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1

Reconnection voltage as a function of IMF clock angle  

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

2

Magnetic merging line and reconnection voltage versus IMF clock angle: Results from global MHD simulations  

NASA Astrophysics Data System (ADS)

This paper proposes diagnosis methods to trace the magnetic merging line and to calculate the electric potential along it for Earth's magnetospheric magnetic fields obtained by global magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere-ionosphere (SMI) system. The points with minimum magnetic field strength along last closed magnetic field lines and properly selected closed field lines are combined to trace the whole merging line, and the radial ray integration of convectional electric field is used to calculate the electric potential on the merging line. The diagnosis methods are then applied to magnetospheric magnetic fields associated with different interplanetary magnetic field (IMF) clock angles, and a preliminary analysis is presented on the clock angle response of the geometry of the merging line and the associated reconnection voltage. The merging line is found to be similar in geometry to that of the compound field superposed by the Earth's dipole field and the IMF, whereas the reconnection voltage is approximately fitted by sin3/2($\\theta$ IMF/2) for its response to the IMF clock angle $\\theta$ IMF. The ionospheric transpolar potential and the voltage along the polar cap boundary show different dependence from that of the reconnection voltage, so it is not justified to take them as substitutes for the reconnection voltage. The length of the sunward merging line between the two peaks of reconnection potential shows a nonmonotonic variation in response to $\\theta$ IMF, peaked at $\\theta$ IMF = 90°, so it is also not justified to take electric fields along the merging line, however defined they may be, to characterize the total reconnection rate and the coupling strength between the solar wind and the magnetosphere. The reconnection nearby magnetic nulls closest to the subsolar point is found to be negligible, which gives support to the component reconnection hypothesis for dayside reconnection of quasi-steady states of the SMI system.

Hu, Y. Q.; Peng, Z.; Wang, C.; Kan, J. R.

2009-08-01

3

Relationship between the IMF azimuthal angle and solar wind velocity  

NASA Astrophysics Data System (ADS)

The relationship between the IMF azimuthal angle and plasma velocity has been studied independently for three types of solar wind streams (recurrent and transient high-speed streams and low-speed background wind) based on the interplanetary medium parameters measured in the near-Earth orbits in 1964-1996. The relationships between the IMF azimuthal angle cotangent and plasma velocity are close to linear but strongly differ from one another and from the theoretical relationship for all types of streams. These differences area caused by the magnetic field disturbance on the time scales smaller than a day, and the effect of this disturbance has been studied quantitatively. The effective periods of rotation of the IMF sources on the Sun, depending on the solar cycle phase, have been obtained from the relations between the IMF azimuthal angle cotangent and plasma velocity. During the most part of the solar cycle, the periods of rotation of the IMF sources are close to the period of rotation of the solar equator but abruptly increase to the values typical of the solar circumpolar zones in the years of solar minimums.

Erofeev, D. V.

2008-04-01

4

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

5

Seasonal and clock angle control of the location of flux transfer events signatures at the magnetopause  

NASA Astrophysics Data System (ADS)

Most models of flux transfer event (FTE) formation produce pairs of structures, which in general move away from the subsolar region and give rise to signatures which can be observed in both the northern and southern hemispheres. The multiple reconnection line (X-line) model is unique as a reconnection-based model that is capable of producing a single flux rope if only two X-lines are present. Raeder [2006] reported the results of an MHD simulation where he studied the effect of the Earth's dipole tilt on reconnection at the dayside magnetopause for a southward IMF orientation; in his simulations, flux ropes were formed by the sequential formation of X-lines, and when the dipole tilt was set to a value representative of solstice the flux ropes moved preferentially towards the winter hemisphere. Some observational evidence has previously been presented for a bias towards FTE signatures being observed in the winter hemisphere; in this presentation, we show further observational evidence for this phenomenon, using an independently-derived data set. Once the seasonal bias is taken into account, we find that the IMF clock angle controls the location of FTE signatures. We also find that the effective dipole tilt (combining the geomagnetic dipole tilt with the IMF tilt angle) provides no clear control of the location of FTE signatures.

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

2012-04-01

6

Seasonal and clock angle control of the location of flux transfer event signatures at the magnetopause  

NASA Astrophysics Data System (ADS)

Most models of flux transfer event (FTE) formation produce pairs of structures which in general move away from the subsolar region and give rise to signatures which can be observed in both the Northern and Southern Hemispheres. The multiple reconnection line (X line) model is unusual as a reconnection-based model that is capable of producing a single flux rope if only two X lines are present. Raeder (2006) reported the results of an MHD simulation where he studied the effect of the Earth's dipole tilt on reconnection at the dayside magnetopause for a southward IMF orientation; in his simulations, flux ropes were formed by the sequential formation of X lines, and when the dipole tilt was set to a value representative of solstice the flux ropes moved preferentially toward the winter hemisphere. Some observational evidence has previously been presented for a bias toward FTE signatures being observed in the winter hemisphere; in this paper, we present further observational evidence for this phenomenon, using an independently derived data set. Once the seasonal bias is taken into account, we find that the IMF clock angle controls the location of FTE signatures. We also find that the effective dipole tilt (combining the geomagnetic dipole tilt with the IMF tilt angle) provides no clear control of the location of FTE signatures.

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

2012-04-01

7

Investigating the IMF cone angle control of Pc3-4 pulsations observed on the ground  

NASA Astrophysics Data System (ADS)

studies have shown that Pc3-4 pulsations (~0.014-0.1 Hz) observed in Earth's magnetosphere during daytime hours originate in the ion foreshock region of the solar wind, just upstream from Earth's bow shock. They occur when the interplanetary magnetic field (IMF) is primarily radial—when the IMF cone angle ?xB ? 45°. However, our knowledge of ion foreshock conditions is often incomplete because of the very limited number of spacecraft providing upstream data. In this study we compared 13 months of wave observations at two widely separated ground stations (Hornsund, Svalbard and Halley, Antarctica) to IMF values in the OMNI database in order to test this relation. Values of ?xB and the empirically predicted wave frequency (fcalc = 0.06 BIMF) were compared to daily Fourier spectrograms displaying pulsation power and frequency. Although there was often good temporal agreement between low ?xB and increased Pc3-4 wave power, numerous counterexamples were also evident. A statistical study of wave activity in quarter hour increments showed that Pc3-4 pulsations were associated with low ?xB values, 81% of the time at Hornsund and 83% at Halley. IMF cone angle data from all available upstream monitors were compared to wave observations for a more limited number of days; many of these showed inconsistent IMF orientations. This study indicates some of the limitations of the existing upstream monitors and provides a quantitative estimate (~80%) of the accuracy of the OMNI data set in characterizing conditions near the nose of Earth's bow shock under predominantly radial IMF conditions.

Bier, Elianna A.; Owusu, Nana; Engebretson, Mark J.; Posch, Jennifer L.; Lessard, Marc R.; Pilipenko, Viacheslav A.

2014-03-01

8

Clocks  

NSDL National Science Digital Library

This is a good resource to expose students to different types of clocks. Ultimately we want our students to be able to apply the skills that they acquire (in this case, telling time) to all situations. It is nice that you can print clocks showing different times or each of the types of clocks. Thank you for sharing.

2012-04-12

9

The IMF dependence of the magnetopause from global MHD simulations  

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

10

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

Microsoft Academic Search

The normalized rate of occurrence of dayside Pc 3,4 pulsations from L = 2.4 to 4.3 has a strong enhancement for low cone angles of the interplanetary magnetic field. When the angle of the IMF to the earth sun line, theta\\/sub BX\\/, in 15° or less the occurrence rate is 7-8 times the average rate at L = 2.4 to

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

1983-01-01

11

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)

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.

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

1983-01-01

12

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

13

Magnetosphere-ionosphere coupling at midmorning local times: Dependence on IMF parameters  

NASA Astrophysics Data System (ADS)

We discuss magnetosphere-ionosphere coupling at ˜0900 magnetic local time based on two conjunctions of Polar with Svalbard on November 30 and December 3, 1997. We document a correspondence between latitudinally separate aurorae with field aligned currents, and identify the source of temporal variability of aurorae and currents. On November 30 under a westward (By<0) and generally northward IMF, a sunward-flowing, mixing region in the boundary plasma sheet is postulated to be the source of the Region 1 (R1) current. Plasma filaments therein are the source of discrete, midmorning arcs. Field line resonances in the Region 2 (R2) current are driven by the Kelvin-Helmholtz instability. When the IMF turned north, all midmorning arcs were replaced by a weak cusp-type form north of zenith. Pulsations in all aurorae correlate with magnetic oscillations at Polar and local ground magnetometers. Under the more southerly and eastward IMF on Dec 3, a pair of cusp current sheets on antisunward convection was observed poleward of R1/R2. Here enhanced, pulsed fluxes of ions of magnetosheath energies perturbed the geomagnetic field and were accompanied by enhanced electron fluxes of magnetosheath energies bidirectionally streaming along the field. The associated aurora is pulsed in response to decreasing IMF Bz. We extend a reconnection model to include time dependence and hypothesize that observations in the regime of cusp currents are due to time-varying reconnection at an X-line tilted from lower (at prenoon) to higher (postnoon) latitudes by IMF By>0. Accordingly, cusp currents appear at prenoon. Ion pulsing ceased when the IMF clock angle ? was ˜60°. All aurorae advance equatorward as ? increases. The observations reveal a complex of relationships sensitively regulated by the IMF, and we can separate dependencies on IMF Bz from those on By.

Farrugia, Charles J.; Sandholt, Per Even

14

Robo Clock  

NSDL National Science Digital Library

Students learn various topics associated with the circle through studying a clock. Topics include reading analog time, understanding the concept of rotation (clockwise vs. counter-clockwise), and identifying right angles and straight angles within circles. Many young students have difficulty telling time in analog format, especially with fewer analog clocks in use (compared to digital clocks). This includes the ability to convert time written in words to a number format, for example, making the connection between "quarter of an hour" to 15 minutes. Students also find it difficult to convert "quarter of an hour" to the number of degrees in a circle. This activity incorporates a LEGO® MINDSTORMS® NXT robot to help students distinguish and visualize the differences in clockwise vs. counter-clockwise rotation and right vs. straight angles, while learning how to tell time on an analog clock. To promote team learning and increase engagement, students work in teams to program and control the robot.

Applying Mechatronics to Promote Science (AMPS) Program GK-12,

15

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)

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.

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

2005-01-01

16

Clock Counting  

NSDL National Science Digital Library

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

Mcduffee, Ms.

2008-11-12

17

Clocks, Angles and Functions  

ERIC Educational Resources Information Center

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…

Kemp, Andy

2006-01-01

18

Interhemispheric Conjugacy of High-Latitude Ionospheric Convection Determined From DMSP IMF-Dependent Models  

NASA Astrophysics Data System (ADS)

In this study we report on a series of new ionospheric convection models constructed from the DMSP thermal ion drift measurements for both the northern and southern polar regions and for the summer, winter, and equinox. Applying the regression analysis technique to the IMF and DMSP data, we first obtained four basic elements of the convection response on 1-nT changes in the corresponding IMF component: (a) the two-cell, ``quasi-viscous'' convection (i.e., for IMF ~0 (b) the lobe convection cell controlled by the IMF azimuthal component; (c) the merging two-cell convection driven by the IMF southward orientation; and (d) the near-pole, two-cell ``reverse'' convection caused by the northward IMF. Then we fitted the obtained distributions of regression coefficients by the spherical harmonics; the resulting DMSP-based ionospheric convection model (DICM) is fully parameterized by the IMF strength and direction. After comparisons with other available high-latitude convection patterns organized by the IMF ``clock-angle'', we concluded that DICM shows all expected features of the solar wind-magnetosphere-ionosphere coupling. A new element in our model is its ``quasi-viscous'' term, which has not been yet obtained in any other satellite or radar-based ionospheric convection studies. Another new elements are the DICM seasonal dependence and interhemispheric symmetry/asymmetry features; for example, we found that the summer cross-polar potentials are 10-15% smaller than the winter potentials. The latter is in agreement with the seasonal dependence of field-aligned currents and with the voltage-current relationship required for the proper magnetosphere-ionosphere coupling. The obtained results justify a need in developing a unified approach for the modeling of high-latitude ionospheric convection from various data sources (i.e., from ground magnetometers, radars, digisondes, and satellite observations) allowing seemliness data assimilation in various ``space weather'' applications. The new models can be run on-line at the SPRL Web site http://www.sprl.umich.edu/mist/.

Papitashvili, V. O.; Rich, F. J.

2001-12-01

19

IMF Staff Papers  

NSDL National Science Digital Library

The quarterly journal IMF Staff Papers "makes available to a wider audience research papers prepared by the members of the IMF staff." The March 1999 issue looks at skilled and unskilled workers in Spain, deindustrialization in advanced economies, and the story of exchange rate deviations from purchasing power parity in two monetary unions.

20

IMF Annual Report 1998  

NSDL National Science Digital Library

Released in September 1998, the IMF Annual Report covers world economic events to April 30, 1998 in 13 searchable files. The effects of key developments such as the Asian Financial Crisis on advanced, developing, and transition economies are discussed as well IMF reaction and structural change.

Fund., International M.

1998-01-01

21

Measuring the IMF  

NSDL National Science Digital Library

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

22

Clock Wise  

NSDL National Science Digital Library

Practice reading a clock, input times for the clock to display, or let the clock generate random times for you to read. Choose from three difficulty levels. Clock Wise is one of the Interactivate assessment explorers.

23

THEMIS Observations of Double-onset Substorms and Their Association with IMF Variations  

NASA Astrophysics Data System (ADS)

On 16 July 2008, two pairs of Pi2 pulsation bursts occurred successively and simultaneously at the ground- based observatory system for the THEMIS mission. The keogram at CHBG (L=3.90, corrected geomagnetic longitude 23.0) showed auroral activations at each Pi2 onset. The ground-based magnetometers and geosynchronous orbit sensed magnetic perturbations like the one affected by the formation of the substorm current wedge. The horizontal magnetic variation vectors, consisting of H and D components, had the vortex patterns like the ones induced by the upward and downward field-aligned currents during substorm times. These observations display two recurrent occurrences of double-onset substorms. Meanwhile the THEMIS-B probe at ~ XGSM 25 Re observed two same variation trends of the interplanetary magnetic field (IMF) with a low clock angle as those in the upstream region shifted to ~1 AU just in front of Earth's magnetopause. The mapping of ground Pi2 onsets to the IMF observations shows that they appear under two variation cycles of north-to-south and then north. Same as previous missions reported, this event manifests that double-onset substorms are externally triggered in association with the IMF variations.

Cheng, C.; Russell, C. T.; Angelopoulos, V.; Mann, I.; Glassmeier, K. H.; Baumjohann, W.; Mende, S.; Donovan, E.

2009-05-01

24

IMF Loan for Russia  

NSDL National Science Digital Library

This week's In the News looks at the International Monetary Fund's recent lending agreement with Russia. The nine resources discussed offer commentary, news, analysis, and background information concerning the IMF's current economic package, and discuss the Russian economic crisis in general. A key player in the New Russian Federation's transition to a market economy, the IMF, agreed to ease Russia's ongoing financial crisis on July 13, 1998 with a loan of 15.1 billion dollars (to be dispersed over two years). According to IMF First Deputy Managing Director Stanley Fischer, this amount is "a very significant draw on our resources," although the IMF has protected its funding carefully via terms outlined in the agreement. Deliberators in Russia's Parliament, however, find the conditions set by the IMF, President Boris Yeltsin, and other international lenders to be too harsh -- particularly a condition to protect the rights of foreign investors. As the debate continues, many fear that future international funding will be withheld, and the ruble will continue its downward spiral set off by the Asian financial crisis in May 1998 (discussed in the January 30, 1998 Scout Report). With 5 billion dollars or more available from the IMF as early as next week, Russian government leaders must agree on a feasible economic plan, before conditions worsen.

Waters, Megan.

1998-01-01

25

Angles  

NSDL National Science Digital Library

Play these games to determine the best angles for success! Alien Angles Set the angle to rescue the alien. Space Angles Target the angle to shoot the alien spaceship. Mini Golf Knowing the angles will help you get the ball in the hole. ...

Clark, Mr

2012-10-31

26

Angles  

NSDL National Science Digital Library

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

Edkins, Jo

2007-01-01

27

A review of the IMF.  

NASA Astrophysics Data System (ADS)

The present-day mass function (PDMF) of field stars in the solar neighborhood is discussed. The IMF is probably not universal; reported IMF variations in open clusters and globular clusters are unlikely to be spurious. Finally the physics of the IMF is discussed.

Zinnecker, H.

28

Angles.  

National Technical Information Service (NTIS)

Shows the Brownstone Kids teaching others how to dance. Illustrates angles as they turn and sing 'Get the Angles.' The group goes to a community center for playing pool in 'Calling Shoots.' Discusses angles showing the 90-degree, 45-degree, and 180-degree...

1994-01-01

29

Observation of mixed ion populations deep inside earth magnetosphere as evidence for reconnection during northward IMF with substantial y-component  

NASA Astrophysics Data System (ADS)

It is widely accepted that plasma from ionospheric and solar wind origin are the two main sources for the hot plasma sheet plasma. Of the possible entry processes magnetic field reconnection is a preferable candidate. To observe in a magnetopause boundary layer on open field lines an admixture of plasmas with different history is a natural consequence of merging between magnetosheath and magnetospheric field lines. However a number of observations of ion regions with mixed magnetosheath - plasma-sheet ion population deep inside the magnetosphere have been reported in the literature, all of them being observed under northward interplanetary magnetic field (IMF). Interball-1 (IB-1) orbit permitted for extensive investigations of the near-Earth high-latitude magnetotail. We have found several cases, observed under northward IMF with substantial By, when plasma in these regions was mixed. We discuss in details one case of prolonged observations of mixed ion region, detected near the dusk terminator at ZGSM ~8.5 to 12.7 RE . Its registration started when IB-1 was 6.35 RE away from the magnetopause and lasted for 6.5 hours till the s/c exited into the magnetosheath. Both ion populations were nearly stagnant, their velocity did not exceed 30 km/s and plasma-sheet electrons were absent. Most of the time IMF clock angle was less than 90 deg, rotating to more than 270 deg at the end of the interval, IMF Bx being positive and dominating. An FTE was registered during clock angle rotation. Plasma characteristics suggest that observations took place at the high-latitude boundary of the near-Earth plasma sheet (near the separatrix) on closed field lines (FL). Data are consistent with the following sequence of events: the FL of the mixed region, because of IMF Bz>0 and the dipole tilt, first reconnected at high latitudes in the southern hemisphere. As a result of the large IMF Bx and By>0 the draped open FL were convected duskward and here reconnected a second time with FL from the northern high-latitude boundary plasma sheet, thus forming a closed FL. The magnetosheath plasma was captured on them, plasma sheet electrons have escaped while they were open. MHD simulations performed by the CCMC facilities prove this hypothesis.

Koleva, R.; Smirnov, V.; Fedorov, A.; Semkova, J.

30

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

NASA Technical Reports Server (NTRS)

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.

Maynard, Nelson C.

2003-01-01

31

The Myth of the IMF  

NASA Astrophysics Data System (ADS)

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!

Melnick, J.

2009-11-01

32

Biological Clocks  

NSDL National Science Digital Library

This lesson, from Science NetLinks, will challenge students to consider the idea of biological clocks. By first observing the opening and closing of a Morning Glory flower, students will be introduced to the concept of biological clocks in a tangible, hands-on way. The teacher will then lead them to identify internal clues they experience at different times of the day and talk about their own biological clocks.

Science Netlinks;

2002-08-05

33

Clock Arithmetic  

NSDL National Science Digital Library

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

2010-01-01

34

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

NASA Technical Reports Server (NTRS)

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.

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

35

Light Clock  

NSDL National Science Digital Library

This simple animation illustrates the principle of time dilation as predicted by special relativity. The simulation consists of two light clocks, one at rest and the other moving at a fraction of the speed of light. The user can change the speed of the moving clock.

Fowler, Michael; Ching, Jacquie H.

2008-07-30

36

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

NASA Astrophysics Data System (ADS)

We present SuperDARN radar observations of the nightside high-latitude ionospheric flow during two 6-hour intervals of quasi-steady northward interplanetary magnetic field (IMF). During both intervals (01:30 07:30 UT on 2 December and 21:00 03:00 UT on 14/15 December 1999), the solar wind and IMF remained relatively steady with Bz positive and By negative, such that the IMF clock angle was ~ - 50° to - 60°. Throughout both intervals the radar data clearly indicate the presence of a highly distorted By-dominated twin cell flow pattern, indicative of an open magnetosphere, which is confirmed by DMSP and auroral data. Estimates of the changes in open flux present during each interval indicate approximately balanced dayside and nightside reconnection at rates of ~ 30 35 kV over the full 6 h. However, strong bursts of flow with speeds of over ~ 1000 ms-1 are observed near magnetic midnight on time scales of ~ 1 h, which are associated with increases in the transpolar voltage. These are indicative of the net closure of open flux by recon-nection in the tail. During one large flow burst, the night-side reconnection rate is estimated to have been ~ 1.5 times the dayside rate, i.e. ~ 45 60 kV compared with ~ 30 40 kV. Magnetic bays, which would indicate the formation of a sub-storm current wedge, are not observed in association with these bursts. In addition, no low-latitude Pi2s or geostationary particle injections were observed, although some local, small amplitude Pi2-band (5 50 mHz) activity does accompany the bursts. Coincident measurements of the flow and of the low amplitude magnetic perturbations reveal nightside ionospheric conductances of no more than a few mho, indicative of little associated precipitation. Therefore, we suggest that the flow bursts are the ionospheric manifestation of bursty reconnection events occurring in the more distant geomagnetic tail. The main implication of these findings is that, under the circumstances examined here, the convection cycle is not equivalent to the usual substorm cycle that occurs for southward IMF.

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

2003-02-01

37

International Monetary Fund (IMF) Data Mapper  

NSDL National Science Digital Library

The IMF publishes a range of time series data on IMF lending, exchange rates and other economic and financial indicators. Manuals, guides, and other material on statistical practices at the IMF, in member countries, and of the statistical community at large are also available. The data mapper allows the user to view IMF data in a variety of ways using differing indicators.

Fund, International M.

38

Recent Advances on IMF Research  

NASA Astrophysics Data System (ADS)

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

Kroupa, Pavel

39

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

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

40

Clock Works.  

ERIC Educational Resources Information Center

A science unit on clocks demonstrates the need to control variables to obtain reliable results from an experiment. Two activities, one for beginners and one for advanced students, are included. Directions for making a sundial are offered. (MT)

Markle, Sandra

1988-01-01

41

Living Clocks  

NSDL National Science Digital Library

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

Moreno, Nancy P.; Tharp, Barbara Z.; Vogt, Greg L.

2009-01-01

42

The Square Light Clock and Special Relativity  

ERIC Educational Resources Information Center

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…

Galli, J. Ronald; Amiri, Farhang

2012-01-01

43

Many happy returns? Recidivism and the IMF  

Microsoft Academic Search

IMF programs are designed to provide a temporary source of finance for countries with balance of payments disequilibria. Consequently, borrowing from the IMF should occur infrequently and be widely distributed among member countries. However, some countries are recurrent users of Fund resources. This paper investigates which variables account for multiple borrowings from the IMF. We use models of count data

Graham Bird; Mumtaz Hussain; Joseph P. Joyce

2004-01-01

44

Time Clocks  

NSDL National Science Digital Library

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

Greb, Stephen

45

The IMF and Civil Society  

NSDL National Science Digital Library

Over the past several decades, the number of civil society organizations (such as labor unions, think tanks, and faith-based associations) has grown exponentially. The International Monetary Fund (IMF) is intimately interested in such organizations, and would like to engage with such groups "through information sharing, dialogue, and consultation at both global and national levels." Visitors to the homepage are encouraged to look at the "Spotlight" area as a starting point, as it contains briefing documents and news releases on the IMF's recent activities in this area. Moving down the homepage, visitors are also encouraged to look at the "News" section, which contains the latest updates from poverty reduction programs in Haiti and other structured initiatives. The site is rounded out by a "Resources" area which contains a basic factsheet, the archives of the Civil Society Newsletter, and transcripts from various events and symposia.

46

IMF control of geomagnetic activity  

NASA Technical Reports Server (NTRS)

Recent work on the IMF control of geomagnetic activity is reviewed. The goal is to quantitatively express the temporal relation between the solar wind input and the ionospheric output from the magnetospheric system. Linear prediction filtering was used which treats the magnetosphere as a black box characterized by an impulse response. It is shown that an average impulse response can account for only about 40 percent of the variance in the AL index.

Mcpherron, R. L.; Bargatze, L. F.; Holzer, R. E.; Baker, D. N.; Clauer, C. R.

1988-01-01

47

CMOS Clock Synchronizer  

NASA Technical Reports Server (NTRS)

Circuit synchronizes clock and gate signals within one-quarter of clock cycle. Clock synchronizer with one-quarter-cycle skew constructed from three flip-flops, three NAND gates, and inverter. In addition gate signal to which clock synchronized, circuit requires square-wave input at twice desired clock frequency.

Kepp, R. B.

1987-01-01

48

Biological clocks  

PubMed Central

Circadian rhythms describe biological phenomena that oscillate with an ?24-hour cycle. These rhythms include blood pressure, body temperature, hormone levels, the number of immune cells in blood, and the sleep-wake cycle. In this paper, we will focus on common genes between species that are responsible for determining the circadian behavior, especially some transcription factors (i.e., switch genes) that serve to regulate many circadian rhythm genes. The intent of this summary is to introduce the common molecular mechanism of biological clocks between flies and humans and then to describe the research from three laboratories that was presented in the session.

Ishida, Norio; Kaneko, Maki; Allada, Ravi

1999-01-01

49

IMF Financial Transactions Plan Quarterly Report  

NSDL National Science Digital Library

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

50

Economic determinants of IMF financial arrangements  

Microsoft Academic Search

We analyze factors that lead to IMF approval of financial arrangements. We account for both economic variables that induce a country to seek an IMF arrangement (‘demand-side’ factors) and macroeconomic policy commitments that the IMF considers when deciding whether to approve it (‘supply-side’ factors). Using a pooled sample of annual observations for 91 developing countries over 1973–1991, we obtain maximum

Malcolm Knight; Julio A. Santaella

1997-01-01

51

IMF: Case of a Dead Theory Walking  

Microsoft Academic Search

The Asian financial crisis has eased, but its reverberations have enmeshed the International Monetary Fund (IMF) in a major legiti- macy crisis over its recently assumed mission and its ability to implement it. That new mission—promoting free capital mobility around the globe—parallels U.S. policy, though deviating sharply from the IMF's original function. The IMF's crisis is thus also a U.S.

David Felix

2000-01-01

52

IMF Length Scales and Predictability: The Two Length Scale Medium  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

53

Does IMF Financing Result in Moral Hazard?  

Microsoft Academic Search

The view that the IMF's financial support gives rise to moral hazard has become increasingly prominent in policy discussions, particularly following the 1995 Mexican crisis. This paper seeks to clarify a number of conceptual issues and bring some basic empirical evidence to bear on this hypothesis. While some element of moral hazard is a logical consequence of the IMF's financial

Steven Phillips

2000-01-01

54

The IMF Approach to Economic Stabilization  

Microsoft Academic Search

This paper explains the IMF approach to economic stabilization. It argues that a Fund-supported program is a process, comprising six broadly defined phases, that evolves along a multiplicity of potential pathways. The paper discusses the three-pronged approach to stabilization at the core of all IMF-supported programs, stresses the iterative character of \\

Michael Mussa; Miguel A. Savastano

1999-01-01

55

The Stellar IMF from turbulent fragmentation  

NASA Technical Reports Server (NTRS)

In this paper they conclude that turbulent fragmentation is unavoidable in super-sonically turbulent molecular clouds, and given the success of the present model to predict the observed shape of the Stellar IMF, they conclude that turbulent fragmentation is essential to the origin of the stellar IMF.

Padoan, P.; Nordlund, A.

