescence. The iodine fluorescence quenching clock reaction can be used in the classroom to explore not only the principles of redox chemistry and reaction kinetics, but also the photophysics of fluorescent pH probes and optical quenching.

  20. Molecular clock on a neutral network.

    PubMed

    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. PMID:17930643

  1. Optimal implementations for reliable circadian clocks.

    PubMed

    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. PMID:25238386

  2. Clock-driven quantum thermal engines

    NASA Astrophysics Data System (ADS)

    Malabarba, Artur S. L.; Short, Anthony J.; Kammerlander, Philipp

    2015-04-01

    We consider an isolated autonomous quantum machine, where an explicit quantum clock is responsible for performing all transformations on an arbitrary quantum system (the engine), via a time-independent Hamiltonian. In a general context, we show that this model can exactly implement any energy-conserving unitary on the engine, without degrading the clock. Furthermore, we show that when the engine includes a quantum work storage device we can approximately perform completely general unitaries on the remainder of the engine. This framework can be used in quantum thermodynamics to carry out arbitrary transformations of a system, with accuracy and extracted work as close to optimal as desired, while obeying the first and second laws of thermodynamics. We thus show that autonomous thermal machines suffer no intrinsic thermodynamic cost compared to externally controlled ones.

  3. The suprachiasmatic nuclei as a seasonal clock.

    PubMed

    Coomans, Claudia P; Ramkisoensing, Ashna; Meijer, Johanna H

    2015-04-01

    In mammals, the suprachiasmatic nucleus (SCN) contains a central clock that synchronizes daily (i.e., 24-h) rhythms in physiology and behavior. SCN neurons are cell-autonomous oscillators that act synchronously to produce a coherent circadian rhythm. In addition, the SCN helps regulate seasonal rhythmicity. Photic information is perceived by the SCN and transmitted to the pineal gland, where it regulates melatonin production. Within the SCN, adaptations to changing photoperiod are reflected in changes in neurotransmitters and clock gene expression, resulting in waveform changes in rhythmic electrical activity, a major output of the SCN. Efferent pathways regulate the seasonal timing of breeding and hibernation. In humans, seasonal physiology and behavioral rhythms are also present, and the human SCN has seasonally rhythmic neurotransmitter levels and morphology. In summary, the SCN perceives and encodes changes in day length and drives seasonal changes in downstream pathways and structures in order to adapt to the changing seasons. PMID:25451984

  4. What Is the Angle?

    NSDL National Science Digital Library

    This activity will help students understand how the angle of the Sun affects temperatures around the globe. After experimenting with a heat lamp and thermometers at differing angles, students apply what they learned to explain temperature variations on Earth. The printable six-page handout includes a series of inquiry-based questions to get students thinking about what they already know about temperature patterns, detailed experiment directions, and a worksheet that will help students use the experiment results to gain a deeper understanding of seasonal temperature changes and why Antarctica is always so cold. The students will explore all the angles of sunlight with a few thermometers and a heat lamp and understand why there is such a dramatic temperature change between the equator and the South Pole.

  5. A Manufacturable Chip-Scale Atomic Clock

    Microsoft Academic Search

    D. W. Youngner; L. Lust; D. R. Carlson; S. T. Lu; L. J. Forner; H. M. Chanhvongsak; T. D. Stark

    2007-01-01

    Several factors are converging to enable atomic clocks to be manufactured with very small dimensions and run at low operating power. MOEMS technology, high-speed vcsels, microelectronics, wafer-scale packaging, and the all-optical CPT method of exciting atomic transitions are key ingredients in the quest to make precision time-keeping devices with chip-scale dimensions. In this paper we report on the design and

  6. Intense, Narrow Atomic-Clock Resonances

    Microsoft Academic Search

    Y.-Y. Jau; A. B. Post; N. N. Kuzma; A. M. Braun; M. V. Romalis; W. Happer

    2004-01-01

    We present experimental and theoretical results showing that magnetic resonance transitions from the ``end'' sublevels of maximum or minimum spin in alkali-metal vapors are a promising alternative to the conventional 0-0 transition for small-size gas-cell atomic clocks. For these ``end resonances,'' collisional spin-exchange broadening, which often dominates the linewidth of the 0-0 resonance, decreases with increasing spin polarization and vanishes

  7. The Circadian Clock, Reward, and Memory

    PubMed Central

    Albrecht, Urs

    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. PMID:22084628

  8. Optical clock signal distribution and packaging optimization

    Microsoft Academic Search

    Linghui Wu

    2002-01-01

    Polymer-based waveguides for optoelectronic interconnects and packagings were fabricated by a fabrication process that is compatible with the Si CMOS packaging process. An optoelectronic interconnection layer (OIL) for the high-speed massive clock signal distribution for the Cray T-90 supercomputer board employing optical multimode channel waveguides in conjunction with surface-normal waveguide grating couplers and a 1-to-2 3 dB splitter was constructed.

  9. The Tick Tock of the Tenure Clock

    E-print Network

    Jean, Vanessa A.

    2014-12-05

    stigma 12 (Williams, 2000) than a faculty member who stays on the traditional tenure track time schedule. Together, these theories and empirical evidence suggest that women who extend the tenure clock will have worse outcomes than men who extend... & Mescher, 2013; Vandello, Hettinger, Bosson, & Siddiqi, 2013), 13 which is thought to be inferior to masculine. This stigma, referred to as femininity stigma, is experienced by men who request family leave which has been found to predict less rewards (i...

  10. Maternal Feeding Controls Fetal Biological Clock

    Microsoft Academic Search

    Hidenobu Ohta; Shanhai Xu; Takahiro Moriya; Masayuki Iigo; Tatsuya Watanabe; Norimichi Nakahata; Hiroshi Chisaka; Takushi Hanita; Tadashi Matsuda; Toshihiro Ohura; Yoshitaka Kimura; Nobuo Yaegashi; Shigeru Tsuchiya; Hajime Tei; Kunihiro Okamura; Naomi Rogers

    2008-01-01

    BackgroundIt 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 FindingsTo 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

  11. Radioisotope Decay Rate Based Counting Clock

    Microsoft Academic Search

    Rajesh Duggirala; Amit Lal; Shankar Radhakrishnan

    \\u000a Precise timing and frequency sources are vital in a wide range electronic-based systems such as communication networks and\\u000a global positioning systems. These applications constantly demand reductions in size, weight and power (SWaP) while improving\\u000a the precision of time or frequency references. Historically, clocks based on electromagnetic oscillations of atoms have provided\\u000a the most precise method of timing events lasting longer

  12. What's the Angle?

    NSDL National Science Digital Library

    American Museum of Natural History

    2002-01-01

    This activity helps learners understand how the angle of the Sun affects temperatures around the globe. After experimenting with a heat lamp and thermometers at differing angles, learners apply what they learned to explain temperature variations on Earth. The printable six-page handout includes a series of inquiry-based questions to get learners thinking about what they already know about temperature patterns, detailed experiment directions, and a worksheet that helps learners use the experiment results to gain a deeper understanding of seasonal temperature changes and why Antarctica is always cold.

