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1

On the IMF clock angle dependence of the dayside magnetopause reconnection rate  

Microsoft Academic Search

We investigate the IMF clock angle dependence of steady magnetic reconnection at Earth's dayside magnetopause. We present results from a series of high resolution global resistive magnetohydrodynamics simulations (64 million computational cells, giving a magnetopause cell size of a couple hundred kilometers in the GSE X coordinate and about five hundred kilometers in the GSE Y and Z coordinates) in

J. C. Dorelli; J. Raeder

2005-01-01

2

Dayside magnetosphere-ionosphere coupling during IMF clock angle ?90°: Longitudinal cusp bifurcation, quasi-periodic cusp-like auroras, and traveling convection vortices  

Microsoft Academic Search

In spite of the great progress achieved in the understanding the Earth's magnetosphere-ionosphere system, its configuration and dynamics during periods with large horizontal interplanetary magnetic field (IMF ?By? $\\\\gg$ 0) is still poorly investigated. In such time intervals, the cusp\\/low-latitude boundary layer (LLBL) entry regions are characterized by a more complex magnetic reconnection topology, than during IMF Bz-dominated periods, which

S. Massetti

2005-01-01

3

The role of CMEs and interplanetary shocks in IMF winding angle statistics  

SciTech Connect

We examine the possible role of CMEs and interplanetary shocks in past analyses of the large-scale winding of the IMF by extracting CME and shock observations from the ISEE-3 dataset and analyzing periods of the disturbed and undisturbed solar wind separately. We use the full ISEE-3 dataset representing the entire L{sub 1} mission (1978{endash}1982). We conclude that CMEs, the shocks upstream of CMEs and other interplanetary shocks are responsible for the apparent overwinding of the IMF spiral relative to the Parker prediction. The IMF winding angle asymmetry appears to be preserved after the removal of the interplanetary disturbances. {copyright} {ital 1996 American Institute of Physics.}

Smith, C.W. [Bartol Research Institute, University of Delaware, Newark (United States); Phillips, J.L. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

1996-07-01

4

Solar wind dependence of energy coupling between solar wind and magnetosphere during intense northward IMFs  

NASA Astrophysics Data System (ADS)

We statistically study the solar wind dependence of the magnetospheric activities during intense northward interplanetary magnetic fields (IMFs) events (Bz>10 nT, last over 3 h). It was found that the energy coupling between solar wind and magnetosphere during intense northward IMFs was mainly controlled by solar wind velocity and IMF clock angle (?). A northward IMF coupling function was derived based on the dimensional analysis and quantitative analysis of the solar wind parameters and the geomagnetic indices. It was shown that when ?>˜45°, the energy input increases obviously as ? increases. Most importantly, it was also found that the relative importance between the viscous interaction and the IMF ?By? effect in controlling the energy input into the magnetosphere during intense northward IMFs mainly depends on IMF clock angle. The viscous interaction will outweigh the IMF ?By? effect in the northward IMF events with ?<˜75°. In contrast, for those northward IMF events with ?>˜75°, the IMF ?By? effect may be more important than the viscous interaction.

Luo, H.; Chen, G. X.; Du, A. M.; Xu, W. Y.

2013-05-01

5

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

Microsoft Academic Search

This paper proposes diagnosis methods to trace the magnetic merging line and to calculate the electric potential along it for Earth's magnetospheric magnetic fields obtained by global magnetohydrodynamic (MHD) simulations of the solar wind-magnetosphere-ionosphere (SMI) system. The points with minimum magnetic field strength along last closed magnetic field lines and properly selected closed field lines are combined to trace the

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

2009-01-01

6

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

Microsoft Academic Search

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

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

1983-01-01

7

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

NASA Astrophysics Data System (ADS)

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

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

8

Reconnection Tailward of the Cusp Under Negative IMF Bz Conditions  

NASA Astrophysics Data System (ADS)

In the recent statistical work of Twitty et al. (2004) based on Cluster observations in the high- and mid-altitude cusp at near-noon local times (MLT), the prevalent opinion that lobe reconnection is exclusively a northward IMF (B_z > 0) phenomenon is given further support. Contrary to this view, we present a case of lobe reconnection during a steady south-easterly IMF (B_z = -5 nT, IMF clock angle = 115°) midway through the passage at Earth of an interplanetary magnetic cloud on April 17, 1999. Robust signatures of lobe reconnection are present in particle data obtained from Polar/HYDRA during an overflight of the southern polar cusp at 08-09 MLT in the form of an inverse energy-versus-latitude dispersion of precipitating ions. From the ground magnetometer records of the Svalbard stations of the IMAGE chain we infer the presence of a long series of pulsed ionospheric flows (PIFs) in both the merging and lobe convection cells in the northern hemisphere. These data provide strong evidence for the occurrence of (pulsed) lobe reconnection during this interval of steady southeast IMF. The interplanetary conditions included a dominant IMF B_y component of 20 nT, a low proton plasma beta (< 0.1) and a low Alfven Mach number (~3) near the center of the cloud. We speculate that these conditions may give rise to a plasma depletion layer next to the high-latitude magnetopause, a circumstance which favors lobe reconnection. Twitty, C. et al., Geophys. Res. lett., 31, L19808, 2004. This work is supported by a grant in NASA's SEC-GI Program

Farrugia, C. J.; Sandholt, P.

2005-12-01

9

What is the IMF.  

National Technical Information Service (NTIS)

This informational pamphlet provides a brief overview of the International Monetary Fund (IMF). The IMF is an organization of 184 countries working together to foster global monetary cooperation, secure financial stability, facilitate international trade,...

2006-01-01

10

IMF lending and geopolitics  

Microsoft Academic Search

There is growing awareness that the distribution of IMF facilities may not be influenced only by the economic needs of the borrowers. This paper focuses on the fact that the IMF may favour geopolitically important countries in the distribution of IMF loans, differentiating between concessional and nonconcessional facilities. To carry out the empirical analysis, we construct a new database that

Julien Reynaud; Julien Vauday

2008-01-01

11

Reform of IMF Conditionality  

Microsoft Academic Search

The IMF has faced criticism of its expansive use of conditionality. The paper proposes a new procedure for IMF lending designed to meet these criticisms by arguing for the legalization and formalization of the procedure for IMF lending in the light of legal concepts derived mainly from national administrative laws. The gist of the procedure is that, rather than have

Ofer Eldar

2005-01-01

12

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

NASA Astrophysics Data System (ADS)

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

Baker, K. B.

2001-12-01

13

Institutional Determinants of IMF Agreements  

Microsoft Academic Search

Do domestic institutions influence decisions to participate in IMF programs? I argue that executives facing more veto players are more likely to turn to the IMF, but the IMF is more likely to conclude agreements when there are fewer veto players. Reform- minded executives often use the IMF's leverage to push through unpopular policies. The more actors in a political

James Raymond Vreeland

14

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

15

IMF's Return to Iraq.  

National Technical Information Service (NTIS)

December 23, 2005, represented a landmark for Iraq. On that day, the Executive Board of the International Monetary Fund (IMF) approved that institution's first ever stand-by arrangement (SBA) for Iraq. The new arrangement is designed to support that natio...

R. Looney

2006-01-01

16

Angles.  

National Technical Information Service (NTIS)

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

1994-01-01

17

Response of Aurorae, Plasma Convection, and Birkeland Currents to Strong IMF By and Negative Bz Conditions  

NASA Astrophysics Data System (ADS)

In a number of case event studies we probe the association between dayside auroral forms/activities and plasma convection channels (pulsed ionospheric flows) located at the dayside polar cap boundary during By-dominated IMF conditions when a negative Bz-component is also present (clock angle range 90-135°). Both polarities of IMF By are included. We base our results on (i) ground auroral observations at high latitudes (70-80° MLAT) and (ii) particle precipitation, ion drift, and Birkeland current measurements made by the DMSP F13 spacecraft. The following auroral types in the system of forms and activities within the merging and lobe convection cells are noted: (i) cusp 1 aurora ("midday gap"), (ii) cusp 2 aurora in the postnoon sector (By > 0 ), (iii) dayside BPS/LLBL aurorae in the pre- and postnoon sectors, (iv) poleward moving auroral forms (PMAFs) in the mantle regime, and (v) polar arcs on the pre- and postnoon sides of the polar cap. We investigate how these auroral forms evolve in space and time during magnetopause reconnection events. Our goal is to obtain a comprehensive picture of the complex system of dayside and polar cap auroral forms and convection channels contributing to the large-scale pattern of plasma convection/precipitation with the dawn-dusk asymmetry imposed by the IMF By-component. Emphasis is placed on small- and medium-scale structures. These are often averaged out in large statistical studies. This work is supported in part by NASA Grants NNG05GG25G and NNG05GC75G

Sandholt, P.; Farrugia, C.

2006-05-01

18

Coupling the Solar-Wind/IMF to the Ionosphere Through the High Latitude CUSPS  

NASA Astrophysics Data System (ADS)

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 from diverse locations and using large-scale MHD models to put the measurements in context, it is possible to constrain our 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, BY bifurcates 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 fact, the small convection cell is generally driven by opposite hemisphere merging. BX 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.

2005-01-01

19

Angles  

NSDL National Science Digital Library

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

Foundation, Shodor E.

2004-01-01

20

Does IMF conditionality benefit lenders?  

Microsoft Academic Search

Conclusions  The purpose of this paper has been to assess whether official and private lenders benefit from IMF participation in rescheduling\\u000a sovereign LDC debt via the Paris Club. If IMF participation increases the expected value of any existing or newly rescheduled\\u000a official or private debt contracts, then lenders benefit. The transmission process can be via the immediate liquidity the\\u000a IMF provides

Stephen T. Easton; Duane W. Rockerbie

1999-01-01

21

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 ...

Greene, Miss

2010-04-26

22

Recent Changes in IMF Lending  

Microsoft Academic Search

IMF lending has risen sharply in the wake of the global financial crisis from the lows in the mid 2000s. Despite increasing recently, the number of new IMF financing arrangements has been relatively small, but the average size of these arrangements is high by historical standards. Much of the new lending has been to Europe, which has resulted in marked

Kim Edwards; Wing Hsieh

2011-01-01

23

International Monetary Fund (IMF) Data Mapper  

NSDL National Science Digital Library

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

Fund, International M.

24

Biological Clocks  

NSDL National Science Digital Library

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

Science Netlinks;

2002-08-05

25

Component reconnection observed by TC-1 at the dawn flank magnetopause with IMF Bz to be about 0  

NASA Astrophysics Data System (ADS)

Generally, the component reconnection process could take place more easily near sub-solar point than flank magnetopause. In this work, an event of component reconnections observed by TC-1 has been investigated. During the interval of IMF Bz0, at the dawn flank of the magnetopause, TC-1 observed a series of accelerated flows of plasmas, with the velocity up to 500 km/s, even more than twice of the background of the magnetosheath flows. The negative Vz component and negative Vx component were the dominant components of the flows. By using MVA method, a series of bipolar signals were found in the normal component BN in local magnetopause coordinates (LMN), corresponding to the series of the high-speed flows. The negative VL components domained the accelerated flows in LMN coordinates, indicating that the merging happened in -L direction. The analysis of the observed features of the high-speed flows shows that a series of reconnections happened at the dayside flank magnetopause during the interval of IMF Bz0. The clock angle between the IMF and the magnetospheric field could be estimated about 62, noticeably smaller than 180, which implies the component reconnection happened at the dawn flank of the magnetopause. Furthermore, the pretty good result of the walén test using DeHoffman Teller analysis further supports the happening of reconnection. Finally, the motions of the reconnected flux tubes predicted by using the Cooling Model could supply more details of the reconnection process, in which the open flux tube reconnected with the north cusp could still move across the south cusp along the magnetopause, and then convected to the north lobe. The observation of TC-1 presents new observational evidence of component reconnection at flank magnetopause far away from sub-solar point.

Qing, Yan Guang

26

Clock Arithmetic  

NSDL National Science Digital Library

This activity and Java applet allows a student to explore modular arithmetic. It is also a tool for finding remainders where all the possible numbers (the numbers less than the divisor) are put in a circle or clock. The learner uses the scroll bar to modify the size of the clock from 2 to 26 hours, sets a starting value and then moves the "clock" forward a number of specified hours to see the resulting sum. Support pages for the learner and the instructor are included.

2005-01-01

27

Comparative Clocks  

Microsoft Academic Search

\\u000a Daily biological clocks have been described in organisms from all phyla. Here, we describe some features of these temporal\\u000a programs in model experimental systems from bacteria to humans, from fungi to plants. The comparative approach initially delivered\\u000a the transcriptional feedback loop as a fundamental clock mechanism. In addition to early reports showing translational regulation\\u000a in the algae, data from several

Martha Merrow; David Lenssen; Till Roenneberg

28

The Politics of IMF Forecasts  

Microsoft Academic Search

Using panel data for 157 countries over the period 1999-2005 we empirically investigate the politics involved in IMF economic forecasts. We find a systematic bias in growth and inflation forecasts. Our results indicate that countries voting in line with the US in the UN General Assembly receive lower inflation forecasts. As the US is the Fund’s major shareholder, this result

Axel Dreher; Silvia Marchesi; James Raymond Vreeland

2007-01-01

29

The Politics of IMF Forecasts  

Microsoft Academic Search

Using panel data for 157 countries over the period 1999-2005 we empirically investigate the politics involved in IMF economic forecasts. We find a systematic bias in growth and inflation forecasts. Our results indicate that countries voting in line with the US in the UN General Assembly receive lower inflation forecasts. As the US is the Fund's major shareholder, this result

Axel Dreher; Silvia Marchesi; James Raymond Vreeland

30

Mobilizing IMF Gold for Multilateral Debt Cancellation  

Microsoft Academic Search

Sony Kapoor examines how using IMF gold sales to fund multilateral debt cancellation could release much needed resources for meeting the millennium development goals (MDGs). He shows why multilateral debt cancellation is so critical and how the sale of IMF gold could finance it for the IMF as well as the World Bank. He addresses the concerns of the gold-producing

Sony Kapoor

2005-01-01

31

IMF Conditionality and Objections: The Russian Case  

Microsoft Academic Search

Emerging economies in crisis typically request assistance from the International Monetary Fund (IMF). After evaluating the situation, the IMF makes a loan available to the country, conditional on certain policy reforms. Governments usually resist many of these measures and negotiation ensues. This paper analyzes the most contentious measures of IMF conditionality in the context of Russia after the August 1998

Jorge Martinez-Vazquez; Felix Rioja; Samuel Skogstad; Neven Valev

2001-01-01

32

The financial benefits of the IMF  

Microsoft Academic Search

The IMF provides loans to countries in financial distress at a relatively low interest rate. In this article we calculate how much the seven largest debtors to the IMF have saved on interest payments during the Asian crisis and its aftermath. We explain how the IMF can charge these low interest rates and at what cost for creditor countries. The

A. F. P. Bakker; Martijn Schrijvers

2000-01-01

33

IMF Conditionality and Objections: The Russian Case  

Microsoft Academic Search

Emerging economies in crisis typically request assistance from the International Monetary Fund (IMF). After evaluating the situation, the IMF makes a loan available to the country conditional on certain policy reforms. Governments usually resist many of these measures and negotiation ensues. This paper analyzes the most contentious measures of IMF conditionality in the context of Russia after the August 1998

Jorge Martinez-Vazquez; Felix Rioja; Samuel Skogstad; Neven Valev

2000-01-01

34

The Square Light Clock and Special Relativity  

ERIC Educational Resources Information Center

|A thought experiment that includes a square light clock is similar to the traditional vertical light beam and mirror clock, except it is made up of four mirrors placed at a 45[degree] angle at each corner of a square of length L[subscript 0], shown in Fig. 1. Here we have shown the events as measured in the rest frame of the square light clock.…

Galli, J. Ronald; Amiri, Farhang

2012-01-01

35

Beat the Clock!  

NSDL National Science Digital Library

Students solve equations to beat the clock. The faster the you work, the better your score! Pick a link below, work as fast as you can, then show me your score! beat the clock: addition equations Beat the clock: subtracting beat the clock: multiplication beat the clock: division beat the clock: two step *Bonus: Pick a partner and have a race! ...

Troff, Ms.

2008-06-23

36

The IMF of Simple and Composite Populations  

NASA Astrophysics Data System (ADS)

The combination of a finite timescale for star formation, rapid early stellar evolution, and rapid stellar dynamical processes imply that the stellar initial mass function (IMF) cannot be inferred for any star cluster independently of its age (the Cluster IMF Theorem). The IMF can nevertheless be constrained statistically by evolving many theoretical populations drawn from one parent distribution and testing these against observed populations. It follows that all known well-resolved stellar populations are consistent with having been drawn from the same parent mass distribution. The IMF Universality Hypothesis cannot therefore be discarded despite the existence of the Cluster IMF Theorem. This means that the currently existing star formation theory fails to describe the stellar outcome because it predicts a dependency of the IMF on the physical boundary conditions, which is not observed. The Integrated Galactic IMF Theorem, however, predicts a variation of galaxy-wide IMFs in dependence on the galaxy's star formation rate even if the IMF Universality Hypothesis is valid. This variation has now been observed in SDSS galaxy data. Detailed analysis of the binary properties in the very low mass star and brown dwarf mass regime on the one hand and in the stellar regime on the other shows there to be a discontinuity in the IMF near 0.1 M? such that brown dwarfs follow a separate distribution function. Very recent observations of the stellar population within 1 pc of the nucleus of the Milky Way do suggest a top-heavy IMF, perhaps hinting at a variation in the star formation outcome with tidal field and temperature, thereby violating the IMF Universality Hypothesis under these physically extreme conditions. Another violation of this hypothesis appears to emerge for extremely metal-poor stars, such that the primordial IMF appears to have been depleted in low mass stars.

Kroupa, P.

2008-06-01

37

Economic determinants of IMF financial arrangements  

Microsoft Academic Search

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

Malcolm Knight; Julio A. Santaella

1997-01-01

38

IMF: Case of a Dead Theory Walking  

Microsoft Academic Search

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

David Felix

2000-01-01

39

Two-Stage Oscillatory Response of the Magnetopause to a Current/Vortex Sheet Followed by Northward IMF: Cluster Observations  

NASA Astrophysics Data System (ADS)

We discuss the motion and structure of the magnetopause/boundary layer observed by Cluster in response to a joint tangential discontinuity/vortex sheet (TD/VS) observed by the ACE spacecraft on December 7, 2000. The observations are then supplemented by theory. Sharp polarity reversals in the east-west components of the field and flow ,By and Vy, occurred at the discontinuity. These rotations were followed by a period of strongly northward IMF. These two factors elicited a two-stage response at the magnetopause, as observed by Cluster situated in the boundary layer at the duskside terminator. First, the magnetopause suffered a large deformation from its equilibrium position, with large-amplitude oscillations of ~3 min period being set up. These are argued to be mainly the result of tangential stresses associated with ? Vy, the contribution of dynamic pressure changes being small in comparison. This strengthens recent evidence of the importance to magnetospheric dynamics of changes in azimuthal solar wind flow. The TD/VS impact caused a global response seen by ground magnetometers in an MLT range spanning at least 12 hours. The response monitored on ground magnetometers is similar to that brought about by magnetopause motions driven by dynamic pressure changes. Second, Cluster recorded higher frequency waves (~79 s). Two clear phases could be distinguished from the spectral power density, which decreased by a factor of ~3 in the second phase. Applying compressible, linearized MHD theory, we show that these perturbations are consistent with surface waves originating from the Kelvin-Helmholtz instability. Varying the local magnetic shear at the Cluster locale, as suggested by the temporal profile of the IMF clock angle, we find that locally stability was reinstated, so that the reduced power in the second phase is argued to be due residual KH activity arriving from locations farther to the dayside.

Farrugia, C.; Gratton, F.; Lund, E.; Torbert, R.; Sandholt, P.; Cowley, S.; Gnavi, G.; Bilbao, L.; Mouikis, C.; Kistler, L.; Mann, I.; Watermann, J.; Singer, H.

2007-12-01

40

IMF Conditionality and Country Ownership of Programs  

Microsoft Academic Search

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

Mohsin S. Khan; Sunil Sharma

2001-01-01

41

The Structural Budget Balance The IMF's Methodology  

Microsoft Academic Search

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

Robert P. Hagemann

1999-01-01

42

The IMF Approach to Economic Stabilization  

Microsoft Academic Search

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

Michael Mussa; Miguel A. Savastano

1999-01-01

43

Does IMF Financing Result in Moral Hazard?  

Microsoft Academic Search

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

Steven Phillips

2000-01-01

44

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

45

Signalling credibility? The IMF and catalytic finance  

Microsoft Academic Search

International Monetary Fund (IMF) programmes are thought to function as a seal of approval to international markets although evidence suggests that Fund programmes do not attract capital inflows. Existing studies fail to address the effects of selection into IMF programmes, which raises questions about the robustness of the findings. Correcting for selection bias, I find that states under Fund programmes

Martin S. Edwards

2003-01-01

46

The effect of IMF programs on labor  

Microsoft Academic Search

Recent work shows that IMF programs hurt economic growth in the short run and finds no evidence that they help in the long run (Przeworski and Vreeland 2000). Why would governments choose to enter into programs that lower growth? It turns out that the damaging effects of IMF programs may not be evenly distributed. Two st udies on the effects

James Raymond Vreeland

2000-01-01

47

On US politics and IMF Lending  

Microsoft Academic Search

The political factors, which shape IMF lending to LDCs, have attracted much attention. The same goes for the role and influence of the US. However, formal modelling is scant. In this paper, we assume that the US is principal within the IMF and seeks to maximize its impact on the policy stance of debtor countries. We derive the optimal loan

Thomas Barnebeck Andersen; Thomas Harr; Finn Tarp

2004-01-01

48

IMF lending and creditor moral hazard  

Microsoft Academic Search

Existing empirical evidence on the effects of IMF intervention on debtor and creditor incentives - so-called moral hazard - is mixed. A new test of creditor moral hazard is developed, which uses some new data and some more stringent identifying restrictions. The test examines the response of the market valuation of UK banks to IMF loan packages. It finds a

Andrew G Haldane; Jorg Scheibe

2004-01-01

49

The Determinants of IMF Loan Programs  

Microsoft Academic Search

This paper focuses on the bargaining process underlying financial arrangements between the IMF and recipient countries. The primary aim is to investigate the relationship between the own country characteristics, both in terms of macroeconomic conditions and bargaining power, and the outcome of the agreement with the Fund. IMF lending practices respond to economic conditions but are also sensitive to other

Matteo Alessandro Bobba

2004-01-01

50

On US politics and IMF lending  

Microsoft Academic Search

The political factors shaping IMF lending to developing countries have attracted attention in recent empirical work. This goes in particular for the role and influence of the US. However, scant formal modelling makes interpretation of empirical results difficult. In this paper, we propose a model in which the US acts as principal within the IMF and seeks to maximize its

Thomas Barnebeck Andersen; Thomas Harr; Finn Tarp

2006-01-01

51

Rank clocks.  