2001-01-01

56

The Structural Budget Balance The IMF's Methodology  

Microsoft Academic Search

This paper describes the methodology used by the IMF staff to calculate the structural budget balance, estimates of which are published regularly in the IMF's World Economic Outlook. The structural budget balance is the government's actual fiscal position purged of the estimated budgetary consequences of the business cycle, and is designed in part to provide an indication of the medium-term

Robert P. Hagemann

1999-01-01

57

IMF Conditionality and Country Ownership of Programs  

Microsoft Academic Search

The paper uses finance and agency theory to establish two main propositions: First, that the conditionality attached to adjustment programs supported by the IMF is justified. Second, that ownership of programs by the borrowing country is crucial for their success. Hence, since both IMF conditionality and country ownership are necessary, the task is one of designing conditionality to maximize program

Mohsin S. Khan; Sunil Sharma

2001-01-01

58

IMF control of the Earth's magnetosphere  

Microsoft Academic Search

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

A. Nishida

1983-01-01

59

Clock Gating and Negative Edge Triggering for Energy Recovery Clock  

Microsoft Academic Search

Energy recovery clocking has been demonstrated as an effective method for reducing the clock power. In this method the conventional square wave clock signal is replaced by a sinusoidal clock generated by a resonant circuit. Such a modification in clock signal prevents application of existing clock gating solutions. In this paper, we propose a clock gating solution for energy recovery

Vishwanadh Tirumalashetty; Hamid Mahmoodi

2007-01-01

60

Dayside auroral emissions controlled by IMF: Surveys for dayside auroral excitation at 557.7 and 630.0 nm in Ny-Ålesund, Svalbard and South Pole, Antarctica  

NASA Astrophysics Data System (ADS)

A survey of dayside 557.7/630.0-nm auroral emission, acquired from the all-sky imagers at the Yellow River station (YRS) in Ny-Ålesund, Svalbard, shows that the dayside auroral oval could be divided into 5 auroral active regions (AARs), i.e., the dawnside (Da/0600-0730 MLT) and duskside (Du/1530-1700 MLT) green aurora sectors, the prenoon (W/0730-1000 MLT) and postnoon (H/1300-1530 MLT) peaks for 557.7/630.0-nm auroral emissions, the midday gap (M/1000-1300 MLT) for green aurora. The 630.0-nm intensities in W, M, and H nearly increase linearly with the Kan-Lee electric field. The 630.0-nm auroral emissions in W and H show a double-peak feature associated with the change of IMF clock angle, one peak at 90° and the other at 270°. The 630.0-nm emission in M, however, is dominantly excited during the clock angle of 90°-270°. It is considered that the 630.0-nm emissions in W/H and M are related to the prenoon/postnoon anti-parallel reconnection at the high-latitude magnetopause and the subsolar component reconnection, respectively. Moreover, the 630.0-nm intensity in the dayside oval shows the monotonic increase with the absolute value of the north-south oriented electric field (Ez), but the increasing rate of the intensity in the postnoon (prenoon) oval is larger than that in the prenoon (postnoon) oval when IMF By is negative (positive). Only the 557.7-nm intensity in region M and H/Du increases gradually with the absolute value of negative Ez. These features should be associated with the change of inter-hemispheric currents produced by Ez. The synoptic distribution of dayside aurora in southern hemisphere, acquired from all-sky imager at South Pole, presents same structure with that in northern hemisphere that there are also two 557.7/630.0-nm auroral emission peaks on the southern-hemispheric dayside oval, i.e., the 0900 MLT and 1400-1500 MLT peaks, and a dramatically midday gap for green line emission on 1000-1300 MLT sector. However, the auroral intensity presents an asymmetry between two hemispheres, namely, the postnoon auroral intensity is less than the prenoon intensity in southern hemisphere, but more than that in northern hemisphere, and that, the hemispheric asymmetry is not changed with the change of IMF's polarity, although 1) when IMF By is changed from positive to negative, the auroral intensity in southern hemisphere decreases at 557.7 and 630.0 nm on postnoon oval, and increases at 630.0 nm on prenoon oval, respectively, which present the opposite change in northern hemisphere; 2) When IMF Bz is changed from positive to negative, the 630.0-nm auroral intensity increases dramatically in two dayside ovals. We consider that the hemispheric asymmetry is not only independent with the interhemispheric current that resulted from the penetration of the IMF into the magnetosphere and should primarily depend on the sign of By, or the difference between ionospheric conductivities in the Northern and Southern hemispheres, but also the hemispheric asymmetry of dayside FACs systems and the topological structure of dayside magnetosphere related with IMF By.

Hu, Z.; Ebihara, Y.; Yang, H.; Hu, H.; Han, D.; Huang, D.; Zhang, B.; Liu, R.

2012-12-01

61

Role of CMEs in IMF winding statistics  

NASA Technical Reports Server (NTRS)

Past studies of the spiral winding of the IMF have revealed an over winding relative to the Parker prediction that is evident in both the omnitape and Pioneer-Venus Orbiter data sets. An asymmetry between the winding of the northern and southern hemispheres is also observed. Both results are seen to be persistent over many years and statistically significant. Both results have implications for cosmic ray propagation in the heliosphere. There has been a suggestion in past analyses that the digression from the Parker prediction is greatest during times of heightened CME activity. We examine the possible role of CMEs in these past analyses by extracting CME observations from the ISEE-3 dataset and analyzing CME and undisturbed periods separately. We use the full ISEE-3 dataset representing the entire L1 mission (1978 1982). This coincides with a period in the solar cycle when CME activity was heightened. Preliminary results are suggestive that CMEs may be responsible for a significant portion of both the spiral angle overwinding and asymmetry. Possible implications for the high latitude fields and cosmic ray propagation will be reviewed in light of this analysis.

Smith, Charles W.; Phillips, John L.

1995-01-01

62

Memory Event Clocks  

NASA Astrophysics Data System (ADS)

We introduce logics and automata based on memory event clocks. A memory clock is not really reset: instead, a new clock is created, while the old one is still accessible by indexing. We can thus constrain not only the time since the last reset (which was the main limitation in event clocks), but also since previous resets. When we introduce these clocks in the linear temporal logic of the reals, we create Recursive Memory Event Clocks Temporal Logic (RMECTL). It turns out to have the same expressiveness as the Temporal Logic with Counting (TLC) of Hirshfeld and Rabinovich. We then examine automata with recursive memory event clocks (RMECA). Recursive event clocks are reset by simpler RMECA, hence the name "recursive". In contrast, we show that for RMECA, memory clocks do not add expressiveness, but only concision. The original RECA define thus a fully decidable, robust and expressive level of real-time expressiveness.

Jerson Ortiz, James; Legay, Axel; Schobbens, Pierre-Yves

63

IMF dependence of the ENAs observed from the dayside magnetosheath  

NASA Astrophysics Data System (ADS)

We report the statistical study of the energy-resolved energetic neutral atoms (ENAs) from the dayside magnetosheath by the Interstellar Boundary Explorer (IBEX) observations correlating with the upstream interplanetary magnetic field (IMF) conditions. We focus on the one-hour-averaged data obtained by the IBEX-Hi instrument of the ENAs at energies between ~0.5 and ~6 keV from January 2009 to May 2011, including about ~1600 inferred plasma spectra from global ENA measurements. We find that the shock angle at the nose of the Earth's bow shock has a significant correlation with the hardening of the spectra at energies above ~2 keV, which typically represents the energy of the solar wind particles. This trend is consistent with the nature of collisionless shocks and/or the variation of the shock downstream turbulence with shock geometry. In addition to the shock angle correlations, we show the magnetosheath spectral-index and flux-intensity dependence on the IMF elevation angle, geomagnetic indices, and solar wind speed to further understand what creates the energetic plasma populations in the magnetosheath.

Ogasawara, K.; Dayeh, M. A.; Funsten, H. O.; Fuselier, S. A.; Livadiotis, G.; McComas, D. J.

2013-05-01

64

Model-based clock synchronization in networks with drifting clocks  

Microsoft Academic Search

This paper examines a clock synchronization algorithm in which processors identify dynamic models of neighboring processor clocks. These models are then used as signature functions to develop a clock synchronization algorithm that functions in the presence of drifting clocks

Michael D. Lemmon; Joydeep Ganguly; Lucia Xia

2000-01-01

65

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

66

The Location of the Magnetopause Reconnection Site during Southward IMF Conditions  

NASA Astrophysics Data System (ADS)

Karlheinz Trattner, karlheinz.j.trattner.dr@lmco.com Lockheed Martin Advanced Technology Lab, CA 94304, California, United States Stephen Fuselier, stephen.a.fuselier@lmco.com Lockheed Martin Advanced Technology Lab, Palo Alto, California, United States Steven Petrinec, steven.m.petrinec@lmco.com Lockheed Martin Advanced Technology Lab, Palo Alto, United States There are two reconnection location scenarios discussed in the literature: a) anti-parallel re-connection where shear angles between the magnetospheric field and the IMF are near 180 degrees, and b) component reconnection where shear angles are as low as 50 degrees. One popular component reconnection model is the tilted neutral line model. Recent studies about the location of the reconnection line with single point measurements under stable solar wind and IMF conditions reveal that the so-called tilted X-line, crossing near the dayside sub-solar region, is the dominant reconnection scenario. Specifically, magnetic reconnection will occur along the line of maximum magnetic shear across the dayside magnetopause. Exceptions to this reconnection location are dominant southward IMF conditions (within 25 of southward IMF) or a dominant IMF BX component (more than 70

Trattner, Karlheinz; Fuselier, Stephen; Petrinec, Steven

67

Solar cycle variations in IMF intensity  

Microsoft Academic Search

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 contered at solar maximum. No systematic variations

Joseph H. King

1979-01-01

68

A Single EU Seat in the IMF?  

Microsoft Academic Search

AbstractThis article examines the rationale for consolidating EU Member States' position in the International Monetary Fund (IMF). Although a substantial amount of co-ordination already takes place, particularly on issues related to the euro area and the single monetary and exchange rate policy, co-operation between EU countries in the IMF remains a relatively new phenomenon and divergences still prevail. The current

Lorenzo Bini Smaghi

2004-01-01

69

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

NASA Technical Reports Server (NTRS)

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.

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

1984-01-01

70

The Glyoxal Clock Reaction  

ERIC Educational Resources Information Center

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…

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

2007-01-01

71

Association of consecutive Pi2-Ps6 band pulsations with earthward fast flows in the plasma sheet in response to IMF variations  

NASA Astrophysics Data System (ADS)

11 March 2009, the H component had four consecutive bay-like variations accompanied by positive and negative deflections in the D component across the Atlantic like those affected by the substorm current wedge formation. A train of pulsations with a frequency range 2-10 mHz (referred to as Pi2-Ps6 band), sensed by Time History of Events and Macroscale Interactions during Substorms (THEMIS)/Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) magnetometers, had clearly three consecutive Pi2s followed by a Ps6 at low latitudes, but first Pi2 and then Ps6 at high latitudes mixed with large-amplitude Ps6 at midlatitudes. The geostationary orbit magnetometers sensed similar magnetic perturbations. THEMIS probes first observed earthward fast flows, magnetic dipolarizations, and modulated energetic particle fluxes at ~ XGSM -9.2 RE, then at ~ XGSM -7.5 RE for Pi2 and at ~ XGSM -18.0 RE only for Ps6. They appeared during a very quiet period for northward interplanetary magnetic field (IMF) with a clock angle variation of low to high and then low. The H spectrum shows two harmonic frequencies ~2-4 mHz and ~8-10 mHz but the D spectrum one dominant frequency ~2-4 mHz. Pi2 can result from a combination of fast magnetospheric and plasmaspheric cavity resonances and Ps6 from a fast magnetospheric cavity resonance. The surface waves at the interface separating braking earthward fast flows from the ambient plasma convection region could lead to large-amplitude Ps6 at midlatitudes. Hence, consecutive Pi2-Ps6 band pulsations can be associated with earthward fast flows in the plasma sheet, expectedly driven by magnetotail reconnection, respectively, in the near-Earth region and the distant Earth one in response to IMF variations as in the two-neutral-point model.

Cheng, Ching-Chang; Mann, Ian R.; Baumjohann, Wolfgang

2014-05-01

72

Type-matching clock tree for zero skew clock gating  

Microsoft Academic Search

Clock skew minimization is always very important in the clock tree synthesis. Due to clock gating, the clock tree may include different types of logic gates, e.g., AND gates, OR gates, and buffer gates. If the logic gates at the same level are in different types, which have different timing behaviors, the control of clock skew becomes difficult. Based on

Chia-ming Chang; Shih-hsu Huang; Yuan-kai Ho; Jia-zong Lin; Hsin-po Wang; Yu-sheng Lu

2008-01-01

73

Clock Arithmetic and Cryptography  

NSDL National Science Digital Library

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

2010-01-01

74

Science Nation: Biological Clocks  

NSDL National Science Digital Library

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

75

Ionospheric convection response to changing IMF direction  

NASA Technical Reports Server (NTRS)

By combining ground-based and satellite-based measurements of ionospheric electric fields, conductivities and magnetic perturbations, it was possible to examine the characteristics of instantaneous, ionospheric convection patterns associated with changing directions of the interplanetary magnetic field (IMF). In response to a rapid southward-to-northward turning of the IMF on July 23, 1983, the ionospheric convection reconfigured over a period of 40 minutes. The configuration changed from a conventional two-cell pattern to a contracted four-cell pattern, with reversed convection cells in the high-latitude dayside, associated with a strong potential drop of about 75 kV. Later, in response to a gradual rotation of the IMF from the +Z through the -Y toward the -Z direction, the nightside cells disappeared and the dawn cell in the reversed pair wrapped around and displaced the dusk cell until a conventional two-cell pattern was reestablished, largely in accord with the qualitative model of Crooker (1988). The results suggest that multiple cells can arise as a result of strong southward to northward transitions in the IMF. They appear to persist for sometime thereafter.

Knipp, D. J.; Richmond, A. D.; Emery, B.; Crooker, N. U.; De La Beaujardiere, O.; Evans, D.

1991-01-01

76

Modulation of Dayside Reconnection During Northward IMF  

NASA Astrophysics Data System (ADS)

On 17 September 2000 the IMF was directed continuously northward for more than three hours. Density fluctuations in the solar wind resulted in quasi-periodic variations in the solar wind dynamic pressure, and correlated fluctuations also occurred in the IMF Bz component. The Northern hemisphere SuperDARN radars observed bursts of high-latitude high-velocity plasma flow during this northward IMF interval, both when ionospheric signatures consistent with low-latitude merging were observed, and when lobe merging was occurring. On average the recurrence period of these flow bursts was ~22 min. During this time the SI-12 spectrographic imager channel on the IMAGE spacecraft observed the dayside proton auroral spot continuously (Frey et al., 2003). The brightness of the auroral spot varied over time. Here we find a direct correlation between the occurrence of bursts of plasma flow and periodic fluctuations in the brightness of the proton auroral spot. Our results suggest that correlated fluctuations in the solar wind dynamic pressure and IMF Bz component modulated ionospheric precipitation and dayside reconnection, resulting in fluctuations in the brightness of the proton auroral spot and periodic variations in the dayside high-latitude plasma flow.

Provan, G.; Lester, M.; Cowley, S. W.; Grocott, A.; Milan, S. E.; Hubert, B.; Khan, H.

2005-12-01

77

IMF Conditionality as a Screening Device  

Microsoft Academic Search

A theoretical model is developed in that both buybacks and the adoption of an IMF program can be used as screening devices that enable a creditor to discriminate between debtor countries that are willing to use debt relief in order to invest and repay and countries that are not. Asymmetric information is assumed. This problem can be solved if the

Silvia Marchesi; Jonathan P. Thomas

1999-01-01

78

The IMF's role in structural adjustment  

Microsoft Academic Search

In the 1980s conditional lending for structural adjustment in developing countries moved the IMF beyond its role of macroeconomic crisis management. Fund-supported adjustment programmes have often been flawed by a lack of distributional analysis and by poor sequencing of reforms, notably premature financial liberalisation. As a result they have caused avoidable hardship. In addition, the attempt to taper out aid

Paul Collier; Jan Willem Gunning

1999-01-01

79

BUGS system clock distributor  

NASA Technical Reports Server (NTRS)

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.

Dietrich, Thomas M.

1991-01-01

80

Number Base Clocks  

NSDL National Science Digital Library

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

81

Radio Controlled Clocks  

Microsoft Academic Search

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

Michael A. Lombardi

82

World Population Clock  

NSDL National Science Digital Library

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

Levine, David

83

Biological Clocks & Circadian Rhythms  

ERIC Educational Resources Information Center

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…

Robertson, Laura; Jones, M. Gail

2009-01-01

84

Plasma wave levels and IMF orientations preceding observations of interplanetary shocks by ISEE-3  

NASA Technical Reports Server (NTRS)

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle of the interplanetary magnetic field (IMF) to the shock normal at the time the shocks cross the spacecraft. It is shown that precursor wave noise level is correlated with field orientation and an extrapolated instantaneous orientation angle throughout the preshock observation interval for two contrasting active and quiet cases, and that intermediate, variable noise levels correspond to intermediate, variable IMF orientations. It is inferred that foreshocks are an intrinsic part of the structure of quasiparallel interplanetary shocks.

Greenstadt, E. W.; Scarf, F. L.; Fredricks, R. W.; Kennel, C. F.; Smith, E. J.

1982-01-01

85

The Salpeter Slope of the IMF Explained  

NASA Astrophysics Data System (ADS)

If we accept a paradigm that star formation is a self-similar, hierarchical process, then the Salpeter slope of the IMF for high-mass stars can be simply and elegantly explained as follows. If the intrinsic IMF at the smallest scales follows a simple -2 power-law slope, then the steepening to the -2.35 Salpeter value results when the most massive stars cannot form in the lowest-mass clumps of a cluster. It is stressed that this steepening must occur if clusters form hierarchically from clumps, and the lowest-mass clumps can form stars. This model is consistent with a variety of observations as well as theoretical simulations.

Oey, M. Sally

86

Circadian Clocks and Metabolism  

PubMed Central

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.

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

2014-01-01

87

Femtosecond optical clock  

SciTech Connect

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

Bagaev, Sergei N; Denisov, Vladimir I; Zakharyash, Valerii F; Kashirsky, Aleksandr V; Klementyev, Vasilii M; Kuznetsov, Sergei A; Korel', I I; Pivtsov, V S [Institute of Laser Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk (Russian Federation)

2004-12-31

88

IMF sector behavior deduced from geomagnetic data  

SciTech Connect

Interplanetary magnetic field (IMF) sector structures, such as 'toward' the sun and 'away' from the sun on each day, have been objectivly estimated from daily and monthly mean values of the horizontal component of the geomagnetic variation field at Godhavn during the period 1926--1970. The agreement between this estimation and actual satellite observations of the sector structures of the interval 1964--1970 is 88, 79, and 58% in summer, equinox, and winter, respectively. A remarkable agreement (more than 95%) is obtained for the summers of 1964, 1969, and 1970. Various types of IMF sector behavior are examined by taking this seasonal factor into consideration. Approximately 27-day recurrences of the same structure are often found, and 5- to 14-day consecutive occurrences of the same sector are frequently noted. Furthermore, the total number of occurrences for each estimated sector in each year shows an apparently good correlation with smoothed sunspot numbers and geomagnetic aa index. After a brief introduction of the production mechanism of sector effects on polar geomagnetic fields the limitations and merits of IMF sector inference from geomagnetic data are emphasized.

Matsushita, S.; Trotter, D.E.

1980-05-01

89

Iodine Clock Reaction.  

ERIC Educational Resources Information Center

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)

Mitchell, Richard S.

1996-01-01

90

Clock genes and sleep  

Microsoft Academic Search

In most species—from cyanobacteria to humans—endogenous clocks have evolved that drive 24-h rhythms of behavior and physiology.\\u000a In mammals, these circadian rhythms are regulated by a hierarchical network of cellular oscillators controlled by a set of\\u000a clock genes organized in a system of interlocked transcriptional feedback loops. One of the most prominent outputs of the\\u000a circadian system is the synchronization

Dominic Landgraf; Anton Shostak; Henrik Oster

91

IMF draping around the geotail - IMP 8 observations  

NASA Technical Reports Server (NTRS)

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.

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

1992-01-01

92

Optical Lattice Clocks  

NASA Astrophysics Data System (ADS)

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

Oates, Chris

2012-06-01

93

Detailed Cusp Study for Northward IMF and Quiet Conditions  

Microsoft Academic Search

On the 17th of March 2001, CLUSTER enters the cusp over the northern hemisphere during a period of northward IMF (Bz ~ 2nT) and quiet solar and magnetospheric conditions(P<1nT, AE ~ 0). No significant variations in the IMF are observed,except a change in the IMF By component from positive to negative over a period of half an hour. PEACE observations

A. VONTRAT-REBERAC; M. G. Taylor; D. Fontaine; N. Cornilleau-Wehrlin; J. Sauvaud; T. Chust; A. N. Fazakerley; H. Rème; M. W. Dunlop

2001-01-01

94

Empirical convection models for northward IMF  

NASA Technical Reports Server (NTRS)

It is clear that polar cap convection during times of northward Interplanetary Magnetic Field (IMF) is more structured and of lower mean speed than at times of southward IMF. This, coupled with the fact that the polar cap is smaller, means that empirical models are more difficult to construct with certainty. It is also clear that sunward flow deep in the polar cap is often observed, but its connection with the rest of the flow pattern is controversial. At present, empirical models are of three types: 'statistical' models wherein data from different days but with similar IMF conditions are averaged together; 'pattern recognition' models, which are built up by examining individually hundreds of passes to derive a 'typical' pattern which embodies features frequently observed; and 'assimilative' models, which use data of different types and from as many locations as possible, but all taken at the same time, in order to derive a snapshot (or series of snapshots) of the entire pattern. Each type of model has its own difficulties. Statistical models, by their very nature, smooth out flow features (e.g. the convection reversal, and the locus of sunward flow deep in the polar cap) which are not found at precisely the same invariant latitudes and magnetic local times on different days. Pattern recognition models are better at reproducing small-scale features, but the large-scale pattern can be a matter of interpretation. Assimilative models (such as AMIE) hold out the best hope for creating instantaneous, global convection patterns; however, the analysis technique tends to be most irregular (and least reliable) in the regions which are not well covered by in situ data. It appears that, at least at times, a four cell model with sunward flow at the highest and lowest latitudes, and antisunward flow in between, is consistent with the observations. At other times, the observations may be consistent with a two-cell convection pattern, but which includes significant meanders within the polar cap.

Moses, Julie J.; Reiff, Patricia H.

1994-01-01

95

Solar cycle variations in IMF intensity  

NASA Technical Reports Server (NTRS)

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.

King, J. H.

1979-01-01

96

Plasma wave levels and IMF orientations preceding observations of interplanetary shocks by ISEE-3  

SciTech Connect

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly-enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle theta/sub B/n of the interplanetary magnetic field (IMF) to the shock normal at the time the shocks cross the spacecraft. We show that precursor wave noise level is correlated with field orientation and an extrapolated theta/sub B/n throughout the preshock observation interval for two contrasting active and quiet cases, and that intermediate, variable noise levels correspond to intermediate, variable IMF orientations. We infer that foreshocks are an intrinsic part of the structure of quasi-parallel interplanetary shocks.

Greenstadt, E.W.; Scarf, F.L.; Kennel, C.F.; Smith, E.J.; Fredricks, R.W.

1982-06-01

97

Anomaly Clock Detection Algorithm for a Robust Clock Ensemble.  

National Technical Information Service (NTIS)

The Anomaly Clock Detection Algorithm is intended to facilitate a monitoring system to better manage a clock system, insuring continuity of operations and limiting the expected degradation of performance due to contingencies and anomalies. A novel ensembl...

P. Rochat Q. Wang

2009-01-01

98

The influence of IMF B(y) on the high-latitude thermospheric circulation during northward IMF  

NASA Technical Reports Server (NTRS)

This paper uses the Dynamics Explorer data set, together with a sufficient quantity of corresponding IMF data, to establish correlations among the observed relationships between the IMF B(y) and the high-latitude thermospheric circulation during periods of northward IMF. Statistical evidence is presented that illustrates a relationship between the respective magnitudes of the B(z) and B(y) components of the IMF and the occurrence of sunward winds in the polar cap. The ion-neutral coupling processes responsible for the observed effects are discussed together with the general implications of the results.

Mccormac, F. G.; Killeen, T. L.; Thayer, J. P.

1991-01-01

99

Somites without a clock.  

PubMed

The formation of body segments (somites) in vertebrate embryos is accompanied by molecular oscillations (segmentation clock). Interaction of this oscillator with a wave traveling along the body axis (the clock-and-wavefront model) is generally believed to control somite number, size, and axial identity. Here we show that a clock-and-wavefront mechanism is unnecessary for somite formation. Non-somite mesoderm treated with Noggin generates many somites that form simultaneously, without cyclic expression of Notch-pathway genes, yet have normal size, shape, and fate. These somites have axial identity: The Hox code is fixed independently of somite fate. However, these somites are not subdivided into rostral and caudal halves, which is necessary for neural segmentation. We propose that somites are self-organizing structures whose size and shape is controlled by local cell-cell interactions. PMID:24407478

Dias, Ana S; de Almeida, Irene; Belmonte, Julio M; Glazier, James A; Stern, Claudio D

2014-02-14

100

Ytterbium Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

We report on an optical clock based on the ^1S0-^3P0 transition in neutral Yb atoms confined to a Stark shift-free optical lattice. Tight confinement of atoms to the Lamb-Dicke regime is shown to suppress Doppler- and recoil-related shifts, while the Stark shift-canceling technique eliminates the clock's first-order sensitivity to lattice intensity. Clocks based on magnetically-induced spectroscopy of ^174Yb (I=0) and state-resolved spectroscopy of ^171Yb (I=1/2) are demonstrated. Comparisons with other optical and microwave frequency standards via a self-referenced femtosecond frequency comb have enabled initial measurements of the absolute frequency and systematic effects with a fractional uncertainty of 10-15, a level that can be reached in 10 seconds of averaging time.

Lemke, Nathan; Barber, Zeb; Poli, Nicola; Oates, Chris; Hollberg, Leo

2008-05-01

101

Optical atomic clocks  

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

102

Einstein's concept of a clock and clock paradox  

Microsoft Academic Search

A geometric illustration of the Lorentz transformations is given. According to similarity between space and time and correspondence between a ruler and a clock, like the division number in a moving ruler, the tick number of a moving clock is independent of its relative speed and hence invariant under the Lorentz transformations. So the hand of the moving clock never

Wang Guowen

2005-01-01

103

The circadian clock goes genomic  

PubMed Central

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

2013-01-01

104

Make a Chemical Clock  

NSDL National Science Digital Library

This lesson for Grades 6-8 combines a short video with three experiments to observe and record chemical changes. The experiments use common household materials to demonstrate chemical reaction -- a change that leads to a transformation of one substance into another substance. In the 3rd experiment, there are two chemical reactions happening at the same time. Through careful observation, learners see that the 3rd reaction represents a "chemical clock", because the time it takes the chemicals to react happens very predictably, like a regular clock. Talking Science is part of National Public Radio's Science Friday initiative.

2011-08-18

105

Dependence of Global Poynting Flux on IMF By  

NASA Astrophysics Data System (ADS)

In this study we present the dependence of the global Poynting flux on the IMF By orientation. The amount of energy that enters the near Earth system from the solar wind and IMF interacting with the geomagnetic field is a function of the solar wind speed and pressure and the IMF orientation. 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 depends on the IMF By polarity. This apparent contrast between input (from the solar wind) and output (energy dissipating Pedersen currents) raises to the question: To what extend is the global Poynting flux dependent on the IMF By polarity. We have performed a large statistical study using abrupt transitions in the IMF By component (polarity changes) as measured by the ACE spacecraft. The effect of other solar wind parameters such as the solar wind pressure is minimized by selecting events where these are nearly constant. We use electric field distribution from SuperDARN and field-aligned current distributions from AMPERE to calculate the global distribution of the Poynting Flux. We show events as well statistical results to answer the science objective. The study emphasizes the global dynamic behavior of the ionosphere in its response to changes in the external driver (IMF).

Humberset, Beate K.; Gjerloev, Jesper W.

2014-05-01

106

IMF Programs: Who is Chosen and What Are the Effects?  

Microsoft Academic Search

IMF lending practices respond to economic conditions but are also sensitive to political-economy variables. Specifically, the sizes and frequencies of loans are influenced by a country's presence at the Fund, as measured by the country's share of quotas and professional staff. IMF lending is also sensitive to a country's political and economic proximity to some major shareholding countries of the

Robert J. Barro; Jong-Wha Lee

2002-01-01

107

The effect of IMF programs on economic growth  

Microsoft Academic Search

Using a bivariate, dynamic version of the Heckman selection model, we estimate the effect of participation in International Monetary Fund (IMF) programs on economic growth. We find evidence that governments enter into agreements with the IMF under the pressures of a foreign reserves crisis but they also bring in the Fund to shield themselves from the political costs of adjustment

Adam Przeworski; James Raymond Vreeland

2000-01-01

108

IMF programs: Who is chosen and what are the effects?  

Microsoft Academic Search

IMF loans react to economic conditions but are also sensitive to political-economy variables. Loans tend to be larger and more frequent when a country has a bigger quota and more professional staff at the IMF and when a country is more connected politically and economically to the United States and major European countries. These results are of considerable interest for

Robert J. Barro; Jong-Wha Lee

2005-01-01

109

Estimating the instability of a composite clock  

NASA Technical Reports Server (NTRS)

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.

Greenhall, Charles A.

