These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

E-print Network

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

Lockwood, Mike

2

Alfvén Mach number and IMF clock angle dependencies of sunward flow channels in the magnetosphere  

NASA Astrophysics Data System (ADS)

Interplanetary coronal mass ejections associated with strong interplanetary magnetic field (IMF) By have been shown to enhance the neutral density in low Earth orbit. The enhancement has been linked to strong downward Poynting fluxes embedded within ionospheric channels of significant sunward ExB drift (2000-3000 m/s). Here we present MHD results describing the magnetospheric counterpart of the ionospheric flow channel that Defense Meteorological Satellite Program (DMSP) encountered on 15 May 2005. It is shown that the clock angle of maximum sunward flow (?FC) depends on the IMF clock angle ?FC = ? * ?IMF - 1.3° with ? = (0.30, 0.38, 0.43, 0.45) at X = (4, 2, 0, -2) RE. This is poleward of the magnetic null point region. The flow also depends on the solar wind Alfvén Mach number Vx = Vx0 - ?v * MA. The critical MA = Vx0 / ?V for Vx = 0 decreases from MA = 3.42 (X = 4 RE) to MA = 2.40 (X = -2 RE). The low MA and ?IMF conditions that characterized the X = 2 RE flow and resulted in strong Poynting flux occurred for 16% of all 167 h in 1998-2008 with Dst < -180 nT.

Eriksson, S.; RastäTter, L.

2013-04-01

3

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

NASA Astrophysics Data System (ADS)

We apply a numerical model of time-dependent ionospheric convection to two directly driven reconnection pulses during a 15-min interval of southward IMF on 26 November 2000. The model requires an input magnetopause reconnection rate variation, which is here derived from the observed variation in the upstream IMF clock angle, ?. The reconnection rate is mapped to an ionospheric merging gap, the MLT extent of which is inferred from the Doppler-shifted Lyman-? emission on newly opened field lines, as observed by the FUV instrument on the IMAGE spacecraft. The model is used to reproduce a variety of features observed during this event: SuperDARN observations of the ionospheric convection pattern and transpolar voltage; FUV observations of the growth of patches of newly opened flux; FUV and in situ observations of the location of the Open-Closed field line Boundary (OCB) and a cusp ion step. We adopt a clock angle dependence of the magnetopause reconnection electric field, mapped to the ionosphere, of the form Enosin4(?/2) and estimate the peak value, Eno, by matching observed and modeled variations of both the latitude, ?OCB, of the dayside OCB (as inferred from the equatorward edge of cusp proton emissions seen by FUV) and the transpolar voltage ?PC (as derived using the mapped potential technique from SuperDARN HF radar data). This analysis also yields the time constant ?OCB with which the open-closed boundary relaxes back toward its equilibrium configuration. For the case studied here, we find ?OCB = 9.7 ± 1.3 min, consistent with previous inferences from the observed response of ionospheric flow to southward turnings of the IMF. The analysis confirms quantitatively the concepts of ionospheric flow excitation on which the model is based and explains some otherwise anomalous features of the cusp precipitation morphology.

Lockwood, M.; Lanchester, B. S.; Morley, S. K.; Throp, K.; Milan, S. E.; Lester, M.; Frey, H. U.

2006-02-01

4

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

5

JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, VOL. 118, 49985007, doi:10.1002/jgra.50479, 2013 Tracing magnetic separators and their dependence on IMF clock  

E-print Network

JOURNAL OF GEOPHYSICAL RESEARCH: SPACE PHYSICS, VOL. 118, 4998­5007, doi:10.1002/jgra.50479, 2013 and their dependence on IMF clock angle in global magnetospheric simulations, J. Geophys. Res. Space Physics, 118, 4998 [Angelopoulos et al., 2008, and references therein]. Deter- mining where reconnection happens as a function

6

Effects of dipole tilt angle on geomagnetic activity  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

7

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

8

Cluster Survey of the Occurrence of Reconnection Tailward of the Cusp and its IMF Dependence: Implications for Component and Anti-Parallel Merging  

NASA Astrophysics Data System (ADS)

We have surveyed the occurrence of earthward directed reconnection jets at the poleward edge of the cusp detected by Cluster as a function of the interplanetary magnetic field (IMF) clock angle. The survey covers 3 years (2001-2003) of cusp and magnetopause crossings and is restricted to periods of relatively stable IMF. Our survey indicates that these jets occur only when the IMF clock angle is within ~90 degrees of the GSM +z direction. This finding at first seems inconsistent with the component merging model which should allow reconnection to occur for large than 90 degree clock angle (or less than 90 degrees in magnetic shear angle). However, it is possible that this is a geophysical rather than a physical effect. When the IMF has a southward component, reconnection equatorward of the cusp could prevent the formation of a plasma depletion layer adjacent to the low- and high-latitude magnetopause, resulting in super-Alfvenic magnetosheath flows next to the high-latitude magnetopause. No accelerated reconnecton jets can be detected sunward of the X-line in this regime. On the other hand, our survey also found that the dawn-dusk location of reconnection jet detection is independent of the IMF By which seems inconsistent with anti-parallel merging.

Phan, T.; Twitty, C.; Paschmann, G.; Carlson, C.; Lavraud, B.; Reme, H.; Dunlop, M.

2004-05-01

9

Cluster Survey of the Occurrence of Reconnection Tailward of the Cusp and its IMF Dependence: Implications for Component and Anti-Parallel Merging  

NASA Astrophysics Data System (ADS)

We have surveyed the occurrence of earthward directed reconnection jets at the poleward edge of the cusp detected by Cluster as a function of the interplanetary magnetic field (IMF) clock angle. The survey covers 3 years (2001-2003) of cusp and magnetopause crossings and is restricted to periods of relatively stable IMF. Our survey indicates that these jets occur only when the IMF clock angle is within ~ 90 degrees of the GSM +z direction. This finding at first seems inconsistent with the component merging model which should allow reconnection to occur for large than 90 degrees clock angle (or less than 90 degrees in magnetic shear angle). However, it is possible that this is a geophysical rather than a physical effect. When the IMF has a southward component, reconnection equatorward of the cusp could prevent the formation of a plasma depletion layer adjacent to the low- and high-latitude magnetopause, resulting in super-Alfvenic magnetosheath flows next to the high-latitude magnetopause. No accelerated reconnecton jets can be detected sunward of the X-line in this regime. On the other hand, our survey also found that the dawn-dusk location of reconnection jet detection is independent of the IMF By which seems inconsistent with anti-parallel merging.

Twitty, C.; Phan, T.; Paschmann, G.; Carlson, C.; Lavraud, B.; Reme, H.; Dunlop, M.; Balogh, A.

10

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

NASA Astrophysics Data System (ADS)

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

Kuznetsova, Tamara

11

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.

12

Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms  

NASA Astrophysics Data System (ADS)

We combine in situ measurements from Cluster with high-resolution 557.7 nm all-sky images from South Pole to investigate the spatial and temporal evolution of merging on the dayside magnetopause. Variations of 557.7 nm emissions were observed at a 6 s cadence at South Pole on 29 April 2003 while significant changes in the Interplanetary Magnetic Field (IMF) clock angle were reaching the magnetopause. Electrons energized at merging sites are the probable sources for 557.7 nm cusp emissions. At the same time Cluster was crossing the pre-noon cusp in the Northern Hemisphere. The combined observations confirm results of a previous study that merging events can occur at multiple sites simultaneously and vary asynchronously on time scales of 10 s to 3 min (Maynard et al., 2004). The intensity of the emissions and the merging rate appear to vary with changes in the IMF clock angle, IMF BX and the dynamic pressure of the solar wind. Most poleward moving auroral forms (PMAFs) reflect responses to changes in interplanetary medium rather than to local processes. The changes in magnetopause position required by increases in dynamic pressure are mediated by merging and result in the generation of PMAFs. Small (15-20%) variations in dynamic pressure of the solar wind are sufficient to launch PMAFs. Changes in IMF BX create magnetic flux compressions and rarefactions in the solar wind. Increases (decreases) in IMF BX strengthens |B| near northern (southern) hemisphere merging sites thereby enhancing merging rates and triggering PMAFs. When correlating responses in the two hemispheres, the presence of significant IMF BX also requires that different lag-times be applied to ACE measurements acquired ~0.1 AU upstream of Earth. Cluster observations set lag times for merging at Northern Hemisphere sites; post-noon optical emissions set times of Southern Hemisphere merging. All-sky images and magnetohydrodynamic simulations indicate that merging occurs in multiple discrete locations, rather than continuously, across the dayside for southward IMF conditions in the presence of dipole tilt. Matching optical signatures with clock-angle, BX, and dynamic pressure variations provides new insights about interplanetary control of dayside merging and associated auroral dynamics.

Maynard, N. C.; Burke, W. J.; Ebihara, Y.; Ober, D. M.; Wilson, G. R.; Siebert, K. D.; Winningham, J. D.; Lanzerotti, L. J.; Farrugia, C. J.; Ejiri, M.; Rème, H.; Balogh, A.; Fazakerley, A.

2006-11-01

13

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

14

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

15

IMF Working Papers  

NSDL National Science Digital Library

As of January, 1997, the International Monetary Fund has begun to provide full text (Adobe Acrobat [.pdf] format only) of its Working Papers. At present 17 papers are available, on such topics as India's saving performance, the effect labor market policies and growth fundamentals have on OECD countries, the Austrian pension system, and business cycles in Asia and Latin America, among others. Print copy price information and selected abstracts are available. As the IMF has produced an average of 127 Working Papers per year since 1991, this promises to be a major economic working paper repository. The IMF also provides other services from its home page, highlighted by its Dissemination Standards Bulletin Board--metadata records about economic, financial, and demographic data.

1997-01-01

16

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

17

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

18

Angles  

NSDL National Science Digital Library

This interactive Flash applet enables students, using estimation and measurement skills, to investigate angles. Teachers can use this page for demonstrating how to read a protractor, and the protractor can be hidden to give students practice in estimating angle measures. The size of the angle can be controlled or chosen randomly.

Bunker, Dan

2011-01-01

19

Angles  

NSDL National Science Digital Library

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

Foundation, Shodor E.

2004-01-01

20

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

21

Angles  

NSDL National Science Digital Library

This lesson is designed to introduce students to different types of angles including acute, obtuse, and right. The lesson also introduces ways to compare angles such as alternate interior, corresponding, and many others. This lesson provides links to discussions and activities related to angles as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one.

2010-01-01

22

Interactive Clock  

NSDL National Science Digital Library

This interactive clock allows users to create time on an analog clock to the closest minute. Teachers can also make the time to the closest five minutes, quarter hour, half hour, or hour. Two answers can be revealed to show the time on a digital clock or to read the time as " --- minutes until ---" or "--- minutes past ---". The clock face can be changed to show more or less information and there is an option to show elapsed time.

Myers, Nathan

2012-08-01

23

Clock Wise  

NSDL National Science Digital Library

In this activity, students can enter a time to be displayed on an analog clock. They can also have the clock display a time then read the clock to figure out what time it says. This activity allows students to practice reading analog clocks. 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

24

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

25

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.

26

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

27

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

28

Competitive Accretion and the IMF  

E-print Network

Competitive accretion occurs when stars in a cluster accrete from a shared reservoir of gas. The competition arises due to the relative attraction of stars as a function of their mass and location in the cluster. The low relative motions of the stars and gas in young, gas dominated clusters results in a tidal limit to the accretion whereas in the stellar dominated cluster cores, the high relative velocities results in Bondi-Hoyle accretion. The combination of these two accretion processes produces a two power-law IMF with $\\gamma \\approx -1.5$, for low-mass stars which accrue their mass in the gas dominated regime, and a steeper, $\\gamma\\approx -2.5$, IMF for higher-mass stars that form in the core of a cluster. Simulations of the fragmentation and formation of a stellar cluster show that the final stellar masses, and IMF, are due to competitive accretion. Competitive accretion also naturally results in a mass segregated cluster and in a direct correlation between the richness of a cluster and the mass of the most massive star therein. The {\\sl knee} where the IMF slope changes occurs near the Jeans mass of the system.

Ian A. Bonnell

2005-01-13

29

Dayside auroral emissions controlled by IMF: A survey for dayside auroral excitation at 557.7 and 630.0 nm in Ny-Ålesund, Svalbard  

NASA Astrophysics Data System (ADS)

A survey of dayside 557.7 and 630.0 nm auroral emission, acquired from the all-sky imagers at the Yellow River Station in Ny-Ålesund, Svalbard, shows that the dayside auroral oval could be divided into five auroral active regions: the dawnside (Da, 06:00-07:30 MLT) and duskside (Du, 15:30-17:00 MLT) green aurora sectors, the prenoon (W, 07:30-10:00 MLT) and postnoon (H, 13:00-15:30 MLT) peaks for 557.7 and 630.0 nm auroral emissions, and the midday gap (M, 10:00-13:00 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 interplanetary magnetic field (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 antiparallel 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 interhemispheric currents produced by Ez.

Hu, Ze-Jun; Yang, Hui-Gen; Han, De-Sheng; Huang, De-Hong; Zhang, Bei-Chen; Hu, Hong-Qiao; Liu, Rui-Yuan

2012-02-01

30

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.

31

Evidence in Favour of IMF Variations  

E-print Network

The stellar initial mass function (IMF) determines the relative number of stars born at a given mass. Despite the tremendous effort to establish a universal IMF, the astronomical literature offers a wealth of diverse evidence for IMF variations. This review was prepared for a controversial debate at the conference ``Starbursts -- Near and Far'' at Ringberg Castle, 2000, and gives a one-sided portrayal in favour of IMF variations. I will summarise the empirical evidence that the IMF varies with time, with environment, and for all stellar masses. While I see no obvious systematic trend in most regions of our Galaxy, there is at least an indication that the IMF is biased towards more massive stars in the early universe and in starbursts.

Frank Eisenhauer

2001-01-18

32

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

33

IMF Prediction with Cosmic Rays  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

34

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

NASA Astrophysics Data System (ADS)

Substorms and storms occurring under conditions of northward IMF (BZN) are commonly examined as "extraordinary events" since they are developed when the efficiency of the interplanetary electric field EY = vBZS (Reiff and Luhmann, 1986) falls to zero. Examination of these events demonstrates that all of them occur, like to ordinary substorms and storms, under conditions that are necessary and sufficient for development of substorms (PC ? 1.5 mV/m) and storms ( >2 mV/m). The specified values of the PC index testify that the magnetosphere is affected by the intense interplanetary electric field EKL=vBTsin2?/2 (Kan and Lee, 1979), where BT is the IMF tangential component and ? is an angle between BT component and the geomagnetic Z-axis. The principal difference between coupling functions EY and EKL lies in the fact that EKL function includes the IMF azimuthal (BY) component. As BY increases relative to BZ, the difference between electric fields EY and EKL quickly grows, and the value of EKL field can be as large as 5-10 mV/m even under conditions of northward IMF orientation, when EY reaches to zero. The same situation is valid for substorms triggered by sharp northward turning of the IMF BZ component following the prolonged period of southward IMF influence. Examination of these substorms demonstrates that they are initiated by increase of coupling function EKL and that the substorm sudden onsets were preceded by the PC index growth. Consistency between the IMF northward turning and substorm sudden onset in these cases is coincidence that explains why substorm are only occasionally initiated by the IMF northward turning. Thus, the "extraordinary" storms and substorms occurring under conditions of ineffective northward IMF component turned out to be events nothing out of the ordinary, if examining them in relation to proper coupling function (EKL) and monitoring them by the PC index.

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

2012-04-01

35

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

36

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

37

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

38

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

39

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

40

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

41

Wolf-Rayet Stars as IMF Probes  

E-print Network

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

Claus Leitherer

2004-08-25

42

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

43

IMF, World Bank programs hinder AIDS prevention.  

PubMed

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

Denoon, D J

1995-07-10

44

Press Conference of Stanley Fischer, First Deputy Managing Director, IMF: IMF aid package to South Korea  

NSDL National Science Digital Library

On December 5, 1997, Stanley Fischer, First Deputy Managing Director of the IMF, gave a press conference on the IMF aid package to South Korea. The beginning of the financial crisis in South Korea can be traced to the collapse of Hanbo Steel Corp., the first in a string of large corporate failures in South Korea. This was followed by the decline in the value of the Korean won against the dollar in October 1997, which persisted until November when the Central Bank of Korea stopped intervening to support the won. The continued decline in won forced the Korean government to seek financial assistance from the International Monetary Fund (IMF). On December 3, the IMF announced a $55 billion aid package for South Korea.

Fischer, Stanley.

1997-01-01

45

Clocks and Time  

E-print Network

A general definition of a clock is proposed, and the role of clocks in establishing temporal pre-conditions in quantum mechanical questions is critically discussed. The different status of clocks as used by theorists external to a system and as used by participant-observers within a system is emphasized. It is shown that the foliation of spacetime into instants of time is necessary to correctly interpret the readings of clocks and that clocks are thus insufficient to reconstruct time in the absence of such a foliation.

Arlen Anderson

1995-07-18

46

Optimizing Passive Quantum Clocks  

E-print Network

We describe protocols for passive atomic clocks based on quantum interrogation of the atoms. Unlike previous techniques, our protocols are adaptive and take advantage of prior information about the clock's state. To reduce deviations from an ideal clock, each interrogation is optimized by means of a semidefinite program for atomic state preparation and measurement whose objective function depends on the prior information. Our knowledge of the clock's state is maintained according to a Bayesian model that accounts for noise and measurement results. We implement a full simulation of a running clock with power-law noise models and find significant improvements by applying our techniques.

Michael Mullan; Emanuel Knill

2014-04-15

47

Optimizing passive quantum clocks  

NASA Astrophysics Data System (ADS)

We describe protocols for passive atomic clocks based on quantum interrogation of the atoms. Unlike previous techniques, our protocols are adaptive and take advantage of prior information about the clock's state. To reduce deviations from an ideal clock, each interrogation is optimized by means of a semidefinite program for atomic state preparation and measurement whose objective function depends on the prior information. Our knowledge of the clock's state is maintained according to a Bayesian model that accounts for noise and measurement results. We implement a full simulation of a running clock with power-law noise models and find significant improvements by applying our techniques.

Mullan, Michael; Knill, Emanuel

2014-10-01

48

A reexamination of long-duration radial IMF events  

NASA Astrophysics Data System (ADS)

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

Pi, Gilbert; Shue, Jih-Hong; Chao, Jih-Kwin; N?me?ek, Zdenek; Å afránková, Jana; Lin, Chia-Hsien

2014-09-01

49

IMF Center: EconEd Online  

NSDL National Science Digital Library

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

50

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

Microsoft Academic Search

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

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

1982-01-01

51

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

Microsoft Academic Search

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

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

1982-01-01

52

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

53

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

E-print Network

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

R. Alba

2005-07-22

54

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.

55

Plausible Clocks: Constant Size Logical Clocks for Distributed Systems  

Microsoft Academic Search

. In a Distributed System with N sites, the precise detection of causalrelationships between events can only be done with vector clocks of size N. Thisgives rise to scalability and efficiency problems for accurate logical clocks. Inthis paper we propose a class of logical clocks called plausible clocks that can beimplemented with a number of components not affected by the

Francisco J. Torres-rojas; Mustaque Ahamad

1996-01-01

56

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. PMID:23604478

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

2014-01-01

57

Maintaining Digital Clocks In Step  

Microsoft Academic Search

We design a stabilizing system of simultaneously triggered clocks: if the clock values ever differ, then the system is guaranteed to converge to a state where all clock values are identical, and are subsequently maintained to be identical. Our design of an N-clock system uses N registers of 2 log N bits each and is guaranteed to converge to identical

Anish Arora; Shlomi Dolev; Mohamed G. Gouda

1991-01-01

58

Connection between dynamically derived IMF normalisation and stellar population parameters  

E-print Network

We report on empirical trends between the dynamically determined stellar initial mass function (IMF) and stellar population properties for a complete, volume-limited sample of 260 early-type galaxies from the Atlas3D project. We study trends between our dynamically-derived IMF normalisation and absorption line strengths, and interpret these via single stellar population- (SSP-) equivalent ages, abundance ratios (measured as [alpha/Fe]), and total metallicity, [Z/H]. We find that old and alpha-enhanced galaxies tend to have on average heavier (Salpeter-like) mass normalisation of the IMF, but stellar population does not appear to be a good predictor of the IMF, with a large range of normalisation at a given population parameter. As a result, we find weak IMF-[alpha/Fe] and IMF-age correlations, and no significant IMF-[Z/H] correlation. The observed trends appear significantly weaker than those reported in studies that measure the IMF normalisation via low-mass star demographics inferred through stellar spectra...

McDermid, Richard M; Alatalo, Katherine; Bayet, Estelle; Blitz, Leo; Bois, Maxime; Bournaud, Frederic; Bureau, Martin; Crocker, Alison F; Davies, Roger L; Davis, Timothy A; de Zeeuw, P T; Duc, Pierre-Alain; Emsellem, Eric; Khochfar, Sadegh; Krajnovic, Davor; Kuntschner, Harald; Morganti, Raffaella; Naab, Thorsten; Oosterloo, Tom; Sarzi, Marc; Scott, Nicholas; Serra, Paolo; Weijmans, Anne-Marie; Young, Lisa M

2014-01-01

59

Crisis Prevention through Global Surveillance: A Task beyond the IMF  

Microsoft Academic Search

In early 2008, the future of the International Monetary Fund was in doubt. The world was awash with dollars since the United States ran an enormous current account deficit, the mirror image of which was trade surpluses in most other countries. Hence, few countries had balance of payments problems, and the IMF had few borrowers. IMF income was insufficient to

Swaminathan S. Anklesaria Aiyar

2010-01-01

60

High-latitude Joule heating response to IMF inputs  

Microsoft Academic Search

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

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

2005-01-01

61

IMF Structural Conditionality: How Much is Too Much?  

Microsoft Academic Search

As suggested above, an active debate has long been underway - and has intensified in the wake of the Asian crisis - about the appropriate scope and intrusiveness of IMF policy conditionality. In this paper, I take up one key element of that debate, namely, the role of structural policies in IMF-supported adjustment programs. By \\

Morris Goldstein

2001-01-01

62

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

63

Resetting Biological Clocks  

ERIC Educational Resources Information Center

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

Winfree, Arthur T.

1975-01-01

64

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

65

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

66

Rockets, clocks, and gravity  

Microsoft Academic Search

Uses of atomic clocks, telemetry, and spacecraft to test predictions of the General Theory of Relativity are described. The number of cycles of a signal being generated by an atomic clock on board a satellite and directed toward earth stations allows precise determination of movements away or toward the receiving station, with an accuracy of 1\\/9,192,631,770 when using the outer

R. F. C. Vessot

1982-01-01

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

68

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

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

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

69

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

70

Study of Rolling Bearing SVM Pattern Recognition Based on Correlation Dimension of IMF  

Microsoft Academic Search

A method of pattern recognition based on correlation of intrinsic mode function (IMF) and Support Vector Machine (SVM) was proposed. Firstly, the rolling bearing vibration signal was decomposed into a finit series of IMFS by EMD. Secondly, useful IMFS which contained main fault information were chosen through correlation coefficient threshold filtering method. Finally, the correlation dimensions of the main IMFS

Qing Jiang; Ting Li; Yan Yao; Jinhui Cai

2012-01-01

71

Tutorial: Clock and Clock Systems Performance Measures  

NASA Technical Reports Server (NTRS)

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

Allan, David W.

1996-01-01

72

IMF programs and human rights, 1981–2003  

Microsoft Academic Search

We examined the effects of International Monetary Fund (IMF) supervised programs on changes in government respect for physical\\u000a integrity rights in developing countries between 1981 and 2003. A longer period under an IMF program increased government\\u000a use of torture and extra judicial killing and also worsened the overall human rights conditions in developing countries. The\\u000a use of a two-stage model

M. Rodwan Abouharb; David L. Cingranelli

2009-01-01

73

Trapped Ion Optical Clocks  

Microsoft Academic Search

For the last fifty years, the international standard of time has been the caesium atomic clock, which is based on the 9.2 GHz microwave absorption in caesium-133 atoms. The recent Nobel Physics award to T W Haensch and J L Hall for their development of widespan femtosecond comb metrology has recognised the major role that femtosecond combs have made to

Patrick Gill

2006-01-01

74

Generalized gravitomagnetic clock effect  

E-print Network

In General Relativity, the rotation of a gravitating body like the Earth influences the motion of orbiting test particles or satellites in a non-Newtonian way. This causes, e.g., a precession of the orbital plane known as the Lense-Thirring effect and a precession of the spin of a gyroscope known as the Schiff effect. Here, we discuss a third effect first introduced by Cohen and Mashhoon called the gravitomagnetic clock effect. It describes the difference in proper time of counterrevolving clocks after a revolution of $2\\pi$. For two clocks on counterrotating equatorial circular orbits around the Earth, the effect is about $10^{-7}$ seconds per revolution, which is quite large. We introduce a general relativistic definition of the gravitomagnetic clock effect which is valid for arbitrary pairs of orbits. This includes rotations in the same direction and different initial conditions, which are crucial if the effect can be detected with existing satellites or with payloads on nondedicated missions. We also derive the post-Newtonian expansion of the general relativistic expression and calculate the effect for the example of a satellite of a Global Navigation Satellite System compared to a geostationary satellite.

Eva Hackmann; Claus Lämmerzahl

2014-06-24

75

Generalized gravitomagnetic clock effect  

NASA Astrophysics Data System (ADS)

In general relativity, the rotation of a gravitating body like the Earth influences the motion of orbiting test particles or satellites in a non-Newtonian way. This causes, e.g., a precession of the orbital plane known as the Lense-Thirring effect and a precession of the spin of a gyroscope known as the Schiff effect. Here, we discuss a third effect first introduced by Cohen and Mashhoon called the gravitomagnetic clock effect. It describes the difference in proper time of counterrevolving clocks after a revolution of 2?. For two clocks on counterrotating equatorial circular orbits around the Earth, the effect is about 10-7 s per revolution, which is quite large. We introduce a general relativistic definition of the gravitomagnetic clock effect which is valid for arbitrary pairs of orbits. This includes rotations in the same direction and different initial conditions, which are crucial if the effect can be detected with existing satellites or with payloads on nondedicated missions. We also derive the post-Newtonian expansion of the general relativistic expression and calculate the effect for the example of a satellite of a global navigation satellite system compared to a geostationary satellite.

Hackmann, Eva; Lämmerzahl, Claus

2014-08-01

76

Iron around the clock.  

PubMed

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

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

2014-07-01

77

Iodine Clock Reaction  

NSDL National Science Digital Library

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

78

Feeding the Clock  

NSDL National Science Digital Library

In mammals, sleeping, feeding, and most other physiological processes are influenced by a circadian system and therefore display daily oscillations. These rhythms are generated by self-sustained and cell-autonomous molecular clocks that exist in virtually all cell types. Lamia et al. propose a molecular mechanism through which metabolic cycles may interact with the circadian clockwork circuitry.

David Suter (National Centre of Competence in Research Frontiers in Genetics;); Ueli Schibler (National Centre of Competence in Research Frontiers in Genetics;)

2009-10-16

79

Rockets, clocks, and gravity  

NASA Astrophysics Data System (ADS)

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

Vessot, R. F. C.

80

Solar wind entry into the magnetosphere under northward IMF conditions  

NASA Astrophysics Data System (ADS)

The state of the plasma sheet in the magnetosphere is usually observed to be hot (1-10 keV) and tenuous (~0.1 cm -3 ). However, sometimes part of it is observed to be colder (< 1 keV) and denser (~1 cm -3 ), and the plasma flow is almost stagnant. Much higher density (~10 cm -3 ) plasma material (superdense plasma sheet) is also sometimes observed near the geosynchronous orbit. The cold dense plasma sheet (CDPS) is usually observed after a period of northward interplanetary magnetic field (IMF), which is also a necessary condition for the formation of a superdense plasma sheet (SDPS). Since the CDPS is generally absent of a cold O + component, and the ionospheric outflow is strong only under southward IMF condition, the source of the CDPS is thought to be the solar wind. Usually, solar wind plasma and energy entry into the magnetosphere is considered to occur mainly during the southward IMF condition through reconnection processes that first occur at the dayside magnetopause and then in the magnetotail. However, the formation of CDPS suggests that there are also certain processes that let solar wind enter the magnetosphere when the IMF is northward. The purpose of this dissertation study is to find out the mechanism that transports solar wind plasma into the magnetosphere under northward IMF conditions, and thus to find out the mechanism of the formation of CDPS and SDPS. To study the solar wind entry mechanism, I use global simulations of the magnetosphere in conjunction with the analysis of observation data. The model used here is the Open Global Geospace Circulation Model (OpenGGCM), which is a magnetosphere MHD model with a stretched grid that has higher grid resolution near the Earth. The simulation is driven by the upstream solar wind input. I run simulations for several CDPS events to validate the model by comparing the simulation results with observations. I then establish that the double high- latitude reconnection process is the dominant process that leads to the entry of solar wind plasma under northward IMF conditions, and that it is sufficient to form the CDPS. With the successful simulation of CDPS events, I continue to study a SDPS event in detail using simulation and observations from a series of spacecraft. I find that the southward IMF following a long period of northward IMF condition compresses the preexisting CDPS, and sets off the near-tail reconnection that causes the compressed CDPS to be pushed and accelerated toward the Earth and form the SDPS near the geosynchronous orbit. I further systematically study how the solar wind plasma enters the magnetosphere due to double high-latitude reconnection for various solar wind, northward IMF and geomagnetic dipole conditions. I trace flow paths from the solar wind and study the variation of the magnetic field line topology along the flow paths. I find that there is an entry window through which the solar wind plasma can enter the magnetosphere as a result of double high-latitude reconnection under northward IMF conditions. I show how the entry window depends on solar wind, IMF and geomagnetic dipole parameters. With the entry window, I estimate the solar wind plasma entry rate for various conditions. I find that the entry rate under northward IMF conditions is of the order of 10 26 to 10 27 particles per second. I also estimate the conditions at which solar wind plasma entry is most efficient.