  13. Atomic clocks with suppressed blackbody radiation shift.

    PubMed

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

    2011-07-15

    We develop a concept of atomic clocks where the blackbody radiation shift and its fluctuations can be suppressed by 1-3 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 ?1 and ?2) which are exposed to the same thermal environment, there exists a "synthetic" frequency ?(syn) ? (?1 - ?12?2) largely immune to the blackbody radiation shift. For example, in the case of 171Yb+ it is possible to create a synthetic-frequency-based clock in which the fractional blackbody radiation shift can be suppressed to the level of 10(-18) in a broad interval near room temperature (300±15??K). We also propose a realization of our method with the use of an optical frequency comb generator stabilized to both frequencies ?1 and ?2, where the frequency ?(syn) is generated as one of the components of the comb spectrum. PMID:21838344

  14. Clock distribution system for digital computers

    DOEpatents

    Wyman, Robert H. (Brentwood, CA); Loomis, Jr., Herschel H. (Davis, CA)

    1981-01-01

    Apparatus for eliminating, in each clock distribution amplifier of a clock distribution system, sequential pulse catch-up error due to one pulse "overtaking" a prior clock pulse. The apparatus includes timing means to produce a periodic electromagnetic signal with a fundamental frequency having a fundamental frequency component V'.sub.01 (t); an array of N signal characteristic detector means, with detector means No. 1 receiving the timing means signal and producing a change-of-state signal V.sub.1 (t) in response to receipt of a signal above a predetermined threshold; N substantially identical filter means, one filter means being operatively associated with each detector means, for receiving the change-of-state signal V.sub.n (t) and producing a modified change-of-state signal V'.sub.n (t) (n=1, . . . , N) having a fundamental frequency component that is substantially proportional to V'.sub.01 (t-.theta..sub.n (t) with a cumulative phase shift .theta..sub.n (t) having a time derivative that may be made uniformly and arbitrarily small; and with the detector means n+1 (1.ltoreq.n

  15. Clock genes: their role in colorectal cancer.

    PubMed

    Karantanos, Theodoros; Theodoropoulos, George; Pektasides, Dimitrios; Gazouli, Maria

    2014-02-28

    Clock genes create a complicated molecular time-keeping system consisting of multiple positive and negative feedback loops at transcriptional and translational levels. This circadian system coordinates and regulates multiple cellular procedures implicated in cancer development such as metabolism, cell cycle and DNA damage response. Recent data support that molecules such as CLOCK1, BMAL1 and PER and CRY proteins have various effects on c-Myc/p21 and Wnt/?-catenin pathways and influence multiple steps of DNA damage response playing a critical role in the preservation of genomic integrity in normal and cancer cells. Notably, all these events have already been related to the development and progression of colorectal cancer (CRC). Recent data highlight critical correlations between clock genes' expression and pathogenesis, progression, aggressiveness and prognosis of CRC. Increased expression of positive regulators of this circadian system such as BMAL1 has been related to decrease overall survival while decreased expression of negative regulators such as PER2 and PER3 is connected with poorer differentiation, increased aggressiveness and worse prognosis. The implications of these molecules in DNA repair systems explain their involvement in the development of CRC but at the same time provide us with novel targets for modern therapeutic approaches for patients with advanced CRC. PMID:24587674

  16. Fractional Brownian sheets run with nonlinear clocks

    NASA Astrophysics Data System (ADS)

    Wu, Dongsheng

    2012-01-01

    Let X=lbrace X(t), tin {R}_+^Nrbrace be an (N, d)-fractional Brownian sheet run with nonlinear clocks, that is, X(t) = BH(F1(t1), …, FN(tN)) for all t=(t_1,ldots,t_N)in {R}_+^N, where BH is an (N, d)-fractional Brownian sheet with Hurst indices H = (H1, …, HN) ? (0, 1)N, and where F_i: {R}_+rArr {R}_+ (i = 1, …, N) are N non-negative nondecreasing functions that satisfy bi-Lipschitz conditions. In this paper, we study sample path properties of fractional Brownian sheet run with nonlinear clocks X. We first derive a sharp modulus of continuity for X, and then determine the Hausdorff and packing dimensions of the range X([0, 1]N), the graph GrX([0, 1]N), and the level sets for the X. We also provide necessary and sufficient conditions for the existence of local times of X and investigate the joint continuity of the local times. Finally, we study the intersection behavior of two independent fractional Brownian sheets run with (possibly different) nonlinear clocks.

  17. The Effects of Clock Drift on the Mars Exploration Rovers

    NASA Technical Reports Server (NTRS)

    Ali, Khaled S.; Vanelli, C. Anthony

    2012-01-01

    All clocks drift by some amount, and the mission clock on the Mars Exploration Rovers (MER) is no exception. The mission clock on both MER rovers drifted significantly since the rovers were launched, and it is still drifting on the Opportunity rover. The drift rate is temperature dependent. Clock drift causes problems for onboard behaviors and spacecraft operations, such as attitude estimation, driving, operation of the robotic arm, pointing for imaging, power analysis, and telecom analysis. The MER operations team has techniques to deal with some of these problems. There are a few techniques for reducing and eliminating the clock drift, but each has drawbacks. This paper presents an explanation of what is meant by clock drift on the rovers, its relationship to temperature, how we measure it, what problems it causes, how we deal with those problems, and techniques for reducing the drift.

  18. Laser clocks and near field gravity of rotating objects

    NASA Technical Reports Server (NTRS)

    Hafele, Joseph C.

    1988-01-01

    This work explores the feasibliity of using high performance laser clocks to detect effects of rotation in the near field region of the Earth's gravitational field. According to general relativity, the time recorded by an independent clock is the proper time of the space-time metric that applies to the system under consideration. If the gravitational source is stationary (nonrotating), proper time involves only the speed of the clocks and the scalar gravitational potential at the position of the clocks. However, if the source is rotating, the motion of the source could have an effect on the metric. Previous attempts to calculate the relativistic timekeeping for terrestrial clocks have used the metric for a nonrotating system, primarily because metrics for a rotating system were not available. This work investigates the specific effects of rotation on the Earth's gravitational field and the corresponding effect on timekeeping of laser clocks in the near field environment.

  19. A LED driver based on the data clock regeneration design

    NASA Astrophysics Data System (ADS)

    Que, Longcheng; Du, Yiying; Zhou, Yun; Lv, Jian; Jiang, Yadong

    2012-10-01

    Recent years witnessed that LEDs have been widely used in many consumer electronics and other areas. However, many applications require a large number of LED cascade drives. When LED driver IC drives cascaded LEDs, the cascade length is often limited because of the insufficient drive capability of the data clock. Once the technology of data clock regeneration is applied in LED driver chip, Signal drive capability is effectively enhanced by the data clock regeneration, thus the cascade length is greatly increased. After the algorithm of data clock regeneration is verified in Quartus II, the circuit and layout of LED driver are designed in Cadence using this technology. In product test, LED driver based on the data clock regeneration drives more than 2,000 points cascaded LEDs at 25 MHz clock. LED drivers with this technique are suitable for a variety of large-scale cascaded LEDs.

  20. Histone lysine demethylase JARID1a activates CLOCK-BMAL1 and influences the circadian clock.

    PubMed

    DiTacchio, Luciano; Le, Hiep D; Vollmers, Christopher; Hatori, Megumi; Witcher, Michael; Secombe, Julie; Panda, Satchidananda

    2011-09-30

    In animals, circadian oscillators are based on a transcription-translation circuit that revolves around the transcription factors CLOCK and BMAL1. We found that the JumonjiC (JmjC) and ARID domain-containing histone lysine demethylase 1a (JARID1a) formed a complex with CLOCK-BMAL1, which was recruited to the Per2 promoter. JARID1a increased histone acetylation by inhibiting histone deacetylase 1 function and enhanced transcription by CLOCK-BMAL1 in a demethylase-independent manner. Depletion of JARID1a in mammalian cells reduced Per promoter histone acetylation, dampened expression of canonical circadian genes, and shortened the period of circadian rhythms. Drosophila lines with reduced expression of the Jarid1a homolog, lid, had lowered Per expression and similarly altered circadian rhythms. JARID1a thus has a nonredundant role in circadian oscillator function. PMID:21960634

  1. Strategies for reducing the light shift in atomic clocks

    NASA Astrophysics Data System (ADS)

    Katori, Hidetoshi; Ovsiannikov, V. D.; Marmo, S. I.; Palchikov, V. G.

    2015-05-01

    Recent progress in optical lattice clocks requires unprecedented precision in controlling systematic uncertainties at the 10-18 level. Tuning of nonlinear light shifts is shown to reduce lattice-induced clock shift for a wide range of lattice intensity. Based on theoretical multipolar, nonlinear, anharmonic, and higher-order light shifts, we numerically demonstrate possible strategies for Sr, Yb, and Hg clocks to achieve lattice-induced systematic uncertainty below 1 ×10-18 .