PubMed

Many objects and events, such as cities, firms and internet hubs, scale with size in the upper tails of their distributions. Despite intense interest in using power laws to characterize such distributions, most analyses have been concerned with observations at a single instant of time, with little analysis of objects or events that change in size through time (notwithstanding some significant exceptions). It is now clear that the evident macro-stability in such distributions at different times can mask a volatile and often turbulent micro-dynamics, in which objects can change their position or rank-order rapidly while their aggregate distribution appears quite stable. Here I introduce a graphical representation termed the 'rank clock' to examine such dynamics for three distributions: the size of cities in the US from ad 1790, the UK from ad 1901 and the world from 430 bc. Our results destroy any notion that rank-size scaling is universal: at the micro-level, these clocks show cities and civilizations rising and falling in size at many times and on many scales. The conventional model explaining such scaling on the basis of growth by proportionate effect cannot replicate these micro-dynamics, suggesting that such models and explanations are considerably less general than has hitherto been assumed. PMID:17136088

Batty, Michael

2006-11-30

52

The Location of the Magnetopause Reconnection Site during Southward IMF Conditions  

NASA Astrophysics Data System (ADS)

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

Trattner, Karlheinz; Fuselier, Stephen; Petrinec, Steven

53

Beat the Clock  

NSDL National Science Digital Library

Students: use these interactive sites to solve linear equations. The faster you solve the equations the better your score. Pick a link below, play the game solving the equations as fast as you can then show me your score. Beat the clock: solving addition equations Beat the clock: subtracting equations Beat the clock: Solving Multiplication equations Beat the clock: Solving Division Equations Beat the clock: Solving two-step equations ...

Wells, Mrs.

2008-06-23

54

A Single EU Seat in the IMF?  

Microsoft Academic Search

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

Lorenzo Bini Smaghi

2004-01-01

55

Solar cycle variations in IMF intensity  

Microsoft Academic Search

Annual averages of logarithms of hourly interplanetary magnetic field (IMF) intensities, obtained from geocentric spacecraft between November 1963 and December 1977, reveal the following solar cycle variation. For 2--3 years at each solar minimum period, the IMF intensity is depressed by 10--15% relative to its mean value realized during a broad 9-year period contered at solar maximum. No systematic variations

Joseph H. King

1979-01-01

56

Does the IMF Help or Hurt? The Effect of IMF programs on the likelihood and outcome of currency crises  

Microsoft Academic Search

Using panel data for 68 countries over the period 1975-2002 this paper examines how IMF programs, disbursed loans, and compliance with conditionality affect the risk of currency crises and the outcome of such crises. Specifically, we investigate whether countries with previous IMF intervention are more likely to experience currency crises. In a second step, we analyze the IMF’s impact on

Axel Dreher; Stefanie Walter

2008-01-01

57

IMF program compliance: Aggregate index versus policy specific research strategies  

Microsoft Academic Search

Consensus has grown that the economic reform programs of the International Monetary Fund (IMF) have failed to promote economic\\u000a development. There is little consensus about how IMF programs should be reformed, however, because we do not understand why\\u000a IMF programs have failed. Some critics contend that the IMF’s austere policy conditions are inappropriate for most program-countries\\u000a and cause economic crises

James R. Vreeland

2006-01-01

58

Memory Event Clocks  

NASA Astrophysics Data System (ADS)

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

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

59

Light Clocks and the Clock Hypothesis  

NASA Astrophysics Data System (ADS)

The clock hypothesis of relativity theory equates the proper time experienced by a point particle along a timelike curve with the length of that curve as determined by the metric. Is it possible to prove that particular types of clocks satisfy the clock hypothesis, thus genuinely measure proper time, at least approximately? Because most real clocks would be enormously complicated to study in this connection, focusing attention on an idealized light clock is attractive. The present paper extends and generalized partial results along these lines with a theorem showing that, for any timelike curve in any spacetime, there is a light clock that measures the curve's length as accurately and regularly as one wishes.

Fletcher, Samuel C.

2013-10-01

60

The Design of IMF-Supported Programs: Does the Balance Sheet of the IMF Matter?  

Microsoft Academic Search

Despite the popularity of the argument that the IMF extends new loans to ensure that existing loans are serviced on schedule, evidence of such defensive-lending behavior is mixed. In this paper, we use a new database on IMF program conditionality and implementation that offers fresh insights on the issue of defensive lending. In particular, we analyze whether a large prominence

Oya Celasun; Rodney Ramcharan

61

Wavefront aberration compensation of projection lens using clocking lens elements.  

PubMed

For extremely high-performance lithographic lenses, the edge level accuracy of the manufacturing process and multicompensation strategies must be applied. Element clocking can be effectively used to compensate for the low-order figure errors of the elements. Considering that commercial optical software is usually incapable of obtaining good convergence for clocking optimization, this paper proposes a mathematical model of a lithographic lens containing the errors of a surface figure, after which a clocking optimization algorithm is programmed. A clocking optimization instance proving that the clocking optimization algorithm is capable of finding the optimized angle of elements and that clocking is an effective compensation strategy. The calculated accuracy of the proposed mathematic model was found to be acceptable for clocking optimization. PMID:23913057

Liu, Chunlai; Huang, Wei; Shi, Zhenguang; Xu, Weicai

2013-08-01

62

Zero skew clock routing for fast clock tree generation  

Microsoft Academic Search

A zero skew clock routing methodology has been developed to help design team speed up their clock tree generation process. The methodology works by breaking up the clock net into smaller partitions, then inserting clock buffers to drive each portion, and lastly, routing the connection from original clock source to each newly inserted clock buffers with zero skew. A few

M. B. I. Reaz; Nowshad Amin; M. I. Ibrahimy; F. Mohd-Yasin; A. Mohammad

2008-01-01

63

Two-stage oscillatory response of the magnetopause to a tangential discontinuity/vortex sheet followed by northward IMF: Cluster observations  

NASA Astrophysics Data System (ADS)

We discuss the motion and structure of the magnetopause/boundary layer observed by Cluster in response to a joint tangential discontinuity/vortex sheet (TD/VS) observed by the Advanced Composition Explorer spacecraft on 7 December 2000. The observations are then supplemented by theory. Sharp polarity reversals in the east-west components of the field and flow By and Vy occurred at the discontinuity. These rotations were followed by a period of strongly northward interplanetary magnetic field (IMF). These two factors elicited a two-stage response at the magnetopause, as observed by Cluster situated in the boundary layer at the duskside terminator. First, the magnetopause suffered a large deformation from its equilibrium position, with large-amplitude oscillations of ˜3-min period being set up. These are argued to be mainly the result of tangential stresses associated with ?Vy the contribution of dynamic pressure changes being small in comparison. This strengthens recent evidence of the importance to magnetospheric dynamics of changes in azimuthal solar wind flow. The TD/VS impact caused a global response seen by ground magnetometers in a magnetic local time range spanning at least 12 h. The response monitored on ground magnetometers is similar to that brought about by magnetopause motions driven by dynamic pressure changes. Second, Cluster recorded higher-frequency waves (˜79 s). Two clear phases could be distinguished from the spectral power density, which decreased by a factor of ˜3 in the second phase. Applying compressible linearized MHD theory, we show that these waves are generated by the Kelvin-Helmholtz (KH) instability. Varying the local magnetic shear at the Cluster locale, as suggested by the temporal profile of the IMF clock angle, we find that locally stability was reinstated, so that the reduced power in the second phase is argued to be due residual KH activity arriving from locations farther to the dayside.

Farrugia, C. J.; Gratton, F. T.; Lund, E. J.; Sandholt, P. E.; Cowley, S. W. H.; Torbert, R. B.; Gnavi, G.; Mann, I. R.; Bilbao, L.; Mouikis, C.; Kistler, L.; Smith, C. W.; Singer, H. J.; Watermann, J. F.

2008-03-01

64

Optical clock recovery  

NASA Astrophysics Data System (ADS)

A scheme for high speed clock and data recovery using an electroabsorption modulated laser and a semiconductor optical amplifiers arranged in an optical-electrical-optical (OEO) loop has been demonstrated. By injecting the 80Gb/s optical data into the OEO ring, the 10GHz clock tone is traced and amplified in the loop. A 10GHz electrical clock and, a 10 GHz optical clock are recovered simultaneously.

Chen, Z.; Sun, H.; Ma, S.; Dutta, N. K.

2009-01-01

65

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

66

Creating a sun clock  

Microsoft Academic Search

An individual project in an early engineering design course is described in which students were required to learn about a simple, ancient system for telling time, namely a sun clock. The students then designed, fabricated and presented for testing both a vertically and horizontally mounted sun clock. These projects were evaluated based on the accuracy of the clocks, the quality

R. Bannerot

2005-01-01

67

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

68

The IMF's role in structural adjustment  

Microsoft Academic Search

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

Paul Collier; Jan Willem Gunning

1999-01-01

69

The Effect of IMF Programs on Labor  

Microsoft Academic Search

Previous studies find that IMF programs have negative effects on income distribution [The International Monetary Fund and Latin America: Economic Stabilization and Class Conflict, Westview Press, Boulder, 1987a; World Dev. 15 (1987b) 365; World Dev. 28 (2000) 1031]. No study, however, has used parametric methods to control for nonrandom selection. Using a dynamic version of the Heckman selection model, I

James Raymond Vreeland

2002-01-01

70

IMF Conditionality as a Screening Device  

Microsoft Academic Search

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

Silvia Marchesi; Jonathan P. Thomas

1999-01-01

71

Jamaica: Macroeconomic Policy, Debt and the IMF  

Microsoft Academic Search

This paper looks at Jamaica’s recent history of indebtedness, its experience during the global economic downturn, and examines its current agreement with the International Monetary Fund (IMF). It finds that Jamaica’s economic and social progress has suffered considerably from the burden of an unsustainable debt; and that even after the debt restructuring of 2010, this burden remains unsustainable and very

Juan Montecino; Jake Johnson

2011-01-01

72

? IMF - development, criti- cisms and future tasks  

Microsoft Academic Search

The activities of the International Monetary Fund (IMF) are a time- honoured matter for debate. In the past decade the focus has been on the Fund's significance for the stability of the international financial sys- tem, in particular its influence and impact on the emerging market eco- nomies in the light of rapidly expanding capital markets. There has been frequent

DAVID FARELIUS

73

How can the IMF catalyse private capital flows? A model  

Microsoft Academic Search

This paper presents a model to explain how IMF programmes can catalyse private capital flows following a financial crisis, a concept that was at the heart of the IMF's strategy for dealing with capital account crises in the late 1990s. In the model, the IMF lends funds below the prevailing market interest rate and it is this subsidy that induces

Adrian Penalver

2004-01-01

74

The role of the IMF in the European debt crisis  

Microsoft Academic Search

This paper gives an overview of the role of the IMF in the European debt crisis. It describes the rescue packages and the involvement of the IMF. The main part discusses the pros and cons of the participation of the IMF in elaborating and monitoring the economic adjustment programs for the countries in crisis. A last section concludes and tries

Franz Seitz; Thomas Jost

2012-01-01

75

The politics of influence: An analysis of IMF surveillance  

Microsoft Academic Search

IMF surveillance is typically thought to have effect because it provides useful information to member countries, because it engages countries in cooperative behaviour or because it piggy-backs the bargaining power the IMF enjoys in some countries. This article explores IMF surveillance by bringing to bear theoretical explanations as to why and how these effects might work. The simplest explanation is

Domenico Lombardi; Ngaire Woods

2008-01-01

76

On the Role and Eects of IMF Seniority  

Microsoft Academic Search

The paper presents a three period model that studies the eects of IMF loans on borrowers’ and lenders’ welfare highlighting the fact that the IMF has both de jure and de facto seniority rights over private creditors. It is shown that an IMF intervention affects borrowers and lenders in different ways. Ex-post, once capital is installed and a liquidity shock

Diego Saravia

2004-01-01

77

IMF surveillance and financial markets—A political economy analysis  

Microsoft Academic Search

The International Monetary Fund (IMF) is in the process of re-inventing itself with bilateral and multilateral surveillance emerging as a key function. The paper analyses how IMF surveillance announcements may be influenced by political power that member countries exert at the IMF. First, we analyze the content of Article IV Public Information Notices (PIN), and second, we use the financial

Marcel Fratzscher; Julien Reynaud

2011-01-01

78

IMF Surveillance and Financial Markets - A Political Economy Analysis  

Microsoft Academic Search

The International Monetary Fund (IMF) is in the process of re-inventing itself with bilateral and multilateral surveillance emerging as a key function. The paper analyses how IMF surveillance announcements may be influenced by political power that member countries exert at the IMF. First, we analyze the content of Article IV Public Information Notices (PIN), and second, we use the financial

Marcel Fratzscher; Julien Reynaud

2010-01-01

79

The Response of Other Lenders to the IMF  

Microsoft Academic Search

Until the late 1980s, it was a stylized fact that when a country adopted an IMF program, additional loans from non-IMF sources would be triggered. Subsequent empirical research cast doubt on this catalytic effect; a country's past involvement with the IMF appeared to be negatively correlated with new lending. This paper examines directly the response of lenders to the presence

Dane Rowlands

2001-01-01

80

Geopolitics and international organizations: An empirical study on IMF facilities  

Microsoft Academic Search

There is growing awareness that the distribution of IMF facilities may not be influenced only by the economic needs of borrowers. This paper focuses on the fact that the IMF may favour geopolitically important countries in the distribution of IMF loans, differentiating between concessional and non-concessional facilities. To carry out the empirical analysis, we construct a new database that compiles

Julien Reynaud; Julien Vauday

2009-01-01

81

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

Microsoft Academic Search

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

Robert J Barro; Jong-Wha Lee

2003-01-01

82

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

83

Does the IMF Help or Hurt? The Effect of IMF Programs on the Likelihood and Outcome of Currency Crises  

Microsoft Academic Search

Using panel data for 68 countries over the period 1975-2002 this paper examines how IMF programs, disbursed loans, and compliance with conditionality affect the risk of currency crises and the outcome of such crises. Specifically, we investigate whether countries with previous IMF intervention are more likely to experience currency crises. In a second step, we analyze the IMF's impact on

Stefanie Walter

2010-01-01

84

Automatic clocking optimization for compensating two-dimensional tolerances.  

PubMed

Clocking of lens elements is frequently used as an effective method of compensating for two-dimensional tolerances such as material inhomogeneity and surface figure errors. Typically, the lens designer has to determine the optimum angles of rotation by manually modeling lens element clocking in the commercial optical design software because the nature of errors resolved by lens clocking does not lead to good convergences for clocking optimization. In this paper, a method of automatic clocking optimization is developed. The method is implemented using a combination of particle swarm optimization algorithm and commercial optical design software. The optimum angles of rotation and predicted imaging performance are automatically calculated using this method. Methods of implementation and optimization examples are also given. PMID:24104106

Xu, Weicai; Huang, Wei; Liu, Chunlai; Shang, Hongbo

2013-09-23

85

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

86

Performance Evaluation of Plausible Clocks  

Microsoft Academic Search

Plausible Clocks do not characterize causality [6] but, under appropriate circumstances, their accuracy is close to vector clocks. This paper explores the effects that several\\u000a factors have on the performance of these clocks.

Francisco J. Torres-rojas

2001-01-01

87

Control of clock signals  

Microsoft Academic Search

Precision and reliability of timescales are of importance in many situations, in particular in satellite navigation systems (i.e., Galileo system). Motivated by the necessity to improve the precision and the reliability of such clock signals, we have explored the possibility to exploit control theory in clock steering methods. First of all we provide a more robust theoretical framework for the

Marcello Farina; Sergio Bittanti; Patrizia Tavella; Lorenzo Galleani

2009-01-01

88

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…

Robertson, Laura; Jones, M. Gail

2009-01-01

89

5 on the Clock  

NSDL National Science Digital Library

This problem reinforces the telling of time on a digital clock, and it requires students to work systematically. The number of 'times' the digit 5 appears in a 24-hour period is a matter of a solver's assumptions. Ideas for implementation, extension and support are included along with a printable poster. A link to an interactive Class Clock (cataloged separately) is provided.

2008-12-01

90

Clock Genes and Cancer  

Microsoft Academic Search

Period genes ( Per2, Per1) are essential circadian clock genes. They also function as negative growth regulators. Per2 mutant mice show de novo and radiation-induced epithelial hyperplasia, tumors, and an abnormal DNA damage response. Human tumors show Period gene mutations or decreased expression. Other murine clock gene mutations are not associated with a tumor prone phenotype. Shift work and nocturnal

Patricia A. Wood; Xiaoming Yang; William J. M. Hrushesky

2009-01-01

91

Active Optical Clocks  

NASA Astrophysics Data System (ADS)

An active optical clock is a special bad cavity laser with perturbation-free medium lasing transition. Spectrum narrowing due to laser mechanism expressed by modified Schawlow-Townes formula improves its high stability of the center frequency of active optical clock by several orders of magnitude is expected. The ultimate limit factor caused by Johnson thermal noise in conventional ultra-stable cavity can be reduced by cavity-pulling effect. In this paper, we will discuss the main features of different configurations of active optical clock, including thermal atomic beam, laser slowed atomic beam, optical lattice and magneto-optical trap trapped atoms. The applications of active optical clock in sub-natural linewidth laser spectroscopy and ultra-long coherence-time laser are discussed here also. Besides the active optical clock, several new concepts including Ramsey laser -- a laser based on Ramsey separated fields method, active atom interferometry, and kilosecond laser are introduced.

Chen, Jingbiao

2009-04-01

92

Plausible Clocks: Constant Size Logical Clocks for Distributed Systems  

Microsoft Academic Search

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

Francisco J. Torres-rojas; Mustaque Ahamad

1996-01-01

93

Clock period optimization technique using multiple clocking domains  

Microsoft Academic Search

The concept of unconstrained clock skew scheduling (CSS) is practically limited due to the difficulties in implementing dedicated clock delays in a reliable manner. This results in a significant limitation of the optimization potential. As an alternative the application of multiple clocking domains with dedicated clock buffer will be implemented. In this paper, an algorithm is proposed for determining the

I. Flavia Princess Nesamani; K Mariya Priyadarshini; A. Sri Devi; V. Lakshmi Prabha

2011-01-01

94

IMF retrospective and prospective: A public goods viewpoint  

Microsoft Academic Search

The paper investigates changes in IMF activities using the analytical framework of international public goods. The IMF promotes\\u000a international financial stability, whose outputs are joint products with varying degrees of publicness. In recent years, IMF\\u000a loans (recipient-specific benefits) have assumed decreased importance, while the Fund’s technical assistance and monitoring\\u000a activities have taken on greater importance. As a consequence, the club

Joseph P. Joyce; Todd Sandler

2008-01-01

95

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

SciTech Connect

Separate studies using the same micropulsation data base in the period range 10--150 s have shown earlier that signal levels recorded during September, October, and November 1969 at Calgary correlated positively with both solar wind alignment of the IMF and solar wind speed, but each correlation contained enough scatter to allow for influence of the other factor. In this report, joint correlations of velocity and field direction with parameters representing hourly distributions rather than minima of IMF orientation angle display the relative effect of the two agents on magnetic pulsation signal levels. The joint correlations reduce the overall scatter and show that solar wind speeds above 200--300 km/s and angles between the IMF and the sun-earth line of less than 50/sup 0/--60/sup 0/ are associated with enlarged magnetic pulsation amplitudes. These threshold effects tend to support both the bow shock origin and the Kelvin-Helmholtz amplification of daytime signal transients in the Pc 3, 4 period ranges.

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

1979-02-01

96

Femtosecond optical clock  

SciTech Connect

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

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

2004-12-31

97

Circadian clocks and metabolism.  

PubMed

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

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

2013-01-01

98

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

99

Space clocks for navigation satellites  

Microsoft Academic Search

The estimation of prediction errors of the Galileo space clocks time is performed via the following steps: a) the determination of errors induced by the geodetic measurement system noise in measuring and predicting the space clock time, based on measurements of GPS clocks produced by the extended GeTT experiment, b) the elaboration of a theoretical model for estimating the clock

G. Busca; C. Frelechoz; Q. Wang; M. R. Merino; U. Hugentobler; R. Dach; G. Dudle; G. Graglia; F. Luongo; P. Rochat; F. Droz; P. Mosset; F. Emma; J. Hahn

2003-01-01

100

Inferring the High Mass Stellar IMF in M31  

NASA Astrophysics Data System (ADS)

I will present results from our ongoing study of the high mass stellar initial mass function (IMF) in M31. I will review the probabilistic technique for inferring the present day mass function (MF) of a resolved young star cluster that avoids many of challenges associated traditional IMF studies (e.g., binning of data, observational completeness), and show how this technique can robustly provide constraints on the high mass IMF. I will show preliminary MF measurements for select young clusters observed with PHAT, and discuss progress toward a secure high mass IMF determination in M31 using ~ 1000 young resolved star clusters.

Weisz, Daniel R.; Fouesneau, M.; Hogg, D. W.; Rix, H.; Dolphin, A. E.; Dalcanton, J.; Lang, D.; Johnson, L. C.; Beerman, L.; Bell, E. F.; Gordon, K. D.; Gouliermis, D.; Kalirai, J. S.; Skillman, E. D.; Williams, B. F.; PHAT Team

2013-01-01

101

Non-radial solar wind flows and IMF B z during 1973-2003  

NASA Astrophysics Data System (ADS)

The characteristics of latitudinal angles of solar wind flow ( ?v) observed near earth have been studied during the period 1973-2003. The average magnitude of ?v shows distinct enhancements during the declining and maximum phases of the sunspot cycles. A close association of B z component of IMF in the GSE system and the orientation of meridional flows in the solar wind is found which depends on the IMF sector polarity. This effect has been studied in typical geomagnetic storm periods. The occurrence of non-radial flows is also found to exhibit heliolatitudinal dependence during the years 1975 and 1985 as a characteristic feature of non-radial solar wind expansion from polar coronal holes.

Pereira, Felix B.; Girish, T. E.

2009-03-01

102

Iodine Clock Reaction.  

ERIC Educational Resources Information Center

|Describes a combination of solutions that can be used in the study of kinetics using the iodine clock reaction. The combination slows down degradation of the prepared solutions and can be used successfully for several weeks. (JRH)|

Mitchell, Richard S.

1996-01-01

103

Clock genes and sleep  

Microsoft Academic Search

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

Dominic Landgraf; Anton Shostak; Henrik Oster

104

The stellar IMF at very low metallicities  

NASA Astrophysics Data System (ADS)

The theory for the formation of the first population of stars (Pop III) predicts a 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 Msolar. 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 H2 as the leading coolant at very high densities. 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 model four clouds with different metallicities (10-4, 10-5, 10-6Zsolar, and 0), and determine the properties of each cloud at the point at which it undergoes gravitational fragmentation. We find evidence for fragmentation in all four cases, and hence conclude that there is no critical metallicity below which fragmentation is impossible. Nevertheless, there is a clear change in the behavior of the clouds at Z = 105Zsolar, caused by the fact that at this metallicity, fragmentation takes longer to occur than accretion, leading to a flat mass function at lower metallicities.

Dopcke, Gustavo; Glover, Simon C. O.; Clark, Paul C.; Klessen, Ralf S.

2012-09-01

105

The Revolving Door: Duration and Recidivism in IMF Programs  

Microsoft Academic Search

Quarterly evidence on participation in IMF programs for the period 1974-2003 is examined using the techniques of hazard analysis and error-correction estimation. Three hypotheses are proposed and tested. An increase in cumulative prior participation in IMF programs is found to cause a reduction on average in the length of a new spell of participation. The length of time between participation

Patrick Conway

2007-01-01

106

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

Microsoft Academic Search

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

Robert J. Barro; Jong-Wha Lee

2002-01-01

107

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

Microsoft Academic Search

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

Robert J. Barro; Jong-Wha Lee

2005-01-01

108

The IMF Rescue Program in Korea: What Went Wrong?  

