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1

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

NASA Astrophysics Data System (ADS)

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

Grocott, A.; Milan, S. E.

2013-12-01

2

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

3

Consecutive bursts of Pi2-band and long-period pulsations during a northward and low-clock-angle IMF period  

NASA Astrophysics Data System (ADS)

On 14 August 2004, four pulsation bursts, in a period up to 200 s from the Pi2 band, consecutively occurred at the SMALL and 210 MM arrays in the post-midnight sector. Meanwhile, the Double Star TC 1 probe in the plasma sheet at ~XGSM -11.0 Re, observed quasi-periodic magnetic fluctuations at each burst onset. The Cluster 4 probe in the north lobe at ~XGSM -14.0 Re, sensed Pi2-band magnetic perturbations at the second burst onset and long-period ones for the third and fourth bursts. No bursty flow activations occurred at the onset of the first and second bursts. Earthward flow bursts first appeared at TC 1 prior to the third burst onset and ~5 min later at Cluster 4. These flows persisted through the end of the last burst and appeared to have a same periodic variation as in the magnetic field at Cluster 4. Except for the second burst, geostationary LANL 97 probe at ~XGSM -2.0 Re also detected wave-like energetic proton fluxes. The mapping of ground pulsations onset timing to the solar wind observation just in front of Earth's magnetopause shows that they appear during a northward IMF period with low clock-angle variations. Spectral analyses show two distinct spectral features in which Pi2-band bursts become two harmonic and long-period ones monochromatic. Waveform comparisons show that Pi2-band bursts can result from a combination of fast magnetospheric and plasmaspheric cavity resonances and long-period ones from a fast magnetospheric cavity resonance. Although they do not have a one-to-one relationship with earthward plasma flows, these pulsations can be fast compressional waves expectedly driven by magnetic reconnection in the distant-Earth magnetotail under northward IMF as in the two-neutral-point model. Fig. 1. (a-b) The IMF By, the IMF Bz, and the IMF clock angle at 1 AU (corresponding to ~XGSM 17 Re) from 1910 UT to 2010 UT on 14 August 2004. (c-d) Three components of the magnetic field and the ion flow velocity at Cluster 4 (~XGSM -14.0Re). (e-f) Same as Figs. 1c-d, except for TC 1 (~XGSM -11.0Re). (g) The energetic proton flux at LANL 97 (~XGSM -2.0Re.) (h) The H component at the SMALL and 210 MM arrays. The vertical dashed lines denote the ground pulsation onsets. Consecutive pulstion onsets are marked with a a serial number for identification.

Cheng, C.; Russell, C. T.; Baumjohann, W.; Yumoto, K.

2013-12-01

4

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

5

Ionospheric convection signatures of the interchange cycle at small interplanetary magnetic field clock angles  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to show a "proof of the existence" of the ionospheric situation that is expected for the interchange cycle, during periods of favorable interplanetary magnetic field (IMF) and dipole tilt conditions. To do so, we present three case studies of dayside high-latitude ionospheric convection that is observed around the equinoxes (near-zero dipole tilt) and at small IMF clock angles (one ?c ˜ -30° event and two ?c ˜ 30° events, where ?c ? Arg(BZ + iBY)), using Super Dual Auroral Radar Network (SuperDARN)/Defense Meteorological Satellite Program (DMSP)/National Oceanic and Atmospheric Administration (NOAA) data in the Northern Hemisphere and, when available, DMSP data in the Southern Hemisphere. The convection pattern exhibits twin reverse cells in both hemispheres, but the constituents of each cell are different. In the Northern Hemisphere, for ?c ˜ 30° (?c ˜ -30°), the center of the dawnside (duskside) cell is located poleward of the polar cap boundary, while the center of the duskside (dawnside) cell is located equatorward of the polar cap boundary. For ?c ˜ 30°, we confirmed that the above-mentioned dawn-dusk relation reverses in the Southern Hemisphere. The north-south asymmetric behavior of the conjugate reverse cells, on the dawnside and duskside each, is consistent with two independent interchange cycles that result from the coupling of IMF-lobe reconnection in one hemisphere with lobe-closed reconnection in the opposite hemisphere.

Watanabe, Masakazu; Sofko, George J.; Yan, Xi; McWilliams, Kathryn A.; St.-Maurice, Jean-Pierre; Koustov, Alexandre V.; Hussey, Glenn C.; Hairston, Marc R.

2010-12-01

6

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

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

7

Robo Clock  

NSDL National Science Digital Library

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

AMPS GK-12 Program,

8

IMF Staff Papers  

NSDL National Science Digital Library

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

9

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.

10

IMF Annual Report 1998  

NSDL National Science Digital Library

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

Fund., International M.

1998-01-01

11

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

12

IMF Loan for Russia  

NSDL National Science Digital Library

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

Waters, Megan.

1998-01-01

13

The massive star IMF  

E-print Network

We review our current knowledge on the IMF in nearby environments, massive star forming regions, super star clusters, starbursts and alike objects from studies of integrated light, and discuss the various techniques used to constrain the IMF. In most cases, including UV-optical studies of stellar features and optical-IR analysis of nebular emission, the data is found to be compatible with a "universal" Salpeter-like IMF with a high upper mass cut-off over a large metallicity range. In contrast, near-IR observations of nuclear starbursts and LIRG show indications of a lower M_up and/or a steeper IMF slope, for which no alternate explanation has yet been found. Also, dynamical mass measurements of seven super star clusters provide so far no simple picture of the IMF. Finally we present recent results of a direct stellar probe of the upper end of the IMF in metal-rich HII regions, showing no deficiency of massive stars at high metallicity, and determining a lower limit on M_up of >~ 60--90 Msun.

Daniel Schaerer

2002-08-12

14

Angles  

NSDL National Science Digital Library

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

Clark, Mr

2012-10-31

15

Angles  

NSDL National Science Digital Library

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

Edkins, Jo

2007-01-01

16

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

17

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

18

Angles  

NSDL National Science Digital Library

In this activity, students practice comparing angles when a transversal intersects two parallel lines. This activity allows students to explore the vocabulary used when comparing angles (e.g., alternate, same-side, interior, corresponding, etc.). 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.

2011-03-04

19

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

20

Clock Time  

NSDL National Science Digital Library

You will have practice reading the time on a clock and pairing it up with its digital or written text match. Complete this as quickly as you can in order to beat the clock! Stop the Clock 1 Stop the Clock 2 Stop the Clock 6 Each of these links varies in degree of difficulty. They progressively go up in difficulty in the time you are telling. The first starts out telling time in half hour intervals. The following activity progress to fifteen minutes. The final activity is matching up the time on the clock to ...

Miss Greene

2010-04-26

21

The IMF and Civil Society  

NSDL National Science Digital Library

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

22

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

23

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

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

24

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.

25

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

26

IMF Length Scales and Predictability: The Two Length Scale Medium  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

27

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

28

Clock Works.  

ERIC Educational Resources Information Center

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

Markle, Sandra

1988-01-01

29

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

30

Living Clocks  

NSDL National Science Digital Library

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

Nancy P. Moreno

2009-01-01

31

Observational evidence of pitch angle isotropization by IMF waves  

Microsoft Academic Search

A statistical analysis of interstellar He+ pickup ion measurements from SOHO\\/CTOF combined with magnetic field data from WIND\\/MFI enable quantitative study of wave-particle interactions in the inner heliosphere for the first time. Magnetic field vector measurements with a time resolution of 3 seconds are used to determine power spectrum characteristics of interplanetary magnetic turbulence. These spectral characteristics are then compared

L. Saul; E. Möbius; C. W. Smith; P. Bochsler; H. Grünwaldt; B. Klecker; F. Ipavich

2004-01-01

32

Observational Evidence of Pitch Angle Isotropization by IMF Waves  

Microsoft Academic Search

A statistical analysis of interstellar He+ pickup ion measurements from\\u000aSOHO\\/CTOF combined with magnetic field data from WIND\\/MFI enable quantitative\\u000astudy of wave-particle interactions in the inner heliosphere for the first\\u000atime. Magnetic field vector measurements with a time resolu-tion of 3 seconds\\u000aare used to determine power spectrum char-acteristics of interplanetary\\u000amagnetic turbulence. These spec-tral characteristics are then compared

L. Saul; E. Möbius; C. W. Smith; P. Bochsler; B. Klecker; Garching Physik

2004-01-01

33

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

34

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

NASA Astrophysics Data System (ADS)

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

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

2006-10-01

35

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

NASA Astrophysics Data System (ADS)

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

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

36

Solar cycle variations in IMF intensity  

NASA Technical Reports Server (NTRS)

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

King, J. H.

1979-01-01

37

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

38

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

39

OPTICAL CLOCK RECOVERY AND CLOCK DIVISION CIRCUIT  

E-print Network

OPTICAL CLOCK RECOVERY AND CLOCK DIVISION CIRCUIT K. Vlachos, T. Papakyriakopoulos, T. Houbavlis, MB suppression of the sub-harmonics of the input data pattern, despite long series of consecutive zero's. The same circuit was also used to perform clock division by 2 and 4. Introduction The ability to perform

Vlachos, Kyriakos G.

40

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

41

A true test: do IMF programs hurt the poor?  

Microsoft Academic Search

This article analyses the effect of IMF programs on poverty with data from 82 countries during 1985–2000. Two indicators of poverty, infant mortality rates and the human development index (HDI), are utilized, and the effects of the IMF's concessionary and nonconcessionary programs are investigated, as well as economic and institutional factors. The results show that the IMF's programs have no

Zlata Hajro; Joseph P. Joyce

2009-01-01

42

Smart clock: a new time  

Microsoft Academic Search

The smart clock provides for the automatic synchronization of any clock to an external standard with a minimum of measurements. The concept covers a range of applications from wrist watches and household clocks to high accuracy clocks. The smart clock enhances the accuracy or stability of a clock or oscillator by comparing it with an external standard. The smart clock

Marc A. Weiss; David W. Allan; Dick D. Davis; Judah Levine

1992-01-01

43

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

44

Angles, Angles and More Angles!  

NSDL National Science Digital Library

Test Your Angle Knowledge! Angles Telescope Star Gazing Help diget to fill up his scrapbook of stars by using his telescope and pointting at each planet during the night! But make sure you hurry before the sun comes up! Shoot The Space Ship Angles Game Try and figure out which angle you need to use to shoot down the aliens spaceship! ...

Smith, Miss

2011-03-23

45

Classification of clock reactions.  

PubMed

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

Horváth, Attila K; Nagypál, István

2015-02-23

46

Smart clock: a new time  

Microsoft Academic Search

A tutorial description is given of the smart clock, which makes it possible for any clock to be automatically synchronized to an external standard with a minimum of measurements. The concept covers a range of applications from wrist watches and household clocks to the specialized world of high-accuracy clocks. The smart clock enhances the accuracy or stability of a clock

Marc A. Weiss; David W. Allan; Dick D. Davis; Judah Levine

1992-01-01

47

Empirical convection models for northward IMF  

NASA Technical Reports Server (NTRS)

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

Moses, Julie J.; Reiff, Patricia H.

1994-01-01

48

Clipart ETC: Clock Menu  

NSDL National Science Digital Library

This website has over 2,000 illustrations of analog clocks. There are clocks with a variety of numeral fonts, and plain faces showing all possible times in one-minute increments. There are also an assortment of antique clocks, pocket watches, pendulums, hour glasses, and the interior devices of time pieces.

Clearinghouse, Educational T.

2010-08-20

49

The Glyoxal Clock Reaction  

ERIC Educational Resources Information Center

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

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

2007-01-01

50

Solar cycle variations in IMF intensity  

NASA Technical Reports Server (NTRS)

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

King, J. H.

1979-01-01

51

The stellar IMF at very low metallicities  

E-print Network

The theory for the formation of the first population of stars (Pop III) predicts an initial mass function (IMF) dominated by high-mass stars, in contrast to the present-day IMF, which tends to yield mostly stars with masses less than 1 M_Sol. The leading theory for the transition in the characteristic stellar mass predicts that the cause is the extra cooling provided by increasing metallicity. In particular, dust can overtake H_2 as the leading coolant at very high densities. The aim of this work is to determine the influence of dust cooling on the fragmentation of very low metallicity gas. To investigate this, we make use of high-resolution hydrodynamic simulations with sink particles to replace contracting protostars, and analyze the collapse and further fragmentation of star-forming clouds. We follow the thermodynamic response of the gas by solving the full thermal energy equation, and also track the behavior of the dust temperature and the chemical evolution of the gas. We model four clouds with different...

Dopcke, Gustavo; Clark, Paul C; Klessen, Ralf S

2012-01-01

52

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

53

Connection between dynamically derived IMF normalisation and stellar populations  

E-print Network

In this contributed talk I present recent results on the connection between stellar population properties and the normalisation of the stellar initial mass function (IMF) measured using stellar dynamics, based on a large sample of 260 early-type galaxies observed as part of the Atlas3D project. This measure of the IMF normalisation is found to vary non-uniformly with age- and metallicity-sensitive absorption line strengths. Applying single stellar population models, there are weak but measurable trends of the IMF with age and abundance ratio. Accounting for the dependence of stellar population parameters on velocity dispersion effectively removes these trends, but subsequently introduces a trend with metallicity, such that `heavy' IMFs favour lower metallicities. The correlations are weaker than those found from previous studies directly detecting low-mass stars, suggesting some degree of tension between the different approaches of measuring the IMF. Resolving these discrepancies will be the focus of future w...

McDermid, Richard M

2015-01-01

54

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

55

Clock Arithmetic and Cryptography  

NSDL National Science Digital Library

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

2011-01-14

56

Science Nation: Biological Clocks  

NSDL National Science Digital Library

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

57

Quantum Clocks and Stopwatches  

Microsoft Academic Search

Time is to clock as mind is to brain. The clock or watch somehow contains the time. And yet time refuses to be bottled up like a genie stuffed in a lamp. Whether it flows as sand or turns on wheels within wheels, time escapes irretrievably, while we watch. Even when the bulbs of the hourglass shatter, when darkness withholds

Rafael Sala Mayato; Daniel Alonso; Iñigo Egusquiza

58

Biological Clocks & Circadian Rhythms  

ERIC Educational Resources Information Center

The study of biological clocks and circadian rhythms is an excellent way to address the inquiry strand in the National Science Education Standards (NSES) (NRC 1996). Students can study these everyday phenomena by designing experiments, gathering and analyzing data, and generating new experiments. As students explore biological clocks and circadian…

Robertson, Laura; Jones, M. Gail

2009-01-01

59

Molecular clock mirages  

Microsoft Academic Search

Summary The hypothesis of the molecular clock proposes that molecular evolution occurs at rates that persist through time and across lineages, for a given gene. The neutral theory of molecular evolution predicts that the clock will be a Poisson process, with equal mean and variance. Experimental data have shown that the variance is typically larger than the mean. Hypotheses have

Francisco J. Ayala

1999-01-01

60

Egyptian "Star Clocks"  

NASA Astrophysics Data System (ADS)

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

Symons, Sarah

61

IMF changes and polar-cap electric fields and currents  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

62

Flies, clocks and evolution.  

PubMed Central

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

Rosato, E; Kyriacou, C P

2001-01-01

63

Optical Atomic Clocks David Hanneke  

E-print Network

-1 32 nHz Calendar Pendulum clock 1 Hz Escapement, gears Quartz watch 32 768 Hz = 215 Hz Microchip Pendulum clock 103 Quartz watch 105 Optical atomic clock 1014 1/Q C. W. Chou, et al., To be published (2010Optical Atomic Clocks David Hanneke Michelson Postdoctoral Prize Lectures 11 May 2010 #12;Hanneke

Hanneke, David

64

Optical clocks and relativity.  

PubMed

Observers in relative motion or at different gravitational potentials measure disparate clock rates. These predictions of relativity have previously been observed with atomic clocks at high velocities and with large changes in elevation. We observed time dilation from relative speeds of less than 10 meters per second by comparing two optical atomic clocks connected by a 75-meter length of optical fiber. We can now also detect time dilation due to a change in height near Earth's surface of less than 1 meter. This technique may be extended to the field of geodesy, with applications in geophysics and hydrology as well as in space-based tests of fundamental physics. PMID:20929843

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

2010-09-24

65

Pulsating dayside aurora in relation to ion upflow events during a northward interplanetary magnetic field (IMF) dominated by a strongly negative IMF BY  

Microsoft Academic Search

We report a study of ion upflow as seen by the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR), initiated by a rotation from interplanetary magnetic field (IMF) BZ negative to IMF BZ positive, under the influence of a strongly negative IMF BY. We combine ground-based instruments, such as meridian scanning photometers (MSP), all-sky imager (ASI) data, and radars, with solar

D. A. Lorentzen; P. M. Kintner; J. Moen; F. Sigernes; K. Oksavik; Y. Ogawa; J. Holmes

2007-01-01

66

Real-time simulation clock  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

67

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

68

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

NASA Astrophysics Data System (ADS)

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

Erofeev, D. V.

2014-12-01

69

Variable frequency microprocessor clock generator  

SciTech Connect

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

Branson, C.N.

1989-04-04

70

The IMF dependence of the local time of transpolar arcs  

NASA Astrophysics Data System (ADS)

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

Fear, R.; Milan, S. E.

2011-12-01

71

Optical atomic clocks  

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

72

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

NASA Astrophysics Data System (ADS)

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

Vedde Fiskerstrand, Tonje; Gjerloev, Jesper W.

2014-05-01

73

The circadian clock goes genomic  

PubMed Central

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

2013-01-01

74

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

75

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

76

What are clock distribution networks?  

Microsoft Academic Search

In a synchronous digital system, the clock signal is used to define a time reference for the movement of data within that system. Since this function is vital to the operation of a synchronous system, much attention has been given to the characteristics of these clock signals and the networks used in their distribution. Clock signals are often regarded as

Eby G. Friedman

2005-01-01

77

On the Effect of IMF Turning on Ion Dynamics  

NASA Astrophysics Data System (ADS)

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×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 IMF 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.

2011-10-01

78

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

79

The response of the high-latitude ionosphere to IMF variations  

Microsoft Academic Search

The convection of plasma in the high-latitude ionosphere is strongly affected by the interplanetary magnetic field (IMF) carried by the solar wind. From numerous statistical studies, it is known that the plasma circulation conforms to patterns that are characteristic of particular IMF states. Following a change in the IMF, the convection responds by reconfiguring into a pattern that is more

J. M. Ruohoniemi; S. G. Shepherd; R. A. Greenwald

2002-01-01

80

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

81

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

82

Clock Reaction: Outreach Attraction  

ERIC Educational Resources Information Center

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

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

2010-01-01

83

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

84

World Food Clock  

NSDL National Science Digital Library

The Scout Staff keeps an eye out for sites that are both informative and interactive, and the World Food Clock does not disappoint. A true feat of graphic design, we loved this site for its innovative and effective presentation of information. The World Food Clock succeeds in providing relevant statistics in an easily digestible manner, with clean and informative visual representations. Likewise, the navigation is both fun and functional, allowing the user to have a stimulating learning experience about global consumption and production.How much food is being consumed around the world right now? It's a vast question that can be answered by the World Food Clock. This interesting website draws on information provided by the Food and Agricultural Organization (FAO) of the United Nations and presents a streaming set of data on global food consumption, global food waste, and other informative topics. It's visually arresting and users can scroll down to look through different "clocks" that track statistics such as the land used to grow wasted food and the stages of food waste, which include production, processing, and consumption. This is a wonderful tool for folks with an interest in food security, environmental studies, public health, and international relations. It could also be used in any number of design courses to illustrate a range of techniques and visualization strategies.

Twyman, Luke

85

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

2014-08-28

86

Telling Time With Analog Clocks.  

NSDL National Science Digital Library

Telling time is an important skill that you will use on a daily basis. It is important to understand and know how to read both analog clocks and digital clocks because they are both still used today. Analog clocks are becoming more out of date, but you don't ever want to be in a situation where you have to say "I can't read that kind of clock! I don't know what time it is." Let's practice your skills of telling time with analog clocks to help you avoid those situations. Move the hands of the clock to show the correct time. Time Clock See if you can match the analog time with the digital time. Match Analog and Digital When you get to this page, click the random button and then practice telling the analog time. If level one is too easy, then try levels ...

Alyssa Nichols

2012-04-27

87

Differing angles on angle  

Microsoft Academic Search

Values of plane angles are expressed with a choice of several units. Historically the quantity needed a unit because it was, and still is, used as a base quantity. ISO\\/TC 12 defines it as a derived, dimensionless quantity, and the International System of Units (SI) gives it the ‘dimensionless unit’ radian, which now means no more than ‘one’. This paper

W H Emerson

2005-01-01

88

Einstein's concept of a clock and clock paradox  

E-print Network

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

Wang Guowen

2005-01-25

89

IMF-driven plasmasphere erosion of 10 July 2000  

NASA Astrophysics Data System (ADS)

On 10 July 2000, the IMAGE EUV imager observed erosion of the nightside plasmasphere that occurred in two bursts during 5-8 UT. The plasmapause radial velocity Vpp at 2.4 MLT was extracted from the time sequence of EUV images. We show that intervals of Vpp < 0 (i.e., erosion) are correlated with intervals of southward (Swd) interplanetary magnetic field (IMF), if the solar wind and IMF data are time-delayed by 30 minutes (in addition to a 3.7-minute delay for propagation to the magnetopause). This suggests that coupling between the solar wind and the plasmapause, involving processes in the ionosphere and magnetotail, takes about 30 minutes. A 6:40 UT magnetosphere compression may have hurried the onset of the second erosion.

Goldstein, J.; Sandel, B. R.; Forrester, W. T.; Reiff, P. H.

2003-02-01

90

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

NSDL National Science Digital Library

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

91

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

92

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

93

The High Mass Stellar IMF in M31  

NASA Astrophysics Data System (ADS)

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

Weisz, Daniel R.; PHAT

2015-01-01

94

Galactic archaeology: IMF and depletion in the "thin disk"  

E-print Network

We determine the initial mass function (IMF) of the ``thin disk'' by means of a direct comparison between synthetic stellar samples (for different matching choices of IMF, star formation rate SFR and depletion) and a complete (volume-limited) sample of single stars near the galactic plane (|z| < 25pc), selected from the Hipparcos catalogue (d < 100pc, M_v < +4.0). Our synthetic samples are computed from first principles: stars are created with a random distribution of mass M_* and age t_* which follow a given (genuine) IMF and SFR(t_*). They are then placed in the HR diagram by means of a grid of empirically well-tested evolution tracks. The quality of the match (synthetic versus observed sample) is assessed by means of star counts in specific regions in the HR diagram. 7 regions are located along the MS (main sequence, mass sensitive), while 4 regions represent different evolved (age-sensitive) stages of the stars. The counts of evolved stars, in particular, give valuable evidence of the history of the ``thin disk'' (apparent) star formation and lift the ambiguities in models restricted to MS star counts.

K. -P. Schröder; B. Pagel

2003-03-02

95

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

96

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

97

Gradient Clock Synchronization in Wireless Sensor Networks  

E-print Network

Gradient Clock Synchronization in Wireless Sensor Networks Philipp Sommer Computer Engineering clocks are crucial for many ap- plications in sensor networks. Existing time synchro- nization algorithms Keywords Sensor Networks, Time Synchronization, Clock Drift, Implementation, Experiments Permission to make

98

Quartz Crystal Clocks  

NASA Technical Reports Server (NTRS)

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

1976-01-01

99

Digital processing clock  

NASA Technical Reports Server (NTRS)

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

Phillips, D. H.