  2. Self-tested self-synchronization circuit for mesochronous clocking

    Microsoft Academic Search

    Fenghao Mu; Christer Svensson

    2001-01-01

    In large-scale and high-speed systems, global synchronization has been commonly used to protect clocked I\\/O from data read failure caused by metastability. There are many drawbacks with global synchronization, which will approach its physical limit in the future as system clock frequency and system scale increase simultaneously. Mesochronous clocking overcomes these drawbacks, but without a proper delay or phase control,

  3. Optimizing Two-Phase, Level-Clocked Circuitry

    Microsoft Academic Search

    1992-01-01

    )Alexander T. IshiiNEC C&C Research LaboratoriesPrinceton, New Jersey 08540Charles E. LeisersonMarios C. PapaefthymiouMIT Laboratory for Computer ScienceCambridge, Massachusetts 02139AbstractWe investigate two strategies for reducing the clock period of a two-phase, levelclockedcircuit: clock tuning, which adjusts the waveforms that clock the circuit,and retiming, which relocates circuit latches. These methods can be used to converta circuit with edge-triggered latches into a...

  4. Optimizing two-phase, level-clocked circuitry

    Microsoft Academic Search

    Alexander T. Ishii; Charles E. Leiserson; Marios C. Papaefthymiou

    1997-01-01

    We investigate two strategies for reducing the clock period of a two-phase, level-clocked circuit: clocktuning, which adjusts the waveforms that clock the circuit, and retiming, which relocates circuit latches.These methods can be used to convert a circuit with edge-triggered latches into a faster level-clockedone.We model a two-phase circuit as a graph G = (V; E) whose vertex set V is

  5. Daily coordination of cancer growth and circadian clock gene expression

    Microsoft Academic Search

    Shaojin You; Patricia A. Wood; Yin Xiong; Minoru Kobayashi; Jovelyn Du-Quiton; William J. M. Hrushesky

    2005-01-01

    Background.Circadian coordination in mammals is accomplished, in part, by coordinate, rhythmic expression of a series of circadian clock genes in the central clock within the suprachiasmatic nuclei (SCN) of the hypothalamus. These same genes are also rhythmically expressed each day within each peripheral tissue.Methods.We measured tumor size, tumor cell cyclin E protein, tumor cell mitotic index, and circadian clock gene

  6. Higher Pole Linear Traps for Atomic Clock Applications

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    We investigate experimentally and theoretically higher pole linear ion traps for frequency standard use. We have built a 12-pole trap and have successfully loaded ions into it from a linear quadrupole trap. By solving the Boltzmann equation describing large ion clouds where space charge interactions are important, we show that clock frequency changes due to ion number fluctuations are much smaller in ion clocks based multipole traps than comparable clocks based on quadrupole linear traps.

  7. A Novel Photonic Clock and Carrier Recovery Device

    NASA Technical Reports Server (NTRS)

    Yao, X. Steve; Lutes, George; Maleki, Lute

    1996-01-01

    As data communication rates climb toward ten Gb/s, clock recovery and synchronization become more difficult, if not impossible, using conventional electronic circuits. We present in this article experimental results of a high speed clock and carrier recovery using a novel device called a photonic oscillator that we recently developed in our laboratory. This device is capable of recovering clock signals up to 70 GHz. To recover the clock, the incoming data is injected into the photonic oscillator either through the optical injection port or the electrical injection port. The free running photonic oscillator is tuned to oscillate at a nominal frequency equal to the clock frequency of the incoming data. With the injection of the data, the photonic oscillator will be quickly locked to clock frequency of the data stream while rejecting other frequency components associated with the data. Consequently, the output of the locked photonic oscillator is a continuous periodical wave synchronized with the incoming data or simply the recovered clock. We have demonstrated a clock to spur ratio of more than 60 dB of the recovered clock using this technique. Similar to the clock recovery, the photonic oscillator can be used to recover a high frequency carrier degraded by noise and an improvement of about 50 dB in signal-to-noise ratio was demonstrated. The photonic oscillator has both electrical and optical inputs and outputs and can be directly interfaced with a photonic system without signal conversion. In addition to clock and carrier recovery, the photonic oscillator can also be used for (1) stable high frequency clock signal generation, (2) frequency multiplication, (3) square wave and comb frequency generation, and (4) photonic phase locked loop.

  8. Obstacle-aware clock-tree shaping during placement

    Microsoft Academic Search

    Dong-Jin Lee; Igor L. Markov

    2011-01-01

    Traditional IC design flows optimize clock networks before signal-net routing and are limited by the quality of register placement. Existing publications also reflect this bias and focus mostly on clock routing. The few known techniques for register placement exhibit significant limitations and do not account for recent progress in large-scale placement and obstacle-aware clock-network synthesis. In this work, we integrate

  9. Ground control system for the midcourse space experiment UTC clock

    NASA Technical Reports Server (NTRS)

    Dragonette, Richard

    1994-01-01

    One goal of the Midcourse Space Experiment (MSX) spacecraft Operations Planning Center is to maintain the onboard satellite UTC clock (UTC(MSX)) to within 1 millisecond of UTC(APL) (the program requirement is 10 msec). The UTC(MSX) clock employs as its time base an APL built 5 MHz quartz oscillator, which is expected to have frequency instabilities (aging rate + drift rate + frequency offset) that will cause the clock to drift approximately two to ten milliseconds per day. The UTC(MSX) clock can be advanced or retarded by the APL MSX satellite ground control center by integer multiples of 1 millisecond. The MSX Operations Planning Center is developing software which records the drift of UTC(MSX) relative to UTC(APL) and which schedules the time of day and magnitude of UTC(MSX) clock updates up to 48 hours in advance. Because of the manner in which MSX spacecraft activities are scheduled, MSX clock updates are planned 24 to 48 hours in advance, and stored in the satellite's computer controller for later execution. Data will be collected on the drift of UTC(MSX) relative to UTC(APL) over a three to five day period. Approximately six times per day, the time offset between UTC(MSX) and UTC(APL) will be measured by APL with a resolution of less than 100 microseconds. From this data a second order analytical model of the clock's drift will be derived. This model will be used to extrapolate the offset of the MSX clock in time from the present to 48 hours in the future. MSX clock updates will be placed on the spacecraft's daily schedule whenever the predicted clock offset exceeds 0.5 milliseconds. The paper includes a discussion of how the empirical model of the MSX clock is derived from satellite telemetry data, as well as the algorithm used to schedule MSX clock updates based on the model.

  10. Casting and Angling.

    ERIC Educational Resources Information Center

    Little, Mildred J.; Bunting, Camille

    The self-contained packet contains background information, lesson plans, 15 transparency and student handout masters, drills and games, 2 objective examinations, and references for teaching a 15-day unit on casting and angling to junior high and senior high school students, either as part of a regular physical education program or as a club…

  11. Ring laser angle encoder

    NASA Technical Reports Server (NTRS)

    Coccoli, J. D.; Lawson, J. R.; Mc Garty, T. P.; Nickles, J. E.

    1969-01-01

    Ring laser angle encoder with a scanning photometer autocollimator and an isolation axis, provides continuous digital readout. It measures the angular difference in inertial attitudes of target /any phenomena generating or reflecting a light beam/ two at a time relative to target one at a time.

  12. Casting and Angling.

    ERIC Educational Resources Information Center

    Smith, Julian W.

    As part of a series of books and pamphlets on outdoor education, this manual consists of easy-to-follow instructions for fishing activities dealing with casting and angling. The manual may be used as a part of the regular physical education program in schools and colleges or as a club activity for the accomplished weekend fisherman or the…

  13. ORTHO- ELIMINATION OF TRACKING SYSTEM CLOCK ERRORS

    NASA Technical Reports Server (NTRS)

    Wu, J. T.