Microsoft Academic Search

The International Monetary Fund (IMF) has recently received heavy criticism for its handling of the Asian financial crises in 1997. Among others, focus has been put upon the IMF's macroeconomic stabilisation measures of tight monetary policy and fiscal policy, and more fundamental measures of structural reform. The purpose of this paper is to clarify the ongoing debate on the role

Hyun-Hoon Lee

109

The Carrington Storm of 1859 IMF, IEF, TPP, and Dst  

Microsoft Academic Search

From the shock transit time of the 1859 Carrington event, we use statistical relations to infer a shock speed, ICME speed, and maximum ICME field strength. Using average upstream solar wind and IMF conditions, we also infer the profiles of the ram pressure and IMF strength through the ICME-sheath. The Bombay magnetogram for the event gives the magnitude of the

G. Siscoe

2004-01-01

110

The effect of IMF programs on economic growth  

Microsoft Academic Search

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

Adam Przeworski; James Raymond Vreeland

2000-01-01

111

The IMF and the Ruble Area, 1991–93  

Microsoft Academic Search

This paper summarizes the IMF advice on the ruble area as it was presented to the national authorities in Russia, the Baltic countries, and other states of the former Soviet Union in 1991-93. In the course of doing so, the paper corrects some misperceptions that have arisen about the IMF's role. The evidence presented in the paper suggests that (i)

John Odling-Smee; Gonzalo Pastor

112

The IMF and the Ruble Area, 1991–93  

Microsoft Academic Search

This paper summarizes the IMF advice on the ruble area as it was presented to the national authorities in Russia, the Baltic countries, and other states of the former Soviet Union in 1991-93. In the course of doing so, the paper corrects some misperceptions that have arisen about the IMF's role. The evidence presented in the paper suggests that (i)

John Odling-Smee; Gonzalo Pastor

2002-01-01

113

Reflections on the Function and Facilities for IMF Lending  

Microsoft Academic Search

When the International Monetary Fund provides financial support to mem- ber countries from its general resources, the IMF is what it is supposed to be—the primary official international lender of final resort to countries fac- ing actual or potential difficulties in meeting their international payments obligations. To a strictly limited extent, the IMF also functions as a pro- vider of

MICHAEL MUSSA

114

Do loans harm? The Effect of IMF Programs on Inequality  

Microsoft Academic Search

IMF programs consist of granting loans, and of conditionality that countries have to follow in order to qualify for them. The paper uses a pooled time-series cross section analysis, covering 98 countries over the period 1970-2000 in order to find out which effect IMF programs have on the personal and wage income distribution of the grant receiving country. Similar to

Niels Gilbert; Brigitte Unger

2009-01-01

115

Asymmetric Venusian Plasma Environment: Role of the IMF Bx Component  

NASA Astrophysics Data System (ADS)

We study the hemispheric asymmetries of the Venusian plasma environment and induced magnetosphere caused by the flow-aligned component (Bx) of the interplanetary magnetic field (IMF). The Venusian induced magnetosphere is formed by piling up of the IMF against the highly conducting ionosphere. Venus is located in the inner Solar System in a region where Bx typically dominates the IMF. The non-zero Bx gives rise to, for example, perpendicular and parallel bow shock regions in hemispheres perpendicular to the convection electric field. We use the HYB-Venus hybrid simulation to study plasma properties around the planet in two cases: 1) the zero IMF Bx case and 2) the nominal case where the IMF Bx is the dominant component. Further, we study the morphology of the magnetic field around Venus in both cases.

Jarvinen, R.; Kallio, E. J.; Fedorov, A.; Zhang, T.; Barabash, S.; Dyadechkin, S.; Janhunen, P.; Sillanpaa, I.

2011-12-01

116

Free-radical clocks  

SciTech Connect

Organic chemists have, for many years, used competing unimolecular radical reactions as qualitative timing devices to investigate the rates of radical-molecule reactions. The relevant information is obtained simply by product analysis. If unimolecular clock reactions are to be used to determine absolute rate constants for radical-molecule reactions in solution, then, for each class of radical, there is a need for clocks, calibrated for solution work, which cover a range of time scales. For calibration of a clock reaction, a general procedure using EPR spectroscopy has been developed which allows absolute rate constants, k/sub 1/ for unimolecular reactions to be measured in solution over a range of temperature. This yields the Arrhenius parameters, which makes it possible for using clock reactions in studies carried out at temperatures other than those at which k/sub 1/ was measured. The number of clock reactions calibrated by EPR spectroscopy has grown rapidly in recent years. This article illustrates the utility of the approach and presents a few examples taken from the literature.

Griller, D.; Ingold, K.U.

1980-09-01

117

On clocks and clouds  

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

118

MarkerClock: A Communicating Augmented Clock for Elderly  

Microsoft Academic Search

This paper presents markerClock, a communication appli- ance embedded into a clock and designed for seniors as a simple and intuitive device. MarkerClock enhances seniors' connectedness to their social networks, particularly friends, neighbors and relatives, therefore increasing the potential of human communication for providing and re- ceiving care. In doing so, markerClock supports reciprocal care behaviors observed during our initial

Yann Riche; Wendy E. Mackay

2007-01-01

119

Plausible Clocks: Constant Size Logical Clocks for Distributed Systems  

Microsoft Academic Search

Summary.   In a Distributed System with N sites, the precise detection of causal relationships between events can only be done with\\u000a vector clocks of size N. This gives rise to scalability and efficiency problems for logical clocks that can be used to order\\u000a events accurately. In this paper we propose a class of logical clocks called plausible clocks that can

Francisco J. Torres-rojas; Mustaque Ahamad

1999-01-01

120

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

121

Thermospheric Neutral Density Responses to Changes in IMF Sector Polarity  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

122

On turbulent fragmentation and the origin of the stellar IMF  

NASA Astrophysics Data System (ADS)

Two varieties of the universal stellar initial mass function (IMF) viz., the Kroupa and the Chabrier IMF, have emerged over the last decade to explain the observed distribution of stellar masses. The possibility of the universal nature of the stellar IMF leads us to the interesting prospect of a universal mode of star-formation. It is well-known that turbulent fragmentation of gas in the interstellar medium produces a lognormal distribution of density which is further reflected by the mass-function for clumps at low and intermediate masses. Stars condense out of unstable clumps through a complex interplay between a number of dynamic processes which must be accounted for when tracing the origin of the stellar IMF. In the present work, applying the theory of gravitational fragmentation we first derive the mass function (MF) for clumps. Then a core mass function (CMF) is derived by allowing the clumps to fragment, having subjected each one to a random choice of gas temperature. Finally, the stellar IMF is derived by applying a random core-to-star conversion efficiency, ?, in the range of 5-15% to each CMF. We obtain a power-law IMF that has exponents within the error-bars on the Kropua IMF. This derived IMF is preceded by a similar core mass function which suggests, gravoturbulent fragmentation plays a key role in assembling necessary conditions that relate the two mass-functions. In this sense the star-formation process, at least at low redshifts where gas cooling is efficient, is likely to be universal. We argue that the observed knee in the CMF and the stellar IMF may alternatively be interpreted in terms of the characteristic temperature at which gas in potential star-forming clouds is likely to be found. Our results also show that turbulence in star-forming clouds is probably driven on large spatial scales with a power-spectrum steeper than Kolmogorov-type.

Anathpindika, S.

2013-01-01

123

GNSS clock prediction and integrity  

Microsoft Academic Search

Estimation of GNSS clocks phase is conventionally carried out by geodetic network adjustment techniques where orbits and all participant clocks are computed in a batch or Kalman filter least square adjustment to a reference time scale and frame. For real time navigation this estimated clock has to be predicted and provided to the user through the broadcasted navigation message or

Francisco Gonzalez Martinez; P. Waller

2009-01-01

124

Cold Dense Plasma Sheet Formation During Northward IMF  

NASA Astrophysics Data System (ADS)

A cold, dense plasma sheet (CDPS) is often observed when the IMF has been northward for an extended time period, usually several hours. One such period occurred October 22/23, 2003. During that period the IMF was strongly northward for approximately 36 hours, while Cluster II observed a cold dense plasma sheet. We present detailed global simulation results for this event that show how the CDPS develops due to lobe reconnection, which causes IMF flux tubes to be captured and subsequently convected into the tail, forming the CDPS.

Raeder, J.; Li, W.; Dorelli, J.; Oieroset, M.; Phan, T.

2004-12-01

125

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

126

Free-radical clocks  

Microsoft Academic Search

Organic chemists have, for many years, used competing unimolecular radical reactions as qualitative timing devices to investigate the rates of radical-molecule reactions. The relevant information is obtained simply by product analysis. If unimolecular clock reactions are to be used to determine absolute rate constants for radical-molecule reactions in solution, then, for each class of radical, there is a need for

David Griller; Keith U. Ingold

1980-01-01

127

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

128

A Statistical Study of IMF Bz Generation in the Solar Wind  

Microsoft Academic Search

It is well known that the interplanetary magnetic field (IMF) Bz component plays an important role in the generation of geomagnetic activity. The origin of IMF Bz is yet not completely understood but some simple cases of coronal mass ejections when the ambient IMF is draping the CME plasma clouds. However, IMF Bz is observed not only during CMEs but

W. Lyatsky; A. Tan

2005-01-01

129

Why Do Governments and the IMF Enter into Agreements? Statistically Selected Cases  

Microsoft Academic Search

Why do governments and the International Monetary Fund (IMF) enter into agreements? Conventional wisdom holds that governments turn to the Fund for a straightforward reason: they need an IMF loan. An alternative argument is that governments want IMF conditions to be imposed to help push through unpopular economic reforms. To illustrate how the desire for IMF conditions can play a

JAMES RAYMOND VREELAND

2000-01-01

130

Why Do Governments and the imf Enter into Agreements? Statistically Selected Cases  

Microsoft Academic Search

Why do governments and the International Monetary Fund (imf) enter into agreements? Conventional wisdom holds that governments turn to the Fund for a straightforward reason: they need an imf loan. An alternative argument is that governments want imf conditions to be imposed to help push through unpopular economic reforms. To illustrate how the desire for imf conditions can play a

James Raymond Vreeland

2003-01-01

131

The moral hazard of IMF lending: Making a fuss about a minor problem?  

Microsoft Academic Search

The International Monetary Fund (IMF) is under serious attack. Some critics blame IMF lending for having contributed to the spreading of financial crises in emerging markets. Consequently, they call for putting an end to IMF lending. This radical proposal rests on the contention that official financial support has discouraged IMF borrowers to pursue appropriate economic policies, and private creditors to

Peter Nunnenkamp

1999-01-01

132

IMF programs and human rights, 1981–2003  

Microsoft Academic Search

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

M. Rodwan Abouharb; David L. Cingranelli

2009-01-01

133

Explaining IMF lending decisions after the Cold War  

Microsoft Academic Search

This paper empirically investigates the economic and political factors that affect a country’s likelihood to sign an arrangement\\u000a with the IMF and the determinants of the financial size of such a program. Arguably the world and the global financial architecture\\u000a underwent structural changes after the ending of Cold War and so did the role of the IMF. Hence, we update

Christoph Moser; Jan-Egbert Sturm

2011-01-01

134

Cold atom clocks  

Microsoft Academic Search

This paper reviews recent progress on microwave clocks using laser cooled neutral atoms. With an ultra-stable cryogenic sapphire oscillator as interrogation oscillator, a cesium fountain operates at the quantum projection noise limit. With 6 105 detected atoms, the relative frequency stability deltanu\\/nu is 4 10-14tau-1\\/2 where tau is the integration time in seconds. This stability is comparable to that of

C. Salomon; Y. Sortais; S. Bize; M. Abgrall; S. Zhang; C. Nicolas; C. Mandache; P. Lemonde; P. Laurent; G. Santarelli; A. Clairon; N. Dimarcq; P. Petit; A. Mann; A. Luiten; S. Chang

2001-01-01

135

On accelerated magnetosheath flows under northward IMF  

NASA Astrophysics Data System (ADS)

We study the acceleration of magnetosheath plasma using a semi-analytical magnetic string approach for a range of solar wind Alfvén Mach numbers, MA, between 2 and 20. We work with an IMF vector perpendicular to the solar wind velocity, Vsw, and pointing north. We do not invoke magnetic reconnection. Our results indicate that magnetosheath speeds can exceed the solar wind speed, and the ratio V/Vsw increases with decreasing MA. Analyzing the dependence of this ratio on MA, we find that for MA = 2, maximum V/Vsw ? 1.6, and for MA = 10-20, maximum V/Vsw varies from 1.21 to 1.13. Maximum speeds occur a few Earth radii (RE) tailward of the dawn-dusk terminator. The thickness of the accelerated flow layer varies as MA-2. Taking the magnetopause subsolar distance as 10 RE, we find typical values for the thickness of ˜4 RE for MA = 3 and 0.35 RE for MA = 10. The physical mechanism is that of draping of the magnetic field lines around the magnetosphere, and the associated magnetic tension and total pressure gradient forces acting on the flow. For lower MA the plasma depletion is stronger, and thus the acceleration produced by the pressure gradient is larger. An additional acceleration is produced by the magnetic tension, which is stronger for smaller MA. At the dayside the pressure gradient and magnetic tension forces both act in the same direction. But tailward of the terminator the magnetic tension starts to act in the opposite direction to the pressure gradient. When the resulting force vanishes, the highest speed is attained.

Erkaev, N. V.; Farrugia, C. J.; Harris, B.; Biernat, H. K.

2011-01-01

136

The Vitamin C Clock Reaction  

NASA Astrophysics Data System (ADS)

An iodine clock reaction that gives a colorless to black result similar to that of the familiar Landolt iodate-bisulfite clock reaction is described. The vitamin C clock reaction uses chemicals that are readily available on the retail market: vitamin C, tincture of iodine, 3% hydrogen peroxide, and laundry starch. Orange juice may be used as the vitamin C source to give an orange to black reaction.

Wright, Stephen W.

2002-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

138

The Carrington Storm of 1859 IMF, IEF, TPP, and Dst  

NASA Astrophysics Data System (ADS)

From the shock transit time of the 1859 Carrington event, we use statistical relations to infer a shock speed, ICME speed, and maximum ICME field strength. Using average upstream solar wind and IMF conditions, we also infer the profiles of the ram pressure and IMF strength through the ICME-sheath. The Bombay magnetogram for the event gives the magnitude of the SSC and the duration of the transit time passed the earth of the ICME sheath. Since this event occurred during Solar Cycle 10, there is a statistical likelihood that the IMF in the ICME went from north to south as it passed the earth. We use these pieces of information, statistical relations and inferences to construct a probable scenario for the time sequence of solar wind and IMF parameters for the event. We feed this sequence of parameters into analytical models that convert upstream solar wind and IMF data into estimates of the position of the stagnation point, the value of the transpolar potential, and the profile of Dst. Some results: This was probably a two-phase Dst storm with the ICME-sheath driving the first phase and the trailing half of the ICME the second phase. The transpolar potential saturated at a value that probably exceeded 400 kV, and Dst probably reached -600 nT during both storm phases. The stagnation point probably moved to within 3 Re of the center of earth.

Siscoe, G.

2004-05-01

139

The Mechanism of the Formaldehyde Clock Reaction.  

ERIC Educational Resources Information Center

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

Burnett, M. G.

1982-01-01

140

Clock modeling for GNSS applications  

NASA Astrophysics Data System (ADS)

The traditional GNSS (Global Navigation Satellite System) data analysis assumes an independent set of clocks for each epoch. This introduces a huge number of parameters that are highly correlated with station height and troposphere parameters. If the number of the clock parameters can be reduced the GNSS processing procedure may be stabilized. Experiments with kinematic solutions for stations equipped with H-Maser clocks have confirmed this. On the other hand, static coordinates do not significantly benefit from changing the strategy in handling the clock parameter. In the current GNSS constellation only GIOVE-B and the GPS Block IIF satellite clocks seems to be good enough to be modeled instead of freely estimated for each epoch without loosing accuracy at the level of phase measurements. With the Galileo constellation this will change in future. In this context, ESA (European Space Agency) sponsored a project on "Satellite and Station Clock Modelling for GNSS". We will present first results from this project. Different deterministic and stochastic clock models have been evaluated, implemented, and assessed for station and satellite clocks. We will demonstrate the performance and benefits that are available also for today's applications, e.g., in (near) real-time monitoring of crustal deformations.

Orliac, E. J.; Dach, R.; Voithenleitner, D.; Hugentobler, U.; Wang, K.; Rothacher, M.; Svehla, D.

2011-12-01

141

Variable molecular clocks in hominoids  

Microsoft Academic Search

Generation time is an important determinant of a neutral molecular clock. There are several human-specific life history traits that led to a substantially longer generation time in humans than in other hominoids. Indeed, a long generation time is considered an important trait that distinguishes humans from their closest relatives. Therefore, humans may exhibit a significantly slower molecular clock as compared

Navin Elango; James W. Thomas; Soojin V. Yi

2006-01-01

142

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

143

USNO Alternate Master Clock Steering.  

National Technical Information Service (NTIS)

The primary mission of the U.S. Naval Observatory (USNO) Alternate Master Clock (AMC) facility, located at Schriever AFB, is to back up the critical functions of the USNO Time Service Department in Washington, D.C. The USNO AMC operates two Master Clocks,...

P. A. Koppang S. T. Hutsell

2000-01-01

144

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

NASA Astrophysics Data System (ADS)

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

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

2013-06-01

145

The IMF Quota Formula: Linchpin of Fund Reform  

Microsoft Academic Search

The current allocation of decision making in the International Monetary Fund (IMF), determined largely by the distribution of members' quotas, has failed to keep up with the changing world economy. The situation undermines the Fund's relevance and legitimacy in promoting global growth and economic and financial stability. A new simplified and transparent formula to guide the distribution of Fund quotas

Richard N. Cooper; Edwin M. Truman

2007-01-01

146

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

147

Making the IMF and the World Bank More accountable  

Microsoft Academic Search

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

Ngaire Woods

2005-01-01

148

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

149

Occurrence frequencies of IMF triggered and nontriggered substorms  

Microsoft Academic Search

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

Tung-Shin Hsu; Robert L. McPherron

2003-01-01

150

Conditionality and Ownership in IMF Lending: A Political Economy Approach  

Microsoft Academic Search

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

Allan Drazen

2002-01-01

151

The IMF: Lender of Last Resort or Scapegoat?  

Microsoft Academic Search

IMF arrangements provide countries with increased access to foreign exchange during balance of payments crises. Because ready access to foreign exchange may lower the incentives of governments to pursue policies which will avoid such crises, the Fund imposes conditions upon countries in return for the loan of foreign exchange. Hence, the conventional understanding is that governments entering arrangements need an

James Raymond Vreeland

1999-01-01

152

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

Microsoft Academic Search

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

Horst Siebert

1999-01-01

153

Debt Sustainability Assessment: The IMF Approach and Alternatives  

Microsoft Academic Search

Debt sustainability is an essential attribute of good macroeconomic policies but its precise definition is elusive and its assessment is even more challenging. The IMF has developed a sophisticated approach but it must be recognized that, because the future is unknown, any debt sustainability assessment is only valid within the bounds of the underlying guesses. There is no support for

Charles Wyplosz

2007-01-01

154

World Bank\\/IMF: Financial and Programme Support for SSR  

Microsoft Academic Search

With the endorsement of The DAC Handbook on Security System Reform by Organisation for Economic Co-operation and Development (OECD) member governments in 2007, the centrality of governance to the security sector reform (SSR) agenda was clearly established within the development community (Box 8.1). The World Bank and the International Monetary Fund (IMF) hold observer status in the Development Assistance Community

Nicole Ball

155

IMF Lending, Maturity of International Debt and Moral Hazard  

Microsoft Academic Search

International Monetary Fund lending continues to be criticized for possibly generating moral hazard in international financial markets. The empirical examination of this issue has focused exclusively on the potential distortions in the pricing of credit, in the form of lower spreads. To date no research has been conducted on the potential impact of IMF lending on the maturity composition of

Wasseem Mina; Jorge Martinez-Vazquez

2002-01-01

156

The Evolution of 'Homegrown Conditionality' in India: IMF Relations  

Microsoft Academic Search

This article explores the historical relationship between the Government of India (GOI) and the International Monetary Fund (IMF) as a successful model for the ways in which a developing country can learn to work with and through multilateral organisations to promote economic and political development while sustaining democratic institutions and relative international political autonomy. In the mid-1960s, India's relations with

PRAVEEN K. CHAUDHRY; VIJAY L. KELKAR; Vikash Yadav

2004-01-01

157

The simultaneous multiple constraints of the IMF and SFR history in star formation complexes  

Microsoft Academic Search

The multiple constraints method of the IMF and SFR history in star formation complexes (SFCs) attempts to match simultaneously the observed UBVR colours, Lyman continuum fluxes and chemical abundances by finding a best set of the IMF parameters (alpha, M_max), age t and SFR history. The method of using simultaneous multiple constraints of the IMF and SFR history in SFCs

F. H. Sakhibov; M. A. Smirnov

2001-01-01

158

The effect of IMF lending on the probability of sovereign debt crises  

Microsoft Academic Search

This paper explores empirically how the adoption of IMF programs affects sovereign risk over the medium term. We find that IMF programs significantly increase the probability of subsequent sovereign defaults by approximately 1.5–2 percentage points. These results cannot be attributed to endogeneity bias as they are supported by specifications that explain sovereign defaults and program participation simultaneously. Furthermore, IMF programs

Markus Jorra

2012-01-01

159

Adoption of an IMF programme and debt rescheduling. An empirical analysis  

Microsoft Academic Search

The existence of an empirical relationship between the adoption of an IMF programme and the concession of a debt rescheduling by commercial creditors is tested using a bivariate probit model. If countries who have arrangements with the IMF are more likely than others to obtain a rescheduling of their external debt, we could conclude that the adoption of an IMF

Silvia Marchesi

2003-01-01

160

IMF concern for reputation and conditional lending failure: theory and empirics  

Microsoft Academic Search

One possible explanation for the unsatisfactory implementation of IMF conditionality has been attributed to the lack of credibility of the IMF threat of interrupting financial assistance in case of non compliance with the negotiated conditions. In this paper we suggest that such lack of credibility might be due to the dual role played by the IMF which acts at the

Silvia Marchesi; Laura Sabani

2005-01-01

161

Adoption of an IMF Programme and Debt Rescheduling. An Empirical Analysis  

Microsoft Academic Search

The existence of an empirical relationship between the adoption of an IMF programme and the concession of a debt rescheduling by commercial creditors is tested using a bivariate probit model. If countries who have arrangements with the IMF are more likely than others to obtain a rescheduling of their external debt we could conclude that the adoption of an IMF

Silvia Marchesi

2001-01-01

162

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

Microsoft Academic Search

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

H. Jin; K. Maezawa; T. Mukai

2008-01-01

163

The Last Frontier? The IMF and the Diffusion of Global Monetary Norms in Central Asia1  

Microsoft Academic Search

This paper examines the IMF's role as an external actor promoting central bank reforms in the 'frontier' economies of the former Soviet Union. While it is commonly assumed that the IMF's influence over national economic policymaking is determined by a state's dependence on the Fund for financial resources, recent evidence suggests that most IMF programs fail to be completed and

André Broome

164

Reform of IMF Conditionality - A Proposal for Self-Imposed Conditionality  

Microsoft Academic Search

The IMF has faced criticism of its expansive use of conditionality. The paper proposes a new procedure for IMF lending designed to meet these criticisms by arguing for the legalization and formalization of the procedure for IMF lending in the light of legal concepts derived mainly from national administrative laws. The gist of the procedure is that, rather than have

Ofer Eldar

2006-01-01

165

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

NASA Astrophysics Data System (ADS)

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

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

2013-10-01

166

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

167

Biological Clocks and Circadian Rhythms  

NSDL National Science Digital Library

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

Robertson, Laura; Jones, M. G.