Li, Wenhui

81

Circadian Clocks in the Ovary  

PubMed Central

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

Sellix, Michael T.; Menaker, Michael

2010-01-01

82

An Active Ion Optical Clock  

NASA Astrophysics Data System (ADS)

We propose a scheme for an active ion optical clock with a detailed description of the pumping method, lasing states, output power, linewidth and light shift. Considering 171Yb+ ions in a Paul trap, we propose utilizing a Fabry—Perot resonator to realize the lasing of active optical frequency standards. The quantum-limited linewidth of an active 171Yb+ ion optical clock is narrower than 1 mHz. Based on the mechanism and the advantages of an active optical clock at the ion optical clock transition frequency, this new laser light source as a stable local oscillator will be beneficial to the single-ion optical clock, which currently is one of the most accurate clocks.

Zhuang, Wei; Zhang, Tong-Gang; Chen, Jing-Biao

2014-09-01

83

Microchip-Based Trapped-Atom Clocks  

E-print Network

This is a chapter of a recently published book entitled Atom Chips, edited by Jakob Reichel and Vladan Vuletic. The contents of this chapter include: Basic Principles; Atomic-Fountain versus Trapped-Atom Clocks; Optical-Transition Clocks versus Microwave Clocks; Clocks with Magnetically Trapped Atoms--Fundamental Limits and Experimental Demonstrations; Readout in Trapped-Atom Clocks; and Spin Squeezing.

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

2011-04-20

84

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

85

Accessories Around the Clock.  

E-print Network

Accessories Around the Clock RHEBA MERLE BOYLES GRAHAM HARD NENA ROBERSON FANNIE BROWN EATON Extension Clothing Specialists k. The Texas A. a M. College System 2? well-dressed woman of today believes a wardrobe of fewer q, well chosen... for a short time and are adapfed- by only a few. Some fads can be practical but often they grade you down on appearance. Good taste is realizing the importance of wearing the right clothes for the occasion and the individual. Acc on l m o HINTS...

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

1958-01-01

86

Robust Clock Synchronization in Wireless Sensor Networks  

E-print Network

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

Saibua, Sawin

2010-10-12

87

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

88

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

89

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

90

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

91

The critical solar wind pressure for IMF penetration into the Venus ionosphere  

Microsoft Academic Search

Early observations and simulations have revealed that the occurrence of IMF penetration into the Venus ionosphere depends on the upstream solar wind pressure, and that IMF is transported into the ionosphere by the downward convection when the solar wind dynamic pressure is relatively large. In this paper, we investigated the critical solar wind pressure for the IMF penetration, by using

H. Jin; K. Maezawa; T. Mukai

2008-01-01

92

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

NASA Astrophysics Data System (ADS)

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

Gennaro, Mario

2014-10-01

93

Dayside boundary layer under northward IMF: A Cluster perspective  

NASA Astrophysics Data System (ADS)

It has been proposed that the Low Latitude Boundary Layer (LLBL) was formed by high-latitude reconnection when the IMF is northward. To study the relationship between the low-latitude boundary layer and high-latitude boundary layer under northward IMF condition, we present statistical results based on 3 years of data obtained by Cluster when these spacecraft were in the vicinity of the dayside magnetopause during northward IMF. In total 341 cases of Cluster crossing of Low Latitude Boundary Layer (LLBL) and High Latitude Boundary Layer (HLBL) (according to the definition by Phan et al [1996a,b]) have been analyzed in detail in order to study the relation between the LLBL and the HLBL. The plasma density, temperature, velocity, energetic particle flux and magnetic field geometry change across the magnetopause under northward IMF were analyzed by a superposed epoch analysis. It has been suggested [Zong et al, 2004] that the solar wind plasma density decreases in the magnetospheric boundary region in an exponential mannerwith an e-folding distance of 1000 km during northward IMF in a case study. In this statistical study, we explore further the relation between the distance to magnetopause and the penetration of solar wind plasma inside the magnetopause. Phan, T. D., and G. Paschmann, Low-latitude dayside magnetopause and boundary layer for high magnetic sheath: 1. Structure and motion, J. Geophys. Res.,101, 7801-7815, 1996 Phan, T. D., G. Paschmann, and B. U. O. Sonnerup, Low-latitude dayside magnetopause and boundary layer for high magnetic sheath: 2. Occurrence of magnetic reconnection, J. Geophys. Res.,101, 7817-7828, 1996 Zong, Q.-G., T. A. Fritz, H. Spence, K. Oksavik, Z.-Y. Pu, A. Korth, and P. W. Daly, Energetic particle sounding of the magnetopause: A contribution by Cluster/RAPID, J. Geophys. Res.,109, A04207, 2004

Zhang, H.; Fritz, T.; Zong, Q.; Daly, P.

2004-12-01

94

The structure of the plasma sheet under northward IMF  

NASA Astrophysics Data System (ADS)

Studies on the properties of the plasma sheet have shown that it becomes cold and dense (T < 2 keV, n > 1 cm-3) during extended northward IMF periods and this change in the plasma status is most prominent close to the flanks. When these Cold and Dense Ions (CDIs) are transported earthward, it is reasonable to expect the compression to keep the density high whereas the temperature is elevated by adiabatic heating upon compression. This process should produce Hot-Dense Ions (HDIs) at the inner-edge of the plasma sheet. By defining HDIs with the criteria T > 2 keV, n > 1 cm-3, HDIs have been searched for using five years data of the Geotail spacecraft. HDIs are indeed found, and when focusing on those HDIs obtained under nominal solar wind dynamic pressures, we find them to appear only on the dawnside plasma sheet inner-edge and that during extended northward IMF intervals. That is, the result supports the idea that HDIs are the inner-magnetosphere extension of CDIs, and further imply that such a connection between the two populations takes place only on dawnside. In this paper, we describe the statistical study that reveals this structure of the plasma sheet. This picture suggesting significant dawn-dusk asymmetry in heating and transport in the magnetotail under northward IMF is also tested by case studies in which we inspect data from fortuitous orbits that transverse more than one key region under steady IMF/SW conditions. We also study data from multi-spacecraft monitoring the key regions simultaneously. Expected features are seen in these independent studies implying that the picture obtained by the statistic study indeed reflects the spatial structure of the plasma sheet under northward IMF.

Fujimoto, M.; Phan, T.; Bonnell, J.; McFadden, J.; Carlson, C.; Seki, K.; Kistler, L.; Reme, H.; Mukai, T.

2004-12-01

95

Clock controls angiogenesis.  

PubMed

Circadian rhythms control multiple physiological and pathological processes, including embryonic development in mammals and development of various human diseases. We have recently, in a developing zebrafish embryonic model, discovered that the circadian oscillation controls developmental angiogenesis. Disruption of crucial circadian regulatory genes, including Bmal1 and Period2, results in marked impairment or enhancement of vascular development in zebrafish. At the molecular level, we show that the circadian regulator Bmal1 directly targets the promoter region of the vegf gene in zebrafish, leading to an elevated expression of VEGF. These findings can reasonably be extended to developmental angiogenesis in mammals and even pathological angiogenesis in humans. Thus, our findings, for the first time, shed new light on mechanisms that underlie circadian clock-regulated angiogenesis. PMID:23324349

Jensen, Lasse Dahl; Cao, Yihai

2013-02-01

96

Clocks around Sgr A*  

NASA Astrophysics Data System (ADS)

The S stars near the Galactic Centre and any pulsars that may be on similar orbits can be modelled in a unified way as clocks orbiting a black hole, and hence are potential probes of relativistic effects, including black hole spin. The high eccentricities of many S stars mean that relativistic effects peak strongly around pericentre; for example, orbit precession is not a smooth effect but almost a kick at pericentre. We argue that concentration around pericentre will be an advantage when analysing redshift or pulse-arrival data to measure relativistic effects, because cumulative precession will be drowned out by Newtonian perturbations from other mass in the Galactic Centre region. Wavelet decomposition may be a way to disentangle relativistic effects from Newton perturbations. Assuming a plausible model for Newtonian perturbations on S2, relativity appears to be strongest in a two-year interval around pericentre, in wavelet modes of time-scale ?6 months.

Angélil, Raymond; Saha, Prasenjit

2014-11-01

97

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

98

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

99

Numerical biases on IMF determinations created by binning  

E-print Network

We detect and quantify significant numerical biases in the determination of the slope of power laws with Salpeter (or similar) indices from uniformly-binned data using chi-square minimization. The biases are caused by the correlation between the number of stars per bin and the assigned weights and are especially important when the number of stars per bin is small. This result implies the existence of systematic errors in the values of IMFs calculated in this way. We propose as an alternative using variable-size bins and dividing the stars evenly among them. Such variable-size bins yield very small biases that are only weakly dependent on the number of stars per bin. Furthermore, we show that they allow for the calculation of reliable IMFs with only a small total number of stars. Therefore, they are a preferred alternative to the standard uniform-size binning.

J. Maíz Apellániz; L. Úbeda

2005-05-01

100

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

101

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

102

The Stellar IMF as a Property of Turbulence  

E-print Network

We propose to interpret the stellar IMF as a property of the turbulence in the star--forming gas. Gravitationally unstable density enhancements in the turbulent flow collapse and form stars. Their mass distribution can be derived analytically from the power spectrum of the turbulent flow and the isothermal shock jump conditions in the magnetized gas. For a power spectrum index \\beta=1.74, consistent with Larson's velocity dispersion--size relation as well as with new numerical and analytic results on supersonic turbulence, we obtain a power law mass distribution of dense cores with a slope equal to 3/(4-\\beta)=1.33, consistent with the slope of Salpeter's stellar IMF. Below one solar mass, the mass distribution flattens and turns around at a fraction of a solar mass, as observed for the stellar IMF in a number of stellar clusters, because only the densest cores are gravitationally unstable. The mass distribution at low masses is determined by the Log--Normal distribution of the gas density. The intermittent nature of this distribution is responsible for the generation of a significant number of collapsing cores of brown dwarf mass.

Paolo Padoan; Ake Nordlund

2004-11-16

103

A quantum network of clocks  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

104

The cyanobacterial clock and metabolism.  

PubMed

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

Pattanayak, Gopal; Rust, Michael J

2014-04-01

105

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

106

A quantum network of clocks  

E-print Network

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

Peter Kómár; Eric M. Kessler; Michael Bishof; Liang Jiang; Anders S. Sørensen; Jun Ye; Mikhail D. Lukin

2013-10-22

107

The effects of IMF programs on U.S. foreign direct investment in the developing world  

Microsoft Academic Search

Given the popular wisdom that the U.S. government influences IMF policies and tends to support the business community, it\\u000a might be expected that IMF programs benefit U.S. firms abroad and thus borrower nations are attractive destinations for U.S.\\u000a foreign direct investment (FDI). Surprisingly, no study has tested the impact of IMF loans on U.S. FDI. Controlling for common\\u000a explanations in

Glen Biglaiser; Karl DeRouen Jr

2010-01-01

108

Angle Sums  

NSDL National Science Digital Library

With this applet, students can examine the angles in a triangle, quadrilateral, pentagon, hexagon, heptagon or octagon. They can change the shape of the figure by dragging the vertices; the size of each angle is shown and the sum of the interior angles calculated. Students are challenged to find a relationship between the number of sides and the sum of the interior angles.

Illuminations, Nctm

2000-01-01

109

IMF biases created by binning and unresolved systems  

E-print Network

I discuss two of the possible sources of biases in the determination of the IMF: binning and the existence of unresolved components. The first source is important for clusters with a small number of stars detected in a given mass bin while the second one is relevant for all clusters located beyond the immediate solar neighborhood. For both cases I will present results of numerical simulations and I will discuss strategies to correct for their effects. I also present a brief description of a third unrelated bias source.

J. Maíz Apellániz

2008-01-24

110

Titan's methane clock  

NASA Astrophysics Data System (ADS)

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

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

2010-04-01

111

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

112

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

113

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

114

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

115

Can clocks really run backwards?  

E-print Network

In an apparently unexplored region of relativistic spacetime, a simple thought experiment demonstrates that conjoined Lorentz transformations predict a proper clock at rest will run backwards and that prediction violates the logical principle of causality. Shown first in a modification of the standard clock paradox thought experiment, this fault carries over to finite accelerations of the moving observer. After re-examination of the standard clock paradox, a logical fault was also found in the concept of spacetime. A two-dimensional treatment of the Earth orbit predicts that our astronomers should measure proper time on distant variable objects in our own Galaxy as impossibly running backwards on approach-then-recede trajectories. The excellent record of relativity aside, we still have much new physics to learn about our spatially three-dimensional universe. It is suggested that space is not a freely stretching medium but is something that is substantive and is being produced.

Charles B. Leffert

2002-08-12

116

Synchronization of Huygens' clocks and the Poincaré method  

NASA Astrophysics Data System (ADS)

We study two models of connected pendulum clocks synchronizing their oscillations, a phenomenon originally observed by Huygens. The oscillation angles are assumed to be small so that the pendulums are modeled by harmonic oscillators, clock escapements are modeled by the van der Pol terms. The mass ratio of the pendulum bobs to their casings is taken as a small parameter. Analytic conditions for existence and stability of synchronization regimes, and analytic expressions for their stable amplitudes and period corrections are derived using the Poincaré theorem on existence of periodic solutions in autonomous quasi-linear systems. The anti-phase regime always exists and is stable under variation of the system parameters. The in-phase regime may exist and be stable, exist and be unstable, or not exist at all depending on parameter values. As the damping in the frame connecting the clocks is increased the in-phase stable amplitude and period are decreasing until the regime first destabilizes and then disappears. The results are most complete for the traditional three degrees of freedom model, where the clock casings and the frame are consolidated into a single mass.

Jovanovic, Vojin; Koshkin, Sergiy

2012-06-01

117

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

118

A generalized gravitomagnetic clock effect  

E-print Network

In General Relativity the rotation of a gravitating body like the Earth influences the motion of orbiting test particles or satellites in a non-Newtonian way. This causes e.g. a precession of the orbital plane, known as the Lense-Thirring effect, and a precession of the spin of a gyroscope, known as the Schiff effect. Here we discuss a third effect, first introduced by Cohen and Mashhoon, called the gravitomagnetic clock effect. It describes the difference in proper time of counter revolving clocks after a revolution of $2\\pi$. For two clocks on counter rotating equatorial circular orbits around the Earth the effect is about $10^{-7}$ seconds per revolution, which is quite large. We introduce a general relativistic definition of the gravitomagnetic clock effect which is valid for arbitrary pairs of orbits. This includes rotations in the same direction and different initial conditions, which is crucial if the effect can be detected with existing satellites or with payloads on non-dedicated missions. We also de...

Hackmann, Eva

2014-01-01

119

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

120

Main Sequence Star Counts as a Probe of IMF Variations with Galactic Environment  

NASA Astrophysics Data System (ADS)

There are many theoretical reasons to expect that the stellar initial mass function {IMF} may not be universal across all types of galaxies and eras of star formation, but the empirical evidence for IMF variations is only now becoming compelling. Recent work using multiple complementary indirect methods is converging on the result that more massive, higher metallicity systems contain more bottom-heavy IMFs. Geha et al. {2013} and Kalirai et al. {2013} have just obtained similarly dramatic results with a much more direct and model-independent method: counting stars below the oldest main sequence turnoff in the closest galaxies to the Milky Way. Reliable IMF measurements using this technique are available in the literature for only four galaxies: the Milky Way, the Small Magellanic Cloud, and two ultra-faint dwarfs, which show extremely bottom-light IMFs. We propose to use identical analysis techniques on archival WFPC2, ACS, and WFC3 imaging to determine the IMF from 0.5 to 0.75 Msun in four additional galaxies: the Large Magellanic Cloud, Sagittarius, Ursa Minor, and Draco. These measurements will substantially improve our knowledge of the dependence of the IMF on different galaxy properties such as metallicity and mass, providing new constraints on the physics responsible for IMF variations.

Adams, Joshua

2013-10-01

121

IMF Lending and Geopolitical Influences: The Articles of Agreements and Beyond  

Microsoft Academic Search

A recent work from Barro and Lee (2003) has nourished the ongoing debate on the IMF governance. Using traditional moral hazard hypothesis, they introduced political economy framework to explain IMF loan programs and found that countries' political connections to the United States and other major shareholding countries are a strong determinant. Our work firstly refines their analysis by studying the

Julien REYNAUD; Julien VAUDAY

2005-01-01

122

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. PMID:23161063

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

2013-01-01

123

Clock Laser System for a Strontium Lattice Clock  

NASA Astrophysics Data System (ADS)

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

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

2009-04-01

124

18-mhz clock distribution system  

SciTech Connect

This paper discusses how designing the high-frequency distribution system to allow HP's new 32-bit VLSI processor to operate at 18 mhz proved to be a significant design challenge. The chips required 6 v, two-phase, nonoverlapping clocks with rise times less than 6 ns and overshoot/undershoot less than 1 v. It was decided early in the project that, because of area constraints, the processor chips would not buffer their clocks. However the RAM chips do provide some buffering. Hence the capacitive loading components vary from approximately 300 pf per phase for a CPU chip to approximately 30 pf per phase for a ram chip. In addition, the capacitive loading presented is highly variable because of the dynamic circuits used and depends on which circuits are active. Worst-case tolerances produce capacitive specifications that can vary +or- 30percent and cause unbalanced loads on each phase.

Lob, C.G.; Elkins, A.O.

1983-08-01

125

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

126

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

127

Silencing the circadian clock gene Clock using RNAi reveals dissociation of the circatidal clock from the circadian clock in the mangrove cricket.  

PubMed

Whether a clock that generates a circatidal rhythm shares the same elements as the circadian clock is not fully understood. The mangrove cricket, Apteronemobius asahinai, shows simultaneously two endogenous rhythms in its locomotor activity; the circatidal rhythm generates active and inactive phases, and the circadian rhythm modifies activity levels by suppressing the activity during subjective day. In the present study, we silenced Clock (Clk), a master gene of the circadian clock, in A. asahinai using RNAi to investigate the link between the circatidal and circadian clocks. The abundance of Clk mRNA in the crickets injected with double-stranded RNA of Clk (dsClk) was reduced to a half of that in control crickets. dsClk injection also reduced mRNA abundance of another circadian clock gene period (per) and weakened diel oscillation in per mRNA expression. Examination of the locomotor rhythms under constant conditions revealed that the circadian modification was disrupted after silencing Clk expression, but the circatidal rhythm remained unaffected. There were no significant changes in the free-running period of the circatidal rhythm between the controls and the crickets injected with dsClk. Our results reveal that Clk is essential for the circadian clock, but is not required for the circatidal clock. From these results we propose that the circatidal rhythm of A. asahinai is driven by a clock, the molecular components of which are distinct from that of the circadian clock. PMID:24995838

Takekata, Hiroki; Numata, Hideharu; Shiga, Sakiko; Goto, Shin G

2014-09-01

128

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

NASA Astrophysics Data System (ADS)

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

Dib, Sami

2014-10-01

129

Angles (elementary)  

NSDL National Science Digital Library

This lesson is designed to introduce students to acute, obtuse, and right angles. This lesson provides links to discussions and activities related to angles as well as suggested ways to integrate them into the lesson. Finally, the lesson provides links to follow-up lessons designed for use in succession with the current one.

2010-01-01

130

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

131

Diversity of Human Clock Genotypes and Consequences  

PubMed Central

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

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

2014-01-01

132

The Circadian Clock Coordinates Ribosome Biogenesis  

PubMed Central

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

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

2013-01-01

133

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

134

Supporting Family Awareness with the Whereabouts Clock  

Microsoft Academic Search

We report the results of a field trial of a situated awareness device for families called the “Whereabouts Clock”. The Clock\\u000a displays the location of family members using cellphone data as one of four privacy-preserving, deliberately coarse-grained\\u000a categories (HOME, WORK, SCHOOL or ELSEWHERE). The results show that awareness of others through the Clock supports not only family communication and coordination

Abigail Sellen; Alex S. Taylor; Barry Brown; Shahram Izadi

2009-01-01

135

Electron channeling, de Broglie's clock and the relativistic time operator  

E-print Network

Electron channeling in silicon crystals has brought forward the possibility of having detected a particle's "internal clock", as an intrinsic oscillation with de Broglie's frequency. The transmission probability along a major axial direction is reduced with respect to neighboring angles, except for a sharp peak at the atomic row direction. The pattern observed is a "W" instead of a "U". This central peak is attributed to a process known as "rosette motion", in which the crossing of successive atoms would be related to the de Broglie frequency. A classical multiple scattering calculation found that, to represent the experimental results, the interaction frequency had to be about twice the de Broglie's clock frequency; that is, the "Zitterbewegung" frequency. In the present paper, the observed characteristics of this process are shown to be consistent with a free particle quantum mechanical motion described by Dirac's Hamiltonian, albeit with an effective mass resulting from the interaction with the crystal atoms. The introduction of a self-adjoint dynamic time operator provides the connection with an internal "system time", the de Broglie clock.

M. Bauer

2014-03-18

136

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

137

Low velocity limits of cold atom clocks  

E-print Network

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

J. Muñoz; I. Lizuain; J. G. Muga

2009-09-08

138

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

E-print Network

GPS clock calibration using an atomic clock Shuei YAMADA,Hans Gerd BERNS Abstract Time di#11;ernece of GPS at SK and KEK was measured by making reference to an atomic clock. Following value was obtained: TGPS@SK TGPS@KEK = 0:115#22;sec: 1 motivation #15; measure time di#11;errence of GPS at SK and KEK #15

Berns, Hans-Gerd

139

The Satellite Clock Bias Forecast Based on Empirical Mode Decomposition and Least Squares Support Vector Machines  

NASA Astrophysics Data System (ADS)

In order to solve the nonlinear and non-stationary characteristics of satellite clock bias (SCB), a hybrid model combining the empirical mode decomposition (EMD) and least squares support vector machines (LSSVM) for the SCB forecasting is proposed in this paper. The main ideas are as follows: the single difference sequence is firstly obtained by making difference between two SCB values of adjacent epoch, and then the EMD is used to decompose the difference sequence into several intrinsic mode function (IMF) components, and one residual component. Secondly, the LSSVM are constructed to forecast these IMFs and residual values individually, and then all these forecasted values are aggregated to produce the forecasted value for the single difference. Finally, the forecasted single difference sequence is recovered to the corresponding predicted SCB. The GPS satellites are taken for example, and the prediction experiments are carried out so as to verify the feasibility and validity of the proposed algorithm. The simulation results show that the proposed EMD-LSSVM model can be employed to predict the SCB effectively, whose predicted accuracy is better than those of the quadratic polynomial (QP) and grey models, as well as the LSSVM model without time series decomposition.

Lei, Y.; Zhao, D. N.

2014-05-01

140

The Influence of the Interplanetary Magnetic Field (IMF) on Atmospheric Escape at Mars  

NASA Astrophysics Data System (ADS)

We present a study on the response of Mars’ atmosphere to changes in the interplanetary magnetic field (IMF) configuration, specifically with respect to the atmospheric escape rate via pick up ions and upcoming MAVEN observations.

Curry, S. M.; Luhmann, J. G.; Ma, Y.; Dong, C. F.; Brain, D. A.

2014-07-01

141

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

NASA Astrophysics Data System (ADS)

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

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

142

Macroeconomic effects of IMF-sponsored programs in Latin America: output costs, program recidivism and the vicious cycle of failed stabilizations  

Microsoft Academic Search

We investigate the effects of IMF stabilization programs, and the reasons behind the unusually high IMF activity and relatively low program completion rates in Latin America. We base our tests on a panel, and distinguish between IMF program approvals and completion. We find that Latin America has higher output costs of IMF programs (especially when completed), no improvement in the

Michael M. Hutchison; Ilan Noy

2003-01-01

143

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

144

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

145

Regionalizing Multilateralism: Estimating the Power of Potential Regional Voting Blocs in the IMF  

Microsoft Academic Search

This paper explores the voting power of hypothetical regional voting blocs in the Executive Board of the International Monetary Fund. We first discuss the prospect of regionally defined groups becoming more significant in the Fund’s decision-making process. After briefly outlining the IMF’s formal decision procedures, including its weighted voting system, use of special majorities, and the function of voting groups

Jonathan R. Strand; David P. Rapkin

2005-01-01

146

IMF By effects in the plasma flow at the polar cap boundary  

NASA Astrophysics Data System (ADS)

We used the dataset obtained from the EISCAT Svalbard Radar during 2000-2008 to study statistically the ionospheric convection in a vicinity of the polar cap boundary as related to IMF By conditions separately for northward and southward IMF. The effect of IMF By is manifested in the intensity and direction of the azimuthal component of ionospheric flow. The most significant effect is observed on the day and night sides whereas on dawn and dusk the effect is essentially less prominent. However, there is an asymmetry with respect to the noon-midnight meridian. On the day side the intensity of By-related azimuthal flow is maximal exactly at noon, whereas on the night side the maximum is shifted toward the post-midnight hours (~03:00 MLT). On the dusk side the relative reduction of the azimuthal flow is much larger than that on the dawn side. Overall, the magnetospheric response to IMF By seems to be stronger in the 00:00-12:00 MLT sector compared to the 12:00-24:00 MLTs. Quantitative characteristics of the IMF By effect are presented and partly explained by the magnetospheric electric fields generated due to the solar wind and also by the position of open-closed boundary for different IMF orientation.

Lukianova, R.; Kozlovsky, A.

2011-07-01

147

Clock Sources for Synchronized Communication Systems  

Microsoft Academic Search

The ideal clock source will have start-stop capability, maintain known phase with respect to a start signal and combine high-frequency stability with voltage tuning to permit phase lock and Doppler correction. These properties define a clock source suitable for synchronized communication systems in which a remote unit must be started in synchronism with the signal received from a local unit.

Richard C. Mackey

1962-01-01

148

Combinatorial Clock Auctions: Price Direction and Performance  

Microsoft Academic Search

This paper addresses three concerns with ascending price Combinatorial Clock Auctions (CCAs); price guidance toward efficiency relevant packages, computational burden, and susceptibility to collusive bidding. We propose a descending price Combinatorial Clock Auction (DCCA) with a newly devised pricing strategy to alleviate all of these concerns. Mimicking bidding behavior of human subjects found in previous laboratory experiments, agent-based simulations of

David R. Munro; Stephen Rassenti

2011-01-01

149

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

150

Orbit determination for next generation space clocks  

NASA Astrophysics Data System (ADS)

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

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

2009-09-01

151

The Ozone-Iodine-Chlorate Clock Reaction  

PubMed Central

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

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

2013-01-01

152

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

153

The Jeans mass and the origin of the knee in the IMF  

E-print Network

We use numerical simulations of the fragmentation of a 1000 solar mass molecular cloud and the formation of a stellar cluster to study how the initial conditions for star formation affect the resulting initial mass function (IMF). In particular, we are interested in the relation between the thermal Jeans mass in a cloud and the knee of the initial mass function, i.e. the mass separating the region with a flat IMF slope from that typified by a steeper, Salpeter-like, slope. In three isothermal simulations with M_J=1 solar mass, M_J=2 solar masses and M_J=5 solar masses, the number of stars formed, at comparable dynamical times, scales roughly with the number of initial Jeans masses in the cloud. The mean stellar mass also increases (though less than linearly) with the initial Jeans mass in the cloud. It is found that the IMF in each case displays a prominent knee, located roughly at the mass scale of the initial Jeans mass. Thus clouds with higher initial Jeans masses produce IMFs which are shallow to higher masses. This implies that a universal IMF requires a physical mechanism that sets the Jeans mass to be near 1 solar mass. Simulations including a barotropic equation of state as suggested by Larson, with cooling at low densities followed by gentle heating at higher densities, are able to produce realistic IMFs with the knee located at approximately 1 solar mass, even with an initial M_J=5 solar masses. We therefore suggest that the observed universality of the IMF in the local Universe does not require any fine tuning of the initial conditions in star forming clouds but is instead imprinted by details of the cooling physics of the collapsing gas.

I. A. Bonnell; C. J. Clarke; M. R. Bate

2006-03-17

154

Evidence for Systematic IMF Variations in the Giant H II Regions of M33  

NASA Astrophysics Data System (ADS)

HST/WFPC2 photometry of the ionizing stellar populations in 6 giant H II regions of M33 reveal a significant steepening of the IMF slope (? ) with increasing galactocentric radius and concurrently decreasing O/H abundance, amounting to d(? )/d[O/H] ~ 1/dex (Park et al. 2001, in preparation). This IMF steepening represents the first strong evidence for a systematic environmental effect on stellar population at the high-mass end. The photoevaporative process, pioneered by J. J. Hester et al. (1996) to explain their HST/WFPC2 observations of the Eagle Nebula (M16), provides a viable mechanism for ablating massive protostellar cores and thus steepening the IMF slope. The ablation is expected to increase with decreasing O/H abundance and associated dust that would otherwise shield the protostellar core from the UV photon field. By contrast, considerations of metallicity-dependent accretion and cooling/fragmentation processes predict a flattening of the IMF slope at lower O/H --- which is not seen. Predictions include the most top-heavy (flattest) IMFs occurring near the metal-rich centers of star-forming galaxies, and the most bottom-heavy (steepest) IMFs occurring in the metal-poor disks of dwarf irregular galaxies at the current epoch and in the disks of larger primeval galaxies at high-z ... as in the Hubble Deep Fields. Such metallicity-dependent IMFs would require adjustment of the total computed star formation rates in these systems, the SFRs decreasing in galaxy centers and increasing in dwarf irregular and primeval disk galaxies. W.H.W., J.W.P., and E.M.M. acknowledge prior support from NASA through its HST GO program.

Waller, W. H.; Lee, M. G.; Park, H. S.; Kim, S. C.; Malumuth, E. M.; Parker, J. Wm.

2001-05-01

155

Circadian clocks are designed optimally  

E-print Network

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

Hasegawa, Yoshihiko

2014-01-01

156

Feynman's Clock for open quantum systems  

E-print Network

We show that Feynman's Clock construction, in which the time-evolution of a closed quantum system is encoded as a ground state problem, can be extended to open quantum systems. In our formalism, the ground states of an ensemble of non-Hermitian Feynman Clock Hamiltonians yield stochastic trajectories, which unravel the evolution of a Lindblad master equation. In this way, one can use Feynman's Clock not only to simulate the evolution of a quantum system, but also it's interaction with an environment such as a heat bath or measuring apparatus. A simple numerical example of a two-level atom undergoing spontaneous emission is presented and analyzed.

