Science.gov

Sample records for imf clock angle

  1. Timescales Of The Influence Of IMF Clock Angle In Controlling The Characteristics Of Magnetospheric Dynamics

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Milan, S. E.

    2013-12-01

    We exploit a database of high-latitude ionospheric electric potential patterns, derived from radar observations of plasma convection in the northern hemisphere from the years 2000 - 2006, to investigate the timescales of interplanetary magnetic field (IMF) penetration into the magnetosphere. We parameterise the convection observations by IMF clock angle, ? (the angle between geocentric solar magnetic (GSM) north and the projection of the IMF vector onto the GSM Y-Z plane), and by an IMF timescale, ?B (the length of time that a similar clock angle has been maintained prior to the convection observations being made). We find that the nature of the ionospheric convection changes with IMF clock angle, as expected from previous time-averaged studies, and that for ?B ~ 30 mins the convection patterns closely resemble their time-averaged counterparts. However, we also find that for certain IMF clock angles, in particular those with a northward BZ component and significant BY (dusk-dawn) component, the patterns evolve with increasing ?B to less resemble their time-averaged counterparts, showing a marked enhancement in dusk-dawn asymmetry as ?B approaches 10 hours. We discuss these findings in terms of the effects of the persistent penetration of a quasi-steady IMF into the magnetosphere, and its implications for understanding different modes of magnetospheric dynamics.

  2. Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle

    E-print Network

    Lockwood, Mike

    Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 1. Persistence of cusp proton aurora K. Throp, M. Lockwood,1 B. S. Lanchester, and S. K employ a numerical model of cusp ion precipitation and proton aurora emission to fit variations

  3. Separator morphology and null location dependence on clock angle in global magnetospheric simulations

    NASA Astrophysics Data System (ADS)

    Komar, C. M.; Cassak, P.; Dorelli, J.; Glocer, A.; Kuznetsova, M. M.

    2012-12-01

    Magnetic separators (single magnetic field lines that separate regions of all different magnetic topologies) and magnetic nulls are important to identify at the dayside magnetopause because they provide valuable information about the global magnetic topology and where magnetic reconnection is likely to occur. Relatively few studies have addressed the changes to the separators and nulls as a function of interplanetary magnetic field (IMF) clock angle. In this study, we present a new highly accurate method for tracing magnetic separators. We confirm the technique with separators from a vacuum superposition model of a dipolar magnetic field added to a uniform background field. Then, we trace separators in global magnetohydrodynamic (MHD) simulations using the three-dimensional BATS-R-US code with a uniform plasma resistivity. The magnetic nulls and separators are found in distinct simulations with IMF clock angles ranging from 0 (parallel) to 180 degrees (antiparallel) in increments of 30 degrees. Trends in the location of the nulls and the structural morphology of the separators are tabulated as a function of clock angle and compared to the vacuum superposition model. While there are many qualitative similarities, deviations of the two models are also noted.

  4. The IMF dependence of the magnetopause from global MHD simulations

    NASA Astrophysics Data System (ADS)

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

    2013-06-01

    Numerical results from a physics-based global magnetohydrodynamic (MHD) model are used to investigate the controlling effects of the interplanetary magnetic field (IMF) components, BY and BZ, on the location and shape of the magnetopause. The subsolar magnetopause is identified by using the plasma density and velocity, the cusp by using the current density, and the other area by streamlines and the current density. These data are fitted with a three-dimensional surface function constructed by Liu et al. (2012), which allows description of the cusp geometry as well as the north-south asymmetry and azimuthal asymmetry of the magnetopause. A new parameter which depends on the IMF BY and BZ is introduced to describe the orientation of the elliptical cross section of the magnetopause. Effects of IMF BY and BZ on the magnetopause configuration parameters are analyzed, and dependence of the magnetopause parameters in the IMF components are obtained. Magnetopause cross section is found to be largely controlled by the IMF clock angle. The stretch direction of the magnetopause cross section is always near the direction of the IMF but is a little closer to the meridional plane than the IMF. Increasing BY or BZincreases the eccentricity of the magnetopause cross section. This effect is larger for southward IMF than for the northward IMF, and the stretching effect of BY is smaller than that of BZ.

  5. 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.

  6. Statistical Comparison of a Southern Auroral Electrojet Index with Northern Hemisphere AE Indices as a Function of Solar Wind and IMF

    NASA Astrophysics Data System (ADS)

    Boudouridis, A.; Weygand, J. M.; Zesta, E.

    2014-12-01

    A Southern Auroral Electrojet (SAE) index has been recently constructed using seven Antarctica magnetometer stations. It has been compared for case studies with the standard Auroral Electrojet (AE) index, and a near-conjugate to the southern stations Northern Auroral Electrojet (NAE) index. Both similarities and differences with the Northern Hemisphere indices have been detected, and they reveal information about the conjugacy of geomagnetic disturbances. In this work we compare the three indices statistically as a function of the accompanying solar wind (SW) and Interplanetary Magnetic Field (IMF) conditions to further explore conjugacy issues. We use 274 days of common north/south data presence between December 2005 and August 2010. We calculate the cross correlation coefficients and differences between all three pairs, AE-SAE, NAE-SAE, and AE-NAE. We estimate the effect of the SW/IMF conditions on the index correlations and differences using three groups of data: 1) the entire data set, 2) periods when there is no station in the Southern Hemisphere located within the 20-02 Magnetic Local Time (MLT) sector where substorms occur, and 3) separately for the four different seasons. We consider the following SW/IMF quantities: IMF By, Bz, clock angle ? = tan-1(|By|/Bz), coupling parameter sin2(?/2), SW dynamic pressure, density, velocity, and electric field. We find that high north-south correlation coefficients are more common during strong SW/IMF driving, e.g., southward IMF, high IMF |By|, high SW dynamic pressure, high SW electric field, and high ? and sin2(?/2). All the above studies are also conducted for the index differences instead of their correlations. We find that the index differences are higher for higher SW/IMF driving, suggesting that the SAE index follows the northern indices trend, but has in general lower values than either the standard AE or the conjugate NAE index. The MLT study shows that the number of high AE/SAE correlations is slightly lower at all clock angles and dynamic pressure levels when no southern station is within 20-02 MLT. Of the four seasons, spring and winter had enough data for their results to be statistically significant. The results show that the number of high correlations is greater during the spring period than the winter period, for various levels of SW pressure, IMF By and IMF Bz.

  7. The Influence of Clocking Angle of the Projectile on the Simulated Impact Response of a Shuttle Leading Edge Wing Panel

    NASA Technical Reports Server (NTRS)

    Jackson, Karen E.; Fasanella, Edwin L.; Lyle, Karen H.; Spellman, Regina L.

    2005-01-01

    An analytical study was conducted to determine the influence of clocking angle of a foam projectile impacting a space shuttle leading edge wing panel. Four simulations were performed using LS-DYNA. The leading edge panels are fabricated of multiple layers of reinforced carbon-carbon (RCC) material. The RCC material was represented using Mat 58, which is a material property that can be used for laminated composite fabrics. Simulations were performed of a rectangular-shaped foam block, weighing 0.23-lb., impacting RCC Panel 9 on the top surface. The material properties of the foam were input using Mat 83. The impact velocity was 1,000 ft/s along the Orbiter X-axis. In two models, the foam impacted on a corner, in one model the foam impacted the panel initially on the 2-in.-long edge, and in the last model the foam impacted the panel on the 7-in.- long edge. The simulation results are presented as contour plots of first principal infinitesimal strain and time history plots of contact force and internal and kinetic energy of the foam and RCC panel.

  8. Coupling the Solar-Wind/IMF to the Ionosphere through the High Latitude Cusps

    NASA Technical Reports Server (NTRS)

    Maynard, Nelson C.

    2003-01-01

    Magnetic merging is a primary means for coupling energy from the solar wind into the magnetosphere-ionosphere system. The location and nature of the process remain as open questions. By correlating measurements form diverse locations and using large-scale MHD models to put the measurements in context, it is possible to constrain out interpretations of the global and meso-scale dynamics of magnetic merging. Recent evidence demonstrates that merging often occurs at high latitudes in the vicinity of the cusps. The location is in part controlled by the clock angle in the interplanetary magnetic field (IMF) Y-Z plane. In fact, B(sub Y) bifurcated the cusp relative to source regions. The newly opened field lines may couple to the ionosphere at MLT locations of as much as 3 hr away from local noon. On the other side of noon the cusp may be connected to merging sites in the opposite hemisphere. In face, the small convection cell is generally driven by opposite hemisphere merging. B(sub X) controls the timing of the interaction and merging sites in each hemisphere, which may respond to planar features in the IMF at different times. Correlation times are variable and are controlled by the dynamics of the tilt of the interplanetary electric field phase plane. The orientation of the phase plane may change significantly on time scales of tens of minutes. Merging is temporally variable and may be occurring at multiple sites simultaneously. Accelerated electrons from the merging process excite optical signatures at the foot of the newly opened field lines. All-sky photometer observations of 557.7 nm emissions in the cusp region provide a "television picture" of the merging process and may be used to infer the temporal and spatial variability of merging, tied to variations in the IMF.

  9. 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.

  10. The Myth of the IMF

    NASA Astrophysics Data System (ADS)

    Melnick, J.

    2009-11-01

    The Myth of Science is the idea that complex phenomena in Nature can be reduced to a set of equations based on the fundamental laws of physics. The Myth of the IMF is the notion that the observed distribution of stellar masses at birth (the IMF) can and must be explained by any successful theory of star formation. In this contribution I argue that the IMF is the result of the complex evolution of the interstellar medium in galaxies, and that as such the IMF preserves very little information, if any, about the detailed physics of star formation. Trying to infer the physics of star formation from the IMF is like trying to understand the personality of Beethoven from the power-spectrum of the Ninth Symphony!

  11. UNDERSTANDING THE IMF Richard B. Larson

    E-print Network

    Larson, Richard B.

    when expressed in terms of the number of stars per unit logarithmic mass interval (Scalo 1986, 1998 of the stellar IMF and in determining a characteristic mass scale. The importance of the thermal physics has been , and at this point the Jeans mass is about 0.3 solar masses, similar to the mass at which the IMF peaks. If most

  12. Angles, Time, and Proportion

    ERIC Educational Resources Information Center

    Pagni, David L.

    2005-01-01

    This article describes an investigation making connections between the time on an analog clock and the angle between the minute hand and the hour hand. It was posed by a middle school mathematics teacher. (Contains 8 tables and 6 figures.)

  13. 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…

  14. 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.

  15. 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.

  16. 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

  17. Solar cycle variations in IMF intensity

    NASA Technical Reports Server (NTRS)

    King, J. H.

    1979-01-01

    Annual averages of logarithms of hourly interplanetary magnetic field (IMF) intensities, obtained from geocentric spacecraft between November 1963 and December 1977, reveal the following solar cycle variation. For 2-3 years at each solar minimum period, the IMF intensity is depressed by 10-15% relative to its mean value realized during a broad 9-year period centered at solar maximum. No systematic variations occur during this 9-year period. The solar minimum decrease, although small in relation to variations in some other solar wind parameters, is both statistically and physically significant.

  18. IMF, World Bank programs hinder AIDS prevention.

    PubMed

    Denoon, D J

    1995-07-10

    International Monetary Fund (IMF) and World Bank structural adjustment programs (SAPs) imposed on developing nations in the 1980s inadvertently helped set the stage for the AIDS epidemic. These programs continue to hinder efforts to prevent HIV transmission. SAPs resulted in the following phenomena which place populations at risk of HIV infection: increased rural-urban migration of cheap labor sparked by a shift to an export-oriented economy, the development of transportation infrastructures in the 1980s to support the changed economy, increased migration and urbanization, and reduced government spending upon health and social services necessitated by the SAPs. For HIV transmission in developing countries to be substantially reduced, the SAP economic policies which may have promoted disease must be modified. An alternative development strategy must satisfy basic human needs such as food, housing, and transport; shift emphasis from the production of a small number of primary commodities for export to diversified agricultural production; support marginal producers and subsistence farmers; emphasize human resource development; end the top-down approach favored by the IMF and World Bank in favor of a truly cooperative development policy; alter the charters of the IMF and World Bank to permit the cancellation or restructuring of debt; and require AIDS Impact Reports of the IMF and World Bank. PMID:12289894

  19. 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.

  20. Solar cycle variations in IMF intensity

    NASA Technical Reports Server (NTRS)

    King, J. H.

    1979-01-01

    Annual averages of logarithms of hourly interplanetary magnetic field intensities, obtained from geocentric spacecraft between November 1963 and December 1977, reveal the following solar cycle variation. For 2 to 3 years at each solar minimum period, the IMF intensity is depressed by 10-15 percent relative to its mean value realized during a broad nine-year period centered at solar maximum. No systematic variations occur during this nine-year period. The solar minimum decrease, although small relative to variations in some other solar wind parameters, is both statistically and physically significant.

  1. 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

  2. Hanle detection for optical clocks.

    PubMed

    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

  3. Galactic-Field IMFs of Massive Stars

    E-print Network

    Pavel Kroupa; Carsten Weidner

    2003-08-20

    Over the past years observations of young and populous star clusters have shown that the stellar IMF appears to be an invariant featureless Salpeter power-law with an exponent alpha=2.35 for stars more massive than a few Msun. A consensus has also emerged that most, if not all, stars form in stellar groups and star clusters, and that the mass function of young star clusters in the solar-neighborhood and in interacting galaxies can be described, over the mass range of a few 10 Msun to 10^7 Msun, as a power-law with an exponent near beta=2. These two results imply that galactic-field IMFs for early-type stars cannot, under any circumstances, be a Salpeter power-law, but that they must have a steeper exponent alpha_field>2.8. This has important consequences for the distribution of stellar remnants and for the chemo-dynamical and photometric evolution of galaxies.

  4. 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.

  5. Testing the Universality of the Stellar IMF with Chandra

    NASA Astrophysics Data System (ADS)

    Coulter, David; Lehmer, Bret; Eufrasio, Rafael T.; Kundu, Arunav; Peacock, Mark; Hornschemeier, Ann E.; Basu-Zych, Antara; Gonzalez, Anthony H.; Maccarone, Tom; Maraston, Claudia; Zepf, Steve E.

    2016-01-01

    The stellar initial mass function (IMF), which is often assumed to be universal, has recently been suggested to vary with elliptical galaxy mass. The observed optical/near-IR spectra of massive ellipticals show evidence for an excess of low-mass stars (based on gravity sensitive absorption lines like Na and FeH) over that expected from a standard Milky Way-like IMF, which is observed in low-mass ellipticals. This suggests that massive ellipticals have a "bottom heavy" IMF with substantially steeper slopes than standard IMFs. An extrapolation of such a steep-slope IMF to high stellar masses would lead to a deficit of black hole and neutron star formation compared to a standard IMF; correspondingly, fewer low-mass X-ray binaries (LMXBs) per unit stellar mass would be expected for the steep-slope IMF. Using new Chandra observations of six low-mass ellipticals plus seven previously observed high-mass ellipticals, we test whether the number of LMXBs per unit K-band luminosity (N/LK) is consistent with a changing IMF with galaxy mass. We find nearly constant values of N/LK over the full mass range, implying there is very little change in the high stellar-mass (>8 Msol) end of the IMF for these galaxies despite the optical/near-IR evidence for changes in the low stellar-mass end of the IMF. We will discuss implications for how the overall IMF shape of elliptical galaxies changes as a function of galaxy mass.

  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. The Glyoxal Clock Reaction

    ERIC Educational Resources Information Center

    Ealy, Julie B.; Negron, Alexandra Rodriguez; Stephens, Jessica; Stauffer, Rebecca; Furrow, Stanley D.

    2007-01-01

    Research on the glyoxal clock reaction has led to adaptation of the clock reaction to a general chemistry experiment. This particular reaction is just one of many that used formaldehyde in the past. The kinetics of the glyoxal clock makes the reaction suitable as a general chemistry lab using a Calculator Based Laboratory (CBL) or a LabPro. The…

  8. 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.

  9. Probabilistic forecasting analysis of geomagnetic indices for southward IMF events

    NASA Astrophysics Data System (ADS)

    Zhang, X.-Y.; Moldwin, M. B.

    2015-03-01

    Geomagnetic disturbances that drive space weather impacts such as ground-induced currents and radiation belt enhancements are usually driven by strong southward interplanetary magnetic field (IMF) intervals. However, current heliospheric models either do not predict or provide low-accuracy forecasts of IMF Bz. Here we examine the probability distribution function of geomagnetic activity indices for southward IMF intervals. We analyze the in situ plasma and magnetic field measurements long-duration large-amplitude southward IMF intervals (called Bs events). The statistical profiles of other solar wind and IMF parameters show significant differences during the periods 1 day before the Bs events for different solar wind transients (such as interplanetary coronal mass ejections and stream interaction regions). As is well known, we find that the solar wind speed is positively correlated with geomagnetic indices and that strong southward IMF is the key in storm triggering but not necessarily for substorms. We find that the solar wind density weakly affects geomagnetic field activity, but the response depends on the type of solar wind transient that includes the strong Bs events. We also find that magnetospheric ultralow-frequency waves are induced by both strong southward IMF and solar wind dynamic pressure disturbances. We suggest that strong Bs events could be predicted from the preceding characteristics of solar wind and IMF changes and that probabilistic forecasting of geomagnetic activity occurrence is potentially useful in space weather forecasting. We present preliminary analysis to demonstrate the out-of-sample ability to predict IMF Bs events with in situ solar wind data.

  10. 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.

  11. magnetosphere can attain when the IMF points REFERENCES AND NOTES

    E-print Network

    Boxer, Steven G.

    magnetosphere can attain when the IMF points northward. REFERENCES AND NOTES 1. J. W. Dungey, Phys Phenomenology and Magnetospheric Processes: Earth and Other Planets, A. Keiling, E. Donovan, F. Bagenal, T

  12. Publications Angling, Angling Records,

    E-print Network

    Publications Angling, Angling Records, and Game Fish Conservation The 1982 edition of "World Record Game Fishes," published by the Inter- national Game Fish Association, 3000 East Las alas Boulevard, Fort Lauder- dale, FL 33316, continues to grow as an important reference work for the serious angler

  13. 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…

  14. BUGS system clock distributor

    NASA Technical Reports Server (NTRS)

    Dietrich, Thomas M.

    1991-01-01

    A printed circuit board which will provide external clocks and precisely measure the time at which events take place was designed for the Bristol University Gas Spectrometer (BUGS). The board, which was designed to interface both mechanically and electrically to the Computer Automated Measurement and Control (CAMAC) system, has been named the BUGS system clock control. The board's design and use are described.

  15. Egyptian "Star Clocks"

    NASA Astrophysics Data System (ADS)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  16. BUGS system clock distributor

    NASA Astrophysics Data System (ADS)

    Dietrich, Thomas M.

    1991-11-01

    A printed circuit board which will provide external clocks and precisely measure the time at which events take place was designed for the Bristol University Gas Spectrometer (BUGS). The board, which was designed to interface both mechanically and electrically to the Computer Automated Measurement and Control (CAMAC) system, has been named the BUGS system clock control. The board's design and use are described.

  17. Variation in the statistical properties of IMF direction fluctuations during the 22-year solar magnetic cycle

    NASA Astrophysics Data System (ADS)

    Erofeev, D. V.

    2014-12-01

    The variation in the IMF direction distribution during the 22-year solar magnetic cycle has been studied. Data obtained in near-Earth orbits and measurements in the heliospheric regions located far from the Earth, performed with the Helios and Ulysses spacecraft devices, have been analyzed. It has been found that the correlation between the azimuth and magnetic field fluctuations is statistically significant in the low-latitude heliospheric region at heliocentric distances of 0.3-5.4 AU, and the sign of this correlation reverses at a change in the polar solar magnetic field orientation. In the polar zones of the heliosphere outside the latitudinal extension of the heliospheric current sheet, the angle correlation coefficient rapidly decreases with increasing heliographic latitude. The angle correlation sign reversal during the 22-year cycle is accompanied by a change of the asymmetry sign of the magnetic field inclination distribution.

  18. Optical Atomic Clocks David Hanneke

    E-print Network

    Hanneke, David

    Optical Atomic Clocks David Hanneke Michelson Postdoctoral Prize Lectures 11 May 2010 #12;Hanneke Optical atomic clock 1 PHz = 1015 Hz Frequency comb http://en.wikipedia.org/wiki/ File:Scappamento.gif T Pendulum clock 103 Quartz watch 105 Optical atomic clock 1014 1/Q C. W. Chou, et al., To be published (2010

  19. 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

  20. Real-time simulation clock

    NASA Technical Reports Server (NTRS)

    Bennington, Donald R. (inventor); Crawford, Daniel J. (inventor)

    1990-01-01

    The invention is a clock for synchronizing operations within a high-speed, distributed data processing network. The clock is actually a distributed system comprising a central clock and multiple site clock interface units (SCIUs) which are connected by means of a fiber optic star network and which operate under control of separate clock software. The presently preferred embodiment is a part of the flight simulation system now in current use at the NASA Langley Research Center.

  1. Resetting Biological Clocks

    ERIC Educational Resources Information Center

    Winfree, Arthur T.

    1975-01-01

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

  2. 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)

  3. 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.

  4. All-optical frame clock recovery from even-multiplexed OTDM signals

    NASA Astrophysics Data System (ADS)

    Yin, Lina; Liu, Guoming; Wu, Jian; Lin, Jintong

    2005-02-01

    Frame clock is useful for packet processing such as header detection and payload demultiplexing. A novel all-optical frame clock recovery scheme based on "intensity reshaper" and mode-locked semiconductor fiber ring laser is demonstrated. The "intensity reshaper" including a polarization controller and a polarizer is the key element to realize frame clock recovery from equal-amplitude even-multiplexed OTDM signals. In theory, a mathematical expression is given to analyze the intensity of harmonic of clock-frequency component. The relative intensity of each clock-frequency component will change with the alterative angle caused by adjusting the PC in the "intensity reshaper", so the desirable clock-frequency component can be enhanced, which is helpful for clock recovery. Moreover, the intensity of harmonic of clock-frequency component is also related to the pulse amplitude, width and period in the multiplexed data. In experiment, 2.5GHz frame clock is extracted from even-multiplexed 4x2.5GHz and 8x2.5GHz OTDM signals respectively. At the same time, bit clock is also recovered by using this scheme. The extracted clock pulses have several desirable features such as low timing jitter, broad wavelength tuning range and polarization independence. This scheme simplifies signal generation and propagation in OTDM systems, which can be applied to clock recovery in high-speed OTDM network.

  5. High-Latitude Ionospheric Dynamics During Conditions of Northward IMF

    NASA Technical Reports Server (NTRS)

    Sharber, J. R.

    1996-01-01

    In order to better understand the physical processes operating during conditions of northward interplanetary magnetic field (IMF), in situ measurements from the Dynamics Explorer-2 (low altitude) polar satellite and simultaneous observations from the auroral imager on the Dynamics Explorer-1 (high altitude) satellite were used to investigate the relationships between optical emissions, particle precipitation, and convective flows in the high-latitude ionosphere. Field aligned current and convective flow patterns during IMF north include polar cap arcs, the theta aurora or transpolar arc, and the 'horse-collar' aurora. The initial part of the study concentrated on the electrodynamics of auroral features in the horse-collar aurora, a contracted but thickened emission region in which the dawn and dusk portions can spread to very high latitudes, while the latter part focused on the evolution of one type of IMF north auroral pattern to another, specifically the quiet-time horse-collar pattern to a theta aurora.

  6. Subtleties of the clock retardation

    NASA Astrophysics Data System (ADS)

    Redži?, D. V.

    2015-11-01

    For a simple electromagnetic model of a clock introduced by Jefimenko (clock # 1 in 1996 Am. J. Phys. 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, dynamical contents of the clock retardation are demonstrated. Somewhat surprisingly, the analysis presented discloses that some familiar relativistic generalizations concerning the retardation of clocks have to be amended.

  7. The Two Sides of the Mental Clock: The Imaginal Hemispatial Effect in the Healthy Brain

    ERIC Educational Resources Information Center

    Conson, Massimiliano; Cinque, Fausta; Trojano, Luigi

    2008-01-01

    When subjects are asked to compare the mental images of two analog clocks telling different times (the mental clock test), they are faster to process angles formed by hands located in the right than in the left half of the dial. In the present paper, we demonstrate that this Imaginal HemiSpatial Effect (IHSE) can be also observed in two modified…

  8. Room 103, transom woodwork and original clock. All clocks are ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    Room 103, transom woodwork and original clock. All clocks are driven by a common signal. - San Bernardino Valley College, Life Science Building, 701 South Mount Vernon Avenue, San Bernardino, San Bernardino County, CA

  9. XRay Emission, Stellar Populations and Determination of IMF

    E-print Network

    X­Ray Emission, Stellar Populations and Determination of IMF S. Sciortino, 1 G. Micela, 1 F the reserved time of Palermo's Observa­ tory scientists will allow us to identify and study their late colors, the more X­ray active stars having photometric indices that make them appear less metallic than

  10. IMF AND EVOLUTION OF CLOSE BINARIES AFTER STARFORMATION BURSTS

    E-print Network

    Popov, Sergei

    IMF AND EVOLUTION OF CLOSE BINARIES AFTER STARFORMATION BURSTS S.B. Popov 1 , M.E. Prokhorov 1 , V the program is avail­ able in WWW: http://xray.sai.msu.ru/ (Nazin et al., 1998)) -- to calculate evolution examined the evolution of 12 types of X­ray sources in close binary systems (both with neutron stars

  11. Possible density dependent local variations in the IMF

    NASA Astrophysics Data System (ADS)

    Kavila, Indulekha; George, Babitha

    2015-08-01

    Variations in the IMF have been reported within open clusters (signifying mass segregation), between globular clusters, within galaxies and between galaxies. Most stars are considered to form in a clustered mode. However, the surface density of YSO's shows a wide range and it is also considered that stars form in the clustered mode only at the peaks of the surface density. The bound cluster formation efficiency in galaxies is observed to be correlated with the Star Formation Rate density which itself is seen to be correlated with the gas surface density by the Kennicutt Schmidt law.Observationally, dense cores in molecular clouds - which go on to produce stars - have a mass spectrum that is broadly consistent with a Salpeter slope of -1.35 at the high mass end. In simulations of clouds with Gaussian fluctuations it is seen that the mass spectrum of peaks which collapse are approximately log-normal, peaking roughly at the average Jeans' mass in the cloud. We explore a possible way in which the IMF could depend on the local gas density. The extent of the variations that can be caused by such a dependence is explored. The IMFs of the sample clusters that are generated are compared with the IMFs of observed clusters and also against radial trends reported in galaxies.

  12. The CMF as provenance of the stellar IMF?

    NASA Astrophysics Data System (ADS)

    Anathpindika, S.

    2011-12-01

    In the present work we examined the hypothesis that, a core mass function (CMF), such as the one deduced for cores in the Orion molecular cloud (OMC), could possibly be the primogenitor of the stellar initial mass function (IMF). Using the rate of accretion of a protostar from its natal core as a free parameter, we demonstrate its quintessential role in determining the shape of the IMF. By varying the rate of accretion, we show that a stellar mass distribution similar to the universal IMF could possibly be generated starting from either a typical CMF such as the one for the OMC, or a uniform distribution of prestellar core masses which leads us to suggest, the apparent similarity in shapes of the CMF and the IMF is perhaps, only incidental. The apodosis of the argument being, complex physical processes leading to stellar birth are crucial in determining the final stellar masses, and consequently, the shape of stellar mass distribution. This work entails partial Monte-Carlo treatment of the problem, and starting with a randomly picked sample of cores, and on the basis of classical arguments which include protostellar feedback and cooling due to emission from warm dust, a theoretical distribution of stellar masses is derived for five realisations of the problem; the magnetic field, though, has been left out of this exercise.

  13. 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.

  14. Observational aspects of IMF draping-related magnetosheath accelerations for northward IMF

    NASA Astrophysics Data System (ADS)

    Harris, B.; Farrugia, C. J.; Erkaev, N. V.; Torbert, R. B.

    2013-10-01

    Acceleration of magnetosheath plasma resulting from the draping of the interplanetary magnetic field (IMF) around the magnetosphere can give rise to flow speeds that exceed that of the solar wind (VSW) by up to ~60%. Three case event studies out of 34 identified events are described. We then present a statistical study of draping-related accelerations in the magnetosheath. Further, we compare the results with the recent theory of Erkaev et al. (2011, 2012). We present a methodology to help distinguish draping-related accelerations from those caused by magnetic reconnection. To rule out magnetopause reconnection at low latitudes, we focus mainly on the positive Bz phase during the passage of interplanetary coronal mass ejections (ICMEs), as tabulated in Richardson and Cane (2010) for 1997-2009, and adding other events from 2010. To avoid effects of high-latitude reconnection poleward of the cusp, we also consider spacecraft observations made at low magnetic latitudes. We study the effect of upstream Alfvén Mach number (MA) and magnetic local time (MLT) on the speed ratio V/VSW. The comparison with theory is good. Namely, (i) flow speed ratios above unity occur behind the dawn-dusk terminator, (ii) those below unity occur on the dayside magnetosheath, and (iii) there is a good general agreement in the dependence of the V ratio on MA.

  15. The IMF of the field population of 30 Doradus

    NASA Astrophysics Data System (ADS)

    Selman, F. J.; Melnick, J.

    2005-12-01

    The star-formation history and IMF of the field population of the 30 Doradus super-association is determined using Wide Field Imager photometry. The cluster NGC 2070 and the OB association LH104 are also studied and used for comparison. The star-formation history of the 30 Doradus super-association appears to be characterized by a large increase in star-formation activity 10 Myr to 20 Myr ago. This seems to be the case across the whole eastern half of the LMC as demonstrated by the ages of stellar populations as far away as 30 Doradus and Shapley's Constellation III. Star-formation appears to be occurring at a constant rate in the field and in loose associations, and in bursts in the clusters. The field IMF is found to have almost the exact Salpeter slope in the range 7 ~M_? ? M ? 40 ~M_?, at odds with previous claims. We find that, for objects with more complex star-formation histories, Be stars and selective incompleteness strongly affect the determination of the IMF for M > 40~ M_?, naturally explaining the observed deviation of the high mass IMF slope from the Salpeter value. The present work supports the idea of a universal IMF. Based on observations obtained with the MPG/ESO 2.2-m telescope at La Silla Observatory. Tables 1-3 are only available in electronic form at http://www.edpsciences.org. Full Table 2 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/443/851

  16. Estimating the instability of a composite clock

    NASA Technical Reports Server (NTRS)

    Greenhall, Charles A.

    2004-01-01

    A composite clock created from a local clock ensemble is known by its time offsets from the ensemble clocks. By a geometrical argument, estimate for the instability of the composite clock are calculated from the instabilities of the ensemble clocks, individually and against the composite clock. The method is illustrated by examples using simulated and real ensembles.

  17. Clock Analysis of X10 Nalini Vasudevan

    E-print Network

    constructs: finish, atomic Focus: Synchronization between activities through clocks async { /* body of asyncClock Analysis of X10 Programs Nalini Vasudevan Mentor: Olivier Tardieu Manager: Vijay Saraswat #12 */ } #12;Clocks in X10 Barriers Declare clocks Share clocks Synchronize next() function All tasks clocked

  18. Tutorial: Clock and Clock Systems Performance Measures

    NASA Technical Reports Server (NTRS)

    Allan, David W.

    1996-01-01

    This tutorial contains basic material - familiar to many. This will be used as a foundation upon which we will build - bringing forth some new material and equations that have been developed especially for this tutorial. These will provide increased understanding toward parameter estimation of clock and clock system's performance. There is a very important International Telecommunications Union (ITU) handbook being prepared at this time which goes much further than this tutorial has time to do. I highly recommend it as an excellent resource document. The final draft is just now being completed, and it should be ready late in 1996. It is an outstanding handbook; Dr. Sydnor proposed to the ITU-R several years ago, and is the editor with my assistance. We have some of the best contributors in the community from around the world who have written the ten chapters in this handbook. The title of the handbook is 'Selection and use of Precise Frequency and Time Systems'. It will be available from the ITU secretariat in Geneva, Switzerland, but NAVTEC Seminars also plans to be a distributor.

  19. Iron around the clock.

    PubMed

    Tissot, Nicolas; Przybyla-Toscano, Jonathan; Reyt, Guilhem; Castel, Baptiste; Duc, Céline; Boucherez, Jossia; Gaymard, Frédéric; Briat, Jean-François; Dubos, Christian

    2014-07-01

    Carbon assimilation, a key determinant of plant biomass production, is under circadian regulation. Light and temperature are major inputs of the plant clock that control various daily rhythms. Such rhythms confer adaptive advantages to the organisms by adjusting their metabolism in anticipation of environmental fluctuations. The relationship between the circadian clock and nutrition extends far beyond the regulation of carbon assimilation as mineral nutrition, and specially iron homeostasis, is regulated through this mechanism. Conversely, iron status was identified as a new and important input regulating the central oscillator, raising the question of the nature of the Fe-dependent signal that modulates the period of the circadian clock. Several lines of evidence strongly suggest that fully developed and functional chloroplasts as well as early light signalling events, involving phytochromes, are essential to couple the clock to Fe responses. Nevertheless, the exact nature of the signal, which most probably involves unknown or not yet fully characterized elements of the chloroplast-to-nucleus retrograde signalling pathway, remains to be identified. Finally, this regulation may also involves epigenetic components. PMID:24908512

  20. Clock Reaction: Outreach Attraction

    ERIC Educational Resources Information Center

    Carpenter, Yuen-ying; Phillips, Heather A.; Jakubinek, Michael B.

    2010-01-01

    Chemistry students are often introduced to the concept of reaction rates through demonstrations or laboratory activities involving the well-known iodine clock reaction. For example, a laboratory experiment involving thiosulfate as an iodine scavenger is part of the first-year general chemistry laboratory curriculum at Dalhousie University. With…

  1. Narrative Clock Sculptures

    ERIC Educational Resources Information Center

    Popp, Linda

    2005-01-01

    Art teacher Linda Popp and artist H. Ed Smith team up to teach about creating sculptural clocks. This lesson shows how a portrait can be created using various media. Students based projects on someone in their lives they have known for a long time. This sculptural problem was part of a series of portrait and self-portrait lessons with a high…

  2. Circadian Clock, Cancer, and Chemotherapy

    PubMed Central

    2015-01-01

    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

  3. The High Mass Stellar IMF in M31

    NASA Astrophysics Data System (ADS)

    Weisz, Daniel R.; PHAT

    2015-01-01

    I will present a progress report on our analysis of the high mass stellar initial mass (IMF) in M31 from the Panchromatic Hubble Andromeda Treasury program (PHAT), an 828-orbit HST survey of 1/3 of M31's star-forming disk. To date, we have measured the present day mass function (MF) above 2 M? for nearly 1000 young star clusters (< 300 Myr) by modeling their resolved star color-magnitude diagrams. The MF slopes of individual clusters show a tremendous degree of scatter, with some clusters differing substantially from Salpeter. There appears to be little correlation between physical properties of the clusters (e.g., mass, age) and their MF slopes. From analysis of the ensemble of clusters, we recover a global MF that is both steeper than Salpeter and one that exhibits a high degree of variance, which, if taken at face value, does not appear comapabilte with a universal IMF model. We are using an extensive suite of artificial clusters, designed to mimic observations, to investigate whether effects such as finite sampling statistics, dynamical evolution (e.g., mass segregation), stellar multiplicity, cluster membership, crowding, and/or completeness can be responsible for the observed MF properties, or if the M31 cluster population has an intrinsically non-universal IMF.

  4. On the IMF in a Triggered Star Formation Context

    E-print Network

    Zhou, Tingtao; Lin, D N C; Gritschneder, Matthias; Lau, Herbert

    2015-01-01

    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. W...