2009-02-01

168

Field-aligned acceleration above the polar caps during prolonged periods of Northward IMF: 1- Ion outflows  

NASA Astrophysics Data System (ADS)

The Cluster spacecraft reveal the presence of successive current sheets of opposite polarity above the polar caps during extended periods of northward IMF. At Cluster altitude (5-7 RE), the upward part of this current system consists of ion beams accelerated by quasi-static electric fields and associated with precipitating electrons. They are surrounded by low energy upflowing electron beams carrying a downward current. In this paper, we focus on Cluster observations of upflowing ion beams in the upward current region. These Polar Cap Ion Beams (PCIB) are accelerated by quasi-static electric fields. A recent statistical study shed new light on these structures. The PCIB have lifetimes that can exceed 20 minutes, they appear after northward turning of the IMF and disappear when it turns southward with a delay estimated to respectively ~2 hours and 20 minutes. Interestingly, about 40% of PCIB are detected together with isotropic plasma clouds located in the magnetospheric lobes. When present, the isotropic plasma population has a strong spatial correlation with PCIB suggesting that it is linked to the observed ion outflows. The temperature and pitch angle distribution of these isotropic ions show that they likely originate from the plasmasheet. The statistical properties of PCIB (size, orientation, IMF dependency...) are similar to those of optical polar cap arcs suggesting that both are different signatures of the same phenomenon. This is further confirmed by a case study combining Cluster in-situ data and TIMED optical observations. Using the high-altitude Cluster data as input to a magnetosphere-ionosphere coupling model we have been able to compute the UV emissions produced by the precipitating electrons associated with the PCIB. The modeled photo-emission is in good agreement with that of a polar cap arc observed by TIMED during the same time period. We'll discuss the new insight these observations give on the interaction between the magnetosphere and ionosphere during prolonged periods of northward IMF.

Maggiolo, R.; Fontaine, D.; Echim, M.; Simon Wedlund, C.; Zhang, Y.

2011-12-01

169

Rubidium Atomic Clock for Galileo.  

National Technical Information Service (NTIS)

The overall performance of navigation payloads is dependent on the performance of the on-board clocks. Better stability leads directly to improved space segment autonomy and simplified ground segment operation. The European Space Agency supports the devel...

A. Jeanmaire F. Emma P. Rochat

1999-01-01

170

Stop the Clock, Level 3  

NSDL National Science Digital Library

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

Cogan, Mark

2002-01-01

171

Complex bird clocks.  

PubMed Central

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

Gwinner, E; Brandstatter, R

2001-01-01

172

MESSENGER observations of Mercury's magnetosphere during northward IMF  

NASA Astrophysics Data System (ADS)

MESSENGER's January 14, 2008, flyby of Mercury has provided new observations of the planet's magnetosphere for northward interplanetary magnetic field (IMF). The dusk magnetopause was located inward from the mean magnetopause surface, possibly due to reduced tail magnetic flux content for IMF Bz > 0 and/or the pressure of planetary pickup ions as they respond to the dawnward - v × B electric field in the magnetosheath. Within the plasma sheet rotations of the magnetic field are observed consistent with, Kelvin-Helmholtz vortices ~1 RM in diameter (RM is Mercury's radius). MESSENGER exited through a 1,000 km-wide boundary layer bordered by inner and outer current sheets that resemble rotational and tangential discontinuities, respectively. The total magnetic field change across this layer is consistent with the predicted solar wind ram pressure at Mercury during the MESSENGER flyby.

Slavin, James A.; Anderson, Brian J.; Zurbuchen, Thomas H.; Baker, Daniel N.; Krimigis, Stamatios M.; Acuña, Mario H.; Benna, Mehdi; Boardsen, Scott A.; Gloeckler, George; Gold, Robert E.; Ho, George C.; Korth, Haje; McNutt, Ralph L.; Raines, Jim M.; Sarantos, Menelaos; Schriver, David; Solomon, Sean C.; Trávní?ek, Pavel

2009-01-01

173

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.

174

Capital-market Liberalization, Globalization, and the IMF  

Microsoft Academic Search

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

Joseph E. Stiglitz

2004-01-01

175

What's Wrong with the IMF? What Would be Better?  

Microsoft Academic Search

he International Monetary Fund (IMF) and the World Bank, created in 1944, reflected the experience of the 1920s and 1930s. The Fund's tasks were to adjust current-account imbalances and manage the exchange-rate system. The Bank's main tasks were to lend for the reconstruction of Europe and to eliminate the alleged bias against lending to developing countries. Whatever conditions might have

Allan H. Meltzer

1999-01-01

176

The Variation of Integrated Star IMFs among Galaxies  

Microsoft Academic Search

The integrated galaxial initial mass function (IGIMF) is the relevant\\u000adistribution function containing the information on the distribution of stellar\\u000aremnants, the number of supernovae and the chemical enrichment history of a\\u000agalaxy. Since most stars form in embedded star clusters with different masses\\u000athe IGIMF becomes an integral of the assumed (universal or invariant) stellar\\u000aIMF over the embedded

C. Weidner; P. Kroupa

2005-01-01

177

Microstructure of the IMF turbulences at 2.5 AU  

Microsoft Academic Search

A detailed analysis of small period (15–900 sec) magnetohydrodynamic (MHD) turbulences of the interplanetary magnetic field (IMF) has been made using Pioneer-11 high time resolution data (0.75 sec) inside a Corotating Interaction Region (CIR) at a heliocentric distance of 2.5 AU in 1973. The metods used are the hodogram analysis, the minimum variance matrix analysis and the coherence analysis. The

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

1995-01-01

178

The IMF of Open Star Clusters with Tycho-2  

NASA Astrophysics Data System (ADS)

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

Sanner, Jörg; Geffert, Michael

179

Canada and the IMF: Trailblazer or Prodigal Son?  

Microsoft Academic Search

Canada played an important role in the establishment of the IMF, yet in 1950 it was also the first major member to abandon\\u000a the Bretton Woods par-value system in favour of a flexible exchange rate. Canada’s trail-blazing experience demonstrated that\\u000a a flexible exchange rate can operate in stable and effective manner under a high degree of capital mobility. Equally important,

Michael D. Bordo; Tamara Gomes; Lawrence L. Schembri

2010-01-01

180

Was the IMF's Imposition of Economic Regime Change Justified? A Critique of the IMF's Economic and Political Role in Korea During and After the Crisis  

Microsoft Academic Search

As late as October 1997 the IMF declared that the Korean economy was experiencing a temporary liquidity squeeze, not a solvency problem. Yet in December 1997 Deputy Managing Director Stanley Fischer declared that Korea suffered from a systemic “breakdown of economic relations” so complete that only radical economic restructuring could restore prosperity. The IMF attached what it called “extreme structural

Kang-Kook Lee; James Crotty

2004-01-01

181

Atomic clock ensemble in space  

NASA Astrophysics Data System (ADS)

Atomic Clock Ensemble in Space (ACES) is a mission using high-performance clocks and links to test fundamental laws of physics in space. Operated in the microgravity environment of the International Space Station, the ACES clocks, PHARAO and SHM, will generate a frequency reference reaching instability and inaccuracy at the 1 · 10-16 level. A link in the microwave domain (MWL) and an optical link (ELT) will make the ACES clock signal available to ground laboratories equipped with atomic clocks. Space-to-ground and ground-to-ground comparisons of atomic frequency standards will be used to test Einstein's theory of general relativity including a precision measurement of the gravitational red-shift, a search for time variations of fundamental constants, and Lorentz Invariance tests. Applications in geodesy, optical time transfer, and ranging will also be supported. ACES has now reached an advanced technology maturity, with engineering models completed and successfully tested and flight hardware under development. This paper presents the ACES mission concept and the status of its main instruments.

Cacciapuoti, L.; Salomon, C.

2011-12-01

182

Circadian clocks and cell division  

PubMed Central

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

2010-01-01

183

Clocks, Metabolism, and the Epigenome  

PubMed Central

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

Feng, Dan; Lazar, Mitchell A.

2012-01-01

184

Methylphenidate Modifies the Motion of the Circadian Clock  

PubMed Central

People with attention-deficit/hyperactivity disorder (ADHD) often experience sleep problems, and these are frequently exacerbated by the methylphenidate they take to manage their ADHD symptoms. Many of the changes to sleep are consistent with a change in the underlying circadian clock. The present study was designed to determine if methylphenidate alone could alter properties of the circadian clock. Young male mice were examined in light–dark cycles and in constant darkness and recordings were performed on behavioral activity, sleep, and electrical activity in the suprachiasmatic nucleus (SCN) of freely moving mice. Methylphenidate in the drinking water (0.08%) significantly increased activity in the mid-to-late night, and led to a delay in the onset of activity and sleep relative to the light–dark cycle. While locomotor levels returned to baseline after treatment ended, the phase angle of entrainment required at least a week to return to baseline levels. In constant darkness, the free-running period of both wheel-running and general locomotor rhythms was lengthened by methylphenidate. When the treatment ended, the free-running period either remained stable or only partially reverted to baseline levels. Methylphenidate also altered the electrical firing rate rhythms in the SCN. It induced a delay in the trough of the rhythm, an increment in rhythm amplitude, and a reduction in rhythm variability. These observations suggest that methylphenidate alters the underlying circadian clock. The observed changes are consistent with clock alterations that would promote sleep-onset insomnia.

Antle, Michael C; van Diepen, Hester C; Deboer, Tom; Pedram, Pardis; Pereira, Rob Rodrigues; Meijer, Johanna H

2012-01-01

185

Advances in understanding the peripheral circadian clocks  

PubMed Central

In the past decade, it has become increasingly evident that the circadian clock system plays an important role in many physiological processes. The circadian clock can be divided into 2 parts: the central clock, residing in the suprachiasmatic nucleus of the hypothalamus, which receives light cues, and the peripheral clocks that reside in various tissues throughout the body. The peripheral clocks play an integral and unique role in each of their respective tissues, driving the circadian expression of specific genes involved in a variety of physiological functions. The goal of this review is to provide an introduction to and overview of the peripheral clocks, including potential mechanisms, targets, and implications for disease states. The peripheral clocks include the cardiovascular, metabolic, endocrine, immune, and reproductive systems.— Richards, J., Gumz, M. L. Advances in understanding the peripheral circadian clocks.

Richards, Jacob; Gumz, Michelle L.

2012-01-01

186

Colloquium: Physics of optical lattice clocks  

SciTech Connect

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

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

2011-04-01

187

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

188

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

Microsoft Academic Search

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

Glen Biglaiser; Karl DeRouen Jr

2010-01-01

189

The use of clock tests in schizophrenia  

Microsoft Academic Search

Though clock drawing tests are well recognized as measures of cognitive function, there is little data on the performance of patients with schizophrenia. We compared 24 patients with schizophrenia to 24 healthy, age-matched controls on clock drawing, copying, and reading. Patients with schizophrenia performed significantly worse on clock drawing and copying despite the fact that the groups had similar scores

Nathan Herrmann; Daphne Kidron; Kenneth I Shulman; Edith Kaplan; Malcolm Binns; Jorge Soni; Larry Leach; Morris Freedman

1999-01-01

190

Clocking and Cell Placement for QCA  

Microsoft Academic Search

In this paper we propose a novel two-dimensional clocking and timing scheme for systems which permit a reduction in the longest line length in each clocking zone. The proposed clocking schemes utilize logic propagation techniques which have been developed for systolic arrays. Placement of QCA cells is modified to ensure correct signal generation and timing. The significant reduction in the

V. Vankamamidi; M. Ottavi; F. Lombardi

2006-01-01

191

Fault-tolerant 3D clock network  

Microsoft Academic Search

Clock tree synthesis is one of the most important and challenging problems in 3D ICs. The clock signals have to be delivered by through-silicon vias (TSVs) to different tiers with minimum skew and latency. While there are a few related works in literature, none of them considers the reliability of TSVs. Accordingly, the failure of any TSV in the clock

Chiao-Ling Lung; Yu-Shih Su; Shih-Hsiu Huang; Yiyu Shi; Shih-Chieh Chang

2011-01-01

192

The Circadian Clock Influences Heart Performance  

Microsoft Academic Search

Circadian clocks are believed to provide the selective advantage of anticipation, thus allowing organisms to respond efficiently to stimuli at the appropriate moment. Disrupted circadian rhythms have been found to affect a variety of basic physiological processes. However, the importance of the circadian clock in regulating heart performance remains undetermined. We hypothesized that the circadian clock plays a crucial role

Xi Wu; Zhiwei Liu; Guangsen Shi; Lijuan Xing; Xiaohan Wang; Xiwen Gu; Zhipeng Qu; Zhen Dong; Jing Xiong; Xiang Gao; Chenyu Zhang; Ying Xu

2011-01-01

193

The Adaptive Value of Circadian Clocks  

Microsoft Academic Search

Circadian clocks are thought to enhance the fitness of organisms by improving their ability to adapt to extrinsic influences, specifically daily changes in environmental factors such as light, temperature, and humidity. Some investigators have proposed that circadian clocks provide an additional “intrinsic adaptive value,” that is, the circadian clock that regulates the timing of internal events has evolved to be

Mark A. Woelfle; Yan Ouyang; Kittiporn Phanvijhitsiri; Carl Hirschie Johnson

2004-01-01

194

A Clock Shock: Mouse CLOCK Is Not Required for Circadian Oscillator Function  

Microsoft Academic Search

Summary The circadian clock mechanism in the mouse is com- posed of interlocking transcriptional feedback loops. Two transcription factors, CLOCK and BMAL1, are believed to be essential components of the circadian clock. We have used the Cre-LoxP system to generate whole-animal knockouts of CLOCK and evaluated the resultant circadian phenotypes. Surprisingly, CLOCK- deficient mice continue to express robust circadian rhythms

Jason P. DeBruyne; Elizabeth Noton; Christopher M. Lambert; Elizabeth S. Maywood; David R. Weaver; Steven M. Reppert

2006-01-01

195

Optical frequency standards and clocks  

Microsoft Academic Search

Optical frequency standards based on single trapped ions or ensembles of neutral atoms have recently demonstrated stability and accuracy superior to that of the current generation of microwave primary frequency standards, with significant potential for further improvements. When combined with femtosecond optical frequency combs, these standards can be operated as optical clocks generating a direct microwave output signal, raising the

H. S. Margolis

2010-01-01

196

Neuroimmunology of the circadian clock  

Microsoft Academic Search

Circadian timekeeping is a ubiquitous feature of all eukaryotes which allows for the imposition of a biologically appropriate temporal architecture on an animal's physiology, behavior and metabolism. There is growing evidence that in mammals the processes of circadian timing are under the influence of the immune system. Such a role for the neuroimmune regulation of the circadian clock has inferences

Andrew N. Coogan; Cathy A. Wyse

2008-01-01

197

Physical aware clock skew rescheduling  

Microsoft Academic Search

Yield driven skew scheduling method leads to a clock tree with much greater wire length and buffer number that is not acceptable by designer. Geometry based register position relationships are converted to skew constraints and are combined with timing constraints harmoniously. With the two kinds of skew constraints together, our algorithm solves the skew scheduling problem for both restrictions and

Xinjie Wei; Yici Cai; Xianlong Hong

2007-01-01

198

EMP stars with high mass IMF and hierarchical galaxy formation  

NASA Astrophysics Data System (ADS)

Extremely metal-poor (EMP) stars in the Galactic halo are stars formed in the very early stage of the chemical evolution of the Galaxy. In previous study, we proposed that typical mass of EMP stars are massive, based on observations of carbon-enhanced EMP stars. In this study, we build a merger tree of the Galaxy semi-analytically and follow the chemical evolution along the merger tree. We also consider the effect of binary and high-mass initial mass function(IMF). Resultant theoretical metallicity distribution function (MDF) and abundance distribution are compared with observed metal-poor halo stars.

Komiya, Yutaka; Suda, Takuma; Habe, Asao; Fujimoto, Masayuki Y.

2010-03-01

199

Analysis of a magnetically trapped atom clock  

SciTech Connect

We consider optimization of a rubidium atom clock that uses magnetically trapped Bose condensed atoms in a highly elongated trap, and determine the optimal conditions for minimum Allan variance of the clock using microwave Ramsey fringe spectroscopy. Elimination of magnetic field shifts and collisional shifts are considered. The effects of spin-dipolar relaxation are addressed in the optimization of the clock. We find that for the interstate interaction strength equal to or larger than the intrastate interaction strengths, a modulational instability results in phase separation and symmetry breaking of the two-component condensate composed of the ground and excited hyperfine clock levels, and this mechanism limits the clock accuracy.

Kadio, D. [Departments of Chemistry and Electro-Optics, and Ilse Katz Center for Nano-Science, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Band, Y. B. [Departments of Chemistry and Electro-Optics, and Ilse Katz Center for Nano-Science, Ben-Gurion University of the Negev, Beer-Sheva 84105 (Israel); Atomic Physics Division, A267 Physics, National Institute of Standards and Technology, Gaithersburg, Maryland 20899 (United States)

2006-11-15

200

Unraveling the circadian clock in Arabidopsis  

PubMed Central

The circadian clock is an endogenous timing system responsible for coordinating an organism’s biological processes with its environment. Interlocked transcriptional feedback loops constitute the fundamental architecture of the circadian clock. In Arabidopsis, three feedback loops, the core loop, morning loop and evening loop, comprise a network that is the basis of the circadian clock. The components of these three loops are regulated in distinct ways, including transcriptional, post-transcriptional and posttranslational mechanisms. The discovery of the DNA-binding and repressive activities of TOC1 has overturned our initial concept of its function in the circadian clock. The alternative splicing of circadian clock-related genes plays an essential role in normal functioning of the clock and enables organisms to sense environmental changes. In this review, we describe the regulatory mechanisms of the circadian clock that have been identified in Arabidopsis.

Wang, Xiaoxue; Ma, Ligeng

2013-01-01

201

The Galaxy-wide IMF - from Star Clusters to Galaxies  

NASA Astrophysics Data System (ADS)

Over the past years observations of young and populous star clusters have shown that the stellar initial mass function (IMF) can be conveniently described by a two-part power-law with an exponent ?2 = 2.3 for stars more massive than about 0.5 M? and an exponent of ?1 = 1.3 for less massive stars. A consensus has also emerged that most, if not all, stars form in stellar groups and star clusters, and that the mass function of these can be described as a power-law (the embedded cluster mass function, ECMF) with an exponent ? ? 2. These two results imply that the integrated galactic IMF (IGIMF) for early-type stars cannot be a Salpeter power-law, but that they must have a steeper exponent. An application to star-burst galaxies shows that the IGIMF can become top-heavy. This has important consequences for the distribution of stellar remnants and for the chemo-dynamical and photometric evolution of galaxies. In this contribution the IGIMF theory is described, and the accompanying contribution by Pflamm-Altenburg, Weidner & Kroupa (this volume) documents the applications of the IGIMF theory to galactic astrophysics.

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

2011-06-01

202

How IMF Bx affects the two polar hemispheres differently  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

203

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

Microsoft Academic Search

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

Ronald L. Rosenberg

1975-01-01

204

Evaluating the effect of IMF lending to low-income countries  

Microsoft Academic Search

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

Louis Dicks-Mireaux; Mauro Mecagni; Susan Schadler

2000-01-01

205

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

Microsoft Academic Search

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

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

1996-01-01

206

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

207

Does Membership on the UN Security Council Influence IMF Decisions? Evidence from Panel Data  

Microsoft Academic Search

We investigate whether temporary members of the UN Security Council receive favorable treatment from the IMF, using panel data for 191 countries over the period 1951 to 2004. Our results indicate a robust positive relationship between temporary UN Security Council membership and participation in IMF programs, even after accounting for economic and political factors, as well as regional and country

Axel Dreher; Jan-Egbert Sturm; James Raymond Vreeland

2006-01-01

208

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

Microsoft Academic Search

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

Gary M. Woller; David Kirkwood Hart

1995-01-01

209

Lending Policies of the IMF: HIPC and Debt Relief in Africa  

Microsoft Academic Search

As the issue of aid effectiveness takes centre stage in the context of the looming deadline of the Millennium Development Goals, a spotlight shines on the International Monetary Fund (IMF) lending practices to low-income countries; particularly those in Africa. The IMF's Poverty Reduction and Growth Strategy (PRGF) is a lending facility fraught with contestation regarding both the conditionalities embedded in

Nancy Dubosse

210

Adoption of an IMF Programme and Debt Rescheduling: An Empirical Analysis  

Microsoft Academic Search

The existence of an empirical relationship between the adoption of an IMF programme and the concession of a debt rescheduling by commer- cial creditors is tested using a bivariate probit model. If countries who have arrangements with the IMF are more likely than others to obtain a rescheduling of their external debt we could conclude that the adoption of an

Silvia Marchesi

2000-01-01

211

The Effect of IMF Lending on the Probability of Sovereign Debt Crises  

Microsoft Academic Search

This paper explores empirically how the adoption of IMF programs affects sovereign risk over the medium term. We nd that IMF programs signifcantly increase the probability of subsequent sovereign defaults by approximately 1.5 to 2 percentage points. These results cannot be attributed to endogeneity bias as they are supported by speci cations that explain sovereign defaults and program participation simultaneously.

Markus Jorra

2010-01-01

212

Adoption of an IMF Programme and Debt Rescheduling. An Empirical Analysis  

Microsoft Academic Search

The existence of an empirical relationship between the adoption of an IMF programme and the concession of a debt rescheduling by commercial and official creditors is tested using a bivariate probit model. If countries who have arrangements with the IMF are more likely than others to obtain a rescheduling of their external debt we could conclude that the adoption of

Silvia Marchesi

1999-01-01

213

Adoption of an IMF Programme and Debt Rescheduling. An empirical test of their relationship  

Microsoft Academic Search

The existence of an empirical relationship between the adoption of an IMF programme and the concession of a debt rescheduling by commercial and o¢cial creditors is tested using a bivariate probit model. If countries who have arrangements with the IMF are more likely than others to obtain a rescheduling of their external debt we could conclude that the adoption of

Silvia Marchesi

214

Vulnerability, Crisis and Debt Maturity: do IMF Interventions Shorten the Length of Borrowing?  