1982-01-01

100

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

101

Fault-tolerant clock synchronization  

Microsoft Academic Search

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

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

1984-01-01

102

Circadian Clock Mutants of Cyanobacteria  

Microsoft Academic Search

A diverse set of circadian clock mutants was isolated in a cyanobacterial strain that carries a bacterial luciferase reporter gene attached to a clock-controlled promoter. Among 150,000 clones of chemically mutagenized bioluminescent cells, 12 mutants were isolated that exhibit a broad spectrum of periods (between 16 and 60 hours), and 5 mutants were found that show a variety of unusual

Takao Kondo; Nicholas F. Tsinoremas; Susan S. Golden; Carl Hirschie Johnson; Shinsuke Kutsuna; Masahiro Ishiura

1994-01-01

103

Optimal Clocking of Circular Pipelines  

Microsoft Academic Search

A timing model for circular pipelines is presented and used to obtain the minimum cycle time in terms of circuit delays and clock skews. The model accounts for short- and long-path delays, the effects of clock skew, and the use of both latches and flip-flops as synchronizing elements. The formulation and implementation of algorithms to find the minimum cycle time

Karem A. Sakallah; Trevor N. Mudge; Timothy M. Burkst; Edward S. Davidson

1991-01-01

104

Variation and power issues in VLSI clock networks  

E-print Network

, (2) Link insertion for buffered clock nets, (3) Methodology and algorithms for rotary clocking and (4) Clock mesh optimization for skew-power trade off. For clock trees this dissertation presents techniques to integrate the different aspects of clock...

Venkataraman, Ganesh

2009-05-15

105

Manchester decoder clock multiplier  

NASA Astrophysics Data System (ADS)

The circuit comprises a differentiator, two a clock decoder, a data flip-flop unit, and a multiphase and frequency logic circuit. The differentiator checks the incoming Manchester encoded signal and divides it into two trigger signals one with data associated with logic O transitions within the Manchester signal and the second trigger signal containing data associated with logic 1 transitions with the Manchester data. One trigger signal is fed to one the nonretriggerable-gated-monostable-multivibrator and the other trigger signal is transmitted to the second similar unit. Within these monostable multivibrator units the signals are a plurality of delayed signals which have waveforms built upon the occurrence of transitions within the Manchester signal associated with the logic O and logic I occurrences. Also within the monostalbe multivibrator, a set/reset latch is utilized to create appropriate signals to aid the control gates in blocking out undesired portions of the input trigger signals from the differentiator. The outputs of the set/reset latches are then fed to a clock decoder and onto a data flip-flop unit which is used to retrieve the data signals from the Manchester encoded signal. Outputs from the tapped delay lines within each monostable multivibrator which emit a plurality of delayed signals are fed to a multiphase and frequency logic unit which combines these delayed signals in a predetermined manner.

Gomez, A. D.; Gennetten, E. W.

1985-04-01

106

Angle Sums  

NSDL National Science Digital Library

"Examine the angles in a triangle, quadrilateral, pentagon, hexagon, heptagon or octagon and find a relationship between the number of sides and the sum of the interior angles." (Source: 2000-2012 National Council of Teachers of Mathematics)

Mathematics, Illuminations N.

2010-05-20

107

The SFR and IMF of the galactic disk  

NASA Astrophysics Data System (ADS)

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

Just, Andreas

2003-04-01

108

A test of convection models for IMF Bz north  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

109

A Superfluid Clock  

NASA Technical Reports Server (NTRS)

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

Penanen, Konstantin

2004-01-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

111

spiral inductors power/clock mesh  

E-print Network

inductors clock tree power/clock mesh Traditional tree-driven grid augmented with spiral inductors to resonate the clock capacitance at the fundamental of the clock frequency. #12;#12;#12;Research Areas Playstation 2 Watch Phone Philips Philips DVD Player TiVo Recorder #12;Long-Term Goal Supplying tools

112

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

113

Enhancing Beneficial Jitter Using Phase Shifted Clock DistributionPhase-Shifted Clock Distribution  

E-print Network

Beneficial Jitter Effect cpf/1 · : Supply noise phase at clock launch · or : Clock path delaycpt res dataclk clean clock case Large : Average supply voltages seen by clock edges closer cpf f cp cp, 11 ­ Large cpf cpf #12;Impact of Delay Sensitivity 65nm, 25°C, 1.2V Vdd 12% Vdd noise · Typical clock path delay

Kim, Chris H.

114

Angle Practice!  

NSDL National Science Digital Library

How well do you know your angles? Check out these games and put your knowledge to the test! They will stump you if you don't pay close attention to the different angles they give you! Alien Angles! - Use the protractor to guess where the alien has flown away to. If you pick the right spot, you can save all the aliens! Squirt the Dog! Angle practice - Move the hose using different measures of angles to try and squirt the dog. To what degree? - Think you're ready to challenge yourself? Check out ...

Hume, Ms.

2012-11-02

115

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.

Laura Robertson

2009-02-01

116

TUTORIAL: Frequency metrology and clocks  

NASA Astrophysics Data System (ADS)

Transitions between discrete energy levels in well-isolated atomic systems are highly reproducible and therefore make ideal references for highly accurate frequency standards or clocks. In particular, a single laser-cooled ion confined in a radiofrequency ion trap closely approximates the spectroscopic ideal of a particle at rest in a perturbation-free environment. Narrow optical transitions in such systems are therefore very promising for the realization of optical clocks with accuracy around 2 orders of magnitude higher than current microwave primary standards. In this paper the fundamental aspects, current performance and applications of trapped ion optical clocks are reviewed and the potential for future improvements is considered.

Margolis, H. S.

2009-08-01

117

Analysis of inhomogeneous-excitation frequency shifts of ytterbium optical lattice clocks  

NASA Astrophysics Data System (ADS)

We have investigated the frequency shifts caused by inhomogeneous excitation in a 171Yb optical lattice clock. The dependences of the inhomogeneity on the temperature of the cold ytterbium atoms and the misaligning angle between the lattice laser and the clock laser are analyzed by numerical calculations. The dependence of the fractional collisional frequency shift on the ground state fraction under different cold atom temperatures, atom numbers, lattice trap depths and unequal transverse and longitudinal temperatures are also shown. The results show that the uncertainty of the ytterbium clocks, contributed by the inhomogeneous excitation, can be reduced to be 10?19 or even lower with certain conditions.

Chen, Ning; Xu, Xinye

2015-01-01

118

Watching from the sidelines? The decline of the IMF's crisis management role  

Microsoft Academic Search

This article compares the International Monetary Fund (IMF)'s crisis management role during the Asian financial crisis in 1997–98 with the role it has played during the ‘credit crunch’ which emerged in the wake of the subprime crisis in the United States. With prominent calls for the construction of new forms of global financial governance to prevent a recurrence of the

Mark Beeson; André Broome

2008-01-01

119

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

120

Clocking design and analysis for a 600MHz Alpha microprocessor  

Microsoft Academic Search

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

Daniel W. Bailey; Bradley J. Benschneider

1998-01-01

121

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

122

IMF control of the azimuthal direction of earthward magnetotail fast flows?  

NASA Astrophysics Data System (ADS)

Cluster magnetotail data together with ACE solar wind data from 2001-2009 are used to investigate the dependence of the azimuthal flow direction of earthward magnetotail fast flows on the interplanetary magnetic field (IMF). We find indication that fast flows have favorable azimuthal directions that are dependent on the IMF. Our results suggest that for positive IMF By the favorable azimuthal direction of the fast flows is dawnward in the northern plasma sheet and duskward in the southern plasma sheet. For negative IMF By an opposite situation takes place, the favorable azimuthal flow directions are then duskward and dawnward in the northern and southern plasma sheet, respectively. The results are in agreement with the idea that untwisting of reconnected magnetic field lines directs the fast flows in the magnetotail, the field line twist itself being controlled by the IMF.

Pitkänen, T.; Hamrin, M.; Norqvist, P.; Karlsson, T.; Nilsson, H.

2013-12-01

123

On the enhancement of the IMF magnitude during 1978-1979  

NASA Astrophysics Data System (ADS)

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

King, J. H.

1981-01-01

124

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

E-print Network

The clock is the important synchronizing element in all synchronous digital systems. The difference in the clock arrival time between sink points is called the clock skew. This uncertainty in arrival times will limit operating frequency and might...

Ramakrishnan, Sundararajan

2010-10-12

125

Molecular Mechanisms Underlying the Arabidopsis Circadian Clock  

PubMed Central

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

Nakamichi, Norihito

2011-01-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

127

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

128

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

129

A Clock Reaction Based on Molybdenum Blue  

E-print Network

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

Neuenschwander, Ulrich

130

Circadian molecular clocks and cancer.  

PubMed

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

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

2014-01-01

131

Telling time on a clock  

NSDL National Science Digital Library

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

Dart, Greg

2007-10-19

132

Acting with the Clock: Clocking Practices in Early Childhood  

ERIC Educational Resources Information Center

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

Pacini-Ketchabaw, Veronica

2012-01-01

133

BMAL1 and CLOCK, Two Essential Components of the Circadian Clock, Are Involved in Glucose Homeostasis  

PubMed Central

Circadian timing is generated through a unique series of autoregulatory interactions termed the molecular clock. Behavioral rhythms subject to the molecular clock are well characterized. We demonstrate a role for Bmal1 and Clock in the regulation of glucose homeostasis. Inactivation of the known clock components Bmal1 (Mop3) and Clock suppress the diurnal variation in glucose and triglycerides. Gluconeogenesis is abolished by deletion of Bmal1 and is depressed in Clock mutants, but the counterregulatory response of corticosterone and glucagon to insulin-induced hypoglycaemia is retained. Furthermore, a high-fat diet modulates carbohydrate metabolism by amplifying circadian variation in glucose tolerance and insulin sensitivity, and mutation of Clock restores the chow-fed phenotype. Bmal1 and Clock, genes that function in the core molecular clock, exert profound control over recovery from insulin-induced hypoglycaemia. Furthermore, asynchronous dietary cues may modify glucose homeostasis via their interactions with peripheral molecular clocks. PMID:15523558

2004-01-01

134

Heterogeneous Genomic Molecular Clocks in Primates  

E-print Network

Heterogeneous Genomic Molecular Clocks in Primates Seong-Ho Kim1[ , Navin Elango1[ , Charles Warden, Georgia, United States of America Using data from primates, we show that molecular clocks in sites) Heterogeneous genomic molecular clocks in primates. PLoS Genet 2(10): e163. DOI: 10.1371/journal.pgen. 0020163

Yi, Soojin

135

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

136

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.

137

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

E-print Network

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

Carsten Weidner; Pavel Kroupa

2004-09-30

138

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

NASA Astrophysics Data System (ADS)

We use numerical simulations of the fragmentation of a 1000Msolar 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 IMF, 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 MJeans= 1, 2 and 5Msolar, 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 1Msolar. 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 ~1Msolar, even with an initial MJeans= 5Msolar. 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.

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

2006-05-01

139

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

NASA Technical Reports Server (NTRS)

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

Bremer, J.

1989-01-01

140

VCSEL polarization control for chip-scale atomic clocks.  

SciTech Connect

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

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

2007-01-01

141

Our Future Clocks and Watches  

Microsoft Academic Search

IF clocks are to strike at all, surely once per hour is insufficient, while four times is excessive; the high hour-numbers even now are inconvenient to count, and with the quarters heard alone it is possible to make a mistake of an hour. I cannot but think, then, on the whole, that the necessities of ship-life have long driven mariners

Edward L. Garbett

1885-01-01

142

Glucocorticoids and the circadian clock.  

PubMed

Glucocorticoids, hormones produced by the adrenal gland cortex, perform numerous functions in body homeostasis and the response of the organism to external stressors. One striking feature of their regulation is a diurnal release pattern, with peak levels linked to the start of the activity phase. This release is under control of the circadian clock, an endogenous biological timekeeper that acts to prepare the organism for daily changes in its environment. Circadian control of glucocorticoid production and secretion involves a central pacemaker in the hypothalamus, the suprachiasmatic nucleus, as well as a circadian clock in the adrenal gland itself. Central circadian regulation is mediated via the hypothalamic-pituitary-adrenal axis and the autonomic nervous system, while the adrenal gland clock appears to control sensitivity of the gland to the adrenocorticopic hormone (ACTH). The rhythmically released glucocorticoids in turn might contribute to synchronisation of the cell-autonomous clocks in the body and interact with them to time physiological dynamics in their target tissues around the day. PMID:18971218

Dickmeis, Thomas

2009-01-01

143

Biological Clocks: Riding the Tides  

PubMed Central

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

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

2015-01-01

144

[Circadian clock disruption and diabetes mellitus].  

PubMed

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

Ando, Hitoshi; Fujimura, Akio

2013-12-01

145

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

146

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

NASA Astrophysics Data System (ADS)

The strength and orientation of the interplanetary magnetic field (IMF) has a strong effect on the high-latitude plasma convection pattern, thereby influencing the speed and direction of polar thermospheric winds. The possibility of similar IMF control over the compositional response of the thermosphere during geomagnetic disturbances has not been fully investigated. This study finds that the y-component of the IMF (IMF By) exerts significant control over the development and subsequent equatorward transport of composition disturbances during periods of heightened geomagnetic activity. This is determined using the NCAR-TIMEGCM to simulate the thermospheric conditions during the first 3 weeks far-ultraviolet (FUV) imaging operations of the Dynamics Explorer 1 (DE-1) mission in 1981. The images reveal changes in the relative thermospheric column abundance of O versus N2 (?O/N2). These changes are reproduced by the model, incorporating variable IMF strength and orientation as inputs. It is found that simple reversal of IMF By leads to subsequent changes in ?O/N2 at middle latitudes by as much as 30%. This is a manifestation of the effect identified in the companion to this report (Crowley et al., 2006). The study confirms the hypothesis of Immel et al. (1997) that IMF-By effects on middle-latitude thermospheric composition are important, though more complex than expected. Contrary to previous predictions, early morning local times are shown to be more likely to suffer large decreases in ?O/N2 when By is negative. However, the overall magnitude of high-latitude Joule heating is found to be greater when By is positive.

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

2006-10-01

147

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

148

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

149

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

150

Our Future Clocks and Watches  

Microsoft Academic Search

I WOULD suggest, as a modification of ``R. B.'s'' suggestion in NATURE (p. 80), that the striking of the clocks on the twenty-four system might be varied at each quarter of the day, so as to indicate the time without so much striking. Thus, 1 (a.m.) to 6 might be indicated by the usual method; 7 could be indicated by

H. H. Clayton

1885-01-01

151

Molecular components of the mammalian circadian clock  

PubMed Central

Mammals synchronize their circadian activity primarily to the cycles of light and darkness in the environment. This is achieved by ocular photoreception relaying signals to the suprachiasmatic nucleus (SCN) in the hypothalamus. Signals from the SCN cause the synchronization of independent circadian clocks throughout the body to appropriate phases. Signals that can entrain these peripheral clocks include humoral signals, metabolic factors, and body temperature. At the level of individual tissues, thousands of genes are brought to unique phases through the actions of a local transcription/translation-based feedback oscillator and systemic cues. In this molecular clock, the proteins CLOCK and BMAL1 cause the transcription of genes which ultimately feedback and inhibit CLOCK and BMAL1 transcriptional activity. Finally, there are also other molecular circadian oscillators which can act independently of the transcription-based clock in all species which have been tested. PMID:23604473

Buhr, Ethan D.; Takahashi, Joseph S.

2013-01-01

152

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

153

Ribonucleoprotein Complexes That Control Circadian Clocks  

PubMed Central

Circadian clocks are internal molecular time-keeping mechanisms that enable organisms to adjust their physiology and behavior to the daily surroundings. Misalignment of circadian clocks leads to both physiological and health impairment. Post-transcriptional regulation and translational regulation of circadian clocks have been extensively investigated. In addition, accumulating evidence has shed new light on the involvement of ribonucleoprotein complexes (RNPs) in the post-transcriptional regulation of circadian clocks. Numerous RNA-binding proteins (RBPs) and RNPs have been implicated in the post-transcriptional modification of circadian clock proteins in different model organisms. Herein, we summarize the advances in the current knowledge on the role of RNP complexes in circadian clock regulation. PMID:23698761

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

2013-01-01

154

Oscillatory Mechanisms Underlying the Drosophila Circadian Clock  

NSDL National Science Digital Library

This animation depicts a schematic of the Drosophila circadian clock mechanism in a single, pacemaking lateral brain neuron. Circadian clocks allow organisms to exhibit rhythmic behaviors and processes based on a nearly 24-hour cycle in the absence of any light stimulation. In the fruit fly, the basic molecular mechanism consists of two intertwined transcription-translation negative feedback loops. One loop--the "positive loop"--controls the rhythmic expression of a positive transcription factor gene, Clock. The second loop--the "negative loop"--controls the transcription of period and timeless, two genes that encode repressor proteins. The loops are intertwined because Period and Timeless repress transcription mediated by the transcription factors Clock and Cycle, whereas the Clock:Cycle heterodimer drives transcription of period and timeless, as well as that of vrille, a repressor of Clock expression. Light cycles can synchronize the Drosophila circadian pathway by directly stimulating cryptochrome-dependent degradation of Timeless.

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

2003-11-18

155

Huygens synchronization of two pendulum clocks  

E-print Network

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

Henrique M. Oliveira; Luís V. Melo

2014-10-29

156

Clock Routing for High-Performance ICs  

Microsoft Academic Search

In this paper we focus on routing techniques for optimizing clock signals in small-cell (e.g., standard-cell, sea-of gate, etc.…) ASICs. In previously reported work, the routing of the clock net has been performed using ordinary global routing techniques based on a minimum spanning or minimal Steiner tree that have little understanding of clock routing problems. We present a novel approach

Michael A. B. Jackson; Arvind Srinivasan; Ernest S. Kuh

1990-01-01

157

What's my angle? : do people with big hands have larger angles between their fingers?  

NSDL National Science Digital Library

This activity challenges students to think about angles as geometric shapes and to find the sizes of the angles between their fingers. It is part of the Figure This! collection of 80 online mathematical challenges emphasizing real world uses of mathematics. For this challenge, the students trace a hand stretched to form an L-shape with the thumb and sketches angles of 90 degrees and 45 degrees between the thumb and index finger. They use the sketches to estimate the angles between their other fingers. Questions extend the challenge to finding the distance a bike wheel travels in one rotation, the headings of compass directions, and the number of degrees between the hands of a clock. Also included are directions for making a protractor by folding a circle of paper and a question about the meaning of negative angles. Copyright 2005 Eisenhower National Clearinghouse

National Action Council for Minorities in Engineering

2002-01-01

158

Clock genes, pancreatic function, and diabetes.  

PubMed

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

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

2014-11-01

159

A transportable strontium optical lattice clock  

E-print Network

We report on a transportable optical clock, based on laser-cooled strontium atoms trapped in an optical lattice. The experimental apparatus is composed of a compact source of ultra-cold strontium atoms including a compact cooling laser set-up and a transportable ultra-stable laser for interrogating the optical clock transition. The whole setup (excluding electronics) fits within a volume of less than 2 m$^3$. The high degree of operation reliability of both systems allowed the spectroscopy of the clock transition to be performed with 10 Hz resolution. We estimate an uncertainty of the clock of $7\\times10^{-15}$ Hz.

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

2014-01-01

160

Song I-Yeong's Armillary Clock  

NASA Astrophysics Data System (ADS)

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

Kim, Sang Hyuk; Lee, Yong Sam

161

IMF Approves SDR 15.5 Billion Stand-by Credit for Korea  

NSDL National Science Digital Library

The "IMF Approves SDR 15.5 Billion Stand-by Credit for Korea" details the aid package put together for Korea and provides a background of the events and the objectives of the aid package. 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

162

Characterizing the brown dwarf formation channels from the IMF and binary-star dynamics  

E-print Network

The stellar initial mass function (IMF) is a key property of stellar populations. There is growing evidence that the classical star-formation mechanism by the direct cloud fragmentation process has difficulties to reproduce the observed abundance and binary properties of brown dwarfs and very-low-mass stars. In particular, recent analytical derivations of the stellar IMF exhibit a deficit of brown dwarfs compared to observational data. Here we derive the residual mass function of brown dwarfs as an empirical measure of the brown dwarf deficiency in recent star-formation models with respect to observations and show that it is compatible with the substellar part of the Thies-Kroupa-IMF and the mass function obtained by numerical simulations. We conclude that the existing models may be further improved by including a substellar correction term accounting for additional formation channels like disk or filament fragmentation. The term "peripheral fragmentation" is introduced here for such additional formation chan...

Thies, Ingo; Kroupa, Pavel; Marks, Michael

2015-01-01

163

Injection-Locked Clocking: A Low-Power Clock Distribution Scheme for High-End Microprocessors  

E-print Network

Injection-Locked Clocking: A Low-Power Clock Distribution Scheme for High-End Microprocessors Hui-performance microprocessors. Clocking circuitry accounts for an overwhelming amount of total power consumption in multi is a crucial aspect of modern multi- GHz microprocessor design. Conventional distribution schemes are more

Wu, Hui

164

Synchronization: from pendulum clocks to chaotic lasers and chemical oscillators  

E-print Network

Synchronization: from pendulum clocks to chaotic lasers and chemical oscillators MICHAEL ROSENBLUM Christiaan Huygens reported on his observation of synchronization of two pendulum clocks which he had briefly described in his memoirs Horologium Oscillatorium (The Pendulum Clock, or Geome- trical

Potsdam, Universität

165

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

166

Gigabit Ethernet Asynchronous Clock Compensation FIFO  

NASA Technical Reports Server (NTRS)

Clock compensation for Gigabit Ethernet is necessary because the clock recovered from the 1.25 Gb/s serial data stream has the potential to be 200 ppm slower or faster than the system clock. The serial data is converted to 10-bit parallel data at a 125 MHz rate on a clock recovered from the serial data stream. This recovered data needs to be processed by a system clock that is also running at a nominal rate of 125 MHz, but not synchronous to the recovered clock. To cross clock domains, an asynchronous FIFO (first-in-first-out) is used, with the write pointer (wprt) in the recovered clock domain and the read pointer (rptr) in the system clock domain. Because the clocks are generated from separate sources, there is potential for FIFO overflow or underflow. Clock compensation in Gigabit Ethernet is possible by taking advantage of the protocol data stream features. There are two distinct data streams that occur in Gigabit Ethernet where identical data is transmitted for a period of time. The first is configuration, which happens during auto-negotiation. The second is idle, which occurs at the end of auto-negotiation and between every packet. The identical data in the FIFO can be repeated by decrementing the read pointer, thus compensating for a FIFO that is draining too fast. The identical data in the FIFO can also be skipped by incrementing the read pointer, which compensates for a FIFO draining too slowly. The unique and novel features of this FIFO are that it works in both the idle stream and the configuration streams. The increment or decrement of the read pointer is different in the idle and compensation streams to preserve disparity. Another unique feature is that the read pointer to write pointer difference range changes between compensation and idle to minimize FIFO latency during packet transmission.

Duhachek, Jeff

2012-01-01

167

Global synchronization of parallel processors using clock pulse width modulation  

DOEpatents

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

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

2013-04-02

168

The physics of clocks and watches  

Microsoft Academic Search

The mode of operation of the component mechanisms of clocks and watches is reviewed, and the errors in timekeeping which they introduce discussed together with the steps which are taken to rectify them. A review of mechanical clocks includes a consideration of the pendulum and circular, temperature, barometric and escapement errors. Specific escapements are discussed.Spring, temperature and escapement errors in

J F W Bishop

1955-01-01

169

Constraining fossil calibrations for molecular clocks  

E-print Network

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

Kumar, Sudhir

170

Progress of the 87Rb Fountain Clock  

NASA Astrophysics Data System (ADS)

A fountain atomic clock based on cold 87 Rb atoms has been in operation in our laboratory for several months. We therefore report the design of the rubidium fountain clock including its physical package, optical system and daily operation. Ramsey fringes have been attained with the signal to noise ratio of about 100.