  5. The Magnetospheric Response to Abrupt Variations in the IMF Orientation

    NASA Astrophysics Data System (ADS)

    Sibeck, D. G.

    2014-12-01

    We run the University of Michigan's BATS-R-US global magnetohydrodynamic model at NASA/GSFC's CCMCto study the magnetospheric response to abrupt variations in the IMF orientation but constant solar wind plasmaparameters. IMF rotations from southward to duskward orientations diminish reconnection rates and the flow ofplasma to the dayside magnetopause, launch Alfven waves that carry strong duskward magnetic field perturbationsto the cusp ionosphere, introduce a weak duskward magnetic field perturbation to the outer dayside magnetosphere, twistthe magnetotail current sheet counterclockwise when viewed from the Sun, flatten the north/south dimensions of the distant magnetotail, andgenerate a broad slow-mode fan on the magnetotail flanks. Southward IMF turnings strengthen the Region 1 Birkelandcurrents, prominently depressing magnetic field strengths in the inner dayside magnetosphere and to a lesserdegree those in the outer magnetosphere, consistent with inward dayside magnetopause erosion. The daysidemagnetopause becomes blunter. As evidenced by enhanced magnetosheath thermal and magnetosphericmagnetic pressures, the magnetopause therefore becomes subject to a greater fraction of the incident solar winddynamic pressure at locations away from the subsolar point.

  6. ZFIRE Survey: Studying the IMF at z~2

    NASA Astrophysics Data System (ADS)

    Nanayakkara, Themiya

    2015-08-01

    The development of sensitive Near Infra-Red instruments has made it possible to study the galaxy properties at z~2, just 3Gy after the Big Bang. This is expected to be the time period where galaxies are actively star forming and evolving rapidly to form the massive galaxies that are observed in our local neighborhood.As a part of the ZFIRE survey we used the MOSFIRE on Keck to study environment, metallicity and ISM properties of galaxies at these redshifts. This allowed us to spectroscopically confirm the highest redshift cluster found so far.In my talk I will present results of the first ever attempt to constrain the Initial Mass Function (IMF) of galaxies at these redshifts using a cluster and a field sample. We have investigated the degeneracy between the star formation histories and the IMF to make strong constrains on the stellar mass distribution of these galaxies using synthetic stellar spectra. Our results will demonstrate the possibility of the universality of the IMF as a function of time and environment.

  7. Measuring time with physical clocks

    E-print Network

    Esteban Castro-Ruiz; Flaminia Giacomini; ?aslav Brukner

    2015-07-07

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

  8. Einstein's concept of a clock and clock paradox

    E-print Network

    Wang Guowen

    2005-01-25

    A geometric illustration of the Lorentz transformations is given. According to similarity between space and time and correspondence between a ruler and a clock, like the division number in a moving ruler, the tick number of a moving clock is independent of its relative speed and hence invariant under the Lorentz transformations. So the hand of the moving clock never runs slow but the time interval between its two consecutive ticks contracts. Thus it is Einstein's concept of slowing of the hands of moving clocks to create the clock paradox or twin paradox. Regrettably, the concept of the clock that Einstein retained is equivalent to Newton's concept of absolute time that he rejected. This is a blemish in Einstein's otherwise perfect special relativity.

  9. MHD simulations using average solar wind conditions for substorms observed under northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Park, K. S.; Lee, D.-Y.; Ogino, T.; Lee, D. H.

    2015-09-01

    Substorms are known to sometimes occur even under northward interplanetary magnetic field (IMF) conditions. In this paper, we perform three-dimensional global magnetohydrodynamic simulations to examine dayside reconnection, tail, and ionospheric signatures for two cases of substorm observations under prolonged northward and dawnward IMF conditions: (1) a strongly northward/dawnward IMF case with BIMF = (0, -20, 20) nT; (2) a weakly northward/dawnward IMF case with BIMF = (0, -2, 2) nT. Throughout the simulations, we used the constant solar wind conditions to reflect the prolonged solar wind conditions around the substorm times. We found that, in both cases, the tail reconnection occurred after the usual high-latitude reconnection on the dayside, providing a possible energy source for later triggered substorm observations under northward IMF conditions. The presence of an equal amount of IMF By allows the high-latitude reconnected magnetic field lines to transport to the tail lobe, eventually leading to the tail reconnection. The simulation results also revealed the following major differences between the two cases: First, the reconnection onset (both on dayside and in the tail) occurs earlier in the strongly northward IMF case than in the weakly northward IMF case. Second, the polar cap size, which is finite in both cases despite the northward IMF conditions and thus supports the lobe energy buildup needed for the substorm occurrences, is larger in the strongly northward IMF case. Accordingly, the polar cap potential is far larger in the strongly northward IMF case (hundreds of kilovolt) than in the weakly northward IMF case (tens of kilovolt). Third, in the strongly northward IMF case, the strong earthward tail plasma flow appears to be caused by the enhanced convection (so enhanced duskward Ey) due to the tail reconnection. In contrast, in the weakly northward IMF case, the earthward tail plasma flow increases gradually in association with a modestly increased duskward electric field. In addition, the inner plasma pressure and the cross tail current near the reconnection site increase significantly in the strongly northward IMF case but less significantly in the weakly northward IMF case after the onset of the tail reconnection. In conclusion, the simulation results support observations of the substorms under northward IMF conditions in the presence of an equal amount of IMF By by demonstrating the energy input via dayside reconnection and the subsequent occurrence of the tail reconnection.

  10. Magnetization dynamics, Bennett clocking and associated energy dissipation in multiferroic logic

    NASA Astrophysics Data System (ADS)

    Salehi Fashami, Mohammad; Roy, Kuntal; Atulasimha, Jayasimha; Bandyopadhyay, Supriyo

    2011-04-01

    It has been recently shown that the magnetization of a multiferroic nanomagnet, consisting of a magnetostrictive layer elastically coupled to a piezoelectric layer, can be rotated by a large angle if a tiny voltage of a few tens of millivolts is applied to the piezoelectric layer. The potential generates stress in the magnetostrictive layer and rotates its magnetization by ~ 90° to implement Bennett clocking in nanomagnetic logic chains. Because of the small voltage needed, this clocking method is far more energy efficient than those that would employ spin transfer torque or magnetic fields to rotate the magnetization. In order to assess if such a clocking scheme can also be reasonably fast, we have studied the magnetization dynamics of a multiferroic logic chain with nearest-neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We find that clock rates of 2.5 GHz are feasible while still maintaining the exceptionally high energy efficiency. For this clock rate, the energy dissipated per clock cycle per bit flip is ~ 52 000 kT at room temperature in the clocking circuit for properly designed nanomagnets. Had we used spin transfer torque to clock at the same rate, the energy dissipated per clock cycle per bit flip would have been ~ 4 × 108 kT, while with current transistor technology we would have expended ~ 106 kT. For slower clock rates of 1 GHz, stress-based clocking will dissipate only ~ 200 kT of energy per clock cycle per bit flip, while spin transfer torque would dissipate about 108 kT. This shows that multiferroic nanomagnetic logic, clocked with voltage-generated stress, can emerge as a very attractive technique for computing and signal processing since it can be several orders of magnitude more energy efficient than current technologies.

  11. Magnetization dynamics, Bennett clocking and associated energy dissipation in multiferroic logic.

    PubMed

    Fashami, Mohammad Salehi; Roy, Kuntal; Atulasimha, Jayasimha; Bandyopadhyay, Supriyo

    2011-04-15

    It has been recently shown that the magnetization of a multiferroic nanomagnet, consisting of a magnetostrictive layer elastically coupled to a piezoelectric layer, can be rotated by a large angle if a tiny voltage of a few tens of millivolts is applied to the piezoelectric layer. The potential generates stress in the magnetostrictive layer and rotates its magnetization by ~90° to implement Bennett clocking in nanomagnetic logic chains. Because of the small voltage needed, this clocking method is far more energy efficient than those that would employ spin transfer torque or magnetic fields to rotate the magnetization. In order to assess if such a clocking scheme can also be reasonably fast, we have studied the magnetization dynamics of a multiferroic logic chain with nearest-neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We find that clock rates of 2.5 GHz are feasible while still maintaining the exceptionally high energy efficiency. For this clock rate, the energy dissipated per clock cycle per bit flip is ~52,000 kT at room temperature in the clocking circuit for properly designed nanomagnets. Had we used spin transfer torque to clock at the same rate, the energy dissipated per clock cycle per bit flip would have been ~4 x 10? kT, while with current transistor technology we would have expended ~10? kT. For slower clock rates of 1 GHz, stress-based clocking will dissipate only ~200 kT of energy per clock cycle per bit flip, while spin transfer torque would dissipate about 10? kT. This shows that multiferroic nanomagnetic logic, clocked with voltage-generated stress, can emerge as a very attractive technique for computing and signal processing since it can be several orders of magnitude more energy efficient than current technologies. PMID:21389584

  12. 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.

  13. 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.

  14. Huygens synchronization of two clocks

    PubMed Central

    Oliveira, Henrique M.; Melo, Luís V.

    2015-01-01

    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 behaviour is observed experimentally, validating the model. PMID:26204557

  15. Huygens synchronization of two clocks.

    PubMed

    Oliveira, Henrique M; Melo, Luís V

    2015-01-01

    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 behaviour is observed experimentally, validating the model. PMID:26204557

  16. Huygens synchronization of two clocks

    NASA Astrophysics Data System (ADS)

    Oliveira, Henrique M.; Melo, Luís V.

    2015-07-01

    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 behaviour is observed experimentally, validating the model.

  17. The story of UGC 11919 - a galaxy which could possess a non-standard stellar IMF

    NASA Astrophysics Data System (ADS)

    Saburova, Anna; Zasov, Anatoly; Uklein, Roman; Katkov, Ivan

    2015-08-01

    We performed long-slit observations of a spiral galaxy UGC11919 with the Russian 6-m telescope to study its kinematics and stellar population. The previous studies allowed to suspect that this galaxy possesses a peculiarly low mass-to-light ratio M/L of stellar population. A bottom-light stellar initial mass function (IMF) could explain the low value of M/L. The performed spectral observations and the estimation of stellar mass-to-light ratio for different evolutionary models using both the broad-band magnitudes and the detailed spectral data confirm this peculiarity if to accept the inclination angle i = 30 or higher, as it was obtained earlier from the optical isophotes and HI velocity field based on the WSRT observations. However we show that the HI isophotes are compatible with the lower value of i, hence the question of peculiarly low M/L remains open. The derived stellar kinematic profiles reveal a signature of kinematically decoupled nuclear disk in the galaxy. We show that the disk of UGC11919 is dynamically overheated independently of the adopted inclination angle - probably as the result of the gravitational interaction with companions which were found in the HI line.

  18. Robust Clock Synchronization in Wireless Sensor Networks 

    E-print Network

    Saibua, Sawin

    2010-10-12

    Clock synchronization between any two nodes in a Wireless Sensor Network (WSNs) is generally accomplished through exchanging messages and adjusting clock offset and skew parameters of each node’s clock. To cope with unknown network message delays...

  19. 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.

  20. 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…

  1. The Response of the Dayside Equatorial Electrojet to Step-like Changes of IMF Bz

    NASA Astrophysics Data System (ADS)

    Ohtani, Shinichi; Uozumi, Teiji; Kawano, Hideaki; Yoshikawa, Akimasa; Utada, Hisashi; Nagatsuma, Tsutomu; Yumoto, Kiyohumi

    2013-04-01

    The equatorial electrojet (EEJ) is driven by zonal electric fields, which are known to be well correlated with the interplanetary electric field and therefore with the interplanetary magnetic field (IMF) Bz component. In the present study we investigate how the equatorial horizontal (H) magnetic component, and therefore the EEJ, responds to step-like changes of IMF Bz. The reduction of southward IMF Bz (northward turnings) and that of northward IMF Bz (southward turning) are examined separately. The result shows that for the northward turnings, the EEJ immediately starts to weaken with the accuracy of the estimates of the travel times of the IMF changes. The time constant of the response is much longer, and the equatorial H component decreases continuously by 40 nT for 30 min after the northward turnings. In contrast, the response of the EEJ to the southward turnings is far less clear in both magnitude and timing. The difference in the EEJ response to the northward and southward turnings presumably reflects the fact that the magnetosphere-ionosphere system is more sensitive to IMF Bz for southward IMF Bz than for northward IMF Bz. It is suggested that there exists a global current system that connects the auroral electrojets and the EEJ, and the electric field penetrates to the dip equator as the polar cap potential extends to lower latitudes. We also address the effect of night-side substorm activity on the EEJ in the context of IMF Bz changes.

  2. Methodologies for steering clocks

    NASA Technical Reports Server (NTRS)

    Chadsey, Harold

    1995-01-01

    One of the concerns of the PTTI community is the coordination of one time scale with another. This is accomplished through steering one clock system to another, with a goal of a zero or constant offset in time and frequency. In order to attain this goal, rate differences are calculated and allowed for by the steering algorithm. This paper will present several of these different methods of determining rate differences. Ideally, any change in rate should not cause the offset to change sign (overshoot) by any amount, but certainly not by as much as its previous absolute value. The advantages and disadvantages of each depend on the user's situation.

  3. The Vitamin C Clock Reaction.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Describes an iodine clock reaction that produces an effect similar to the Landolt clock reaction. This reaction uses supermarket chemicals and avoids iodate, bisulfite, and mercury compounds. Ascorbic acid and tincture of iodine are the main reactants with alternate procedures provided for vitamin C tablets and orange juice. (DDR)

  4. Ideal clocks - a convenient fiction

    E-print Network

    Krzysztof Lorek; Jorma Louko; Andrzej Dragan

    2015-08-24

    We show that no device built according to the rules of quantum field theory can measure proper time along its path. Highly accelerated quantum clocks experience the Unruh effect, which inevitably influences their time rate. This contradicts the concept of an ideal clock, whose rate should only depend on the instantaneous velocity.

  5. 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

  6. The financial crisis and global health: the International Monetary Fund's (IMF) policy response.

    PubMed

    Ruckert, Arne; Labonté, Ronald

    2013-09-01

    In this article, we interrogate the policy response of the International Monetary Fund (IMF) to the global financial crisis, and discuss the likely global health implications, especially in low-income countries. In doing so, we ask if the IMF has meaningfully loosened its fiscal deficit targets in light of the economic challenges posed by the financial crisis and adjusted its macro-economic policy advice to this new reality; or has the rhetoric of counter-cyclical spending failed to translate into additional fiscal space for IMF loan-recipient countries, with negative health consequences? To answer these questions, we assess several post-crisis IMF lending agreements with countries requiring financial assistance, and draw upon recent academic studies and civil society reports examining policy conditionalities still being prescribed by the IMF. We also reference recent studies examining the health impacts of these conditionalities. We demonstrate that while the IMF has been somewhat more flexible in its crisis response than in previous episodes of financial upheaval, there has been no meaningful rethinking in the application of dominant neoliberal macro-economic policies. After showing some flexibility in the initial crisis response, the IMF is pushing for excessive contraction in most low and middle-income countries. We conclude that there remains a wide gap between the rhetoric and the reality of the IMF's policy and programming advice, with negative implications for global health. PMID:22504946

  7. Probabilistic Forecasting Analysis of Geomagnetic Indices for IMF Bs-events

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Moldwin, M.

    2014-12-01

    Strong southward interplanetary magnetic field (IMF Bs) intervals are important to drive disturbances in the Earth's magnetosphere. However, high-accuracy forecast of IMF Bz is not available from current heliospheric models. Here we perform a follow-up study of McPherron and Siscoe [2004] to examine the statistical characteristics of interplanetary plasma/magnetic field and probability distribution function of geomagnetic activity indices for strong IMF Bs intervals. It is shown that the occurrence of long-duration, large-amplitude IMF Bs intervals, related with different solar wind transients (such as ICME, SIR), are preceded by and change with a distinctive set of other solar wind/IMF parameters. We find that solar wind speed is positively correlated with geomagnetic indices, and that strong IMF Bs is the key to trigger storm but not necessarily substorm. We also find that solar wind density weakly affects geomagnetic activity, and the response depends on different kinds of solar wind transients that include the strong IMF Bs-events. We also find that magnetospheric ULF waves are induced by both strong southward IMF intervals and solar wind dynamic pressure disturbances.

  8. 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.

  9. 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

  10. 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.

  11. Acceleration effects on atomic clocks

    E-print Network

    F. Dahia; P. J. Felix de Araujo

    2015-07-27

    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.

  12. Acceleration effects on atomic clocks

    NASA Astrophysics Data System (ADS)

    Dahia, F.; da Silva, P. J. Felix

    2015-09-01

    We consider a free massive particle inside a box that 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 instantaneous acceleration on the rate of atomic clocks. We argue that our result does not violate the clock hypothesis.

  13. The IMF-sensitive 1.14-?m Na I doublet in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Smith, Russell J.; Alton, Padraig; Lucey, John R.; Conroy, Charlie; Carter, David

    2015-11-01

    We present J-band spectroscopy of passive galaxies focusing on the Na I doublet at 1.14 ?m. Like the Na I 0.82 ?m doublet, this feature is strong in low-mass stars and hence may provide a useful probe of the initial mass function (IMF). From high signal-to-noise composite spectra, we find that Na I 1.14 ?m increases steeply with increasing velocity dispersion, ?, and for the most massive galaxies (? ? 300 km s-1) is much stronger than predicted from synthetic spectra with Milky Way-like IMFs and solar abundances. Reproducing Na I 1.14 ?m at high ? likely requires either a very high [Na/H], or a bottom-heavy IMF, or a combination of both. Using the Na D line to break the degeneracy between IMF and abundance, we infer [Na/H] ? +0.5 and a steep IMF (single-slope-equivalent x ? 3.2, where x = 2.35 for Salpeter), for the high-? galaxies. At lower mass (? = 50-100 km s-1), the line strengths are compatible with Milky Way (MW)-like IMFs and near-solar [Na/H]. We highlight two galaxies in our sample where strong gravitational lensing masses favour MW-like IMFs. Like the high-? sample on average, these galaxies have strong Na I 1.14 ?m; taken in isolation their sodium indices imply bottom-heavy IMFs which are hard to reconcile with the lensing masses. An alternative full-spectrum-fitting approach, applied to the high-? sample, recovers an IMF less heavy than Salpeter, but under-predicts the Na I 1.14 ?m line at the 5? level. We conclude that current models struggle to reproduce this feature in the most massive galaxies without breaking other constraints, and caution against over-reliance on the sodium lines in spectroscopic IMF studies.

  14. IMF / World Bank boards of governors discuss population, migration.

    PubMed

    1994-05-01

    A brief presentation was given of the statements Dr. Nafis Sadik, Executive Director of the UN Fund for Population Activities (UNFPA) and Secretary General of the 1994 International Conference on Population and Development (ICPD), made before a meeting of the International Monetary Fund (IMF) and the World Bank on resource flows to developing countries, population, international trade, and migration. The meeting was attended by finance ministers from 24 countries. The IMF Managing Director gave an overview at the meeting of the world economic situation and the need for international assistance for effective population and family planning programs. Dr. Sadik emphasized this need as a requirement for implementation of the 20-year ICPD Programme of Action. The increased investment was considered beneficial because it would increase life expectancy, lower demand for health and education services, reduce pressure in the job market, reduce economic hardship, and increase social stability. The growth of prosperity was considered by Dr. Sadik to be tied to increased demand for housing, energy, and utilities. A slower and more balanced population growth would allow for government services to meet demands and for the world to adjust to increasing numbers of people. Several ministers supported the call for increased funding of population programs and poverty reduction programs. A special communique by ministers recognized that the connections between economic growth, population, poverty reduction, health, investment in human resources, and environmental degradation must be integrated into population policy. Ministers urged the ICPD to emphasize improvements in primary school enrollment in low income countries, in access to family planning and health services, and in maternal and child mortality rates. Ministers wanted to see increases in the proportion of aid directed to population programs above the current 1.25%. Requests were made for more research into the social, political, and economic impact of international migration among both host and origin countries. PMID:12179004

  15. 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.

  16. Response of reverse convection to fast IMF transitions

    NASA Astrophysics Data System (ADS)

    Taguchi, S.; Tawara, A.; Hairston, M. R.; Slavin, J. A.; Le, G.; Matzka, J.; Stolle, C.

    2015-05-01

    The nature of the transition that high-latitude reverse convection makes in response to fast interplanetary magnetic field (IMF) changes is investigated using observations from multiple spacecraft and a ground magnetometer array. We focused on two fast IMF-transition events on 22 April 2006. Immediately after the first event, three ST5 spacecraft identified a clear change in the distribution of the polar cap field-aligned current. Coordinate observations with the Greenland magnetometer chain showed that the near-noon Hall current distribution, which is closely related to the polar cap field-aligned current or reverse convection, was in a transition state for about 10 min. For the second event, the Greenland magnetic perturbations also showed that a transition state occurred in the near-noon sector for 10-15 min. Three DMSP spacecraft that traversed the polar cap provided evidence showing that variations of the ground magnetic perturbations were produced by the transition from clockwise plasma circulation to the anticlockwise circulation over the polar cap. A simple calculation based on the Biot-Savart law shows that the near-noon transition state is consistent with the approach of a new convection region to the near-noon sector at the speed of 0.5-1 km s-1, which is coupled with the moving away of the old convection region at a similar speed. For the higher-latitude sunward flow region, it is found that the convection takes a transition state almost simultaneously (within 1 min) with that in the near-noon sector, i.e., quasi-instantaneous response.

  17. Radio Controlled Clocks Speaker/Author: Michael A. Lombardi

    E-print Network

    to their radio controlled clocks as "atomic clocks", but that description isn't true. A real atomic clock has receives a signal sent from a place where an atomic clock is located. And as we shall see, radio clocks existed long before atomic clocks were invented. Radio time signals were referenced to pendulum clocks

  18. Clock genes and female reproduction 

    E-print Network

    Chen, Cynthia

    2009-01-01

    The involvement of clock genes in the temporal regulation of the function and lifespan of the corpus luteum (CL) has not been investigated in detail. Immunohistochemistry and real-time quantitative PCR techniques were used ...

  19. 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.

  20. The IMF dependence of the local time of transpolar arcs: Implications for formation mechanism

    NASA Astrophysics Data System (ADS)

    Fear, R. C.; Milan, S. E.

    2012-03-01

    Transpolar arcs are auroral features that extend from the nightside auroral oval into the polar cap. It is well established that they occur predominantly when the interplanetary magnetic field (IMF) has a northward component (Bz > 0). Results concerning how the magnetic local time at which transpolar arcs form might depend upon the IMF dawn-dusk component (BY) are more mixed. Some studies have found a correlation between these two variables, with Northern Hemisphere arcs forming predominantly premidnight when BY > 0 and postmidnight when BY < 0 and vice versa in the Southern Hemisphere. However, a more recent statistical study found that there was no significant correlation, and other studies find that the formation of moving arcs is triggered by a change in the sign of the IMF BY component. In this paper, we investigate the relationship between the magnetic local time at which transpolar arcs form and the IMF BY component. It is found that there is indeed a correlation between the magnetic local time at which transpolar arcs form and the IMF BY component, which acts in opposite senses in the Northern and Southern hemispheres. However, this correlation is weak if the IMF is only averaged over the hour before the first emergence of the arc and becomes stronger if the IMF is averaged 3-4 h beforehand. This is consistent with a mechanism where the magnetic local time at which the arc first forms depends on the BY component in the magnetotail adjacent to the plasma sheet, which is determined by the IMF BY component during intervals of dayside reconnection in the hours preceding the first emergence of the arc. We do not find evidence for the triggering of arcs by an IMF BY sign change.

  1. Complex bird clocks.

    PubMed Central

    Gwinner, E; Brandstätter, R

    2001-01-01

    The circadian pacemaking system of birds comprises three major components: (i) the pineal gland, which rhythmically synthesizes and secretes melatonin; (ii) a hypothalamic region, possibly equivalent to the mammalian suprachiasmatic nuclei; and (iii) the retinae of the eyes. These components jointly interact, stabilize and amplify each other to produce a highly self-sustained circadian output. Their relative contribution to overt rhythmicity appears to differ between species and the system may change its properties even within an individual depending, for example, on its state in the annual cycle or its photic environment. Changes in pacemaker properties are partly mediated by changes in certain features of the pineal melatonin rhythm. It is proposed that this variability is functionally important, for instance, for enabling high-Arctic birds to retain synchronized circadian rhythms during the low-amplitude zeitgeber conditions in midsummer or for allowing birds to adjust quickly their circadian system to changing environmental conditions during migratory seasons. The pineal melatonin rhythm, apart from being involved in generating the avian pacemaking oscillation, is also capable of retaining day length information after isolation from the animal. Hence, it appears to participate in photoperiodic after-effects. Our results suggest that complex circadian clocks have evolved to help birds cope with complex environments. PMID:11710987

  2. Pitfalls of Insulin Pump Clocks

    PubMed Central

    Reed, Amy J.

    2014-01-01

    The objective was to raise awareness about the importance of ensuring that insulin pumps internal clocks are set up correctly at all times. This is a very important safety issue because all commercially available insulin pumps are not GPS-enabled (though this is controversial), nor equipped with automatically adjusting internal clocks. Special attention is paid to how basal and bolus dose errors can be introduced by daylight savings time changes, travel across time zones, and am-pm clock errors. Correct setting of insulin pump internal clock is crucial for appropriate insulin delivery. A comprehensive literature review is provided, as are illustrative cases. Incorrect setting can potentially result in incorrect insulin delivery, with potential harmful consequences, if too much or too little insulin is delivered. Daylight saving time changes may not significantly affect basal insulin delivery, given the triviality of the time difference. However, bolus insulin doses can be dramatically affected. Such problems may occur when pump wearers have large variations in their insulin to carb ratio, especially if they forget to change their pump clock in the spring. More worrisome than daylight saving time change is the am-pm clock setting. If this setting is set up incorrectly, both basal rates and bolus doses will be affected. Appropriate insulin delivery through insulin pumps requires correct correlation between dose settings and internal clock time settings. Because insulin pumps are not GPS-enabled or automatically time-adjusting, extra caution should be practiced by patients to ensure correct time settings at all times. Clinicians and diabetes educators should verify the date/time of insulin pumps during patients’ visits, and should remind their patients to always verify these settings. PMID:25355713

  3. How chemistry influences cloud structure, star formation, and the IMF

    E-print Network

    Hocuk, S; Spaans, M; Caselli, P

    2015-01-01

    In the earliest phases of star-forming clouds, stable molecular species, such as CO, are important coolants in the gas phase. Depletion of these molecules on dust surfaces affects the thermal balance of molecular clouds and with that their whole evolution. For the first time, we study the effect of grain surface chemistry (GSC) on star formation and its impact on the initial mass function (IMF). We follow a contracting translucent cloud in which we treat the gas-grain chemical interplay in detail, including the process of freeze-out. We perform 3d hydrodynamical simulations under three different conditions, a pure gas-phase model, a freeze-out model, and a complete chemistry model. The models display different thermal evolution during cloud collapse. The equation of state (EOS) of the gas becomes softer with CO freeze-out and the results show that at the onset of star formation, the cloud retains its evolution history such that the number of formed stars differ (by 7%) between the three models. While the stel...

  4. 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.

  5. Monte-Carlo experiments on star-cluster induced integrated-galaxy IMF variations

    E-print Network

    Carsten Weidner; Pavel Kroupa

    2004-09-30

    As most if not all stars are born in stellar clusters the shape of the mass function of the field stars is not only determined by the initial mass function of stars (IMF) but also by the cluster mass function (CMF). In order to quantify this Monte-Carlo simulations were carried out by taking cluster masses randomly from a CMF and then populating these clusters with stars randomly taken from an IMF. Two cases were studied. Firstly the star masses were added randomly until the cluster mass was reached. Secondly a number of stars, given by the cluster mass divided by an estimate of the mean stellar mass and sorted by mass, were added until the desired cluster mass was reached. Both experiments verified the analytical results of Kroupa & Weidner (2003) that the resulting integrated stellar initial mass function is a folding of the IMF with the CMF and therefore steeper than the input IMF above 1 Msol.

  6. Dark matter and IMF normalization in Virgo dwarf early-type galaxies

    NASA Astrophysics Data System (ADS)

    Tortora, C.; La Barbera, F.; Napolitano, N. R.

    2016-01-01

    In this work, we analyse the dark matter (DM) fraction, fDM, and mass-to-light ratio mismatch parameter, ?IMF (computed with respect to a Milky Way-like initial mass function), for a sample of 39 dwarf early-type galaxies in the Virgo cluster. Both fDM and ?IMF are estimated within the central (one effective radius) galaxy regions, with a Jeans dynamical analysis that relies on galaxy velocity dispersions, structural parameters, and stellar mass-to-light ratios from the SMAKCED survey. In this first attempt to constrain, simultaneously, the initial mass function (IMF) normalization and the DM content, we explore the impact of different assumptions on the DM model profile. On average, for an Navarro, Frenk & White (NFW) profile, the ?IMF is consistent with a Chabrier-like normalization ({? _IMF}˜ 1), with {f_DM}˜ 0.35. One of the main results of this work is that for at least a few systems the ?IMF are heavier than the Milky Way-like value (i.e. either top- or bottom-heavy). When introducing tangential anisotropy, larger ?IMF and smaller fDM are derived. Adopting a steeper concentration-mass relation than that from simulations, we find lower ?IMF ( ? 1) and larger fDM. A constant M/L profile with null fDM gives the heaviest ?IMF (˜2). In the MONDian framework, we find consistent results to those for our reference NFW model. If confirmed, the large scatter of ?IMF for dEs would provide (further) evidence for a non-universal IMF in early-type systems. On average, our reference fDM estimates are consistent with those found for low-?e (˜ 100 km s^{-1}) early-type galaxies (ETGs). Furthermore, we find fDM consistent with values from the SMAKCED survey, and find a double-value behaviour of fDM with stellar mass, which mirrors the trend of dynamical M/L and global star formation efficiency (from abundance matching estimates) with mass.

  7. A critique of vole clocks

    NASA Astrophysics Data System (ADS)

    Martin, Robert A.

    2014-06-01

    Recent attempts to estimate the age of deposition of European fossil localities using mathematical equations derived from size change of the first lower molar in arvicolid rodent lineages as a function of time prompted an assessment of the value of this approach. The accuracy of “vole clocks” depends on accurate dating of a fossil system and establishment of a directional size change pattern through time in a given species from the dated system. Results of this review suggest that vole clocks have limited value for biochronology. In addition to several methodological and statistical problems with published studies, vole clocks in general are untenable because paleontological systems cannot resolve dating to the level of accuracy necessary to construct an accurate equation, size and shape change is never monotonic (constant velocity) in lineages, and size commonly reverses direction in lineages on all time scales.

  8. 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.

  9. Primary Atomic Clock Reference System

    NASA Technical Reports Server (NTRS)

    2001-01-01

    An artist's concept of the Primary Atomic Clock Reference System (PARCS) plarned to fly on the International Space Station (ISS). PARCS will make even more accurate atomic time available to everyone, from physicists testing Einstein's Theory of Relativity, to hikers using the Global Positioning System to find their way. In ground-based atomic clocks, lasers are used to cool and nearly stop atoms of cesium whose vibrations are used as the time base. The microgravity of space will allow the atoms to be suspended in the clock rather than circulated in an atomic fountain, as required on Earth. PARCS is being developed by the Jet Propulsion Laboratory with principal investigators at the National Institutes of Standards and Technology and the University of Colorado, Boulder. See also No. 0103191

  10. Primary Atomic Clock Reference System

    NASA Technical Reports Server (NTRS)

    2001-01-01

    An artist's concept of the Primary Atomic Clock Reference System (PARCS) plarned to fly on the International Space Station (ISS). PARCS will make even more accurate atomic time available to everyone, from physicists testing Einstein's Theory of Relativity, to hikers using the Global Positioning System to find their way. In ground-based atomic clocks, lasers are used to cool and nearly stop atoms of cesium whose vibrations are used as the time base. The microgravity of space will allow the atoms to be suspended in the clock rather than circulated in an atomic fountain, as required on Earth. PARCS is being developed by the Jet Propulsion Laboratory with principal investigators at the National Institutes of Standards and Technology and the University of Colorado, Boulder. See also No. 0100120.

  11. 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.

  12. Operation-triggered quantum clock synchronization

    NASA Astrophysics Data System (ADS)

    Yue, Jie-Dong; Zhang, Yu-Ran; Fan, Heng

    2015-09-01

    We present a quantum clock synchronization scheme of multiple parties which uses operation as the trigger to start the evolution of the initial state. In comparison, the existing protocols use measurement to start the evolution. We show that our protocol links the problem to a multiple-phase estimation problem, such that we have provided a general framework for the study of quantum clock synchronization. We can use the Fisher information to give the precision of the synchronization, and we explicitly show that the Heisenberg scale of synchronization is achieved in the two-party case. We prove that the measurement-triggered quantum clock synchronization is included in the operation-triggered quantum clock synchronization, so the operation-triggered quantum clock synchronization is, in general, more powerful than measurement-triggered quantum clock synchronization. We show that our protocol is very efficient in synchronizing a clock to the average time of other clocks.

  13. PLL-based active optical clock distribution

    E-print Network

    Kern, Alexandra M., 1979-

    2004-01-01

    Reducing the timing uncertainty associated with clock edges has become an exceedingly difficult problem as clock frequencies in high-performance processors increase past several gigahertz. Absolute quantities of skew and ...

  14. A Clock Reaction Based on Molybdenum Blue

    E-print Network

    Neuenschwander, Ulrich

    Clock reactions are rare kinetic phenomena, so far limited mostly to systems with ionic oxoacids and oxoanions in water. We report a new clock reaction in cyclohexanol that forms molybdenum blue from a noncharged, yellow ...

  15. Advances in understanding the peripheral circadian clocks

    PubMed Central

    Richards, Jacob; Gumz, Michelle L.

    2012-01-01

    In the past decade, it has become increasingly evident that the circadian clock system plays an important role in many physiological processes. The circadian clock can be divided into 2 parts: the central clock, residing in the suprachiasmatic nucleus of the hypothalamus, which receives light cues, and the peripheral clocks that reside in various tissues throughout the body. The peripheral clocks play an integral and unique role in each of their respective tissues, driving the circadian expression of specific genes involved in a variety of physiological functions. The goal of this review is to provide an introduction to and overview of the peripheral clocks, including potential mechanisms, targets, and implications for disease states. The peripheral clocks include the cardiovascular, metabolic, endocrine, immune, and reproductive systems.— Richards, J., Gumz, M. L. Advances in understanding the peripheral circadian clocks. PMID:22661008

  16. Colloquium: Physics of optical lattice clocks

    SciTech Connect

    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{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.

  17. Proton Aurora Dynamics in Response to the IMF and Solar Wind Variations

    NASA Technical Reports Server (NTRS)

    Chang, S.; Mende, S.; Frey, H.; Gallagher, D. L.; Lepping, R. P.; Six, N. Frank (Technical Monitor)

    2002-01-01

    On May 23, 2000, proton auroras observed by IMAGE (Imager for Magnetopause to Aurora Global Exploration) FUV (Far Ultraviolet) on the dayside were very dynamic. Auroral pattern in the cusp is well correlated with Interplanetary Magnetic Field (IMF) and solar wind parameters. When IMF were northward, cusp proton aurora appeared at high latitude poleward from the auroral oval. A high-latitude proton aurora brightened after solar wind ion temperature increased and it disappeared after IMF turned southward. Under the southward IMF condition, auroral activity occurred only in the dayside auroral oval. As IMF $B_z$ reverted to northward, cusp proton aurora reappeared at high latitude. The magnetic local time of the cusp proton aurora changes with the IMF $B_y$ polarity, consistent with previous reports. These results suggest an upstream source of the high-latitude cusp proton aurora for this event. One possible explanation is that bow shock energetic ions are transported into the cusp via the high-latitude magnetic merging process to induce optical emissions in the ionosphere.