David G. Tempel; Alan Aspuru-Guzik

2014-06-21

157

Chemo-dynamical evolution of tidal dwarf galaxies. I. Method and IMF dependence  

NASA Astrophysics Data System (ADS)

We present high-resolution simulations of tidal dwarf galaxies (TDGs) to investigate their early chemo-dynamical evolution and test their survivability. In this work, the simulation setup is introduced and the response of TDGs to self-consistent star formation (SF) and an external tidal field is examined. Throughout the simulation star cluster particles with variable masses down to 5 M? form, depending on the local gas reservoir. For low cluster masses Mcl, the stellar initial mass function (IMF) is considered to be either filled or truncated at a maximal star mass mmax to represent the observed mmax-Mcl relation (IGIMF theory). The evolution of TDGs with fully populated and truncated IMFs are compared to study the impact of stellar energy feedback on their survivability. Both TDGs experience an initial starburst but after a dynamical time they evolve into dwarf galaxies with self-regulated and continuous SF. At this stage, the truncated-IMF model contains about six times more stellar mass than the invariant IMF models, but the final bound gas mass is comparable in both models. In spite of their significantly different SF histories, both TDG models are not disrupted within the first 500 Myr. We conclude that TDGs can survive an early starburst, independent of the underlying IMF description, even though they do not harbour a stabilizing dark matter halo.

Ploeckinger, S.; Hensler, G.; Recchi, S.; Mitchell, N.; Kroupa, P.

2014-02-01

158

Fast and accurate clock recovery in packet switched networks  

Microsoft Academic Search

Real-time periodic transmission across packet switched networks requires clock recovery at the destination. The stochastic nature of packet traffic makes clock recovery difficult. A new packet network clock recovery algorithm is proposed for fast and accurate synchronization. The algorithm has the ability to filter out buffer level fluctuations efficiently and remove the negative contribution of delay jitter in clock recovery.

G. Shen; M. H. M. Nizam; E. Liu; L. Gui; X. Xu

2004-01-01

159

Zero-Dead-Time Operation of Interleaved Atomic Clocks  

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

160

Decentralized Fault-Tolerant Clock Pulse Generation in VLSI Chips  

E-print Network

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

Szmolyan, Peter

161

Transition time bounded low-power clock tree construction  

Microsoft Academic Search

Recently power becomes a significant issue in clock network design for high-performance ICs because the clock network consumes a large portion of the total power in the whole system. Also, clock signal is the signal with the highest frequency in the whole system, which makes the transition time bound of the clock signal extremely tight. Hence, it is necessary to

Min Pan; Chris Chong-Nuen Chu; J. Morris Chang

2005-01-01

162

The Fault Tolerant Daisy Chain Clock Synchronization Algorithm  

Microsoft Academic Search

In this report we present a new fault tolerant clock synchronization algorithm called the Fault Tolerant Daisy Chain algorithm. It is intended for internal clock synchronization of systems using a broadcast bus with Time Division Multiple Access (TDMA) communication, or other systems where clock readings are broadcast at regular intervals. The algorithm allows synchronization after each clock reading and is

Henrik Lönn

163

Angle detector  

NASA Technical Reports Server (NTRS)

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

Parra, G. T. (inventor)

1978-01-01

164

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. PMID:24075994

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

2013-01-01

165

Connecting the Circadian Clock with Chemosensation  

E-print Network

responses are under control of the circadian clock. I found that local oscillators in afferent (primary) chemosensory neurons drive rhythms in physiological and behavioral responses to attractive and aversive chemical signals. During the middle of the night...

Chatterjee, Abhishek

2012-07-16

166

Thermoplasticity in the plant circadian clock  

PubMed Central

In the March 2012 issue of The Plant Cell we describe extensive alternative splicing (AS) of Arabidopsis circadian clock genes. Notably these distinct post-transcriptional events associate with different steady-state temperatures and also with plants undergoing temperature transitions leading us to propose that temperature-associated AS is an additional mechanism involved in the operation and control of the plant circadian clock. Here we show that temperature associated AS also extends to REVEILLE 8 (RVE8), demonstrating a hitherto unrecognized link between the expression of this clock associated gene and temperature. Finally we discuss our observations of the plastic nature of clock gene expression at the post-transcriptional level in the context of the ongoing fascination of how plants respond to temperature. PMID:22902701

James, Allan B.; Syed, Naeem Hasan; Brown, John W. S.; Nimmo, Hugh G.

2012-01-01

167

The epigenetic language of circadian clocks.  

PubMed

Epigenetic control, which includes DNA methylation and histone modifications, leads to chromatin remodeling and regulated gene expression. Remodeling of chromatin constitutes a critical interface of transducing signals, such as light or nutrient availability, and how these are interpreted by the cell to generate permissive or silenced states for transcription. CLOCK-BMAL1-mediated activation of clock-controlled genes (CCGs) is coupled to circadian changes in histone modification at their promoters. Several chromatin modifiers, such as the deacetylases SIRT1 and HDAC3 or methyltransferase MLL1, have been shown to be recruited to the promoters of the CCGs in a circadian manner. Interestingly, the central element of the core clock machinery, the transcription factor CLOCK, also possesses histone acetyltransferase activity. Rhythmic expression of the CCGs is abolished in the absence of these chromatin modifiers. Here we will discuss the evidence demonstrating that chromatin remodeling is at the crossroads of circadian rhythms and regulation of metabolism and cellular proliferation. PMID:23604474

Sahar, Saurabh; Sassone-Corsi, Paolo

2013-01-01

168

Techniques for low jitter clock multiplication  

E-print Network

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

Helal, Belal M., 1971-

2008-01-01

169

Phase measurement system using a dithered clock  

DOEpatents

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

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

1991-05-28

170

Biological clocks and the practice of psychiatry  

PubMed Central

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

Schulz, Pierre

2007-01-01

171

Progress in Building NRC's Cesium Fountain Clock.  

National Technical Information Service (NTIS)

We report recent progress made on the construction of a cesium fountain atomic clock at the Frequency and Time Group of the National Research Council (NRC) Canada. We also future design plans and operation scheme of the fountain.

C. Gigault, L. Marmet, P. Dube

2005-01-01

172

Quantum clock synchronization and quantum error correction  

E-print Network

I consider quantum protocols for clock synchronization, and investigate in particular whether entanglement distillation or quantum error-correcting codes can improve the robustness of these protocols. I also draw attention to some unanswered questions about the relativistic theory of quantum measurement. This paper is based on a talk given at the NASA-DoD Workshop on Quantum Information and Clock Synchronization for Space Applications (QuICSSA), September 25-26, 2000.

John Preskill

2000-10-29

173

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

174

Clock gene variation in Tachycineta swallows  

PubMed Central

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

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

2012-01-01

175

Response of the convection electric field on southward turning of the IMF  

NASA Astrophysics Data System (ADS)

We have investigated the response of convection electric fields in the inner magnetosphere on southward turning of the interplanetary magnetic field (IMF), and its spatial dependence using the CRRES spacecraft data measured in the inner magnetosphere. When the southward turning of IMF to -20 nT was measured by IMP-8 twice at 3:12 and 5:52 UT, which was accompanied by a storm with the minimum SYM-H of -216 nT, the CRRES spacecraft was located in the dusk inner magnetosphere and detected enhancements of the convection electric field within 1 min after the southward IMF Bz reaches the dayside magnetopause. The amplitude of the electric field is well reproduced by the Weimer model. These results indicate that plasma convection in the inner magnetosphere quickly responds to the energy input from the solar wind to the magnetosphere, and the time variation can be described by simple mapping of two-cell convection in the ionosphere. However, when the spacecraft is located in the midnight sector, convection electric fields do not quickly respond to southward turning of the IMF. CRRES measured a 20 min delay of enhancements of the electric field at 6.6 RE and 21.5 MLT on March 21, 1991. The amplitude is about a half of the Weimer model electric field mapped onto the spacecraft location. A statistical analysis using 165 events of southward and northward turning of the IMF has clarified that the electric field quickly (< 5 min) responds to IMF variations at the earthward of the inner edge of the electron plasma sheet, while it takes more than 30 min in the plasma sheet. This tendency indicates that plasma convection has a different behavior in and earthward of the plasmasheet.

Nishimura, Y.; Kikuchi, T.; Wygant, J.; Shinbori, A.; Brautigam, D.; Ono, T.; Iizima, M.; Kumamoto, A.

2008-12-01

176

Improving Quantum Clocks via Semidefinite Programming  

E-print Network

The accuracies of modern quantum logic clocks have surpassed those of standard atomic fountain clocks. These clocks also provide a greater degree of control, because before and after clock queries, we are able to apply chosen unitary operations and measurements. Here, we take advantage of these choices and present a numerical technique designed to increase the accuracy of these clocks. We use a greedy approach, minimizing the phase variance of a noisy classical oscillator with respect to a perfect frequency standard after an interrogation step; we do not optimize over successive interrogations or the probe times. We consider arbitrary prior frequency knowledge and compare clocks with varying numbers of ions and queries interlaced with unitary control. Our technique is based on the semidefinite programming formulation of quantum query complexity, a method first developed in the context of deriving algorithmic lower bounds. The application of semidefinite programming to an inherently continuous problem like that considered here requires discretization; we derive bounds on the error introduced and show that it can be made suitably small.

Michael Mullan; Emanuel Knill

2011-07-26

177

Network Features of the Mammalian Circadian Clock  

PubMed Central

The mammalian circadian clock is a cell-autonomous system that drives oscillations in behavior and physiology in anticipation of daily environmental change. To assess the robustness of a human molecular clock, we systematically depleted known clock components and observed that circadian oscillations are maintained over a wide range of disruptions. We developed a novel strategy termed Gene Dosage Network Analysis (GDNA) in which small interfering RNA (siRNA)-induced dose-dependent changes in gene expression were used to build gene association networks consistent with known biochemical constraints. The use of multiple doses powered the analysis to uncover several novel network features of the circadian clock, including proportional responses and signal propagation through interacting genetic modules. We also observed several examples where a gene is up-regulated following knockdown of its paralog, suggesting the clock network utilizes active compensatory mechanisms rather than simple redundancy to confer robustness and maintain function. We propose that these network features act in concert as a genetic buffering system to maintain clock function in the face of genetic and environmental perturbation. PMID:19278294

Baggs, Julie E; Price, Tom S; DiTacchio, Luciano; Panda, Satchidananda; FitzGerald, Garret A; Hogenesch, John B

2009-01-01

178

Republic of Korea: IMF Stand-by Arrangement: Summary of the Economic Program: December 5, 1997  

NSDL National Science Digital Library

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

1997-01-01

179

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

180

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

181

Massive star populations and the IMF in metal-rich starbursts  

E-print Network

We present new spectroscopic observations of Mkn 309, a starburst galaxy with one of the largest WR populations known. A highly super solar metallicity is derived. Using additional objects we analyse a sample of five metal-rich WR galaxies with the main goal of constraining the basic properties of the massive star populations (IMF slope, M_up) and the star formation history (age, burst duration) of these objects by quantitative comparisons with evolutionary synthesis models. The following main results are obtained: 1) The observations are well explained by extended bursts of star formation or a superposition of several bursts. Ages and burst durations are estimated. This naturally explains both the observed WR populations (including WN and WC stars) and the presence of red supergiants. 2) The fitted SEDs indicate that the stellar light suffers from a smaller extinction than that of the gas, confirming independent earlier findings. 3) All the considered observational constraints are compatible with a Salpeter IMF extending to masses >~ 40 Msun. Adopting a conservative approach we derive a LOWER LIMIT of Mup >~ 30 Msun for the Salpeter IMF. From more realistic assumptions on the metallicity and SF history we favour a lower limit Mup >~ 30-40 Msun, which is also in agreement with Hbeta equivalent width measurements of metal-rich HII regions in spiral galaxies indicating an upper mass cut-off of at least ~ 35 - 50 Msun. Steep IMF slopes (alpha >~ 3.3) are very unlikely. (abridged/modified abstract)

Daniel Schaerer; Natalia G. Guseva; Yuri I. Izotov; Trinh X. Thuan

2000-08-31

182

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

E-print Network

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

California at Berkeley, University of

183

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

E-print Network

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

California at Berkeley, University of

184

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF  

E-print Network

The dynamic cusp aurora on 30 November 1997: response to southward turning of the IMF P. E a Accepted: 26 January 1999 Abstract. We document the detailed dynamics of the dayside aurora in the $1200®cation of both the red (630.0 nm) and green (557.7 nm) line emissions in the cusp aurora near 1200 MLT and $100

Paris-Sud XI, Université de

185

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

186

may 7, 2011 vol xlvi no 19 EPW Economic & Political Weekly12 The IMF, Capital Controls  

E-print Network

exchange rate volatility, avoid maturity mismatches, limit speculative activity in an economy, and provideCOMMENTARY may 7, 2011 vol xlvi no 19 EPW Economic & Political Weekly12 The IMF, Capital Controls be effective, arguing that they should be part of the toolkit to promote financial stability, and outlining

Tufts University

187

IMF conditionality and rule of law: exceptional powers and banking in Malaysia and Venezuela  

Microsoft Academic Search

The 1990s was a decade marked by the implementation of market reforms worldwide. Countries in Latin America and Asia experimented with neoliberal programs sponsored by international financial institutions (IFIs) in order to adopt the arrangements required for the functioning of a market economy. The International Monetary Fund (IMF) joined in these efforts and incorporated structural requirements in its programs as

Gabriel Garcia

2009-01-01

188

Modeling of cusp ion structures during southward and northward IMF with particle tracing code  

Microsoft Academic Search

Cusp ion structures have been used to infer the location and properties of reconnection at the Earth's magnetopause. However, satellite movement relative to reconnection sites creates a temporal\\/spatial ambiguity in the observations, and empirical models have difficulty to account for the constantly changing magnetospheric phenomena. In this study, we model the cusp ion structures during southward and northward IMF by

H. Kim; J. Raeder

2008-01-01

189

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

190

MOND and IMF variations in early-type galaxies from ATLAS3D  

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

191

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

192

Compact, Highly Stable Ion Atomic Clock  

NASA Technical Reports Server (NTRS)

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

Prestage, John

2008-01-01

193

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. PMID:20712885

2010-01-01

194

The superoxide dismutase molecular clock revisited.  

PubMed Central

The Cu,Zn superoxide dismutase (SOD) was examined earlier and found to behave in a very unclock-like manner despite (accepted point mutation, or PAM) corrections for multiple replacements per site. Depending upon the time span involved, rates could differ 5-fold. We have sought to determine whether the data might be clock-like if a covarion model were used. We first determined that the number of concomitantly variable codons (covarions) in SOD is 28. With that value fixed we found that the observations for SOD could fit reasonably well a molecular clock if, given 28 covarions, (i) there are approximately six replacements every 10 million years, (ii) the total number of codons is 162, (iii) the number of codons that are permanently invariable across the range of taxa from fungi to mammals is 44, and (iv) the persistence of variability is quite low (0.01). Thus, the inconsistent number of amino acid differences between various pairs of descendent sequences could well be the result of a fairly accurate molecular clock. The general conclusion has two sides: (i) the inference that a given gene is a bad clock may sometimes arise through a failure to take all the relevant biology into account and (ii) one should examine the possibility that different subsets of amino acids are evolving at different rates, because otherwise the assumption of a clock may yield erroneous estimates of divergence times on the basis of the observed number of amino acid differences. PMID:8041700

Fitch, W M; Ayala, F J

1994-01-01

195

Dual-wavelength active optical clock  

E-print Network

We experimentally realize the dual-wavelength active optical clock for the first time. As the Cs cell temperature is kept between 118 $^{\\circ }C$ and 144 $^{\\circ }C$, both the 1359 nm and the 1470 nm stimulated emission output of Cs four-level active optical clock are detected. The 1470 nm output linewidth of each experimental setup of Cs four-level active optical clock is measured to be 590 Hz with the main cavity length unstabilized. To stabilize the cavity length of active optical clock, the experimental scheme of 633 nm and 1359 nm good-bad cavity dual-wavelength active optical clock is proposed, where 633 nm and 1359 nm stimulated emission is working at good-cavity and bad-cavity regime respectively. The cavity length is stabilized by locking the 633 nm output frequency to a super-cavity with the Pound-Drever-Hall (PDH) technique. The frequency stability of 1359 nm bad-cavity stimulated emission output is then expected to be further improved by at least 1 order of magnitude than the 633 nm PDH system d...

Xu, Zhichao; Zhuang, Wei; Chen, Jingbiao

2014-01-01

196

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

197

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

198

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

199

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

PubMed

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

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

2014-01-01

200

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

201

Detection of the gravitomagnetic clock effect  

E-print Network

The essence of the gravitomagnetic clock effect is properly defined showing that its origin is in the topology of world lines with closed space projections. It is shown that, in weak field approximation and for a spherically symmetric central body, the loss of synchrony between two clocks counter-rotating along a circular geodesic is proportional to the angular momentum of the source of the gravitational field. Numerical estimates are presented for objects within the solar system. The less unfavorable situation is found around Jupiter.

A. Tartaglia

1999-09-02

202

A relativistic analysis of clock synchronization  

NASA Technical Reports Server (NTRS)

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

Thomas, J. B.

1974-01-01

203

Caring around the Clock: rounding in practice.  

PubMed

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

Hutchings, Marie

204

The Large Water-Clock of Amphiaraeion  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

205

Regulation of Circadian Clocks by Redox Homeostasis*  

PubMed Central

Living organisms possess biological clocks that resonate with environmental cycles in light, temperature, and food availability. Recently, circadian oscillations in the redox state of peroxiredoxin have been described as an additional non-transcriptional timekeeping mechanism. Of note, this redox cycle is conserved in both prokaryotes and eukaryotes. How the classical “transcription-translation feedback loop” model and this redox oscillation are related is still poorly understood. In this minireview, we describe the most recent evidence pointing to cross-talk between the circadian clock and the redox status of the cell. PMID:23861436

Stangherlin, Alessandra; Reddy, Akhilesh B.

2013-01-01

206

An electronic clock for correlated noise corrections  

NASA Astrophysics Data System (ADS)

An inexpensive and portable approach is presented to measure the time of occurrence of an experimental event as measured by a specific electronic clock. The clock resets in active synchronization with the experimental AC-power cycle. This allows an efficient and complete correction for correlated noise contributions to pulse area and time measurements of detector channels equipped with PhotoMultiplier Tubes. The electronic board that was developed will be described. The performance for the treatment of correlated noise in experimental data taken at the BNL-AGS facility, and analyses of spectral decompositions of this noise, will also be described.

Llope, W. J.; Adams, N.; Kainz, K. K.

2000-04-01

207

Effects of Pinealectomy on Hypothalamic Metabolic and Clock Gene Rhythms  

E-print Network

the validity of the neuroendocrine loop model by suggesting that although melatonin administration affects overt clock function, (Lu and Cassone, 1993) it has no effect on the transcription of clock genes (Yasuo et al., 2002). Thus, expression of these genes...

Clauson, Amanda

2006-07-11

208

Intrachip clock signal distribution via si-based optical interconnect  

E-print Network

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

Ahn, Donghwan

2007-01-01

209

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. ...

210

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. PMID:23012586

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

2012-01-01

211

Spread spectrum clock generation for the reduction of radiated emissions  

Microsoft Academic Search

A method is presented for reducing the radiated emissions of an electronic device by frequency modulating (FM) the system clock. This method, referred to as spread spectrum clock generation, or SSCG, is applicable to most microprocessor based systems. A unique waveform used to frequency modulate a digital clock signal results in a spectrum with sideband harmonics that are nearly uniform

Keith B. Hardin; John T. Fessler; Donald R. Bush

1994-01-01

212

Spoofing GPS Receiver Clock Offset of Phasor Measurement Units  

E-print Network

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

Liberzon, Daniel

213

Sun Watching Lesson 4: Making a Sun Clock  

E-print Network

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

Maxwell, Bruce D.

214

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

E-print Network

cause functional errors. Various clock routing techniques can be broadly categorized into 'balanced tree' and 'fixed mesh' methods. The skew and delay using the balanced tree method is higher compared to the fixed mesh method. Although fixed mesh...

Ramakrishnan, Sundararajan

2010-10-12

215

Optimal Clock Synchronization in Networks Christoph Lenzen  

E-print Network

applications depend on network nodes having a precisely Permission to make digital or hard copies of all 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

216

Compact microwave cavity for hydrogen atomic clock  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

217

An Iodine Fluorescence Quenching Clock Reaction  

Microsoft Academic Search

A fluorescent clock reaction is described that is based on the principles of the Landolt iodine reaction but uses the potent fluorescence quenching properties of triiodide to abruptly extinguish the ultraviolet fluorescence of optical brighteners present in liquid laundry detergents. The reaction uses easily obtained household products. One variation illustrates the sequential steps and mechanisms of the reaction; other variations

Richard B. Weinberg

2007-01-01

218

Blackbody radiation shifts in optical atomic clocks.  

PubMed

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

Safronova, Marianna; Kozlov, Mikhail; Clark, Charles

2012-03-01

219

Systems Biology of the Mammalian Circadian Clock  

E-print Network

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

Spang, Rainer

220

Energy efficient lighting for the biological clock  

Microsoft Academic Search

Unexpectedly the existence of a formerly unknown type of photoreceptor in the human eye has been proven about 10 years ago. Primarily sensitive in the blue spectral range it is responsible for transducing light signals directly into the brain, controlling essential biological functions like setting of the circadian clock or daytime activation. Recent scientific research has enabled beneficial applications. The

Dieter Lang

2011-01-01

221

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

222

Associative skew clock routing for difficult instances  

E-print Network

including difficult instances based on an improved delay model. Experimental results show that our algorithm can reduce the total clock routing wirelength by 9%Â?15% compared to greedy-DME, which is one of the best zero skew routing algorithms....

Kim, Min-seok

2006-08-16

223

Molecular Bases for Circadian Clocks Review  

Microsoft Academic Search

first decades of genetic and molecular genetic analysis of clocks) and the fact that the Drosophila timeless gene, tim, was still in the process of arriving. This era was Life is a cyclical chemical process that is regulated in spent convincing ourselves that such genes really were four dimensions. We distinguish parts of the cycle: de- the key to understanding

Jay C. Dunlap

224

Desynchronization of Noisy Multicellular Clocks Underlies the Population-level Singularity Behavior of Mammalian Circadian Clock  

Microsoft Academic Search

The singularity behavior of circadian clocks defined as the suppression of circadian oscillation by critical perturbation is one of the intriguing dynamical properties of circadian rhythms. Although the singularity behaviors have been observed in various organisms, its mechanism has not yet been elucidated, because the hierarchical structure of multi-cell-level circadian clocks exists behind the organism-level circadian rhythm. In vitro light-responsible

Tetsuya J. Kobayashi; Hideki Ukai; Hiroki R. Ueda

2007-01-01

225

A role for timely nuclear translocation of clock repressor proteins in setting circadian clock speed.  

PubMed

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

Lee, Euna; Kim, Eun Young

2014-09-01

226

Standard emitters (clocks) and calibrated standard emitters (clocks) in spaces with affine connections and metrics  

E-print Network

It is shown that the general belief that the frequency and the absolute value of the velocity of periodic signals sent by a standard emitter do not change on the world line of the emitter needs to be revised and new conditions for the existence of a calibrted standard emitter should be taken into account. The notions of a standard clock and of a calibrated standard clock are introduced in a space with affine connections and metrics. The variation of the velocity and of the frequency of a standard clock could be compared with the constant velocity and the constant frequency of a calibrated standard clock along the world line of the observer. This calibrated standard clock is transported by meand of a generalized Fermi-Walker transport along the same world line of the observer. Some remarks about the synchronization of standard clocks in spaces with affine connections and metrics are given. PACS numbers: 95.30.Sf; 04.90.+h; 04.20.Cv; 04.90.+e

Sawa Manoff

2005-05-12

227

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

PubMed Central

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

Lee, Euna

2014-01-01

228

The monetary approach to the balance of payments and the IMF model of financial programming  

Microsoft Academic Search

The monetary approach to the balance of payments has, in essence, two theorems: (i) The foreign assets of the central bank are negatively related to its domestic assets; (ii) the excess supply of money causes, and is equivalent to, the trade deficit. This paper tests these theorems for India using OLS, 2SLS, and co-integration, error-correction modelling. The IMF-supported adjustment programs

RANJIT SAU

1994-01-01

229

s-Wave Collisional Frequency Shift of a Fermion Clock  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

231

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

232

Arabidopsis circadian clock and photoperiodism: time to think about location  

PubMed Central

Summary of recent advances Plants possess a circadian clock that enables them to coordinate internal biological events with external daily changes. Recent studies in Arabidopsis revealed that tissue specific clock components exist and that the clock network architecture also varies within different organs. These findings indicate that the makeup of circadian clock(s) within a plant is quite variable. Plants utilize the circadian clock to measure day-length changes for regulating seasonal responses, such as flowering. To ensure that flowering occurs under optimum conditions, the clock regulates diurnal CONSTANS (CO) expression. Subsequently, CO protein induces FLOWERING LOCUS T (FT) expression which leads to flowering. It is emerging that both CO and FT expression are intricately controlled by groups of transcription factors with overlapping functions. PMID:19836294

Imaizumi, Takato

2009-01-01

233

Network news: prime time for systems biology of the plant circadian clock truncated form of the title: Plant circadian clocks  

PubMed Central

Summary Whole-transcriptome analyses have established that the plant circadian clock regulates virtually every plant biological process and most prominently hormonal and stress response pathways. Systems biology efforts have successfully modeled the plant central clock machinery and an iterative process of model refinement and experimental validation has contributed significantly to the current view of the central clock machinery. The challenge now is to connect this central clock to the output pathways for understanding how the plant circadian clock contributes to plant growth and fitness in a changing environment. Undoubtedly, systems approaches will be needed to integrate and model the vastly increased volume of experimental data in order to extract meaningful biological information. Thus, we have entered an era of systems modeling, experimental testing, and refinement. This approach, coupled with advances from the genetic and biochemical analyses of clock function, is accelerating our progress towards a comprehensive understanding of the plant circadian clock network. PMID:20889330

McClung, C. Robertson; Gutierrez, Rodrigo A.

2011-01-01

234

Atmospheric limitations to clock synchronization at microwave frequencies  

NASA Technical Reports Server (NTRS)

Clock synchronization schemes utilizing microwave signals that pass through the Earth's atmosphere are ultimately limited by our ability to correct for the variable delay imposed by the atmosphere. The atmosphere is non-dispersive at microwave frequencies and imposes a delay of roughly 8 nanosec times the cosecant of the elevation angle. This delay is composed of two parts, the delay due to water vapor molecules (i.e., the wet delay), and the delay due to all other atmospheric constituents (i.e., the dry delay). Water vapor contributes approximately 5 to 10% of the total atmospheric delay but is highly variable, not well mixed, and difficult to estimate from surface air measurements. However, the techniques of passive remote sensing using microwave radiometry can be used to estimate the line of sight delay due to water vapor with potential accuracies of 10 to 20 picosec. The devices that are used are called water vapor radiometers and simply measure the power emitted by the water vapor molecule at the 22.2 GHz spectral line. An additional power measurement is usually included at 31.4 GHz in order to compensate for the effect of liquid water (e.g., clouds). The dry atmosphere is generally in something close to hydrostatic equilibrium and its delay contribution at zenith can be estimated quite well from a simple barometric measurement. At low elevation angles one must compensate for refractive bending and possible variations in the vertical refractivity profile. With care these effects can be estimated with accuracies on the order of 30 picosec down to elevation angles of 10 degree.

Resch, G. M.

1984-01-01

235

An Iodine Fluorescence Quenching Clock Reaction  

NASA Astrophysics Data System (ADS)

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

Weinberg, Richard B.

2007-05-01

236

Circadian clock control of endocrine factors.  

PubMed

Organisms experience dramatic fluctuations in demands and stresses over the course of the day. In order to maintain biological processes within physiological boundaries, mechanisms have evolved for anticipation of, and adaptation to, these daily fluctuations. Endocrine factors have an integral role in homeostasis. Not only do circulating levels of various endocrine factors oscillate over the 24 h period, but so too does responsiveness of target tissues to these signals or stimuli. Emerging evidence suggests that these daily endocrine oscillations do not occur solely in response to behavioural fluctuations associated with sleep-wake and feeding-fasting cycles, but are orchestrated by an intrinsic timekeeping mechanism known as the circadian clock. Disruption of circadian clocks by genetic and/or environmental factors seems to precipitate numerous common disorders, including the metabolic syndrome and cancer. Collectively, these observations suggest that strategies designed to realign normal circadian rhythmicities hold potential for the treatment of various endocrine-related disorders. PMID:24863387

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

2014-08-01

237

Optimal implementations for reliable circadian clocks.  

PubMed

Circadian rhythms are acquired through evolution to increase the chances for survival through synchronizing with the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. We find by using a phase model with multiple inputs that achieving the maximal limit of regularity and entrainability entails many inherent features of the circadian mechanism. At the molecular level, we demonstrate the role sharing of two light inputs, phase advance and delay, as is well observed in mammals. At the behavioral level, the optimal phase-response curve inevitably contains a dead zone, a time during which light pulses neither advance nor delay the clock. We reproduce the results of phase-controlling experiments entrained by two types of periodic light pulses. Our results indicate that circadian clocks are designed optimally for reliable clockwork through evolution. PMID:25238386

Hasegawa, Yoshihiko; Arita, Masanori

2014-09-01

238

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.

239

Optimal Implementations for Reliable Circadian Clocks  

NASA Astrophysics Data System (ADS)

Circadian rhythms are acquired through evolution to increase the chances for survival through synchronizing with the daylight cycle. Reliable synchronization is realized through two trade-off properties: regularity to keep time precisely, and entrainability to synchronize the internal time with daylight. We find by using a phase model with multiple inputs that achieving the maximal limit of regularity and entrainability entails many inherent features of the circadian mechanism. At the molecular level, we demonstrate the role sharing of two light inputs, phase advance and delay, as is well observed in mammals. At the behavioral level, the optimal phase-response curve inevitably contains a dead zone, a time during which light pulses neither advance nor delay the clock. We reproduce the results of phase-controlling experiments entrained by two types of periodic light pulses. Our results indicate that circadian clocks are designed optimally for reliable clockwork through evolution.

