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Sample records for imf clock angle

  1. 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.

  2. Magnetospheric sash dependence on IMF direction

    NASA Astrophysics Data System (ADS)

    Siscoe, G. L.; Erickson, G. M.; Ö Sonnerup, B. U.; Maynard, N. C.; Siebert, K. D.; Weimer, D. R.; White, W. W.

    The magnetospheric sash is a ribbon of weak field shaped like a horseshoe with its open ends adjacent to the north and south dayside, magnetopause cusps and its closed end forming the cross-tail current sheet. The clock angle of the sash in the dawn-dusk meridian plane (as seen from the sun) rotates from 0° to 90° as the clock angle of the interplanetary magnetic field (IMF) rotates from 0° to 180°. We use a global MHD simulation to obtain the sash clock angles for IMF clock angles of 45°, 90°, and 135°. Remarkably, the results are very close to the clock angle of the magnetic null points obtained by superposing a uniform field representing the IMF on a dipole field representing the earth. Contours of magnetic field strength on cross sections perpendicular to the solar wind flow direction show how the sash evolves tailward from the dayside cusps.

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

    NASA Astrophysics Data System (ADS)

    Förster, M.; Rentz, S.; Köhler, 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.

  4. The rate of occurrence of dayside Pc 3,4 pulsations - The L-value dependence of the IMF cone angle effect

    NASA Technical Reports Server (NTRS)

    Russell, C. T.; Luhmann, J. G.; Odera, T. J.; Stuart, W. F.

    1983-01-01

    When the angle of the IMF to the earth sun line is 15 deg or less, the occurrence rate of dayside Pc 3,4 pulsations in 7-8 times the average at L values of 2.4-2.8, and 2.2-3.5 times the average at L of 4-4.3. These waves disappear when the IMF is nearly at right angles to the sun-earth line. Such observations are consistent with a source originating in the waves upstream of the subsolar bow shock, which are transported by convection to the magnetopause. There, they couple to oscillations of magnetospheric field lines. Because the magnetospheric plasma's index of refraction decreases with radial distance except at the plasmapause, inwardly propagating waves should be refracted away from the radial direction. To reach low L values, the waves should therefore couple near the stagnation point and propagate nearly radially inwards. The streamline geometry and its connection to the foreshock region is illustrated for various IMF orientations, using a simple approximation to the magnetosheath flow field.

  5. Solar wind plasma entry into the magnetosphere under northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Li, Wenhui; Raeder, Joachim; Thomsen, Michelle F.; Lavraud, Benoit

    2008-04-01

    This study examines how solar wind plasma enters the magnetosphere under northward interplanetary magnetic field (IMF) conditions, using the Open Geospace General Circulation Model (OpenGGCM) for various solar wind, IMF, and geomagnetic dipole conditions. We trace flow paths of individual fluid elements from the solar wind and study the variation of the topology of the magnetic field line along those flow paths. We find that there is an entry window through which the solar wind plasma can enter the magnetosphere as a result of double high-latitude reconnection under northward IMF conditions. We investigate how the entry window depends on solar wind, IMF, and geomagnetic dipole parameters, and we estimate the solar wind plasma entry rate for various conditions. We find that the effective entry rate under northward IMF conditions is of the order of 1026 to 1027 particles per second. We also estimate the conditions for which solar wind plasma entry is most efficient. The newly created flux tubes with closed-field topology are subsequently convected to the nightside and consequently cause magnetosheath plasma to be captured and enter the magnetosphere. Some captured dayside plasma takes about 90 min to convect along the magnetopause to a near tail flank region of the central plasma sheet, thus forming a cold dense plasma sheet. Double high-latitude reconnection can also release the captured plasma. Thus a balance of inflow and outflow of the captured plasma is eventually established under prolonged northward IMF conditions. We find that high-latitude reconnection is common under northward IMF conditions in our simulations. It occurs for IMF with any clock angle within [-90°, 90°], measured in front of the bow shock, and for any geomagnetic dipole tilt angle within [-30°, 30°]. An IMF field line with a zero x component usually first reconnects with a geomagnetic field line at the northern high-latitude boundary when the geomagnetic dipole tilts positive toward the

  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

  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

  8. The dependence of the LLBL thickness on IMF Bz and By components

    NASA Astrophysics Data System (ADS)

    Znatkova, S. S.; Antonova, E. E.; Pulinets, M. S.; Kirpichev, I. P.; Riazantseva, M. O.

    2016-07-01

    The thickness of the low latitude boundary layer (LLBL) is studied as a function of interplanetary magnetic field (IMF) using the data of THEMIS mission. The data from intersections of LLBL by Themis-A and -C satellites are analyzed. Solar wind parameters are provided by Themis-B satellite located before the bow shock. We use earlier developed method of LLBL thickness determination based on the analysis of the variation of plasma velocity in the layer perpendicular to the magnetopause. The database for the present analysis consists of 109 single satellite LLBL crossings where the values of LLBL thickness are obtained. The time shift of solar wind propagation from the spacecraft performing measurements outside the bow shock to the LLBL is taken into account. We analyze the dependence of LLBL thickness on IMF Bz and By using data of IMF measurements with 3 s resolution and produce the 180 s averaging of these data. Large scattering of the values of LLBL thickness and the weak dependence on IMF is demonstrated. Dawn-dusk asymmetry of LLBL thickness is not observed. The dependence of LLBL thickness on IMF clock angle is discussed.

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

    NASA Astrophysics Data System (ADS)

    Haaland, S. E.; Paschmann, G.; Förster, 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.

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

    NASA Astrophysics Data System (ADS)

    Förster, 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

  11. High-Latitude Plasma Convection as a Function of Solar Wind and IMF Using a Simple Parameterization

    NASA Astrophysics Data System (ADS)

    Baker, K. B.

    2001-12-01

    A simple parameterization of high-latitude ionospheric plasma convection patterns has been developed to study the relationship of the convection patterns to the speed and density of the solar wind and the interplanetary magnetic field (IMF). The parameterization includes the overall size of the convection pattern, the total potential drop, the orientation of the pattern, and the relative sizes of the dawn and dusk convection cells. The spherical harmonic fitting analysis of Ruohoniemi and Baker [1998] was applied to two years (1999, 2000) of SuperDARN HF-Radar data from the northern hemisphere. Solar Wind and IMF data were take from the definitive ACE key parameter data. Linear regression analysis was applied to determine the relationship of the convection pattern parameters to various combinations of solar wind and IMF parameters. The polar cap potential drop was found to be most strongly correlated to vBz, but a weaker correlation to v*abs(By) was also noted. The orientation of the convection pattern was well correlated with either By alone or the IMF clock angle. Ruohoniemi, J. M., and K. B. Baker, Large-scale imaging of high-latitude convection with SuperDARN HF-radar observations, J. Geophys. Res., 103, 20,797-20,811, 1998.

  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. On magnetopause inflation under radial IMF

    NASA Astrophysics Data System (ADS)

    Suvorova, A. V.; Dmitriev, A. V.

    2016-07-01

    Full understanding of the magnetosphere interaction with radial IMF structures embedded in the solar wind flow is far from completeness. In order to analyze the effects of radial IMF, we use THEMIS observations of the magnetopause and magnetosheath together with upstream data acquired from ACE and Wind monitors as well as from the OMNI data base. We demonstrate a prominent magnetopause inflation and low pressure magnetosheath (LPM) mode under long-lasting radial IMF. We propose that these phenomena result from a kinetic effect of energetic ions taking the energy away from the pressure balance at the magnetopause. We show that strict quantitative determination of the inflation and LPM mode as a function of the cone angle is difficult because of the problems with reliable determination of the upstream and magnetosheath conditions. The shortcomings are caused by such effects as ambiguous time delay for the solar wind propagation, THEMIS orbital bias and model-dependent estimations of the magnetopause inflation.

  14. Clocks, Angles and Functions

    ERIC Educational Resources Information Center

    Kemp, Andy

    2006-01-01

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

  15. 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!

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

    NASA Technical Reports Server (NTRS)

    Maynard, Nelson C.

    2003-01-01

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

  17. 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.

  18. 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.

  19. A review of IMF theories

    NASA Astrophysics Data System (ADS)

    Cayrel, R.

    An overview is presented of theories of the initial mass function (IMF), starting from those essentially based on stochastic arguments to those involving more physics. Consideration is given to the scheme of Auluck and Kothari (1960, 1965), hierarchical theories, the predicted IMF, coalescence theories, DiFazio's theory (1986), fragmentation from sheets and filaments (bimodal star formation), and the criteria for determining stellar masses. The following concepts are proposed as being the most likely to survive: the general statistical arguments supporting log-normal laws, or power laws; the opacity-limited fragmentation concept; and the concept that the IMF is not a pure product of cloud fragmentation processes but also depends on internal properties of the object itself.

  20. 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.

  1. IMF Prediction with Cosmic Rays

    NASA Astrophysics Data System (ADS)

    Bieber, J. W.; Evenson, P. A.; Kuwabara, T.; Pei, C.

    2013-12-01

    Cosmic rays impacting Earth have passed through and interacted with the interplanetary magnetic field (IMF) surrounding Earth, and in some sense they carry information on the three-dimensional structure of that field. This work uses neutron monitor data in an effort to extract that information and use it to predict the future behavior of the IMF, especially the north-south component (Bz) which is so crucial in determining geomagnetic activity. We consider 161 events from a published list of interplanetary coronal mass ejections and compare hourly averages of the predicted field with the actual field measured later. We find that the percentage of events with 'good' predictions of Bz (in the sense of having a positive correlation between the prediction and the subsequent measurement) varies from about 85% for predictions 1 hour into the future to about 60% for predictions 4 hours into the future. We present several ideas for how the method might be improved in future implementations. Supported by NASA grant NNX08AQ01G and NSF grant ANT-0739620.

  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. 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.

  4. 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.

  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. 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…

  7. 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.

  8. On the use of a sunward-libration-point orbiting spacecraft as an IMF monitor for magnetospheric studies

    NASA Technical Reports Server (NTRS)

    Kelly, T. J.; Crooker, N. U.; Siscoe, G. L.; Russell, C. T.; Smith, E. J.

    1984-01-01

    Magnetospheric studies often require knowledge of the orientation of the IMF. In order to test the accuracy of using magnetometer data from a spacecraft orbiting the sunward libration point for this purpose, the angle between the IMF at ISEE 3, when it was positioned around the libration point, and at ISEE 1, orbiting Earth, has been calculated for a data set of two-hour periods covering four months. For each period, a ten-minute average of ISEE 1 data is compared with ten-minute averages of ISEE 3 data at successively lagged intervals. At the lag time equal to the time required for the solar wind to convect from ISEE 3 to ISEE 1, the median angle between the IMF orientation at the two spacecraft is 20 deg, and 80% of the cases have angles less than 38 deg. The results for the angles projected on the y-z plane are essentially the same.

  9. 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.)

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

    NASA Astrophysics Data System (ADS)

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

    Although the Mars Express (MEX) does not carry a magnetometer, it is in principle possible to derive the interplanetary magnetic field (IMF) orientation from the three dimensional velocity distribution of pick-up ions measured by the Ion Mass Analyser (IMA) on board MEX because pick-up ions' orbits, in velocity phase space, are expected to gyrate around the IMF when the IMF is relatively uniform on a scale larger than the proton gyroradius. Upstream of bow shock, MEX often observed cycloid distributions (two dimensional partial ring distributions in velocity phase space) of protons in a narrow channel of the IMA detector (only one azimuth for many polar angles). We show two such examples. Three different methods are used to derive the IMF orientation from the observed cycloid distributions. One method is intuitive (intuitive method), while the others derive the minimum variance direction of the velocity vectors for the observed ring ions. These velocity vectors are selected either manually (manual method) or automatically using simple filters (automatic method). While the intuitive method and the manual method provide similar IMF orientations by which the observed cycloid distribution is well arranged into a partial circle (representing gyration) and constant parallel velocity, the automatic method failed to arrange the data to the degree of the manual method, yielding about a 30° offset in the estimated IMF direction. The uncertainty of the derived IMF orientation is strongly affected by the instrument resolution. The source population for these ring distributions is most likely newly ionized hydrogen atoms, which are picked up by the solar wind.