Microsoft Academic Search

This paper studies how IMF lending affects countries' bonds maturity. Debt maturity was claimed to be one of the causes of the crisis of recent years: Too much short-term debt would be the seed of self-fulfilling crises. In turn, one of the goals of the IMF is to prevent crises and to alleviate their effects once they occur. I find

Diego Saravia

2010-01-01

215

IMF concern for reputation and conditional lending failure: theory and empirics  

Microsoft Academic Search

The IMF is entrusted with the twofold task of enforcing conditionality and deciding whether or not to continue financial assistance. In this paper we examine the implications on IMF lending behaviour of the existence of uncertainty about its ability to monitor governments’ actions and to enforce conditionality. It is shown that the existence of an even small degree of uncertainty

Silvia Marchesi; Laura Sabani

2005-01-01

216

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

Microsoft Academic Search

It is well known that a persistent southward Interplanetary Magnetic Field (IMF) produces increased geomagnetic activity. It has recently been shown that a sudden increase in solar wind pressure results in poleward expansion of the auroral oval and closing of the polar cap over a wide range of MLTs, and this effect is more pronounced under southward IMF orientation. We

A. Boudouridis; E. Zesta; L. R. Lyons; P. C. Anderson; D. Lummerzheim

2005-01-01

217

THE IMF AND WORLD BANK APPROACHES TO MACROECONOMIC MANAGEMENT IN DEVELOPING COUNTRIES  

Microsoft Academic Search

Abstract:An half a century has just passed since the creation of the Bretton Woods Institutions, the IMF and World Bank. As in the past decades, both institutions are still on the economic as well as political agenda of a number of countries, in particular, developing countries. This paper gives the analytical descriptions of both the IMF and World Bank approaches,to

Huseyin Sen

218

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

Microsoft Academic Search

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

Julien REYNAUD; Julien VAUDAY

2005-01-01

219

WHY IS THE FISCAL POLICY IMPOSED BY IMF PRO-CYCLIC?  

Microsoft Academic Search

The economies which appealed to the IMF loan faced difficulties related to financing the public and the private foreign debt. IMF imposed the promoting of a restrictive fiscal policy to the beneficiary countries, in order to decrease the budget deficit, e

Marinas Marius-Corneliu

2009-01-01

220

Political Determinants Of IMF Balance of Payments Lending: The Curse of Carabosse?  

Microsoft Academic Search

How do political interests shape International Monetary Fund balance of payments lending decisions? We suggest that the institutional structure governing IMF decision- making creates an opportunity for American policymakers to influence IMF lending decisions. We then suggest two reasons, one based on interest group politics and one based on foreign policy objectives, why American policymakers have an incentive to exploit

Thomas Oatley; Jason Yackee

2000-01-01

221

Are IMF Loans More Effective without Policy Advice? A Switching VAR Assessment  

Microsoft Academic Search

Since the current global financial crisis started in 2008, the international Monetary Fund (IMF) has been gaining power again. Before this crisis, the IMF appeared to be sliding towards terminal irrelevance. For several years, emerging economies had been making fewer and fewer demands on its rescue services. The economic emergency room with nearly no patients a year ago is now

Shigeru Iwata; Hiroshi Murao

2009-01-01

222

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

Microsoft Academic Search

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

Axel Dreher; Nathan Jensen

2005-01-01

223

IMF and Economic Growth: The Effects of Programs, Loans, and Compliance with Conditionality  

Microsoft Academic Search

In theory, the IMF could influence economic growth via several channels, among them advice to policy makers, money disbursed under its programs, and its conditionality. This paper tries to separate those effects empirically. Using panel data for 98 countries over the period 1970-2000 it analyzes whether IMF involvement influences economic growth in program countries. Consistent with the results of previous

Axel Dreher

2004-01-01

224

IMF and Economic Growth: The Effects of Programs, Loans, and Compliance with Conditionality  

Microsoft Academic Search

In theory, the IMF could influence economic growth via several channels, among them advice to policy makers, money disbursed under its programs, and its conditionality. This paper tries to disentangle those effects empirically. Using panel data for 98 countries over the period 1970-2000 it analyzes whether IMF involvement influences economic growth in program countries. Consistent with the results of previous

Axel Dreher

2005-01-01

225

IMF and economic growth: The effects of programs, loans, and compliance with conditionality  

Microsoft Academic Search

In theory, the IMF could influence economic growth via several channels, among them advice to policy makers, money disbursed under its programs, and its conditionality. This paper tries to separate those effects empirically. Using panel data for 98 countries over the period 1970- 2000 it analyzes whether IMF involvement influences economic growth in program countries. Consistent with the results of

Axel Dreher

2006-01-01

226

Predicting interplanetary magnetic field (IMF) propagation delay times using the minimum variance technique  

Microsoft Academic Search

It has been known that the fluctuations in the interplanetary magnetic field (IMF) may be oriented in approximately planar structures that are tilted with respect to the solar wind propagation direction along the Sun-Earth line. This tilting causes the IMF propagating from a point of measurement to arrive at other locations with a timing that may be significantly different from

D. R. Weimer; D. M. Ober; N. C. Maynard; M. R. Collier; D. J. McComas; N. F. Ness; C. W. Smith; J. Watermann

2003-01-01

227

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

228

A VMEbus clock system for accelerator control  

SciTech Connect

Because an accelerator has many systems which must operate with a high degree of synchronization, a clock signal is typically generated which carries timing information to the various accelerator components. This paper discusses two VMEbus modules designed to generate and receive this clock signal. Together they implement a clock system which can generate timing markers with 200 nanosecond resolution and can generate timing delays of over one hour with one microsecond resolution. The Clock Generator module contains both a time line generator programmed to produce clock events at specific times and eight programmable input channels to produce clock events when externally triggered. Additional clock events are generated directly from the VMEbus. Generators can be cascaded for added capability. The Clock Timer module receives the signal from the generator. It can be programmed to recognize specific clock events which act as triggers to the eight timing channels on the module. Each timing channel is programmed with a 32-bit delay value. The channels are clocked at 1 MHz. At the end of the delay period, a timer channel produces an output pulse and optionally can generate a bus interrupt.

Beechy, D.G.; McClure, C.R. (Fermi National Accelerator Lab., Batavia, IL (US))

1992-04-01

229

Impact of IMF-related news on capital markets: Further evidence from bond spreads in Indonesia and Korea  

Microsoft Academic Search

The IMF's effects on private capital markets have attracted increasing attention in the literature. This paper examines whether IMF-related news during the Asian crisis contains information regarding the changes in sovereign bond spreads of Indonesia and Korea. Our results indicate that other countries’ IMF-related news increases these countries’ bond spreads. Both in Indonesia and Korea, the countries’ own news associated

Ay?e Y. Evrensel; Ali M. Kutan

2008-01-01

230

Angle Hunting  

NSDL National Science Digital Library

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

Exploratorium

2010-01-01

231

Ribonucleoprotein Complexes That Control Circadian Clocks  

PubMed Central

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

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

2013-01-01

232

Molecular components of the mammalian circadian clock  

PubMed Central

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

Buhr, Ethan D.; Takahashi, Joseph S.

2013-01-01

233

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

234

Low Cost Scheme for On-Line Clock Skew Compensation  

Microsoft Academic Search

In this paper we propose a novel buffer scheme that is able to compensate undesired skews between clocks of a synchronous system in a negligible time upon skew occurrence, thus being suitable also for on-line clock-skew correction. Clock signals are aligned one with respect to the other, starting from a reference clock, and moving forward among physically adjacent clock signals,

Martin Omaña; Daniele Rossi; Cecilia Metra

2005-01-01

235

Dayside magnetic topology at the Earth's magnetopause for northward IMF  

NASA Astrophysics Data System (ADS)

When the Interplanetary Magnetic Field is northward, magnetic reconnection occurs at the Earth's high latitude magnetopause in regions poleward of the Earth's magnetospheric cusps. Observations at the high latitude magnetopause appear to support reconnection poleward of both northern and southern hemisphere cusps, forming closed field lines in the magnetosheath. However, observations at the dayside low latitude magnetopause and in the low altitude cusp do not support this reconnection scenario. Using plasma and magnetic field data from the Cluster spacecraft, signatures of reconnection poleward of both cusps were investigated as a function of latitude. It was found that reconnection in at least one hemisphere occurs essentially all the time for northward IMF. This investigation also confirmed the apparent discrepancy between high and low latitude observations. A scenario for reconnection in both cusps whereby the field line reconnected poleward of one cusp convects away from the dayside magnetopause before reconnecting in the opposite hemisphere is consistent with observations at all latitudes.

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

2012-08-01

236

Accelerated magnetosheath flows caused by IMF draping: Dependence on latitude  

NASA Astrophysics Data System (ADS)

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

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

2012-01-01

237

Polar convection and birkeland currents during strongly positive IMF By  

NASA Astrophysics Data System (ADS)

The TRIAD satellite passed directly over the field of view of the Scandinavian Twin Auroral Radar Experiment (STARE) radar on May 1, 1978, at approximately 0618 UT when the By component of the interplanetary magnetic field (IMF) was unusually large in comparison to the other two component on this day were Bx=-1.8 nT, Bv=8.7 nT, and Bz=-0.2 nT (King, 1979). The TRIAD magnetic field perturbations revealed the presence of a very intense (?B ~ 500 nT) region 1 downward-flowing Birkeland current near 0930 MLT and poleward of a much weaker upward-flowing region 2 current. This ``net'' (unbalanced) Birkeland current was observed at a 67° magnetic latitude in this morning sector (near 0930 MLT). The net Birkeland current was located equatorward of a region of intense westward (antisunward) ionospheric convection flow detected by the STARE radar. We conclude that the polar cap convection flow is distorted and displaced to low latitudes (<67° magnetic latitude) in the morning sector during this period of strongly positive By and almost negligible Bx and Bz. The large net region 1 Birkeland current is associated with the convection flow reversal. Convection velocity data acquired by the AE-C satellite on October 29, 1978, near 1723 UT when Bx=-0.5 nT, By= 8.3 nT, and Bz=-2.7 nT (average values during the 1700 to 1800 UT interval) show the convection reversal near 67° invariant latitude and 0800 MLT (King, 1979). These two examples support previous suggestions for the important influence that the By component of IMF has on the intensity and location of high-latitude convection and Birkeland currents.

Min-Yun, Zi; Nielsen, E.; Hanson, W. B.; Potemra, T. A.

1987-04-01

238

RESULTS OF MODELLING GPS SATELLITE CLOCKS  

Microsoft Academic Search

The IGS (International GPS Service) Analysis Centers (ACs) provide GPS satellite clock offsets to GPS-Time (GPST) in the form of standard ephemeris in sp3-format or clock- RINEX files on a daily basis. These clock offsets, used mainly in GPS post-processing software along with consistent precise satellite ephemeris, are output to a least squares estimation process based on tracking data of

V. Bröderbauer; R. Weber

239

The chlorate-iodine clock reaction.  

PubMed

A clock reaction produced by mixing chlorate and iodine solutions in perchloric acid media is reported. This is the first example of a clock reaction using chlorate as a reagent. Increasing chlorate and acid concentration reduces the induction period. Changing the initial iodine concentration does not affect the length of the induction period. The discovery of this clock reaction opens the possibility that a new family of oscillation reactions can be built using chlorate as reagent. PMID:16366551

Oliveira, André P; Faria, Roberto B

2005-12-28

240

Legitimate Skew Clock Routing with Buffer Insertion  

Microsoft Academic Search

In this paper, we propose a new quick and effective legitimate skew clock routing with buffer insertion algorithm. We analyze\\u000a the optimal buffer position in the clock path, and conclude the sufficient condition and heuristic condition for buffer insertion\\u000a in clock net. During the routing process, this algorithm integrates buffer insertion and node merging together, and performs\\u000a them in parallel.

Xinjie Wei; Yici Cai; Meng Zhao; Xianlong Hong

2006-01-01

241

Systems biology of mammalian circadian clocks.  

PubMed

Systems Biology is a natural extension of molecular biology and can be defined as biology after identification of key gene(s). Systems-biological research is hence seen as a multistage process, beginning with the comprehensive identification and quantitative analysis of individual system components and their networked interactions and leading to the ability to control existing systems toward the desired state and design new ones based on an understanding of structure and underlying dynamical principles. In this chapter, we take mammalian circadian clocks as a model system and describe systems-biological approaches, including the identification of clock-controlled genes, clock-controlled cis elements, and clock transcriptional circuits driven by functional genomics; the parameter change of clock components followed by quantitative measurement; and the dynamic and quantitative perturbation of the clock and its application to one of the fundamental but yet-unsolved questions: singularity behavior of clocks. As perspective for systems-biological investigations, we also introduce the system-level dynamical questions related to the core of clocks, including delay, nonlinearity, temperature-compensation and synchronization of mammalian circadian oscillator(s), and the system-level information problems related to clocks in the environment, including the internal representation of light change through perfect adaptation and internal representation of day length through photoperiodism in mammals. PMID:18419294

Ueda, H R

2007-01-01

242

Multi-domain clock skew scheduling-aware register placement to optimize clock distribution network  

Microsoft Academic Search

Multi-domain clock skew scheduling is a cost effective technique for performance improvement. However, the required wire length and area overhead due to phase shifters for realizing such clock scheduler may be considerable if registers are placed without considering assigned skews. Focusing on this issue, in this paper, we propose a skew scheduling-aware register placement algorithm that enables clock tree optimization

Naser Mohammadzadeh; Minoo Mirsaeedi; Ali Jahanian; Morteza Saheb Zamani

2009-01-01

243

The Panchromatic Hubble Andromeda Treasury: A Bayesian Method for Constraining the High Mass Stellar IMF  

NASA Astrophysics Data System (ADS)

The high mass stellar initial mass function (IMF) underpins virtually all of extragalactic astrophysics. However, measurements of the IMF above a few solar masses exhibit significant dispersion, and recent evidence is suggestive of environmentally dependent IMF variations. The Panchromatic Hubble Andromeda Treasury (PHAT)program is a multi-wavelength survey including hundreds of resolved young clusters extending from the near-UV to near-IR, allowing for a systematic study of the high mass stellar IMF for a large set of clusters over a wide range of environments. Here, we present a new Bayesian technique aimed at constraining the properties of the high mass IMF for resolved stars in individual clusters. This method probabilistically considers uncertainties in stellar mass, completeness, and cluster membership, and uses a Markov Chain Monte Carlo (MCMC) to sample the posterior probability distribution. The MCMC analysis allows us to constrain both the slope of the IMF and the upper stellar mass limit for a single cluster, while fully exploring all associated uncertainties and degeneracies. We present simulations that explore the potential biases introduced by the number of observed stars, stellar mass uncertainties, completeness, aging effects and age spread, and binary stars. The application of this technique to the young cluster population in the PHAT survey will result in the one the most comprehensive investigations of the high mass stellar IMF to date. PHAT is supported by HST GO-12055 administered by NASA.

Weisz, Daniel R.; Fouesneau, M.; Hogg, D. W.; Rix, H. W.; Dalcanton, J. J.; Johnson, L. C.; PHAT Collaboration

2012-01-01

244

Vagaries of the molecular clock  

PubMed Central

The hypothesis of the molecular evolutionary clock asserts that informational macromolecules (i.e., proteins and nucleic acids) evolve at rates that are constant through time and for different lineages. The clock hypothesis has been extremely powerful for determining evolutionary events of the remote past for which the fossil and other evidence is lacking or insufficient. I review the evolution of two genes, Gpdh and Sod. In fruit flies, the encoded glycerol-3-phosphate dehydrogenase (GPDH) protein evolves at a rate of 1.1 × 10?10 amino acid replacements per site per year when Drosophila species are compared that diverged within the last 55 million years (My), but a much faster rate of ?4.5 × 10?10 replacements per site per year when comparisons are made between mammals (?70 My) or Dipteran families (?100 My), animal phyla (?650 My), or multicellular kingdoms (?1100 My). The rate of superoxide dismutase (SOD) evolution is very fast between Drosophila species (16.2 × 10?10 replacements per site per year) and remains the same between mammals (17.2) or Dipteran families (15.9), but it becomes much slower between animal phyla (5.3) and still slower between the three kingdoms (3.3). If we assume a molecular clock and use the Drosophila rate for estimating the divergence of remote organisms, GPDH yields estimates of 2,500 My for the divergence between the animal phyla (occurred ?650 My) and 3,990 My for the divergence of the kingdoms (occurred ?1,100 My). At the other extreme, SOD yields divergence times of 211 My and 224 My for the animal phyla and the kingdoms, respectively. It remains unsettled how often proteins evolve in such erratic fashion as GPDH and SOD.

Ayala, Francisco J.

1997-01-01

245

Giove-A Apparent Clock Assessment and Results.  

National Technical Information Service (NTIS)

The performance of the Galileo space-borne clocks is of importance for navigation and integrity at the corresponding user level. Clock estimation and prediction errors are directly mapped into the User Equivalent Range Error (UERE). The clock quality also...

D. Navarro- Reyes F. Gonzalez J. H. Hahn P. Waller R. Piriz

2007-01-01

246

IMF By and seasonal dependence of the electric field in the inner magnetosphere  

NASA Astrophysics Data System (ADS)

It is known that the electric field pattern at high-latitudes depends on the polarity of the Y component of the interplanetary magnetic field (IMF By) and season. In this study we investigate the above relationships in the inner magnetosphere by using the perigee data from Cluster passing through the magnetic equator. The data consist of both components of the electric field perpendicular to the magnetic field obtained by the electron drift instrument (EDI). These data are sorted by polarities of IMF By and Bz and by seasons or hemispheres. The possible causes of the dependence of the electric fields on IMF By and seasons are discussed.

Matsui, H.; Quinn, J. M.; Torbert, R. B.; Jordanova, V. K.; Puhl-Quinn, P. A.; Paschmann, G.

2004-12-01

247

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

248

Space clock missions and orbitography requirements  

Microsoft Academic Search

In this paper, we study in detail the requirements on orbitography compatible with operation of next generation space clocks at the required uncertainty, and based on a completely relativistic model. We show that the required accuracy goal can be reached with relatively modest constraints on the orbitography of the space clock, much less stringent than expected from \\

L. Duchayne; F. Mercier; P. Wolf

2007-01-01

249

Time prediction accuracy for a space clock  

Microsoft Academic Search

For the Galileo system it is required that a space clock time prediction be performed, covering the time interval (Tp) between two uploads. The time prediction accuracy of the space clock is therefore an important issue. The predictability of the Space Passive Hydrogen Maser (S-PHM) time error is evaluated by the RMS of the predicted time errors at the prediction

G. Busca; Q. Wang

2003-01-01

250

"Molecular Clock" Analogs: A Relative Rates Exercise  

ERIC Educational Resources Information Center

|Although molecular clock theory is a commonly discussed facet of evolutionary biology, undergraduates are rarely presented with the underlying information of how this theory is examined relative to empirical data. Here a simple contextual exercise is presented that not only provides insight into molecular clocks, but is also a useful exercise for…

Wares, John P.

2008-01-01

251

A colorful model of the circadian clock.  

PubMed

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

Reppert, Steven M

2006-01-27

252

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

253

Designing the best clock distribution network  

Microsoft Academic Search

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

Phillip J. Restle; Alina Deutsch

1998-01-01

254

Natural Selection and the Molecular Clock  

Microsoft Academic Search

This paper concludes that the statistical properties of protein evolution are com- patible with a particular model of evolution by natural selection. The argument begins with a statistical description of the molecular clock based on a Poisson process with a randomly varying tick rate. If the time scale of the change of the tick rate of the molecular clock is

John H. Gillespie

1986-01-01

255

Quality monitoring in clock synchronized distributed systems  

Microsoft Academic Search

Clock synchronization in distributed computer systems is an enabler for the introduction of real-time. So far, many approaches are published which implement clock synchronization on a protocol basis over state of the art packet oriented networks. One very recent example is the introduction of real-time into industrial Ethernet net- works, like in Profinet or Powerlink. In addition to this usually

Georg Gaderer; Patrick Loschmidt; Thilo Sauter

2006-01-01

256

Clocks not winding down: unravelling circadian networks  

Microsoft Academic Search

An intrinsic clock enables an organism to anticipate environmental changes and use energy sources more efficiently, thereby conferring an adaptive advantage. Having an intrinsic clock to orchestrate rhythms is also important for human health. The use of systems biology approaches has advanced our understanding of mechanistic features of circadian oscillators over the past decade. The field is now in a

Eric E. Zhang; Steve A. Kay

2010-01-01

257

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

258

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

259

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

Microsoft Academic Search

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

Michael M. Hutchison; Ilan Noy

2003-01-01

260

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

261

Star Forming Regions and the IMF Along the Hubble Sequence  

NASA Astrophysics Data System (ADS)

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

Bresolin, Fabio

262

A clock reaction based on molybdenum blue.  

PubMed

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 molybdenum complex as precursor, in the presence of hydrogen peroxide. Interestingly, the concomitant color change is reversible, enabling multiple clock cycles to be executed consecutively. The kinetics of the clock reaction were experimentally characterized, and by adding insights from quantum chemical calculations, a plausible reaction mechanism was postulated. Key elementary reaction steps comprise sigmatropic rearrangements with five-membered or bicyclo[3.1.0] transition states. Importantly, numerical kinetic modeling demonstrated the mechanism's ability to reproduce the experimental findings. It also revealed that clock behavior is intimately connected to the sudden exhaustion of hydrogen peroxide. Due to the stoichiometric coproduction of ketone, the reaction bears potential for application in alcohol oxidation catalysis. PMID:23634968

Neuenschwander, Ulrich; Negron, Arnaldo; Jensen, Klavs F

2013-05-15

263

Optical Atomic Clock Technology for Space Applications  

NASA Astrophysics Data System (ADS)

Within our work, we investigate the use of optical atomic clocks in spacecraft equipment. The primary goal is to identify optical clocks, which are best suited for satellite implementation. Not only high performance concerning stability and accuracy of the frequency standards but also the possibility to space-qualify such a clock is necessary. Therefore, we analyze different optical clock technologies developed by European and international research facilities in terms of performance and space qualification levels. An optical frequency comb as one subsystem of an optical clock was in this context examined in detail during an ESA funded project. Within this project, two commercially available mode-locked lasers based on rare-earth doped fibers have been analysed and tested under space relevant environmental conditions. We present our test results of thermal, thermal-vacuum and radiation tests and compare the principles of mode locking with respect to their ability for space qualification. Detailed analysis of benefits in positioning accuracy by the use of optical clocks in future global navigation satellite systems as an example application for space-borne optical clocks has been carried out in a study performed for DLR. Thereby a sophisticated simulation has been performed, taking into account not only higher accuracy and stability of optical clocks but also the net result in positioning accuracy when atmospheric influences and orbit deviations are considered. From the space-engineering point of view, main issues for optical clocks in space are stand-alone operation, space environment like radiation and required lifetime of all equipment. The final goal of all our efforts is to identify key technologies that are necessary for the implementation of an optical atomic clock in space. Therefore, a compromise has to be found between technologies that promise highest performance and others that are able to be further developed to a space qualified system within a given time frame and budget.

Plattner, Markus; Kemmerle, Kurt; Stuffler, Timo

264

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

Microsoft Academic Search

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

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

2005-01-01

265

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

SciTech Connect

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

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

1996-03-01

266

IMF Initiatives to Reduce Poverty: Social Marketing to Make Globalization Work Better for All  

Microsoft Academic Search

Abstract In the face of considerable international concern and debate, the International Monetary Fund (IMF) has undertaken a fundamental repositioning during 1997-2002. One integral part of the institution's new role in the so-called \\

Alfred C. Holden

267

Comparison of LFM Simulation Results with Observation for Strongly Northward IMF  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

268

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

Microsoft Academic Search

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

Axel Dreher; Nathan Jensen

2003-01-01

269

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

Microsoft Academic Search

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

Ozlem Arpac; Graham Bird

2009-01-01

270

How can IMF policy eliminate country moral hazard and account for externalities?  

Microsoft Academic Search

Costly crisis prevention has positive external effects, which leads to free-riding of governments on each other's efforts. “Ordinary” IMF loans aggravate existing externalities, reinforcing the under-investment problem. We consider the reform proposals of the “Meltzer commission” in both loan and insurance models and show how the IMF can eliminate country moral. The efficiency-ensuring loan policy accounts for given externalities and

Thomas Weithöner

2006-01-01

271

Democracies only: When do IMF agreements serve as a seal of approval?  