  18. 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.

  19. Optimized multiparty quantum clock synchronization

    SciTech Connect

    Ben-Av, Radel; Exman, Iaakov

    2011-07-15

    A multiparty protocol for distributed quantum clock synchronization has been claimed to provide universal limits on the clock accuracy, viz., that accuracy monotonically decreases with the number n of party members. But this is only true for synchronization when one limits oneself to W states. This work shows that the usage of Z (Symmetric Dicke) states, a generalization of W states, results in improved accuracy, having a maximum when Left-Floor n/2 Right-Floor of its members have their qubits with a |1> eigenstate.

  20. VCSEL polarization control for chip-scale atomic clocks.

    SciTech Connect

    Geib, Kent Martin; Peake, Gregory Merwin; Wendt, Joel Robert; Serkland, Darwin Keith; Keeler, Gordon Arthur

    2007-01-01

    Sandia National Laboratories and Mytek, LLC have collaborated to develop a monolithically-integrated vertical-cavity surface-emitting laser (VCSEL) assembly with controllable polarization states suitable for use in chip-scale atomic clocks. During the course of this work, a robust technique to provide polarization control was modeled and demonstrated. The technique uses deeply-etched surface gratings oriented at several different rotational angles to provide VCSEL polarization stability. A rigorous coupled-wave analysis (RCWA) model was used to optimize the design for high polarization selectivity and fabrication tolerance. The new approach to VCSEL polarization control may be useful in a number of defense and commercial applications, including chip-scale atomic clocks and other low-power atomic sensors.

  1. Policy on Tenure Clock Extension Policy on Tenure Clock

    E-print Network

    Sridhar, Srinivas

    chair and college dean) to a faculty member either because of a birth or adoption; or because documentation submitted to HRM/Benefits at the same time as the written request for tenure clock extensions is submitted to the Office of the Provost. Medical documentation will be maintained confidentially in HRM/Benefits

  2. Naming Analog Clocks Conceptually Facilitates Naming Digital Clocks

    ERIC Educational Resources Information Center

    Meeuwissen, Marjolein; Roelofs, Ardi; Levelt, Willem J. M.

    2004-01-01

    This study investigates how speakers of Dutch compute and produce relative time expressions. Naming digital clocks (e.g., 2:45, say ''quarter to three'') requires conceptual operations on the minute and hour information for the correct relative time expression. The interplay of these conceptual operations was investigated using a repetition…

  3. Acting with the Clock: Clocking Practices in Early Childhood

    ERIC Educational Resources Information Center

    Pacini-Ketchabaw, Veronica

    2012-01-01

    In this article, the author addresses intra-actions that take place among humans and non-human others--the physical world, the materials--in early childhood education's everyday practices. Her object of study is the clock. Specifically, she provides an example of what it might mean to account for the intra-activity of the material-discursive…

  4. 47 CFR 80.935 - Station clock.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  5. 47 CFR 80.935 - Station clock.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  6. 47 CFR 80.935 - Station clock.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  7. 47 CFR 80.935 - Station clock.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  8. 47 CFR 80.935 - Station clock.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Station clock. 80.935 Section 80.935... MARITIME SERVICES Compulsory Radiotelephone Installations for Small Passenger Boats § 80.935 Station clock. Each station subject to this subpart must have a working clock or timepiece readily available to...

  9. 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.

  10. 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.

  11. 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

  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. Analysis of a magnetically trapped atom clock

    SciTech Connect

    Kadio, D.; Band, Y. B.

    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.

  14. 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.

  15. Automatic control of clock duty cycle

    NASA Technical Reports Server (NTRS)

    Feng, Xiaoxin (Inventor); Roper, Weston (Inventor); Seefeldt, James D. (Inventor)

    2010-01-01

    In general, this disclosure is directed to a duty cycle correction (DCC) circuit that adjusts a falling edge of a clock signal to achieve a desired duty cycle. In some examples, the DCC circuit may generate a pulse in response to a falling edge of an input clock signal, delay the pulse based on a control voltage, adjust the falling edge of the input clock signal based on the delayed pulse to produce an output clock signal, and adjust the control voltage based on the difference between a duty cycle of the output clock signal and a desired duty cycle. Since the DCC circuit adjusts the falling edge of the clock cycle to achieve a desired duty cycle, the DCC may be incorporated into existing PLL control loops that adjust the rising edge of a clock signal without interfering with the operation of such PLL control loops.

  16. A tunable artificial circadian clock in clock-defective mice

    PubMed Central

    D'Alessandro, Matthew; Beesley, Stephen; Kim, Jae Kyoung; Chen, Rongmin; Abich, Estela; Cheng, Wayne; Yi, Paul; Takahashi, Joseph S.; Lee, Choogon

    2015-01-01

    Self-sustaining oscillations are essential for diverse physiological functions such as the cell cycle, insulin secretion and circadian rhythms. Synthetic oscillators using biochemical feedback circuits have been generated in cell culture. These synthetic systems provide important insight into design principles for biological oscillators, but have limited similarity to physiological pathways. Here we report the generation of an artificial, mammalian circadian clock in vivo, capable of generating robust, tunable circadian rhythms. In mice deficient in Per1 and Per2 genes (thus lacking circadian rhythms), we artificially generate PER2 rhythms and restore circadian sleep/wake cycles with an inducible Per2 transgene. Our artificial clock is tunable as the period and phase of the rhythms can be modulated predictably. This feature, and other design principles of our work, might enhance the study and treatment of circadian dysfunction and broader aspects of physiology involving biological oscillators. PMID:26617050

  17. A tunable artificial circadian clock in clock-defective mice.

    PubMed

    D'Alessandro, Matthew; Beesley, Stephen; Kim, Jae Kyoung; Chen, Rongmin; Abich, Estela; Cheng, Wayne; Yi, Paul; Takahashi, Joseph S; Lee, Choogon

    2015-01-01

    Self-sustaining oscillations are essential for diverse physiological functions such as the cell cycle, insulin secretion and circadian rhythms. Synthetic oscillators using biochemical feedback circuits have been generated in cell culture. These synthetic systems provide important insight into design principles for biological oscillators, but have limited similarity to physiological pathways. Here we report the generation of an artificial, mammalian circadian clock in vivo, capable of generating robust, tunable circadian rhythms. In mice deficient in Per1 and Per2 genes (thus lacking circadian rhythms), we artificially generate PER2 rhythms and restore circadian sleep/wake cycles with an inducible Per2 transgene. Our artificial clock is tunable as the period and phase of the rhythms can be modulated predictably. This feature, and other design principles of our work, might enhance the study and treatment of circadian dysfunction and broader aspects of physiology involving biological oscillators. PMID:26617050

  18. Are the total mass density and the low-mass end slope of the IMF anticorrelated?

    NASA Astrophysics Data System (ADS)

    Spiniello, C.; Barnabè, M.; Koopmans, L. V. E.; Trager, S. C.

    2015-09-01

    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 Very Large Telescope (VLT) X-Shooter 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_{low, 250}= 0.131^{+0.023}_{-0.026} M_{?}, respectively, for a reference point with ?? ? 250 km s-1 and Reff ? 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 anticorrelation between total dynamical mass density and low-mass IMF slope at the 87 per cent CL [dx/d log (?) = -0.19^{+0.15}_{-0.15}]. This anticorrelation is consistent with the low-redshift lenses found by Smith et al. that have high velocity dispersions and high stellar mass densities but surprisingly shallow IMF slopes.

  19. Strong Gravitational Lensing and the Stellar IMF of Early-type Galaxies

    E-print Network

    Leier, Dominik; Saha, Prasenjit; Charlot, Stéphane; Bruzual, Gustavo; La Barbera, Francesco

    2015-01-01

    The stellar initial mass function is an important ingredient in galaxy formation, mainly linking the luminosity of a galaxy to its stellar mass, and driving chemical enrichment. In recent years there has been an ongoing discussion about systematic variations of the IMF in early-type galaxies and its connection with possible drivers such as velocity dispersion or metallicity. Strong gravitational lensing over galaxy scales in combination with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the IMF. We combine photometric and spectroscopic constraints from the latest set of population synthesis models of Charlot & Bruzual, including a varying IMF, with a non-parametric analysis of the lensing mass in a sample of 18 early-type lens galaxies from the SLACS survey, with velocity dispersions in the range 200-300 km/s. We find that very bottom-heavy IMFs are excluded. However, the upper limit to the IMF slope ($\\mu \\lesss...

  20. Genomic clocks and evolutionary timescales

    NASA Technical Reports Server (NTRS)

    Blair Hedges, S.; Kumar, Sudhir

    2003-01-01

    For decades, molecular clocks have helped to illuminate the evolutionary timescale of life, but now genomic data pose a challenge for time estimation methods. It is unclear how to integrate data from many genes, each potentially evolving under a different model of substitution and at a different rate. Current methods can be grouped by the way the data are handled (genes considered separately or combined into a 'supergene') and the way gene-specific rate models are applied (global versus local clock). There are advantages and disadvantages to each of these approaches, and the optimal method has not yet emerged. Fortunately, time estimates inferred using many genes or proteins have greater precision and appear to be robust to different approaches.

  1. Mitigating aliasing in atomic clocks

    NASA Astrophysics Data System (ADS)

    Uys, Hermann; Akhalwaya, Ismail; Sastrawan, Jarrah; Biercuk, Michael

    2015-05-01

    Passive atomic clocks periodically calibrate a classical local oscillator against an atomic quantum reference through feedback. The periodic nature of this correction leads to undesirable aliasing noise. The Dick Effect, is a special case of aliasing noise consisting of the down-conversion of clock noise at harmonics of the correction frequency to a frequency of zero. To combat the Dick effect and aliasing noise in general, we suggest an extension to the usual feedback protocol, in which we incorporate information from multiple past measurements into the correction after the most recent measurement, approximating a crude low pass anti-aliasing filter of the noise. An analytical frequency domain analysis of the approach is presented and supported by numerical time domain simulations.

  2. Conveyor-belt clock synchronization

    SciTech Connect

    Giovannetti, Vittorio; Maccone, Lorenzo; Shapiro, Jeffrey H.; Wong, Franco N.C.; Lloyd, Seth

    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.

  3. The LASSO experiment. [clock synchronization

    NASA Technical Reports Server (NTRS)

    Serene, B.

    1979-01-01

    An international coordinated experimental assessment of a system which promises to provide a synchronization of clocks bound to time and frequency standard laboratories, with an accuracy of one nanosecond using existing or near ground-based laser stations via a geostationary satellite (SIRIO-2) is detailed. The system performance and the technical details concerning the on-board equiment, the ground segment, and the operational configuration are discussed. Finally, the future prospects of the LASSO experiment and possible implementations are examined together.

  4. 29 CFR 785.48 - Use of time clocks.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 3 2012-07-01 2012-07-01 false Use of time clocks. 785.48 Section 785.48 Labor Regulations... clocks. (a) Differences between clock records and actual hours worked. Time clocks are not required. In those cases where time clocks are used, employees who voluntarily come in before their regular...

  5. 29 CFR 785.48 - Use of time clocks.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 3 2011-07-01 2011-07-01 false Use of time clocks. 785.48 Section 785.48 Labor Regulations... clocks. (a) Differences between clock records and actual hours worked. Time clocks are not required. In those cases where time clocks are used, employees who voluntarily come in before their regular...

  6. 29 CFR 785.48 - Use of time clocks.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 3 2013-07-01 2013-07-01 false Use of time clocks. 785.48 Section 785.48 Labor Regulations... clocks. (a) Differences between clock records and actual hours worked. Time clocks are not required. In those cases where time clocks are used, employees who voluntarily come in before their regular...

  7. 29 CFR 785.48 - Use of time clocks.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 3 2014-07-01 2014-07-01 false Use of time clocks. 785.48 Section 785.48 Labor Regulations... clocks. (a) Differences between clock records and actual hours worked. Time clocks are not required. In those cases where time clocks are used, employees who voluntarily come in before their regular...

  8. 29 CFR 785.48 - Use of time clocks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false Use of time clocks. 785.48 Section 785.48 Labor Regulations... clocks. (a) Differences between clock records and actual hours worked. Time clocks are not required. In those cases where time clocks are used, employees who voluntarily come in before their regular...

  9. Bennett clocking of nanomagnetic logic using multiferroic single-domain nanomagnets

    NASA Astrophysics Data System (ADS)

    Atulasimha, J.; Bandyopadhyay, S.

    2010-10-01

    The authors show that it is possible to rotate the magnetization of a multiferroic (strain-coupled two-layer magnetostrictive-piezoelectric) nanomagnet by a large angle with a small electrostatic potential. This can implement Bennett clocking [Int. J. Theor. Phys. 21, 905 (1982)] in nanomagnetic logic arrays resulting in unidirectional propagation of logic bits from one stage to another. This method is potentially more energy efficient than using spin-transfer torque for magnetization rotation. For realistic parameters, it is shown that a potential of ˜0.2 V applied to a multiferroic nanomagnet can rotate magnetization by nearly 90° to implement Bennett clocking.

  10. Diversity of Human Clock Genotypes and Consequences

    PubMed Central

    Zhang, Luoying; Ptá?ek, Louis J.; Fu, Ying-Hui

    2014-01-01

    The molecular clock consists of a number of genes that form transcriptional and post-transcriptional feedback loops, which function together to generate circadian oscillations that give rise to circadian rhythms of our behavioral and physiological processes. Genetic variations in these clock genes have been shown to be associated with phenotypic effects in a repertoire of biological processes, such as diurnal preference, sleep, metabolism, mood regulation, addiction, and fertility. Consistently, rodent models carrying mutations in clock genes also demonstrate similar phenotypes. Taken together, these studies suggest that human clock-gene variants contribute to the phenotypic differences observed in various behavioral and physiological processes, although to validate this requires further characterization of the molecular consequences of these polymorphisms. Investigating the diversity of human genotypes and the phenotypic effects of these genetic variations shall advance our understanding of the function of the circadian clock and how we can employ the clock to improve our overall health. PMID:23899594

  11. 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.

  12. 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.

  13. Clock tree synthesis for prescribed skew specifications 

    E-print Network

    Chaturvedi, Rishi

    2005-08-29

    of our bu?ered clock tree routing and an extension to the NS algorithm [13]. : : : : : : : : : : : : : : : : : : : : : : : : : 37 III Wirelength from our MAT algorithm and CL algorithm in [13]. The number in each parentheses is the ratio with respect... obtained by NS. : : : : : : : : : : : : : : : : : : : : : : : 32 19 Clock tree obtained by minimum merging cost based algorithm - MIC. 33 20 Clock tree obtained by maximum delay target based ordering al- gorithm - MAT...

  14. The chlorate-iodine clock reaction.

    PubMed

    Oliveira, André P; Faria, Roberto B

    2005-12-28

    A clock reaction produced by mixing chlorate and iodine solutions in perchloric acid media is reported. This is the first example of a clock reaction using chlorate as a reagent. Increasing chlorate and acid concentration reduces the induction period. Changing the initial iodine concentration does not affect the length of the induction period. The discovery of this clock reaction opens the possibility that a new family of oscillation reactions can be built using chlorate as reagent. PMID:16366551

  15. Collisionally induced atomic clock shifts and correlations

    SciTech Connect

    Band, Y. B.; Osherov, I.

    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.

  16. Optical lattice clocks and quantum metrology

    NASA Astrophysics Data System (ADS)

    Katori, Hidetoshi

    2011-04-01

    The 'magic wavelength' protocol has made it possible to design atomic clocks based on well-engineered perturbations. Such 'optical lattice clocks' will allow extremely high stability using a large number of atoms and fractional uncertainties of ~10-18 by sharing particular 'magic' wavelengths. This Review covers the experimental realizations of such clocks, the optimal design of optical lattices and recent demonstrations of improved stability for large numbers of atoms. Possible impacts and future applications of optical lattice clocks are also discussed, such as testing the fundamental laws of physics and developing relativistic geodesy.

  17. Experimental validation of clock synchronization algorithms

    NASA Technical Reports Server (NTRS)

    Palumbo, Daniel L.; Graham, R. Lynn

    1992-01-01

    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 Midpoint 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 behavior of the clock system. It is found that a 100 percent 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 three clock ticks. Clock skew grows to six 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.

  18. A transportable strontium optical lattice clock

    E-print Network

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

    2014-01-01

    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 set-up and a transportable ultra-stable laser for interrogating the optical clock transition. The whole setup (excluding electronics) fits within a volume of less than 2 m$^3$. 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 an uncertainty of the clock of $7\\times10^{-15}$ Hz.

  19. Spin-1/2 Optical Lattice Clock

    SciTech Connect

    Lemke, N. D.; Ludlow, A. D.; Barber, Z. W.; Fortier, T. M.; Diddams, S. A.; Jiang, Y.; Jefferts, S. R.; Heavner, T. P.; Parker, T. E.; Oates, C. W.

    2009-08-07

    We experimentally investigate an optical clock based on {sup 171}Yb (I=1/2) atoms confined in an optical lattice. We have evaluated all known frequency shifts to the clock transition, including a density-dependent collision shift, with a fractional uncertainty of 3.4x10{sup -16}, limited principally by uncertainty in the blackbody radiation Stark shift. We measured the absolute clock transition frequency relative to the NIST-F1 Cs fountain clock and find the frequency to be 518 295 836 590 865.2(0.7) Hz.

  20. 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.

  1. Case Studies on Clock Gating and Local Routign for VLSI Clock Mesh 

    E-print Network

    Ramakrishnan, Sundararajan

    2010-10-12

    . This thesis deals with the introduction of 'reconfigurability' by using control structures like transmission gates between sub-clock meshes, thus enabling clock gating in clock mesh. By using the optimum value of size for PMOS and NMOS of transmission gate...

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

    E-print Network

    Pikovsky, Arkady

    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

  3. 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.

  4. The nonlinear response of AE to the IMF Bs driver - A spectral break at 5 hours

    NASA Technical Reports Server (NTRS)

    Tsurutani, Bruce T.; Goldstein, Bruce E.; Sugiura, Masahisa; Iyemori, Toshihiko; Gonzalez, Walter D.

    1990-01-01

    The existence of a sharp break in the power spectrum of AE at about 5 hours is demonstrated. Several possible explanations of the nonlinear response of AE to the IMF Bs driver are briefly discussed, including: variable ionospheric conductivity (increasing with Bs) for the high frequency regime, and several AE saturation mechanisms for the low frequency regime.

  5. 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

  6. MOND and IMF variations in early-type galaxies from ATLAS3D

    NASA Astrophysics Data System (ADS)

    Tortora, C.; Romanowsky, A. J.; Cardone, V. F.; Napolitano, N. R.; Jetzer, Ph.

    2014-02-01

    Modified Newtonian Dynamics (MOND) represents a phenomenological alternative to dark matter (DM) for the missing mass problem in galaxies and clusters of galaxies. We analyse the central regions of a local sample of ˜220 early-type galaxies from the ATLAS3D survey, to see if the data can be reproduced without recourse to DM. We estimate dynamical masses in the MOND context through Jeans analysis and compare to ATLAS3D stellar masses from stellar population synthesis. We find that the observed stellar mass-velocity dispersion relation is steeper than expected assuming MOND with a fixed stellar initial mass function (IMF) and a standard value for the acceleration parameter a0. Turning from the space of observables to model space (a) fixing the IMF, a universal value for a0 cannot be fitted, while, (b) fixing a0 and leaving the IMF free to vary, we find that it is `lighter' (Chabrier like) for low-dispersion galaxies and `heavier' (Salpeter like) for high dispersions. This MOND-based trend matches inferences from Newtonian dynamics with DM and from the detailed analysis of spectral absorption lines, adding to the converging lines of evidence for a systematically varying IMF.

  7. Proton aurora in the cusp during southward IMF H. U. Frey and S. B. Mende

    E-print Network

    Mende, Stephen B.

    Proton aurora in the cusp during southward IMF H. U. Frey and S. B. Mende Space Sciences Laboratory 2003. [1] One of the most distinct aurorae in the high-latitude dayside region occurs at the footprint-duration observations of the proton aurora in this region and thus enables morphological and quantitative studies

  8. Transpolar auroras, their particle precipitation, and IMF B sub y component

    SciTech Connect

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

    1991-08-01

    Transpolar auroras, their associated particle precipitation, and their occurrence with respect to the IMF B{sub y} polarity are examined on the basis of DMSP F6 auroral images and the corresponding particle data. It is found that the transpolar arcs are located in the poleward edge of the soft particle precipitation region extending from either the dawn or dusk part of the auroral oval precipitation; they are not embedded in the polar rain region. This finding suggests that the transpolar arcs are located along the poleward boundary of the closed field line region (or the equatorward boundary of the open region) as suggested by Meng. Further, the appearance of the extended precipitation region from the oval depends on the polarity of the IMF B{sub y}, in the northern hemisphere morning sector for IMF B{sub y} < 0 or in the evening sector for IMF B{sub y} > 0. In general, the precipitating particle flux in the extended precipitation region is not high enough to produce appreciable luminosity. Thus only the transpolar arcs (associated with relatively intense precipitation) near the poleward boundary tend to become much more luminous, forming the so-called theta aurora.

  9. 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

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

    E-print Network

    Mende, Stephen B.

    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

  11. 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

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

    DOEpatents

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

    2013-04-02

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

  13. The Global Response of Dayside Ionospheric Currents to Changes of IMF Bz

    NASA Astrophysics Data System (ADS)

    Ohtani, S.; Uozumi, T.; Kawano, H.; Yoshikawa, A.; Yumoto, K.

    2012-12-01

    In the present study we examine the global response of dayside ionospheric currents to step-like changes of the interplanetary magnetic field (IMF) BZ component. The magnetopause can be magnetically traced toward the ionosphere to the dayside auroral region and therefore, it is expected that the change of the IMF Bz component, if it interacts with the magnetosphere, directly affects auroral electrojet in the midday sector. At the dip equator the equatorial electrojet is driven by zonal electric fields, which are also known to be well correlated with the interplanetary electric field and therefore with the IMF Bz component. The EEJ changes in intensity with local time and it has a sharp peak in the midday sector. Therefore, from the continuity of current, we infer that the EEJ is a part of a larger current system. In this study we observationally address the closure of the EEJ by examining ground magnetic variations associated with the steplike changes of IMF Bz. First we statistically confirm that the EEJ indeed changes responding to IMF Bz. Then, in an event study, we test if the associated variations can be identified at different parts of the ionosphere (e.g., mid latitudes, auroral zone, and polar cap). The preliminary study found similar magnetic variations in the east-west magnetic component at mid latitudes at both dusk and dawn but with opposite signs, which suggests that mid-latitude meridional currents connect auroral electrojets and EEJ forming a global current system. We discuss the result in terms of the formation of a Cowling channel along the terminator, the model recently proposed by Yoshikawa et al. [2012; also submitted to this special session].

  14. THE INTRINSIC CIRCADIAN CLOCK WITHIN THE CARDIOMYOCYTE

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Circadian clocks are intracellular molecular mechanisms that allow the cell to anticipate the time of day. We have previously reported that the intact rat heart expresses the major components of the circadian clock, of which its rhythmic expression in vivo is consistent with the operation of a fully...

  15. Ideal clocks—a convenient fiction

    NASA Astrophysics Data System (ADS)

    Lorek, Krzysztof; Louko, Jorma; Dragan, Andrzej

    2015-09-01

    We show that no device built according to the rules of quantum field theory can measure proper time along its path. Highly accelerated quantum clocks experience the Unruh effect, which inevitably influences their time rate. This contradicts the concept of an ideal clock, whose rate should only depend on the instantaneous velocity.

  16. Constraining fossil calibrations for molecular clocks

    E-print Network

    Kumar, Sudhir

    Constraining fossil calibrations for molecular clocks Sir, In a recent paper, Mu¨ller and Reisz(1) proposed how fossil calibrations should be selected for application in molecular clock studies. The topic molecules. Nonetheless, we believe that these authors have erred both in their proposal of fossil

  17. An Iodine Fluorescence Quenching Clock Reaction

    ERIC Educational Resources Information Center

    Weinberg, Richard B.; Muyskens, Mark

    2007-01-01

    Clock reactions based upon competing oxidation and reduction reactions of iodine and starch as the most popular type of chemistry example is presented to illustrate the redox phenomena, reaction kinetics, and principles of chemical titration. The examination of the photophysical principles underlying the iodine fluorescence quenching clock

  18. "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…

  19. The Ozone-Iodine-Chlorate Clock Reaction

    PubMed Central

    Sant'Anna, Rafaela T. P.; Monteiro, Emily V.; Pereira, Juliano R. T.; Faria, Roberto B.

    2013-01-01

    This work presents a new clock reaction based on ozone, iodine, and chlorate that differs from the known chlorate-iodine clock reaction because it does not require UV light. The induction period for this new clock reaction depends inversely on the initial concentrations of ozone, chlorate, and perchloric acid but is independent of the initial iodine concentration. The proposed mechanism considers the reaction of ozone and iodide to form HOI, which is a key species for producing non-linear autocatalytic behavior. The novelty of this system lies in the presence of ozone, whose participation has never been observed in complex systems such as clock or oscillating reactions. Thus, the autocatalysis demonstrated in this new clock reaction should open the possibility for a new family of oscillating reactions. PMID:24386257

  20. The ozone-iodine-chlorate clock reaction.

    PubMed

    Sant'Anna, Rafaela T P; Monteiro, Emily V; Pereira, Juliano R T; Faria, Roberto B

    2013-01-01

    This work presents a new clock reaction based on ozone, iodine, and chlorate that differs from the known chlorate-iodine clock reaction because it does not require UV light. The induction period for this new clock reaction depends inversely on the initial concentrations of ozone, chlorate, and perchloric acid but is independent of the initial iodine concentration. The proposed mechanism considers the reaction of ozone and iodide to form HOI, which is a key species for producing non-linear autocatalytic behavior. The novelty of this system lies in the presence of ozone, whose participation has never been observed in complex systems such as clock or oscillating reactions. Thus, the autocatalysis demonstrated in this new clock reaction should open the possibility for a new family of oscillating reactions. PMID:24386257

  1. Nutrient Sensing and the Circadian Clock

    PubMed Central

    Peek, Clara B.; Ramsey, Kathryn M.; Marcheva, Biliana; Bass, Joseph

    2012-01-01

    The circadian system synchronizes behavioral and physiologic processes with daily changes in the external light-dark cycle, optimizing energetic cycles with the rising and setting of the sun. Molecular clocks are organized hierarchically, with neural clocks orchestrating the daily switch between periods of feeding and fasting, and peripheral clocks generating 24hr oscillations of energy storage and utilization. Recent studies indicate that clocks respond to nutrient signals, and that high-fat diet influences the period of locomotor activity under free-running conditions, a core property of the clock. A major goal is to identify the molecular basis for the reciprocal relationship between metabolic and circadian pathways. Here, we highlight the role of peptidergic hormones and macromolecules as nutrient signals integrating circadian and metabolic systems. PMID:22424658

  2. The dependence of transpolar arc location on IMF By: a comparison of two large transpolar arc datasets

    NASA Astrophysics Data System (ADS)

    Kullen, Anita; Fear, Rob; Milan, Steve

    2014-05-01

    It is well-known that transpolar arc occurrence and motion depends strongly on the interplanetary magnetic field (IMF). The dawn-duskward motion of these arcs is strongly controlled by the IMF By component. Fear and Milan (2012) showed that not only the transpolar arc motion but also the dawn-duskward displacement of the original nightside connection point depends on the direction of IMF By. The best correlations between IMF By and location of transpolar arc nighside connection point was found for a 3-4 hour time delay between these. The results of their study are here reinvestigated using a similar dataset by Kullen et al. (2002) covering another time period. The analysis of the results shows several interesting features. It confirms many of the statistical results in the Fear and Milan (2012) study. However, the best correlation between IMF By and transpolar arc location is found to be with IMF conditions 1-2 hours before the arc occurs. Furthermore, one class of transpolar arcs (bending arcs, splitting from dawn- or dusk oval side around 21 and 3 UT) shows no correlation with IMF By at all. This indicates, bending arcs may form in a different way. A possible connection between bending transpolar arcs and dayside flux transfer events is investigated with help of ionospheric plasma flow patterns using SuperDARN data.

  3. Multi-Fault Detection of Rolling Element Bearings under Harsh Working Condition Using IMF-Based Adaptive Envelope Order Analysis

    PubMed Central

    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

  4. 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

  5. The molecular clock as a metabolic rheostat.

    PubMed

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

    2015-09-01

    Circadian clocks are biologic oscillators present in all photosensitive species that produce 24-h cycles in the transcription of rate-limiting metabolic enzymes in anticipation of the light-dark cycle. In mammals, the clock drives energetic cycles to maintain physiologic constancy during the daily switch in behavioural (sleep/wake) and nutritional (fasting/feeding) states. A molecular connection between circadian clocks and tissue metabolism was first established with the discovery that 24-h transcriptional rhythms are cell-autonomous and self-sustained in most tissues and comprise a robust temporal network throughout the body. A major window in understanding how the clock is coupled to metabolism was opened with discovery of metabolic syndrome pathologies in multi-tissue circadian mutant mice including susceptibility to diet-induced obesity and diabetes. Using conditional transgenesis and dynamic metabolic testing, we have pinpointed tissue-specific roles of the clock in energy and glucose homeostasis, with our most detailed understanding of this process in endocrine pancreas. Here, we review evidence for dynamic regulation of insulin secretion and oxidative metabolic functions by the clock transcription pathway to regulate homeostatic responses to feeding and fasting. These studies indicate that clock transcription is a determinant of tissue function and provide a reference for understanding molecular pathologies linking circadian desynchrony to metabolic disease. PMID:26332974

  6. Circadian clocks are designed optimally

    E-print Network

    Hasegawa, Yoshihiko

    2014-01-01

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

  7. Lutetium +: A better clock candidate

    NASA Astrophysics Data System (ADS)

    Arnold, Kyle; Paez, Eduardo; Haciyev, Elnur; Arifin, Arifin; Cazan, Radu; Barrett, Murray

    2015-05-01

    With the extreme precision now reached by optical clocks it is reasonable to consider redefinition of the frequency standard. In doing so it is important to look beyond the current best-case efforts and have an eye on future possibilities. We will argue that singly ionized Lutetium is a strong candidate for the next generation of optical frequency standards. Lu + has a particularly narrow optical transition in combination with several advantageous properties for managing systematic uncertainties compared to the other atomic species. We summarize these properties and our specific strategies for managing the uncertainties due to external perturbations. Finally, we present the status of our ongoing experiments with trapped Lu +, including the results of precision measurements of its atomic structure.

  8. Clock time is absolute and universal

    NASA Astrophysics Data System (ADS)

    Shen, Xinhang

    2015-09-01

    A critical error is found in the Special Theory of Relativity (STR): mixing up the concepts of the STR abstract time of a reference frame and the displayed time of a physical clock, which leads to use the properties of the abstract time to predict time dilation on physical clocks and all other physical processes. Actually, a clock can never directly measure the abstract time, but can only record the result of a physical process during a period of the abstract time such as the number of cycles of oscillation which is the multiplication of the abstract time and the frequency of oscillation. After Lorentz Transformation, the abstract time of a reference frame expands by a factor gamma, but the frequency of a clock decreases by the same factor gamma, and the resulting multiplication i.e. the displayed time of a moving clock remains unchanged. That is, the displayed time of any physical clock is an invariant of Lorentz Transformation. The Lorentz invariance of the displayed times of clocks can further prove within the framework of STR our earth based standard physical time is absolute, universal and independent of inertial reference frames as confirmed by both the physical fact of the universal synchronization of clocks on the GPS satellites and clocks on the earth, and the theoretical existence of the absolute and universal Galilean time in STR which has proved that time dilation and space contraction are pure illusions of STR. The existence of the absolute and universal time in STR has directly denied that the reference frame dependent abstract time of STR is the physical time, and therefore, STR is wrong and all its predictions can never happen in the physical world.

  9. The circadian clock in cancer development and therapy

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The...

  10. Byzantine Self-Stabilizing Clock Distribution with HEX

    E-print Network

    Waldmann, Uwe

    cell library. Their purpose is to (i) forward synchronized clock signals throughout the grid and (ii for Byzantine fault-tolerant and self-stabilizing clock distribution in multi-synchronous GALS architectures. Fault-tolerant clock generation and clock distribution is a mandatory prerequisite for highly dependable

  11. Understanding Neutral Genomic Molecular Clocks Soojin V. Yi

    E-print Network

    Yi, Soojin

    ESSAY Understanding Neutral Genomic Molecular Clocks Soojin V. Yi Received: 24 July 2007 / Accepted genomics, understanding the neutral genomic molecular clock occupies a critical place. It has been and recombination rates are important determinants of neutral genomic molecular clocks. Keywords Molecular clock Á

  12. Concurrent Reading and Writing of Clocks LESLIE LAMPORT

    E-print Network

    Lamport ,Leslie

    "atomic" when they read "regular". There are two different kinds of clocks--monotonic clocks that neverConcurrent Reading and Writing of Clocks LESLIE LAMPORT Digital Equipment Corporation a monotonic and a cyclic multiple-word clock that is updated by one process and read by one or more other

  13. 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

  14. Concurrent Reading and Writing of Clocks LESLIE LAMPORT

    E-print Network

    Lamport ,Leslie

    ``atomic'' when they read ``regular''. There are two di#erent kinds of clocks---monotonic clocks that neverConcurrent Reading and Writing of Clocks LESLIE LAMPORT Digital Equipment Corporation a monotonic and a cyclic multiple­word clock that is updated by one process and read by one or more other

  15. The investigation of the interplanetary magnetic field (IMF) sector structure's influence on a upper mesosphere - lower thermosphere (80 — 110 km) neutral wind during Earth's passing through the sector boundary of the IMF

    NASA Astrophysics Data System (ADS)

    Elakhov, Max; Fahrutdinova, Antonina; Maksyutin, Sergey

    As part of determining the possible mechanism of the interplanetary magnetic field (IMF) relationship with neutral wind, lower atmosphere and the upper mesosphere - lower termosphere (MLT, 80 — 110 km) neutral wind velocities data analysis is carried out during the IMF changing events. The prevailing zonal and meridional wind data was obtained by the radiometeoric measurements in Kazan (Volga Region) Federal University, at Kazan (55 N, 49 E) during 1986-1990, 1993-1995, 1998-2002. The analysis revealed the correlation between the responses of the prevailing neutral wind within the altitude interval of the lower atmosphere and of the MLT region to the Earth's passing through the IMF sector boundary. Effects have a seasonal variation and depend on IMF direction.

  16. 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.

  17. Light clocks in strong gravitational fields

    E-print Network

    Raffaele Punzi; Frederic P. Schuller; Mattias N. R. Wohlfarth

    2009-02-11

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

  18. Entangled optical clocks via Rydberg blockade

    NASA Astrophysics Data System (ADS)

    Komar, Peter; Kessler, Eric; Topcu, Turker; Derevianko, Andrei; Lukin, Mikhail

    2015-05-01

    We present an analysis of a protocol for creating fully entangled GHZ-type states of atoms in spatially separated optical atomic clocks. In our scheme, local operations make use of the strong dipole-dipole interaction between Rydberg excitations, which give rise to fast and reliable quantum operations involving all atoms in the ensemble. The necessary entanglement between distant ensembles is mediated by single-photon quantum channels and collectively enhanced light-matter couplings. These techniques can be used to create the recently proposed quantum clock network based on neutral atom optical clocks. We specifically analyze the realization of this scheme based on neutral Yb atoms.