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

    NASA Astrophysics Data System (ADS)

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

    2006-10-01

    Although the Mars Express (MEX) does not carry a magnetometer, it is in principle possible to derive the interplanetary magnetic field (IMF) orientation from the three dimensional velocity distribution of pick-up ions measured by the Ion Mass Analyser (IMA) on board MEX because pick-up ions' orbits, in velocity phase space, are expected to gyrate around the IMF when the IMF is relatively uniform on a scale larger than the proton gyroradius. During bow shock outbound crossings, MEX often observed cycloid distributions (two dimensional partial ring distributions in velocity phase space) of protons in a narrow channel of the IMA detector (only one azimuth for many polar angles). We show two such examples. Three different methods are used to derive the IMF orientation from the observed cycloid distributions. One method is intuitive (intuitive method), while the others derive the minimum variance direction of the velocity vectors for the observed ring ions. These velocity vectors are selected either manually (manual method) or automatically using simple filters (automatic method). While the intuitive method and the manual method provide similar IMF orientations by which the observed cycloid distribution is well arranged into a partial circle (representing gyration) and constant parallel velocity, the automatic method failed to arrange the data to the degree of the manual method, yielding about a 30° offset in the estimated IMF direction. The uncertainty of the derived IMF orientation is strongly affected by the instrument resolution. The source population for these ring distributions is most likely newly ionized hydrogen atoms, which are picked up by the solar wind.

  12. 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.

  13. Solar cycle variations in IMF intensity

    NASA Technical Reports Server (NTRS)

    King, J. H.

    1979-01-01

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

  14. Atomic Clocks

    NASA Astrophysics Data System (ADS)

    Wynands, Robert

    Time is a strange thing. On the one hand it is arguably the most inaccessible physical phenomenon of all: both in that it is impossible to manipulate or modify—for all we know—and in that even after thousands of years mankind's philosophers still have not found a fully satisfying way to understand it. On the other hand, no other quantity can be measured with greater precision. Today's atomic clocks allow us to reproduce the length of the second as the SI unit of time with an uncertainty of a few parts in 1016—orders of magnitude better than any other quantity. In a sense, one can say [1

  15. Molecular clocks.

    PubMed

    Lee, Michael S Y; Ho, Simon Y W

    2016-05-23

    In the 1960s, several groups of scientists, including Emile Zuckerkandl and Linus Pauling, had noted that proteins experience amino acid replacements at a surprisingly consistent rate across very different species. This presumed single, uniform rate of genetic evolution was subsequently described using the term 'molecular clock'. Biologists quickly realised that such a universal pacemaker could be used as a yardstick for measuring the timescale of evolutionary divergences: estimating the rate of amino acid exchanges per unit of time and applying it to protein differences across a range of organisms would allow deduction of the divergence times of their respective lineages (Figure 1). PMID:27218841

  16. Special Relativistic Clock Comparisons

    NASA Astrophysics Data System (ADS)

    Morton, Tom

    2007-03-01

    Time mappings of a stationary clock's time points onto a moving clock's time line heuristically resolve certain temporal asymmetries in time dilation. Time mapping postulates are identified and transforms are derived. `Clock Re-phasing' vs. `Time Leap' is discussed.

  17. 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.

  18. 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.

  19. 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.

  20. 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…

  1. The IMF at intermediate masses from Galactic Cepheids

    NASA Astrophysics Data System (ADS)

    Mor, R.; Robin, A. C.; Figueras, F.; Lemasle, B.

    2014-07-01

    Aims: To constrain the Initial Mass Function (IMF) of the Galactic young (<1 Gyr) thin Disc population using Cepheids. Methods: We have optimized the flexibility of the new Besançon Galaxy Model (Czekaj 2014) to simulate magnitude and distance complete samples of young intermediate mass stars assuming different IMFs and Star Formation Histories (SFH). Comparing the simulated synthetic catalogues with the observational data we studied which IMF reproduces better the observational number of Cepheids in the Galactic thin Disc. We analysed three different IMF: (1) Salpeter, (2) Kroupa-Haywood and (3) Haywood-Robin IMFs with a decreasing SFH from Aumer & Binney (2009). Results: For the first time the Besançon Galaxy Model is used to characterize the galactic Cepheids. We found that for most of the cases the Salpeter IMF overestimates the number of observed Cepheids and Haywood-Robin IMF underestimates it. The Kroupa-Haywood IMF, with a slope α = 3.2, is the one that best reproduces the observed Cepheids. From the comparison of the predicted and observed number of Cepheids up to V = 12, we point that the model might underestimate the scale height of the young population. Conclusions: In agreement with Kroupa & Weidner (2003) our study shows that the Salpeter IMF (α = 2.35) overestimates the star counts in the range 4 ≤ M/M⊙≤ 10 and supports the idea that the slope of the intermediate and massive stars IMF is steeper than the Salpeter IMF. The poster can be found online at: https://gaia.ub.edu/Twiki/pub/GREATITNFC/ProgramFinalconference/Poster_R._Mor_Great.pdf.

  2. 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

  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. 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.

  5. Connection between dynamically derived IMF normalisation and stellar populations

    NASA Astrophysics Data System (ADS)

    McDermid, Richard M.

    2015-04-01

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

  6. Thermospheric Neutral Density Responses to Changes in IMF Sector Polarity

    NASA Astrophysics Data System (ADS)

    Kwak, Y.; Kim, K.; Forbes, J.; Lee, S.

    2008-12-01

    The thermospheric density is important not only for satellite orbital tracking, but also in understanding the thermosphere-ionosphere coupling process as well. Thermospheric density variations are controlled by various sources such as Joule/particle heating, Lorentz force, thermal expansion, upwelling and horizontal wind circulation. These sources are directly or indirectly associated with the direction and/or strength of the interplanetary magnetic field (IMF). That is, there is an intimate relationship between IMF variation and thermospheric density variation. In order to examine how thermospheric density variations are influenced on the orientation and/or strength of the IMF, we used total mass density around 400 km, derived from the high- accuracy accelerometer on board the Challenging Minisatellite Payload (CHAMP) spacecraft, in 2003 when the IMF exhibited a well-defined sector polarity change with a ~27-day periodicity; directed toward the Sun (i.e., +Bx and -By) and away the Sun (-Bx and +By). It has been known that the IMF By in GSE coordinates makes a positive or negative IMF Bz offset in GSM coordinate. We discuss whether the thermospheric total mass density from CHAMP changes with the IMF sector polarity.

  7. First nuclear clock?

    NASA Astrophysics Data System (ADS)

    2016-06-01

    A nuclear clock that is more precise than any atomic clock available today could soon be a reality after physicists in Germany detected a crucial low-energy transition in the thorium-229 nucleus, which could be used to create a new frequency standard.

  8. 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.

  9. 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…

  10. 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.

  11. Flies, clocks and evolution.

    PubMed Central

    Rosato, E; Kyriacou, C P

    2001-01-01

    The negative feedback model for gene regulation of the circadian mechanism is described for the fruitfly, Drosophila melanogaster. The conservation of function of clock molecules is illustrated by comparison with the mammalian circadian system, and the apparent swapping of roles between various canonical clock gene components is highlighted. The role of clock gene duplications and divergence of function is introduced via the timeless gene. The impressive similarities in clock gene regulation between flies and mammals could suggest that variation between more closely related species within insects might be minimal. However, this is not borne out because the expression of clock molecules in the brain of the giant silk moth, Antheraea pernyi, is not easy to reconcile with the negative feedback roles of the period and timeless genes. Variation in clock gene sequences between and within fly species is examined and the role of co-evolution between and within clock molecules is described, particularly with reference to adaptive functions of the circadian phenotype. PMID:11710984

  12. Response of the Reverse Convection to Sharp IMF Turnings

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    How strongly the dayside high-latitude convection is controlled by the orientation of the IMF for periods of the steady IMF is well established. However, the nature of the transition that the convection makes when the IMF changes sharply is still not fully understood. In the present paper, we report the characteristics of the transient nature of the reverse convection on the basis of observations from multi-spacecraft and ground magnetometer stations. During a period of northward IMF on 22 April 2006 the magnetic field observations from three ST-5 spacecraft identified distribution change in the polar cap field-aligned current which responds to a quick IMF turning from the purely northward orientation to the duskward orientation. At this time ST-5 flew over one of the Greenland magnetometer stations located near 1200 MLT. The analysis of the ground magnetic perturbations shows that the field-aligned current distribution, which is closely related to the reverse convection pattern, was changing gradually during about 10 min before reaching a steady state. When the steady state was going on, the IMF changed sharply from the duskward orientation to the dawnward orientation. Immediately after this IMF turning, three DMSP spacecraft (F13, F15, and F16) traversed the dayside polar cap in the northern hemisphere. The ion drift observation indicates that the polar cap convection changed from the clockwise circulation to the counter-clockwise circulation during about 10 min. The data from the Greenland magnetometer stations show that a transient state, i.e., deformation or reduction of the clockwise circulation started in the near-noon and postnoon sectors almost simultaneously when the ion drift consisting of the clockwise circulation is still seen in the prenoon polar cap by the DMSP spacecraft. We discuss the changing global patterns that occurred over the whole dayside polar cap during the course of the 10-min transient state for both cases.

  13. 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

  14. 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

  15. 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)

  16. 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)

  17. 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.

  18. 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.

  19. Temporal Cusp Ion Signatures and Magnetopause Reconnection during Northward IMF

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Dispersed ion signatures observed in the magnetospheric cusps have been used to understand the locations and properties of magnetopause reconnection. Whether a cusp structure is spatial or temporal is an important question because these structures reveal the spatial and temporal nature of magnetopause reconnection. We study temporal cusp ion signatures and their relation to the magnetopause processes during northward IMF using the Open Global Geospace Circulation Model (OpenGGCM) and the Liouville Theorem Particle Tracer (LTPT). OpenGGCM produces dayside reconnection within the framework of resistive MHD, while the LTPT calculates cusp ion signatures caused by the simulated reconnection. Our model produces temporal cusp ion dispersions with ion energies that increase with decreasing latitude during northward IMF, although these signatures are commonly associated with subsolar reconnection during southward IMF. We investigate which magnetopause process is responsible for the temporal cusp signatures.

  20. 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.

  1. The IMF dependence of the local time of transpolar arcs

    NASA Astrophysics Data System (ADS)

    Fear, R.; Milan, S. E.

    2011-12-01

    Transpolar arcs or polar cap arcs are auroral features which are observed within the polar cap. They occur predominantly during intervals of northward IMF (Berkey et al., 1976). There is mixed evidence for IMF BY control of the local time at which the arcs initially form; Gussenhoven (1982) found that polar cap arcs formed preferentially post-midnight when BY < 0 (evaluated over 1 or 2 hours preceding the start of the arc) and pre-midnight when BY > 0, whereas Valladares et al (1991) found no clear dependency. The only previous statistical study of globally-imaged transpolar arcs (Kullen et al., 2002) found differing results for moving and non-moving arcs, concluding that three different models were required to identify (i) moving arcs, (ii) stationary arcs near the dawn/dusk portion of the main oval, and (iii) stationary arcs in the midnight sector. In this presentation, we show the results of a statistical study of 131 transpolar arcs observed by the FUV cameras on the IMAGE satellite between June 2000 and September 2005. We find that arcs tend to form following the same dependency on BY as identified by Gussenhoven (1982), whether moving or not. We find that the correlation between the magnetic local time at which the arc forms and the IMF BY component is relatively weak if the IMF is only averaged over the hour preceding the arc formation, but becomes stronger if the IMF is evaluated between 1 and 4 hours before the arc first forms. This is consistent with the timescale that is expected for newly-opened magnetospheric flux to reach the magnetotail plasma sheet (Dungey, 1961; Milan et al., 2007), and is therefore consistent with the suggestion that transpolar arcs map to the plasma sheet. We suggest that the similar dependence of stationary and moving arcs on the IMF BY component might imply that it is possible to explain both types of arc in terms of a single mechanism.

  2. The IMF as a function of supersonic turbulence

    NASA Astrophysics Data System (ADS)

    Bertelli Motta, C.; Clark, P. C.; Glover, S. C. O.; Klessen, R. S.; Pasquali, A.