    1994-01-01

    ORTHO is part of the Global Positioning System (GPS) being developed by the U.S. Air Force, a navigational system that will use 18 NAVSTAR satellites to broadcast navigation messages and achieve worldwide coverage. The normal positioning technique uses one receiver which receives signals from at least four GPS satellites. For higher accuracy work it is often necessary to use a differential technique in which more than one receiver is used. The geodetic measurement has all receivers on the ground and allows the determination of the relative locations of the ground sites. The main application of the ORTHO program is in the elimination of clock errors in a GPS based tracking system. The measured distance (pseudo-range) from a GPS receiver contains errors due to differences in the receiver and satellite clocks. The conventional way of eliminating clock errors is to difference pseudo-ranges between different GPS satellites and receivers. The Householder transformation used in this program performs a function similar to the conventional single differencing or double differencing. This method avoids the problem of redundancy and correlation encountered in a differencing scheme. It is able to keep all information contained in the measurements within the scope of a least square estimation. For multiple transmitter and receiver GPS tracking network, this method is in general more accurate than the differencing technique. This program assumes that the non-clock measurement partial derivatives for the particular application are computed earlier by another program. With the partial derivatives and information to identify the transmitters and receivers as the input, the program performs the Householder transformation on the partial derivatives. The transformed partials are output by the program and may be used as an input to the filter program in the subsequent estimation process. Clock partial derivatives are generated internally and are not part of the input to the program. ORTHO is written completely in FORTRAN 77 on the DEC VAX operating under VMS 4.5 and requires 805K of central memory. LINPACK, a public domain subroutine package distributed by Argonne National Laboratory and IMSL subroutine library, is required. ORTHO was released in 1988.

  14. Micromagic Clock: Microwave Clock Based on Atoms in an Engineered Optical Lattice

    SciTech Connect

    Beloy, K.; Derevianko, A.; Dzuba, V. A.; Flambaum, V. V. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States); School of Physics, University of New South Wales, Sydney, 2052 (Australia)

    2009-03-27

    We propose a new class of atomic microwave clocks based on the hyperfine transitions in the ground state of aluminum or gallium atoms trapped in optical lattices. For such elements magic wavelengths exist at which both levels of the hyperfine doublet are shifted at the same rate by the lattice laser field, canceling its effect on the clock transition. A similar mechanism for the magic wavelengths may work in microwave hyperfine transitions in other atoms which have the fine-structure multiplets in the ground state.

  15. Micromagic clock: microwave clock based on atoms in an engineered optical lattice.

    PubMed

    Beloy, K; Derevianko, A; Dzuba, V A; Flambaum, V V

    2009-03-27

    We propose a new class of atomic microwave clocks based on the hyperfine transitions in the ground state of aluminum or gallium atoms trapped in optical lattices. For such elements magic wavelengths exist at which both levels of the hyperfine doublet are shifted at the same rate by the lattice laser field, cancelling its effect on the clock transition. A similar mechanism for the magic wavelengths may work in microwave hyperfine transitions in other atoms which have the fine-structure multiplets in the ground state. PMID:19392262

  16. The efficiency of 'viscous interaction' between the solar wind and the magnetosphere during intense northward IMF events

    NASA Technical Reports Server (NTRS)

    Tsurutani, Bruce T.; Gonzalez, W. D.

    1995-01-01

    We examined 11 cases when the interplanetary magnetic field (IMF) was intensely northward (greater than 10 nT) for long durations of time (greater than 3 hours), to quantitatively determine an uppler limit on the efficiency of solar wind energy injection into the magnetosphere. We have specifically selected these large B(sub N) events to minimize the effects of magnetic reconnection. Many of these cases occurred during intervals of high-speed streams associated with coronal mass ejections when viscous interaction effects might be at a maximum. It is found that the typical efficiency of solar wind energy injection into the magnetosphere is 1.0 x 10(exp -3) to 4.0 x 10(exp -3), 100 to 30 times less efficient than during periods of intense southward IMFs. Other energy sinks not included in these numbers are discussed. Estimates of their magnitudes are provided.

  17. Response of the M-I current system for two successive interplanetary shocks during the southward and northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Du, Aimin; Zhang, Tielong; Zhao, Xudong; Zhang, Ying; Wang, Yuan; Luo, Hao

    2015-04-01

    When strong interplanetary shock interacts with the magnetosphere, the behavior of the current system is changed in magnetosphere and ionosphere. In this study, the dual SIs were triggered by the compressional region of two successive solar flares on August 1-3, 2010. They were corresponding to the interplanetary source between the two CMEs with outstanding high density impulse. One SI occurred during the northward IMF, while fifteen minutes later the other SI took place under southward IMF conditions. By using ground- and space-based measurements from 145 global observatories and multiple satellites, respectively, we compared the global current distribution of the double SIs on the ground, in the Earth's synchronous orbit and inner plasmasphere, and discussed the variations of magnetosphere-ionosphere current system associated with the two kinds of SIs.

  18. N/O-trends in Late-Type Galaxies: AGB-stars, IMFs, Abundance Gradients and the Origin of Nitrogen

    E-print Network

    Lars Mattsson

    2008-08-15

    Models of galactic chemical evolution (CEMs) show that the shape of the stellar initial mass function (IMF) and other assumptions regarding star formation affect the resultant abundance gradients in models of late-type galaxies. Furthermore, intermediate mass (IM) stars undeniably play an important role in the buildup of nitrogen abundances in galaxies. Here I specifically discuss the nitrogen contribution from IM/AGB stars and how it affects the N/O-gradient. For this purpose I have modelled the chemical evolution of a few nearby disc galaxies using different IMFs and star formation prescriptions. It is demonstrated that N/O-gradients may be used to constrain the nitrogen contribution from IM/AGB-stars.

  19. IMF By-dependent plasma flow and Birkeland currents in the dayside magnetosphere. I - Dynamics Explorer observations

    NASA Technical Reports Server (NTRS)

    Burch, J. L.; Reiff, P. H.; Menietti, J. D.; Winningham, J. D.; Heelis, R. A.; Hanson, W. B.; Shawhan, S. D.; Shelley, E. G.; Sugiura, M.

    1985-01-01

    Plasma, magnetic-field, and dc electric-field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar-wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By-dependent global convection model for southward IMF. A significant element of the model is the coexistence of three types of convection cells ('merging cells', 'viscous cells', and 'lobe cells'). This model can account for observations of a nearly stationary (in local time) convection 'throat', a sunward-antisunward convection reversal zone at the polar-cap boundary in both the morning and afternoon quadrants, the morphology of solar-wind ion injection and transport in the mid-altitude polar cusp, and the By-dependent dawn-dusk asymmetry of polar-cap electron fluxes.

  20. Continuous Nondemolition Measurement of the Cs Clock Transition Pseudospin

    SciTech Connect

    Chaudhury, Souma; Smith, Greg A.; Schulz, Kevin; Jessen, Poul S. [College of Optical Sciences, University of Arizona, Tucson, Arizona 85721 (United States)

    2006-02-03

    We demonstrate a weak continuous measurement of the pseudospin associated with the clock transition in a sample of Cs atoms. Our scheme uses an optical probe tuned near the D{sub 1} transition to measure the sample birefringence, which depends on the z component of the collective pseudospin. At certain probe frequencies the differential light shift of the clock states vanishes, and the measurement is nonperturbing. In dense samples the measurement can be used to squeeze the collective clock pseudospin and has the potential to improve the performance of atomic clocks and interferometers.

  1. Prospects for Optical Clocks with a Blue-Detuned Lattice

    SciTech Connect

    Takamoto, M.; Katori, H.; Marmo, S. I.; Ovsiannikov, V. D.; Pal'chikov, V. G. [Department of Applied Physics, Graduate School of Engineering, University of Tokyo, Bunkyo-ku, 113-8656 Tokyo (Japan); CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, 332-0012 Saitama (Japan); Physics Department, Voronezh State University, Universitetskaya pl.1, 394006, Voronezh (Russian Federation); Institute of Metrology for Time and Space at National Research Institute for Physical-Technical and Radiotechnical Measurements, Mendeleevo, Moscow Region, 141579 (Russian Federation)

    2009-02-13

    We investigated the properties of optical lattice clocks operated with a repulsive light-shift potential. The magic wavelength, where light-shift perturbation for the clock transition cancels, was experimentally determined to be 389.889(9) nm for {sup 87}Sr. The hyperpolarizability effects on the clock transition were investigated theoretically. With minimal trapping field perturbation provided by the blue-detuned lattice, the fractional uncertainty due to the hyperpolarizability effects was found to be 2x10{sup -19} in the relevant clock transition.

