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Sample records for imf clock angle

  1. Reconnection voltage as a function of IMF clock angle

    NASA Technical Reports Server (NTRS)

    Fedder, J. A.; Mobarry, C. M.; Lyon, J. G.

    1991-01-01

    Magnetic reconnection between the IMF and the geomagnetic field is thought to play a major role in the transfer of solar wind momentum and energy to the magnetosphere. Both analytic modeling and analysis of geophysical data have shown that this coupling process should be a sensitive function of the clock angle of the IMF. Results are presented from a three-dimensional, MHD, global numerical simulation code for the reconnection voltage between the closed geomagnetic field and the IMF as a function of the IMF clock angle. These results are consistent with a sin(theta/2) functional behavior.

  2. The influence of IMF clock angle timescales on the morphology of ionospheric convection

    NASA Astrophysics Data System (ADS)

    Grocott, A.; Milan, S. E.

    2014-07-01

    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) control of ionospheric convection and associated magnetospheric dynamics. We parameterize 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 ?B30 min, the convection patterns closely resemble their time-averaged counterparts. However, as ?B increases we find that the convection evolves away from the time-averaged patterns to reveal modified characteristic flow features. We discuss these findings in terms of solar wind-magnetosphere-ionosphere coupling and consider their implications for understanding the time-dependent nature of magnetospheric dynamics.

  3. Relation between cusp ion structures and dayside reconnection for four IMF clock angles: OpenGGCM-LTPT results

    NASA Astrophysics Data System (ADS)

    Connor, H. K.; Raeder, J.; Sibeck, D. G.; Trattner, K. J.

    2015-06-01

    When, where, and which type of reconnection (antiparallel or component) happens on the dayside magnetopause are long-standing unsolved questions due to insufficient in situ observation of reconnection sites. Previous studies showed that the dispersed ion signatures observed in the magnetospheric cusps depend on the reconnection mechanism, suggesting that cusp ion signatures can be a good tool to investigate the locations and properties of dayside reconnection. We investigate this close relation between cusp signatures and magnetopause reconnection for four different interplanetary magnetic field (IMF) clock angles (CA) using the Open Global Geospace Circulation Model (OpenGGCM) and the Liouville Theorem Particle Tracer(LTPT). OpenGGCM produces dayside reconnection under the resistive MHD theory, and LTPT calculates cusp ion signatures caused by the simulated reconnection. Our model results show that for CA = 0, antiparallel reconnection at both the northern and southern lobes causes a reverse dispersion in which ion energies increase with increasing latitude. For CA = 60, unsteady antiparallel reconnection at both the northern and southern lobes causes double reverse dispersions. For CA = 120, component reconnection near the subsolar point produces a dispersionless signature in the low-latitude cusp, and antiparallel reconnection on the duskside northern magnetopause produces a normal dispersion in the high-latitude cusp in which ion energies decrease with increasing latitude. For CA = 180, antiparallel reconnection near the subsolar point causes a normal dispersion.

  4. IMF dependence of high-latitude thermospheric wind pattern derived from CHAMP cross-track measurements

    NASA Astrophysics Data System (ADS)

    Frster, M.; Rentz, S.; Khler, W.; Liu, H.; Haaland, S. E.

    2008-06-01

    Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern obtained from the Cluster EDI plasma drift measurements under the same sorting conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for ByIMF+ (ByIMF-) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for ByIMF+ than for ByIMF- and is systematically larger (~5) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for BzIMF-/ByIMF- conditions at the Northern Hemisphere, but for BzIMF-/ByIMF+ conditions at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.

  5. MHD simulation of energy transfer across magnetopause during sudden changes of the IMF orientation

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    A three-dimensional adaptive magnetohydrodynamic (MHD) model is used to investigate the energy flow from the solar wind to the magnetosphere in response to sudden turnings of the interplanetary magnetic field (IMF) on 5 June 1998. During this dynamic period, the size of magnetospheric cavity and the energy input fluctuated enormously. Due to the positive earth dipole tilt angle during the event, the distribution of energy transfer between northern and southern hemispheres of magnetopause is asymmetrical, with most energy transferred in the north hemisphere sunward of XGSE>0RE. The electromagnetic and mechanical energy inputs increase rapidly after the arrival of an interplanetary shock, while the electromagnetic energy rises much more slowly after IMF turns from north to south. With a nearly invariable By component of IMF, under southward IMF the most electromagnetic energy is transferred near the plane anti-parallel to IMF clock angle, the most significant mechanical energy input occurs in the polar cusp of north hemisphere. In contrast, for northward IMF the electromagnetic energy is mostly transferred near the plane perpendicular to IMF clock angle, mechanical transferred energy occurs near equatorial plane of dayside magnetopause. Analyzing the distribution of the Poynting flux we show that the high-latitude reconnection causes different types of electromagnetic energy transfers into the magnetosphere during northward IMF especially with a large By component. It is also shown that the traditional energy transfer parameters from solar wind conditions do not include any of residual or hysteresis effects; therefore sometimes they do not reflect the right response to the solar wind variations.

  6. IMF Dependence of High-Latitude Thermospheric Wind Pattern Derived from CHAMP Cross-Track Accelerometer Data and the Corresponding Magnetospheric Convection from Cluster EDI Measurements

    NASA Astrophysics Data System (ADS)

    Foerster, Matthias; Haaland, Stein E.; Rentz, Stefanie; Liu, Huixin

    Neutral thermospheric wind pattern at high latitudes obtained from cross-track acceleration measurements of the CHAMP satellite above both North and South polar regions are statistically analyzed in their dependence on the Interplanetary Magnetic Field (IMF) direction in the GSM y-z plane (clock angle). We compare this dependency with magnetospheric convection pattern using 1-min-averages of Cluster/EDI electric drift observations and the same IMF and solar wind sorting conditions. The spatially distributed Cluster/EDI measurements are mapped to a the common reference level at ionospheric F-region heights in a magnetic latitude/MLT grid. We obtained both regular thermospheric wind and plasma drift pattern according to the various IMF conditions. The IMF-dependency shows some similarity with the corresponding high-latitude plasma convection insofar that the larger-scale convection cells, in particular the round-shaped dusk cell for IMF By+ (By-) conditions at the Northern (Southern) Hemisphere, leave their marks on the dominant general transpolar wind circulation from the dayside to the nightside. The direction of the transpolar circulation is generally deflected toward a duskward flow, in particular in the evening to nighttime sector. The degree of deflection correlates with the IMF clock angle. It is larger for IMF By+ than for Byand is systematically larger (about 5 deg) and appear less structured at the Southern Hemisphere compared with the Northern. Thermospheric cross-polar wind amplitudes are largest for IMF Bz-/Byconditions (corresponding to sector 5) at the Northern Hemisphere, but for IMF Bz-/By+ conditions (sector 3) at the Southern because the magnetospheric convection is in favour of largest wind accelerations over the polar cap under these conditions. The overall variance of the thermospheric wind magnitude at Southern high latitudes is larger than for the Northern. This is probably due to a larger "stirring effect" at the Southern Hemisphere because of the larger distance between the geographic and geomagnetic frameworks.

  7. 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 Е =[VхB], 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.

  8. High-latitude plasma convection from Cluster EDI measurements: method and IMF-dependence

    NASA Astrophysics Data System (ADS)

    Haaland, S. E.; Paschmann, G.; Frster, M.; Quinn, J. M.; Torbert, R. B.; McIlwain, C. E.; Vaith, H.; Puhl-Quinn, P. A.; Kletzing, C. A.

    2007-02-01

    We have used vector measurements of the electron drift velocity made by the Electron Drift Instrument (EDI) on Cluster between February 2001 and March 2006 to derive statistical maps of the high-latitude plasma convection. The EDI measurements, obtained at geocentric distances between ~4 and ~20 RE over both hemispheres, are mapped into the polar ionosphere, and sorted according to the clock-angle of the interplanetary magnetic field (IMF), measured at ACE and propagated to Earth, using best estimates of the orientation of the IMF variations. Only intervals of stable IMF are used, based on the magnitude of a "bias-vector" constructed from 30-min averages. The resulting data set consists of a total of 5862 h of EDI data. Contour maps of the electric potential in the polar ionosphere are subsequently derived from the mapped and averaged ionospheric drift vectors. Comparison with published statistical results based on Super Dual Auroral Radar Network (SuperDARN) radar and low-altitude satellite measurements shows excellent agreement between the average convection patterns, and in particular the lack of mirror-symmetry between the effects of positive and negative IMF By, the appearance of a duskward flow component for strongly southward IMF, and the general weakening of the average flows and potentials for northerly IMF directions. This agreement lends credence to the validity of the assumption underlying the mapping of the EDI data, namely that magnetic field lines are equipotentials. For strongly northward IMF the mapped EDI data show the clear emergence of two counter-rotating lobe cells with a channel of sunward flow between them. The total potential drops across the polar caps obtained from the mapped EDI data are intermediate between the radar and the low-altitude satellite results.

  9. High-latitude plasma convection during Northward IMF as derived from in-situ magnetospheric Cluster EDI measurements

    NASA Astrophysics Data System (ADS)

    Frster, M.; Haaland, S. E.; Paschmann, G.; Quinn, J. M.; Torbert, R. B.; Vaith, H.; Kletzing, C. A.

    2008-09-01

    In this study, we investigate statistical, systematic variations of the high-latitude convection cell structure during northward IMF. Using 1-min-averages of Cluster/EDI electron drift observations above the Northern and Southern polar cap areas for six and a half years (February 2001 till July 2007), and mapping the spatially distributed measurements to a common reference plane at ionospheric level in a magnetic latitude/MLT grid, we obtained regular drift patterns according to the various IMF conditions. We focus on the particular conditions during northward IMF, where lobe cells at magnetic latitudes >80 with opposite (sunward) convection over the central polar cap are a permanent feature in addition to the main convection cells at lower latitudes. They are due to reconnection processes at the magnetopause boundary poleward of the cusp regions. Mapped EDI data have a particular good coverage within the central part of the polar cap, so that these patterns and their dependence on various solar wind conditions are well verified in a statistical sense. On average, 4-cell convection pattern are shown as regular structures during periods of nearly northward IMF with the tendency of a small shift toward negative clock angles. The positions of these high-latitude convection foci are within 79 to 85 magnetic latitude and 09:00 15:00 MLT. The MLT positions are approximately symmetric 2 h about 11:30 MLT, i.e. slightly offset from midday toward prenoon hours, while the maximum (minimum) potential of the high-latitude cells is at higher magnetic latitudes near their maximum potential difference at ?-10 to -15 clock angle for the North (South) Hemisphere. With increasing clock angle distances from ?IMFBz+, a gradual transition occurs from the 4-cell pattern via a 3-cell to the common 2-cell convection pattern, in the course of which one of the medium-scale high-latitude dayside cells diminishes and disappears while the other intensifies and merges with the opposite main cell of the same polarity to form the large "round-shaped" convection cell when approaching a well-known IMFBy-dominated configuration. Opposite scenarios with interchanged roles of the respective cells occur for the opposite turning of the clock angle and at the Southern Hemisphere. The high-latitude dayside cells become more pronounced with increasing magnitude of the IMF vector.

  10. 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.

  11. Separator reconnection at the magnetopause for predominantly northward and southward IMF: Techniques and results

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    In this work, we demonstrate how to track magnetic separators in three-dimensional simulated magnetic fields with or without magnetic nulls, apply these techniques to enhance our understanding of reconnection at the magnetopause. We present three methods for locating magnetic separators and apply them to 3-D resistive MHD simulations of the Earth's magnetosphere using the Block-Adaptive-Tree Solar-wind Roe-type Upwind Scheme code. The techniques for finding separators and determining the reconnection rate are insensitive to interplanetary magnetic field (IMF) clock angle and can in principle be applied to any magnetospheric model. Moreover, the techniques have a number of advantages over prior separator finding techniques applied to the magnetosphere. The present work examines cases of high and low resistivity for two clock angles. We go beyond previous work examine the separator during Flux Transfer Events (FTEs). Our analysis of reconnection on the magnetopause yields a number of interesting conclusions: Reconnection occurs all along the separator even during predominately northward IMF cases. Multiple separators form in low-resistivity conditions, and in the region of an FTE the separator splits into distinct branches. Moreover, the local contribution to the reconnection rate, as determined by the local parallel electric field, drops in the vicinity of the FTE with respect to the value when there are none.

  12. 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.

  13. 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!

  14. 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.

  15. Recent Advances on IMF Research

    NASA Astrophysics Data System (ADS)

    Kroupa, Pavel

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    It was demonstrated that an interplanetary magnetic field (IMF) sense dependent 2nd order anisotropy is produced by the diffusion convection of cosmic rays in the heliomagnetosphere. The result implies that the anisotropy cannot be expressed only by the pitch angle with respect to the IMF axis.

  17. Polar, Cluster and SuperDARN Evidence for High-Latitude Merging during Southward IMF: Temporal/Spatial Evolution

    NASA Technical Reports Server (NTRS)

    Maynard, N. C.; Ober, D. M.; Burke, W. J.; Scudder, J. D.; Lester, M.; Dunlap, M.; Wild, J. A.; Grocott, A.; Farrugia, C. J.; Lund, E. J.; Russell, C. T.

    2003-01-01

    Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walen tests, are necessary, but not sufficient, conditions, for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the SuperDARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than approximately 150 degrees. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole tilt angle increases or when IMF B(sub X) increases the effective dipole tilt.

  18. Observations at Low Latitudes of Magnetic Merging Signatures Within a Flux Transfer Event During a Northward IMF

    NASA Technical Reports Server (NTRS)

    Chandler, M. O.; Avanov, L. A.

    2003-01-01

    Flux transfer events (FTE) have been postulated to result from transient magnetic merging. If so, the ion distributions within an event should exhibit features known to result from merging. Observations of a FTE by instruments on the Polar spacecraft revealed classical merging signatures that included: 1) D-shaped, accelerated, magnetosheath ion distributions, 2) a well defined de Hoffman-Teller frame, 3) local stress balance, and 4) a P-N magnetic field signature. This FTE was observed near the magnetic equator at approx. 13 MLT under conditions of a moderately northward interplanetary magnetic field (IMF) (clock angle of less than 10 deg). The nature of the ion distributions and the consistency of the measured cutoff speed with that calculated from the measured local magnetic field and the derived de Hoffman-Teller speed show the ion injection to be local. Coupled with the northward IMF these results lead to the conclusion that component merging in the low latitude region was responsible for the FTE.

  19. MARSIS Observations of the Martian Nightside Ionosphere Depending on Solar Wind and IMF Conditions

    NASA Astrophysics Data System (ADS)

    Dieval, C.; Nemec, F.; Morgan, D. D.; Gurnett, D. A.

    2013-12-01

    Despite the absence of solar radiation on the Martian nightside, a weak, irregular and variable ionosphere is produced there. The nightside ionosphere is produced by two main sources: plasma transport from the dayside to the nightside, and precipitation of solar wind electrons. The latter mechanism was proposed for explaining the observation of localized ionospheric reflections on the nightside of Mars by the MARSIS radar onboard the Mars Express orbiter. These ionospheric reflections were observed in regions of strong and vertical remanent crustal magnetic field. The common interpretation is that in such regions, open magnetic field lines form, that connect the Martian crustal magnetic fields to the solar wind. These open field lines allow the precipitating suprathermal electrons to reach low altitudes and to cause localized heating and ionization of the atmosphere. Observations by Mars Express and Mars Global Surveyor (MGS) have shown that the precipitation of suprathermal electrons depends strongly on the crustal field strength and orientation. They have also shown that the electron precipitation depends on external parameters, such as the solar wind dynamic pressure and the orientation of the interplanetary magnetic field (IMF). In this work, we look at the effect of these two external parameters on the occurrence rate of observing nightside ionospheric reflections with MARSIS. To estimate the solar wind dynamic pressure and the IMF clock angle, we use the proxies developed by the MGS team. This statistical study extends from November 2005 to November 2006, when MGS ceased to operate. The variable external drivers are expected to influence the supply of plasma to the nightside, and therefore to influence the formation of the irregular nightside ionosphere.

  20. Digital aspect clock

    NASA Technical Reports Server (NTRS)

    Bartley, W. C.

    1971-01-01

    Digital clock precisely set and reset by pulses from a solar sensor, combined with a logic system, provides accurate time-sector division of spin-stabilized satellite. Integral times for viewing physical phenomena from various directions are equal and mean angles of viewing can be determined.

  1. Magnetopause reconnection and energy conversion as influenced by the dipole tilt and the IMF Bx

    NASA Astrophysics Data System (ADS)

    Hoilijoki, Sanni; Souza, Vitor M.; Walsh, Brian M.; Janhunen, Pekka; Palmroth, Minna

    2014-06-01

    We study the effect of Earth's dipole tilt angle and interplanetary magnetic field (IMF) Bx and By components on the location of reconnection and the energy conversion at the magnetopause. We simulate southward IMF satisfying both inward- and outward-type Parker spiral conditions during three different dipole tilt angles using a global magnetohydrodynamic model GUMICS-4. We find that positive (negative) Bx contributes to the magnetopause reconnection line location by moving northward (southward) and positive (negative) dipole tilt angle by moving it southward (northward). The tilt shifts the dayside load region toward the winter hemisphere and the summer cusp toward the equatorial plane. Magnetic flux hence piles effectively in the summer hemisphere leading to increased magnetopause currents that enhance the Poynting flux through the magnetopause. We find that the intensity of the energy conversion in the generators is strongly affected by the dipole tilt angle, whereas intensity in the load region is mainly affected by IMF Bx.

  2. IMF-lending programs and suicide mortality.

    PubMed

    Goulas, Eleftherios; Zervoyianni, Athina

    2016-03-01

    While the economic consequences of IMF programs have been extensively analyzed in the literature, much less is known about how key welfare indicators, including suicide-mortality rates, correlate with countries' participation in such programs. This paper examines the impact of IMF lending on suicide mortality, using data from 30 developing and transition countries that received non-concessionary IMF loans during 1991-2008. Our results support the hypothesis of a positive causal relationship between suicide mortality and participation in IMF programs but reveal no systematic suicide-increasing effect from the size of IMF loans. This holds after accounting for self-selection into programs, resulting from the endogeneity of a country's decision to resort to the IMF for funding, and after controlling for standard socio-economic influences on suicidal behaviour. In particular, we find a positive aggregate suicide-mortality differential due to IMF-program participation of between 4 and 14 percentage points. We also find that the positive association between suicides and program participation is stronger and more robust among males. Comparing age groups, individuals belonging to the age group 45-to-64 exhibit the highest increase in suicide due to program-participation, which amounts to over 18 percentage points. Overall, our results imply that when countries are exposed to IMF programs in an attempt to resolve their economic problems, social-safety nets need to be designed to protect the adversely-affected part of the population. PMID:26874823

  3. Laser clock

    NASA Astrophysics Data System (ADS)

    Facklam, R. L.

    1984-11-01

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

  4. Relation of PC index to magnetic disturbances developing under conditions of northward IMF

    NASA Astrophysics Data System (ADS)

    Podorozhkina, N.; Sormakov, D.; Troshichev, O.

    2012-04-01

    Substorms and storms occurring under conditions of northward IMF (BZN) are commonly examined as "extraordinary events" since they are developed when the efficiency of the interplanetary electric field EY = vBZS (Reiff and Luhmann, 1986) falls to zero. Examination of these events demonstrates that all of them occur, like to ordinary substorms and storms, under conditions that are necessary and sufficient for development of substorms (PC ≥ 1.5 mV/m) and storms ( >2 mV/m). The specified values of the PC index testify that the magnetosphere is affected by the intense interplanetary electric field EKL=vBTsin2θ/2 (Kan and Lee, 1979), where BT is the IMF tangential component and θ is an angle between BT component and the geomagnetic Z-axis. The principal difference between coupling functions EY and EKL lies in the fact that EKL function includes the IMF azimuthal (BY) component. As BY increases relative to BZ, the difference between electric fields EY and EKL quickly grows, and the value of EKL field can be as large as 5-10 mV/m even under conditions of northward IMF orientation, when EY reaches to zero. The same situation is valid for substorms triggered by sharp northward turning of the IMF BZ component following the prolonged period of southward IMF influence. Examination of these substorms demonstrates that they are initiated by increase of coupling function EKL and that the substorm sudden onsets were preceded by the PC index growth. Consistency between the IMF northward turning and substorm sudden onset in these cases is coincidence that explains why substorm are only occasionally initiated by the IMF northward turning. Thus, the "extraordinary" storms and substorms occurring under conditions of ineffective northward IMF component turned out to be events nothing out of the ordinary, if examining them in relation to proper coupling function (EKL) and monitoring them by the PC index.

  5. 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.

  6. Control of lunar external magnetic enhancements by IMF polarity: A case study

    NASA Astrophysics Data System (ADS)

    Nishino, Masaki N.; Fujimoto, Masaki; Tsunakawa, Hideo; Matsushima, Masaki; Shibuya, Hidetoshi; Shimizu, Hisayoshi; Takahashi, Futoshi; Saito, Yoshifumi; Yokota, Shoichiro

    2012-12-01

    We study an interaction between the solar wind and crustal magnetic fields on the lunar surface using SELENE (Kaguya) data. It has been known that magnetic enhancements are at times detected near the limb external to the lunar wake, which is thus called lunar external magnetic enhancement (LEME), as a result of direct interaction between the solar wind and lunar crustal fields. Although previous observational studies showed that LEMEs in the high solar zenith angle region favor stronger interplanetary magnetic field (IMF) and higher solar wind density, the relation between the IMF and the crustal field orientation has not been taken into account. We show evidence that the relation between the IMF and crustal field orientation is also one of the key factors that control the extent of LEME, focusing on one-day observations at 100 km altitude that include data above strong crustal fields around South Pole-Aitken (SPA) basin. Strong LEMEs are detected at 100 km altitude around SPA basin under the stronger and northward IMF condition, while they weaken under southward IMF. All LEME's peaks are located in the region where unperturbed crustal fields at 300 km altitude are directed northward while they are less related to unperturbed crustal fields at 100 km or lower, which suggests that lunar crustal fields are compressed by the solar wind dynamic pressure, and its large scale component parallel to the IMF is essential to the formation of the LEME.

  7. 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

  8. 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…

  9. 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.

  10. 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.)

  11. Magnetic substorms and northward IMF turning

    NASA Astrophysics Data System (ADS)

    Troshichev, Oleg; Podorozhkina, Nataly

    To determine the relation of the northward IMF turnings to substorm sudden onsets, we separated all events with sharp northward IMF turnings observed in years of solar maximum (1999-2002) and solar minimum (2007-2008). The events (N=261) have been classified in 5 groups in accordance with average magnetic activity in auroral zone (low, moderate or high levels of AL index) at unchanged or slightly changed PC index and with dynamics of PC (steady distinct growth or distinct decline) at arbitrary values of AL index. Statistical analysis of relationships between the IMF turning and changes of PC and AL indices has been fulfilled separately for each of 5 classes. Results of the analysis showed that, irrespective of geophysical conditions and solar activity epoch, the magnetic activity in the polar caps and in the auroral zone demonstrate no response to the sudden northward IMF turning, if the moment of northward turning is taken as a key date. Sharp increases of magnetic disturbance in the auroral zone are observed only under conditions of the growing PC index and statistically they are related to moment of the PC index exceeding the threshold level (~1.5 mV/m), not to northward turnings timed, as a rule, after the moment of sudden onset. Magnetic disturbances observed in these cases in the auroral zone (magnetic substorms) are guided by behavior of the PC index, like to ordinary magnetic substorms or substorms developed under conditions of the prolonged northward IMF impact on the magnetosphere. The evident inconsistency between the sharp IMF changes measured outside of the magnetosphere and behavior of the ground-based PC index, the latter determining the substorm development, provides an additional argument in favor of the PC index as a ground-based proxy of the solar wind energy that entered into magnetosphere.

  12. Optical atomic clocks

    NASA Astrophysics Data System (ADS)

    Ludlow, Andrew D.; Boyd, Martin M.; Ye, Jun; Peik, E.; Schmidt, P. O.

    2015-04-01

    Optical atomic clocks represent the state of the art in the frontier of modern measurement science. In this article a detailed review on the development of optical atomic clocks that are based on trapped single ions and many neutral atoms is provided. Important technical ingredients for optical clocks are discussed and measurement precision and systematic uncertainty associated with some of the best clocks to date are presented. An outlook on the exciting prospect for clock applications is given in conclusion.