Microsoft Academic Search

Conditional lending by the IMF is predicated, in part, on the belief that IMF programs are associated with increased capital\\u000a inflows to participating countries. This belief is generally consistent with theoretical arguments in the academic literature\\u000a (e.g., Bird and Rowlands 1997; Bordo et al. 2004) but the empirical literature often finds otherwise (e.g., Jensen 2004). This paper argues that the

Molly E. Bauer; Cesi Cruz; Benjamin A. T. Graham

2012-01-01

272

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

Microsoft Academic Search

At A.A. Bochvar Institute a novel conception of IMF to burn civil and weapon’s grade Pu is currently accepted. It consists in the fact, that instead of using pelletized IMF, that features low serviceability and dust forming route of fuel element fabrication, the usage is made of dispersion type fuel element with aluminium or zirconium matrices.Dispersion fuels feature a high

A. M. Savchenko; A. V. Vatulin; E. M. Glagovsky; I. I. Konovalov; A. V. Morozov; A. V. Kozlov; S. A. Ershov; V. A. Mishunin; G. V. Kulakov; V. I. Sorokin; A. P. Simonov; Z. N. Petrova; V. V. Fedotov

2010-01-01

273

Estimating Angles  

NSDL National Science Digital Library

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

2007-06-01

274

Critical Angle  

NSDL National Science Digital Library

This website from the Exploratorium provides a demonstration of total internal reflection. The activity uses a fish aquarium to illustrate how a transparent material like water can act as a reflector. The site provides a thorough description of what to do, an explanation of what is happening, including the critical angle, and examples of its applications to optical fibers.

2008-06-23

275

Congruence of two Kalman filter composite clocks  

NASA Astrophysics Data System (ADS)

This paper compares the estimation results of two composite clock algorithms based on Kalman filtering of measured clock differences: the original Jones-Tryon algorithm and Greenhall's covariance-reduction modification. The theory is carried out for a general clock model that includes the model introduced by Davis et al: the sum of the three-state linear model and a set of Markov processes used to approximate flicker-frequency noise. Since measurement noise is allowed, at each measurement time the corrected clock offsets (the difference between the clock offsets and their estimates) do not coincide but form a set of values, different for the two algorithms. The core result is that these two sets are congruent, that is, they differ by a common scalar shift. As a function of time the value of the shift behaves as a random walk. Moreover, the two Kalman filters have the same measurement residuals. Therefore, any detector algorithm that uses the measurement residuals is not impacted by the covariance reduction. The congruency holds for time-varying measurement matrices. Therefore, the result is applicable to the measurement setup of laboratories as well as that of a Global Navigation Satellite System with varying visibilities of satellite clocks at ground stations. These results are illustrated by a simulated ensemble of three caesium clocks and two active hydrogen masers, measured against one of the masers.

Suess, Matthias; Greenhall, Charles A.

2013-10-01

276

[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

277

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

278

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

279

HORACE: A compact cold atom clock for Galileo  

Microsoft Academic Search

HORACE (HOrloge à Refroidissement d’Atomes en Cellule=clock based on atoms cooled from vapour cell) is a compact cold caesium atom clock developed in SYRTE at Paris Observatory. This clock can operate both on ground and in microgravity environment. Design of HORACE is based on isotropic light cooling, allowing performing the whole clock sequence (cooling, atomic preparation, Ramsey interrogation and detection)

F. X. Esnault; N. Rossetto; D. Holleville; J. Delporte; N. Dimarcq

2011-01-01

280

Characterization and modeling of clock skew with process variations  

Microsoft Academic Search

A new compact model for on-chip clock skew as a function of device, interconnect, and system parameter variations is derived. Unlike previous models that describe qualitative behavior of clock skew components, the new model provides a closed form expression for each clock skew component. An example of clock skew components for a typical design using 0.18 ?m CMOS technology is

Payman Zarkesh-Ha; Tony Mule; James D. Meindl

1999-01-01

281

Evaluation of nano biological clock activity capsulated by lipid layer  

Microsoft Academic Search

In this paper, we try to establish newly technique that the components of the biological clock are reconstituted into the liposome. In other words, we try to produce a nano size clock, capsulated into the liposome, made by protein molecules. The circadian clock is a basic cellular system found in almost all organisms. This clock generates self-sustained oscillations under constant

Masaru Kojima; Masahiro Nakajima; Michio Homma; Kingo Takiguchi; Takao Kondo; Toshio Fukuda

2010-01-01

282

Reconstitution of biological clock into phospholipid-coated microdroplet  

Microsoft Academic Search

In this paper, we try to establish newly technique that the components of the biological clock are reconstituted into the liposome. In other words, we try to produce a nano size clock, capsulated into the liposome, made by protein molecules. The biological clock is a basic cellular system found in almost all organisms. This clock generates self-sustained oscillations under constant

Masaru Kojima; Masae Ohno; Masahiro Nakajima; Michio Homma; Kingo Takiguchi; Takao Kondo; Toshio Fukuda

2009-01-01

283

The circadian Clock mutant mouse: impaired masking response to light  

Microsoft Academic Search

Synchronization of an internal clock (entrainment) and a direct response to light (masking) are complementary ways of restricting activity of an animal to day or night. The protein CLOCK has an important role in the oscillatory mechanism of mammalian pacemakers. Our data show that it is also involved in masking responses. Mice with the Clock\\/Clock mutation reduced their wheel running

Uwe Redlin; Samer Hattar; N. Mrosovsky

2005-01-01

284

Nano size biological clock capsulated by lipid layer: Reconstitution of biological clock into phospholipid-coated microdroplets  

Microsoft Academic Search

We propose a nano size clock, capsulated into micro size liposome, made by protein molecules. The circadian clock is a basic cellular system found in almost all organisms. This clock generates self-sustained oscillations under constant conditions with a ¿24-hour (circadian) period. In cyanobacteria, circadian clock was reconstituted by only three proteins. We reconstitute these proteins and adenosine triphosphate (ATP; energy

Masaru Kojima; Masae Ohno; Masahiro Nakajima; Michio Homma; Kingo Takiguchi; Takao Kondo; Toshio Fukuda

2009-01-01

285

Atomic clock error modeling for GNSS software platform  

Microsoft Academic Search

This paper presents satellite atomic clock error model for generating the satellite clock error in GNSS software platform for the GPS Ll C\\/A code signal, L2 civil signal, L5 signal, and Galileo El, E5a signals. Scheme to simulate the clock error through phase error characteristics of the atomic clock are given. Rubidium, cesium and hydrogen maser clock are considered for

M. Y. Shin; S. J. Lee

2008-01-01

286

Modular Clock Algorithm for Blind Rendezvous.  

National Technical Information Service (NTIS)

A new algorithm, the modular clock algorithm, is developed and analyzed as a solution for the simple rendezvous environment model, coupled with a modified version for environment models with less information. This thesis examines the rendezvous problem as...

N. C. Theis

2009-01-01

287

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

Schulz, Pierre

2007-01-01

288

The circadian clock of Neurospora crassa.  

PubMed

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

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

2011-08-01

289

Compact Microwave Cavity for Hydrogen Atomic Clock.  

National Technical Information Service (NTIS)

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

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

1992-01-01

290

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

291

New IGS Station and Satellite Clock Combination  

Microsoft Academic Search

  Following the principles set forth in the Position Paper #3 at the 1998 Darmstadt Analysis Center (AC) Workshop on the new\\u000a International GPS Service (IGS) International Terrestrial Reference Frame (ITRF) realization and discussions at the 1999 La\\u000a Jolla AC workshop, a new clock combination program was developed. The program allows for the input of both SP3 and the new\\u000a clock

Jan Kouba; Tim Springer

2001-01-01

292

Deep Space Atomic Clock Ticks Toward Success  

NASA Video Gallery

Dr. Todd Ely, principal investigator for NASA's Deep Space Atomic Clock at the Jet Propulsion Laboratory in Pasadena, Calif., spotlights the paradigm-busting innovations now in development to revolutionize spaceflight navigation. The Deep Space Atomic Clock project is one of nine critical Technology Demonstration Missions now under way across the agency -- bridging the gap between laboratory development of valuable new technologies and full-scale testing in the space environment. (NASA/JPL)

Sydney B

2012-12-04

293

CLOX: an executive clock drawing task  

Microsoft Academic Search

OBJECTIVETo describe a clock drawing task (CLOX) designed to elicit executive impairment and discriminate it from non-executive constructional failure.SUBJECTS90 elderly subjects were studied (45 elderly and well persons from the independent living apartments of a continuing care retirement community and 45 patients with probable Alzheimer’s disease). The clock drawing performance of elderly patients was compared with that of 62 young

Donald R Royall; Jeffrey A Cordes; Marsha Polk

1998-01-01

294

Circadian clock, cancer and lipid metabolism  

Microsoft Academic Search

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

Norio Ishida

2007-01-01

295

The MAC - a miniature atomic clock  

Microsoft Academic Search

The authors are developing a chip-scale atomic clock (CSAC), more than two orders of magnitude smaller and lower power than any existing technology. As an intermediate milestone, en route to the ultimate CSAC objectives, we have developed a miniature atomic clock (MAC), combining the low-power CSAC physics package with a low-parts count, low-power digital control and microwave system. The MAC

R. Lutwak; P. Vlitas; M. Varghese; M. Mescher; D. K. Serkland; G. M. Peake

2005-01-01

296

Downloading central clock information in Drosophila  

Microsoft Academic Search

Pigment-disprsing factor (PDF) neuropeptide is an important neurochemical that carries circadian timing information originating\\u000a from the central oscillator in Drosophila. Several core-clock factors function as upstream pdf regulators; the dClock and cycle genes control pdf transcription, whereas the period and timeless genes regulate post-translational processes of PDF via unknown mechanisms. For a downstream neural path, PDF most likely\\u000a acts as

Jae H. Park

2002-01-01

297

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.

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

2012-01-01

298

Coupling governs entrainment range of circadian clocks  

PubMed Central

Circadian clocks are endogenous oscillators driving daily rhythms in physiology and behavior. Synchronization of these timers to environmental light–dark cycles (‘entrainment') is crucial for an organism's fitness. Little is known about which oscillator qualities determine entrainment, i.e., entrainment range, phase and amplitude. In a systematic theoretical and experimental study, we uncovered these qualities for circadian oscillators in the suprachiasmatic nucleus (SCN—the master clock in mammals) and the lung (a peripheral clock): (i) the ratio between stimulus (zeitgeber) strength and oscillator amplitude and (ii) the rigidity of the oscillatory system (relaxation rate upon perturbation) determine entrainment properties. Coupling among oscillators affects both qualities resulting in increased amplitude and rigidity. These principles explain our experimental findings that lung clocks entrain to extreme zeitgeber cycles, whereas SCN clocks do not. We confirmed our theoretical predictions by showing that pharmacological inhibition of coupling in the SCN leads to larger ranges of entrainment. These differences between master and the peripheral clocks suggest that coupling-induced rigidity in the SCN filters environmental noise to create a robust circadian system.

Abraham, Ute; Granada, Adrian E; Westermark, Pal O; Heine, Markus; Kramer, Achim; Herzel, Hanspeter

2010-01-01

299

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

300

The simultaneous multiple constraints of the IMF and SFR history in star formation complexes  

NASA Astrophysics Data System (ADS)

The multiple constraints method of the IMF and SFR history in star formation complexes (SFCs) attempts to match simultaneously the observed UBVR colours, Lyman continuum fluxes and chemical abundances by finding a best set of the IMF parameters (?, M_max), age t and SFR history. The method of using simultaneous multiple constraints of the IMF and SFR history in SFCs (SMC method) is based on the evolutionary synthesis models of stellar clusters, in which the SFR was either an instantaneous burst of age t (simultaneous star formation - SSF model) or a constant with duration t (constant star formation - CSF model) and, parameterized the IMF as a power law of index ? with upper and lower mass limits M_max, M_min. This procedure results in large uncertainties for individual star forming regions (?=0.35, ?M_max=30M_odot, ?_log(t)=0.20), but may be adequate for a study of the average properties of a large sample. The simultaneous multiple constraints of the IMF and SFR history in star formation complexes resolved the IMF-SFR ambiguity in 100 SFCs in 20 galaxies. Star formation episodes proceed either instantaneously or at continuous rate in individual regions. There are correlations between the parameters that define the star formation process (IMF, SFR), and the local properties of the parent galaxy (density, metallicity). The dependence of ages on linear sizes (S in parsec) of star forming regions derived from independent observations of star clusters in LMC (Efremov and Elmegreen: 1998, MNRAS 299, 588) is confirmed. SFR history depends on the star density of SFC. Low density regions demonstrate instantaneous starburst, while in high density SFCs one can see a continuous star formation process. A trend towards greater ages at high stellar densities in the case of constant SFR history indicates that the lifetimes of SFCs are longer than corresponding dynamical time scales of clouds, and that star formation seems to be no fast process on every scale The mechanisms that triggered the burst of star formation depend on the star density and metallicity of SFC. There is a trend toward flatter IMFs at low densities in both cases of SFR history. The density dependence of IMF indicates the role of interactions in protostellar clouds. Dust plays an important role in the transport and redistribution of the Lyc photons emitted by the OB stars; a fraction (1-f) of the Lyc photons escapes, not absorbed by gas in individual SFCs varies from 0 to 90% with a mean = (50+/-30)%. Different star formation episodes (SSF or CSF) show different correlations between the observed parameters (L, S, Z, f). Estimated empirical relations between IMF, ages and observed luminosities, sizes, and colour indices, allow to constrain integrated (cumulative) IMF in a parent galaxy between two extreme versions of star formation regimes SSF and CSF. It is shown that the integrated IMF in the parent galaxy depends not only on the distribution of IMF slopes in individual SFCs but also on the luminosity (size) distribution of SFCs.

Sakhibov, F. H.; Smirnov, M. A.

301

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

NASA Astrophysics Data System (ADS)

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

Greissl, Julia Jennifer

2010-12-01

302

A Comprehensive Study of Relationship Between Subsolar Standoff Distance of the Magnetopause and Cone Angle of Interplanetary Magnetic Field  

Microsoft Academic Search

The subsolar standoff distance of the Earth's magnetopause is an important parameter in studying interactions between the solar wind and the magnetosphere. Its value is mainly controlled by the north-south component (Bz) of the interplanetary magnetic field (IMF) and solar wind dynamic pressure (Dp). Recent studies have found that the subsolar standoff distance is large for small cone angle of

C. Huang; J. Shue; W. Hsieh; B. Lee

2010-01-01

303

N+CPT clock resonance  

SciTech Connect

In a typical compact atomic time standard a current modulated semiconductor laser is used to create the optical fields that interrogate the atomic hyperfine transition. A pair of optical sidebands created by modulating the diode laser become the coherent population trapping (CPT) fields. At the same time, other pairs of optical sidebands may contribute to other multiphoton resonances, such as three-photon N-resonance [Phys. Rev. A 65, 043817 (2002)]. We analyze the resulting joint CPT and N-resonance (hereafter N+CPT) analytically and numerically. Analytically we solve a four-level quantum optics model for this joint resonance and perturbatively include the leading ac Stark effects from the five largest optical fields in the laser's modulation comb. Numerically we use a truncated Floquet solving routine that first symbolically develops the optical Bloch equations to a prescribed order of perturbation theory before evaluating. This numerical approach has, as input, the complete physical details of the first two excited-state manifolds of {sup 87}Rb. We test these theoretical approaches with experiments by characterizing the optimal clock operating regimes.

Crescimanno, M. [Department of Physics and Astronomy, Youngstown State University, Youngstown, Ohio 44555 (United States); Hohensee, M. [MS-59, Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts 02138 (United States)

2008-12-15

304

Signal processing in cellular clocks  

PubMed Central

Many biochemical events within a cell need to be timed properly to occur at specific times of day, after other events have happened within the cell or in response to environmental signals. The cellular biochemical feedback loops that time these events have already received much recent attention in the experimental and modeling communities. Here, we show how ideas from signal processing can be applied to understand the function of these clocks. Consider two signals from the network s(t) and r(t), either two variables of a model or two experimentally measured time courses. We show how s(t) can be decomposed into two parts, the first being a function of r(t), and the second the derivative of a function of r(t). Geometric principles are then derived that can be used to understand when oscillations appear in biochemical feedback loops, the period of these oscillations, and their time course. Specific examples of this theory are provided that show how certain networks are prone or not prone to oscillate, how individual biochemical processes affect the period, and how oscillations in one chemical species can be deduced from oscillations in other parts of the network.

Forger, Daniel B.

2011-01-01

305

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

306

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

NASA Astrophysics Data System (ADS)

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

Lei, Yaguo; Zuo, Ming J.

2009-12-01

307

Solar Wind and IMF Control of the Recovery Phase of Substorms  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

308

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

309

Using IEEE 1588 and boundary clocks for clock synchronization in telecom networks  

Microsoft Academic Search

This article describes the use of IEEE 1588 and boundary clocks for clock distribution (phase\\/time transfer) in telecom networks. The technology is primarily used to serve the radio interface synchronization requirements of mobile systems such as WiMAX and LTE, and to reduce the deployment and dependence of GPS systems in base stations. We discuss the most important functions that are

Michel Ouellette; Kuiwen Ji; Song Liu; Han Li

2011-01-01

310

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

SciTech Connect

In order to better understand the physical processes operating during conditions of northward interplanetary magnetic field (IMF), in situ measurements from the Dynamics Explorer-2 (low altitude) polar satellite and simultaneous observations from the auroral imager on the Dynamics Explorer-1 (high altitude) satellite were used to investigate the relationships between optical emissions, particle precipitation, and convective flows in the high-latitude ionosphere. Field aligned current and convective flow patterns during IMF north include polar cap arcs, the theta aurora or transpolar arc, and the `horse-collar` aurora. The initial part of the study concentrated on the electrodynamics of auroral features in the horse-collar aurora, a contracted but thickened emission region in which the dawn and dusk portions can spread to very high latitudes, while the latter part focused on the evolution of one type of IMF north auroral pattern to another, specifically the quiet-time horse-collar pattern to a theta aurora.

Sharber, J.R.

1996-01-01

311

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

312

Dependence of the electric field in the inner magnetosphere on the IMF BY component  

NASA Astrophysics Data System (ADS)

It is known that the electric field pattern at high-latitudes depends on the polarity of IMF BY. The potential cell at the duskside (dawnside) is larger than that at the other side for IMF BY>0 (BY<0) in the northern hemisphere. This asymmetry of the potential cell appears oppositely in the southern hemisphere. In this study we investigate the above problem by using the perigee data from Cluster passing through the magnetic equator. The data consist of both components of the electric field perpendicular to the magnetic field obtained by the electron drift instrument (EDI). These data are sorted by IMF BY and discussed in terms of the seasonal variation of the orbits and the possible locations of the reconnection at the dayside magnetopause.

Matsui, H.; Quinn, J. M.; Torbert, R. B.; Jordanova, V. K.; Paschmann, G.

2003-12-01

313

Latitudinal and longitudinal displacement of cusp ion precipitation controlled by IMF By and Bz  

NASA Astrophysics Data System (ADS)

Dependence of the location of the cusp precipitation on the orientation of interplanetary magnetic field (IMF) is investigated using data from the Akebono satellite taken at altitudes of several thousands of km. More than a hundred cusp precipitation events have been identified with the low-energy particle detector (LEP) onboard Akebono. The observed energy spectra of ions precipitating at the cusp are dispersed by the convection motion of field lines. We pay special attention to the location where precipitating ions have the highest energy in the energy dispersion curve as recorded along the satellite's path; such location would represent the one nearest to the foot point of the dayside reconnection line (we here assume that the cusp ion injection is triggered by the magnetopause reconnection). We study this location as a proxy for the foot point of the reconnection line and call it "ion entry point" in this paper. Our analysis shows that the location of the "ion entry point" has a strong dependence on the sign and magnitude of IMF By and Bz . By and Bz have almost orthogonal effects on the location of the entry point, with the latitudinal displacement linearly related to Bz, and the longitudinal displacement linearly related to By . We find that the Bz dependence of the ion entry point is represented by a single regression line for entire range of Bz irrespective of its north/south polarity. We also find that the By dependence is larger for positive Bz than for negative Bz . The distribution of ion entry points for positive IMF By is almost a mirror image of that for negative IMF By with respect to the noon-midnight meridian plane. We discuss the dependence of the "ion entry point" on the IMF from the viewpoint of where and how the magnetopause reconnection (merging) occurs for various orientations of IMF.

Asai, K. T.; Maezawa, K.; Mukai, T.; Hayakawa, H.

2005-07-01

314

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

315

Stochastic properties of the plant circadian clock  

PubMed Central

Circadian clocks are gene regulatory networks whose role is to help the organisms to cope with variations in environmental conditions such as the day/night cycle. In this work, we explored the effects of molecular noise in single cells on the behaviour of the circadian clock in the plant model species Arabidopsis thaliana. The computational modelling language Bio-PEPA enabled us to give a stochastic interpretation of an existing deterministic model of the clock, and to easily compare the results obtained via stochastic simulation and via numerical solution of the deterministic model. First, the introduction of stochasticity in the model allowed us to estimate the unknown size of the system. Moreover, stochasticity improved the description of the available experimental data in several light conditions: noise-induced fluctuations yield a faster entrainment of the plant clock under certain photoperiods and are able to explain the experimentally observed dampening of the oscillations in plants under constant light conditions. The model predicts that the desynchronization between noisy oscillations in single cells contributes to the observed damped oscillations at the level of the cell population. Analysis of the phase, period and amplitude distributions under various light conditions demonstrated robust entrainment of the plant clock to light/dark cycles which closely matched the available experimental data.

Guerriero, Maria Luisa; Pokhilko, Alexandra; Fernandez, Aurora Pinas; Halliday, Karen J.; Millar, Andrew J.; Hillston, Jane

2012-01-01

316

Multi-spacecraft THEMIS - Geotail observations of magnetosheath plasma penetration deep into the low-latitude dayside and nightside magnetosphere for equal northward and dawnward IMF  

NASA Astrophysics Data System (ADS)

On June 3, 2007 the five THEMIS spacecraft traversed the dayside post-noon magnetosphere like pearls on a string in a near-equatorial orbit with a 15.4 RE apogee. The leading (probe B) and trailing (probe A) spacecraft were separated by ~~3 RE. While THEMIS B monitored the magnetosheath THEMIS A, C, D, and E were still located inside the magnetosphere and observed an extended layer of mixed cold magnetosheath and hot plasma sheet plasmas. The plasma temperature and density were intermediate between the magnetosheath and hot plasma sheet values. The electron pitch angle distributions in this cold and dense plasma sheet (CDPS) display perfectly balanced field-aligned counter-streaming electrons at all energies, indicating that this region is located on closed magnetic field lines. The CDPS was observed sequentially by the four THEMIS spacecraft, which allows the determination of the thickness and spatial evolution of this region. The dayside post-noon magnetopause appeared to be a stable boundary during this interval, with no evidence for Kelvin-Helmholtz waves. During the same interval Geotail observed CDPS in the dawn flank magnetotail, indicating that the magnetosheath plasma penetration was a global phenomenon. The CDPS observations were associated with an interval of equal northward and dawnward IMF. These observations may suggest that the capturing of the magnetosheath plasma by double-cusp reconnection occurs even with a significant IMF By component.