    2016-08-01

    Recent studies seem to suggest that the stellar initial mass function (IMF) in early-type galaxies might be different from a classical Kroupa or Chabrier IMF, i.e. contain a larger fraction of the total mass in low-mass stars. From a theoretical point of view, supersonic turbulence has been the subject of interest in many analytical theories proposing a strong correlation with the characteristic mass of the core mass function (CMF) in star forming regions, and as a consequence with the stellar IMF. Performing two suites of smoothed particles hydrodynamics (SPH) simulations with different mass resolutions, we aim at testing the effects of variations in the turbulent properties of a dense, star forming molecular cloud on the shape of the system mass function in different density regimes. While analytical theories predict a shift of the peak of the CMF towards lower masses with increasing velocity dispersion of the cloud, we observe in the low-density regime the opposite trend, with high Mach numbers giving rise to a top-heavy mass distribution. For the high-density regime we do not find any trend correlating the Mach number with the characteristic mass of the resulting IMF, implying that the dynamics of protostellar accretion discs and fragmentation on small scales is not strongly affected by turbulence driven at the scale of the cloud. Furthermore, we suggest that a significant fraction of dense cores are disrupted by turbulence before stars can be formed in their interior through gravitational collapse. Although this particular study has limitations in its numerical resolution, we suggest that our results, along with those from other studies, cast doubt on the turbulent fragmentation models on the IMF that simply map the CMF to the IMF.

  3. Kelvin-Helmholtz Instability under southward IMF: THEMIS observations and OpenGGCM simulations

    NASA Astrophysics Data System (ADS)

    Kavosi, S.; Raeder, J.

    2015-12-01

    While Kelvin-Helmholtz (KH) waves for southward IMF were long thought to be non-existent, both the Kavosi and Raeder [2015] study, and two other independent studies [Hwang et al., 2011; Yan et al., 2014] have found southward IMF KH events. It still remains a mystery, though, why KH under southward IMF occurs only at one quarter of the rate compared to northward IMF [Kavosi and Raeder, 2015], and whether or not such waves occur only under specific conditions. The previous study [Hwang et al., 2011] suggested that the irregular and temporally intermittent structure of KH waves due to dynamically active sub solar behavior under southward IMF condition may explain the preferential in situ detection of KH waves under northward IMF. This explanation is also consistent with the KH events under southward IMF in our database. The majority of the events during southward IMF are irregular, short and polychromatic in compare to regular, long lasting and monochromatic waves under northward IMF. To effectively isolate these differences, we have used both our extensive THEMIS KH event database and OpenGGCM simulations. Our simulation results show that the KH waves under southward IMF are irregular, higher frequency, lower amplitude, and polychromatic compared to northward IMF. Additionally, our statistical analysis shows that occurrence rate of KH wave as a function of solar wind plasma parameters is different under southward IMF compared to northward IMF.

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

    NASA Astrophysics Data System (ADS)

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

    2005-02-01

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

  5. VCSELs for atomic clocks

    NASA Astrophysics Data System (ADS)

    Serkland, Darwin K.; Peake, Gregory M.; Geib, Kent M.; Lutwak, Robert; Garvey, R. Michael; Varghese, Mathew; Mescher, Mark

    2006-02-01

    The spectroscopic technique of coherent population trapping (CPT) enables an all-optical interrogation of the groundstate hyperfine splitting of cesium (or rubidium), compared to the optical-microwave double resonance technique conventionally employed in atomic frequency standards. All-optical interrogation enables the reduction of the size and power consumption of an atomic clock by two orders of magnitude, and vertical-cavity surface-emitting lasers (VCSELs) are preferred optical sources due to their low power consumption and circular output beam. Several research teams are currently using VCSELs for DARPA's chip-scale atomic clock (CSAC) program with the goal of producing an atomic clock having a volume < 1 cm^3, a power consumption < 30 mW, and an instability (Allan deviation) < 1x10^-11 during a 1-hour averaging interval. This paper describes the VCSEL requirements for CPT-based atomic clocks, which include single mode operation, single polarization operation, modulation bandwidth > 4 GHz, low power consumption (for the CSAC), narrow linewidth, and low relative intensity noise (RIN). A significant manufacturing challenge is to reproducibly obtain the required wavelength at the specified VCSEL operating temperature and drive current. Data are presented that show the advantage of operating at the D1 (rather than D2) resonance of the alkali atoms. Measurements of VCSEL linewidth will be discussed in particular, since atomic clock performance is especially sensitive to this parameter.

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2009-05-01

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

  8. Distinct Magnetospheric Responses to Southward IMF in Two Substorms

    NASA Technical Reports Server (NTRS)

    El-Alaoui, Mostafa; Ashour-Abdalla, M.; Richard, R. L.; Frank, L. A.; Paterson, W. R.; Sigwarth, J. B.

    2003-01-01

    Solar wind plasma parameters and the Interplanetary Magnetic Field (IMF) observed by the WIND spacecraft upstream of the bow shock were used as input to magnetohydrodynamic (MHD) simulations of two substorm events. The power deposited into the ionosphere due to electron precipitation was calculated both from VIS observations and from the simulations.

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

    NASA Astrophysics Data System (ADS)

    Aikio, A. T.; Pitkänen, 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.

  10. Optical atomic clocks

    NASA Astrophysics Data System (ADS)

    Poli, N.; Oates, C. W.; Gill, P.; Tino, G. M.

    2013-12-01

    In the last ten years extraordinary results in time and frequency metrology have been demonstrated. Frequency-stabilization techniques for continuous-wave lasers and femtosecond optical frequency combs have enabled a rapid development of frequency standards based on optical transitions in ultra-cold neutral atoms and trapped ions. As a result, today's best performing atomic clocks tick at an optical rate and allow scientists to perform high-resolution measurements with a precision approaching a few parts in 1018. This paper reviews the history and the state of the art in optical-clock research and addresses the implementation of optical clocks in a possible future redefinition of the SI second as well as in tests of fundamental physics.

  11. A fault-tolerant clock

    NASA Technical Reports Server (NTRS)

    Daley, W. P.; Mckenna, J. F., Jr.

    1973-01-01

    Computers must operate correctly even though one or more of components have failed. Electronic clock has been designed to be insensitive to occurrence of faults; it is substantial advance over any known clock.

  12. 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⊙.

  13. 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.

  14. 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.

  15. 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.

  16. 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…

  17. 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…

  18. 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…

  19. Pulsed Optically Pumped Rb clock

    NASA Astrophysics Data System (ADS)

    Micalizio, S.; Levi, F.; Godone, A.; Calosso, C. E.; François, B.; Boudot, R.; Affolderbach, C.; Kang, S.; Gharavipour, M.; Gruet, F.; Mileti, G.

    2016-06-01

    INRIM demonstrated a Rb vapour cell clock based on pulsed optical pumping (POP) with unprecedented frequency stability performances, both in the short and in the medium-long term period. In the frame of a EMRP project, we are developing a new clock based on the same POP principle but adopting solutions aimed at reducing the noise sources affecting the INRIM clock. At the same time, concerning possible technological applications, particular care are devoted in the project to reduce the size and the weight of the clock, still keeping the excellent stability of the INRIM clock. The paper resumes the main results of this activity.

  20. 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.

  1. 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.

  2. Rockets, clocks, and gravity

    NASA Astrophysics Data System (ADS)

    Vessot, R. F. C.

    Uses of atomic clocks, telemetry, and spacecraft to test predictions of the General Theory of Relativity are described. The number of cycles of a signal being generated by an atomic clock on board a satellite and directed toward earth stations allows precise determination of movements away or toward the receiving station, with an accuracy of 1/9,192,631,770 when using the outer shell electron to nucleus magnetic interaction of a cesium 133 isotope. Doppler radar serves the same purpose when reflected off the surface of a spacecraft, and radio transmitters landed on Mars have provided a source of signals which are deflected by the sun when orbital positions of earth and Mars are in favorable positions. Goals of the NASA Starprobe mission to measure the gravitational flattening and time/space warping occurring around the sun are outlined.

  3. 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

  4. 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.

  5. Statistical study of the effect of ULF fluctuations in the IMF on the cross polar cap potential drop for northward IMF

    NASA Astrophysics Data System (ADS)

    Kim, H.-J.; Lyons, L.; Boudouridis, A.; Pilipenko, V.; Ridley, A. J.; Weygand, J. M.

    2011-10-01

    Recent studies showed that, regardless of the orientation of the Interplanetary Magnetic Field (IMF), ULF wave activity in the solar wind can substantially enhance the convection in the high latitude ionosphere, suggesting that ULF fluctuations may also be an important contributor to the coupling of the solar wind to the magnetosphere-ionosphere system. We conduct a statistical study to understand the effect of ULF power in the IMF on the cross polar cap potential, primarily focusing on northward IMF. We have analyzed the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) calculations of the polar cap potential, a IMF ULF index that is defined as the logarithm of Pc5 ULF power in IMF, and solar wind velocity and dynamic pressure for 249 days in 2003. We find that, separated from the effects of solar wind speed and dynamic pressure, the average cross polar cap potentials show a roughly linear dependence on the ULF index, with a partial correlation coefficient of 0.19. Highly structured convection flow patterns with a number of localized vortices are often observed under fluctuating northward IMF. For such a convection configuration, it is hard to estimate properly the cross polar cap potential drop, as the enhanced flows around the vortices that may be associated with IMF fluctuations do not necessarily yield a large potential drop. Thus, despite the relatively small correlation coefficient, the linear trend we found gives support to the significant role of IMF ULF fluctuations on the coupling of the solar wind to the magnetosphere-ionosphere system.

  6. 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

  7. Simulation of the geospace response to a sudden change in IMF orientation.

    NASA Astrophysics Data System (ADS)

    Lopez, R. E.; Pham, K. H.; Wiltberger, M. J.

    2015-12-01

    We have conducted simulations of the response of the geospace system to a sudden change in the orientation of the interplanetary magnetic field (IMF) using the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamic code. Specifically, we have explored a sudden change in the IMF orientation from an extended period during which it was steady northward, to a steady southward IMF. The change in the IMF orientation first causes a reversal in the direction of the bow shock current, which launches a fast mode wave that propagates through the system, causing changes in the overall current pattern even before the southward IMF arrives at the dayside magnetopause to initiate low latitude merging. When the southward IMF does arrive at the magnetopause, the preceding northward IMF in the solar wind flow is still driving high latitude merging poleward of the cusp. Even when the two-cell convection pattern in the ionosphere becomes the dominant convection, the LFM results show that there is still some remnant of the high latitude reverse cell convection that is associated with northward IMF that had previously merged with the geomagnetic field and which takes some time to be cleared out of the system. We will present a detailed account of the timescales and changes in the magnetic topologies, current systems, magnetospheric plasma flows, and ionospheric potential patterns associated with the transition from northward to southward IMF. We will also discuss the implications of these findings for understanding the effect of transient changes in IMF orientations.

  8. IMF By-controlled field-aligned currents in the magnetotail during northward interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Cheng, Z. W.; Shi, J. K.; Dunlop, M.; Liu, Z. X.

    2014-08-01

    The influence of the interplanetary magnetic field (IMF) By component on the field-aligned currents (FACs) in the plasma sheet boundary layer (PSBL) in the magnetotail during the northward IMF were investigated using the data from Cluster. There are 748 FACs cases selected to do analysis. We present that the IMF By component plays a very important role in controlling the flow direction of the FACs in the PSBL in the magnetotail. In the northern hemisphere, the influence of the positive (negative) IMF By is an earthward (tailward) FACs. To the contrary, in the southern hemisphere, the effect of the positive (negative) IMF By is a tailward (earthward) FACs. There is a clear north-south asymmetry of the polarity of the FACs in the PSBL when IMF By is positive or negative, and this asymmetry of the polarity is more distinct when IMF By is positive. The FAC density is controlled by IMF By only when |IMF By| is large. When |IMF By| is more than 10 nT the absolute FAC density in the PSBL has an obvious positive correlation with the |IMF By|. When |IMF By| is less than 10 nT, there is no correlation between the absolute FAC density and |IMF By|. There is a clear dusk-dawn asymmetry in the current densities for the FACs in the PSBL, with the dawn currents appearing larger than the dusk currents. The FAC with the largest (smallest) density is located in the range of 0100≤MLT<0200 (2100≤MLT<2200).

  9. 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

  10. 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

  11. A mixed relaxed clock model.

    PubMed

    Lartillot, Nicolas; Phillips, Matthew J; Ronquist, Fredrik

    2016-07-19

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

  12. 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.