  13. Classification of clock reactions.

    PubMed

    Horvth, Attila K; Nagypl, Istvn

    2015-02-23

    Autocatalytic systems are sometimes designated as clock reactions or reactions that exhibit clock behavior. To resolve the recent dispute over the term clock reaction, we describe a new approach to classify systems featuring clock behavior into three distinct groups: substrate-depletive clock reactions, autocatalysis-driven clock reactions, and systems that have pseudo clock behavior. Many of the well-known classical and recently discovered reactions can conveniently be put into these categories. We also provide a convincing argument for classifying some autocatalytic processes as clock reactions, but it does not necessarily mean that all autocatalytic processes should be classified as autocatalysis-driven clock reactions. This classification can be conveniently performed if the kinetic nature of the given system has been completely elucidated and understood. PMID:25425415

  14. IMF draping around the geotail - IMP 8 observations

    NASA Technical Reports Server (NTRS)

    Kaymaz, Zerefsan; Siscoe, George; Luhmann, Janet G.

    1992-01-01

    The draping pattern for the full range of IMF directions is mapped in the GSM yz-plane using a large data set for studying magnetic field draping around the tail. Based on the maps, it is concluded that the dominant pattern is draping as found by Ohtani and Kokubun (1991) and Sanchez and Siscoe (1990). A new finding is that the draping pattern is rotated relative to the plane formed by the IMF and the aberrated x-axis, with the degree of rotation varying from zero for strongly northward and southward IMF to a peak of 17 deg for moderately southward IMF. It is also found that the tail radius is bigger for southward IMF than for northward IMF.

  15. 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.

  16. An Observational Perspective of the IMF: Progress and Challenges

    NASA Astrophysics Data System (ADS)

    Offner, Stella

    2015-08-01

    The stellar initial mass function (IMF) is a fundamental astrophysical quantity that impacts a wide range of astrophysical problems from heavy element distribution to galactic evolution to planetary system formation. However, the origin and universality of the IMF are hotly debated both observationally and theoretically. I review recent observations of the IMF across a variety of environments. These suggest the IMF is surprisingly invariant between star-forming regions, star clusters, and spiral galaxies but that it may also vary under extreme conditions, including within the Galactic center and early type galaxies.

  17. The Pendulum Clock.

    ERIC Educational Resources Information Center

    Carlson, John E.

    1991-01-01

    The development and function of the pendulum clock is discussed from a historical perspective. Computations for the period of and forces acting on a pendulum are presented. The remarkable workmanship of early clock makers is described. (CW)

  18. 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.

  19. IMF orientation, solar wind velocity, and Pc 3-4 signals - A joint distribution

    NASA Technical Reports Server (NTRS)

    Greenstadt, E. W.; Singer, H. J.; Russell, C. T.; Olson, J. V.

    1979-01-01

    Separate studies using the same micropulsation data base in the period range 10-150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar-wind alignment of the IMF and solar-wind speed, but each correlation contained enough scatter to allow for the influence of the other factor. In this report, joint correlations of velocity and field direction with parameters representing hourly distributions rather than minima of IMF orientation angle display the relative effect of the two agents on magnetic pulsation signal levels. The joint correlations reduce the overall scatter and show that solar-wind speeds above 200-300 km/s and angles between the IMF and the sun-earth line of less than 50-60 deg are associated with enlarged magnetic pulsation amplitudes. These threshold effects tend to support both the bow-shock origin and the Kelvin-Helmholtz amplification of daytime signal transients in the Pc 3, 4 period ranges.

  20. 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.

  1. 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…

  2. 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

  3. 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

  4. 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

  5. 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.

  6. Connection between dynamically derived IMF normalisation and stellar populations

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.

    2015-04-01

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

  7. 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.

  8. Human clock genes.

    PubMed

    Piggins, Hugh D

    2002-01-01

    Rhythmic variations in physiological and behavioural processes are mediated by both endogenous and exogenous factors. Endogenous factors include self-sustaining biological pacemakers or clocks which in the absence of strong external influences self-sustain periodic rhythms in such diverse physiological and psychological processes as core body temperature, food intake, cognitive performance and mood. Clocks with endogenous periods near or at 24 h (called circadian clocks from the Latin, circa dies, meaning about one day) have been documented from prokaryotes to single cell eukaryotes to multi-cellular, complex animals such as flies, rodents and humans. Over the past few years, a revolution in the understanding of the molecular basis of these clocks has led to the identification of a number of core clock genes and their proteins, and the development of elegant feedback models to explain the molecular gears of circadian clocks. At least eight human orthologs of mouse core clock genes have been identified, and polymorphisms in two of these, hClock and hPer2, have been implicated in human sleep disorders. Remarkably, knowledge of these core clock genes and the development of sophisticated reporter systems to monitor clock gene promoter activity have led to the astonishing observation that our body is actually composed of millions of cellular clocks and oscillators whose co-ordinated activity gives rise to pronounced daily, monthly, and seasonal rhythms in physiology and behaviour. An idea that is gaining favour is that our physical and mental well-being is probably determined by the appropriate phasing of these millions of cellular clocks with recurring, meaningful events in the environment. PMID:12452483

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

    NASA Astrophysics Data System (ADS)

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

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

  10. IMF changes and polar-cap electric fields and currents

    NASA Technical Reports Server (NTRS)

    Burch, J. L.; Heelis, R. A.

    1980-01-01

    The polar cap, defined as the region of the auroral oval, is magnetically connected to the solar wind; currents may flow easily between the two regions, and polar cap electric fields and currents respond sensitively to variations in the interplanetary magnetic field (IMF). In the present paper, the response of polar cap electric field and currents to variations in IMF x, y, and z components is discussed.

  11. 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…

  12. Electronically Calibratable Clock

    NASA Technical Reports Server (NTRS)

    Davidson, J. R.; Heyman, J. S.

    1982-01-01

    Calibration circuit corrects apparent clock rate (ACR) of digital clock without altering oscillator frequency. Calibration circuit does not require iterative adjustments to reference frequency or rate, and correction to ACR is controlled by pushbuttons. Technique is applicable to any timer or counter that counts up to predetermined number then outputs a pulse to a readout register or to control another device.

  13. 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.

  14. 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

  15. 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.

  16. 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.

  17. 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

  18. Circadian Clocks and Metabolism

    PubMed Central

    Marcheva, Biliana; Ramsey, Kathryn M.; Peek, Clara B.; Affinati, Alison; Maury, Eleonore; Bass, Joseph

    2014-01-01

    Circadian clocks maintain periodicity in internal cycles of behavior, physiology, and metabolism, enabling organisms to anticipate the 24-h rotation of the Earth. In mammals, circadian integration of metabolic systems optimizes energy harvesting and utilization across the light/dark cycle. Disruption of clock genes has recently been linked to sleep disorders and to the development of cardiometabolic disease. Conversely, aberrant nutrient signaling affects circadian rhythms of behavior. This chapter reviews the emerging relationship between the molecular clock and metabolic systems and examines evidence that circadian disruption exerts deleterious consequences on human health. PMID:23604478

  19. Femtosecond optical clock

    SciTech Connect

    Bagaev, Sergei N; Denisov, Vladimir I; Zakharyash, Valerii F; Kashirsky, Aleksandr V; Klementyev, Vasilii M; Kuznetsov, Sergei A; Korel', I I; Pivtsov, V S

    2004-12-31

    New advances in the field of synthesis of optical frequencies and the development of a new generation of optical clocks are considered. The use of mode-locked femtosecond lasers and fibre emission-spectrum stretchers allows the synthesis of any frequencies (from radio-frequencies to the UV region) and drastically simplifies the structure of an optical clock. The schemes of femtosecond optical clock are presented and the application of tapered optical fibres in them is described. (optical metrology and quantum frequency standards)

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  1. 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.

  2. 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)

  3. 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)

  4. 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.

  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. Variable frequency microprocessor clock generator

    SciTech Connect

    Branson, C.N.

    1989-04-04

    A microprocessor-based system is described comprising: a digital central microprocessor provided with a clock input and having a rate of operation determined by the frequency of a clock signal input thereto; memory means operably coupled to the central microprocessor for storing programs respectively including a plurality of instructions and addressable by the central microprocessor; peripheral device operably connected to the central microprocessor, the first peripheral device being addressable by the central microprocessor for control thereby; a system clock generator for generating a digital reference clock signal having a reference frequency rate; and frequency rate reduction circuit means connected between the clock generator and the clock input of the central microprocessor for selectively dividing the reference clock signal to generate a microprocessor clock signal as an input to the central microprocessor for clocking the central microprocessor.

  7. 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.

  8. On clocks and clouds

    NASA Astrophysics Data System (ADS)

    Witte, M. K.; Chuang, P. Y.; Feingold, G.

    2014-07-01

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

  9. On clocks and clouds

    NASA Astrophysics Data System (ADS)

    Witte, M. K.; Chuang, P. Y.; Feingold, G.

    2013-09-01

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

  10. Quantum primordial standard clocks

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

    In this paper, we point out and study a generic type of signals existing in the primordial universe models, which can be used to model-independently distinguish the inflation scenario from alternatives. These signals are generated by massive fields that function as standard clocks. The role of massive fields as standard clocks has been realized in previous works. Although the existence of such massive fields is generic, the previous realizations require sharp features to classically excite the oscillations of the massive clock fields. Here, we point out that the quantum fluctuations of massive fields can actually serve the same purpose as the standard clocks. We show that they are also able to directly record the defining property of the scenario type, namely, the scale factor of the primordial universe as a function of time a(t), but through shape-dependent oscillatory features in non-Gaussianities. Since quantum fluctuating massive fields exist in any realistic primordial universe models, these quantum primordial standard clock signals are present in any inflation models, and should exist quite generally in alternative-to-inflation scenarios as well. However, the amplitude of such signals is very model-dependent.

  11. 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 (Kppen 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.

  12. On the IMF in a Triggered Star Formation Context

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  13. 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.

  14. 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.

  15. 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

  16. IMF effect on the polar cap contraction and expansion during a period of substorms

    NASA Astrophysics Data System (ADS)

    Aikio, A. T.; Pitknen, T.; Honkonen, I.; Palmroth, M.; Amm, O.

    2013-06-01

    The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase. In addition, we suggest that the IMF Bz component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further.

  17. Modern yields per stellar generation: the effect of the IMF

    NASA Astrophysics Data System (ADS)

    Vincenzo, F.; Matteucci, F.; Belfiore, F.; Maiolino, R.

    2016-02-01

    Gaseous and stellar metallicities in galaxies are nowadays routinely used to constrain the evolutionary processes in galaxies. This requires the knowledge of the average yield per stellar generation, yZ, i.e. the quantity of metals that a stellar population releases into the interstellar medium (ISM), which is generally assumed to be a fixed fiducial value. Deviations of the observed metallicity from the expected value of yZ are used to quantify the effect of outflows or inflows of gas, or even as evidence for biased metallicity calibrations or inaccurate metallicity diagnostics. Here, we show that y_{Z} depends significantly on the initial mass function (IMF), varying by up to a factor larger than three, for the range of IMFs typically adopted in various studies. Varying the upper mass cutoff of the IMF implies a further variation of yZ by an additional factor that can be larger than two. These effects, along with the variation of the gas mass fraction restored into the ISM by supernovae (R, which also depends on the IMF), may yield to deceiving results, if not properly taken into account. In particular, metallicities that are often considered unusually high can actually be explained in terms of yield associated with commonly adopted IMFs such as the Kroupa or Chabrier. We provide our results for two different sets of stellar yields (both affected by specific limitations) finding that the uncertainty introduced by this assumption can be as large as 0.2 dex. Finally, we show that yZ is not substantially affected by the initial stellar metallicity as long as Z > 10-3 Z?.

  18. The circadian clock goes genomic

    PubMed Central

    2013-01-01

    Large-scale biology among plant species, as well as comparative genomics of circadian clock architecture and clock-regulated output processes, have greatly advanced our understanding of the endogenous timing system in plants. PMID:23796230

  19. 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.

  20. Investigating the low-mass slope and possible turnover in the LMC IMF

    NASA Astrophysics Data System (ADS)

    Gennaro, Mario

    2014-10-01

    We propose to derive the Initial Mass Function (IMF) of the field population of the Large Magellanic Cloud (LMC) down to 0.2 solar masses, probing the mass regime where the characteristic IMF turnover is observed in our Galaxy. The power of the HST, using the WFC3 IR channel, is necessary to obtain photometric mass estimates for the faint, cool, dwarf stars with masses below the expected IMF turnover point. Only by probing the IMF down to such masses, it will be possible to clearly distinguish between a bottom-heavy or bottom-light IMF in the LMC. Recent studies, using the deepest available observations for the Small Magellanic Cloud, cannot find clear evidence of a turnover in the IMF for this galaxy, suggesting a bottom-heavy IMF in contrast to the Milky Way. A similar study of the LMC is needed to confirm a possible dependence of the low-mass IMF with galactic environment. Studies of giant ellipticals have recently challenged the picture of a universal IMF, and suggest an enviromental dependence of the IMF, with the most massive galaxies having a larger fraction of low mass stars and no IMF turnover. A study of possible IMF variations from resolved stellar populations in nearby galaxies is of great importance in sheding light on this issue. Our simple approach, using direct evidence from basic star counts, is much less prone to systematic errors with respect to studies of more distant objects which have to rely on the observations of integrated properties.

  1. Clock asynchrony and mass variation

    SciTech Connect

    Gruber, R.P.; Brahm, D.E.

    1993-04-01

    Many theories have been proposed in which particle masses vary with time. In a world with varying particle masses, clocks become asynchronous and metersticks inconsistent. By combining two or more clocks with different known dependences on mass, one can construct a nearly invariant clock, and measure the rate of mass variation. If the proton and electron masses vary differently, then certain equations must be applied to predict a clock's dependence on each. 8 refs.

  2. 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.

  3. Cultivated tomato clock runs slow.

    PubMed

    Kay, Steve A; Remigereau, Marie-Stanislas

    2015-12-29

    The plant circadian clock is a complex network of genes crucial for plant survival. A new study finds that domestication gradually slowed down the circadian clock of tomato via selection on two major genes-one that delayed phasing of the clock with daylight, whereas the other induced a longer period. PMID:26711110

  4. Iron around the clock.

    PubMed

    Tissot, Nicolas; Przybyla-Toscano, Jonathan; Reyt, Guilhem; Castel, Baptiste; Duc, Cline; Boucherez, Jossia; Gaymard, Frdric; Briat, Jean-Franois; 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

  5. 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

  6. 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

  7. 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…

  8. 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…

  9. 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

  10. Auroral Asymmetries in the Conjugate Hemispheres During Strong IMF Bx

    NASA Astrophysics Data System (ADS)

    Laundal, K.; Ostgaard, N.

    2008-12-01

    Simultaneous UV images of the conjugate aurora, taken from the IMAGE and Polar spacecraft reveal prominent differences between the two hemispheres. During a period of 1.5 hours of continuous measurements, we observe: 1) An intense arc in the dusk sector which extends further towards midnight in the southern hemisphere than in the northern hemisphere, 2) A much more severe poleward expansion in the southern hemisphere during a substorm growth phase, and 3) An asymmetric intensity distribution, with the most intense aurora at dusk in the southern hemisphere, and at dawn in the northern hemisphere. Throughout this period, the IMF was stable, with Bz negative (?-4 nT), By slowly increasing from ?-2 to ? 2 nT, and Bx positive (? 10 nT). Previous studies suggest that penetration of positive IMF Bx into the magnetosphere may explain at least part of the observations presented here.

  11. Photic resetting and entrainment in CLOCK-deficient mice.

    PubMed

    Dallmann, Robert; DeBruyne, Jason P; Weaver, David R

    2011-10-01

    Mice lacking the CLOCK protein have a relatively subtle circadian phenotype, including a slightly shorter period in constant darkness, differences in phase resetting after 4-hour light pulses in the early and late night, and a variably advanced phase angle of entrainment in a light-dark (LD) cycle. The present series of experiments was conducted to more fully characterize the circadian phenotype of Clock(-/-) mice under various lighting conditions. A phase-response curve (PRC) to 4-hour light pulses in free-running mice was conducted; the results confirm that Clock(-/-) mice exhibit very large phase advances after 4-hour light pulses in the late subjective night but have relatively normal responses to light at other phases. The abnormal shape of the PRC to light may explain the tendency of CLOCK-deficient mice to begin activity before lights-out when housed in a 12-hour light:12-hour dark lighting schedule. To assess this relationship further, Clock(-/-) and wild-type control mice were entrained to skeleton lighting cycles (1L:23D and 1L:10D:1L:12D). Comparing entrainment under the 2 types of skeleton photoperiods revealed that exposure to 1-hour light in the morning leads to a phase advance of activity onset (expressed the following afternoon) in Clock(-/-) mice but not in the controls. Constant light typically causes an intensity-dependent increase in circadian period in mice, but this did not occur in CLOCK-deficient mice. The failure of Clock(-/-) mice to respond to the period-lengthening effect of constant light likely results from the increased functional impact of light falling in the phase advance zone of the PRC. Collectively, these experiments reveal that alterations in the response of CLOCK-deficient mice to light in several paradigms are likely due to an imbalance in the shape of the PRC to light. PMID:21921293

  12. 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.

  13. 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.

  14. 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.

  15. Pulsed Red-aurora Transients and Boundary Layer Modulation During Imf Bz~0 and Large Imf By Conditions.

    NASA Astrophysics Data System (ADS)

    Massetti, S.; Orsini, S.; Candidi, M.; Kauristie, K.; de Angelis, E.; Milillo, A.; Mura, A.

    Dayside recurrent red-aurora activity, recorded between 76 and 78 invariant latitude from Ny-Ålesund, during the November 30, 1999, exhibits a short (5 min) and long- term (20-25 min) modulation that seems to be not directly associable to solar wind variations ahead the bow-shock. A similar behaviour has been reported by analysing high latitude magnetograms data. The phenomena seem to be associated with the par- ticular IMF configuration present during the events, characterised by a large By com- ponent (≈10 nT) and Bz close to zero. Magnetic reconnection occurring at the dayside magnetopause during this IMF configuration, could drive the LLBL insta- ble and induce short and/or long-period modulation in the magnetosphere-ionosphere coupling. This work compare optical auroral observations with satellite, ionospheric radar and magnetograms data.

  16. Clocks in algae.

    PubMed

    Noordally, Zeenat B; Millar, Andrew J

    2015-01-20

    As major contributors to global oxygen levels and producers of fatty acids, carotenoids, sterols, and phycocolloids, algae have significant ecological and commercial roles. Early algal models have contributed much to our understanding of circadian clocks at physiological and biochemical levels. The genetic and molecular approaches that identified clock components in other taxa have not been as widely applied to algae. We review results from seven species: the chlorophytes Chlamydomonas reinhardtii, Ostreococcus tauri, and Acetabularia spp.; the dinoflagellates Lingulodinium polyedrum and Symbiodinium spp.; the euglenozoa Euglena gracilis; and the red alga Cyanidioschyzon merolae. The relative simplicity, experimental tractability, and ecological and evolutionary diversity of algal systems may now make them particularly useful in integrating quantitative data from "omic" technologies (e.g., genomics, transcriptomics, metabolomics, and proteomics) with computational and mathematical methods. PMID:25379817

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  18. Foucault pendulum ``wall clock''

    NASA Astrophysics Data System (ADS)

    Crane, H. Richard

    1995-01-01

    Details are given for the construction of a 70-cm-long Foucault pendulum to be mounted on the wall, and for a simple modification that will make it display local clock time. The possibility of having a Foucault pendulum of such short length is the result of finding new or improved ways of reducing four perturbing effects that become more severe as the length is decreased. They relate to: precession due to ellipticity in the motion, the drive system for maintaining the amplitude, the means of limiting the growth of ellipticity, and the method of gripping the suspending wire at the top. With those improvements, successful Foucault operation was attained in pendulums as short as 15 cm, support to center of bob. Following that severe test, the length for the ``wall clock'' was set at a conservative 70 cm. At that length it is highly reliable, and accurate to within 2% when timed for the full revolution. Uniformity in rate when comparing different intervals of azimuth is of course less. A simple method of making the pendulum read local time is described. Two clocks, one in the author's office and one at home, have been in continuous operation for more than ten years.

  19. 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.

  20. 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

  1. Circadian Clocks in the Ovary

    PubMed Central

    Sellix, Michael T.; Menaker, Michael

    2010-01-01

    Clock gene expression has been observed in tissues of the hypothalamic-pituitary-gonadal (HPG) axis. While the contribution of hypothalamic oscillators to the timing of reproductive biology is well known, the role of peripheral oscillators like those in the ovary is less clear. Circadian clocks in the ovary may play a role in the timing of ovulation. Disruption of the clock in ovarian cells or desynchrony between ovarian clocks and circadian oscillators elsewhere in the body may contribute to the onset and progression of various reproductive pathologies. Here we review evidence for clock function in the ovary across multiple species and offer a novel perspective on the role of this clock in normal ovarian physiology and in diseases that negatively impact fertility. PMID:20599392

  2. The configuration of the auroral distribution for interplanetary magnetic field B sub z northward. 1. IMF B sub x and B sub y dependencies as observed by the Viking satellite

    SciTech Connect

    Eliphinstone, R.D.; Jankowska, K.; Murphree, J.S.; Cogger, L.L. )

    1990-05-01

    Viking images obtained throughout 1986 have been utilized in combination with IMP 8 satellite measurements of the interplanetary magnetic fields (IMF) to determine typical northern hemisphere auroral distributions for a variety of IMF B{sub z} positive conditions. Varying B{sub y} has an effect which is consistent with expected results. That is, B{sub y} positive implies high-latitude auroral arcs in the dusk sector while negative B{sub y} gives dawn sector polar arcs. A new result gives significant importance to the B{sub x} component of the IMF. B{sub x} toward the Sun (B{sub y} = 0) gives polar arcs on both dawn and dusk with comparatively weak UV emissions. With B{sub x} away from the Sun (B{sub y} = 0) a single Sun-aligned morning sector polar arc dominates the auroral distribution. Azimuthal angle changes to the IMF of only 45{degree} seem to affect the global auroral distribution with time scales of less than 2-3 hours. Poleward boundaries of the aurora were found to have a strong dependence on the IMF azimuthal angle which varied according to the magnetic local time investigated.

  3. Huygens synchronization of two clocks.

    PubMed

    Oliveira, Henrique M; Melo, Lus 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

  4. 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

  5. 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.

  6. 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.

  7. Optical atomic clocks and metrology

    NASA Astrophysics Data System (ADS)

    Ludlow, Andrew

    2014-05-01

    The atomic clock has long demonstrated the capability to measure time or frequency with very high precision. Consequently, these clocks are used extensively in technological applications such as advanced synchronization or communication and navigation networks. Optical atomic clocks are next- generation timekeepers which reference narrowband optical transitions between suitable atomic states. Many optical time/frequency standards utilize state-of-the-art quantum control and precision measurement. Combined with the ultrahigh quality factors of the atomic resonances at their heart, optical atomic clocks have promised new levels of timekeeping precision, orders of magnitude higher than conventional atomic clocks based on microwave transitions. Such measurement capability enables and/or enhances many of the most exciting applications of these clocks, including the study of fundamental laws of physics through the measurement of time evolution. Here, I will highlight optical atomic clocks and their utility, as well as review recent advances in their development and performance. In particular, I will describe in detail the optical lattice clock and the realization of frequency measurement at the level of one part in 1018. To push the performance of these atomic timekeepers to such a level and beyond, several key advances are being explored worldwide. These will be discussed generally, with particular emphasis on our recent efforts at NIST in developing the optical lattice clock based on atomic ytterbium.

  8. IMF sector behavior estimated from geomagnetic data at South Pole

    SciTech Connect

    Matsushita, S.; Xu, W.h.

    1981-05-01

    IMF sector behavior which has previously been estimated from the geomagnetic data at Godhavn is confirmed by study of the data at South Pole for 1959--1970 with the same estimation technique, taking the difference between northern and southern hemispheres into consideration. A method to improve (about 18%) the agreement between assigned and actual sector structures by study of the data at the two stations is suggested. Geomagnetic disturbance effects on sector estimation are discussed, and reversed sector effects in winter are given special emphasis.