2004-01-01

110

Locally clocked microprocessor  

Microsoft Academic Search

A 2-?m CMOS locally clocked sequential microprocessor designed for a self-timed environment is described. The processor's synchronization is based on a pulse that runs through the system. The pulse is channeled through a delay block that simulates the processing time of the instruction to be executed. Since it accrues the average delay, rather than the longest delay of the instructions

S. J. Muscato; A. Albicki

1993-01-01

111

The pulsed rubidium clock  

Microsoft Academic Search

In this paper, we describe a laboratory proto-type of pulsed optically pumped clock based on a rubidium vapor cell with buffer gas. The measured frequency stability (overlapping Allan deviation) is ?y(?) = 3 × 10-12 ? -1\\/2 and the level of 4 × 10-14 is reached for averaging time of ? = 3 × 104 s. For the same set

Aldo Godone; Salvatore Micalizio; Claudio E. Calosso; Filippo Levi

2006-01-01

112

Interaction of the IP shock with the magnetosphere: Effects of the IMF rotation  

NASA Astrophysics Data System (ADS)

Interaction of interplanetary (IP) shocks with the Earth's magnetosphere is a key problem of the Space Weather Program because their interaction often (but not always) leads to major geomagnetic storms. According to already published papers, a fast forward shock passing through the bow shock would generate a train of new discontinuities that differ along the bow shock surface. However, IP shocks are often accompanied with a rotation of the interplanetary magnetic field (IMF) over a large angle and this rotation modifies the interaction process. Since the huge interaction region can be covered by simultaneous spacecraft observations only sporadically, global MHD modeling can help in our understanding of these processes. Using one IP shock observed by Geotail, we compare its passage through the magnetosphere with a model prediction of the global BATS-R-US MHD code. We slightly change upstream conditions in several model runs to order to separate effects of the IP shock itself from the effects of the IMF rotation. The results show that IMF rotations intensify the IP shock influence and lead to a more complex character of the resulting discontinuities.

Nemecek, Zdenek; Safrankova, Jana; Goncharov, Oleksandr; Merka, Jan; Koval, Andrei

113

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

ERIC Educational Resources Information Center

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…

Conson, Massimiliano; Cinque, Fausta; Trojano, Luigi

2008-01-01

114

Dependence of the polar cap geometry on the IMF  

NASA Technical Reports Server (NTRS)

The geometry of the open field line region in the polar region is computed for a variety of the interplanetary magnetic field (IMF) orientation. The open field line region can be identified as the area bounded by the auroral oval, namely the polar cap. The polar cap geometry varies considerably with the orientation of the IMF and magnitude, particularly when the IMF Bz component is positive and large. The corresponding exit points of the open field lines on the magnetopause are also examined. The results are useful in interpreting various upper atmospheric phenomena in the highest latitude region of the earth and also in observing chemical releases outside the magnetopause.

Akasofu, S.-I.; Roederer, M.

1984-01-01

115

World Food Clock  

NSDL National Science Digital Library

How much food is being consumed around the world right now? It's a vast question that can be answered by the World Food Clock. This interesting website draws on information provided by the Food and Agricultural Organization (FAO) of the United Nations and presents a streaming set of data on global food consumption, global food waste, and other informative topics. It's visually arresting and users can scroll down to look through different "clocks" that track statistics such as the land used to grow wasted food and the stages of food waste, which include production, processing, and consumption. This is a wonderful tool for folks with an interest in food security, environmental studies, public health, and international relations. It could also be used in any number of design courses to illustrate a range of techniques and visualization strategies.

Twyman, Luke

116

Distributed Differential Oscillators for Global Clock Networks  

Microsoft Academic Search

This paper presents a distributed differential oscillator global clock network where the clock capacitance is rendered resonant with a set of on-chip spiral inductors. The clock amplitude and clock phase are both uniform across the entire global distribution, making this design scalable and compatible with existing local clocking methodologies. The resonant network, combined with phase averaging of the distributed oscillator,

Steven C. Chan; Kenneth L. Shepard; Phillip J. Restle

2006-01-01

117

Understanding Neutral Genomic Molecular Clocks  

Microsoft Academic Search

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

Soojin V. Yi

2007-01-01

118

A review of the Initial Mass Function (IMF)  

NASA Astrophysics Data System (ADS)

The present-day mass function (PDMF) of field stars in the solar neighborhood is discussed. Major uncertainties in the derivation exist, in particular the luminosity-mass relation and the bolometric corrections. Consequently, it is not clear whether the PDMF turns over at very low masses (M less than 0.3 M solar mass), and the slope at the high-mass end (M more than 10 M solar mass) is more uncertain than usually assumed. The reality of two features in the PDMF (at M = 1.2 M solar mass and M = 3 M solar mass respectively) is an open question. The concept of a bimodal IMF is critically examined. Gusten and Mezger's (1983) and Larson's (1986) bimodal models may run into problems. If the effects of high-mass stars prevent low-mass stars from forming, the term biased IMF is a better description of the situation than bimodal IMF. The IMF is probably not universal; reported IMF variations in open clusters and globular clusters are unlikely to be spurious. The fact that the mass of a star in the making depends on many random-valued (multiplicative) input parameters suggests a stochastic rather than a deterministic approach for the origin of the IMF.

Zinnecker, Hans

1988-02-01

119

Master/slave clock arrangement for providing reliable clock signal  

NASA Technical Reports Server (NTRS)

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.

Abbey, Duane L. (Inventor)

1977-01-01

120

A Light Clock Satisfying the Clock Hypothesis of Special Relativity  

ERIC Educational Resources Information Center

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…

West, Joseph

2007-01-01

121

The Mechanism of the Formaldehyde Clock Reaction.  

ERIC Educational Resources Information Center

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)

Burnett, M. G.

1982-01-01

122

Clock Distribution Scheme for Large RSFQ Circuits.  

National Technical Information Service (NTIS)

A primary issue for maximizing the performance of large scale synchronous digital systems is the clock distribution scheme. We present a novel clocking scheme, developed specifically for RSFQ logic, which is based on the concurrent flow of clock and data....

K. Gaj E. G. Friedman M. J. Feldman A. Krasniewski

1995-01-01

123

Quartz Crystal Clocks  

NASA Technical Reports Server (NTRS)

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

1976-01-01

124

Methodologies for steering clocks  

NASA Technical Reports Server (NTRS)

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.

Chadsey, Harold

1995-01-01

125

Biological switches and clocks  

PubMed Central

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.

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

2008-01-01

126

A design for digital, dynamic clock deskew  

Microsoft Academic Search

Unintentional clock skews between clock domains represent an increasing and costly overhead in high-performance VLSI chips. We describe a novel yet easy-to-implement design that reduces skew between local clock domains dynamically or statically by sensing clock-delay differences and then tuning the clock of each domain relative to its neighbors. Lowering local clock skew is accomplished without compromising worst-case global skew.

Charles E. Dike; Nasser A. Kurd; Priyadarsan Patra; Javed Barkatullah

2003-01-01

127

A selectively driven molecular clock  

Microsoft Academic Search

The problem of whether mutations that increase a species' fitness are incorporated into the genome as a function of generation interval or as a function of absolute time is of some interest because of the clock-like nature of amino acid substitutions known to have occurred in the evolution of certain well studied proteins. The molecular clock features a rate of

Daniel Hartl; Daniel Dykhuizen

1979-01-01

128

Fault-tolerant clock synchronization  

Microsoft Academic Search

This paper gives two simple efficient distributed algorithms: one for keeping clocks in a network synchronized and one for allowing new processors to join the network with their clocks synchronized. The algorithms tolerate both link and node failures of any type. The algorithm for maintaining synchronization will work for arbitrary networks (rather than just completely connected networks) and tolerates any

Joseph Y. Halpern; Barbara Simons; Ray Strong; Danny Dolev

1984-01-01

129

Optimal clock synchronization in networks  

Microsoft Academic Search

Having access to an accurate time is a vital building block in all networks; in wireless sensor networks even more so, because wireless media access or data fusion may depend on it. Starting out with a novel analysis, we show that or- thodox clock synchronization algorithms make fundamental mistakes. The state-of-the-art clock synchronization algo- rithm FTSP exhibits an error that

Christoph Lenzen; Philipp Sommer; Roger Wattenhofer

2009-01-01

130

The Vitamin C Clock Reaction.  

ERIC Educational Resources Information Center

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)

Wright, Stephen W.

2002-01-01

131

Monitoring atomic clocks on board GNSS satellites  

NASA Astrophysics Data System (ADS)

A method for monitoring atomic clocks on board Global Navigation Satellites System (GNSS) satellites is described to address the issue of clock related signal integrity in safety-critical applications of GNSS. The carrier-phase time transfer is employed in the clock monitoring method which enables tight tracking of the satellite onboard clocks and thus improves detectability of clock anomalies. Detecting onboard clock anomalies requires the ability to monitor clocks in real time, and a Kalman filter can then be utilized to estimate the phase offsets between the satellite clocks and ground clocks. This study, using the difference between the measured and predicted phase offset as a test statistic, sets a threshold for clock anomalies based on the prediction interval approach. Finally the validity of the monitoring method is examined by processing a set of real GNSS data that includes two recent incidents of clock anomalies in GNSS satellites.

Lee, Seung-Woo; Kim, Jeongrae; Jeong, Myeong-Sook; Lee, Young Jae

2011-05-01

132

The pulsed rubidium clock.  

PubMed

In this paper, we describe a laboratory prototype of pulsed optically pumped clock based on a rubidium vapor cell with buffer gas. The measured frequency stability (overlapping Allan deviation) is sigma(y)(tau) = 3 x 10(-12)tau(-1/2) and the level of 4 x 10(-14) is reached for averaging time of r = 3 x 10(14) s. For the same set of data, the statistical tool Theol predicts a frequency stability of 2 x 10(-14) for tau = 10(5) s. This result confirms the theoretical predictions regarding this kind of frequency standard and makes it very attractive for satellite navigation and space applications in which a simple and reliable implementation is required, and the short and medium term stability (till one day) is the main concern. PMID:16555760

Godone, Aldo; Micalizio, Salvatore; Calosso, Claudio E; Levi, Filippo

2006-03-01

133

High-Latitude Ionospheric Dynamics During Conditions of Northward IMF  

NASA Technical Reports Server (NTRS)

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.

Sharber, J. R.

1996-01-01

134

Biological Clocks and Circadian Rhythms  

NSDL National Science Digital Library

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

Robertson, Laura; Jones, M. G.

2009-02-01

135

Synchronizing clocks in the presence of faults  

Microsoft Academic Search

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

Leslie Lamport; P. M. Melliar-Smith

1985-01-01

136

WFPC2 CYCLE 10 Clocks ON Check  

NASA Astrophysics Data System (ADS)

Closure calibration for clocks ON mode. This serial clocks ON calibration program obtains dark frames with clocks ON in order to provide data to create a clocks on super dark calibration reference file, to monitor and characterize the evolution of hot pixels, and to obtain standard star observations for photometric calibration.

Schultz, Alfred

2001-07-01

137

The Ionospheric current response to an abrupt southward turning of the IMF  

NASA Astrophysics Data System (ADS)

In this large statistical study we answer the fundamental question: How does the ionospheric current system respond to abrupt changes in the solar wind driving? For the solar wind driver we use ACE data propagated to the front of the magnetosphere and for the ionospheric response we use SuperMAG SMU/SML indices (equivalent to AU/AL). To answer the science objective we have identified over 1000 events from the years 1998-2009. The events were selected as: 45 minutes continuous positive IMF Bz followed by 45 minutes continuous negative IMF Bz. Following the southward turning we identify two times: 1) the time before any response is seen in SMU/SML (response time), and 2) the time before the SMU/SML has found a new steady level (reconfiguration time). We find a surprisingly large spread in the response and reconfiguration times, and we attribute this to other controlling parameters. For example solar zenith angle, By and Bz strength, in addition to density, pressure and speed of the solar wind. Finally, non uniform ground station distribution also plays a role. We find a wide distribution with a maximum at 10 min and 30 min for response and reconfiguration times respectively.

Vedde Fiskerstrand, Tonje; Gjerloev, Jesper W.

2014-05-01

138

Calibrating the avian molecular clock.  

PubMed

Molecular clocks are widely used to date phylogenetic events, yet evidence supporting the rate constancy of molecular clocks through time and across taxonomic lineages is weak. Here, we present 90 candidate avian clock calibrations obtained from fossils and biogeographical events. Cross-validation techniques were used to identify and discard 16 inconsistent calibration points. Molecular evolution occurred in an approximately clock-like manner through time for the remaining 74 calibrations of the mitochondrial gene, cytochrome b. A molecular rate of approximately 2.1% (+/- 0.1%, 95% confidence interval) was maintained over a 12-million-year interval and across most of 12 taxonomic orders. Minor but significant variance in rates occurred across lineages but was not explained by differences in generation time, body size or latitudinal distribution as previously suggested. PMID:18422932

Weir, J T; Schluter, D

2008-05-01

139

History of early atomic clocks  

Microsoft Academic Search

This review of the history of early atomic clocks includes early atomic beam magnetic resonance, methods of separated and successive oscillatory fields, microwave absorption, optical pumping and atomic masers.

Norman F. Ramsey

2005-01-01

140

Microfabricated atomic clocks and magnetometers  

Microsoft Academic Search

We demonstrate the critical subsystems of a compact atomic clock based on a microfabricated physics package. The clock components have a total volume below 10 cm3, a fractional frequency instability of 6 × 10-10\\/tau1\\/2, and consume 200 mW of power. The physics package is easily adapted to function as a magnetometer with sensitivity below 50 pT Hz-1\\/2 at 10 Hz.

S. Knappe; P. D. D. Schwindt; V. Gerginov; V. Shah; L. Liew; J. Moreland; H. G. Robinson; L. Hollberg; J. Kitching

2006-01-01

141

Stop the Clock, Level 5  

NSDL National Science Digital Library

This interactive game gives students practice in comparing digital and analog clock times to the nearest minute. The digital displays are based on the 24-hour system. They are presented with five displays of each and must drag each digital time to the matching analog clock. They are given feedback and encouraged to improve their time in doing the task. Please note: precision levels 1, 2, 3, and 4 (cataloged separately) are available at Oswego Interactive Games (see related resources).

Cogan, Mark

2002-01-01

142

Stop the Clock, Level 2  

NSDL National Science Digital Library

This interactive game gives students practice in comparing digital and analog clock times to the nearest fifteen minutes. They are presented with five displays of each and must drag each digital time to the matching analog clock. They are given feedback and encouraged to improve their time in doing the task. Please note: precision levels 1, 3, 4, and 5 (cataloged separately) are available at Oswego Interactive Games (see related resources).

Cogan, Mark

2002-01-01

143

Stop the Clock, Level 1  

NSDL National Science Digital Library

This interactive game gives students practice in comparing digital and analog clock times to the nearest half hour. They are presented with five displays of each and must drag each digital time to the matching analog clock. They are given feedback and encouraged to improve their time in doing the task. Please note: precision levels 2, 3, 4, and 5 (cataloged separately) are available at Oswego Interactive Games (see related resources).

Cogan, Mark

2002-01-01

144

Stop the Clock, Level 3  

NSDL National Science Digital Library

This interactive game gives students practice in comparing digital and analog clock times to the nearest five minutes. They are presented with five displays of each and must drag each digital time to the matching analog clock. They are given feedback and encouraged to improve their time in doing the task. Please note: precision levels 1, 2, 4, and 5 (cataloged separately) are available at Oswego Interactive Games (see related resources).

Cogan, Mark

2002-01-01

145

Stop the Clock, Level 4  

NSDL National Science Digital Library

This interactive game gives students practice in comparing digital and analog clock times to the nearest minute. They are presented with five displays of each and must drag each digital time to the matching analog clock. They are given feedback and encouraged to improve their time in doing the task. Please note: precision levels 1, 2, 3, and 5 (cataloged separately) are available at Oswego Interactive Games (see related resources).

Cogan, Mark

2002-01-01

146

Clocking design and analysis for a 600MHz Alpha microprocessor  

Microsoft Academic Search

Design, analysis, and verification of the clock hierarchy on a 600 MHz Alpha microprocessor is presented. The clock hierarchy includes a gridded global clock, gridded major clocks, and many local clocks and local conditional clocks, which together improve performance and power at the cost of verification complexity. Performance is increased with a windowpane arrangement of global clock drivers for lowering

Daniel W. Bailey; Bradley J. Benschneider

1998-01-01

147

Gravitational Wave Search with the Clock Mission  

NASA Technical Reports Server (NTRS)

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.

Armstrong, J. W.

1997-01-01

148

Complex bird clocks.  

PubMed Central

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

Gwinner, E; Brandstatter, R

2001-01-01

149

Conditionality and Ownership in IMF Lending: A Political Economy Approach  

Microsoft Academic Search

The relation between IMF conditionality and country ownership of assistance programs is considered from a political economy perspective, focusing on the question of why conditionality is needed if it is in a country’s best interests to undertake the reform program. It is argued that heterogeneity of interests must form the basis of any discussion of conditionality and ownership. The Paper

Allan Drazen

2002-01-01

150

Distinct Magnetospheric Responses to Southward IMF in Two Substorms  

NASA Technical Reports Server (NTRS)

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.

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

2003-01-01

151

Occurrence frequencies of IMF triggered and nontriggered substorms  

Microsoft Academic Search

The occurrence of triggered and nontriggered substorm are examined in light of current interest in such issues as substorm identification, IMF By variations, and potentially undetected small-scale solar wind perturbation. Global substorms are identified using a sudden, persistent decrease in the AL index. The onset of this global expansion is taken to be the time of the Pi 2 burst

Tung-Shin Hsu; Robert L. McPherron

2003-01-01

152

Making the IMF and the World Bank More accountable  

Microsoft Academic Search

Accused of being secretive, unaccountable and ineffective, both the IMF and the World Bank are seeking to become more transparent, more participatory and more accountable. Yet few attempts have been made to dissect the existing structure of accountability within the international financial institutions (IFIs). This paper critically examines the existing accountability of the institutions, and offers some recommendations for making

Ngaire Woods

2005-01-01

153

IMF Committee on Balance of Payments Statistics: Annual Report 1997  

NSDL National Science Digital Library

The IMF Committee on Balance of Payments Statistics has released its 1997 Annual Report. The report points to sizable discrepancies in the global balance of payments statistics. Central to this report are the efforts that attempt to account for the discrepancies such as the coordinated portfolio investment survey.

1998-01-01

154

BA?IMSIZLIK SONRASI AZERBAYCAN IMF ?L??K?LER?  

Microsoft Academic Search

After the independence of Azerbaijan and as a result of interactions with international monetary organisations, there has been great success in the country's economy. Within the framework, of the IMFs order towards monetary systems and policies towards under- development countries in the last decade, a partnership with Azerbaijan has been achieved. Through that partnership essential, positive effect has been achieved.

Elçin SÜLEYMANOV

2002-01-01

155

Improving the world's financial architecture : the role of the IMF  

Microsoft Academic Search

The IMF must change its sanction and incentive systems so that the next crisis is more likely to be prevented. It should concentrate more on ex ante prevention, which can be done by clearly specifying the rules that will be applied ex post. It should also rely more on automatic mechanisms that operate through the market in order to get

Horst Siebert

1999-01-01

156

Effect of IMF By on thermospheric composition at high and middle latitudes: 2. Data comparisons  

Microsoft Academic Search

The strength and orientation of the interplanetary magnetic field (IMF) has a strong effect on the high-latitude plasma convection pattern, thereby influencing the speed and direction of polar thermospheric winds. The possibility of similar IMF control over the compositional response of the thermosphere during geomagnetic disturbances has not been fully investigated. This study finds that the y-component of the IMF

Thomas J. Immel; Geoff Crowley; Chris L. Hackert; John D. Craven; Ray G. Roble

2006-01-01

157

Occurrence frequencies of IMF triggered and nontriggered substorms  

NASA Technical Reports Server (NTRS)

The occurrence of triggered and nontriggered substorm are examined in light of current interest in such issues as substorm identification, IMF By variations, and potentially undetected small-scale solar wind perturbation. Global substorms are identified using a sudden, persistent decrease in the AL index. The onset of this global expansion is taken to be the time of the Pi 2 burst nearest in time to the beginning of the AL, decrease. IMF triggers were identified both subjectively through visual scanning of the data and automatically with a computer algorithm. Both northward turnings of the IMF Bz and decreases in the amplitude of the By component were considered as possible triggers. Two different solar wind monitors were used in the investigation: IMP-8 in a circular orbit with a distance 12 to approx.35 Re to the Earth-Sun line and ISEE-2 in an elliptical orbit with a distance only 5 to approx.10 Re to the Earth-Sun line. The IMP-8 results show that the triggering probability does not depend on the distance of the monitor from the Earth-Sun line in the range 12-35 Re. The ISEE dataset shows that closer than 12 Re the triggering probability is the same as it is in the IMP-8 data set. Thus there appears to be no dependence of triggering on the location of the monitor provided it is within 35 Re of the Earth. We also demonstrate that including the By component does not significantly increase the probability of substorm triggering. Approximately 60% of all substorms appear to be triggered. Of the 40% for which we could not identify a trigger, 10% occurred while the IMF was northward. The data suggest that substorm onset is a consequence of an internal magnetospheric instability that is highly sensitive to changes in magnetospheric convection induced by a sudden change in the IMF, but that these changes are not always necessary.

Hsu, Tung-Shin; McPherron, Robert L.

2003-01-01

158

Dependence of O+ escape rate from the Venusian upper atmosphere on IMF directions  

NASA Astrophysics Data System (ADS)

investigate the dependence of the O+ escape rate on the upstream interplanetary magnetic field (IMF) direction by using data from the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) instrument and the magnetometer (MAG) onboard Venus Express. We consider two cases, namely the perpendicular IMF case (167 events) and the parallel IMF case (82 events), where IMF is nearly perpendicular to the Venus-Sun line and nearly parallel to it. By integrating O+ fluxes observed on the nightside, total O+ escape rates of (5.8 ± 2.9) × 1024 s-1 (perpendicular IMF case) and (4.9 ± 2.2) × 1024 s-1 (parallel IMF case) are obtained. As these values are not significantly different, the upstream IMF direction does not affect the total amount of O+ outflow from Venus. The different acceleration mechanisms must balance each other in order to keep the escape rate the same.

Masunaga, K.; Futaana, Y.; Stenberg, G.; Barabash, S.; Zhang, T. L.; Fedorov, A.; Okano, S.; Terada, N.

2013-05-01

159

Primary Atomic Clock Reference System  

NASA Technical Reports Server (NTRS)

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

2001-01-01

160

Primary Atomic Clock Reference System  

NASA Technical Reports Server (NTRS)

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.

2001-01-01

161

Clocks, Metabolism, and the Epigenome  

PubMed Central

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.

Feng, Dan; Lazar, Mitchell A.

2012-01-01

162

A critique of vole clocks  

NASA Astrophysics Data System (ADS)

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

Martin, Robert A.

2014-06-01

163

Synchronous clock stopper for microprocessor  

NASA Technical Reports Server (NTRS)

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.

Kitchin, David A. (Inventor)

1985-01-01

164

Circadian molecular clocks and cancer.  

PubMed

Physiological processes such as the sleep-wake cycle, metabolism and hormone secretion are controlled by a circadian rhythm adapted to 24h day-night periodicity. This circadian synchronisation is in part controlled by ambient light decreasing melatonin secretion by the pineal gland and co-ordinated by the suprachiasmatic nucleus of the hypothalamus. Peripheral cell autonomous circadian clocks controlled by the suprachiasmatic nucleus, the master regulator, exist within every cell of the body and are comprised of at least twelve genes. These include the basic helix-loop-helix/PAS domain containing transcription factors; Clock, BMal1 and Npas2 which activate transcription of the periodic genes (Per1 and Per2) and cryptochrome genes (Cry1 and Cry2). Points of coupling exist between the cellular clock and the cell cycle. Cell cycle genes which are affected by the molecular circadian clock include c-Myc, Wee1, cyclin D and p21. Therefore the rhythm of the circadian clock and cancer are interlinked. Molecular examples exist including activation of Per2 leads to c-myc overexpression and an increased tumor incidence. Mice with mutations in Cryptochrome 1 and 2 are arrhythmic (lack a circadian rhythm) and arrhythmic mice have a faster rate of growth of implanted tumors. Epidemiological finding of relevance include 'The Nurses' Health Study' where it was established that women working rotational night shifts have an increased incidence of breast cancer. Compounds that affect circadian rhythm exist with attendant future therapeutic possibilities. These include casein kinase I inhibitors and a candidate small molecule KL001 that affects the degradation of cryptochrome. Theoretically the cell cycle and malignant disease may be targeted vicariously by selective alteration of the cellular molecular clock. PMID:24099911

Kelleher, Fergal C; Rao, Aparna; Maguire, Anne

2014-01-01

165

Colloquium: Physics of optical lattice clocks  

NASA Astrophysics Data System (ADS)

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

Derevianko, Andrei; Katori, Hidetoshi

2011-04-01

166

Spectral analysis of clock noise: a primer  

NASA Astrophysics Data System (ADS)

The statistical characterization of clock noise is important for understanding how well a clock can perform in applications where timekeeping is important. The usual frequency domain characterization of clock noise is the power spectrum. We present a primer on how to estimate the power spectrum of clock noise given a finite sequence of measurements of time (or phase) differences between two clocks. The simplest estimator of the spectrum is the periodogram. Unfortunately this estimator is often problematic when applied to clock noise. Three estimators that overcome the deficiencies of the periodogram are the sinusoidal multitaper spectral estimator, Welch's overlapped segment averaging estimator and Burg's autoregressive estimator. We give complete details on how to calculate these three estimators. We apply them to two examples of clock noise and find that they all improve upon the periodogram and give comparable results. We also discuss some of the uses for the spectrum and its estimates in the statistical characterization of clock noise.

Percival, Donald B.

2006-08-01

167

Colloquium: Physics of optical lattice clocks  

SciTech Connect

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.

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

2011-04-01

168

Telling time on a clock  

NSDL National Science Digital Library

Students who complete this exercise will know how to tell time on an analog clock. Being able to tell time is great! You will know when school starts (and when it gets out!), when it\\'s time to play and even when it\\'s bed time. Complete the following exercises: 1. Visit Clock Wise and put in the following five times: 3:45 a.m. 12:30 p.m. 3:05 p.m. 6:45 p.m. 8:20 a.m. Draw a picture of each ...

Dart, Greg

2007-10-19

169

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

Microsoft Academic Search

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

Peter Nilsson; Mats Torkelson

1996-01-01

170

Acting with the Clock: Clocking Practices in Early Childhood  

ERIC Educational Resources Information Center

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…

Pacini-Ketchabaw, Veronica

2012-01-01

171

Auroral Substorm Time Scales: Seasonal and IMF Variations  

NASA Technical Reports Server (NTRS)

The time scales and phases of auroral substorm, activity are quantied in this study using the hemispheric power computed from Polar Ultraviolet Imager (UVI) images. We have applied this technique to several hundred substorm events and we are able to quantify how the characterist act, of substorms vary with season and IMF Bz orientation. We show that substorm time scales vary more strongly with season than with IMF Bz orientation. The recovery time for substorm. activity is well ordered by whether or not the nightside oral zone is sunlit. The recovery time scales for substorms occurring in the winter and equinox periods are similar and are both roughly a factor of two longer than in summer when the auroral oval is sunlit. Our results support the hypothesis that the ionosphere plays an active role in governing the dynamics of the aurora.

Chua, D.; Parks, G. K.; Brittnacher, M.; Germany, G. A.; Spann, J. F.; Six, N. Frank (Technical Monitor)

2002-01-01

172

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

NSDL National Science Digital Library

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

173

Capital-market Liberalization, Globalization, and the IMF  

Microsoft Academic Search

One of the most controversial aspects of globalization is capital-market liberalization--not so much the liberalization of rules governing foreign direct investment, but those affecting short-term capital flows, speculative hot capital that can come into and out of a country. In the 1980s and 1990s, the IMF and the US Treasury tried to push capital-market liberalization around the world, encountering enormous

Joseph E. Stiglitz

2004-01-01

174

Magnetotail Structure and its Internal Particle Dynamics During Northward IMF  

NASA Technical Reports Server (NTRS)

This study uses Global magnetohydrodynamic (MHD) simulations driven by solar wind data along with Geotail observations of the magnetotail to investigate the magnetotail's response to changes in the interplanetary magnetic field (IMF); observed events used in the study occurred on March 29, 1993 and February 9, 1995. For events from February 9, 1995, we also use the time-dependent MHD magnetic and electric fields and the large-scale kinetic (LSK) technique to examine changes in the Geotail ion velocity distributions. Our MHD simulation shows that on March 29, 1993, during a long period of steady northward IMF, the tail was strongly squeezed and twisted around the Sun-Earth axis in response to variations in the IMF B(sub y) component. The mixed (magnetotail and magnetosheath) plasma observed by Geotail results from the spacecraft's close proximity to the magnetopause and its frequent crossings of this boundary. In our second example (February 9, 1995) the IMF was also steady and northward, and in addition had a significant B(sub y) component. Again the magnetotail was twisted, but not as strongly as on March 29, 1993. The Geotail spacecraft, located approximately 30 R(sub E) downtail, observed highly structured ion distribution functions. Using the time-dependent LSK technique, we investigate the ion sources and acceleration mechanisms affecting the Geotail distribution functions during this interval. At 1325 UT most ions are found to enter the magnetosphere on the dusk side earthward of Geotail with a secondary source on the dawn side in the low latitude boundary layer (LLBL). A small percentage come from the ionosphere. By 1347 UT the majority of the ions come from the dawn side LLBL. The distribution functions measured during the later time interval are much warmer, mainly because particles reaching the spacecraft from the dawnside are affected by nonadiabatic scattering and acceleration in the neutral sheet.

Ashour-Abdalia, M.; El-Alaoui, M.; Peroomian, V.