Hasegawa, Yoshihiko; Arita, Masanori

2014-09-01

240

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

241

Clock synchronization for mobile ad hoc networks  

E-print Network

University in partial fulfillment for the designation of UNIVERSITY UNDERGRADUATE RESEARCH FELLOW Approved as to style and content by: Jennifer L. Welch (Fellows Advisor) Edward A. Funkhouser (Executive Director) April 2003 Group: Engineering... and Physics 1 ABSTRACT Clock Synchronization in Mobile Ad Hoc Networks. (April 2003) Rajan Chandra Department of Electrical Engineering Texas A&M University Fellows Advisor: Dr. Jennifer L. Welch Department of Computer Science As mobile networking...

Chandra, Rajan

2013-02-22

242

Ionospheric Response to the Changes in the Interplanetary Magnetic Field (IMF) Bz Under Strong Positive IMF By Conditions, as Seen using SuperDARN and PolarDARN Radars.  

NASA Astrophysics Data System (ADS)

The interplanetary magnetic field (IMF) is known to have a profound influence on the ionospheric convection pattern at high latitudes. Thus, when the IMF has a dominant southward (Bz) component, the convection over the central polar cap is anti-sunward and closes through the dawn and dusk sectors to produce a familiar 2-cell convection pattern. For strong northward IMF conditions, the pattern is thought to break into four cells, with sunward convection taking place over the noon sector of the polar cap. For strong IMF By conditions the standard 2-cell convection pattern is believed to become asymmetric and/or to rotate from its basic alignment with the noon-to- midnight meridian to a more dusk-to-dawn or dawn-to-dusk alignment. With the help of the new PolarDARN radar in combination with other SuperDARN radar data, we have been able to observe changes occurring deep into the polar cap during a period of strong sustained positive IMF By, when the Bz component was always less than 20% of the By component in magnitude. The basic shape of the convection pattern was highly reminiscent of the Heppner-Maynard `BC' convection pattern predicted for strong positive By conditions ( Heppner and Maynard, JGR, 92, 4467, 1987). We note that we observed very clear changes in the convection pattern as Bz changed signs, with a distinct sub-cell on the evening side being present while the IMF Bz component was greater than zero. The sub-cell completely vanished when the Bz component changed sign. These variations were unexpected in view of the relatively small IMF Bz magnitudes involved. Interestingly enough, this feature would have been missed, had the PolarDARN radar data not been added to the data obtained with the rest of the SuperDARN radars. We will discuss the implications of our findings for our understanding of ionospheric/magnetospheric convection in response to solar wind inputs.

Choudhary, R.; St.-Maurice, J.; Sofko, G. J.

2007-12-01

243

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. PMID:24270424

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

244

The hepatic circadian clock modulates xenobiotic metabolism in mice.  

PubMed

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

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

2014-08-01

245

Regulated DNA Methylation and the Circadian Clock: Implications in Cancer  

PubMed Central

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

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

2014-01-01

246

Particle entry through "Sash" groove simulated by Global 3D Electromagnetic Particle code with duskward IMF By  

NASA Astrophysics Data System (ADS)

We made our efforts to parallelize the global 3D HPF Electromagnetic particle model (EMPM) for several years and have also reported our meaningful simulation results that revealed the essential physics involved in interaction of the solar wind with the Earth's magnetosphere using this EMPM (Nishikawa et al., 1995; Nishikawa, 1997, 1998a, b, 2001, 2002) in our PC cluster and supercomputer(D.S. Cai et al., 2001, 2003). Sash patterns and related phenomena have been observed and reported in some satellite observations (Fujumoto et al. 1997; Maynard, 2001), and have motivated 3D MHD simulations (White and al., 1998). We also investigated it with our global 3D parallelized HPF EMPM with dawnward IMF By (K.-I. Nishikawa, 1998) and recently new simulation with dusk-ward IMF By was accomplished in the new VPP5000 supercomputer. In the new simulations performed on the new VPP5000 supercomputer of Tsukuba University, we used larger domain size, 305×205×205, smaller grid size (? ), 0.5R E(the radium of the Earth), more total particle number, 220,000,000 (about 8 pairs per cell). At first, we run this code until we get the so-called quasi-stationary status; After the quasi-stationary status was established, we applied a northward IMF (B z=0.2), and then wait until the IMF arrives around the magnetopuase. After the arrival of IMF, we begin to change the IMF from northward to duskward (IMF B y=-0.2). The results revealed that the groove structure at the day-side magnetopause, that causes particle entry into inner magnetosphere and the cross structure or S-structure at near magneto-tail are formed. Moreover, in contrast with MHD simulations, kinetic characteristic of this event is also analyzed self-consistently with this simulation. The new simulation provides new and more detailed insights for the observed sash event.

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

2004-12-01

247

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

248

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

249

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

E-print Network

We investigate the magneto-optical effect of cold atoms in an integrating sphere both experimentally and theoretically. The dependence of magneto-optical rotation angle on the biased magnetic field, the probe light intensity, and the probe light detuning are investigated. The probe light background is blocked and the shot noise is strongly suppressed. This detection scheme may provide a new approach for high contrast cold atom clock and cold atom optical magnetometer.

Wan, Jinyin; Meng, Yanling; Xiao, Ling; Liu, Peng; Wang, Xiumei; Wang, Yaning; Liu, Liang

2014-01-01

250

Clock rates, clock settings and the physics of the space-time Lorentz transformation  

E-print Network

A careful study is made of the operational meaning of the time symbols appearing in the space-time Lorentz transformation. Four distinct symbols, with different physical meanings, are needed to describe reciprocal measurements involving stationary and uniformly-moving clocks. Physical predictions concern only the observed rate of a clock as a function of its relative speed, not its setting. How the failure to make this distinction leads to the conventional predictions of spurious `relativity of simultaneity' and `length contraction' effects in special relativity is explained.

J. H. Field

2006-06-12

251

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

PubMed

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

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

2009-03-27

252

Initial results from global MHD simulations of magnetospheric ULF pulsations driven by IMF fluctuations  

NASA Astrophysics Data System (ADS)

The physical mechanisms responsible for electron energization, loss, and transport in the outer radiation belt are not well-understood. Several studies have established a link between high solar wind speeds and electron flux enhancements in the outer radiation belt. In particular, high speed stream (HSS)-driven and corotating interaction region (CIR)-driven geomagnetic storms, which typically do not produce Dst depressions comparable to their CME-driven counterparts, often times generate high levels of energetic electron flux in the outer radiation belt. The mechanism(s) that produces such a strong response of the outer radiation belt during HSS- and CIR-driven events remains elusive. We note that interplanetary magnetic field (IMF) fluctuations are often embedded in HSSs and CIRs, in the form of Alfvenic fluctuations. We also note that there is evidence that solar wind driven ultra-low frequency (ULF) waves are associated with electron flux enhancements in the outer radiation belt. Thus, we have explored the possibility that IMF-fluctuation-driven ULF waves are the intermediary physical mechanism responsible for such energetic electron flux enhancements during high solar wind speed events, via drift-resonant wave-particle interactions (e.g. ULF-enhanced radial diffusion). We present an initial set of results from Lyon-Fedder-Mobarry (LFM) global, three-dimensional magnetohydrodynamic (MHD) simulations of the solar wind/magnetosphere interaction. These simulations are driven with synthetic IMF-fluctuations in the upstream solar wind, as an idealization of solar wind Alfvenic fluctuations. The global nature of the LFM simulation permits a full consideration of the spatial distribution and spectral character of the ULF pulsations generated. Knowledge of these wave characteristics is crucial in quantifying the role that ULF waves play in radiation belt electron dynamics.

Claudepierre, S. G.; Elkington, S. R.; Wiltberger, M. J.; Mann, I. R.; Gosling, J. T.

2012-12-01

253

Polar convection and Birkeland currents during strongly positive IMF B sub y  

SciTech Connect

The TRIAD satellite passed directly over the field of view of the Scandinavian Twin Auroral Radar Experiment (STARE) radar on May 1, 1978, at approximately 0618 UT when the B{sub y} component of the interplanetary magnetic field (IMF) was unusually large in comparison to the other two components. The average IMF values in the interval from 0600 to 0700 UT on this day were B{sub x} = {minus}1.8 nT, B{sub y} = 8.7 nT, and B{sub z} = {minus}0.2 nT (King, 1979). The TRIAD magnetic field perturbations revealed the presence of a very intense ({Delta}B {approximately} 500 nT) region 1 downward-flowing Birkeland current near 0930 MLT and poleward of a much weaker upward-flowing region 2 current. This net Birkeland current was located equatorward of a region of intense westward ionospheric convection flow detected by the STARE radar. The authors conclude that the polar cap convection flow is distorted and displaced to low latitudes (< 67{degree} magnetic latitude) in the morning sector during this period of strongly positive B{sub y} and almost negligible B{sub x} and B{sub z}. The large net region 1 Birkeland current is associated with the convection flow reversal. Convection velocity data acquired by the AE-C satellite on October 29, 1978, near 1723 UT when B{sub x} = {minus}0.5 nT, B{sub y} = 8.3 nT, and B{sub z} = {minus}2.7 nT show the convection reversal near 67{degree} invariant latitude and 0800 MLT. These two examples support previous suggestions for the important influence that the B{sub y} component of IMF has on the intensity and location of high-latitude convection and Birkeland currents.

Zi Minyun (Peking Univ. (China)); Nielsen, E. (Max-Planck-Inst. for Aeronomy, Lindau (West Germany)); Hanson, W.B. (Univ. of Texas, Richardson (United States)); Potemra, R.A. (Johns Hopkins Univ., Laurel, MD (United States))

1987-04-01

254

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

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

2004-01-01

255

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

256

Clock Synchronisation in Inertial Frames and Gravitational Fields  

E-print Network

The special relativistic test theory of Mansouri and Sexl is sketched. Theories based on different clock synchronisations are found to be equivalent to special relativity, as regards experimental results. The conventionality of clock synchronisation is shown not to hold, by means of an example, in a simple accelerated system and through the principle of equivalence in gravitational fields, especially when the metric is not static. Experimental implications on very precise clock synchronisation on earth are discussed.

François Goy

1996-07-20

257

[Physiological and pathophysiological role of the circadian clock system].  

PubMed

It has been well known for ages that in living organisms the rhythmicity of biological processes is linked to the ~ 24-hour light-dark cycle. However, the exact function of the circadian clock system has been explored only in the past decades. It came to light that the photosensitive primary "master clock" is situated in the suprachiasmatic photosensitive nuclei of the special hypothalamic region, and that it is working according to ~24-hour changes of light and darkness. The master clock sends its messages to the peripheral "slave clocks". In many organs, like pancreatic ?-cells, the slave clocks have autonomic functions as well. Two essential components of the clock system are proteins encoded by the CLOCK and BMAL1 genes. CLOCK genes are in interaction with endonuclear receptors such as peroxisoma-proliferator activated receptors and Rev-erb-?, as well as with the hypothalamic-pituitary-adrenal axis, regulating the adaptation to stressors, energy supply, metabolic processes and cardiovascular system. Melatonin, the product of corpus pineale has a significant role in the functions of the clock system. The detailed discovery of the clock system has changed our previous knowledge about the development of many diseases. The most explored fields are hypertension, cardiovascular diseases, metabolic processes, mental disorders, cancers, sleep apnoe and joint disorders. CLOCK genes influence ageing as well. The recognition of the periodicity of biological processes makes the optimal dosing of certain drugs feasible. The more detailed discovery of the interaction of the clock system might further improve treatment and prevention of many disorders. PMID:22935429

Halmos, Tamás; Suba, Ilona

2012-09-01

258

Transmutation of Transuranic Elements in Advanced MOX and IMF Fuel Assemblies Utilizing Multi-recycling Strategies  

E-print Network

material in the spent fuel. As indicated in Figure 1.1, the long-term toxicity is associated with actinides, particularly the Transuranium elements (TRUs) while the short-term risks are due to fission products (FPs) [2]. 5 Figure 1.1 Ingestion... Assemblies: IMF is a relatively new concept[6]. It contains Plutonium and Minor Actinides (MA) in a fertile-free matrix. By doing this, the possibility of producing new Plutonium from neutron capture on Uranium (e.g., U- 238?Pu -239) is excluded, and...

Zhang, Yunhuang

2011-02-22

259

A study of the dusk convection cell's response to an IMF southward turning  

NASA Astrophysics Data System (ADS)

One example of the response of ionospheric convection and the polar cap boundary to a sudden change in the interplanetary magnetic field (IMF) orientation has been studied by using ground magnetometers, the Super Dual Auroral Radar Network (SuperDARN), and Defense Meteorological Satellite Program (DMSP) particle detectors when the IMF suddenly changed from northward (+6 nT) to strongly southward (-19 nT) at 1716 UT on 5 September 1995. The Bz component was fairly constant for ~2 hours before and ~25 min after the sudden IMF change. The convection flow changed almost simultaneously over a global extent. This initial change of the convection pattern can be characterized by a sudden formation of a large flow vortex in the afternoon sector. This agrees with the earlier findings by Ruohoniemi and Greenwald [1998] and Ridley et al. [1998]. On the other hand, the response of the polar cap boundary (or its proxy) is more complicated. The Saskatoon radar, located in the late morning sector, observed an equatorward shift of the cusp scatter region simultaneously with the initial response of the convection flows. The DMSP particle data also showed a simultaneous equatorward expansion of the auroral oval in the 2100 magnetic local time (MLT) sector. The radar and particle data indicate the immediate equatorward expansion of the precipitation regions in the noon and premidnight sectors. About 10-20 min after the initial change, there were changes observed in the dusk region, namely, an equatorward expansion of the current reversal boundary observed by the Greenland magnetometer chain in the dusk sector between 1740 and 1750 UT and an equatorward expansion of the convection reversal boundary detected by the Stokkseyri, Halley, and Syowa radars. The delayed responses were observed 18-8 min before a substorm onset was recorded at midlatitude stations at 1756 UT. These observations indicate that there were two kinds of ionospheric responses to the southward turning of the IMF; the first response is the formation of the convection vortex and the equatorward shift of the polar cap boundary at noon and at ~2100 MLT, and the second response is the equatorward expansion of the convection reversal boundary in the dusk sector. We make the case that the first response is associated with the propagation of magnetosonic waves and that the second response is consistent with the Cowley and Lockwood [1992] picture of the redistribution of the newly created open flux in the polar cap region.

Nishitani, Nozomu; Ogawa, Tadahiko; Sato, Natsuo; Yamagishi, Hisao; Pinnock, Mike; Villain, Jean-Paul; Sofko, George; Troshichev, Oleg

2002-03-01

260

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

261

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

262

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. PMID:22750052

Jordan, Sabine D.; Lamia, Katja A.

2012-01-01

263

Derivation and experimental verification of clock synchronization theory  

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 Mid-Point Algorithm. Special clock circuitry was designed and built so that several operating conditions and failure modes (including malicious failures) could be tested. Both theories are shown to predict conservative upper bounds (i.e., measured values of clock skew were always less than the theory prediction). Insight gained during experimentation led to alternative derivations of the theories. These new theories accurately predict the clock system's behavior. It is found that a 100% penalty is paid to tolerate worst case failures. It is also shown that under optimal conditions (with minimum error and no failures) the clock skew can be as much as 3 clock ticks. Clock skew grows to 6 clock ticks when failures are present. Finally, it is concluded that one cannot rely solely on test procedures or theoretical analysis to predict worst case conditions. conditions.

Palumbo, Daniel L.

1994-01-01

264

Global MHD modeling of ionospheric convection and field-aligned currents associated with IMF By triggered theta auroras  

NASA Astrophysics Data System (ADS)

numerical magnetohydrodynamic simulations, we investigate the evolution of ionospheric convection and field-aligned currents (FACs) when ? auroras are formed in response to interplanetary magnetic field (IMF) By transitions. When the polarity of IMF By switches abruptly during northward IMF periods, the crossbar of the ? aurora is isolated from the flankside auroral oval and drifts into the polar cap. This drift motion is involved in a large round cell associated with new IMF By, with sunward convection residing only on the dayside tip of the crossbar. There exists an IMF By-controlled large-scale FAC system on the crossbar. When the ? aurora is drifting duskward (dawnward), the FACs are located on the dawnside (duskside) boundary of the crossbar adjacent to the "new" lobe. In contrast, the magnetospheric source region of the crossbar FAC system is located on the duskside (dawnside) boundary of the protruded plasma sheet adjacent to the "old" lobe. In the source region, plasma thermal pressure feeds the electromagnetic energy of FACs, and these processes can be interpreted as coupling of slow mode and Alfvén mode disturbances. In the ionosphere, the crossbar-associated FACs close with part of the region 1 currents associated with the new crescent cell. The magnetospheric source of that part of the region 1 FACs is located on the plasma sheet boundary and the magnetopause both adjacent to the new lobe. Dynamo processes in the old-lobe side and the new-lobe side work together to drive the ionospheric drift motion of the crossbar.

Watanabe, Masakazu; Sakito, Shintaro; Tanaka, Takashi; Shinagawa, Hiroyuki; Murata, Ken T.

2014-08-01

265

Quantum mechanics, matter waves, and moving clocks  

E-print Network

This paper is divided into three parts. In the first (section 1), we demonstrate that all of quantum mechanics can be derived from the fundamental property that the propagation of a matter wave packet is described by the same gravitational and kinematic time dilation that applies to a clock. We will do so in several steps, first deriving the Schroedinger equation for a nonrelativistic particle without spin in a weak gravitational potential, and eventually the Dirac equation in curved space-time describing the propagation of a relativistic particle with spin in strong gravity. In the second part (sections 2-4), we present interesting consequences of the above quantum mechanics: that it is possible to use wave packets as a reference for a clock, to test general relativity, and to realize a mass standard based on a proposed redefinition of the international system of units, wherein the Planck constant would be assigned a fixed value. The clock achieved an absolute accuracy of 4 parts per billion (ppb). The experiment yields the fine structure constant $\\alpha = 7.297\\,352\\,589(15) \\times 10^{-3}$ with 2.0 ppb accuracy. We present improvements that have reduced the leading systematic error about 8-fold and improved the statistical uncertainty to 0.33 ppb in 6 hours of integration time, referred to $\\alpha$. In the third part (sections 5-7), we present possible future experiments with atom interferometry: A gravitational Aharonov-Bohm experiment and its application as a measurement of Newton's gravitational constant, antimatter interferometry, interferometry with charged particles, and interferometry in space. We will give a review of previously published material when appropriate, but will focus on new aspects that haven't been published before.

Holger Mueller

2013-12-23

266

Clocks And Dynamics In Quantum Mechanics  

E-print Network

We argue that (1) our perception of time through change and (2) the gap between reality and our observation of it are at the heart of both quantum mechanics and the dynamical mechanism of physical systems. We suggest that the origin of quantum uncertainty lies with the absence of infinities or infinitesimals in observational data and that our concept of time derives from observing changing data (events). We argue that the fundamentally important content of the Superposition Principle is not the "probability amplitude" of posterior state observation but future state availability conditional only on prior information. Since event detection also implies posterior conditions (e.g. a specific type of detectable event occurred) as well as prior conditions, the probabilities of detected outcomes are also conditional on properties of the posterior properties of the observation. Such posterior conditions cannot affect the prior state availabilities and this implies violation of counter-factual definiteness. A component of a quantum system may be chosen to represent a clock and changes in other components can then be expected to be correlated with clocks with which they are entangled. Instead of traditional time-dependent equations of motion we provide a specific mechanism whereby evolution of data is instead quasi-causally related to the relative \\availability\\ of states and equations of motion are expressed in terms of quantized clock variables. We also suggest that time-reversal symmetry-breaking in weak interactions is an artifice of a conventional choice of co-ordinate time-function. Analysis of a "free" particle suggests that conventional co-ordinate space-time emerges from how we measure the separation of objects and events.

Michael York

2014-05-05

267

Gravity Probe C(lock) - Probing the gravitomagnetic field of the Earth by means of a clock experiment  

E-print Network

We outline a mission with the aim of directly detecting the gravitomagnetic field of the Earth. This mission is called Gravity Probe C. Gravity Probe C(lock) is based on a recently discovered and surprisingly large gravitomagnetic clock effect. The main idea is to compare the proper time of two standard clocks in direct and retrograde orbits around the Earth. After one orbit the proper time difference of two such clocks is predicted to be of the order of $2\\times 10^{-7}$ s. The conceptual difficulty to perform Gravity Probe C is expected to be comparable to that of the Gravity Probe B--mission.

Frank Gronwald; Eleonora Gruber; Herbert Lichtenegger; Roland A. Puntigam

1997-12-11

268

Science 101: How do atomic clocks work?  

NSDL National Science Digital Library

You might be wondering why in the world we need such precise measures of time. Well, many systems we use everyday, such as Global Positioning Systems, require precise synchronization of time. This comes into play in telecommunications and wireless communications, also. For purely scientific reasons, we can use precise measurement of time to determine whether or not fundamental constants in the universe appear to be changing over time. Not something that keeps the average person awake at night, but a big deal to theoretical physicists. Before addressing atomic clocks, the author discusses the ways we measure time, in this month's column.

2008-11-01

269

The Mackworth Clock Test: a computerized version.  

PubMed

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

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

2000-03-01

270

Laser Cooled Atomic Clocks in Space  

NASA Technical Reports Server (NTRS)

The goals of the Glovebox Laser-cooled Atomic Clock Experiment (GLACE) are: (1) first utilization of tunable, frequency-stabilized lasers in space, (2) demonstrate laser cooling and trapping in microgravity, (3) demonstrate longest 'perturbation-free' interaction time for a precision measurement on neutral atoms, (4) Resolve Ramsey fringes 2-10 times narrower than achievable on Earth. The approach taken is: the use of COTS components, and the utilization of prototype hardware from LCAP flight definition experiments. The launch date is scheduled for Oct. 2002. The Microgravity Science Glovebox (MSG) specifications are reviewed, and a picture of the MSG is shown.

Thompson, R. J.; Kohel, J.; Klipstein, W. M.; Seidel, D. J.; Maleki, L.

2000-01-01

271

The Circadian Clock Modulates Enamel Development  

PubMed Central

Fully mature enamel is about 98% mineral by weight. While mineral crystals appear very early during its formative phase, the newly secreted enamel is a soft gel-like matrix containing several enamel matrix proteins of which the most abundant is amelogenin (Amelx). Histological analysis of mineralized dental enamel reveals markings called cross-striations associated with daily increments of enamel formation, as evidenced by injections of labeling dyes at known time intervals. The daily incremental growth of enamel has led to the hypothesis that the circadian clock might be involved in the regulation of enamel development. To identify daily rhythms of clock genes and Amelx, we subjected murine ameloblast cells to serum synchronization to analyze the expression of the circadian transcription factors Per2 and Bmal1 by real-time PCR. Results indicate that these key genetic regulators of the circadian clock are expressed in synchronized murine ameloblast cell cultures and that their expression profile follows a circadian pattern with acrophase and bathyphase for both gene transcripts in antiphase. Immunohistological analysis confirms the protein expression of Bmal and Cry in enamel cells. Amelx expression in 2-day postnatal mouse molars dissected every 4 hours for a duration of 48 hours oscillated with an approximately 24-hour period, with a significant approximately 2-fold decrease in expression during the dark period compared to the light period. The expression of genes involved in bicarbonate production (Car2) and transport (Slc4a4), as well as in enamel matrix endocytosis (Lamp1), was greater during the dark period, indicating that ameloblasts express these proteins when Amelx expression is at the nadir. The human and mouse Amelx genes each contain a single nonconserved E-box element within 10 kb upstream of their respective transcription start sites. We also found that within 2 kb of the transcription start site of the human NFYA gene, which encodes a positive regulator of amelogenin, there is an E-box element that is conserved in rodents and other mammals. Moreover, we found that Nfya expression in serum-synchronized murine ameloblasts oscillated with a strong 24-hour rhythm. Taken together, our data support the hypothesis that the circadian clock temporally regulates enamel development. PMID:22653892

Lacruz, Rodrigo S.; Hacia, Joseph G.; Bromage, Timothy G.; Boyde, Alan; Lei, Yaping; Xu, Yucheng; Miller, Joseph D.; Paine, Michael L.; Snead, Malcolm L.

2012-01-01

272

Atomic physics with vapor-cell clocks  

NASA Astrophysics Data System (ADS)

The most widely used atomic frequency standards (or clocks) are based on the microwave resonant frequencies of optically pumped vapors of alkali-metal atoms in glass cells filled with buffer gas. These vapor-cell clocks are secondary, not primary frequency standards mainly because of the light and pressure shifts, which alter the resonant frequencies of the alkali-metal atoms. This dissertation presents studies of atomic physics important to vapor-cell clocks and, in particular, their accuracy. First, we report a simple method to suppress the light shift in optical pumping systems. This method uses only frequency modulation of a radio frequency or microwave source, which excites an atomic resonance, to simultaneously lock the source frequency to the atomic resonance and lock the pumping light frequency to suppress the light shift. This technique can be applied to many optical pumping systems that experience light shifts. It is especially useful for atomic clocks because it improves the long-term performance, reduces the influence of a pumping laser, and requires less equipment than previous methods. Next, we present three studies of the pressure shift, starting with an estimation of the hyperfine-shift potential that is responsible for most of the pressure shift. We then show that the microwave resonant frequencies of ground-state Rb and Cs atoms in Xe buffer gas have a relatively large nonlinear dependence on the Xe pressure, presumably because of short-lived RbXe and CsXe van der Waals molecules. The Xe data show striking discrepancies with the previous theory for nonlinear shifts, most of which is eliminated by accounting for the spin-rotation interaction in addition to the hyperfine-shift interaction in the molecules. To the limit of our experimental accuracy, the shifts of Rb and Cs in He, Ne, and N2 were linear with pressure. We then consider the prospects for suppressing the pressure shift with buffer-gas mixtures and feedback. Finally, we report an investigation of the potential for integrating spheres to enhance absorption in optically thin alkali-metal vapor cells. We demonstrate a roughly ten-fold increase of the optical absorption that seems to be limited by the glass cell required to contain the alkali-metal vapor.

McGuyer, Bart Hunter

273

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

274

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

NASA Astrophysics Data System (ADS)

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

Azhar, Hanif; Giraudet, Guillaume; Faubert, Jocelyn

2013-03-01

275

Reliability of Prediction of Magnetosheath Magnetic Field Components from IMF Observations  

NASA Astrophysics Data System (ADS)

In the present statistical study, we discuss a probability of observations of the same sign of magnetic field components in the solar wind and magnetosheath. The analysis is based on 5-minute data from four spacecraft (Interball-1, IMP 8, Cluster, and Themis) operating in different phases of the solar cycle in the magnetosheath. Their measurements are compared with Wind interplanetary magnetic field observations and other available upstream monitors (ACE, Themis B, and OMNI database) are tested for some sets. For example, we demonstrate that the probability of observations of the same Bz sign in the solar wind and in the magnetosheath is surprisingly very low from general point of view. The probability changes through the solar cycle being larger at the solar minimum. Regardless of the solar cycle phase, this probability is close to 0.5 (random coincidence) for IMF Bz ~ 1 nT and it is a rising function of the Bz value. Distant solar wind monitors don't guarantee the prediction of the Bz even for values of IMF Bz exceeding 9 nT but such large values are observed only a few percent of time. A better probability profile is reached for a monitor located just upstream as it is demonstrated for the Themis project. Through the paper, we show probabilities of observations of all magnetic field components and the dependence of these observations on locations of a particular magnetosheath spacecraft and upstream conditions.

Safrankova, J.; Nemecek, Z.; Gutynska, O.; Hayosh, M.

2009-12-01

276

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

SciTech Connect

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

Henderson, M.G.; Reeves, G.D.; Belian, R.D. [Los Alamos National Lab., NM (United States); Murphree, J.S. [Univ. of Calgary, Alberta (Canada)

1996-03-01

277

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

NASA Astrophysics Data System (ADS)

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

Loewenstein, Michael

2013-04-01

278

Observations of IMF and seasonal effects in high-latitude convection  

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

279

High performance of a DMTD system used in a composite clock including a Cs clock, a H-maser (clock) and a VCO  

NASA Astrophysics Data System (ADS)

We present a composite clock based on servoing a voltage controlled oscillator (VCO) by both a caesium beam clock and a hydrogen maser. We wish to obtain a physical realization of a new reference timescale with an output signal which combines the long term stability of the caesium clock, the middle term stability of the H maser and the short term stability of the VCO. The system contribution at 100 MHz to the middle term frequency instabilities is expected to be around 10-15 at 1 s. This paper describes the dual-mixer time-difference (DMTD) system used to obtain the information needed for the control of the VCO.

Plantard, C.; Mbaye, P. M.; Vernotte, F.

2008-12-01

280

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

281

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

282

The Renaissance or the cuckoo clock.  

PubMed

'…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. PMID:22084388

Pines, Jonathon; Hagan, Iain

2011-12-27

283

Animal clocks: when science meets nature  

PubMed Central

Daily rhythms of physiology and behaviour are governed by an endogenous timekeeping mechanism (a circadian ‘clock’), with the alternation of environmental light and darkness synchronizing (entraining) these rhythms to the natural day–night cycle. Our knowledge of the circadian system of animals at the molecular, cellular, tissue and organismal levels is remarkable, and we are beginning to understand how each of these levels contributes to the emergent properties and increased complexity of the system as a whole. For the most part, these analyses have been carried out using model organisms in standard laboratory housing, but to begin to understand the adaptive significance of the clock, we must expand our scope to study diverse animal species from different taxonomic groups, showing diverse activity patterns, in their natural environments. The seven papers in this Special Feature of Proceedings of the Royal Society B take on this challenge, reviewing the influences of moonlight, latitudinal clines, evolutionary history, social interactions, specialized temporal niches, annual variation and recently appreciated post-transcriptional molecular mechanisms. The papers emphasize that the complexity and diversity of the natural world represent a powerful experimental resource. PMID:23825215

Kronfeld-Schor, Noga; Bloch, Guy; Schwartz, William J.

2013-01-01

284

Epidemiology of the human circadian clock.  