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

    ERIC Educational Resources Information Center

    West, Joseph

    2007-01-01

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

  10. 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

  11. Digital processing clock

    NASA Technical Reports Server (NTRS)

    Phillips, D. H.

    1982-01-01

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

  12. Clocks and cardiovascular function

    PubMed Central

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

    2016-01-01

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

  13. Quartz Crystal Clocks

    NASA Technical Reports Server (NTRS)

    1976-01-01

    General Time Corporation, under contract to NASA, developed a quartz crystal for obtaining a stable time base from which all mission times could be derived. This later became basis of consumer clocks and watches with accuracy of one minute a year, watches useful in timing sports events as well as general use. When quartz is electrically stimulated it can vibrate millions of times a second. Since timepieces use a vibrating body to keep up time, incredibly fast vibration of a quartz crystal--up to 4,194,304 beats a second opened a new horizon in accuracy.

  14. Biological switches and clocks

    PubMed Central

    Tyson, John J.; Albert, Reka; Goldbeter, Albert; Ruoff, Peter; Sible, Jill

    2008-01-01

    To introduce this special issue on biological switches and clocks, we review the historical development of mathematical models of bistability and oscillations in chemical reaction networks. In the 1960s and 1970s, these models were limited to well-studied biochemical examples, such as glycolytic oscillations and cyclic AMP signalling. After the molecular genetics revolution of the 1980s, the field of molecular cell biology was thrown wide open to mathematical modellers. We review recent advances in modelling the geneprotein interaction networks that control circadian rhythms, cell cycle progression, signal processing and the design of synthetic gene networks. PMID:18522926

  15. 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.

  16. The Mechanism of the Formaldehyde Clock Reaction.

    ERIC Educational Resources Information Center

    Burnett, M. G.

    1982-01-01

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

  17. 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)

  18. The SFR and IMF of the galactic disk

    NASA Astrophysics Data System (ADS)

    Just, Andreas

    2003-04-01

    There is a long term dynamical heating of stellar populations with age observed in the age velocity dispersion relation (AVR). This effect allows a determination of the star formation history SFR(t) from local kinematical data of main sequence stars. Using a self-consistent disk model for the vertical structure of the disk, we find from the kinematics of the stars in the solar neighbourhood that the SFR shows a moderate star burst about 10 Gyr ago followed by a continuous decline to the present day value consistent with the observed number of OB stars. The gravitational potential of the gas component and of the Dark Matter Halo is included and the effect of chemical enrichment, finite lifetime of the stars and mass loss of the stellar component are taken into account. The scale heights for main sequence stars together with the SFR is then used to determine constistently the IMF from the observed local luminosity function. The main new result is that the power law break in the present day mass function (PDMF) around 1 M ? is entirely due to evolutionary effects of the disk and does not appear in the IMF.

  19. How IMF Bx affects the two polar hemispheres differently

    NASA Astrophysics Data System (ADS)

    Reistad, Jone Peter; stgaard, Nikolai; Magnus Laundal, Karl; Oksavik, Kjellmar

    2013-04-01

    From studying the aurora in both hemispheres simultaneously, mechanisms responsible for producing asymmetric aurora have earlier been identified. One such mechanism believed to be responsible for large-scale asymmetries on auroral brightness between the hemispheres is the solar wind dynamo (E ? j < 0). In the presence of a significant Bx-component in the interplanetary magnetic field during Bz negative, the solar wind dynamo is suggested to be more prominent in one hemisphere compared to the other. By utilizing the large IMAGE WIC database of global imaging of the aurora from the Northern Hemisphere, we derive patterns of auroral intensities for a) when the efficiency of this mechanism is believed to be important compared to other mechanisms, and b) during similar conditions when the efficiency of the solar wind dynamo is believed to be important in the opposite (southern) hemisphere. First results indicate a distinct difference in intensity between the two cases. In order to investigate the expected similar effect in the Southern Hemisphere, a similar analysis on the much smaller dataset from the Polar VIS Earth camera will be conducted. In the Southern Hemisphere we expect to see the same IMF Bx intensity dependence but for opposite sign of IMF Bx. Also, MHD simulations of the magnetosphere system might be utilized to further investigate any asymmetric flow speeds between the northern and southern magnetosheaths expected from the suggested asymmetric dynamo action.

  20. The circadian clock and asthma.

    PubMed

    Durrington, Hannah J; Farrow, Stuart N; Loudon, Andrew S; Ray, David W

    2014-01-01

    It is characteristic of asthma that symptoms worsen overnight, particularly in the early hours of the morning. Nocturnal symptoms in asthma are common and are an important indicator for escalation of treatment. An extensive body of research has demonstrated that nocturnal symptoms of cough and dyspnea are accompanied by circadian variations in airway inflammation and physiologic variables, including airflow limitation and airways hyper-responsiveness. The molecular apparatus that underpins circadian variations, controlled by so called 'clock' genes, has recently been characterised. Clock genes control circadian rhythms both centrally, in the suprachiasmatic nucleus of the brain and peripherally, within every organ of the body. Here, we will discuss how clock genes regulate circadian rhythms. We will focus particularly on the peripheral lung clock and the peripheral immune clock and discuss how these might relate to both the pathogenesis and treatment of asthma. PMID:23704227

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  2. Dependence of Large-Scale Global Poynting Flux on IMF By Polarity Change

    NASA Astrophysics Data System (ADS)

    Humberset, B. K.; Gjerloev, J. W.

    2014-12-01

    In this study we present the dependence of the global Poynting flux on the IMF By polarity change. The amount of energy that enters the magnetosphere from the solar wind is a function of the solar wind speed and pressure and the IMF orientation and magnitude. All the various published coupling models show that the polarity of the IMF By component does not change the energy input. In contrast the global convection patterns, and thus the ionospheric Pedersen currents, depend on IMF By polarity. This seems to imply that the ionospheric energy deposition is a function of IMF By polarity. Thus, there appear to be a fundamental difference between the input (from the solar wind) and the output (energy dissipating Pedersen currents). We, therefore, ask the question: To what extend is the global Poynting flux dependent on the IMF By polarity? We have performed a statistical study evaluating 59 abrupt transitions in the IMF By component (polarity changes) as measured by the ACE spacecraft. The effect of other solar wind coupling parameters, such as the IMF Bz component, are minimized by selecting events where these are nearly constant. We use electric field distributions from SuperDARN and field-aligned current distributions from AMPERE to calculate the global distribution of the Poynting Flux. To minimize the effect of magnetospheric energy unloading we focus on the 06-18 MLT region. We further investigate the dependence on solar induced conductivity. We find that the Poynting flux is slightly larger for positive IMF By compared to negative By conditions. For a low conductivity (not sunlit) ionosphere the Poynting flux is smaller than in the high conductivity (sunlit) ionosphere and we find a smaller dependence on IMF By polarity. The study emphasizes the global dynamic behavior of the ionosphere in its response to changes in the external driver (IMF).

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

    NASA Astrophysics Data System (ADS)

    Hocuk, S.; Cazaux, S.; Spaans, M.; Caselli, P.

    2016-03-01

    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 as also indicated in Hocuk, Cazaux & Spaans, but to a lesser degree because of a different dust temperature treatment, which is more accurate for cloud cores. 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 per cent) between the three models. While the stellar mass distribution results in a different IMF when we consider pure freeze-out, with the complete treatment of the GSC, the divergence from a pure gas-phase model is minimal. We find that the impact of freeze-out is balanced by the non-thermal processes; chemical and photodesorption. We also find an average filament width of 0.12 pc (±0.03 pc), and speculate that this may be a result from the changes in the EOS caused by the gas-dust thermal coupling. We conclude that GSC plays a big role in the chemical composition of molecular clouds and that surface processes are needed to accurately interpret observations, however, that GSC does not have a significant impact as far as star formation and the IMF is concerned.

  4. A Superfluid Clock

    NASA Technical Reports Server (NTRS)

    Penanen, Konstantin

    2004-01-01

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

  5. A microfabricated atomic clock

    SciTech Connect

    Knappe, Svenja; Shah, Vishal; Schwindt, Peter D.D.; Hollberg, Leo; Kitching, John; Liew, Li-Anne; Moreland, John

    2004-08-30

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

  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. 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.

  8. Response of the Magnetosphere-Ionosphere system to a sudden southward turning of IMF

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Ridley, A.

    2008-05-01

    A sudden southward turning of IMF is simulated by the University of Michigan BATSRUS model. After the northward to southward transition of IMF at a solar wind speed of 400km/s encounters the bow shock, it takes about 6 minutes to propagate to the magnetopause, eating up the northward IMF inside the magnetosheath and excites the dayside reconnection. The ionospheric response to this sudden southward IMF transition is delayed by another ~4 minutes, during which, conversions from the cusp reconnection to dayside reconnection and Alf'ven wave propagation take place, carrying dayside plasma down to the Earth; thereafter changes in the ionosphere and ground magnetic perturbations associated with the southward IMF are observed. These responses appear to be globally onset. The time it takes from the bow shock hitness to the ionospheric reaction varies with the solar wind speed.

  9. 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 earths 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.

  10. Accelerated magnetosheath flows caused by IMF draping: Dependence on latitude

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Farrugia, C. J.; Mezentsev, A. V.; Torbert, R. B.; Biernat, H. K.

    2012-01-01

    In previous work we used a semi-analytical treatment to describe accelerated magnetosheath flows caused by the draping of interplanetary magnetic field (IMF) lines around the magnetosphere. Here, we use the same approach, i.e., modeling the magnetic field lines as elastic strings, to examine how the magnetic tension force, one of the two agents responsible for producing these flows, varies along field lines away from the equatorial plane. The bend in the field line caused by the draping mechanism propagates as two oppositely-directed waves to higher latitudes. For a due northward IMF - the case we consider here - these propagate symmetrically north/south of the equatorial plane. As a result, a two-peaked latitude velocity profile develops as we go further downtail and the velocity peaks migrate along the magnetic field line to higher latitudes. We examine this velocity-profile for two Alfvn Mach numbers (MA = 8 and 3), representative of conditions in the solar wind at 1 AU (normal solar wind and solar transients). Qualitatively, the picture is the same but quantitatively there are important differences: (i) the flows reach higher values for the lower MA (maximum V/VSW = 1.6) than for the higher MA (V/VSW = 1.3); (ii) asymptotic values are reached farther downstream of the dawn-dusk terminator for the lower MA (-50 RE vs -15 RE); (iii) For the lower MA the highest speeds are reached away from the equatorial plane. We predict two channels of fast magnetosheath flow next to the magnetopause at off-equatorial latitudes that exceed the solar wind speed.

  11. A quantum network of clocks

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  12. The Cyanobacterial Clock and Metabolism

    PubMed Central

    Pattanayak, Gopal; Rust, Michael J.

    2014-01-01

    Cyanobacteria possess the simplest known circadian clock, which presents a unique opportunity to study how rhythms are generated and how input signals from the environment reset the clock time. The kaiABC locus forms the core of the oscillator, and the remarkable ability to reconstitute oscillations using purified KaiABC proteins has allowed researchers to study mechanism using the tools of quantitative biochemistry. Autotrophic cyanobacteria experience major shifts in metabolism following a light-dark transition, and recent work suggests that input mechanisms that couple the day-night cycle to the clock involve energy and redox metabolites acting directly on clock proteins. We offer a summary of the current state of knowledge in this system and present a perspective for future lines of investigation. PMID:24667330

  13. Quantum clock synchronization: Multiparty protocol

    NASA Astrophysics Data System (ADS)

    Kr?o, Marko; Paul, Prabasaj

    2002-08-01

    We present a multiparty quantum clock synchronization protocol that utilizes shared prior entanglement and broadcast of classical information to synchronize spatially separated clocks. Notably, it is necessary only for any one party to publish classical information. Consequently, the efficacy of the method is independent of the relative location of the parties. The suggested protocol is robust and does not require precise sequencing of procedural steps.

  14. 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

  15. Application of IMF screws to assist internal rigid fixation of jaw fractures: our experiences of 168 cases

    PubMed Central

    Bai, Zhenxi; Gao, Zhibiao; Xiao, Xia; Zhang, Wenjuan; Fan, Xing; Wang, Zhaoling

    2015-01-01

    Intermaxillary fixation (IMF) screws were first introduced to achieve IMF as a kind of bone borne appliance for jaw fractures in 1989. Because this method can overcome many disadvantages associated with tooth borne appliance, IMF screws have been popularly used for jaw fractures since then. From March 2011 to February 2014, we treated 168 cases with single or multiple jaw fractures by open reduction and a total of 705 IMF screws were intraoperatively applied in all the cases to achieve IMF and maintain dental occlusion as an adjuvant to open reduction. The numbers, implantation sites and complications of IMF screws were retrospectively analyzed. In our experience, we found that IMF screws were important to assist open reduction of jaw fractures but their roles should be objectively assessed and the reliability of open reduction and internal rigid fixation must be emphasized. Much attention should be paid when implanting. PMID:26617892

  16. Comparison of LFM Simulation Results with Observation for Strongly Northward IMF

    NASA Astrophysics Data System (ADS)

    Bhattarai, S. K.; Lopez, R. E.; Bruntz, R. J.

    2011-12-01

    The dynamics involved in solar wind magnetosphere coupling when interplanetary magnetic field (IMF) is northward is still poorly understood. When IMF is northward the coupling occurs at high latitude poleward of the cusp region. One of the methods of measuring this coupling is to calculate the polar cap potential (PCP). PCP is the difference between the maximum and minimum potential in the polar cap region. In this paper we show results obtained from Lyon Feeder Mobbary (LFM) simulation as well as satellite observation showing saturation of polar cap potential for strongly northward IMF. Furthermore, we compare the overall magnetosphere geometry obtained from ideal LFM simulation result with various satellite data during similar conditions of strongly northward IMF.

  17. Why brown dwarfs are special . Arguments from IMF theory vs. observations

    NASA Astrophysics Data System (ADS)

    Thies, I.; Pflamm-Altenburg, J.; Kroupa, P.

    The lower end of the stellar initial mass function (IMF) is the topic of an ongoing debate. Among the most popular myths is the assumption of a continuous fall off from stars to brown dwarfs in both the IMF itself and the binary statistics of stars and BDs. However, recent analytical star-formation models by Hennebelle & Chabrier (2008) or Padoan & Nordlund (2002) could model the stellar part quite well while failing to reproduce the substellar region satisfactorily. We show that the deviation of these model IMFs to the observed ones is essentially just the IMF of the separate substellar population introduced in Thies & Kroupa (2007) and later confirmed numerically in Thies et al. (2010). In addition, new estimates to the binarity and companion mass-ratio distribution resulting directly from the two-population model are presented.

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

    NASA Astrophysics Data System (ADS)

    Martn-Navarro, Ignacio; Vazdekis, Alexandre; La Barbera, Francesco; Falcn-Barroso, Jess; Lyubenova, Mariya; van de Ven, Glenn; Ferreras, Ignacio; Snchez, S. F.; Trager, S. C.; Garca-Benito, R.; Mast, D.; Mendoza, M. A.; Snchez-Blzquez, P.; Gonzlez Delgado, R.; Walcher, C. J.; The CALIFA Team

    2015-06-01

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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. Massive Elliptical Galaxies: BH Scouring or a Bottom-Heavy IMF?

    NASA Astrophysics Data System (ADS)

    Thomas, Jens; Saglia, Roberto; Bender, Ralf; Erwin, Peter; Fabricius, Maximilian

    2015-04-01

    We present indirect constraints on the stellar initial-mass-function (IMF) in nine massive elliptical galaxies with ? ~ 300 km/s, via a comparison of dynamical and stellar-population based stellar masses. We use adaptive-optics assisted, high resolution kinematical data from the SINFONI Search for Supermassive Black Holes that allow us to constrain the dynamical stellar mass-to-light ratio in the very centre of each galaxy. Hence we measure the IMF in a galaxy region where the stellar mass dominates over dark matter, minimising any potential degeneracy between the two mass components. In six of our galaxies - those which have depleted stellar cores - we find an IMF consistent with the one measured in the Milky-Way via direct star counts. The three remaining, power-law galaxies have instead stellar masses about a factor of two times larger than expected from a Milky-Way type IMF, indicating either a more bottom-heavy IMF (like, e.g., the Salpeter IMF) or a dark-matter distribution that is degenerate with the stellar mass down to the very centres of these galaxies. The bottom-light IMF in our core galaxies is surprising in view of previous studies that suggested a systematic IMF variation where early-type galaxies with ? ~ 300 km/s have a Salpeter or even more dwarf-dominated IMF. Core galaxies are particularly important since their unique central orbital structure offers an independent crosscheck for the dynamical models. Our models with a bottom-light IMF are consistent with the distribution of orbits predicted by SMBH-binary core-formation models. This indicates that spatially well resolved central kinematical data are important for determining unbiased dynamical stellar mass-to-light ratios. Our results imply either that the IMF in massive galaxies varies over a wider range than previously anticipated, and is not the same in core and power-law ellipticals, or else that there are systematic variations in the distribution of dark matter among massive early-type galaxies.

  4. 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, δIMF (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 δIMF 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 δIMF is consistent with a Chabrier-like normalization ({δ _IMF}˜ 1), with {f_DM}˜ 0.35. One of the main results of this work is that for at least a few systems the δIMF are heavier than the Milky Way-like value (i.e. either top- or bottom-heavy). When introducing tangential anisotropy, larger δIMF and smaller fDM are derived. Adopting a steeper concentration-mass relation than that from simulations, we find lower δIMF ( ≲ 1) and larger fDM. A constant M/L profile with null fDM gives the heaviest δIMF (˜2). In the MONDian framework, we find consistent results to those for our reference NFW model. If confirmed, the large scatter of δIMF 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-σe (˜ 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

  10. 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.

  11. 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

  12. 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

  13. 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…

  14. 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.

  15. Quasars as very-accurate clock synchronizers

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  16. 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 10dB of squeezing in large ensembles within a few microseconds and without degrading the subsequent clock interrogation. PMID:24679291

  17. 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.

  18. 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...

  19. 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...

  20. 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...

  1. 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...

  2. 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...

  3. Clock Drawing in Developmental Dyslexia.

    ERIC Educational Resources Information Center

    Eden, Guinevere F.; Wood, Frank B.; Stein, John F.

    2003-01-01

    A study involving 93 children (ages 10-12), 295 with poor reading skills, found many children with dyslexia and some garden-variety poor readers showed significant left neglect on the Clock Drawing Test. In poor readers with dyslexia, spatial construction deficits were observed like those of parents with acquired right-hemisphere lesions.…

  4. Biological Clocks: Riding the Tides

    PubMed Central

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

    2015-01-01

    Animals with habitats in the intertidal zone often display biological rhythms that coordinate with both the tidal and the daily environmental cycles. Two recent studies show that the molecular components of the biological clocks mediating tidal rhythms are likely different from the phylogenetically conserved components that mediate circadian (daily) rhythms. PMID:24156810

  5. [Circadian clock disruption and diabetes mellitus].

    PubMed

    Ando, Hitoshi; Fujimura, Akio

    2013-12-01

    Recent studies have demonstrated relationships between the dysfunction of circadian clocks and the development of obesity and type 2 diabetes. In humans, both shift work and the genetic variations of clock genes increase the risk of these disorders. In mice, the light conditions which induce chronic jet lag and modifications of the clock genes cause obesity and/or type 2 diabetes. Moreover, circadian clocks in peripheral tissues are impaired in both patients with type 2 diabetes and genetically obese diabetic mice. Therefore, circadian clocks are important new therapeutic targets for preventing and treating obesity and type 2 diabetes. PMID:24437264

  6. Molecular Mechanisms Underlying the Arabidopsis Circadian Clock

    PubMed Central

    Nakamichi, Norihito

    2011-01-01

    A wide range of biological processes exhibit circadian rhythm, enabling plants to adapt to the environmental day–night cycle. This rhythm is generated by the so-called ‘circadian clock’. Although a number of genetic approaches have identified >25 clock-associated genes involved in the Arabidopsis clock mechanism, the molecular functions of a large part of these genes are not known. Recent comprehensive studies have revealed the molecular functions of several key clock-associated proteins. This progress has provided mechanistic insights into how key clock-associated proteins are integrated, and may help in understanding the essence of the clock's molecular mechanisms. PMID:21873329

  7. 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.

  8. 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.

  9. 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.

  10. Why two clocks synchronize: Energy balance of the synchronized clocks

    NASA Astrophysics Data System (ADS)

    Czołczyński, Krzysztof; Perlikowski, Przemysław; Stefański, Andrzej; Kapitaniak, Tomasz

    2011-06-01

    We consider the synchronization of two clocks which are accurate (show the same time) but have pendulums with different masses. We show that such clocks hanging on the same beam beside the complete (in-phase) and antiphase synchronizations perform the third type of synchronization in which the difference of the pendulums' displacements is a periodic function of time. We identify this period to be a few times larger than the period of pendulums' oscillations in the case when the beam is at rest. Our approximate analytical analysis allows to derive the synchronizations conditions, explains the observed types of synchronizations, and gives the approximate formula for both the pendulums' amplitudes and the phase shift between them. We consider the energy balance in the system and show how the energy is transferred between pendulums via oscillating beam allowing pendulums' synchronization.

  11. 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

  12. Solar Wind and IMF Control of the Recovery Phase of Substorms

    NASA Astrophysics Data System (ADS)

    Bryant, C. R.; Murphree, J. S.; Weygand, J.; Mende, S. B.; Donovan, E. F.

    2007-12-01

    The IMF and solar wind dynamic pressure can affect the onset location and phenomenon such as transpolar arcs and the overall substorm process. It is unclear, however, if the IMF, solar wind density and/or dynamic pressure have any effect on the substorm recovery phase. Using the IMAGE FUV WIC and SI-12 instruments a selection of 138 isolated substorms was determined. Using Weimer-mapped ACE IMF and solar wind measurements, the controlling effect on various aspects of the recovery phase global auroral evolution are examined. In particular, the effect of IMF By component is of interest due to its significant effect on transpolar arcs and onset location. The results clearly show that there is no significant effect of the IMF on the recovery phase. There is a tendency for the solar wind density and dynamic pressure to effect the recovery phase process as manifested in the global aurora. In particular, the proton aurora as measured with the SI-12 instrument is more heavily influenced by the density and pressure than the largely electron aurora measured with the WIC instrument.

  13. 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 σ⋆ ≡ 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 (ρ) = -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.

  14. Upstream energetic ions under radial IMF - A critical test of the Fermi model

    NASA Technical Reports Server (NTRS)

    Sarris, E. T.; Krimigis, S. M.

    1988-01-01

    Eight years of interplanetary magnetic field (IMF) and energetic particle observations obtained by the IMP-8 spacecraft upstream from the bow shock have been surveyed, and 63 cases when the upstream IMF remained radial for extended periods of time (greater than 1 hour) have been accumulated. Of these, two cases have been selected during which measurable fluxes of ambient solar or corotating energetic particle events were absent. These conditions provide an excellent test to the theories of the origin of upstream energetic ions. It is shown that there are extended periods with radial IMF when no upstream energetic ions were detected. It is further shown that energetic ions in the range E of between 50 keV and 1 MeV, inclusive, are not continuously present but appear in bursts of intensities varying by more than an order of magnitude under persistently radial IMF. These measurements contradict a fundamental prediction of the Fermi mechanism for the origin of the upstream energetic ions, namely that such ions should always be present on radial IMF lines. The observations are consistent with the hypothesis that energetic (greater than about 50 keV) ions leak out from, and appear in the upstream medium sporadically, following the onset of magnetic activity within the magnetosphere.

  15. 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.

  16. 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.

  17. 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.

  18. An epigenetic clock controls aging.

    PubMed

    Mitteldorf, Josh

    2016-02-01

    We are accustomed to treating aging as a set of things that go wrong with the body. But for more than twenty years, there has been accumulating evidence that much of the process takes place under genetic control. We have seen that signaling chemistry can make dramatic differences in life span, and that single molecules can significantly affect longevity. We are frequently confronted with puzzling choices the body makes which benefit neither present health nor fertility nor long-term survival. If we permit ourselves a shift of reference frame and regard aging as a programmed biological function like growth and development, then these observations fall into place and make sense. This perspective suggests that aging proceeds under control of a master clock, or several redundant clocks. If this is so, we may learn to reset the clocks with biochemical interventions and make an old body behave like a young body, including repair of many of the modes of damage that we are accustomed to regard as independent symptoms of the senescent phenotype, and for which we have assumed that the body has no remedy. PMID:26608516

  19. High-Latitude Ionospheric Dynamics During Conditions of Northward IMF. Final report

    SciTech Connect

    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.