  2. Crosstalk between the circadian clock and innate immunity in Arabidopsis.

    PubMed

    Zhang, Chong; Xie, Qiguang; Anderson, Ryan G; Ng, Gina; Seitz, Nicholas C; Peterson, Thomas; McClung, C Robertson; McDowell, John M; Kong, Dongdong; Kwak, June M; Lu, Hua

    2013-01-01

    The circadian clock integrates temporal information with environmental cues in regulating plant development and physiology. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine this role of the circadian clock, we tested disease resistance in mutants disrupted in CCA1 and LHY, which act synergistically to regulate clock activity. We found that cca1 and lhy mutants also synergistically affect basal and resistance gene-mediated defense against Pseudomonas syringae and Hyaloperonospora arabidopsidis. Disrupting the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GRP7, a key constituent of a slave oscillator regulated by the circadian clock and previously shown to influence plant defense and stomatal activity. We show that the defense role of CCA1 and LHY against P. syringae is at least partially through circadian control of stomatal aperture but is independent of defense mediated by salicylic acid. Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity. Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity. PMID:23754942

  3. Space Clocks to Test Relativity: ACES and Beyond

    NASA Astrophysics Data System (ADS)

    Wolf, Peter

    2009-05-01

    Atomic clocks are an outstanding tool for the experimental verification of general relativity and more generally for fundamental astronomy (VLBI, pulsar timing, navigation, etc). Recent years have seen a rapid improvement in the performance of such clocks, promising new improved tests of relativity, in particular onboard terrestrial and interplanetary space missions. However, the use of such high accuracy clocks onboard spacecraft also requires detailed modelling and data analysis within the frame of general relativity and/or alternative theoretical frameworks. In this talk I present the Atomic Clock Ensemble in Space (ACES) mission, a joint ESA/CNES project to be launched in 2012, with particular emphasis on relativistic aspects and the corresponding data analysis. The mission consists of two high accuracy atomic clocks (a hydrogen maser and a laser cooled Cs atomic clock) to be installed onboard the International Space Station (ISS) and a high performance microwave link (MWL) allowing the comparison between ground and space clocks. The second part of the talk will be devoted to future missions making use of the more recent development of optical clocks and optical comparison methods, in particular the SAGAS project (Search for Anomalous Gravitation using Atomic Sensors), that aims to fly an optical atomic clock on a solar system escape trajectory with science objectives in fundamental physics and solar system science (arXiv: 0711.0304).

  4. Working around the clock: circadian rhythms and skeletal muscle

    PubMed Central

    Zhang, Xiping; Dube, Thomas J.

    2009-01-01

    The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to understand the contribution of circadian factors to normal metabolism, metabolic responses to muscle training, and contribution of the molecular clock in muscle-to-muscle disease (e.g., insulin resistance). Consistent with the potential for the skeletal muscle molecular clock modulating skeletal muscle physiology, there are findings in the literature that there is significant time-of-day effects for strength and metabolism. Additionally, there is some recent evidence that temporal specificity is important for optimizing training for muscular performance. While these studies do not prove that the molecular clock in skeletal muscle is important, they are suggestive of a circadian contribution to skeletal muscle function. The application of well-established models of skeletal muscle research in function and metabolism with available genetic models of molecular clock disruption will allow for more mechanistic understanding of potential relationships. PMID:19696362

  5. Prospects for atomic clocks based on large ion crystals

    E-print Network

    Kyle Arnold; Elnur Haciyev; Eduardo Paez; Chern Hui Lee; John Bollinger; M. D. Barrett

    2015-07-08

    We investigate the feasibility of precision frequency metrology with large ion crystals. For clock candidates with a negative differential static polarisability, we show that micromotion effects should not impede the performance of the clock. Using Lu+ as a specific example, we show that quadrupole shifts due to the electric fields from neighbouring ions do not significantly affect clock performance. We also show that effects from the tensor polarisability can be effectively managed with a compensation laser at least for a small number of ions (ion-based atomic clocks, allowing them to achieve stability levels comparable to neutral atoms in optical lattices and a viable path to greater levels of accuracy.

  6. Prospects for atomic clocks based on large ion crystals

    E-print Network

    Arnold, Kyle; Paez, Eduardo; Lee, Chern Hui; Bollinger, John; Barrett, M D

    2015-01-01

    We investigate the feasibility of precision frequency metrology with large ion crystals. For clock candidates with a negative differential static polarisability, we show that micromotion effects should not impede the performance of the clock. Using Lu+ as a specific example, we show that quadrupole shifts due to the electric fields from neighbouring ions do not significantly affect clock performance. We also show that effects from the tensor polarisability can be effectively managed with a compensation laser at least for a small number of ions (ion-based atomic clocks, allowing them to achieve stability levels comparable to neutral atoms in optical lattices and a viable path to greater levels of accuracy.

  7. Derivation and experimental verification of clock synchronization theory

    NASA Technical Reports Server (NTRS)

    Palumbo, Daniel L.

    1994-01-01

    The objective of this work is to validate mathematically derived clock synchronization theories and their associated algorithms through experiment. Two theories are considered, the Interactive Convergence Clock Synchronization Algorithm and the Mid-Point Algorithm. Special clock circuitry was designed and built so that several operating conditions and failure modes (including malicious failures) could be tested. Both theories are shown to predict conservative upper bounds (i.e., measured values of clock skew were always less than the theory prediction). Insight gained during experimentation led to alternative derivations of the theories. These new theories accurately predict the clock system's behavior. It is found that a 100% penalty is paid to tolerate worst case failures. It is also shown that under optimal conditions (with minimum error and no failures) the clock skew can be as much as 3 clock ticks. Clock skew grows to 6 clock ticks when failures are present. Finally, it is concluded that one cannot rely solely on test procedures or theoretical analysis to predict worst case conditions. conditions.

  8. 36. FLAG TOWER CLOCK ZONE FROM SOUTH TOWER ROOF, LOOKING ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    36. FLAG TOWER CLOCK ZONE FROM SOUTH TOWER ROOF, LOOKING NORTH - Smithsonian Institution Building, 1000 Jefferson Drive, between Ninth & Twelfth Streets, Southwest, Washington, District of Columbia, DC

  9. Derivation and experimental verification of clock synchronization theory

    NASA Astrophysics Data System (ADS)

    Palumbo, Daniel L.

    1994-06-01

    The objective of this work is to validate mathematically derived clock synchronization theories and their associated algorithms through experiment. Two theories are considered, the Interactive Convergence Clock Synchronization Algorithm and the Mid-Point Algorithm. Special clock circuitry was designed and built so that several operating conditions and failure modes (including malicious failures) could be tested. Both theories are shown to predict conservative upper bounds (i.e., measured values of clock skew were always less than the theory prediction). Insight gained during experimentation led to alternative derivations of the theories. These new theories accurately predict the clock system's behavior. It is found that a 100% penalty is paid to tolerate worst case failures. It is also shown that under optimal conditions (with minimum error and no failures) the clock skew can be as much as 3 clock ticks. Clock skew grows to 6 clock ticks when failures are present. Finally, it is concluded that one cannot rely solely on test procedures or theoretical analysis to predict worst case conditions. conditions.

  10. Angle Sense: A Valuable Connector.

    ERIC Educational Resources Information Center

    Rubenstein, Rheta N.; And Others

    1993-01-01

    Proposes angle sense as a fundamental connector between mathematical concepts for middle grade students. Introduces the use of pattern blocks and a goniometer, a tool to measure angles, to help students develop angle sense. Discusses connections between angle measurement and the concepts of rational numbers, circles, area, number theory,…

  11. A Different Angle on Perspective

    ERIC Educational Resources Information Center

    Frantz, Marc

    2012-01-01

    When a plane figure is photographed from different viewpoints, lengths and angles appear distorted. Hence it is often assumed that lengths, angles, protractors, and compasses have no place in projective geometry. Here we describe a sense in which certain angles are preserved by projective transformations. These angles can be constructed with…

  12. Effects of Pinealectomy on Metabolic Activity and Clock Gene Expression in Passer domesticus 

    E-print Network

    McCormick, Ryan

    2008-08-19

    suggest two differentially regulated oscillatory mechanisms at the cellular level: a metabolic clock that rapidly responds to melatonin and a transcriptional clock that likely responds to the entrainment of the metabolic clock. Here we examine...