Zhou, Zi-Chao; Wei, Rong; Shi, Chun-Yan; Lv, De-Sheng; Li, Tang; Wang, Yu-Zhu

2009-12-01

171

Does clock-watching make you clockwise?  

PubMed

French and Richards (1993) found that subjects asked to draw from memory a clock that had Roman numerals on its face typically represented the number four on the clock face as "IV" rather than the correct "IIII", whereas those merely asked to copy it typically drew "IIII". The current experiments followed the methodology of French and Richards, but then went on to examine the subsequent memorial representation of the number four. Subjects drew a clock with Roman numerals on its face, either from memory (with or without forewarning) or while the clock remained in full view. Subsequently, subjects were asked to recall the exact form in which the numbers were represented on the clock (Experiment 1) or were asked to recognise which of two clocks had been presented earlier (Experiment 2). Findings supported the idea that subjects in the copy condition were more likely than subjects in other conditions to draw the clock without invoking schematic knowledge of Roman numerals. The basic effect reported by French and Richards was replicated in both experiments. Furthermore, in both experiments, subjects who correctly drew the clock with the number four represented as "IIII" were more likely to misrepresent it as "IV" in the subsequent memory task if they were in the copy condition rather than the two memory conditions. The results are interpreted in terms of schema theory. PMID:8821085

Richards, A; French, C C; Harris, P

1996-01-01

172

An Iodine Fluorescence Quenching Clock Reaction  

ERIC Educational Resources Information Center

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

Weinberg, Richard B.; Muyskens, Mark

2007-01-01

173

A clock distribution network for microprocessors  

Microsoft Academic Search

A global clock distribution strategy used on several microprocessor chips is described. The clock network consists of buffered tunable trees or treelike networks, with the final level of trees all driving a single common grid covering most of the chip. This topology combines advantages of both trees and grids. A new tuning method was required to efficiently tune such a

Phillip J. Restle; Timothy G. McNamara; David A. Webber; Peter J. Camporese; Kwok F. Eng; Keith A. Jenkins; David H. Allen; Michael J. Rohn; Michael P. Quaranta; David W. Boerstler; Charles J. Alpert; Craig A. Carter; Roger N. Bailey; John G. Petrovick; Byron L. Krauter; Bradley D. McCredie

2001-01-01

174

THE INTRINSIC CIRCADIAN CLOCK WITHIN THE CARDIOMYOCYTE  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

175

Resonating Circadian Clocks Enhance Fitness in Cyanobacteria  

Microsoft Academic Search

In some organisms longevity, growth, and developmental rate are improved when they are maintained on a light\\/dark cycle, the period of which ``resonates'' optimally with the period of the endogenous circadian clock. However, to our knowledge no studies have demonstrated that reproductive fitness per se is improved by resonance between the endogenous clock and the environmental cycle. We tested the

Yan Ouyang; Carol R. Andersson; Takao Kondo; Susan S. Golden; Carl Hirschie Johnson

1998-01-01

176

The Welch-Lynch Clock Synchronization Algorithm  

E-print Network

The Welch-Lynch Clock Synchronization Algorithm Bruno Dutertre Technical Report 747 March 27, 1998 E1 4NS, UK #12; Abstract This note describes the Welch-Lynch fault-tolerant algorithm for clock. #12; Contents 1 Introduction 1 2 Algorithm 2 3 Formal Analysis 4 3.1 Overview

Dutertre, Bruno

177

A tale of two synchronizing clocks  

Microsoft Academic Search

A specific application for wastewater monitoring and ac- tuation, called CSOnet, deployed city-wide in a mid-sized US city, South Bend, Indiana, posed some challenges to a time synchronization protocol. The nodes in CSOnet have a low duty cycle (2% in current deployment) and use an ex- ternal clock, called the Real Time Clock (RTC), for trigger- ing the sleep and

Jinkyu Koo; Rajesh Krishna Panta; Saurabh Bagchi; Luis Antonio Montestruque

2009-01-01

178

Trapped ion optical clocks for space applications  

NASA Astrophysics Data System (ADS)

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

Gill, Patrick

179

Nutrient Sensing and the Circadian Clock  

PubMed Central

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

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

2012-01-01

180

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

181

Catalyzing Private Capital Flows: Do IMF Programs Work as Commitment Devices?  

Microsoft Academic Search

An objective of IMF programs is to help countries improve their access to international capital markets. In this paper, we examine if Fund programs influence the ability of developing country issuers to tap international bond markets and whether they improve spreads paid on the bonds issued. We find that Fund programs do not provide a uniformly favorable signaling effect, i.e.,

Ashoka Mody; Diego Saravia

2005-01-01

182

Enhanced solar wind geoeffectiveness after a sudden increase in dynamic pressure during southward IMF orientation  

E-print Network

Enhanced solar wind geoeffectiveness after a sudden increase in dynamic pressure during southward increase in solar wind pressure results in poleward expansion of the auroral oval and closing of the polar show that southward IMF conditions combined with high solar wind dynamic pressure immediately after

Lummerzheim, Dirk

183

Do IMF and World Bank programs induce government crises? An empirical analysis  

E-print Network

Do IMF and World Bank programs induce government crises? An empirical analysis Axel Drehera Martin of the German Economic Association for helpful comments, Richard Jong-A-Pin for valuable input to an earlier, and CESifo. E-mail: mail@axel-dreher.de. b ETH Zurich, KOF Swiss Economic Institute, Weinbergstrasse 35, CH

Krivobokova, Tatyana

184

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

185

Actual voting power of the IMF members based on their political-economic integration  

Microsoft Academic Search

A voting power analysis was made to estimate the power of IMF members within the Executive Board and the Fund in general through the existing constituency system.For this purpose we introduced two absolute power indices extending the classical Penrose (non-normalized Banzhaf) and Coleman (“the power of the body to act”) indices by taking into account the members’ preferences to coalesce,

Fuad Aleskerov; Valeriy Kalyagin; Kirill Pogorelskiy

2008-01-01

186

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

187

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

188

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

189

On the Effect of IMF Turning on Ion Dynamics at Mercury  

NASA Astrophysics Data System (ADS)

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 ExB 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 gyration periods 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 IMF 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. H.

2011-12-01

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

Triangle Geometry: Angles  

NSDL National Science Digital Library

This interactive math site teaches students about angles and triangles. There are interactive activities for measuring angles, exploring types of angles, and adding angles. By using a Java applet and pictures, a proof of the Pythagorean Theorem is demonstrated.

Math Cove

2007-12-12

192

[Molecular mechanisms of circadian clock functioning].  

PubMed

Most physiological processes of all organisms are rhythmic with a period of about 24 h and are generated by an endogenous biological CLOCK present in all cells. However, there is also a central CLOCK--the primary circadian pacemaker which is localized in the suprachiasmatic nuclei of the mammalian hypothalamus. Factors of groups Period (PER1, PER2 and PER3), BMAL (BMAL1 and BMAL2), CRYptochromes (CRY1 and CRY2) as well as some other factors are the components of this circadian CLOCK system. Some of these genes contain E-box sequences and their expression is regulated by a transcription factor complex CLOCK-BMAL1. The enzymes responsible for the post-translational modification of circadian gene products are also the components of circadian CLOCK system. These enzymes define CLOCK's work and determine the duration of circadian biorhythm and functional state of the whole organism. The most important of these enzymes are casein kinase-1epsilon and -1delta. We have analysed data about the interconnection between the circadian CLOCK system, cell cycle, and cancerogenesis as well as about the sensitivity of circadian gene expression to the action of toxic agents and nanomaterials. PMID:21888051

Karbovsky?, L L; Minchenko, D O; Garmash, Ia A; Minchenko, O G

2011-01-01

193

Picosecond MIXSEL for clocking applications  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

194

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

NASA Astrophysics Data System (ADS)

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

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

2001-12-01

195

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

PubMed Central

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

196

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

197

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

NASA Astrophysics Data System (ADS)

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

Kullen, Anita; Fear, Rob; Milan, Steve

2014-05-01

198

Self-Calibrating Clocks for Globally Asynchronous Locally Synchronous Systems  

Microsoft Academic Search

We present a local clocking mechanism based on a tunable delay line which calibrates itself from a low frequency global clock. After initial tuning, the local clock remains calibrated when environmental conditions change. Each module of a large system on a chip can use one of these clock generators running at the optimal frequency for the module. Communication between locally

Simon W. Moore; George S. Taylor; Paul A. Cunningham; Robert D. Mullins; Peter Robinson

2000-01-01

199

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

200

Sleep: the sound of a local alarm clock.  

PubMed

Besides the master clock located in the suprachiasmatic nucleus (SCN) of the brain, additional clocks are distributed across the central nervous system and the body. The role of these 'secondary' clocks remains unclear. A new study shows that the lack of an internal clock in histamine neurons profoundly perturbs sleep. PMID:25562304

Adamantidis, Antoine R

2015-01-01

201

Precision of the Gonyaulax circadian clock.  

PubMed

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

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

1981-09-01

202

Light clocks in strong gravitational fields  

E-print Network

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

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

2009-02-11

203

Atomic Clock Based On Linear Ion Trap  

NASA Technical Reports Server (NTRS)

Highly stable atomic clock based on excitation and measurement of hyperfine transition in 199Hg+ ions confined in linear quadrupole trap by radio-frequency and static electric fields. Configuration increases stability of clock by enabling use of enough ions to obtain adequate signal while reducing non-thermal component of motion of ions in trapping field, reducing second-order Doppler shift of hyperfine transition. Features described in NPO-17758 "Linear Ion Trap for Atomic Clock." Frequency standard based on hyperfine transition described in NPO-17456, "Trapped-Mercury-Ion Frequency Standard."

Prestage, John D.; Dick, G. John

1992-01-01

204

Model of a mechanical clock escapement  

NASA Astrophysics Data System (ADS)

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

Moline, David; Wagner, John; Volk, Eugene

2012-07-01

205

[Comment on “Accurate clock for remote areas” by J. Bonanomi] For clock watchers  

NASA Astrophysics Data System (ADS)

Your news item in Eos (63(4), January 26, 1982, p. 129) refers to an accurate clock for remote areas that utilizes Omega signals to synchronize clocks to 0.01 s.A system utilizing GPS satellite signals is also currently available for synchronizing remote clocks to an accuracy of better than 100 ns! GPS is presently in its validation phase and can now provide worldwide time transfer capability. The very stable satellite atomic clocks are routinely monitored and correction parameters are broadcast as part of the GPS message.

Perreault, Paul D.

206

Circadian clock circuitry in colorectal cancer  

PubMed Central

Colorectal cancer is the most prevalent among digestive system cancers. Carcinogenesis relies on disrupted control of cellular processes, such as metabolism, proliferation, DNA damage recognition and repair, and apoptosis. Cell, tissue, organ and body physiology is characterized by periodic fluctuations driven by biological clocks operating through the clock gene machinery. Dysfunction of molecular clockworks and cellular oscillators is involved in tumorigenesis, and altered expression of clock genes has been found in cancer patients. Epidemiological studies have shown that circadian disruption, that is, alteration of bodily temporal organization, is a cancer risk factor, and an increased incidence of colorectal neoplastic disease is reported in shift workers. In this review we describe the involvement of the circadian clock circuitry in colorectal carcinogenesis and the therapeutic strategies addressing temporal deregulation in colorectal cancer. PMID:24764658

Mazzoccoli, Gianluigi; Vinciguerra, Manlio; Papa, Gennaro; Piepoli, Ada

2014-01-01

207

Clock synchronization for mobile ad hoc networks  

E-print Network

As mobile networking advances, there is a need for services such as clock synchronization that improve performance and support the development of higher-level applications. This can be achieved by adapting existing algorithms (such as the Network...

Chandra, Rajan

2013-02-22

208

Avian Circadian Organization: A Chorus of Clocks  

PubMed Central

In birds, biological clock function pervades all aspects of biology, controlling daily changes in sleep: wake, visual function, song, migratory patterns and orientation, as well as seasonal patterns of reproduction, song and migration. The molecular bases for circadian clocks are highly conserved, and it is likely the avian molecular mechanisms are similar to those expressed in mammals, including humans. The central pacemakers in the avian pineal gland, retinae and SCN dynamically interact to maintain stable phase relationships and then influence downstream rhythms through entrainment of peripheral oscillators in the brain controlling behavior and peripheral tissues. Birds represent an excellent model for the role played by biological clocks in human neurobiology; unlike most rodent models, they are diurnal, they exhibit cognitively complex social interactions, and their circadian clocks are more sensitive to the hormone melatonin than are those of nocturnal rodents. PMID:24157655

Cassone, Vincent M

2013-01-01

209

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

210

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

211

Mission-Clock-Display Software Tool  

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

212

Using Atomic Clocks to Detect Gravitational Waves  

E-print Network

Atomic clocks have recently reached a fractional timing precision of $gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

Loeb, Abraham

2015-01-01

213

Circadian Clock Proteins in Mood Regulation  

PubMed Central

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

Partonen, Timo

2015-01-01

214

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

215

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

216

The aging biological clock in Neurospora crassa.  

PubMed

The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response. PMID:25535564

Case, Mary E; Griffith, James; Dong, Wubei; Tigner, Ira L; Gaines, Kimberly; Jiang, James C; Jazwinski, S Michal; Arnold, Jonathan

2014-09-01

217

Towards Self-Clocked Gated OCDMA Receiver  

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

218

Circadian clocks, food intake, and metabolism.  

PubMed

Circadian rhythmicity that has been shaped by evolution over millions of years generates an internal timing controlling the sleep-wake and metabolism cycles. The daily variations between sleep/fasting/catabolism and wakefulness/feeding/anabolism are coordinated by a master hypothalamic clock, mainly reset by ambient light. Secondary clocks, including liver and adipose tissue, are normally synchronized by the master clock, but they are also sensitive to feeding time, especially when meals take place during the usual resting period. Cellular metabolism and circadian clocks are tightly interconnected at the molecular levels. Although the suprachiasmatic clock is not shifted by mealtime under light-dark conditions, nutritional cues can feedback onto it and modulate its function under hypo- and hypercaloric (high-fat) conditions. Food-related reward cues are other modulators of the master clock. Circadian disturbances (e.g., desynchronization induced by shift work or chronic jet lag) are frequently associated with metabolic dysfunctions (chronobesity) and vice versa. Pharmacological tools and natural synchronizers (i.e., light and mealtime) can be useful as chronotherapeutic treatments to limit the occurrence of metabolic risk factors. PMID:23899596

Challet, Etienne

2013-01-01

219

The Circadian Clock Modulates Renal Sodium Handling  

PubMed Central

The circadian clock contributes to the control of BP, but the underlying mechanisms remain unclear. We analyzed circadian rhythms in kidneys of wild-type mice and mice lacking the circadian transcriptional activator clock gene. Mice deficient in clock exhibited dramatic changes in the circadian rhythm of renal sodium excretion. In parallel, these mice lost the normal circadian rhythm of plasma aldosterone levels. Analysis of renal circadian transcriptomes demonstrated changes in multiple mechanisms involved in maintaining sodium balance. Pathway analysis revealed the strongest effect on the enzymatic system involved in the formation of 20-HETE, a powerful regulator of renal sodium excretion, renal vascular tone, and BP. This correlated with a significant decrease in the renal and urinary content of 20-HETE in clock-deficient mice. In summary, this study demonstrates that the circadian clock modulates renal function and identifies the 20-HETE synthesis pathway as one of its principal renal targets. It also suggests that the circadian clock affects BP, at least in part, by exerting dynamic control over renal sodium handling. PMID:22440902

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

2012-01-01

220

The aging biological clock in Neurospora crassa  

PubMed Central

The biological clock affects aging through ras-1 (bd) and lag-1, and these two longevity genes together affect a clock phenotype and the clock oscillator in Neurospora crassa. Using an automated cell-counting technique for measuring conidial longevity, we show that the clock-associated genes lag-1 and ras-1 (bd) are true chronological longevity genes. For example, wild type (WT) has an estimated median life span of 24 days, while the double mutant lag-1, ras-1 (bd) has an estimated median life span of 120 days for macroconidia. We establish the biochemical function of lag-1 by complementing LAG1 and LAC1 in Saccharomyces cerevisiae with lag-1 in N. crassa. Longevity genes can affect the clock as well in that, the double mutant lag-1, ras-1 (bd) can stop the circadian rhythm in asexual reproduction (i.e., banding in race tubes) and lengthen the period of the frequency oscillator to 41 h. In contrast to the ras-1 (bd), lag-1 effects on chronological longevity, we find that this double mutant undergoes replicative senescence (i.e., the loss of replication function with time), unlike WT or the single mutants, lag-1 and ras-1 (bd). These results support the hypothesis that sphingolipid metabolism links aging and the biological clock through a common stress response PMID:25535564

Case, Mary E; Griffith, James; Dong, Wubei; Tigner, Ira L; Gaines, Kimberly; Jiang, James C; Jazwinski, S Michal; Arnold, Jonathan

2014-01-01

221

[Dysfunctions of biological clocks and their treatments].  

PubMed

Biological rhythms are periodic phenomena entrained to environmental changes by exogenous factors called synchronizers or entraining agents namely the light-dark cycle, the rest-activity cycle and the seasons, among others. In humans the major synchronizers are the light-dark and rest activity cycles. The endogenous component of a biological rhythm is dependent upon a number of clock genes. The main biological clock (oscillator or pacemaker) is the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. The photoperiod (light-dark cycle) perceived by the retina acts on the SCN genes. Peripheral clocks have also been described in a number of tissues e.g. retina, adrenals. In a number of occurrences the synchronizers are badly perceived (transmeridian flights, shiftwork, nightwork...) or are not at all perceived (blindness). This situation is named rhythm desynchronization, it is external when the desynchronization is strictly related to the environment or internal when it is related to a dysfunction of the clock like in e.g. aging, Alzheimer disease, seasonal affective disorders (SAD) or hormone-dependent cancers which results in fatigue, sleep and mood disorders... A number of drugs called resynchronizing agents or chronobiotics which act on the biological clock are able to resynchronize the clock and to improve the patients' condition. Bright light is used in the treatment of SAD, melatonin, the pineal hormone, is also of interest when administered at precise timings in the 24hours scale. Other drugs like B12 vitamin or psychotropic drugs have also been proposed as chronobiotics. PMID:18706343

Touitou, Y

2008-06-01

222

Circadian clocks and mood-related behaviors.  

PubMed

Circadian clocks are present in nearly all tissues of an organism, including the brain. The brain is not only the site of the master coordinator of circadian rhythms located in the suprachiasmatic nuclei (SCN) but also contains SCN-independent oscillators that regulate various functions such as feeding and mood-related behavior. Understanding how clocks receive and integrate environmental information and in turn control physiology under normal conditions is of importance because chronic disturbance of circadian rhythmicity can lead to serious health problems. Genetic modifications leading to disruption of normal circadian gene functions have been linked to a variety of psychiatric conditions including depression, seasonal affective disorder, eating disorders, alcohol dependence, and addiction. It appears that clock genes play an important role in limbic regions of the brain and influence the development of drug addiction. Furthermore, analyses of clock gene polymorphisms in diseases of the central nervous system (CNS) suggest a direct or indirect influence of circadian clock genes on brain function. In this chapter, I will present evidence for a circadian basis of mood disorders and then discuss the involvement of clock genes in such disorders. The relationship between metabolism and mood disorders is highlighted followed by a discussion of how mood disorders may be treated by changing the circadian cycle. PMID:23604481

Albrecht, Urs

2013-01-01

223

Origin of the prestellar core mass function and link to the IMF - Herschel first results  

NASA Astrophysics Data System (ADS)

We briefly review ground-based (sub)millimeter dust continuum observations of the prestellar core mass function (CMF) and its connection to the stellar initial mass function (IMF). We also summarize the first results obtained on this topic from the Herschel Gould Belt survey, one of the largest key projects with the Herschel Space Observatory. Our early findings with Herschel confirm the existence of a close relationship between the CMF and the IMF. Furthermore, they suggest a scenario according to which the formation of prestellar cores occurs in two main steps: 1) complex networks of long, thin filaments form first, probably as a result of interstellar MHD turbulence; 2) the densest filaments then fragment and develop prestellar cores via gravitational instability.

André, Ph.; Men'shchikov, A.; Könyves, V.; Arzoumanian, D.

2011-04-01

224

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

225

Modulated reconnection rate and energy conversion at the magnetopause under steady IMF conditions  

Microsoft Academic Search

We use the multi-spacecraft mission Cluster to make observational estimates of the local energy conversion across the dayside high-latitude magnetopause. The energy conversion is estimated during eleven complete magnetopause crossings under steady south-dawnward interplanetary magnetic field (IMF). We describe a new method to determine the reconnection rate from the magnitude of the local energy conversion. The reconnection rate as well

L. Rosenqvist; A. Vaivads; A. Retinò; T. Phan; H. J. Opgenoorth; I. Dandouras; S. Buchert

2008-01-01

226

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

227

Do the IMF and the World Bank influence voting in the UN General Assembly?  

Microsoft Academic Search

Using panel data for 188 countries over the 1970–2008 period, this paper analyzes empirically the influence of the IMF and\\u000a the World Bank on voting patterns in the UN General Assembly. Countries receiving adjustment projects and larger non-concessional\\u000a loans from the World Bank vote more frequently in line with the average G7 country. The same is true for countries obtaining

Axel Dreher; Jan-Egbert Sturm

2006-01-01

228

A definitive census of the IMF of a nearby young massive cluster  

NASA Astrophysics Data System (ADS)

Over the past years, we have performed one of the most extensive study of the young (lambda)-Orionis star forming region, combining photometric data from the xray to the mid-IR, as well as wide field and high spatial resolution imaging. This effort allowed us to identify hundreds of very low mass stars, brown dwarfs and isolated planetary mass candidate members in the three clusters present in this region: Collinder 69, Barnard 30 and Barnard 35, with the ultimate aim to perform a detailed study of the very low mass end of the IMF from the core of the clusters to their periphery. We now propose to use the unique capabilities of IMACS to perform spectroscopic follow-up observations of these candidates members. The spectra will allow us to: i) determine the spectral type - and therefore the T_eff - of our candidates; ii) assess their membership to the clusters using various complementary diagnostics (presence or absence of H(alpha), gravity sensitive lines such as K I, Na I); iii) draw a definitive census of the IMF of the cluster over the entire mass spectrum, from its core to its edges. The proposed observations will allow us to make a unique comprehensive study of the IMF of a nearby young massive cluster down to M=15~20 M_Jup and of the properties (discs, accretion) of its substellar members, and a benchmark result for all the models of formation and evolution.

Bouy, Herve; Martin, Eduardo L.; Barrado Y Navascues, David; Stauffer, John

2009-08-01

229

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

230

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

PubMed

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

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

2015-02-01

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

Modeling the mammalian circadian clock  

NASA Astrophysics Data System (ADS)

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

Jolley, Craig; Ueda, Hiroki

2012-02-01

233

Evolutionary Links Between Circadian Clocks and Photoperiodic Diapause in Insects  

PubMed Central

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

Meuti, Megan E.; Denlinger, David L.

2013-01-01

234

Microwave Atomic Clock in the Optical Lattice with Specific Frequency  

NASA Astrophysics Data System (ADS)

A scheme for a microwave atomic clock is proposed for Cs or Rb atoms trapped in a blue detuned optical lattice. The ac Stark shift of the clock transition due to a trapping laser is calculated. We analyze it at some specific laser wavelength. Compared with the case of the fountain clock, the cavity related shifts, the collision shift and the Doppler effect are eliminated or suppressed dramatically in an atomic lattice clock. By analyzing various sources of clock uncertainty, a microwave atomic lattice clock with a high accuracy and small volume is feasible.