  20. Future Laser-Cooled Microwave Clock Performance

    NASA Technical Reports Server (NTRS)

    Gibble, Kurt

    1997-01-01

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

  1. 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.

  2. The Circadian Clock Coordinates Ribosome Biogenesis

    PubMed Central

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

    2013-01-01

    Biological rhythms play a fundamental role in the physiology and behavior of most living organisms. Rhythmic circadian expression of clock-controlled genes is orchestrated by a molecular clock that relies on interconnected negative feedback loops of transcription regulators. Here we show that the circadian clock exerts its function also through the regulation of mRNA translation. Namely, the circadian clock influences the temporal translation of a subset of mRNAs involved in ribosome biogenesis by controlling the transcription of translation initiation factors as well as the clock-dependent rhythmic activation of signaling pathways involved in their regulation. Moreover, the circadian oscillator directly regulates the transcription of ribosomal protein mRNAs and ribosomal RNAs. Thus the circadian clock exerts a major role in coordinating transcription and translation steps underlying ribosome biogenesis. PMID:23300384

  3. Clock genes control cortical critical period timing.

    PubMed

    Kobayashi, Yohei; Ye, Zhanlei; Hensch, Takao K

    2015-04-01

    Circadian rhythms control a variety of physiological processes, but whether they may also time brain development remains largely unknown. Here, we show that circadian clock genes control the onset of critical period plasticity in the neocortex. Within visual cortex of Clock-deficient mice, the emergence of circadian gene expression was dampened, and the maturation of inhibitory parvalbumin (PV) cell networks slowed. Loss of visual acuity in response to brief monocular deprivation was concomitantly delayed and rescued by direct enhancement of GABAergic transmission. Conditional deletion of Clock or Bmal1 only within PV cells recapitulated the results of total Clock-deficient mice. Unique downstream gene sets controlling synaptic events and cellular homeostasis for proper maturation and maintenance were found to be mis-regulated by Clock deletion specifically within PV cells. These data demonstrate a developmental role for circadian clock genes outside the suprachiasmatic nucleus, which may contribute mis-timed brain plasticity in associated mental disorders. PMID:25801703

  4. Mechanism of the circadian clock in physiology

    PubMed Central

    Richards, Jacob

    2013-01-01

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

  5. 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...

  6. 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...

  7. 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...

  8. 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...

  9. 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...

  10. Low Power Gated Clock Tree Driven Placement

    NASA Astrophysics Data System (ADS)

    Shen, Weixiang; Cai, Yici; Hong, Xianlong; Hu, Jiang

    As power consumption of the clock tree dominates over 40% of the total power in modem high performance VLSI designs, measures must be taken to keep it under control. One of the most effective methods is based on clock gating to shut off the clock when the modules are idle. However, previous works on gated clock tree power minimization are mostly focused on clock routing and the improvements are often limited by the given registers placement. The purpose of this work is to navigate the registers during placement to further reduce the clock tree power based on clock gating. Our method performs activity-aware register clustering that reduces the clock tree power not only by clumping the registers into a smaller area, but also by pulling the registers with the similar activity patterns closely to shut off the clock more time for the resultant subtrees. In order to reduce the impact of signal nets wirelength and power due to register clustering, we apply the timing and activity based net weighting in [14], which reduces the nets switching power by assigning a combination of activity and timing weights to the nets with higher switching rates or more critical timing. To tradeoff the power dissipated by the clock tree and the control signal, we extend the idea of local ungating in [6] and propose an algorithm of gate control signal optimization, which still sets the gate enable signal high if a register is active for a number of consecutive clock cycles. Experimental results on a set of MCNC benchmarks show that our approach is able to reduce the power and total wirelength of clock tree greatly with minimal overheads.

  11. The chlorate-iodine clock reaction.

    PubMed

    Oliveira, Andr 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

  12. 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.

  13. The molecular clock may be an episodic clock.

    PubMed Central

    Gillespie, J H

    1984-01-01

    It is argued that the apparent constancy of the rate of molecular evolution may be an artifact due to the very slow rate of evolution of individual amino acids. A statistical analysis of protein evolution using a stationary point process as the null hypothesis leads to the conclusion that molecular evolution is episodic, with short bursts of rapid evolution followed by long periods of slow evolution. Such dynamics are incompatible with the neutral allele theory and require a revision of the standard interpretation of the molecular clock. PMID:6595674

  14. 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.

  15. 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.

  16. Song I-Yeong's Armillary Clock

    NASA Astrophysics Data System (ADS)

    Kim, Sang Hyuk; Lee, Yong Sam

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

  17. The impact of solar wind ULF Bz fluctuations on geomagnetic activity for viscous timescales during strongly northward and southward IMF

    NASA Astrophysics Data System (ADS)

    Osmane, A.; Dimmock, A. P.; Naderpour, R.; Pulkkinen, T. I.; Nykyri, K.

    2015-11-01

    We analyze more than 17 years of OMNI data to statistically quantify the impact of IMF Bz fluctuations on AL by using higher-order moments in the AL-distribution as a proxy. For strongly southward interplanetary magnetic field (IMF), the AL distribution function is characterized by a decrease of the skewness, a shift of its peak from -30 nT to -200 nT, and a broadening of the distribution core. During northward IMF, the distribution of AL is characterized by a significant reduction of the standard deviation and weight in the tail. Following this characterization of AL for southward and northward IMF, we show that IMF fluctuations enhance the driving on timescales smaller than those of substorms by shifting the peak of the probability distribution function by more than 150 nT during southward IMF, and by narrowing the distribution function by a factor of 2 during northward IMF. For both southward and northward IMF, we demonstrate that high power fluctuations in Bz systematically result in a greater level of activity on timescales consistent with viscous processes. Our results provide additional quantitative evidence of the role of the solar wind fluctuations in geomagnetic activity. The methodology presented also provides a framework to characterize short timescale magnetospheric dynamics taking place on the order of viscous timescales ? ? 1 hour.

  18. Sleep, Clocks and Synaptic Plasticity

    PubMed Central

    2014-01-01

    Sleep is widely believed to play an essential role in synaptic plasticity. However, the precise mechanisms governing this presumptive function are largely unknown. There is also evidence for independent circadian oscillations in synaptic strength and morphology. Therefore, synaptic changes observed after sleep reflect interactions between state-dependent (e.g. wake vs. sleep) and state-independent (circadian) processes. In this article we review how sleep and biological clocks influence synaptic plasticity. We discuss these findings in the context of current plasticity-based theories of sleep function and propose a new model that integrates circadian and brain state influences on synaptic plasticity. PMID:25087980

  19. Circadian molecular clock in lung pathophysiology.

    PubMed

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

    2015-11-15

    Disrupted daily or circadian rhythms of lung function and inflammatory responses are common features of chronic airway diseases. At the molecular level these circadian rhythms depend on the activity of an autoregulatory feedback loop oscillator of clock gene transcription factors, including the BMAL1:CLOCK activator complex and the repressors PERIOD and CRYPTOCHROME. The key nuclear receptors and transcription factors REV-ERB? and ROR? regulate Bmal1 expression and provide stability to the oscillator. Circadian clock dysfunction is implicated in both immune and inflammatory responses to environmental, inflammatory, and infectious agents. Molecular clock function is altered by exposomes, tobacco smoke, lipopolysaccharide, hyperoxia, allergens, bleomycin, as well as bacterial and viral infections. The deacetylase Sirtuin 1 (SIRT1) regulates the timing of the clock through acetylation of BMAL1 and PER2 and controls the clock-dependent functions, which can also be affected by environmental stressors. Environmental agents and redox modulation may alter the levels of REV-ERB? and ROR? in lung tissue in association with a heightened DNA damage response, cellular senescence, and inflammation. A reciprocal relationship exists between the molecular clock and immune/inflammatory responses in the lungs. Molecular clock function in lung cells may be used as a biomarker of disease severity and exacerbations or for assessing the efficacy of chronotherapy for disease management. Here, we provide a comprehensive overview of clock-controlled cellular and molecular functions in the lungs and highlight the repercussions of clock disruption on the pathophysiology of chronic airway diseases and their exacerbations. Furthermore, we highlight the potential for the molecular clock as a novel chronopharmacological target for the management of lung pathophysiology. PMID:26361874

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  2. 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.

  3. Deregulation of the circadian clock constitutes a significant factor in tumorigenesis: a clockwork cancer. Part I: clocks and clocking machinery

    PubMed Central

    Uth, Kristin; Sleigh, Roger

    2014-01-01

    Many physiological processes occur in a rhythmic fashion, consistent with a 24-h cycle. The central timing of the day/night rhythm is set by a master clock, located in the suprachiasmatic nucleus (a tiny region in the hypothalamus), but peripheral clocks exist in different tissues, adjustable by cues other than light (temperature, food, hormone stimulation, etc.), functioning autonomously to the master clock. Presence of unrepaired DNA damage may adjust the circadian clock so that the phase in which checking for damage and DNA repair normally occurs is advanced or extended. The expression of many of the genes coding for proteins functioning in DNA damage-associated response pathways and DNA repair is directly or indirectly regulated by the core clock proteins. Setting up the normal rhythm of the circadian cycle also involves oscillating changes in the chromatin structure, allowing differential activation of various chromatin domains within the 24-h cycle. PMID:26019503

  4. Substorms under northward IMF conditions and their implications on the question of energy availability in the tail

    NASA Astrophysics Data System (ADS)

    Lee, D.; Choi, K.; Ohtani, S.; Lee, J.; Kim, K.

    2008-12-01

    A southward IMF condition is generally considered as the most natural precondition for a substorm to occur. The condition is preferred for effective energy entry from the solar wind into the magnetosphere that is to be released via substorm occurrence. But it has been previously reported by some researchers that substorms sometimes occur under northward IMF conditions as well. Based on the IMAGE WIC aurora observations and the solar wind data from ACE and Geotail, we found that the occurrence of substorms under preceding northward IMF conditions is indeed not uncommon. In this paper, we present details of several such substorms that occurred in 2000 and 2001. In selecting these events, we have imposed a distinguishing condition that an identified substorm is preceded by another substorm, both being under northward IMF conditions, so that the later one is indeed a northward IMF substorm in the sense that it is not affected directly by any earlier southward IMF condition that can easily supply solar wind energy. Surprisingly, the substorms identified this way are major substorms, i.e., those with clear auroral breakup followed by substantial auroral expansion. For some of the events, we find that they occurred during the recovery phase of a magnetic storm (the IMF turned and remained northward). This implies the possibility that the availability of the magnetospheric energy for the northward IMF substorms of this kind is related to the preceding magnetic storm. For other northward IMF substorms, however, they indicated no obvious association with preceding magnetic storm activity. We use various data sets and models to address the fundamental question, i.e., what process can effectively transfer the solar wind energy into the magnetosphere under northward IMF conditions to lead to a major substorm, and also the question whether the tail is left with sufficient energy for a substorm occurrence even after major energy release by an earlier substorm occurrence.

  5. 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].

  6. Asymmetrical response of dayside ion precipitation to a large rotation of the IMF

    NASA Astrophysics Data System (ADS)

    Berchem, J.; Richard, R. L.; Escoubet, C. P.; Wing, S.; Pitout, F.

    2016-01-01

    We have carried out global magnetohydrodynamics (MHD) simulations together with large-scale kinetic simulations to investigate the response of the dayside magnetospheric ion precipitation to a large rotation (135°) of the interplanetary magnetic field (IMF). The study uses simplified global MHD model (no dipole tilt and constant ionospheric conductance) and idealized solar wind conditions where the IMF rotates smoothly from a southward toward a northward direction (BX = 0) to clearly identify the effects of the impact of the discontinuity on the magnetopause. Results of the global simulations reveal that a strong north-south asymmetry develops in the pattern of precipitating ions during the interaction of the IMF rotation with the magnetopause. For a counterclockwise IMF rotation from its original southward direction (BY < 0), a spot of high-energy particle injections occurs in the Northern Hemisphere but not in the Southern Hemisphere. The spot moves poleward and dawnward as the interacting field rotates. In that case, reconnection is found close to the poleward edge of the northern cusp, while it occurs farther tailward in the Southern Hemisphere. Tracing magnetic field lines shows an asymmetry in the tilt of the cusps and indicates that the draping and subsequent double reconnection of newly opened field lines from the Southern Hemisphere over the dayside magnetosphere cause the symmetry breaking. The reverse north-south asymmetry is found for a clockwise IMF rotation from its original southward direction (BY > 0). Trends observed in the ion dispersions predicted from the simulations are in good agreement with Cluster observations of the midaltitude northern cusp, which motivated the study.

  7. Young and embedded clusters in Cygnus-X: evidence for building up the IMF?

    NASA Astrophysics Data System (ADS)

    Maia, F. F. S.; Moraux, E.; Joncour, I.

    2016-02-01

    We provide a new view on the Cygnus-X north complex by accessing for the first time the low mass content of young stellar populations in the region. CFHT/WIRCam camera was used to perform a deep near-IR survey of this complex, sampling stellar masses down to ˜0.1 M⊙. Several analysis tools, including a extinction treatment developed in this work, were employed to identify and uniformly characterise a dozen unstudied young star clusters in the area. Investigation of their mass distributions in low-mass domain revealed a relatively uniform log-normal IMF with a characteristic mass of 0.32±0.08 M⊙ and mass dispersion of 0.40±0.06. In the high mass regime, their derived slopes showed that while the youngest clusters (age < 4 Myr) presented slightly shallower values with respect to the Salpeter's, our older clusters (4 Myr < age < 18 Myr) showed IMF compliant values and a slightly denser stellar population. Although possibly evidencing a deviation from an 'universal' IMF, these results also supports a scenario where these gas dominated young clusters gradually 'build up' their IMF by accreting low-mass stars formed in their vicinity during their first ˜3 Myr, before the gas expulsion phase, emerging at the age of ˜4 Myr with a fully fledged IMF. Finally, the derived distances to these clusters confirmed the existence of at least 3 different star forming regions throughout Cygnus-X north complex, at distances of 500-900 pc, 1.4-1.7 kpc and 3.0 kpc, and revealed evidence of a possible interaction between some of these stellar populations and the Cygnus-OB2 association.

  8. A colorful model of the circadian clock.

    PubMed

    Reppert, Steven M

    2006-01-27

    The migration of the colorful monarch butterfly provides biologists with a unique model system with which to study the cellular and molecular mechanisms underlying a sophisticated circadian clock. The monarch circadian clock is involved in the induction of the migratory state and navigation over long distances, using the sun as a compass. PMID:16439193

  9. 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...

  10. Fast Clock Recovery for Digital Communications

    NASA Technical Reports Server (NTRS)

    Tell, R. G.

    1985-01-01

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

  11. 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

  12. Ideal clocksa 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.

  13. "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…

  14. 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.

  15. 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

  16. Hypothalamic clocks and rhythms in feeding behaviour.

    PubMed

    Bechtold, David A; Loudon, Andrew S I

    2013-02-01

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

  17. 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

  18. 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

  19. 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

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

    NASA Technical Reports Server (NTRS)

    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 Bz 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 BZ 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 By 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.

  1. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  4. On the Predictability of Substorms Following Sharp Northward Turnings of the IMF

    NASA Technical Reports Server (NTRS)

    Blanchard, G. T.; Lyons, Larry R.; Spann, James F., Jr.; Reeves, G. D.

    1998-01-01

    It has been shown that there is an association between changes of the interplanetary magnetic field (IMF) that are expected to lead to a reduction in magnetospheric convection (northward turnings, reductions) and the onset of the expansion phase of substorms. This has been previously demonstrated by analyses of IMF data during time intervals associated with identified substorm onsets. Here we examine whether observations of northward turnings of the IMF can be used to predict the occurrence of substorms. We first identified sharp northward turnings that follow an interval of steady, southward IMF using measurements from the Wind spacecraft during the first 180 days of 1997. We also required that the northward turning be observed by either IMP-8 or GEOTAIL, in addition to Wind, and that one of the observing satellites be sufficiently close to the Earth-Sun line, or that the two observing satellites be sufficiently separated, that we are reasonably certain that the northward turning affected the magnetosphere. We also used the dual observations to estimate the arrival of the northward turning at the Earth. Using these criteria, we predicted 17 substorms. We then searched for the following signatures of substorm onset around the time of the predicted onset: auroral brightening followed by auroral bulge expansion observed by Polar UVI, geosynchronous particle injection, geosynchronous magnetic field dipolarization, and an appropriate magnetic disturbance at the surface of the Earth. Of the 17 predictions of substorms, 10 were successful in that a substorm onset was observed within 12 min of the predicted onset, 1 is indeterminate due to a lack of data at the Earth, 1 had unusual activity that we have not been able to identify, and 5 were unsuccessful. The failure of these last 5 predictions is explicable. Two of the northward turnings that failed to produce substorms were preceded by the lowest average of the set. The remaining 3 were the only cases in which the northward turning was accompanied by a simultaneous sharp increase. The increase would be expected to offset the decrease in convection that would otherwise be expected to be associated with a northward turning. These results indicate that it is an IMF change that leads to a reduction in convection, rather than just a northward turning or reduction that is associated with substorms, and that at least some substorms can be predicted by measurements of the IMF.

  5. Miniaturized laser magnetometers and clocks

    NASA Astrophysics Data System (ADS)

    Wynands, Robert; Affolderbach, C.; Hollberg, Leo W.; Kitching, John E.; Knappe, Svenja A.; Staehler, M.

    2002-04-01

    We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision applications like magnetometry or atomic frequency standards, using the D lines in thermal Cs or Rb vapor. The magnetometer operates by monitoring the position of the Zeeman-shifted outermost resonance component. The central Zeeman component is well suited for frequency standard applications because its position is shifted by magnetic fields only in second order. We derive the required pair of laser fields form a special diode laser by direct modulation of the injection current. Magneto metric sensitivity down to a picotesla and 10-12 relative instability for a finger-sized clock have been achieved in this way. Use of a magnetic gradiometer allows to cancel fluctuations of ambient magnetic fields to a large degree, making possible sensitive measurements even outside magnetically shielded rooms.

  6. 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.

  7. 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.

  8. Transmission delays in hardware clock synchronization

    NASA Technical Reports Server (NTRS)

    Shin, Kang G.; Ramanathan, P.

    1988-01-01

    Various methods, both with software and hardware, have been proposed to synchronize a set of physical clocks in a system. Software methods are very flexible and economical but suffer an excessive time overhead, whereas hardware methods require no time overhead but are unable to handle transmission delays in clock signals. The effects of nonzero transmission delays in synchronization have been studied extensively in the communication area in the absence of malicious or Byzantine faults. The authors show that it is easy to incorporate the ideas from the communication area into the existing hardware clock synchronization algorithms to take into account the presence of both malicious faults and nonzero transmission delays.

  9. 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."

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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...

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

    PubMed

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

    2013-10-25

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

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. 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, AndrewD.; 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 worms forebrain. The worms 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

  1. Slow mode structure in the nightside magnetosheath related to IMF draping

    NASA Astrophysics Data System (ADS)

    Erkaev, N. V.; Farrugia, C. J.; Mezentsev, A. V.; Torbert, R. B.; Biernat, H. K.

    2014-02-01

    We apply a semianalytic magnetohydrodynamic approach to describe effects in the nightside magnetosheath related to accelerated magnetosheath flows caused by the draping of interplanetary magnetic field (IMF). Assuming a northward IMF direction, we show the development of slow mode fronts in the far tail (tailward of approximately -60 RmE). We find that accelerated flows north and south of the equator start to converge toward lower latitudes. The ensuing plasma compression gives rise to slow mode waves in the equatorial region which, further down the tail, evolve into slow mode shocks. These fronts propagating along the magnetic field lines are characterized by sharp increases of plasma density, pressure, and temperature and a decrease in the magnetic field strength. The magnetic pressure exhibits an anticorrelation with the plasma pressure, but the total pressure is fairly constant across the fronts. The field-aligned plasma velocity component anticorrelates with the plasma density, while the perpendicular velocity component does not have sharp variations at the fronts. For northward IMF, these fronts appear near the equatorial region and then propagate to higher latitudes. This effect is not very sensitive to the particular shape of the magnetopause. Lowering the upstream Alfvn Mach number increases the strength of the slow mode waves, which also develop closer to Earth. We predict that this effect can be observed by space probes skimming the far tail.

  2. 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.

  3. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  5. 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

  6. The IMF in galaxy clusters: What is needed to account for high metal production?

    NASA Astrophysics Data System (ADS)

    Morsony, Brian; Heath, Caitlin; Workman, Jared

    2015-08-01

    The gas in galaxy clusters is enriched in metal, typically to about 30% of solar metallicity. However, stars a relatively rare in clusters, meaning that the amount of metal produced per star is about 3 times as much as in the Milky Way. We set out to determine what changes to standard star formation are needed to reproduce the observed metal enhancement. Modifications include expanding the IMF to high mass (>130 M_sun) stars and including metal production from pair-instability supernovae, using an enhanced type-Ia SN rate, and using various modifications of the IMF to make it more top-heavy. For each set of assumptions, we use theoretical nucleosynthesis models to calculate the expected total metal yield per mass of star formation, and to predict the relative abundances of different elements. Including pair-instability supernovae will dramatically increase the amount of metal produced, and, combined with a slightly flatter IMF, can lead to 3 times the metal production per solar mass of star formation, along with an increase abundance of intermediate-mass elements.

  7. 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+).

  8. Reconnection and Energy Conversion at the Magnetopause as Influenced by Earth's Dipole Tilt Angle and Interplanetary Magnetic Field

    NASA Astrophysics Data System (ADS)

    Hoilijoki, S.; Palmroth, M.

    2013-12-01

    We study the effect of Earth's dipole tilt angle and interplanetary magnetic field (IMF) Bx and By components on the location of reconnection and the energy conversion at the magnetopause. We simulate southward IMF satisfying both inward- and outward-type Parker spiral conditions during three different dipole tilt angles using a global magnetohydrodynamic model GUMICS-4. Different combinations of dipole tilt angle and IMF Bx and By components change the magnetopause reconnection morphology and magnitude. This can be studied by comparing the location of the reconnection line and the location and strength of the energy conversion for different parameter combinations. We find that the IMF Bx and the dipole tilt angle modify the reconnection line location and both magnitude and location of the energy conversion. We discuss the relative role of the non-zero Bx and the dipole tilt angle in dayside reconnection first separately and then by letting the parameters change simultaneously. We find that positive (negative) Bx moves the reconnection line northward (southward) and positive (negative) tilt angle moves the line southward (northward). When both tilt angle and Bx are positive or negative they reverse each others effect so that the reconnection line location is almost the same as it is when both Bx and tilt angle are zero. When these two parameters have opposite signs they enhance each other's effects. We find evidence that reconnection-induced processes modify the shape of the magnetopause, which in turn has and effect on the reconnection location. Therefore intrinsic processes within the magnetosphere - the magnetic flux transfer to nightside and the subsequent return of the closed flux - can influence the basic reconnection processes within the dayside magnetopause.

  9. Navigating more precisely with laser clocks

    NASA Astrophysics Data System (ADS)

    Mileti, Gaetano; Affolderbach, Christoph; Droz, Fabien; Murphy, Eamonn

    2005-05-01

    The development of the key technologies, particularly in terms of reliable diode lasers and atomic vapour cells, will pave the way towards low-power and miniature - ultimately chip-scale - atomic clocks for industrial and domestic use.

  10. The circadian clock of Neurospora crassa

    PubMed Central

    Baker, Christopher L.; Loros, Jennifer J.; Dunlap, Jay C.