  13. Huygens synchronization of two clocks.

    PubMed

    Oliveira, Henrique M; Melo, Luís V

    2015-01-01

    The synchronization of two pendulum clocks hanging from a wall was first observed by Huygens during the XVII century. This type of synchronization is observed in other areas, and is fundamentally different from the problem of two clocks hanging from a moveable base. We present a model explaining the phase opposition synchronization of two pendulum clocks in those conditions. The predicted behaviour is observed experimentally, validating the model. PMID:26204557

  14. 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.

  15. Steady reconnection during intervals of northward IMF: Implications for magnetosheath properties

    NASA Astrophysics Data System (ADS)

    Petrinec, S. M.; Trattner, K. J.; Fuselier, S. A.

    2003-12-01

    This study examines the location of the reconnection site on the magnetopause for conditions of northward interplanetary magnetic field (IMF) and its implications for properties of the magnetosheath. Ion distribution functions from the Toroidal Imaging Mass Angle Spectrometer (TIMAS) instrument on board the Polar spacecraft during passes through the dayside cusp region when the IMF was steady and northward are used. Cutoff velocities are determined from these distributions and the distance from the Polar spacecraft to the site of reconnection is estimated. A magnetospheric magnetic field model is used to map these determined distances to a location on the magnetopause where reconnection is believed to have occurred. Nearly all of these reconnection sites lie in places where the magnetosheath flow is estimated to be super-Alfvénic (using hydrodynamic theory and an analytic magnetosheath magnetic field model). However, there exist strict constraints on the speed of the ambient magnetosheath flow at the reconnection site, in order for this particular type of particle distribution to have been observed by TIMAS. Different physical models are discussed, including the possibility of nonstationary reconnection sites and the existence of a plasma depletion layer which significantly increases the magnetosheath Alfvén speed close to the magnetopause. From the observations and mapped reconnection locations, we estimate statistically how much the average ion density must decrease (and the magnetic field must increase) in the plasma depletion layer to be consistent with the cusp region observations. The resulting range of values is consistent with the theoretical estimates of Zwan and Wolf [1976] (k >= 2).

  16. X lines in the magnetotail for southward and northward IMF conditions

    NASA Astrophysics Data System (ADS)

    Zhang, L. Q.; Wang, J. Y.; Baumjohann, W.; Rème, H.; Dai, L.; Dunlop, M. W.; Chen, T.; Huang, Y.

    2015-09-01

    Utilizing associated observations of Geotail and ACE satellites from the year of 1998 to 2005, we investigated the X lines in the near-Earth tail under different interplanetary magnetic field (IMF) conditions. The X lines are recognized by the tailward fast flows with negative Bz. Statistically, the X lines in the tail can be observed for southward as well as northward IMF, but more frequently observed for southward IMF. A typical case on 26 April 2005 showed clear evidence that the X line can occur for northward IMF while the geomagnetic activity is particularly quiet. Further analysis showed that the X line-related solar wind has stronger Ey and Bz components for southward than northward IMF. In addition, the X line-related geomagnetic activities are stronger for southward than northward IMF.

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

    NASA Technical Reports Server (NTRS)

    Abbey, Duane L. (Inventor)

    1977-01-01

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

  18. 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…

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

    PubMed

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

    2011-04-15

    It has been recently shown that the magnetization of a multiferroic nanomagnet, consisting of a magnetostrictive layer elastically coupled to a piezoelectric layer, can be rotated by a large angle if a tiny voltage of a few tens of millivolts is applied to the piezoelectric layer. The potential generates stress in the magnetostrictive layer and rotates its magnetization by ~90° to implement Bennett clocking in nanomagnetic logic chains. Because of the small voltage needed, this clocking method is far more energy efficient than those that would employ spin transfer torque or magnetic fields to rotate the magnetization. In order to assess if such a clocking scheme can also be reasonably fast, we have studied the magnetization dynamics of a multiferroic logic chain with nearest-neighbor dipole coupling using the Landau-Lifshitz-Gilbert (LLG) equation. We find that clock rates of 2.5 GHz are feasible while still maintaining the exceptionally high energy efficiency. For this clock rate, the energy dissipated per clock cycle per bit flip is ~52,000 kT at room temperature in the clocking circuit for properly designed nanomagnets. Had we used spin transfer torque to clock at the same rate, the energy dissipated per clock cycle per bit flip would have been ~4 x 10⁸ kT, while with current transistor technology we would have expended ~10⁶ kT. For slower clock rates of 1 GHz, stress-based clocking will dissipate only ~200 kT of energy per clock cycle per bit flip, while spin transfer torque would dissipate about 10⁸ kT. This shows that multiferroic nanomagnetic logic, clocked with voltage-generated stress, can emerge as a very attractive technique for computing and signal processing since it can be several orders of magnitude more energy efficient than current technologies. PMID:21389584

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

    NASA Astrophysics Data System (ADS)

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

    2011-04-01

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

  1. 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 gene–protein interaction networks that control circadian rhythms, cell cycle progression, signal processing and the design of synthetic gene networks. PMID:18522926

  2. 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).

  3. 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.

  4. Einstein’s Clocks

    SciTech Connect

    Lincoln, Don

    2015-09-09

    One of the most non-intuitive physics theories ever devised is Einstein’s Theory of Special Relativity, which claim such crazy-sounding things as two people disagreeing on such familiar concepts as length and time. In this video, Fermilab’s Dr. Don Lincoln shows that every single day particle physicists prove that moving clocks tick more slowly than stationary ones. He uses an easy to understand example of particles that move for far longer distances than you would expect from combining their velocity and stationary lifetime.

  5. 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)

  6. A mixed relaxed clock model

    PubMed Central

    2016-01-01

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

  7. Statistical study of influence of the IMF cone angle on foreshock processes

    NASA Astrophysics Data System (ADS)

    Urbar, Jaroslav; Nemecek, Zdenek; Safrankova, Jana; Prech, Lubomir

    2016-07-01

    The parameters of the solar wind plasma are modified upstream the Earth's bow shock, in the ion foreshock region, which is typically observed at quasi-parallel bow shock. Associated ULF waves are created due to the interaction of the solar wind plasma with the ions reflected at the bow shock where they generate fast magnetosonic waves with an in-phase relationship between the ion flux and magnetic field fluctuations. Using multipoint observations from the THEMIS spacecraft located in the vicinity of the bow shock or in the foreshock, we present statistical maps of a modification of solar wind parameters due to foreshock processes (solar wind heating and deceleration, enhancements of electric and magnetic field fluctuation levels, etc.). At the paper, a special attention is devoted to intervals of the radial interplanetary magnetic field that creates the foreshock upstream of a whole dayside bow shock.

  8. Strong gravitational lensing and the stellar IMF of early-type galaxies

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    Systematic variations of the initial mass function (IMF) in early-type galaxies, and their connection with possible drivers such as velocity dispersion or metallicity, have been much debated in recent years. Strong lensing over galaxy scales combined with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the IMF. We combine photometric and spectroscopic constraints from the latest set of population synthesis models of Charlot & Bruzual, including a varying IMF, with a non-parametric analysis of the lens masses of 18 ETGs from the SLACS survey, with velocity dispersions in the range 200-300 km s-1. We find that very bottom-heavy IMFs are excluded. However, the upper limit to the bimodal IMF slope (μ ≲ 2.2, accounting for a dark matter fraction of 20-30 per cent, where μ = 1.3 corresponds to a Kroupa-like IMF) is compatible at the 1σ level with constraints imposed by gravity-sensitive line strengths. A two-segment power-law parametrization of the IMF (Salpeter-like for high masses) is more constrained (Γ ≲ 1.5, where Γ is the power index at low masses) but requires a dark matter contribution of ≳25 per cent to reconcile the results with a Salpeter IMF. For a standard Milky Way-like IMF to be applicable, a significant dark matter contribution is required within 1Re. Our results reveal a large range of allowed IMF slopes, which, when interpreted as intrinsic scatter in the IMF properties of ETGs, could explain the recent results of Smith et al., who find Milky Way-like IMF normalizations in a few massive lensing ETGs.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Systematic variations of the IMF in early-type galaxies, and their connection with possible drivers such as velocity dispersion or metallicity, have been much debated in recent years. Strong lensing over galaxy scales combined with photometric and spectroscopic data provides a powerful method to constrain the stellar mass-to-light ratio and hence the functional form of the IMF. We combine photometric and spectroscopic constraints from the latest set of population synthesis models of Charlot & Bruzual, including a varying IMF, with a non-parametric analysis of the lens masses of 18 ETGs from the SLACS survey, with velocity dispersions in the range 200-300 km s-1. We find that very bottom-heavy IMFs are excluded. However, the upper limit to the bimodal IMF slope (μ ≲ 2.2, accounting for a dark matter fraction of 20-30%, where μ = 1.3 corresponds to a Kroupa-like IMF) is compatible at the 1 σ level with constraints imposed by gravity-sensitive line strengths. A two-segment power law parameterisation of the IMF (Salpeter-like for high masses) is more constrained (Γ ≲ 1.5, where Γ is the power index at low masses) but requires a dark matter contribution of ≲ 25% to reconcile the results with a Salpeter IMF. For a standard Milky Way-like IMF to be applicable, a significant dark matter contribution is required within 1Re. Our results reveal a large range of allowed IMF slopes, which, when interpreted as intrinsic scatter in the IMF properties of ETGs, could explain the recent results of Smith et al., who find Milky Way-like IMF normalisations in a few massive lensing ETGs.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  11. 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)

  12. Circadian clocks: lessons from fish.

    PubMed

    Idda, M Laura; Bertolucci, Cristiano; Vallone, Daniela; Gothilf, Yoav; Sánchez-Vázquez, Francisco Javier; Foulkes, Nicholas S

    2012-01-01

    Our understanding of the molecular and cellular organization of the circadian timing system in vertebrates has increased enormously over the past decade. In large part, progress has been based on genetic studies in the mouse as well as on fundamental similarities between vertebrate and Drosophila clocks. The zebrafish was initially considered as a potentially attractive genetic model for identifying vertebrate clock genes. However, instead, fish have ultimately proven to be valuable complementary models for studying various aspects of clock biology. For example, many fish can shift from diurnal to nocturnal activity implying specific flexibility in their clock function. We have learned much about the function of light input pathways, and the ontogeny and function of the pineal organ, the fish central pacemaker. Finally, blind cavefish have also provided new insight into the evolution of the circadian clock under extreme environmental conditions. PMID:22877658

  13. 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.

  14. 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).

  15. 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.

  16. 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

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

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Moldwin, M.

    2014-12-01

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

  18. 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.

  19. Circadian clocks and breast cancer.

    PubMed

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

    2016-01-01

    Circadian clocks respond to environmental time cues to coordinate 24-hour oscillations in almost every tissue of the body. In the breast, circadian clocks regulate the rhythmic expression of numerous genes. Disrupted expression of circadian genes can alter breast biology and may promote cancer. Here we overview circadian mechanisms, and the connection between the molecular clock and breast biology. We describe how disruption of circadian genes contributes to cancer via multiple mechanisms, and link this to increased tumour risk in women who work irregular shift patterns. Understanding the influence of circadian rhythms on breast cancer could lead to more efficacious therapies, reformed public health policy and improved patient outcome. PMID:27590298

  20. End-resonance clock and all-photonic clock

    NASA Astrophysics Data System (ADS)

    Jau, Yuan-Yu; Happer, William; Gong, Fei; Braun, Alan; Kwakernaak, Martin

    2008-02-01

    The end-resonance clock uses strong hyperfine end transition to stabilize the frequency of the local oscillator. Comparing to the conventional 0-0 atomic clock, end resonance has very small spin-exchange broadening effect. The spin-exchange rate is proportional to the number density of the alkali-metal atoms. By using the end resonance, we are able to use very high dense vapor to obtain a much better signal to noise ratio. On the other hand, the end resonance suffers from the first-order magnetic field dependence. This problem, however, can be solved by simultaneously using a Zeeman end resonance to stabilize the magnetic field. Here, we report the most recent result of the end-resonance clock. In addition, we report a whole new technique, push-pull laser-atomic oscillator, which can be thought as all-photonic clock. This new clock requires no local oscillator. It acts like a photonic version of maser, which spontaneously generates modulated laser light and modulated voltage signals. The modulation serves as the clock signal, which is automatically locked to the ground-state hyperfine frequency of alkali-metal atoms.