1998-01-01

175

Magnetotail Structure and its Internal Particle Dynamics During Northward IMF  

NASA Technical Reports Server (NTRS)

This study uses Global magnetohydrodynamic (MHD) simulations driven by solar wind data along with Geotail observations of the magnetotail to investigate the magnetotail's response to changes in the interplanetary magnetic field (IMF); observed events used in the study occurred on March 29, 1993 and February 9, 1995. For events from February 9, 1995, we also use the time-dependent MHD magnetic and electric fields and the large-scale kinetic (LSK) technique to examine changes in the Geotail ion velocity distributions. Our MHD simulation shows that on March 29, 1993, during a long period of steady northward IMF, the tail was strongly squeezed and twisted around the Sun-Earth axis in response to variations in the IMF B(sub y) component. The mixed (magnetotail and magnetosheath) plasma observed by Geotail results from the spacecraft's close proximity to the magnetopause and its frequent crossings of this boundary. In our second example (February 9, 1995) the IMF was also steady and northward, and in addition had a significant B(sub y) component. Again the magnetotail was twisted, but not as strongly as on March 29, 1993. The Geotail spacecraft, located approximately 30 R(sub E) downtail, observed highly structured ion distribution functions. Using the time-dependent LSK technique, we investigate the ion sources and acceleration mechanisms affecting the Geotail distribution functions during this interval. At 1325 UT most ions are found to enter the magnetosphere on the dusk side earthward of Geotail with a secondary source on the dawn side in the low latitude boundary layer (LLBL). A small percentage come from the ionosphere. By 1347 UT the majority of the ions come from the dawn side LLBL. The distribution functions measured during the later time interval are much warmer, mainly because particles reaching the spacecraft from the dawn side are affected by nonadiabatic scattering and acceleration in the neutral sheet.

Ashour-Abdalla, M.; Raeder, J.; El-Alaoui, M.; Peroomian, V.

1998-01-01

176

The IMF of Open Star Clusters with Tycho-2  

NASA Astrophysics Data System (ADS)

We present the stellar initial mass function (IMF) of several nearby open star clusters derived on the basis of the Tycho-2 catalogue (Høg et al., 2000, A&A 355, L27). Tycho-2, computed from the original Tycho catalogue (ESA, 1997, SP-1200) and ground based first epoch data, provides positions, stellar proper motions, and BT and VT photometric data. With the help of the proper motions, we distinguished between the members and non-members of the clusters; from the stellar magnitudes we derived the initial stellar masses. Since the catalogue becomes incomplete around VT=11 mag, we were restricted to a small magnitude (and hence mass) interval, so that we chose to study nearby ((m-M)0 <= 7.5 mag) open star clusters with - according to Robichon et al. (1999, A&A 345, 471) - a clear separation of field and cluster proper motions, restricting our sample to 8 objects. The IMF computed from m ? 1 Msolar up to the main sequence turn off point could be well represented by power laws with exponents from ?=-0.85 to ?=-2.36 (when Salpeter's (1955, ApJ 121, 161) value is ?=-1.35). Within the errors (which are comparably high for some of the objects due to their low numbers of members), this is in good agreement with the range of IMF slopes as given, e.g., by Scalo (1998, ASP Conf. Series 142, 201). Regarding upcoming missions of astrometry satellites (FAME, DIVA, GAIA), this kind of IMF study based on a uniform all-sky data sample will play a more important role in the future: The limiting magnitudes of these instruments will be fainter, proper motions will be available for all detected objects (in contrary to, e.g., the HIPPARCOS catalogue, the proper motions of which were determined for the stars of an input catalogue only) and will become independent of ground based observations, so that their quality will be higher.

Sanner, Jörg; Geffert, Michael

177

Wielen dip and IMF for the solar neighborhood stars  

NASA Astrophysics Data System (ADS)

The Wielen dip at M v 7 in the Wielen (1974) luminosity function (LF) for the solar neighborhood stars yields a corresponding dip at m 0.7m o in the present day mass function (PDMF) of main sequence (MS) stars. This Wielen dip suggests that two different initial mass functions (IMF) have been operative after the initial phase of disk evolution and the age of the solar neighborhood is about 13 billion years.

Lee, See-Woo

178

Adaptive clock synchronization in sensor networks  

Microsoft Academic Search

Recent advances in technology have made low cost, low power wireless sensors a reality. Clock synchronization is an important service in any distributed system, including sensor network systems. Applications of clock synchronization in sensor networks include data integration in sensors, sensor reading fusion, TDMA medium access scheduling, and power mode energy saving. However, for a number of reasons, standard clock

Santashil PalChaudhuri; Amit Kumar Saha; David B. Johnson

2004-01-01

179

Spin Squeezing in a Rydberg Lattice Clock  

NASA Astrophysics Data System (ADS)

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.

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

2014-03-01

180

From circadian clock gene expression to pathologies  

Microsoft Academic Search

In most organisms, circadian rhythms are generated by a molecular clockwork involving so-called clock genes. These circadian clock genes participate in regulatory feedback loops, in which proteins regulate their own expression. The outcome is that ribonucleic acids (RNAs) and proteins produced from many of these genes oscillate with a circadian rhythm. Here, we describe the regulation of clock genes and

Elaine Waddington Lamont; Francine O. James; Diane B. Boivin; Nicolas Cermakian

2007-01-01

181

The observed North-South Asymmetry of IMF spiral  

NASA Technical Reports Server (NTRS)

We appraise the finding, reported in the literature, that a small but finite north-south asymmetry (NSA) exists in the interplanetary magnetic field (IMF) spiral at Earth's orbit. We have analyzed the data available on the Omnitape for the 1963 to 1993 period. The coverage is very uneven, ranging from less than 40% to greater than 80%. The magnitude of NSA fluctuates considerably during the period of our analysis. This is true even if one considers the period 1967 to 1982 when the coverage is greater than 50%. The values of NSA derived from 27-day averages of the hourly data points range from greater than +50 deg to less than -40 deg. If one arranges the data according to the magnetic polarity epochs of the solar polar field, the epoch averages gives the magnitude of NSA less than approximately 2 deg. This is also true, if one considers the average magnitude of NSA for the 1965 to 1993 period, when the coverage is greater than 25%. A genuine, persistent, NSA of IMF spiral is likely to affect the cosmic ray modulation, on either side of the current sheet, by introducing a corresponding change in the radial diffusion coefficient of energetic particle transport in the heliosphere. The annual mean values of the observed NSA of IMF spiral are compared with the observed off-ecliptic contributions to cosmic ray modulation.

Ahluwalia, H. S.; Xue, S. S.

1995-01-01

182

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

Microsoft Academic Search

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

Hamid Mahmoodi; Vishy Tirumalashetty; Matthew Cooke; Kaushik Roy

2009-01-01

183

Real-Time Simulation Clock.  

National Technical Information Service (NTIS)

A real time simulation clock is decribed for generating frame tics that synchronize computations to the real time and to other computations in a system that has a central computer and multiple remote sites that utilize the central computer. Timing tics ar...

D. R. Bennington D. J. Crawford

1987-01-01

184

Genomic clocks and evolutionary timescales  

Microsoft Academic Search

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

S. Blair Hedges; Sudhir Kumar

2003-01-01

185

Clock Drawing in Developmental Dyslexia.  

ERIC Educational Resources Information Center

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.…

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

2003-01-01

186

Molecular Clock and Gene Function  

Microsoft Academic Search

Molecular phylogenies based on the molecular clock require the comparison of orthologous genes. Orthologous and paralogous genes usually have very different evolutionary fates. In general, orthologs keep the same functions in species, whereas, particularly over a long time span, paralogs diverge functionally and may become pseudogenes or get lost. In eukaryotic genomes, because of the degree of redundancy of genetic

Cecilia Saccone; Corrado Caggese; Anna Maria D’Erchia; Cecilia Lanave; Marta Oliva; Graziano Pesole

2003-01-01

187

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

NASA Astrophysics Data System (ADS)

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).

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

2014-08-01

188

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

NASA Technical Reports Server (NTRS)

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.

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

2001-01-01

189

Automatic control of clock duty cycle  

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

190

Small Molecule Modifiers of Circadian Clocks  

PubMed Central

Circadian clocks orchestrate 24-h oscillations of essential physiological and behavioral processes in response to daily environmental changes. These clocks are remarkably precise under constant conditions yet highly responsive to resetting signals. With the molecular composition of the core oscillator largely established, recent research has increasingly focused on clock modifying mechanisms/molecules. In particular, small-molecule modifiers, intrinsic or extrinsic, are emerging as powerful tools for understanding basic clock biology as well as developing putative therapeutic agents for clock-associated diseases. In this review, we will focus on synthetic compounds capable of modifying the period, phase or amplitude of circadian clocks, with particular emphasis on the mammalian clock. We will discuss the potential of exploiting these small-molecule modifiers in both basic and translational research.

Chen, Zheng; Yoo, Seung-Hee; Takahashi, Joseph S.

2013-01-01

191

VCSEL polarization control for chip-scale atomic clocks.  

SciTech Connect

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.

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

2007-01-01

192

On the enhancement of the IMF magnitude during 1978-1979  

NASA Technical Reports Server (NTRS)

The magnitude of the interplanetary magnetic field (IMF) exhibits an enhancement during 1978-1979 relative to all years back to 1963. It is shown that IMF magnitude variations over the 1966-1979 period represent the combined effect of variations in both the radial flux density of the IMF and the degree of spiraling of the IMF, consistent with the theoretical model of Parker. The 1978-1979 IMF magnitude enhancement is due to an enhancement of radial flux which was in turn related to an increase of magnetic flux leaving solar active regions. It is also shown that during the corotating stream dominated years 1973-1976, the IMF was less wound up than it was during other years, and that 1973-1974 were years of enhanced radial flux.

King, J. H.

1981-01-01

193

What's Your Angle on Angles?  

ERIC Educational Resources Information Center

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…

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

2007-01-01

194

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

NASA Technical Reports Server (NTRS)

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

Lennartsson, W.

1988-01-01

195

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

196

Genomic clocks and evolutionary timescales  

NASA Technical Reports Server (NTRS)

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.

Blair Hedges, S.; Kumar, Sudhir

2003-01-01

197

Comment on ‘The smallest clock  

NASA Astrophysics Data System (ADS)

It has been suggested that Wigner's clock inequalities can be applied to biological systems. Peši? was the first to suggest this by applying these inequalities to the reproduction time of a mycoplasma (1993 Eur. J. Phys. 14 90). More recently, Goel applied Wigner's clock inequalities to the system formed by a Taq DNA polymerase reading a phage lambda DNA strand, concluding that the behaviour of polymerases is governed by quantum mechanical processes. By means of a counterexample, using a Pfu DNA polymerase, I show that current experimental evidence does not allow us to conclude that Wigner's inequalities govern the behaviour of polymerases. Furthermore, both works are based on an incorrect interpretation of the concept of position uncertainty.

Brualla, Lorenzo

2013-05-01

198

The mammalian clock and chronopharmacology.  

PubMed

Increases in our understanding of the molecular control of circadian rhythms and subsequent signaling pathways has allowed for new therapeutic drug targets to be identified as well as for a better understanding of how to more efficaciously and safely utilize current drugs. Here, we review recent advances in targeting components of the molecular clock in mammals for the development of novel therapeutics as well as describe the impact of the circadian rhythm on drug efficacy and toxicity. PMID:23481644

Griffett, Kristine; Burris, Thomas P

2013-04-01

199

Biologic clocks and the gut  

Microsoft Academic Search

The gastrointestinal tract displays biologic rhythms in basal gastric acid output, epithelial cell proliferation, gastrointestinal\\u000a motility, and appetite regulation. Furthermore, the development of gastrointestinal complications after administration of\\u000a aspirin and after chemo- and radiotherapy for metastatic colon cancer depends on the time of administration. Biologic rhythms\\u000a are driven by so-called clock genes. Thus, it is conceivable that subsets of genes

Willemijntje A. Hoogerwerf

2006-01-01

200

Mechanism of the circadian clock in physiology  

PubMed Central

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.

Richards, Jacob

2013-01-01

201

Ribonucleoprotein Complexes That Control Circadian Clocks  

PubMed Central

Circadian clocks are internal molecular time-keeping mechanisms that enable organisms to adjust their physiology and behavior to the daily surroundings. Misalignment of circadian clocks leads to both physiological and health impairment. Post-transcriptional regulation and translational regulation of circadian clocks have been extensively investigated. In addition, accumulating evidence has shed new light on the involvement of ribonucleoprotein complexes (RNPs) in the post-transcriptional regulation of circadian clocks. Numerous RNA-binding proteins (RBPs) and RNPs have been implicated in the post-transcriptional modification of circadian clock proteins in different model organisms. Herein, we summarize the advances in the current knowledge on the role of RNP complexes in circadian clock regulation.

Wang, Dongni; Liang, Xiaodi; Chen, Xianyun; Guo, Jinhu

2013-01-01

202

Future Laser-Cooled Microwave Clock Performance  

NASA Technical Reports Server (NTRS)

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.

Gibble, Kurt

1997-01-01

203

Molecular components of the mammalian circadian clock  

PubMed Central

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

Buhr, Ethan D.; Takahashi, Joseph S.

2013-01-01

204

Angle Hunting  

NSDL National Science Digital Library

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

Exploratorium

2010-01-01

205

How IMF Bx affects the two polar hemispheres differently  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

206

A test of convection models for IMF Bz north  

NASA Technical Reports Server (NTRS)

The Utah State University Ionospheric Model was run to obtain diurnally reproducible ionospheric densities and temperatures for summer and winter conditions using both distorted two-cell and three-cell convection patterns. Differences due to the different convection patterns manifest themselves in the depth and location of polar holes in the F-region electron density. While the total depth of the model holes is a characteristic of the diurnally reproducible pattern, the features appear and are recognizable within 0.5 h. Langmuir probe data from 41 DE-2 passes, during which the IMF Bz component was northward, have been qualitatively checked against the model predictions. The cross polar cap electron density profiles of a large majority of the passes more closely conform to the distorted two-cell runs for both polarities of the IMF By component. This test can be generalized to rule out proposed convection patterns based on the presence/absence and position of polar electron density holes.

Maynard, N. C.; Sojka, J. J.; Schunk, R. W.; Heppner, J. P.; Brace, L. H.

1990-01-01

207

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

NASA Astrophysics Data System (ADS)

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

Smarandache, Florentin

2013-03-01

208

Spin-1/2 Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

We experimentally investigate an optical clock based on Yb171 (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 3.4×10-16, 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.

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.

2009-08-01

209

Experimental validation of clock synchronization algorithms  

NASA Technical Reports Server (NTRS)

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.

Palumbo, Daniel L.; Graham, R. Lynn

1992-01-01

210

Circadian clock genes, ovarian development and diapause  

PubMed Central

Insects, like most organisms, have an internal circadian clock that oscillates with a daily rhythmicity, and a timing mechanism that mediates seasonal events, including diapause. In research published in BMC Biology, Ikeno et al. show that downregulation of the circadian clock genes period and cycle affects expression of ovarian diapause in the insect Riptortus pedestris. They interpret these important results as support for Erwin Bünning's (1936) hypothesis that the circadian clock constitutes the basis of photoperiodism. However, their observations could also be the result of pleiotropic effects of the individual clock genes. See research article http://www.biomedcentral.com/1741-7007/8/116

2010-01-01

211

Circadian clock genes, ovarian development and diapause.  

PubMed

Insects, like most organisms, have an internal circadian clock that oscillates with a daily rhythmicity, and a timing mechanism that mediates seasonal events, including diapause. In research published in BMC Biology, Ikeno et al. show that downregulation of the circadian clock genes period and cycle affects expression of ovarian diapause in the insect Riptortus pedestris. They interpret these important results as support for Erwin Bünning's (1936) hypothesis that the circadian clock constitutes the basis of photoperiodism. However, their observations could also be the result of pleiotropic effects of the individual clock genes.See research article http://www.biomedcentral.com/1741-7007/8/116. PMID:20828372

Bradshaw, William E; Holzapfel, Christina M

2010-01-01

212

Evaluating the effect of IMF lending to low-income countries  

Microsoft Academic Search

The purpose of this paper is twofold: to apply to a group of low-income borrowers from the IMF, the most commonly used technique for measuring the independent effects on economic developments of IMF support; and to develop a minimum set of diagnostic tests for determining whether necessary conditions for using the methodology exist. The modified control-group methodology is used to

Louis Dicks-Mireaux; Mauro Mecagni; Susan Schadler

2000-01-01

213

International Monetary Fund's (IMF) Proposed Quota Increase: Issues for Congress. CRS Report for Congress.  

National Technical Information Service (NTIS)

The International Monetary Fund (IMF) is the international lender-of-last-resort. Each of the 182 members of the IMF have a quota, which broadly reflects the size of its economy and its relative position in the world economy. Among other things, quotas de...

P. A. Wertman

1998-01-01

214

Heliographic latitude dependence of the IMF dominant polarity in 1972--1973 using Pioneer 10 data  

Microsoft Academic Search

The heliographic latitude dependence of the interplanetary magnetic ; field (IMF) was studied by using Pioneer 10 data taken from March 1972 through ; June 1973 over Bartels solar rotation (SR) periods 1896--1913. The daily IMF ; sector polarities were plotted for each of these SR periods. Then the number of ; days of positive polarity (''away'' directed fields) per

Ronald L. Rosenberg

1975-01-01

215

Evidence of high-latitude reconnecting during northward IMF: Hawkeye observations  

Microsoft Academic Search

Reconnection is accepted as an important process for driving the solar wind\\/magnetospheric interaction although it is not fully understood. In particular, reconnection for northward interplanetary magnetic field (IMF) at high-latitudes tailward of the cusp, has received little attention in comparison with equatorial reconnection for southward IMF. Using Hawkeye data the authors present the first direct observations of reconnection at the

R. L. Kessel; J. L. Green; S. F. Fung; S. A. Boardsen; L. C. Tan; T. E. Eastman; J. D. Craven; L. A. Frank

1996-01-01

216

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

PubMed

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

Ruckert, Arne; Labonté, Ronald

2013-09-01

217

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

Microsoft Academic Search

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

Gary M. Woller; David Kirkwood Hart

1995-01-01

218

Evolution of the Global Aurora During Positive IMF B(sub z) and Varying IMF B(sub y) Conditions  

NASA Technical Reports Server (NTRS)

The DE 1 imaging instrumentation provides a full view of the entire auroral oval every 12 min for several hours during each orbit. We examined five examples of global evolution of the aurora that occurred during the northern hemisphere winter of 1981-1982 when the z component of the interplanetary magnetic field (IMF) was positive and the y component was changing sign. Evolution of an expanded auroral emission region into a theta aurora appears to require a change in the sign of B(sub y) during northward Interplanetary Magnetic Field. Theta aurora are formed both from expanded duskside emission regions (B(sub y) changes from positive to negative) and dawnside emission regions (B(sub y) changes from negative to positive), however the dawnside-originating and duskside-originating evolutions are not mirror images. The persistence of a theta aurora after its formation suggests that there may be no clear relationship between the theta aurora pattern and the instantaneous configuration of the IMF.

Cumnock, J. A.; Sharber, J. A.; Heelis, R. A.; Hairston, M. R.; Craven, J. D.

1997-01-01

219

On the enhancement of the IMF magnitude during 1978-1979  

NASA Technical Reports Server (NTRS)

The magnitude of the interplanetary magnetic field (IMF) exhibits an enhancement during 1978 to 1979 relative to all years back to 1963. It is shown that IMF magnitude variations over the 1966 to 1979 period represent the combined effect of variations in both the radial flux density of the IMF and the degree of spiraling of the IMG, consistent with the theoretical model of Parker. The 1978 to 1979 IMF magnitude enhancement is due to an enhancement of radial flux which was in turn related to an increase of magnetic flux leaving solar active regions. It is also shown that during the corotating stream dominated years 1973 to 1976, the IMF was less wound up than during other years, and that 1973 to 1974 were years of enhanced radial flux.

King, J. H.

1981-01-01

220

Gigabit Ethernet Asynchronous Clock Compensation FIFO  

NASA Technical Reports Server (NTRS)

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.

Duhachek, Jeff

2012-01-01

221

Angle Measurer  

NSDL National Science Digital Library

This Flash applet gives students practice in creating an angle measuring between zero and 180 degrees. Two buttons control the increase or decrease of the opening between two rays. Points are awarded for accuracy.

2011-01-01

222

Right Angle  

NSDL National Science Digital Library

This article gives teachers background information on right angles. It provides geometric and practical examples, a paper folding construction method, and some history of the usage of the term 'right.'

Goldenberg, Paul

2011-06-09

223

An all-digital clock generator for dynamic frequency scaling  

Microsoft Academic Search

An all-digital clock generator for dynamic frequency scaling is presented by using a cyclic clock multiplier. It realizes the fractional or multiplied output clock within four reference clock cycles. The frequency of the output clock can be programmed as Mfref\\/N (fref is the reference clock frequency, 1lesMles7, and 1lesNles8). It has been fabricated in a 0.18 um CMOS process. The

Wei-Ming Lin; Chao-Chyun Chen; Shen-Iuan Liu

2009-01-01

224

Microstructure of the IMF turbulences at 2.5 AU  

NASA Technical Reports Server (NTRS)

A detailed analysis of small period (15-900 sec) magnetohydrodynamic (MHD) turbulences of the interplanetary magnetic field (IMF) has been made using Pioneer-11 high time resolution data (0.75 sec) inside a Corotating Interaction Region (CIR) at a heliocentric distance of 2.5 AU in 1973. The methods used are the hodogram analysis, the minimum variance matrix analysis and the cohenrence analysis. The minimum variance analysis gives evidence of linear polarized wave modes. Coherence analysis has shown that the field fluctuations are dominated by the magnetosonic fast modes with periods 15 sec to 15 min. However, it is also shown that some small amplitude Alfven waves are present in the trailing edge of this region with characteristic periods (15-200 sec). The observed wave modes are locally generated and possibly attributed to the scattering of Alfven waves energy into random magnetosonic waves.

Mavromichalaki, H.; Vassilaki, A.; Marmatsouri, L.; Moussas, X.; Quenby, J. J.; Smith, E. J.

1995-01-01

225

Global synchronization of parallel processors using clock pulse width modulation  

DOEpatents

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.

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

226

Designing the best clock distribution network  

Microsoft Academic Search

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

Phillip J. Restle; Alina Deutsch

1998-01-01

227

Conjugate-Phase, Remote-Clock Synchronizer.  

National Technical Information Service (NTIS)

This invention relates to a method for synchronizing a master clock and a remote slave clock which nominally has the same pulse frequency but may be out of time-phase. The method consists of transmitting a master pulse to the slave, measuring the time del...

W. M. Waters

1980-01-01

228

Conjugate-Phase, Remote-Clock Synchronizer.  

National Technical Information Service (NTIS)

A method for synchronizing a master clock and a remote slave clock which nominally has the same pulse frequency but may be out of time-phase comprising transmitting a master pulse to the slave, measuring the time delay, delta tau, between the received pul...

W. M. Waters

1983-01-01

229

Multi-time zoned digital clock  

Microsoft Academic Search

A digital clock capable of displaying the time in any one of four different time zones and in any one of four different language numerals is presented. Two different implementations of the clock are reported. The first implementation, designed for four time zones, makes use of counters, EPROMs, and multinumeric display decoders described by K.B. Balasubramanian and P.K. Rajan (1989).

K. Balasubramanian

1991-01-01

230

[Internal clock desynchronization, light and melatonin].  

PubMed

The internal clock is synchronized by environmental factors. In humans the main factors are the light-dark alternation, the sleep-wake cycle, and social life. Rhythm desynchronization occurs when the clock is no longer in phase (harmony) with the environment, resulting in a phase shift (phase advance or phase delay) which can produce fatigue, sleep disorders and mood disorders. Clock desynchronization is related to a a loss of adaptation between the clock and synchronizers, to an inability of the clock to be entrained, or to a dysfunction of the clock itself Shiftwork and nightwork, transmeridian flights, depressive states and other psychiatric disorders, as well as blindness, aging and intake in some medications and psychoactive agents like alcohol are among the numerous causes of rhythm desynchronization. Melatonin and light exposure are able to control and resynchronize the clock. The phase response curve (PRC) clearly demonstrates that light exposure and/or melatonin administration are able to shift (advance or delay, depending on their timing) and thereby reset the clock. PMID:22812159

Touitou, Yvan

2011-10-01

231

"Molecular Clock" Analogs: A Relative Rates Exercise  

ERIC Educational Resources Information Center

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…

Wares, John P.

2008-01-01

232

A Test Of Precision GPS Clock Synchronization  

NASA Technical Reports Server (NTRS)

This paper will describe tests of precision GPS time transfer using geodetic-quality TurboRogue receivers. The GPS data are processed with the GIPSY-OASIS II software, which simultaneously estimates the GPS satellite orbits and clocks, receiver locations and clock offsets, as well as other parameters such as earth orientation.

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

1996-01-01

233

GPS SIGNAL INTEGRITY DEPENDENCIES ON ATOMIC CLOCKS  

Microsoft Academic Search

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

Marc Weiss; Pradipta Shome; Ron Beard

234

O-GlcNAc signaling entrains the circadian clock by inhibiting BMAL1/CLOCK ubiquitination  

PubMed Central

SUMMARY Circadian clocks are coupled to metabolic oscillations through nutrient-sensing pathways. Nutrient flux into the hexosamine biosynthesis pathway triggers covalent protein modification by O-linked ?-D-N-acetylglucosamine (O-GlcNAc). Here we show that the hexosamine/O-GlcNAc pathway modulates peripheral clock oscillation. O-GlcNAc transferase (OGT) promotes expression of BMAL1/CLOCK target genes and affects circadian oscillation of clock genes in vitro and in vivo. Both BMAL1 and CLOCK are rhythmically O-GlcNAcylated and this protein modification stabilizes BMAL1 and CLOCK by inhibiting their ubiquitination. In vivo analysis of genetically modified mice with perturbed hepatic OGT expression shows aberrant circadian rhythms of glucose homeostasis. These results establish the counteraction between O-GlcNAcylation and ubiquitination as a key mechanism that regulates the circadian clock and suggest a crucial role for O-GlcNAc signaling in transducing nutritional signals to the core circadian timing machinery.

Li, Min-Dian; Ruan, Hai-Bin; Hughes, Michael E.; Lee, Jeong-Sang; Singh, Jay P.; Jones, Steven P.; Nitabach, Michael N.; Yang, Xiaoyong

2013-01-01

235

A Blind Circadian Clock in Cavefish Reveals that Opsins Mediate Peripheral Clock Photoreception  

PubMed Central

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.

Cavallari, Nicola; Frigato, Elena; Vallone, Daniela; Frohlich, Nadine; Lopez-Olmeda, Jose Fernando; Foa, Augusto; Berti, Roberto; Sanchez-Vazquez, Francisco Javier; Bertolucci, Cristiano; Foulkes, Nicholas S.

2011-01-01

236

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

PubMed

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

1994-05-01

237

Trapped ion optical clocks for space applications  

NASA Astrophysics Data System (ADS)

The last two decades have seen Cs fountain microwave clocks reach a level of better than 10-15 uncertainty per day, and the Pharao Cs space clock due for launch on the ISS in 2013 should provide improvement to the ground-based fountain clocks. However, the rapid pace of development of optical atomic clocks has reached a stage where they now challenge the accuracy and stability of the microwave clocks, and in some cases, out-perform them, primarily due to the much higher clock operating frequency and resultant improved stability. Optical clock uncertainty levels of 10-18 are now being projected, and the Al+ ion quantum logic clock is already demonstrating an inaccuracy of 9x10-18 [1] and points the way forward for a host of other ion (eg Yb+ and Sr+ ) and atom (eg Sr) clocks to emulate such leading performance. With the advent of such accuracies, the space research community and the European Space Agency have become focused on the potential to deploy such optical clocks in space with application to a number of areas ranging from fundamental physics to earth observation, satellite navigation and communications. On the fundamental physics front, opportunities exist for significantly improved tests of the Einstein equivalence principle and general relativity, including time and gravitational variations in fundamental constants, all of which can offer insights to the development of a unified model of quantum mechanics and gravitation. On the technology side, optical atomic clocks offer possibilities for improved location, deep space ranging, Earth geodetic mapping and secure satellite communications. Set against all these possibilities, there remains the necessity to demonstrate clock technology that is com-mensurate with space mission satellite payloads and operational constraints. Ion clocks have good characteristics in respect of payload considerations such as mass, size and power. This talk will review the state-of-the-art performance of ion optical clocks and their relativities to space applications and potential missions. [1] C W Chou et al. Phys. Rev. Lett. 104 070802 (2010)

Gill, Patrick

238

How changes in the tilt angle of the geomagnetic dipole affect the coupled magnetosphere-ionosphere-thermosphere system  

NASA Astrophysics Data System (ADS)

The orientation of the Earth's magnetic field has changed dramatically during the geological past. We have investigated the effects of changes in dipole tilt angle on the magnetosphere, ionosphere, and thermosphere, using the Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model. The dipole tilt angle modulates the efficiency of solar wind-magnetosphere coupling, by influencing the diurnal variation in the angle ? between the dipole axis and the GSM z axis. This influences how much Joule heating occurs at high magnetic latitudes. The dipole tilt angle also controls the geographic distribution of the Joule heating, as it determines the geographic latitude of the magnetic poles. Changes in the amount and distribution of Joule heating with tilt an`gle produce further changes in temperature and neutral winds. The latter affect the O/N2 ratio, which in turn modifies the peak electron density of the F2 layer, NmF2. All these effects are most important when the Interplanetary Magnetic Field (IMF) is southward, while being almost negligible under northward IMF. However, a change in dipole tilt also changes the inclination of the magnetic field, which affects the vertical component of ionospheric plasma diffusion along the magnetic field, regardless of the IMF direction. Changes in vertical plasma diffusion are responsible for ?2/3 of the changes in NmF2 and most of the low to midlatitude changes in hmF2 under southward IMF and for most of the changes in both variables under northward IMF. Thermal contraction may be responsible for high-latitude decreases in hmF2 with increasing tilt angle under southward IMF.