Oieroset, M.; Phan, T. D.; Angelopoulos, V.; McFadden, J. P.; Carlson, C. W.; Larson, D.; Glassmeier, K.; Fujimoto, M.; Nishino, M.; Raeder, J.; Li, W.; Bonnell, J. W.

2007-12-01

317

Role of clock genes in gastrointestinal motility  

PubMed Central

Biological rhythms coordinate the timing of our internal bodily functions. Colonic motility follows a rhythm as well: most people will have a bowel movement in the morning and rarely during the night. Recent work provides a potential mechanism for this observation: the mouse colon possesses a functional circadian clock as well as a subset of rhythmically expressed genes that may directly impact on colonic motility. Furthermore, measures of colonic motility such as the colonic tissue contractile response to acetylcholine, stool output, and intracolonic pressure changes vary as a function of the time of day, but these variations are attenuated in mice with disrupted clock function. These laboratory findings are supported by clinical observations. Gastrointestinal symptoms such as diarrhea or constipation are prevalent among shift workers and time-zone travelers, both of which are conditions associated with disruptions in biological rhythms. This review will discuss new insights into the role of clock genes in colonic motility and their potential clinical relevance.

2010-01-01

318

Systems biology of mammalian circadian clocks.  

PubMed

Systems biology is a natural extension of molecular biology; it can be defined as biology after identification of key gene(s). Systems-biological research is a multistage process beginning with (a) the comprehensive identification and (b) quantitative analysis of individual system components and their networked interactions, which lead to the ability to (c) control existing systems toward the desired state and (d) design new ones based on an understanding of the underlying structure and dynamical principles. In this review, we use the mammalian circadian clock as a model system and describe the application of systems-biological approaches to fundamental problems in this model. This application has allowed the identification of transcriptional/posttranscriptional circuits, the discovery of a temperature-insensitive period-determining process, and the discovery of desynchronization of individual clock cells underlying the singularity behavior of mammalian clocks. PMID:20148689

Ukai, Hideki; Ueda, Hiroki R

2010-01-01

319

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.

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

2013-01-01

320

Recent atomic clock comparisons at NIST  

NASA Astrophysics Data System (ADS)

The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg+ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant ? to less than 2 · 10-6yr-1 and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al+ and Hg+ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10-17. The record of such measurements over the last year sensitively tests for a temporal variation of ? and constrains dot{?}/? = (-1.6 ± 2.3) . 10^{-17} yr^{-1}, consistent with zero.

Lorini, L.; Ashby, N.; Brusch, A.; Diddams, S.; Drullinger, R.; Eason, E.; Fortier, T.; Hastings, P.; Heavner, T.; Hume, D.; Itano, W.; Jefferts, S.; Newbury, N.; Parker, T.; Rosenband, T.; Stalnaker, J.; Swann, W.; Wineland, D.; Bergquist, J.

2008-10-01

321

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

322

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...

323

Cold Atom Clocks in Space:. Pharao and Aces  

Microsoft Academic Search

The interest of space environment for cold atom clocks is outlined. We discuss the scientific objectives of the European space mission ACES which will fly onboard the international space station in 2005-2007 with a cold atom clock, PHARAO.

P. Laurent; M. Abgrall; A. Clairon; P. Lemonde; G. Santarelli; P. Uhrich; N. Dimarcq; L. G. Berner; G. Busca; A. Jornod; P. Thomann; E. Samain; P. Wolf; F. Gonzalez; Ph. Guillemot; F. Nouel; Ch. Sirmain; S. Feltham; C. Salomon

2002-01-01

324

Real clocks and the Zeno effect  

SciTech Connect

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

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

2003-08-01

325

The Fermilab D0 Master Clock System  

SciTech Connect

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

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

1991-11-01

326

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

Microsoft Academic Search

A Hilbert-Huang transform (HHT) is a time-frequency technique and has been widely applied to analyzing vibration signals in the field of fault diagnosis of rotating machinery. It analyzes the vibration signals using intrinsic mode functions (IMFs) extracted using empirical mode decomposition (EMD). However, EMD sometimes cannot reveal the signal characteristics accurately because of the problem of mode mixing. Ensemble empirical

Yaguo Lei; Ming J. Zuo

2009-01-01

327

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 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. H.

2011-06-01

328

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

Microsoft Academic Search

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

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

2001-01-01

329

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

Microsoft Academic Search

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

Graham Bird; Dane Rowlands

2001-01-01

330

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

Microsoft Academic Search

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

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

1995-01-01

331

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

Microsoft Academic Search

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

Ngaire Woods

2000-01-01

332

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

Microsoft Academic Search

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

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

1990-01-01

333

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

Microsoft Academic Search

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

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

1979-01-01

334

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

Microsoft Academic Search

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

T. Iijima; T. Shibaji

1987-01-01

335

Beyond the IMF Medicine: Thailand's Response to the 1997 Financial Crisis  

Microsoft Academic Search

From the summer of 1997 through summer 1999, Thailand's economy took a steep plunge into recession and economic collapse. Only in the third-quarter of 1999, did the economy give signs of a fragile, if hesitant recovery. Almost immediately the International Monetary Fund(IMF) took credit, arguing that its policies and programs were finally producing results. How valid is this claim. This

Shalendra D. Sharma

2002-01-01

336

Current Structure and Motion of a Northward IMF X-Line  

Microsoft Academic Search

On March 18, 2002, between 14:50 and 15:03 UT, Cluster passed from the tail lobe northward and sunward into the magnetosheath. The IMAGE FUV instrument observed a proton emission, northward of the auroral zone, that endured for a period of hours, including the time of the Cluster crossing. The location is consistent with the footprint of a northward IMF reconnection

D. E. Wendel; P. H. Reiff; A. Fazakerley; S. Schwartz; S. Mende; J. D. Winningham; M. Goldstein

2004-01-01

337

THE ROLE OF THE IMF IN DEBT RESTRUCTURINGS: LENDING INTO ARREARS, MORAL HAZARD AND SUSTAINABILITY CONCERNS  

Microsoft Academic Search

In recent years the IMF has made efforts to build an improved “crisis prevention and resolution framework” that minimizes the size and frequency of bailouts, largely out of a concern with the possible moral hazard consequences of its interventions. This framework, however, which includes an emphasis on greater private sector involvement, the encouragement of the use of collective action clauses

Lucio SIMPSON

2006-01-01

338

Managing Turkish debt: An OLG investigation of the IMF's fiscal programming model for Turkey  

Microsoft Academic Search

In this paper we investigate the fiscal policy alternatives on domestic debt management, cohort welfare, and growth for the Turkish economy. We utilize a model of exogenous growth in the overlapping generations (OLG) tradition with intertemporally optimizing agents and open capital markets, calibrated to the Turkish economy in 1990s. We examine the macroeconomic effects of the current IMF-led austerity program

Ebru Voyvoda; Erinc Yeldan

2005-01-01

339

The Paris OECD-IMF Workshop on Real Estate Price Indexes: Conclusions and Future Directions  

Microsoft Academic Search

The paper summarizes the main ideas suggested in OECD-IMF Workshop on Real Estate Price Indexes which was held in Paris, November 6-7, 2006. The paper discusses possible uses and target indexes for real estate price indexes and notes that a major problem is that it is not possible to exactly match the quality of dwelling units over time due to

Erwin Diewert

2007-01-01

340

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

341

Understanding Pathways Through Financial Crises and the Impact of the IMF: An Introduction  

Microsoft Academic Search

The International Monetary Fund is often perceived as imposing harsh policies on countries facing financial crisis. A comparison of six countries affected by the pressures of the 1990s suggests more subtle effects. In Malaysia, India, and South Africa, policymakers kept the IMF at arms length to permit a more gradual and heterodox adjustment, including cap- ital controls in India and

Ngaire Woods

2006-01-01

342

Effect of IMF Structural Adjustment Programs on Expectations: The Case of Transition Economies  

Microsoft Academic Search

We analyze the effect of IMF programs on economic agents' expectations about the economy in transitional countries using survey data from the Central and Eastern Eurobarometer poll, an annual general public survey monitoring the evolution of public opinion from 1990 to 1997. Previous studies, in contrast, have looked at indirect measures, such as capital flows or yield spreads, to assess

Patrick A. Imam

2007-01-01

343

Electrical and optical clock distribution networks for gigascale microprocessors  

Microsoft Academic Search

A summary of electrical and optical approaches to clock distribution within high-performance microprocessors is presented. System-level properties of intrachip electrical clock distribution networks corresponding to three microprocessor families are summarized. It is found that global clock interconnect performance and short-term jitter present the greatest challenges to the continued use of conventional clock distribution methodologies. An extrapolation of trends describing the

Anthony V. Mule; Elias N. Glytsis; Thomas K. Gaylord; James D. Meindl

2002-01-01

344

Transcripts from the Circadian Clock: Telling Time and Season  

Microsoft Academic Search

We all know it when we wake mere moments before an alarm clock is scheduled to wake us: our\\u000abody clock made the alarm clock redundant. This phenomenon is driven by an endogenous\\u000atimer known as the biological, or circadian clock. Each revolution of the Earth about its own\\u000aaxis produces periods of light and dark which define what we

K. Brand

2011-01-01

345

Over GHz low-power RF clock distribution for a multiprocessor digital system  

Microsoft Academic Search

Conventional digital clock distribution interconnection causes a severe power consumption problem for GHz clock distribution because of transmission line losses, and it exhibits difficult signal integrity problems due to clock skew, clock jitter and signal reflection. To overcome these conventional digital clock distribution limitations, optical clock distribution techniques, based on guided-wave optics and free-space optics, have been proposed. However, the

Woonghwan Ryu; Albert Lu Chee Wai; Fan Wei; Wai Lai Lai; Joungho Kim

2001-01-01

346

Determining the Sub-stellar IMF in the Most Massive Young Milky Way Cluster, Westerlund 1  

NASA Astrophysics Data System (ADS)

Despite over 50 years of active research, a key question in galactic astronomy remains unanswered: is the initial mass function {IMF} of stars and sub-stellar objects universal, or does it depend on initial conditions? The answer has profound consequences for the evolution of galaxies as well as a predictive theory of star formation. Work to date suggests that certain environments {high densities, e.g. Elmegreen 2004; low metallicity, e.g. Larson 2005} should produce a top-heavy IMF, and there are hints from unresolved star-bursts that this might be the case. Yet, there is no clear evidence for an IMF that differs from that characterizing the Galactic field stars in a resolved stellar population down to one solar mass. Westerlund 1 is the most massive young star cluster known in the Milky Way. With an estimated mass of 5x10^4 Msun, an age of 3-5 Myr, and located at a distance of 3-4 kpc, it presents a unique opportunity to test whether the IMF in such a cluster deviates from the norm well down into the brown dwarf regime. We propose WFC3 near-IR imaging to probe the IMF down to 40 Jupiter masses. The data will enable use to: 1} provide a stringent test of the universality of the IMF under conditions approximating those of star-bursts; 2} search for primordial or dynamic mass segregation in the clusters; and 3} assess whether the cluster is likely to remain bound {as a massive open cluster} or disperse into the field. We will obtain images in the F125W, F160W, and F139M filters. The F139M filter covers a strong water absorption feature and the color F125W/F139M is a powerful temperature diagnostic in the range 2800-4000 K. This information will enable us to: a} confirm membership for low mass stars suspected on the basis of their position in the color-magnitude diagram; b} place the members in the HR diagram; and c} estimate the masses and ages of cluster members for low-mass stars and sub-stellar objects. This new capability offered with the WFC3 {through a novel combination of filter complement, high spatial resolution, and large field of view} will enable us to make a fundamental test of whether the IMF is universal on a unique resolved stellar population, as well as assess the clusters structure, dynamics, and ultimate fate.;

Andersen, Morten

2008-07-01

347

Microsecond Clock Comparison by Means of TV Synchronizing Pulses  

Microsoft Academic Search

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

Jiri Tolman; Vladimir Ptacek; Antonin Soucek; Rudolf Stecher

1967-01-01

348

Simulating synchronized clocks and common knowledge in distributed systems  

Microsoft Academic Search

Time and knowledge are studied in synchronous and asynchronous distributed systems. A large class of problems that can be solved using logical clocks as if they were perfectly synchronized clocks is formally characterized. For the same class of problems, a broadcast primitive that can be used as if it achieves common knowledge is also proposed. Thus, logical clocks and the

Gil Neiger; Sam Toueg

1993-01-01

349

A Novel Consumer Clock Device Based on Grey Relational Analysis  

Microsoft Academic Search

People have the need to use a novel consumer clock device for home automation, personal security and convenience. This paper presents the design and implementation of the innovative system. The system architecture which is controlled by micro-controller unit (MCU) includes main alarm clock module, lucky module and security module. In the main alarm clock module, we create a novel hourglass

Po-Lun Chang; Ying-Kuei Yang; Wei-Lieh Hsu; Fei-Hu Hsieh; Mu-der Jeng; Yu-Xin Guo

2009-01-01

350

Wireless Clock Distribution System Using an External Antenna  

Microsoft Academic Search

A compact wireless clock distribution system with an external planar array antenna which can provide phase and amplitude distributions suitable for synchronizing circuits over a 35-mm diameter circular area at 3 GHz is proposed. The computer systems using this wireless clock distribution can have a comparable form factor as systems using a conventional clock network. The system is composed of

Ran Li; Xiaoling Guo; Dong-Jun Yang; K. O. Kenneth

2007-01-01

351

Hardware-Assisted Software Clock Synchronization for Homogeneous Distributed Systems  

Microsoft Academic Search

Abstmct- Clock synchronization in the presence of faults has been studied extensively in recent years and several software and hardware solutions have been proposed. Software solutions re- quire nodes to exchange and adjust their individual clock values periodically. Since the clock values are exchanged via message passing, the time overhead induced by the software solutions can be substantial, especially if

Parameswaran Ramanathan; Dilip D. Kandlur; Kang G. Shin

1990-01-01

352

Circadian clocks — the fall and rise of physiology  

Microsoft Academic Search

Circadian clocks control the daily life of most light-sensitive organisms — from cyanobacteria to humans. Molecular processes generate cellular rhythmicity, and cellular clocks in animals coordinate rhythms through interaction (known as coupling). This hierarchy of clocks generates a complex, ?24-hour temporal programme that is synchronized with the rotation of the Earth. The circadian system ensures anticipation and adaptation to daily

Martha Merrow; Till Roenneberg

2005-01-01

353

Signs of the time: environmental input to the circadian clock  

Microsoft Academic Search

The circadian clock forms one of the most fascinat- ing adaptations to life on earth. Organisms can not only anticipate the day\\/night cycle but can make use of an internal clock to measure daylength as an indi- cator of the changing of the seasons. The innate per- iod of the clock is not exactly equal to 24 h, but is

Paul F. Devlin

2002-01-01

354

Tuning the Mammalian Circadian Clock: Robust Synergy of Two Loops  

Microsoft Academic Search

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

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

2011-01-01

355

Noise-resistant and synchronized oscillation of the segmentation clock  

Microsoft Academic Search

Periodic somite segmentation in vertebrate embryos is controlled by the `segmentation clock', which consists of numerous cellular oscillators. Although the properties of a single oscillator, driven by a hairy negative-feedback loop, have been investigated, the system-level properties of the segmentation clock remain largely unknown. To explore these characteristics, we have examined the response of a normally oscillating clock in zebrafish

Kazuki Horikawa; Kana Ishimatsu; Eiichi Yoshimoto; Shigeru Kondo; Hiroyuki Takeda

2006-01-01

356

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

NASA Astrophysics Data System (ADS)

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

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

2013-01-01

357

IMF-induced escape of molecular ions from the Martian ionosphere  

NASA Astrophysics Data System (ADS)

Since Mars does not possess a significant global intrinsic magnetic field, the solar wind interacts directly with the Martian ionosphere and can induce ion escapes from it. Phobos-2 and recent Mars Express (MEX) observations have shown that the escaping ions are O+ as well as molecular O2+ and CO2+. While O+ escape can be understood by the ion pick-up of non-thermal O corona extended around the planet, regarding the heavy molecular O2+ and CO2+, which are buried in the lower ionosphere, a novel escape mechanism needs to considered. Here we attack this problem by global magnetohydrodynamic (MHD) simulations. First, we clarify the global structure of the streamlines that result from the interaction with the solar wind. Then, by focusing on the streamlines that dip into the low-altitude part of the dayside ionosphere, we investigate the escape path of the molecular ions. The effects of the interplanetary magnetic field (IMF) on the molecular ion escape process are investigated by comparing the results with and without IMF. IMF has little effect on O+ escape via ion pick-up mediated by solar wind electron impact ionization of the O corona. O2+ and CO2+ are shoveled from the low-altitude regions of the dayside ionosphere by magnetic tension in the presence of IMF. These ions are pulled by the U-shaped field lines to the north and south poles, and at the terminator, they are concentrated in the noon-midnight meridian plane. These ions remain confined to the noon-midnight plane as they are transported to the nightside to form the tail ray. Then they escape along the streamlines open to the interplanetary space. Under a typical solar wind and IMF condition expected at Mars, O+, O2+ and CO2+ escape fluxes are 8.0 × 1023, 3.5 × 1023 and 5.0 × 1022 ion s-1, respectively, which are in good agreement with the MEX observations.

Kubota, Y.; Maezawa, K.; Jin, H.; Fujimoto, M.

2013-08-01

358

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

359

Dynamic IPC\\/Clock Rate Optimization  

Microsoft Academic Search

Current microprocessor designs set the functionality and clock rate of the chip at design time based on the configuration that achieves the best overall performance over a range of target applications. The result may be poor performance when running applications whose requirements are not well-matched to the particular hardware organization chosen. We present a new approach called Complexity-Adaptive Processors (CAPs)

David H. Albonesi

1998-01-01

360

Bunch clock for the Advanced Photon Source.  

National Technical Information Service (NTIS)

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 co...

F. R. Lenkszus R. J. Laird

1997-01-01

361

Neutralism and selectionism: the molecular clock  

Microsoft Academic Search

The neutrality theory predicts that the rate of molecular evolution will be constant over time, and thus that there is a molecular clock for timing evolutionary events. It has been observed that the variance of the rate of evolution is generally larger than expected according to the neutrality theory. Several modifications of the theory have been proposed to account for

Francisco J. Ayala

2000-01-01

362

Oscillatory Mechanisms Underlying the Murine Circadian Clock  

NSDL National Science Digital Library

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

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

2003-11-18

363

Molecular Bases for Circadian Clocks Review  

Microsoft Academic Search

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

Jay C. Dunlap

364

EMCS Modules/Intelligent Time Clock (ITC).  

National Technical Information Service (NTIS)

The CEL has developed a microprocessor-based intelligent time clock (ITC) for control of HVAC equipment. The ITC has the capability of operating as a stand-alone controller, or as part of a distributed large-scale Energy Monitoring and Control System (EMC...

D. Shiroma

1980-01-01

365

Tick Tock, a Vitamin C Clock.  

ERIC Educational Resources Information Center

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

Wright, Stephen W.

2002-01-01

366

Circadian clocks in human red blood cells  

Microsoft Academic Search

Circadian (?24 hour) clocks are fundamentally important for coordinated physiology in organisms as diverse as cyanobacteria and humans. All current models of the molecular circadian 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

John S. O’Neill; Akhilesh B. Reddy

2011-01-01

367

Circadian clocks in human red blood cells  

Microsoft Academic Search

Circadian (~24 hour) clocks are fundamentally important for coordinated physiology in organisms as diverse as cyanobacteria and humans. All current models of the molecular circadian 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

John S. O'Neill; Akhilesh B. Reddy

2011-01-01

368

The U. S. Naval Observatory Clock Time Reference and the Performance of a Sample of Atomic Clocks.  

National Technical Information Service (NTIS)

The U.S. Naval Observatory (USNO) uses clock averaging of about 16 selected cesium beam clocks for the derivation of an extremely uniform clock time scale. Frequency stabilities of better than 2 x 10 to the minus 14th power for very long intervals are bei...

G. M. R. Winkler R. G. Hall D. B. Percival

1970-01-01

369

Frequency Comparison of Two High-Accuracy Al+ Optical Clocks  

NASA Astrophysics Data System (ADS)

We have constructed an optical clock with a fractional frequency inaccuracy of 8.6×10-18, based on quantum logic spectroscopy of an Al+ ion. A simultaneously trapped Mg+ ion serves to sympathetically laser cool the Al+ ion and detect its quantum state. The frequency of the S01?P03 clock transition is compared to that of a previously constructed Al+ optical clock with a statistical measurement uncertainty of 7.0×10-18. The two clocks exhibit a relative stability of 2.8×10-15?-1/2, and a fractional frequency difference of -1.8×10-17, consistent with the accuracy limit of the older clock.

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

2010-02-01

370

Photoperiodic plasticity in circadian clock neurons in insects.  

PubMed

Since Bünning's observation of circadian rhythms and photoperiodism in the runner bean Phaseolus multiflorus in 1936, many studies have shown that photoperiodism is based on the circadian clock system. In insects, involvement of circadian clock genes or neurons has been recently shown in the photoperiodic control of developmental arrests, diapause. Photoperiod sets peaks of period (per) or timeless (tim) mRNA abundance at lights-off in Sarcophaga crassipalpis, Chymomyza costata and Protophormia terraenovae. Abundance of per and Clock mRNA changes by photoperiod in Pyrrhocoris apterus. Subcellular Per distribution in circadian clock neurons changes with photoperiod in P. terraenovae. Although photoperiodism is not known in Leucophaea maderae, under longer day length, more stomata and longer commissural fibers of circadian clock neurons have been found. These plastic changes in the circadian clock neurons could be an important constituent for photoperiodic clock mechanisms to integrate repetitive photoperiodic information and produce different outputs based on day length. PMID:23986711

Shiga, Sakiko

2013-08-23

371

Entangling the lattice clock: Towards Heisenberg-limited timekeeping  

NASA Astrophysics Data System (ADS)

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

2010-03-01

372

Entangling the lattice clock: Towards Heisenberg-limited timekeeping  

NASA Astrophysics Data System (ADS)

We present a scheme 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

2010-03-01

373

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

374

Solar Wind Transport Into Magnetosphere Caused by Magnetic Reconnection During Southward and Northward IMF  

NASA Astrophysics Data System (ADS)

Reconnection is considered as the dominant mechanism of the solar wind transport into magnetosphere. Here, two cases under southward and northward IMF respectively are analyzed, with the results as follows: Firstly, by analyzing measurements from Cluster, an event of magnetopause crossing has been investigated. At the latitude of about 40' and MLT of 13:20 during southward IMF, a transition layer was observed, with the magnetospheric field configuration and cold dense plasma features of magnetosheath. The particle energy- time spectrograms inside the layer were similar to but still a little different from those in magnetosheath, obviously indicating solar wind entry into magnetosphere. The direction and magnitude of the accelerated ion flow implied that reconnection might possibly cause such a solar wind entry phenomenon. The bipolar signature of the normal magnetic component BN in magnetopause coordinates further supported happening of reconnection there. Solar wind plasma flowed toward magnetopause and entered magnetosphere along the reconnected flux tube. The magnetospheric branch of the reconnected flux tube was still inside the magnetosphere after reconnection and supplied the path for solar wind entry into the dayside magnetosphere. Secondly, an event of Cluster-Double Star conjunction observations of magnetic reconnection at high latitude magnetopause nightside of the cusp and solar wind transport into magnetosphere caused by such a reconnection process has been investigated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; reconnection can heat plasma more in parallel direction than in perpendicular direction, to a level of about 4 keV; with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magnetosphere. The case analysis gave more detail and observational evidence of the solar wind transport into magnetosphere by reconnection under southward or northward IMF.