PubMed

Humans show large inter-individual differences in organising their behaviour within the 24-h day-this is most obvious in their preferred timing of sleep and wakefulness. Sleep and wake times show a near-Gaussian distribution in a given population, with extreme early types waking up when extreme late types fall asleep. This distribution is predominantly based on differences in an individuals' circadian clock. The relationship between the circadian system and different "chronotypes" is formally and genetically well established in experimental studies in organisms ranging from unicells to mammals. To investigate the epidemiology of the human circadian clock, we developed a simple questionnaire (Munich ChronoType Questionnaire, MCTQ) to assess chronotype. So far, more than 55,000 people have completed the MCTQ, which has been validated with respect to the Horne-Østberg morningness-eveningness questionnaire (MEQ), objective measures of activity and rest (sleep-logs and actimetry), and physiological parameters. As a result of this large survey, we established an algorithm which optimises chronotype assessment by incorporating the information on timing of sleep and wakefulness for both work and free days. The timing and duration of sleep are generally independent. However, when the two are analysed separately for work and free days, sleep duration strongly depends on chronotype. In addition, chronotype is both age- and sex-dependent. PMID:17936039

Roenneberg, Till; Kuehnle, Tim; Juda, Myriam; Kantermann, Thomas; Allebrandt, Karla; Gordijn, Marijke; Merrow, Martha

2007-12-01

285

How to fix a broken clock  

PubMed Central

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

Schroeder, Analyne M.; Colwell, Christopher S.

2013-01-01

286

Circadian Clocks in Human Red Blood Cells  

PubMed Central

Summary Circadian (~24 hour) clocks are fundamentally important for coordinated physiology in organisms as diverse as cyanobacteria and humans. All current models of the clockwork in eukaryotic cells are based on transcription-translation feedback loops. Non-transcriptional mechanisms in the clockwork have been difficult to study in mammalian systems. We circumvented these problems by developing novel assays using human red blood cells (RBCs), which have no nucleus (or DNA), and therefore cannot perform transcription. Our results show that transcription is, in fact, not required for circadian oscillations in humans, and that non-transcriptional events appear sufficient to sustain cellular circadian rhythms. Using RBCs, we found that peroxiredoxins, highly conserved antioxidant proteins, undergo ~24 hour redox cycles, which persist for many days under constant conditions (i.e. in the absence of external cues). Moreover, these rhythms are entrainable (i.e. tunable by environmental stimuli), and temperature-compensated, both key features of circadian rhythms. We anticipate our findings will facilitate more sophisticated cellular clock models, highlighting the interdependency of transcriptional and non-transcriptional oscillations in potentially all eukaryotic cells. PMID:21270888

O'Neill, John S.; Reddy, Akhilesh B.

2010-01-01

287

Local receptors as novel regulators for peripheral clock expression.  

PubMed

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

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

2014-11-01

288

Fundamentals of Large Sensor Networks: Connectivity, Capacity, Clocks and Computation  

E-print Network

1 Fundamentals of Large Sensor Networks: Connectivity, Capacity, Clocks and Computation Nikolaos M and operational issues related to large sensor networks - connectivity, capacity, clocks and function computation needs to study optimal strategies for in-network aggregation of data, in order to reliably compute

289

Local receptors as novel regulators for peripheral clock expression  

PubMed Central

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

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

2014-01-01

290

A critical analysis of application-adaptive multiple clock processors  

Microsoft Academic Search

Enabled by the continuous advancement in fabrication technology, present day synchronous microprocessors include more than 100 million transistors and have clock speeds well in excess of the 1GHz mark. Distributing a low-skew clock signal in this frequency range to all areas of a large chip is a task of growing complexity. As a solution to this problem, designers have recently

Emil Talpes; Diana Marculescu

2003-01-01

291

Orchestrating time: arrangements of the brain circadian clock  

E-print Network

Orchestrating time: arrangements of the brain circadian clock Michael C. Antle1 and Rae Silver2 Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, 630 West 168- lated by a brain clock located in the suprachiasmatic nucleus (SCN). Individual cells within

Silver, Rae

292

Clock genes in the heart: characterization and attenuation with hypertrophy.  

PubMed

We investigated whether the heart, like other mammalian organs, possesses internal clocks, and, if so, whether pressure overload-induced hypertrophy alters the clock mechanism. Clock genes are intrinsically maintained, as shown by rhythmic changes even in single cells. Clocks are believed to confer a selective advantage by priming the cell for the expected environmental stimulus. In this way, clocks allow anticipation, thereby synchronizing responsiveness of the cell with the timing of the stimulus. We have found that in rat heart all mammalian homologues of known Drosophila clock genes (bmal1, clock, cry1, cry2, per1, per2, per3, dbp, hlf, and tef) show circadian patterns of expression and that the induction of clock output genes (the PAR [rich in proline and acidic amino acid residues] transcription factors dbp, hlf, and tef) is attenuated in the pressure-overloaded hypertrophied heart. The results expose a new dynamic regulatory system in the heart, which is partially lost with hypertrophy. Although the target genes of these PAR transcription factors are not known in the heart, the results provide evidence for a diminished ability of the hypertrophied heart to anticipate and subsequently adapt to physiological alterations during the day. PMID:11397780

Young, M E; Razeghi, P; Taegtmeyer, H

2001-06-01

293

Verge and Foliot Clock Escapement: A Simple Dynamical System  

ERIC Educational Resources Information Center

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

Denny, Mark

2010-01-01

294

Frequency comparison of optical lattice clocks beyond the Dick limit  

NASA Astrophysics Data System (ADS)

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

Takamoto, Masao; Takano, Tetsushi; Katori, Hidetoshi

2011-05-01

295

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

296

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

297

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

298

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

299

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

300

Initial atomic coherences and Ramsey frequency pulling in fountain clocks  

NASA Astrophysics Data System (ADS)

In the uncertainty budget of primary atomic cesium fountain clocks, evaluations of frequency-pulling shifts of the hyperfine clock transition caused by unintentional excitation of its nearby transitions (Rabi and Ramsey pulling) have been based so far on an approach developed for cesium beam clocks. We re-evaluate this type of frequency pulling in fountain clocks and pay particular attention to the effect of initial coherent atomic states. We find significantly enhanced frequency shifts caused by Ramsey pulling due to sublevel population imbalance and corresponding coherences within the state-selected hyperfine component of the initial atom ground state. Such shifts are experimentally investigated in an atomic fountain clock and quantitative agreement with the predictions of the model is demonstrated.

Gerginov, Vladislav; Nemitz, Nils; Weyers, Stefan

2014-09-01

301

Quantum Limit on Stability of Clocks in a Gravitational Field  

E-print Network

Good clocks are of importance both to fundamental physics and for applications in astronomy, metrology and global positioning systems. In a recent technological breakthrough, researchers at NIST have been able to achieve a stability of 1 part in $10^{18}$ using an Ytterbium clock. This naturally raises the question of whether there are fundamental limits to the stability of clocks. In this paper we point out that gravity and quantum mechanics set a fundamental limit on the stability of clocks. This limit comes from a combination of the uncertainty relation, the gravitational redshift and the relativistic time dilation effect. For example, a single ion hydrogen maser clock in a terrestrial gravitational field cannot achieve a stability better than one part in $10^{22}$. This observation has implications for laboratory experiments involving both gravity and quantum theory.

Supurna Sinha; Joseph Samuel

2014-01-04

302

Standard Clock in Primordial Density Perturbations and Cosmic Microwave Background  

E-print Network

Standard Clocks in the primordial epoch leave a special type of features in the primordial perturbations, which can be used to directly measure the scale factor of the primordial universe as a function of time a(t), thus discriminating between inflation and alternatives. We have started to search for such signals in the Planck 2013 data using the key predictions of the Standard Clock. In this Letter, we summarize the key predictions of the Standard Clock and present an interesting candidate example in Planck 2013 data. Motivated by this candidate, we construct and compute full Standard Clock models and use the more complete prediction to make more extensive comparison with data. Although this candidate is not yet statistically significant, we use it to illustrate how Standard Clocks appear in Cosmic Microwave Background and how they can be further tested by future data. We also use it to motivate more detailed theoretical model building.

Xingang Chen; Mohammad Hossein Namjoo

2014-04-06

303

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. PMID:22389588

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

2009-01-01

304

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? PMID:24135705

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

2013-01-01

305

A mechanosensory pathway to the Drosophila circadian clock.  

PubMed

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

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

2014-01-31

306

Picking out parallels: plant circadian clocks in context.  

PubMed Central

Molecular models have been described for the circadian clocks of representatives of several different taxa. Much of the work on the plant circadian system has been carried out using the thale cress, Arabidopsis thaliana, as a model. We discuss the roles of genes implicated in the plant circadian system, with special emphasis on Arabidopsis. Plants have an endogenous clock that regulates many aspects of circadian and photoperiodic behaviour. Despite the discovery of components that resemble those involved in the clocks of animals or fungi, no coherent model of the plant clock has yet been proposed. In this review, we aim to provide an overview of studies of the Arabidopsis circadian system. We shall compare these with results from different taxa and discuss them in the context of what is known about clocks in other organisms. PMID:11710980

McWatters, H G; Roden, L C; Staiger, D

2001-01-01

307

Remote atomic clock synchronization via satellites and optical fibers  

E-print Network

In the global network of institutions engaged with the realization of International Atomic Time (TAI), atomic clocks and time scales are compared by means of the Global Positioning System (GPS) and by employing telecommunication satellites for two-way satellite time and frequency transfer (TWSTFT). The frequencies of the state-of-the-art primary caesium fountain clocks can be compared at the level of 10e-15 (relative, 1 day averaging) and time scales can be synchronized with an uncertainty of one nanosecond. Future improvements of worldwide clock comparisons will require also an improvement of the local signal distribution systems. For example, the future ACES (atomic clock ensemble in space) mission shall demonstrate remote time scale comparisons at the uncertainty level of 100 ps. To ensure that the ACES ground instrument will be synchronized to the local time scale at PTB without a significant uncertainty contribution, we have developed a means for calibrated clock comparisons through optical fibers. An un...

Piester, D; Fujieda, M; Feldmann, T; Bauch, A

2011-01-01

308

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

309

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

310

Angles All Around  

NSDL National Science Digital Library

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

Bennett, Mrs.

2011-12-14

311

Desynchronization of Noisy Multi-cellular Clocks Underlies the Population-level Singularity Behavior of Mammalian Circadian Clock  

NASA Astrophysics Data System (ADS)

The singularity behavior of circadian clocks defined as the suppression of circadian oscillation by critical perturbation is one of the intriguing dynamical properties of circadian rhythms. Although the singularity behaviors have been observed in various organisms, its mechanism has not yet been elucidated, because the hierarchical structure of multi-cell-level circadian clocks exists behind the organism-level circadian rhythm. In vitro light-responsible circadian system is indispensable for extracting the underlying mechanism of the singularity behavior behind the hierarchical structure of multi-cell organisms. To obtain such in vitro system, we synthetically constructed light-responsible mammalian clock cells by exogenously introducing a photo-responsible receptor. By using this synthetic system and population-level high-throughput promoter activity assay, we found that a light pulse with critical timing and strength can induce population-level singularity behavior of the light-responsible mammalian clock cells. Subsequent single-cell measurement revealed that desynchronization of multi-cellular clocks underlies the population-level singularity. A mathematical model consistently explains our population-level and single-cell-level experimental data, and also demonstrates that the synchronization and desynchronization of cellular clocks is the underlying mechanism of population-level response of circadian clocks to external perturbation. In addition, our model suggests that fluctuation in single-cell-level behavior of the clock cells is the key determinant of the observable singularity behavior.

Kobayashi, Tetsuya J.; Ukai, Hideki; Ueda, Hiroki R.

2007-07-01

312

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

PubMed

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

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

2014-09-15

313

Stochastic stellar cluster IMFs: Models and impact on integrated cluster parameter determination  

E-print Network

Stellar clusters are regularly used to study the evolution of their host galaxy. Except for a few nearby galaxies, these studies rely on the interpretation of integrated cluster properties, especially integrated photometry observed using multiple filters (i.e. the Spectral Energy Distribution SED). To allow interpretation of such observations, we present a large set of GALEV cluster models using the realistic approach of adopting stochastically-sampled stellar IMFs. We provide models for a wide range of cluster masses (10^3 - 2 * 10^5$ Msun), metallicities (-2.3 <= [Fe/H] <= +0.18 dex), foreground extinction, and 184 regularly used filters. We analyze various sets of stochastic cluster SEDs by fitting them with non-stochastic models, which is the procedure commonly used in this field. We identify caveats and quantify the fitting uncertainties associated with this standard procedure. We show that this can yield highly unreliable fitting results, especially for low-mass clusters.

Anders, P; de Grijs, R; Wicker, J

2013-01-01

314

The scale-free character of the cluster mass function and the universality of the stellar IMF  

E-print Network

Our recent determination of a Salpeter slope for the IMF in the field of 30 Doradus (Selman and Melnick 2005) appears to be in conflict with simple probabilistic counting arguments advanced in the past to support observational claims of a steeper IMF in the LMC field. In this paper we re-examine these arguments and show by explicit construction that, contrary to these claims, the field IMF is expected to be exactly the same as the stellar IMF of the clusters out of which the field was presumably formed. We show that the current data on the mass distribution of clusters themselves is in excellent agreement with our model, and is consistent with a single spectrum {\\it by number of stars} of the type $n^\\beta$ with beta between -1.8 and -2.2 down to the smallest clusters without any preferred mass scale for cluster formation. We also use the random sampling model to estimate the statistics of the maximal mass star in clusters, and confirm the discrepancy with observations found by Weidner and Kroupa (2006). We argue that rather than signaling the violation of the random sampling model these observations reflect the gravitationally unstable nature of systems with one very large mass star. We stress the importance of the random sampling model as a \\emph{null hypothesis} whose violation would signal the presence of interesting physics.

Fernando J. Selman; Jorge Melnick

2008-05-16

315

Control That Capital It is time for the IMF and the United States to fully support capital  

E-print Network

yanked their funds and retreated to the "safe" haven of the United States. Capital controls help smooth the inflows and outflows of capital and protect developing economies. Most controls target highly shortControl That Capital It is time for the IMF and the United States to fully support capital controls

Tufts University

316

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

Microsoft Academic Search

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

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

2006-01-01

317

Radial (L) profiles of MHD wave power and energetic electron flux during high-speed streams: dependence on IMF Bz  

NASA Astrophysics Data System (ADS)

During the passage of solar wind high-speed streams, normally characterized by a weak IMF, historic observations [e.g. Rostoker et al., JGR 1998] have shown that a peak of both ULF wave power and electron flux is formed at high L (5-6), measurable from geosynchronous orbit (6.6). Recurrence of the streams leads to a driven oscillation in the magnetospheric field and particle distributions between an excited and a quiet state, with a delay time of 2 days following the solar wind speed. Here we show that, in the presence of Southward IMF Bz, the new peak will form instead at low L (~3) and in some events within the slot L range (2-3). In addition to the change in the magnetospheric configuration resulting from a steady IMF BSouth, it is the fluctuations in the field power and therefore in the wave-particle interaction that are significant in changing the wave power and particle flux profiles. The timescale for those interactions is reduced from 2 days to several hours or tens of minutes. The effect is compared both to effects during low-IMF high-speed streams and to interplanetary coronal mass ejections (Vassiliadis et al., submitted to GRL).

Koepke, M.; Vassiliadis, D.; Baker, D.; Weigel, R.; Zhang, J.; Poomvises, W.

2007-12-01

318

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

NASA Astrophysics Data System (ADS)

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

van Dokkum, Pieter

2014-10-01

319

Dynamics and performance of clock pendulums  

NASA Astrophysics Data System (ADS)

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

Hoyng, Peter

2014-11-01

320

Probing unification scenarios with atomic clocks  

NASA Astrophysics Data System (ADS)

We discuss the usage of measurements of the stability of nature’s fundamental constants coming from comparisons between atomic clocks as a means to constrain coupled variations of these constants in a broad class of unification scenarios. After introducing the phenomenology of these models, we provide updated constraints based on a global analysis of the latest experimental results. We obtain null results for the proton-to-electron mass ratio ??/?=(0.68±5.79)×10-16yr-1 and for the gyromagnetic factor g?p/gp=(-0.72±0.89)×10-16yr-1 (both of these being at the 95% confidence level). These results are compatible with theoretical expectations on unification scenarios, but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

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

2012-12-01

321

Diurnal oscillations of soybean circadian clock and drought responsive genes.  

PubMed

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

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

2014-01-01

322

Direct regulation of CLOCK expression by REV-ERB.  

PubMed

Circadian rhythms are regulated at the cellular level by transcriptional feedback loops leading to oscillations in expression of key proteins including CLOCK, BMAL1, PERIOD (PER), and CRYPTOCHROME (CRY). The CLOCK and BMAL1 proteins are members of the bHLH class of transcription factors and form a heterodimer that regulates the expression of the PER and CRY genes. The nuclear receptor REV-ERB? plays a key role in regulation of oscillations in BMAL1 expression by directly binding to the BMAL1 promoter and suppressing its expression at certain times of day when REV-ERB? expression levels are elevated. We recently demonstrated that REV-ERB? also regulates the expression of NPAS2, a heterodimer partner of BMAL1. Here, we show that REV-ERB? also regulates the expression another heterodimer partner of BMAL1, CLOCK. We identified a REV-ERB? binding site within the 1(st) intron of the CLOCK gene using a chromatin immunoprecipitation - microarray screen. Suppression of REV-ERB? expression resulted in elevated CLOCK mRNA expression consistent with REV-ERB?'s role as a transcriptional repressor. A REV-ERB response element (RevRE) was identified within this region of the CLOCK gene and was conserved between humans and mice. Additionally, the CLOCK RevRE conferred REV-ERB responsiveness to a heterologous reporter gene. Our data suggests that REV-ERB? plays a dual role in regulation of the activity of the BMAL1/CLOCK heterodimer by regulation of expression of both the BMAL1 and CLOCK genes. PMID:21479263

Crumbley, Christine; Burris, Thomas P

2011-01-01

323

The bird of time: cognition and the avian biological clock  

PubMed Central

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

Cassone, Vincent M.; Westneat, David F.

2012-01-01

324

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

SciTech Connect

Two conjugate HF radars are currently operating at Goose Bay, Labrador, and Halley Station, Antarctica, and are providing continuous, high temporal resolution measurements of plasma convection over large areas of the high-latitude ionosphere. In this paper, data from these radars for a single 45-min period about local noon on 22 April 1988 are examined to study near-instantaneous, conjugate, two-dimensional patterns of plasma convection in the vicinity of the cusp and their response to changes in the B{sub y} component of the interplanetary magnetic field (IMF). The observations indicate that under quasi-stationary IMF conditions, the conjugate convection patterns are quite similar to the synthesized patterns of Heppner and Maynard (1987). The patterns respond rapidly to changes in the IMF B{sub y} component. The average response time was 8 min between an IMF transition at the IMP-8 satellite and the beginning of a convection reconfiguration in the ionosphere. Typically, the newly reconfigured convection pattern filled the radar field of view (10{degree} to 15{degree} of invariant latitude and 2.5 h of local time) within 6 min of reconfiguration onset. For the examples studied the reconfiguration onsets began over an extended local time sector in the invariant latitude range from 73{degree} to 75{degree} and proceeded by means of a poleward expansion of the reconfigured pattern into a region containing fossil convection associated with the prior IMF state. The authors interpret the onset region in the ionosphere as being associated with cusp field lines and the poleward region as being associated with open field lines in the plasma mantle and tail lobe.

Greenwald, R.A.; Baker, K.B.; Ruohoniemi, J.M. (Johns Hopkins Univ., Laurel, MD (USA)); Dudeney, J.R.; Pinnock, M.; Mattin, N.; Leonard, J.M. (Natural Environment Research Council, Cambridge (England)); Lepping, R.P. (NASA Goddard Space Flight Center, Greenbelt, MD (USA))

1990-06-01

325

The Chlorate-Iodine-Nitrous Acid Clock Reaction  

PubMed Central

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

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

2014-01-01

326

A review of reduced Kalman filters for clock ensembles.  

PubMed

This paper reviews the author's previous work on free-running timescales based on Kalman filters that act upon clock comparisons. The natural Kalman clock ensemble algorithm tends to optimize long-term timescale stability at the expense of short-term stability. By subjecting each postmeasurement error covariance matrix to a non-transparent reduction operation, one obtains corrected clocks with improved short-term stability and little sacrifice of long-term stability. A new result on covariance matrix reduction is also stated. PMID:22481783

Greenhall, Charles

2012-03-01

327

x0000 -xx xxxx 2006 metrologia Spectral Analysis of Clock Noise: A Primer  

E-print Network

x0000 - xx xxxx 2006 metrologia Spectral Analysis of Clock Noise: A Primer Donald B Percival present a primer on how to estimate the power spectrum of clock noise given a finite sequence: A Primer of clock noise. In this context the difference in time as kept by two clocks (or, equivalently

Percival, Don

328

A Role for the PERIOD:PERIOD Homodimer in the Drosophila Circadian Clock  

Microsoft Academic Search

Circadian clocks in eukaryotes rely on transcriptional feedback loops, in which clock genes repress their own transcription resulting in molecular oscillations with a period of ?24 h. In Drosophila, the clock proteins Period (PER) and Timeless (TIM) operate in such a feedback loop, whereby they first accumulate in the cytoplasm of clock cells as a heterodimer. Nuclear translocation of the

Johannes Landskron; Ko Fan Chen; Eva Wolf; Ralf Stanewsky

2009-01-01

329

A Fault Tolerant Clock Synchronization Algorithm for Systems with Low-Precision Oscillators  

Microsoft Academic Search

In this paper we present a new fault tolerant clock synchronization algorithm called the Fault Tolerant Daisy Chain algorithm. It is intended for internal clock synchronization of systems using a broadcast bus with Time Division Multiple Access (TDMA) communication, or other systems where clock readings are broadcast at regular intervals. The algorithm allows synchronization after each clock reading and is

Henrik Lönn

1999-01-01

330

Control of rhythmic output from the circadian clock in Neurospora crassa  

E-print Network

xi LIST OF TABLES TABLE Page 1 Summary of clock-controlled genes ....................................... 19 2 N. crassa clock-controlled genes revealed by microarray analysis... xi LIST OF TABLES TABLE Page 1 Summary of clock-controlled genes ....................................... 19 2 N. crassa clock-controlled genes revealed by microarray analysis...

Lewis, Zachary Austin

2005-02-17

331

Fast Self-Stabilizing Byzantine Tolerant Digital Clock Synchronization  

E-print Network

their memory in an arbitrary fashion. Within the context of this model, we are interested in the digital clock in the Twenty-Seventh Annual ACM SIGACT-SIGOPS Symposium on Principles of Distributed Comput- ing (PODC'08

Dolev, Danny

332

Photosynthetic entrainment of the Arabidopsis thaliana circadian clock  

E-print Network

genes display a novel and visible phenotype as to light responses during de-etiolation of Arabidopsis thaliana seedlings. Biosci., Biotech. and Biochem. 71, 834–839 (2007). 20. Fukushima, A. et al. Impact of clock-associated Arabidopsis pseudo...

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

2013-10-23

333

9. CONCRETE CLOCK ADDITION, INTERIOR, LOOKING NORTH FROM SOUTH END ...  

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

9. CONCRETE CLOCK ADDITION, INTERIOR, LOOKING NORTH FROM SOUTH END (INTERIOR OF SECOND FLOOR OF MAIN BUILDING VISIBLE TO THE RIGHT) - Gerber Sheet Metal Works Building, 128 Porthand Avenue, South, Minneapolis, Hennepin County, MN

334

3.3 Gigahertz Clocked Quantum Key Distribution System  

Microsoft Academic Search

A fibre-based quantum key distribution system operating up to a clock frequency of 3.3GHz is presented. The system demonstrates significantly increased key exchange rate potential and operates at a wavelength of 850nm.

Karen J. Gordon; Veronica Fernandez; Robert J. Collins; Ivan Rech; Sergio D. Cova; Paul D. Townsend; Gerald S. Buller

2006-01-01

335

Gigahertz clocked quantum key distribution system using FPGA  

Microsoft Academic Search

An implementation of 1-GHz clocked differential-phase-shift quantum key distribution system is reported. High speed signal generation and its storage were realized by using FPGA. A stable operation was demonstrated for over a 1-hour.

Toshimori Honjo; Morinosato Wakamiya

2009-01-01

336

A quantum key distribution system operating at gigahertz clock rates  

Microsoft Academic Search

A fiber-optic based quantum key distribution system, operating at a wavelength of 850 nm, has been developed capable of operating up to a clock frequency of 1 GHz, creating significantly increased key exchange rates

K. J. Gordon; V. Fernandez; G. S. Buller; P. D. Townsend; S. D. Cova; S. Tisa

2004-01-01

337

3.3 Gigahertz Clocked Quantum Key Distribution System  

E-print Network

A fibre-based quantum key distribution system operating up to a clock frequency of 3.3GHz is presented. The system demonstrates significantly increased key exchange rate potential and operates at a wavelength of 850nm.

Karen J. Gordon; Veronica Fernandez; Robert J. Collins; Ivan Rech; Sergio D. Cova; Paul D. Townsend; Gerald S. Buller

2006-05-05

338

22. SOUTHWEST CORNER OF BANKING ROOM, FROM EAST, SHOWING CLOCK ...  

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

22. SOUTHWEST CORNER OF BANKING ROOM, FROM EAST, SHOWING CLOCK ON SOUTH WALL AND TWO MEZZANINES BEYOND COLUMNS - Philadelphia Saving Fund Society, Twelfth & Market Streets, Philadelphia, Philadelphia County, PA

339

Speed of light as measured by two terrestrial stable clocks  

NASA Technical Reports Server (NTRS)

Despite the recent criticism within the special theory of relativity, there exists an arrangement of stable clocks rotating with the earth which predicts diurnal variations of the one-way speed of light, as suggested previously.

Hsu, J. P.; Sherry, T. N.; Chiu, C. B.

1977-01-01

340

Compact Microwave Mercury Ion Clock for Space Applications  

NASA Technical Reports Server (NTRS)

We review progress in developing a small Hg ion clock for space operation based on breadboard ion-clock physics package where Hg ions are shuttled between a quadrupole and a 16-pole rf trap. With this architecture we have demonstrated short-term stability approx.1-2x10(exp -13) at 1 second, averaging to 10-15 at 1 day. This development shows that H-maser quality stabilities can be produced in a small clock package, comparable in size to an ultra-stable quartz oscillator required or holding 1-2x10(exp -13) at 1 second. We have completed an ion clock physics package designed to withstand vibration of launch and are currently building a approx. 1 kg engineering model for test. We also discuss frequency steering software algorithms that simultaneously measure ion signal size and lamp light output, useful for long term operation and self-optimization of microwave power and return engineering data.

Prestage, John D.; Tu, Meirong; Chung, Sang K.; MacNeal, Paul

2007-01-01

341

A bunch clock for the Advanced Photon Source  

SciTech Connect

A bunch clock timing module has been developed for use by Advanced Photon Source beamlines. The module provides bunch pattern and timing information that can be used to trigger beamline data collection equipment. The module is fully integrated into the control system software (EPICS) which automatically loads it with the storage ring fill pattern at injection time. Fast timing outputs (1 ns FWHM) for each stored bunch are generated using the storage ring low-level rf and revolution clock as input references. Fiber-optic-based transmitters and receivers are used to transmit a 352-MHz low-level rf reference to distributed bunch clock modules. The bunch clock module is a single-width VME module and may be installed in a VME crate located near beamline instrumentation. A prototype has been in use on the SRI CAT beamline for over a year. The design and integration into the control system timing software along with measured performance results are presented.

Lenkszus, F.R.; Laird, R.J. [Argonne National Lab., IL (United States). Advanced Photon Source

1997-06-01

342

Functional independence of circadian clocks that regulate plant gene expression  

E-print Network

Functional independence of circadian clocks that regulate plant gene expression Simon C. Thain and behaviour of most eukaryotes, controlling an orderly succession of physiological processes in plants. Peripheral plant and animal tissues also maintain circadian rhythms when isolated in culture

Millar, Andrew J.

343

Clock Technology Development in the Laser Cooling and Atomic Physics (LCAP) Program  

NASA Technical Reports Server (NTRS)

This paper presents the Laser Cooling and Atomic Physics (LCAP) program. It focuses on clock technology development. The topics include: 1) Overview of LCAP Flight Projects; 2) Space Clock 101; 3) Physics with Clocks in microgravity; 4) Space Clock Challenges; 5) LCAP Timeline; 6) International Space Station (ISS) Science Platforms; 7) ISS Express Rack; 8) Space Qualification of Components; 9) Laser Configuration; 10) Clock Rate Comparisons: GPS Carrier Phase Frequency Transfer; and 11) ISS Model Views. This paper is presented in viewgraph form.

Seidel, Dave; Thompson, R. J.; Klipstein, W. M.; Kohel, J.; Maleki, L.

2000-01-01

344

Two static 4K clocked and nonclocked RAM designs  

Microsoft Academic Search

A detailed description of both a clocked and a nonclocked n-channel MOS 4K static RAM is presented. The clocked device is a three-supply (+12 V, +5 V, -5 V) RAM which uses bootstrapping circuitry for signal driving, and sustaining resistors for low memory array power dissipation and infinite chip select length. The nonclocked device is a single supply (+5 V)

T. R. O'Connell; JOHN M. HARTMAN; E. B. Errett; G. S. Leach

1977-01-01

345

On chip clock synchronization for large digital systems  

E-print Network

ON CHIP CLOCK SYNCHRONIZATION FOR I ARGE DIGITAL SYSTEMS A Thesis by DANIEL BRUESKE Submitted to the Oflice of Graduate Studies of Texas ARM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 1994... Major Subject: Electrical Engineering ON CHIP CLOCK SYNCHRONIZATION FOR LARGE DIGITAL SYSTEMS A Thesis by DANIEL BRUESKE Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved...

Brueske, Daniel

2012-06-07

346

Peripheral clocks and the regulation of cardiovascular and metabolic function.  

PubMed

Circadian rhythms generated by cell autonomous biological clocks allow for the appropriate temporal synchronization of physiology and behavior, optimizing the efficiency of biological systems. Circadian oscillators and functions have been uncovered in both central and peripheral tissues. This article describes methodology, experimental design, and technical challenges pertaining to studies of circadian rhythms in the periphery. Experimental approaches are focused upon revealing the role of peripheral clocks in cardiovascular and metabolic function using in vitro and in vivo techniques. PMID:15817310

Rudic, R Daniel; Curtis, Anne M; Cheng, Yan; FitzGerald, Garret

2005-01-01

347

Tissue-intrinsic dysfunction of circadian clock confers transplant arteriosclerosis.  