Cnossen, Ingrid; Richmond, Arthur D.

2012-10-01

239

Dependence of O+ escape rate from the Venusian upper atmosphere on IMF directions  

NASA Astrophysics Data System (ADS)

We investigate the dependence of the O+ escape rate from the Venusian upper atmosphere on the upstream interplanetary magnetic field (IMF) direction. Using the data obtained from the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) instrument and the magnetometer (MAG) onboard Venus Express, O+ fluxes observed in the night side region is statistically calculated. The data is classified into two cases: the perpendicular IMF case and the parallel IMF case, where IMF is nearly perpendicular to the solar wind velocity and nearly parallel to it. In the period between June 21 2006 and May 31, 2010, the O+ escape rates of (5.8 ± 2.9) × 10^24 s^-1 (perpendicular IMF case) and (4.9 ± 2.2) × 10^24 s^-1 (parallel IMF case) are obtained. Since these values are not significantly different, we conclude that the IMF direction does not affect the total amount of O+ outflow from Venus. Several acceleration mechanisms must balance each other in order to keep the escape rate constant.

Masunaga, K.; Futaana, Y.; Stenberg, G.; Barabash, S.; Zhang, T. L.; Fedorov, A.; Okano, S.; Terada, N.

2013-09-01

240

Estimating Angles  

NSDL National Science Digital Library

This Flash game for one or two players gives students practice in estimating the size of angles. A circle and a radius pointing in a random direction are given. The student activates a second sweeping radius, which can move in either direction, and tries to stop it at the specified measure. Three difficulty levels control the range of angle measures. Points are awarded based on closeness of the estimate. The Teachers' Notes page includes suggestions for implementation, discussion questions, ideas for extension and support.

2007-06-01

241

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

NASA Astrophysics Data System (ADS)

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

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

2012-03-01

242

Observational study of the IMF spiral north and south of the current sheet  

NASA Technical Reports Server (NTRS)

We have analyzed 23 years of spacecraft observations spanning 27 AU. Our analysis reveals both an overwinding of the interplanetary magnetic field (IMF) and a sustained asymmetry between the northern and southern hemispheres of the heliosphere. Nonzero azimuthal field components at the source boundary may account for the observed overwinding. The north-south asymmetry, whereby the IMF spiral north of the current sheet is more tightly wound than the IMF spiral south of the current sheet, persists due to unknown sources. It is also shown that there exist significant, correlated departures from the Parker theory in the azimuthal component of the field.

Smith, C. W.; Bieber, J. W.

1992-01-01

243

Picosecond MIXSEL for clocking applications  

NASA Astrophysics Data System (ADS)

The MIXSEL combines the gain of a VECSEL with the saturable absorber of a SESAM in one semiconductor structure to achieve fundamental modelocking in a simple straight cavity. We present a high-power MIXSEL with sub-10-ps pulse durations that can be scaled easily in repetition rate from a few GHz to <100 GHz. At 5.1 GHz repetition rate an average output power of 1.05 W in 2.4-ps-pulses was achieved. By scaling the repetition rate to 10 GHz (3.9-ps-pulses at 1.29 W), then to 20.7 GHz (2.35-ps-pulses at 607 mW) and most recently to even more than 100 GHz makes this high-power MIXSEL an attractive source suitable for applications such as optical clocking or optical sampling.

Mangold, M.; Wittwer, V. J.; Zaugg, C. A.; Link, S. M.; Golling, M.; Tilma, B. W.; Keller, U.

2014-03-01

244

Precision of the Gonyaulax circadian clock.  

PubMed

Under constant conditions, the circadian bioluminescent glow rhythm in populations (10(5) cells) of Gonyaulax polyedra is accurate to within 2 min/day. On successive days following the transfer to constant conditions, however, the glow exhibits a progressively broader waveform, implying that individual clocks in the population are drifting out of synchrony. Analysis of the glow waveform suggests that the standard deviation in circadian period among individual clocks is about 18 min and that the period of a given clock varies by less than this from one day to the next. PMID:6170441

Njus, D; Gooch, V D; Hastings, J W

1981-09-01

245

Transmission delays in hardware clock synchronization  

NASA Technical Reports Server (NTRS)

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

Shin, Kang G.; Ramanathan, P.

1988-01-01

246

On the possibility and impossibility of achieving clock synchronization  

Microsoft Academic Search

It is known that clock synchronization can be achieved in the presence of faulty clocks numbering more than one-third of the total number of participating clocks provided that some authentication technique is used. Without authentication the number of faults that can be tolerated has been an open question. Here we show that if we restrict logical clocks to running within

Danny Dolev; Joseph Y. Halpern; H. Raymond Strong

1984-01-01

247

Moving clocks, reference frames and the twin paradox  

Microsoft Academic Search

It is the act of moving a clock out of one inertial frame of reference (IFR) and into another IFR which causes the clock to slow. But what of identical clocks constructed and calibrated in different IFRs? This paper takes a look at such a scenario, demonstrating that two such clocks would tick synchronously and concludes with a new look

C. Renshaw

1996-01-01

248

A Novel Low-Power Clock Skew Compensation Circuit  

Microsoft Academic Search

The clock is a periodic synchronization signal used as a time reference for data transfers in synchronous digital systems. However, the clock skew constrains the improvement of clock frequencies and affects the reliability of systems. One skew reduction technique is the use of clock deskew circuits. They can be classified into two methods: delay-locked loop (DLL) deskewing and synchronous mirror

Rong Ji; Liang Chen; Gang Luo; Xianjun Zeng; Junfeng Zhang; Yingjie Feng

2008-01-01

249

Star Forming Regions and the IMF Along the Hubble Sequence  

NASA Astrophysics Data System (ADS)

This thesis examines the properties of star forming regions in galaxies across the Hubble sequence. It focuses on the stellar populations of giant extragalactic H scII regions and OB associations, addressing in particular the question of Initial Mass Function (IMF) variations with metallicity and/or galaxy morphology. This work is composed of three main sections: (a) 3650-10,000 A spectroscopy of nearly 100 H scII regions in 20 spiral galaxies (Sa through Sm). Two indicators of the ionizing cluster effective temperature (T*) are analyzed: the intensity of the He I ?5876 line, and the 'radiation softness' parameter ?=(O+/O++)/(S+/S++). The interpretation of the data relies on CLOUDY photoionization models. A positive T* gradient of 7000-8000 K is found between 2 Zsolar and 0.2 Zsolar. The diagnostic diagrams and the T* - metallicity relation are consistent with an upper mass limit of the IMF of ~100 Msolar and an age of ~1 Myr, irrespective of chemical abundance or Hubble type. (b) An investigation of extragalactic OB associations, based on Hubble Space Telescope images. The size distribution of the associations (found with an automated search algorithm) is similar in all galaxies examined, with a mean size around 80 pc. An indication is found that the average number of bright blue stars depends on the parent galaxy Hubble type. The upper stellar V luminosity function is comparable among galaxies, with slope dlog N/dMV=0.61±0.03. A few star cluster candidates are identified. (c) UBVR and H? photometry of 266 H scII regions in 10 spiral galaxies (Sa through Sd). The H? equivalent width is independent of Hubble type. The continuum and H? luminosity functions show similar trends, namely a steeper slope and a smaller characteristic luminosity for early-type galaxies. These results lead to the conclusion that changes in the properties of H scII regions and associations along the Hubble sequence are most likely due to variations in the number of stars per star forming region and in the number of regions per unit area, rather than the mass function.

Bresolin, Fabio

250

Transactivation mechanisms of mouse clock transcription factors, mClock and mArnt3  

Microsoft Academic Search

Background: The Arnt3 (also termed as BMAL1 or MOP3)\\/Clock heterodimer is a positive regulator of circadian rhythm and activates the transcription of target genes such as per1 and vasopressin. Results: We investigated the transcriptional mechan- ism of mArnt3\\/mClock heterodimer. While mClock did not possess any distinct activation domain, mArnt3 contained a transcriptional activation domain at the most C-terminal end, the

Sho Takahata; Takahiro Ozaki; Junsei Mimura; Yasuo Kikuchi; Kazuhiro Sogawa; Yoshiaki Fujii-Kuriyama

2000-01-01

251

Circadian and Circalunar Clock Interactions in a Marine Annelid  

PubMed Central

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

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

2013-01-01

252

Circadian and circalunar clock interactions in a marine annelid.  

PubMed

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

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

2013-10-17

253

Comparison of LFM Simulation Results with Observation for Strongly Northward IMF  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

254

Conjunction observations of global magnetosphere respond to solar wind and IMF variations during an intense storm  

NASA Astrophysics Data System (ADS)

Magnetic fluctuations of the globe magnetosphere driven by the sharp increase of the solar wind dynamic pressure or IMF significant change observed by Cluster, THEMIS, Geotail and ground stations are investigated. Comparing with characteristics of those magnetic disturbances observed around the dayside low-latitude magnetopause, night-side high-latitude magnetopause and in the mid-tail during an intense storm, it is found that those fluctuations responds to the solar wind and IMF variations observed at dayside and night-side are different. The magnetic fluctuations around dayside magnetopause have both respond to the changes of the IMF and Solar wind dynamic pressure. Whereas magnetic fluctuations around night-side high-latitude magnetopause, mid-tail and low latitude station have significant respond to the solar wind dynamic respond but almost no respond to the IMF variations. Our results present a clear route of energy transfer from solar wind to the magnetosphere during storms.

Duan, Su-ping; Liu, Zhenxing; He, Zhaohai; Dandouras, Iannis; Reme, Henri; Angelopoulos, Vassilis

2014-05-01

255

Evidence of high-latitude reconnecting during northward IMF: Hawkeye observations  

SciTech Connect

Reconnection is accepted as an important process for driving the solar wind/magnetospheric interaction although it is not fully understood. In particular, reconnection for northward interplanetary magnetic field (IMF) at high-latitudes tailward of the cusp, has received little attention in comparison with equatorial reconnection for southward IMF. Using Hawkeye data the authors present the first direct observations of reconnection at the high-latitude magnetopause (75{degrees}) during northward IMF in the form of sunward flowing protons. This flow is nearly field aligned, approximately Alfvenic, and roughly obeys tangential momentum balance. The magnetic field shear is large at the magnetopause and there is a non-zero B{sub N} component suggesting the existence of a rotational discontinuity and reconnection. The Hawkeye observations support several recent simulations at least qualitatively in terms of flow directions expected for high-latitude reconnection during northward IMF. 16 refs., 3 figs.

Kessel, R.L.; Chen, S.H.; Green, J.L. [NASA Goddard Space Flight Center, Greenbelt, MD (United States)] [and others] [NASA Goddard Space Flight Center, Greenbelt, MD (United States); and others

1996-03-01

256

Global Financial Crisis: The Role of the International Monetary Fund (IMF). (Updated February 4, 2009).  

National Technical Information Service (NTIS)

This report discusses two potential roles the International Monetary Fund (IMF) may have in helping to resolve the current global financial crisis: (1) immediate crisis control through balance of payments lending to emerging market and less-developed coun...

M. A. Weiss

2009-01-01

257

Global Financial Crisis: The Role of the International Monetary Fund (IMF).  

National Technical Information Service (NTIS)

This report discusses two potential roles the International Monetary Fund (IMF) may have in helping to resolve the current global financial crisis: (1) immediate crisis control through balance of payments lending to emerging market and less-developed coun...

M. A. Weiss

2008-01-01

258

IMF: interconnect-driven multilevel floorplanning for large-scale building-module designs  

Microsoft Academic Search

We present in this paper a new interconnect-driven multi- level floorplanning, called IMF, to handle large-scale building-module designs. Unlike the traditional multilevel framework that adopts the \\

Tung-chieh Chen; Yao-wen Chang; Shyh-chang Lin

2005-01-01

259

Quality variation of GPS satellite clocks on-orbit using IGS clock products  

NASA Astrophysics Data System (ADS)

Over 60% clocks on board of the GPS satellites are working longer than their designed life. Therefore realizing their stabilities in a long time scales is essential to GPS navigation and positioning plus IGS time scale maintaining. IGS clock products from 2001 to 2010 are used to analyze the GPS satellite clock qualities such as frequency stabilities and clock noise level. We find out that for the clocks of Block IIA satellites the frequency stabilities and clock noise are 10 times worse than that of the Block IIR and IIR-M satellites. Moreover, the linear relationships between frequency stabilities and clock residuals have been deduced with an accuracy of better than 0.02 ns. Specially, it is noticed that the clock of the PRN27 is instable and the relationship between the frequency stability and residuals is at least a quadratic curve. Therefore, we suggested that GPS satellite clocks should be weighted by their quality levels in application, and the observations of the Block IIA should not be used for real-time positioning which required precision better than one meter.

Huang, G.; Zhang, Q.; Li, H.; Fu, W.

2013-03-01

260

The effects of northward IMF on the structure of the magnetosphere  

NASA Astrophysics Data System (ADS)

Effects of northward IMF on the structure of the magnetosphere were studied by using a global MHD model. The model suggests a mechanism for creating high latitude sunward convection. The mechanism is not due to magnetic merging over the cusp region. Instead, the model indicates that the northward IMF field lines, which move around the magnetosphere, tend to squeeze the magnetotail at the boundary. This leads to formation of vortex flows in the tail and the observed sunward convection in the polar cap.

Wu, C. C.

1985-12-01

261

Independent Actor or Agent? An Empirical Analysis of the impact of US interests on IMF Conditions  

Microsoft Academic Search

In this paper we analyze whether IMF conditionality is exclusively designed in line with observable economic indicators or, alternatively, whether it is partly driven by its major shareholder, the United States. A panel data analysis of 206 letters of intent from 38 countries from 4\\/1997-2\\/2003 reveals that the number of conditions on an IMF loan depends on a borrowing country’s

Axel Dreher; Nathan Jensen

2003-01-01

262

The effects of northward IMF on the structure of the magnetosphere  

NASA Technical Reports Server (NTRS)

Effects of northward IMF on the structure of the magnetosphere were studied by using a global MHD model. The model suggests a mechanism for creating high latitude sunward convection. The mechanism is not due to magnetic merging over the cusp region. Instead, the model indicates that the northward IMF field lines, which move around the magnetosphere, tend to squeeze the magnetotail at the boundary. This leads to formation of vortex flows in the tail and the observed sunward convection in the polar cap.

Wu, C. C.

1985-01-01

263

The influence of IMF on the lower ionosphere plasma in high and middle latitudes  

NASA Technical Reports Server (NTRS)

As shown by ground-based absorption measurements, the lower ionospheric plasma is markedly controlled by the structure of the IMF. Whereas in high auroral and subauroral latitudes this effect is very pronounced, in midlatitudes its influence is less important. A comparison of these results with satellite data of the IMF and the solar wind speed confirms the important role of these components, not only during special events but also for the normal state of the ionospheric D region plasma.

Bremer, J.

1989-01-01

264

Turkey and the IMF: A case study in the political economy of policy implementation  

Microsoft Academic Search

Research into IMF program implementation has usually taken the form of large sample regression analyses. A more detailed explanation\\u000a is offered in this paper through a case study of program implementation in Turkey between 1999 and 2004. Our research is based\\u000a on a series of in-depth interviews with policy makers, program negotiators, bureaucrats, interest groups and IMF personnel.\\u000a Our results

Ozlem Arpac; Graham Bird

2009-01-01

265

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...

266

Spacetime and Quantum Propagation From Digital Clocks  

NASA Astrophysics Data System (ADS)

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.

Ord, Garnet. N.

2013-09-01

267

Compact Microwave Cavity for Hydrogen Atomic Clock.  

National Technical Information Service (NTIS)

A summary is presented that introduces the compact microwave cavity used in the hydrogen atomic clock. Special emphasis is placed on derivation of theoretical calculating equations of main parameters of the microwave cavity. A brief description is given o...

D. Zhang Y. Zhang Y. Fu Y. Zhang

1992-01-01

268

Circadian clock, cancer and lipid metabolism  

Microsoft Academic Search

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

Norio Ishida

2007-01-01

269

Mission-Clock-Display Software Tool  

NASA Technical Reports Server (NTRS)

Displays including images of alarm clocks illustrate temporal statuses of multiple events. MCLK is customizable clock-display computer program with Motif user interface. Used to keep track of such multiple "milestone" events as those occurring during countdowns in spacecraft launches, and alerts user when event time reached. In addition, program displays time from several time zones. Real time measured in Coordinated Universal Time. Written in C language.

Aguilera, Christine; Murphy, Susan C.; Miller, Kevin J.; Guerrero, Ana Maria P.

1993-01-01

270

Clock schedule verification under process variations  

Microsoft Academic Search

With aggressive scaling down of feature sizes in VLSI fab- rication, process variations have become a critical issue in designs, especially for high-performance ICs. Usually having level-sensitive latches for their speed, high-performance IC designs need to verify the clock schedules. With process vari- ations, the verification needs to compute the probability of correct clocking. Because of complex statistical correlations, traditional

Ruiming Chen; Hai Zhou

2004-01-01

271

Tests of Lorentz invariance with atomic clocks  

NASA Astrophysics Data System (ADS)

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.

Mohan, Lakshmi

272

Clock gene variation in Tachycineta swallows.  

PubMed

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

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

2012-01-01

273

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

NASA Astrophysics Data System (ADS)

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.

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

2014-07-01

274

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

275

The Neurospora circadian clock: simple or complex?  

PubMed Central

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

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

2001-01-01

276

The Circadian Clock Modulates Renal Sodium Handling  

PubMed Central

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

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

2012-01-01

277

Towards Self-Clocked Gated OCDMA Receiver  

NASA Astrophysics Data System (ADS)

A novel incoherent OCDMA receiver with incorporated all-optical clock recovery for self-synchronization of a time gate for the multi access interferences (MAI) suppression and minimizing the effect of data time jitter in incoherent OCDMA system was successfully developed and demonstrated. The solution was implemented and tested in a multiuser environment in an out of the laboratory OCDMA testbed with two-dimensional wavelength-hopping time-spreading coding scheme and OC-48 (2.5 Gbp/s) data rate. The self-clocked all-optical time gate uses SOA-based fibre ring laser optical clock, recovered all-optically from the received OCDMA traffic to control its switching window for cleaning the autocorrelation peak from the surrounding MAI. A wider eye opening was achieved when the all-optically recovered clock from received data was used for synchronization if compared to a static approach with the RF clock being generated by a RF synthesizer. Clean eye diagram was also achieved when recovered clock is used to drive time gating.

Idris, S.; Osadola, T.; Glesk, I.

2013-02-01

278

Hydrogen Maser Clock (HMC) Experiment  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

279

Drawing Clocks and Driving Cars  

PubMed Central

OBJECTIVE The purpose of the study was to determine whether a new method of scoring the Clock Drawing Test (CDT) is a reliable and valid method for identifying older adults with declining driving competence. DESIGN Prospective cohort study. SETTING An outpatient driving evaluation clinic. PARTICIPANTS One hundred nineteen community-dwelling, active drivers with a valid driver's license, aged 60 and older referred for driving evaluation. MAIN OUTCOME MEASURES The CDT and a driving test using a STISIM Drive simulator. RESULTS The CDT showed a high level of accuracy in predicting driving simulation outcome (area under the receiver-operator curve, 0.90; 95% confidence interval, 0.82 to 0.95). CDT scoring scales were comparable and all correlations between CDT scores and driving performance were negative, implying that as the CDT score decreases, the number of errors increases. Interrater reliability of CDT scores was 0.95. Subjects scoring less than 5 out of 7 points on the CDT made significantly more driving errors, hazardous and in total (P <.001). CONCLUSIONS The CDT can help establish problems with executive function and indicate the need for a formal driving evaluation. Our CDT scoring scale is a reliable, valid, and time-effective screening tool for identifying elderly drivers in need of further evaluation.

Freund, Barbara; Gravenstein, Stefan; Ferris, Rebecca; Burke, Bonnie L; Shaheen, Elias

2005-01-01

280

On the relationships between double-onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event  

NASA Astrophysics Data System (ADS)

The relationships between double-onset substorm, pseudobreakup, and IMF variation were investigated with magnetic, auroral, and particle observations from space to the ground during 0200-0600 UT on 4 September 1999. There were five consecutive bursts of Pi2 pulsations on the ground during the time of interest. The onset time of ground Pi2s maps to the same variation sequence in the IMF structure seen propagating to the Earth in multiple satellite observations in the upstream region. The comparison of auroral and energetic particle data with IMF observations shows that a sequence of two double-onset substorms intervened by a pseudobreakup appears in two distinct cycles of southward IMF followed by a northward interval. For the first substorm, the first onset begins when the By magnitude declines after the IMF turns southward for about 90 min, and the second onset occurs after northward turning of the IMF accompanied by an increasing By magnitude. The pseudobreakup appears while the IMF turns southward and the By magnitude slightly decreases. For the second substorm, the first onset commences while the IMF remains southward with a steady By magnitude, and the second onset occurs after the IMF becomes strongly northward and the By magnitude decreases instead. These observations can be explained with the two-neutral-point model. The first onset occurs when the IMF turns southward. Reconnection at the near-Earth neutral point first begins on closed field lines within the plasma sheet, and the second onset occurs when the IMF turns northward and reconnection at the distant neutral point ceases and reconnection at the near-Earth neutral point may reach the open flux of the tail lobes. In addition, a decrease in the By magnitude may help reduce magnetotail convection and release all the built-up flux to allow the onset to commence after northward turning of the IMF. If the IMF remains southward, the reduction of magnetotail convection due to a decreasing By would lead to a pseudobreakup instead. In contrast, an increasing By magnitude would increase magnetotail convection and weaken magnetospheric substorm after the IMF turns northward. Consequently, for the occurrence of double-onset substorms and pseudobreakups, not only the first onset begins spontaneously during steady southward IMF and the second onset appears after northward turning of the IMF but the By change also affects magnetotail convection which may evoke (or abate) the substorm-related activation while the IMF turns southward (or northward).

Cheng, Ching-Chang; Russell, Christopher T.; Reeves, Geoff D.; Connors, Martin; Moldwin, Mark B.

2005-07-01

281

Evolutionary Links Between Circadian Clocks and Photoperiodic Diapause in Insects  

PubMed Central

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

Meuti, Megan E.; Denlinger, David L.

2013-01-01

282

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

283

A contribution to ULF activity in the Pc 3-4 range correlated with IMF radial orientation. [geomagnetic micropulsations  

NASA Technical Reports Server (NTRS)

The paper describes an experiment to determine whether the radial orientation of the interplanetary magnetic field (IMF) is associated with ULF activity in the Pc 3-4 range. Data are obtained from base levels, undisturbed intervals, IMF and disturbance selection, and trigonometric correlation. The results obtained are discussed, noting particularly that for low Kp, the probability of enhanced amplitude noise rises as IMF orientation with respect to the nominal solar wind flow decreases in both Pc 3 and Pc 4 channels.

Greenstadt, E. W.; Olson, J. V.

1977-01-01

284

A high-speed photonic clock and carrier regenerator  

NASA Technical Reports Server (NTRS)

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

Yao, X. S.; Lutes, G.

1995-01-01

285

Body weight, metabolism and clock genes  

PubMed Central

Biological rhythms are present in the lives of almost all organisms ranging from plants to more evolved creatures. These oscillations allow the anticipation of many physiological and behavioral mechanisms thus enabling coordination of rhythms in a timely manner, adaption to environmental changes and more efficient organization of the cellular processes responsible for survival of both the individual and the species. Many components of energy homeostasis exhibit circadian rhythms, which are regulated by central (suprachiasmatic nucleus) and peripheral (located in other tissues) circadian clocks. Adipocyte plays an important role in the regulation of energy homeostasis, the signaling of satiety and cellular differentiation and proliferation. Also, the adipocyte circadian clock is probably involved in the control of many of these functions. Thus, circadian clocks are implicated in the control of energy balance, feeding behavior and consequently in the regulation of body weight. In this regard, alterations in clock genes and rhythms can interfere with the complex mechanism of metabolic and hormonal anticipation, contributing to multifactorial diseases such as obesity and diabetes. The aim of this review was to define circadian clocks by describing their functioning and role in the whole body and in adipocyte metabolism, as well as their influence on body weight control and the development of obesity.

2010-01-01

286

Nuclear receptors rock around the clock.  

PubMed

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

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

2014-05-01

287

Generalized clocks in timeless canonical formalism  

NASA Astrophysics Data System (ADS)

Hamiltonian dynamics is recast in a timeless formalism in which parameter time ? is derived from the generalized coordinates, the Hamiltonian invariance on trajectories, and the Maupertuis principle. In order to define a time variable T in macroscopic systems, the cyclicity in the phase space replaces the self consistent assumption of time periodicity generally adopted for real clocks. Generalized clocks are defined in physical systems of sufficient complexity. Under suitable assumptions, physical systems can be separated in a subsystem to be dynamically described, and another cyclic subsystem which has the role of generalized clock. The latter provides a discrete approximation of the parameter time, called metric time. The stability prescription of generalized clocks guarantees that dynamics is expressed by the same equations of motion parametrized by the parameter time, in terms of metric time at the desired approximation. The timeless Hamiltonian framework, together with the definition of generalized clock, provide a ground to account the fundamental timelessness of nature, and the experimental evidence of time evolution in macroscopic systems experienced by the observers.

Prati, Enrico

2011-07-01

288

Clock synchronization on the RAX spacecraft  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

289

Constraints on the low-mass IMF in young super-star clusters in starburst galaxies  

NASA Astrophysics Data System (ADS)

As evidence for variations in the initial mass function (IMF) in nearby star forming regions remains elusive we are forced to expand our search to more extreme regions of star formation. Starburst galaxies, which contain massive young clusters have in the past been reported to have IMFs different than that characterizing the field star IMF. In this thesis we use high signal-to-noise near-infrared spectra to place constraints on the shape of the IMF in extreme regions of extragalactic star formation and also try to understand the star formation history in these regions. Through high signal-to-noise near-infrared spectra it is possible to directly detect low-mass PMS stars in unresolved young super-star clusters, using absorption features that trace cool stars. Combining Starburst99 and available PMS tracks it is then possible to constrain the IMF in young super-star clusters using a combination of absorption lines each tracing different ranges of stellar masses and comparing observed spectra to models. Our technique can provide a direct test of the universality of the IMF compared to the Milky Way. We have obtained high signal-to-noise H- and K-band spectra of two young super-star clusters in the starburst galaxies NGC 4039/39 and NGC 253 in order to constrain the low-mass IMF and star formation history in the clusters. The cluster in NGC 4038/39 shows signs of youth such as thermal radio emission and strong hydrogen emission lines as well as late-type absorption lines indicative of cool stars. The strength and ratio of these absorption lines cannot be reproduced through either late-type pre-main sequence stars or red supergiants alone. We interpret the spectrum as a superposition of two star clusters of different ages over the physical region of 90 pc our spectrum represents. One cluster is young (? 3 Myr) and is responsible for part of the late-type absorption features, which are due to PMS stars in the cluster, and the hydrogen emission lines. The second cluster is older (6 Myr - 18 Myr) and is needed to reproduce the overall depth of the late-type absorption features in the spectrum. While the superposition of clusters does not allow us to place stringent constraints on the IMF there is no evidence of a low-mass cutoff in the cluster and the IMF is consistent with a Chabrier and Kroupa IMF typical of the field. The cluster in NGC 253 shows the same signs of youth as the cluster in NGC 4038/39 and sits in front of a background population of older stars. The background population has an age of ? 12 Myr and thus contains red supergiants. After carefully subtracting this background we model the spectrum of the young cluster. We find that its IMF is consistent with a Chabrier and Kroupa IMF with a best-fit power-law slope of 1.0 in linear units. Slopes of 0.0 - 1.5 are also formally consistent with the cluster spectrum. We conclude that there is no strong evidence for an unusual IMF or a lack of low-mass stars (? 1 M? ) in either of these galaxies.

Greissl, Julia Jennifer

2010-12-01

290

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

NASA Astrophysics Data System (ADS)

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.

Lei, Yaguo; Zuo, Ming J.