Zhou, Xiao-Ji; Chen, Xu-Zong; Chen, Jing-Biao; Wang, Yi-Qiu; Li, Jia-Ming

2009-09-01

235

A high-speed photonic clock and carrier regenerator  

NASA Technical Reports Server (NTRS)

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

Yao, X. S.; Lutes, G.

1995-01-01

236

Three errors in the article: "The OPERA neutrino velocity result and the synchronisation of clocks"  

E-print Network

We found three mistakes in the article " The OPERA neutrino velocity result and the synchronisation of clocks" by Contaldi \\cite{Contaldi}. First, the definition of the angle of the latitude in the geoid description leads to a prolate spheroid (rugby ball shape) instead of an oblate spheroid with the usual equatorial flattening. Second, Contaldi forgot a cosine of the latitude in the centripetal contribution term. And last but not least, a profound conceptual mistake was done in believing that an atomic clock or any timekeeper apparatus was carried in a journey by car or plane between CERN and Gran Sasso; instead of that atomic clocks are continuously resynchronized through a GPS device, and the variation of the potential term applies only for the neutrino travel itself. Thus instead of a $\\Delta t \\approx 30ns $ correction claimed by the author in a travel of 12 hours plus 4 days at rest for an atomic clock, we have found a time correction only for the neutrino itself $\\Delta t=3.88 \\, 10^{-16} s$! That means, that this paper \\cite{Contaldi} does not give the right explanation why the neutrino is seen travelling faster than the speed of light in the OPERA neutrino experiment.

Olivier Besida

2011-10-13

237

Dating Phylogenies with Hybrid Local Molecular Clocks  

PubMed Central

Background Because rates of evolution and species divergence times cannot be estimated directly from molecular data, all current dating methods require that specific assumptions be made before inferring any divergence time. These assumptions typically bear either on rates of molecular evolution (molecular clock hypothesis, local clocks models) or on both rates and times (penalized likelihood, Bayesian methods). However, most of these assumptions can affect estimated dates, oftentimes because they underestimate large amounts of rate change. Principal Findings A significant modification to a recently proposed ad hoc rate-smoothing algorithm is described, in which local molecular clocks are automatically placed on a phylogeny. This modification makes use of hybrid approaches that borrow from recent theoretical developments in microarray data analysis. An ad hoc integration of phylogenetic uncertainty under these local clock models is also described. The performance and accuracy of the new methods are evaluated by reanalyzing three published data sets. Conclusions It is shown that the new maximum likelihood hybrid methods can perform better than penalized likelihood and almost as well as uncorrelated Bayesian models. However, the new methods still tend to underestimate the actual amount of rate change. This work demonstrates the difficulty of estimating divergence times using local molecular clocks. PMID:17849008

Aris-Brosou, Stéphane

2007-01-01

238

Nuclear receptors rock around the clock  

PubMed Central

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

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

2014-01-01

239

Changes in the Gonial Angle Following Bilateral Sagittal Split Osteotomy and Vertical Ramus Osteotomy for Mandibular Excess  

PubMed Central

Aim: The gonial angle plays an important role in ensuring a harmonious facial profile. Changes in this angle after surgery may be an esthetic concern for both the patient and the surgeon. The aim of the present study was to evaluate gonial angle changes after mandibular setback by the bilateral sagittal split osteotomy (BSSO) and vertical ramus osteotomy (VRO) techniques. Methods: Fifty-eight male patients with mandibular prognathism only were treated from 2004 to 2006 (deformities such as discrepancy of jaws, mandibular setback of more than 10 mm, asymmetry, and vertical discrepancy were excluded). Patients were randomly divided into 2 groups. In the first group, mandibular setback was performed using the Obwegeser technique and wire osteosynthesis with 4 weeks' fixation (IMF), and in the second group, mandibular setback via VRO without wire osteosynthesis and 4 weeks' IMF was carried out. Lateral cephalograms were obtained for all the patients before surgery (T0) and 1 year after surgery (T1). Gonial angle and occlusal plane-SN in T0 and T1 were evaluated. Results: After surgery, the gonial angle had decreased in all patients. Decrease in the gonial angle in the VRO group was greater than the BSSO group. The average decrease in the gonial angle was significantly more (P < 0.05) in the VRO group (7°) than in the BSSO group (2°). Conclusion: Gonial angle decrease was observed in the present study following mandibular setback by the VRO and BSSO techniques. This decrease in the VRO group was significantly greater. PMID:20204060

Yazdani, Javad; Talesh, Kourosh Taheri; Motamedi, Mohammad Hosein Kalantar; Ghavimi, Mohammad Ali

2010-01-01

240

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

241

CENTRAL AND PERIPHERAL CIRCADIAN CLOCKS IN MAMMALS  

PubMed Central

The circadian system of mammals is composed of a hierarchy of oscillators that function at the cellular, tissue and systems levels. A common molecular mechanism underlies the cell autonomous circadian oscillator throughout the body, yet this clock system is adapted to different functional contexts. In the central suprachiasmatic nucleus (SCN) of the hypothalamus, a coupled population of neuronal circadian oscillators acts as a master pacemaker for the organism to drive rhythms in activity and rest, feeding, body temperature and hormones. Coupling within the SCN network confers robustness to the SCN pacemaker which in turn provides stability to the overall temporal architecture of the organism. Throughout the majority of the cells in the body, cell autonomous circadian clocks are intimately enmeshed within metabolic pathways. Thus, an emerging view for the adaptive significance of circadian clocks is their fundamental role in orchestrating metabolism. PMID:22483041

Mohawk, Jennifer A.; Green, Carla B.; Takahashi, Joseph S.

2013-01-01

242

Supporting Family Awareness with the Whereabouts Clock  

NASA Astrophysics Data System (ADS)

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

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

243

Models of the Primordial Standard Clock  

E-print Network

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

Xingang Chen; Mohammad Hossein Namjoo; Yi Wang

2015-01-10

244

Sugars, the clock and transition to flowering  

PubMed Central

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

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

2013-01-01

245

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

246

Clock mechanisms and their effects, leads into steam engine  

E-print Network

In a clock-maker’s shop, Simon Schaffer explains the great precision needed to make clocks, and the development of standardized parts. The feed-back mechanisms or governors are absolutely essential in the first stationary steam engines....

Dugan, David

2004-08-17

247

Watching the clock: Studying variation in rates of molecular evolution  

E-print Network

Watching the clock: Studying variation in rates of molecular evolution between species Robert at different rates in different species. Indeed, contrary to hopes that molecular evolution would be clock

Hohenlohe, Paul A.

248

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

249

Role of cardiomyocyte circadian clock in myocardial metabolic adaptation  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

250

DCS: Distributed Asynchronous Clock Synchronization in Delay Tolerant Networks  

E-print Network

in the number of hops and the intercontact durations [9] results in a need for large guard periods that cause synchronized clocks and use extra awake periods, called guard periods, to compensate for uncertainty in clock

Shen, Xuemin "Sherman"

251

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

PubMed Central

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

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

2014-01-01

252

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

253

Water-Powered Astronomical Clock Tower  

NASA Astrophysics Data System (ADS)

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

Sun, Xiaochun

254

Quantum clock synchronization with a single qudit.  

PubMed

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

Tavakoli, Armin; Cabello, Adán; ?ukowski, Marek; Bourennane, Mohamed

2015-01-01

255

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

256

Quantum Clock Synchronization with a Single Qudit  

NASA Astrophysics Data System (ADS)

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

Tavakoli, Armin; Cabello, Adán; ?ukowski, Marek; Bourennane, Mohamed

2015-01-01

257

Quantum Clock Synchronization with a Single Qudit  

PubMed Central

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

Tavakoli, Armin; Cabello, Adán; ?ukowski, Marek; Bourennane, Mohamed

2015-01-01

258

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

259

Timescale algorithms combining cesium clocks and hydrogen masers  

NASA Technical Reports Server (NTRS)

The United States Naval Observatory (USNO) atomic timescale, formerly based on an ensemble of cesium clocks, is now produced by an ensemble of cesium clocks and hydrogen masers. In order to optimize stability and reliability, equal clock weighting has been replaced by a procedure reflecting the relative, time-varying noise characteristics of the two different types of clocks. Correlation of frequency drift is required, and residual drift is avoided by the eventual complete deweighting of the masers.

Breakiron, Lee A.

1992-01-01

260

Positional Cloning of the Mouse Circadian Clock Gene  

Microsoft Academic Search

We used positional cloning to identify the circadian Clock gene in mice. Clock is a large transcription unit with 24 exons spanning ?100,000 bp of DNA from which transcript classes of 7.5 and ?10 kb arise. Clock encodes a novel member of the bHLH–PAS family of transcription factors. In the Clock mutant allele, an A?T nucleotide transversion in a splice

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

1997-01-01

261

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

262

The Circadian Clock Starts Ticking at a Developmentally Early Stage  

Microsoft Academic Search

Although overt diurnal rhythms of behavior do not begin until well after birth, molecular studies suggest that the circadian clock may begin much earlier at a cellular level: mouse embryonic fibroblasts, for example, already possess robust clocks. By multiple criteria, we found no circadian clock present in mouse embryonic stem cells. Nevertheless, upon their differentiation into neurons, circadian gene expression

Elzbieta Kowalska; Ermanno Moriggi; Christoph Bauer; Charna Dibner; Steven A. Brown

2010-01-01

263

Self Calibrating Clocks for Globally Asynchronous Locally Synchronous Systems  

E-print Network

. A low frequency clock (e.g. a 32kHz watch crystal) is used as a reference source and a measurementSelf Calibrating Clocks for Globally Asynchronous Locally Synchronous Systems S.W. Moore, G a local clocking mechanism based on a tunable delay line which calibrates itself from a low frequency

Mullins, Robert

264

Origin and evolution of the anchor clock escapement  

Microsoft Academic Search

The escapement is a feedback regulator that controls the speed of a mechanical clock. The first anchor escapement used in a mechanical clock was designed and applied by Robert Hooke around 1657. Its application catalyzed a rapid succession in clock and watch escapement designs over the next 50 years that revolutionized timekeeping. In this article, I consider the advances this

M. V. Headrick

2002-01-01

265

Restoration of an 18th century English clock  

Microsoft Academic Search

The background knowledge and the steps required to repair ancient clocks and watches are described. The restoration of old clocks and watches involves the problem of making them work. The wear that results from years of use and the fact that parts are lost or broken leads the restorer to replace certain component parts of the watch or clock. The

Daniel Curtit; Jean-Michel Piguet

1992-01-01

266

A new fault-tolerant algorithm for clock synchronization  

Microsoft Academic Search

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

Jennifer Lundelius; Nancy A. Lynch

1984-01-01

267

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.

268

Clock generation and distribution for the first IA64 microprocessor  

Microsoft Academic Search

The clock design for the first implementation of the IA-64 microprocessor is presented. A clock distribution with an active distributed deskewing technique is used to achieve a low skew of 28 ps. This technique is capable of compensating skews caused by within-die process variations that are becoming a sig- nificant factor of the clock design. The global, regional and local

Simon Tam; Stefan Rusu; Robert Kim; Ji Zhang; Ian Young

2000-01-01

269

Evaluation of clock synchronization protocols for Wireless Sensor Networks  

Microsoft Academic Search

In this paper we compare three clock synchronization protocols for Wireless Sensor Networks and evaluate their performances under different operating conditions. The ¿Dynamic Continuous Clock Synchronization¿ (DCCS), here is compared with the ¿Reference Broadcast Synchronization¿ (RBS) and the ¿Continuous Clock Synchronization¿ (CCS). The performance evaluation of the three protocols has been carried out via simulation using the OMNeT++ discrete event

O. Mirabella; M. Brischetto; A. Raucea

2009-01-01

270

Jitter Amplification Considerations for PCB Clock Channel Design  

Microsoft Academic Search

Jitter Amplification is a real concern in the design of PCB clock channels if the frequency of the clock is high and the PCB trace is relatively long. In this paper, we confirm the earlier finding of clock channel jitter amplification [1], using a multiple edge response (MER) simulation method instead of jitter impulse response for the channel. However, we

C. Madden; Sam Chang; Dan Oh; Chuck Yuan

2007-01-01

271

Molecular genetics of the fruit-fly circadian clock  

Microsoft Academic Search

The circadian clock percolates through every aspect of behaviour and physiology, and has wide implications for human and animal health. The molecular basis of the Drosophila circadian clock provides a model system that has remarkable similarities to that of mammals. The various cardinal clock molecules in the fly are outlined, and compared to those of their actual and ‘functional’ homologues

Ezio Rosato; Eran Tauber; Charalambos P Kyriacou

2006-01-01

272

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

SciTech Connect

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

Geha, Marla [Astronomy Department, Yale University, New Haven, CT 06520 (United States); Brown, Thomas M.; Tumlinson, Jason; Kalirai, Jason S.; Avila, Roberto J.; Ferguson, Henry C. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Simon, Joshua D. [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Kirby, Evan N. [Department of Physics and Astronomy, University of California Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States); VandenBerg, Don A. [Department of Physics and Astronomy, University of Victoria, P.O. Box 3055, Victoria, BC V8W 3P6 (Canada); Munoz, Ricardo R. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Guhathakurta, Puragra, E-mail: marla.geha@yale.edu, E-mail: tbrown@stsci.edu, E-mail: tumlinson@stsci.edu [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

2013-07-01

273

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

274

Relationship between the IMF magnitude and Pc 3 magnetic pulsations in the magnetosphere  

NASA Technical Reports Server (NTRS)

The relationships between the IMF magnitude and pulsation frequencies in the Pc 3-4 range simultaneously observed both at synchronous orbit and at low latitudes on the ground are statistically described. A theoretical discussion is given on how these observations can be interpreted in terms of the characteristic frequency of compressional Pc 3-4 magnetic pulsations in the magnetosphere, based on the well-established ion cyclotron resonance mechanism between magnetosonic mode of low-frequency upstream waves and narrowly reflected ion beams in the earth's foreshock.

Yumoto, K.; Saito, T.; Tsurutani, B. T.; Smith, E. J.; Akasofu, S.-I.

1984-01-01

275

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

276

Optimal Clock Synchronization in Networks Christoph Lenzen  

E-print Network

, and go back to sleep. If they need to exchange information, they will go back to sleep as soon Laboratory ETH Zurich, Switzerland wattenhofer@tik.ee.ethz.ch Abstract Having access to an accurate time Keywords Sensor Networks, Time Synchronization, Clock Drift, Lower Bound 1 Introduction Without doubt

277

European plans for new clocks in space  

NASA Technical Reports Server (NTRS)

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

Leschiutta, Sigfrido M.; Tavella, Patrizia

1995-01-01

278

Clock Synchronization for Multihop Wireless Sensor Networks  

ERIC Educational Resources Information Center

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

Solis Robles, Roberto

2009-01-01

279

Circadian Clock Proteins in Prokaryotes: Hidden Rhythms?  

PubMed Central

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

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

2010-01-01

280

Oscillatory Mechanisms Underlying the Murine Circadian Clock  

NSDL National Science Digital Library

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

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

2003-11-18

281

^87Sr Clock Comparisons at JILA  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

282

Evolving Biological Clocks using Genetic Regulatory Networks  

Microsoft Academic Search

We study the evolvability and dynamics of artificial genetic regulatory networks (GRNs), as active control systems, real- izing simple models of biological clocks that have evolved to respond to periodic environmental stimuli of various kinds with appropriate periodic behaviors. GRN models may differ in the evolvability of expressive regulatory dynamics. A new class of artificial GRNs with an evolvable number

Johannes F. Knabe; Chrystopher L. Nehaniv; Maria J. Schilstra; Tom Quick

283

Distant Clock Synchronization Using Entangled Photon Pairs  

E-print Network

We report a proof-of-principle experiment on distant clock synchronization. Besides the achievement of picosecond resolution at 3 kilometer distance, this experiment demonstrated a novel concept for high accuracy non-local timing and positioning based on the quantum feature of entangled states.

Alejandra Valencia; Giuliano Scarcelli; Yanhua Shih

2004-07-26

284

On the Sun, Earth, and Clocks.  

ERIC Educational Resources Information Center

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

Easton, D.

1985-01-01

285

Current Status of the Molecular Clock Hypothesis  

ERIC Educational Resources Information Center

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

Hermann, Gilbert

2003-01-01

286

Circadian Clock Function in the Mammalian Ovary.  

PubMed

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

Sellix, Michael T

2014-11-01

287

The mammalian retina as a clock  

NASA Technical Reports Server (NTRS)

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

Tosini, Gianluca; Fukuhara, Chiaki

2002-01-01

288

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. PMID:25258565

Lee, Euna

2014-01-01

289

Application of immersed MF (IMF) followed by reverse osmosis (RO) membrane for wastewater reclamation: A case study in Malaysia.  

PubMed

A pilot scale membrane plant was constructed and monitored in Shah Alam, Malaysia for municipal wastewater reclamation for industrial application purposes. The aim of this study was to verify its suitability under the local conditions and environmental constraints for secondary wastewater reclamation. Immersed-type crossflow microfiltration (IMF) was selected as the pretreatment step before reverse osmosis filtration. Secondary wastewater after chlorine contact tank was selected as feed water. The results indicated that the membrane system is capable of producing a filtrate meeting the requirements of both WHO drinking water standards and Malaysian Effluent Standard A. With the application of an automatic backwash process, IMF performed well in hydraulic performance with low fouling rate being achieved. The investigations showed also that chemical cleaning is still needed because of some irreversible fouling by microorganisms always remains. RO treatment with IMF pretreatment process was significantly applicable for wastewater reuse purposes and promised good hydraulic performance. PMID:18025737

Ujang, Z; Ng, K S; Tg Hamzah, Tg Hazmin; Roger, P; Ismail, M R; Shahabudin, S M; Abdul Hamid, M H

2007-01-01

290

The stellar IMF in early-type galaxies from a non-degenerate set of optical line indices  

NASA Astrophysics Data System (ADS)

We investigate the optical spectral region of spectra of ˜1000 stars searching for initial mass function (IMF)-sensitive features to constrain the low-mass end of the IMF slope in elliptical galaxies. The use of indicators bluer than near-infrared features (NaI, CaT, Wing-Ford FeH) is crucial if we want to compare our observations to optical simple stellar population (SSP) models. We use the MILES stellar library (Sánchez-Blázquez et al.) in the wavelength range 3500-7500 Å to select indices that are sensitive to cool dwarf stars and that do not or only weakly depend on age and metallicity. We find several promising indices of molecular TiO and CaH lines. In this wavelength range, the response of a change in the effective temperature of the cool red giant (RGB) population is similar to the response of a change in the number of dwarf stars in the galaxy. We therefore investigate the degeneracy between IMF variation and ?Teff, RGB, and show that it is possible to break this degeneracy with the new IMF indicators defined here. In particular, we define a CaH1 index around ?6380 Å that arises purely from cool dwarfs, does not strongly depend on age and is anticorrelated with [?/Fe]. This index allows the determination of the low-mass end of the IMF slope from integrated-light measurements when combined with different TiO lines and age- and metallicity-dependent features such as H?, Mgb, Fe5270 and Fe5335. The use of several indicators is crucial to break degeneracies between IMF variations, age, abundance pattern and effective temperature of the cool red giant (RGB) population. We measure line-index strengths of our new optical IMF indicators in the Conroy & van Dokkum SSP models and compare these with index strengths of the same spectral features in a sample of stacked Sloan Digital Sky Survey early-type galaxy spectra with varying velocity dispersions. Using different indicators, we find a clear trend of a steepening IMF with increasing velocity dispersion from 150 to 310 km s-1 described by the linear equation x = (2.3 ± 0.1) log ?200 + (2.13 ± 0.15), where x is the IMF slope and ?200 is the central stellar velocity dispersion measured in units of 200 km s-1. We test the robustness of this relation by repeating the analysis with 10 different sets of indicators. We found that the NaD feature has the largest impact on the IMF slope, if we assume solar [Na/Fe] abundance. By including NaD, the slope of the linear relation increases by 0.3 (2.6 ± 0.2). We compute the `IMF mismatch' parameter as the ratio of stellar mass-to-light ratio predicted from the x-?200 relation to that inferred from SSP models assuming a Salpeter IMF and find good agreement with independent published results.

Spiniello, Chiara; Trager, Scott; Koopmans, Léon V. E.; Conroy, Charlie

2014-02-01

291

Angles of Reflection  

NSDL National Science Digital Library

This interactive simulation shows what happens to light when it hits a mirror. The simluation allows the user to change the angle of the incoming or incident light wave and see the corresponding reflected angle.

Davidson, Michael W.; Tchourioukanov, Kirill I.

2006-06-15

292

The Stellar IMF, Core Mass Function, & The Last-Crossing Distribution  

E-print Network

Hennebelle & Chabrier 2008 (HC08) attempted to derive the stellar IMF as a consequence of turbulent density fluctuations, using an argument similar to Press & Schechter 1974 for Gaussian random fields. Like that example, however, this solution does not resolve the 'cloud in cloud' problem; it also does not extend to large scales that dominate the velocity/density fluctuations. In principle, these can change the results at the order-of-magnitude level. Here, we use the results from Hopkins 2011 (H11) to generalize the excursion set formalism and derive the exact solution in this regime. We argue that the stellar IMF and core mass function (CMF) should be associated with the last-crossing distribution, i.e. the mass spectrum of bound objects defined on the smallest scale on which they are self-gravitating. This differs from the first-crossing distribution (mass function on the largest self-gravitating scale) which is defined cosmologically and which H11 show corresponds to the GMC mass function in disks...

Hopkins, Philip F

2012-01-01

293

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

294

On the importance of IMF |BY| on polar cap patch formation  

NASA Astrophysics Data System (ADS)

A number of poleward-moving events were observed between 1130-1300 UT on 11 Feb 2004, during periods of southward interplanetary magnetic field (IMF), while the steerable antenna of the EISCAT Svalbard Radar (ESR) and the Tromsø VHF Radar pointed nearly northward at low elevation. In this interval, simultaneous SuperDARN CUTLASS Finland radar measurements showed poleward-moving radar aurora forms (PMRAFs) which appeared very similar to the density enhancements observed by the ESR northward-pointing antenna. These events appeared quasi-periodically with a period of about 10 minutes. Comparing the observations from the above three radars, it is inferred that there is an almost one-to-one correspondence between the Poleward-Moving Plasma Concentration Enhancements (PMPCEs) observed by the ESR and the VHF radar, and the PMRAFs measured by the CUTLASS Finland radar. These observations are consistent with the interpretation that the polar cap patch material was generated by photo-ionisation at sub-auroral latitudes, and that the plasma was structured by bursts of magnetopause reconnection giving access to the polar cap. There is clear evidence that plasma structuring into patches was dependent on the variability in IMF |BY|. The duration of these events implies that the average evolution time of the newly opened flux tubes from the sub-auroral region to the polar cap was about 33 minutes.

Zhang, Q.-H.; Zhang, B.-C.; Liu, R.-Y.; Dunlop, M. W.; Lockwood, M.; Moen, J.; Yang, H.-G.; Hu, H.-Q.; Hu, Z.-J.; Liu, S.-L.; McCrea, I.; Lester, M.