  1. Response of reverse convection to fast IMF transitions

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Maruyama, Takashi; Jin, Hidekatsu

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

  3. A transportable optical lattice clock

    NASA Astrophysics Data System (ADS)

    Vogt, Stefan; Häfner, Sebastian; Grotti, Jacopo; Koller, Silvio; Al-Masoudi, Ali; Sterr, Uwe; Lisdat, Christian

    2016-06-01

    We present the experimental setup and first results of PTB's transportable 87Sr clock. It consists of a physics package, several compact laser breadboards, and a transportable high finesse cavity for the clock laser. A comparison of the transportable system with our stationary optical lattice clock yields an instability of 2.2 x 10-15 √s/τ for the transportable clock. The current fractional uncertainty of 1 × 10-15 is still limited by the not yet fully evaluated light shift from the free running optical lattice laser operated near the magic wavelength. We are currently improving our transportable system to reach an uncertainty at or below the 10-17 level, which will finaly be limited by the uncertainty in blackbody radiation shift correction.

  4. 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

  5. Circadian Clocks, Stress, and Immunity

    PubMed Central

    Dumbell, Rebecca; Matveeva, Olga; Oster, Henrik

    2016-01-01

    In mammals, molecular circadian clocks are present in most cells of the body, and this circadian network plays an important role in synchronizing physiological processes and behaviors to the appropriate time of day. The hypothalamic–pituitary–adrenal endocrine axis regulates the response to acute and chronic stress, acting through its final effectors – glucocorticoids – released from the adrenal cortex. Glucocorticoid secretion, characterized by its circadian rhythm, has an important role in synchronizing peripheral clocks and rhythms downstream of the master circadian pacemaker in the suprachiasmatic nucleus. Finally, glucocorticoids are powerfully anti-inflammatory, and recent work has implicated the circadian clock in various aspects and cells of the immune system, suggesting a tight interplay of stress and circadian systems in the regulation of immunity. This mini-review summarizes our current understanding of the role of the circadian clock network in both the HPA axis and the immune system, and discusses their interactions. PMID:27199894

  6. Stochastic models for atomic clocks

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

  7. Physical Time and Thermal Clocks

    NASA Astrophysics Data System (ADS)

    Borghi, Claudio

    2016-07-01

    In this paper I discuss the concept of time in physics. I consider the thermal time hypothesis and I claim that thermal clocks and atomic clocks measure different physical times, whereby thermal time and relativistic time are not compatible with each other. This hypothesis opens the possibility of a new foundation of the theory of physical time, and new perspectives in theoretical and philosophical researches.

  8. Gravitational Wave Search with the Clock Mission

    NASA Technical Reports Server (NTRS)

    Armstrong, J. W.

    1997-01-01

    Doppler tracking of distant spacecraft is the only method currently available to search for gravitational waves in the low-frequency (approx. 0.0001-0.1 Hz) band. In this technique the Doppler system measures the relative dimensionless velocity 2(delta)v/c = (delta)f/f(sub o) between the earth and the spacecraft as a function of time, where (delta)f is the frequency perturbation and f(sub o) is the nominal frequency of the radio link. A gravitational wave of amplitude h incident on this system causes small frequency perturbations, of order h in (delta)f/f(sub o), replicated three times in the observed record (Estabrook and Wahlquist 1975). All experiments to date and those planned for the near future involve only 'two-way' Doppler-i.e., uplink signal coherently transponded by the spacecraft with Doppler measured using a frequency standard common to the transmit and receive chains of the ground station. If, as on the proposed Clock Mission, there is an additional frequency standard on the spacecraft and a suitable earth-spacecraft radio system, some noise sources can be isolated and removed from the data (Vessot and Levine 1978). Supposing that the Clock Mission spacecraft is transferred into a suitable interplanetary orbit, I discuss here how the on-board frequency standard could be employed with an all-Ka-band radio system using the very high stability Deep Space Network station DSS 25 being instrumented for Cassini. With this configuration, the Clock Mission could search for gravitational waves at a sensitivity limited by the frequency standards, rather than plasma or tropospheric scintillation effects, whenever the sun-earth-spacecraft angle is greater than 90 degrees.

  9. Common features in diverse insect clocks.

    PubMed

    Numata, Hideharu; Miyazaki, Yosuke; Ikeno, Tomoko

    2015-01-01

    This review describes common features among diverse biological clocks in insects, including circadian, circatidal, circalunar/circasemilunar, and circannual clocks. These clocks control various behaviors, physiological functions, and developmental events, enabling adaptation to periodic environmental changes. Circadian clocks also function in time-compensation for celestial navigation and in the measurement of day or night length for photoperiodism. Phase response curves for such clocks reported thus far exhibit close similarities; specifically, the circannual clock in Anthrenus verbasci shows striking similarity to circadian clocks in its phase response. It is suggested that diverse biological clocks share physiological properties in their phase responses irrespective of period length. Molecular and physiological mechanisms are best understood for the optic-lobe and mid-brain circadian clocks, although there is no direct evidence that these clocks are involved in rhythmic phenomena other than circadian rhythms in daily events. Circadian clocks have also been localized in peripheral tissues, and research on their role in various rhythmic phenomena has been started. Although clock genes have been identified as controllers of circadian rhythms in daily events, some of these genes have also been shown to be involved in photoperiodism and possibly in time-compensated celestial navigation. In contrast, there is no experimental evidence indicating that any known clock gene is involved in biological clocks other than circadian clocks. PMID:26605055

  10. Gradient in the IMF slope and Sodium abundance of M87 with MUSE

    NASA Astrophysics Data System (ADS)

    Spiniello, C.; Sarzi, M.; Krajnovic, D.

    2016-06-01

    We present evidence for a radial variation of the stellar initial mass function IMF) in the giant elliptical NGC~4486 based on integral-field MUSE data acquired during the first Science Verification run for this instrument. A steepening of the low-mass end of the IMF towards the centre of this galaxy is necessary to explain the increasing strength of several of the optical IMF sensitive features introduced by Spiniello et al., which we observe in high-quality spectra extracted in annular apertures. The need for a varying slope of the IMF emerges when the strength of these IMF-sensitive features, together with that other classical Lick indices mostly sensitive to stellar metallicity and the bundance of α-elements, are fitted with the state-of-the-art stellar population models from Conroy & van Dokkum and Vazdekis et al., which we modified in order to allow variations in IMF slope, metallicity and α-elements abundance. More specifically, adopting 13-Gyr-old, single-age stellar population models and an unimodal IMF we find that the slope of the latter increases from x=1.8 to x=2.6 in the central 25 arcsec of NGC~4486. Varying IMF accompanied by a metallicity gradient, whereas the abundance of α-element appears constant throughout the MUSE field of view. We found metallicity and α-element abundance gradients perfectly consistent with the literature. A sodium over-abundance is necessary (according to CvD12 models) at all the distances (for all the apertures) and a slight gradient of increasing [Na/Fe] ratio towards the center can be inferred. However, in order to completely break the degeneracies between Na-abundance, total metallicity and IMF variation a more detailed investigation that includes the redder NaI line is required.

  11. 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

  12. Precision measurements with an ultracold molecular clock

    NASA Astrophysics Data System (ADS)

    Zelevinsky, Tanya

    2014-05-01

    High-precision spectroscopy has been instrumental in the progress of atomic physics. In this talk, we extend precision spectroscopy techniques to ultracold diatomic strontium molecules tightly trapped in an optical lattice, and discuss the results from the point of view of molecular and fundamental science. For weakly bound molecules near the atomic threshold corresponding to the narrow intercombination transition, we observe peculiar and unexpected physics, including multiply forbidden transitions and anomalously large linear and quadratic Zeeman shifts. The Zeeman shifts are highly sensitive to nonadiabatic mixing angles of the molecular wave functions. For the first time, we quantitatively compare the electric- and magnetic-dipole transition strengths for forbidden transitions in molecules, and discuss the dependence on the internuclear separation. In addition, we study ground state molecules, and discuss the present status of the molecular lattice clock and the physics it is able to probe. Magic-wavelength spectroscopy is successfully demonstrated for a range of narrow molecular transitions.

  13. What's Your Angle on Angles?

    ERIC Educational Resources Information Center

    Browning, Christine A.; Garza-Kling, Gina; Sundling, Elizabeth Hill

    2007-01-01

    Although the nature of the research varies, as do concepts of angle, research in general supports the supposition that angle is a complex idea, best understood from a variety of perspectives. In fact, the concept of angle tends to be threefold, consisting of: (1) the traditional, static notion of two rays meeting at a common vertex; (2) the idea…

  14. Dawn-dusk asymmetry in the northward IMF plasma sheet

    NASA Astrophysics Data System (ADS)

    Wing, S.; Johnson, J. R.; Newell, P. T.; Meng, C.

    2005-05-01

    During periods of northward IMF, as a result of large influx of the magnetosheath ions, the plasma sheet becomes cold and dense. During these periods, a large number of the plasma sheet ions have two components: hot (magnetospheric origin) and cold (magnetosheath origin). Based on their spectral distributions: one-component Maxwellian, two-component Maxwellian, and kappa (k), the characteristics of the plasma sheet ions were studied with DMSP satellites and a method of inferring plasma sheet ion properties from the ionospheric observations. The cold-component constituent of the two-component ions is hotter in the dawn than the dusk sector, consistent with the in situ studies that suggest that the magnetosheath ion is heated upon its entry along the plasma sheet dawn flank. This temperature asymmetry leads to a dawn-dusk asymmetry in the ion spectral distribution. The cold and hot components are closer together in temperature space, which increases the proportion of ions having (apparent) one-component distribution in the dawn flank while, in the dusk flank, the influx of the magnetosheath ions increase the density of the two-component ions. The dawn-dusk asymmetry in the cold magnetosheath ion profile should help determine the roles of various proposed magnetosheath entry mechanisms.

  15. Titan's methane clock

    NASA Astrophysics Data System (ADS)

    Nixon, C. A.; Jennings, D. E.; Romani, P. N.; Teanby, N. A.; Irwin, P. G. J.; Flasar, F. M.

    2010-04-01

    Measurements of the 12C/13C and D/H isotopic ratios in Titan's methane show intriguing differences from the values recorded in the giant planets. This implies that either (1) the atmosphere was differently endowed with material at the time of formation, or (2) evolutionary processes are at work in the moon's atmosphere - or some combination of the two. The Huygens Gas Chromatograph Mass Spectrometer Instrument (GCMS) found 12CH4/13CH4 = 82 +/- 1 (Niemann et al. 2005), some 7% lower than the giant planets' value of 88 +/- 7 (Sada et al. 1996), which closely matches the terrestrial inorganic standard of 89. The Cassini Composite Infrared Spectrometer (CIRS) has previously reported 12CH4/13CH4 of 77 +/-3 based on nadir sounding, which we now revise upwards to 80 +/- 4 based on more accurate limb sounding. The CIRS and GCMS results are therefore in agreement about an overall enrichment in 13CH4 of ~10%. The value of D/H in Titan's CH4 has long been controversial: historical measurements have ranged from about 8-15 x 10-5 (e.g. Coustenis et al. 1989, Coustenis et al. 2003). A recent measurement based on CIRS limb data by Bezard et al. (2007) puts the D/H in CH4 at (13 +/- 1) x 10-5, very much greater than in Jupiter and Saturn, ~2 x 10-5 (Mahaffy et al. 1998, Fletcher et al. 2009). To add complexity, the 12C/13C and D/H vary among molecules in Titan atmosphere, typically showing enhancement in D but depletion in 13C in the daughter species (H2, C2H2, C2H6), relative to the photochemical progenitor, methane. Jennings et al. (2009) have sought to interpret the variance in carbon isotopes as a Kinetic Isotope Effect (KIE), whilst an explanation for the D/H in all molecules remains elusive (Cordier et al. 2008). In this presentation we argue that evolution of isotopic ratios in Titan's methane over time forms a ticking 'clock', somewhat analogous to isotopic ratios in geochronology. Under plausible assumptions about the initial values and subsequent replenishment, various

  16. 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

  17. 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.