    2011-01-01

    Summary Circadian clocks organize our inner physiology with respect to the external world providing life with the ability to anticipate and thereby better prepare for major fluctuations in its environment. Circadian systems are widely represented in nearly all major branches of life except archaebacteria, and within the eukaryotes the filamentous fungus Neurospora crassa has served for nearly half a century as a durable model organism for uncovering the basic circadian physiology and molecular biology. Studies using Neurospora have clarified our fundamental understanding of the clock as nested positive and negative feedback loops regulated through transcriptional and post-transcriptional processes. These feedback loops are centered on a limited number of proteins that form molecular complexes, and their regulation provides a physical explanation for nearly all clock properties. This review will introduce the basics of circadian rhythms, the model filamentous fungus Neurospora crassa, and provide an overview of the molecular components and regulation of the circadian clock. PMID:21707668

  11. 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.

  12. 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.

  13. 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.

  14. 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

  15. 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

  16. 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

  17. 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.

  18. Circadian Clock Proteins in Mood Regulation

    PubMed Central

    Partonen, Timo

    2015-01-01

    Mood regulation is known to be affected by the change of seasons. Recent research findings have suggested that mood regulation may be influenced by the function of circadian clocks. In addition, the activity of brown adipocytes has been hypothesized to contribute to mood regulation. Here, the overarching link to mood disorders might be the circadian clock protein nuclear receptor subfamily 1, group D, member 1. PMID:25610405

  19. 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.

  20. Clock gene variation in Tachycineta swallows

    PubMed Central

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

    2012-01-01

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

  1. 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 Donnes 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.

  2. Maser and secondary clock in telecommunications networks

    NASA Technical Reports Server (NTRS)

    Risley, A.

    1984-01-01

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

  3. The Neurospora circadian clock: simple or complex?

    PubMed Central

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

  4. Miniature atomic clock for space applications

    NASA Astrophysics Data System (ADS)

    Maleki, Lute; Savchenkov, Anatoliy; Liang, Wei; Eliyahu, Danny; Ilchenko, Vladimir; Dale, Elijah; Matsko, Andrey

    2015-09-01

    This paper presents a novel architecture for a high performance atomic clock based on the use of miniature optical whispering gallery mode (WGM) resonators. Following the approach of stabilizing a laser local oscillator to an optical transition in an atom or ion, as used in advanced atomic clock, a semiconductor laser is used for stabilization to the D1 line of Rb atoms, held in a small vapor cell. The laser is self-injection locked to a WGM resonator to reduce its linewidth. To produce the RF output of the clock, a second WGM resonator excited with a second cw semiconductor laser produces an optical frequency comb that is demodulated on a fast photodiode. Locking the resonator that generates the frequency comb to the laser stabilized to the Rb transition transfers the stability of the atomic transition to the RF output of the clock. In this way, a miniature all-optical atomic clock is realized. Details of the operation of the clock and application of the architecture to other atomic systems, such as a ytterbium ion, will be described.

  5. 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.

  6. Adipose Clocks: Burning the Midnight Oil.

    PubMed

    Henriksson, Emma; Lamia, Katja A

    2015-10-01

    Circadian clocks optimize the timing of physiological processes in synchrony with daily recurring and therefore predictable changes in the environment. Until the late 1990s, circadian clocks were thought to exist only in the central nervous systems of animals; elegant studies in cultured fibroblasts and using genetically encoded reporters in Drosophila melanogaster and in mice showed that clocks are ubiquitous and cell autonomous. These findings inspired investigations of the advantages construed by enabling each organ to independently adjust its function to the time of day. Studies of rhythmic gene expression in several organs suggested that peripheral organ clocks might play an important role in optimizing metabolic physiology by synchronizing tissue-intrinsic metabolic processes to cycles of nutrient availability and energy requirements. The effects of clock disruption in liver, pancreas, muscle, and adipose tissues support that hypothesis. Adipose tissues coordinate energy storage and utilization and modulate behavior and the physiology of other organs by secreting hormones known as "adipokines." Due to behavior- and environment-driven diurnal variations in supply and demand for chemical and thermal energy, adipose tissues might represent an important peripheral location for coordinating circadian energy balance (intake, storage, and utilization) over the whole organism. Given the complexity of adipose cell types and depots, the sensitivity of adipose tissue biology to age and diet composition, and the plethora of known and yet-to-be-discovered adipokines and lipokines, we have just begun to scratch the surface of understanding the role of circadian clocks in adipose tissues. PMID:25926681

  7. Maser and secondary clock in telecommunications networks

    NASA Astrophysics Data System (ADS)

    Risley, A.

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

  8. 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

  9. Secure network of entangled atomic clocks

    NASA Astrophysics Data System (ADS)

    Komar, Peter; Bishof, Michael; Jiang, Liang; Ye, Jun; Lukin, Mikhail

    2013-05-01

    We propose a scheme for entangling atomic clocks separated by large distances using the concept of quantum networks. The protocol allows the clocks at different locations to be used in a network for a ``supreme clock signal'' with a stability set by the Heisenberg limit for the total number of atoms in the network. The realization we consider consists of multiple optical clock qubits at each location, as well as entanglement links created by sharing EPR photon pairs using quantum repeaters. We analyze the effect of local oscillator phase noise, time delays, and decoherence on the overall stability using different feedback schemes. We show that, for the current-state-of-the-art laser noise spectrum, the network is able to utilize a fully entangled GHZ state for a large number of clock qubits. We show that such a network can be made completely secure by preventing outside parties and individual participants from taking unfair advantage, while at the same time, providing access to the ``supreme clock signal'' for all honest contributors. Our protocol could serve as the backbone for a future global positioning system that will greatly surpass the accuracy and stability of the current GPS network.

  10. 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.

  11. Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF

    SciTech Connect

    Hairston, M.R.; Heelis, R.A.

    1995-03-01

    A three-day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP-8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined following each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit time for the IMF to travel from the position of the IMP-8 satellite to the magnetopause, a further time lag of about 17 to 25 minutes is observed for the five cases where the IMF turned from northward to southward. A longer lag of between 28 and 44 minutes is observed for the two cases where the IMF turned from southward to northward. These lags are interpreted as the inertial response time of the ionosphere in reacting to the change in the IMF. 16 refs., 4 figs.

  12. Modeling the mammalian circadian clock

    NASA Astrophysics Data System (ADS)

    Jolley, Craig; Ueda, Hiroki

    2012-02-01

    In biology, important processes often depend on a temporal schedule. The 24-hour periodicity of solar illumination caused by the earth's rotation has consequences for environmental factors such as temperature and humidity as well as ecological factors such as the presence of food, predators, or potential mates. As a result, many organisms have evolved to develop a circadian clock that allows them to anticipate these environmental changes in the absence of direct temporal cues. In recent years, extensive efforts have been made to deconstruct the biological clockwork from various organisms, develop mathematical models of circadian function, and construct synthetic analogues to test our understanding. My present work has two major foci. First, we have used regulatory principles revealed by recent experimental work to construct a model of the core genetic oscillator of the mammalian circadian system that captures key system-level behaviors. Second, we are exploring the possibility of a post-translational phosphorylation-based oscillator that is coupled to the core oscillator, conferring enhanced robustness and stability on the complete system. A simple model of this post-translational oscillator reveals key design constraints that must be satisfied by any such oscillator.

  13. 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.

  14. 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.

  15. The IMF-sensitive 1.14-μm 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 μm. Like the Na I 0.82 μm 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 μm increases steeply with increasing velocity dispersion, σ, and for the most massive galaxies (σ ≳ 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 μm at high σ 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-σ galaxies. At lower mass (σ = 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-σ sample on average, these galaxies have strong Na I 1.14 μm; 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-σ sample, recovers an IMF less heavy than Salpeter, but under-predicts the Na I 1.14 μm line at the 5σ 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.

  16. 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 bHLHPAS 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 domaincontaining clock protein (besides Drosophila PERIOD), which suggests that this motif may define an evolutionarily conserved feature of the circadian clock mechanism. PMID:9160755

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

    PubMed Central

    Meuti, Megan E.; Denlinger, David L.

    2013-01-01

    In this article, we explore links between circadian clocks and the clock involved in photoperiodic regulation of diapause in insects. Classical resonance (NandaHamner) and night interruption (Bnsow) experiments suggest a circadian basis for the diapause response in nearly all insects that have been studied. Neuroanatomical studies reveal physical connections between circadian clock cells and centers controlling the photoperiodic diapause response, and both mutations and knockdown of clock genes with RNA interference (RNAi) point to a connection between the clock genes and photoperiodic induction of diapause. We discuss the challenges of determining whether the clock, as a functioning module, or individual clock genes acting pleiotropically are responsible for the photoperiodic regulation of diapause, and how a stable, central circadian clock could be linked to plastic photoperiodic responses without compromising the clocks essential functions. Although we still lack an understanding of the exact mechanisms whereby insects measure day/night length, continued classical and neuroanatomical approaches, as well as forward and reverse genetic experiments, are highly complementary and should enable us to decipher the diverse ways in which circadian clocks have been involved in the evolution of photoperiodic induction of diapause in insects. The components of circadian clocks vary among insect species, and diapause appears to have evolved independently numerous times, thus, we anticipate that not all photoperiodic clocks of insects will interact with circadian clocks in the same fashion. PMID:23615363

  18. 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

  19. 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.

  20. 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.

  1. Circadian Clock Control of Liver Metabolic Functions.

    PubMed

    Reinke, Hans; Asher, Gad

    2016-03-01

    The circadian clock is an endogenous biological timekeeping system that synchronizes physiology and behavior to day/night cycles. A wide variety of processes throughout the entire gastrointestinal tract and notably the liver appear to be under circadian control. These include various metabolic functions such as nutrient uptake, processing, and detoxification, which align organ function to cycle with nutrient supply and demand. Remarkably, genetic or environmental disruption of the circadian clock can cause metabolic diseases or exacerbate pathological states. In addition, modern lifestyles force more and more people worldwide into asynchrony between the external time and their circadian clock, resulting in a constant state of social jetlag. Recent evidence indicates that interactions between altered energy metabolism and disruptions in the circadian clock create a downward spiral that can lead to diabetes and other metabolic diseases. In this review, we provide an overview of rhythmic processes in the liver and highlight the functions of circadian clock genes under physiological and pathological conditions; we focus on their roles in regulation of hepatic glucose as well as lipid and bile acid metabolism and detoxification and their potential effects on the development of fatty liver and nonalcoholic steatohepatitis. PMID:26657326

  2. 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

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

    NASA Astrophysics Data System (ADS)

    Palmroth, M.; Archer, M.; Vainio, R.; Hietala, H.; Pfau-Kempf, Y.; Hoilijoki, S.; Hannuksela, O.; Ganse, U.; Sandroos, A.; Alfthan, S. von; Eastwood, J. P.

    2015-10-01

    For decades, monochromatic large-scale ultralow frequency (ULF) waves with a period of about 30 s have been observed upstream of the quasi-parallel bow shock. These waves typically propagate obliquely with respect to the interplanetary magnetic field (IMF), while the growth rate for the instability causing the waves is maximized parallel to the magnetic field. It has been suggested that the mechanism for the oblique propagation concerns wave refraction due to the spatial variability of the suprathermal ions, originating from the E B drift component. We investigate the ULF foreshock under a quasi-radial IMF with Vlasiator, which is a newly developed global hybrid-Vlasov simulation solving the Vlasov equation for protons, while electrons are treated as a charge-neutralizing fluid. We observe the generation of the 30 s ULF waves and compare their properties to previous literature and multipoint Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft observations. We find that Vlasiator reproduces the foreshock ULF waves in all reported observational aspects. We conclude that the variability of the density and velocity of the reflected back streaming ions determines the large-scale structure of the foreshock, which affects the wave frequency, wavelength, and oblique propagation. We conclude that the wave refraction may also be at work for radial IMF conditions, which has earlier been thought of as an exception to the refraction mechanism due to the small E B drift component. We suggest that additional refraction may be caused by the large-scale spatial variability of the density and velocity of the back streaming ions.

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

    NASA Technical Reports Server (NTRS)

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

    2004-01-01

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

  5. 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.

  6. Simultaneous observations of polar cap patches and Sun-aligned arcs during transitions of the IMF

    NASA Astrophysics Data System (ADS)

    Valladares, C. E.; Fukui, K.; Sheehan, R.; Carlson, H. C., Jr.; Bullett, T.

    1998-11-01

    This paper presents the first observations of simultaneous polar cap patches and polar cap arcs in a single common 1000-km field of view, and identifies a model that explains the interplanetary magnetic field (IMF) dependencies of the observed phenomenology. To study the characteristics of the polar cap optical emissions in the 630.0 nm line during transitions of the IMF Bz, we have scanned images taken at Qaanaaq, Greeland, between 1989 and 1994. We found that on a few occasions, when Bz changed from a south to a north orientation, a particular pattern of polar cap patches and Sun-aligned arcs coexisted. No similar pattern of coexisting arcs and patches was found during north-to-south IMF transitions. The detailed analyses of three of these events are presented here in which patches and polar cap arcs are clearly identified to reside simultaneously within the Qaanaaq imager field of view. The digisonde located also at Qaanaaq is used to confirm that the optical patches correspond to enhancements in the number density and a simultaneous decrease of the hmF2 value. These two factors increase the capability of the imager to differentiate between patches and the background airglow. Data collected by the DMSP F8 satellite during one of the events reaffirm the appearance of polar cap precipitation during the Bz positive period. The J4 sensor on board DMSP F8 detected typical electron fluxes commonly associated with polar cap arcs. The coexistence of patches and arcs is due to a slower response of the patches in exiting the polar cap, and then the relatively sudden appearance of polar cap arcs presumably driven by dayside reconnection between the IMF and open flux drawn initially equatorward toward the cusp. This model, of dayside reconnection switching from equatorward of the cusp for Bz south to poleward of the cusp for Bz north, likewise explains why arcs and patches are seen by the imager to coexist for rapid Bz reversals only from south to north and not from north to south.

  7. A global MHD simulation study of the vortices at the magnetosphere boundary under the southward IMF condition

    NASA Astrophysics Data System (ADS)

    Park, K.; Ogino, T.; Lee, D.; Walker, R. J.; Kim, K.

    2013-12-01

    One of the significant problems in magnetospheric physics concerns the nature and properties of the processes which occur at the magnetopause boundary; in particular how energy, momentum, and plasma the magnetosphere receives from the solar wind. Basic processes are magnetic reconnection [Dungey, 1961] and viscouslike interaction, such as Kelvin-Helmholtz instability [Dungey 1955, Miura, 1984] and pressure-pulse driven [Sibeck et al. 1989]. In generally, magnetic reconnection occurs efficiently when the IMF is southward and the rate is largest where the magnetosheath magnetic field is antiparallel to the geomagnetic field. [Sonnerup, 1974; Crooker, 1979; Luhmann et al., 1984; Park et al., 2006, 2009]. The Kelvin-Helmholtz instability is driven by the velocity shear at the boundary, which occur frequently when the IMF is northward. Also variation of the magnetic field and the plasma properties is reported to be quasi-periodic with 2-3min [Otto and Fairfield, 2000] and period of vortex train with 3 to 4 minutes by global MHD simulation [Ogino, 2011]. The pressure-pulse is driven by the solar wind. And the observations of the magnetospheric magnetic field response show quasi-periodic with a period of 8 minutes [Sibeck et al., 1989; Kivelson and Chen, 1995]. There have been few studies of the vortices in the magnetospheric boundary under southward IMF condition. However it is not easy to find the generation mechanism and characteristic for vortices in complicated 3-dimensional space. Thus we have performed global MHD simulation for the steady solar wind and southward IMF conditions. From the simulation results, we find that the vortex occurs at R= 11.7Re (IMF Bz = -2 nT) and R= 10.2Re (IMF Bz = -10 nT) in the dayside magnetopause boundary. Also the vortex rotates counterclockwise in duskside magnetopause (clockwise in dawnside) and propagates tailward. Across the vortex, magnetic field and plasma properties clearly show quasi-periodic fluctuations with a period of 8~10 minutes under the weak southward IMF and 4~8 minutes for strong southward IMF conditions. Magnetic reconnection favorably occurs in anti-parallel field region with slower shear velocity in the magnetosheath. The magnetic field lines are highly bent by parallel vorticity (Omega||) in the flanks of the magnetopause boundary. Also, similar vortices are formed in a grid spacing of 0.3Re and 0.2Re. A small structure vortices are generated in higher resolution (0.1Re) and two vortices are mixed after 1m30s We suggest that the reconnection is a mechanism of generating vortex with a periodicity in the dayside during the southward IMF.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    SciTech Connect

    Geha, Marla; 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. Winding up the cyanobacterial circadian clock.

    PubMed

    Mackey, Shannon R; Golden, Susan S

    2007-09-01

    The endogenous circadian clock of the cyanobacterium Synechococcus elongatus controls many cellular processes and confers an adaptive advantage on this organism in a competitive environment. To be advantageous, this internal biological oscillator must be reset daily to remain in synchrony with its environment and to transduce temporal information to control behaviors at appropriate times of day. Recent studies have discovered new components of these input and output pathways of the clock that help to 'wind up' our understanding of the clock system as a whole. Here we review the mechanisms by which S. elongatus maintains internal time, discuss how external stimuli affect this oscillation, and evaluate the mechanisms underlying circadian controlled cellular events. PMID:17804240

  11. Quantum clock: A critical discussion on spacetime

    NASA Astrophysics Data System (ADS)

    Burderi, Luciano; Di Salvo, Tiziana; Iaria, Rosario

    2016-03-01

    We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time interval Δ t that this clock can measure scales as the inverse of its size Δ r . This implies an uncertainty relation between space and time: Δ r Δ t >G ℏ/c4, where G , ℏ, and c are the gravitational constant, the reduced Planck constant, and the speed of light, respectively. We outline and briefly discuss the implications of this uncertainty conjecture.

  12. 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.

  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. 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.

  15. Sugars, the clock and transition to flowering

    PubMed Central

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

    2013-01-01

    Sugars do not only act as source of energy, but they also act as signals in plants. This mini review summarizes the emerging links between sucrose-mediated signaling and the cellular networks involved in flowering time control and defense. Cross-talks with gibberellin and jasmonate signaling pathways are highlighted. The circadian clock fulfills a crucial role at the heart of cellular networks and the bilateral relation between sugar signaling and the clock is discussed. It is proposed that important factors controlling plant growth (DELLAs, PHYTOCHROME INTERACTING FACTORS, invertases, and trehalose-6-phosphate) might fulfill central roles in the transition to flowering as well. The emerging concept of sweet immunity, modulated by the clock, might at least partly rely on a sucrose-specific signaling pathway that needs further exploration. PMID:23420760

  16. Supporting Family Awareness with the Whereabouts Clock

    NASA Astrophysics Data System (ADS)

    Sellen, Abigail; Taylor, Alex S.; Kaye, Joseph Jofish'; Brown, Barry; Izadi, Shahram

    We report the results of a field trial of a situated awareness device for families called the Whereabouts Clock. The Clock displays the location of family members using cellphone data as one of four privacy-preserving, deliberately coarse-grained categories ( HOME, WORK, SCHOOL or ELSEWHERE). The results show that awareness of others through the Clock supports not only family communication and coordination but also more emotive aspects of family life such as reassurance, connectedness, identity and social touch. We discuss how the term awareness means many things in practice and highlight the importance of designing not just for family activities, but in order to support the emotional, social and even moral aspects of family life.

  17. 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

  18. The circadian clock in old Drosophila melanogaster.

    PubMed

    Driver, C

    2000-01-01

    A growing body of evidence indicates that one of the age-associated changes in the central nervous system that affect most old people is the loss of function of the circadian clock system. This loss results in impaired timing and quality of sleep, with consequent cognitive and other behavior problems. Failure of the clock contributes to the difficulties encountered with Alzheimer's disease. It also results in adverse changes in the hormonal regulation of intermediary metabolism, stress resistance and sexual function. Drosophila melanogaster is proposed as a model organism where this age-related change may be studied more readily. Circadian patterns are disrupted in Drosophila, with considerable differences between strains. In addition a fusion gene product of a key gene involved in the clock (per), and Green Fluorescent Protein, shows a 50% fall with age. PMID:11707931

  19. Which came first, spacetime or clocks?

    NASA Astrophysics Data System (ADS)

    Ord, G. N.

    2014-04-01

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

  20. 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.

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

    PubMed Central

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

    2014-01-01

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

  2. Light shift reduction in atomic clocks

    NASA Astrophysics Data System (ADS)

    Affolderbach, C.; Andreeva, Ch.; Cartaleva, Stefka S.; Karaulanov, Todor S.; Mileti, Gaetano; Slavov, Dimitar G.

    2004-06-01

    In this paper we present a detailed description of a method for reduction of the light shift in laser-pumped gas-cell atomic clocks. The method consists in using a multi-frequency optical pumping obtained through frequency modulation of the laser spectrum with precisely controllable parameters. Experimental evidence of a strong reduction of the frequency dependence of the LS in an optical pumping Rb gas-cell clock is demonstrated in a large frequency interval, which is in a very good agreement with the numerical estimations reported.

  3. 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.

  4. 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

  5. Water-Powered Astronomical Clock Tower

    NASA Astrophysics Data System (ADS)

    Sun, Xiaochun

    The construction of water-powered astronomical instruments was a long tradition of instrument making that started in the second century AD with Zhang Heng's water-powered celestial globe. The technology reached a peak when, in the eleventh century, Su Song and his team constructed the Water-Powered Astronomical Clock Tower which combined the armillary sphere, the celestial globe, and the time-keeping mechanism into a large automatic structure. Su Song's instrument contained a mechanism for controlling the water-powered movements of its wheels that amounts to an "escapement mechanism" for a mechanical clock. A new reconstruction of the mechanism is introduced in this chapter.

  6. Quantum Clock Synchronization with a Single Qudit

    PubMed Central

    Tavakoli, Armin; Cabello, Adán; Żukowski, Marek; Bourennane, Mohamed

    2015-01-01

    Clock synchronization for nonfaulty processes in multiprocess networks is indispensable for a variety of technologies. A reliable system must be able to resynchronize the nonfaulty processes upon some components failing causing the distribution of incorrect or conflicting information in the network. The task of synchronizing such networks is related to Byzantine agreement (BA), which can classically be solved using recursive algorithms if and only if less than one-third of the processes are faulty. Here we introduce a nonrecursive quantum algorithm, based on a quantum solution of the detectable BA, which achieves clock synchronization in the presence of arbitrary many faulty processes by using only a single quantum system. PMID:25613754

  7. Using GLONASS signal for clock synchronization

    NASA Technical Reports Server (NTRS)

    Gouzhva, Yuri G.; Gevorkyan, Arvid G.; Bogdanov, Pyotr P.; Ovchinnikov, Vitaly V.

    1994-01-01

    Although in accuracy parameters GLONASS is correlated with GPS, using GLONASS signals for high-precision clock synchronization was, up to the recent time, of limited utility due to the lack of specialized time receivers. In order to improve this situation, in late 1992 the Russian Institute of Radionavigation and Time (RMT) began to develop a GLONASS time receiver using as a basis the airborne ASN-16 receiver. This paper presents results of estimating user clock synchronization accuracy via GLONASS signals using ASN-16 receiver in the direct synchronization and common-view modes.

  8. The Large Water-Clock of Amphiaraeion

    NASA Astrophysics Data System (ADS)

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

    2010-07-01

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

  9. 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.

  10. 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. ...

  11. 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...

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

    MedlinePLUS

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

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

    PubMed

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

    2015-01-01

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

  14. 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.

  15. Interhemispheric Geomagnetic Field Response to Sudden Change in Solar Wind Pressure and IMF Orientation

    NASA Astrophysics Data System (ADS)

    Kim, H.; Cai, X.; Clauer, C. R.; Stolle, C.; Matzka, J.

    2011-12-01

    Preliminary investigation of geomagnetic field response to sudden change in solar wind pressure and IMF orientation is presented using data from satellite and ground magnetometer array in both northern and southern hemispheres. Some data sets in this study have been provided by AGO (Automatic Geophysical Observatory) and AAL-PIP (Autonomous Adaptive Low-Power Instrument Platform) stations deployed in Antarctica along the 40 magnetic meridian. These stations facilitate high-latitude multi-point magnetic conjugate observation pairs to the Greenland West Coast magnetometer chain for interhemispheric investigations, which have been rarely made because of the difficulty in accessing the Antarctic regions. Geomagnetic field perturbations in response to solar wind pressure impulse events, in which the solar wind pressure changes are more than 5 nPa in less than ~16 minutes and the pressures are steady for ~1 hour before and ~20 minutes after the pressure changes, have been examined using the data sets obtained from 1998 to 2010 to show global local time distribution of the ground response, timing response between the two hemispheres and its seasonal variation, and the relationship between IMF orientation and the ground response accompanied by the solar wind sudden pressure change.