2012-04-01

295

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

296

Type IIn Supernova Detections in z˜2 Lyman Break Galaxies: Probing the IMF Directly  

NASA Astrophysics Data System (ADS)

Type IIn supernovae (SNe IIn) exhibit luminous ultraviolet continua during outburst and luminous, long-lived narrow ultraviolet and optical emission lines attributed to circumstellar interaction. These properties have enabled successful detections at z˜2 in archival imaging and continued investigations from late-time spectroscopy. Because SNe IIn are believed to have massive (?50M?) progenitors, searches in the well-studied Lyman break galaxy (LBG) host population offer the prospect of testing the form of the high-redshift stellar initial mass function (IMF) in a high density star formation environment directly. I briefly discuss our z˜2 photometric detection method targeting LBGs in the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) and present data from the first 6 confirmed z˜2 SNe IIn pulled from 30 photometric SN candidates. A comparison of the color and magnitude distributions of the SN host galaxies to that of the full LBG sample finds that z˜2 SNe preferentially occur in bluer, fainter galaxies. I conclude with a discussion of an approach that uses the CFHTLS pilot sample to provide a first estimate of the form of the high-redshift IMF. Upcoming deep synoptic imaging surveys will greatly improve z˜2 SNe IIn statistics from ˜105 expected detections and future large aperture space- and ground-based telescopes will have the sensitivities to extend this work to ?6.

Cooke, J.; Sullivan, M.; Barton, E. J.; Ellis, R. S.; Gal-Yam, A.

2011-06-01

297

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

NASA Astrophysics Data System (ADS)

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

Lu, Jessica

2014-10-01

298

Clock gene variants differentiate mood disorders.  

PubMed

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

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

2014-09-26

299

Entangling the lattice clock: Towards Heisenberg-limited timekeeping  

SciTech Connect

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

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

2010-03-15

300

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

301

Near-earth magnetotail shape and size as determined from the magnetopause flaring angle  

SciTech Connect

Knowledge of the average size and shape of the near-Earth magnetotail is an essential element for our understanding of the magnetospheric response to the influence of the solar wind. An empirical model of the near-Earth magnetotail has been developed, which depends upon distance downtail (x{sub GSM}), the solar wind momentum flux ({rho}v{sup 2}{sub SW}), and the Z{sub GSM} component of the interplanetary magnetic field (IMF B{sub z}). This model has been created by using the pressure balance relation to calculate a set of flare angles for the nightside magnetopause in the region {minus}22 R{sub E} {le}X{sub GSM} {le}{minus}10 R{sub E}. Observations of the magnetic field in the lobe by ISEE 2 and simultaneous observations of the magnetic field and plasma properties of the solar wind by IMP 8 were used to determine the internal and external pressure components, respectively. Examination of calculated flare angle values reveal a dependence upon downtail distance and {rho}v{sup 2}{sub SW}. Normalized to the median downtail distance and dynamic pressure, the angle of flare of the magnetopause is found to increase linearly with decreasing B{sub Z} when the IMF is southward, but there is little variation when the IMF is northward. The empirical function derived for the flaring angle of the magnetotail is used to determine a relation for the radius of the tail. Comparisons with previous empirical models and results are also performed. In addition, values of magnetic flux within the magnetotail are calculated for times of sudden impulse events. 43 refs., 17 figs., 4 tabs.

Petrinec, S.M.; Russell, C.T. [Univ. of California, Los Angeles, CA (United States)] [Univ. of California, Los Angeles, CA (United States)

1996-01-01

302

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

303

The response of the large scale ionospheric convection pattern to changes in the IMF and substorms - Results from the SUNDIAL 1987 campaign  

Microsoft Academic Search

Multipoint observations of ionospheric convection, made during the SUNDIAL 1987 campaign (May 29 to June 8) which included two intervals of variable IMF Bz and By and several substorms, are used to examine the response of the ionospheric convection in the postdusk and midnight sectors to changes in the IMF Bz component, as well as the effect of substorms on

M. Lester; O. de La Beaujardiere; J. C. Foster; M. P. Freeman; H. Luehr; J. M. Ruohoniemi; W. Swider

1993-01-01

304

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

305

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

306

The IMF of the open star cluster NGC 581 (M103): A deviation from Salpeter's law?  

NASA Astrophysics Data System (ADS)

Membership determination is an essential tool to derive the initial mass function (IMF, for comprehensive reviews see Scalo 1986, 1998) of open star clusters, as the contamination of the data with field stars is a major problem. Two methods are in use nowadays and each of them has its advantages and disadvantages: The classical method is to distinguish between cluster and field stars by their proper motions: We can expect that all the cluster stars move in the same way, whereas the field stars show different proper motions. Therefore, we can derive a membership probability for each detected star. As both old and recent photographic plates are needed to measure the proper motions, this method is limited by the poor sensitivity (compared with CCD) of the old plates. With the introduction of CCD imaging to astronomy, the method of statistical field star subtraction became more popular. Assuming that the field stars within the cluster area are distributed in a similar way compared to those nearby, the distribution of the field stars can be subtracted from that of the (contaminated) cluster area. This makes sense for fainter stars only because of small number statistics for the bright stars. Our project aims at a combination of these two methods for the membership determination: For the bright stars in a field of a cluster, a proper motion study is made while the faint members are selected by a statistical field star subtraction. From the cleaned data we will derive the luminosity and mass functions of the clusters. The shape of the IMF is to be studied as well as a possible inhomogenity of the mass distribution within the clusters. Finally, the universality of the IMF is to be tested. We presented proper motions and CCD photometry of stars in the region of the open star cluster NGC 581 (M 103). Fitting isochrones of the Padua group (Bertelli et al. 1994) to the colour-magnitude diagram, we derived the following parameters for the object: log t = 7.3 (i.e. t = 2107 years), Z = 0.02, EB-V = 0.40 mag, m - M = 12.3 mag (which leads to a distance of r = 1.6 kpc). We found a very steep slope of ? = -2.05 ± 0.09 for the initial mass function of NGC 581. This result is in good agreement with previous studies of Phelps & Janes (1993, 1994) who found ? = -1.78 for NGC 581, but does not fit to the value of ? = -1.35 for the solar neigbourhood (Salpeter 1955).

Sanner, Jörg; Geffert, Michael; Schmoll, Jürgen

307

Tissue-specific clocks in Arabidopsis show asymmetric coupling.  

PubMed

Many organisms rely on a circadian clock system to adapt to daily and seasonal environmental changes. The mammalian circadian clock consists of a central clock in the suprachiasmatic nucleus that has tightly coupled neurons and synchronizes other clocks in peripheral tissues. Plants also have a circadian clock, but plant circadian clock function has long been assumed to be uncoupled. Only a few studies have been able to show weak, local coupling among cells. Here, by implementing two novel techniques, we have performed a comprehensive tissue-specific analysis of leaf tissues, and show that the vasculature and mesophyll clocks asymmetrically regulate each other in Arabidopsis. The circadian clock in the vasculature has characteristics distinct from other tissues, cycles robustly without environmental cues, and affects circadian clock regulation in other tissues. Furthermore, we found that vasculature-enriched genes that are rhythmically expressed are preferentially expressed in the evening, whereas rhythmic mesophyll-enriched genes tend to be expressed in the morning. Our results set the stage for a deeper understanding of how the vasculature circadian clock in plants regulates key physiological responses such as flowering time. PMID:25363766

Endo, Motomu; Shimizu, Hanako; Nohales, Maria A; Araki, Takashi; Kay, Steve A

2014-11-20

308

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

309

Tissue-specific clocks in Arabidopsis show asymmetric coupling  

PubMed Central

Many organisms rely on a circadian clock system to adapt to daily and seasonal environmental changes. The mammalian circadian clock consists of a central clock in the suprachiasmatic nucleus that is tightly coupled and synchronizes other clocks in peripheral tissues1, 2. Plants also have a circadian clock, but plant circadian clock function has long been assumed to be uncoupled3. Only a few studies have been able to show a weak, local coupling among cells4, 5, 6, 7. Here, by implementing two novel techniques, we have performed a comprehensive tissue-specific analysis of leaf tissues, and we have discovered that the vasculature and mesophyll clocks asymmetrically regulate each other in Arabidopsis. The circadian clock in the vasculature has characteristics distinct from other tissues, cycles robustly without environmental cues, and affects circadian clock regulation in other tissues. Furthermore, we found that vasculature-enriched genes that are rhythmic are preferentially expressed in the evening, whereas rhythmic mesophyll-enriched genes tend to be expressed in the morning. Our results set the stage for a deeper understanding of how the vasculature circadian clock in plants regulates key physiological responses such as flowering time. PMID:25363766

Endo, Motomu; Shimizu, Hanako; Nohales, Maria A.; Araki, Takashi; Kay, Steve A.

2014-01-01

310

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

311

Genetic Analysis of Ectopic Circadian Clock Induction in Drosophila  

PubMed Central

Cell-autonomous feedback loops underlie the molecular oscillations that define circadian clocks. In Drosophila the transcription factor Clk activates multiple clock components of feedback loops many of which feed back and regulate Clk expression or activity. Previously the authors evoked similar molecular oscillations in putatively naïve neurons in Drosophila by ectopic expression of a single gene, Clk, suggesting a master regulator function. Using molecular oscillations of the core clock component PERIOD (PER), the authors observed dramatic and widespread molecular oscillations throughout the brain in flies expressing ectopic Clk. Consistent with the master regulator hypothesis, they found that Clk is uniquely capable of inducing ectopic clocks as ectopic induction of other clock components fails to induce circadian rhythms. Clk also induces oscillations even when expression is adult restricted, suggesting that ectopic clocks can even be induced in differentiated cells. However, if transgene expression is discontinued, PER expression disappears, indicating that Clk must be continually active to sustain ectopic clock function. In some cases Clk-mediated PER induction was observed without apparent synchronous cycling, perhaps due to desynchronization of rhythms between clocks or truly cell autonomous arrhythmic PER expression, indicating that additional factors may be necessary for coherent rhythms in cells ectopically expressing Clk. To determine minimal requirements for circadian clock induction by Clk, the authors determined the genetic requirements of ectopic clocks. No ectopic clocks are induced in mutants of Clk’s heterodimeric partner cyc. In addition, noncycling PER is observed when ectopic Clk is induced in a cryb mutant background. While other factors may contribute, these results indicate that persistent Clock induction is uniquely capable of broadly inducing ectopic rhythms even in adults, consistent with a special role at the top of a clock gene hierarchy. PMID:19755582

Kilman, Valerie L.; Allada, Ravi

2011-01-01

312

Metabolism and the Circadian Clock Converge  

PubMed Central

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

Eckel-Mahan, Kristin

2013-01-01

313

Clock-Driven Quantum Thermal Engines  

E-print Network

We consider an isolated autonomous quantum machine, where an explicit quantum clock is responsible for performing all transformations on an arbitrary quantum system (the engine), via a time-independent Hamiltonian. In a general context, we show that this model can exactly implement any energy-conserving unitary on the engine, without degrading the clock. Furthermore, we show that when the engine includes a quantum work storage device we can approximately perform completely general unitaries on the remainder of the engine. This framework can be used in quantum thermodynamics to carry out arbitrary transformations of a system, with accuracy and extracted work as close to optimal as desired, whilst obeying the first and second laws of thermodynamics. We thus show that autonomous thermal machines suffer no intrinsic thermodynamic cost compared to externally controlled ones.

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

2014-12-03

314

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.

315

The suprachiasmatic nuclei as a seasonal clock.  

PubMed

In mammals, the suprachiasmatic nucleus (SCN) contains a central clock that synchronizes daily (i.e., 24-h) rhythms in physiology and behavior. SCN neurons are cell-autonomous oscillators that act synchronously to produce a coherent circadian rhythm. In addition, the SCN helps regulate seasonal rhythmicity. Photic information is perceived by the SCN and transmitted to the pineal gland, where it regulates melatonin production. Within the SCN, adaptations to changing photoperiod are reflected in changes in neurotransmitters and clock gene expression, resulting in waveform changes in rhythmic electrical activity, a major output of the SCN. Efferent pathways regulate the seasonal timing of breeding and hibernation. In humans, seasonal physiology and behavioral rhythms are also present, and the human SCN has seasonally rhythmic neurotransmitter levels and morphology. In summary, the SCN perceives and encodes changes in day length and drives seasonal changes in downstream pathways and structures in order to adapt to the changing seasons. PMID:25451984

Coomans, Claudia P; Ramkisoensing, Ashna; Meijer, Johanna H

2014-11-20

316

Analysis of atom-interferometer clocks  

NASA Astrophysics Data System (ADS)

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

Peil, Steven; Ekstrom, Christopher R.

2014-01-01

317

Clock distribution system for digital computers  

DOEpatents

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

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

1981-01-01

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

The response of the high-latitude dayside ionosphere to an abrupt northward transition in the IMF  

NASA Technical Reports Server (NTRS)

We examine the response of the high-latitude ionosphere in the prenoon sector to a northward turning of the IMF. The event was observed in the 11-13 UT interval on June 1, 1987, in the course of a multiday SUNDIAL campaign. The transition in the IMF was observed by the IMP-8 satellite which was located upstream of the earth at a distance of 36 Re. The ionospheric response in the 70-80 deg invariant latitude interval was monitored by two radars. The preexisting plasma convection observed by the radars exhibited large velocities (500-1000 m/s) and stable longterm trends, consistent with the inertial rotation of the convection pattern expected of the conditions then prevailing, B(z) less than 0, B(y) greater than 0. The plasma flow rapidly abated in response to the IMF transition. The electron density measurements made by radar in the meridional plane showed that the ionosphere had been rich in structure with the active deposition of ionization by particle precipitation. Subsequently it resembled an inactive, unstructured mid-latitude configuration. There was a dramatic decrease in the amount of backscatter observed by the HF radar. We analyze the times of transition in the various data sets and show that the ionosphere began to show the effects of the IMF transition about 2 min after its probable arrival at the magnetopause boundary.

Ruohoniemi, J. M.; Greenwald, R. A.; De La Beaujardiere, O.; Lester, M.

1993-01-01

320

The response of the high-latitude dayside ionosphere to an abrupt northward transition in the IMF  

NASA Astrophysics Data System (ADS)

We examine the response of the high-latitude ionosphere in the prenoon sector to a northward turning of the IMF. The event was observed in the 11-13 UT interval on June 1, 1987, in the course of a multiday SUNDIAL campaign. The transition in the IMF was observed by the IMP-8 satellite which was located upstream of the earth at a distance of 36 Re. The ionospheric response in the 70-80 deg invariant latitude interval was monitored by two radars. The preexisting plasma convection observed by the radars exhibited large velocities (500-1000 m/s) and stable longterm trends, consistent with the inertial rotation of the convection pattern expected of the conditions then prevailing, B(z) less than 0, B(y) greater than 0. The plasma flow rapidly abated in response to the IMF transition. The electron density measurements made by radar in the meridional plane showed that the ionosphere had been rich in structure with the active deposition of ionization by particle precipitation. Subsequently it resembled an inactive, unstructured mid-latitude configuration. There was a dramatic decrease in the amount of backscatter observed by the HF radar. We analyze the times of transition in the various data sets and show that the ionosphere began to show the effects of the IMF transition about 2 min after its probable arrival at the magnetopause boundary.

Ruohoniemi, J. M.; Greenwald, R. A.; de La Beaujardiere, O.; Lester, M.

1993-07-01

321

Statistical Properties of the Solar Wind and IMF at 1 AU  

NASA Astrophysics Data System (ADS)

During the declining phase of the solar cycle the evolution of the solar magnetic field produces large regions of unipolar magnetic field that create coronal holes and are the sources of high speed solar wind streams. These streams overtake and interact with slow solar wind emitted from the equatorial belt of closed magnetic field lines. These interaction regions corotate (CIR) with the Sun and sweep across the Earth once per solar rotation. Inside a CIR the properties of the solar wind are well organized by time relative to the interface between the two streams (epoch time). We have compiled lists of stream interfaces in solar cycle #22 (1994- 1996) and in cycle #23 (2003-2005) and used them to study the systematic properties of the solar wind and interplanetary magnetic field at 1 AU. We present the results as dynamic cumulative probability distributions (cdf) for different variables and as traces of the quartiles of these distributions as function of epoch time. We find that the solar wind is highly organized relative to the stream interface and therefore that geomagnetic activity driven by this wind is organized as well. This systematic behavior provides the basis for probabilistic forecasting by air mass climatology. If one can predict the arrival of a stream interface then within certain limits one can predict the probability that various measures of geomagnetic activity will lie within a given range. We also find that the climatology of the solar wind as measured at the Earth has a semiannual variation as a consequence of two different effects: the axial effect that causes the Earth to be at high or low heliographic latitude near equinoxes and the Rosenberg-Coleman (R-C) effect which states that the fraction of time the Earth samples a particular polarity of the IMF is dominated by the polar magnetic field of the Sun emanating from the hemisphere in which the Earth is located. A third phenomenon the Russell-McPherron (R-M) effect is important for the Earth and geomagnetic activity. In GSM coordinates the azimuthal component of the IMF (By) will have a negative projection on the Z-axis according to the rule "Spring to Fall away". A negative projection allows magnetic reconnection between the IMF and the Earth's magnetic field. The R-M effect in combination with the R-C and axial effects leads to the semiannual variation of geomagnetic activity. Another important effect is the 22-year Hale cycle of the solar magnetic field. Each solar cycle the dipole moment of the Sun reverses shortly after solar maximum. This has the effect of reversing the sector structure of the IMF at the Earth reversing the sign of the projection of By and hence decreasing the probability of reconnection. This makes the declining phase of even solar cycles (1995) slightly more geoeffective that of odd cycles (2006). Finally there is evidence that there is a real difference in the nature of solar magnetic activity between odd and even cycles further influencing the properties of the solar wind at 1 AU.

McPherron, R. L.

2006-12-01

322

Around the Tarantula and into the Arches: A Salpeter IMF in the Field and in Clusters  

NASA Astrophysics Data System (ADS)

We propose that NGC 2070, the ionizing cluster of the Tarantula nebula, has the best determined stellar initial mass function (IMF), and that with a power-law slope at 2.17±0.05 it defines what we call Salpeter. The result of a Bayesian analysis of data for the field of the 30 Doradus super-association and for the Arches cluster near the galactic center, previously thought as counter-examples to the universality hypothesis, show that both of them are consitent with a Salpeter slope. We also show that there is no contradiction in principle to have the same stellar mass function in clusters and in the field population independently of what the cluster mass function is.

Selman, F. J.; Espinoza, P.; Melnick, J.

2011-06-01

323

Case Study of Solar Wind and IMF Influence on Ionospheric Outflow  

NASA Technical Reports Server (NTRS)

We examine ionospheric outflows in the high attitude magnetospheric polar cap during the POLAR satellite's apogee on 04/19/96 using the TIDE instrument. The pass has a fairly constant flux of H+ which is similar to many other passes, but there is a large amount of O+ present. The elevated levels of O+ may be due both to the geophysical conditions during the apogee pass (Kp=5) and prior to the pass. When the outflows for many high altitude polar cap passes are analyzed the O+ density correlates well with the dynamic pressure. There are several aspects of this pass which are interesting besides the abundance of O+ relative to H+. In this pass both the H+ and O+ outflow velocity correlate with both the solar wind speed and Interplanetary Magnetic Field (IMF) Bx. The geophysical conditions are such that the solar wind speed and IMF Bx are highly correlated with each other. For this case the dynamic pressure of the solar wind is fairly constant and has an average value of about 2.5 nPa which is typical for the solar wind, but the average solar wind speed is about 695 km/s which is greater than 450 km/s which is typical for the solar wind at I AU. The ion outflow measurements themselves are interrelated. The H+ density and parallel speed are anticorrelated which results in the constant flux. The 0+ density does not have as large of a anticorrelation with its parallel speed as H+ does with its parallel speed.

Elliott, H. A.; Comfort, R. H.; Craven, P. D.; Chandler, M. O.; Moore, T. E.; Rose, M. Franklin (Technical Monitor)

2000-01-01

324

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

NASA Astrophysics Data System (ADS)

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

Tang, Baitian; Worthey, Guy

2015-01-01

325

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

Microsoft Academic Search

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

Yibin Ye; Kaushik Roy; Georgios I. Stamoulis

1997-01-01

326

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

Microsoft Academic Search

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

Yibin Ye; K. Roy; G. I. Stamoulis

1997-01-01

327

Circadian Clocks in Antennal Neurons Are Necessary and Sufficient for Olfaction Rhythms in Drosophila  

Microsoft Academic Search

Background: The Drosophila circadian clock is controlled by interlocked transcriptional feedback loops that operate in many neuronal and nonneuronal tissues. These clocks are roughly divided into a central clock, which resides in the brain and is known to control rhythms in locomotor activity, and peripheral clocks, which comprise all other clock tissues and are thought to control other rhythmic outputs.

Shintaro Tanoue; Parthasarathy Krishnan; Balaji Krishnan; Stuart E Dryer; Paul E Hardin

2004-01-01

328

Solidifying the solid angle.  

PubMed

This paper evaluates the position of the solid angle in its application to modeling in electrocardiology. Particular attention is paid to the use of the solid angle for linking cardiac electric activity to the potentials observed on the body surface. In this application, the solid angle is a dominant factor in the expression of the sources during depolarization known as the uniform double layer. In the related equivalent double layer model, the contributions of the elementary sources are also expressed in terms of solid angles, their strength not being uniform. A recently developed theory allows the equivalent double layer to be applied to both depolarization and repolarization. PMID:12539116

van Oosterom, A

2002-01-01

329

Universal IMF versus dark halo response in early-type galaxies: breaking the degeneracy with the Fundamental Plane  

NASA Astrophysics Data System (ADS)

We use the relations between aperture stellar velocity dispersion (?ap), stellar mass (MSPS) and galaxy size (Re) for a sample of ˜150 000 early-type galaxies from Sloan Digital Sky Survey/DR7 to place constraints on the stellar initial mass function (IMF) and dark halo response to galaxy formation. We build ? cold dark matter-based mass models that reproduce, by construction, the relations between galaxy size, light concentration and stellar mass, and use the spherical Jeans equations to predict ?ap. Given our model assumptions (including those in the stellar population synthesis models), we find that reproducing the median ?ap versus MSPS relation is not possible with both a universal IMF and a universal dark halo response. Significant departures from a universal IMF and/or dark halo response are required, but there is a degeneracy between these two solutions. We show that this degeneracy can be broken using the strength of the correlation between residuals of the velocity-mass (?log ?ap) and size-mass (?log Re) relations. The slope of this correlation, ?VR ? ?log ?ap/?log Re, varies systematically with galaxy mass from ?VR ? -0.45 at MSPS ˜ 1010 M? to ?VR ? -0.15 at MSPS ˜ 1011.6 M?. The virial Fundamental Plane (FP) has ?VR = -1/2, and thus we find that the tilt of the observed FP is mass dependent. Reproducing this tilt requires both a non-universal IMF and a non-universal halo response. Our best model has mass-follows-light at low masses (MSPS ? 1011.2 M?) and unmodified Navarro, Frenk and White haloes at MSPS ˜ 1011.5 M?. The stellar masses imply a mass-dependent IMF which is `lighter' than Salpeter at low masses and `heavier' than Salpeter at high masses.