  18. Circadian clocks and cell division

    PubMed Central

    2010-01-01

    Evolution has selected a system of two intertwined cell cycles: the cell division cycle (CDC) and the daily (circadian) biological clock. The circadian clock keeps track of solar time and programs biological processes to occur at environmentally appropriate times. One of these processes is the CDC, which is often gated by the circadian clock. The intermeshing of these two cell cycles is probably responsible for the observation that disruption of the circadian system enhances susceptibility to some kinds of cancer. The core mechanism underlying the circadian clockwork has been thought to be a transcription and translation feedback loop (TTFL), but recent evidence from studies with cyanobacteria, synthetic oscillators and immortalized cell lines suggests that the core circadian pacemaking mechanism that gates cell division in mammalian cells could be a post-translational oscillator (PTO). PMID:20890114

  19. 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.

  20. Clocks, Metabolism, and the Epigenome

    PubMed Central

    Feng, Dan; Lazar, Mitchell A.

    2012-01-01

    Many behaviors and physiological activities in living organisms display circadian rhythms, allowing them to anticipate and prepare for the diurnal changes in the living environment. In this way, metabolic processes are aligned with the periodic environmental changes and behavioral cycles, such as the sleep/wake and fasting/feeding cycles. Disturbances of this alignment significantly increase the risk of metabolic diseases. Meanwhile, the circadian clock receives signals from the environment and feedback from metabolic pathways, and adjusts its activity and function. Growing evidence connects the circadian clock with epigenomic regulators. Here we review the recent advances in understanding the crosstalk between the circadian clock and energy metabolism through epigenomic programming and transcriptional regulation. PMID:22841001

  1. Sr+ single-ion clock

    NASA Astrophysics Data System (ADS)

    Dubé, P.; Madej, A. A.; Jian, B.

    2016-06-01

    The evaluated uncertainty of the 88Sr+ ion optical clock has decreased by several orders of magnitude during the last 15 years, currently reaching a level of 1.2 x 10-17. In this paper, we review the methods developed to control very effectively the largest frequency shifts that once were the main sources of uncertainty for the 88Sr+ single-ion clock. These shifts are the micromotion shifts, the electric quadrupole shift and the blackbody radiation shift. With further improvements to the evaluation of the systematic shifts, especially the blackbody radiation shift, it is expected that the total uncertainty of the single-ion clock transition frequency will reach the low 10-18 level in the near future.

  2. Convection dynamics and driving mechanism of a small substorm during dominantly IMF By+, Bz+ conditions

    NASA Astrophysics Data System (ADS)

    Liang, Jun; Sofko, G. J.; Donovan, E. F.; Watanabe, M.; Greenwald, R. A.

    2004-04-01

    Ground-based optical, magnetic and radar measurements detected a small substorm on October 9, 2000. Solar wind observations on GEOTAIL revealed a prolonged dominant Bz+ and steady By+ interplanetary magnetic field (IMF) prior to the substorm onset, except for a southward excursion at 0645-0655 UT, and a ``square-wave'' IMF Bx-By structure at 0727-0735 UT. We find that the IMF southward excursion led to the dayside convection enhancement and energy transport into the magnetosphere. When the dayside convection decreased, two pseudobreakups occurred as the consequence of the release of magnetospheric energy into the ionosphere. The substorm onset was associated with the IMF Bx-By structure in ``directly driven'' fashion. There was also a Stage-2 expansion which was internally driven within the magnetotail.

  3. 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.

  4. 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.

  5. 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.

  6. 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…

  7. 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…

  8. Single-transistor-clocked flip-flop

    DOEpatents

    Zhao, Peiyi; Darwish, Tarek; Bayoumi, Magdy

    2005-08-30

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

  9. 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. 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.

  12. 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.

  13. Spin squeezing in a Rydberg lattice clock.

    PubMed

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

    2014-03-14

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

  14. 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...

  15. A quantum network of clocks

    NASA Astrophysics Data System (ADS)

    Komar, Peter; Kessler, Eric; Bishof, Michael; Jiang, Liang; Sorensen, Anders; Ye, Jun; Lukin, Mikhail

    2014-05-01

    Shared timing information constitutes a key resource for positioning and navigation with a direct correspondence between timing accuracy and precision in applications such as the Global Positioning System (GPS). By combining precision metrology and quantum networks, we propose here a quantum, cooperative protocol for the operation of a network consisting of geographically remote optical atomic clocks. Using non-local entangled states, we demonstrate an optimal utilization of the global network resources, and show that such a network can be operated near the fundamental limit set by quantum theory yielding an ultra-precise clock signal. Furthermore, the internal structure of the network, combined with basic techniques from quantum communication, 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. See also: Komar et al. arXiv:1310.6045 (2013) and Kessler et al. arXiv:1310.6043 (2013).

  16. 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.…

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. Clock Laser System for a Strontium Lattice Clock

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  2. Fault diagnosis of rotating machinery using an improved HHT based on EEMD and sensitive IMFs

    NASA Astrophysics Data System (ADS)

    Lei, Yaguo; Zuo, Ming J.

    2009-12-01

    A Hilbert-Huang transform (HHT) is a time-frequency technique and has been widely applied to analyzing vibration signals in the field of fault diagnosis of rotating machinery. It analyzes the vibration signals using intrinsic mode functions (IMFs) extracted using empirical mode decomposition (EMD). However, EMD sometimes cannot reveal the signal characteristics accurately because of the problem of mode mixing. Ensemble empirical mode decomposition (EEMD) was developed recently to alleviate this problem. The IMFs generated by EEMD have different sensitivity to faults. Some IMFs are sensitive and closely related to the faults but others are irrelevant. To enhance the accuracy of the HHT in fault diagnosis of rotating machinery, an improved HHT based on EEMD and sensitive IMFs is proposed in this paper. Simulated signals demonstrate the effectiveness of the improved HHT in diagnosing the faults of rotating machinery. Finally, the improved HHT is applied to diagnosing an early rub-impact fault of a heavy oil catalytic cracking machine set, and the application results prove that the improved HHT is superior to the HHT based on all IMFs of EMD.

  3. 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.

  4. 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.

  5. Tectonic blocks and molecular clocks.

    PubMed

    De Baets, Kenneth; Antonelli, Alexandre; Donoghue, Philip C J

    2016-07-19

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

  6. 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

  7. Design principles underlying circadian clocks.

    PubMed Central

    Rand, D. A.; Shulgin, B. V.; Salazar, D.; Millar, A. J.

    2004-01-01

    A fundamental problem for regulatory networks is to understand the relation between form and function: to uncover the underlying design principles of the network. Circadian clocks present a particularly interesting instance, as recent work has shown that they have complex structures involving multiple interconnected feedback loops with both positive and negative feedback. While several authors have speculated on the reasons for this, a convincing explanation is still lacking.We analyse both the flexibility of clock networks and the relationships between various desirable properties such as robust entrainment, temperature compensation, and stability to environmental variations and parameter fluctuations. We use this to argue that the complexity provides the flexibility necessary to simultaneously attain multiple key properties of circadian clocks. As part of our analysis we show how to quantify the key evolutionary aims using infinitesimal response curves, a tool that we believe will be of general utility in the analysis of regulatory networks. Our results suggest that regulatory and signalling networks might be much less flexible and of lower dimension than their apparent complexity would suggest. PMID:16849158

  8. The Sr optical lattice clock at JILA: A new record in atomic clock performance

    NASA Astrophysics Data System (ADS)

    Nicholson, Travis; Bloom, Benjamin; Williams, Jason; Campbell, Sara; Bishof, Michael; Zhang, Xibo; Zhang, Wei; Bromley, Sarah; Hutson, Ross; McNally, Rees; Ye, Jun

    2014-05-01

    The exquisite control exhibited over quantum states of individual particles has revolutionized the field of precision measurement, as exemplified by highly accurate atomic clocks. Optical clocks have been the most accurate frequency standards for the better part of a decade, surpassing even the cesium microwave fountains upon which the SI second is based. Two classes of optical clocks have outperformed cesium: single-ion clocks and optical lattice clocks. Historically ion clocks have always been more accurate, and the precision of ion clocks and lattice clocks has been comparable. For years it has been unclear if lattice clocks can overcome key systematics and become more accurate than ion clocks. In this presentation I report the first lattice clock that has surpassed ion clocks in both precision and accuracy. These measurements represent a tenfold improvement in precision and a factor of 20 improvement in accuracy over the previous best lattice clock results. This work paves the way for a better realization of SI units, the development of more sophisticated quantum sensors, and precision tests of the fundamental laws of nature.

  9. A Variable IMF Slope To Fit The LCDM Picture To Observed High-z Submillimeter Sources

    NASA Astrophysics Data System (ADS)

    Muñoz, A. M.; Navarrete, F. P.; Lagos, C. Del P.; Padilla, N. D.; Cora, S. A.; Tecce, T. E.

    2011-10-01

    Using a Salpeter initial mass function (IMF) allows to describe fairly well a large variety of properties in galaxies. However, some studies have found that it is necessary to change it for a top-heavy IMF in starbursts to give an adequate prediction in the abundance of submillimeter galaxies (SMGs) at high redshifts. We show preliminary results of an implementation of a star formation intensity dependent IMF slope in a semi-analytic model of galaxy formation, which has been connected with a spectrophotometric code that provides an adequate treatment of reprocessed starlight by dust. We also explore systematic effects on the counts of submm sources coming from the beamsize of the receiver taking into account the spatial correlation of sources and foreground objects. This helps alleviate the discrepancies found between the model and the observations.

  10. 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

  11. Precise time dissemination via portable atomic clocks

    NASA Technical Reports Server (NTRS)

    Putkovich, K.

    1982-01-01

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

  12. Future Laser-Cooled Microwave Clock Performance

    NASA Technical Reports Server (NTRS)

    Gibble, Kurt

    1997-01-01

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

  13. Diversity of Human Clock Genotypes and Consequences

    PubMed Central

    Zhang, Luoying; Ptáček, Louis J.; Fu, Ying-Hui

    2014-01-01

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

  14. The NIM Sr Optical Lattice Clock

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Wang, Q.; Li, Y.; Meng, F.; Lin, B.; Zang, E.; Sun, Z.; Fang, F.; Li, T.; Fang, Z.

    2016-06-01

    A 87Sr optical lattice clock is built at the National Institute of Metrology (NIM) of China. The atoms undergo two stages of laser cooling before being loaded into a horizontal optical lattice at the magic wavelength of 813 nm. After being interrogated by a narrow linewidth 698 nm clock laser pulse, the normalized excitation rate is measured to get the frequency error, which is then used to lock the clock laser to the ultra-narrow 1S0-3P0 clock transition. The total systematic uncertainty of the clock is evaluated to be 2.3 × 10-16, and the absolute frequency of the clock is measured to be 429 228 004 229 873.7(1.4) Hz with reference to the NIM5 cesium fountain.

  15. 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...

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

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

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

  17. The plant circadian clock looks like a traditional Japanese clock rather than a modern Western clock

    PubMed Central

    Mizuno, Takeshi; Yamashino, Takafumi

    2015-01-01

    Life cycle adaptation to seasonal changes in photoperiod and ambient temperature is a major determinant of the ecological success behind the widespread domestication of flowering plants. The circadian clock plays a role in the underlying mechanism for adaptation through generating endogenous rhythms that allow plants to adapt and adjust to both the 24 h diurnal rotation and 365 d seasonal revolution. Nevertheless, the mechanism by which the circadian clock tracks seasonal changes in photoperiod and temperature is a longstanding subject in the field. Recently, we have begun to understand the question of how the light and ambient temperature signals feed into the circadian clock transcriptional circuitry in day-night cycles in order to track seasonal changes in photoperiod and ambient temperature.1-4 Our results collectively indicate that the evening complex (EC) nighttime repressor consisting of LUX-ELF3-ELF4 plays a crucial role in this respect. Here, we discuss about these recent studies to add further implications. PMID:26382718

  18. 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.

  19. Peripheral circadian clocks--a conserved phenotype?

    PubMed

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

    2013-05-01

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

  20. 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 (宋以穎, 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 (仁村) Kim Seong-Su (金性洙, 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.

  1. 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.

  2. 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.

  3. Angle detector

    NASA Technical Reports Server (NTRS)

    Parra, G. T. (Inventor)

    1978-01-01

    An angle detector for determining a transducer's angular disposition to a capacitive pickup element is described. The transducer comprises a pendulum mounted inductive element moving past the capacitive pickup element. The capacitive pickup element divides the inductive element into two parts L sub 1 and L sub 2 which form the arms of one side of an a-c bridge. Two networks R sub 1 and R sub 2 having a plurality of binary weighted resistors and an equal number of digitally controlled switches for removing resistors from the networks form the arms of the other side of the a-c bridge. A binary counter, controlled by a phase detector, balances the bridge by adjusting the resistance of R sub 1 and R sub 2. The binary output of the counter is representative of the angle.