  13. PUBLISHED ONLINE: 15 JUNE 2014 | DOI: 10.1038/NPHYS3000 A quantum network of clocks

    E-print Network

    Loss, Daniel

    ) with unprecedented stability and accuracy. W ith the advances of highly phase coherent lasers, optical atomic clocks-limited clocks separated by large distances-- as appropriate, for example, for satellite-based clocks possibly op

  14. A Band-Reject Nested-PLL Phase-Noise Reduction Scheme for Clock-Cleaners

    E-print Network

    Ayazi, Farrokh

    , Barranquilla, Colombia Email: mpardo@gatech.edu Abstract--This paper proposes a clock-conditioner architecture purity of the clock signal in communication systems. A phase-locked loop (PLL) can be used as a clock

  15. Auroras in the region of the near-polar boundary of the cusp in the case the northward IMF

    Microsoft Academic Search

    I. P. Gabis; M. I. Pudovkin

    1992-01-01

    All-sky camera data from the Antarctic station Vostok are used to analyze the characteristics of auroras associated with midday anomalous ionization in the E-layer appearing in the case of the northward IMF. Arc-type auroras, single or multiple, are shown to appear in the corrected geomagnetic-latitude interval of 80-83 deg a few minutes before or simultaneously with the anomalous ionization in

  16. Predictions of magnetosheath merging between IMF field lines of opposite polarity

    NASA Astrophysics Data System (ADS)

    Maynard, N. C.; Sonnerup, B. U. Ã.-.; Siscoe, G. L.; Weimer, D. R.; Siebert, K. D.; Erickson, G. M.; White, W. W.; Schoendorf, J. A.; Ober, D. M.; Wilson, G. R.; Heinemann, M. A.

    2002-12-01

    Magnetohydrodynamic (MHD) simulations using the Integrated Space Weather Prediction Model (ISM) show merging in the magnetosheath between interplanetary magnetic field (IMF) field lines on opposite sides of a directional discontinuity. As the discontinuity passes the bow shock and traverses the magnetosheath, the magnetic field gradients on either side become steeper, and the geometry is distorted by the nonuniform flow speed in the magnetosheath. Associated current densities are intensified. In a location isolated from the magnetopause, we use the appearance of an X magnetic field configuration, associated dissipation electric fields, and increases in plasma velocity in the exhaust direction from the X as evidence for merging in the magnetosheath. We suggest that these signatures might be observable by Polar, as it now traverses the magnetosheath near the nose or by the Cluster spacecraft when the discontinuity is tilted away from the YZ plane. Merging signatures are seen in simulations with both 90° and 180° rotations of the field across the discontinuity. Magnetosheath merging creates a hole in the directional discontinuity, allowing the magnetosphere to penetrate through the structure as the discontinuity passes downstream. Magnetosheath merging has the potential to affect ionospheric convection pattern changes, open-closed boundaries, and magnetotail dynamics. A possible association with hot flow anomalies (HFA) is also indicated.

  17. Solar Wind and IMF Control of Large-Scale Ionospheric Currents and Their Time Variations

    NASA Astrophysics Data System (ADS)

    Juusola, L.; Kauristie, K.; Tanskanen, E.; Partamies, N.; Viljanen, A.; Andréeová, K.; van de Kamp, M.; Vanhamäki, H.; Milan, S. E.; Lester, M.; Grocott, A.; Imber, S. M.

    2014-12-01

    Patterns of high-latitude ionospheric currents are a manifestation of the solar wind-magnetosphere-ionosphere coupling. Rapid variations of the currents are associated with geomagnetically induced currents (GIC) in technological conductor systems and displays of bright, diverse auroras. One advantage of a ground-based magnetometer network over a low-orbit satellite is the possibility to distinguish between temporal and spatial variations in the data. Although ground magnetic field data can only yield distributions of ionospheric equivalent currents instead of the full horizontal and field-aligned current density, estimates for these can be obtained, under certain assumptions. We use data (1994-2013) from the ground-based IMAGE magnetometer network to derive statistical distributions of the large-scale ionospheric equivalent current density and its time-derivative as well as estimates for the field-aligned current density. These are compared with and validated against horizontal and field-aligned current density distributions obtained from low-orbit CHAMP satellite magnetic field data (2000-2010) and convection maps obtained from SuperDARN radar data (2000-2010). The ground-based distributions reveal a strong dependence of the dayside variations on radial interplanetary magnetic field (IMF) orientation and solar wind speed. The spatial distribution of enhanced nightside activity agrees with that of the average substorm bulge and depends on solar wind energy input into the magnetosphere. The most intense time variation events are related to substorm activity and occur on the nightside.

  18. Observations of a transient event in the subsolar magnetosheath during strongly northward IMF

    NASA Astrophysics Data System (ADS)

    Dias Silveira, M. V.; Sibeck, D. G.; Gonzalez, W. D.; Koga, D.

    2013-12-01

    We present multipoint THEMIS observation of a transient event in the subsolar magnetosheath on July 10, 2007. The event exhibits some features of a flux transfer event, such as a bipolar variation in the magnetic field component normal to the nominal magnetopause centered on a peak in the total magnetic field strength. Four THEMIS spacecraft were in the magnetosheath and one in the magnetosphere. Timing analysis and the absence of flow perturbation suggest that the event is a small scale structure (~0.12 Re in the direction of the flow) moving with the background magnetosheath flow. Despite the inferred small size of the event, THC and THD both observed large amplitude (~40 nT) bipolar magnetic field signatures normal to the nominal magnetopause. Nearby spacecraft THE (only 0.2 Re further outward in the Xgsm direction) observed no significant magnetic field perturbation. Neither did THB or THA, located further away in the magnetosheath and magnetosphere, respectively. During the event, the IMF was strongly northward (approximately 20nT), which does not favor subsolar magnetic reconnection. Inside the structure, the magnetic field briefly rotates 90° away from northward to dawnward. Ions stream antiparallel to the magnetic field in the magnetosheath, parallel to the magnetic field in the event.

  19. The Space Optical Clocks Project: Development of high-performance transportable and breadboard optical clocks and advanced subsystems

    E-print Network

    S. Schiller; A. Görlitz; A. Nevsky; S. Alighanbari; S. Vasilyev; C. Abou-Jaoudeh; G. Mura; T. Franzen; U. Sterr; S. Falke; Ch. Lisdat; E. Rasel; A. Kulosa; S. Bize; J. Lodewyck; G. M. Tino; N. Poli; M. Schioppo; K. Bongs; Y. Singh; P. Gill; G. Barwood; Y. Ovchinnikov; J. Stuhler; W. Kaenders; C. Braxmaier; R. Holzwarth; A. Donati; S. Lecomte; D. Calonico; F. Levi

    2012-06-17

    The use of ultra-precise optical clocks in space ("master clocks") will allow for a range of new applications in the fields of fundamental physics (tests of Einstein's theory of General Relativity, time and frequency metrology by means of the comparison of distant terrestrial clocks), geophysics (mapping of the gravitational potential of Earth), and astronomy (providing local oscillators for radio ranging and interferometry in space). Within the ELIPS-3 program of ESA, the "Space Optical Clocks" (SOC) project aims to install and to operate an optical lattice clock on the ISS towards the end of this decade, as a natural follow-on to the ACES mission, improving its performance by at least one order of magnitude. The payload is planned to include an optical lattice clock, as well as a frequency comb, a microwave link, and an optical link for comparisons of the ISS clock with ground clocks located in several countries and continents. Undertaking a necessary step towards optical clocks in space, the EU-FP7-SPACE-2010-1 project no. 263500 (SOC2) (2011-2015) aims at two "engineering confidence", accurate transportable lattice optical clock demonstrators having relative frequency instability below 1\\times10^-15 at 1 s integration time and relative inaccuracy below 5\\times10^-17. This goal performance is about 2 and 1 orders better in instability and inaccuracy, respectively, than today's best transportable clocks. The devices will be based on trapped neutral ytterbium and strontium atoms. One device will be a breadboard. The two systems will be validated in laboratory environments and their performance will be established by comparison with laboratory optical clocks and primary frequency standards. In this paper we present the project and the results achieved during the first year.