PubMed

The suprachiasmatic nucleus of the brain is the circadian center, relaying rhythmic environmental and behavioral information to peripheral tissues to control circadian physiology. As such, central clock dysfunction can alter systemic homeostasis to consequently impair peripheral physiology in a manner that is secondary to circadian malfunction. To determine the impact of circadian clock function in organ transplantation and dissect the influence of intrinsic tissue clocks versus extrinsic clocks, we implemented a blood vessel grafting approach to surgically assemble a chimeric mouse that was part wild-type (WT) and part circadian clock mutant. Arterial isografts from donor WT mice that had been anastamosed to common carotid arteries of recipient WT mice (WT:WT) exhibited no pathology in this syngeneic transplant strategy. Similarly, when WT grafts were anastamosed to mice with disrupted circadian clocks, the structural features of the WT grafts immersed in the milieu of circadian malfunction were normal and absent of lesions, comparable to WT:WT grafts. In contrast, aortic grafts from Bmal1 knockout (KO) or Period-2,3 double-KO mice transplanted into littermate control WT mice developed robust arteriosclerotic disease. These lesions observed in donor grafts of Bmal1-KO were associated with up-regulation in T-cell receptors, macrophages, and infiltrating cells in the vascular grafts, but were independent of hemodynamics and B and T cell-mediated immunity. These data demonstrate the significance of intrinsic tissue clocks as an autonomous influence in experimental models of arteriosclerotic disease, which may have implications with regard to the influence of circadian clock function in organ transplantation. PMID:21969583

Cheng, Bo; Anea, Ciprian B; Yao, Lin; Chen, Feng; Patel, Vijay; Merloiu, Ana; Pati, Paramita; Caldwell, R William; Fulton, David J; Rudic, R Daniel

2011-10-11

348

Tissue-intrinsic dysfunction of circadian clock confers transplant arteriosclerosis  

PubMed Central

The suprachiasmatic nucleus of the brain is the circadian center, relaying rhythmic environmental and behavioral information to peripheral tissues to control circadian physiology. As such, central clock dysfunction can alter systemic homeostasis to consequently impair peripheral physiology in a manner that is secondary to circadian malfunction. To determine the impact of circadian clock function in organ transplantation and dissect the influence of intrinsic tissue clocks versus extrinsic clocks, we implemented a blood vessel grafting approach to surgically assemble a chimeric mouse that was part wild-type (WT) and part circadian clock mutant. Arterial isografts from donor WT mice that had been anastamosed to common carotid arteries of recipient WT mice (WT:WT) exhibited no pathology in this syngeneic transplant strategy. Similarly, when WT grafts were anastamosed to mice with disrupted circadian clocks, the structural features of the WT grafts immersed in the milieu of circadian malfunction were normal and absent of lesions, comparable to WT:WT grafts. In contrast, aortic grafts from Bmal1 knockout (KO) or Period-2,3 double-KO mice transplanted into littermate control WT mice developed robust arteriosclerotic disease. These lesions observed in donor grafts of Bmal1-KO were associated with up-regulation in T-cell receptors, macrophages, and infiltrating cells in the vascular grafts, but were independent of hemodynamics and B and T cell-mediated immunity. These data demonstrate the significance of intrinsic tissue clocks as an autonomous influence in experimental models of arteriosclerotic disease, which may have implications with regard to the influence of circadian clock function in organ transplantation. PMID:21969583

Cheng, Bo; Anea, Ciprian B.; Yao, Lin; Chen, Feng; Patel, Vijay; Merloiu, Ana; Pati, Paramita; Caldwell, R. William; Fulton, David J.; Rudic, R. Daniel

2011-01-01

349

GIOVE Orbit and Clock Determination Based on the CONGO Network  

NASA Astrophysics Data System (ADS)

As a prototype for the satellites of the future European Global Navigation Satellite System (GNSS) Galileo, the European Space Agency (ESA) launched two satellites (GIOVE-A and GIOVE-B) as part of the Galileo in Orbit Validation Element (GIOVE). To gain experience with the signals transmitted by these satellites and to estimate satellite orbit and clock parameters, a global network of GIOVE-capable receivers was established. This Cooperative Network for GIOVE Observations (CONGO) is operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR, Oberpfaffenhofen, Germany) and Bundesamt für Kartographie und Geodäsie (BKG, Frankfurt, Germany) in cooperation with several local station hosts. The CONGO network currently consists of 10 globally distributed stations providing their observations in real-time. This network is used by Technische Universität München for an operational daily orbit and clock determination of the GIOVE satellites including orbit predictions. The strategy of the combined GPS and GIOVE processing is presented. The quality of the estimated GIOVE satellite orbits is evaluated by orbit fits and satellite laser ranging (SLR). The quality of the GIOVE satellite clocks, in particular the hydrogen maser of GIOVE-B, is discussed. As three different receiver types and two different satellite systems are considered in the CONGO processing, a special focus has to be put on the biases between the different receivers and GNSSs. Additionally, DLR's Real-Time Clock Estimation (RETICLE) system has been extended to provide clock offset estimates for the GIOVE satellites based on the real-time data streams from the CONGO network. The GIOVE clocks are estimated based on the predicted orbits mentioned above. The paper introduces the real-time clock estimation process and presents real-time clock results.

Steigenberger, Peter; Hauschild, André; Montenbruck, Oliver; Hugentobler, Urs; Hessels, Uwe; Weber, Georg; Noack, Thoralf

2010-05-01

350

Comparison of various clocks at LANL LAPP facility  

SciTech Connect

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 operationally from 2005 to the present show variations of {approx} 35 nsec. SLRE variability is xxx +/- yyy sec (std dev). SLRE occasionally show unusual events such as those discussed by Pongratz. We will continue to study and monitor.

Dighe, Kalpak Arvind [Los Alamos National Laboratory

2010-10-29

351

Clock Face Drawing Test Performance in Children with ADHD  

PubMed Central

Introduction The utility and discriminatory pattern of the clock face drawing test in ADHD is unclear. This study therefore compared Clock Face Drawing test performance in children with ADHD and controls. Methods 95 school children with ADHD and 191 other children were matched for gender ratio and age. ADHD symptoms severities were assessed using DSM-IV ADHD checklist and their intellectual functioning was assessed. The participants completed three clock-drawing tasks, and the following four functions were assessed: Contour score, Numbers score, Hands setting score, and Center score. Results All the subscales scores of the three clock drawing tests of the ADHD group were lower than that of the control group. In ADHD children, inattention and hyperactivity/ impulsivity scores were not related to free drawn clock test scores. When pre-drawn contour test was performed, inattentiveness score was statistically associated with Number score while none of the other variables of age, gender, intellectual functioning, and hand use preference were associated with that kind of score. In pre-drawn clock, no association of ADHD symptoms with any CDT subscales found significant. In addition, more errors are observed with free drawn clock and Pre-drawn contour than pre-drawn clock. Discussion Putting Numbers and Hands setting are more sensitive measures to screen ADHD than Contour and Center drawing. Test performance, except Hands setting, may have already reached a developmental plateau. It is probable that Hand setting deficit in children with ADHD may not decrease from age 8 to 14 years. Performance of children with ADHD is associated with complexity of CDT. PMID:25337328

Ghanizadeh, Ahmad; Safavi, Salar; Berk, Michael

2013-01-01

352

Master Clock and Time-Signal-Distribution System  

NASA Technical Reports Server (NTRS)

A timing system comprising an electronic master clock and a subsystem for distributing time signals from the master clock to end users is undergoing development to satisfy anticipated timing requirements of NASA s Deep Space Network (DSN) for the next 20 to 30 years. This system has a modular, flexible, expandable architecture that is easier to operate and maintain than the present frequency and timing subsystem (FTS).

Tjoelker, Robert; Calhoun, Malcolm; Kuhnle, Paul; Sydnor, Richard; Lauf, John

2007-01-01

353

Geometrical Model of Solar Radiation Pressure Based on High-Performing Galileo Clocks - First Geometrical Mapping of the Yarkowsky effect  

NASA Astrophysics Data System (ADS)

Solar radiation pressure is the main source of errors in the precise orbit determination of GNSS satellites. All deficiencies in the modeling of Solar radiation pressure map into estimated terrestrial reference frame parameters as well as into derived gravity field coefficients and altimetry results when LEO orbits are determined using GPS. Here we introduce a new approach to geometrically map radial orbit perturbations of GNSS satellites using highly-performing clocks on board the first Galileo satellites. Only a linear model (time bias and time drift) needs to be removed from the estimated clock parameters and the remaining clock residuals map all radial orbit perturbations along the orbit. With the independent SLR measurements, we show that a Galileo clock is stable enough to map radial orbit perturbations continuously along the orbit with a negative sign in comparison to SLR residuals. Agreement between the SLR residuals and the clock residuals is at the 1 cm RMS for an orbit arc of 24 h. Looking at the clock parameters determined along one orbit revolution over a period of one year, we show that the so-called SLR bias in Galileo and GPS orbits can be explained by the translation of the determined orbit in the orbital plane towards the Sun. This orbit translation is due to thermal re-radiation and not accounting for the Sun elevation in the parameterization of the estimated Solar radiation pressure parameters. SLR ranging to GNSS satellites takes place typically at night, e.g. between 6 pm and 6 am local time when the Sun is in opposition to the satellite. Therefore, SLR observes only one part of the GNSS orbit with a negative radial orbit error that is mapped as an artificial bias in SLR observables. The Galileo clocks clearly show orbit translation for all Sun elevations: the radial orbit error is positive when the Sun is in conjuction (orbit noon) and negative when the Sun is in opposition (orbit midnight). The magnitude of this artificial negative SLR bias depends on the orbit quality and should rather be called GNSS orbit bias instead of SLR bias. When LEO satellite orbits are estimated using GPS, this GPS orbit bias is mapped into the antenna phase center. All LEO satellites, such as CHAMP, GRACE and JASON-1/2, need an adjustment of the radial antenna phase center offset. GNSS orbit translations towards the Sun in the orbital plane do not only propagate into the estimated LEO orbits, but also into derived gravity field and altimetry products. Geometrical mapping of orbit perturbations using an on board GNSS clock is a new technique to monitor orbit perturbations along the orbit and was successfully applied in the modeling of Solar radiation pressure. We show that CODE Solar radiation pressure parameterization lacks dependency with the Sun's elevation, i.e. elongation angle (rotation of Solar arrays), especially at low Sun elevations (eclipses). Parameterisation with the Sun elongation angle is used in the so-called T30 model (ROCK-model) that includes thermal re-radiation. A preliminary version of Solar radiation pressure for the first five Galileo and the GPS-36 satellite is based on 2×180 days of the MGEX Campaign. We show that Galileo clocks map the Yarkowsky effect along the orbit, i.e. the lag between the Sun's illumination and thermal re-radiation. We present the first geometrical mapping of anisotropic thermal emission of absorbed sunlight of an illuminated satellite. In this way, the effects of Solar radiation pressure can be modelled with only two paramaters for all Sun elevations.

Svehla, Drazen; Rothacher, Markus; Hugentobler, Urs; Steigenberger, Peter; Ziebart, Marek

2014-05-01

354

Polygon Angle Applet  

NSDL National Science Digital Library

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

Exner, Nicholas

2000-05-31

355

What's My Angle?  

NSDL National Science Digital Library

This interactive module offers learners the opportunity to check their knowledge of angle measure and estimation, and the use of a protractor. There are ten activities that vary the tasks and the degree of precision. The site is designed for whiteboard demonstration as well, and it includes a tutorial on angle types and protractor use.

2011-01-01

356

SunAngle Calculator  

NSDL National Science Digital Library

SunAngle is an on-line tool that calculates solar angles and related information for a given location, date, and time. It computes the declination of the Sun, sunrise and sunset times, azimuth of the Sun, solar time and more. Complete instructions and definitions of variables are included.

Gronbeck, Christopher

357

The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole  

NASA Astrophysics Data System (ADS)

Star formation in the centers of galaxies is thought to yield massive stars with a possibly top-heavy stellar mass distribution. It is likely that magnetic fields play a crucial role in the distribution of stellar masses inside star-forming molecular clouds. In this context, we explore the effects of magnetic fields, with a typical field strength of 38 ?G, such as in RCW 38, and a field strength of 135 ?G, similar to NGC 2024 and the infrared dark cloud G28.34+0.06, on the initial mass function (IMF) near (? 10 pc) a 107 solar mass black hole. Using these conditions, we perform a series of numerical simulations with the hydrodynamical code FLASH to elucidate the impact of magnetic fields on the IMF and the star-formation efficiency (SFE) emerging from an 800 solar mass cloud. We find that the collapse of a gravitationally unstable molecular cloud is slowed down with increasing magnetic field strength and that stars form along the field lines. The total number of stars formed during the simulations increases by a factor of 1.5-2 with magnetic fields. The main component of the IMF has a lognormal shape, with its peak shifted to sub-solar (? 0.3 M?) masses in the presence of magnetic fields, due to a decrease in the accretion rates from the gas reservoir. In addition, we see a top-heavy, nearly flat IMF above ~2 solar masses, from regions that were supported by magnetic pressure until high masses are reached. We also consider the effects of X-ray irradiation if the central black hole is active. X-ray feedback inhibits the formation of sub-solar masses and decreases the SFEs even further. Thus, the second contribution is no longer visible. We conclude that magnetic fields potentially change the SFE and the IMF both in active and inactive galaxies, and need to be taken into account in such calculations. The presence of a flat component of the IMF would be a particularly relevant signature for the importance of magnetic fields, as it is usually not found in hydrodynamical simulations.

Hocuk, S.; Schleicher, D. R. G.; Spaans, M.; Cazaux, S.

2012-09-01

358

Laser Ranging Experiment on Lunar Reconnaissance Orbiter: Clocks and Ranges  

NASA Astrophysics Data System (ADS)

Accurate ranges from Earth to the Lunar Reconnaissance Orbiter (LRO) spacecraft Laser Ranging (LR) system supplement the precision orbit determination (POD) of LRO. LRO is tracked by ten LR stations from the International Laser Ranging Service (ILRS), using H-maser, GPS steered Rb, and Cs standard oscillators as reference clocks. The LR system routinely makes one-way range measurements via laser time-of-flight from Earth to LRO. Uplink photons are received by a telescope mounted on the high-gain antenna on LRO , transferred through a fiber optic cable to the Lunar Orbiter Laser Altimeter (LOLA), and timed-tagged by the spacecraft clock. The range from the LR Earth station to LRO is derived from paired outgoing and received times. Accurate ranges can only be obtained after solving for both the spacecraft and ground station clock errors. The drift rate and aging rate of the LRO clock are calculated from data provided by the primary LR station, NASA's Next Generation Satellite Laser Ranging System (NGSLR) in Greenbelt, Maryland. The results confirm the LRO clock oscillator mid to long term stability measured during ground testing. These rates also agree well with those determined through POD. Simultaneous and near-simultaneous ranging to LRO from multiple LR stations in America, Europe, and Australia has been successfully achieved within a 10 hour window. Data analysis of these ranging experiments allows for precision modeling of the clock behaviors of each LR ground station and characterization of the station ground fire times.

Mao, D.; Rowlands, D. D.; McGarry, J.; Zuber, M. T.; Smith, D. E.; Torrence, M. H.; Neumann, G. A.; Mazarico, E.; Sun, X.; Zagwodzki, T. W.; Cavanaugh, J. F.; Ramos-Izquierdo, L.

2010-12-01

359

Casein kinase 1 promotes synchrony of the circadian clock network.  

PubMed

Casein kinase 1, known as DOUBLETIME (DBT) in Drosophila melanogaster, is a critical component of the circadian clock that phosphorylates and promotes degradation of the PERIOD (PER) protein. However, other functions of DBT in circadian regulation are not clear, in part because severe reduction of dbt causes preadult lethality. Here we report the molecular and behavioral phenotype of a viable dbt(EY02910) loss-of-function mutant. We found that DBT protein levels are dramatically reduced in adult dbt(EY02910) flies, and the majority of mutant flies display arrhythmic behavior, with a few showing weak, long-period (?32 h) rhythms. Peak phosphorylation of PER is delayed, and both hyper- and hypophosphorylated forms of the PER and CLOCK proteins are present throughout the day. In addition, molecular oscillations of the circadian clock are dampened. In the central brain, PER and TIM expression is heterogeneous and decoupled in the canonical clock neurons of the dbt(EY02910) mutants. We also report an interaction between dbt and the signaling pathway involving pigment dispersing factor (PDF), a synchronizing peptide in the clock network. These data thus demonstrate that overall reduction of DBT causes long and arrhythmic behavior, and they reveal an unexpected role of DBT in promoting synchrony of the circadian clock network. PMID:24820422

Zheng, Xiangzhong; Sowcik, Mallory; Chen, Dechun; Sehgal, Amita

2014-07-01

360

Serum factors in older individuals change cellular clock properties  

PubMed Central

Human aging is accompanied by dramatic changes in daily sleep–wake behavior: Activity shifts to an earlier phase, and the consolidation of sleep and wake is disturbed. Although this daily circadian rhythm is brain-controlled, its mechanism is encoded by cell-autonomous circadian clocks functioning in nearly every cell of the body. In fact, human clock properties measured in peripheral cells such as fibroblasts closely mimic those measured physiologically and behaviorally in the same subjects. To understand better the molecular mechanisms by which human aging affects circadian clocks, we characterized the clock properties of fibroblasts cultivated from dermal biopsies of young and older subjects. Fibroblast period length, amplitude, and phase were identical in the two groups even though behavior was not, thereby suggesting that basic clock properties of peripheral cells do not change during aging. Interestingly, measurement of the same cells in the presence of human serum from older donors shortened period length and advanced the phase of cellular circadian rhythms compared with treatment with serum from young subjects, indicating that a circulating factor might alter human chronotype. Further experiments demonstrated that this effect is caused by a thermolabile factor present in serum of older individuals. Thus, even though the molecular machinery of peripheral circadian clocks does not change with age, some age-related circadian dysfunction observed in vivo might be of hormonal origin and therefore might be pharmacologically remediable. PMID:21482780

Pagani, Lucia; Schmitt, Karen; Meier, Fides; Izakovic, Jan; Roemer, Konstanze; Viola, Antoine; Cajochen, Christian; Wirz-Justice, Anna; Brown, Steven A.; Eckert, Anne

2011-01-01

361

Quantum arrival and dwell times via idealized clocks  

SciTech Connect

A number of approaches to the problem of defining arrival- and dwell-time probabilities in quantum theory makes use of idealized models of clocks. An interesting question is the extent to which the probabilities obtained in this way are related to standard semiclassical results. In this paper, we explore this question using a reasonably general clock model, solved using path-integral methods. We find that, in the weak-coupling regime, where the energy of the clock is much less than the energy of the particle it is measuring, the probability for the clock pointer can be expressed in terms of the probability current in the case of arrival times, and the dwell-time operator in the case of dwell times, the expected semiclassical results. In the regime of strong system-clock coupling, we find that the arrival-time probability is proportional to the kinetic-energy density, consistent with an earlier model involving a complex potential. We argue that, properly normalized, this may be the generically expected result in this regime. We show that these conclusions are largely independent of the form of the clock Hamiltonian.

Yearsley, J. M.; Downs, D. A.; Halliwell, J. J.; Hashagen, A. K. [Blackett Laboratory, Imperial College, London SW7 2BZ (United Kingdom)

2011-08-15

362

Applications of Clocks to Space Navigation & "Planetary GPS"  

NASA Technical Reports Server (NTRS)

The ability to fly atomic clocks on GPS satellites has profoundly defined the capabilities and limitations of GPS in near-Earth applications. It is likely that future infrastructure for Lunar and Mars applications will be constrained by financial factors. The development of a low cost, small, high performance space clock -- or ultrahigh performance space clocks -- could revolutionize and drive the entire approach to GPS-like systems at the Moon (or Mars), and possibly even change the future of GPS at Earth. Many system trade studies are required. The performance of future GPS-like tracking systems at the Moon or Mars will depend critically on clock performance, availability of inertial sensors, and constellation coverage. Example: present-day GPS carry 10(exp -13) clocks and require several updates per day. With 10(exp -15) clocks, a constellation at Mars could operate autonomously with updates just once per month. Use of GPS tracking at the Moon should be evaluated in a technical study.

Lichten, Stephen M.

2004-01-01

363

Special Angle Pairs Discovery Activity  

NSDL National Science Digital Library

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

Henry, Barbara

2012-04-16

364

Laser Technology in Commercial Atomic Clocks  

NASA Astrophysics Data System (ADS)

Commercial atomic frequency standards (AFS) are deployed in diverse civilian, military, and aerospace applications, ranging from high-precision measurement and calibration to navigation, communications and, of course, timekeeping. Currently, commercially available AFS include magnetically-selected cesium beam frequency standards and hydrogen masers and lamp-pumped rubidium oscillators. Despite the revolution in atomic physics and laboratory-scale AFS brought about by the advent of the tunable laser in the early 1970s, commercial AFS invariably rely on more conventional atomic physics technology developed in the 1950s. The reason for this lack of advancement of commercial AFS technology is the relatively poor reliability and environmental sensitivity of narrow-linewidth single-mode laser sources at atomic resonance wavelengths. Over the past 8 years, Symmetricom, in collaboration with laser manufacturers, has developed specialized laser sources for commercial AFS applications. These laser devices, optimized for high spectral purity and long-term reliability, will enable a new generation of commercial AFS. This talk will briefly describe two laser-based atomic frequency standard development programs at Symmetricom. The Chip-Scale Atomic Clock, two orders of magnitude smaller and lower power than any commercial AFS, will enable atomic timing accuracy in portable battery-powered applications. The Optically-Pumped Cesium Beam Frequency Standard, under development for deployment onboard the GPS-III satellite constellation, will provide enhanced short-term stability and longer lifetime compared to magnetically-selected cesium beam AFS.

Lutwak, R.

2006-05-01

365

Entrainment of the human circadian clock.  

PubMed

Humans are an excellent model system for studying entrainment of the circadian clock in the real world. Unlike the situation in laboratory experiments, entrainment under natural conditions is achieved by different external signals as well as by internal signals generated by multiple feedbacks within the system (e.g., behavior-dependent light and temperature changes, melatonin levels, or regular nutrient intake). Signals that by themselves would not be sufficient zeitgebers may contribute to entrainment in conjunction with other self-sufficient zeitgeber signals (e.g., light). The investigation of these complex zeitgeber interactions seems to be problematic in most model systems and strengthens the human system for circadian research. Here, we review our endeavors measuring human entrainment in real life, predominantly with the help of the Munich ChronoType Questionnaire (MCTQ). The large number of participants in our current MCTQ database allows accurate quantification of the human phase of entrainment (chronotype) and how it depends on age or sex. We also present new data showing how chronotype depends on natural light exposure. The results indicate the importance of zeitgeber strength on human entrainment and help in understanding the differences in chronotype, e.g., between urban and rural regions. PMID:18419286

Roenneberg, T; Merrow, M

2007-01-01

366

Fossilized gravitational wave relic and primordial clocks  

NASA Astrophysics Data System (ADS)

If long-wavelength primordial tensor modes are coupled to short-wavelength scalar modes, the scalar curvature two-point function will have an off-diagonal component. This "fossil" remnant is a signature of a mode coupling that cannot be achieved in single-clock inflation. Any constraint on its presence allows a cross-check of the relationship between the dynamical generation of the fluctuations and the evolution of the inflationary background. We use the example of non—Bunch-Davies initial states for the tensor and scalar modes to demonstrate that physically reasonable fossils, consistent with current data, can be observable in the near future. We illustrate how the fossil off-diagonal power spectrum is a complementary probe to the squeezed limit bispectra of the scalar and tensor sectors individually. We also quantify the relation between the observable signal and the squeezed limit bispectrum for a general scalar-scalar-fossil coupling and note the effect of superhorizon tensor modes on the anisotropy in scalar modes.

Brahma, Suddhasattwa; Nelson, Elliot; Shandera, Sarah

2014-01-01

367

Cardiovascular tissues contain independent circadian clocks.  

PubMed

Acute cardiovascular events exhibit a circadian rhythm in the frequency of occurrence. The mechanisms underlying these phenomena are not yet fully understood, but they may be due to rhythmicity inherent in the cardiovascular system. We have begun to characterize rhythmicity of the clock gene mPer1 in the rat cardiovascular system. Luciferase activity driven by the mPer1 gene promoter is rhythmic in vitro in heart tissue explants and a wide variety of veins and arteries cultured from the transgenic Per1-luc rat. The tissues showed between 3 and 12 circadian cycles of gene expression in vitro before damping. Whereas peak per1-driven bioluminescence consistently occurred during the late night in the heart and all arteries sampled, the phases of the rhythms in veins varied significantly by anatomical location. Varying the time of the culture procedure relative to the donor animal's light:dark cycle revealed that, unlike some other rat tissues such as liver, the phases of in vitro rhythms of arteries, veins, and heart explants were affected by culture time. However, phase relationships among tissues were consistent across culture times; this suggests diversity in circadian regulation among components of the cardiovascular system. PMID:15835394

Davidson, A J; London, B; Block, G D; Menaker, M

2005-01-01

368

A Two-Photon E1-M1 Optical Clock  

NASA Astrophysics Data System (ADS)

Innovations in precision frequency measurement advance popular technologies such as global positioning systems (GPS), permit the testing of fundamental physics constants, and have the potential to measure local variations in gravity. Driving optical transitions for frequency measurement using an E1-M1 excitation scheme in a hot mercury (Hg) vapor cell is viable and could be the basis of a portable optical frequency standard with comparable accuracy to the most precise atomic clocks in the world. This dissertation explores the fundamental physics of the new E1-M1 method of high-precision frequency measurement in an optical, atomic clock and describes the construction of a high-power E1-M1 clock laser. The value of this new scheme compared to existing optical frequency standards is the simplicity and portability of the experimental setup. Such an optical frequency standard would permit frequency measurement in far-flung locations on earth and in space. Analysis of both the E1-M1 optical transition and thermal properties of the candidate clock atoms are presented. These models allow a stability estimate of an E1-M1 optical clock and recommend experimental settings to optimize the standard. The experimental work that has been performed in pursuit of observing the E1-M1 clock transition in Hg is also discussed. An optical clock operates by making a precision frequency measurement of a laser that has been brought into resonance with a clock atom's oscillator: a high quality atomic level transition. Group II type atoms, such as Hg, have the 1S0-3P0 transition that is an ideal basis for a clock. The E1-M1 excitation is performed by driving the two-photon allowed transition 1S0-3P1-3P0. This is in contrast to the single-photon E1 transition used in other systems. Single-photon schemes must use ultracold atoms to reduce atomic motion to attain high levels of accuracy. Driving the clock transition with a pair of degenerate counter-propagating photons in an E1-M1 scheme reduces Doppler broadening effects without the need for ultracold atoms. This allows frequency measurement to be performed at temperatures that produce large atomic number densities, increasing the statistical accuracy and portability of the E1-M1 system compared to cold systems.

Alden, Emily A.

369

Cluster-II Multi-Spacecraft Observations of Continuous Reconnection at the Dayside Magnetopause under Steady IMF Conditions  

NASA Astrophysics Data System (ADS)

We use data from the Cluster Ion Spectrometry (CIS) and magnetic field (FGM) experiments to survey Cluster-II crossings of the dayside magnetopause. The focus of this presentation is on the detection by consecutive spacecraft of accelerated flows at the dayside magnetopause under steady IMF conditions. The agreement between the observed flow acceleration and reconnection theory is better than 95% in many events, indicating that these flows are produced by reconnection. The detection of reconnection jets by consecutive spacecraft crossing the magnetopause implies that reconnection occurs continuously over an extended period of time. Furthermore, the observed flow direction tends to be steady during the same period of time, indicating the presence of a stable reconnection line across the dayside magnetopause. Our observations thus suggest that reconnection is continuous and well-organized, rather than patchy and random, under steady IMF conditions

Phan, T.; Carlson, C.; Parks, G.; Twitty, C.; McFadden, J.; Reme, H.; Balogh, A.; Bosqued, J. M.; Dandouras, I.; Sauvaud, J. A.; aoustin, C.; Kistler, L.; Moebius, E.; Mouikis, C.; Klecker, B.; Paschmann, G.; McCarthy, M.; Formisano, V.; Bavassano-Cattaneo, M.; Dilellis, D.; Korth, A.; Lundin, R.

2001-12-01

370

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

E-print Network

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

Lars Mattsson

2008-08-15

371

A global magnetohydrodynamic simulation of magnetospheric dynamics when the IMF is southward: Mapping to the auroral zone  

NASA Technical Reports Server (NTRS)

A high resolution global magnetohydrodynamic simulation model is used to investigate magnetospheric dynamics during intervals with southward interplanetary magnetic field (IMF). When the southward IMF reaches the dayside magnetopause reconnection begins and magnetic flux is convected into the tail lobes. After about 35 m, reconnection begins within the plasma sheet near midnight at x = -14 RE. Later the x-line moves towards the magnetopause. The reconnection occurs just tailward of the region where the tail attaches onto the dipole dominated inner magnetosphere. Later when all the plasma sheet field lines have reconnected a plasmoid moves down the tail. The region of the ionosphere where the energy flux from the magnetosphere is greatest is calculated. The energy flux is confined to a region which approximates the auroral oval.

Walker, Raymond J.; Ogino, Tatsuki; Ashour-Abdalla, Maha; Raeder, Joachim

1992-01-01

372

The Role of Periodic Loading-Unloading in the Magnetotail vs IMF Bz Flipping in the Ring Current Buildup  

NASA Astrophysics Data System (ADS)

We use the global MHD code BATS-R-US output to drive Fok Ring Current (FRC) model. Introducing of kinetic corrections to BATS-R-US code in the magnetotail region leads to fast reconnection rates observed in kinetic simulations and quasi-periodic loading-unloading cycles in the magnetotail during a long period of steady southward IMF B_z. Running of FRC model in this case correspondingly leads to quasi-periodic oscillations of geosynchronous energetic particle fluxes, similar to "sawtooth" profile injections. We compare these results with the results of the FRC model driven by BATS-R-US code for periodically flipping IMF B_z component, without kinetic corrections.