  19. Model of a mechanical clock escapement

    NASA Astrophysics Data System (ADS)

    Moline, David; Wagner, John; Volk, Eugene

    2012-07-01

    The mechanical tower clock originated in Europe during the 14th century to sound hourly bells and later display hands on a dial. An important innovation was the escapement mechanism, which converts stored energy into oscillatory motion for fixed time intervals through the pendulum swing. Previous work has modeled the escapement mechanism in terms of inelastic and elastic collisions. We derive and experimentally verify a theoretical model in terms of impulsive differential equations for the Graham escapement mechanism in a Seth Thomas tower clock. The model offers insight into the clock's mechanical behavior and the functionality of the deadbeat escapement mechanism.

  20. Polarizabilities of the 87Sr clock transition

    NASA Astrophysics Data System (ADS)

    Shi, C.; Robyr, J.-L.; Eismann, U.; Zawada, M.; Lorini, L.; Le Targat, R.; Lodewyck, J.

    2015-07-01

    In this paper, we propose an in-depth review of the vector and tensor polarizabilities of the two energy levels of the 87Sr clock transition whose measurement was reported in P. G. Westergaard et al. [Phys. Rev. Lett. 106, 210801 (2011), 10.1103/PhysRevLett.106.210801]. We conduct a theoretical calculation that reproduces the measured coefficients. In addition, we detail the experimental conditions used for their measurement in two Sr optical lattice clocks and exhibit the quadratic behavior of the vector and tensor shifts with the depth of the trapping potential and evaluate their impact on the accuracy of the clock.

  1. Magic wavelengths for terahertz clock transitions

    SciTech Connect

    Zhou Xiaoji; Xu Xia; Chen Xuzong; Chen Jingbiao

    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.

  2. 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."

  3. 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.

  4. 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

  5. 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

  6. IMF or Abundance Variations? Steep Gradients at the Centers of Elliptical Galaxies

    NASA Astrophysics Data System (ADS)

    McConnell, Nicholas J.; Lu, Jessica R.; Mann, Andrew

    2016-01-01

    We present high signal-to-noise spectra for six early-type galaxies with Keck/LRIS, covering 350-1050 nm and probing spatial scales from 100 pc to several kpc. Some of our objects exhibit steep absorption-line gradients within the central ~300 pc, indicating a rapid increase in [Na/Fe] and [N/Fe] toward the galaxy center. While stellar population synthesis (SPS) modeling may address whether the stellar initial mass function (IMF) varies as a function of radius, we caution that the competing effects of chemical abundance variations and IMF variations demands extreme care in interpreting SPS models of integrated-light spectra. The steep abundance variations themselves may offer insight to star formation and gas retention in progenitors of today's early-type galaxies, including the possible overabundance of stars above ~3 Msun.

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

    E-print Network

    Vincenzo, Fiorenzo; Recchi, Simone; Calura, Francesco; McWilliam, Andrew; Lanfranchi, Gustavo A

    2015-01-01

    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 $\\alpha$-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 [$\\alpha$/Fe] ratios than classical IMFs and lower [hydrostatic/explosive] $\\alpha$-element ratios, in qualitative agreement with observations...

  8. Toward a Complete Census of the Low Mass IMF in the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Robberto, Massimo; Andersen, Morten; Barman, Travis; Bellini, Andrea; da Rio, Nicola; de Mink, Selma; Hillenbrand, Lynne A.; Lu, Jessica R.; Luhman, Kevin; Felice Manara, Carlo; Meyer, Michael; Platais, Imants; Pueyo, Laurent; Soderblom, David; Soummer, Remi; Stahler, Steve; Tan, Jonathan Charles

    2015-08-01

    A 52-orbit Hubble Treasury Program is currently under way to investigate two fundamental questions of star formation: a) the low- mass tail of the IMF, down to a few Jupiter masses; b) the dynamical evolution of clusters, as revealed by stellar proper motions. The program targets the Orion Nebula Cluster using WFC3 and ACS in coordinated parallel mode to perform a synoptic survey in the 1.345micron H2O feature and in the F775W Ic broad-band. In this poster we present early results from the IR survey, aimed at discovering and classify all brown dwarfs and planetary-mass objects in the field, extending the IMF down to lowest masses formed by gravitational collapse. Using the latest generation of high contrast image processing we are also searching for faint companions, reaching down to sub-arcsecond separations and 10-4 flux ratios.

  9. The IMF in Extreme Star-Forming Environments: Searching for Variations vs. Initial Conditions

    E-print Network

    Morten Andersen; M. R. Meyer; J. Greissl; B. D. Oppenheimer; M. A. Kenworthy; D. W. McCarthy; H. Zinnecker

    2005-06-14

    Any predictive theory of star formation must explain observed variations (or lack thereof) in the initial mass function. Recent work suggests that we might expect quantitative variations in the IMF as a function of metallicity (Larson 2005) or magnetic field strength (Shu et al. 2004). We summarize results from several on-going studies attempting to constrain the ratio of high to low mass stars, as well as stars to sub- stellar objects, in a variety of different environments, all containing high mass stars. First, we examine the ratio of stars to sub--stellar objects in the nearby Mon R2 region utilizing NICMOS/HST data. We compare our results to the IMF by Kroupa (2002)]} and to the observed ratios for IC 348 and Orion. Second, we present preliminary results for the ratio of high to low mass stars in W51, the most luminous HII region in the galaxy. Based on ground--based multi--colour images of the cluster obtained with the MMT adaptive optics system, we derive a lower limit to the ratio of high-mass to low-mass stars and compare it to the ratios for nearby clusters. Finally, we present the derived IMF for the R136 region in the LMC where the metallicity is 1/4 solar using HST/NICMOS data. We find that the IMF is consistent with that characterizing the field (Chabrier 2003), as well as nearby star--forming regions, down to 1.0 Msun outside 2 pc. Whereas the results for both Mon R2 and R136 are consistent with the nearby clusters, the ratio of high to low mass stars in W51 tentatively indicates a lack of low--mass objects.

  10. The effects of IMF sector boundary crossings on the induced magnetosphere of Venus

    NASA Astrophysics Data System (ADS)

    Vech, D.; Stenberg, G.; Nilsson, H.; Edberg, N. J. T.; Opitz, A.; Szeg?, K.; Zhang, T. L.; Futaana, Y.

    2015-10-01

    The induced planetary magnetosphere is the result of the interaction between the streaming solar wind plasma and an unmagnetized planetary body with an ionosphere acting as an obstacle. The structure of the induced magnetosphere highly depends on the upstream solar wind parameters including the direction and magnitude of the Interplanetary Magnetic Field (IMF). (e.g. Zhang et al., 2009; Masunaga et al., 2011). Not only the upstream conditions but also temporal variations of the upstream conditions are expected to cause changes in the structure of induced magnetospheres. For example, Niedner and Brandt [1978] reported that the cometary ion tail was lost due to reconnection after an IMF sector boundary crossing. Edberg et al. [2011] studied the effects of Interplanetary Coronal Mass Ejections (ICME) and Co-rotating Interaction Regions (CIR) at Venus. They suggested that the change in the magnetic field polarity during IMF sector boundary crossings contribute to an increased ion outflow. In addition, they speculated that this might be due to dayside magnetic reconnection. In this study we aim to understand the effects of the varying upstream conditions on the Venusian induced magnetosphere. Using the entire Venus Express/ASPERA-4 and MAG datasets, we first produce the spatial distribution of ions in the plasma environment of Venus during ICME and CIR passages together with that during the average condition. In addition to ICME/CIR passages, we focus on the Heliospheric Current Sheet (HCS) crossings, which can also change the polarity of the induced magnetosphere. By comparing HCS events and ICME/CIR events, we may be able to distinguish the contribution of IMF polarity change on the Venusian induced magnetosphere, because the solar wind is less disturbed during HCS events. We will compare the signatures associated with the sector boundary crossings found at the magnetotail of Venus with that is previously reported from comet studies.

  11. Is coverage a factor in non-Gaussianity of IMF parameters?

    NASA Technical Reports Server (NTRS)

    Ahluwalia, H. S.; Fikani, M. M.

    1995-01-01

    Recently, Feynman and Ruzmaikin (1994) showed that IMF parameters for the 1973 to 1990 period are not log-normally distributed as previously suggested by Burlaga and King (1979) for the data obtained over a shorter time period (1963-75). They studied the first four moments, namely: mean, variance, skewness, and kurtosis. For a Gaussian distribution, moments higher than the variance should vanish. In particular, Feynman and Ruzmaikin obtained very high values of kurtosis during some periods of their analysis. We note that the coverage for IMF parameters is very uneven for the period analyzed by them, ranging from less than 40% to greater than 80%. So a question arises as to whether the amount of coverage is a factor in their analysis. We decided to test this for the B(sub z) component of IMF, since it is an effective geoactive parameter for short term disturbances. Like them, we used 1-hour averaged data available on the Omnitape. We studied the scatter plots of the annual mean values of B(sub z)(nT) and its kurtosis versus the percent coverage for the year. We obtain a correlation coefficient of 0.48 and 0.42 respectively for the 1973-90 period. The probability for a chance occurrence of these correlation coefficients for 18 pair of points is less than 8%. As a rough measure of skewness, we determined the percent asymmetry between the areas of the histograms representing the distributions of the positive and the negative values of B(sub z) and studied its correlation with the coverage for the year. This analysis yields a correlation coefficient of 0.41 When we extended the analysis for the whole period for which IMF data are available (1963-93) the corresponding correlation coefficients are 0.59, 0.14, and 0.42. Our findings will be presented and discussed

  12. Simultaneous conjugate observations of dynamic variations in high-latitude dayside convection due to changes in IMF By

    NASA Technical Reports Server (NTRS)

    Greenwald, R. A.; Baker, K. B.; Ruohoniemi, J. M.; Dudeney, J. R.; Pinnock, M.; Mattin, N.; Leonard, J. M.; Lepping, R. P.

    1990-01-01

    Data from two conjugate HF radars currently operating at Goose Bay (Labrador) and the Halley Station (Antarctica), obtained for a single 45-min period about local noon on April 22, 1988, were used to study the near-instantaneous conjugate two-dimensional patterns of plasma convection in the vicinity of the cusp. In particular, the response of these plasma convection patterns to changes in the By component of the IMF was examined. Results indicate that, under quasi-stationary IMF conditions, the conjugate convection patterns are quite similar to the synthesized patterns of Heppner and Maynard (1987) and that the patterns respond rapidly to changes in the IMF By component. Results also show that transitions between convection states begin to occur within minutes of the time that an IMF state change is incident on the magnetospheric boundary, and that the convection reconfigurations expand poleward, completely filling the field of view of an HF radar within 6 min of the time of onset.

  13. Evidence for Depletion Layers at the Dayside Magnetopause for IMF Orientations with Southward Components

    NASA Astrophysics Data System (ADS)

    Maynard, N. C.; Ober, D. M.; Burke, W. J.; Scudder, J. D.; Mozer, F. S.; Russell, C. T.; Siscoe, G. L.; Erickson, G. M.; Sonnerup, B. U.; Weimer, D. R.; Siebert, K. D.; White, W. W.

    2002-05-01

    The equatorward precession of Polar's apogee allowed the satellite to execute prolonged south-to-north skimming orbits along the dayside magnetopause during the equinoctial months of 2000 and 2001. Particle and field measurements during these skimming passes give new perspectives of the magnetopause and adjacent magnetosheath. Correlations between magnetic field variations observed at an upstream monitor and in the magnetosheath were established, considering variable lag times due to tilted phase fronts in the solar wind. Combining these results with MHD simulation results using the MRC Integrated Space Weather Model, we predict and observe depletion layers for two categories of events with southward IMF components, in addition to those normally observed with northward IMF. Depletion was seen at the velocity separator connecting the two high-latitude merging sites in each hemisphere. Flux piles up in this stagnation region until the field lines drape to the high-latitude merging site. This is enhanced by the presence of dipole tilt or a BX component. In addition the simulations show that the high-altitude cusps move toward the equator and shoulders develop in the open magnetic field configuration above the cusp for strongly driven conditions. The shoulder will be strongest in the hemisphere tilted toward the Sun. The shoulder slows the flux approaching the magnetopause, and the resulting pile up creates a depletion layer above the cusp during active events with large southward IMF. Observations from the March 31, 2001 storm are consistent with the existence of these shoulder depletion layers.

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

    NASA Astrophysics Data System (ADS)

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

    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 irradiation resistance and reliability; they can consequently reach high burnups and be serviceable under transient conditions. Three basic fuel element versions are under development in VNIINM for both thermal and fast reactors. The first version is a fuel element with a heterogeneous arrangement of fuel (PuO 2 or YSZ granules) within an Al or Zr matrix. The second version of a fuel element has a heat conducting Al or Zr alloy matrix and an isolated arrangement of PuO 2 in a fuel minielement more fully meets the 'Rock Fuel' requirements. According to the third version a porous meat of zirconium metallurgically bonded to a fuel cladding is formed through which a PuO 2 powder is introduced. All the versions are technologically simple to fabricate and require minimal quantities of process operations related to treating MA and Pu. Preliminary in-pile tests of IMF prototypes are presented.

  15. Structural adjustment and public spending on health: evidence from IMF programs in low-income countries.

    PubMed

    Kentikelenis, Alexander E; Stubbs, Thomas H; King, Lawrence P

    2015-02-01

    The relationship between health policy in low-income countries (LICs) and structural adjustment programs devised by the International Monetary Fund (IMF) has been the subject of intense controversy over past decades. While the influence of the IMF on health policy can operate through various pathways, one main link is via public spending on health. The IMF has claimed that its programs enhance government spending for health, and that a number of innovations have been introduced to enable borrowing countries to protect health spending from broader austerity measures. Critics have pointed to adverse effects of Fund programs on health spending or to systematic underfunding that does not allow LICs to address health needs. We examine the effects of Fund programs on government expenditures on health in low-income countries using data for the period 1985-2009. We find that Fund programs are associated with higher health expenditures only in Sub-Saharan African LICs, which historically spent less than any other region. This relationship turns negative in LICs in other regions. We outline the implications of these findings for health policy in a development context. PMID:25576997

  16. 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.

  17. On the Effect of IMF Turning on Ion Dynamics at Mercury

    NASA Technical Reports Server (NTRS)

    Delcourt, D. C.; Moore, T. E.; Fok, M.-C. H.

    2011-01-01

    We investigate the effect of a rotation of the Interplanetary Magnetic Field (IMF) on the transport of magnetospheric ion populations at Mercury. We focus on ions of planetary origin and investigate their large-scale circulation using three-dimensional single-particle simulations. We show that a nonzero Bx component of the IMF leads to a pronounced asymmetry in the overall circulation pattern . In particular, we demonstrate that the centrifugal acceleration due to curvature of the E x B drift paths is more pronounced in one hemisphere than the other, leading to filling of the magnetospheric lobes and plasma sheet with more or less energetic material depending upon the hemisphere of origin. Using a time-varying electric and magnetic field model, we investigate the response of ions to rapid (a few tens of seconds) re-orientation of the IMF. We show that, for ions with gyroperiods comparable to the field variation time scale, the inductive electric field should lead to significant nonadiabatic energization, up to several hundreds of eVs or a few keVs. It thus appears that IMP turning at Mercury should lead to localized loading of the magnetosphere with energetic material of planetary origin (e.g., Na+).

  18. Circadian clocks, obesity and cardiometabolic function.

    PubMed

    Scott, E M

    2015-09-01

    Life on earth is governed by the continuous 24-h cycle of light and dark. Organisms have adapted to this environment with clear diurnal rhythms in their physiology and metabolism, enabling them to anticipate predictable environmental fluctuations over the day and to optimize the timing of relevant biological processes to this cycle. These rhythms are regulated by molecular circadian clocks, and current evidence suggests that interactions between the central and peripheral molecular clocks are important in metabolic and vascular functions. Disrupting this process through mutations in the core clock genes or by interfering with the environmental zeitgebers that entrain the clock appear to modulate the function of cells and tissues, leading to an increased risk for cardiometabolic disease. PMID:26332972

  19. Spacetime and Quantum Propagation From Digital Clocks

    NASA Astrophysics Data System (ADS)

    Ord, Garnet. N.

    2013-09-01

    Minkowski spacetime predates quantum mechanics and is frequently regarded as an extension of the classical paradigm of Newtonian physics, rather than a harbinger of quantum mechanics. By inspecting how discrete clocks operate in a relativistic world we show that this view is misleading. Discrete relativistic clocks implicate classical spacetime provided a continuum limit is taken in such a way that successive ticks of the clock yield a smooth worldline. The classical picture emerges but does so by confining unitary propagation into spacetime regions between ticks that have zero area in the continuum limit. Clocks allowed a continuum limit that does not force inter-event intervals to zero, satisfy the Dirac equation. This strongly suggests that the origin of quantum propagation is to be found in the shift from Newton's absolute time to Minkowski's frame dependent time and is ultimately relativistic in origin.

  20. 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 (such as the Network...

  1. Techniques for low jitter clock multiplication

    E-print Network

    Helal, Belal M., 1971-

    2008-01-01

    Phase realigning clock multipliers, such as Multiplying Delay-Locked Loops (MDLL), offer significantly reduced random jitter compared to typical Phase-Locked Loops (PLL). This is achieved by introducing the reference signal ...

  2. Biological clocks and the practice of psychiatry

    PubMed Central

    Schulz, Pierre

    2007-01-01

    Endogenous biological clocks enable living species to acquire some independence in relation to time. They improve the efficiency of biological systems, by allowing them to anticipate future constraints on major physyological systems and cell energy metabolism. The temporal organization of a giwen biological function can be impaired in its coordination with astronomical time or with other biological function. There are also external conditions that influence biological clocks. This temporal organization is complex, and it is possible that a series of psychiatric disorders and syndromes involve primary or secondary changes in biological clocks: seasonal and other mood disorders, premenstrual syndromes, social jet lag, free-running rhythms, and several sleep disorders are among them. In this review, we describe the main concepts relevant to chronobiology and explore the relevance of knowledge about biological clocks to the clinical practice of psychiatry PMID:17969862

  3. Tuning Genetic Clocks Employing DNA Binding Sites

    E-print Network

    Del Vecchio, Domitilla

    Periodic oscillations play a key role in cell physiology from the cell cycle to circadian clocks. The interplay of positive and negative feedback loops among genes and proteins is ubiquitous in these networks. Often, delays ...

  4. Method and system for downhole clock synchronization

    DOEpatents

    Hall, David R.; Bartholomew, David B.; Johnson, Monte; Moon, Justin; Koehler, Roger O.

    2006-11-28

    A method and system for use in synchronizing at least two clocks in a downhole network are disclosed. The method comprises determining a total signal latency between a controlling processing element and at least one downhole processing element in a downhole network and sending a synchronizing time over the downhole network to the at least one downhole processing element adjusted for the signal latency. Electronic time stamps may be used to measure latency between processing elements. A system for electrically synchronizing at least two clocks connected to a downhole network comprises a controlling processing element connected to a synchronizing clock in communication over a downhole network with at least one downhole processing element comprising at least one downhole clock. Preferably, the downhole network is integrated into a downhole tool string.

  5. Elite athletes refine their internal clocks.

    PubMed

    Chen, Yin-Hua; Cesari, Paola

    2015-01-01

    Evaluating time properly is crucial for everyday activities from fundamental behaviors to refined coordinative movements such as in sport playing. Lately the concept of the existence of a unique internal clock for evaluating time in different scales has been challenged by recent neurophysiology studies. Here we provide evidence that individuals evaluate time durations below and above a second based on two different internal clocks for sub- and suprasecond time ranges: a faster clock for the subsecond range and a slower one for suprasecond time. Interestingly, the level of precision presented by these two clocks can be finely tuned through long-term sport training: Elite athletes, independently from their sport domains, generate better time estimates than nonathletes by showing higher accuracy and lower variability, particularly for subsecond time. We interpret this better time estimation in the short durations as being due to their extraordinary perceptual and motor ability in fast actions. PMID:25029090

  6. Phase measurement system using a dithered clock

    DOEpatents

    Fairley, C.R.; Patterson, S.R.

    1991-05-28

    A phase measurement system is disclosed which measures the phase shift between two signals by dithering a clock signal and averaging a plurality of measurements of the phase differences between the two signals. 8 figures.

  7. 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

  8. Connecting the Circadian Clock with Chemosensation 

    E-print Network

    Chatterjee, Abhishek

    2012-07-16

    in T1 sensillae ............................................................................................. 40 14 Or83b and Gprk2 mutants show no rhythm in spike amplitude................. 41 15 Representative traces of sucrose-evoked single...-helix?loop?helix (bHLH) PER- ARNT-SIM (PAS) partners CLOCK (CLK) and CYCLE (CYC), which bind to E-box (CACGTG) enhancer elements and stimulate transcription of period (per) and timeless (tim) in a time-dependant manner (Fig. 1), along with other key clock...

  9. Tests of Lorentz invariance with atomic clocks

    NASA Astrophysics Data System (ADS)

    Mohan, Lakshmi

    Lorentz invariance has been the cornerstone of special relativity. Recent theories have been proposed which suggest violations of Lorentz invariance. Experiments have been conducted using clocks that place the strictest limits on these theories. The thesis focuses on the Mansouri and Sexl formulation and I calculate using this framework the Doppler effect, Compton effect, Maxwell's equations, Hydrogen energy levels and other effects. I conclude the thesis by suggesting a possible method of testing my results using atomic clocks.

  10. Reduced Kalman Filters for Clock Ensembles

    NASA Technical Reports Server (NTRS)

    Greenhall, Charles A.

    2011-01-01

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

  11. Frequency comparison of optical lattice clocks

    NASA Astrophysics Data System (ADS)

    Takamoto, Masao; Takano, Tetsushi; Katori, Hidetoshi

    2011-10-01

    We demonstrate the frequency comparison of two optical lattice clocks at the relative stabilities close to the quantum projection noise (QPN) limit of optical lattice clocks. This stable frequency comparison is accomplished by synchronous interrogations of two clocks by a common probe laser, which allows us to cancel out the probe laser's frequency noise. We perform the frequency comparison of a one-dimensional (1D) optical lattice clock with spin-polarized fermions 87Sr and a three-dimensional (3D) optical lattice clock with unity-occupation bosons 88Sr and achieve the Allan standard deviation of ??(?)=4×10-16 ?-1/2, which corresponds to the QPN limited stability for N=1,000 atoms and the spectrum linewidth ?=8 Hz. The relative stability reaches 1×10-17 with an averaging time of 1,600 s. Finally, we discuss the prospects to realize 10-18 fractional inaccuracies and the possible application of frequency comparison with synchronous interrogations to remote clocks' comparison for relativistic geodesy.

  12. The Neurospora circadian clock: simple or complex?

    PubMed Central

    Bell-Pedersen, D; Crosthwaite, S K; Lakin-Thomas, P L; Merrow, M; Økland, M

    2001-01-01

    The fungus Neurospora crassa is being used by a number of research groups as a model organism to investigate circadian (daily) rhythmicity. In this review we concentrate on recent work relating to the complexity of the circadian system in this organism. We discuss: the advantages of Neurospora as a model system for clock studies; the frequency (frq), white collar-1 and white collar-2 genes and their roles in rhythmicity; the phenomenon of rhythmicity in null frq mutants and its implications for clock mechanisms; the study of output pathways using clock-controlled genes; other rhythms in fungi; mathematical modelling of the Neurospora circadian system; and the application of new technologies to the study of Neurospora rhythmicity. We conclude that there may be many gene products involved in the clock mechanism, there may be multiple interacting oscillators comprising the clock mechanism, there may be feedback from output pathways onto the oscillator(s) and from the oscillator(s) onto input pathways, and there may be several independent clocks coexisting in one organism. Thus even a relatively simple lower eukaryote can be used to address questions about a complex, networked circadian system. PMID:11710976

  13. 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

  14. Short-term GNSS satellite clock stability

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  15. [Clock genes, circadian rhythms and food intake].

    PubMed

    Challet, E

    2007-01-01

    The molecular clockwork in mammals involves various clock genes with specific temporal patterns of expression. Synchronization of the master circadian clock located in the suprachiasmatic nuclei is accomplished mainly via daily resetting of the phase of the clock by light stimuli. Phase shifting responses to light are correlated with induction of Per1 and Per2 within the suprachiasmatic cells. The timing of peripheral oscillators is controlled by the suprachiasmatic clock when food is available ad libitum. Time of feeding, as modulated by temporal restricted feeding, is a potent Zeitgeber (synchronizer) for peripheral oscillators with no clear synchronizing influence on the suprachiasmatic clockwork. However, a timed calorie restriction (i.e. when only a hypocaloric diet is given each day at the same time) can modify the temporal organization generated by the suprachiasmatic nuclei and reset by the light-dark cycle. Such a situation of conflict between photic and feeding synchronizers alters timing of clock gene expression within the suprachiasmatic nuclei and timing of circadian outputs, indicating that the suprachiasmatic clock is sensitive to nutritional cues. PMID:17412526

  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

    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. Polar cap ion beams during periods of northward IMF: Cluster statistical results

    NASA Astrophysics Data System (ADS)

    Maggiolo, R.; Echim, M.; de Keyser, J.; Fontaine, D.; Jacquey, C.; Dandouras, I.

    2011-05-01

    Above the polar caps and during prolonged periods of northward IMF, the Cluster satellites detect upward accelerated ion beams with energies up to a few keV. They are associated with converging electric field structures indicating that the acceleration is caused by a quasi-static field-aligned electric field that can extend to altitudes higher than 7 RE (Maggiolo et al., 2006; Teste et al., 2007). Using the AMDA science analysis service provided by the Centre de Données de la Physique des Plasmas, we have been able to extract about 200 events of accelerated upgoing ion beams above the polar caps from the Cluster database. Most of these observations are taken at altitudes lower than 7 RE and in the Northern Hemisphere. We investigate the statistical properties of these ion beams. We analyze their geometry, the properties of the plasma populations and of the electric field inside and around the beams, as well as their dependence on solar wind and IMF conditions. We show that ~40 % of the ion beams are collocated with a relatively hot and isotropic plasma population. The density and temperature of the isotropic population are highly variable but suggest that this plasma originates from the plasma sheet. The ion beam properties do not change significantly when the isotropic, hot background population is present. Furthermore, during one single polar cap crossing by Cluster it is possible to detect upgoing ion beams both with and without an accompanying isotropic component. The analysis of the variation of the IMF BZ component prior to the detection of the beams indicates that the delay between a northward/southward turning of IMF and the appearance/disappearance of the beams is respectively ~2 h and 20 min. The observed electrodynamic characteristics of high altitude polar cap ion beams suggest that they are closely connected to polar cap auroral arcs. We discuss the implications of these Cluster observations above the polar cap on the magnetospheric dynamics and configuration during prolonged periods of northward IMF.

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

    NASA Astrophysics Data System (ADS)

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

    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 of a complete sample of dense molecular cores in a single cloud employing a robust method that uses uses extinction of background starlight to measure core masses and enables the reliable extension of such measurements to lower masses than previously possible. Methods: We use a map of near-infrared extinction in the nearby Pipe dark cloud to identify the population of dense cores in the cloud and measure their masses. Results: We identify 159 dense cores and construct the mass function for this population. We present the first robust evidence for a departure from a single power-law form in the mass function of a population of cores and find that this mass function is surprisingly similar in shape to the stellar IMF but scaled to a higher mass by a factor of about 3. This suggests that the distribution of stellar birth masses (IMF) is the direct product of the dense core mass function and a uniform star formation efficiency of 30%±10%, and that the stellar IMF may already be fixed during or before the earliest stages of core evolution. These results are consistent with previous dust continuum studies which suggested that the IMF directly originates from the core mass function. The typical density of ~104 cm-3 measured for the dense cores in this cloud suggests that the mass scale that characterizes the dense core mass function may be the result of a simple process of thermal (Jeans) fragmentation. Table of core positions is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/462/L17

  19. Hydrogen Maser Clock (HMC) Experiment

    NASA Technical Reports Server (NTRS)

    Vessot, Robert F. C.; Mattison, Edward M.

    1997-01-01

    The Hydrogen Maser Clock (HMC) project was originally conceived to fly on a reflight of the European Space Agency (ESA) free flying platform, the European Recoverable Carrier (EURECA) that had been launched into space and recovered by NASA's Space Transportation System (STS). A Phase B study for operation of HMC as one of the twelve EURECA payload components was begun in July 1991, and completed a year later. Phase C/D of HMC began in August 1992 and continued into early 1995. At that time ESA decided not to refly EURECA, leaving HMC without access to space. Approximately 80% of the flight support electronics are presently operating the HMC's physics package in a vacuum tank at the Smithsonian Astrophysical Observatory, and are now considered to be well-tested flight electronics. The package will continue to be operated until the end of 1997 or until a flight opportunity becomes avaiable. Appendices: letters and trip report; proceedings of the symposium on frequency standards and metrology; milli-celsius-stability thermal control for an orbiting frequency standard.

  20. N+CPT clock resonance

    SciTech Connect

    Crescimanno, M.; Hohensee, M.

    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.

  1. Positional Cloning of the Mouse Circadian Clock Gene

    PubMed Central

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

    2013-01-01

    Summary 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 donor site causes exon skipping and deletion of 51 amino acids in the CLOCK protein. Clock is a unique gene with known circadian function and with features predicting DNA binding, protein dimerization, and activation domains. CLOCK represents the second example of a PAS domain–containing clock protein (besides Drosophila PERIOD), which suggests that this motif may define an evolutionarily conserved feature of the circadian clock mechanism. PMID:9160755

  2. Structure of the Outer Cusp and Sources of the Cusp Precipitation during Intervals of a Horizontal IMF

    NASA Technical Reports Server (NTRS)

    Berchem, Jean; Nemecek, Z.; Safrankova, J.; Prech, L.; Simunek, J.; Sauvaud, J.-A.; Fedorov, A.; Stenuit, H.; Fuselier, S. A.; Savin, S.; Zelenyi, L.

    2003-01-01

    The cusp represents a place where the magnetosheath plasma can directly penetrate into the magnetosphere. Since the main transport processes are connected with merging of the interplanetary and magnetospheric field lines: the interplanetary magnetic field (IMF) Orientation plays a decisive role in the formation of the high-altitude cusp. The importance of the sign of the IMF B(sub Z) component for this process was suggested about 40 years ago and later it was documented by many experimental investigations. However, situations when IMF Bz is the major IMF component are rather rare. The structure of the cusp during periods of a small IMF B(sub Z) is generally unknown, probably due to the fully 3-D nature of the interaction. The present case study reveals the importance of horizontal IMF components on the global magnetospheric configuration as well as on small-scale processes at the cusp-magnetosheath interface. We have used simultaneous measurements of several spacecraft (ISTP program) operating in different regions of interplanetary space and two closely spaced satellites (INTERBALL-1/MAGION-4) crossing the cusp-magnetosheath boundary to show the connection between the short- and large-scale phenomena. In the northern hemisphere, observations suggest a presence of two spots of cusp-like precipitation supplied by reconnection occurring simultaneously in both hemispheres. A source of this bifurcation is the positive IMF B(sub y) component further enhanced by the field draping in the magnetosheath. This magnetic field component shifts the entry point far away from the local noon but in opposite sense in either hemisphere. The cusp represents a place where the magnetosheath plasma can directly

  3. 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.

  4. Clock synchronization on the RAX spacecraft

    NASA Astrophysics Data System (ADS)

    Springmann, John C.; Kempke, Benjamin P.; Cutler, James W.; Bahcivan, Hasan

    2014-05-01

    The Radio Aurora Explorer (RAX) is a CubeSat that was developed to study space weather in Earth's ionosphere. The scientific payload is a bistatic radar system in which an onboard receiver works in cooperation with a ground-based transmitter. Accuracy of the onboard clock is critical for processing the radar measurements. The RAX timing system utilizes commercial off-the-shelf components integrated into custom subsystems. GPS is used to maintain absolute timing accuracy better than 1 ?s, but the subsystem is not always available due to power constraints, so a method has been developed to correct the onboard clock error without the use of GPS. The clock correction utilizes range measurements extracted from the pulses emitted by the transmitter, and resulting absolute clock accuracies of better than 0.20 s with drift of less than 21 ns/s have been demonstrated. The RAX timing system and the clock correction algorithm are presented as a reference for other spacecraft designers and are critical for those analyzing RAX data.

  5. Nuclear receptors rock around the clock

    PubMed Central

    Zhao, Xuan; Cho, Han; Yu, Ruth T; Atkins, Annette R; Downes, Michael; Evans, Ronald M

    2014-01-01

    Circadian rhythms characterize almost every aspect of human physiology, endocrinology, xenobiotic detoxification, cell growth, and behavior. Modern lifestyles that disrupt our normal circadian rhythms are increasingly thought to contribute to various disease conditions ranging from depression and metabolic disorders to cancer. This self-sustained time-keeping system is generated and maintained by an endogenous molecular machine, the circadian clock, which is a transcriptional mechanism composed of the transcription factors CLOCK and BMAL and their co-repressors, PER and CRY. Nuclear receptors (NRs) represent a large family of hormone-sensitive transcriptional regulators involved in a myriad of biological processes such as development, energy metabolism, reproduction, inflammation, and tissue homeostasis. Recent studies point not only to NR regulation by the clock, but also to NR regulation of the clock itself. Here, we discuss recent studies that functionally and mechanistically implicate NRs as key components of both the universal and adaptive circadian clock mechanisms. As proven pharmacological targets, nuclear receptors are promising targets for therapeutic control of many pathological conditions associated with the disruption of circadian rhythm. PMID:24737872

  6. 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

  7. A dynamical model of highlatitude convection derived from SuperDARN plasma drift measurements

    E-print Network

    Shepherd, Simon

    sufficient spatial coverage to define the complete pattern of convection. In these cases, an empirical model; Ruohoniemi et al., 2002; Lester et al., 2006] have led to the use of the IMF clock angle, the IMF transverse incoherent backscatter radars [Foster et al., 1986; Holt et al., 1987; Zhang et al., 2007] and coherent

  8. 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.

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

    SciTech Connect

    Geha, Marla; Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.; Avila, Roberto J.; Ferguson, Henry C.; Simon, Joshua D.; Kirby, Evan N.; VandenBerg, Don A.; Munoz, Ricardo R.; Guhathakurta, Puragra E-mail: tbrown@stsci.edu

    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. Statistical properties and solar wind source of long-duration and amplitude southward IMF intervals and their geomagnetic effectiveness

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Moldwin, M.

    2012-12-01

    It is well known that extended periods of large amplitude southward Interplanetary Magnetic Field (IMF) are geoeffective. This study determines the statistical properties of these intervals and identifies their corresponding solar wind source. We use 1-min WIND magnetometer data from 1995 - 2011. It is noted that IMF Bz changes polarity from north-to-south or south-to-north at high-frequency (every 3-4 mins) by counting. Long intervals of southward IMF are mainly imbedded in MC (> 2 hrs), SMFR (1-2 hrs) or SIR (0.5-1 hr). About 29% of the long duration (> 2 hrs) strong southward IMF (< -5 nT) are associated with these structures. We also examined the statistical properties and geoeffectiveness for the solar wind and IMF conditions with long duration southward Bz not related to any of these structures. We found that these intervals are related to Heliospheric Current Sheet (HCS) or unidirectional magnetic field or ambiguous variations. Using geomagnetic activity indices obtained from ground magnetometers most of these intervals corresponded to large increases of substorm activity, but not geomagnetic storms. There is a strong solar cycle dependence on the occurrence frequency of strong southward Bz (less than -5 nT).

  11. Models of the Primordial Standard Clock

    NASA Astrophysics Data System (ADS)

    Chen, Xingang; Namjoo, Mohammad Hossein; Wang, Yi

    2015-02-01

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

  12. Intact Interval Timing in Circadian CLOCK Mutants

    PubMed Central

    Cordes, Sara; Gallistel, C. R.