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

    SciTech Connect

    Lastovicka, J.

    1984-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Lastovicka, J.

    1984-05-01

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

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

    NASA Technical Reports Server (NTRS)

    Lastovicka, J.

    1984-01-01

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

  19. IMF b/sub y/ control of ionization and electric fields measured by the Sondrestrom radar

    SciTech Connect

    Robinson, R.M.; Clauer, C.R.; De La Beaujardiere, O.; Kelly, J.D.; Evans, D.S.

    1986-01-01

    The pattern of ionization and electric fields measured in the dayside auroral zone by the Sondrestrom incoherent scatter radar is compared with interplanetary magnetic field (IMF) data from the IMP-8 spacecraft. The electric-field configuration is most sensitive to the B/sub y/ component of the IMF. For B/sub y/ < 0 there is a strong reversal in convective flow between 1300 and 1600 MLT with a region of enhanced F-region ionization associated with low-energy particle precipitation at the reversal. For B/sub y/ > 0 the convention reversal is most apparent on the morning side. Ionization produced by particle precipitation for B/sub y/ > 0. is much less conspicuous than that observed on the afternoon side for B/sub y/ <0. We show radar measurements of ionization, electric fields and electron temperatures associated with two distinct types of particle precipitation in the pre-noon local time sector for B/sub y/> 0. The patterns of precipitation for B/sub y/ < 0 and B/sub y/ > 0 are consistent with the distribution of field-aligned currents, in that precipitation occurs primarily in the upward current regions. With this interpretation, only the precipitation associated with the cusp-field-aligned currents on the dawn side may be intense enough to produce ionospheric signatures observable from the ground.

  20. 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.

  1. Formation of an F3 layer in the equatorial ionosphere: A result from strong IMF changes

    NASA Astrophysics Data System (ADS)

    Paznukhov, V. V.; Reinisch, B. W.; Song, P.; Huang, X.; Bullett, T. W.; Veliz, O.

    2007-07-01

    We analyzed ionospheric observations made with digisondes in Jicamarca, Ramey, Wallops Island, Ascension Island, and Kwajalein Island during the major magnetic storm of November 9 10, 2004, which was associated with rapid interplanetary magnetic field (IMF) Bz changes. The strongest ionospheric responses to the southward IMF Bz turning were observed at the dip equator at Jicamarca where during the magnetic disturbance a dramatic F2 peak density depletion occurred at around 15:00 local time, accompanied by a fast upward motion of the plasma. In this process, an additional ionospheric layer, the F3 layer, formed with peak densities NmF3 exceeding NmF2. This observation may be considered evidence of an equatorial plasma fountain enhancement caused by the magnetic field disturbance. Responses were observed in a large range of latitudes and local times. The best indicator of the responses appears to be the peak height of the F layer, since competing processes determine the peak densities. The observed responses at low latitude locations in the morning and dusk sectors pose challenges to the simple penetrating electric field model because the upward motion is inconsistent with the E×B drift associated with a dawn dusk electric field. Clear responses in the Jicamarca local time sector occurred at latitudes as high as 28°, at Ramey, Puerto Rico. This latitude range appears to be beyond the range of the flux tube corresponding to the 900 km F3 layer peak height at Jicamarca, indicating a more extended uplifting of flux tubes.

  2. The mmax-Mecl relation, the IMF and IGIMF: probabilistically sampled functions

    NASA Astrophysics Data System (ADS)

    Weidner, C.; Kroupa, P.; Pflamm-Altenburg, J.

    2013-09-01

    We introduce a new method to measure the dispersion of mmax values of star clusters and show that the observed sample of mmax is inconsistent with random sampling from a universal stellar initial mass function (IMF) at a 99.9 per cent confidence level. The scatter seen in the mmax-Mecl data can be mainly (76 per cent) understood as being the result of observational uncertainties only. The scatter of mmax values at a given Mecl is consistent with mostly being measurement uncertainties such that the true (physical) scatter may be very small. Additionally, new data on the local star-formation regions Taurus-Auriga and L1641 in Orion make stochastically formed stellar populations rather unlikely. The data are however consistent with the local integrated galactic stellar initial mass function theory according to which a stellar population is a sum of individual star-forming events each of which is described by well-defined physical laws. Randomly sampled IMFs and henceforth scale-free star formation seems to be in contradiction to observed reality.

  3. The structure of the distanct geomagnetic tail during long periods of northward IMF

    NASA Technical Reports Server (NTRS)

    Raeder, J.; Walker, R. J.; Ashour-Abdalla, M.

    1995-01-01

    We have used a newly developed, parallelized, global MHD magnetosphere - ionosphere simulation model with a 400 R(sub E) long tail to study the evolution, structure, and dynamics of the distant magnetotail during extended periods of northward interplanetary magnetic field (IMF). We find that the tail evolves to a nearly time stationary structure about one solar wind transit time after the IMF turns northward. Four regions of different magnetic topology can be distinguished which extend at least to the end of the simulation box at 400 R(sub E). Besides lobe field lines and open solar wind field lines tailward of an X-line, there is a broad boundary layer of closed field lines which we call the tail flank boundary layer (TFBL). Just inside the TFBL there is a region of closed field loops. Besides the X-line we find two O-lines which are enclosed by the closed field loops and are roughly aligned with the tail axis. Together they form a U shaped separator between the northward and the southward plasma sheet fields.

  4. Observations of magnetospheric substorms occurring with no apparent solar wind/IMF trigger

    SciTech Connect

    Henderson, M.G.; Reeves, G.D.; Belian, R.D.; Murphree, J.S.

    1996-03-01

    An outstanding topic in magnetospheric physics is whether substorms are always externally triggered by disturbances in either the interplanetary magnetic field or solar wind, or whether they can also occur solely as the result of an internal magnetospheric instability. Over the past decade, arguments have been made on both sides of this issue. Horwitz and McPherron have shown examples of substorm onsets which they claimed were not externally triggered. However, as pointed out by Lyons, there are several problems associated with these studies that make their results somewhat inconclusive. In particular, in the McPherron et al. study, fluctuations in the B{sub y} component were not considered as possible triggers. Furthermore, Lyons suggests that the sharp decreases in the AL index during intervals of steady IMF/solar wind, are not substorms at all but rather that they are just enhancements of the convection driven DP2 current system that are often observed to occur during steady magnetospheric convection events. In the present study, we utilize a much more comprehensive dataset (consisting of particle data from the Los Alamos energetic particle detectors at geosynchronous orbit, IMP 8 magnetometer and plasma data, Viking UV auroral imager data, mid-latitude Pi2 pulsation data, ground magnetometer data and ISEE1 magnetic field and energetic particle data) to show as unambiguously as possible that typical substorms can indeed occur in the absence of an identifiable trigger in the solar wind/IMF.

  5. 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.

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

    PubMed

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

    2015-01-01

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

  7. Global Observations of the Effect of a Sustained North-South Oscillation in the IMF

    NASA Astrophysics Data System (ADS)

    Nemec, B. J.; Bering, E. A.; Nellums, R.

    2005-05-01

    This paper presents a preliminary study of what appears to be the first IMF event initially identified as interesting on the basis of ground based atmospheric electricity data. On Jan 2, 1993, the electric field mill and air-earth current meters at South Pole Station detected a sustained oscillation in the earth-ionosphere potential at South Pole with a quasi-period of 1 hour and duration of more than 8 hours. Similar oscillations were found in both local and conjugate magnetometer data. This event was recorded all over the earth and by satellite. In addition, the event occurred during the PPB and ELBBO balloon campaigns. Periodic electric field fluctuations associated with the event were observed on most of the balloons. The solar wind and IMF conditions were only available from GEOTAIL, which was located in the magnetosheath at x~-120 Re. The global electrodynamics of the event was modeled using plots generated by AMIE, (Assimilative Mapping of Ionospheric Electrodynamics). The convection pattern variations during the event were a combination of periodic positive turnings of the convection pattern, and periodic intensifications of the electric potential. The auroral energy flux was observed to intensify periodically during the same period, with a major peak at about 1100 UT.

  8. 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.

  9. 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.

  10. The Role of Circadian Clocks in Metabolic Disease

    PubMed Central

    Li, Min-Dian; Li, Chao-Min; Wang, Zhong

    2012-01-01

    The circadian clock is a highly conserved timing system, resonating physiological processes to 24-hour environmental cycles. Circadian misalignment is emerging as a risk factor of metabolic disease. The molecular clock resides in all metabolic tissues, the dysfunction of which is associated with perturbed energy metabolism. In this article, we will review current knowledge about molecular mechanisms of the circadian clock and the role of clocks in the physiology and pathophysiology of metabolic tissues. PMID:23012586

  11. 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.)...

  12. 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.)...

  13. 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.)...

  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, 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.)...

  16. 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.

  17. 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…

  18. 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

  19. On the Sun, Earth, and Clocks.

    ERIC Educational Resources Information Center

    Easton, D.

    1985-01-01

    Discusses motions of the sun and earth in relation to the accuracy of clocks. Effect of eccentricity of the earth's orbit, efect of inclination of the earth's axis, and combination of these two effects are considered. The accuracy of sundials is also discussed. (DH)

  20. 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)

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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…

  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. European plans for new clocks in space

    NASA Astrophysics Data System (ADS)

    Leschiutta, Sigfrido M.; Tavella, Patrizia

    1995-05-01

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

  8. 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

  9. 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.

  10. ^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)

  11. 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

  12. Entrainment of peripheral clock genes by cortisol

    PubMed Central

    Mavroudis, Panteleimon D.; Scheff, Jeremy D.; Calvano, Steve E.; Lowry, Stephen F.

    2012-01-01

    Circadian rhythmicity in mammals is primarily driven by the suprachiasmatic nucleus (SCN), often called the central pacemaker, which converts the photic information of light and dark cycles into neuronal and hormonal signals in the periphery of the body. Cells of peripheral tissues respond to these centrally mediated cues by adjusting their molecular function to optimize organism performance. Numerous systemic cues orchestrate peripheral rhythmicity, such as feeding, body temperature, the autonomic nervous system, and hormones. We propose a semimechanistic model for the entrainment of peripheral clock genes by cortisol as a representative entrainer of peripheral cells. This model demonstrates the importance of entrainer's characteristics in terms of the synchronization and entrainment of peripheral clock genes, and predicts the loss of intercellular synchrony when cortisol moves out of its homeostatic amplitude and frequency range, as has been observed clinically in chronic stress and cancer. The model also predicts a dynamic regime of entrainment, when cortisol has a slightly decreased amplitude rhythm, where individual clock genes remain relatively synchronized among themselves but are phase shifted in relation to the entrainer. The model illustrates how the loss of communication between the SCN and peripheral tissues could result in desynchronization of peripheral clocks. PMID:22510707

  13. Macroscopic perturbations of the Interplanetary Magnetic Field (IMF) by P/Halley as seen by the Giotto magnetometer

    NASA Technical Reports Server (NTRS)

    Raeder, J.; Neubauer, F. M.; Ness, N.; Burlaga, L. F.

    1986-01-01

    Giotto magnetic field data were used to analyze the macroscopic field structure in the vicinity of P/Halley. During the Giotto flyby at comet P/Halley the IMF showed a quite stable away polarity. Draping of magnetic field lines is clearly observed along the outbound leg of the trajectory. Inside the magnetic pile-up region the field reverses its polarity several times. A symmetry of oppositely magnetized sheets with respect to the nucleus is found and explained in terms of convected IMF features.

  14. Clock gene variants differentiate mood disorders.

    PubMed

    Dmitrzak-Weglarz, Monika Paulina; Pawlak, Joanna Maria; Maciukiewicz, Malgorzata; Moczko, Jerzy; Wilkosc, Monika; Leszczynska-Rodziewicz, Anna; Zaremba, Dorota; Hauser, Joanna

    2015-01-01

    Genetic variations in clock-related genes were hypothesized to be involved to in the susceptibility of mood disorders MD (both unipolar (UPD) and bipolar (BPD) disorders). In our work we investigated role of gene variants form four core period proteins: CLOCK, ARNTL, TIM and PER3. The total sample comprised from 744 mood disorders inpatients (UPD = 229, BPD = 515) and 635 healthy voluntary controls. The 42 SNPs from four genes of interest were genotyped. We used single polymorphisms, haplotypes, SNPs interactions and prediction analysis using classical statistical and machine learning methods. We observed association between two polymorphisms of CLOCK (rs1801260 and rs11932595) with BPDII and two polymorphisms of TIM (rs2291739, rs11171856) with UPD. We also detected ARNTL haplotype variant (rs1160996C/rs11022779G/rs1122780T) to be associated with increased risk of MD, BPD (both types). We established significant epistatic interaction between PER3 (rs2172563) and ARNTL (rs4146388 and rs7107287) in case of BPD. Additionally relation between PER3 (rs2172563) and CLOCK (rs1268271 and rs3805148) appeared in case of UPD. Classification and Regression Trees (C and RT) showed significant predictive value for 10 polymorphisms in all analyzed genes. However we failed to obtain model with sufficient predictive power. During analyses of sleep disturbances sample, we found carriers of homozygote variants (ARNTL: rs11022778 TT, rs1562438 TT, rs1982350 AA and PER3: rs836755 CC) showing more frequent falling asleep difficulties when compare to other genotypes carriers. Our study suggested a putative role of the CLOCK, TIM, ARNTL and PER3 and polymorphisms in MD susceptibility. In our analyses we showed association of specific gene variants with particular types of MD. We also confirmed necessity of performing separate analyzes for BPD and UPD patients. Comprehensive statistical approach is required even with individual symptoms analyses. PMID:25258123

  15. 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.

  16. 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

  17. 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.

  18. Submillimetre galaxies in a hierarchical universe: number counts, redshift distribution and implications for the IMF

    NASA Astrophysics Data System (ADS)

    Hayward, Christopher C.; Narayanan, Desika; Kereš, Dušan; Jonsson, Patrik; Hopkins, Philip F.; Cox, T. J.; Hernquist, Lars

    2013-01-01

    High-redshift submillimetre galaxies (SMGs) are some of the most rapidly star-forming galaxies in the Universe. Historically, galaxy formation models have had difficulty explaining the observed number counts of SMGs. We combine a semi-empirical model with 3D hydrodynamical simulations and 3D dust radiative transfer to predict the number counts of unlensed SMGs. Because the stellar mass functions, gas and dust masses, and sizes of our galaxies are constrained to match observations, we can isolate uncertainties related to the dynamical evolution of galaxy mergers and the dust radiative transfer. The number counts and redshift distributions predicted by our model agree well with observations. Isolated disc galaxies dominate the faint (S1.1 ≲ 1 or S850 ≲ 2 mJy) population. The brighter sources are a mix of merger-induced starbursts and galaxy-pair SMGs; the latter subpopulation accounts for ˜30-50 per cent of all SMGs at all S1.1 ≳ 0.5 mJy (S850 ≳ 1 mJy). The mean redshifts are ˜3.0-3.5, depending on the flux cut, and the brightest sources tend to be at higher redshifts. Because the galaxy-pair SMGs will be resolved into multiple fainter sources by the Atacama Large Millimeter/submillimeter Array (ALMA), the bright ALMA counts should be as much as two times less than those observed using single-dish telescopes. The agreement between our model, which uses a Kroupa initial mass function (IMF), and observations suggests that the IMF in high-redshift starbursts need not be top heavy; if the IMF were top heavy, our model would overpredict the number counts. We conclude that the difficulty some models have reproducing the observed SMG counts is likely indicative of more general problems - such as an underprediction of the abundance of massive galaxies or a star formation rate and stellar mass relation normalization lower than that observed - rather than a problem specific to the SMG population.

  19. Controlling the Cyanobacterial Clock by Synthetically Rewiring Metabolism.

    PubMed

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

    2015-12-22

    Circadian clocks are oscillatory systems that 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 light and dark. We found that feeding sugar to cultures blocked the clock-resetting effect of a dark pulse. Furthermore, 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

  20. 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

  1. 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.

  2. Multiple Cusps under Northward IMF Conditions: Observations and MHD Simulations Compared

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Siscoe, G.; Fritz, T. A.; Zong, Q.; Daly, P. W.; Reme, H.; Balogh, A.; Ridley, A. J.; Raeder, J.

    2007-12-01

    Multiple cusps have been observed by the Cluster spacecraft when the satellites were traveling outbound on Mar 21 and Mar 22, 2001. We conclude that multiple cusps are a temporal effect which is due to the change of the solar wind azimuthal flow (the wind sock effect). The cusp properties derived from two MHD codes, Open GGCM and BATSRUS, have been compared with the Cluster observations. We find that although the simulated magnetospheres are smaller than the real magnetosphere, the simulated magnetic fields and the amplitude of the model-derived plasma parameters (velocity, density, temperature and thermal pressure) agree well with Cluster observations. The MHD code successfully simulated the responses of the cusp positions to the solar wind azimuthal flow. This event is under northward IMF condition. The Geotail spacecraft observed the cold dense plasma when it crossed the dusk flank of the magnetotail. MHD code successfully simulated the formation of the cold sense plasma sheet on the flanks.

  3. Structure of the subsolar magnetopause regions during northward IMF: First results from THEMIS

    NASA Astrophysics Data System (ADS)

    McFadden, J. P.; Phan, T. D.; Carlson, C. W.; Angelopoulos, V.; Glassmeier, K.-H.; Auster, U.

    2008-05-01

    THEMIS observations at the sub-solar magnetopause reveal the structure of the low latitude boundary layer (LLBL) and magnetosheath boundary layer (MSBL) during northward IMF. Unlike previous single spacecraft observations of this region, four of the five THEMIS spacecraft were able to capture the transition of magnetosheath plasma with no electron heating to uni-directional heated electrons followed by bi-directional heated electrons, demonstrating that this electron structure is spatial. Furthermore, the sequence of these transitions shows that the bi-directional heated electrons appear at the outer edge of the weak magnetopause current sheet. Since heated magnetosheath electrons outside the magnetopause current layer are used as an indicator of lobe reconnection in the hemisphere radiating these electrons, reconnection in both lobes is observed before the flux tubes cross the magnetopause. In essence, these observations provide convincing evidence that the LLBL was formed by dual-lobe reconnection.

  4. 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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

    van Dokkum, Pieter

    2014-10-01

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

  8. 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.

  9. Are there auroral signatures related to asymmetric generation of field-aligned currents in the tail due to an IMF By induced twist?

    NASA Astrophysics Data System (ADS)

    Reistad, Jone Peter; stgaard, Nikolai; Tenfjord, Paul; Snekvik, Kristian; Milan, Steve; Oksavik, Kjellmar

    2015-04-01

    It is well known that the IMF influences the Earth's magnetic field. For the case of a dawn-dusk component in the IMF, the magnetic pressure in the lobes will experience a dawn-dusk asymmetry being oppositely directed in the two hemispheres. These asymmetric magnetic pressure distributions forced by the IMF will affect also closed field-lines, and the result is an added By-component in the closed magnetosphere in the same direction as the IMF By. This is known in the literature as IMF By penetration and has frequently been suggested to be responsible for observed differences in the nightside auroral brightness during By dominated IMF. However, a detailed description of how the asymmetric stresses in the tail can propagate to the ionosphere(s) and eventually affect the aurora is presently lacking. Also, the earlier statistical studies indicating this IMF By influence on the global aurora have focused on only one hemisphere. Therefore, the precise mechanism and extent of the IMF By influence on the global aurora in both hemispheres are not fully understood. We present a statistical analysis of the nightside auroral brightness from both hemispheres during carefully selected IMF By dominated events using the FUV-WIC camera on-board the IMAGE spacecraft. Performing the same analysis in both hemispheres with the same camera will provide further insight to these questions. This will help us determine if the stress in the tail imposed by IMF By can affect the Northern and Southern ionospheres differently. If so, these results would be important for understanding the mechanism for asymmetric stress propagation from the tail to the ionospheres.

  10. 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.

  11. Metabolic and Nontranscriptional Circadian Clocks: Eukaryotes

    PubMed Central

    Reddy, Akhilesh B.; Rey, Guillaume

    2016-01-01

    Circadian clocks are cellular timekeeping mechanisms that coordinate behavior and physiology around the 24-h day in most living organisms. Misalignment of an organism’s clock with its environment is associated with long-term adverse fitness consequences, as exemplified by the link between circadian disruption and various age-related diseases in humans. Current eukaryotic models of the circadian oscillator rely on transcription/translation feedback loop mechanisms, supplemented with accessory cytosolic loops that connect them to cellular physiology. However, there is mounting evidence questioning the absolute necessity of transcription-based oscillators for circadian rhythmicity, supported by the recent discovery of oxidation-reduction cycles of peroxiredoxin proteins, which persist even in the absence of transcription. A more fundamental mechanism based on metabolic cycles could thus underlie circadian transcriptional and cytosolic rhythms, thereby promoting circadian oscillations to integral properties of cellular metabolism. PMID:24606143

  12. Analysis of atom-interferometer clocks

    NASA Astrophysics Data System (ADS)

    Peil, Steven; Ekstrom, Christopher R.

    2014-01-01

    We analyze the nature and performance of clocks formed by stabilizing an oscillator to the phase difference between two paths of an atom interferometer. The phase evolution has been modeled as being driven by the proper-time difference between the two paths, although it has an ambiguous origin in the nonrelativistic limit and it requires a full quantum-field-theory treatment in the general case. We present conditions for identifying deviations from the nonrelativistic limit as a way of testing the proper-time-driven phase evolution model. We show that the system performance belies the premise that an atom-interferometer clock is referenced to a divided-down Compton oscillation, and we suggest that this implies there is no physical oscillation at the Compton frequency.

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  20. Effects of clock monitoring on electroencephalographic activity: is unconscious movement initiation an artifact of the clock?

    PubMed

    Miller, Jeff; Shepherdson, Peter; Trevena, Judy

    2011-01-01

    Electroencephalographic (EEG) activity was recorded while participants waited to make spontaneous key-press movements (Experiment 1) or waited for tones in a pitch judgment task (Experiment 2). In one condition of each experiment, participants also had to report the position of a spot traveling on a clock at the crucial time point (i.e., when they decided to move or when the tone was presented), mimicking a procedure used to assess the time of conscious awareness of an event of interest. In a second condition, there was no clock or temporal judgment. Average EEG activity preceding key presses was substantially different when participants had to monitor the clock than when they did not. Smaller clock-related differences in average EEG activity were also present preceding tone onsets. The effects of clock monitoring on EEG activity could be responsible for previous reports that movement-related brain activity begins before participants have consciously decided to move (e.g., Libet, Gleason, Wright, & Pearl, 1983). PMID:21123855

  1. 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.