Taktakishvili, A.; Kuznetsova, M. M.; Fok, M.; Hesse, M.; Rastaetter, L.; Chulaki, A.; Maddox, M.; Gombosi, T.; Dezeeuw, D.

2006-12-01

373

Daily variation at Concordia station (Antarctica) and its dependence on IMF conditions  

NASA Astrophysics Data System (ADS)

After some short test surveys, during the 2004-2005 summer expedition in Antarctica, a geomagnetic French-Italian observatory was installed on the plateau (geographic coordinates: 75.1° S, 123.4° E; corrected geomagnetic coordinates: 88.9° S, 54.3° E; UT=LT-8) very close to the geomagnetic pole. In this paper we present some peculiarities of the daily variation as observed at this polar cap observatory during the years 2005 and 2006, taking into account the different Loyd seasons and different interplanetary magnetic field conditions. Some interesting results emerge from the analysis, confirming the dependence of the daily variation (and of the associated polar current systems) on the IMF Bz and By components. In particular the analysis showed that different Bz conditions correspond to different contribution to daily variation of ionospheric and field aligned currents, while particular By conditions lead to a time shift of the diurnal variation, indicating an asymmetry with respect to the noon meridian.

Cafarella, L.; di Mauro, D.; Lepidi, S.; Meloni, A.; Pietrolungo, M.; Santarelli, L.; Schott, J. J.

2007-10-01

374

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

375

Time Scales Of Auroral Intensifications Measured By Polar Uvi: Seasonal And Imf Dependence  

NASA Astrophysics Data System (ADS)

The hemispheric power of auroral electron precipitation measured by the Polar Ul- traviolet Imager (UVI) is used to quantify the time scales of auroral intensifications. It is shown that the auroral power during substorms is sustained above pre-onset lev- els for longer time scales during events that occur during southward interplanetary magnetic field (IMF). Furthermore, it is demonstrated that the characteristic time for substorm activity is roughly a factor of three longer for events that occur in darkness than for those when the ionosphere is sunlit. It is shown that the longer time scale of substorms occurring in darkness is sustained by discrete auroral features associated with field-aligned potential drops and inertial Alfven waves. These discrete structures exist for shorter time scales if they are observed at all during substorms that occur in sunlight. These results provide further evidence for the emerging view that the iono- spheric boundary conditions at the foot of auroral field lines play a significant role in determining both the synoptic scale structure of the aurora and its dynamical time scales.

Chua, D.; Parks, G.; Brittnacher, M.; Germany, G.; Spann, J.; Carlson, C.

376

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

NASA Astrophysics Data System (ADS)

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 the same time IMAGE observed a bright spot poleward of the dayside auroral oval resulting from precipitating protons into the atmosphere. The intensity of the proton spot is consistent with the energy flux contained in the plasma jets observed by Cluster. Using the Tsyganenko-01 magnetic field model with enhanced solar wind pressure, the Cluster MP location is mapped to the vicinity of the IMAGE proton spot. Mapping the auroral spot out to the MP implies an X-line of at least 3.6 RE in yGSM. In addition to confirming the reconnection source of the dayside auroral proton spot, the Cluster observations also reveal sub-Alfvénic flows and a plasma depletion layer in the magnetosheath next to the MP, in a region where gas dynamic models predict super-Alfvénic flows.

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

2003-05-01

377

Properties, Structure and Dynamics of the Exterior Cusp Under Northward IMF, Cluster Multi Event Analysis  

NASA Astrophysics Data System (ADS)

We have studied in detail multi-spacecraft observations of four Cluster exterior cusp passes during the years 2001 and 2002. All of them occurred during northward Interplanetary Magnetic Field (IMF) intervals. A well-bounded region where the magnetic field exhibits very low diamagnetic values and the ions display high levels of isotropisation is sampled. We refer to this region as the Stagnant Exterior Cusp (SEC). We show that the overall picture of the region is compatible with a reconnection site poleward of the cusp for all four events. The global topology of the exterior cusp and SEC can be inferred and reveals that the solar-wind plasma at least partly gets access to the magnetosphere through a sharp boundary delimiting the SEC from the unperturbed magnetosheath. Multi spacecraft data analysis further permits to highlight that the whole region is highly dynamic. The SEC-magnetosheath boundary presents abrupt changes in the magnetic field and plasma parameters and is shown to be rotational in nature. We will put particular emphasis on the exact characteristics and possible nature of this key boundary of the magnetosphere.

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

2002-12-01

378

Observations of a transient event in the subsolar magnetosheath during strongly northward IMF  

NASA Astrophysics Data System (ADS)

We present multipoint THEMIS observation of a transient event in the subsolar magnetosheath on July 10, 2007. The event exhibits some features of a flux transfer event, such as a bipolar variation in the magnetic field component normal to the nominal magnetopause centered on a peak in the total magnetic field strength. Four THEMIS spacecraft were in the magnetosheath and one in the magnetosphere. Timing analysis and the absence of flow perturbation suggest that the event is a small scale structure (~0.12 Re in the direction of the flow) moving with the background magnetosheath flow. Despite the inferred small size of the event, THC and THD both observed large amplitude (~40 nT) bipolar magnetic field signatures normal to the nominal magnetopause. Nearby spacecraft THE (only 0.2 Re further outward in the Xgsm direction) observed no significant magnetic field perturbation. Neither did THB or THA, located further away in the magnetosheath and magnetosphere, respectively. During the event, the IMF was strongly northward (approximately 20nT), which does not favor subsolar magnetic reconnection. Inside the structure, the magnetic field briefly rotates 90° away from northward to dawnward. Ions stream antiparallel to the magnetic field in the magnetosheath, parallel to the magnetic field in the event.

Dias Silveira, M. V.; Sibeck, D. G.; Gonzalez, W. D.; Koga, D.

2013-12-01

379

Observations of Magnetic Reconnection From Multiple Merging Sites Along the Same Field Lines Under Northward IMF Conditions  

NASA Astrophysics Data System (ADS)

Several researchers have shown that when the interplanetary magnetic field (IMF) is northward, magnetic reconnection occurs at the Earth's high latitude magnetopause in regions poleward of the magnetospheric cusps for both the northern and southern hemispheres. With a non-zero By component there is also the possibility for reconnection to occur equatorward of the cusp [e.g., Moore et al., 2002; Chandler et al., 2008]. This paper reexamines the observations of Chandler et al., 2008 in the context of several newly identified, similar events from the Thermal Ion Dynamics Experiment (TIDE) onboard the Polar spacecraft. The observations consist of distinct, overlapping populations of velocity-dispersed magnetosheath ion distributions and outflowing ionospheric ions and occur under a variety of northward IMF conditions. In each case, evidence will be presented to show that the observations are consistent with interactions with separate reconnection sites and plausible scenarios are explored for the location of the sites. The objective is to show that the Chandler et al., 2008 observation is not unique and that the interpretation of these events can be reconciled with those of other investigators studying the dayside magnetic topology for northward IMF.

Giles, B. L.; Avanov, L. A.; Chandler, M. O.; Pollock, C. J.

2013-12-01

380

Ripple Clock Schemes for Quantum-dot Cellular Automata Circuits  

NASA Astrophysics Data System (ADS)

Quantum-dot cellular automata (QCA) is an emerging technology for building digital circuits at nano-scale. It is considered as an alternative to widely used complementary metal oxide semiconductor (CMOS) technology because of its key features, which include low power operation, high density and high operating frequency. Unlike conventional logic circuits in which information is transferred by electrical current, QCA operates with the help of coulomb interaction between two adjacent QCA cells. A QCA cell is a set of four quantum-dots that are placed near the corners of a square. Due to the fact that clocking provides power and control of data flow in QCA, it is considered to be the backbone of QCA operation. This thesis presents the design and simulation of a ripple clock scheme and an enhanced ripple clock scheme for QCA circuits. In the past, different clock schemes were proposed and studied which were focused on data flow in particular direction or reducing delay. This proposed thesis will study the design and simulation of new clock schemes which are more realistic for implementation, give a freedom to propagate logic in all directions, suitable for both combinational and sequential circuits and has potential to support testing and reconfiguration up to some extent. A variety of digital circuits including a 2--to--1 multiplexer, a 1--bit memory, an RS latch, a full adder, a 4--bit adder and a 2--to--4 decoder are implemented and simulated using these clock schemes. A 2--to--4 decoder is used to demonstrate the testing capabilities of these clock schemes. All QCA layouts are drawn and simulated in QCADesigner.

Purohit, Prafull

381

Global cooling and densification of the plasma sheet during an extended period of purely northward IMF on October 22-24, 2003  

Microsoft Academic Search

The October 22-24, 2003 interplanetary magnetic cloud was characterized by an exceptionally long interval (~32 hours) of nearly purely northward interplanetary magnetic field (IMF). Following the northward IMF turning Cluster observed a gradual transition to a cold (<1 keV) and dense (~1-2 cm-3) plasma sheet (CDPS). Cluster observed CDPS continuously for the following ~30 hours while passing through the neutral

M. Øieroset; J. Raeder; T. D. Phan; S. Wing; J. P. McFadden; W. Li; M. Fujimoto; M. Øieroset; A. Balogh

2005-01-01

382

Global cooling and densification of the plasma sheet during an extended period of purely northward IMF on October 22–24, 2003  

Microsoft Academic Search

The October 22–24, 2003 interplanetary magnetic cloud was characterized by an exceptionally long interval (?32 hours) of nearly purely northward interplanetary magnetic field (IMF). Following the northward IMF turning Cluster observed a gradual transition to a cold (<1 keV) and dense (?1–2 cm?3) plasma sheet (CDPS). Cluster observed CDPS continuously for the following ?30 hours while passing through the neutral

M. Øieroset; J. Raeder; T. D. Phan; S. Wing; J. P. McFadden; W. Li; M. Fujimoto; A. Balogh

2005-01-01

383

PROBLEM 8 CLOCK SYNCHRONISATION Consider a set of C clocks. Each clock has a single hour hand that can only point to  

E-print Network

of moving the hand of each clock in the subset clockwise by 3 hours. Your task is to find a minimal sequence solution, the block numbers making up the minimal solution (in the required length/dictionary order 7 ­ SPREADING GOSSIP We have a remote village with n 20 houses (h0, h1, h2, ... hn-1) and several

Goodman, James R.

384

'Magic Angle Precession'  

SciTech Connect

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

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

2008-01-21

385

Differentially timed extracellular signals synchronize pacemaker neuron clocks.  

PubMed

Synchronized neuronal activity is vital for complex processes like behavior. Circadian pacemaker neurons offer an unusual opportunity to study synchrony as their molecular clocks oscillate in phase over an extended timeframe (24 h). To identify where, when, and how synchronizing signals are perceived, we first studied the minimal clock neural circuit in Drosophila larvae, manipulating either the four master pacemaker neurons (LNvs) or two dorsal clock neurons (DN1s). Unexpectedly, we found that the PDF Receptor (PdfR) is required in both LNvs and DN1s to maintain synchronized LNv clocks. We also found that glutamate is a second synchronizing signal that is released from DN1s and perceived in LNvs via the metabotropic glutamate receptor (mGluRA). Because simultaneously reducing Pdfr and mGluRA expression in LNvs severely dampened Timeless clock protein oscillations, we conclude that the master pacemaker LNvs require extracellular signals to function normally. These two synchronizing signals are released at opposite times of day and drive cAMP oscillations in LNvs. Finally we found that PdfR and mGluRA also help synchronize Timeless oscillations in adult s-LNvs. We propose that differentially timed signals that drive cAMP oscillations and synchronize pacemaker neurons in circadian neural circuits will be conserved across species. PMID:25268747

Collins, Ben; Kaplan, Harris S; Cavey, Matthieu; Lelito, Katherine R; Bahle, Andrew H; Zhu, Zhonghua; Macara, Ann Marie; Roman, Gregg; Shafer, Orie T; Blau, Justin

2014-09-01

386

A mammalian circadian clock model incorporating daytime expression elements.  

PubMed

Models of the mammalian clock have traditionally been based around two feedback loops-the self-repression of Per/Cry by interfering with activation by BMAL/CLOCK, and the repression of Bmal/Clock by the REV-ERB proteins. Recent experimental evidence suggests that the D-box, a transcription factor binding site associated with daytime expression, plays a larger role in clock function than has previously been understood. We present a simplified clock model that highlights the role of the D-box and illustrate an approach for finding maximum-entropy ensembles of model parameters, given experimentally imposed constraints. Parameter variability can be mitigated using prior probability distributions derived from genome-wide studies of cellular kinetics. Our model reproduces predictions concerning the dual regulation of Cry1 by the D-box and Rev-ErbA/ROR response element (RRE) promoter elements and allows for ensemble-based predictions of phase response curves (PRCs). Nonphotic signals such as Neuropeptide Y (NPY) may act by promoting Cry1 expression, whereas photic signals likely act by stimulating expression from the E/E' box. Ensemble generation with parameter probability restraints reveals more about a model's behavior than a single optimal parameter set. PMID:25229153

Jolley, Craig C; Ukai-Tadenuma, Maki; Perrin, Dimitri; Ueda, Hiroki R

2014-09-16

387

CLOCK in breast tumorigenesis: genetic, epigenetic, and transcriptional profiling analyses.  

PubMed

The transcription factors responsible for maintaining circadian rhythm influence a variety of biological processes. Recently, it has been suggested that the core circadian genes may play a role in breast tumorigenesis, possibly by influencing hormone regulation or other pathways relevant to cancer. To evaluate this hypothesis, we conducted a genetic and epigenetic association study, as well as a transcriptional profiling array and a pathway-based network analysis. We report significant correlations between single nucleotide polymorphisms associated with the central circadian regulator CLOCK and breast cancer risk, with apparent effect modification by estrogen receptor/progesterone receptor status. We also found that hypermethylation in the CLOCK promoter reduced the risk of breast cancer, and lower levels of CLOCK expression were documented in healthy controls relative to normal or tumor tissue from patients with breast cancer. Finally, we silenced CLOCK in vitro and performed a whole-genome expression microarray and pathway analysis, which identified a cancer-relevant network of transcripts with altered expression following CLOCK gene knockdown. Our findings support the hypothesis that circadian genes influence tumorigenesis, and identify a set of circadian gene variants as candidate breast cancer susceptibility biomarkers. PMID:20124474

Hoffman, Aaron E; Yi, Chun-Hui; Zheng, Tongzhang; Stevens, Richard G; Leaderer, Derek; Zhang, Yawei; Holford, Theodore R; Hansen, Johnni; Paulson, Jennifer; Zhu, Yong

2010-02-15

388

Towards on-chip clocking of perpendicular Nanomagnetic Logic  

NASA Astrophysics Data System (ADS)

Perpendicular Nanomagnetic Logic (pNML) is a computing concept, where the local magnetization and fringing fields of ferromagnets are used to store and process information. Most commonly, pNML devices have been operated at millisecond time scales. In this work, pNML magnets are clocked by a planar on-chip inductor at frequencies ranging from 100 kHz to 40 MHz. The inherent switching field (SF) and SF distribution (SFD) of an individual magnet is determined. An Arrhenius equation is used in order to model the SFD especially suited for compact modeling of the NML devices. Furthermore, a magnetic power-clock, implemented by an on-chip inductor with ferromagnetic cladding, is proposed and analyzed by finite element simulations. Clocking frequencies up to 100 MHz at low power are within reach. An estimate of the power density of a scaled pNML computing system extracted from the data is given. The power efficiency of the on-chip field-clock is calculated to be 17%, remarkable for a current-driven clocking concept.

Becherer, M.; Kiermaier, J.; Breitkreutz, S.; Eichwald, I.; Žiemys, G.; Csaba, G.; Schmitt-Landsiedel, D.

2014-12-01

389

Logical synchronization: how evidence and hypotheses steer atomic clocks  

NASA Astrophysics Data System (ADS)

A clock steps a computer through a cycle of phases. For the propagation of logical symbols from one computer to another, each computer must mesh its phases with arrivals of symbols from other computers. Even the best atomic clocks drift unforeseeably in frequency and phase; feedback steers them toward aiming points that depend on a chosen wave function and on hypotheses about signal propagation. A wave function, always under-determined by evidence, requires a guess. Guessed wave functions are coded into computers that steer atomic clocks in frequency and position—clocks that step computers through their phases of computations, as well as clocks, some on space vehicles, that supply evidence of the propagation of signals. Recognizing the dependence of the phasing of symbol arrivals on guesses about signal propagation elevates `logical synchronization.' from its practice in computer engineering to a dicipline essential to physics. Within this discipline we begin to explore questions invisible under any concept of time that fails to acknowledge the unforeseeable. In particular, variation of spacetime curvature is shown to limit the bit rate of logical communication.

Myers, John M.; Madjid, F. Hadi

2014-05-01

390

A new trapped ion atomic clock based on 201Hg+.  

PubMed

High-resolution spectroscopy has been performed on the ground-state hyperfine transitions in trapped (201)Hg+ ions as part of a program to investigate the viability of (201)Hg+ for clock applications. Part of the spectroscopy work was directed at magnetic-field-sensitive hyperfine lines with delta m(F) = 0, which allow accurate Doppler-free measurement of the magnetic field experienced by the trapped ions. Although it is possible to measure Doppler-free magnetic-field-sensitive transitions in the commonly used clock isotope, (199)Hg+, it is more difficult. In this paper, we discuss how this (199)Hg+ feature may be exploited to produce a more stable clock or one requiring less magnetic shielding in environments with magnetic field fluctuations far in excess of what is normally found in the laboratory. We have also determined that in discharge-lamp-based trapped mercury ion clocks, the optical pumping time for (201)Hg+ is about 3 times shorter than that of (199)Hg+ This can be used to reduce dead time in the interrogation cycle for these types of clocks, thereby reducing the impact of local oscillator noise aliasing effects. PMID:20211781

Burt, Eric A; Taghavi-Larigani, Shervin; Tjoelker, Robert L

2010-03-01

391

Hunting for topological dark matter with atomic clocks  

E-print Network

The cosmological applications of atomic clocks so far have been limited to searches of the uniform-in-time drift of fundamental constants. In this paper, we point out that a transient in time change of fundamental constants can be induced by dark matter objects that have large spatial extent, and are built from light non-Standard Model fields. The stability of this type of dark matter can be dictated by the topological reasons. We point out that correlated networks of atomic clocks, some of them already in existence, can be used as a powerful tool to search for the topological defect dark matter, thus providing another important fundamental physics application to the ever-improving accuracy of atomic clocks. During the encounter with a topological defect, as it sweeps through the network, initially synchronized clocks will become desynchronized. Time discrepancies between spatially-separated clocks are expected to exhibit a distinct signature, encoding defect's space structure and its interaction strength with the Standard Model fields.

A. Derevianko; M. Pospelov

2013-11-05

392

Differentially Timed Extracellular Signals Synchronize Pacemaker Neuron Clocks  

PubMed Central

Synchronized neuronal activity is vital for complex processes like behavior. Circadian pacemaker neurons offer an unusual opportunity to study synchrony as their molecular clocks oscillate in phase over an extended timeframe (24 h). To identify where, when, and how synchronizing signals are perceived, we first studied the minimal clock neural circuit in Drosophila larvae, manipulating either the four master pacemaker neurons (LNvs) or two dorsal clock neurons (DN1s). Unexpectedly, we found that the PDF Receptor (PdfR) is required in both LNvs and DN1s to maintain synchronized LNv clocks. We also found that glutamate is a second synchronizing signal that is released from DN1s and perceived in LNvs via the metabotropic glutamate receptor (mGluRA). Because simultaneously reducing Pdfr and mGluRA expression in LNvs severely dampened Timeless clock protein oscillations, we conclude that the master pacemaker LNvs require extracellular signals to function normally. These two synchronizing signals are released at opposite times of day and drive cAMP oscillations in LNvs. Finally we found that PdfR and mGluRA also help synchronize Timeless oscillations in adult s-LNvs. We propose that differentially timed signals that drive cAMP oscillations and synchronize pacemaker neurons in circadian neural circuits will be conserved across species. PMID:25268747

Collins, Ben; Kaplan, Harris S.; Cavey, Matthieu; Lelito, Katherine R.; Bahle, Andrew H.; Zhu, Zhonghua; Macara, Ann Marie; Roman, Gregg; Shafer, Orie T.; Blau, Justin

2014-01-01

393

Buffer Gas Experiments in Mercury (Hg+) Ion Clock  

NASA Technical Reports Server (NTRS)

We describe the results of the frequency shifts measured from various buffer gases that might be used as a buffer gas to increase the loading efficiency and cooling of ions trapped in a small mercury ion clock. The small mass, volume and power requirement of space clock precludes the use of turbo pumps. Hence, a hermetically sealed vacuum system, incorporating a suitable getter material with a fixed amount of inert buffer gas may be a practical alternative to the groundbased system. The collision shifts of 40,507,347.996xx Hz clock transition for helium, neon and argon buffer gases were measured in the ambient earth magnetic field. In addition to the above non-getterable inert gases we also measured the frequency shifts due to getterable, molecular hydrogen and nitrogen gases which may be used as buffer gases when incorporated with a miniature ion pump. We also examined the frequency shift due to the low methane gas partial pressure in a fixed higher pressure neon buffer gas environment. Methane gas interacted with mercury ions in a peculiar way as to preserve the ion number but to relax the population difference in the two hyperfine clock states and thereby reducing the clock resonance signal. The same population relaxation was also observed for other molecular buffer gases (N H,) but at much reduced rate.

Chung, Sang K.; Prestage, John D.; Tjoelker, Robert L.; Maleki, Lute

2004-01-01

394

Progress Toward a Compact, Highly Stable Ion Clock  

NASA Technical Reports Server (NTRS)

There was an update on the subject of two previous NASA Tech Briefs articles: Compact, Highly Stable Ion Clock (NPO-43075), Vol. 32, No. 5 (May 2008), page 63; and Neon as a Buffer Gas for a Mercury-Ion Clock (NPO-42919), Vol. 32, No. 7 (July 2008), page 62. To recapitulate: A developmental miniature mercury-ion clock has stability comparable to that of a hydrogen-maser clock. The ion-handling components are housed in a sealed vacuum tube, wherein a getter pump maintains the partial vacuum, and the evacuated tube is backfilled with mercury vapor in a neon buffer gas. There was progress in the development of the clock, with emphasis on the design, fabrication, pump-down, and bake-out of the vacuum tube (based on established practice in the travelingwave- tube-amplifier industry) and the ability of the tube to retain a vacuum after a year of operation. Other developments include some aspects of the operation of mercury-vapor source (a small appendage oven containing HgO) so as to maintain the optimum low concentration of mercury vapor, and further efforts to miniaturize the vacuum and optical subsystems to fit within a volume of 2 L.

Prestage, John; Chung, Sang

2009-01-01

395

Circadian clock gene expression regulates cancer cell growth through glutaminase.  

PubMed

Glutamine is an essential amino acid for malignant tumor cells. Glutaminase that metabolizes glutamine reaches a maximum expression in tumors immediately before the maximum proliferation rate. Tumor cells grow at different rates during the day. We postulated that the activity of glutaminase in tumor cells is subject to the regulation of circadian clock gene. We measured glutaminase by western blot analysis and circadian clock gene expression by real-time polymerase chain reaction in the liver and tumor cells at six equispaced time points of the day in individual mice of a 12/12 h light/dark schedule. The results showed that the tumor-bearing mice, under normal diurnal conditions, are circadianly entrained, as reflected by the normal host locomotor activity rhythms and rhythmic liver clock gene expression. The tumors within these mice are also circadianly organized, as reflected by circadian clock gene (Bmal1) expression. What is most remarkable is that kidney-type glutaminase also showed circadian rhythms in the same pattern with tumor circadian clock gene expression in liver cancer xenograft model, indicating that conditionally inhibiting glutaminase activity may provide a new target for cancer therapy. PMID:24681885

Huang, Aixia; Bao, Bingbo; Gaskins, H Rex; Liu, Haijun; Zhang, Xueli; Lu, Liwen; Gao, Shan; Shi, Yihai; Zhang, Ming; Shan, Yuanzhou; Feng, Jing; Yao, Guoxiang

2014-05-01

396

Design of clock recovery circuits for optical clocking in DSM CMOS  

NASA Astrophysics Data System (ADS)

CMOS technology scaling especially in the sub-100 nm regime has made signaling in long global a challenge, resulting in a need for an improved interconnect technology. Optical signalling is a promising alternative to existing global interconnects and alleviates interconnect bottle-neck. This paper presents a design of a CMOS trans-impedance amplifier (TIA) that is intended for a truly CMOS compatible on-chip optical clock distribution system. This TIA employs replica biasing technique to achieve stability while maximizing its bandwidth and gain. The design was implemented in a 0.35?m CMOS process and is currently under probe testing. The simulation results show that the design achieved a bandwidth of 1GHz and gain of 128dB-?. Extensive Monte-Carlo simulations indicate the superior characteristics of stability under a variety of process and environmental variations.

Thangaraj, Charles; Stephenson, Kevin; Chen, Tom; Lear, Kevin; Raza, Abdul Matheen

2007-05-01

397

The Chemical and Educational Appeal of the Orange Juice Clock  

NASA Astrophysics Data System (ADS)

The Orange Juice Clock, in which a galvanic cell is made from the combination of a magnesium strip, a copper strip, and juice in a beaker, has been a popular classroom, conference, and workshop demonstration for nearly 10 years. It is widely enjoyed because it shows visually how chemistry - or more precisely, electrochemistry - is responsible for the very common phenomenon of a clock ticking. The chemistry of the process can also be understood on a variety of levels, from middle school (simple electron flow in a circuit, Ohm's law) and high school (reduction/oxidation and standard cell potentials) to first-year college (cell potential at nonideal conditions) and graduate school courses (overpotential and charge transfer across interfaces.) The discussion that follows considers the recent history, chemistry, and educational uses of the demonstration. The History The demonstration was devised by one of us (PK) in 1986, after reading an activity in Hubert Alyea's 1947 compendium of chemical demonstrations from this Journal (1). In that activity, Alyea hooked a magnesium strip to the negative battery terminal of an electric bell and hooked a copper strip to the positive terminal. He placed the loose ends of the strips into a 1M 2SO4 solution and the bell rang. After trying the demonstration, it seemed to make sense to modify the electrolyte to orange juice because it is safe, readily available, and would be a mixture in which the magnesium would oxidize more slowly than in sulfuric acid. Further, a clock was substituted for the bell because a clock is easier on the ears than a bell. A video of the orange-juice clock setup is given as Figure 1. Figure 1.The orange juice clock set up. Video of orange juice clock was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. The apparatus was presented in 1987 as part of a teacher workshop led by Irwin Talesnick, then of Queen's University in Canada. Talesnick, whose distinguished career has been characterized by seeing educational possibilities in so many things, created a modified version of the clock, with the atomic numbers of the elements representing the hours in the day (see Fig. 2) in his internationally popular workshops. Due largely to Talesnick's efforts, the orange juice clock is a standard demonstration in many chemistry programs and presentations. Figure 2.Irwin Talesnick represents the hours of the day by the corresponding elements in his clock. The Procedure This can be done as a demonstration or as an activity, although at about 10 per clock, expense does become an issue. There are no unusual safety precautions with this demonstration. We know of no accidents that have occurred with the orange juice clock. The demonstration requires: a single AA-cell battery-operated wall clock with a sweep-second hand a medium-sized beaker (600 mL is fine) enough orange juice or other electrolyte mixture or solution to fill the beaker about 2/3 full (tap water often works fine!) a 20-30-cm magnesium strip, coiled at one end or wrapped around a popsicle stick a 20-30-cm copper strip, coiled at one end alligator clips to connect the strips to the battery terminals on the clock a stand against which to lean the setup The demonstration is put together as shown in Figure 3. Connect the magnesium to the "-" contact of the clock and the copper to the "+" contact. Immerse the other ends of the strips into the solution. The clock will start to tick within a few seconds. If it does not work within a short period of time, check that the strips are well connected to the battery terminals, are hooked to the proper poles, and are not touching each other. The clock should keep reasonably close time (in orange juice) for a couple of days, or until the magnesium is nearly completely oxidized. Figure 3.A schematic of the orange juice clock seup. Video of orange juice clock. In video, the copper electrode is on the left and the magnesium electrode is on the right. Video was filmed and editted by Jerry Jacobson at the University of Wisconsin - Madison. The

Kelter, Paul B.; Carr, James D.; Johnson, Tanya; Mauricio Castro-Acuña, Carlos

1996-12-01

398

A magnetic Signature of the solar Core in IMF Variations and geophysical Data?  

NASA Astrophysics Data System (ADS)

Based on the successful reconstruction of the global solar magnetic field by a number of investigators it seems clear that the field strength B nT has increased significantly during the last 300 years However it has been demonstrated that a weak field strength has unexpected consequences for the near-Earth environment since under those conditions very large fluence SPE-nitrate events have an enhanced probability to be observed in the earth s ice caps These results were explicable in terms of the linear dependence of the Alfven velocity upon the strength of the IMF leading to higher shock compressions in the past For this reason emphasis has been placed on evaluating the minimum values Bmin of the total magnetic flux Solanki et al 2000 which upon rough examination seems to resemble variations between sequential states of equilibrium which extend over several Schwabe cycles Whereas the magnetic field strength B nT increases with decreasing cycle length an inverse relationship can be demonstrated for the field strength with decreasing cycle length if the magnetic flux Bmax is expressed as a fraction of Bmin This type of variation will be examined in view of varying contributions to the field strength by low and high order multipoles 2l-poles of the magnetic flux of the solar magnetic field The current understanding of this field is based on the dynamo action generated at the tachocline as revealed by helioseismic data Such data have not yet revealed detailed structural information about the core However modulation of magnetic energy

Dreschhoff, G.

399

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

400

Circadian clocks optimally adapt to sunlight for reliable synchronization  

PubMed Central

Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to synchronize internal time with periodic stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist, because better entrainability favours higher sensitivity which may sacrifice regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase–response curve with a variational method. Our results indicate an existence of a dead zone, i.e. a time period during which input stimuli neither advance nor delay the clock. A dead zone appears only when input stimuli obey the time course of actual solar radiation, but a simple sine curve cannot yield a dead zone. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle. PMID:24352677

Hasegawa, Yoshihiko; Arita, Masanori

2014-01-01

401

Heisenberg-Limited Atom Clocks Based on Entangled Qubits  

NASA Astrophysics Data System (ADS)

We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time.