Dutton, Aaron A.; Macciò, Andrea V.; Mendel, J. Trevor; Simard, Luc

2013-07-01

330

Integrated power clock generators for low energy logic  

Microsoft Academic Search

Low-energy (adiabatic) logic families have been proposed to reduce energy consumption of VLSI logic devices. Instead of the conventional DC power supply, these logic families require AC power supplies (power clocks) that allow energy recovery and also serve as timing clocks for the logic. In this paper, high-frequency resonant DC\\/AC inverters are proposed as power clock generators where all power

D. Maksimovic; V. G. Oklobdzija

1995-01-01

331

Circadian clocks and phosphorylation: Insights from computational modeling  

Microsoft Academic Search

Circadian clocks are based on a molecular mechanism regulated at the transcriptional, translational and post-translational\\u000a levels. Recent experimental data unravel a complex role of the phosphorylations in these clocks. In mammals, several kinases\\u000a play differential roles in the regulation of circadian rhythmicity. A dysfunction in the phosphorylation of one clock protein\\u000a could lead to sleep disorders such as the Familial

Jean-Christophe Leloup

2009-01-01

332

Higher Pole Linear Traps for Atomic Clock Applications  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

333

All-Optical NRZ-DPSK Clock Recovery Using Chromatic-Dispersion-Induced Clock Tone  

Microsoft Academic Search

All-optical clock recovery (CR) from 10-Gb\\/s nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signal is demonstrated experimentally by introducing the chromatic-dispersion-induced clock tone into a free-running semiconductor optical amplifier (SOA)-based fiber ring laser for achieving mode-locking. Since no special component is required for NRZ-DPSK demodulation, our proposed method is very promising because of its simple configuration and better stability. The good performance of

Songnian Fu; M. Tang; Wen-De Zhong; Yang Jing Wen; P. Shum

2007-01-01

334

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

SciTech Connect

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

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

2013-01-01

335

Prospects for Optical Clocks with a Blue-Detuned Lattice  

SciTech Connect

We investigated the properties of optical lattice clocks operated with a repulsive light-shift potential. The magic wavelength, where light-shift perturbation for the clock transition cancels, was experimentally determined to be 389.889(9) nm for {sup 87}Sr. The hyperpolarizability effects on the clock transition were investigated theoretically. With minimal trapping field perturbation provided by the blue-detuned lattice, the fractional uncertainty due to the hyperpolarizability effects was found to be 2x10{sup -19} in the relevant clock transition.

Takamoto, M.; Katori, H.; Marmo, S. I.; Ovsiannikov, V. D.; Pal'chikov, V. G. [Department of Applied Physics, Graduate School of Engineering, University of Tokyo, Bunkyo-ku, 113-8656 Tokyo (Japan); CREST, Japan Science and Technology Agency, 4-1-8 Honcho Kawaguchi, 332-0012 Saitama (Japan); Physics Department, Voronezh State University, Universitetskaya pl.1, 394006, Voronezh (Russian Federation); Institute of Metrology for Time and Space at National Research Institute for Physical-Technical and Radiotechnical Measurements, Mendeleevo, Moscow Region, 141579 (Russian Federation)

2009-02-13

336

The circadian clock starts ticking at a developmentally early stage.  

PubMed

Although overt diurnal rhythms of behavior do not begin until well after birth, molecular studies suggest that the circadian clock may begin much earlier at a cellular level: mouse embryonic fibroblasts, for example, already possess robust clocks. By multiple criteria, we found no circadian clock present in mouse embryonic stem cells. Nevertheless, upon their differentiation into neurons, circadian gene expression was observed. In the first steps along the pathway from ES cells to neurons, a neural precursor cell (NPC) line already showed robust circadian oscillations. Therefore, at a cellular level, the circadian clock likely begins at the very earliest stages of mammalian development. PMID:21135160

Kowalska, Elzbieta; Moriggi, Ermanno; Bauer, Christoph; Dibner, Charna; Brown, Steven A

2010-12-01

337

Crosstalk between the Circadian Clock and Innate Immunity in Arabidopsis  

PubMed Central

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

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

2013-01-01

338

Clock distribution and synchronization in large digital systems  

E-print Network

). As shown in Fig. 1, the clock distribution network is formed by a pair of closely matched rings, and clock signals are assumed to be propagated at a constant speed. Each clock signal generated by the master node is fanned out into a pair of twin signals..., and the twin signals are transmitted on the two rings in opposite direction. Unless a node is located exactly at the middle of the ring, the node reccivcs the twin signals at different time instants. Then, the difference of clock receiving times between...

Hung, Tzu-Chien

1991-01-01

339

Space Clocks to Test Relativity: ACES and Beyond  

NASA Astrophysics Data System (ADS)

Atomic clocks are an outstanding tool for the experimental verification of general relativity and more generally for fundamental astronomy (VLBI, pulsar timing, navigation, etc). Recent years have seen a rapid improvement in the performance of such clocks, promising new improved tests of relativity, in particular onboard terrestrial and interplanetary space missions. However, the use of such high accuracy clocks onboard spacecraft also requires detailed modelling and data analysis within the frame of general relativity and/or alternative theoretical frameworks. In this talk I present the Atomic Clock Ensemble in Space (ACES) mission, a joint ESA/CNES project to be launched in 2012, with particular emphasis on relativistic aspects and the corresponding data analysis. The mission consists of two high accuracy atomic clocks (a hydrogen maser and a laser cooled Cs atomic clock) to be installed onboard the International Space Station (ISS) and a high performance microwave link (MWL) allowing the comparison between ground and space clocks. The second part of the talk will be devoted to future missions making use of the more recent development of optical clocks and optical comparison methods, in particular the SAGAS project (Search for Anomalous Gravitation using Atomic Sensors), that aims to fly an optical atomic clock on a solar system escape trajectory with science objectives in fundamental physics and solar system science (arXiv: 0711.0304).

Wolf, Peter

2009-05-01

340

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

341

A Cavity Enhanced ^87Sr Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

Optical lattice clocks based on alkaline earth atoms have the potential to outperform single atomic ion clocks (the best clocks to date) [1,2]. The promise of lattice clocks is due to their larger atom numbers, for quantum projection noise limited atomic clocks average down like 1 / ?Natoms. Our new ^87Sr optical lattice clock utilizes a cavity enhanced 1D magic wavelength lattice to further improve our atom number [3]. The circulating power in our cavity allows us to operate at larger trap volumes than our previous retroreflected configuration while maintaining reasonable trap depths. These larger trap volumes enable us to transfer many more atoms into our lattice, improving our signal to noise. We will discuss our new cavity lattice clock system, and progress toward a comparison of two JILA lattice clocks will also be discussed. We will also touch on our goal of a 3D cavity enhanced lattice clock geometry. [4pt] [1] A.D. Ludlow et al, Science 319, 1805 (2008)[0pt] [2] T. Rosenband et al, Science 319, 1808 (2008)[0pt] [3] P.G. Westergaard et al, PRL 106, 210801 (2011)

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

2012-06-01

342

Prospects for Optical Clocks with a Blue-Detuned Lattice  

NASA Astrophysics Data System (ADS)

We investigated the properties of optical lattice clocks operated with a repulsive light-shift potential. The magic wavelength, where light-shift perturbation for the clock transition cancels, was experimentally determined to be 389.889(9) nm for Sr87. The hyperpolarizability effects on the clock transition were investigated theoretically. With minimal trapping field perturbation provided by the blue-detuned lattice, the fractional uncertainty due to the hyperpolarizability effects was found to be 2×10-19 in the relevant clock transition.

Takamoto, M.; Katori, H.; Marmo, S. I.; Ovsiannikov, V. D.; Pal'Chikov, V. G.

2009-02-01

343

Clock genes show circadian rhythms in salivary glands.  

PubMed

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

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

2012-08-01

344

DIP ANGLE MEASURING DEVICE  

E-print Network

tude of the angle between the true horizon and the visible horizon known as the angle .... chred within the bearing by a support member 38 which is screwed onto the ... and the bearing. 55 to prevent a metal to metal contact, and a steel spring.

Boris J. Gavrisheff

345

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

346

Reading Angles in Maps  

ERIC Educational Resources Information Center

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

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

2014-01-01

347

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.

Barbara Henry

2012-04-16

348

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

PubMed Central

In mammals, immediate-early transcription of the Period 1 (Per1) gene is crucial for resetting the mammalian circadian clock. Here, we show that CLOCK is a real signalling molecule that mediates the serum-evoked rapid induction of Per1 in fibroblasts through the Ca2+-dependent protein kinase C (PKC) pathway. Stimulation with serum rapidly induced nuclear translocation, heterodimerization and Ser/Thr phosphorylation of CLOCK just before the surge of Per1 transcription. Serum-induced CLOCK phosphorylation was abolished by treatment with PKC inhibitors but not by other kinase inhibitors. Consistently, the interaction between CLOCK and PKC was markedly increased shortly after serum shock, and the Ca2+-dependent PKC isoforms PKC? and PKC? phosphorylated CLOCK in vitro. Furthermore, phorbol myristic acetate treatment triggered immediate-early transcription of Per1 and also CLOCK phosphorylation, which were blocked by a Ca2+-dependent PKC inhibitor. These findings indicate that CLOCK activation through the Ca2+-dependent PKC pathway might have a substantial role in phase resetting of the circadian clock. PMID:17347670

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

2007-01-01

349

Observation of Spin Polarized Clock Transition in 87Sr Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

We report our observation of the spin polarized 1S0 ? 3P0 clock transition spectrum in an optical lattice clock based on fermionic 87Sr. The atoms are trapped and pre-cooled to about 2 ?K with two stages of laser cooling at 461 nm and 689 nm, respectively. Then the atoms are loaded into an optical lattice formed by the interference of counter-propagating laser beams at 813 nm. An external cavity diode laser at 698 nm, which is stabilized to a high finesse cavity with a linewidth of about 5 Hz and a drift rate of less than 0.2 Hz/s, is used to excite the atoms to the 3P0 state. The ?-polarized clock transition spectrum of resolvable mF states is obtained by applying a small bias magnetic field along the polarization axis of the probe beam. A spin polarized clock transition spectrum as narrow as 10 Hz with an 80 ms probe pulse is obtained.

Wang, Qiang; Lin, Yi-Ge; Li, Ye; Lin, Bai-Ke; Meng, Fei; Zang, Er-Jun; Li, Tian-Chu; Fang, Zhan-Jun

2014-12-01

350

Development and entrainment of the colonic circadian clock during ontogenesis.  

PubMed

Colonic morphology and function change significantly during ontogenesis. In mammals, many colonic physiological functions are temporally controlled by the circadian clock in the colon, which is entrained by the central circadian clock in the suprachiasmatic nuclei (SCN). The aim of this present study was to ascertain when and how the circadian clock in the colon develops during the perinatal period and whether maternal cues and/or the developing pup SCN may influence the ontogenesis of the colonic clock. Daily profiles of clock genes Per1, Per2, Cry1, Cry2, Rev-erb?, Bmal1, and Clock expression in the colon underwent significant modifications since embryonic day 20 (E20) through postnatal days (P) 2, 10, 20, and 30 via changes in the mutual phasing among the individual clock gene expression rhythms, their relative phasing to the light-dark regime, and their amplitudes. An adult-like state was achieved around P20. The foster study revealed that during the prenatal period, the maternal circadian phase may partially modulate development of the colonic clock. Postnatally, the absence and/or presence of rhythmic maternal care affected the phasing of the clock gene expression profiles in pups at P10 and P20. A reversal in the colonic clock phase between P10 and P20 occurred in the absence of rhythmic signals from the pup SCN. The data demonstrate ontogenetic maturation of the colonic clock and stress the importance of prenatal and postnatal maternal rhythmic signals for its development. These data may contribute to the understanding of colonic function-related diseases in newborn children. PMID:24337008

Polidarová, Lenka; Olejníková, Lucie; Paušlyová, Lucia; Sládek, Martin; Soták, Matúš; Pácha, Ji?í; Sumová, Alena

2014-02-15

351

Comparisons of Synchronous-Clocking SFQ Adders  

NASA Astrophysics Data System (ADS)

Recent advances of superconducting single-flux-quantum (SFQ) circuit technology make it attractive to investigate computing systems using SFQ circuits, where arithmetic circuits play important roles. In order to develop excellent SFQ arithmetic circuits, we have to design or select their underlying algorithms, called hardware algorithms, from different point of view than CMOS circuits, because SFQ circuits work by pulse logic while CMOS circuits work by level logic. In this paper, we compare implementations of hardware algorithms for addition by synchronous-clocking SFQ circuits. We show that a set of individual bit-serial adders and Kogge-Stone adder are superior to others.

Takagi, Naofumi; Tanaka, Masamitsu

352

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

353

Miniaturized optical system for atomic fountain clock  

NASA Astrophysics Data System (ADS)

Using modularized components, we have built a miniaturized optical system for 87Rb atomic fountain clock that is fitted on an 80 cm × 60 cm optical breadboard. Compared with the conventional optical setup on the table, our system is more compact, more robust and miniaturized. Taking advantage of this system, laser beams are transmitted through eight optical fibre patch cords from the optical breadboard to an ultra high vacuum system. This optical setup has operated for five months in our fountain system and required no alignment.

Lü, De-Sheng; Qu, Qiu-Zhi; Wang, Bin; Zhao, Jian-Bo; Li, Tang; Liu, Liang; Wang, Yu-Zhu

2011-06-01

354

The circadian clock modulates enamel development.  

PubMed

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

2012-06-01

355

Polarizabilities of the beryllium clock transition  

NASA Astrophysics Data System (ADS)

The polarizabilities of the three lowest states of the beryllium atom are determined from a large basis configuration interaction calculation. The polarizabilities of the 2s2 1Se ground state (37.73a03) and the 2s2p 3P0o metastable state (39.04a03) are found to be very similar in size and magnitude. This leads to an anomalously small blackbody radiation shift at 300 K of -0.018(4) Hz for the 2s2 1Se-2s2p 3P0o clock transition. Magic wavelengths for simultaneous trapping of the ground and metastable states are also computed.

Mitroy, J.

2010-11-01

356

Laser angle sensor development  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

357

From sundials to atomic clocks: Understanding time and frequency  

Microsoft Academic Search

A historical review of clocks and watches leads into a discussion of today's most sophisticated time piece, the atomic clock. The need for highly accurate atomic time to a millonth of a second or better, is described as it relates to a number of modern-day activities and systems such as advanced electronic communication systems, satellite navigation systems, and precise scientific

J. Jespersen; J. Fitz-Randolph

1977-01-01

358

Atomic clocks: new prospects in metrology and geodesy  

E-print Network

We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.

Delva, Pacôme

2013-01-01

359

Atomic clocks: new prospects in metrology and geodesy  

E-print Network

We present the latest developments in the field of atomic clocks and their applications in metrology and fundamental physics. In the light of recent advents in the accuracy of optical clocks, we present an introduction to the relativistic modelization of frequency transfer and a detailed review of chronometric geodesy.

Pacôme Delva; Jérôme Lodewyck

2013-08-29

360

Wide-area clock distribution using controlled delay lines  

Microsoft Academic Search

This paper describes a clock distribution strategy adequate for wide-area synchronisation, applicable to VLSI, WSI and MCM systems. This strategy is described in terms of Controlled Delay Lines. Local clock multiplication is proposed to solve possible phase ambiguities. Implementation issues are also discussed. Simulations using DLLs with extreme parameter variations are presented in the last section. Sub-nanosecond phase accuracy is

Rui L. Aguiar; Dinis M. Santos

1998-01-01

361

Coordination of the maize transcriptome by a conserved circadian clock  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

362

Chronobiology: Biological Clocks and Rhythms of the Skin  

Microsoft Academic Search

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

A. Mehling; J. W. Fluhr

2006-01-01

363

Enhancing Beneficial Jitter Using Phase-Shifted Clock Distribution  

E-print Network

Affecting Beneficial Jitter Effect cpf/1 dataclk s,s · : Supply noise phase at clock launch · or : Clock edges closer · Up to 58ps (11.6% Tclk) slack improvement with proper cpf cpf cpf - 120 - 100 0 0.4 0.8 1

Kim, Chris H.

364

Improving the Dynamic Continuous Clock Synchronization for WSNs  

Microsoft Academic Search

Clock synchronization is an important feature in Wireless Sensor Networks, as a common vision of time can be required in order to perform synchronous operations. In this paper we present a new version of the Dynamic Continuous Clock Synchronization protocol which offers a greater robustness and requires less power than the original protocol. The role of the Reference Node which

O. Mirabella; M. Brischetto; A. Raucea; F. Banno?; N. Caruso

2010-01-01

365

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

366

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

367

Time, Clocks and the Speed of Light Vasco Guerra  

E-print Network

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

Guerra, Vasco

368

Quantum key distribution with 1.25 Gbps clock synchronization  

E-print Network

Quantum key distribution with 1.25 Gbps clock synchronization J. C. Bienfang, A. J. Gross, A. Mink the exchange of sifted quantum cryptographic key over a 730 meter free-space link at rates of up to 1.0 Mbps operates in parallel with a quantum channel at 845 nm. Clock recovery techniques on the classical channel

369

Wetting and Contact Angle  

NSDL National Science Digital Library

Students are presented with the concepts of wetting and contact angle. They are also introduced to the distinction between hydrophobic and hydrophilic surfaces. Students observe how different surfaces are used to maintain visibility under different conditions.

NSF CAREER Award and RET Program, Mechanical Engineering and Material Science,

370

Temperature-Compensated Clock Skew Adjustment  

PubMed Central

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

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

2013-01-01

371

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

372

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

373

Similarities in the circadian clock and photoperiodism in plants  

PubMed Central

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

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

2010-01-01

374

Restoration of an 18th century English clock  

NASA Astrophysics Data System (ADS)

The background knowledge and the steps required to repair ancient clocks and watches are described. The restoration of old clocks and watches involves the problem of making them work. The wear that results from years of use and the fact that parts are lost or broken leads the restorer to replace certain component parts of the watch or clock. The parts are made in such a way that they fit in with the appearance of the object. This work requires the watchmaker/restorer to have a thorough knowledge of all the mechanisms used in watchmaking and knowhow which covers the whole field, from watches to monumental clocks. An example of a restoration carried out on a Bracket clock is given.

Curtit, Daniel; Piguet, Jean-Michel

375

Lattice-induced nonadiabatic frequency shifts in optical lattice clocks  

SciTech Connect

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

Beloy, K. [Centre for Theoretical Chemistry and Physics, New Zealand Institute for Advanced Study, Massey University Auckland, Private Bag 102904, 0745 Auckland (New Zealand)

2010-09-15

376

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

377

Hunting for topological dark matter with atomic clocks  

NASA Astrophysics Data System (ADS)

The cosmological applications of atomic clocks so far have been limited to searches for the uniform-in-time drift of fundamental constants. We point out that a transient-in-time change of fundamental constants can be induced by dark-matter objects that have large spatial extent, such as stable topological defects built from light non-Standard Model fields. Networks of correlated atomic clocks, some of them already in existence, such as the Global Positioning System, can be used as a powerful tool to search for topological defect dark matter, thus providing another important fundamental physics application for the ever-improving accuracy of atomic clocks. During the encounter with an extended dark-matter object, 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 the defect's space structure and its interaction strength with atoms.

Derevianko, A.; Pospelov, M.

2014-12-01

378

Standard Clock in primordial density perturbations and cosmic microwave background  

NASA Astrophysics Data System (ADS)

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 (CMB) and how they can be further tested by future data. We also use it to motivate more detailed theoretical model building.

Chen, Xingang; Namjoo, Mohammad Hossein

2014-12-01

379

Circadian Clock Control of the Cellular Response to DNA Damage  

PubMed Central

Mammalian cells possess a cell-autonomous molecular clock which controls the timing of many biochemical reactions and hence the cellular response to environmental stimuli including genotoxic stress. The clock consists of an autoregulatory transcription-translation feedback loop made up of four genes/proteins, BMal1, Clock, Cryptochrome, and Period. The circadian clock has an intrinsic period of about 24 hours, and it dictates the rates of many biochemical reactions as a function of the time of the day. Recently, it has become apparent that the circadian clock plays an important role in determining the strengths of cellular responses to DNA damage including repair, checkpoints, and apoptosis. These new insights are expected to guide development of novel mechanism-based chemotherapeutic regimens. PMID:20227409

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

2010-01-01

380

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

2014-03-21

381

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

382

'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

383

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

384

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

385

The crisis of neoliberalism and the future of international institutions: A comparison of the IMF and the WTO  

Microsoft Academic Search

The current crisis of neoliberalism is calling into question the relevance of key international institutions. We analyze the\\u000a origins, nature, and possible impacts of the crisis through comparing two such institutions: the International Monetary Fund\\u000a (IMF) and the World Trade Organization (WTO). Both originated in the post-World War II U.S.-led hegemonic order and were transformed\\u000a as part of the transition

Nitsan Chorev; Sarah Babb

2009-01-01

386

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

387

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

388

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

389

Equivalent ionospheric current systems representing IMF sector effects on the polar geomagnetic field  

NASA Astrophysics Data System (ADS)

Equivalent ionospheric current systems representing IMF sector effects on the geomagnetic field in high latitudes are examined for each of the twelve calendar months by spherical harmonic analyses of geomagnetic hourly data at 13 northern polar stations for seven years. The main feature of obtained equivalent current systems includes circular currents at about 80 deg invariant latitude mostly in the daytime in summer and reversed circular currents at about 70 deg invariant latitude mainly at night in winter. Field-aligned current distributions responsible for equivalent currents, as well as vector distributions of electric fields and ionospheric currents, are approximated numerically from current functions of equivalent current systems by taking assumed distributions of the ionospheric conductivity. Two sets of upward and downward field-aligned current pairs in the auroral region, and also a field-aligned current region near the pole show seasonal variations. Also, ionospheric electric-field propagation along geomagnetic field lines from the summer hemisphere to the winter hemisphere with auroral Hall-conductivity effects may provide an explanation for the winter reversal of sector effects.

Matsushita, S.; Xu, W.-Y.

1982-07-01

390

Disruption of the circadian clock due to the Clock mutation has discrete effects on aging and carcinogenesis  

PubMed Central

The mammalian circadian system has been implicated in the regulation of various biological processes including those involved in genotoxic stress responses and tumor suppression. Here we report that mice with the functional deficiency in circadian transcription factor CLOCK (Clock/Clock mutant mice) do not display predisposition to tumor formation both during their normal lifespan or when challenged by ?-radiation. This phenotype is consistent with high apoptotic and low proliferation rate in lymphoid tissues of Clock mutant mice and is supported by the gene expression profiling of a number of apoptosis and cell cycle-related genes, as well as by growth inhibition of cells with CLOCK downregulation. At the same time, Clock mutant mice respond to low-dose irradiation by accelerating their aging program, and develop phenotypes that are reminiscent of those in Bmal1-deficient mice. Taken together, our results demonstrate the dichotomy in biological consequences of the disruption of the circadian clock with respect to ageing and cancer. They also highlight the existence of a complex interconnection between ageing, carcinogenesis and individual components of the circadian clock machinery. PMID:18418054

Antoch, Marina P.; Gorbacheva, Victoria Y.; Vykhovanets, Olena; Toshkov, Illia A.; Kondratov, Roman V.; Kondratova, Anna A.; Lee, Choogon; Nikitin, Alexander Yu.

2009-01-01

391

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

NASA Astrophysics Data System (ADS)

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

Andriyas, T.; Spencer, E. A.

2010-12-01

392

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

393

Global view of dayside magnetic reconnection with the dusk-dawn IMF orientation: A statistical study for Double Star and Cluster data  

Microsoft Academic Search

Double Star\\/TC-1 and Cluster data show that both component reconnection and anti-parallel reconnection occur at the magnetopause when the interplanetary magnetic field (IMF) is predominantly dawnward. The occurrence of these different features under these very similar IMF conditions are further confirmed by a statistical study of 290 fast flows measured in both the low and high latitude magnetopause boundary layers.