  4. 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 τ ≪ 1 hour.

  5. 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-ERBα and RORα regulate Bmal1 expression and provide stability to the oscillator. Circadian clock dysfunction is implicated in both immune and inflammatory responses to environmental, inflammatory, and infectious agents. Molecular clock function is altered by exposomes, tobacco smoke, lipopolysaccharide, hyperoxia, allergens, bleomycin, as well as bacterial and viral infections. The deacetylase Sirtuin 1 (SIRT1) regulates the timing of the clock through acetylation of BMAL1 and PER2 and controls the clock-dependent functions, which can also be affected by environmental stressors. Environmental agents and redox modulation may alter the levels of REV-ERBα and RORα in lung tissue in association with a heightened DNA damage response, cellular senescence, and inflammation. A reciprocal relationship exists between the molecular clock and immune/inflammatory responses in the lungs. Molecular clock function in lung cells may be used as a biomarker of disease severity and exacerbations or for assessing the efficacy of chronotherapy for disease management. Here, we provide a comprehensive overview of clock-controlled cellular and molecular functions in the lungs and highlight the repercussions of clock disruption on the pathophysiology of chronic airway diseases and their exacerbations. Furthermore, we highlight the potential for the molecular clock as a novel chronopharmacological target for the management of lung pathophysiology. PMID:26361874

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

    Tsao, Wen-Chang; Pan, Min-Chun

    2014-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  10. 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.

  11. 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.

  12. Impact of the uncertainties of the ISM when studying the IMF at intermediate masses

    NASA Astrophysics Data System (ADS)

    Mor, R.; Robin, A. C.; Lemasle, B.; Figueras, F.

    We evaluate the impact of the uncertainties in the 3D structure of the Interstellar Medium (ISM) when studying the Initial Mass Function (IMF) at intermediate masses using classical Galactic Cepheids. For that we use the Besan\\c{c}on Galaxy Model (BGM, \\citealt{Robin2003} and \\citealt{Czekaj2014}) and assume different IMFs and different interstellar structure maps to simulate magnitude limited samples of young intermediate mass stars. As our strategy to derive the IMF is based on star counts (in proceedings \\cite{Mor2015} and Mor et al. 2016 in prep.), we quantify the differences in star counts by comparing the whole-sky simulations with Tycho-2 catalogue up to V_T=11 and using Healpix maps. Moreover we compare simulations with different extinction models up to Gaia magnitude G=20. As expected, larger discrepancies between simulations and observations are found in the Galactic Plane, showing that the interstellar extinction in the plane is one of the major source of uncertainty in our study. We show how even with the uncertainties due to the ISM we are able to distinguish between different IMFs.

  13. Tectonic blocks and molecular clocks

    PubMed Central

    2016-01-01

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

  14. Temperature influences in receiver clock modelling

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  15. Eliminating Tracking-System Clock Errors

    NASA Technical Reports Server (NTRS)

    Wu, Jiun-Tsong; Bertiger, William I.

    1989-01-01

    Problems of redundancy and correlation avoided. ORTHO computer program eliminates effect of clock errors in differential solutions for positions of users of Global Positioning System (GPS). Main application, elimination of clock errors in tracking system based on GPS. Written in FORTRAN 77.

  16. 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

  17. Systematic Effects in Atomic Fountain Clocks

    NASA Astrophysics Data System (ADS)

    Gibble, Kurt

    2016-06-01

    We describe recent advances in the accuracies of atomic fountain clocks. New rigorous treatments of the previously large systematic uncertainties, distributed cavity phase, microwave lensing, and background gas collisions, enabled these advances. We also discuss background gas collisions of optical lattice and ion clocks and derive the smooth transition of the microwave lensing frequency shift to photon recoil shifts for large atomic wave packets.

  18. 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).

  19. 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...

  20. "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…

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

    SciTech Connect

    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.

  2. A blind circadian clock in cavefish reveals that opsins mediate peripheral clock photoreception.

    PubMed

    Cavallari, Nicola; Frigato, Elena; Vallone, Daniela; Fröhlich, Nadine; Lopez-Olmeda, Jose Fernando; Foà, Augusto; Berti, Roberto; Sánchez-Vázquez, Francisco Javier; Bertolucci, Cristiano; Foulkes, Nicholas S

    2011-09-01

    The circadian clock is synchronized with the day-night cycle primarily by light. Fish represent fascinating models for deciphering the light input pathway to the vertebrate clock since fish cell clocks are regulated by direct light exposure. Here we have performed a comparative, functional analysis of the circadian clock involving the zebrafish that is normally exposed to the day-night cycle and a cavefish species that has evolved in perpetual darkness. Our results reveal that the cavefish retains a food-entrainable clock that oscillates with an infradian period. Importantly, however, this clock is not regulated by light. This comparative study pinpoints the two extra-retinal photoreceptors Melanopsin (Opn4m2) and TMT-opsin as essential upstream elements of the peripheral clock light input pathway. PMID:21909239

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

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

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

  4. 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.

  5. A low maintenance Sr optical lattice clock

    NASA Astrophysics Data System (ADS)

    Hill, I. R.; Hobson, R.; Bowden, W.; Bridge, E. M.; Donnellan, S.; Curtis, E. A.; Gill, P.

    2016-06-01

    We describe the Sr optical lattice clock apparatus at NPL with particular emphasis on techniques used to increase reliability and minimise the human requirement in its operation. Central to this is a clock-referenced transfer cavity scheme for the stabilisation of cooling and trapping lasers. We highlight several measures to increase the reliability of the clock with a view towards the realisation of an optical time-scale. The clock contributed 502 hours of data over a 25 day period (84% uptime) in a recent measurement campaign with several uninterrupted periods of more than 48 hours. An instability of 2 x 10-17 was reached after 105 s of averaging in an interleaved self-comparison of the clock.

  6. 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

  7. Double-modulation CPT cesium compact clock

    NASA Astrophysics Data System (ADS)

    Yun, Peter; Mejri, Sinda; Tricot, Francois; Abdel Hafiz, Moustafa; Boudot, Rodolphe; de Clercq, Emeric; Guérandel, Stéphane

    2016-06-01

    Double-modulation coherent population trapping (CPT) is based on a synchronous modulation of Raman phase and laser polarization, which allows the atomic population to accumulate in a common dark state. The high contrast signal obtained on the clock transition with a relative compact and robust laser system is interesting as basis of a high performance microwave clock. Here we study the parameters of a double-modulation CPT Cs clock working in cw mode. The optimal polarization modulation frequency and cell temperature for maximum contrast of clock transition are investigated. The parameters of the detection are also studied. With the optimal parameters, we observe a CPT signal with contrast of 10% and linewidth of 492 Hz, which is well suited for implementing a cw atomic clock.

  8. 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

  9. 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.

  10. 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.

  11. 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.

  12. Impact of the IMF rotation on the cusp dynamics on the dayside: Global 3D PIC simulations

    NASA Astrophysics Data System (ADS)

    Huang, Z.; Cai, D.; Lembege, B.; Nishikawa, K.-I.

    The dynamics of the cusp region is analyzed with a new version of a global three-dimensional full particle simulation with changing the interplanetary magnetic field IMF direction progressively from northward to duskward then duskward to southward With the initial northward IMF bands of weak magnetic field sash form poleward of the cusp at high latitudes in each hemisphere and at high altitudes these sashes are located approximately around the pole axis As the IMF rotates duskward these sashes move toward the equator within opposite quadrants Then as the duskward-oriented IMF continue to rotate toward southward these sashes move further and reach the dayside magnetopause at the equator During the progressive rotation of the IMF from northward to duskward i the sash region widens towards lower latitudes banana-shape and with the duskward IMF ii the size of the banana-shape region becomes minimum and its location stops around a maximum deviation of 45degree from the polar axis It should be noted that the sashes are extended from the dayside to the nightside tailward The motion of the sashes is also analyzed during the IMF rotation form duskward to southward

  13. 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

  14. The effect of a brief northward turning in IMF Bz on solar wind-magnetosphere coupling in a global MHD simulation

    NASA Astrophysics Data System (ADS)

    Pham, Kevin H.; Lopez, Ramon E.; Bruntz, Robert

    2016-05-01

    In this paper we examine the response of the magnetosphere-ionopshere (M-I) system to a transient northward excursion in the interplanetary magnetic field (IMF) using the Lyon-Fedder-Mobarry (LFM) global MHD simulation. The simulated IMF transitions hold from a steady southward IMF to a steady northward IMF before suddenly transitioning back to southward IMF after 20 min. Once the IMF returns southward, the M-I system is in a state of reduced energy dissipation for approximately an hour as it reconfigures back into a standard southward IMF configuration. We find that the northward IMF excursion affects both the viscous and reconnection interactions with the solar wind. The flow of plasma in the magnetosphere is significantly disrupted by the reconnection cycle under northward IMF. This reduce the transfer of mechanical energy from the solar wind due to the viscous interaction, and the magnetosphere-ionosphere system is in a mixed topological configuration containing elements produced by both of southward IMF reconnection and the Dungey cycle, as well as northward IMF reconnection and the presence of reverse cell convection at high latitudes. The effects of the transient northward IMF must be completely cleared out before the system can return to an optimal state of energy transfer characteristic of steady southward IMF. As a result, a simple 20 min excursion of northward IMF can put the magnetosphere-ionosphere system into a reduced state of coupling to the solar wind for some time following the return to steady southward IMF; for LFM we saw a reduced state lasting an hour

  15. 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.

  16. Time clock requirements for hospital physicians.

    PubMed

    Shapira, Chen; Vilnai-Yavetz, Iris; Rafaeli, Anat; Zemel, Moran

    2016-06-01

    An agreement negotiated following a doctors' strike in 2011 introduced a requirement that physicians in Israel's public hospitals clock in and out when starting and leaving work. The press reported strong negative reactions to this policy and predicted doctors deserting hospitals en masse. This study examines physicians' reactions toward the clock-in/clock-out policy 6 months after its implementation, and assesses the relationship between these reactions and aspects of their employment context. 676 physicians in 42 hospitals responded to a survey assessing doctor's reactions toward the clock, hospital policy makers, and aspects of their work. Reactions to the clock were generally negative. Sense of calling correlated positively with negative reactions to the clock, and the latter correlated positively with quit intentions. However, overall, respondents reported a high sense of calling and low quit intentions. We suggest that sense of calling buffers and protects physicians from quit intentions. Differences in reactions to the clock were associated with different employment characteristics, but sense of calling did not vary by hospital size or type or by physicians' specialty. The findings offer insights into how physicians' working environment affects their reactions to regulatory interventions, and highlight medical professionalism as buffering reactions to unpopular regulatory policies. PMID:27142179

  17. Circadian clock system in the pineal gland.

    PubMed

    Fukada, Yoshitaka; Okano, Toshiyuki

    2002-02-01

    The pineal gland is a neuroendocrine organ that functions as a central circadian oscillator in a variety of nonmammalian vertebrates. In many cases, the pineal gland retains photic input and endocrinal-output pathways both linked tightly to the oscillator. This contrasts well with the mammalian pineal gland equipped only with the output of melatonin production that is subject to neuronal regulation by central circadian oscillator located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Molecular studies on animal clock genes were performed first in Drosophila and later developed in rodents. More recently, clock genes such as Per, Cry, Clock, and Bmal have been found in a variety of vertebrate clock structures including the avian pineal gland. The profiles of the temporal change of the clock gene expression in the avian pineal gland are more similar to those in the mammalian SCN rather than to those in the mammalian pineal gland. Avian pineal gland and mammalian SCN seem to share a fundamental molecular framework of the clock oscillator composed of a transcription/translation-based autoregulatory feedback loop. The circadian time-keeping mechanism also requires several post-translational events, such as protein translocation and degradation processes, in which protein phosphorylation plays a very important role for the stable 24-h cycling of the oscillator and/or the photic-input pathway for entrainment of the clock. PMID:11890455

  18. Highly precise clocks to test fundamental physics

    NASA Astrophysics Data System (ADS)

    Bize, S.; Wolf, P.