  2. A Compact Model for the Complex Plant Circadian Clock.

    PubMed

    De Caluw, Jolle; Xiao, Qiying; Hermans, Christian; Verbruggen, Nathalie; Leloup, Jean-Christophe; Gonze, Didier

    2016-01-01

    The circadian clock is an endogenous timekeeper that allows organisms to anticipate and adapt to the daily variations of their environment. The plant clock is an intricate network of interlocked feedback loops, in which transcription factors regulate each other to generate oscillations with expression peaks at specific times of the day. Over the last decade, mathematical modeling approaches have been used to understand the inner workings of the clock in the model plant Arabidopsis thaliana. Those efforts have produced a number of models of ever increasing complexity. Here, we present an alternative model that combines a low number of equations and parameters, similar to the very earliest models, with the complex network structure found in more recent ones. This simple model describes the temporal evolution of the abundance of eight clock gene mRNA/protein and captures key features of the clock on a qualitative level, namely the entrained and free-running behaviors of the wild type clock, as well as the defects found in knockout mutants (such as altered free-running periods, lack of entrainment, or changes in the expression of other clock genes). Additionally, our model produces complex responses to various light cues, such as extreme photoperiods and non-24 h environmental cycles, and can describe the control of hypocotyl growth by the clock. Our model constitutes a useful tool to probe dynamical properties of the core clock as well as clock-dependent processes. PMID:26904049

  3. The regulation of central and peripheral circadian clocks in humans.

    PubMed

    Cermakian, N; Boivin, D B

    2009-11-01

    Many circadian rhythms are controlled by the central clock of the suprachiasmatic nucleus of the hypothalamus, as well as clocks located in other brain regions and most peripheral tissues. These central and peripheral clocks are based on clock genes and their protein products. In recent years, the expression of clock genes has started to be investigated in human samples, primarily white blood cells, but also skin, oral mucosa, colon cells, adipose tissue as well as post-mortem brain tissue. The expression of clock genes in those peripheral tissues offers a way to monitor human peripheral clocks and to compare their function and regulation with those of the central clock, which is followed by markers such as melatonin, cortisol and core body temperature. We have recently used such an approach to compare central and peripheral rhythms in subjects under different lighting conditions. In particular, we have monitored the entrainment of the clock of blood cells in subjects undergoing a simulated night shift protocol with bright light treatment, known to efficiently reset the central clock. This line of research will be helpful for learning more about the human circadian system and to find ways to alleviate health problems of shift workers, and other populations experiencing altered circadian rhythms. PMID:19849799

  4. The hepatic circadian clock modulates xenobiotic metabolism in mice.

    PubMed

    DeBruyne, Jason P; Weaver, David R; Dallmann, Robert

    2014-08-01

    The circadian clock generates daily cycles of gene expression that regulate physiological processes. The liver plays an important role in xenobiotic metabolism and also has been shown to possess its own cell-based clock. The liver clock is synchronized by the master clock in the brain, and a portion of rhythmic gene expression can be driven by behavior of the organism as a whole even when the hepatic clock is suppressed. So far, however, there is relatively little evidence indicating whether the liver clock is functionally important in modulating xenobiotic metabolism. Thus, mice lacking circadian clock function in the whole body or specifically in liver were challenged with pentobarbital and acetaminophen, and pentobarbital sleep time (PBST) and acetaminophen toxicity, respectively, was assessed at different times of day in mutant and control mice. The results suggest that the liver clock is essential for rhythmic changes in xenobiotic detoxification. Surprisingly, it seems that the way in which the clock is disrupted determines the rate of xenobiotic metabolism in the liver. CLOCK-deficient mice are remarkably resistant to acetaminophen and exhibit a longer PBST, while PERIOD-deficient mice have a short PBST. These results indicate an essential role of the tissue-intrinsic peripheral circadian oscillator in the liver in regulating xenobiotic metabolism. PMID:25238856

  5. A Compact Model for the Complex Plant Circadian Clock

    PubMed Central

    De Caluwé, Joëlle; Xiao, Qiying; Hermans, Christian; Verbruggen, Nathalie; Leloup, Jean-Christophe; Gonze, Didier

    2016-01-01

    The circadian clock is an endogenous timekeeper that allows organisms to anticipate and adapt to the daily variations of their environment. The plant clock is an intricate network of interlocked feedback loops, in which transcription factors regulate each other to generate oscillations with expression peaks at specific times of the day. Over the last decade, mathematical modeling approaches have been used to understand the inner workings of the clock in the model plant Arabidopsis thaliana. Those efforts have produced a number of models of ever increasing complexity. Here, we present an alternative model that combines a low number of equations and parameters, similar to the very earliest models, with the complex network structure found in more recent ones. This simple model describes the temporal evolution of the abundance of eight clock gene mRNA/protein and captures key features of the clock on a qualitative level, namely the entrained and free-running behaviors of the wild type clock, as well as the defects found in knockout mutants (such as altered free-running periods, lack of entrainment, or changes in the expression of other clock genes). Additionally, our model produces complex responses to various light cues, such as extreme photoperiods and non-24 h environmental cycles, and can describe the control of hypocotyl growth by the clock. Our model constitutes a useful tool to probe dynamical properties of the core clock as well as clock-dependent processes. PMID:26904049

  6. 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

  7. Abiotic stress and the plant circadian clock

    PubMed Central

    Sanchez, Alfredo; Shin, Jieun

    2011-01-01

    In this review, we focus on the interaction between the circadian clock of higher plants to that of metabolic and physiological processes that coordinate growth and performance under a predictable, albeit changing environment. In this, the phytochrome and cryptochrome photoreceptors have shown to be important, but not essential for oscillator control under diurnal cycles of light and dark. From this foundation, we will examine how emerging findings have firmly linked the circadian clock, as a central mediator in the coordination of metabolism, to maintain homeostasis. This occurs by oscillator synchronization of global transcription, which leads to a dynamic control of a host of physiological processes. These include the determination of the levels of primary and secondary metabolites, and the anticipation of future environmental stresses, such as mid-day drought and midnight coldness. Interestingly, metabolic and stress cues themselves appear to feedback on oscillator function. In such a way, the circadian clock of plants and abiotic-stress tolerance appear to be firmly interconnected processes. PMID:21325898

  8. 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

  9. 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

  10. 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; Mehlstubler, 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 (30015??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

  11. Histone Lysine Demethylase JARID1a Activates CLOCK-BMAL1 and Influences the Circadian Clock

    PubMed Central

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

    2011-01-01

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

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

    PubMed

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

    2011-09-30

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

  13. ORTHO- ELIMINATION OF TRACKING SYSTEM CLOCK ERRORS

    NASA Technical Reports Server (NTRS)

    Wu, J. T.

    1994-01-01

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

  14. Laser clocks and near field gravity of rotating objects

    NASA Technical Reports Server (NTRS)

    Hafele, Joseph C.

    1988-01-01

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

  15. Estimating the stability of N clocks with correlations.

    PubMed

    Torcaso, F; Ekstrom, C R; Burt, E A; Matsakis, D N

    2000-01-01

    Estimation of an atomic clock's frequency stability, separate from its reference, is often done using a three-cornered hat procedure. A major requirement for the success of this method is that clocks be uncorrelated. If this requirement is not satisfied, the three-cornered hat procedure can lead to misleading or even negative variance estimates. Others have considered this problem and developed an analysis that allows for the possibility of cross correlation between clocks. We have extended and applied these ideas to obtain mathematically consistent frequency stability estimates on atomic clock data from the U.S. Naval Observatory. In addition, we derived an expression for the clock weights that produce a minimum variance combination of clocks in the presence of correlations. PMID:18238659

  16. Inexpensive programmable clock for a 12-bit computer

    NASA Technical Reports Server (NTRS)

    Vrancik, J. E.

    1972-01-01

    An inexpensive programmable clock was built for a digital PDP-12 computer. The instruction list includes skip on flag; clear the flag, clear the clock, and stop the clock; and preset the counter with the contents of the accumulator and start the clock. The clock counts at a rate determined by an external oscillator and causes an interrupt and sets a flag when a 12-bit overflow occurs. An overflow can occur after 1 to 4096 counts. The clock can be built for a total parts cost of less than $100 including power supply and I/O connector. Slight modification can be made to permit its use on larger machines (16 bit, 24 bit, etc.) and logic level shifting can be made to make it compatible with any computer.

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

    PubMed

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

    2016-01-22

    We propose the use of optical lattice clocks operated with fermionic alkaline-earth atoms to study spin-orbit coupling (SOC) in interacting many-body systems. The SOC emerges naturally during the clock interrogation, when atoms are allowed to tunnel and accumulate a phase set by the ratio of the "magic" lattice wavelength to the clock transition wavelength. We demonstrate how standard protocols such as Rabi and Ramsey spectroscopy that take advantage of the sub-Hertz resolution of state-of-the-art clock lasers can perform momentum-resolved band tomography and determine SOC-induced s-wave collisions in nuclear-spin-polarized fermions. With the use of a second counterpropagating clock beam, we propose a method for engineering controlled atomic transport and study how it is modified by p- and s-wave interactions. The proposed spectroscopic probes provide clean and well-resolved signatures at current clock operating temperatures. PMID:26849600

  18. 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.

  19. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  1. Clock Genes in Hypertension: Novel Insights from Rodent Models

    PubMed Central

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

    2014-01-01

    The circadian clock plays an integral role in the regulation of physiological processes, including the regulation of blood pressure. However, deregulation of the clock can lead to pathophysiological states including hypertension. Recent work has implicated the circadian clock genes in the regulation of processes in the heart, kidney, vasculature, and the metabolic organs, which are all critical in the regulation of the blood pressure. The goal of this review is to provide an introduction and general overview into the role of circadian clock genes in the regulation of blood pressure with a focus on their deregulation in the etiology of hypertension. This review will focus on the core circadian clock genes CLOCK, BMAL1, Per, and Cry. PMID:25025868

  2. 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.

  3. 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.

  4. 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.

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

    NASA Technical Reports Server (NTRS)

    Dragonette, Richard

    1994-01-01

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

  6. Higher Pole Linear Traps for Atomic Clock Applications

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

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

  7. 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 .

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

    SciTech Connect

    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.

  9. 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 μm. PMID:26365754

  10. 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.

  11. 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 μm.

  12. 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 μm. PMID:26365754

  13. 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.

  14. Working around the clock: circadian rhythms and skeletal muscle

    PubMed Central

    Zhang, Xiping; Dube, Thomas J.

    2009-01-01

    The study of the circadian molecular clock in skeletal muscle is in the very early stages. Initial research has demonstrated the presence of the molecular clock in skeletal muscle and that skeletal muscle of a clock-compromised mouse, Clock mutant, exhibits significant disruption in normal expression of many genes required for adult muscle structure and metabolism. In light of the growing association between the molecular clock, metabolism, and metabolic disease, it will also be important to understand the contribution of circadian factors to normal metabolism, metabolic responses to muscle training, and contribution of the molecular clock in muscle-to-muscle disease (e.g., insulin resistance). Consistent with the potential for the skeletal muscle molecular clock modulating skeletal muscle physiology, there are findings in the literature that there is significant time-of-day effects for strength and metabolism. Additionally, there is some recent evidence that temporal specificity is important for optimizing training for muscular performance. While these studies do not prove that the molecular clock in skeletal muscle is important, they are suggestive of a circadian contribution to skeletal muscle function. The application of well-established models of skeletal muscle research in function and metabolism with available genetic models of molecular clock disruption will allow for more mechanistic understanding of potential relationships. PMID:19696362

  15. Timing by rhythms: Daily clocks and developmental rulers.

    PubMed

    Webb, Alexis B; Oates, Andrew C

    2016-01-01

    Biological rhythms are widespread, allowing organisms to temporally organize their behavior and metabolism in advantageous ways. Such proper timing of molecular and cellular events is critical to their development and health. This is best understood in the case of the circadian clock that orchestrates the daily sleep/wake cycle of organisms. Temporal rhythms can also be used for spatial organization, if information from an oscillating system can be recorded within the tissue in a manner that leaves a permanent periodic pattern. One example of this is the "segmentation clock" used by the vertebrate embryo to rhythmically and sequentially subdivide its elongating body axis. The segmentation clock moves with the elongation of the embryo, such that its period sets the segment length as the tissue grows outward. Although the study of this system is still relatively young compared to the circadian clock, outlines of molecular, cellular, and tissue-level regulatory mechanisms of timing have emerged. The question remains, however, is it truly a clock? Here we seek to introduce the segmentation clock to a wider audience of chronobiologists, focusing on the role and control of timing in the system. We compare and contrast the segmentation clock with the circadian clock, and propose that the segmentation clock is actually an oscillatory ruler, with a primary function to measure embryonic space. PMID:26542934

  16. Power and Skew Aware Point Diffusion Clock Network

    NASA Astrophysics Data System (ADS)

    Jung, Gunok; Kim, Chunghee; Chae, Kyoungkuk; Park, Giho; Park, Sung Bae

    This letter presents point diffusion clock network (PDCN) with local clock tree synthesis (CTS) scheme. The clock network is implemented with ten times wider metal line space than typical mesh networks for low power and utilized to nine times smaller area CTS execution for minimized clock skew amount. The measurement results show that skew amount of PDCN with local CTS is reduced to 36% and latency is shrunk to 45% of the amount in a 4.81mm2 CortexA-8 core with 65nm Samsung process.

  17. Continuous nondemolition measurement of the Cs clock transition pseudospin.

    PubMed

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

    2006-02-01

    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 D1 transition to measure the sample birefringence, which depends on the 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. PMID:16486816

  18. Crosstalk between the Circadian Clock and Innate Immunity in Arabidopsis

    PubMed Central

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

    2013-01-01

    The circadian clock integrates temporal information with environmental cues in regulating plant development and physiology. Recently, the circadian clock has been shown to affect plant responses to biotic cues. To further examine this role of the circadian clock, we tested disease resistance in mutants disrupted in CCA1 and LHY, which act synergistically to regulate clock activity. We found that cca1 and lhy mutants also synergistically affect basal and resistance gene-mediated defense against Pseudomonas syringae and Hyaloperonospora arabidopsidis. Disrupting the circadian clock caused by overexpression of CCA1 or LHY also resulted in severe susceptibility to P. syringae. We identified a downstream target of CCA1 and LHY, GRP7, a key constituent of a slave oscillator regulated by the circadian clock and previously shown to influence plant defense and stomatal activity. We show that the defense role of CCA1 and LHY against P. syringae is at least partially through circadian control of stomatal aperture but is independent of defense mediated by salicylic acid. Furthermore, we found defense activation by P. syringae infection and treatment with the elicitor flg22 can feedback-regulate clock activity. Together this data strongly supports a direct role of the circadian clock in defense control and reveal for the first time crosstalk between the circadian clock and plant innate immunity. PMID:23754942

  19. 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.

  20. 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.

  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. Glucocorticoids entrain molecular clock components in human peripheral cells.

    PubMed

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

    2015-04-01

    In humans, shift work induces a desynchronization between the circadian system and the outside world, which contributes to shift work-associated medical disorders. Using a simulated night shift experiment, we previously showed that 3 d of bright light at night fully synchronize the central clock to the inverted sleep schedule, whereas the peripheral clocks located in peripheral blood mononuclear cells (PBMCs) took longer to reset. This underlines the need for testing the effects of synchronizers on both the central and peripheral clocks. Glucocorticoids display circadian rhythms controlled by the central clock and are thought to act as synchronizers of rodent peripheral clocks. In the present study, we tested whether the human central and peripheral clocks were sensitive to exogenous glucocorticoids (Cortef) administered in the late afternoon. We showed that 20 mg Cortef taken orally acutely increased PER1 expression in PBMC peripheral clocks. After 6 d of Cortef administration, the phases of central markers were not affected, whereas those of PER2-3 and BMAL1 expression in PBMCs were shifted by ? 9.5-11.5 h. These results demonstrate, for the first time, that human peripheral clocks are entrained by glucocorticoids. Importantly, they suggest innovative interventions for shift workers and jet-lag travelers, combining synchronizing agents for the central and peripheral clocks. PMID:25500935

  3. The role of the mechanical clock in medieval science.

    PubMed

    lvarez, Vctor Prez

    2015-03-01

    The invention and spread of the mechanical clock is a complex and multifaceted historical phenomenon. Some of these facets, such as its social impact, have been widely studied, but their scientific dimensions have often been dismissed. The mechanical clock was probably born as a scientific instrument for driving a model of the universe, and not only natural philosophers but also kings, nobles and other members of the social elites showed an interest in clocks as scientific instruments. Public clocks later spread a new way of telling time based on equal hours, laying the foundations for changes in time consciousness that would accelerate scientific thinking. PMID:25802023

  4. Individual trial analysis evidences clock and non-clock based conditioned suppression behaviors in rats.

    PubMed

    Tallot, Lucille; Capela, Daphn; Brown, Bruce L; Doyre, Valrie

    2016-03-01

    We analyzed the temporal pattern of conditioned suppression of lever-pressing for food in rats conditioned with tone-shock pairings using either a 10 or 15s conditioned stimulus (CS)-unconditioned stimulus (US) interval with a CS duration that was three times the CS-US interval. The analysis of average suppression and of individual trials was performed during Probe CS-alone trials and when a short gap was inserted during the CS. The pattern of suppression followed the classical temporal rules: (1) scalar property, (2) a shift in peak suppression due to a gap, compatible with a Stop rule, (3) a three-state pattern of lever-pressing in individual trials, with abrupt start and stop of suppression. The peak of the average suppression curve, but not the middle time, was anticipatory to the programmed US time. The pattern of lever-pressing in individual trials unraveled two types of start of suppression behavior: a clock-based biphasic responding, with a burst of lever-pressing before suppression, and a non-clock based monophasic reduction of lever-pressing close to the CS onset. The non-clock based type of behavior may be responsible for the anticipatory peak time, and the biphasic pattern of lever-pressing may reflect the decision stage described in clock models. PMID:26772780

  5. Polar cap response to the solar wind density jump under constant southward IMF

    NASA Astrophysics Data System (ADS)

    Belenkaya, E. S.; Kalegaev, V. V.; Blokhina, M. S.

    2014-11-01

    Sharp changes of the solar wind parameters determining the dynamic pressure jump lead to strong magnetosphere-ionosphere disturbances. Here the effect on the Earth's ionospheric high latitudes of the solar wind dynamic pressure pulse caused only by the increase of the interplanetary plasma density under southward constant IMF is considered. We investigate reaction of the cross-polar cap potential on the increase of AL index and/or jump of the solar wind density. It is found that for the case of 10 January 1997 the main contribution to the polar cap potential drop increase gave the growth of AL index relative to the input of the solar wind density jump. We also study the influence of the solar wind density increase on the crosspolar cap potential for the quiet magnetospheric conditions. It occurred that the polar cap potential difference decreases with the great increase of the interplanetary plasma density. For the disturbed magnetosphere the main role in the polar cap potential drop increase plays increase of AL. Thus, we found the change of the cross-polar cap potential due to the AL index variations and/or the solar wind density drop even in a case when the interplanetary electric field is constant.

  6. 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 Hα 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.

  7. 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.

  8. Scaling of electric field fluctuations associated with the aurora during northward IMF

    NASA Astrophysics Data System (ADS)

    Kozelov, B. V.; Golovchanskaya, I. V.

    2006-10-01

    We present a statistical study of scaling features of the electric field fluctuations measured by the DE2 satellite in the polar region during positive Bz IMF when the theta-aurora was observed by the DE1 satellite. It is demonstrated that the power spectra of the fluctuations have a power-law form at spatial scales from ~0.5 km (the limit of resolution) to several thousands of kilometers, with a break near 100 km. The scaling properties of the field are studied by examining the generalized structure functions (GSFs) and probability density functions (PDFs) of the fluctuations. The observed PDFs have a non-Gaussian shape with heavy tails. We also demonstrate a collapse of the re-scaled PDFs onto a single curve. A relation of PDF shape to solar wind conditions is revealed. The same analysis is performed on the TV observations of the theta-aurora. The scaling characteristics of the field and auroral fluctuations are compared.

  9. 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.

  10. 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.

  11. The Mackworth Clock Test: a computerized version.

    PubMed

    Lichstein, K L; Riedel, B W; Richman, S L

    2000-03-01

    The Mackworth Clock Test (MCT; N. H. Mackworth, 1948) was developed to evaluate vigilance in British Air Force radar technicians during World War II. Homemade versions of the MCT have since varied with respect to both the characteristics of the device and the procedures of its administration. This article is a report on a computerized version of the MCT developed by the authors to closely emulate Mackworth's test. MCT data were collected from 25 undergraduate students; their performance was found to be equivalent to Mackworth's participants' data. This is the first MCT version that has been validated against the original. PMID:10766107

  12. Large scale temporal and radial gradients in the IMF - Helios 1, 2, ISEE-3, and Pioneer 10, 11

    NASA Technical Reports Server (NTRS)

    Slavin, J. A.; Smith, E. J.; Thomas, B. T.

    1984-01-01

    Recent investigations using measurements at 1 AU have discovered three types of long term variation in the interplanetary magnetic field: solar minimum decreases, solar maximum enhancements, and small decreases around solar reversal. In this study the 1972-1982 Helios 1, 2, ISEE-3, and Pioneer 10, 11 observations between 0.3 and 12 AU are examined to further investigate these changes. It was found that all three IMF solar cycle effects are also present in the Helios and Pioneer measurements, confirming that these variations occur throughout the low latitude heliosphere. In addition, the comparison of measurements by identical magnetometers on ISEE-3, Pioneer 10 and Pioneer 11 has revealed a more rapid decrease in IMF intensity than predicted by classical Parker theory. Causes and ramifications of both the long term variations and steeper-than-expected radial gradients in the interplanetary magnetic field are discussed.

  13. First polar and 1995-034 observations of the midaltitude cusp during a persistent northward IMF condition

    NASA Astrophysics Data System (ADS)

    Grande, M.; Fennell, J.; Livi, S.; Kellett, B.; Perry, C.; Anderson, P.; Roeder, J.; Spence, H.; Fritz, T.; Wilken, B.

    We present the first observations by Polar and 1995-034 of the mid-altitude cusp. On May 29, 1996, the Polar and 1995-034 spacecraft crossed into an extended cusp region. The region was characterized by intense fluxes of solar wind like ions in the energy range 1-10 keV that had angular distributions that showed evidence of flows and trapping. The ion composition data are combined with energetic proton observations from Polar and plasma observations from 1995-034 and DMSP satellites to examine the spatial and temporal extent and plasma characteristics of the cusp during a persistent northward IMF condition. The composition data is consistent with expected solar wind composition with a source temperature of 1.25 106 K. The combined spacecraft observations show an extended cusp-like region, probably produced by northward IMF.

  14. 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.

  15. Heme-based Sensing by the Mammalian Circadian Protein, CLOCK

    PubMed Central

    Lukat-Rodgers, Gudrun S.; Correia, Cristina; Botuyan, Maria Victoria; Mer, Georges; Rodgers, Kenton R.

    2010-01-01

    Heme is emerging as a key player in the synchrony of circadian-coupled transcriptional regulation. Current evidence suggests that levels of circadian-linked transcription are regulated in response to both the availability of intracellular heme and by heme-based sensing of carbon monoxide and possibly nitric oxide. The protein CLOCK is central to the regulation and maintenance of circadian rhythms in mammals. CLOCK comprises two PAS domains, each with a heme binding site. Our studies focus on the functionality of the Murine CLOCK PASA domain (residues 103-265). We show that CLOCK PASA binds Fe(III) protoporhyrin IX to form a complex with 1:1 stoichiometry. Optical absorbance and resonance Raman studies reveal that the heme of ferric CLOCK PASA is a six-coordinate, low spin complex whose resonance Raman signature is insensitive to pH over the range of protein stability. Ferrous CLOCK PASA is a mixture of five-coordinate, high spin and six-coordinate, low spin complexes. Ferrous CLOCK PASA forms complexes with CO and NO. Ferric CLOCK PASA undergoes reductive nitrosylation in the presence of NO to generate a CLOCK PASANO, which is a pentacoordinate {FeNO}7 complex. Formation of the highly stable {FeNO}7 heme complex from either ferrous or ferric heme makes possible the binding of NO at very low concentration, a characteristic of NO sensors. Comparison of the spectroscopic properties and CO binding kinetics of CLOCK PASA with other CO sensor proteins reveals that CLOCK PASA exhibits chemical properties consistent with a heme-based gas sensor protein. PMID:20666392

  16. 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.

  17. Reading Angles in Maps

    ERIC Educational Resources Information Center

    Izard, Vronique; 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 47:15-53:30months) were presented with fragments of geometric maps, in which angle sections

  18. Magnetopause surface waves triggered by a rotating IMF with the global MHD SWMF/BAT-S-RUS model

    NASA Astrophysics Data System (ADS)

    Andriyas, T.; Spencer, E. A.

    2010-12-01

    The solar wind driving of magnetopause surface waves is only partly understood. In particular we do not have a picture of the magnetopause surface wave properties and behavior when a magnetic cloud event, which sometimes involves a rotating IMF, impinges on the magnetosphere. Here we investigate the effect of a twisting or rotational IMF under moderate solar wind velocity (about 500 km/s) upon the magnetosphere with the Global MHD BATS-R-US code. Synthetic solar wind data is constructed to simulate the most important features of a magnetic cloud event, but without including shock features. A sinusoidally varying By component accompanied by a cosinusoidally varying Bz component of the IMF is input into the model with magnitude 10-20 nT. The synthetic data is representative of the magnetic cloud event that occurred on October 3-7 2000. We use the results of the simulation to infer the modes, properties, and particularly the phase speed and wavelength of the surface wave structures.

  19. 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.