    2008-01-01

    While progress has been made in determining the molecular basis for the circadian clock, the mechanism by which mammalian brains time intervals measured in seconds to minutes remains a mystery. An obvious question is whether the interval timing mechanism shares molecular machinery with the circadian timing mechanism. In the current study, we trained circadian CLOCK +/? and ?/? mutant male mice in a peak-interval procedure with 10 and 20-s criteria. The mutant mice were more active than their wild-type littermates, but there were no reliable deficits in the accuracy or precision of their timing as compared with wild-type littermates. This suggests that expression of the CLOCK protein is not necessary for normal interval timing. PMID:18602902

  13. Biogeographic calibrations for the molecular clock.

    PubMed

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

    2015-09-01

    Molecular estimates of evolutionary timescales have an important role in a range of biological studies. Such estimates can be made using methods based on molecular clocks, including models that are able to account for rate variation across lineages. All clock models share a dependence on calibrations, which enable estimates to be given in absolute time units. There are many available methods for incorporating fossil calibrations, but geological and climatic data can also provide useful calibrations for molecular clocks. However, a number of strong assumptions need to be made when using these biogeographic calibrations, leading to wide variation in their reliability and precision. In this review, we describe the nature of biogeographic calibrations and the assumptions that they involve. We present an overview of the different geological and climatic events that can provide informative calibrations, and explain how such temporal information can be incorporated into dating analyses. PMID:26333662

  14. 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.

  15. 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 ...

  16. 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....

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

    MedlinePLUS

    ... Science Home Page Tick Tock: New Clues About Biological Clocks and Health By Emily Carlson, Alisa Machalek, ... Posted November 1, 2012 Genes and proteins run biological clocks that help keep daily rhythms in synch. ...

  18. Photosynthetic entrainment of the Arabidopsis thaliana circadian clock

    E-print Network

    Haydon, Michael J.; Mielczarek, Olga; Robertson, Fiona C.; Hubbard, Katherine E.; Webb, Alex A. R.

    2013-10-23

    of the circadian clock in plants. Here we show that these rhythmic, endogenous sugar signals can entrain circadian rhythms in Arabidopsis thaliana by regulating the gene expression of circadian clock components early in the photoperiod, thus defining a ‘metabolic...

  19. Role of cardiomyocyte circadian clock in myocardial metabolic adaptation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Marked circadian rhythmicities in cardiovascular physiology and pathophysiology exist. The cardiomyocyte circadian clock has recently been linked to circadian rhythms in myocardial gene expression, metabolism, and contractile function. For instance, the cardiomyocyte circadian clock is essential f...

  20. 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

  1. 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.

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

    SciTech Connect

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

    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. 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.

  5. Caring around the Clock: rounding in practice.

    PubMed

    Hutchings, Marie

    A large acute trust in the East Midlands looked to the US to inform its implementation of hourly rounding, otherwise known as intentional rounding. A combination of transformational leadership and meaningful interactions form the basis of a new approach to rounding--Caring around the Clock. The trust piloted the concept on 10 wards with results showing a 32% reduction in call lights. The successful change in practice required an investment in staff education to equip staff with the necessary skills. The trust is currently rolling out Caring around Hourly rounding can reducethe Clock to 79 inpatient wards. PMID:23342834

  6. Real clocks and the Zeno effect

    SciTech Connect

    Egusquiza, Inigo L.; Garay, Luis J.

    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.

  7. 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.

  8. Orchestrating time: arrangements of the brain circadian clock

    E-print Network

    Silver, Rae

    in regulating the overall activity of the circadian clock: some cells within the SCN rhythmically express `clock time: how to synchronize 20 000 clocks Biological processes exhibit daily rhythms that enable organisms generated by the 20 000 neurons [1] that constitute the master circadian pacemaker located in the SCN

  9. A Clock and Ephemeris Algorithm for Dual Frequency SBAS

    E-print Network

    Stanford University

    A Clock and Ephemeris Algorithm for Dual Frequency SBAS Juan Blanch, Todd Walter, Per Enge the clock and ephemeris error bounds. In addition, new SBAS messages will be broadcast in the L5 channel performance. In this work, we propose an algorithm to compute the error bounds on the clock and ephemeris

  10. Sun Watching Lesson 4: Making a Sun Clock

    E-print Network

    Lawrence, Rick L.

    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

  11. Optimal Infinite Runs in One-Clock Priced Timed Automata

    E-print Network

    David, Alexandre

    Optimal Infinite Runs in One-Clock Priced Timed Automata Alexandre David1 , Daniel Ejsing-Duun2-time ratio in a one-clock priced timed automaton and pro- vide an algorithmic solution. Through refinements of the one-clock priced timed automaton. 1 Introduction Timed automata, introduced in 1990 by Alur and Dill

  12. Modeling the circadian clock: from molecular mechanism to

    E-print Network

    Goldbeter, Albert

    Modeling the circadian clock: from molecular mechanism to physiological disorders Jean of circadian rhythms, a computa- tional model for the mammalian circadian clock is used to examine the dynamical bases of circadian-clock-related physiological disorders in humans. Entrainment by the light

  13. 47 CFR 80.865 - Radiotelephone station clock.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 47 Telecommunication 5 2010-10-01 2010-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  14. 47 CFR 80.865 - Radiotelephone station clock.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 47 Telecommunication 5 2013-10-01 2013-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  15. 47 CFR 80.865 - Radiotelephone station clock.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 47 Telecommunication 5 2014-10-01 2014-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  16. 47 CFR 80.865 - Radiotelephone station clock.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 47 Telecommunication 5 2012-10-01 2012-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  17. 47 CFR 80.865 - Radiotelephone station clock.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 47 Telecommunication 5 2011-10-01 2011-10-01 false Radiotelephone station clock. 80.865 Section 80.865 Telecommunication FEDERAL COMMUNICATIONS COMMISSION (CONTINUED) SAFETY AND SPECIAL RADIO SERVICES... W § 80.865 Radiotelephone station clock. A clock having a face of at least 12.7 cm (5 in.)...

  18. Spoofing GPS Receiver Clock Offset of Phasor Measurement Units

    E-print Network

    Dominguez-Garcia, Alejandro

    1 Spoofing GPS Receiver Clock Offset of Phasor Measurement Units Xichen Jiang, Jiangmeng Zhang the feasibility of a spoofing attack on the GPS receiver of a Phasor Measurement Unit (PMU). We formulate's receiver clock offset (with respect to the GPS time measured by the onboard satellite clocks) before

  19. Building a Better Atomic Clock Benjamin J. Bloom

    E-print Network

    Jin, Deborah

    Building a Better Atomic Clock by Benjamin J. Bloom B.S., Massachusetts Institute of Technology thesis entitled: Building a Better Atomic Clock written by Benjamin J. Bloom has been approved a Better Atomic Clock Thesis directed by Prof. Jun Ye Since 1967, the Second has been defined by the CGPM

  20. 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

  1. Optical atomic clocks Andrew D. Ludlow,1,2

    E-print Network

    Jin, Deborah

    Optical atomic clocks Andrew D. Ludlow,1,2 Martin M. Boyd,1,3 and Jun Ye1 1 JILA, National Hannover, Welfengarten 1, 30167 Hannover, Germany (published 26 June 2015) Optical atomic clocks represent on the development of optical atomic clocks that are based on trapped single ions and many neutral atoms is provided

  2. Compile-Time Analysis and Specialization of Clocks in

    E-print Network

    executed at p2 / } · Synchronization between activities through · finish · atomic · clocks ComplileCompile-Time Analysis and Specialization of Clocks in Concurrent Programs Nalini Vasudevan (Columbia University) Complile-Time Analysis and Specialization of Clocks in Concurrent Programs ­ p. 1

  3. Atomic Clocks and Frequency Standards The Battel for Exactness

    E-print Network

    Peters, Achim

    Atomic Clocks and Frequency Standards The Battel for Exactness Matthias Reggentin Humboldt 2 Atomic Clock Concept 3 Microwave Frequency Standards 4 Outlook M. Reggentin (HU-Berlin) Atomic://ageofsail.wordpress.com/ M. Reggentin (HU-Berlin) Atomic Clocks and Frequency Standards July 07, 2010 3 / 39 #12;Importance

  4. A new record in atomic clock performance Travis L. Nicholson

    E-print Network

    Jin, Deborah

    A new record in atomic clock performance by Travis L. Nicholson B.A., University of Colorado, 2006 thesis entitled: A new record in atomic clock performance written by Travis L. Nicholson has been) A new record in atomic clock performance Thesis directed by Dr. Jun Ye The pursuit of better atomic

  5. Optical lattice clocks with non-interacting bosons and fermions

    E-print Network

    Loss, Daniel

    -precision atomic clocks that operate at a fractional uncertainty of 10-15 or less, quantum statistics and therefore the spins of the interrogated atoms have an essential role in determining the clocks' ultimate performance in atomic clocks. A single ion1 in a Paul trap offers such a system and demonstrates the most accurate

  6. 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.

  7. On the IMF BY dependence on polar cap patch exits at night

    NASA Astrophysics Data System (ADS)

    Moen, J.; Hosokawa, K.; Gulbrandsen, N.

    2012-04-01

    Polar cap patches are islands of enhanced F-region electron density within the polar cap. They form near the cusp inflow region at day, transit the polar cap when frozen into twin-cell convection, and finally exit the polar cap at night into the night time auroras. When exiting they change status from patches to blobs. Monitoring the presence of F-region plasma structures and their travel path is essential in order to develop reliable space weather forecasts for the high latitude ionosphere in future. This paper presents a comprehensive study of a sequence of polar cap patches that exit the polar cap. Superimposing satellite images of the auroral oval and all-sky camera observations of airglow patches onto SuperDARN convection maps for an extended time period around magnetic midnight, provides an unparalleled opportunity to examine how plasma exits the polar cap. Under conditions of IMF BY predominantly positive (+5nT) we find that the patches exit both into the oval on the dusk cell pre midnight and on the dusk cell post midnight. This event study concurs with a statistical result also presented. The statistics show that the MLT distribution of patch exits, which is a ~10 hours broad bell shaped function cantered on ~23:30 MLT, is just marginally sensitive to the IMF BY polarity. This makes us conclude that the patches do not memorize on which cell they entered the polar cap.

  8. Particle injections observed at the morning sector as a response to IMF turning

    NASA Astrophysics Data System (ADS)

    Kozelova, T. V.; Kozelov, B. V.

    2015-11-01

    We report a detailed case study of substorm on January 6, 2008 in the interval 13-15 UT using data from four THEMIS satellites located in the morning sector magnetosphere eastward the onset location. The substorm of interest presents the ground-based magnetic disturbance consisted from the large-scale pulsations (4-5 min) superposed on the substorm bay. One can distinguish at least two significant activations at different spatial regions. First activation, which follow after a short-living burst of the IMF Bz, developed westward of second one, which was sequent after the northward turning IMF Bz. We show the existence of fast magnetosonic mode after second activation. This mode was observed at 7.5 RE in the morning sector at region of transition from dipole to tail-like configuration of the magnetic field. The increase of z-component of the magnetic field observed in magnetosphere during the non-diamagnetic structure is interpreted as an enhancement of westward ring (or partial-ring) current at closer to Earth distances. The appearance of the sub-keV plasma at ?5.8 RE (used as a tracer of substorm injection) supports this supposition.

  9. Impact of Magnetic Draping, Convection, and Field Line Tying on Magnetopause Reconnection Under Northward IMF

    NASA Technical Reports Server (NTRS)

    Wendel, Deirdre E.; Reiff, Patricia H.; Goldstein, Melvyn L.

    2010-01-01

    We simulate a northward IMF cusp reconnection event at the magnetopause using the OpenGGCM resistive MHD code. The ACE input data, solar wind parameters, and dipole tilt belong to a 2002 reconnection event observed by IMAGE and Cluster. Based on a fully three-dimensional skeleton separators, nulls, and parallel electric fields, we show magnetic draping, convection, ionospheric field line tying play a role in producing a series of locally reconnecting nulls with flux ropes. The flux ropes in the cusp along the global separator line of symmetry. In 2D projection, the flux ropes the appearance of a tearing mode with a series of 'x's' and 'o's' but bearing a kind of 'guide field' that exists only within the magnetopause. The reconnecting field lines in the string of ropes involve IMF and both open and closed Earth magnetic field lines. The observed magnetic geometry reproduces the findings of a superposed epoch impact parameter study derived from the Cluster magnetometer data for the same event. The observed geometry has repercussions for spacecraft observations of cusp reconnection and for the imposed boundary conditions reconnection simulations.

  10. Identifying Variations to the IMF at High-$z$ Through Deep Radio Surveys

    E-print Network

    Murphy, Eric J

    2010-01-01

    In this article I briefly describe how deep radio surveys may provide a means to identify variations in the upper end of the initial mass function (IMF) in star-forming galaxies at high redshifts (i.e., $z\\gtrsim$3). At such high redshifts, I argue that deep radio continuum observations at frequencies $\\gtrsim$10 GHz using next generation facilities (e.g., EVLA, MeerKAT, SKA/NAA) will likely provide the most accurate measurements for the ionizing photon rates (star formation rates; SFRs) of normal galaxies since their non-thermal emission should be highly suppressed due to the increased inverse Compton (IC) losses from the cosmic microwave background (CMB), leaving only thermal (free-free) emission detectable. Thus, a careful analysis of such observations in combination with future ALMA and JWST data, measuring the rest-frame far-infrared and UV emission from the same population of galaxies, may yield the best means to search for variability in the stellar IMF at such epochs.

  11. The Turbulent ISM of Galaxies 10 Gyrs ago: Star Formation, Gas Accretion, and IMF

    NASA Astrophysics Data System (ADS)

    Le Tiran, Loïc; Lehnert, Matthew D.

    2011-12-01

    The utilization of integral-field spectroscopy has led us to a new understanding of the physical conditions in galaxies within the first few billion years after the Big Bang. In this proceedings, we analyze observations of ~50 massive galaxies as seen as they were 10 Gyrs ago using SINFONI from the ESO-VLT. We show that the large line width they exhibit can be explained by the intense mechanical energy output from the young stars. We also study the influence of cold gas accretion upon these galaxies: We show that an unrealistic amount of shocked gas would be needed in order to explain the H? emission from these galaxies through shocks from gas accretion with velocity about the H? line widths of these galaxies. We also use DEEP2 photometric measurements for a sub-sample of 10 of these galaxies to evaluate their ratio of H? to FUV flux as a function of their H? and R-band luminosity surface brightnesses. Our data suggests that perhaps their initial mass function (IMF) is flatter than Salpeter at the high mass end, as has been suggested recently for some local galaxies. It may be that high turbulence is responsible for skewing the IMF towards more massive stars as suggested by some theories of star-formation. Much work is however needed to accredit this hypothesis.

  12. The IMF and Internal Kinematics of the Massive Young Star Cluster, Westerlund 1

    NASA Astrophysics Data System (ADS)

    Lu, Jessica

    2014-10-01

    The most massive young star cluster known in the Milky Way, Westerlund 1, represents a far more extreme environment for star formation than nearby, well-studied, and lower-mass star forming regions such as Taurus and Orion. We propose to construct a complete photometric and kinematic census of Westerlund 1 in order to identify cluster members down to 0.1 solar masses, precisely determine the initial mass function (IMF), and measure the internal kinematic structure of the cluster. With these measurements, we will test whether the IMF is universal, as may be the case for nearby lower-mass star forming regions, or favors high-mass star formation, as has been suggested theoretically and from some observational results. We will observe Wd 1 with WFC3-IR, which is the only instrument capable of delivering high spatial resolution, a well-characterized and stable PSF, and a wide field of view at infrared wavelengths. We exploit WFC3's capabilities to cover the full extent of the cluster with photometry, to correct for variable extinction and derive stellar masses, and with proper motions, to distinguish between cluster members and contaminating field stars. Our proposed observations of Westerlund 1 will help determine whether the star formation process, and the emergent stellar mass distribution, varies with initial cloud conditions.

  13. Observations of IMF and seasonal effects in high-latitude convection

    NASA Technical Reports Server (NTRS)

    Ruohoniemi, J. M.; Greenwald, R. A.

    1995-01-01

    Strong interplanetary magnetic field (IMF) and seasonal effects in the convection of nightside ionospheric plasma are described. The findings are based on a statistical analysis of observations made with the Johns Hopkins University/ Applied Physics Lab (JHU/APL) HF radar located at Goose Bay, Labrador. For positive sign of the IMF dusk-dawn component, By greater than 0 the dawn cell is more crescent shaped and the dusk cell more round while for BY less than 0 these pairings of size and shape are reversed. The more extreme crescent /round cell dichotomy is obtained for BY greater than 0. The return flows associated with the crescent-shaped cell dominate at midnight MLT (magnetic local time); the reversal in the zonal velocity in the 67 deg-69 deg lambda (magnetic latitude) interval occurs 2.5 hr earlier in summer than in winter. The maximum effects are obtained on the nightside for the pairings By greater than 0, summer and BY less than 0, winter; the first produces the more structured cell in the morning, the second in the evening, and this cell dominates the return flow at midnight. The difference in the zonal flow reversals for these pairings exceeds 4 hr in MLT.

  14. 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.

  15. Ionospheric and geomagnetic responses to changes in IMF B Z : a superposed epoch study

    NASA Astrophysics Data System (ADS)

    Davis, C. J.; Wild, M. N.; Lockwood, M.; Tulunay, Y. K.

    1997-02-01

    Superposed epoch studies have been carried out in order to determine the ionospheric response at mid-latitudes to southward turnings of the interplanetary magnetic field (IMF). This is compared with the geomagnetic response, as seen in the indices Kp, AE and Dst. The solar wind, IMF and geomagnetic data used were hourly averages from the years 1967-1989 and thus cover a full 22-year cycle in the solar magnetic field. These data were divided into subsets, determined by the magnitudes of the southward turnings and the concomitant increase in solar wind pressure. The superposed epoch studies were carried out using the time of the southward turning as time zero. The response of the mid-latitude ionosphere is studied by looking at the F-layer critical frequencies, foF2, from hourly soundings by the Slough ionosonde and their deviation from the monthly median values, foF2. For the southward turnings with a change in Bz of Bz<>\\ > 11.5<> nT accompanied by a solar wind dynamic pressure P exceeding 5 nPa, the F region critical frequency, foF2, shows a marked decrease, reaching a minimum value about 20 h after the southward turning. This recovers to pre-event values over the subsequent 24 h, on average. The Dst index shows the classic storm-time decrease to about -60 nT. Four days later, the index has still to fully recover and is at about -25 nT. Both the Kp and AE indices show rises before the southward turnings, when the IMF is strongly northward but the solar wind dynamic pressure is enhanced. The average AE index does register a clear isolated pulse (averaging 650 nT for 2 h, compared with a background peak level of near 450 nT at these times) showing enhanced energy deposition at high latitudes in substorms but, like Kp, remains somewhat enhanced for several days, even after the average IMF has returned to zero after 1 day. This AE background decays away over several days as the Dst index recovers, indicating that there is some contamination of the currents observed at the AE stations by the continuing enhanced equatorial ring current. For data averaged over all seasons, the critical frequencies are depressed at Slough by 1.3 MHz, which is close to the lower decile of the overall distribution of foF2 values. Taking 30-day periods around summer and winter solstice, the largest depression is 1.6 and ␣ 1.2 MHz, respectively. This seasonal dependence is confirmed by a similar study for a Southern Hemisphere station, Argentine Island, giving peak depressions of 1.8 MHz and 0.5 MHz for summer and winter. For the subset of turnings where Bz<>\\ > 11.5<> nT and P<>\\ <=\\ <>5 nPa, the response of the geomagnetic indices is similar but smaller, while the change in foF2 has all but disappeared. This confirms that the energy deposited at high latitudes, which leads to the geomagnetic and ionospheric disturbances following a southward turning of the IMF, increases with the energy density (dynamic pressure) of the solar wind flow. The magnitude of all responses are shown to depend on Bz. At Slough, the peak depression always occurs when Slough rotates into the noon sector. The largest ionospheric response is for southward turnings seen between 15-21 UT.

  16. Reading Angles in Maps

    ERIC Educational Resources Information Center

    Izard, Véronique; O'Donnell, Evan; Spelke, Elizabeth S.

    2014-01-01

    Preschool children can navigate by simple geometric maps of the environment, but the nature of the geometric relations they use in map reading remains unclear. Here, children were tested specifically on their sensitivity to angle. Forty-eight children (age 47:15-53:30 months) were presented with fragments of geometric maps, in which angle sections…

  17. ^87Sr Clock Comparisons at JILA

    NASA Astrophysics Data System (ADS)

    Williams, Jason; Nicholson, Travis; Bloom, Benjamin; Campbell, Sara; Martin, Michael; Swallows, Matthew; Bishof, Michael; Ye, Jun

    2012-06-01

    Great advances are being realized with optical lattice clocks, where spectroscopy at optical frequencies and large ensembles of neutral atoms combine to offer extremely high frequency precision and stability. Recent results from the Strontium 87 optical atomic clock at JILA have demonstrated that strong interactions among fermions confined in a two-dimensional (2D) optical lattice suppress the collisional frequency shift and its uncertainty to the level of 10-17 [1]. We report on the progress of a second optical lattice clock at JILA, in which fermionic ^87Sr atoms are confined in a lattice potential derived from optical buildup cavities to provide strong confinement over a very large volume in one, two, and three dimensional lattices. Intercomparisons of the two clocks at JILA will be used to explore in greater detail the physics governing the transition shifts and uncertainties in our two ^87Sr optical lattice systems and will provide a significant improvement of our systematic errors.[4pt] [1] M D. Swallows et al. Science, 331, 1043 (2011)

  18. Clock Synchronization for Multihop Wireless Sensor Networks

    ERIC Educational Resources Information Center

    Solis Robles, Roberto

    2009-01-01

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

  19. Tick Tock, a Vitamin C Clock.

    ERIC Educational Resources Information Center

    Wright, Stephen W.

    2002-01-01

    Presents an activity that uses supermarket chemicals to perform a clock reaction in which the endpoint is signaled by an abrupt change in the appearance from colorless to blue-black. This activity can be used to explore reaction kinetics and the effect of reactant concentrations on the apparent rate of reaction. (DDR)

  20. Systems Biology of the Mammalian Circadian Clock

    E-print Network

    Spang, Rainer

    Molecular Chronobiology #12;The circadian oscillator Circadian rhythm Oster et al., 2002 Feedback loops rhythms disrupted -TrCP1-Mediated Degradation of PERIOD2 Is Essential for Circadian Dynamics Reischl et alSystems Biology of the Mammalian Circadian Clock Hanspeter Herzel Institute for Theoretical Biology

  1. Longitudinal light clock vs special relativity

    E-print Network

    Giovanni Zanella

    2015-11-13

    In order to respect the Principle of Relativity, the analysis of the behavior of the longitudinal light clock reveals the necessity to extend the Doppler effect also to space and time. As a consequence, the bodies in inertial motion must dilate along the direction of their movement.

  2. Circadian Clock Proteins in Prokaryotes: Hidden Rhythms?

    PubMed Central

    Loza-Correa, Maria; Gomez-Valero, Laura; Buchrieser, Carmen

    2010-01-01

    Circadian clock genes are vital features of eukaryotes that have evolved such that organisms can adapt to our planet's rotation in order to anticipate the coming day or night as well as unfavorable seasons. This circadian clock uses oscillation as a timekeeping element. However, circadian clock mechanisms exist also in prokaryotes. The circadian clock of Cyanobacteria is well studied. It is regulated by a cluster of three genes: kaiA, kaiB, and kaiC. In this review, we will discuss the circadian system in cyanobacteria, and provide an overview and updated phylogenetic analysis of prokaryotic organisms that contain the main circadian genes. It is evident that the evolution of the kai genes has been influenced by lateral transfers but further and deeper studies are needed to get an in depth understanding of the exact evolutionary history of these genes. Interestingly, Legionella pneumophila an environmental bacterium and opportunistic human pathogen that parasitizes protozoa in fresh water environments also contains kaiB and kaiC, but their functions are not known. All of the residues described for the biochemical functions of the main pacemaker KaiC in Synechococcus elongatus are also conserved in the L. pneumophila KaiC protein. PMID:21687756

  3. Circadian clock function in the mammalian ovary.

    PubMed

    Sellix, Michael T

    2015-02-01

    Rhythmic events in the female reproductive system depend on the coordinated and synchronized activity of multiple neuroendocrine and endocrine tissues. This coordination is facilitated by the timing of gene expression and cellular physiology at each level of the hypothalamo-pituitary-ovarian (HPO) axis, including the basal hypothalamus and forebrain, the pituitary gland, and the ovary. Central to this pathway is the primary circadian pacemaker in the suprachiasmatic nucleus (SCN) that, through its myriad outputs, provides a temporal framework for gonadotropin release and ovulation. The heart of the timing system, a transcription-based oscillator, imparts SCN pacemaker cells and a company of peripheral tissues with the capacity for daily oscillations of gene expression and cellular physiology. Although the SCN sits comfortably at the helm, peripheral oscillators (such as the ovary) have undefined but potentially critical roles. Each cell type of the ovary, including theca cells, granulosa cells, and oocytes, harbor a molecular clock implicated in the processes of follicular growth, steroid hormone synthesis, and ovulation. The ovarian clock is influenced by the reproductive cycle and diseases that perturb the cycle and/or follicular growth can disrupt the timing of clock gene expression in the ovary. Chronodisruption is known to negatively affect reproductive function and fertility in both rodent models and women exposed to shiftwork schedules. Thus, influencing clock function in the HPO axis with chronobiotics may represent a novel avenue for the treatment of common fertility disorders, particularly those resulting from chronic circadian disruption. PMID:25367899

  4. Current Status of the Molecular Clock Hypothesis

    ERIC Educational Resources Information Center

    Hermann, Gilbert

    2003-01-01

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

  5. Circadian Clocks in the Immune System.

    PubMed

    Labrecque, Nathalie; Cermakian, Nicolas

    2015-08-01

    The immune system is a complex set of physiological mechanisms whose general aim is to defend the organism against non-self-bodies, such as pathogens (bacteria, viruses, parasites), as well as cancer cells. Circadian rhythms are endogenous 24-h variations found in virtually all physiological processes. These circadian rhythms are generated by circadian clocks, located in most cell types, including cells of the immune system. This review presents an overview of the clocks in the immune system and of the circadian regulation of the function of immune cells. Most immune cells express circadian clock genes and present a wide array of genes expressed with a 24-h rhythm. This has profound impacts on cellular functions, including a daily rhythm in the synthesis and release of cytokines, chemokines and cytolytic factors, the daily gating of the response occurring through pattern recognition receptors, circadian rhythms of cellular functions such as phagocytosis, migration to inflamed or infected tissue, cytolytic activity, and proliferative response to antigens. Consequently, alterations of circadian rhythms (e.g., clock gene mutation in mice or environmental disruption similar to shift work) lead to disturbed immune responses. We discuss the implications of these data for human health and the areas that future research should aim to address. PMID:25900041

  6. European plans for new clocks in space

    NASA Technical Reports Server (NTRS)

    Leschiutta, Sigfrido M.; Tavella, Patrizia

    1995-01-01

    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.

  7. CLOCK, an essential pacemaker component, controls expression

    E-print Network

    Halazonetis, Thanos

    , is expressed according to a robust daily rhythm in the suprachiasmatic nucleus and several peripheral tissues expression. Here we present evidence that circadian Dbp transcription requires the basic helix­loop­helix­PAS protein CLOCK, an essential component of the negative-feedback circuitry generating circadian oscillations

  8. The mammalian retina as a clock

    NASA Technical Reports Server (NTRS)

    Tosini, Gianluca; Fukuhara, Chiaki

    2002-01-01

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

  9. Biochemical basis for the biological clock

    NASA Technical Reports Server (NTRS)

    Morre, D. James; Chueh, Pin-Ju; Pletcher, Jake; Tang, Xiaoyu; Wu, Lian-Ying; Morre, Dorothy M.

    2002-01-01

    NADH oxidases at the external surface of plant and animal cells (ECTO-NOX proteins) exhibit stable and recurring patterns of oscillations with potentially clock-related, entrainable, and temperature-compensated period lengths of 24 min. To determine if ECTO-NOX proteins might represent the ultradian time keepers (pacemakers) of the biological clock, COS cells were transfected with cDNAs encoding tNOX proteins having a period length of 22 min or with C575A or C558A cysteine to alanine replacements having period lengths of 36 or 42 min. Here we demonstrate that such transfectants exhibited 22, 36, or 40 to 42 h circadian patterns in the activity of glyceraldehyde-3-phosphate dehydrogenase, a common clock-regulated protein, in addition to the endogenous 24 h circadian period length. The fact that the expression of a single oscillatory ECTO-NOX protein determines the period length of a circadian biochemical marker (60 X the ECTO-NOX period length) provides compelling evidence that ECTO-NOX proteins are the biochemical ultradian drivers of the cellular biological clock.

  10. Realisation of a compact methane optical clock

    SciTech Connect

    Gubin, M A; Kireev, A N; Konyashchenko, A V; Kryukov, P G; Tausenev, A V; Tyurikov, D A; Shelkovnikov, A S

    2008-07-31

    A compact optical clock based on a double-mode He-Ne/CH{sub 4} optical frequency standard and a femtosecond Er{sup 3+} fibre laser is realised and its stability against a commercial hydrogen frequency standard is measured. (letters)

  11. The peripheral clock regulates human pigmentation.

    PubMed

    Hardman, Jonathan A; Tobin, Desmond J; Haslam, Iain S; Farjo, Nilofer; Farjo, Bessam; Al-Nuaimi, Yusur; Grimaldi, Benedetto; Paus, Ralf

    2015-04-01

    Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies. PMID:25310406

  12. Distant clock synchronization using entangled photon pairs

    SciTech Connect

    Valencia, Alejandra; Scarcelli, Giuliano; Shih, Yanhua

    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.

  13. 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.

  14. 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.

  15. 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

  16. Field operations with cesium clocks in HF navigation systems

    NASA Technical Reports Server (NTRS)

    Christy, E. H.; Clayton, D. A.

    1982-01-01

    Networks of HF phase comparison marine navigation stations employing cesium clocks are discussed. The largest permanent network is in the Gulf of Mexico where some fourteen base stations are continuously active and others are activated as needed. These HF phase comparison systems, which operate on a single transmission path, require a clock on the mobile unit as well. Inventory consists of upwards of 70 clocks from two different manufacturers. The maintenance of this network as an operating system requires a coordinated effort involving clock preparation, clock environment control, station performance monitoring and field service.

  17. 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.

  18. 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

  19. A Role for Timely Nuclear Translocation of Clock Repressor Proteins in Setting Circadian Clock Speed

    PubMed Central

    Lee, Euna

    2014-01-01

    By means of a circadian clock system, all the living organisms on earth including human beings can anticipate the environmental rhythmic changes such as light/dark and warm/cold periods in a daily as well as in a yearly manner. Anticipating such environmental changes provide organisms with survival benefits via manifesting behavior and physiology at an advantageous time of the day and year. Cell-autonomous circadian oscillators, governed by transcriptional feedback loop composed of positive and negative elements, are organized into a hierarchical system throughout the organisms and generate an oscillatory expression of a clock gene by itself as well as clock controlled genes (ccgs) with a 24 hr periodicity. In the feedback loop, hetero-dimeric transcription factor complex induces the expression of negative regulatory proteins, which in turn represses the activity of transcription factors to inhibit their own transcription. Thus, for robust oscillatory rhythms of the expression of clock genes as well as ccgs, the precise control of subcellular localization and/or timely translocation of core clock protein are crucial. Here, we discuss how sub-cellular localization and nuclear translocation are controlled in a time-specific manner focusing on the negative regulatory clock proteins. PMID:25258565

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

    E-print Network

    Jonathan D. Weinstein; Kyle Beloy; Andrei Derevianko

    2009-12-06

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

  1. Controlling the Cyanobacterial Clock by Synthetically Rewiring Metabolism

    PubMed Central

    Pattanayak, Gopal K.; Lambert, Guillaume; Bernat, Kevin; Rust, Michael J.

    2015-01-01

    Summary Circadian clocks are oscillatory systems and allow organisms to anticipate rhythmic changes in the environment. Several studies have shown that circadian clocks are connected to metabolism, but it is not generally clear whether metabolic signaling is one voice among many that influence the clock, or whether metabolic cycling is the major clock synchronizer. To address this question in cyanobacteria, we used a synthetic biology approach to make normally autotrophic cells capable of growth on exogenous sugar. This allowed us to manipulate metabolism independently from the light and dark. We found that feeding sugar to cultures blocked the clock-resetting effect of a dark pulse. Further, in the absence of light, the clock efficiently synchronizes to metabolic cycles driven by rhythmic feeding. We conclude that metabolic activity, independent of its source, is the primary clock driver in cyanobacteria. PMID:26686627

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

    SciTech Connect

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

    2010-03-15

    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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Multispacecraft study on the dynamics of the dusk-flank magnetosphere under northward IMF: 1011 January 1997

    E-print Network

    Bonnell, John W.

    Multispacecraft study on the dynamics of the dusk-flank magnetosphere under northward IMF: 10 the magnetosheath plasma onto the magnetospheric field lines. Three candidate processes are discussed, but none Magnetospheric Physics: Plasma sheet; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2724

  8. Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and the IMF

    E-print Network

    J. R. Rigby; G. H. Rieke

    2004-01-13

    Determining the properties of starbursts requires spectral diagnostics of their ultraviolet radiation fields, to test whether very massive stars are present. We test several such diagnostics, using new models of line ratio behavior combining Cloudy, Starburst99 and up-to-date spectral atlases. For six galaxies we obtain new measurements of HeI 1.7 um / Brackett 10, a difficult to measure but physically simple (and therefore reliable) diagnostic. We obtain new measurements of HeI 2.06 um / Brackett gamma in five galaxies, and find that it and [OIII]/Hbeta are generally unreliable diagnostics in starbursts. The heteronuclear and homonuclear mid--infrared line ratios (notably [NeIII] 15.6 um / [NeII] 12.8 um) consistently agree with each other and with HeI 1.7 um / Br10; this argues that the mid-infrared line ratios are reliable diagnostics of spectral hardness. In a sample of 27 starbursts, [NeIII]/[NeII] ratios are significantly less excited than model predictions for a Salpeter IMF extending to 100 solar masses. Plausible model alterations strengthen this conclusion. By contrast, the low-mass and low-metallicity galaxies II Zw 40 and NGC 5253 show relatively high neon line ratios, compatible with a Salpeter slope extending to at least 40--60 Msol. One solution for the low neon line ratios in the high--metallicity starbursts would be that they are deficient in >40 Msol stars compared to a Salpeter IMF. An alternative explanation, which we prefer, is that massive stars in high--metallicity starbursts spend much of their lives embedded within ultra--compact HII regions that prevent the near- and mid-infrared nebular lines from forming and escaping. This hypothesis has important consequences for starburst modelling and interpretation.

  9. Investigating [X/Fe], IMF, and compositeness in integrated-light models

    NASA Astrophysics Data System (ADS)

    Tang, Baitian; Worthey, Guy

    2015-01-01

    Modelling elliptical galaxy integrated-light characteristics with old, metal-rich stellar populations is a common and promising way to study these distant objects. However, different model parameters may change the characteristics in a similar way, causing degeneracy, e.g., the age-metallicity degeneracy. Here, we investigate several under-appreciated effects with the evolving Worthey models, and discuss their detectabilities.We model composite stellar populations with realistic abundance distribution functions (ADFs), tracking the trends of individual elements as a function of overall heavy element abundance as observed in MW bulge stars in addition to solar neighborhood stars. Comparing bulge versus elliptical galaxies, Fe, Ti, and Mg trend about the same for both but C, Na, and Ca seem irreconcilably different.Exploring the behavior of abundance compositeness leads to the concepts of ``red lean'' where a narrower ADF appears more metal rich than a wide one, and ``red spread'' where the spectral difference between wide and narrow ADFs increases as the ADF peak is moved to more metal-rich values. The prospects of measuring the width of the ADF of an old stellar population were investigated and seem bright using UV to IR photometry.Next, we try to disentangle the effects of 1) low-mass cut-off; 2) IMF slope; and 3) AGB strength in several IMF-sensitive indices and NIR colors. In most of the NIR-optical colors, varying low-mass cut-off and AGB strength leads to about 0.03 mag drift, which is comparable to the observable limits. Using a mix of photometric and spectral absorption indices (e.g. [MgFe], Wing-Ford, V-K, and B-V) degeneracy can be lifted, although at an observationally challenging amplitude. We go on to include ADF width and abundance ratio effects, and discuss the accuracy of disentangling multiple effects from integrated-light measurements.