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

2014-05-01

402

Fault-tolerant clock synchronization validation methodology. [in computer systems  

NASA Technical Reports Server (NTRS)

A validation method for the synchronization subsystem of a fault-tolerant computer system is presented. The high reliability requirement of flight-crucial systems precludes the use of most traditional validation methods. The method presented utilizes formal design proof to uncover design and coding errors and experimentation to validate the assumptions of the design proof. The experimental method is described and illustrated by validating the clock synchronization system of the Software Implemented Fault Tolerance computer. The design proof of the algorithm includes a theorem that defines the maximum skew between any two nonfaulty clocks in the system in terms of specific system parameters. Most of these parameters are deterministic. One crucial parameter is the upper bound on the clock read error, which is stochastic. The probability that this upper bound is exceeded is calculated from data obtained by the measurement of system parameters. This probability is then included in a detailed reliability analysis of the system.

Butler, Ricky W.; Palumbo, Daniel L.; Johnson, Sally C.

1987-01-01

403

Synchronizing computer clocks using a local area network  

NASA Technical Reports Server (NTRS)

Researchers completed the first tests of a method to synchronize the clocks of networked computers to the National Institute of Standards and Technology (NIST) time scale. The method uses a server computer to disseminate the time to other clients on the same local-area network. The server is synchronized to NIST using the ACTS protocol over a dial-up telephone line. The software in both the server and the parameters of this model are used to adjust the time of the local clock and the interval between calibration requests in a statistically optimum way. The algorithm maximizes the time between calibrations while at the same time keeping the time of the local clock correct within a specific tolerance. The method can be extended to synchronize computers linked over wide-area networks, and an experiment to test the performance of the algorithms over such networks is being planned.

Levine, Judah

1990-01-01

404

The circadian clock gates the intestinal stem cell regenerative state.  

PubMed

The intestine has evolved under constant environmental stresses, because an animal may ingest harmful pathogens or chemicals at any time during its lifespan. Following damage, intestinal stem cells (ISCs) regenerate the intestine by proliferating to replace dying cells. ISCs from diverse animals are remarkably similar, and the Wnt, Notch, and Hippo signaling pathways, important regulators of mammalian ISCs, are conserved from flies to humans. Unexpectedly, we identified the transcription factor period, a component of the circadian clock, to be critical for regeneration, which itself follows a circadian rhythm. We discovered hundreds of transcripts that are regulated by the clock during intestinal regeneration, including components of stress response and regeneration pathways. Disruption of clock components leads to arrhythmic ISC divisions, revealing their underappreciated role in the healing process. PMID:23583176

Karpowicz, Phillip; Zhang, Yong; Hogenesch, John B; Emery, Patrick; Perrimon, Norbert

2013-04-25

405

The twin paradox with macroscopic clocks in superconducting circuits  

E-print Network

Time dilation, a striking prediction of Einstein's relativity, plays an important role in applications such as the Global Positioning System. One of the most compelling consequences of time dilation is known as the twin paradox, where a twin at rest ages more than her sibling travelling at relativistic speeds. In this paper, we propose an implementation of the twin paradox in superconducting circuits with velocities as large as a few percent of the speed of light. Ultrafast modulation of the boundary conditions for the electromagnetic field in a microwave cavity simulates a clock moving at relativistic speeds. While previous demonstrations of this effect involve point-like clocks, our superconducting cavity has a finite length, allowing us to investigate the role of clock size as well as interesting quantum effects on time dilation. In particular, our theoretical results show that the travelling twin ages slower for larger cavity lengths and that quantum particle creation, known in this context as the dynamic...

Lindkvist, Joel; Fuentes, Ivette; Dragan, Andrzej; Svensson, Ida-Maria; Delsing, Per; Johansson, Göran

2014-01-01

406

Th17 cell differentiation is regulated by the circadian clock  

PubMed Central

Circadian clocks regulate numerous physiological processes that vary across the day-night (diurnal) cycle, but if and how the circadian clock regulates the adaptive immune system is mostly unclear. Interleukin-17-producing CD4+ T helper (Th17) cells are proinflammatory immune cells that protect against bacterial and fungal infections at mucosal surfaces. Their lineage specification is regulated by the orphan nuclear receptor ROR?t. We show that the transcription factor NFIL3 suppresses Th17 cell development by directly binding and repressing the Ror?t promoter. NFIL3 links Th17 cell development to the circadian clock network through the transcription factor REV-ERB?. Accordingly Th17 lineage specification varies diurnally and is altered in Rev-erb??/? mice. Light cycle disruption elevated intestinal Th17 cell frequencies and increased susceptibility to inflammatory disease. Thus, lineage specification of a key immune cell is under direct circadian control. PMID:24202171

Yu, Xiaofei; Rollins, Darcy; Ruhn, Kelly A.; Stubblefield, Jeremy J.; Green, Carla B.; Kashiwada, Masaki; Rothman, Paul B.; Takahashi, Joseph S.; Hooper, Lora V.

2014-01-01

407

Heisenberg-limited atom clocks based on entangled qubits.  

PubMed

We present a quantum-enhanced atomic clock protocol based on groups of sequentially larger Greenberger-Horne-Zeilinger (GHZ) states that achieves the best clock stability allowed by quantum theory up to a logarithmic correction. Importantly the protocol is designed to work under realistic conditions where the drift of the phase of the laser interrogating the atoms is the main source of decoherence. The simultaneous interrogation of the laser phase with a cascade of GHZ states realizes an incoherent version of the phase estimation algorithm that enables Heisenberg-limited operation while extending the coherent interrogation time beyond the laser noise limit. We compare and merge the new protocol with existing state of the art interrogation schemes, and identify the precise conditions under which entanglement provides an advantage for clock stabilization: it allows a significant gain in the stability for short averaging time. PMID:24877919

Kessler, E M; Kómár, P; Bishof, M; Jiang, L; Sørensen, A S; Ye, J; Lukin, M D

2014-05-16

408

Circadian clocks optimally adapt to sunlight for reliable synchronization  

E-print Network

Circadian oscillation provides selection advantages through synchronization to the daylight cycle. However, a reliable clock must be designed through two conflicting properties: entrainability to properly respond to external stimuli such as sunlight, and regularity to oscillate with a precise period. These two aspects do not easily coexist because better entrainability favors higher sensitivity, which may sacrifice the regularity. To investigate conditions for satisfying the two properties, we analytically calculated the optimal phase-response curve with a variational method. Our result indicates an existence of a dead zone, i.e., a time during which external stimuli neither advance nor delay the clock. This result is independent of model details and a dead zone appears only when the input stimuli obey the time course of actual insolation. Our calculation demonstrates that every circadian clock with a dead zone is optimally adapted to the daylight cycle. Our result also explains the lack of a dead zone in osc...

Hasegawa, Yoshihiko

2014-01-01

409

Two-photon E1-M1 optical clock  

NASA Astrophysics Data System (ADS)

An allowed E1-M1 excitation scheme creates optical access to the 1S0?3P0 clock transition in group-II-type atoms. This method does not require the hyperfine mixing or application of an external magnetic field of other optical clock systems. The advantages of this technique include a Doppler-free excitation scheme and increased portability with the use of vapor cells. We will discuss technical mechanisms of a monochromatic excitation scheme for a hot E1-M1 clock and briefly discuss a bichromatic scheme to eliminate light shifts. We determine the optimal experimental parameters for Hg, Yb, Ra, Sr, Ba, Ca, Mg, and Be and calculate that neutral Hg has ideal properties for a hot, portable frequency standard.

Alden, E. A.; Moore, K. R.; Leanhardt, A. E.

2014-07-01

410

Interactions of the Circadian CLOCK System and the HPA Axis  

PubMed Central

Organisms have developed concurrent behavioral and physiological adaptations to the strong influence of day/night cycles, as well as to unforeseen, random stress stimuli. These circadian and stress-related responses are achieved by two highly conserved and interrelated regulatory networks, the circadian CLOCK and stress systems, which respectively consist of oscillating molecular pacemakers, the Clock/Bmal1 transcription factors, and the hypothalamic-pituitary-adrenal (HPA) axis and its end-effector, the glucocorticoid receptor. These systems communicate with each other at different signaling levels, and dysregulation of either system may lead to development of pathologic conditions. In this review, we summarize the mutual physiologic interactions between the circadian CLOCK system and the HPA axis, and discuss their clinical implications. PMID:20106676

Nader, Nancy; Chrousos, George P.; Kino, Tomoshige

2010-01-01

411

Speed control: cogs and gears that drive the circadian clock  

PubMed Central

In most organisms, an intrinsic circadian (~24 h) timekeeping system drives rhythms of physiology and behavior. Within cells that contain a circadian clock, specific transcriptional activators and repressors reciprocally regulate each other to generate a basic molecular oscillator. A mismatch of the period generated by this oscillator with the external environment creates circadian disruption, which can have adverse effects on neural function. Although several clock genes have been extensively characterized, a fundamental question remains: how do these genes work together to generate a ~24 h period? Period altering mutations in clock genes can affect any of multiple, regulated steps in the molecular oscillator. In this review, we examine the regulatory mechanisms that contribute to setting the pace of the circadian oscillator. PMID:22748426

Zheng, Xiangzhong; Sehgal, Amita

2012-01-01

412

Conservation of Arabidopsis thaliana circadian clock genes in Chrysanthemum lavandulifolium.  

PubMed

In Arabidopsis, circadian clock genes play important roles in photoperiod pathway by regulating the daytime expression of CONSTANS (CO), but related reports for chrysanthemum are notably limited. In this study, we isolated eleven circadian clock genes, which lie in the three interconnected negative and positive feedback loops in a wild diploid chrysanthemum, Chrysanthemum lavandulifolium. With the exception of ClELF3, ClPRR1 and ClPRR73, most of the circadian clock genes are expressed more highly in leaves than in other tested tissues. The diurnal rhythms of these circadian clock genes are similar to those of their homologs in Arabidopsis. ClELF3 and ClZTL are constitutively expressed at all time points in both assessed photoperiods. The expression succession from morning to night of the PSEUDO RESPONSE REGULATOR (PRR) gene family occurs in the order ClPRR73/ClPRR37, ClPRR5, and then ClPRR1. ClLHY is expressed during the dawn period, and ClGIs is expressed during the dusk period. The peak expression levels of ClFKF1 and ClGIs are synchronous in the inductive photoperiod. However, in the non-inductive night break (NB) condition or non-24 h photoperiod, the peak expression level of ClFKF1 is significantly changed, indicating that ClFKF1 itself or the synchronous expression of ClFKF1 and ClGIs might be essential to initiate the flowering of C. lavandulifolium. This study provides the first extensive evaluation of circadian clock genes, and it presents a useful foundation for dissecting the functions of circadian clock genes in C. lavandulifolium. PMID:24844451

Fu, Jianxin; Yang, Liwen; Dai, Silan

2014-07-01

413

Ras-mediated deregulation of the circadian clock in cancer.  

PubMed

Circadian rhythms are essential to the temporal regulation of molecular processes in living systems and as such to life itself. Deregulation of these rhythms leads to failures in biological processes and eventually to the manifestation of pathological phenotypes including cancer. To address the questions as to what are the elicitors of a disrupted clock in cancer, we applied a systems biology approach to correlate experimental, bioinformatics and modelling data from several cell line models for colorectal and skin cancer. We found strong and weak circadian oscillators within the same type of cancer and identified a set of genes, which allows the discrimination between the two oscillator-types. Among those genes are IFNGR2, PITX2, RFWD2, PPAR?, LOXL2, Rab6 and SPARC, all involved in cancer-related pathways. Using a bioinformatics approach, we extended the core-clock network and present its interconnection to the discriminative set of genes. Interestingly, such gene signatures link the clock to oncogenic pathways like the RAS/MAPK pathway. To investigate the potential impact of the RAS/MAPK pathway - a major driver of colorectal carcinogenesis - on the circadian clock, we used a computational model which predicted that perturbation of BMAL1-mediated transcription can generate the circadian phenotypes similar to those observed in metastatic cell lines. Using an inducible RAS expression system, we show that overexpression of RAS disrupts the circadian clock and leads to an increase of the circadian period while RAS inhibition causes a shortening of period length, as predicted by our mathematical simulations. Together, our data demonstrate that perturbations induced by a single oncogene are sufficient to deregulate the mammalian circadian clock. PMID:24875049

Relógio, Angela; Thomas, Philippe; Medina-Pérez, Paula; Reischl, Silke; Bervoets, Sander; Gloc, Ewa; Riemer, Pamela; Mang-Fatehi, Shila; Maier, Bert; Schäfer, Reinhold; Leser, Ulf; Herzel, Hanspeter; Kramer, Achim; Sers, Christine

2014-05-01

414

One year of Galileo IOV orbit and clock determination  

NASA Astrophysics Data System (ADS)

With activation of the fourth Galileo satellite, the Galileo In-Orbit Validation (IOV) phase was achieved in December 2012. The Galileo IOV constellation consists of Proto Flight Model (PFM) and Flight Model 2 (FM2) launched in October 2011 and FM3 and FM4 launched in October 2012. Although the satellites are transmitting navigation signals on all designated frequencies, transmission of the navigation message has not yet started. However, the availability of an orbit product is a prerequisite for most user applications. To support early applications of Galileo, IOV orbit and clock parameters are estimated from observations of the Cooperative Network for GNSS Observation (CONGO) and the Multi-GNSS Experiment (MGEX) of the International GNSS Service (IGS). The quality of these GNSS-only orbits as evaluated by internal consistency tests and Satellite Laser Ranging (SLR) residuals is in general on the one decimeter level. However, the orbits suffer from systematic errors depending on the elevation of the Sun above the orbital plane. These errors show up, e.g., as a bump in the Allan deviation of the estimated clock parameters at the orbital frequency. We started with the Galileo orbit and clock determination in January 2012 and 2013 for PFM/FM2 and FM3/FM4, respectively. The time period of more than one year for PFM/FM2 allows for a proper analysis of the systematic errors. The impact of including SLR observations for a combined GNSS+SLR orbit determination, namely a reduction of the systematic errors, is demonstrated. Finally, the performance of the different clocks on board the IOV satellites (Rubidium clocks and Hydrogen masers) is evaluated and compared with other state-of-the-art GNSS satellite clocks.

Steigenberger, Peter; Hackel, Stefan; Hugentobler, Urs; Montenbruck, Oliver

2013-04-01

415

Ras-Mediated Deregulation of the Circadian Clock in Cancer  

PubMed Central

Circadian rhythms are essential to the temporal regulation of molecular processes in living systems and as such to life itself. Deregulation of these rhythms leads to failures in biological processes and eventually to the manifestation of pathological phenotypes including cancer. To address the questions as to what are the elicitors of a disrupted clock in cancer, we applied a systems biology approach to correlate experimental, bioinformatics and modelling data from several cell line models for colorectal and skin cancer. We found strong and weak circadian oscillators within the same type of cancer and identified a set of genes, which allows the discrimination between the two oscillator-types. Among those genes are IFNGR2, PITX2, RFWD2, PPAR?, LOXL2, Rab6 and SPARC, all involved in cancer-related pathways. Using a bioinformatics approach, we extended the core-clock network and present its interconnection to the discriminative set of genes. Interestingly, such gene signatures link the clock to oncogenic pathways like the RAS/MAPK pathway. To investigate the potential impact of the RAS/MAPK pathway - a major driver of colorectal carcinogenesis - on the circadian clock, we used a computational model which predicted that perturbation of BMAL1-mediated transcription can generate the circadian phenotypes similar to those observed in metastatic cell lines. Using an inducible RAS expression system, we show that overexpression of RAS disrupts the circadian clock and leads to an increase of the circadian period while RAS inhibition causes a shortening of period length, as predicted by our mathematical simulations. Together, our data demonstrate that perturbations induced by a single oncogene are sufficient to deregulate the mammalian circadian clock. PMID:24875049

Relogio, Angela; Thomas, Philippe; Medina-Perez, Paula; Reischl, Silke; Bervoets, Sander; Gloc, Ewa; Riemer, Pamela; Mang-Fatehi, Shila; Maier, Bert; Schafer, Reinhold; Leser, Ulf; Herzel, Hanspeter; Kramer, Achim; Sers, Christine

2014-01-01

416

Using Inscribed Angles and Polygons  

NSDL National Science Digital Library

This unit will teach you about inscribed angles, intercepted arcs, their measures, inscribed polygons, and their associated theorems. OK, time for notes! Define Inscribed Angles, using the following website (Only define the inscribed angle from this site): Inscribed Angle Definition Using this new idea, you can use the following activity to figure out the formula for the measure of an inscribed angle: Inscribed Angle Formula Discovery The whole lesson depends upon this definition. Define Intercepted Arc, Inscribed polygons, ...

Neubert, Mrs.

2011-03-10

417

What Is the Angle?  

NSDL National Science Digital Library

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

418

The role of clocks in operating deep space missions  

NASA Technical Reports Server (NTRS)

Operation of deep space missions requires stable frequency references and clocks to perform several mission critical functions. These references are used in generating the telecommunication links to maintain communications between earth and spacecraft, in generating accurate doppler, range, and very long baseline interferometry (VLBI) observables for determining the spacecraft's time varying position, and to generate on-board timing information for clocking out timed commands and time tagging instrument data. In addition, science applications exist, particularly those utilizing radio instrumentation, which can require additional functions and levels of performance. The design necessary to support these functions affects both the spacecraft and the ground tracking stations.

Asmar, Sami W.; Kursinski, E. R.

1992-01-01

419

A CMOS clock and data recovery circuit for intraocular microsystems.  

PubMed

This paper presents the implementation of a clock and data recovery circuit (CDR) for intraocular microsystems. The CDR was designed to minimize chip area and power consumption and to recover the clock and data signals from the incoming data stream. Since the CDR has been designed without any external components it is well suited for being integrated in an intraocular microsystem. Simulation results show that this CDR works with power dissipation of less than 2.4 mW with a single 3.3 V power supply. The simulations are based on a 0.6 micron n-well CMOS single-polysilicon, three-metal technology. PMID:12451805

Prämassing, F; Püttjer, D; Buss, R; Jäger, D

2002-01-01

420

Obesity May Shut Down Circadian Clock in the Cardiovascular System  

NSDL National Science Digital Library

Researchers at the Georgia Health Sciences University in Augusta have found that a master clock gene ÃÂ which regulates the cardiovascular system ÃÂ does not fluctuate regularly as it does in non-obese animals. This means that a key gene clock of the cardiovascular system does not work properly when obesity is present. These findings are believed to be the first of their kind. The study was conducted by Shuiqing Qiu, Eric Belin de Chantemele, James Mintz, David J. Fulton, R. Daniel Rudic and David W. Stepp.

APS Communications Office (American Physiological Society Communications Office)

2011-04-10

421

On electron channeling and the de Broglie internal clock  

E-print Network

Electron channeling in silicon crystals has brought forward the possibility of having detected the particle's "de Broglie internal clock", as giving rise to the observed resonance peak at the center of the expected transmission probability dip. A classical multiple scattering calculation fails to represent the experimental results unless, surprisingly, the interaction frequency is twice the de Broglie's clock frequency, that is, the "Zitterbewegung" frequency. In the present paper, the observed characteristics of this process are shown to be consistent with a free particle quantum mechanical motion described by Dirac's Hamiltonian.

M. Bauer

2014-09-02

422

Oscillator-free atomic clock using a multimode laser  

NASA Astrophysics Data System (ADS)

We developed an atomic clock using two modes from a single extended-cavity diode laser in multimode operation. The two modes are phase locked with reference to a dispersion signal from a coherent population trapping (CPT) resonance of R85b at 3.036 GHz. The design is in principle free from an oscillator and a modulator and it is a significant simplification over a conventional CPT-based atomic clock. Allan deviation of the beat frequency is 1×10-10 at 200 s integration time.

Yim, Sin Hyuk; Cho, D.

2010-05-01

423

Efficient Atomic Clocks Operated with Several Atomic Ensembles  

NASA Astrophysics Data System (ADS)

Atomic clocks are typically operated by locking a local oscillator (LO) to a single atomic ensemble. In this Letter, we propose a scheme where the LO is locked to several atomic ensembles instead of one. This results in an exponential improvement compared to the conventional method and provides a stability of the clock scaling as (?N)-m/2 with N being the number of atoms in each of the m ensembles and ? a constant depending on the protocol being used to lock the LO.

Borregaard, J.; Sørensen, A. S.

2013-08-01

424

RH1020 Single Event Clock Upset Summary Report  

NASA Technical Reports Server (NTRS)

This report summarizes the testing and analysis of "single event clock upset' in the RH1020. Also included are SEU-rate predictions and design recommendations for risk analysis and reduction. The subject of "upsets" in the RH1020 is best understood by using a model consisting of a global clock buffer and a D-type flip-flop as the basic memory unit. The RH1020 is built on the ACT 1 family architecture. As such, it has one low-skew global clock buffer with a TTL-level input threshold that is accessed via a single dedicated pin. The clock signal is driven to full CMOS levels, buffered, and sent to individual row buffers with one buffer per channel. For low-skew performance, the outputs of all of the RH1020 row buffers are shorted together via metal lines, as is done in the A1020B. All storage in the RH1020 consists of routed flip-flops, constructed with multiplexors and feedback through the routing segments. A simple latch can be constructed from a single (combinatorial or C) module; an edge-triggered flip-flop is constructed using two concatenated latches. There is no storage in the I/O modules. The front end of the clock buffering circuitry, at a common point relative to the row buffer, is a sub-circuit that was determined to be the most susceptible to heavy ions. This is due, in part, to its smaller transistors compared to the rest of the circuitry. This conclusion is also supported by SPICE simulations and an analysis of the heavy ion data, described in this report. The edge triggered D flip-flop has two single-event-upset modes. Mode one, called C-module upset, is caused by a heavy ion striking the C-module's sensitive area on the silicon and produces a soft single bit error at the output of the flip-flop. Mode two, called clock upset, is caused by a heavy ion strike on the clock buffer, generating a runt pulse interpreted as a false clock signal and consequently producing errors at the flip-flop outputs. C-module upset sensitivity in the RH1020 is essentially the same as that of its ACT 1 siblings (A1020, A1020A and A1020B), which were well tested, analyzed, and documented in the literature.

Katz, Richard B.; Wang, J. J.

1998-01-01

425

What's the Angle?  

NSDL National Science Digital Library

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

426

A noise-gated PLL for clock recovery in a free-space laser communication system  

E-print Network

In this thesis, I developed a phase-locked loop system for data clock recovery in a free-space laser communication application. The clock recovery unit is designed to operate at extremely low optical received power, tolerate ...

Lund, Gavin

2012-01-01

427

Identification and initial characterization of circadian clock mutants in Neurospora crassa  

E-print Network

Circadian clocks in organisms provide a means to coordinate behavioral, physiological, and biochemical activities to the appropriate time of day. For example, in Neurospora crassa, the circadian clock controls asexual spore formation (conidiation...

March, Irene Jennifer

2012-06-07

428

The development of the time-keeping clock with TS-1 single chip microcomputer.  

NASA Astrophysics Data System (ADS)

The authors have developed a time-keeping clock with Intel 8751 single chip microcomputer that has been successfully used in time-keeping station. The hard-soft ware design and performance of the clock are introduced.

Zhou, Jiguang; Li, Yongan

429

The development of the time-keeping clock with TS1 single chip microcomputer  

Microsoft Academic Search

The authors have developed a time-keeping clock with Intel 8751 single chip microcomputer that has been successfully used in time-keeping station. The hard-soft ware design and performance of the clock are introduced.

Jiguang Zhou; Yongan Li

1996-01-01

430

Regulation and Synchronization of the Master Circadian Clock by Purinergic Signaling from Suprachiasmatic Nucleus Astrocytes  

E-print Network

Molecular, cellular, and physiological processes within an organism are set to occur at specific times throughout the day. The timing of these processes is under control of a biological clock. Nearly all organisms on Earth have biological clocks...

Womac, Alisa Diane

2012-10-19

431

Identification and Validation of Cryptochrome Inhibitors That Modulate the Molecular Circadian Clock  

E-print Network

the circadian oscillation of Per2-Luc and Bmal1-dLuc activities in cultured fibroblasts, indicating molecular oscillators, and these are referred to as peripheral clocks. These clocks have molecular makeup

Suh, Young-Ger

432

Precision Synchronization of Computer Network Clocks 1,2,3 David L. Mills  

E-print Network

in the Internet [MIL91a], modeling and analysis of computer clocks [MIL92b], the chronology and metrology clock 1 Sponsored by: Advanced Research Projects Agency under NASA Ames Research Center contract NAG 2

Mills, David L.

433

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

E-print Network

Ramond Ball Aero. ·$$ NIST, DARPA-MTO, ONR-CU-MURI, NASA-microgravity physics, LANL Mercury Standard Jim laser and length metrology Richard Fox #12;Types of Clocks Ruler Clock Decay Stable Oscillator Atomic

Van Stryland, Eric

434

Circadian Clock genes Per2 and clock regulate steroid production, cell proliferation, and luteinizing hormone receptor transcription in ovarian granulosa cells  

SciTech Connect

Highlights: {yields} Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression. {yields}Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom. {yields} Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. {yields}Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. {yields} The expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. -- Abstract: Circadian Clock genes are associated with the estrous cycle in female animals. Treatment with Per2 and Clock siRNAs decreased the number of granulosa cells and LHr expression in follicle-stimulating hormone FSH-treated granulosa cells. Per2 siRNA treatment did not stimulate the production of estradiol and expression of P450arom, whereas Clock siRNA treatment inhibited the production of estradiol and expression of P450arom mRNA. Per2 and Clock siRNA treatment increased and unchanged, respectively, progesterone production in FSH-treated granulosa cells. Similarly, expression of StAR mRNA was increased by Per2 siRNA and unchanged by Clock siRNA. Our data provide a new insight that Per2 and Clock have different action on ovarian granulosa cell functions.

Shimizu, Takashi, E-mail: shimizut@obihiro.ac.jp [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan)] [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan); Hirai, Yuko; Murayama, Chiaki; Miyamoto, Akio [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan)] [Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555 (Japan); Miyazaki, Hitoshi [Gene Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8572 (Japan)] [Gene Research Center, University of Tsukuba, Tsukuba, Ibaraki 305-8572 (Japan); Miyazaki, Koyomi [Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) Central 6, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566 (Japan)] [Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST) Central 6, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566 (Japan)

2011-08-19

435

Power-Aware At-Speed Scan Test Methodology for Circuits with Synchronous Clocks  

Microsoft Academic Search

The BurstModetrade test clocking methodology, first presented in, is improved to handle circuits with synchronous clocks of different frequencies. An on-chip clock controller allows to select a large number of clock waveforms necessary to test synchronous cross-domain paths at-speed and control supply voltage variations. The methodology is applicable to both ATPG and BIST and only requires combinational analysis tools. The

Benoit Nadeau-Dostie; Kiyoshi Takeshita; Jean-François Côté

2008-01-01

436

Light signaling to the zebrafish circadian clock by Cryptochrome 1a.  

PubMed

Zebrafish tissues and cells have the unusual feature of not only containing a circadian clock, but also being directly light-responsive. Several zebrafish genes are induced by light, but little is known about their role in clock resetting or the mechanism by which this might occur. Here we show that Cryptochrome 1a (Cry1a) plays a key role in light entrainment of the zebrafish clock. Intensity and phase response curves reveal a strong correlation between light induction of Cry1a and clock resetting. Overexpression studies show that Cry1a acts as a potent repressor of clock function and mimics the effect of constant light to "stop" the circadian oscillator. Yeast two-hybrid analysis demonstrates that the Cry1a protein interacts directly with specific regions of core clock components, CLOCK and BMAL, blocking their ability to fully dimerize and transactivate downstream targets, providing a likely mechanism for clock resetting. A comparison of entrainment of zebrafish cells to complete versus skeleton photoperiods reveals that clock phase is identical under these two conditions. However, the amplitude of the core clock oscillation is much higher on a complete photoperiod, as are the levels of light-induced Cry1a. We believe that Cry1a acts on the core clock machinery in both a continuous and discrete fashion, leading not only to entrainment, but also to the establishment of a high-amplitude rhythm and even stopping of the clock under long photoperiods. PMID:17785416

Tamai, T Katherine; Young, Lucy C; Whitmore, David

2007-09-11

437

Entrainment of peripheral clock genes by cortisol.1 Panteleimon D. Mavroudis,a  

E-print Network

1 Entrainment of peripheral clock genes by cortisol.1 Authors:2 Panteleimon D. Mavroudis,a Jeremy D clock genes by cortisol15 16 * Corresponding author:17 Ioannis P. Androulakis18 Biomedical Engineering of peripheral clock genes by cortisol as a33 representative entrainer of peripheral cells. This model

Androulakis, Ioannis (Yannis)

438

Profile-based dynamic voltage and frequency scaling for a multiple clock domain microprocessor  

Microsoft Academic Search

A Multiple Clock Domain (MCD) processor addresses the challenges of clock distribution and power dissipation by dividing a chip into several (coarse-grained) clock domains, allowing frequency and voltage to be reduced in domains that are not currently on the application's critical path. Given a reconfiguration mechanism capable of choosing appropriate times and values for voltage\\/frequency scaling, an MCD processor has

Grigorios Magklis; Michael L. Scott; Greg Semeraro; David H. Albonesi; Steven Dropsho

2003-01-01

439

DOI: 10.1093/jxb/erh034 Input signals to the plant circadian clock  

E-print Network

. Key words: Arabidopsis thaliana, biological clock, Circadian rhythm, cryptochrome, light regulation in circadian rhythms are uncovering the signalling web that sets the endogenous clock to local time example. Circadian clocks evolved as an adaptation to the planet's 24 h rotation and its attendant rhythms

Millar, Andrew J.

440

Non-Invariant Velocity of Light and Clock Synchronisation in Accelerated Systems  

E-print Network

Clock synchronisation is conventional when inertial systems are involved. This statement is no longer true in accelerated systems. A demonstration is given in the case of a rotating platform. We conclude that theories based on the Einstein's clock synchronisation procedure are unable to explain, for example, the Sagnac effect on the platform. Implications on very precise clock synchronisation on earth are discussed.

François Goy

1996-07-22