X. G. Zhang; X. G. Wang; J. Wang; X.-Z. Zhou; M. W. Dunlop; L. Xie; C. J. Xiao; Q. G. Zong; S. Y. Fu; Z. X. Liu; C. Carr; Z. W. Ma; C. Shen; E. Lucek; H. Rème; P. Escoubet

2007-01-01

394

Application of NARX neural network in storm-time SYM-H index prediction from IMF and solar wind data  

NASA Astrophysics Data System (ADS)

In this study the NARX neural network has been used for the first time to predict high-resolution magnetic storm index of SYM-H from solar wind (SW) and IMF parameters. In total 73 great storm events with IMF/SW data available from ACE satellite during 1998 to 2006 are used to establish the ANN model. Out of them, 67 are used to train the network and the other 6 samples for test. Additionally, the NARX prediction model is also validated using IMF/SW data from WIND satellite for 7 great storms during 1995-1997 and 2005, as well as for the July 2000 Bastille day storm and November 2001 superstorm using Geotail and OMNI data at 1AU. Five interplanetary parameters of IMF Bz, By and total B components along with proton density and velocity of solar wind are used as the original external inputs of the neural network to predict the SYM-H index about one hour or an even longer time ahead. For the 6 test storms registered by ACE including two super-storms with minimum SYM-H less than -200 nT, the correlation coefficient between observed and NARX network predicted SYM-H is 0.95 as a whole, even as high as 0.95 and 0.98 with average relative variance of 13.2 percent and 7.4 percent for the two super-storms, respectively. The prediction for the 7 storms with WIND data is also satisfactory, showing averaged correlation coefficient about 0.91 and RMSE of 14.2 nT. The newly developed NARX model shows much better capability than Elman network for SYM-H prediction, which can partly be attributed to a key feedback to the input layer from the output neuron with a suitable length (about 120 min). This feedback means that nearly real information of the ring current status is effectively brought to taking part in the prediction of SYM-H index by ANN. The proper history length of the output-feedback may mainly reflect on average the characteristic time of ring current decay which involves various decay mechanisms with ion lifetimes from tens of minutes to tens of hours. Besides, it is verified that this kind of model is also capable of providing satisfactory predictions of the SYM-H index 3 hours ahead from IMF/SW data with less physical parameters observed at L1 position, enhancing significantly the practicality of the model in space weather forecasting.

Cai, Lei; Ma, S. Y.; Zhou, Yunliang; Cai, Hongtao

395

Diurnal Oscillations of Soybean Circadian Clock and Drought Responsive Genes  

PubMed Central

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

396

CREB Influences Timing and Entrainment of the SCN Circadian Clock  

PubMed Central

The transcriptional feedback circuit, which is at the core of the suprachiasmatic nucleus (SCN) circadian (i.e., 24 h) clock, is tightly coupled to both external entrainment cues, such as light, as well as rhythmic cues that arise on a system-wide level within the SCN. One potential signaling pathway by which these cues are conveyed to the molecular clock is the CREB/CRE transcriptional cascade. In this study, we employed a tetracycline-inducible CREB repressor mouse strain, in which approximately 60% of the SCN neurons express the transgene, to test CREB functionality in the clock and its effects on overt rhythmicity. We show that attenuated CREB signaling in the SCN led to a significant reduction in light-evoked clock entrainment. An examination of circadian timing revealed that CREB repressor mice exhibited normal free-running rhythms in the absence of external lighting cues. However, under conditions of constant light, which typically leads to a lengthening of the circadian period, CREB repressor mice exhibited a dramatic arrhythmic phenotype, which could be reversed with doxycycline. At a cellular level, the repression of CREB led to a significant reduction in both the expression of the circadian clock proteins PERIOD1 and PERIOD2 and the clock output hormones AVP and VIP. Together, these data support the idea that the CRE transcriptional pathway orchestrates transcriptional events that are essential for both the maintenance of SCN timing and light entrainment of the circadian clock. PMID:21135157

Lee, Boyoung; Li, Aiqing; Hansen, Katelin F.; Cao, Ruifeng; Yoon, Jae Hwa; Obrietan, Karl

2011-01-01

397

The Circadian Clock in Cancer Development and Therapy  

PubMed Central

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

Fu, Loning; Kettner, Nicole M.

2014-01-01

398

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

399

Polarizabilities of the beryllium clock transition  

SciTech Connect

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

Mitroy, J. [School of Engineering, Charles Darwin University, Darwin NT 0909 (Australia)

2010-11-15

400

Mass Loading Characteristics of Crystal Clock Oscillators  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

401

Clock Agreement Among Parallel Supercomputer Nodes  

SciTech Connect

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

Jones, Terry R.; Koenig, Gregory A.

2014-04-30

402

Tuning the Mammalian Circadian Clock: Robust Synergy of Two Loops  

PubMed Central

The circadian clock is accountable for the regulation of internal rhythms in most living organisms. It allows the anticipation of environmental changes during the day and a better adaptation of physiological processes. In mammals the main clock is located in the suprachiasmatic nucleus (SCN) and synchronizes secondary clocks throughout the body. Its molecular constituents form an intracellular network which dictates circadian time and regulates clock-controlled genes. These clock-controlled genes are involved in crucial biological processes including metabolism and cell cycle regulation. Its malfunction can lead to disruption of biological rhythms and cause severe damage to the organism. The detailed mechanisms that govern the circadian system are not yet completely understood. Mathematical models can be of great help to exploit the mechanism of the circadian circuitry. We built a mathematical model for the core clock system using available data on phases and amplitudes of clock components obtained from an extensive literature search. This model was used to answer complex questions for example: how does the degradation rate of Per affect the period of the system and what is the role of the ROR/Bmal/REV-ERB (RBR) loop? Our findings indicate that an increase in the RNA degradation rate of the clock gene Period (Per) can contribute to increase or decrease of the period - a consequence of a non-monotonic effect of Per transcript stability on the circadian period identified by our model. Furthermore, we provide theoretical evidence for a potential role of the RBR loop as an independent oscillator. We carried out overexpression experiments on members of the RBR loop which lead to loss of oscillations consistent with our predictions. These findings challenge the role of the RBR loop as a merely auxiliary loop and might change our view of the clock molecular circuitry and of the function of the nuclear receptors (REV-ERB and ROR) as a putative driving force of molecular oscillations. PMID:22194677

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

2011-01-01

403

Synthesizing genetic sequential logic circuit with clock pulse generator  

PubMed Central

Background Rhythmic clock widely occurs in biological systems which controls several aspects of cell physiology. For the different cell types, it is supplied with various rhythmic frequencies. How to synthesize a specific clock signal is a preliminary but a necessary step to further development of a biological computer in the future. Results This paper presents a genetic sequential logic circuit with a clock pulse generator based on a synthesized genetic oscillator, which generates a consecutive clock signal whose frequency is an inverse integer multiple to that of the genetic oscillator. An analogous electronic waveform-shaping circuit is constructed by a series of genetic buffers to shape logic high/low levels of an oscillation input in a basic sinusoidal cycle and generate a pulse-width-modulated (PWM) output with various duty cycles. By controlling the threshold level of the genetic buffer, a genetic clock pulse signal with its frequency consistent to the genetic oscillator is synthesized. A synchronous genetic counter circuit based on the topology of the digital sequential logic circuit is triggered by the clock pulse to synthesize the clock signal with an inverse multiple frequency to the genetic oscillator. The function acts like a frequency divider in electronic circuits which plays a key role in the sequential logic circuit with specific operational frequency. Conclusions A cascaded genetic logic circuit generating clock pulse signals is proposed. Based on analogous implement of digital sequential logic circuits, genetic sequential logic circuits can be constructed by the proposed approach to generate various clock signals from an oscillation signal. PMID:24884665

2014-01-01

404

Embryonic development and maternal regulation of murine circadian clock function.  

PubMed

The importance of circadian clocks in the regulation of adult physiology in mammals is well established. In contrast, the ontogenesis of the circadian system and its role in embryonic development are still poorly understood. Although there is experimental evidence that the clock machinery is present prior to birth, data on gestational clock functionality are inconsistent. Moreover, little is known about the dependence of embryonic rhythms on maternal and environmental time cues and the role of circadian oscillations for embryonic development. The aim of this study was to test if fetal mouse tissues from early embryonic stages are capable of expressing endogenous, self-sustained circadian rhythms and their contribution to embryogenesis. Starting on embryonic day 13, we collected precursor tissues for suprachiasmatic nucleus (SCN), liver and kidney from embryos carrying the circadian reporter gene Per2::Luc and investigated rhythmicity and circadian traits of these tissues ex vivo. We found that even before the respective organs were fully developed, embryonic tissues were capable of expressing circadian rhythms. Period and amplitude of which were determined very early during development and phases of liver and kidney explants are not influenced by tissue preparation, whereas SCN explants phasing is strongly dependent on preparation time. Embryonic circadian rhythms also developed in the absence of maternal and environmental time signals. Morphological and histological comparison of offspring from matings of Clock-?19 mutant and wild-type mice revealed that both fetal and maternal clocks have distinct roles in embryogenesis. While genetic disruptions of maternal and embryonic clock function leads to increased fetal fat depots, abnormal ossification and organ development, Clock gene mutant newborns from mothers with a functional clock showed a larger body size compared to wild-type littermates. These data may contribute to the understanding of the ontogenesis of circadian clocks and the risk of disturbed maternal or embryonic circadian rhythms for embryonic development. PMID:25431080

Landgraf, Dominic; Achten, Christian; Dallmann, Franziska; Oster, Henrik

2014-11-28

405

Regulation of core clock genes in human islets.  

PubMed

Nearly all mammalian cells express a set of genes known as clock genes. These regulate the circadian rhythm of cellular processes by means of negative and positive autoregulatory feedback loops of transcription and translation. Recent genomewide association studies have demonstrated an association between a polymorphism near the circadian clock gene CRY2 and elevated fasting glucose. To determine whether clock genes could play a pathogenetic role in the disease, we examined messenger RNA (mRNA) expression of core clock genes in human islets from donors with or without type 2 diabetes mellitus. Microarray and quantitative real-time polymerase chain reaction analyses were used to assess expression of the core clock genes CLOCK, BMAL-1, PER1 to 3, and CRY1 and 2 in human islets. Insulin secretion and insulin content in human islets were measured by radioimmunoassay. The mRNA levels of PER2, PER3, and CRY2 were significantly lower in islets from donors with type 2 diabetes mellitus. To investigate the functional relevance of these clock genes, we correlated their expression to insulin content and glycated hemoglobin levels: mRNA levels of PER2 (? = 0.33, P = .012), PER3 (? = 0.30, P = .023), and CRY2 (? = 0.37, P = .0047) correlated positively with insulin content. Of these genes, expression of PER3 and CRY2 correlated negatively with glycated hemoglobin levels (? = -0.44, P = .0012; ? = -0.28, P = .042). Furthermore, in an in vitro model mimicking pathogenetic conditions, the PER3 mRNA level was reduced in human islets exposed to 16.7 mmol/L glucose per 1 mmol/L palmitate for 48 hours (P = .003). Core clock genes are regulated in human islets. The data suggest that perturbations of circadian clock components may contribute to islet pathophysiology in human type 2 diabetes mellitus. PMID:22304835

Stamenkovic, Jelena A; Olsson, Anders H; Nagorny, Cecilia L; Malmgren, Siri; Dekker-Nitert, Marloes; Ling, Charlotte; Mulder, Hindrik

2012-07-01

406

Spread spectrum clock Generator with delay cell array to reduce electromagnetic interference  

Microsoft Academic Search

In high-speed digital systems, most of the electromagnetic interference (EMI) from the system is caused by high-speed digital clock drivers and synchronized circuits. To reduce the EMI from the system clocks, spread spectrum clock (SSC) techniques that modulate the system clock frequency have been proposed. A conventional SSC generator (SSCG) has been implemented with a phase locked loop (PLL) by

Jonghoon Kim; Dong Gun Kam; Pil Jung Jun; Joungho Kim

2005-01-01

407

Can the Salecker-Wigner clock be microscopic?  

E-print Network

Half a century ago H. Salecker and E. P. Wigner examined the functioning of a quantum clock of very simple construction [1]. They raised the question whether such a clock can be microscopic or not, but no clear-cut answer has been reached in [1] (see also [2]). In this note it is shown that their clock can have a microscopic mass and size only if its accuracy is poor, but if the size is macroscopic, a decent accuracy can be achieved even if the mass is microscopic.

Andor Frenkel

2005-03-21

408

Genomics and Systems Approaches in the Mammalian Circadian Clock  

PubMed Central

Summary The circadian clock is an endogenous oscillator that regulates daily rhythms in behavior and physiology. In recent years, systems biology and genomics approaches re-shaped our view of the clock. Our understanding of outputs that regulate behavior and physiology has been enhanced through gene expression profiling and proteomic analyses. Systems approaches uncovered underlying principles of transcriptional regulation and robustness of the oscillator through perturbation analysis and synthetic methods. Finally, new clock components and modifiers were identified through cell-based screening efforts and proteomics. PMID:20926286

Baggs, Julie E.; Hogenesch, John B.

2010-01-01

409

Intracellular and intercellular processes determine robustness of the circadian clock  

PubMed Central

Circadian clocks are present in most organisms and provide an adaptive mechanism to coordinate physiology and behavior with predictable changes in the environment. Genetic, biochemical, and cellular experiments have identified more than a dozen component genes and a signal transduction pathway that support cell-autonomous, circadian clock function. One of the hallmarks of biological clocks is their ability to reset to relevant stimuli while ignoring most others. We review recent results showing intracellular and intercellular mechanisms that convey this robust timekeeping to a variety of circadian cell types. PMID:21536033

Hogenesch, John B.; Herzog, Erik D.

2011-01-01

410

Metabolism control by the circadian clock and vice versa  

PubMed Central

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

Eckel-Mahan, Kristin; Sassone-Corsi, Paolo

2014-01-01

411

Chapter 10: Optical Atomic Clocks in Ion Traps  

NASA Astrophysics Data System (ADS)

Narrow optical transitions in single laser-cooled trapped ions are highly reproducible in frequency and therefore make ideal references for accurate atomic clocks. This chapter provides an introduction to trapped ion optical clocks, covering their principles of operation and describing the different systems being studied at present. The performance of state-of-the-art trapped ion optical clocks is discussed and the various contributions to their frequency uncertainty budgets are outlined. Finally the further developments likely to occur over the next few years are considered.

Margolis, Helen S.

2014-01-01

412

An atomic clock with 10(-18) instability.  

PubMed

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

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

2013-09-13

413

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

414

Daily oscillation and photoresponses of clock gene, Clock, and clock-associated gene, arylalkylamine N-acetyltransferase gene transcriptions in the rat pineal gland.  

PubMed

This study was conducted to investigate the circadian rhythms and light responses of Clock and arylalkylamine N-acetyltransferase (NAT) gene expressions in the rat pineal gland under the environmental conditions of a 12 h light (05:00-17:00 h): 12 h-dark (17:00-05:00 h) cycle (LD) and constant darkness (DD). The pineal gland of Sprague-Dawley rats housed under a LD regime (n=42) for four weeks and of a regime (n=42) for eight weeks were sampled at six different times, every 4 h (n=7 animals per time point), during a 24 h period. Total RNA was extracted from each sample, and the semiquantitative reverse transcription polymerase chain reaction (RT-PCR) was used to determine temporal changes in mRNA levels of Clock and NAT genes during different circadian or zeitgeber times. The data and parameters were analyzed by the cosine function software, Clock Lab software, and the amplitude F test was used to reveal the circadian rhythm. In the DD or LD condition, both the Clock and NAT mRNA levels in the pineal gland showed robust circadian oscillation (p<0.05) with the peak at the subjective night or at nighttime. In comparison with the DD regime, the amplitudes and mRNA levels at the peaks of Clock and NAT expressions in LD in the pineal gland were significantly reduced (p<0.05). In the DD or LD condition, the circadian expressions of NAT were similar in pattern to those of Clock in the pineal gland (p>0.05). These findings indicate that the transcriptions of Clock and NAT genes in the pineal gland not only show remarkably synchronous endogenous circadian rhythmic changes, but also respond to the ambient light signal in a reduced manner. PMID:17364576

Wang, Guo-Qing; Du, Yu-Zhen; Tong, Jian

2007-01-01

415

Taxicab Angles and Trigonometry  

E-print Network

A natural analogue to angles and trigonometry is developed in taxicab geometry. This structure is then analyzed to see which, if any, congruent triangle relations hold. A nice application involving the use of parallax to determine the exact (taxicab) distance to an object is also discussed.

Thompson, Kevin

2011-01-01

416

Casting and Angling.  

ERIC Educational Resources Information Center

As part of a series of books and pamphlets on outdoor education, this manual consists of easy-to-follow instructions for fishing activities dealing with casting and angling. The manual may be used as a part of the regular physical education program in schools and colleges or as a club activity for the accomplished weekend fisherman or the…

Smith, Julian W.

417

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

418

Energy-Efficient Processor Design Using Multiple Clock Domains with Dynamic Voltage and Frequency Scaling  

Microsoft Academic Search

As clock frequency increases and feature size decreases, clock distribution and wire delays present a growing chal- lenge to the designers of singly-clocked, globally syn- chronous systems. We describe an alternative approach, which we call aMultiple Clock Domain (MCD) processor, in which the chip is divided into several (coarse-grained) clock domains, within which independent voltage and fre- quency scaling can

Greg Semeraro; Grigorios Magklis; Rajeev Balasubramonian; David H. Albonesi; Sandhya Dwarkadas; Michael L. Scott

2002-01-01

419

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

420

Circadian clock regulates the host response to Salmonella  

PubMed Central

Organisms adapt to day–night cycles through highly specialized circadian machinery, whose molecular components anticipate and drive changes in organism behavior and metabolism. Although many effectors of the immune system are known to follow daily oscillations, the role of the circadian clock in the immune response to acute infections is not understood. Here we show that the circadian clock modulates the inflammatory response during acute infection with the pathogen Salmonella enterica serovar Typhimurium (S. Typhimurium). Mice infected with S. Typhimurium were colonized to higher levels and developed a higher proinflammatory response during the early rest period for mice, compared with other times of the day. We also demonstrate that a functional clock is required for optimal S. Typhimurium colonization and maximal induction of several proinflammatory genes. These findings point to a clock-regulated mechanism of activation of the immune response against an enteric pathogen and may suggest potential therapeutic strategies for chronopharmacologic interventions. PMID:23716692

Bellet, Marina M.; Deriu, Elisa; Liu, Janet Z.; Grimaldi, Benedetto; Blaschitz, Christoph; Zeller, Michael; Edwards, Robert A.; Sahar, Saurabh; Dandekar, Satya; Baldi, Pierre; George, Michael D.; Raffatellu, Manuela; Sassone-Corsi, Paolo

2013-01-01

421

Preliminary results of the trapped atom clock on a chip.  

PubMed

We present an atomic clock based on the interrogation of magnetically trapped (87)Rb atoms. Two photons, in the microwave and radiofrequency domain, excite the clock transition. At a magnetic field of 3.23 G the clock transition from |F = 1, m(F) = -1> to |F = 2, m(F) = 1> is 1st-order insensitive to magnetic field variations. Ramsey interrogation times longer than 2 s can be achieved, leading to a projected clock stability in the low 10(-13) at 1 s for a cloud of 10(5) atoms. We use an atom chip to cool and trap the atoms. A coplanar waveguide is integrated to the chip to carry the Ramsey interrogation signal, making the physics package as small as (5 cm)(3). We describe the experimental setup and show preliminary Ramsey fringes of line width 1.25 Hz. PMID:20040433

Lacroute, Clement; Reinhard, Friedemann; Ramirez-Martinez, Fernando; Deutsch, Christian; Schneider, Tobias; Reichel, Jakob; Rosenbusch, Peter

2010-01-01

422

Cold-atom double-? coherent population trapping clock  

NASA Astrophysics Data System (ADS)

Miniature atomic clocks based on coherent population trapping (CPT) states in thermal atoms are an important component in many field applications, particularly where satellite frequency standards are not accessible. Cold-atom CPT clocks promise improved accuracy and stability over existing commercial technologies. Here we demonstrate a cold-atom CPT clock based on 87Rb using a high-contrast double-? configuration. Doppler frequency shifts are explained using a simple model and canceled by interrogating the atoms with counterpropagating light beams. We realize a compact cold-atom CPT clock with a fractional frequency stability of 4×10-11?-1/2, thus demonstrating the potential of these devices. We also show that the long-term stability is currently limited by the second-order Zeeman shift to 2×10-12 at 1000 s.

Esnault, F.-X.; Blanshan, E.; Ivanov, E. N.; Scholten, R. E.; Kitching, J.; Donley, E. A.

2013-10-01

423

Circadian biology: a 2.5 billion year old clock.  

PubMed

A recent study suggests that circadian clocks may have evolved at the time of the Great Oxidation Event 2.5 billion years ago in order to drive detoxification of reactive oxygen species. PMID:22835791

Loudon, Andrew S I

2012-07-24

424

Enhanced: Running a Clock Requires Quality Time Together  

NSDL National Science Digital Library

Access to the article is free, however registration and sign-in are required: The strictly timed disassembly of a protein complex before entry of its constituents into the nucleus influences the 24-hour period of the circadian clock.

Jay C. Dunlap (Dartmouth Medical School;Department of Genetics)

2006-01-13

425

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

426

The development of a Kalman filter clock predictor  

NASA Technical Reports Server (NTRS)

A Kalman filter based clock predictor is developed, and its performance evaluated using both simulated and real data. The clock predictor is shown to possess a neat to optimal Prediction Error Variance (PEV) when the underlying noise consists of one of the power law noise processes commonly encountered in time and frequency measurements. The predictor's performance is the presence of multiple noise processes is also examined. The relationship between the PEV obtained in the presence of multiple noise processes and those obtained for the individual component noise processes is examined. Comparisons are made with a simple linear clock predictor. The clock predictor is used to predict future values of the time offset between pairs of NPL's active hydrogen masers.

Davis, John A.; Greenhall, Charles A.; Boudjemaa, Redoane

2005-01-01

427

Tick Tock: New Clues about Biological Clocks and Health  

MedlinePLUS

... clocks that help keep daily rhythms in synch. Credit: Wikimedia Commons. View larger image After you roll ... exhibit sleep patterns fairly similar to our own. Credit: Laurie Tompkins, NIH's National Institute of General Medical ...

428

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.

Gordon, K J; Collins, R J; Rech, I; Cova, S D; Townsend, P D; Buller, G S; Gordon, Karen J.; Fernandez, Veronica; Collins, Robert J.; Rech, Ivan; Cova, Sergio D.; Townsend, Paul D.; Buller, Gerald S.

2006-01-01

429

Quantum Atomic Clock Synchronization: An Entangled Concept of Nonlocal Simultaneity  

NASA Technical Reports Server (NTRS)

We demonstrate that two spatially separated parties (Alice and Bob) can utilize shared prior quantum entanglement, as well as a classical information channel, to establish a synchronized pair of atomic clocks.

Abrams, D.; Dowling, J.; Williams, C.; Jozsa, R.

2000-01-01

430

Modeling a synthetic multicellular clock: Repressilators coupled by quorum sensing  

E-print Network

Modeling a synthetic multicellular clock: Repressilators coupled by quorum sensing Jordi Garcia of such genetic oscillators interacting through a quorum-sensing mechanism should self-synchronize in a robust way

Elowitz, Michael

431

Atomic Clocks and Variations of the FIne Structure Constant  

NASA Technical Reports Server (NTRS)

We describe a new test for possible variations of the fine structure constant alpha by comparisons of rates between clocks based on hyperfine transitions in alkali atoms with different atomic number Z. H-maser, Cs, and Hg(+) clocks have a different dependence on alpha via relativistic contributions of order (Z-alpha)(sup 2). Recent H-maser vs Hg(+) clock comparison data improve laboratory limits on a time variation by 100-fold to give dot-alpha less than or equal to 3.7 x 10(exp -14)/yr. Future laser cooled clocks (Be(+), Rb, Cs, Hg(+), etc.), when compared, will yield the most sensitive of all tests for dot-alpha/alpha.

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

1995-01-01

432

Biological clocks: who in this place set up a sundial?  