    2012-12-01

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

  19. 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.

  20. 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.

  1. 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."

  2. 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.

  3. 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...

  4. 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/τ whereas a clock with dead time integrates as 1/τ(1/2) under identical conditions. We contend that a similar scheme may be applied to improve the stability of optical clocks. PMID:24206471

  5. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

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

  7. Circadian and Circalunar Clock Interactions in a Marine Annelid

    PubMed Central

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

    2013-01-01

    Summary Life is controlled by multiple rhythms. Although the interaction of the daily (circadian) clock with environmental stimuli, such as light, is well documented, its relationship to endogenous clocks with other periods is little understood. We establish that the marine worm Platynereis dumerilii possesses endogenous circadian and circalunar (monthly) clocks and characterize their interactions. The RNAs of likely core circadian oscillator genes localize to a distinct nucleus of the worm’s forebrain. The worm’s forebrain also harbors a circalunar clock entrained by nocturnal light. This monthly clock regulates maturation and persists even when circadian clock oscillations are disrupted by the inhibition of casein kinase 1δ/ε. Both circadian and circalunar clocks converge on the regulation of transcript levels. Furthermore, the circalunar clock changes the period and power of circadian behavior, although the period length of the daily transcriptional oscillations remains unaltered. We conclude that a second endogenous noncircadian clock can influence circadian clock function. PMID:24075994

  8. 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.; Szegő, 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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

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

  10. Abundance ratios and IMF slopes in the dwarf elliptical galaxy NGC 1396 with MUSE

    NASA Astrophysics Data System (ADS)

    Mentz, J. J.; La Barbera, F.; Peletier, R. F.; Falcón-Barroso, J.; Lisker, T.; van de Ven, G.; Loubser, S. I.; Hilker, M.; Sánchez-Janssen, R.; Napolitano, N.; Cantiello, M.; Capaccioli, M.; Norris, M.; Paolillo, M.; Smith, R.; Beasley, M. A.; Lyubenova, M.; Munoz, R.; Puzia, T.

    2016-08-01

    Deep observations of the dwarf elliptical (dE) galaxy NGC 1396 (MV = -16.60, Mass ˜4 × 108 M⊙), located in the Fornax cluster, have been performed with the VLT/ MUSE spectrograph in the wavelength region from 4750 - 9350 Å. In this paper we present a stellar population analysis studying chemical abundances, the star formation history (SFH) and the stellar initial mass function (IMF) as a function of galacto-centric distance. Different, independent ways to analyse the stellar populations result in a luminosity-weighted age of ˜ 6 Gyr and a metallicity [Fe/H]˜ -0.4, similar to other dEs of similar mass. We find unusually overabundant values of [Ca/Fe] ˜+0.1, and under-abundant Sodium, with [Na/Fe] values around -0.1, while [Mg/Fe] is overabundant at all radii, increasing from ˜+0.1 in the centre to ˜+0.2 dex. We notice a significant metallicity and age gradient within this dwarf galaxy. To constrain the stellar IMF of NGC 1396, we find that the IMF of NGC 1396 is consistent with either a Kroupa-like or a top-heavy distribution, while a bottom-heavy IMF is firmly ruled out. An analysis of the abundance ratios, and a comparison with galaxies in the Local Group, shows that the chemical enrichment history of NGC 1396 is similar to the Galactic disc, with an extended star formation history. This would be the case if the galaxy originated from a LMC-sized dwarf galaxy progenitor, which would lose its gas while falling into the Fornax cluster.

  11. The Distant Magnetotail Under Long Duration, Very Northward IMF Conditions: October 22-24, 2003

    NASA Technical Reports Server (NTRS)

    Fairfield, Donald H.; Oieroset, M.; Raeder, J.; Lepping, R. P.; Newell, P. T.; Wind, S.

    2006-01-01

    A unique 32 hour interval of very northward Interplanetary Magnetic Field (IMF) on October 22-24, 2003 created a exceptionally thick cold dense magnetotail plasma sheet, a small polar cap and accompanying small tail lobe. These features were detected by the Cluster DMSP and FAST spacecraft and modeled by a global simulation as described in papers by Oieroset et al. (2005) and Li et al. (2005). During the same interval the Wind spacecraft was passing through the center of the magnetotail about 130 Re downstream of Earth. Wind results will be described that reveal a very unusual magnetotail characterized by (1) continual tailward flow of 200-400 km/s with densities in the range 0.2-3/cc, both of whch are clearly less than those expected in the magnetosheath, (2) a mostly northward Bz but with a predominant Bx field component with sign reversals indicating crossings between the two hemispheres of the tail, and (3) velocity waves superposed on the downstream flow with peak-to-peak amplitudes of 100 to 200 km/s, periods of 10 to 20 minutes and clockwise polarization. Low altitude DMSP and Fast measurements reveal an auroral oval with enhanced latitudinal thickness and a small polar cap filled with structured precipitzting electrons and few ions. A new global MHD simulation of the event exhibits a highly elliptical tail of diminished cross-section at 130 Re with major axis aligned with the northward IMF. The tail current sheet also tends to be aligned in a north-south direction with the two tail hemispheres to the east and west with their polarities depending on prior history of the IMF. The simulation appears to be consistent with many, but not all, of the observations. High latitude cusp reconnection and subsequent downtail flow of closed field lines may explain the tail structure, but the waves are more likely due to the Kelvin-Helmholtz instability often thought to occur during northward IMF conditions.

  12. Influence of Geomagnetic and IMF conditions on High Latitude Upper Atmospheric winds and Temperatures

    NASA Astrophysics Data System (ADS)

    Dhadly, M. S.; Conde, M.; Emmert, J. T.

    2015-12-01

    We analyzed the climatological behavior of upper atmospheric winds (horizontal and vertical) and temperatures above Alaska by combining line-of-sight Doppler shifts of 630 nm optical emissions recorded during the 2011 and 2012 winters using a ground based all-sky wavelength scanning Doppler Fabry-Perot interferometer (SDI) located at Poker Flat (65.12N, 147.47W). The wide field of view covered a large geographic region above Alaska. This field was divided in software into multiple zones (115 used here), allowing independent spectra to be sampled from many directions simultaneously. As a result, it is capable of recording the wind field's spatial variations over a wide geographic region with high spatial resolution, and to resolve these variations over time. Although such climatological studies have been performed previously using satellites, models, and narrow field Fabry-Perot interferometers, there are no published climatological studies of thermospheric winds and temperatures using either SDI data or any other technique with comparable geographic coverage and resolution. Wind summary dial plots were produced to depict the climatology of the horizontal winds and temperatures for different geomagnetic conditions and orientation of interplanetary magnetic field (IMF). Results show that horizontal winds and temperatures had a strong dependence on geospace activity and orientation of IMF. The latitudinal shears in horizontal winds were stronger when geomagnetic conditions were active compared to the latitudinal shears for quiet conditions. Also, shears appeared earlier over Poker Flat when geomagnetic conditions were active. The latitudinal shears showed more dependence on IMF when geomagnetic conditions were active than they did during quieter conditions. F-region temperatures were higher under active geomagnetic conditions than during quiet conditions. They were also observed to be higher in pre-magnetic midnight sector (duskside) than they were post

  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. Deep Space Atomic Clock Ticks Toward Success

    NASA Video Gallery

    Dr. Todd Ely, principal investigator for NASA's Deep Space Atomic Clock at the Jet Propulsion Laboratory in Pasadena, Calif., spotlights the paradigm-busting innovations now in development to revol...

  15. Clock genes, pancreatic function, and diabetes.

    PubMed

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

    2014-12-01

    Circadian physiology is responsible for the temporal regulation of metabolism to optimize energy homeostasis throughout the day. Disturbances in the light/dark cycle, sleep/wake schedule, or feeding/activity behavior can affect the circadian function of the clocks located in the brain and peripheral tissues. These alterations have been associated with impaired glucose tolerance and type 2 diabetes. Animal models with molecular manipulation of clock genes and genetic studies in humans also support these links. It has been demonstrated that the endocrine pancreas has an intrinsic self-sustained clock, and recent studies have revealed an important role of clock genes in pancreatic β cells, glucose homeostasis, and diabetes. PMID:25457619

  16. 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.

  17. 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

  18. Frequency Metrology with Optical Lattice Clocks

    NASA Astrophysics Data System (ADS)

    Hong, Feng-Lei; Katori, Hidetoshi

    2010-08-01

    The precision measurement of time and frequency is of great interest for a wide range of applications, including fundamental science and technologies that support broadband communication networks and the navigation with global positioning systems (GPSs). The development of optical frequency measurement based on frequency combs has revolutionized the field of frequency metrology, especially research on optical frequency standards. The proposal and realization of the optical lattice clock have further stimulated studies in the field of optical frequency metrology. Optical carrier transfer using optical fibers has been used to disseminate optical frequencies or compare two optical clocks without degrading their stability and accuracy. In this paper, we review the state-of-the-art development of optical frequency combs, standards, and transfer techniques with emphasis on optical lattice clocks. We address recent results achieved at the University of Tokyo and the National Metrology Institute of Japan in respect of frequency metrology with Sr and Yb optical lattice clocks.

  19. Avian circadian organization: a chorus of clocks.

    PubMed

    Cassone, Vincent M

    2014-01-01

    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

  20. 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

  1. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

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

  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. Cloning and Expression of SFRP5 in Tibetan Chicken and its Relationship with IMF Deposition.

    PubMed

    Li, Qian; Zuo, Lu-Lu; Lin, Ya-Qiu; Xu, Ya-Ou; Zhu, Jiang-Jiang; Liao, Hong-Hai; Lin, Sen; Xiong, Xian-Rong; Wang, Yong

    2016-10-01

    Secreted frizzled related protein 5 (SFRP5), an anti-inflammatory adipokine, is relevant to the adipocyte differentiation. In order to clarify its role in regulating intramuscular fat (IMF) deposition in Tibetan chicken, the full-length sequence of the Tibetan chicken SFRP5 gene was cloned. The relative expression of SFRP5 gene was detected using quantitative RT-PCR in various tissues of 154 days old Tibetan chicken, as well as in breast muscle, thigh muscle, and adipose tissue at different growth stages. The results showed that SFRP5 gene was expressed in all examined tissues but highly enriched in adipose tissue. Temporal expression profile showed that the expression of SFRP5 was gradually decreased in breast muscle, but was fluctuated in thigh muscle and adipose tissue with the growth of Tibetan chicken. Furthermore, correlation analysis demonstrated that the expression of SFRP5 in breast muscle, thigh muscle and adipose tissue was correlated with IMF content at different levels. The results indicated that Tibetan chicken SFRP5 is involved in IMF deposition. PMID:27565866

  5. 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.

  6. 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+).

  7. 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.

  8. Acceleration and injection of particles inside the magnetosphere changes during duskward IMF By: statistical approach

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    The change of the interplanetary magnetic field (IMF) direction from northward to duskward has an important impact on the inner magnetosphere as analyzed in a recent paper [Yan et al, GRL, to appear] . This impact is analyzed with the help of a new parallel version of the global three-dimensional full particle simulation. As the newly duskward-oriented IMF interacts with the magnetosphere, bands of weak magnetic field (sash) move to the equator (within opposite quadrants), reach lower latitude and merge into each other to form characteristic ``Crosstail-S" structures within the neutral sheet of the magnetotail. The analysis of particle fluxes shows that ``sashs" and ``Crosstail-S" act as magnetic groove to facilitate the entry and injection of magnetosheath particles into the inner magnetosphere. Injected particles are accelerated after the IMF changes its direction from northward to duskward. Characteristic times associated to the changes of the particle dynamics are estimated from the simulations. These informations are thought to be helpful as pre-signatures announcing the triggering of magnetic substorms.

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

    NASA Astrophysics Data System (ADS)

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

    1996-05-01

    An outstanding topic in magnetospheric physics is whether substorms are always externally triggered by disturbances in either the interplanetary magnetic field (IMF) 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 the both sides of this issue. Horwitz [1985] and McPherron et al. [1986] have shown examples of substorm onsets which they claimed were not externally triggered. However, as pointed out by Lyons [1995, 1996], 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 By 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 DP 2 current system that are often observed to occur during steady magnetospheric convection events. In the present study, we utilize a much more comprehensive data set (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, midlatitude Pi 2 pulsation data, ground magnetometer data, and ISEE 1 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.

  10. 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.