  20. Dependence of the time-reading process of the Salecker--Wigner quantum clock on the size of the clock

    E-print Network

    Andor Frenkel

    2015-01-05

    It is shown in the present note that the degree of the complexity of the time-reading process of the Salecker--Wigner clock depends on the size of the clock. This dependence leads to a relation between the size and the accuracy of the clock, and suggests a precise optimal value for the size in agreement with the order of magnitude value established by Salecker and Wigner.

  1. Global view of dayside magnetic reconnection with the dusk-dawn IMF orientation: A statistical study for Double Star and Cluster data

    Microsoft Academic Search

    X. G. Zhang; X. G. Wang; J. Wang; X.-Z. Zhou; M. W. Dunlop; L. Xie; C. J. Xiao; Q. G. Zong; S. Y. Fu; Z. X. Liu; C. Carr; Z. W. Ma; C. Shen; E. Lucek; H. Rème; P. Escoubet

    2007-01-01

    Double Star\\/TC-1 and Cluster data show that both component reconnection and anti-parallel reconnection occur at the magnetopause when the interplanetary magnetic field (IMF) is predominantly dawnward. The occurrence of these different features under these very similar IMF conditions are further confirmed by a statistical study of 290 fast flows measured in both the low and high latitude magnetopause boundary layers.

  2. The Non-universality of the Low-mass End of the IMF is Robust against the Choice of SSP Model

    NASA Astrophysics Data System (ADS)

    Spiniello, C.; Trager, S. C.; Koopmans, L. V. E.

    2015-04-01

    We perform a direct comparison of two state-of-the art single stellar population (SSP) models that have been used to demonstrate the non-universality of the low-mass end of the initial mass function (IMF) slope. The two public versions of the SSP models are restricted to either solar abundance patterns or solar metallicity, too restrictive if one aims to disentangle elemental enhancements, metallicity changes, and IMF variations in massive early-type galaxies (ETGs) with star formation histories different from those in the solar neighborhood. We define response functions (to metallicity and ?-abundance) to extend the parameter space for each set of models. We compare these extended models with a sample of Sloan Digital Sky Survey (SDSS) ETG spectra with varying velocity dispersions. We measure equivalent widths of optical IMF-sensitive stellar features to examine the effect of the underlying model assumptions and ingredients, such as stellar libraries or isochrones, on the inference of the IMF slope down to ?0.1 M?. We demonstrate that the steepening of the low-mass end of the IMF based on a non-degenerate set of spectroscopic optical indicators is robust against the choice of the stellar population model. Although the models agree in a relative sense (i.e., both imply more bottom-heavy IMFs for more massive systems), we find non-negligible differences in the absolute values of the IMF slope inferred at each velocity dispersion by using the two different models. In particular, we find large inconsistencies in the quantitative predictions of the IMF slope variations and abundance patterns when sodium lines are used. We investigate the possible reasons for these inconsistencies.

  3. A positive feedback loop links circadian clock factor CLOCK-BMAL1 to the basic transcriptional machinery

    PubMed Central

    Lande-Diner, Laura; Boyault, Cyril; Kim, Jin Young; Weitz, Charles J.

    2013-01-01

    Circadian clocks in mammals are built on a negative feedback loop in which the heterodimeric transcription factor circadian locomotor output cycles kaput (CLOCK)-brain, muscle Arnt-like 1 (BMAL1) drives the expression of its own inhibitors, the PERIOD and CRYPTOCHROME proteins. Reactivation of CLOCK-BMAL1 occurs at a specific time several hours after PERIOD and CRYPTOCHROME protein turnover, but the mechanism underlying this process is unknown. We found that mouse BMAL1 complexes include TRAP150 (thyroid hormone receptor-associated protein-150; also known as THRAP3). TRAP150 is a selective coactivator for CLOCK-BMAL1, which oscillates under CLOCK-BMAL1 transcriptional control. TRAP150 promotes CLOCK-BMAL1 binding to target genes and links CLOCK-BMAL1 to the transcriptional machinery at target-gene promoters. Depletion of TRAP150 caused low-amplitude, long-period rhythms, identifying it as a positive clock element. The activity of TRAP150 defines a positive feedback loop within the clock and provides a potential mechanism for timing the reactivation of circadian transcription. PMID:24043798

  4. Heme-based Sensing by the Mammalian Circadian Protein, CLOCK

    PubMed Central

    Lukat-Rodgers, Gudrun S.; Correia, Cristina; Botuyan, Maria Victoria; Mer, Georges; Rodgers, Kenton R.

    2010-01-01

    Heme is emerging as a key player in the synchrony of circadian-coupled transcriptional regulation. Current evidence suggests that levels of circadian-linked transcription are regulated in response to both the availability of intracellular heme and by heme-based sensing of carbon monoxide and possibly nitric oxide. The protein CLOCK is central to the regulation and maintenance of circadian rhythms in mammals. CLOCK comprises two PAS domains, each with a heme binding site. Our studies focus on the functionality of the Murine CLOCK PAS–A domain (residues 103-265). We show that CLOCK PAS–A binds Fe(III) protoporhyrin IX to form a complex with 1:1 stoichiometry. Optical absorbance and resonance Raman studies reveal that the heme of ferric CLOCK PAS–A is a six-coordinate, low spin complex whose resonance Raman signature is insensitive to pH over the range of protein stability. Ferrous CLOCK PAS–A is a mixture of five-coordinate, high spin and six-coordinate, low spin complexes. Ferrous CLOCK PAS–A forms complexes with CO and NO. Ferric CLOCK PAS–A undergoes reductive nitrosylation in the presence of NO to generate a CLOCK PAS–A–NO, which is a pentacoordinate {FeNO}7 complex. Formation of the highly stable {FeNO}7 heme complex from either ferrous or ferric heme makes possible the binding of NO at very low concentration, a characteristic of NO sensors. Comparison of the spectroscopic properties and CO binding kinetics of CLOCK PAS–A with other CO sensor proteins reveals that CLOCK PAS–A exhibits chemical properties consistent with a heme-based gas sensor protein. PMID:20666392

  5. Angling hydraulic jumps

    NASA Astrophysics Data System (ADS)

    Belmonte, Andrew; Thiffeault, Jean-Luc

    2008-11-01

    We present an experimental and mathematical study of the normal impact of a jet onto an inclined solid surface, focusing on the characteristics of the hydraulic jump. The angle of the surface is varied between vertical and horizontal positions, using both flat and curved (patterned) surfaces. Comparisons of the outer envelope of the hydraulic jump are made with the ballistic theory and the model of Edwards, Howison, Ockendon, & Ockendon.

  6. Laser angle sensor

    NASA Technical Reports Server (NTRS)

    Pond, C. R.; Texeira, P. D.

    1985-01-01

    A laser angle measurement system was designed and fabricated for NASA Langley Research Center. The instrument is a fringe counting interferometer that monitors the pitch attitude of a model in a wind tunnel. A laser source and detector are mounted above the model. Interference fringes are generated by a small passive element on the model. The fringe count is accumulated and displayed by a processor in the wind tunnel control room. This report includes optical and electrical schematics, system maintenance and operation procedures.

  7. A Predictive Synchronizer for Periodic Clock Domains Uri Frank and Ran Ginosar

    E-print Network

    Ginosar, Ran

    relative phase, and mesochronous domains have exactly the same frequency. The simplest solution for inter typical with periodic clock domains where the clock frequencies are different. Mesochronous synchronizers

  8. Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Lin, Yi-Ge; Li, Ye; Lin, Bai-Ke; Meng, Fei; Zang, Er-Jun; Li, Tian-Chu; Fang, Zhan-Jun

    2014-12-01

    We report our observation of the spin polarized 1S0 ? 3P0 clock transition spectrum in an optical lattice clock based on fermionic 87Sr. The atoms are trapped and pre-cooled to about 2 ?K with two stages of laser cooling at 461 nm and 689 nm, respectively. Then the atoms are loaded into an optical lattice formed by the interference of counter-propagating laser beams at 813 nm. An external cavity diode laser at 698 nm, which is stabilized to a high finesse cavity with a linewidth of about 5 Hz and a drift rate of less than 0.2 Hz/s, is used to excite the atoms to the 3P0 state. The ?-polarized clock transition spectrum of resolvable mF states is obtained by applying a small bias magnetic field along the polarization axis of the probe beam. A spin polarized clock transition spectrum as narrow as 10 Hz with an 80 ms probe pulse is obtained.