PubMed

How do circadian rhythms, alarm clocks and the light/dark cycle interact? The concept of social jetlag is informing our appreciation of the tensions and consequences of imposing an artificial temporal order upon our biology. PMID:22625858

Foster, Russell G

2012-05-22

433

Spin Squeezing on AN Atomic-Clock Transition  

NASA Astrophysics Data System (ADS)

We generate input states with reduced quantum uncertainty (spin-squeezed states) for a hyperfine atomic clock by collectively coupling an ensemble of laser-cooled and trapped 87Rb atoms to an optical resonator. A quantum non-demolition measurement of the population difference between the two clock states with far-detuned light produces an entangled state whose projection noise is reduced by as much as 9.4(8) dB below the standard quantum limit (SQL) for uncorrelated atoms. When the observed decoherence is taken into account, we attain 4.2(8) dB of spin squeezing, confirming entanglement, and 3.2(8) dB of improvement in clock precision over the SQL. The method holds promise for improving the performance of optical-frequency clocks.

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

2009-03-01

434

A Clock Enhanced Loop for Simultaneous Error-Free Demultiplexing and Clock Recovery of 160 Gb/s OTDM Signal Single-Channel Transmission over 100 km  

NASA Astrophysics Data System (ADS)

A simple clock enhanced loop of cascaded electro-absorption modulators (EAMs) and 10 GHz clock recovery modules is presented. The intensity of harmonic of clock-frequency component is analyzed theoretically and verified experimentally in a 160 Gb/s OTDM 100 km transmission system. The 10 GHz clock component is enhanced obviously before launching into the clock recovery module and the recovered clock signal exhibits low rms jitter of < 400 fs. Moreover, completely error-free (10-12) transmission is observed for more than two hours without using forward error correction technology. The power penalty is about 3.6 dB. The proposed loop has merits of enhancing base clock component, simultaneously de-multiplexing and clock recovery, which make the performance of this loop more stable and high suppression of non-target channels.

Jia, Nan; Li, Tang-Jun; Zhong, Kang-Ping; Wang, Mu-Guang; Chen, Ming; Li, Jing; Chi, Jian-Feng

2010-11-01

435

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

436

Rethinking transcriptional activation in the Arabidopsis circadian clock.  

PubMed

Circadian clocks are biological timekeepers that allow living cells to time their activity in anticipation of predictable daily changes in light and other environmental factors. The complexity of the circadian clock in higher plants makes it difficult to understand the role of individual genes or molecular interactions, and mathematical modelling has been useful in guiding clock research in model organisms such as Arabidopsis thaliana. We present a model of the circadian clock in Arabidopsis, based on a large corpus of published time course data. It appears from experimental evidence in the literature that most interactions in the clock are repressive. Hence, we remove all transcriptional activation found in previous models of this system, and instead extend the system by including two new components, the morning-expressed activator RVE8 and the nightly repressor/activator NOX. Our modelling results demonstrate that the clock does not need a large number of activators in order to reproduce the observed gene expression patterns. For example, the sequential expression of the PRR genes does not require the genes to be connected as a series of activators. In the presented model, transcriptional activation is exclusively the task of RVE8. Predictions of how strongly RVE8 affects its targets are found to agree with earlier interpretations of the experimental data, but generally we find that the many negative feedbacks in the system should discourage intuitive interpretations of mutant phenotypes. The dynamics of the clock are difficult to predict without mathematical modelling, and the clock is better viewed as a tangled web than as a series of loops. PMID:25033214

Fogelmark, Karl; Troein, Carl

2014-07-01

437

Rethinking Transcriptional Activation in the Arabidopsis Circadian Clock  

PubMed Central

Circadian clocks are biological timekeepers that allow living cells to time their activity in anticipation of predictable daily changes in light and other environmental factors. The complexity of the circadian clock in higher plants makes it difficult to understand the role of individual genes or molecular interactions, and mathematical modelling has been useful in guiding clock research in model organisms such as Arabidopsis thaliana. We present a model of the circadian clock in Arabidopsis, based on a large corpus of published time course data. It appears from experimental evidence in the literature that most interactions in the clock are repressive. Hence, we remove all transcriptional activation found in previous models of this system, and instead extend the system by including two new components, the morning-expressed activator RVE8 and the nightly repressor/activator NOX. Our modelling results demonstrate that the clock does not need a large number of activators in order to reproduce the observed gene expression patterns. For example, the sequential expression of the PRR genes does not require the genes to be connected as a series of activators. In the presented model, transcriptional activation is exclusively the task of RVE8. Predictions of how strongly RVE8 affects its targets are found to agree with earlier interpretations of the experimental data, but generally we find that the many negative feedbacks in the system should discourage intuitive interpretations of mutant phenotypes. The dynamics of the clock are difficult to predict without mathematical modelling, and the clock is better viewed as a tangled web than as a series of loops. PMID:25033214

Fogelmark, Karl; Troein, Carl

2014-01-01

438

Space clocks to test relativiy: ACES and SAGAS  

NASA Astrophysics Data System (ADS)

Atomic clocks are an outstanding tool for the experimental verification of general relativity and more generally for fundamental astronomy (VLBI, pulsar timing, navigation, etc). Recent years have seen a rapid improvement in the performance of such clocks, promising new improved tests of relativity, in particular onboard terrestrial and interplanetary space missions. We present the scientific motivations of such tests taking the ACES Salomon et al. and SAGAS Wolf et al. (2009) projects as particular examples.

Wolf, Peter; Salomon, Christophe; Reynaud, Serge

2010-01-01

439

Systems Biology of the Clock in Neurospora crassa  

PubMed Central

A model-driven discovery process, Computing Life, is used to identify an ensemble of genetic networks that describe the biological clock. A clock mechanism involving the genes white-collar-1 and white-collar-2 (wc-1 and wc-2) that encode a transcriptional activator (as well as a blue-light receptor) and an oscillator frequency (frq) that encodes a cyclin that deactivates the activator is used to guide this discovery process through three cycles of microarray experiments. Central to this discovery process is a new methodology for the rational design of a Maximally Informative Next Experiment (MINE), based on the genetic network ensemble. In each experimentation cycle, the MINE approach is used to select the most informative new experiment in order to mine for clock-controlled genes, the outputs of the clock. As much as 25% of the N. crassa transcriptome appears to be under clock-control. Clock outputs include genes with products in DNA metabolism, ribosome biogenesis in RNA metabolism, cell cycle, protein metabolism, transport, carbon metabolism, isoprenoid (including carotenoid) biosynthesis, development, and varied signaling processes. Genes under the transcription factor complex WCC (?=?WC-1/WC-2) control were resolved into four classes, circadian only (612 genes), light-responsive only (396), both circadian and light-responsive (328), and neither circadian nor light-responsive (987). In each of three cycles of microarray experiments data support that wc-1 and wc-2 are auto-regulated by WCC. Among 11,000 N. crassa genes a total of 295 genes, including a large fraction of phosphatases/kinases, appear to be under the immediate control of the FRQ oscillator as validated by 4 independent microarray experiments. Ribosomal RNA processing and assembly rather than its transcription appears to be under clock control, suggesting a new mechanism for the post-transcriptional control of clock-controlled genes. PMID:18769678

Dong, Wubei; Tang, Xiaojia; Yu, Yihai; Nilsen, Roger; Kim, Rosemary; Griffith, James; Arnold, Jonathan; Schüttler, H.-Bernd

2008-01-01

440

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

441

Clock distribution architectures for 3-D SOI integrated circuits  

Microsoft Academic Search

Three topologies to globally distribute a clock signal in 3-D circuits have been evaluated. A 3-D test circuit, based on the MITLL 3-D IC manufacturing process, has been designed, fabricated, and measured and is shown to operate at 1.4 GHz. Clock skew measurements indicate that a topology that combines the symmetry of an H-tree on the second plane and local

Vasilis F. Pavlidis; Ioannis Savidis; Eby G. Friedman

2008-01-01

442

Metrological characterization of the pulsed Rb clock with optical detection  

NASA Astrophysics Data System (ADS)

We report on the implementation and metrological characterization of a vapour-cell Rb frequency standard working in a pulsed regime. The three main parts of the clock, physics package, optics and electronics, are described in detail in this paper. The prototype is designed and optimized to detect the clock transition in the optical domain. Specifically, the reference atomic transition, excited with a Ramsey scheme, is detected by observing the interference pattern on a laser absorption signal. The metrological analysis includes the observation and characterization of the clock signal and the measurement of frequency stability and drift. In terms of Allan deviation, the measured frequency stability is as low as 1.7 × 10-13?-1/2, ? being the averaging time, and reaches the value of a few units of 10-15 for ? = 104 s, an unprecedented result for a vapour-cell clock. We discuss the physical effects leading to this result in this paper with particular care to laser and microwave noises transferred to the clock signal. The frequency drift, probably related to temperature, stays below 10-14 per day, and no evidence of flicker floor is observed. We also mention some possible improvements that in principle would lead to a clock stability below the 10-13 level at 1 s and to a drift of a few units of 10-15 per day.

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

2012-08-01

443

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

444

Inexpensive Clock for Displaying Planetary or Sidereal Time  

NASA Technical Reports Server (NTRS)

An inexpensive wall clock has been devised for displaying solar time or sidereal time as it would be perceived on a planet other than the Earth, or for displaying sidereal time on the Earth. The concept of a wall clock synchronized to a period other than the terrestrial mean solar day is not new in itself. What is new here is that the clock is realized through a relatively simple electronic modification of a common battery-powered, quartz-crystal-oscillator-driven wall clock. The essence of the modification is to shut off the internal oscillator of the clock and replace the internal-oscillator output signal with a signal of the required frequency generated by an external oscillator. The unmodified clock electronic circuitry includes a quartz crystal connected to an integrated circuit (IC) that includes, among other parts, a buffer amplifier that conditions the oscillator output. The modification is effected by removing the quartz crystal and connecting the output terminal of the external oscillator, via a capacitor, to the input terminal of the buffer amplifier

Lux, James

2007-01-01

445

A Connection Between MAPK Pathways and Circadian Clocks  

PubMed Central

Circadian clocks and mitogen-activated protein kinase (MAPK) signaling pathways are fundamental features of eukaryotic cells. Both pathways provide mechanisms for cells to respond to environmental stimuli, and links between them are known. We recently reported that the circadian clock in Neurospora crassa regulates daily rhythms in accumulation of phosphorylated, and thus active, OS-2 MAPK, a relative of mammalian p38 MAPK, when cells are grown in constant conditions. In the absence of acute stress, rhythmically activated MAPK then signals to downstream effector molecules to regulate rhythmic expression of target genes of the pathway. Clock regulation of MAPK signaling pathways provides a mechanism to coordinately control major groups of genes such that they peak at the appropriate times of day to provide a growth and survival advantage to the organism by anticipating stresses. MAPK pathways are well known for their role in cell proliferation and tumor suppression. New evidence reveals that some mammalian clock components also function as tumor suppressors and rhythms in phospho-MAPK have been observed in higher eukaryotes. Thus, the role of the clock in regulation of the activity of MAPK pathways provides important clues into the function of the circadian clock as a tumor suppressor. PMID:18728391

de Paula, Renato M.; Lamb, Teresa M.; Bennett, Lindsay; Bell-Pedersen, Deborah

2008-01-01

446

Casein Kinase 1 Promotes Synchrony of the Circadian Clock Network  

PubMed Central

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 dbtEY02910 loss-of-function mutant. We found that DBT protein levels are dramatically reduced in adult dbtEY02910 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 dbtEY02910 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

2014-01-01

447

Frequency noise processes in a strontium ion optical clock  

NASA Astrophysics Data System (ADS)

A recent comparison of the frequencies of a pair of optical clocks based on the 674 nm 2S1/2–2D5/2 optical clock transition in 88Sr+ has highlighted the need to understand factors affecting frequency instability. We have developed statistical models to show that our clock is capable of reaching the quantum projection noise limit; for our clock using 100 ms probe pulses, this is ?3 × 10?15/??. However, this optical clock uses atomic transitions with a linear Zeeman shift, which can lead to a degradation in stability in the presence of magnetic field noise. We show that this generally leads to an increase in white frequency noise, even in cases dominated by magnetic field flicker or random walk noise. By taking into account both the quantum projection and magnetic field noise we are able to explain our observed frequency instabilities. This analysis will relate to any optical clock with a linear Zeeman shift where cancellation of this shift is achieved by interrogating pairs of components. Furthermore, implementing automatic control of lasers and minimization of micromotion requires pausing of the frequency servo occasionally; this leads to only a small degradation of frequency stability.

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

2015-02-01

448

Ejs Brewsterâs Angle Model  

NSDL National Science Digital Library

The Ejs Brewsterâs Angle model displays the electric field of an electromagnetic wave incident on a change of index of refraction. The simulation allows an arbitrarily linearly (in parallel and perpendicular components) polarized wave to encounter the change of index of refraction. The initial electric field and incidence angle change of index of refraction can all be changed via sliders. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. Ejs Brewsterâs Angle model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_ehu_waves_brewster.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models for wave optics are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Aguirregabiria, Juan

2008-08-20

449

Kelvin-Helmholtz instability during northward IMF conditions: Global 3-Dimensional MHD simulations (Invited)  

NASA Astrophysics Data System (ADS)

The Kelvin-Helmholtz Instability (KHI) has long been suggested to operate on the magnetospheric boundary, where the magnetosheath plasma streams past the magnetosphere. The instability is thought to be responsible for inducing various wave populations in the magnetosphere and for mass, momentum and energy transport across the magnetospheric boundary. Waves attributed to the KHI have been observed at the Earth's magnetosphere flanks as well as at Saturn and Mercury during spacecraft crossings, and remotely at boundaries of Coronal Mass Ejections (CMEs). Recent high-resolution global 3D magnetohydrodynamic (MHD) simulations of the magnetosphere confirm the existence of pronounced perturbations of the magnetospheric boundary, which are thought to be due to KHI. Such global simulations had been challenging in the past because of the need to encompass the entire magnetosphere, while sufficiently resolving the boundary layer. Here we present results of such a high-resolution simulation of the magnetosphere, using the Lyon-Fedder-Mobarry (LFM) model, under steady northward Interplanetary Magnetic Field (IMF) conditions. We find the magnetospheric boundary to be globally unstable, including the high-latitude boundary layer (meridional plane), where magnetic tension is apparently not sufficient to stabilize the growth of oscillations. Roughly beyond the terminator, global modes, coupled into the surface modes, become apparent, so that the entire body of the magnetosphere is engaged in an oscillatory motion. The wave vector of the surface oscillations has a component perpendicular to the background flow and tangential to the shear layer (in the equatorial plane, k_z component of the wave vector), which is consistent with the generation of field-aligned currents that flow on closed field lines between the inner portion of the boundary layer and the ionosphere. We calculate the distribution of wave power in the equatorial plane and find it consistent with the existence of a double-vortex sheet, with vortex trains propagating along the inner and outer edges of the boundary layer. The double-vortex sheet is most apparent in the simulation past the terminator plane, but is transient and appears to be unstable, and is most likely a consequence of non-linear development of the velocity shear layer with a finite width. We compute the salient characteristics of the KH waves, including phase speeds, spectra and growth rates. The latter are compared with linear theory and found to be in excellent agreement. Finally, we find that the plasma compressibility is a key factor in controlling the growth rate of the KHI at the magnetosphere flanks in our simulations.

Merkin, V. G.; Lyon, J.; Claudepierre, S. G.

2013-12-01

450

All-optical NRZ-DPSK clock recovery using linearly chirped fiber Bragg grating induced clock tone  

Microsoft Academic Search

All-optical clock recovery (CR) from 10 Gbps nonreturn-to-zero differential phase-shift-keying (NRZ-DPSK) signal is experimentally demonstrated, by introducing the chromatic dispersion induced clock tone into a free-running semiconductor optical amplifier (SOA) based fiber ring laser for achieving mode-locking. Since no special component is required for NRZ-DPSK demodulation, our proposed method is very promising because of its simple configuration and better stability.

Songnian Fu; Wen-De Zhong; M. Tang; P. Shum; Xia Li

2008-01-01

451

The design and analysis of the clock distribution network for a 1.2 GHz Alpha microprocessor  

Microsoft Academic Search

Single-wire, synchronous clocking systems for increasingly large and complex microprocessors present major technical challenges: Die size increases whereas target clock skew and jitter typically remain a constant percentage of a decreasing cycle time. The clocking methodology of the present Alpha microprocessor handles such challenges by radically departing from a single chip-wide clock distribution, to better control clock skew, jitter and

Thucydides Xanthopoulos; Daniel W. Bailey; Atul K. Gangwar; Michael K. Gowan; Anil K. Jain; Brian K. Prewitt

2001-01-01

452

Fossilized Gravitational Wave Relic and Primordial Clocks  

E-print Network

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.

Suddhasattwa Brahma; Elliot Nelson; Sarah Shandera

2014-05-01

453

Cardiovascular tissues contain independent circadian clocks  

NASA Technical Reports Server (NTRS)

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.

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

2005-01-01

454

Ra+ ion trapping: toward an atomic parity violation measurement and an optical clock  

NASA Astrophysics Data System (ADS)

A single Ra+ ion stored in a Paul radio frequency ion trap has excellent potential for a precision measurement of the electroweak mixing angle at low momentum transfer and as the most stable optical clock. The effective transport and cooling of singly charged ions of the isotopes 209Ra to 214Ra in a gas filled radio frequency quadrupole device is reported. The absolute frequencies of the transition 7s2S1/2-7d2D3/2 at wavelength 828 nm have been determined in 212-214Ra+ with ?19 MHz uncertainty using laser spectroscopy on small samples of ions trapped in a linear Paul trap at the online facility Trapped Radioactive Isotopes: µicrolaboratories for fundamental Physics (TRIµP) of the Kernfysisch Versneller Instituut.

Nuñez Portela, M.; Dijck, E. A.; Mohanty, A.; Bekker, H.; van den Berg, J. E.; Giri, G. S.; Hoekstra, S.; Onderwater, C. J. G.; Schlesser, S.; Timmermans, R. G. E.; Versolato, O. O.; Willmann, L.; Wilschut, H. W.; Jungmann, K.

2014-01-01

455

40. CENTRAL PAVILION OF WEST FACADESLIGHTLY ANGLED, FRONTAL, NORMAL ANGLE ...  

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

40. CENTRAL PAVILION OF WEST FACADE--SLIGHTLY ANGLED, FRONTAL, NORMAL ANGLE Copy photograph of photogrammetric plate LC-HABS-FS13-B-1974-839R. - St. Mary's Seminary, 600 North Paca Street, Baltimore, Independent City, MD

456

Wide Angle Movie  

NASA Technical Reports Server (NTRS)

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

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

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

1999-01-01

457

Quantum metrology -- optical atomic clocks and many-body physics.  

NASA Astrophysics Data System (ADS)

Optical clocks based on atoms confined in optical lattices provide a unique opportunity for precise study and measurement of quantum many- body systems. The state-of-the-art optical lattice clock has reached an overall fractional frequency uncertainty of 1 x 10-16 [1]. One dominant contribution to this uncertainty is clock frequency shift arising from atomic collisions. Collisions between initially identical fermionic Sr atoms can occur when they are subject to slightly inhomogeneous optical excitations during the clock operation [2]. We have recently implemented a seemingly paradoxical solution to the collisionshift problem: with a strong atomic confinement in one-dimensional tube-shaped optical traps, we dramatically increase the atomic interactions. Instead of a naively expected increase of collisional frequency shifts, these shifts are increasingly suppressed [3]. The large atomic interaction strength creates an effective energy gap in the system such that inhomogeneous excitations can no longer drive fermions into a pseudo-spin antisymmetric state, and hence their collisions and the corresponding frequency shifts are suppressed. We demonstrate the effectiveness of this approach by reducing the density-related frequency shift to the level of 10-17, representing more than a factor of ten reduction from the previous record [1, 2]. In addition, we have observed well-resolved interaction sidebands separated from the main peak of the clock transition, giving a direct evidence for the removal of the interaction energy from the clock carrier transition. Control of atomic interactions at the level of 1 x 10-17 is a testimony to our understanding of a quantum many-body system and it removes an important obstacle for building an optical atomic clock based on such systems with high accuracy. [4pt] [1] A. D. Ludlow et al., Science 319, 1805 (2008). [0pt] [2] G. K. Campbell et al., Science 324, 360 (2009). [0pt] [3] M. D. Swallows et al., Science 331, 1043 (2011).

Ye, Jun

2011-10-01

458

Shapes and Angles  

NSDL National Science Digital Library

In this activity (page 7 of PDF), learners will identify the general two-dimensional geometric shape of the uppermost cross section of an impact crater. They will also draw connections between the general two-dimensional geometric shape of an impact crater and the projectile's angle of impact. There are two versions of this activity: Challenge, where students construct a launcher and create their own craters; and Non-Challenge where students analyze pictures of craters. The Moon Math: Craters! guide follows a 5E approach, applying concepts of geometry, modeling, data analysis to the NASA lunar spacecraft mission, LCROSS.

NASA

2012-05-08

459

The costovertebral angle.  

PubMed

Because the anatomy of the costovertebral angle is complex and often unfamiliar to the operating thoracic surgeon, surgical procedures performed in that area must be performed by a surgical team rather than by individual surgeons, and such a team usually includes either an orthopedic surgeon or a neurosurgeon. This is the case, for example, of Pancoast's tumors invading the roots of the brachial plexus or the spine itself where the help of an orthopedic surgeon is invaluable not only to achieve a complete resection but also to prevent catastrophic complications. PMID:18271164

Vallières, Eric

2007-11-01

460

Angles and Area  

NSDL National Science Digital Library

In this activity (page 10 of PDF), learners approximate the area of the uppermost cross section of an impact crater using a variety of square grids. They conclude which angle of impact results in the greatest area. There are two versions of this activity: Challenge, where students construct a launcher and create their own craters; and Non-Challenge where students analyze pictures of craters. Includes a pre-lesson activity (p54). The Moon Math: Craters! guide follows a 5E approach, applying concepts of geometry, modeling, data analysis to the NASA lunar spacecraft mission, LCROSS.

Nasa

2012-05-08

461

The response of the large scale ionospheric convection pattern to changes in the IMF and substorms - Results from the SUNDIAL 1987 campaign  

NASA Astrophysics Data System (ADS)

Multipoint observations of ionospheric convection, made during the SUNDIAL 1987 campaign (May 29 to June 8) which included two intervals of variable IMF Bz and By and several substorms, are used to examine the response of the ionospheric convection in the postdusk and midnight sectors to changes in the IMF Bz component, as well as the effect of substorms on ionospheric convection. It was found that the primary ionospheric effect of a change in the IMF from positive Bz to negative Bz is an enhancement in plasma flow magnitude. The response time of the ionospheric convection to each southward turning varies from 15 min near 1800 MLT to 30 min near 2100 MLT and close to one hour near midnight. During one of the substorms, which consisted of several intensifications, the nightside flow reversal moved progressively to earlier local times in response to each substorm intensification.

Lester, M.; de La Beaujardiere, O.; Foster, J. C.; Freeman, M. P.; Luehr, H.; Ruohoniemi, J. M.; Swider, W.

1993-07-01

462

IMF B(y) and day-night conductivity effects in the expanding polar cap convection model  

NASA Technical Reports Server (NTRS)

During southward B(z) periods the open field line region in the ionosphere (polar cap) expands due to increased dayside merging. Ionospheric plasma flow patterns result which can be classified by the sign of the interplanetary magnetic field (IMF) B(y) component. In this paper, a time-dependent ionospheric convection model is constructed to simulate these flows. The model consists of a spiral boundary with a gap in it. The sign of the IMF B(y) component determines the geometry of the gap. A potential is applied across the gap and distributed around the boundary. A flow results which enters the polar cap t