  10. Observations of IMF and seasonal effects in high-latitude convection

    SciTech Connect

    Ruohoniemi, J.M.; Greenwald, R.A.

    1995-05-01

    The authors describe strong interplanetary magnetic field (IMF) and seasonal effects in the convection of nightside ionospheric plasma. The findings are based on a statistical analysis of observations made with the JHU/APL HF radar located at Goose Bay, Labrador. For positive sign of the IMF dawn-dusk component, i.e., B{sub y}>0, the dawn cell is more crescent-shaped and the dusk cell more round while for B{sub y}<0 these pairings of size and shape are reversed. The more extreme crescent/round cell dichotomy is obtained for B{sub y}>0. The return flows associated with the crescent-shaped cell dominate at midnight MLT (Magnetic Local Time); the reversal in the zonal velocity in the 67{degrees}-69{degrees}{Lambda} (magnetic latitude) interval occurs 2 1/2 hr earlier for B{sub y}>0. The seasonal dependence of nightside convection resembles in important respects the B{sub y} dependence. Greater latitudinal velocity shears occur in the morning/afternoon sector for summer/winter and the return flow of this sector dominates at midnight. The zonal flow reversal occurs 2 1/2 hr earlier in summer than in winter. The maximum effects are obtained on the nightside for the pairings [B{sub y}>0, summer] and [B{sub y}<0, winter]; the first produces the more structured cell in the morning, the second in the evening, and this cell dominates the return flow at midnight. The difference in the zonal flow reversals for these pairings exceeds 4 hr in MLT. 15 refs., 4 figs.

  11. 'Magic Angle Precession'

    SciTech Connect

    Binder, Bernd

    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.

  12. 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

  13. Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration

    PubMed Central

    Musiek, Erik S.; Lim, Miranda M.; Yang, Guangrui; Bauer, Adam Q.; Qi, Laura; Lee, Yool; Roh, Jee Hoon; Ortiz-Gonzalez, Xilma; Dearborn, Joshua T.; Culver, Joseph P.; Herzog, Erik D.; Hogenesch, John B.; Wozniak, David F.; Dikranian, Krikor; Giasson, Benoit I.; Weaver, David R.; Holtzman, David M.; FitzGerald, Garret A.

    2013-01-01

    Brain aging is associated with diminished circadian clock output and decreased expression of the core clock proteins, which regulate many aspects of cellular biochemistry and metabolism. The genes encoding clock proteins are expressed throughout the brain, though it is unknown whether these proteins modulate brain homeostasis. We observed that deletion of circadian clock transcriptional activators aryl hydrocarbon receptor nuclear translocator–like (Bmal1) alone, or circadian locomotor output cycles kaput (Clock) in combination with neuronal PAS domain protein 2 (Npas2), induced severe age-dependent astrogliosis in the cortex and hippocampus. Mice lacking the clock gene repressors period circadian clock 1 (Per1) and period circadian clock 2 (Per2) had no observed astrogliosis. Bmal1 deletion caused the degeneration of synaptic terminals and impaired cortical functional connectivity, as well as neuronal oxidative damage and impaired expression of several redox defense genes. Targeted deletion of Bmal1 in neurons and glia caused similar neuropathology, despite the retention of intact circadian behavioral and sleep-wake rhythms. Reduction of Bmal1 expression promoted neuronal death in primary cultures and in mice treated with a chemical inducer of oxidative injury and striatal neurodegeneration. Our findings indicate that BMAL1 in a complex with CLOCK or NPAS2 regulates cerebral redox homeostasis and connects impaired clock gene function to neurodegeneration. PMID:24270424

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

    PubMed Central

    Joska, Tammy M.; Zaman, Riasat; Belden, William J.

    2014-01-01

    Since the cloning and discovery of DNA methyltransferases (DNMT), there has been a growing interest in DNA methylation, its role as an epigenetic modification, how it is established and removed, along with the implications in development and disease. In recent years, it has become evident that dynamic DNA methylation accompanies the circadian clock and is found at clock genes in Neurospora, mice and cancer cells. The relationship among the circadian clock, cancer and DNA methylation at clock genes suggests a correlative indication that improper DNA methylation may influence clock gene expression, contributing to the etiology of cancer. The molecular mechanism underlying DNA methylation at clock loci is best studied in the filamentous fungi, Neurospora crassa, and recent data indicate a mechanism analogous to the RNA-dependent DNA methylation (RdDM) or RNAi-mediated facultative heterochromatin. Although it is still unclear, DNA methylation at clock genes may function as a terminal modification that serves to prevent the regulated removal of histone modifications. In this capacity, aberrant DNA methylation may serve as a readout of misregulated clock genes and not as the causative agent. This review explores the implications of DNA methylation at clock loci and describes what is currently known regarding the molecular mechanism underlying DNA methylation at circadian clock genes. PMID:25198253

  15. Clocking-optimization method for figure-error balancing in complex optical systems

    NASA Astrophysics Data System (ADS)

    Liu, Xiaolin; Li, Yanqiu; Liu, Ke

    2015-05-01

    Figure errors of optical surfaces degrade the performance of optical systems. When predicting the performance and performing system assembly, compensation by clocking of optical components around the optical axis is a conventional but user-dependent method. Commercial optical software cannot optimize this clocking, and existing automatic figure-error balancing methods have limitations. To overcome these limitations, a global and general optimization method based on analyzing the precise relationships between the figure errors and the wavefront error (WFE) is proposed. Using the footprint data of each optical surface, the resulting WFE is calculated. Direct map operation is used for intercepting and rotating the figure-error maps. The simulated annealing algorithm is used to seek the optimal combination of clocking angles for the optical components. This method can be applied to most coaxial optics systems, including dioptric, catoptrics, and catadioptric complex lenses. It is successfully implemented for a catadioptric immersion lithographic optics system with artificial figure errors, and for an experimental lithographic optics system with actual manufacturing figure errors.

  16. Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications

    NASA Astrophysics Data System (ADS)

    Chutani, Ravinder; Maurice, Vincent; Passilly, Nicolas; Gorecki, Christophe; Boudot, Rodolphe; Abdel Hafiz, Moustafa; Abbé, Philippe; Galliou, Serge; Rauch, Jean-Yves; de Clercq, Emeric

    2015-09-01

    This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23?kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17?kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600??m.

  17. Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications.

    PubMed

    Chutani, Ravinder; Maurice, Vincent; Passilly, Nicolas; Gorecki, Christophe; Boudot, Rodolphe; Abdel Hafiz, Moustafa; Abbé, Philippe; Galliou, Serge; Rauch, Jean-Yves; de Clercq, Emeric

    2015-01-01

    This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23?kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17?kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600??m. PMID:26365754

  18. Laser light routing in an elongated micromachined vapor cell with diffraction gratings for atomic clock applications

    PubMed Central

    Chutani, Ravinder; Maurice, Vincent; Passilly, Nicolas; Gorecki, Christophe; Boudot, Rodolphe; Abdel Hafiz, Moustafa; Abbé, Philippe; Galliou, Serge; Rauch, Jean-Yves; de Clercq, Emeric

    2015-01-01

    This paper reports on an original architecture of microfabricated alkali vapor cell designed for miniature atomic clocks. The cell combines diffraction gratings with anisotropically etched single-crystalline silicon sidewalls to route a normally-incident beam in a cavity oriented along the substrate plane. Gratings have been specifically designed to diffract circularly polarized light in the first order, the latter having an angle of diffraction matching the (111) sidewalls orientation. Then, the length of the cavity where light interacts with alkali atoms can be extended. We demonstrate that a longer cell allows to reduce the beam diameter, while preserving the clock performances. As the cavity depth and the beam diameter are reduced, collimation can be performed in a tighter space. This solution relaxes the constraints on the device packaging and is suitable for wafer-level assembly. Several cells have been fabricated and characterized in a clock setup using coherent population trapping spectroscopy. The measured signals exhibit null power linewidths down to 2.23?kHz and high transmission contrasts up to 17%. A high contrast-to-linewidth ratio is found at a linewidth of 4.17?kHz and a contrast of 5.2% in a 7-mm-long cell despite a beam diameter reduced to 600??m. PMID:26365754

  19. 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.

  20. Millisecond pulsars - Nature's most stable clocks

    NASA Astrophysics Data System (ADS)

    Taylor, Joseph H., Jr.

    1991-07-01

    The author describes the role pulsars might play in time and frequency technology. Millisecond pulsars are rapidly rotating neutron stars: spherical flywheels some 20 km in diameter, 1.4 times as massive as the Sun, and spinning as fast as several thousand radians per second. Radio noise generated in a pulsar's magnetosphere by a highly beamed process is detectable over interstellar distances, as a periodic sequence of pulses similar to the ticks of an excellent clock. High-precision comparisons between pulsar time and terrestrial atomic time show that over intervals of several years, some millisecond pulsars have fractional stabilities comparable to those of the best atomic clocks. The author briefly reviews the physics of pulsars, discusses the techniques of pulsar timing measurements, and summarizes the results of careful studies of pulsar stabilities.

  1. 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.

  2. 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

  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. 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.

  5. 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.

  6. The Large Built Water Clock Of Amphiaraeion.

    NASA Astrophysics Data System (ADS)

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

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

  7. Metabolism and the Circadian Clock Converge

    PubMed Central

    Eckel-Mahan, Kristin

    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

  8. 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.

  9. Clock-Driven Quantum Thermal Engines

    E-print Network

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

    2015-04-09

    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, whilst 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.

  10. Sagnac Interferometry with a Single Atomic Clock.

    PubMed

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

    2015-10-16

    The Sagnac effect enables interferometric measurements of rotation with high precision. Using matter waves instead of light promises resolution enhancement by orders of magnitude that scales with particle mass. So far, the paradigm for matter wave Sagnac interferometry relies on de Broglie waves and thus on free propagation of atoms either in free fall or within waveguides. However, the Sagnac effect can be expressed as a proper time difference experienced by two observers moving in opposite directions along closed paths and has indeed been measured with atomic clocks flown around Earth. Inspired by this, we investigate an interferometer comprised of a single atomic clock. The Sagnac effect manifests as a phase shift between trapped atoms in different internal states after transportation along closed paths in opposite directions, without any free propagation. With analytic models, we quantify limitations of the scheme arising from atomic dynamics and finite temperature. Furthermore, we suggest an implementation with previously demonstrated technology. PMID:26550871

  11. Sagnac Interferometry with a Single Atomic Clock

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

    The Sagnac effect enables interferometric measurements of rotation with high precision. Using matter waves instead of light promises resolution enhancement by orders of magnitude that scales with particle mass. So far, the paradigm for matter wave Sagnac interferometry relies on de Broglie waves and thus on free propagation of atoms either in free fall or within waveguides. However, the Sagnac effect can be expressed as a proper time difference experienced by two observers moving in opposite directions along closed paths and has indeed been measured with atomic clocks flown around Earth. Inspired by this, we investigate an interferometer comprised of a single atomic clock. The Sagnac effect manifests as a phase shift between trapped atoms in different internal states after transportation along closed paths in opposite directions, without any free propagation. With analytic models, we quantify limitations of the scheme arising from atomic dynamics and finite temperature. Furthermore, we suggest an implementation with previously demonstrated technology.

  12. 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.

  13. GLONASS orbit/clock combination in VNIIFTRI

    NASA Astrophysics Data System (ADS)

    Bezmenov, I.; Pasynok, S.

    2015-08-01

    An algorithm and a program for GLONASS satellites orbit/clock combination based on daily precise orbits submitted by several Analytic Centers were developed. Some theoretical estimates for combine orbit positions RMS were derived. It was shown that under condition that RMS of satellite orbits provided by the Analytic Centers during a long time interval are commensurable the RMS of combine orbit positions is no greater than RMS of other satellite positions estimated by any of the Analytic Centers.

  14. Optimal Prediction of Clocks from Finite Data

    NASA Technical Reports Server (NTRS)

    Greenhall, Charles A.

    2005-01-01

    This talk is about optimal linear prediction of processes with stationary dth increments, which serve as a class of models for random clock disturbances. The predictor is obtained by orthogonal projection on the affine space of estimators whose errors are invariant to additive polynomials of degree < d. The projection conditions give a system of linear equations thatcan be solved straightforwardly for the regression coefficients. If the data are equally spaced, then the predictor can be obtained by an extension of Levinson's algorithm.

  15. 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

  16. A microresonator frequency comb optical clock

    E-print Network

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

    2013-01-01

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

  17. Clock gene evolution and functional divergence.

    PubMed

    Tauber, Eran; Last, Kim S; Olive, Peter J W; Kyriacou, C P

    2004-10-01

    In considering the impact of the earth's changing geophysical conditions during the history of life, it is surprising to learn that the earth's rotational period may have been as short as 4 h, as recently as 1900 million years ago (or 1.9 billion years ago). The implications of such figures for the origin and evolution of clocks are considerable, and the authors speculate on how this short rotational period might have influenced the development of the "protoclock" in early microorganisms, such as the Cyanobacteria, during the geological periodsin which they arose and flourished. They then discuss the subsequent duplication of clock genes that took place around and after the Cambrian period, 543 million years ago, and its consequences. They compare the relative divergences of the canonical clock genes, which reveal the Per family to be the most rapidly evolving. In addition, the authors use a statistical test to predict which residues within the PER and CRY families may have undergone functional specialization. PMID:15534324

  18. Tuning genetic clocks employing DNA binding sites.

    PubMed

    Jayanthi, Shridhar; Del Vecchio, Domitilla

    2012-01-01

    Periodic oscillations play a key role in cell physiology from the cell cycle to circadian clocks. The interplay of positive and negative feedback loops among genes and proteins is ubiquitous in these networks. Often, delays in a negative feedback loop and/or degradation rates are a crucial mechanism to obtain sustained oscillations. How does nature control delays and kinetic rates in feedback networks? Known mechanisms include proper selection of the number of steps composing a feedback loop and alteration of protease activity, respectively. Here, we show that a remarkably simple means to control both delays and effective kinetic rates is the employment of DNA binding sites. We illustrate this design principle on a widely studied activator-repressor clock motif, which is ubiquitous in natural systems. By suitably employing DNA target sites for the activator and/or the repressor, one can switch the clock "on" and "off" and precisely tune its period to a desired value. Our study reveals a design principle to engineer dynamic behavior in biomolecular networks, which may be largely exploited by natural systems and employed for the rational design of synthetic circuits. PMID:22859962

  19. Tuning Genetic Clocks Employing DNA Binding Sites

    PubMed Central

    Jayanthi, Shridhar; Del Vecchio, Domitilla

    2012-01-01

    Periodic oscillations play a key role in cell physiology from the cell cycle to circadian clocks. The interplay of positive and negative feedback loops among genes and proteins is ubiquitous in these networks. Often, delays in a negative feedback loop and/or degradation rates are a crucial mechanism to obtain sustained oscillations. How does nature control delays and kinetic rates in feedback networks? Known mechanisms include proper selection of the number of steps composing a feedback loop and alteration of protease activity, respectively. Here, we show that a remarkably simple means to control both delays and effective kinetic rates is the employment of DNA binding sites. We illustrate this design principle on a widely studied activator-repressor clock motif, which is ubiquitous in natural systems. By suitably employing DNA target sites for the activator and/or the repressor, one can switch the clock “on” and “off” and precisely tune its period to a desired value. Our study reveals a design principle to engineer dynamic behavior in biomolecular networks, which may be largely exploited by natural systems and employed for the rational design of synthetic circuits. PMID:22859962

  20. 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

  1. Serial Reconfigurable Mismatch-tolerant Clock Distribution Atanu Chattopadhyay Zeljko Zilic

    E-print Network

    Zilic, Zeljko

    -die temperature and process variances. Our clock distribution provides control over regional clock skew, permits in [3,4]. Our clock network is the first to use it to mitigate mismatch effects in a clock network. 2 are broadcast through an integrated circuit, as is the case with clock trees. The extent of flexibility

  2. 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

  3. A clock network for geodesy and fundamental science

    E-print Network

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

    2015-01-01

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

  4. Increased Anxiety in Offspring Reared by Circadian Clock Mutant Mice

    PubMed Central

    Koizumi, Hiroko; Kurabayashi, Nobuhiro; Watanabe, Yuto; Sanada, Kamon

    2013-01-01

    The maternal care that offspring receive from their mothers early in life influences the offspring’s development of emotional behavior in adulthood. Here we found that offspring reared by circadian clock-impaired mice show elevated anxiety-related behavior. Clock mutant mice harboring a mutation in Clock, a key component of the molecular circadian clock, display altered daily patterns of nursing behavior that is fragmented during the light period, instead of long bouts of nursing behavior in wild-type mice. Adult wild-type offspring fostered by Clock mutant mice exhibit increased anxiety-related behavior. This is coupled with reduced levels of brain serotonin at postnatal day 14, whose homeostasis during the early postnatal period is critical for normal emotional behavior in adulthood. Together, disruption of the circadian clock in mothers has an adverse impact on establishing normal anxiety levels in offspring, which may increase their risk of developing anxiety disorders. PMID:23776596

  5. 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.

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

    E-print Network

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

    2015-01-01

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

  7. Responsiveness of the aging circadian clock to light

    PubMed Central

    Benloucif, S.; Green, K.; L’Hermite-Balériaux, M.; Weintraub, S.; Wolfe, L.F.; Zee, P. C.

    2007-01-01

    The present study assessed whether advances in sleep times and circadian phase in older adults might be due to decreased responsiveness of the aging circadian clock to light. Sixteen young (29.3 ± 5.6 yrs) and 14 older adults (67.1 ± 7.4 yrs) were exposed to 4 hours of control dim (10 lux) or bright light (3,500 lux) during the night. Phase shifts of the melatonin rhythm were assessed from the nights before and after the light exposure. Bright light delayed the melatonin midpoint in both young and older adults (p < 0.001). Phase delays for the older subjects were not significantly different from those of the young subjects for either the bright or dim light conditions. The magnitude of phase delays was correlated with both sleep offset and phase angle in the older, but not the younger subjects. The present results indicate that at light intensities commonly used in research as well as clinical practice older adults are able to phase delay to the same extent as younger subjects. PMID:16309797

  8. On the Clock Paradox in the case of circular motion of the moving clock

    E-print Network

    Lorenzo Iorio

    2004-06-27

    In this paper we deal analytically with a version of the so called clock paradox in which the moving clock performs a circular motion of constant radius. The rest clock is denoted as (1), the rotating clock is (2), the inertial frame in which (1) is at rest and (2) moves is I and, finally, the accelerated frame in which (2) is at rest and (1) rotates is A. By using the General Theory of Relativity in order to describe the motion of (1) as seen in A we will show the following features. I) A differential aging between (1) and (2) occurs at their reunion and it has an absolute character, i.e. the proper time interval measured by a given clock is the same both in I and in A. II) From a quantitative point of view, the magnitude of the differential aging between (1) and (2) does depend on the kind of rotational motion performed by A. Indeed, if it is uniform there is no any tangential force in the direction of motion of (2) but only normal to it. In this case, the proper time interval reckoned by (2) does depend only on its constant velocity v=romega. On the contrary, if the rotational motion is uniformly accelerated, i.e. a constant force acts tangentially along the direction of motion, the proper time intervals $do depend$ on the angular acceleration alpha. III) Finally, in regard to the sign of the aging, the moving clock (2) measures always a $shorter$ interval of proper time with respect to (1).

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

    E-print Network

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

    2015-01-01

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

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

    DOEpatents

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

    2015-05-19

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

  11. 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.

  12. 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 .

  13. Clock Synchronization in High-end Computing Environments: A Strategy for Minimizing Clock Variance at Runtime

    SciTech Connect

    Jones, Terry R; Koenig, Gregory A

    2013-01-01

    We present a new software-based clock synchronization scheme that provides high precision time agreement among distributed memory nodes. The technique is designed to minimize variance from a reference chimer during runtime and with minimal time-request latency. Our scheme permits initial unbounded variations in time and corrects both slow and fast chimers (clock skew). An implementation developed within the context of the MPI message passing interface is described, and time coordination measurements are presented. Among our results, the mean time variance for a set of nodes improved from 20.0 milliseconds under standard Network Time Protocol (NTP) down to 2.29 secs under our scheme.

  14. A Clock Synchronization Strategy for Minimizing Clock Variance at Runtime in High-end Computing Environments

    SciTech Connect

    Jones, Terry R; Koenig, Gregory A

    2010-01-01

    We present a new software-based clock synchronization scheme designed to provide high precision time agreement among distributed memory nodes. The technique is designed to minimize variance from a reference chimer during runtime and with minimal time-request latency. Our scheme permits initial unbounded variations in time and corrects both slow and fast chimers (clock skew). An implementation developed within the context of the MPI message passing interface is described and time coordination measurements are presented. Among our results, the mean time variance among a set of nodes improved from 20.0 milliseconds under standard Network Time Protocol (NTP) to 2.29 secs under our scheme.

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

    SciTech Connect

    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, 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.

  16. 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 (atomic clocks, allowing them to achieve stability levels comparable to neutral atoms in optical lattices and a viable path to greater levels of accuracy.

  17. 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.

  18. 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.

  19. Timing molecular motion and production with a synthetic transcriptional clock

    E-print Network

    Winfree, Erik

    properly. Digital clock generators synchronize the states of millions of transistors in silicon circuits previously constructed and analyzed synthetic in vitro DNA switches ("genelets") that can be regulated

  20. Methods to study molecular mechanisms of the Neurospora circadian clock.

    PubMed

    Cha, Joonseok; Zhou, Mian; Liu, Yi

    2015-01-01

    Eukaryotic circadian clocks are comprised of interlocked autoregulatory feedback loops that control gene expression at the levels of transcription and translation. The filamentous fungus Neurospora crassa is an excellent model for the complex molecular network of regulatory mechanisms that are common to all eukaryotes. At the heart of the network, posttranslational regulation and functions of the core clock elements are of major interest. This chapter discusses the methods used currently to study the regulation of clock molecules in Neurospora. The methods range from assays of gene expression to phosphorylation, nuclear localization, and DNA binding of clock proteins. PMID:25662455

  1. 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

  2. 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 (atomic clocks, allowing them to achieve stability levels comparable to neutral atoms in optical lattices and a viable path to greater levels of accuracy.

  3. Continuous Nondemolition Measurement of the Cs Clock Transition Pseudospin

    SciTech Connect

    Chaudhury, Souma; Smith, Greg A.; Schulz, Kevin; Jessen, Poul S.

    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.

  4. 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.

    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.

  5. Dependence of the Time-Reading Process of the Salecker-Wigner Quantum Clock on the Size of the Clock

    NASA Astrophysics Data System (ADS)

    Frenkel, Andor

    2015-12-01

    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.

  6. Time Clock Procedures Each employee is required to have a record of hours worked. In departments using time clocks or the

    E-print Network

    Hung, I-Kuai

    Time Clock Procedures Each employee is required to have a record of hours worked. In departments using time clocks or the web-based time keeping system, the following regulations will apply: 1. Employees are required to clock in prior to their assigned start time, and must clock out when they go off

  7. An Iterative Angle Trisection

    ERIC Educational Resources Information Center

    Muench, Donald L.

    2007-01-01

    The problem of angle trisection continues to fascinate people even though it has long been known that it can't be done with straightedge and compass alone. However, for practical purposes, a good iterative procedure can get you as close as you want. In this note, we present such a procedure. Using only straightedge and compass, our procedure…

  8. Automatic Multi-Stage Clock Gating Optimization Using ILP Formulation

    NASA Astrophysics Data System (ADS)

    Man, Xin; Horiyama, Takashi; Kimura, Shinji

    Clock gating is supported by commercial tools as a power optimization feature based on the guard signal described in HDL (structural method). However, the identification of control signals for gated registers is hard and designer-intensive work. Besides, since the clock gating cells also consume power, it is imperative to minimize the number of inserted clock gating cells and their switching activities for power optimization. In this paper, we propose an automatic multi-stage clock gating algorithm with ILP (Integer Linear Programming) formulation, including clock gating control candidate extraction, constraints construction and optimum control signal selection. By multi-stage clock gating, unnecessary clock pulses to clock gating cells can be avoided by other clock gating cells, so that the switching activity of clock gating cells can be reduced. We find that any multi-stage control signals are also single-stage control signals, and any combination of signals can be selected from single-stage candidates. The proposed method can be applied to 3 or more cascaded stages. The multi-stage clock gating optimization problem is formulated as constraints in LP format for the selection of cascaded clock-gating order of multi-stage candidate combinations, and a commercial ILP solver (IBM CPLEX) is applied to obtain the control signals for each register with minimum switching activity. Those signals are used to generate a gate level description with guarded registers from original design, and a commercial synthesis and layout tools are applied to obtain the circuit with multi-stage clock gating. For a set of benchmark circuits and a Low Density Parity Check (LDPC) Decoder (6.6k gates, 212 F.F.s), the proposed method is applied and actual power consumption is estimated using Synopsys NanoSim after layout. On average, 31% actual power reduction has been obtained compared with original designs with structural clock gating, and more than 10% improvement has been achieved for some circuits compared with single-stage optimization method. CPU time for optimum multi-stage control selection is several seconds for up to 25k variables in LP format. By applying the proposed clock gating, area can also be reduced since the multiplexors controlling register inputs are eliminated.

  9. 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…

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

    E-print Network

    Wu, Hui

    the circuitry faster, the supply voltage is raised, therefore increasing energy consumption. Conversely, any conventional buffered trees with the additional benefit of built- in deskewing. Unlike other alternatives, ILC is fully compatible with conventional clock distribution. In this paper, a quantitative study based

  11. 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.

  12. 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.

  13. 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.

  14. The Space Environment of Mercury: Solar Wind and IMF Modeling of Upstream Conditions

    NASA Astrophysics Data System (ADS)

    Baker, D. N.; Odstrcil, D.; Anderson, B. J.; Benna, M.; Gloeckler, G.; Raines, J. M.; Schriver, D.; Slavin, J. A.; Solomon, S. C.; Killen, R.; Zurbuchen, T. H.

    2008-05-01

    The first Mercury flyby on 14 January 2008 by the MESSENGER spacecraft has re-intensified interest in the solar wind interaction with Mercury's miniature (Earth-like) magnetosphere and extensive planetary exosphere. In order to provide a broad knowledge of the solar wind properties and also some estimate of the interplanetary magnetic field (IMF) near Mercury we have used an empirical modeling technique combined with a physics-based solar wind model. The empirical technique is based on the Wang-Sheeley-Arge (WSA) method that uses solar photospheric magnetic field observations (from Earth-based instruments) in order to estimate inner heliospheric boundary conditions at about 10 solar radii. This information is then used as inputs to the global magnetohydrodynamic (MHD) model, ENLIL, which calculates solar wind velocity, density, temperature, and magnetic field strength throughout the inner heliosphere, In this presentation we show WSA-ENLIL conditions computed for the period around the Mercury flyby. This information is used in conjunction with MESSENGER magnetometer, plasma, ultraviolet spectrometer, and other sensor data to understand the context of the Mercury flyby results. Such in situ data can also be used iteratively to improve the model accuracy for inner heliospheric "space weather" purposes. More generally we discuss how we can estimate relatively continuously the solar wind properties near Mercury and at the cruise location of MESSENGER now, for future flybys, and toward the time of spacecraft orbit insertion in 2011.

  15. The Space Environment of Mercury: Solar Wind and IMF Modeling of Upstream Conditions

    NASA Astrophysics Data System (ADS)

    Baker, D. N.; Odstrcil, D.; Anderson, B. J.; Arge, C. N.; Benna, M.; Gloeckler, G.; Raines, J. M.; Schriver, D.; Slavin, J. A.; Solomon, S. C.; Killen, R. M.; Zurbuchen, T. H.

    2008-12-01

    In order to provide a broad knowledge of the solar wind properties and also some estimate of the interplanetary magnetic field (IMF) near the planet Mercury, we have used an empirical modeling technique combined with a physics-based solar wind model. The empirical approach is the Wang-Sheeley-Arge (WSA) method that uses solar photospheric magnetic field observations (from Earth-based instruments) in order to estimate inner heliospheric boundary conditions out to about 21.5 solar radii. This information is then used as input to the global magnetohydrodynamic (MHD) model, ENLIL, which calculates solar wind velocity, density, temperature, and magnetic field strength throughout the inner heliosphere. WSA-ENLIL conditions were computed for the periods around MESSENGER's flybys of Mercury in January and October of this year. This information has been used in conjunction with MESSENGER Magnetometer measurements and available MESSENGER solar wind data to understand the context of the Mercury flyby results. The in situ spacecraft data can also be used iteratively to improve the model accuracy for inner heliospheric "space weather" purposes. More generally we show how we can estimate relatively continuously the solar wind properties near Mercury and at the cruise location of MESSENGER now, for future flybys, and toward the time of spacecraft insertion into orbit about Mercury in 2011.

  16. 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.

  17. Missing Massive Stars in Starbursts: Stellar Temperature Diagnostics and the IMF

    E-print Network

    Rigby, J R

    2004-01-01

    Determining the properties of starbursts requires spectral diagnostics of their ultraviolet radiation fields, to test whether very massive stars are present. We test several such diagnostics, using new models of line ratio behavior combining Cloudy, Starburst99 and up-to-date spectral atlases. For six galaxies we obtain new measurements of HeI 1.7 um / Brackett 10, a difficult to measure but physically simple (and therefore reliable) diagnostic. We obtain new measurements of HeI 2.06 um / Brackett gamma in five galaxies, and find that it and [OIII]/Hbeta are generally unreliable diagnostics in starbursts. The heteronuclear and homonuclear mid--infrared line ratios (notably [NeIII] 15.6 um / [NeII] 12.8 um) consistently agree with each other and with HeI 1.7 um / Br10; this argues that the mid-infrared line ratios are reliable diagnostics of spectral hardness. In a sample of 27 starbursts, [NeIII]/[NeII] ratios are significantly less excited than model predictions for a Salpeter IMF extending to 100 solar mass...

  18. The Turbulent ISM of Galaxies about 10 Gyrs Ago: An Impact on their IMF?

    NASA Astrophysics Data System (ADS)

    Le Tiran, L.; Lehnert, M. D.

    2011-06-01

    The utilization of integral-field spectroscopy has led us to a new understanding of the physical conditions in galaxies within the first few billion years after the Big Bang. The combination of the kinematics and emission line diagnostics is a powerful technique to discern the physical processes that are at work in distant galaxies. In these proceedings, we present observations of 10 massive galaxies as seen as they were 9 Gyrs ago using SINFONI from the ESO-VLT, combined with photometry from the DEEP2 Survey. We first portray a brief picture of the physical conditions in the warm ionized medium of these galaxies; they exhibit complex morphologies, high star formation and are so pressure dominated they are likely to drive winds and high turbulence. Moreover, their ratio of H? to FUV flux to their R-band luminosity surface brightnesses indicates that perhaps their initial mass function is flatter than Salpeter at the high mass end, as has been suggested recently for some local galaxies. It may be that high turbulence is responsible for skewing the IMF towards more massive stars as suggested by some theories of star-formation.

  19. Dependence of the ionospheric convection pattern on the conductivity and the southward IMF. Ph.D. Thesis

    SciTech Connect

    Shue, J.

    1993-12-31

    Electric field measurements from the DE-2 satellite were used to determine the location of the convection reversal boundary and the potential around this boundary under a combination of interplanetary magnetic field (IMF) and auroral electrojet conditions. The electric potential is obtained by the integration of the electric fields. The convection reversal boundary is defined in this study as where the potential has its absolute maximum and minimum values. The data were sorted into 18 categories according to two levels of the negative IMF B(sub z), three ranges of IMF B(sub y), and two substorm phases. The data were fit with both continuous and discontinuous boundaries to get a functional representation of boundary potentials and locations. A simple model is constructed by solving Laplace`s equation in order to illustrate the obtained boundary potentials and locations. The results show that the enhanced electric field in the midnight sector is associated with an intense westward electrojet current. It can also be seen that the convection reversal boundary is found to be discontinuous near midnight. The discontinuous convection reversal boundary on the dayside is related to the merging near dayside cusp region. The discontinuous convection reversal boundary on the nightside is related to the conductivity enhancement. The intrusion of the dawn cell into the dusk cell is due to nonuniformity of the Hall conductivity in the ionosphere. Another model is constructed by solving the current continuity equation with field-aligned current and nonuniform conductivity added. It can be found that a secondary convection reversal, which is detached from the dusk-cell convection reversal, appears in the evening-midnight sector within the polar cap when the IMF B(sub y) is positive and the conductivity is nonuniform. This convection reversal is attributed to the B x V dynamo.

  20. Associative skew clock routing for difficult instances 

    E-print Network

    Kim, Min-seok

    2006-08-16

    stream_source_info etd-tamu-2006A-CEEN-Kim.pdf.txt stream_content_type text/plain stream_size 30458 Content-Encoding ISO-8859-1 stream_name etd-tamu-2006A-CEEN-Kim.pdf.txt Content-Type text/plain; charset=ISO-8859...-1 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...

  1. 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).

  2. 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.

  3. The relationship between the IMF B(y) and the distant tail (150-238 Re) lobe and plasmasheet B(y) fields

    NASA Technical Reports Server (NTRS)

    Tsurutani, B. T.; Smith, E. J.; Jones, D. E.; Lepping, R. P.; Sibeck, D. G.

    1984-01-01

    The relationships between the Solar Magnetospheric (SM) y-component of the interplanetary magnetic field (IMF) and the lobe and plasmasheet magnetic fields have been studied for the two ISEE-3 deep tail passes. It is found that for positive sector IMFs, 13 percent of the interplanetary magnetic field penetrates into the aberrated north-dawn and south-dusk lobe quadrants, and about the same amount in the north-dusk and south-dawn lobe quadrants for negative sector IMFs. For the above cases, field penetration is significantly less for opposite polarity IMFs. The former results are generally consistent with open magnetospheric models, but the latter (the lack of response in certain quadrants) are unexplained by theory at this time. If the magnitude of the plasmasheet B(y) fields are related to plasma pressure anisotropies, very small anisotropies of about 1.01 are expected.

  4. Twisting and Bending of the Geomagnetic Tail under Northward IMF: OpenGGCM Simulations and Predictions for ARTEMIS

    NASA Astrophysics Data System (ADS)

    Raeder, J.; Li, W.; Ge, Y. S.; Germaschewski, K.; Oieroset, M.