2009-12-01

291

High-latitude convection on open and closed field lines for large IMF B(y)  

NASA Technical Reports Server (NTRS)

S3-3 electric field observations for August 23, 1976, show a single convection cell engulfing the northern polar cap. The flow direction is that for a positive IMF B(y) component. The particle data indicate that nearly half the duskside sunward flow occurs on closed field lines whereas the dawnside flow is entirely on open field lines. This is interpreted in terms of an IMF B(y)-induced deformation in the polar cap boundary, where the deformation moves with the convective flow. Thus, convection streamlines cross the deformed polar cap boundary, but no flow crosses the boundary because it is carried by the flow. Since southern hemisphere convection is expected to occur with the opposite sense of rotation, closed field lines that will be forced to tilt azimuthally are predicted. On the nightside the tilt produces a y component of the magnetic field in the same direction as the IMF for either sign of IMF B(y). This interpretation is consistent with observations of a greater y component in the plasma sheet than the tail lobes, which are difficult to understand in terms of the common explanation of IMF penetration. Alternatives to this interpretation are also discussed.

Moses, J. J.; Crooker, N. U.; Gorney, D. J.; Siscoe, G. L.

1985-01-01

292

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

293

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

294

Star high rate link model: Clock regeneration  

NASA Astrophysics Data System (ADS)

The receiving part of this module, used in spacecraft transmission through a relay satellite, requires a very accurate clock reference in the extraction of data from a QPSK modulated signal at a bit rate of 100 MHz. The results achieved to improve this accuracy working on the nonlinear treatment and the narrow band filtering are described. The chosen clock detector is based on a delay line and a multiplier. The multiplication is assured in ECL logic by an exclusive or. The filter is based on a narrow band phase loop. It is shown that the performance degradation introduced by the clock regenerator is 0.2 dB if the static phase error is kept within 5 deg.

Soldermann, J. P.; Grondin, M.

1984-11-01

295

Predictions for laser-cooled Rb clocks  

NASA Astrophysics Data System (ADS)

Using information from a recent 85Rb two-color photoassociation experiment, we evaluate the merits of fountain clocks based on 87Rb and 85Rb isotopes as alternatives to 133Cs and find that they offer significant advantages. In the case of 87Rb the collisionally induced fractional frequency shift is 15 times smaller than for 133Cs. This small shift is associated with a small difference in the triplet and singlet scattering lengths for 87Rb. For 85Rb, the shift produced by the two mf=0 clock states may have opposite signs allowing the shift to be eliminated by controlling the relative populations of these states. We also present collision quantities relevant to atomic fountain clocks containing multiply launched groups of atoms, and for evaporative cooling of 85Rb atoms.

Kokkelmans, S. J. J. M. F.; Verhaar, B. J.; Gibble, K.; Heinzen, D. J.

1997-12-01

296

Sharp World Clock 4.55  

NSDL National Science Digital Library

What time is it in Nairobi? Or Iowa City? And who can forget St. Petersburg? All of these pesky timekeeping problems become a thing of the past with the help of the Sharp World Clock application. The program allows users to set up any number of digital or analog clocks in a row or grid, and visitors can also customize the clocks to show different national flags and backgrounds. The program also gives users the ability to show sunrise and sunset times, lunar phases, and day or night indicators. This version is compatible with computers running Windows 98 and newer. The program offers a free 15-day trial version, and then visitors can elect to purchase the program.

Wallroth, Johannes

297

Which came first, spacetime or clocks?  

NASA Astrophysics Data System (ADS)

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

Ord, G. N.

2014-04-01

298

O-GlcNAc signaling entrains the circadian clock by inhibiting BMAL1/CLOCK ubiquitination.  

PubMed

Circadian clocks are coupled to metabolic oscillations through nutrient-sensing pathways. Nutrient flux into the hexosamine biosynthesis pathway triggers covalent protein modification by O-linked ?-D-N-acetylglucosamine (O-GlcNAc). Here we show that the hexosamine/O-GlcNAc pathway modulates peripheral clock oscillation. O-GlcNAc transferase (OGT) promotes expression of BMAL1/CLOCK target genes and affects circadian oscillation of clock genes in vitro and in vivo. Both BMAL1 and CLOCK are rhythmically O-GlcNAcylated, and this protein modification stabilizes BMAL1 and CLOCK by inhibiting their ubiquitination. In vivo analysis of genetically modified mice with perturbed hepatic OGT expression shows aberrant circadian rhythms of glucose homeostasis. These results establish the counteraction between O-GlcNAcylation and ubiquitination as a key mechanism that regulates the circadian clock and suggest a crucial role for O-GlcNAc signaling in transducing nutritional signals to the core circadian timing machinery. PMID:23395176

Li, Min-Dian; Ruan, Hai-Bin; Hughes, Michael E; Lee, Jeong-Sang; Singh, Jay P; Jones, Steven P; Nitabach, Michael N; Yang, Xiaoyong

2013-02-01

299

Sample-Clock Phase-Control Feedback  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

300

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

PubMed Central

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

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

2014-01-01

301

Tick Tock: New Clues about Biological Clocks and Health  

MedlinePLUS

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

302

Metabolism: Tick, tock, a beta-cell clock  

Microsoft Academic Search

The daily light-dark cycle affects many aspects of normal physiology through the activity of circadian clocks. It emerges that the pancreas has a clock of its own, which responds to energy fluctuations.

Katja A. Lamia; Ronald M. Evans

2010-01-01

303

Using GLONASS signal for clock synchronization  

NASA Technical Reports Server (NTRS)

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

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

1994-01-01

304

The Fermilab D0 Master Clock System  

SciTech Connect

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

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

1991-11-01

305

Real clocks and the Zeno effect  

SciTech Connect

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

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

2003-08-01

306

Poleward expansion of the westward electrojet depending on the solar wind and IMF parameters  

NASA Astrophysics Data System (ADS)

The effect of the interplanetary parameters on the latitudinal position of the substorm westward electrojet is studied in the work. The data from the IMAGE chain of magnetic stations and POLAR and WIND satellites for the period close to the solar activity minimum (1995-1996) and for the period of the solar activity maximum (2000) have been used for this purpose. It has been indicated that the electrojet poleward edge reaches, on average, higher latitudes at a higher solar wind velocity and at a larger ( B s ) IMF southward component. It has been indicated that the average latitude of the westward electrojet center increases with increasing solar wind velocity and decreases with increasing IMF southward component, as a result of which the electrojet center is, specifically, not observed at high geomagnetic latitudes at large values of the IMF southward component.

Despirak, I. V.; Lubchich, A. A.; Biernat, H. K.; Yahnin, A. G.

2008-06-01

307

Resveratrol regulates circadian clock genes in Rat-1 fibroblast cells.  

PubMed

Circadian clocks, especially peripheral clocks, can be strongly entrained by daily feedings, but few papers have reported the effects of food components on circadian rhythm. The effects of resveratrol, a natural polyphenol, on circadian clocks of Rat-1 cells were analyzed. A dose of 100 muM resveratrol, which did not show cytotoxicity, regulated the expression of clock genes Per1, Per2, and Bmal1. PMID:18997419

Oike, Hideaki; Kobori, Masuko

2008-11-01

308

The Role of Circadian Clocks in Metabolic Disease  

PubMed Central

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

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

2012-01-01

309

Microsecond Clock Comparison by Means of TV Synchronizing Pulses  

Microsoft Academic Search

A new method for precise clocks comparison is described making use of the short rise time of the synchronizing pulse of a current TV picture signal. It is shown that by measuring simultaneously the time interval between one and the same selected TV frame synchropulse and the pulses derived from the respective clocks, these clocks may be compared with microsecond

Jiri Tolman; Vladimir Ptacek; Antonin Soucek; Rudolf Stecher

1967-01-01

310

Time zones: a comparative genetics of circadian clocks  

Microsoft Academic Search

The circadian clock is a widespread cellular mechanism that underlies diverse rhythmic functions in organisms from bacteria and fungi, to plants and animals. Intense genetic analysis during recent years has uncovered many of the components and molecular mechanisms comprising these clocks. Although autoregulatory genetic networks are a consistent feature in the design of all clocks, the weight of evidence favours

Michael W. Young; Steve A. Kay

2001-01-01

311

A new fault-tolerant algorithm for clock synchronization  

Microsoft Academic Search

We describe a new fault-tolerant algorithm for solving a variant of Lamport's clock synchronization problem. The algorithm is designed for a system of distributed processes that communicate by sending messages. Each process has its own read-only physical clock whose drift rate from real time is very small. By adding a value to its physical clock time, the process obtains its

Jennifer Lundelius; Nancy A. Lynch

1984-01-01

312

Clock Synchronization: Open Problems in Theory and Practice  

Microsoft Academic Search

Clock synchronization is one of the most basic building blocks for many applications in computer science and engineering. The purpose of clock synchronization is to provide the constituent parts of a distributed system with a common notion of time. While the problem of synchronizing clocks in distributed systems has already received con- siderable attention from researchers and practitioners alike, we

Christoph Lenzen; Thomas Locher; Philipp Sommer; Roger Wattenhofer

2010-01-01

313

Knock, knock to reset the clock: mechanosensation and circadian rhythms.  

PubMed

Circadian clocks, which underlie the daily rhythms in virtually all organisms, are entrained by diurnal changes in light, temperature, nutrients, and even sound. Simoni et al. (2014) demonstrate that diurnal variation in mechanical vibrations can reset circadian clock phase, providing a potential mechanism for integrating diverse clock-entraining stimuli. PMID:24807220

van Alphen, Bart; Allada, Ravi

2014-05-01

314

Tuning the Mammalian Circadian Clock: Robust Synergy of Two Loops  

Microsoft Academic Search

The circadian clock is accountable for the regulation of internal rhythms in most living organisms. It allows the anticipation of environmental changes during the day and a better adaptation of physiological processes. In mammals the main clock is located in the suprachiasmatic nucleus (SCN) and synchronizes secondary clocks throughout the body. Its molecular constituents form an intracellular network which dictates

Angela Relógio; Pal O. Westermark; Thomas Wallach; Katja Schellenberg; Achim Kramer; Hanspeter Herzel

2011-01-01

315

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

NASA Astrophysics Data System (ADS)

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

Hoilijoki, S.; Palmroth, M.

2013-12-01

316

Biochemical basis for the biological clock  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

317

Developmental Alcohol and Circadian Clock Function  

Microsoft Academic Search

Studies in rats found that alcohol exposure during the early postnatal period, particularly during the brain-growth-spurt period, can result in cell loss in various brain regions and persistent behavioral impairments. Some investigators have speculated that the body's internal clock, which is located in the suprachiasmatic nuclei (SCN) in the brain, may also be affected by developmental alcohol exposure. For example,

David J. Earnest; Wei-Jung A. Chen; James R. West

318

Understanding the somitogenesis clock: what's missing?  

PubMed

The segmentation of vertebrate embryos depends on a complex genetic network that generates highly dynamic gene expression. Many of the elements of the network have been identified, but their interaction and their influence on segmentation remain poorly understood. A few mathematical models have been proposed to explain the dynamics of subsets of the network, but the mechanistic bases remain controversial. This review focuses on outstanding problems with the generation of somitogenesis clock oscillations, and the ways they could regulate segmentation. Proposals that oscillations are generated by a negative feedback loop formed by Lunatic fringe and Notch signaling are weighed against a model based on positive feedback, and the experimental basis for models of simple negative feedback involving Her/Hes genes or Wnt targets is evaluated. Differences are then made explicit between the many 'clock and wavefront' model variants that have been proposed to explain how the clock regulates segmentation. An understanding of the somitogenesis clock will require addressing experimentally the many questions that arise from the study of simple models. PMID:17643270

Cinquin, Olivier

2007-08-01

319

Clocked molecular quantum-dot cellular automata  

Microsoft Academic Search

Quantum-dot cellular automata (QCA) is an approach to computing that eliminates the need for current switches by representing binary information as the configuration of charge among quantum dots. For molecular QCA, redox sites of molecules serve as the quantum dots. The Coulomb interaction between neighboring molecules provides device-device coupling. By introducing clocked control of the QCA cell, power gain, reduced

Craig S. Lent; Beth Isaksen

2003-01-01

320

On the Sun, Earth, and Clocks.  

ERIC Educational Resources Information Center

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

Easton, D.

1985-01-01

321

Tick Tock, a Vitamin C Clock.  

ERIC Educational Resources Information Center

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

Wright, Stephen W.

2002-01-01

322

Analysis of Atom-Interferometer Clocks.  

National Technical Information Service (NTIS)

We analyze the nature and performance of clocks formed by stabilizing an oscillator to the phase difference between two paths of an atom interferometer. The phase evolution has been modeled as being driven by the proper-time difference between the two pat...

C. R. Ekstrom S. Peil

2014-01-01

323

Building a Capillary Action Water Clock.  

ERIC Educational Resources Information Center

Describes a lesson plan for teachers of grades 2-8 to build a capillary action water clock. Includes a list of objectives, a list of skills/concepts addressed, a rationale for inclusion in the curriculum, and an illustrated lesson outline. (Author/MM)

Tracy, Dyanne M.

2002-01-01

324

Realisation of a compact methane optical clock  

SciTech Connect

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

Gubin, M A; Kireev, A N; Konyashchenko, A V; Kryukov, P G; Tausenev, A V; Tyurikov, D A; Shelkovnikov, A S [P. N. Lebedev Physics Institute, Russian Academy of Sciences, Moscow (Russian Federation)

2008-07-31

325

Oscillatory Mechanisms Underlying the Murine Circadian Clock  

NSDL National Science Digital Library

This animation depicts a schematic of the murine circadian clock mechanism in a single, pacemaking neuron in the suprachiasmatic nucleus (SCN) of the hypothalamus, where the master pacemaker is located. Circadian clocks allow organisms to display behaviors and processes with a 24-hour rhythm even in the absence of light input. The basic molecular mechanism consists of two intertwined transcription-translation negative feedback loops. One loop--the "positive loop"--controls the rhythmic expression of a positive transcription factor gene, Bmal1 (also called Mop3). The second loop--the "negative loop"--controls the transcription of genes in the Period and Cryptochrome families, which encode repressor proteins. The loops are intertwined because the proteins PERIOD and CRYPTOCHROME directly repress transcription mediated by the transcription factors CLOCK and BMAL1, whereas the CLOCK:BMAL1 heterodimer drives transcription of the Period and Cryptochrome genes, as well as that of Rev-erb-alpha, which represses Bmal1 expression. Other proteins, such as casein kinase I ε (CKIε) play essential modulatory roles in mammalian circadian timekeeping.

Russell N. Van Gelder (Washington University Medical School;Department of Ophthalmology and Visual Sciences, Department of Molecular Biology and Pharmacology REV); Erik D. Herzog (Washington University;Department of Biology REV)

2003-11-18

326

The mammalian retina as a clock  

NASA Technical Reports Server (NTRS)

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

Tosini, Gianluca; Fukuhara, Chiaki

2002-01-01

327

Circadian Clock Proteins in Prokaryotes: Hidden Rhythms?  

PubMed Central

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

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

2010-01-01

328

Clock Synchronization for Multihop Wireless Sensor Networks  

ERIC Educational Resources Information Center

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

Solis Robles, Roberto

2009-01-01

329

The response of the dayside equatorial electrojet to step-like changes of IMF BZ  

NASA Astrophysics Data System (ADS)

The equatorial electrojet (EEJ) is driven by zonal electric fields, which are known to be well correlated with the interplanetary electric field and therefore with the interplanetary magnetic field (IMF) BZ component. In the present study, we investigate how the equatorial H magnetic component, and therefore the EEJ, responds to step-like changes of IMF BZ. The reduction of southward IMF BZ (northward turning) and that of northward IMF BZ (southward turning) are examined separately. The result shows that for the northward turnings, the EEJ immediately starts to weaken with the accuracy of the estimates of the travel times of the IMF changes. The time constant of the response is much longer, and the equatorial H component decreases continuously by 40 nT for 30 min after the northward turnings. In contrast, the response of the EEJ to the southward turnings is far less clear in both magnitude and timing, and it does not depend on whether or not IMF BZ actually becomes southward. The difference in the EEJ response to the northward and southward turnings reflects at least partially the fact that the magnetosphere-ionosphere system is more sensitive to IMF BZ when IMF is southward than northward. It is suggested that the electric field penetrates from the polar region to the dip equator through a global current system that connects the auroral electrojets and the EEJ, and the ionospheric conductance in the polar region may play an important role in the formation of such a current system.

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

2013-06-01

330

Circadian Rhythms in the CNS and Peripheral Clock Disorders: Human Sleep Disorders and Clock Genes  

Microsoft Academic Search

Genetic analyses of circadian rhythm sleep disorders (CRSD), such as familial advanced sleep phase syndrome (ASPS) and delayed sleep phase syndrome (DSPS), and morningness-eveningness revealed the relationship between variations in clock genes and diurnal change in human behaviors. Variations such as T3111C in the Clock gene are reportedly associated with morningness-eveningness. Two of the pedigrees of familial ASPS (FASPS) are

Takashi Ebisawa

2007-01-01

331

Field operations with cesium clocks in HF navigation systems  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

332

Entangling the lattice clock: Towards Heisenberg-limited timekeeping  

SciTech Connect

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

Weinstein, Jonathan D.; Beloy, Kyle; Derevianko, Andrei [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States)

2010-03-15

333

Photoperiodic plasticity in circadian clock neurons in insects  

PubMed Central

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

Shiga, Sakiko

2013-01-01

334

Uneven patterns of governance: how developing countries are represented in the IMF  

Microsoft Academic Search

The IMF is governed by a 24-member Executive Board which represents 184 countries. Although often prized as a small and efficient decision-making body, the Board represents some countries more effectively than others. This is due to the institutional structure and incentives within which the Board operates. Prime among them is a system of constituencies which have formed and evolved as

Ngaire Woods; Domenico Lombardi

2006-01-01

335

Mapping the Present-Day Prestellar Core Mass Function into the Stellar IMF  

NASA Astrophysics Data System (ADS)

The fact that the shapes of the Present-Day Prestellar Core Mass Function (PDPCMF) and the Stellar Initial Mass Function (StIMF) appear to be very similar is purely coincidental, unless the mapping from the PDPCMF to the StIMF is statistically self similar. Either way, there is a huge amount of physics that occurs between a prestellar core and a protostar, and theories for the genesis of the PDPCMF should be presented as such, not as theories for the origin of the StIMF. Here we explore the constraints that the observed statistical properties of stars place on self-similar mappings. We find a simple mapping that is able to deliver the observed StIMF, the binary frequency as a function of primary mass, and the distribution of mass ratios for binaries with Sun-like primaries. This mapping implies that the local efficiency is high (typically a core spawns ˜ 4 stars, and these stars comprise ˜ 87% of the core's initial mass); that most of the stars spawned by a single core have masses within a factor ˜ 4 of each other; that most cores deliver one long-lasting binary into the field, and in ˜ 75% of cases this binary involves the two most massive stars formed in the core; that the remaining ˜ 25% of binaries involve random pairings of the stars formed in the core.

Holman, Katy; Walch, Stefanie K.; Goodwin, Simon; Whitworth, Anthony Peter

336

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

Microsoft Academic Search

We have used a newly developed, parallelized, global MHD magnetosphere - ionosphere simulation model with a 400 R(sub E) long tail to study the evolution, structure, and dynamics of the distant magnetotail during extended periods of northward interplanetary magnetic field (IMF). We find that the tail evolves to a nearly time stationary structure about one solar wind transit time after

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

1995-01-01

337

Comparison of Magnetic Field Perturbations at High Latitudes with Charged Particle and IMF Measurements  

Microsoft Academic Search

The magnetometer aligned along the spin axis of the Isis 2 satellite has been used to study magnetic field perturbations in the dawn-dusk sectors of the auroral oval and in the polar cap. The field perturbations have been compared with simultaneous particle measurements and with measurements of the interplanetary magnetic field (IMF). Northern hemisphere passes were selected during a period

I. B. McDiarmid; J. R. Burrows; Margaret D. Wilson

1978-01-01

338

Observation of IMF and seasonal effects in the location of auroral substorm onset  

Microsoft Academic Search

We use Polar ultraviolet imager (UVI) and Wind observations to study the location of 648 well-defined Northern Hemisphere auroral breakups (substorm onsets) in response to interplanetary magnetic field (IMF) orientation and season. The most likely onset location is at 2230 MLT and 67° Lambdam with half-maximum widths of 3 hours of MLT and 2° Lambdam, respectively. The onset latitude depends

K. Liou; P. T. Newell; D. G. Sibeck; C.-I. Meng; M. Brittnacher; G. Parks

2001-01-01

339

The Challenge of Good Governance for the IMF and the World Bank Themselves  

Microsoft Academic Search

Over the last decade, the International Monetary Fund (IMF) and the World Bank have embraced “good governance” as a set of principles to guide their objectives in member countries. Both institutions now face pressures to apply some similar standards of transparency, accountability and participation to themselves. This paper examines the challenges this poses for the organizations, beyond the steps they

Ngaire Woods

2000-01-01

340

Cluster observations of the exterior cusp and its surrounding boundaries under northward IMF  

Microsoft Academic Search

We have studied in detail multi-spacecraft observations of the exterior cusp on 04 February 2001, during a steady northward Interplanetary Magnetic Field (IMF) interval. At a radial distance of 11 Re, Cluster encountered a well-bounded region where the magnetic field exhibited very low diamagnetic values and the ions displayed high levels of isotropisation. We refer to this region as the

B. Lavraud; M. W. Dunlop; T. D. Phan; H. Rème; J.-M. Bosqued; I. Dandouras; J.-A. Sauvaud; R. Lundin; M. G. G. T. Taylor; P. J. Cargill; C. Mazelle; C. P. Escoubet; C. W. Carlson; J. P. McFadden; G. K. Parks; E. Moebius; L. M. Kistler; M.-B. Bavassano-Cattaneo; A. Korth; B. Klecker; A. Balogh

2002-01-01

341

Global characteristics of northward IMF-associated (NBZ) field-aligned currents  

Microsoft Academic Search

Some global characteristics of large-scale field-aligned current (FAC) systems are determined by analyzing the magnetic disturbances acquired with the MAGSAT satellite in the southern summer hemisphere during November 1979 through January 1980. The characteristics consist of a dayside part and a nightside part. During IMF periods where Bz is greater than zero, the dayside part is characterized by a large

T. Iijima; T. Shibaji

1987-01-01

342

Structure and properties of the subsolar magnetopause for northward IMF: ISEE observations  

Microsoft Academic Search

Detailed magnetopause structure and properties for the magnetic field, electric field and plasma are examined for an ISEE 1 magnetopause crossing which occurred near the subsolar point when the interplanetary magnetic field (IMF) was strongly northward. Because the crossing is slow, the spatial variations in the plasma are clearly resolved. This example illustrates the nature of the steady state interface

P. Song; C. T. Russell; J. T. Gosling; C. A. Cattell

1990-01-01

343

IMF lending: how is it affected by economic, political and institutional factors?  

Microsoft Academic Search

In seeking to understand IMF lending early large sample econometric studies tended to focus on economic factors. Political and institutional influences were often deemed to be reflected in the frequently large residual. At the same time increasing anecdotal evidence was being amassed to suggest that political factors were indeed important. However, more recent studies have claimed that, by using superior

Graham Bird; Dane Rowlands

2001-01-01

344

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

345

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

Microsoft Academic Search

Separate studies using the same micropulsation data base in the period range 10--150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar wind alignment of the IMF and solar wind speed, but each correlation contained enough scatter to allow for influence of the other factor. In this report,

Eugene W. Greenstadt; Howard J. Singer; Christopher T. Russell; John V. Olson

1979-01-01

346

How useful are the forecasts of intergovernmental agencies? The IMF and OECD versus the consensus  

Microsoft Academic Search

This study compares the accuracy and information content of economic forecasts for G7 countries made in the 1990s by the OECD and IMF. The benchmarks for comparison are the average forecasts of private sector economists published by Consensus Economics. With few exceptions, the private sector forecasts are less biased and more accurate in terms of mean absolute error and root

Roy Batchelor

2001-01-01

347

Once Bitten: The Effect of IMF Programs on Subsequent Reserve Behaviour  

Microsoft Academic Search

Traditional models have encountered problems in explaining the ac- cumulation of international reserves, particularly in Asia, in the period since the late 1990s. One suggestion has been that countries have sought to self insure against future crises, either because of a perceived increase in the cost of crises or because of the perceived conditionality costs of using IMF credits. This

Graham Bird; Alex Mandilaras

2009-01-01

348

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

NASA Astrophysics Data System (ADS)

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.

Tsao, Wen-Chang; Pan, Min-Chun

2014-03-01

349

The Evolution of the Solar Neighborhood: II Time-Dependent IMF and Present Day Mass Function  

NASA Astrophysics Data System (ADS)

According to the star formation rate and metal enrichment rate given by the disk-halo model of Lee and Ann(1981). the two different forms of time-dependent initial mass function(IMF) and the present day mass function(PDMF) of nearly stars have been examined. It was shown that the constraint for the initial rapid metal enrichment requires the time-dependence of IMF at the very early phase ( t<=3*10^8 yrs) of the solar neighborhood. The computes PDMF's show that the PDMF is nearly independent of any specific functional form of IMF as long as the latter includes a Gaussian distribution of log m. This result is due to the very small fractional mass (~5%) of stars formed at the very early period during which the IMF is time-dependent. The computed PDMF suggests the presence of more numerous low mass stars than shown in Miller and Scalo's(1979) PDMF, supporting the possibility of the existence of low-velocity M dwarfs. According to the number distribution of stars with respect to [Fe/H], the mean age of these low mass star must be very old so as to yield the mean metal abundance <[Fe/H]> = -0.15 for the stars in the solar neighborhood.

Lee, See-Woo; Hong, Seung Soo

1982-12-01

350

Do Gravity-Sensitive Absorption Features in Elliptical Galaxy Spectra Trace Abundance Patterns or the IMF?  

NASA Astrophysics Data System (ADS)

Recent work by van Dokkum & Conroy and others has presented significant evidence from gravity-sensitive near-infrared absorption features and dynamical mass-to-light ratios that the stellar initial mass function (IMF) in giant elliptical galaxies is extremely bottom-heavy and varies systematically with galaxy mass. We present a new stellar template library based on spectra of stars in the old open cluster M67 at red and near-IR wavelengths that can be used to place further constraints on such IMF variations across different galactic environments. Unlike existing template sets, M67 stars have a known and homogeneous age and metallicity that is as closely matched to the typical stellar populations in elliptical galaxies as possible. We build population synthesis models from the M67 templates, comparing several absorption features from different atomic and molecular species for consistency against the possibility of chemical enrichment patterns that are not represented in local template samples, and finally measure the IMF variation in a range of spheroids, from dwarf spheroidals and dwarf ellipticals to bulges and giant ellipticals. In particular, we compare the extensively discussed Na I 8183,8195 Å doublet to two rather under-exploited tracers, the redder component of the K I doublet at 7699 Å and the broad swath of CaH features from 6815-6920 Å. The IMF variation inferred from the Na I equivalent widths is greater than those derived from the K I and CaH measurements. We therefore suggest that the sodium abundance in massive ellipticals may be higher than expected, and we place limits on the IMF non-uniformity from the K I and CaH tracers.

Simon, Joshua D.; Adams, J. J.

2013-01-01

351

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

352

Optical Atomic Clocks for Ground and Space Applications  

NASA Astrophysics Data System (ADS)

Optical atomic clocks on ground have now matured to a status where they compete favourably with the best caesium atomic clocks that realize the unit of time in the International System of Units (SI). Optical clocks can have orders of magnitude better short term stability than their radio-frequency counterparts. Even though optical clocks cannot realize the second in the SI better than the best caesium clocks (as long as the definition of the SI second is based on the caesium transition) they can realize the unperturbed center of a quantum transition with much better accuracy and stability. Optical atomic clocks now represent the most accurate measuring devices for applications in technology and basic science. Three alternative routes are followed by optical atomic clocks: In the first approach -the single ion clock -a single quantum absorber is trapped in a field-free region for virtually unlimited time. In neutral atom clocks a large number of atoms trapped in a light field can interrogated in parallel which allows for unprecedented high short-term stability. A very promising third avenue relies on ions where the quantum transition is read out by means of quantum logic techniques. This approach allows to use nearly ideal transitions that are otherwise not accessible. In the first part of this presentation the principles and status of the different types of clocks will be outlined using examples of the PTB's Y b+ single ion clock and the Sr neutral atom lattice clock. Particular emphasis is given to the application of such clocks for advanced applications in science and technology. A number of proposals has been made to utilize the superior properties of optical clocks also for novel science and applications in space and several attempts are under way to realize optical clocks for space applications. Thus, the second part of this contribution will deal with the special requirements for optical clocks in space and the associated similarities and differences of optical clocks for ground and space applications. Furthermore typical applications for optical space clocks for the different approaches will be given.

Riehle, Fritz

353

Metabolism and the circadian clock converge.  

PubMed

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

Eckel-Mahan, Kristin; Sassone-Corsi, Paolo

2013-01-01

354

Analysis of atom-interferometer clocks  

NASA Astrophysics Data System (ADS)

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

Peil, Steven; Ekstrom, Christopher R.

2014-01-01

355

Metabolism and the Circadian Clock Converge  

PubMed Central

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

Eckel-Mahan, Kristin

2013-01-01

356

The Large Built Water Clock Of Amphiaraeion.  