  9. Health Sciences New Employee Orientation Home Department Clock In/ Out Clock Code

    E-print Network

    Gleeson, Joseph G.

    clock code 9 when you leave. Basic Procedure 1. To Access HBS: Dial 286 2. Hear the time message shift and 9 if you are ending your shift. 5. Hear the message: "Verifying". If the number entered was correct, proceed to the next step. If not, you will hear the message, "that number was invalid", try again

  10. Small Angle Neutron Scattering

    SciTech Connect

    Urban, Volker S [ORNL

    2012-01-01

    Small Angle Neutron Scattering (SANS) probes structural details at the nanometer scale in a non-destructive way. This article gives an introduction to scientists who have no prior small-angle scattering knowledge, but who seek a technique that allows elucidating structural information in challenging situations that thwart approaches by other methods. SANS is applicable to a wide variety of materials including metals and alloys, ceramics, concrete, glasses, polymers, composites and biological materials. Isotope and magnetic interactions provide unique methods for labeling and contrast variation to highlight specific structural features of interest. In situ studies of a material s responses to temperature, pressure, shear, magnetic and electric fields, etc., are feasible as a result of the high penetrating power of neutrons. SANS provides statistical information on significant structural features averaged over the probed sample volume, and one can use SANS to quantify with high precision the structural details that are observed, for example, in electron microscopy. Neutron scattering is non-destructive; there is no need to cut specimens into thin sections, and neutrons penetrate deeply, providing information on the bulk material, free from surface effects. The basic principles of a SANS experiment are fairly simple, but the measurement, analysis and interpretation of small angle scattering data involves theoretical concepts that are unique to the technique and that are not widely known. This article includes a concise description of the basics, as well as practical know-how that is essential for a successful SANS experiment.

  11. Testing General Relativity with Atomic Clocks

    NASA Astrophysics Data System (ADS)

    Reynaud, S.; Salomon, C.; Wolf, P.

    2009-12-01

    We discuss perspectives for new tests of general relativity which are based on recent technological developments as well as new ideas. We focus our attention on tests performed with atomic clocks and do not repeat arguments present in the other contributions to the present issue (Space Sci. Rev. 2009, This Issue). In particular, we present the scientific motivations of the space projects ACES (Salomon et al. in CR Acad. Sci. IV-2:1313, 2001) and SAGAS (Wolf et al. in Exp. Astron. 23:651, 2009).

  12. Laser Cooled Atomic Clocks in Space

    NASA Technical Reports Server (NTRS)

    Thompson, R. J.; Kohel, J.; Klipstein, W. M.; Seidel, D. J.; Maleki, L.

    2000-01-01

    The goals of the Glovebox Laser-cooled Atomic Clock Experiment (GLACE) are: (1) first utilization of tunable, frequency-stabilized lasers in space, (2) demonstrate laser cooling and trapping in microgravity, (3) demonstrate longest 'perturbation-free' interaction time for a precision measurement on neutral atoms, (4) Resolve Ramsey fringes 2-10 times narrower than achievable on Earth. The approach taken is: the use of COTS components, and the utilization of prototype hardware from LCAP flight definition experiments. The launch date is scheduled for Oct. 2002. The Microgravity Science Glovebox (MSG) specifications are reviewed, and a picture of the MSG is shown.

  13. Precision of a Mammalian Circadian Clock

    NASA Astrophysics Data System (ADS)

    Kumar Sharma, Vijay; Chandrashekaran, Maroli K.

    This paper reports study of day-to-day instability in the locomotor activity rhythm of the nocturnal field mouse Mus booduga. The free-running period (?) of this rhythm was estimated in constant darkness in n=347 adult male mice. The "onset" and "offset" of locomotor activity rhythm were used as phase markers of the circadian clock. The precision of the onset of locomotor activity was observed to be a non-linear function of ?, with maximal precision at ? close to 24h. The precision of the offset of locomotor activity was found to increase with increasing ?. These results suggest that the homeostasis of ? is tighter when ? is close to 24h.

  14. Precision of Genetic Oscillators and Clocks

    NASA Astrophysics Data System (ADS)

    Morelli, Luis G.; Jülicher, Frank

    2007-06-01

    We develop a stochastic description of feedback oscillators in which functional molecules are produced by an assembly line consisting of many identical steps. The initiation rate of this assembly is regulated by its products via a negative feedback. This model is motivated by genetic oscillators such as circadian clocks. We show that precise oscillations of high quality are possible even when the number of product molecules is low and the fluctuations of amplitude are large. We discuss parameter values which can account for high quality oscillations as observed in single cells. Furthermore, we discuss effects of stochastic amplification steps on precision to account for translational bursting.

  15. A Heuristic Model of Long-Term Atomic Clock Behavior

    Microsoft Academic Search

    D. B. Percival

    1976-01-01

    Summary A class of conceptually simple models for the long-term frequency variations of atomic clocks is presented. The basic model simulates the average fractional frequency deviation of a frequency standard as the sum of a normally distributed random variable, E and a random variable, l~ , which represents the spontaneous changes in the mean frequency of an atomic t clock

  16. A mathematical model for the atomic clock error

    Microsoft Academic Search

    L. Galleani; L. Sacerdote; P. Tavella; C. Zucca

    2003-01-01

    A mathematical model for the clock phase and frequency deviation based on the theory of stochastic differential equations (SDEs) is discussed. In particular, we consider a model that includes what are called the `white and random walk frequency noises' in time metrology, which give rise in a mathematical context to a Wiener and an integrated Wiener process on the clock

  17. Nuclear magnetic resonance implementation of a quantum clock synchronization algorithm

    SciTech Connect

    Zhang Jingfu; Long, G.C; Liu Wenzhang [Key Laboratory For Quantum Information and Measurements, Tsinghua University, Beijing, 100084 (China); Department of Physics, Tsinghua University, Beijing 100084 (China); Deng Zhiwei [Testing and Analytical Center, Beijing Normal University, Beijing, 100875 (China); Lu Zhiheng [Department of Physics, Beijing Normal University, Beijing, 100875 (China)

    2004-12-01

    The quantum clock synchronization (QCS) algorithm proposed by Chuang [Phys. Rev. Lett. 85, 2006 (2000)] has been implemented in a three qubit nuclear magnetic resonance quantum system. The time difference between two separated clocks can be determined by measuring the output states. The experimental realization of the QCS algorithm also demonstrates an application of the quantum phase estimation.

  18. Atomic clocks: new prospects in metrology and geodesy

    E-print Network

    Pacôme Delva; Jérôme Lodewyck

    2013-08-29

    We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.

  19. Atomic-based stabilization for laser-pumped atomic clocks

    Microsoft Academic Search

    V. Gerginov; V. Shah; S. Knappe; L. Hollberg; J. Kitching

    2006-01-01

    We describe a novel technique for stabilizing frequency shifts in laser-interrogated vapor-cell atomic clocks. The method suppresses frequency shifts due to changes in the laser frequency, intensity, and modulation index as well as atomic vapor density. The clock operating parameters are monitored by using the atoms themselves, rather than by using conventional schemes for laser frequency and cell temperature control.

  20. Detection of Anomalies in the Behavior of Atomic Clocks

    Microsoft Academic Search

    Emilia Nunzi; Lorenzo Galleani; Patrizia Tavella; Paolo Carbone

    2007-01-01

    In this paper, the problem of identifying variations in the nature of atomic clock noise is addressed. Two methods are proposed. One method is based on a generalized likelihood ratio test (GLRT), and the other is based on the dynamic Allan variance (DAVAR), which is a representation of the instantaneous clock stability that is able to point out possible nonstationary