    2011-12-01

    The structure of the geomagnetic tail under northward IMF conditions has long been controversial. Various global magnetosphere models predict either a closed tail of relatively short extent or a tail that still contains some open flux but mostly closed flux that extends hundreds of RE down tail. A fortuitous encounter of the Wind spacecraft 125 RE down tail during a 32 hour interval of nearly constant northward IMF occurred October 22-24, 2003 (Oieroset et al., JGR, 113, A04206, 2008). While the observations confirmed the presence of a tail, the plasma parameters were unusual. OpenGGCM simulations agreed fairly well with the observations and showed a severely flattened and twisted tail. However, the single point observations were not sufficient to constrain the model. The pair of ARTEMIS satellites, which have just entered lunar orbit, will provide much more powerful constraints. In this paper we present predictions of the tail structure at lunar orbit as they are expected to be seen by ARTEMIS. We will consider several scenarios of IMF and solar wind conditions, and where appropriate, we will compare simulation results with ARTEMIS data.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Takamoto, Masao; Takano, Tetsushi; Katori, Hidetoshi

    2011-05-01

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

  7. Quantum Memory, Single Photons, and a Nuclear Clock Alex Kuzmich

    E-print Network

    Vallette, Bruno

    Physics and Quantum Optics #12;Towards a nuclear clock #12;Low-lying nuclear levels of 229Th 229Th isomer Transitions 2 5 6 State-of-the-Art Nuclear Models 3 For = 100 , 3+ = 2 × 1019 Measure and 2Quantum Memory, Single Photons, and a Nuclear Clock Alex Kuzmich Georgia Tech Ultra-Cold Atomic

  8. Stable Kalman filters for processing clock measurement data

    NASA Technical Reports Server (NTRS)

    Clements, P. A.; Gibbs, B. P.; Vandergraft, J. S.

    1989-01-01

    Kalman filters have been used for some time to process clock measurement data. Due to instabilities in the standard Kalman filter algorithms, the results have been unreliable and difficult to obtain. During the past several years, stable forms of the Kalman filter have been developed, implemented, and used in many diverse applications. These algorithms, while algebraically equivalent to the standard Kalman filter, exhibit excellent numerical properties. Two of these stable algorithms, the Upper triangular-Diagonal (UD) filter and the Square Root Information Filter (SRIF), have been implemented to replace the standard Kalman filter used to process data from the Deep Space Network (DSN) hydrogen maser clocks. The data are time offsets between the clocks in the DSN, the timescale at the National Institute of Standards and Technology (NIST), and two geographically intermediate clocks. The measurements are made by using the GPS navigation satellites in mutual view between clocks. The filter programs allow the user to easily modify the clock models, the GPS satellite dependent biases, and the random noise levels in order to compare different modeling assumptions. The results of this study show the usefulness of such software for processing clock data. The UD filter is indeed a stable, efficient, and flexible method for obtaining optimal estimates of clock offsets, offset rates, and drift rates. A brief overview of the UD filter is also given.

  9. Local receptors as novel regulators for peripheral clock expression

    PubMed Central

    Wu, Changhao; Sui, Guiping; Archer, Simon N.; Sassone-Corsi, Paolo; Aitken, Karen; Bagli, Darius; Chen, Ying

    2014-01-01

    Mammalian circadian control is determined by a central clock in the brain suprachiasmatic nucleus (SCN) and synchronized peripheral clocks in other tissues. Increasing evidence suggests that SCN-independent regulation of peripheral clocks also occurs. We examined how activation of excitatory receptors influences the clock protein PERIOD 2 (PER2) in a contractile organ, the urinary bladder. PERIOD2::LUCIFERASE-knock-in mice were used to report real-time PER2 circadian dynamics in the bladder tissue. Rhythmic PER2 activities occurred in the bladder wall with a cycle of ?24 h and peak at ?12 h. Activation of the muscarinic and purinergic receptors by agonists shifted the peak to an earlier time (7.2±2.0 and 7.2±0.9 h, respectively). PER2 expression was also sensitive to mechanical stimulation. Aging significantly dampened PER2 expression and its response to the agonists. Finally, muscarinic agonist-induced smooth muscle contraction also exhibited circadian rhythm. These data identified novel regulators, endogenous receptors, in determining local clock activity, in addition to mediating the central control. Furthermore, the local clock appears to reciprocally align receptor activity to circadian rhythm for muscle contraction. The interaction between receptors and peripheral clock represents an important mechanism for maintaining physiological functions and its dysregulation may contribute to age-related organ disorders.—Wu, C., Sui, G., Archer, S. N., Sassone-Corsi, P., Aitken, K., Bagli, D., Chen, Y. Local receptors as novel regulators for peripheral clock expression. PMID:25145629

  10. Nuclear magnetic resonance implementation of a quantum clock synchronization algorithm

    SciTech Connect

    Zhang Jingfu; Long, G.C; Liu Wenzhang; Deng Zhiwei; Lu Zhiheng

    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.

  11. Symmetric Clock Synchronization in Sensor Networks Philipp Sommer

    E-print Network

    , and maybe even more importantly, clock synchronization plays a major role in energy efficiency. State-Communication Networks]: Net- work Architecture and Design General Terms Algorithms, Experimentation, Performance Efficiency 1 Introduction Clock synchronization is a major building block in wire- less sensor networks

  12. Clock Synchronization: Open Problems in Theory and Practice

    E-print Network

    Waldmann, Uwe

    Clock Synchronization: Open Problems in Theory and Practice Christoph Lenzen, Thomas Locher must synchronize their drift- ing hardware clocks by perpetually exchanging messages containing that all messages arrive after an unknown and variable delay. Even if the message delays were always

  13. Self-stabilizing clock phase synchronization in a distributed ring 

    E-print Network

    Pancholi, Alok

    1994-01-01

    This thesis deals with the synchronization of phases of digital clocks or periodic events in a distributed system which has a ring topology. The clocks considered are bounded and synchronous i.e., run at the same rate. And if some periodic event...

  14. Efficient Design and Clocking for a Network-on-Chip 

    E-print Network

    Mandal, Ayan

    2013-05-02

    approach to synthesize a low jitter, low power buffered H-tree for clock distribution. In the second part of this dissertation, we use these efficient clock distribution schemes to present a novel fast NoC design that relies on source synchronous data...

  15. The Circadian Clock in Oral Health and Diseases

    PubMed Central

    Papagerakis, S.; Zheng, L.; Schnell, S.; Sartor, M.A.; Somers, E.; Marder, W.; McAlpin, B.; Kim, D.; McHugh, J.; Papagerakis, P.

    2014-01-01

    Most physiological processes in mammals display circadian rhythms that are driven by the endogenous circadian clock. This clock is comprised of a central component located in the hypothalamic suprachiasmatic nucleus and subordinate clocks in peripheral tissues. Circadian rhythms sustain 24-hour oscillations of a large number of master genes controlling the correct timing and synchronization of diverse physiological and metabolic processes within our bodies. This complex regulatory network provides an important communication link between our brain and several peripheral organs and tissues. At the molecular level, circadian oscillations of gene expression are regulated by a family of transcription factors called “clock genes”. Dysregulation of clock gene expression results in diverse human pathological conditions, including autoimmune diseases and cancer. There is increasing evidence that the circadian clock affects tooth development, salivary gland and oral epithelium homeostasis, and saliva production. This review summarizes current knowledge of the roles of clock genes in the formation and maintenance of oral tissues, and discusses potential links between “oral clocks” and diseases such as head and neck cancer and Sjögren’s syndrome. PMID:24065634

  16. CLOCK SKEW ON DRAM/LOGIC MERGED TECHNOLOGY BASED SYSTEMS

    E-print Network

    Ayers, Joseph

    due to power rail IR drop. The H-tree cgck structure has effectively provided a synchronous clocks buffers due to process variations, temperature differences on the same chip, and power sup ly differences buffers to reduce the dampenin effect of the distributed RC lines on the shape olthe clock signal. Buffers

  17. MULTIPLE CLOCK DOMAIN SYNCHRONIZATION FOR NETWORK ON CHIP ARCHITECTURES

    E-print Network

    Nyathi, Jabulani

    to effectively communicate among the constituent Intellectual Property (IP) blocks/Embedded cores, as well SYNCHRONIZATION Multiple clocks are necessary for communication among IPs firstly because different IP cores many IP Blocks or groups of blocks with completely independent clock domains. One of several possible

  18. Quantitative Trait Loci for the Circadian Clock in Neurospora crassa

    PubMed Central

    Kim, Tae-Sung; Logsdon, Benjamin A.; Park, Sohyun; Mezey, Jason G.; Lee, Kwangwon

    2007-01-01

    Neurospora crassa has been a model organism for the study of circadian clocks for the past four decades. Among natural accessions of Neurospora crassa, there is significant variation in clock phenotypes. In an attempt to investigate natural allelic variants contributing to quantitative variation, we used a quantitative trait loci mapping approach to analyze three independent mapping populations whose progenitors were collected from geographically isolated locations. Two circadian clock phenotypes, free-running period and entrained phase, were evaluated in the 188 F1 progeny of each mapping population. To identify the clock QTL, we applied two QTL mapping analyses: composite interval mapping (CIM) and Bayesian multiple QTL analysis (BMQ). When controlling false positive rates ?0.05, BMQ appears to be the more sensitive of the two approaches. BMQ confirmed most of the QTL from CIM (18 QTL) and identified 23 additional QTL. While 13 QTL colocalize with previously identified clock genes, we identified 30 QTL that were not linked with any previously characterized clock genes. These are candidate regions where clock genes may be located and are expected to lead to new insights in clock regulation. PMID:17947430

  19. What Is The Role of ATP in Molecular Clock Synchronization?

    E-print Network

    Rowell, Eric C.

    What Is The Role of ATP in Molecular Clock Synchronization? Joseph Donnelly July 23, 2015 Abstract of brain cells in mice suggests a synchro- nizing role of ATP in the mammalian clock. The biochemical mechanism of synchronization via ATP remains unknown. Furthermore, instances in which ATP behaves

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

    ERIC Educational Resources Information Center

    Denny, Mark

    2010-01-01

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

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

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system i...

  2. Toward a detailed computational model for the mammalian circadian clock

    E-print Network

    Goldbeter, Albert

    Toward a detailed computational model for the mammalian circadian clock Jean-Christophe Leloup a computational model for the mammalian circadian clock based on the intertwined positive and negative regulatory observations, the model can give rise to sustained circadian oscillations in continuous darkness, characterized

  3. Coordination of the maize transcriptome by a conserved circadian clock

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The plant circadian clock orchestrates 24-hour rhythms in internal physiological processes to coordinate these activities with daily and seasonal changes in the environment. The circadian clock has a profound impact on many aspects of plant growth and development, including biomass accumulation and ...

  4. Atomic clocks: new prospects in metrology and geodesy

    E-print Network

    Delva, Pacôme

    2013-01-01

    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.

  5. Characterization of GPS Clock and Ephemeris Errors to Support ARAIM

    E-print Network

    Boneh, Dan

    . They are dominated by ionospheric error, tropospheric error, multipath, and receiver antenna biases. For dualCharacterization of GPS Clock and Ephemeris Errors to Support ARAIM Todd Walter and Juan Blanch of GPS clock and ephemeris errors to determine appropriate estimates for the probability of independent

  6. Time, Clocks and the Speed of Light Vasco Guerra

    E-print Network

    Guerra, Vasco

    Time, Clocks and the Speed of Light Vasco Guerra and Rodrigo de Abreu Departamento de Física are a direct consequence of the fundamental notions of time and clocks. They can be obtained without any time, independently of the periodic physical phenomena they are built upon and of the machinery

  7. 29 CFR 778.204 - “Clock pattern” premium pay.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 29 Labor 3 2010-07-01 2010-07-01 false âClock patternâ premium pay. 778.204 Section 778.204 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL... Excluded From the âRegular Rateâ Extra Compensation Paid for Overtime § 778.204 “Clock pattern” premium...

  8. 29 CFR 778.204 - “Clock pattern” premium pay.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 29 Labor 3 2013-07-01 2013-07-01 false âClock patternâ premium pay. 778.204 Section 778.204 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL... Excluded From the âRegular Rateâ Extra Compensation Paid for Overtime § 778.204 “Clock pattern” premium...

  9. 29 CFR 778.204 - “Clock pattern” premium pay.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 29 Labor 3 2011-07-01 2011-07-01 false âClock patternâ premium pay. 778.204 Section 778.204 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL... Excluded From the âRegular Rateâ Extra Compensation Paid for Overtime § 778.204 “Clock pattern” premium...

  10. Circadian clock genes universally control key agricultural traits

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Circadian clocks are endogenous timers that enable plants to synchronize biological processes with daily and seasonal environmental conditions in order to allocate resources during the most beneficial times of day and year. The circadian clock regulates a number of central plant activities, includin...

  11. 29 CFR 778.204 - “Clock pattern” premium pay.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 29 Labor 3 2012-07-01 2012-07-01 false âClock patternâ premium pay. 778.204 Section 778.204 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL... Excluded From the âRegular Rateâ Extra Compensation Paid for Overtime § 778.204 “Clock pattern” premium...

  12. 29 CFR 778.204 - “Clock pattern” premium pay.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 29 Labor 3 2014-07-01 2014-07-01 false âClock patternâ premium pay. 778.204 Section 778.204 Labor Regulations Relating to Labor (Continued) WAGE AND HOUR DIVISION, DEPARTMENT OF LABOR STATEMENTS OF GENERAL... Excluded From the âRegular Rateâ Extra Compensation Paid for Overtime § 778.204 “Clock pattern” premium...

  13. TTL> 32bit RS485 Driver 32bit Clock Counter

    E-print Network

    Berns, Hans-Gerd

    0...1240 nsec (*) = selectable (*) NIM TTL­> 32­bit RS485 Driver 32­bit Clock Counter Internal Clock Oscillator 50 MHz TTL­> RS485 Logic Select VME BUS P2 = USER rollover flag GPS pulse GPS signals to V533 (NIM) LOCAL TIME 32­bit to V533 input (RS485) GPS FLAG to V533 input (RS485) TRIGGER to V533

  14. 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.

  15. Clocking in the face of unpredictability beyond quantum uncertainty

    NASA Astrophysics Data System (ADS)

    Madjid, F. Hadi; Myers, John M.

    2015-05-01

    In earlier papers we showed unpredictability beyond quantum uncertainty in atomic clocks, ensuing from a proven gap between given evidence and explanations of that evidence. Here we reconceive a clock, not as an isolated entity, but as enmeshed in a self-adjusting communications network adapted to one or another particular investigation, in contact with an unpredictable environment. From the practical uses of clocks, we abstract a clock enlivened with the computational capacity of a Turing machine, modified to transmit and to receive numerical communications. Such "live clocks" phase the steps of their computations to mesh with the arrival of transmitted numbers. We lift this phasing, known in digital communications, to a principle of logical synchronization, distinct from the synchronization defined by Einstein in special relativity. Logical synchronization elevates digital communication to a topic in physics, including applications to biology. One explores how feedback loops in clocking affect numerical signaling among entities functioning in the face of unpredictable influences, making the influences themselves into subjects of investigation. The formulation of communications networks in terms of live clocks extends information theory by expressing the need to actively maintain communications channels, and potentially, to create or drop them. We show how networks of live clocks are presupposed by the concept of coordinates in a spacetime. A network serves as an organizing principle, even when the concept of the rigid body that anchors a special-relativistic coordinate system is inapplicable, as is the case, for example, in a generic curved spacetime.

  16. Clocking in the face of unpredictability beyond quantum uncertainty

    E-print Network

    F. Hadi Madjid; John M. Myers

    2015-04-16

    In earlier papers we showed unpredictability beyond quantum uncertainty in atomic clocks, ensuing from a proven gap between given evidence and explanations of that evidence. Here we reconceive a clock, not as an isolated entity, but as enmeshed in a self-adjusting communications network adapted to one or another particular investigation, in contact with an unpredictable environment. From the practical uses of clocks, we abstract a clock enlivened with the computational capacity of a Turing machine, modified to transmit and to receive numerical communications. Such "live clocks" phase the steps of their computations to mesh with the arrival of transmitted numbers. We lift this phasing, known in digital communications, to a principle of \\emph{logical synchronization}, distinct from the synchronization defined by Einstein in special relativity. Logical synchronization elevates digital communication to a topic in physics, including applications to biology. One explores how feedback loops in clocking affect numerical signaling among entities functioning in the face of unpredictable influences, making the influences themselves into subjects of investigation. The formulation of communications networks in terms of live clocks extends information theory by expressing the need to actively maintain communications channels, and potentially, to create or drop them. We show how networks of live clocks are presupposed by the concept of coordinates in a spacetime. A network serves as an organizing principle, even when the concept of the rigid body that anchors a special-relativistic coordinate system is inapplicable, as is the case, for example, in a generic curved spacetime.

  17. Angles in the Sky?

    NASA Astrophysics Data System (ADS)

    Behr, Bradford

    2005-09-01

    Tycho Brahe lived and worked in the late 1500s before the telescope was invented. He made highly accurate observations of the positions of planets, stars, and comets using large angle-measuring devices of his own design. You can use his techniques to observe the sky as well. For example, the degree, a common unit of measurement in astronomy, can be measured by holding your fist at arm's length up to the sky. Open your fist and observe the distance across the sky covered by the width of your pinky fingernail. That is, roughly, a degree! After some practice, and knowing that one degree equals four minutes, you can measure elapsed time by measuring the angle of the distance that the Moon appears to have moved and multiplying that number by four. You can also figure distances and sizes of things. These are not precise measurements, but rough estimates that can give you a "close-enough" answer.

  18. Small Angle Neutron Scattering

    SciTech Connect

    Urban, Volker S

    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.

  19. Primary cerebellopontine angle angiosarcoma.

    PubMed

    Guode, Zhai; Qi, Pang; Hua, Guo; Shangchen, Xu; Hanbin, Wang

    2008-08-01

    Primary intracranial angiosarcomas are rare. Only a few cases have been reported in the literature. All cases reported were located in the supratentorial areas. To our knowledge, no cerebellopontine (CP) angle angiosarcoma has been reported. We report a 16-year-old girl who had mild headache, right-sided tinnitus and amblyacousia of 1-year's duration. She later developed abruptly severe headache and vomiting, accompanied by left hemiparesis, numbness, ataxia and bucking, and computerized tomography scan and magnetic resonance imaging were performed. There was a lesion in the right CP angle with haemorrhage and edema. The preoperative diagnosis was neurogenic tumor with haemorrhage. The patient underwent an emergency suboccipital craniectomy, and the lesion was excised completely. Histopathology and immunohistochemistry revealed an angiosarcoma. Postoperative radiotherapy was given. At the time of hospital discharge, she was in better clinical and neurological condition than her preoperative state. She has been followed up for 6 months and is is still in excellent condition without any sign of recurrence. This case report highlights that clinicians should be aware of the characteristics of angiosarcoma, and also stresses the need to include angiosarcoma in the differential diagnosis of rare lesions located in the CP angle. PMID:18314334

  20. Circadian Clock Control of the Cellular Response to DNA Damage

    PubMed Central

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

    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 24 hours, and it dictates the rates of many biochemical reactions as a function of the time of the day. Recently, it has become apparent that the circadian clock plays an important role in determining the strengths of cellular responses to DNA damage including repair, checkpoints, and apoptosis. These new insights are expected to guide development of novel mechanism-based chemotherapeutic regimens. PMID:20227409

  1. Noise and instability of an optical lattice clock

    E-print Network

    Al-Masoudi, Ali; Häfner, Sebastian; Sterr, Uwe; Lisdat, Christian

    2015-01-01

    We present an analysis of the different types of noise from the detection and interrogation laser in our strontium lattice clock. We develop a noise model showing that in our setup quantum projection noise limited detection is possible if more than 130~atoms are interrogated. Adding information about the noise spectrum of our clock laser with sub-$10^{-16}$ fractional frequency instability allows to infer the clock stability for different operational modes. Excellent agreement with experimental observations for the instability of the difference between two interleaved stabilizations is found. We infer a clock instability of $1.6 \\times 10^{-16}/\\sqrt{\\tau / \\rm{s}}$ as a function of averaging time $\\tau$ for normal clock operation.

  2. Calcium and SOL Protease Mediate Temperature Resetting of Circadian Clocks.

    PubMed

    Tataroglu, Ozgur; Zhao, Xiaohu; Busza, Ania; Ling, Jinli; O'Neill, John S; Emery, Patrick

    2015-11-19

    Circadian clocks integrate light and temperature input to remain synchronized with the day/night cycle. Although light input to the clock is well studied, the molecular mechanisms by which circadian clocks respond to temperature remain poorly understood. We found that temperature phase shifts Drosophila circadian clocks through degradation of the pacemaker protein TIM. This degradation is mechanistically distinct from photic CRY-dependent TIM degradation. Thermal TIM degradation is triggered by cytosolic calcium increase and CALMODULIN binding to TIM and is mediated by the atypical calpain protease SOL. This thermal input pathway and CRY-dependent light input thus converge on TIM, providing a molecular mechanism for the integration of circadian light and temperature inputs. Mammals use body temperature cycles to keep peripheral clocks synchronized with their brain pacemaker. Interestingly, downregulating the mammalian SOL homolog SOLH blocks thermal mPER2 degradation and phase shifts. Thus, we propose that circadian thermosensation in insects and mammals share common principles. PMID:26590423

  3. Dissecting the mechanisms of the clock in Neurospora.

    PubMed

    Hurley, Jennifer; Loros, Jennifer J; Dunlap, Jay C

    2015-01-01

    The circadian clock exists to synchronize inner physiology with the external world, allowing life to anticipate and adapt to the continual changes that occur in an organism's environment. The clock architecture is highly conserved, present in almost all major branches of life. Within eukaryotes, the filamentous fungus Neurospora crassa has consistently been used as an excellent model organism to uncover the basic circadian physiology and molecular biology. The Neurospora model has elucidated our fundamental understanding of the clock as nested positive and negative feedback loop, regulated by transcriptional and posttranscriptional processes. This review will examine the basics of circadian rhythms in the model filamentous fungus N. crassa as well as highlight the output of the clock in Neurospora and the reasons that N. crassa has continued to be a strong model for the study of circadian rhythms. It will also synopsize classical and emerging methods in the study of the circadian clock. PMID:25662450

  4. A New Trapped Ion Clock Based on Hg-201(+)

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

    There are two stable odd isotopes of mercury with singly ionized hyperfine structure suitable for a microwave clock: Hg-199(+) and Hg-201(+). Virtually all trapped mercury ion clocks to date have used the 199 isotope. We have begun to investigate the viability of a trapped ion clock based on Hg-201(+). We have measured the unperturbed frequency of the (S-2)(sub 1/2) F = 1, m(sub F) = 0 to (S-2)(sub 1/2) F = 2, m(sub F) = 0 clock transition to be 29.9543658211(2) GHz. In this paper we describe initial measurements with Hg-201(+) and new applications to clocks and fundamental physics.

  5. Quantum Algorithmic Readout in Multi-Ion Clocks

    E-print Network

    Schulte, Marius; Leroux, Ian D; Schmidt, Piet O; Hammerer, Klemens

    2015-01-01

    Optical clocks based on ensembles of trapped ions offer the perspective of record frequency uncertainty with good short-term stability. Most suitable atomic species lack closed transitions for fast detection such that the clock signal has to be read out indirectly through transferring the quantum state of clock ions to co-trapped logic ions by means of quantum logic operations. For ensembles of clock ions existing methods for quantum logic readout require a linear overhead in either time or the number of logic ions. Here we report a quantum algorithmic readout whose overhead scales logarithmically with the number of clock ions in both of these respects. We show that the readout algorithm can be implemented with a single application of a multi-species quantum gate, which we describe in detail for a crystal of Aluminum and Calcium ions.

  6. Lattice-induced nonadiabatic frequency shifts in optical lattice clocks

    SciTech Connect

    Beloy, K.

    2010-09-15

    We consider the frequency shift in optical lattice clocks which arises from the coupling of the electronic motion to the atomic motion within the lattice. For the simplest of three-dimensional lattice geometries this coupling is shown to affect only clocks based on blue-detuned lattices. We have estimated the size of this shift for the prospective strontium lattice clock operating at the 390-nm blue-detuned magic wavelength. The resulting fractional frequency shift is found to be on the order of 10{sup -18} and is largely overshadowed by the electric quadrupole shift. For lattice clocks based on more complex geometries or other atomic systems, this shift could potentially be a limiting factor in clock accuracy.

  7. A self-interfering clock as a "which path" witness.

    PubMed

    Margalit, Yair; Zhou, Zhifan; Machluf, Shimon; Rohrlich, Daniel; Japha, Yonathan; Folman, Ron

    2015-09-11

    In Einstein's general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global-all clocks "tick" uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets "tick" at different rates, to simulate a gravitational time lag, the clock time along each path yields "which path" information, degrading the pattern's visibility. In contrast, in standard interferometry, time cannot yield "which path" information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world. PMID:26249229

  8. A self-interfering clock as a “which path” witness

    NASA Astrophysics Data System (ADS)

    Margalit, Yair; Zhou, Zhifan; Machluf, Shimon; Rohrlich, Daniel; Japha, Yonathan; Folman, Ron

    2015-09-01

    In Einstein’s general theory of relativity, time depends locally on gravity; in standard quantum theory, time is global—all clocks “tick” uniformly. We demonstrate a new tool for investigating time in the overlap of these two theories: a self-interfering clock, comprising two atomic spin states. We prepare the clock in a spatial superposition of quantum wave packets, which evolve coherently along two paths into a stable interference pattern. If we make the clock wave packets “tick” at different rates, to simulate a gravitational time lag, the clock time along each path yields “which path” information, degrading the pattern’s visibility. In contrast, in standard interferometry, time cannot yield “which path” information. This proof-of-principle experiment may have implications for the study of time and general relativity and their impact on fundamental effects such as decoherence and the emergence of a classical world.

  9. Quantum Algorithmic Readout in Multi-Ion Clocks

    E-print Network

    Marius Schulte; Niels Lörch; Ian D. Leroux; Piet O. Schmidt; Klemens Hammerer

    2015-02-02

    Optical clocks based on ensembles of trapped ions offer the perspective of record frequency uncertainty with good short-term stability. Most suitable atomic species lack closed transitions for fast detection such that the clock signal has to be read out indirectly through transferring the quantum state of clock ions to co-trapped logic ions by means of quantum logic operations. For ensembles of clock ions existing methods for quantum logic readout require a linear overhead in either time or the number of logic ions. Here we report a quantum algorithmic readout whose overhead scales logarithmically with the number of clock ions in both of these respects. We show that the readout algorithm can be implemented with a single application of a multi-species quantum gate, which we describe in detail for a crystal of Aluminum and Calcium ions.

  10. Spin-orbit Larmor clock for ionization times in one-photon and strong-field regimes

    NASA Astrophysics Data System (ADS)

    Kaushal, Jivesh; Morales, Felipe; Torlina, Lisa; Ivanov, Misha; Smirnova, Olga

    2015-12-01

    Photoionization is a process where absorption of one or several photons liberates an electron and creates a hole in a quantum system, such as an atom or a molecule. Is it faster to remove an electron using one or many photons, and how to define this time? Here we introduce a clock that allows us to define ionization time for both one-photon and many-photon ionization regimes. The clock uses the interaction of the electron or hole spin with the magnetic field created by their orbital motion, known as the spin-orbit interaction. The angle of spin precession in the magnetic field records time. We use the combination of analytical theory and ab initio calculations to show how ionization delay depends on the number of absorbed photons, how it appears in the experiment and what electron dynamics it signifies. In particular, we apply our method to calculate the derived time delays in tunneling regime of strong-field ionization.

  11. Temperature-Compensated Clock Skew Adjustment

    PubMed Central

    Castillo-Secilla, Jose María; Palomares, Jose Manuel; Olivares, Joaquín

    2013-01-01

    This work analyzes several drift compensation mechanisms in wireless sensor networks (WSN). Temperature is an environmental factor that greatly affects oscillators shipped in every WSN mote. This behavior creates the need of improving drift compensation mechanisms in synchronization protocols. Using the Flooding Time Synchronization Protocol (FTSP), this work demonstrates that crystal oscillators are affected by temperature variations. Thus, the influence of temperature provokes a low performance of FTSP in changing conditions of temperature. This article proposes an innovative correction factor that minimizes the impact of temperature in the clock skew. By means of this factor, two new mechanisms are proposed in this paper: the Adjusted Temperature (AT) and the Advanced Adjusted Temperature (A2T). These mechanisms have been combined with FTSP to produce AT-FTSP and A2T-FTSP Both have been tested in a network of TelosB motes running TinyOS. Results show that both AT-FTSP and A2T-FTSP improve the average synchronization errors compared to FTSP and other temperature-compensated protocols (Environment-Aware Clock Skew Estimation and Synchronization for WSN (EACS) and Temperature Compensated Time Synchronization (TCTS)). PMID:23966192

  12. Grand-mother clocks and quiet lasers

    E-print Network

    Jacques Arnaud; Laurent Chusseau; Fabrice Philippe

    2009-01-08

    Galileo noted in the 16th century that the period of oscillation of a pendulum is almost independent of the amplitude. However, such a pendulum is damped by air friction. The latter may be viewed as resulting from air molecules getting in contact with the pendulum. It follows that air friction, not only damps the oscillation, but also introduces randomness. In the so-called ``grand-mother'' clock, discovered by Huygens in the 18th century, damping is compensated for, on the average, by an escapement mechanism driven by a falling weight. The purpose of this paper is to show that such a clock is, in its idealized form, a quiet oscillator. By ``quiet'' we mean that in spite of the randomness introduced by damping, the dissipated power (viewed as the oscillator output) does not fluctuate slowly. Comparison is made with quiet laser oscillators discovered theoretically in 1984. Because the input power does not fluctuate in both the mechanical oscillator and the quiet laser oscillator, the output power does not fluctuate at small Fourier frequencies, irrespectively of the detailed mechanisms involved.

  13. How to fix a broken clock

    PubMed Central

    Schroeder, Analyne M.; Colwell, Christopher S.

    2013-01-01

    Fortunate are those who rise out of bed to greet the morning light well rested with the energy and enthusiasm to drive a productive day. Others however, depend on hypnotics for sleep and require stimulants to awaken lethargic bodies. Sleep/wake disruption is a common occurrence in healthy individuals throughout their lifespan and is also a comorbid condition to many diseases (neurodegenerative) and psychiatric disorders (depression and bipolar). There is growing concern that chronic disruption of the sleep/wake cycle contributes to more serious conditions including diabetes (type 2), cardiovascular disease and cancer. A poorly functioning circadian system resulting in misalignments in the timing of clocks throughout the body may be at the root of the problem for many people. In this article, we discuss environmental (light therapy) and lifestyle changes (scheduled meals, exercise and sleep) as interventions to help fix a broken clock. We also discuss the challenges and potential for future development of pharmacological treatments to manipulate this key biological system. PMID:24120229

  14. Dual modes of CLOCK:BMAL1 inhibition mediated by Cryptochrome and Period proteins in the mammalian circadian clock.

    PubMed

    Ye, Rui; Selby, Cristopher P; Chiou, Yi-Ying; Ozkan-Dagliyan, Irem; Gaddameedhi, Shobhan; Sancar, Aziz

    2014-09-15

    The mammalian circadian clock is based on a transcription-translation feedback loop (TTFL) in which CLOCK and BMAL1 proteins act as transcriptional activators of Cryptochrome and Period genes, which encode proteins that repress CLOCK-BMAL1 with a periodicity of ? 24 h. In this model, the mechanistic roles of CRY and PER are unclear. Here, we used a controlled targeting system to introduce CRY1 or PER2 into the nuclei of mouse cells with defined circadian genotypes to characterize the functions of CRY and PER. Our data show that CRY is the primary repressor in the TTFL: It binds to CLOCK-BMAL1 at the promoter and inhibits CLOCK-BMAL1-dependent transcription without dissociating the complex ("blocking"-type repression). PER alone has no effect on CLOCK-BMAL1-activated transcription. However, in the presence of CRY, nuclear entry of PER inhibits transcription by displacing CLOCK-BMAL1 from the promoter ("displacement"-type repression). In light of these findings, we propose a new model for the mammalian circadian clock in which the negative arm of the TTFL proceeds by two different mechanisms during the circadian cycle. PMID:25228643

  15. Wide Angle Movie

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This brief movie illustrates the passage of the Moon through the Saturn-bound Cassini spacecraft's wide-angle camera field of view as the spacecraft passed by the Moon on the way to its closest approach with Earth on August 17, 1999. From beginning to end of the sequence, 25 wide-angle images (with a spatial image scale of about 14 miles per pixel (about 23 kilometers)were taken over the course of 7 and 1/2 minutes through a series of narrow and broadband spectral filters and polarizers, ranging from the violet to the near-infrared regions of the spectrum, to calibrate the spectral response of the wide-angle camera. The exposure times range from 5 milliseconds to 1.5 seconds. Two of the exposures were smeared and have been discarded and replaced with nearby images to make a smooth movie sequence. All images were scaled so that the brightness of Crisium basin, the dark circular region in the upper right, is approximately the same in every image. The imaging data were processed and released by the Cassini Imaging Central Laboratory for Operations (CICLOPS)at the University of Arizona's Lunar and Planetary Laboratory, Tucson, AZ.

    Photo Credit: NASA/JPL/Cassini Imaging Team/University of Arizona

    Cassini, launched in 1997, is a joint mission of NASA, the European Space Agency and Italian Space Agency. The mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Space Science, Washington DC. JPL is a division of the California Institute of Technology, Pasadena, CA.

  16. A Note on Angle Construction

    ERIC Educational Resources Information Center

    Francis, Richard L.

    1978-01-01

    The author investigates the construction of angles (using Euclidean tools) through a numerical approach. He calls attention to the surprising impossibility of constructing the conventional units of angle measure--the degree, minute, second, radian, and mil. (MN)

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

    PubMed

    Marcolino-Gomes, Juliana; Rodrigues, Fabiana Aparecida; Fuganti-Pagliarini, Renata; Bendix, Claire; Nakayama, Thiago Jonas; Celaya, Brandon; Molinari, Hugo Bruno Correa; de Oliveira, Maria Cristina Neves; Harmon, Frank G; Nepomuceno, Alexandre

    2014-01-01

    Rhythms produced by the endogenous circadian clock play a critical role in allowing plants to respond and adapt to the environment. While there is a well-established regulatory link between the circadian clock and responses to abiotic stress in model plants, little is known of the circadian system in crop species like soybean. This study examines how drought impacts diurnal oscillation of both drought responsive and circadian clock genes in soybean. Drought stress induced marked changes in gene expression of several circadian clock-like components, such as LCL1-, GmELF4- and PRR-like genes, which had reduced expression in stressed plants. The same conditions produced a phase advance of expression for the GmTOC1-like, GmLUX-like and GmPRR7-like genes. Similarly, the rhythmic expression pattern of the soybean drought-responsive genes DREB-, bZIP-, GOLS-, RAB18- and Remorin-like changed significantly after plant exposure to drought. In silico analysis of promoter regions of these genes revealed the presence of cis-elements associated both with stress and circadian clock regulation. Furthermore, some soybean genes with upstream ABRE elements were responsive to abscisic acid treatment. Our results indicate that some connection between the drought response and the circadian clock may exist in soybean since (i) drought stress affects gene expression of circadian clock components and (ii) several stress responsive genes display diurnal oscillation in soybeans. PMID:24475115

  18. Hunting for dark matter with GPS and atomic clocks

    NASA Astrophysics Data System (ADS)

    Derevianko, Andrei

    2015-05-01

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

  19. Redox rhythm reinforces the circadian clock to gate immune response.

    PubMed

    Zhou, Mian; Wang, Wei; Karapetyan, Sargis; Mwimba, Musoki; Marqués, Jorge; Buchler, Nicolas E; Dong, Xinnian

    2015-07-23

    Recent studies have shown that in addition to the transcriptional circadian clock, many organisms, including Arabidopsis, have a circadian redox rhythm driven by the organism's metabolic activities. It has been hypothesized that the redox rhythm is linked to the circadian clock, but the mechanism and the biological significance of this link have only begun to be investigated. Here we report that the master immune regulator NPR1 (non-expressor of pathogenesis-related gene 1) of Arabidopsis is a sensor of the plant's redox state and regulates transcription of core circadian clock genes even in the absence of pathogen challenge. Surprisingly, acute perturbation in the redox status triggered by the immune signal salicylic acid does not compromise the circadian clock but rather leads to its reinforcement. Mathematical modelling and subsequent experiments show that NPR1 reinforces the circadian clock without changing the period by regulating both the morning and the evening clock genes. This balanced network architecture helps plants gate their immune responses towards the morning and minimize costs on growth at night. Our study demonstrates how a sensitive redox rhythm interacts with a robust circadian clock to ensure proper responsiveness to environmental stimuli without compromising fitness of the organism. PMID:26098366

  20. The Circadian Clock in Cancer Development and Therapy

    PubMed Central

    Fu, Loning; Kettner, Nicole M.