NASA Astrophysics Data System (ADS)

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

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

357

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

PubMed

Circadian rhythms are endogenous and self-sustained oscillations of multiple biological processes with approximately 24-h rhythmicity. Circadian genes and their protein products constitute the molecular components of the circadian oscillator that form positive/negative feedback loops and generate circadian rhythms. The circadian regulation extends from core clock genes to various clock-controlled genes that include various cell cycle genes. Aberrant expression of circadian clock genes, therefore, may lead to genomic instability and accelerated cellular proliferation potentially promoting carcinogenesis. The current study encompasses the investigation of simultaneous expression of four circadian clock genes (Bmal1, Clock, Per1 and Per2) and three clock-controlled cell cycle genes (Myc, Cyclin D1 and Wee1) at mRNA level and determination of serum melatonin levels in peripheral blood samples of 37 CLL (chronic lymphocytic leukemia) patients and equal number of age- and sex-matched healthy controls in order to indicate association between deregulated circadian clock and manifestation of CLL. Results showed significantly down-regulated expression of Bmal1, Per1, Per2 and Wee1 and significantly up-regulated expression of Myc and Cyclin D1 (P < 0.0001) in CLL patients as compared to healthy controls. When expression of these genes was compared between shift-workers and non-shift-workers within the CLL group, the expression was found more aberrant in shift-workers as compared to non-shift-workers. However, this difference was found statistically significant for Myc and Cyclin D1 only (P < 0.05). Serum melatonin levels were found significantly low (P < 0.0001) in CLL subjects as compared to healthy controls whereas melatonin levels were found still lower in shift-workers as compared to non-shift-workers within CLL group (P < 0.01). Our results suggest that aberrant expression of circadian clock genes can lead to aberrant expression of their downstream targets that are involved in cell proliferation and apoptosis and hence may result in manifestation of CLL. Moreover, shift-work and low melatonin levels may also contribute in etiology of CLL by further perturbing of circadian clock. PMID:24190490

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

2014-01-01

358

Determination of the Sector Structure of IMF from Ground-Based Data: Recent Results and Usage Prospects.  

NASA Astrophysics Data System (ADS)

The determination of sector structure of IMF ( SS IMF ) was continued on the base of data from pair of magnetic observatories Vostok - Resolute Bay. Now the SS IMF in the form of standard table for period of 1957-2000 is displayed on the http://charley.izmiran.rssi.ru/magnetism/ssimf.htm. Now the determination is performed by semiautomatic method based on previous results and new improvements. We make some modifications into the basic technique of SS IMF definition that greatly improves the performance and reliability of results. We consider our method as the most reliable data source for magnetospheric research as it already includes results of interaction of SS IMF with the Earth magnetic field. Moreover we make attempt to infer the SS IMF from data of Moscow magnetic observatory. The analysis of data for period of minimum of solar activity at 1995 confirmed that in the toward sector ( By \\textless 0, Bx \\textgreater 0 ) geomagnetic activity dominates in comparison with the away sector ( By \\textgreater 0, Bx \\textless 0 ). Usually in the toward sector we get Bz \\textless 0. Large scale spatial variations and evolution of SS IMF in connection with the general development of solar activity and dynamics of the heliospheric current sheet into maximum of solar cycle 23 are discussed. We also analyze the usage prospects of our data in view of similar information obtained from ACE satellite and ground solar observatories. >http://charley.izmiran.rssi.ru/magnetism/ssimf.htm.

Zaitzev, A. N.; Odintsov, V. I.; Trichtchenko, L. N.; Boteler, D. H.; Coles, R. L.

2001-12-01

359

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

NASA Astrophysics Data System (ADS)

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.

Kullen, Anita; Fear, Rob; Milan, Steve

2014-05-01

360

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

NASA Technical Reports Server (NTRS)

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.

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

361

The Circadian Clock, Reward, and Memory  

PubMed Central

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

Albrecht, Urs

2011-01-01

362

Heterogeneous Genomic Molecular Clocks in Primates  

Microsoft Academic Search

Using data from primates, we show that molecular clocks in sites that have been part of a CpG dinucleotide in recent past (CpG sites) and non-CpG sites are of markedly different nature, reflecting differences in their molecular origins. Notably, single nucleotide substitutions at non-CpG sites show clear generation-time dependency, indicating that most of these substitutions occur by errors during DNA

Seong-Ho Kim; Navin Elango; Charles Warden; Eric Vigoda; Soojin V. Yi

2006-01-01

363

Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration  

PubMed Central

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

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

2013-01-01

364

Tuning Genetic Clocks Employing DNA Binding Sites  

PubMed Central

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

Jayanthi, Shridhar; Del Vecchio, Domitilla

2012-01-01

365

Tuning genetic clocks employing DNA binding sites.  

PubMed

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

Jayanthi, Shridhar; Del Vecchio, Domitilla

2012-01-01

366

Clock genes at the heart of depression.  

PubMed

The rhythms of life are ever pervasive, touching almost every aspect of our lives. We are finely tuned to the cycle of light and dark, so that we normally sleep during the night and are active during the day. Physiological rhythms are, however, not just slaves to the solar day, but are actually generated endogenously within the suprachiasmatic nuclei in the hypothalamus and are entrained via the retina. The circadian timing system is organized hierarchically with the suprachiasmatic nuclei providing neural and/or hormonal cues to the various organ systems, allowing them to express their own rhythmic physiological output. There is now a substantial body of evidence emerging that disruption of rhythmicity through altered sleep/wake patterns and exposure to light, or through endogenous disruption of key determinants of endogenous rhythms, can be detrimental to health. Circadian rhythm disturbances have long been associated with mood disorders, especially delayed sleep onset, and evidence is accumulating that alterations to the cellular timing system may underpin some aspects of the disorders. For example, mice carrying mutations in either Clock or per2 spend less time immobile in swim tests, which has been suggested as mimicking mania. In humans, single nucleotide polymorphisms in Clock and other clock genes have been associated with depression. With this increasing knowledge we may predict that new antidepressant drugs will emerge that, as a primary or secondary mechanism of action, target and correct abnormalities in the circadian timing system. PMID:20663803

Kennaway, David J

2010-08-01

367

Clock distribution system for digital computers  

DOEpatents

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

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

1981-01-01

368

Abiotic stress and the plant circadian clock  

PubMed Central

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

Sanchez, Alfredo; Shin, Jieun

2011-01-01

369

Atomic clocks with suppressed blackbody radiation shift.  

PubMed

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

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

2011-07-15

370

Clock gene evolution and functional divergence.  

PubMed

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

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

2004-10-01

371

ORTHO- ELIMINATION OF TRACKING SYSTEM CLOCK ERRORS  

NASA Technical Reports Server (NTRS)

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

Wu, J. T.

1994-01-01

372

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

NASA Technical Reports Server (NTRS)

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

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

1998-01-01

373

Inexpensive programmable clock for a 12-bit computer  

NASA Technical Reports Server (NTRS)

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

Vrancik, J. E.

1972-01-01

374

Race:. a High Performance Rubidium Clock for the Iss  

NASA Astrophysics Data System (ADS)

The design for RACE, a Rb clock flight experiment for the ISS, is described. The cold collision shift and multiple launching (juggling) have important implications for the design and the resulting clock accuracy and stability. We demonstrate a prototype laser-cooled 87Rb fountain clock and measure the frequency shift due to cold collisions. We observe a density dependent pulling by the microwave cavity and use it to cancel the collision shift. We have also demonstrated a juggling atomic fountain to study cold collisions and we discuss the importance of juggling for future fountain clocks. We present and discuss the double clock design for RACE. This design reduces the noise contributions of the local oscillator and simplifies and enhances an accuracy evaluation of the clock.

Fertig, C.; Rees, I.; Gibble, K.; Prestage, J.; Klipstein, B.; Thompson, R.

2002-02-01

375

Clock-drawing test and unilateral spatial neglect.  

PubMed

We investigated the ability of 25 patients with left unilateral spatial neglect to make a clock face by putting numbers inside a printed circle. Impairment seen in this clock-drawing test did not parallel neglect severity as judged by results of the line-cancellation and line-bisection tests, as well as the copying of a daisy. The score for clock drawing correlated highly with the verbal WAIS score. Most neglect patients with a verbal IQ of 87 or more could draw a clock face fairly well and used planning in placing the numbers 12, 3, 6, and 9 before the others. In clock drawing, verbal intelligence may compensate for left unilateral spatial neglect. We therefore recommend use of the line-cancellation and line-bisection tests, as well as the copying test, but do not recommend use of the clock-drawing test in the diagnosis of left unilateral spatial neglect. PMID:8423871

Ishiai, S; Sugishita, M; Ichikawa, T; Gono, S; Watabiki, S

1993-01-01

376

Quasi-static energy recovery logic and supply-clock generation circuits  

Microsoft Academic Search

A Quasi-Static Energy Recovery Logic family (QSERL) us- ing two complementary sinusoidal supply clocks is proposed in this paper. A high-efficiency clock generation circuitry which generates two complementary sinusoidal clocks re- quired by QSERL is also presented. The clock circuitry locks both frequency and phase of clock signals, which makes it possible to integrate adiabatic module into a VLSI system.

Yibin Ye; Kaushik Roy; Georgios I. Stamoulis

1997-01-01

377

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

SciTech Connect

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

Jones, Terry R [ORNL] [ORNL; Koenig, Gregory A [ORNL] [ORNL

2013-01-01

378

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

SciTech Connect

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

Jones, Terry R [ORNL; Koenig, Gregory A [ORNL

2010-01-01

379

PHYSIOLOGY: Biological Clocks Coordinately Keep Life on Time  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required: Many biological processes, including cell division, metabolism, and seasonal flowering, are controlled by cycles of activity. Mechanisms called biological clocks maintain these cycles. In their Perspective, Gillette and Sejnowski discuss how some clocks do not operate independently of others. Rather, clocks may interact such that the state of one system can alter another.

Martha U. Gillette (University of Illinois;Department of Cell and Developmental Biology and the Neuroscience Program); Terrence J. Sejnowski (Howard Hughes Medical Institute; University of California, San Diego;Salk Institute for Biological Studies; Department of Biology)

2005-08-19

380

A Fine-Grain Clock Synchronization Mechanism for Myrinet Clusters  

Microsoft Academic Search

Clock synchronization is a fundamental requirement for any real-time distributed system operating with global schedules. The presence of a global clock permits co-scheduling, enhances the degree of synchronization between cooperating tasks of parallel programs, and permits implementation of quality of service (QoS) based communication. This paper describes the design and implementation of a high accuracy (±5?s) global clock on a

Srigurunath Chakravarthi; Anand Pillai; Jothi P. Neelamegam; Manoj Apte; Anthony Skjellum

2002-01-01

381

Comment on ``Phase-invariant clock hypothesis for accelerating systems''  

NASA Astrophysics Data System (ADS)

In this paper the phase-invariant clock hypothesis for accelerating systems suggested by F. V. Kowalski [Phys. Rev. A 46, 2261 (1992)] is investigated in detail. It is pointed out that in Kowalski's derivation of the most distinctive result of the hypothesis, predicting no frequency shift between two spatially separated clocks rigidly accelerating, there are a few points needing further discussion. In addition, it is shown that the generalized phase-invariant clock hypothesis denies the existence of the usual twin paradox.

Guangda, Meng; Guangwen, Ma; Youlin, Wu; Guomin, Zhang

1996-06-01

382

Ground control system for the midcourse space experiment UTC clock  

NASA Technical Reports Server (NTRS)

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

Dragonette, Richard

1994-01-01

383

A Novel Photonic Clock and Carrier Recovery Device  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

384

Optimizing Two-Phase, Level-Clocked Circuitry  

Microsoft Academic Search

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

1992-01-01

385

AMPK at the crossroads of circadian clocks and metabolism  

PubMed Central

Circadian clocks coordinate behavior and physiology with daily environmental cycles and thereby optimize the timing of metabolic processes such as glucose production and insulin secretion. Such circadian regulation of metabolism provides an adaptive advantage in diverse organisms. Mammalian clocks are primarily based on a transcription and translation feedback loop in which a heterodimeric complex of the transcription factors CLOCK (circadian locomotor output cycles kaput) and BMAL1 (brain and muscle Arnt-like protein 1) activates the expression of its own repressors, the period (PER1-3) and cryptochrome (CRY1,2) proteins. Posttranslational modification of these core clock components is critical for setting clock time or adjusting the speed of the clock. AMP-activated protein kinase (AMPK) is one of several metabolic sensors that have been reported to transmit energy-dependent signals to the mammalian clock. AMPK does so by driving the phosphorylation and destabilization of CRY and PER proteins. In addition, AMPK subunit composition, sub-cellular localization, and substrate phosphorylation are dependent on clock time. Given the well-established role of AMPK in diverse aspects of metabolic physiology, the reciprocal regulation of AMPK and circadian clocks likely plays an important role in circadian metabolic regulation.

Jordan, Sabine D.; Lamia, Katja A.

2012-01-01

386

Power and Skew Aware Point Diffusion Clock Network  

NASA Astrophysics Data System (ADS)

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

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

387

Crosstalk between the Circadian Clock and Innate Immunity in Arabidopsis  

PubMed Central

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

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

2013-01-01

388

Clock genes show circadian rhythms in salivary glands.  

PubMed

Circadian rhythms are endogenous self-sustained oscillations with 24-hour periods that regulate diverse physiological and metabolic processes through complex gene regulation by "clock" transcription factors. The oral cavity is bathed by saliva, and its amount and content are modified within regular daily intervals. The clock mechanisms that control salivary production remain unclear. Our objective was to evaluate the expression and periodicity of clock genes in salivary glands. Real-time quantitative RT-PCR, in situ hybridization, and immunohistochemistry were performed to show circadian mRNA and protein expression and localization of key clock genes (Bmal1, Clock, Per1, and Per2), ion and aqua channel genes (Ae2a, Car2, and Aqp5), and salivary gland markers. Clock gene mRNAs and clock proteins were found differentially expressed in the serous acini and duct cells of all major salivary glands. The expression levels of clock genes and Aqp5 showed regular oscillatory patterns under both light/dark and complete-dark conditions. Bmla1 overexpression resulted in increased Aqp5 expression levels. Analysis of our data suggests that salivary glands have a peripheral clock mechanism that functions both in normal light/dark conditions and in the absence of light. This finding may increase our understanding of the control mechanisms of salivary content and flow. PMID:22699207

Zheng, L; Seon, Y J; McHugh, J; Papagerakis, S; Papagerakis, P

2012-08-01

389

An evolution of antiparallel merging. [of geomagnetic field and IMF at dayside magnetopause  

NASA Technical Reports Server (NTRS)

It has been suggested (Crooker, 1979) that the geomagnetic field and the merge at the dayside magnetopause along lines formed by the loci of points where the fields are antiparallel. These antiparallel merging lines curve outward from the cusps, one in each hemisphere. Here a three-dimensional magnetopause model in which the antiparallel merging lines become chains of neutral points is described. The model is constructed by overlapping shielding currents of the geomagnetic field and the IMF in a layer of finite thickness. The global topology of the model explains the observed disappearance of flux-transfer events when the IMF turns northward and the dearth of flux-transfer events in the subsolar region.

Crooker, N. U.

1986-01-01

390

Study and effect of IMF and solar wind velocity in CR modulation  

NASA Astrophysics Data System (ADS)

The high amplitude wave train events HAEs of cosmic ray intensity observed during 1981-1994 were analyzed We have studied the effect of southward component Bz of interplanetary magnetic field IMF and solar wind velocity on cosmic ray diurnal anisotropy The neutron monitor data of Deep River station has been used in the present analysis It has been observed that HAEs are weakly dependent on high-speed solar wind velocity The occurrence of HAE is dominant for positive polarity of southward component Bz of IMF The diurnal time of maximum significantly shifts towards earlier hours as compared to the azimuthal corotational direction for majority of the HAEs during the period of investigation

Mishra, R. K.; Mishra, R. A.

391

Alfvén waves as a possible source of long-duration, large-amplitude, and geoeffective southward IMF  

NASA Astrophysics Data System (ADS)

The southward component (Bs) of the interplanetary magnetic field (IMF) is a strong driver of geomagnetic activity. Well-defined solar wind structures such as magnetic clouds and corotating interaction regions are the main sources of long-duration, large-amplitude IMF Bs. Here we analyze IMF Bsevents (t> 1 h, Bz<-5nT) unrelated with any well-defined solar wind structure at 1 AU using ACE spacecraft observations from 1998 to 2004. We find that about one third of these Bs events show Alfvénic wave features; therefore, those Alfvén waves in the solar wind are also an important source of long-duration, large-amplitude IMF southward component. We find that more than half of the Alfvén wave (AW)-related Bs events occur in slow solar wind (Vsw < 400 km/s). One third of the AW-type Bsevents triggered geomagnetic storms, and half triggered substorms.

Zhang, X.-Y.; Moldwin, M. B.; Steinberg, J. T.; Skoug, R. M.

2014-05-01

392

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

NASA Technical Reports Server (NTRS)

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.

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

393

Cluster and Ground-based Observations of The Cusp For Variable Imf and Quiet Conditions  

Microsoft Academic Search

The multi-satellite mission Cluster is an opportunity to study structure and dynamics of the polar cusp. On the 17th of March 2001, Cluster enters the high altitude cusp over the northern hemisphere during variable interplanetary magnetic field (IMF) and quiet conditions(P<1nT, AEsim0). PEACE observations throughout the cusp cross- ing, lasting more than one hour, reveal structured electron fluxes. With electrons

A. Vontrat-Reberac; J. M. Bosqued; M. G. G. T. Taylor; B. Lavraud; D. Fontaine; N. Cornilleau-Wehrlin; H. Laakso; M. Dunlop; P. Canu; A. Fazakerley; A. Marchaudon; K. Oksavik; J. C. Cerisier; P. L. Blelly; J. Moen; P. Décréau

2002-01-01

394

Global simulations of the response of the cusp to a large rotation of the IMF  

NASA Astrophysics Data System (ADS)

Ion dispersions observed by the Cluster spacecraft as they cross the polar cusps offer a unique opportunity to investigate the large-scale topology and dynamics of magnetic reconnection at the dayside magnetosphere. In particular, consecutive crossings of the cusp resulting from the string of pearl configuration of the Cluster spacecraft in that region are well suited for investigating the temporal evolution as well as the spatial extent of ion dispersions as solar wind discontinuities interact with the dayside magnetopause. We have revisited our simulation study of the response of the cusp to a large rotation of the interplanetary magnetic field (IMF), which was observed by the Cluster spacecraft on 23 September 2004. During that event the four satellites crossed the polar cusp within 2-16 minutes of each other while the IMF rotated from a southward to a northward direction. When simulating such events, we first run a three-dimensional global magnetohydrodynamic (MHD) simulation to determine the global topology of the magnetic field at different times during the event and then use a large-scale particle (LSK) simulation to determine the regions where ions enter the magnetosphere and to predict their energy-latitude dispersion in the cusp. We present the results of new simulations of the event that used idealized rotation of the IMF for input instead of the actual IMF observations that were used in our previous study. Comparing the results of the two sets of simulations allows us to determine whether ion injections' transient features identified in our previous study result from the large-scale reconfiguration of the magnetic field topology of the dayside magnetosphere as the discontinuity interacts with the magnetopause or from smaller scale fluctuations in upstream conditions.

Berchem, Jean; Richard, Robert; Escoubet, Philippe; Pitout, Frederic; Taylor, Matthew G. G. T.; Laakso, Harri; Masson, Arnaud; Dandouras, Iannis; Reme, Henri

2014-05-01

395

Anomalous geomagnetic storm of 21–22 January 2005: A storm main phase during northward IMFs  

Microsoft Academic Search

The major (minimum Dst = ?105 nT) magnetic storm which occurred on 21–22 January 2005 is highly anomalous because the storm main phase (identified by the SYM-H indices) developed during northward interplanetary magnetic fields (IMFs). We believe this to be the first event of its type to be reported in the literature. Interplanetary ACE and Cluster C1 data are used

A. M. Du; B. T. Tsurutani; W. Sun

2008-01-01

396

Global simulations of dynamic magnetosphere response to steady southward IMF driving  

NASA Astrophysics Data System (ADS)

We utilize the global MHD model BATS-R-US with incorporated nongyrotropic effects in diffusion regions to investigate the dynamic magnetosphere response to southward interplanetary magnetic field (IMF) driving. We analyze relative importance of the solar wind conditions, ionosphere conductance and dissipation mechanisms supporting the magnetotail reconnection in controlling the mode of magnetic energy release. The conditions for the quasi-periodic loading/unloading sawtooth response will be discussed.

Patel, K.; Kuznetsova, M. M.; Hesse, M.; Rastaetter, L.; Toth, G.; de Zeeuw, D.; Gombosi, T. I.

2009-12-01

397

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

398

Imf, a Novel Myogenic Repressor, Interacts with Members of the MyoD Family  

Microsoft Academic Search

During embryogenesis, cells from the ventral and dorsal parts of the somites give rise to sclerotome and dermomyotome, respectively. Dermomyotome contains skeletal muscle precursors that are determined by the MyoD family of myogenic factors. We have isolated a novel myogenic repressor, I-mf (Inhibitor of MyoD family), which is highly expressed in the sclerotome. In contrast, MyoD family members are concentrated

C.-M. Amy Chen; Norbert Kraut; Mark Groudine; Harold Weintraub

1996-01-01

399

The nonlinear response of AE to the IMF BS driver: A spectral break at 5 hours  

Microsoft Academic Search

We demonstrate the existence of a sharp break in the power spectrum of AE at ? 5 hours. At frequencies below the break, AE has a ? f?1.0 dependence, and at higher frequencies it has a f?2.2 to f?2.4 dependence. The power spectrum of the IMF Bs for the same time interval has a ? f?1.4 dependence with no spectral

Bruce T. Tsurutanil; Masahisa Sugiura; Toshihiko Iyemori; Bruce E. Goldstein; Walter D. Gonzalez; Syun I. Akasofu; Edward J. Smith

1990-01-01

400

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

NASA Technical Reports Server (NTRS)

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.

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

2006-01-01

401

Simultaneous Cluster and IMAGE observations of cusp reconnection and auroral proton spot for northward IMF  

Microsoft Academic Search

On March 18, 2002, under northward interplanetary magnetic field (IMF) and high (~15 nPa) solar wind dynamic pressure conditions, Cluster observed reconnection signatures and the passage of an X-line at the large (~175°) magnetic-shear high-latitude magnetopause (MP). The observations are consistent with the occurrence of a reconnection site tailward of the cusp and in the vicinity of the spacecraft. At

T. Phan; H. U. Frey; S. Frey; L. Peticolas; S. Fuselier; C. Carlson; H. Rème; J.-M. Bosqued; A. Balogh; M. Dunlop; L. Kistler; C. Mouikis; I. Dandouras; J.-A. Sauvaud; S. Mende; J. McFadden; G. Parks; E. Moebius; B. Klecker; G. Paschmann; M. Fujimoto; S. Petrinec; M. F. Marcucci; A. Korth; R. Lundin

2003-01-01

402

Predictions of Substorms and Intensifications Following Northward Turnings of the IMF  

NASA Technical Reports Server (NTRS)

Substorms are often observed to occur at the end of intervals of Southward interplanetary magnetic field (IMF), i.e. following the northward turning. Despite the significant correlation between northward turning and substorms, no direct causal relationship between northward turnings and substorms has been demonstrated. Assuming such a causal relationship, we predict that substorms will occur within a particular interval following the observation of a northward turning in the IMF. We observe 16 northward turnings following steady, southward IMF in data taken by the WIND spacecraft magnetic field instrument (MFI). To ensure that the northward turning was observed at the magnetosphere, we require that the northward turning also be observed by instruments on either one of Geotail or IMP-8 while the separation of the second spacecraft from WIND was more that 10 R(sub E). These two-spacecraft observations also allow us to predict more accurately the arrival time of the northward turning at the Earth. Of the predictions substorms, 10 predictions were clearly successful to within +/- 12 min. Five predictions failed, but the failures reveal clear shortcomings in the criteria for a northward turning that we correct. The failures were caused by an increase in the absolute value of B(sub YGSM) simultaneous with the northward turning in 3 cases, and a weak southward IMF preceding the northward turning in 2 cases. The final northward turning arrived in the recovery phase of an ongoing substorm, and resulted in unusual auroral activity. The implication of the predictability of substorms following sharp northward turnings is that the postulated causal relationship between northward turnings and substorm onset exists. The effect of increases in the absolute value of B(sub YGSM) to negate the triggering ability of northward turnings suggests that the triggering mechanism involves sharp reductions in the magnetospheric convection electric field.

Blanchard, G. T.; Lyons, L. R.; Spann, J.

1999-01-01

403

Once Bitten: The Effect of IMF Programs on Subsequent Reserve Behavior  

Microsoft Academic Search

AbstractTraditional models have encountered problems in explaining the accumulation of international reserves, particularly in Asia, in the period since the late 1990s. One suggestion has been that countries have sought to self-insure against future crises, either because of a perceived increase in the cost of crises or because of the perceived conditionality costs of using IMF credits. This paper offers

Graham Bird; Alex Mandilaras

2011-01-01

404

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

Microsoft Academic Search

This paper presents a preliminary study of what appears to be the first IMF event initially identified as interesting on the basis of ground based atmospheric electricity data. On Jan 2, 1993, the electric field mill and air-earth current meters at South Pole Station detected a sustained oscillation in the earth-ionosphere potential at South Pole with a quasi-period of 1

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

2005-01-01

405

Rapid activation of CLOCK by Ca2+-dependent protein kinase C mediates resetting of the mammalian circadian clock  

Microsoft Academic Search

In mammals, immediate-early transcription of the Period 1 (Per1) gene is crucial for resetting the mammalian circadian clock. Here, we show that CLOCK is a real signalling molecule that mediates the serum-evoked rapid induction of Per1 in fibroblasts through the Ca2+-dependent protein kinase C (PKC) pathway. Stimulation with serum rapidly induced nuclear translocation, heterodimerization and Ser\\/Thr phosphorylation of CLOCK just

Hong Seok Shim; Hyunjung Kim; Jiwon Lee; Gi Hoon Son; Sehyung Cho; Tae H Oh; Sang Hyeon Kang; Dong-Seung Seen; Kun Ho Lee; Kyungjin Kim

2007-01-01

406

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

Microsoft Academic Search

Plasma, magnetic-field, and dc electric-field observations from Dynamics Explorers 1 and 2 are used to investigate the morphology of solar-wind ion injection, Birkeland currents, and plasma convection in the morning sector for both positive and negative interplanetary magnetic field (IMF) By components. The results of the study are used to construct a By-dependent global convection model for southward IMF. A

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

1985-01-01

407

Effects of Magnetotail Stretching and IMF on the Orientation of Quiet Auroral Arcs  

NASA Astrophysics Data System (ADS)

We present results from one of the first extensive studies of the orientation of over 7,500 quiet auroral arcs using the THEMIS ground-based all-sky camera array. Arcs were observed to be within ? = +/- 7.7 degrees of east-west alignment near the southern edge of the auroral oval, with more variation at higher latitudes, which strongly suggests that overall arc morphology is governed by the large-scale structure of the magnetosphere as opposed to localized processes within the ionosphere. We also found that arcs tend to deflect a few degrees southward of geomagnetic east prior to 2300 MLT, and a few degrees northward thereafter. This pattern is consistent with magnetotail stretching as represented by T87 and T89 magnetic field models for quiet (Kp=1,3) conditions, in that arc deflection approximately follows modeled lines of constant B in the equatorial plane mapped to the ionosphere. This again suggests that auroral arc orientation is strongly influenced by large-scale magnetospheric processes. In addition, we studied the effects of the interplanetary magnetic field (IMF) on the location (in magnetic local time) of the reversal of the auroral arc deflection. We found that negative IMF B_x and B_y conditions cause the reversal location to shift duskward of 23 MLT. Alternately, a positive IMF B_x, coupled with a negative B_y, results in a shift in reversal location towards magnetic midnight.

Gillies, D.; Knudsen, D. J.; Donovan, E.; Spanswick, E.

2013-12-01

408

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

NASA Technical Reports Server (NTRS)

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.

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

2004-01-01

409

On the Effect of IMF Turning on Ion Dynamics at Mercury  

NASA Technical Reports Server (NTRS)

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+).

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

2011-01-01

410

Do Sub-Millimeter Galaxy Number Counts Provide Evidence for a Top-Heavy IMF?  

NASA Astrophysics Data System (ADS)

Theoretical models have had difficulty matching the observed number density of sub-millimeter galaxies (SMGs), causing some authors (e.g., Baugh et al. 2005) to suggest that SMGs provide evidence for a top-heavy initial mass function (IMF). To test this claim, we have, for the first time, combined high-resolution 3-D hydrodynamic simulations of isolated and merging massive, gas-rich galaxies, radiative transfer, and a semi-empirical merger rate model to predict the number density of SMGs. Our model can reproduce the observed SMG number density even when using a standard (Kroupa) IMF. The agreement is due to a combination of relatively long sub-mm duty cycles for mergers (a few times 108 years for our most massive models), which owe to our combination of high-resolution 3-D hydrodynamic simulations and dust radiative transfer; sufficient number densities of massive, gas-rich mergers; and the decrease in sub-mm counts observed by recent deep/wide surveys (e.g., Austermann et al. 2010) relative to previous surveys. Our results suggest that the observed SMG number counts do not provide evidence for a top-heavy IMF at high redshift.