  20. Temperature-Compensated Clock Skew Adjustment

    PubMed Central

    Castillo-Secilla, Jose Mara; Palomares, Jose Manuel; Olivares, Joaqun

    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

  1. 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

  2. Circadian Clock Control of Endocrine Factors

    PubMed Central

    Gamble, Karen L.; Berry, Ryan; Frank, Stuart J.; Young, Martin E.

    2015-01-01

    Organisms experience dramatic fluctuations in demands/stresses over the course of the day. In order to maintain biological processes within physiologic boundaries, it is imperative that mechanisms have evolved for anticipation of, and adaptation to, these daily fluctuations. Endocrine factors undoubtedly play an integral role in homeostasis. Not only do circulating levels of various endocrine factors oscillate over the 24 period, but so too does responsiveness of target tissues to these signals/stimuli. Emerging evidence suggests that these daily oscillations do not occur solely in response to behavioral fluctuations associated with sleep/wake and feeding/fasting cycles, but are orchestrated in part by an intrinsic timekeeping mechanism known as the circadian clock. Disruption of circadian clocks, through genetic and/or environmental means, appears to precipitate numerous common disorders, including cardiometabolic diseases and cancer. Collectively, these observations, which are reviewed within the current article, have led to suggestion that strategies designed to realign normal circadian rhythmicities hold a therapeutic potential for the treatment of various endocrine-related disorders. PMID:24863387

  3. 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.

  4. Velocity response curves demonstrate the complexity of modeling entrainable clocks.

    PubMed

    Taylor, Stephanie R; Cheever, Allyson; Harmon, Sarah M

    2014-12-21

    Circadian clocks are biological oscillators that regulate daily behaviors in organisms across the kingdoms of life. Their rhythms are generated by complex systems, generally involving interlocked regulatory feedback loops. These rhythms are entrained by the daily light/dark cycle, ensuring that the internal clock time is coordinated with the environment. Mathematical models play an important role in understanding how the components work together to function as a clock which can be entrained by light. For a clock to entrain, it must be possible for it to be sped up or slowed down at appropriate times. To understand how biophysical processes affect the speed of the clock, one can compute velocity response curves (VRCs). Here, in a case study involving the fruit fly clock, we demonstrate that VRC analysis provides insight into a clock׳s response to light. We also show that biochemical mechanisms and parameters together determine a model׳s ability to respond realistically to light. The implication is that, if one is developing a model and its current form has an unrealistic response to light, then one must reexamine one׳s model structure, because searching for better parameter values is unlikely to lead to a realistic response to light. PMID:25193284

  5. 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...

  6. Variable-clock-rate A/D converter

    NASA Technical Reports Server (NTRS)

    Lipoma, P. C.

    1980-01-01

    Analog-to-digital (A/D) converter operates at two different rates (slow and fast) so that low amplitude noise is reduced without loss of transient response. During tracking, when sensitivity is important, slow clock reduces noise. In search mode, when signal may change rapidly, fast clock ensures rapid response.

  7. 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.

  8. 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.

  9. 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

  10. 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 Clock pattern 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 Regular Rate Extra Compensation Paid for Overtime 778.204 Clock pattern premium...

  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 Clock pattern 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 Regular Rate Extra Compensation Paid for Overtime 778.204 Clock pattern premium...

  12. 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 Clock pattern 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 Regular Rate Extra Compensation Paid for Overtime 778.204 Clock pattern premium...

  13. 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 Clock pattern 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 Regular Rate Extra Compensation Paid for Overtime 778.204 Clock pattern premium...

  14. 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 Clock pattern 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 Regular Rate Extra Compensation Paid for Overtime 778.204 Clock pattern premium...

  15. 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 ...

  16. [The role of biological clock in glucose homeostasis].

    PubMed

    Chrościcki, Piotr; Usarek, Michał; Bryla, Jadwiga

    2013-01-01

    The mechanism of the biological clock is based on a rhythmic expression of clock genes and clock-controlled genes. As a result of their transcripto-translational associations, endogenous rhythms in the synthesis of key proteins of various physiological and metabolic processes are created. The major timekeeping mechanism for these rhythms exists in the central nervous system. The master circadian clock, localized in suprachiasmatic nucleus (SCN), regulates multiple metabolic pathways, while feeding behavior and metabolite availability can in turn regulate the circadian clock. It is also suggested that in the brain there is a food entrainable oscillator (FEO) or oscillators, resulting in activation of both food anticipatory activity and hormone secretion that control digestion processes. Moreover, most cells and tissues express autonomous clocks. Maintenance of the glucose homeostasis is particularly important for the proper function of the body, as this sugar is the main source of energy for the brain, retina, erythrocytes and skeletal muscles. Thus, glucose production and utilization are synchronized in time. The hypothalamic excited orexin neurons control energy balance of organism and modulate the glucose production and utilization. Deficiency of orexin action results in narcolepsy and weight gain, whereas glucose and amino acids can affect activity of the orexin cells. Large-scale genetic studies in rodents and humans provide evidence for the involvement of disrupted clock gene expression rhythms in the pathogenesis of obesity and type 2 diabetes. In general, the current lifestyle of the developed modern societies disturbs the action of biological clock. PMID:23799401

  17. 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...

  18. 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.

  19. 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 α-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.

  20. A mechanosensory pathway to the Drosophila circadian clock.

    PubMed

    Simoni, Alekos; Wolfgang, Werner; Topping, Matthew P; Kavlie, Ryan G; Stanewsky, Ralf; Albert, Joerg T

    2014-01-31

    Circadian clocks attune the physiology of virtually all living organisms to the diurnal cycles of their environments. In metazoan animals, multiple sensory input pathways have been linked to clock synchronization with the environmental cycle (entrainment). Extrinsic entrainment cues include light and temperature. We show that (12-hour:12-hour) cycles of vibration and silence (VS) are sufficient to synchronize the daily locomotor activity of wild-type Drosophila melanogaster. Behavioral synchronization to VS cycles required a functional clock and functional chordotonal organs and was accompanied by phase-shifts of the daily oscillations of PERIOD protein concentrations in brain clock neurons. The feedback from mechanosensory-and particularly, proprioceptive-organs may help an animal to keep its circadian clock in sync with its own, stimulus-induced activities. PMID:24482478

  1. 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

  2. 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 Einsteins general theory of relativity, time depends locally on gravity; in standard quantum theory, time is globalall 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 patterns 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.

  3. STRESSing the role of the plant circadian clock.

    PubMed

    Seo, Pil Joon; Mas, Paloma

    2015-04-01

    The circadian clock is a timekeeper mechanism that is able to regulate biological activities with a period of 24h. Proper matching of the internal circadian time with the environment not only confers fitness advantages but also allows the clock to temporally gate the responses to environmental stresses. By restricting the time of maximal responsiveness, the circadian gating defines an efficient way to increase resistance to stress without substantially decreasing plant growth. Stress signaling in turn appears to influence the clock activity. The feedback regulation might be important to maximize metabolic efficiency under challenging environmental conditions. This review focuses on recent research advances exploring the intricate connection between the clock and osmotic stresses. The role of the circadian clock favoring the proper balance between immune responses and cellular metabolism is also discussed. PMID:25631123

  4. Dissecting the Mechanisms of the Clock in Neurospora

    PubMed Central

    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

  5. Clock Synchronization in Wireless Sensor Networks: An Overview

    PubMed Central

    Rhee, Ill-Keun; Lee, Jaehan; Kim, Jangsub; Serpedin, Erchin; Wu, Yik-Chung

    2009-01-01

    The development of tiny, low-cost, low-power and multifunctional sensor nodes equipped with sensing, data processing, and communicating components, have been made possible by the recent advances in micro-electro-mechanical systems (MEMS) technology. Wireless sensor networks (WSNs) assume a collection of such tiny sensing devices connected wirelessly and which are used to observe and monitor a variety of phenomena in the real physical world. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. This paper reviews the existing clock synchronization protocols for WSNs and the methods of estimating clock offset and clock skew in the most representative clock synchronization protocols for WSNs. PMID:22389588

  6. Residual discrete symmetry of the five-state clock model

    NASA Astrophysics Data System (ADS)

    Baek, Seung Ki; Mkel, Harri; Minnhagen, Petter; Kim, Beom Jun

    2013-07-01

    It is well known that the q-state clock model can exhibit a Kosterlitz-Thouless (KT) transition if q is equal to or greater than a certain threshold, which has been believed to be five. However, recent numerical studies indicate that helicity modulus does not vanish in the high-temperature phase of the five-state clock model as predicted by the KT scenario. By performing Monte Carlo calculations under the fluctuating twist boundary condition, we show that it is because the five-state clock model does not have the fully continuous U(1) symmetry even in the high-temperature phase while the six-state clock model does. We suggest that the upper transition of the five-state clock model is actually a weaker cousin of the KT transition so that it is q?6 that exhibits the genuine KT behavior.

  7. Similarities in the circadian clock and photoperiodism in plants

    PubMed Central

    Song, Young Hun; Ito, Shogo; Imaizumi, Takato

    2010-01-01

    Summary of recent advances Plants utilize circadian clocks to synchronize their physiological and developmental events with daily and yearly changes in the environment. Recent advances in Arabidopsis research have provided a better understanding of the molecular mechanisms of the circadian clock and photoperiodism. One of the most important questions is whether the mechanisms studied in Arabidopsis are conserved in other plants. Homologs of many Arabidopsis clock genes have been identified in various plants and some gene functions have been characterized. It seems that the circadian clocks in plants are similar. Recent success in molecular genetics has also revealed the mechanisms of photoperiodic flowering in cereals. The day-length sensing mechanisms appear to have diverged more between long-day plants and short-day plants than the circadian clock. PMID:20620097

  8. Noise and instability of an optical lattice clock

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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 one to infer the clock stability for different modes of operation. 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 ×10-16/√{τ } as a function of averaging time τ expressed in seconds for normal clock operation.

  9. Quantum Algorithmic Readout in Multi-Ion Clocks

    NASA Astrophysics Data System (ADS)

    Schulte, M.; Lörch, N.; Leroux, I. D.; Schmidt, P. O.; Hammerer, K.

    2016-01-01

    Optical clocks based on ensembles of trapped ions promise record frequency accuracy with good short-term stability. Most suitable ion species lack closed transitions, so the clock signal must be read out indirectly by transferring the quantum state of the clock ions to cotrapped logic ions of a different species. Existing methods of quantum logic readout require a linear overhead in either time or the number of logic ions. Here we describe a quantum algorithmic readout whose overhead scales logarithmically with the number of clock ions in both of these respects. The scheme allows a quantum nondemolition readout of the number of excited clock ions using a single multispecies gate operation which can also be used in other areas of ion trap technology such as quantum information processing, quantum simulations, metrology, and precision spectroscopy.

  10. 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

  11. 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.

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

    PubMed Central

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

    2015-01-01

    Summary 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

  13. 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.

  14. Quantum Algorithmic Readout in Multi-Ion Clocks.

    PubMed

    Schulte, M; Lrch, N; Leroux, I D; Schmidt, P O; Hammerer, K

    2016-01-01

    Optical clocks based on ensembles of trapped ions promise record frequency accuracy with good short-term stability. Most suitable ion species lack closed transitions, so the clock signal must be read out indirectly by transferring the quantum state of the clock ions to cotrapped logic ions of a different species. Existing methods of quantum logic readout require a linear overhead in either time or the number of logic ions. Here we describe a quantum algorithmic readout whose overhead scales logarithmically with the number of clock ions in both of these respects. The scheme allows a quantum nondemolition readout of the number of excited clock ions using a single multispecies gate operation which can also be used in other areas of ion trap technology such as quantum information processing, quantum simulations, metrology, and precision spectroscopy. PMID:26799016

  15. Response time of the polar ionospheric convection pattern to changes in the north-south direction of the IMF. Scientific report No. 1

    SciTech Connect

    Hairston, M.R.; Heelis, R.A.

    1995-03-01

    A three day period from January 27 through January 29, 1992 is analyzed using one minute resolution solar wind data from the IMP8 satellite and the ionospheric convection pattern data derived from the four operational DMSP satellites. During this period there were several clear reversals of the sign of the z component of the interplanetary magnetic field (IMF) which is known to have a direct effect on the convection patterns observed in the polar ionosphere. Polar convection patterns observed by the frequent passes of four DMSP satellites are examined following each sign change to determine the time lag between the change in the IMF at the magnetopause and the establishment of a new global convection signature in the ionosphere. After removing the transit time for the IMF to travel from the position of the IMP-8 satellite to the magnetopause, a further time lag of about 17 to 25 minutes is observed for the five cases where the IMF turned from northward to southward. A longer lag of between 28 and 44 minutes is observed for the two cases where the IMF turned from southward to northward. These lags are interpreted as the inertial response time of the ionosphere in reacting to the change in the IMF.

  16. Laser angle sensor development

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

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

  17. Response of Saturn's Current Sheet Structure to Changes in the Solar Wind Dynamic Pressure and IMF

    NASA Astrophysics Data System (ADS)

    Hansen, K. C.; Jia, X.; Gombosi, T. I.

    2010-12-01

    Using our global MHD model of Saturns magnetosphere, we investigate the location, shape and motion of Saturns current sheet under a variety of situations. Our global MHD model self consistently treats the entire magnetosphere and includes magnetospheric plasma sources from a major disk-like source from Enceladus and the rings and a secondary toroidal plasma source from Titan. The model produces solutions which are not constrained to be symmetric therefore the results are quite useful in trying to extend previous models that have been generated using Cassini data. Because we can carefully control the inputs to our MHD model, we do not have to worry about separating variations due to local time, varying upstream conditions, spacecraft motion or changes in the mass loading rate that often make interpreting the data complicated. We will present results for both steady state, as well as time varying solar wind conditions. Simulations with constant solar wind conditions allow us to study the effect that upsteam dynamic pressure has on both the shape and size of the current sheet. In addition, we will present results from simulations that include sudden changes in the solar wind dynamics pressure as well as the IMF direction. These simulations will allow us to study the current sheet response and to look for features such as current sheet flapping. Our previous studies have shown that the current sheet in our model does in fact reproduce the bowl-like behavior expect at most local times. However, at dusk, the current sheet is often quite warped. We will examine the cause of this warping and under what conditions it occurs.

  18. From nearby low-mass protostars to high redshift starbursts: protostellar outflows tracing the IMF

    NASA Astrophysics Data System (ADS)

    Kristensen, Lars E.; Bergin, Edwin

    2015-08-01

    Embedded low-mass protostars are notoriously difficult to observe even in the nearest Galactic high-mass clusters where they outnumber the high-mass protostars by orders of magnitude. Thus, without a good tracer of the low-mass population, we do not have a good handle on the shape of the initial (core) mass function, leaving little hope for extrapolating to extragalactic regions where we will never have neither the sensitivity nor the resolution to directly observe this population. A good tracer of the low-mass population is needed.One such physical tracer is outflows. Outflow emission is directly proportional to envelope mass, and outflows are predominantly active during the deeply embedded phases of star formation. What is required for this method to work is species and transitions tracing outflows uniquely such that any signal is not diluted by the surrounding cloud, such as certain methanol transitions, water, high-J CO (J > 10).I will present a statistical model of a forming high-mass cluster. The model includes what we currently know about Galactic high-mass clusters and incorporates outflow emission from low-mass protostars. The latter component is obtained from observations of tens of nearby embedded low-mass protostellar outflows in the above-mentioned tracers. The model is benchmarked against ALMA and Herschel-HIFI observations of Galactic clusters proving the concept, and preliminary extrapolations to the extragalactic regime are presented. With this new probe, and traditional probes of the distant star formation which predominantly trace high mass stars, we will be able to explore the IMF in starburst galaxies from low to high redshift.

  19. Sr lattice clock at 1 x 10(-16) fractional uncertainty by remote optical evaluation with a Ca clock.

    PubMed

    Ludlow, A D; Zelevinsky, T; Campbell, G K; Blatt, S; Boyd, M M; de Miranda, M H G; Martin, M J; Thomsen, J W; Foreman, S M; Ye, Jun; Fortier, T M; Stalnaker, J E; Diddams, S A; Le Coq, Y; Barber, Z W; Poli, N; Lemke, N D; Beck, K M; Oates, C W

    2008-03-28

    Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 x 10(-16) fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts. PMID:18276849

  20. The eCDR-PLL, a radiation-tolerant ASIC for clock and data recovery and deterministic phase clock synthesis

    NASA Astrophysics Data System (ADS)

    Leitao, P.; Francisco, R.; Llopart, X.; Tavernier, F.; Baron, S.; Bonacini, S.; Moreira, P.

    2015-03-01

    A radiation-tolerant CDR/PLL ASIC has been developed for the upcoming LHC upgrades, featuring clock Frequency Multiplication (FM) and Clock and Data Recovery (CDR), showing deterministic phase and low jitter. Two FM modes have been implemented: either generating 40, 60, 120 and 240 MHz clock outputs for GBT-FPGA applications or providing 40, 80, 160 and 320 MHz clocks for TTC and e-link applications. The CDR operates with 40, 80, 160 or 320 Mbit/s data rates while always generating clocks at 40, 80, 160 and 320 MHz, regardless of the data rate. All the outputs are phase programmable with a resolution of 195 ps or 260 ps, depending on the selected mode. The ASIC has been designed using radiation-tolerant techniques in a 130 nm CMOS technology and operates at a 1.2 V supply voltage.

  1. Reading Angles in Maps

    PubMed Central

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

    2013-01-01

    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 47:1553:30 months) were presented with fragments of geometric maps, in which angle sections appeared without any relevant length or distance information. Children were able to read these map fragments and compare 2D to 3D angles. However, this ability appeared both variable and fragile among the youngest children of the sample. These findings suggest that 4-year-old children begin to form an abstract concept of angle that applies both to 2D and 3D displays and that serves to interpret novel spatial symbols. PMID:23647223

  2. '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.

  3. 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.

  4. Ferrodroplets: a Global Clock for Droplet Microfluidics

    NASA Astrophysics Data System (ADS)

    Katsikis, Georgios; Prakash, Manu

    2012-11-01

    A fluidic analogue to magnetic bubble computer memory is proposed as a novel propagation mechanism for droplet microfluidics. We designed a prototype microfluidic device where ferrofluid droplets are actuated along a 2-D plane using soft magnet patterns under the influence of rotating magnetic fields. The state of the system is dependent on occupancy of fluid droplets and the track geometry. The propagation characteristics of droplets are studied experimentally by varying operation parameters such as the magnitude and frequency of in-plane magnetic fields and the length scale of the device. The experimental findings are juxtaposed with scaling arguments and numerical simulations. Applications for this device as a universal clocking mechanism for droplet microfluidics are discussed.

  5. Dynamics and performance of clock pendulums

    NASA Astrophysics Data System (ADS)

    Hoyng, Peter

    2014-11-01

    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.

  6. 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.

  7. Asthma: Chronopharmacotherapy and the molecular clock.

    PubMed

    Burioka, Naoto; Fukuoka, Yasushi; Koyanagi, Satoru; Miyata, Masanori; Takata, Miyako; Chikumi, Hiroki; Takane, Hiroshi; Watanabe, Masanari; Endo, Masahiro; Sako, Takanori; Suyama, Hisashi; Ohdo, Shigehiro; Shimizu, Eiji

    2010-07-31

    Bronchial asthma is characterized by chronic airways inflammation and reversible airflow limitation. In patients with asthma, symptoms generally worsen during the early hours of the morning, and pulmonary function often deteriorates at the same time, suggesting a role for chronopharmacotherapy. Several drugs for asthma have been developed based on chronopharmacology. Most medications employed for the chronotherapy of asthma are administered once at night with the goal of preventing chronic airway inflammation or development of airflow limitation. In addition to bronchodilators, the inhaled glucocorticosteroid ciclesonide is now available with once-daily dosing, which also improves patients' compliance. Numerous investigations have demonstrated the usefulness of chronotherapy for asthma, especially for patients with nocturnal asthma. This review focuses on chronotherapy of asthma, and also provides a molecular biological explanation for the influence of asthma medications on the clock genes. PMID:20359514

  8. Cosmic time dilation: The clock paradox revisited

    NASA Astrophysics Data System (ADS)

    Tomaschitz, Roman

    2004-05-01

    The relativistic time dilation is reviewed in a cosmological context. We show that a clock or twin paradox does not arise if cosmic time is properly taken into account. The receding galaxy background provides a unique frame of reference, and the proper times of geodesic as well as accelerated observers can be linked to the universal cosmic time parameter. This suggests to compare the proper time differentials of the respective observers by determining their state of motion in the galaxy grid. In this way, each observer can figure out whether his proper time is dilated or contracted relative to any other. In particular one can come to unambiguous conclusions on the aging of uniformly moving observers, without reference to asymmetries in measurement procedures or accelerations they may have undergone.

  9. 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.

  10. Evolutionary plasticity of segmentation clock networks

    PubMed Central

    Krol, Aurlie J.; Roellig, Daniela; Dequant, Mary-Lee; Tassy, Olivier; Glynn, Earl; Hattem, Gaye; Mushegian, Arcady; Oates, Andrew C.; Pourqui, Olivier

    2011-01-01

    The vertebral column is a conserved anatomical structure that defines the vertebrate phylum. The periodic or segmental pattern of the vertebral column is established early in development when the vertebral precursors, the somites, are rhythmically produced from presomitic mesoderm (PSM). This rhythmic activity is controlled by a segmentation clock that is associated with the periodic transcription of cyclic genes in the PSM. Comparison of the mouse, chicken and zebrafish PSM oscillatory transcriptomes revealed networks of 40 to 100 cyclic genes mostly involved in Notch, Wnt and FGF signaling pathways. However, despite this conserved signaling oscillation, the identity of individual cyclic genes mostly differed between the three species, indicating a surprising evolutionary plasticity of the segmentation networks. PMID:21652651

  11. 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.

  12. 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.

  13. 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.

  14. 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''.

  15. 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

  16. Transcriptional Control of Antioxidant Defense by the Circadian Clock

    PubMed Central

    Patel, Sonal A.; Velingkaar, Nikkhil S.

    2014-01-01

    Abstract Significance: The circadian clock, an internal timekeeping system, is implicated in the regulation of metabolism and physiology, and circadian dysfunctions are associated with pathological changes in model organisms and increased risk of some diseases in humans. Recent Advances: Data obtained in different organisms, including humans, have established a tight connection between the clock and cellular redox signaling making it among the major candidates for a link between the circadian system and physiological processes. Critical Issues: In spite of the recent progress in understanding the importance of the circadian clock in the regulation of reactive oxygen species homeostasis, molecular mechanisms and key regulators are mostly unknown. Future Directions: Here we review, with an emphasis on transcriptional control, the circadian-clock-dependent control of oxidative stress response system as a potential mechanism in age-associated diseases. We will discuss the roles of the core clock components such as brain and muscle ARNT-like 1, Circadian Locomotor Output Cycles Kaput, the circadian-clock-controlled transcriptional factors such as nuclear factor erythroid-2-related factor, and peroxisome proliferator-activated receptor and circadian clock control chromatin modifying enzymes from sirtuin family in the regulation of cellular and organism antioxidant defense. Antioxid. Redox Signal. 20, 29973006. PMID:24111970

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

  18. Pressure sensitivity of the vapor-cell atomic clock.

    PubMed

    Iyanu, Gebriel; Wang, He; Camparo, James

    2009-06-01

    Although atomic clocks have very low levels of frequency instability, they are nonetheless sensitive (albeit slightly) to various environmental parameters, including temperature, power supply voltage, and dc magnetic fields. In the terrestrial environment, however, atmospheric pressure (i.e., the air's molecular density) is not generally included in this list, because the air's density variations near the surface of the earth will typically have a negligible effect on the clock's performance. The situation is different, however, for clocks onboard satellites like Galileo, where manufacturing and testing are done at atmospheric pressure, while operation is in vacuum. The pressure sensitivity of atomic clocks, in particular vapor-cell atomic clocks, can therefore be of significance. Here, we discuss some of the ways in which changes in atmospheric pressure affect vapor-cell atomic clocks, and we demonstrate that, for one device, the pressure-sensitivity traces back to a pressure-induced change in the temperature of the clock's filter and resonance cells. PMID:19574121

  19. 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:

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

    PubMed Central

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

    2015-01-01

    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 activities1–3. 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 investigated4–7. 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 (SA) 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