    2014-01-01

    Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The central and peripheral clocks coordinately generate rhythmic gene expression in a tissue-specific manner in vivo to couple diverse physiological and behavioral processes to periodic changes in the environment. However, as the world industrialized, activities that disrupt endogenous homeostasis with external circadian cues have increased. This change in lifestyle has been linked to increased risk of diseases in all aspects of human health, including cancer. Studies in humans and animal models have revealed that cancer development in vivo is closely associated with the loss of circadian homeostasis in energy balance, immune function and aging that are supported by cellular functions important for tumor suppression including cell proliferation, senescence, metabolism and DNA damage response. The clock controls these cellular functions both locally in cells of peripheral tissues and at the organismal level via extracellular signaling. Thus, the hierarchical mammalian circadian clock provides a unique system to study carcinogenesis as a deregulated physiological process in vivo. The asynchrony between host and malignant tissues in cell proliferation and metabolism also provides new and exciting options for novel anti-cancer therapies. PMID:23899600

  1. Angle performance on optima MDxt

    SciTech Connect

    David, Jonathan; Kamenitsa, Dennis

    2012-11-06

    Angle control on medium current implanters is important due to the high angle-sensitivity of typical medium current implants, such as halo implants. On the Optima MDxt, beam-to-wafer angles are controlled in both the horizontal and vertical directions. In the horizontal direction, the beam angle is measured through six narrow slits, and any angle adjustment is made by electrostatically steering the beam, while cross-wafer beam parallelism is adjusted by changing the focus of the electrostatic parallelizing lens (P-lens). In the vertical direction, the beam angle is measured through a high aspect ratio mask, and any angle adjustment is made by slightly tilting the wafer platen prior to implant. A variety of tests were run to measure the accuracy and repeatability of Optima MDxt's angle control. SIMS profiles of a high energy, channeling sensitive condition show both the cross-wafer angle uniformity, along with the small-angle resolution of the system. Angle repeatability was quantified by running a channeling sensitive implant as a regular monitor over a seven month period and measuring the sheet resistance-to-angle sensitivity. Even though crystal cut error was not controlled for in this case, when attributing all Rs variation to angle changes, the overall angle repeatability was measured as 0.16 Degree-Sign (1{sigma}). A separate angle repeatability test involved running a series of V-curves tests over a four month period using low crystal cut wafers selected from the same boule. The results of this test showed the angle repeatability to be <0.1 Degree-Sign (1{sigma}).

  2. Calibration of angle standards

    NASA Astrophysics Data System (ADS)

    Henrique Brum Vieira, Luiz; Stone, Jack; Viliesid, Miguel; Gastaldi, Bruno R.; Przybylska, Joanna; Chaudhary, K. P.

    2015-01-01

    In 2000, a key comparison, CCL-K3 (optical polygon and angle blocks) was started, piloted by NMISA. Based on it, in 2007, the SIM metrological region started a SIM.L-K3 key comparison piloted by INMETRO. The results of this regional comparison (RMO key comparison) contribute to the Mutual Recognition Arrangement (MRA) between the national metrology institutes of the Metre Convention. It is linked with the CCL-K3 key comparison via laboratories that participated in both the CIPM and the RMO comparisons. This common participation establishes the link between the comparisons and ensures equivalence of national metrology institutes, according to the MRA between NMIs. The SIM NMIs that took part in the CCL-K3 were NIST, NRC and CENAM. However, NRC withdrew from it. GUM from Poland (EURAMET) and NPLI from India (APMP) were invited to participate in the SIM.L-K3 key comparison. The circulation of artefacts (a 12 faces polygon and 4 angle blocks) started in 2008 and was completed in 2009. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

  3. Glancing angle RF sheaths

    NASA Astrophysics Data System (ADS)

    D'Ippolito, D. A.; Myra, J. R.

    2013-10-01

    RF sheaths occur in tokamaks when ICRF waves encounter conducting boundaries. The sheath plays an important role in determining the efficiency of ICRF heating, the impurity influxes from the edge plasma, and the plasma-facing component damage. An important parameter in sheath theory is the angle ? between the equilibrium B field and the wall. Recent work with 1D and 2D sheath models has shown that the rapid variation of ? around a typical limiter can lead to enhanced sheath potentials and localized power deposition (hot spots) when the B field is near glancing incidence. The physics model used to obtain these results does not include some glancing-angle effects, e.g. possible modification of the angular dependence of the Child-Langmuir law and the role of the magnetic pre-sheath. Here, we report on calculations which explore these effects, with the goal of improving the fidelity of the rf sheath BC used in analytical and numerical calculations. Work supported by US DOE grants DE-FC02-05ER54823 and DE-FG02-97ER54392.

  4. Variable angle correlation spectroscopy

    SciTech Connect

    Lee, Y K

    1994-05-01

    In this dissertation, a novel nuclear magnetic resonance (NMR) technique, variable angle correlation spectroscopy (VACSY) is described and demonstrated with {sup 13}C nuclei in rapidly rotating samples. These experiments focus on one of the basic problems in solid state NMR: how to extract the wealth of information contained in the anisotropic component of the NMR signal while still maintaining spectral resolution. Analysis of the anisotropic spectral patterns from poly-crystalline systems reveal information concerning molecular structure and dynamics, yet in all but the simplest of systems, the overlap of spectral patterns from chemically distinct sites renders the spectral analysis difficult if not impossible. One solution to this problem is to perform multi-dimensional experiments where the high-resolution, isotropic spectrum in one dimension is correlated with the anisotropic spectral patterns in the other dimensions. The VACSY technique incorporates the angle between the spinner axis and the static magnetic field as an experimental parameter that may be incremented during the course of the experiment to help correlate the isotropic and anisotropic components of the spectrum. The two-dimensional version of the VACSY experiments is used to extract the chemical shift anisotropy tensor values from multi-site organic molecules, study molecular dynamics in the intermediate time regime, and to examine the ordering properties of partially oriented samples. The VACSY technique is then extended to three-dimensional experiments to study slow molecular reorientations in a multi-site polymer system.

  5. Mass Loading Characteristics of Crystal Clock Oscillators

    NASA Technical Reports Server (NTRS)

    Cobb, Janel; Morris, V. R.; Thorpe, A. N.

    1997-01-01

    The 10-MHz piezoelectric quartz-crystal microbalance (QCM) has been used extensively for stratospheric aerosol sampling. We have undertaken laboratory studies of the QCM response to mass loading by trace gases. However, this device requires dual oscillator circuitry and the mass sensitivity can often be affected by the electronics. The coatings on the quartz crystals are sometimes difficult to remove after they have reacted with a particular gas and a disposable crystal system would be desirable. The cost of the dual oscillator-based QCM makes this a prohibitive option. Since our goal is to develop a cost-effective microbalance system with stable electronics we have begun testing of crystal clock oscillators, which are assembled with their own circuitry. We have been using chemically specific coatings for ozone to determine if the sensitivity and mass-frequency ratios are comparable to that of the 10-MHz QCM.

  6. Dynamics and performance of clock pendulums

    E-print Network

    Hoyng, Peter

    2015-01-01

    We analyze the dynamics of a driven, damped pendulum as used in mechanical clocks. We derive equations for the amplitude and phase of the oscillation, on time scales longer than the pendulum period. The equations are first order ODEs and permit fast simulations of the joint effects of circular and escapement errors, friction, and other disturbances for long times. The equations contain two averages of the driving torque over a period, so that the results are not very sensitive to the fine structure of the driving. We adopt a constant-torque escapement and study the stationary pendulum rate as a function of driving torque and friction. We also study the reaction of the pendulum to a sudden change in the driving torque, and to stationary noisy driving. The equations for the amplitude and phase are shown to describe the pendulum dynamics quite well on time scales of one period and longer. Our emphasis is on a clear exposition of the physics.

  7. Polarizabilities of the beryllium clock transition

    SciTech Connect

    Mitroy, J.

    2010-11-15

    The polarizabilities of the three lowest states of the beryllium atom are determined from a large basis configuration interaction calculation. The polarizabilities of the 2s{sup 2} {sup 1}S{sup e} ground state (37.73a{sub 0}{sup 3}) and the 2s2p {sup 3}P{sub 0}{sup o} metastable state (39.04a{sub 0}{sup 3}) are found to be very similar in size and magnitude. This leads to an anomalously small blackbody radiation shift at 300 K of -0.018(4) Hz for the 2s{sup 2} {sup 1}S{sup e}-2s2p {sup 3}P{sub 0}{sup o} clock transition. Magic wavelengths for simultaneous trapping of the ground and metastable states are also computed.

  8. Clock Agreement Among Parallel Supercomputer Nodes

    DOE Data Explorer

    Jones, Terry R.; Koenig, Gregory A.

    2014-04-30

    This dataset presents measurements that quantify the clock synchronization time-agreement characteristics among several high performance computers including the current world's most powerful machine for open science, the U.S. Department of Energy's Titan machine sited at Oak Ridge National Laboratory. These ultra-fast machines derive much of their computational capability from extreme node counts (over 18000 nodes in the case of the Titan machine). Time-agreement is commonly utilized by parallel programming applications and tools, distributed programming application and tools, and system software. Our time-agreement measurements detail the degree of time variance between nodes and how that variance changes over time. The dataset includes empirical measurements and the accompanying spreadsheets.

  9. Clock comparison based on laser ranging technologies

    NASA Astrophysics Data System (ADS)

    Samain, Etienne

    2015-06-01

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

  10. Energy efficient lighting for the biological clock

    NASA Astrophysics Data System (ADS)

    Lang, Dieter

    2011-03-01

    Unexpectedly the existence of a formerly unknown type of photoreceptor in the human eye has been proven about 10 years ago. Primarily sensitive in the blue spectral range it is responsible for transducing light signals directly into the brain, controlling essential biological functions like setting of the circadian clock or daytime activation. Recent scientific research has enabled beneficial applications. The paradigms for good lighting design are shifting and standardization activities have been started to build up a sound base for description and application of biologically effective lighting. Latest improvements of LED technology are now allowing realizeation of advanced lighting solutions based on SSL. Optimization of biological effects is possible while demands on good vision are maintained. As biologically effective lighting is addressing a second system besides vision in the human body a measure beyond lumen per watt is required for a proper description of energy efficiency.

  11. Neural modeling of an internal clock.

    PubMed

    Yamazaki, Tadashi; Tanaka, Shigeru

    2005-05-01

    We studied a simple random recurrent inhibitory network. Despite its simplicity, the dynamics was so rich that activity patterns of neurons evolved with time without recurrence due to random recurrent connections among neurons. The sequence of activity patterns was generated by the trigger of an external signal, and the generation was stable against noise. Moreover, the same sequence was reproducible using a strong transient signal, that is, the sequence generation could be reset. Therefore, a time passage from the trigger of an external signal could be represented by the sequence of activity patterns, suggesting that this model could work as an internal clock. The model could generate different sequences of activity patterns by providing different external signals; thus, spatiotemporal information could be represented by this model. Moreover, it was possible to speed up and slow down the sequence generation. PMID:15829099

  12. Probing unification scenarios with atomic clocks

    E-print Network

    M. C. Ferreira; M. D. Julião; C. J. A. P. Martins; A. M. R. V. L. Monteiro

    2012-12-17

    We discuss the usage of measurements of the stability of nature's fundamental constants coming from comparisons between atomic clocks as a means to constrain coupled variations of these constants in a broad class of unification scenarios. After introducing the phenomenology of these models we provide updated constraints, based on a global analysis of the latest experimental results. We obtain null results for the proton-to-electron mass ratio ${\\dot\\mu}/{\\mu}=(0.68\\pm5.79)\\ti mes10^{-16}\\, {\\rm yr}{}^{-1}$ and for the gyromagnetic factor ${\\dot g_p}/{g_p} =(-0.72\\pm0.89)\\times10^{-16}\\, {\\rm yr}{}^{-1}$ (both of these being at the 95 % confidence level). These results are compatible with theoretical expectations on unification scenarios, but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

  13. Probing Unification Scenarios with Atomic Clocks

    E-print Network

    M. D. Julião; M. C. Ferreira; C. J. A. P. Martins; A. M. R. V. L. Monteiro

    2013-09-30

    We make use of the comparison between measurements of various pairs of atomic clocks to impose constraints on coupled variations of fundamental constants in severs unification scenarios. We obtain null results for the proton-to-electron mass ratio ${\\dot\\mu}/{\\mu}=(0.68\\pm5.79)\\times10^{-16}\\, {\\rm yr}{}^{-1}$ and for the gyromagnetic factor ${\\dot g_p}/{g_p}=(-0.72\\pm0.89)\\times10^{-16}\\, {\\rm yr}{}^{-1}$ (both of these being at the 95% confidence level). These results are compatible with theoretical expectations on unification scenarios (which we briefly describe), but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

  14. Circadian Rhythms, the Molecular Clock, and Skeletal Muscle

    PubMed Central

    Lefta, Mellani; Wolff, Gretchen; Esser, Karyn A.

    2015-01-01

    Almost all organisms ranging from single cell bacteria to humans exhibit a variety of behavioral, physiological, and biochemical rhythms. In mammals, circadian rhythms control the timing of many physiological processes over a 24-h period, including sleep-wake cycles, body temperature, feeding, and hormone production. This body of research has led to defined characteristics of circadian rhythms based on period length, phase, and amplitude. Underlying circadian behaviors is a molecular clock mechanism found in most, if not all, cell types including skeletal muscle. The mammalian molecular clock is a complex of multiple oscillating networks that are regulated through transcriptional mechanisms, timed protein turnover, and input from small molecules. At this time, very little is known about circadian aspects of skeletal muscle function/metabolism but some progress has been made on understanding the molecular clock in skeletal muscle. The goal of this chapter is to provide the basic terminology and concepts of circadian rhythms with a more detailed review of the current state of knowledge of the molecular clock, with reference to what is known in skeletal muscle. Research has demonstrated that the molecular clock is active in skeletal muscles and that the muscle-specific transcription factor, MyoD, is a direct target of the molecular clock. Skeletal muscle of clock-compromised mice, Bmal1?/? and Clock?19 mice, are weak and exhibit significant disruptions in expression of many genes required for adult muscle structure and metabolism. We suggest that the interaction between the molecular clock, MyoD, and metabolic factors, such as PGC-1, provide a potential system of feedback loops that may be critical for both maintenance and adaptation of skeletal muscle. PMID:21621073

  15. The bird of time: cognition and the avian biological clock

    PubMed Central

    Cassone, Vincent M.; Westneat, David F.

    2012-01-01

    Avian behavior and physiology are embedded in time at many levels of biological organization. Biological clock function in birds is critical for sleep/wake cycles, but may also regulate the acquisition of place memory, learning of song from tutors, social integration, and time-compensated navigation. This relationship has two major implications. First, mechanisms of the circadian clock should be linked in some way to the mechanisms of all these behaviors. How is not yet clear, and evidence that the central clock has effects is piecemeal. Second, selection acting on characters that are linked to the circadian clock should influence aspects of the clock mechanism itself. Little evidence exists for this in birds, but there have been few attempts to assess this idea. At its core, the avian circadian clock is a multi-oscillator system comprising the pineal gland, the retinae, and the avian homologs of the suprachiasmatic nuclei, whose mutual interactions ensure coordinated physiological functions, which are in turn synchronized to ambient light cycles (LD) via encephalic, pineal, and retinal photoreceptors. At the molecular level, avian biological clocks comprise a genetic network of “positive elements” clock and bmal1 whose interactions with the “negative elements” period 2 (per2), period 3 (per3), and the cryptochromes form an oscillatory feedback loop that circumnavigates the 24 h of the day. We assess the possibilities for dual integration of the clock with time-dependent cognitive processes. Closer examination of the molecular, physiological, and behavioral elements of the circadian system would place birds at a very interesting fulcrum in the neurobiology of time in learning, memory, and navigation. PMID:22461765

  16. Synchronous Sampling and Clock Recovery of Internal Oscillators for Side Channel Analysis and Fault Injection

    E-print Network

    International Association for Cryptologic Research (IACR)

    Synchronous Sampling and Clock Recovery of Internal Oscillators for Side Channel Analysis and Fault analysis typically uses an oscilloscope, which mea- sures the data relative to an internal sample clock. By synchronizing the sampling clock to the clock of the target device, the sample rate requirements are con

  17. CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL Function Synergistically in

    E-print Network

    Tobin, Elaine

    CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL Function Synergistically in the Circadian Angeles, California 90095 The circadian clock is an endogenous mechanism that coordinates biological is an important way of controlling clock function in several different circadian systems. CIRCADIAN CLOCK

  18. Using atomic broadcast to implement a posteriori agreement for clock synchronization

    E-print Network

    Rodrigues, Luís E.T.

    Using atomic broadcast to implement a posteriori agreement for clock synchronization L. Rodrigues P - INESC y Abstract In a recent paper we presented a new clock synchro- nization algorithm, dubbed a virtual clock in each node of the distributed system, which is synchronized with all other virtual clocks

  19. PHYSICAL REVIEW A 87, 012509 (2013) Blackbody-radiation shift in the Sr optical atomic clock

    E-print Network

    Safronova, Marianna

    2013-01-01

    PHYSICAL REVIEW A 87, 012509 (2013) Blackbody-radiation shift in the Sr optical atomic clock M. S of optical atomic clocks. The Sr clock transition has the largest BBR shift of all optical frequency optical lattice clock. We suggest future experiments that could further reduce the present uncertainties

  20. Recent Developments in Microwave Ion Clocks

    NASA Astrophysics Data System (ADS)

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

    We review the development of microwave-frequency standards based on trapped ions. Following two distinct paths, microwave ion clocks have evolved greatly in the last twenty years since the earliest Paul-trap-based units. Laser-cooled ion frequency standards reduce the second-order Doppler shift from ion micromotion and thermal secular motion achieving good signal-to-noise ratios via cycling transitions where as many as ~10^8 photons per second per ion may be scattered. Today, laser-cooled ion standards are based on linear Paul traps which hold ions near the node line of the trapping electric field, minimizing micromotion at the trapping-field frequency and the consequent second-order Doppler frequency shift. These quadrupole (radial) field traps tightly confine tens of ions to a crystalline single-line structure. As more ions are trapped, space charge forces some ions away from the node-line axis and the second-order Doppler effect grows larger, even at negligibly small secular temperatures. Buffer-gas-cooled clocks rely on large numbers of ions, typically ~10^7, optically pumped by a discharge lamp at a scattering rate of a few photons per second per ion. To reduce the second-order Doppler shift from space charge repulsion of ions from the trap node line, novel multipole ion traps are now being developed where ions are weakly bound with confining fields that are effectively zero through the trap interior and grow rapidly near the trap electrode ``walls''.

  1. Formal development of a clock synchronization circuit

    NASA Technical Reports Server (NTRS)

    Miner, Paul S.

    1995-01-01

    This talk presents the latest stage in formal development of a fault-tolerant clock synchronization circuit. The development spans from a high level specification of the required properties to a circuit realizing the core function of the system. An abstract description of an algorithm has been verified to satisfy the high-level properties using the mechanical verification system EHDM. This abstract description is recast as a behavioral specification input to the Digital Design Derivation system (DDD) developed at Indiana University. DDD provides a formal design algebra for developing correct digital hardware. Using DDD as the principle design environment, a core circuit implementing the clock synchronization algorithm was developed. The design process consisted of standard DDD transformations augmented with an ad hoc refinement justified using the Prototype Verification System (PVS) from SRI International. Subsequent to the above development, Wilfredo Torres-Pomales discovered an area-efficient realization of the same function. Establishing correctness of this optimization requires reasoning in arithmetic, so a general verification is outside the domain of both DDD transformations and model-checking techniques. DDD represents digital hardware by systems of mutually recursive stream equations. A collection of PVS theories was developed to aid in reasoning about DDD-style streams. These theories include a combinator for defining streams that satisfy stream equations, and a means for proving stream equivalence by exhibiting a stream bisimulation. DDD was used to isolate the sub-system involved in Torres-Pomales' optimization. The equivalence between the original design and the optimized verified was verified in PVS by exhibiting a suitable bisimulation. The verification depended upon type constraints on the input streams and made extensive use of the PVS type system. The dependent types in PVS provided a useful mechanism for defining an appropriate bisimulation.

  2. Circadian rhythms in urinary functions: possible roles of circadian clocks?

    PubMed

    Noh, Jong-Yun; Han, Dong-Hee; Yoon, Ji-Ae; Kim, Mi-Hee; Kim, Sung-Eun; Ko, Il-Gyu; Kim, Khae-Hawn; Kim, Chang-Ju; Cho, Sehyung

    2011-06-01

    Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In this review, we briefly introduce circadian clocks and their organization in mammals. We then summarize known daily or circadian variations in urinary function. Importantly, recent findings by others as well as results obtained by us suggest an active role of circadian clock genes in various urinary functions. Finally, we discuss possible research avenues for the circadian control of urinary function. PMID:21811695

  3. Circadian Rhythms in Urinary Functions: Possible Roles of Circadian Clocks?

    PubMed Central

    Noh, Jong-Yun; Han, Dong-Hee; Yoon, Ji-Ae; Kim, Mi-Hee; Kim, Sung-Eun; Ko, Il-Gyu; Kim, Khae-Hawn; Kim, Chang-Ju

    2011-01-01

    Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In this review, we briefly introduce circadian clocks and their organization in mammals. We then summarize known daily or circadian variations in urinary function. Importantly, recent findings by others as well as results obtained by us suggest an active role of circadian clock genes in various urinary functions. Finally, we discuss possible research avenues for the circadian control of urinary function. PMID:21811695

  4. Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders.

    PubMed

    Barandas, Rita; Landgraf, Dominic; McCarthy, Michael J; Welsh, David K

    2015-12-01

    Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms. PMID:26483181

  5. The problem of clock synchronization - A relativistic approach

    NASA Astrophysics Data System (ADS)

    Klioner, Sergei A.

    1992-03-01

    The problem of synchronization of the earth-based clocks has been discussed in the framework of General Relativity Theory. The synchronization is considered as the transformation of the observers' proper time scales to the coordinate time scale of local inertial geocentric reference system, which is single for all the observers. The formulas for the relativistic corrections occurring in some methods of earth-based clock synchronization (transported clock, duplex communication via geostationary satellite and meteor-burst link, LASSO experiments) have been derived enabling one to attain the accuracy of 0.1 ns.

  6. Demonstration of a dual alkali Rb/Cs fountain clock.

    PubMed

    Guéna, Jocelyne; Rosenbusch, Peter; Laurent, Philippe; Abgrall, Michel; Rovera, Daniele; Santarelli, Giorgio; Tobar, Michael E; Bize, Sébastien; Clairon, André

    2010-03-01

    We report the operation of a dual Rb/Cs atomic fountain clock. (133)Cs and (87)Rb atoms are cooled, launched, and detected simultaneously in LNE-SYRTE's FO2 double fountain. The dual clock operation occurs with no degradation of either the stability or the accuracy. We describe the key features for achieving such a simultaneous operation. We also report on the results of the first Rb/Cs frequency measurement campaign performed with FO2 in this dual atom clock configuration, including a new determination of the absolute (87)Rb hyperfine frequency. PMID:20211784

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

    PubMed

    Huang, Xinming; Gong, Hang; Ou, Gang

    2014-05-01

    In this paper, a weak frequency jump detection method is developed for onboard clocks in global navigation satellite systems (GNSS). A Kalman filter is employed to facilitate the onboard real-time processing of atomic clock measurements, whose N-step prediction residuals are used to construct the weak frequency jump detector. Numerical simulations show that the method can successfully detect weak frequency jumps. The detection method proposed in this paper is helpful for autonomous integrity monitoring of GNSS satellite clocks, and can also be applied to other frequency anomalies with an appropriately modified detector. PMID:24802723

  8. Metabolism control by the circadian clock and vice versa

    PubMed Central

    Eckel-Mahan, Kristin; Sassone-Corsi, Paolo

    2014-01-01

    Circadian rhythms govern a wide variety of physiological and metabolic functions in most organisms. At the heart of these regulatory pathways in mammals is the clock machinery, a remarkably coordinated transcription-translation system that relies on dynamic changes in chromatin states. Recent findings indicate that regulation also goes the other way, as specific elements of the clock can sense changes in the cellular metabolism. Understanding in full detail the intimate links between cellular metabolism and the circadian clock machinery will provide not only crucial insights into system physiology but also new avenues toward pharmacological intervention of metabolic disorders. PMID:19421159

  9. The chlorate-iodine-nitrous acid clock reaction.

    PubMed

    Sant'Anna, Rafaela T P; Faria, Roberto B

    2014-01-01

    A new clock reaction based on chlorate, iodine and nitrous acid is presented. The induction period of this new clock reaction decreases when the initial concentrations of chlorate, nitrous acid and perchloric acid increase, but it is independent on the initial iodine concentration. The proposed mechanism is based on the LLKE autocatalytic mechanism for the chlorite-iodide reaction and the initial reaction between chlorate and nitrous acid to produce nitrate and chlorite. This new clock reaction opens the possibility for a new family of oscillating reactions containing chlorate or nitrous acid, which in both cases has not been observed until now. PMID:25313803

  10. The Chlorate-Iodine-Nitrous Acid Clock Reaction

    PubMed Central

    Sant'Anna, Rafaela T. P.; Faria, Roberto B.

    2014-01-01

    A new clock reaction based on chlorate, iodine and nitrous acid is presented. The induction period of this new clock reaction decreases when the initial concentrations of chlorate, nitrous acid and perchloric acid increase, but it is independent on the initial iodine concentration. The proposed mechanism is based on the LLKE autocatalytic mechanism for the chlorite-iodide reaction and the initial reaction between chlorate and nitrous acid to produce nitrate and chlorite. This new clock reaction opens the possibility for a new family of oscillating reactions containing chlorate or nitrous acid, which in both cases has not been observed until now. PMID:25313803

  11. Stability of atomic clocks based on entangled atoms

    E-print Network

    A. Andre; A. S. Sorensen; M. D. Lukin

    2004-01-21

    We analyze the effect of realistic noise sources for an atomic clock consisting of a local oscillator that is actively locked to a spin-squeezed (entangled) ensemble of $N$ atoms. We show that the use of entangled states can lead to an improvement of the long-term stability of the clock when the measurement is limited by decoherence associated with instability of the local oscillator combined with fluctuations in the atomic ensemble's Bloch vector. Atomic states with a moderate degree of entanglement yield the maximal clock stability, resulting in an improvement that scales as $N^{1/6}$ compared to the atomic shot noise level.

  12. Hyperpolarizability Effects in a Sr Optical Lattice Clock

    SciTech Connect

    Brusch, Anders; Le Targat, Rodolphe; Baillard, Xavier; Fouche, Mathilde; Lemonde, Pierre

    2006-03-17

    We report the observation of a higher-order frequency shift due to the trapping field in a {sup 87}Sr optical lattice clock. We show that, at the magic wavelength of the lattice, where the first-order term cancels, the higher-order shift will not constitute a limitation to the fractional accuracy of the clock at a level of 10{sup -18}. This result is achieved by operating the clock at very high trapping intensity up to 400 kW/cm{sup 2} and by a specific study of the effect of the two two-photon transitions near the magic wavelength.

  13. An atomic clock with 10(-18) instability.

    PubMed

    Hinkley, N; Sherman, J A; Phillips, N B; Schioppo, M; Lemke, N D; Beloy, K; Pizzocaro, M; Oates, C W; Ludlow, A D

    2013-09-13

    Atomic clocks have been instrumental in science and technology, leading to innovations such as global positioning, advanced communications, and tests of fundamental constant variation. Timekeeping precision at 1 part in 10(18) enables new timing applications in relativistic geodesy, enhanced Earth- and space-based navigation and telescopy, and new tests of physics beyond the standard model. Here, we describe the development and operation of two optical lattice clocks, both using spin-polarized, ultracold atomic ytterbium. A measurement comparing these systems demonstrates an unprecedented atomic clock instability of 1.6 × 10(-18) after only 7 hours of averaging. PMID:23970562

  14. Small Mercury Ion Clock for On-board Spacecraft Navigation

    NASA Technical Reports Server (NTRS)

    Prestage, John D.; Chung, Sang; Le, Thanh; Hamell, R.; Maleki, Lute; Tjoelker, Robert

    2004-01-01

    I.Small Ion Clock Approach and Heritage: a) No lasers, uwave cavities, cryogenics, atomic beams, etc. b) Ions are electrically shuttled between separate optical and microwave traps. II. Each trap is optimized for its task: quadrupole for optical state selection; multi-pole for microwave clock. a) Very good stability shown in USNO. Timescale running "open loop." III. "Open loop" operation means no self-measurements of frequency offsets: (Zeeman, ion temperature,... etc.) a) Fewer parts and procedures, produces stable output continuously. IV. Ion clock is not so sensitive to temperature fluctuations a) Measured u:nshielded temperature coefficient of few 10(exp -15) per C. b) No bulky temperature isolation needed.

  15. Modeling Cleft-Region Particle Precipitation Using the Interplanetary Magnetic Field and Generalized Auroral Electrojet Indices

    NASA Astrophysics Data System (ADS)

    Mitchell, E. J.; Newell, P. T.; Ridley, A. J.

    2013-12-01

    Cleft-region particle precipitation affects several ionospheric processes including ionospheric outflow and ionospheric plasma formations. Cleft-region particle precipitation has been shown to be dependent on the interplanetary magnetic field (IMF) clock angle, the dayside-merging rate/local magnetic field changes, and the characteristic energy of the particles. The OVATION-SM particle precipitation model between 0800 and 1600 MLT is modified to include IMF clock angle effects and model individual characteristic energies. The resulting cleft-region particle precipitation model will be shown as well as data-model comparisons with Polar UVI dayside data. The inclusion of characteristic energy dependence and IMF clock angle effects is expected to provide better dayside auroral power predictions and better spatial-temporal location of the cleft-region.

  16. The role of clock genes and circadian rhythm in the development of cardiovascular diseases.

    PubMed

    Takeda, Norihiko; Maemura, Koji

    2015-09-01

    The time of onset of cardiovascular disorders such as myocardial infarctions or ventricular arrhythmias exhibits a circadian rhythm. Diurnal variations in autonomic nervous activity, plasma cortisol level or renin-angiotensin activity underlie the pathogenesis of cardiovascular diseases. Transcriptional-translational feedback loop of the clock genes constitute a molecular clock system. In addition to the central clock in the suprachiasmatic nucleus, clock genes are also expressed in a circadian fashion in each organ to make up the peripheral clock. The peripheral clock seems to be beneficial for anticipating external stimuli and thus contributes to the maintenance of organ homeostasis. Loss of synchronization between the central and peripheral clocks also augments disease progression. Moreover, accumulating evidence shows that clock genes affect inflammatory and intracellular metabolic signaling. Elucidating the roles of the molecular clock in cardiovascular pathology through the identification of clock controlled genes will help to establish a novel therapeutic approach for cardiovascular disorders. PMID:25972277

  17. Entanglement and spin-squeezing in a network of distant optical lattice clocks

    E-print Network

    Eugene S. Polzik; Jun Ye

    2015-12-04

    We propose an approach for collective enhancement of precision for remotely located optical lattice clocks and a way of generation of the Einstein-Podolsky-Rosen state of remote clocks. Close to Heisenberg scaling of the clock precision with the number of clocks M can be achieved even for an optical channel connecting clocks with substantial losses. This scenario utilizes a collective quantum nondemolition measurement on clocks with parallel Bloch vectors for enhanced measurement precision. We provide an optimal network solution for distant clocks as well as for clocks positioned in close proximity of each other. In the second scenario, we employ collective dissipation to drive two clocks with oppositely oriented Bloch vectors into a steady state entanglement. The corresponding EPR entanglement provides enhanced time sharing beyond the projection noise limit between the two quantum synchronized clocks protected from eavesdropping, as well as allows better characterization of systematic effects.

  18. Particle entry through sash in the magnetopause with a dawndard IMF as simulated by a 3-D EM particle code

    NASA Astrophysics Data System (ADS)

    Cai, D.; Yan, X.; Lembege, B.; Nishikawa, K.

    2003-12-01

    We report a new progress in the long-term effort to represent the global interaction of the solar wind with the Earth's magnetosphere using a three-dimensional electromagnetic particle code with the improved resolutions using the HPF Tristan code. After a quasi-steady state is established with an unmagnetized solar wind we gradually switch on a northward interplanetary magnetic field (IMF), which causes a magnetic reconnection at the nightside cusps and the magnetosphere to be depolarized. In the case that the northward IMF is switched gradually to dawnward, there is no signature of reconnection in the near-Earth magnetotail as in the case with the southward turning. On the contrary analysis of magnetic fields in the magnetopause confirms a signature of magnetic reconnection at both the dawnside and duskside. And the plasma sheet in the near-Earth magnetotail clearly thins as in the case of southward turning. Arrival of dawnward IMF to the magnetopause creates a reconnection groove which cause particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. This deep connection is more fully recognized tailward of Earth. The flank weak-field fan joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross-tail S that structurally integrates the magnetopause and the tail interior. This structure contributes to direct plasma entry between the magnetosheath to the inner magnetosphere and plasma sheet, in which the entry process heats the magnetosheath plasma to plasma sheet temperatures. These phenomena have been found by Cluster observations. Further investigation with Cluster observations will provide new insights for unsolved problems such as hot flow anomalies (HFAs), substorms, and storm-substorm relationship. 3-D movies with sash structure will be presented at the meeting.

  19. Heterodyne Interferometer Angle Metrology

    NASA Technical Reports Server (NTRS)

    Hahn, Inseob; Weilert, Mark A.; Wang, Xu; Goullioud, Renaud

    2010-01-01

    A compact, high-resolution angle measurement instrument has been developed that is based on a heterodyne interferometer. The common-path heterodyne interferometer metrology is used to measure displacements of a reflective target surface. In the interferometer setup, an optical mask is used to sample the measurement laser beam reflecting back from a target surface. Angular rotations, around two orthogonal axes in a plane perpendicular to the measurement- beam propagation direction, are determined simultaneously from the relative displacement measurement of the target surface. The device is used in a tracking telescope system where pitch and yaw measurements of a flat mirror were simultaneously performed with a sensitivity of 0.1 nrad, per second, and a measuring range of 0.15 mrad at a working distance of an order of a meter. The nonlinearity of the device is also measured less than one percent over the measurement range.

  20. Cerebellopontine Angle Lipoma

    PubMed Central

    Schuhmann, Martin U.; Lüdemann, Wolf O.; Schreiber, Hartwig; Samii, Madjid

    1997-01-01

    Intracranial lipomas in an infratentorial and extra-axial location are extremely rare. The presented case of an extensive lipoma of the cerebellopontine angle (CPA) represents 0.05% of all CPA tumors operated on in our department from 1978 to 1996. The lipoma constitutes an important differential diagnosis because the clinical management differs significantly from other CPA lesions. The clinical presentation and management of the presented case are analyzed in comparison to all previously described cases of CPA lipomas. The etiology and the radiological features of CPA lipomas are reviewed and discussed. CPA lipomas are maldevelopmental lesions that may cause slowly progressive symptoms. Neuroradiology enables a reliable preoperative diagnosis. Attempts of complete lipoma resection usually result in severe neurological deficits. Therefore, we recommend a conservative approach in managing these patients. Limited surgery is indicated if the patient has an associated vascular compression syndrome or suffers from disabling vertigo. ImagesFigure 1Figure 2Figure 3Figure 4 PMID:17171031