Hayward, C. C.; Narayanan, D.; Jonsson, P.; Cox, T. J.; Kereš, D.; Hopkins, P. F.; Hernquist, L.

2011-06-01

411

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

NASA Astrophysics Data System (ADS)

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.

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

412

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

NASA Astrophysics Data System (ADS)

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

Yamaguchi, Atsushi; Shiga, Nobuyasu; Nagano, Shigeo; Li, Ying; Ishijima, Hiroshi; Hachisu, Hidekazu; Kumagai, Motohiro; Ido, Tetsuya

2012-02-01

413

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

SciTech Connect

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

Hairston, M.R.; Heelis, R.A. [Univ. of Texas at Dallas, Richardson, TX (United States)] [Univ. of Texas at Dallas, Richardson, TX (United States)

1995-03-01

414

Interhemispheric observations of nightside ionospheric electric fields in response to IMF B z and B y changes and substorm pseudobreakup  

NASA Astrophysics Data System (ADS)

HF radar data during equinoctial, small IMF By conditions have enabled the ionospheric convection during the substorm growth phase and substorm pseudobreakup to be studied in both hemispheres. This has revealed both conjugate and non-conjugate convection behaviour during the substorm growth phase before and after the pseudobreakup onset. The nightside convection pattern is found to respond promptly to the southward turning of the interplanetary magnetic field (IMF) which impacts on the dusk flank of the magnetosphere due to an inclined phase front in the IMF in the case study presented. The subsequent interhemispheric observations of nightside convection are controlled by the IMF By polarity. The time scale for the response to changes in the IMF By component is found to be a little longer than for Bz, and the full impact of the IMF By is not apparent in the nightside convection until after substorm pseudobreakup has occurred. The pseudobreakup itself is found to result in a transitory suppression in the ionospheric electric field in both hemispheres. This flow suppression is very similar to that observed in HF radar observations of full substorm onset, with the exception of a lack of subsequent poleward expansion.

Yeoman, T. K.; Lewis, R. V.; Khan, H.; Cowley, S. W. H.; Ruohoniemi, J. M.

2000-08-01

415

Entanglement of trapped-ion clock states  

SciTech Connect

A Moelmer-Soerensen entangling gate is realized for pairs of trapped {sup 111}Cd{sup +} ions using magnetic-field insensitive 'clock' states and an implementation offering reduced sensitivity to optical phase drifts. The gate is used to generate the complete set of four entangled states, which are reconstructed and evaluated with quantum-state tomography. An average target-state fidelity of 0.79 is achieved, limited by available laser power and technical noise. The tomographic reconstruction of entangled states demonstrates universal quantum control of two ion qubits, which through multiplexing can provide a route to scalable architectures for trapped-ion quantum computing.

Haljan, P. C.; Lee, P. J.; Brickman, K-A.; Acton, M.; Deslauriers, L.; Monroe, C. [FOCUS Center and Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

2005-12-15

416

Probing unification scenarios with atomic clocks .  

NASA Astrophysics Data System (ADS)

We make use of the comparison between measurements of various pairs of atomic clocks to impose constraints on coupled variations of fundamental constants in severs unification scenarios. We obtain null results for the proton-to-electron mass ratio {dot mu }/{mu }=(0.68±5.79)×10-16 yr-1 and for the gyromagnetic factor {dot g_p}/{g_p}=(-0.72±0.89)×10-16 yr-1 (both of these being at the 95% confidence level). These results are compatible with theoretical expectations on unification scenarios (which we briefly describe), but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

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

417

Entanglement of trapped-ion clock states  

NASA Astrophysics Data System (ADS)

A Mølmer-Sørensen entangling gate is realized for pairs of trapped Cd+111 ions using magnetic-field insensitive “clock” states and an implementation offering reduced sensitivity to optical phase drifts. The gate is used to generate the complete set of four entangled states, which are reconstructed and evaluated with quantum-state tomography. An average target-state fidelity of 0.79 is achieved, limited by available laser power and technical noise. The tomographic reconstruction of entangled states demonstrates universal quantum control of two ion qubits, which through multiplexing can provide a route to scalable architectures for trapped-ion quantum computing.

Haljan, P. C.; Lee, P. J.; Brickman, K.-A.; Acton, M.; Deslauriers, L.; Monroe, C.

2005-12-01

418

Automatic Multi-Stage Clock Gating Optimization Using ILP Formulation  

NASA Astrophysics Data System (ADS)

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

Man, Xin; Horiyama, Takashi; Kimura, Shinji

419

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

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

420

Maps of precipitation by source region, binned by IMF, with inertial convection streamlines  

NASA Astrophysics Data System (ADS)

We present maps of ionospheric precipitation regions, based on 11 years of DMSP particle data, binned by the interplanetary magnetic field (IMF), with superposed SuperDARN convection streamlines gathered under similar conditions. The convection patterns are transformed into an inertial coordinate system. The maps, which include both the nightside and dayside, are created in a fully automated fashion, with, for example, the cusp centered at its centroid latitude for each half hour bin of MLT, with a latitudinal width equal to the statistical difference between the poleward and equatorward edges. The mantle asymmetry about noon does not fit the pattern expected from simple theoretical considerations (namely, that the mantle should be thicker postnoon for positive By in the Northern Hemisphere). The mantle is appreciably thicker prenoon than postnoon, especially for positive By but also even for negative By. This asymmetry matches the SuperDARN convection flows, in which, irrespective of the sign of By, most of the conversion of closed field lines to open occurs prenoon. Quantitatively expressed, for southward IMF, the potential encompassed by flux crossing the open-closed boundary prenoon (0600-1200 MLT) exceeds that for postnoon (1200-1800 MLT) by 30 kV to 15 kV for By > 3 nT and by 30 kV to 20 kV for By < -3 nT. The mantle shape thus matches convection pattern variations. Only ˜25-35% of the dayside open-closed field line conversion occurs within the particle cusp, with the lower number appropriate to northward IMF. Most closed-to-open field line conversion occurs away from noon. Merging is thus active throughout the frontside magnetosphere. Field lines that merge well away from noon do not experience enough particle inflow against the solar wind velocity to produce anything more than a weak, deenergized (mantle) precipitation. The boundary between the dusk cell and dawn cells consistently coincides with one edge of the cusp. IMF By also controls where most of the nightside reconnection occurs. For positive Bz and By > 3 nT, 31 kV reconnects from 1800 to 2400 MLT, but only 14 kV reconnects from 0000 to 06000 MLT. The convection reversal boundary (CRB) consistently coincides with the nightside open-closed particle boundary (OCB). On the dayside, the CRB lies equatorward (poleward) of the OCB in the postnoon (prenoon) sector for By < 0 (By > 0). This shift is consistent with the effects of an interhemispheric current produced by the partial penetration of the IMF By into the frontside magnetosphere.

Newell, P. T.; Ruohoniemi, J. M.; Meng, C.-I.

2004-10-01

421

MITOCHONDRIAL DNA CLOCKS AND THE PHYLOGENY OF DANAUS BUTTERFLIES  

Microsoft Academic Search

Molecular clocks based on sequence change in mitochondrial (mt) DNA have been useful for placing molecular phylogenies in their historical context, thereby enhancing evolutionary insight. Nonetheless, despite their importance to phylogeographers, the methodology is controversial. Here we report on two mitochondrial clocks for the butterfly genus Danaus based on sequences from the cytochrome c oxidase subunit I (COI) and small

GUGS LUSHAI; DAVID A. S. SMITH; DAVE GOULSON; JOHN A. ALLEN; NORMAN MACLEAN

422

A rate-transparent, self-clocking line code  

NASA Technical Reports Server (NTRS)

A reliable and economical new transmission code is presented with the following properties: zero dc content, baseband bandwidth conservation, self-clocking capability, and data-rate-transparent decoding and synchronization. Simple encoder/decoder and clock extractor circuits are given. The code is demonstrated in a wavelength-multiplexed fiber-optic communication system.

Prucnal, Paul R.; Perrier, Philippe A.

1987-01-01

423

Coordination of the maize transcriptome by a conserved circadian clock  

Microsoft Academic Search

BACKGROUND: The plant circadian clock orchestrates 24-hour rhythms in internal physiological processes to coordinate these activities with daily and seasonal changes in the environment. The circadian clock has a profound impact on many aspects of plant growth and development, including biomass accumulation and flowering time. Despite recent advances in understanding the circadian system of the model plant Arabidopsis thaliana, the

Sadaf Khan; Scott C Rowe; Frank G Harmon

2010-01-01

424

Robust synchronization of absolute and difference clocks over networks  

Microsoft Academic Search

We present a detailed re-examination of the problem of inexpensive yet accurate clock synchronization for networked devices. Based on an empirically validated, parsimonious abstraction of the CPU oscillator as a timing source, accessible via the TSC register in popular PC architectures, we build on the key observation that the measurement of time differences, and absolute time, requires separate clocks, both

Darryl Veitch; Julien Ridoux; Satish Babu Korada

2009-01-01

425

Robust synchronization of absolute and difference clocks over networks  

Microsoft Academic Search

We present a detailed re-examination of the problem of inexpensive yet accurate clock synchronization for networked devices. Based on an empirically validated, parsimonious ab- straction of the CPU oscillator as a timing source, accessible via the TSC register in popular PC architectures, we build on the key observation that the measurement of time differences, and absolute time, requires separate clocks,

Darryl Veitch; Julien Ridoux; Satish Babu Korada

2009-01-01

426

Mass, Time, and Clock (Twin) Paradox in Relativity Theory  

Microsoft Academic Search

The paper is intended to clarify operational meaning of mass and time quantities as main characteristics of an atomic clock, which is considered a quantum oscillator in association with the de Broglie wave concept. The specification of the concept of clock in quantum terms reflects the idea of relativistic mass and time complementarity, which is important for avoiding ambiguity of

Anatoli Vankov

2006-01-01

427

Clocked quantum-dot cellular automata shift register  

Microsoft Academic Search

The quantum-dot cellular automata (QCA) computational paradigm provides a means to achieve ultimately low limits of power dissipation by replacing binary coding in currents and voltages with single-electron switching within arrays of quantum dots (“cells”). Clocked control over the cells allows the realization of power gain, memory and pipelining in QCA circuits. We present an experimental demonstration of a clocked

Alexei O. Orlov; Ravi Kummamuru; R. Ramasubramaniam; Craig S. Lent; Gary H. Bernstein; Gregory L. Snider

2003-01-01

428

AMPK Regulates the Circadian Clock by Cryptochrome Phosphorylation and Degradation  

Microsoft Academic Search

Circadian clocks coordinate behavioral and physiological processes with daily light-dark cycles by driving rhythmic transcription of thousands of genes. Whereas the master clock in the brain is set by light, pacemakers in peripheral organs, such as the liver, are reset by food availability, although the setting, or ``entrainment,'' mechanisms remain mysterious. Studying mouse fibroblasts, we demonstrated that the nutrient-responsive adenosine

Katja A. Lamia; Uma M. Sachdeva; Luciano DiTacchio; Elliot C. Williams; Jacqueline G. Alvarez; Daniel F. Egan; Debbie S. Vasquez; Henry Juguilon; Satchidananda Panda; Reuben J. Shaw; Craig B. Thompson; Ronald M. Evans

2009-01-01

429

Stable Kalman filters for processing clock measurement data  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

430

Sub-nanosecond clock synchronization and precision deep space tracking  

NASA Technical Reports Server (NTRS)

Interferometric spacecraft tracking is accomplished at the NASA Deep Space Network (DSN) by comparing the arrival time of electromagnetic spacecraft signals to ground antennas separated by baselines on the order of 8000 km. Clock synchronization errors within and between DSN stations directly impact the attainable tracking accuracy, with a 0.3 ns error in clock synchronization resulting in an 11 nrad angular position error. This level of synchronization is currently achieved by observing a quasar which is angularly close to the spacecraft just after the spacecraft observations. By determining the differential arrival times of the random quasar signal at the stations, clock synchronization and propagation delays within the atmosphere and within the DSN stations are calibrated. Recent developments in time transfer techniques may allow medium accuracy (50-100 nrad) spacecraft observations without near-simultaneous quasar-based calibrations. Solutions are presented for a global network of GPS receivers in which the formal errors in clock offset parameters are less than 0.5 ns. Comparisons of clock rate offsets derived from GPS measurements and from very long baseline interferometry and the examination of clock closure suggest that these formal errors are a realistic measure of GPS-based clock offset precision and accuracy. Incorporating GPS-based clock synchronization measurements into a spacecraft differential ranging system would allow tracking without near-simultaneous quasar observations. The impact on individual spacecraft navigation error sources due to elimination of quasar-based calibrations is presented. System implementation, including calibration of station electronic delays, is discussed.

Dunn, Charles; Lichten, Stephen; Jefferson, David; Border, James S.

1992-01-01

431

Variable-clock-rate A/D converter  

NASA Technical Reports Server (NTRS)

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

Lipoma, P. C.

1980-01-01

432

Compatible Radio Controlled Clock Technology for Radio Broadcasting Data Transceiver  

Microsoft Academic Search

Radio controlled clock (RCC) is a kind of time measuring technique that uses wireless radio to transmit time signals, purposing on synchronizing the signals of wireless receivers and solving the precision and synchronization problems of clocks between different ranges. This paper has thoroughly analyzed the transmitting characteristics and the encoding principle of RCC and based on the existing technique, a

Kuang-Hao Lin; Kuang-Hui Tang; Shi-Yan Huang; Jan-Dong Tseng

2012-01-01

433

The mercury clock of the Libros del Saber  

Microsoft Academic Search

The Libros del Saber de Astronomia is a compilation of various Arabic astronomical works translated into Castilian in the second half of the thirteenth century, under the direction of King Alfonso X of Spain. A section describing a mercury clock has been suggested to be of particular significance in view of the likely invention of the mechanical clock around this

A. A. Mills

1988-01-01

434

The Circadian Clock Regulates Auxin Signaling and Responses in Arabidopsis  

PubMed Central

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

Covington, Michael F; Harmer, Stacey L

2007-01-01

435

GPS IIR Rubidium Clocks: In-Orbit Performance Aspects.  

National Technical Information Service (NTIS)

The GPS Block IIR rubidium clocks have proved to be the best performers in the current GPS constellation, starting with the first IIR operational clock (launched on July 23, 1997). This discussion covers a number of topics, including the frequency accurac...

M. Epstein G. Freed J. Rajan

2004-01-01

436

Carbon nanotubes for quantum-dot cellular automata clocking  

Microsoft Academic Search

Quantum-dot cellular automata (QCA) is a computing model that has shown great promise for efficient molecular computing. The QCA clock signal consists of an electric field being raised and lowered. The wires needed to generate the clocking field have been thought to be the limiting factor in the density of QCA circuits. This paper explores the feasibility of using single

S. E. Frost; T. J. Dysart; P. M. Kogge; Craig S. Lent

2004-01-01

437

Clock synchronisation experiment in India using symphonie satellite  

NASA Technical Reports Server (NTRS)

A recent clock synchronization experiment between the National Physical Laboratory (NPL), New Delhi and Space Applications Center (SAC), Ahemedabad, in India via geostationary satellite symphonie 2, stationed at 49 E longitude, is reported. A two-way transmission using a microwave transponder considered to provide the greatest precision in synchronization of two remote clocks is described.

Somayajulu, Y. V.; Mathur, B. S.; Banerjee, P.; Garg, S. C.; Singh, L.; Sood, P. C.; Tyagi, T. R.; Jain, C. L.; Kumar, K.

1979-01-01

438

Comparison of Various Clocks at the LANL LAPP Facility.  

National Technical Information Service (NTIS)

Several 40+ hour data records obtained in Oct 2010 from the Los Alamos Portable Pulser Facility (LAPP) Operational clocks show variations of (approx) 27 nsec. Several 16+ hour data records obtained in Aug 2010 from non-operational clocks like those used o...

K. A. Dighe

2010-01-01

439

Comparison of various clocks at LANL LAPP facility  

Microsoft Academic Search

Several 40+ hour data records obtained in Oct 2010 from the Los Alamos Portable Pulser Facility (LAPP) Operational clocks show variations of â 27 nsec. Several 16+ hour data records obtained in Aug 2010 from non-operational clocks like those used operationally from 2005 to the present show variations of â 35 nsec. SLRE variability is xxx +\\/- yyy sec (std

Dighe; Kalpak Arvind

2010-01-01

440

Stochastic modeling of pseudolite clock errors using enhanced AR methods  

Microsoft Academic Search

In a pseudolites based real-time locating system, autoregressive (AR) techniques are applied to model the stochastic behavior of the pseudolite clocks errors. A stable model to predict the clock deviations is obtained from the AR parameters of a process smoothed by a Kalman filter. A performance comparison of the proposed scheme with an approach based on a Markov model is

Mohammad Alawieh; Lucila Patino-Studencka; Dirk Dahlhaus

2010-01-01

441

Metrological characterization of the pulsed Rb clock with optical detection  

Microsoft Academic Search

We report on the implementation and metrological characterization of a vapour-cell Rb frequency standard working in a pulsed regime. The three main parts of the clock, physics package, optics and electronics, are described in detail in this paper. The prototype is designed and optimized to detect the clock transition in the optical domain. Specifically, the reference atomic transition, excited with

S Micalizio; C E Calosso; A Godone; F Levi

2012-01-01

442

Electronics for the Pulsed Rubidium Clock: Design and Characterization  

Microsoft Academic Search

Pulsing the different operation phases of a vapor-cell clock (optical pumping, interrogation, and detection) has been recognized as one of the most effective techniques to reduce light shift and then to improve the stability perspectives of vapor cell clocks. However, in order to take full advantage of the pulsed scheme, a fast-gated electronics is required, the times involved being of

Claudio E. Calosso; Salvatore Micalizio; Aldo Godone; Elio K. Bertacco; Filippo Levi

2007-01-01

443

Chronobiology: Biological Clocks and Rhythms of the Skin  

Microsoft Academic Search

The cyclicity of time affects virtually all aspects of our being and is the basis of the underlying rhythmicity which is typical of our lives. To ‘tell time’, most living organisms use internal timing mechanisms known as ‘biological clocks’. These ‘clocks’ coordinate our physiological and behavioral functions and interactions with our environment. One of the strongest influences on rhythmicity is

A. Mehling; J. W. Fluhr

2006-01-01

444

Cryptographic Combinatorial Clock-Proxy Auctions  

NASA Astrophysics Data System (ADS)

We present a cryptographic protocol for conducting efficient, provably correct and secrecy-preserving combinatorial clock-proxy auctions. The “clock phase” functions as a trusted auction despite price discovery: bidders submit encrypted bids, and prove for themselves that they meet activity rules, and can compute total demand and thus verify price increases without revealing any information about individual demands. In the sealed-bid “proxy phase”, all bids are revealed the auctioneer via time-lapse cryptography and a branch-and-bound algorithm is used to solve the winner-determination problem. Homomorphic encryption is used to prove the correctness of the solution, and establishes the correctness of the solution to any interested party. Still an NP-hard optimization problem, the use of homomorphic encryption imposes additional computational time on winner-determination that is linear in the size of the branch-and-bound search tree, and thus roughly linear in the original (search-based) computational time. The result is a solution that avoids, in the usual case, the exponential complexity of previous cryptographically-secure combinatorial auctions.

Parkes, David C.; Rabin, Michael O.; Thorpe, Christopher

445

Femtosecond fiber laser based methane optical clock  

NASA Astrophysics Data System (ADS)

An optical clock based on an Er3+ fiber femtosecond laser and a two-mode He-Ne/CH4 optical frequency standard ( ?=3.39 ?m) is realized. Difference-frequency generation is used to down convert the 1.5-?m frequency comb of the Er3+ femtosecond laser to the 3.4-?m range. The generated infrared comb overlaps with the He-Ne/CH4 laser wavelength and does not depend on the carrier-envelope offset frequency of the 1.5-?m comb. In this way a direct phase-coherent connection between the optical frequency of the He-Ne/CH4 standard and the radio frequency pulse repetition rate of the fiber laser is established. The stability of the optical clock is measured against a commercial hydrogen maser. The measured relative instability is 1×10-12 at 1 s and for averaging times less than 50 s it is determined by the microwave standard, while for longer times a drift of the He-Ne/CH4 optical standard is dominant.

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

2009-06-01

446

From atomic clocks to coordinate times  

NASA Astrophysics Data System (ADS)

The IAU'1991 Resolution A4, complemented by IAU'2000 Resolution B1.3-4, provide rigorous definitions for barycentric and geocentric reference systems in a relativistic framework and define the coordinate times of these systems as TCB and TCG, respectively. Other coordinate times in use are TT, defined from TCG through IAU'2000 Resolution B1.9, and TDB, whose rigorous definition from TCB is now proposed. For practical use, these coordinate times must be realized and the proper time provided by atomic clocks (Atomic time AT) is used to generate all coordinate times. The present sequence is AT => TT ||> TCG -> TCB ||> TDB, where the sign => indicates the complex series of operations involved in generating International atomic time TAI and where ||> is an exact transformation. The paper examines the uncertainty of realization of TAI and the uncertainty brought by the transformation TCG -> TCB. On-going and future evolutions of atomic clocks are reviewed along with their impact on the diagram of time transformations.

Petit, G.

2006-08-01

447

The Renaissance or the cuckoo clock  

PubMed Central

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

Pines, Jonathon; Hagan, Iain

2011-01-01

448

Heisenberg Limited Two Species Ion Clock  

NASA Astrophysics Data System (ADS)

Motivated by recent experiments [1, 2] we propose a new method that attains nearly Heisenberg limited precision clock measurement, exploiting new techniques for environment assisted metrology [3]. Our method makes use of two species of trapped ions in a linear Paul trap, a logic ion for coherent control and readout and multiple spectroscopy ions with stable clock transitions, to achieve Heisnberg limited sensing. It does not require individual addressability of the spectroscopy ions and uses only multi-chromatic (Sorensen-Molmer) gates for entangling operations between the ions, as opposed to the Cirac-Zoller gates used so far. This allows one to use multiple spectroscopy ions in a single Paul trap, improving on previous methods that could use only one ion at a time. Furthermore we find that many of the sources of noise that act as decoherence in regular multi-chromatic gates do not effect the sensitivity of the proposed metrology method. [4pt] [1] T. Rosenband et al., Science 319, 1808 (2008)[0pt] [2] P. O. Schmidt et al., Science 309, 749 (2005)[0pt] [3] G. Goldstein et al., Arxiv 1001.0089

Goldstein, Garry; Cappellaro, Paola; Jiang, Liang; Sorensen, Anders; Lukin, Mikhail

2010-03-01

449

Temperature-compensated clock skew adjustment.  

PubMed

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

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

2013-01-01

450

Circadian clock-regulated physiological outputs: dynamic responses in nature  

PubMed Central

The plant circadian clock is involved in the regulation of numerous processes. It serves as a timekeeper to ensure that the onset of key developmental events coincides with the appropriate conditions. Although internal oscillating clock mechanisms likely evolved in response to the earth’s predictable day and night cycles, organisms must integrate a range of external and internal cues to adjust development and physiology. Here we introduce three different clock outputs to illustrate the complexity of clock control. Clock-regulated diurnal growth is altered by environmental stimuli. The complexity of the photoperiodic flowering pathway highlights numerous nodes through which plants may integrate information to modulate the timing of phenological outputs. Comparative analyses among ecotypes that differ in flowering response reveal additional environmental cues and molecular processes that have developed to influence flowering. We also explore the process of cold acclimation, where circadian inputs, light quality, and stress responses converge to improve freezing tolerance in anticipation of colder temperatures.

Kinmonth-Schultz, Hannah A.; Golembeski, Greg S.; Imaizumi, Takato

2013-01-01

451

Could ROS signals drive tissue-specific clocks?  

PubMed Central

Circadian clocks have emerged to tune the physiology of organisms to periodic changes in the environment in a dynamic fashion. Negative implications of circadian disruptions in humans, animals and plants have encouraged extensive studies of clock-controlled biological processes in various model species. Recently, it has been shown that the transcription-dependent and -independent biological oscillators are largely driven by cellular oxidative cycles that are intrinsically linked with metabolism. Essentially, the clock is viewed as an integrated network that encompasses cytosolic, genetic and metabolic dimensions. Furthermore, in multicellular organisms, the clock network is organized in a tissue-specific manner. Here we discuss questions that remain unanswered: How do these dimensions communicate with each other and how do tissue-specific clocks exchange temporal information within multicellular organisms?

Schippers, Jos HM; Lai, Alvina G; Mueller-Roeber, Bernd; Dijkwel, Paul P

2013-01-01

452

Clock Synchronization in Wireless Sensor Networks: An Overview  

PubMed Central

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

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

2009-01-01

453

Frequency comparison of two high-accuracy Al+ optical clocks.  

PubMed

We have constructed an optical clock with a fractional frequency inaccuracy of 8.6x10{-18}, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the {1}S{0}<-->{3}P{0} clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0x10{-18}. The two clocks exhibit a relative stability of 2.8x10{-15}tau{-1/2}, and a fractional frequency difference of -1.8x10{-17}, consistent with the accuracy limit of the older clock. PMID:20366869

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

2010-02-19

454

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

455

Describe Angle Pair Relationships  

NSDL National Science Digital Library

This lesson will explain the types of pairs of angles you will find in Geometry. Note taking time on page 5: Angle Information Now, let's see if you get it: Angle Relationship Quiz (fun) Ok! Now for your assignment, #8 on page 38! Class Zone Geometry Textbook ...

Neubert, Mrs.

2011-09-01

456

What's Your Angle?  

NSDL National Science Digital Library

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

2010-01-01

457

CLOCK is a substrate of SUMO and sumoylation of CLOCK upregulates the transcriptional activity of estrogen receptor-?.  

PubMed

Disruption of the circadian rhythm is now believed to associate with a number of hormone-related cancers, such as breast cancer, in which aberrant estrogen receptor-? (ER?) signaling is a major contributor. However, the molecular mechanisms underlying the function of core clock proteins in cancer are still largely undefined. In this study, we showed that circadian locomotor output cycles kaput (CLOCK), a key circadian protein, can interact with ER?. Furthermore, this interaction was enhanced by estrogen. We also showed that CLOCK can be sumoylated and sumoylation of CLOCK, which is also stimulated by estrogen, had two consequences: (1) it increased the transcriptional activity of CLOCK; and (2) it increased the CLOCK-modulated transcriptional activity of ER?, as shown by increased transcription of cyclin D1. Sumoylation of CLOCK occurred at two lysine residues, K67 and K851. The enhancement of ER? transcriptional activity exerted by wild-type but not mutant (2K/2R) CLOCK in response to estrogen indicated that sumoylation of CLOCK may have an important role in estrogen-dependent signaling. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay conducted with breast cancer cell lines (MCF-7 and T47D) demonstrated that sumoylation of CLOCK stimulated cell growth and increased the proportion of S phase cells in the cell cycle. The results of this study uncovered new insight into the connection between a major circadian protein and a major estrogen-dependent transcription factor, providing the basis for further research into the involvement of circadian proteins in breast cancer. PMID:23160374

Li, S; Wang, M; Ao, X; Chang, A K; Yang, C; Zhao, F; Bi, H; Liu, Y; Xiao, L; Wu, H

2013-10-10

458

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

PubMed

The CREB/CRE transcriptional pathway has been implicated in circadian clock timing and light-evoked clock resetting. To date, much of the work on CREB in circadian physiology has focused on how changes in the phosphorylation state of CREB regulate the timing processes. However, beyond changes in phosphorylation, CREB-dependent transcription can also be regulated by the CREB coactivator CRTC (CREB-regulated transcription coactivator), also known as TORC (transducer of regulated CREB). Here we profiled both the rhythmic and light-evoked regulation of CRTC1 and CRTC2 in the murine suprachiasmatic nucleus (SCN), the locus of the master mammalian clock. Immunohistochemical analysis revealed rhythmic expression of CRTC1 in the SCN. CRTC1 expression was detected throughout the dorsoventral extent of the SCN in the middle of the subjective day, with limited expression during early night, and late night expression levels intermediate between mid-day and early night levels. In contrast to CRTC1, robust expression of CRTC2 was detected during both the subjective day and night. During early and late subjective night, a brief light pulse induced strong nuclear accumulation of CRTC1 in the SCN. In contrast with CRTC1, photic stimulation did not affect the subcellular localization of CRTC2 in the SCN. Additionally, reporter gene profiling and chromatin immunoprecipitation analysis indicated that CRTC1 was associated with CREB in the 5' regulatory region of the period1 gene, and that overexpression of CRTC1 leads to a marked upregulation in period1 transcription. Together, these data raise the prospect that CRTC1 plays a role in fundamental aspects of SCN clock timing and entrainment. PMID:23699513

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

2013-05-22

459

Evolutionary plasticity of segmentation clock networks.  

PubMed

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

Krol, Aurélie J; Roellig, Daniela; Dequéant, Mary-Lee; Ta