Yan, G.; Shen, C.; Liu, Z.; Dunlop, M. W.; Lucek, E.; Reme, H.; Carr, C.; Bogdanova, Y. V.; Zhang, T.; Balogh, A.; Fazakerley, A.

2009-05-01

375

The Role of the IMF in Forecasting CME-Induced Terrestrial Space Weather  

NASA Astrophysics Data System (ADS)

The interplanetary magnetic field (IMF) is the major contributor to terrestrial space weather induced by coronal mass ejections (CME). Nowcasting of these events has become quite successful. Our ability to forecast such events on significant time scales (on the order of one day), however, remains a rather elusive goal. In situ observations of the solar wind at the L1 point provide an advance warning of no more than 1 hour. The auto-correlation times of the solar wind are usually too short to enable data driven predictions with sufficient lead times. The resolution of both solar wind propagation modeling from Sun to Earth and solar remote sensing observations is insufficient to predict the CME internal structure at the level needed to predict terrestrial space weather conditions. A practical terrestrial space weather forecast for CMEs will require an integrated approach where remote sensing, modeling and in situ components work together to make the resulting framework stronger than the sum of the individual parts. In this presentation, we will concentrate on in situ observations of the IMF viewed in this context. Ultimately, our goal is to enable the development of integrated, data-driven space weather forecasting. For this, we need to understand the temporal patterns of the IMF inside CMEs at relevant time scales. To uncover these patterns we are classifying solar wind time series segments of various lengths using specially trained neural networks (Kohonen Self-Organizing Maps). We present how well our networks can classify CMEs and their subclasses as a function of the length of these time series segments and the variable types (IMF, solar wind properties) we use. Then we discuss the probability with which the future temporal development of the solar wind can be predicted using those time segment patterns. To close the presentation, we discuss how we envision to correlate our purely empirical CME time segment classifications of the IMF and solar wind measurements with remote sensing solar observations. Combining these correlations with solar wind propagation estimates could lead to probability estimates of IMF temporal developments at L1 and Earth based on remote sensing solar observations alone.

Jahn, J.; Elliott, H. A.

2009-12-01

376

hClock gene expression in human colorectal carcinoma.  

PubMed

In this study, we aimed to investigate changes in the expression of human Clock (hClock), a gene at the core of the circadian gene family, in colorectal carcinomas (CRCs) and to discuss the possible effects. Previous studies have revealed that the disruption of circadian rhythms is one of the endogenous factors that contribute to the initiation and development of CRCs. However, the underlying molecular changes to the circadian genes associated with CRCs have not been explored. Immunofluorescence and quantitative polymerase chain reaction (qPCR) analysis of the hCLOCK protein and gene expression were performed in 30 cases of CRC. The hCLOCK protein was expressed in all specimens obtained from 30 CRC patients. Higher levels of hCLOCK expression were observed in human CRC tissues compared with the paired non-cancerous tissues. hCLOCK expression was significantly higher in poorly differentiated, or late-stage, Dukes' grade tumors and in 64.3% of tumor cases with lymph node metastasis. The hClock gene was expressed in all specimens. A significantly higher expression of hClock was found in human CRC cases compared with paired non-cancerous tissues. There was a strong positive linear correlation between hClock gene expression and protein expression in human CRCs. A strong positive linear correlation was also found between hClock gene expression and ARNT, HIF-1? and VEGF expression in human CRCs. There was no significant correlation between hClock and Bak, Bax, Bid, tumor necrosis factor receptor I (TNFR I) and TNFR II. The circadian gene hClock was stably expressed in human colorectal mucosa and was important in regulating the expression of downstream clock-controlled genes. hCLOCK may interact with HIF-1?/ARNT and activate VEGF to stimulate tumor angiogenesis and metastasis. PMID:23970287

Wang, Liying; Chen, Bozan; Wang, Yaping; Sun, Ning; Lu, Chao; Qian, Ruizhe; Hua, Luchun

2013-08-16

377

Longitude and IMF By Effects on Stormtime Low-Latitude Prompt-Penetration Electric Fields  

NASA Astrophysics Data System (ADS)

During geomagnetically disturbed periods, transient large-scale electric fields of magnetospheric origin, known as prompt penetration electric fields, are known to strongly affect ionospheric dynamics. We examine storm-associated prompt-penetration electric fields in the low-latitude ionosphere using a recently reformulated version of the Rice Convection Model (RCM), a numerical model of the inner magnetosphere and its coupling to the ionosphere. This reformulated version of the RCM was designed to accept an arbitrary intrinsic geomagnetic field and to represent the lack of symmetry in the magnetospheric magnetic field due to the partial penetration of IMF By. In this study we assume an IGRF internal magnetic field together with an event-driven storm-time Tsyganenko external field to investigate the longitudinal dependence of the prompt penetration electric field pattern and the effects of IMF By penetration.

Spiro, R. W.; Sazykin, S.; Song, Y.; Toffoletto, F.; Wolf, R. A.

2010-12-01

378

Solar wind and IMF parameters associated with geomagnetic storms with Dst < - 50 nT  

NASA Astrophysics Data System (ADS)

A correlative study between the intensity of a geomagnetic storm (given by the Dst index) and the peak value reached by some solar wind parameters (velocity and density) and the southward component of the interplanetary magnetic field (IMF) is made. This study has been performed by using hourly values of the Dst index and measurements taken by the ACE spacecraft in the period 2000-2005, for which 72 geomagnetic storms were considered. It is confirmed that peak Dst is correlated to the maximum negative component Bz of the IMF better than the maxima of n and V (solar wind number density and speed, respectively). By considering all the storms, the correlation coefficient was found to be 0.88. If we consider the geomagnetic storms for which - 200 nT < peak Dst < - 60 nT, a lower correlation coefficient of 0.63 is obtained.

Mansilla, Gustavo A.

2008-10-01

379

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

380

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.

381

Molecular clock on a neutral network.  

PubMed

The number of fixed mutations accumulated in an evolving population often displays a variance that is significantly larger than the mean (the overdispersed molecular clock). By examining a generic evolutionary process on a neutral network of high-fitness genotypes, we establish a formalism for computing all cumulants of the full probability distribution of accumulated mutations in terms of graph properties of the neutral network, and use the formalism to prove overdispersion of the molecular clock. We further show that significant overdispersion arises naturally in evolution when the neutral network is highly sparse, exhibits large global fluctuations in neutrality, and small local fluctuations in neutrality. The results are also relevant for elucidating aspects of neutral network topology from empirical measurements of the substitution process. PMID:17930643

Raval, Alpan

2007-09-28

382

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

Microsoft Academic Search

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

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

1990-01-01

383

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

Microsoft Academic Search

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

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

1996-01-01

384

How soon is now? The effects of the IMF on economic reforms in Latin America  

Microsoft Academic Search

This study assesses the effects of IMF loans on economic liberalization in Latin America. Specifically, we are interested\\u000a in whether the Fund receives greater cooperation from Latin American borrowers in the initiation of some economic reforms\\u000a over others. Using a two-stage treatment effects model as well as panel-corrected standard error (PCSE) regression for 15\\u000a Latin American countries from 1980 to

Glen Biglaiser; Karl DeRouen Jr

2011-01-01

385

The IMF as a Lender of Last Resort: Implications for Debt Structures, Pricing and  

Microsoft Academic Search

We present a model of sovereign debt issuance with endogenous liq- uidity crises and maturity mismatches due to …nancial underdevelopment which can rationalize this observation. Within the model IMF assistance is able to catalyze ‡ows as investors'expectations of a bail-out in case of …nancial troubles can facilitate debt roll-overs by reassuring private creditors. The drawback is that such assistance creates

Aitor Erce-Dominguezy

386

Stellar populations in the CFHTLS. I. New constraints on the IMF at low mass  

NASA Astrophysics Data System (ADS)

We present a stellar populations analysis of the first release of the CFHTLS (Canada-France-Hawai Telescope Legacy Survey) data. A detailed comparison between the Besançon model of the Galaxy and the first data release of the CFHTLS-Deep survey is performed by implementing the MEGACAM photometric system in this model using stellar atmosphere model libraries. The reliability of the theoretical libraries to reproduce the observed colours in the MEGACAM system is investigated. The locations of various stellar species like subdwarfs, white dwarfs, late-type and brown dwarfs, binary systems are identified. The contamination of the stellar sample by quasars and compact galaxies is quantified using spectroscopic data from the VIMOS-VLT Deep Survey (VVDS) as a function of i' magnitude and r'-i' colour. A comparison between simulated counts using the standard IMF at low masses show that the number of very low mass dwarfs may have been underestimated in previous studies. These observations favour a power law IMF following d(n)/dm propto m-? with ?=2.5 for m < 0.25 M? or ?=3.0 for m < 0.2 M? for single stars. The resulting LF is in agreement with the local LF as measured from the 5 or 25 pc samples. It is in strong disagreement with the Zheng et al. (2001) LF measured from deep HST data. We show that this discrepancy can be understood as an indication of a different IMF at low masses at early epochs of the Galaxy compared to the local thin disc IMF.

Schultheis, M.; Robin, A. C.; Reylé, C.; McCracken, H. J.; Bertin, E.; Mellier, Y.; Le Fèvre, O.

2006-02-01

387

Chemical consequences of low star formation rates: stochastically sampling the IMF  

Microsoft Academic Search

When estimating the abundances which result from a given star formation\\u000aevent, it is customary to treat the IMF as a series of weight factors to be\\u000aapplied to the stellar yields, as a function of mass, implicitly assuming one\\u000ais dealing with an infinite population. However, when the stellar population is\\u000asmall, the standard procedure would imply the inclusion

Leticia Carigi; Xavier Hernandez

2008-01-01

388

Multiple cusps during an extended northward IMF period with a significant By component  

Microsoft Academic Search

On 21-22 March 2001, four cusp-like regions were observed consecutively in about five hours by all four Cluster spacecraft when the interplanetary magnetic field (IMF) was northward with a significant B y component. All four cusp-like encounters were characterized by turbulent magnetic fields, high-density plasma, and plasma flow significantly slower than the magnetosheath level. The cusp-like regions are associated with

H. Zhang; T. A. Fritz; M. L. Goldstein; S. Wing; W. Keith; J. D. Winningham; R. Frahm; M. W. Dunlop; A. Korth; P. W. Daly; H. Rème; A. Balogh; A. N. Fazakerley

2008-01-01

389

Multiple cusps during an extended northward IMF period with a significant By component  

Microsoft Academic Search

On 21–22 March 2001, four cusp-like regions were observed consecutively in about five hours by all four Cluster spacecraft when the interplanetary magnetic field (IMF) was northward with a significant By component. All four cusp-like encounters were characterized by turbulent magnetic fields, high-density plasma, and plasma flow significantly slower than the magnetosheath level. The cusp-like regions are associated with thermalized,

Q.-G. Zong; H. Zhang; T. A. Fritz; M. L. Goldstein; S. Wing; W. Keith; J. D. Winningham; R. Frahm; M. W. Dunlop; A. Korth; P. W. Daly; A. Balogh; A. N. Fazakerley

2008-01-01

390

Influence of IMF draping direction and crustal magnetic field location on Martian ion beams  

Microsoft Academic Search

Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite onboard Mars Express and data from the Magnetometer\\/Electron Reflectometer (MAG\\/ER) on Mars Global Surveyor have been analyzed to determine whether ion beam events (IBEs) are correlated with the direction of the draped interplanetary magnetic field (IMF) or the proximity of strong crustal magnetic fields to the subsolar

E. Carlsson; D. Brain; J. Luhmann; S. Barabash; A. Grigoriev; H. Nilsson; R. Lundin

2008-01-01

391

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

392

Dynamical machinery of a biochemical clock  

Microsoft Academic Search

Closed positive feedback loops of catalytic reactions between macromolecules, or hypercycles, provide a kinetic mechanism\\u000a whereby each Species serves to catalyze selfreproduction of its successor in the loop. Hypercycles of five members or more\\u000a evolve into limit cycles characteristic of a biochemical clock. Computer study of the coupled non-linear differential equations\\u000a which describe these systems shows that the periodT\\u000a n

Paul E. Phillipson; Peter Schuster; Fritz Kemler

1984-01-01

393

Orthometric height determination using optical clocks  

NASA Astrophysics Data System (ADS)

General relativity theory predicts that there exists a gravity frequency shift (gravitational red shift) if an electromagnetic signal propagates from one point to another point, and the frequency shift depends on the geopotential difference between these two points. Inversely, by measuring the gravity frequency shift between arbitrary two points we may determine the geopotential and consequently the orthometric height difference between these two points. To improve our previous investigations (Shen and Peng 2012), the present study provides further foundation of the optical-fiber frequency transfer approach (OFTA; Shen and Peng 2012) and describes in details how to determine the orthometric height between two points using optical clocks via optical fiber. Optical clocks have achieved a stability of 10E-17 to 10E-18. In another aspect, remote optical fiber communication (e.g. Predehl et al. 2012) demonstrates a frequency comparison accuracy at the level of 10E-18 (or better), which is equivalent to a height variation of 1cm. The quick development of time-frequency science, including the high-precise optical clocks, provides potential of determining the orthometric height between arbitrary two points which are connected by optical fiber. This study suggests that determining the orthometric height difference between two points using optical clocks via optical fiber frequency transfer communication technique is prospective and potential. The realization of the OFTA may greatly contribute to the unification of the world height system (WHS). This work was supported partly by the NSFC (grant No. 41174011), National 973 Project China (grant No. 2013CB733305), NSFC (grant No. 41210006, 41128003, 41021061, 40974015).

Shen, WenBin

2013-04-01

394

The circadian clock, reward, and memory.  

PubMed

During our daily activities, we experience variations in our cognitive performance, which is often accompanied by cravings for small rewards, such as consuming coffee or chocolate. This indicates that the time of day, cognitive performance, and reward may be related to one another. This review will summarize data that describe the influence of the circadian clock on addiction and mood-related behavior and put the data into perspective in relation to memory processes. PMID:22084628

Albrecht, Urs

2011-11-09

395

Recent Developments in Microwave Ion Clocks  

Microsoft Academic Search

We review the development of microwave-frequency standards based on trapped ions. Following two distinct paths, microwave ion clocks have evolved greatly in the last twenty years since the earliest Paul-trap-based units. Laser-cooled ion frequency standards reduce the second-order Doppler shift from ion micromotion and thermal secular motion achieving good signal-to-noise ratios via cycling transitions where as many as ~10^8 photons

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

2001-01-01

396

Clock retardation, absolute space, and special relativity  

Microsoft Academic Search

We consider a sequence of absolute-space kinematical theories which differ more or less from the special theory of relativity (STR) in the amount of clock retardation which they predict, but which agree with STR with respect to roundtrip light experiments, such as Michelson-Morley and Kennedy-Thorndike. This sequence of theories is imbedded in the synchrony-free formulation of STR developed by Winnie

Carlo Giannoni

1979-01-01

397

Light and the human circadian clock.  

PubMed

The circadian clock can only reliably fulfil its function if it is stably entrained. Most clocks use the light-dark cycle as environmental signal (zeitgeber) for this active synchronisation. How we think about clock function and entrainment has been strongly influenced by the early concepts of the field's pioneers, and the astonishing finding that circadian rhythms continue a self-sustained oscillation in constant conditions has become central to our understanding of entrainment.Here, we argue that we have to rethink these initial circadian dogmas to fully understand the circadian programme and how it entrains. Light is also the prominent zeitgeber for the human clock, as has been shown experimentally in the laboratory and in large-scale epidemiological studies in real life, and we hypothesise that social zeitgebers act through light entrainment via behavioural feedback loops (zeitnehmer). We show that human entrainment can be investigated in detail outside of the laboratory, by using the many 'experimental' conditions provided by the real world, such as daylight savings time, the 'forced synchrony' imposed by the introduction of time zones, or the fact that humans increasingly create their own light environment. The conditions of human entrainment have changed drastically over the past 100 years and have led to an increasing discrepancy between biological and social time (social jetlag). The increasing evidence that social jetlag has detrimental consequences for health suggests that shift-work is only an extreme form of circadian misalignment, and that the majority of the population in the industrialised world suffers from a similarly 'forced synchrony'. PMID:23604485

Roenneberg, Till; Kantermann, Thomas; Juda, Myriam; Vetter, Céline; Allebrandt, Karla V

2013-01-01

398

DNA microenvironments and the molecular clock  

Microsoft Academic Search

Summary  A few years ago we presented a stationary Markov model of gene evolution according to which only homologous genes from not\\u000a too divergent species obeying the condition of being stationary may behave as reliable molecular clocks. A compartmentalized\\u000a model of the nuclear genome in which the genes are distributed in compartments, the isochores, defined by their G+C content\\u000a has been

C. Saccone; G. Pesole; G. Preparata

1989-01-01

399

The role of the IMF in recent sovereign debt restructurings: Implications for the policy of lending into arrears  

Microsoft Academic Search

This paper analyzes the role played by the IMF in eight recent sovereign debt restructurings from a comparative perspective: Argentina (2001-2005), the Dominican Republic (2004-2005), Ecuador (1999-2000), Pakistan (1998-2001), the Russian Federation (1998-2001), Serbia (2000-2004), Ukraine (1998-2000) and Uruguay (2004). Our objective is to identify the various dimensions of the IMF's potential involvement during those processes, and to extract some

Javier Díaz-Cassou; Aitor Erce-Domínguez; Juan J. Vázquez-Zamora

2008-01-01

400

Deterministic and Stochastic Receiver Clock Modeling in Precise Point Positioning  

NASA Astrophysics Data System (ADS)

The traditional GNSS (Global Navigation Satellite System) data analysis assumes an independent set of clock corrections for each epoch. This introduces a huge number of parameters that are highly correlated with station height and troposphere parameters. If the number of clock parameters can be reduced, the GNSS processing procedure may be stabilized. Experiments with kinematic solutions for stations equipped with H-Maser clocks have confirmed this. On the other hand, static coordinates do not significantly benefit from changing the strategy in handling the clock parameter. In the current GNSS constellation only GIOVE-B and the GPS Block IIF satellite clocks seem to be good enough to be modeled instead of freely estimated for each epoch without losing accuracy at the level of phase measurements. With the Galileo constellation this will change in future. In this context, ESA (European Space Agency) funded a project on "Satellite and Station Clock Modelling for GNSS". In the frame of this project, various deterministic and stochastic clock models have been evaluated, implemented and assessed for both, station and satellite clocks. In this paper we focus on the impact of modeling the receiver clock in the processing of GNSS data in static and kinematic precise point positioning (PPP) modes. Initial results show that for stations connected to an H-Maser clock the stability of the vertical position for kinematic PPP could be improved by up to 60%. The impact of clock modeling on the estimation of troposphere parameters is also investigated, along with the role of the tropospheric modeling itself, by testing various sampling rates and relative constraints for the troposphere parameters. Finally, we investigate the convergence time of PPP when deterministic or stochastic clock modeling is applied to the receiver clock.

Orliac, E.; Dach, R.; Wang, K.; Rothacher, M.; Voithenleitner, D.; Hugentobler, U.; Heinze, M.; Svehla, D.

2012-04-01

401

Tuning genetic clocks employing DNA binding sites.  

PubMed

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

Jayanthi, Shridhar; Del Vecchio, Domitilla

2012-07-31

402

Does "Clock" Matter in Prostate Cancer?  

PubMed Central

The ancient adaptation of a 24-hour circadian clock has profound effect on our daily biochemical, physiologic, and behavioral processes, including the monitoring of sex hormone levels. Although the disruption of the circadian cycle has been implicated in the etiology of hormone-related female breast cancer, few studies have been undertaken to determine if a link exists in the development of the most common cancer type among men whose etiology remains largely unknown: hormone-related prostate cancer. Here, we hypothesize that both altered-lighted environments and genetic variations in genes responsible for maintaining circadian rhythms may result in deregulation of clock-associated biological processes, such as androgen expression, and consequently influence an individual’s risk of prostate cancer. There is also a potential for the interaction of genetic variants and exposures, such as evening shift work. Confirmation of this hypothesis will add to our understanding of the role of the circadian clock in prostate tumorigenesis and further facilitate the development of novel risk and prognostic biomarkers for prostate cancer.

Zhu, Yong; Zheng, Tongzhang; Stevens, Richard G.; Zhang, Yawei; Boyle, Peter

2008-01-01

403

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

404

Influence of the Stellar IMF on the Population of Double White Dwarf Stars in the Galaxy  

NASA Astrophysics Data System (ADS)

The primary aim of this exercise is to compare populations of Double White Dwarf (DWD) systems generated by using different published forms of the Galaxy's Initial Mass Function (IMF) and Star Formation Rate (SFR). We focus on writing a numerical code to synthesize a population of stars based on analytic expressions of the Galaxy's IMF and SFR. We then use a stellar evolution code developed by Hurley et al. (2002) to evolve these stars to the present epoch. We concentrate on the population of DWD systems that are expected to be strong sources of Gravitational Wave Radiation (GWR) and hence, ideal targets for the space-based GWR detector LISA. We analyze the distributions of these different DWD populations by plotting them in the GWR strain-frequency parameter space. We also compare the relative numbers of the different species (He-He, He-CO, CO-CO etc.) of DWD systems obtained using the different forms of the IMF. This material is based upon work supported by the National Science Foundation under Grant No. 0431664.

Haralson, Zach; Gokhale, V.

2010-01-01

405

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

SciTech Connect

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

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

1995-03-01

406

A classification of dayside auroral forms and activities as a function of interplanetary magnetic field orientation  

Microsoft Academic Search

We present a classification of auroral forms in the dayside high-latitude ionosphere, based on ground observations from Svalbard. Having sorted the different auroral forms by magnetic local time (MLT) and morphological and optical spectral characteristics, we then study them as a function of the orientation of the interplanetary magnetic field (IMF). We find that the IMF clock angle theta is

Per Even Sandholt; Charles J. Farrugia; Jøran Moen; Øystein Noraberg; Bjørn Lybekk; Torleif Sten; Truls Hansen

1998-01-01

407

Zebrafish cell clocks feel the heat and see the light!  

PubMed

The zebrafish has rapidly become established as one of the most valuable vertebrate models for studying circadian clock function. A major initial attraction was its utility in large-scale genetic screens. It subsequently emerged that most zebrafish cells possess circadian clocks that can be entrained directly by exposure to temperature or light dark cycles, a property shared by several zebrafish cell lines. This is not the case for mammals, where the retina is the primary source of light input to the clock. Furthermore, mammalian cell culture clocks can only be entrained by acute culture treatments such as serum shocks. Thus, the zebrafish is proving invaluable to study light and temperature input to the vertebrate clock. In addition, the accessibility of its early developmental stages has placed the zebrafish at the forefront of studies aimed at understanding how the circadian clock is established during embryogenesis. PMID:18248192

Vallone, Daniela; Lahiri, Kajori; Dickmeis, Thomas; Foulkes, Nicholas S

2005-01-01

408

Race:. a High Performance Rubidium Clock for the Iss  

NASA Astrophysics Data System (ADS)

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

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

2002-02-01

409

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

SciTech Connect

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

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

2010-01-01

410

IGS Clock Products for Accurate Geodetic and Timing Applications  

Microsoft Academic Search

The performance of any GNSS is intimately related to the characteristics of the satellite clocks, so an understanding of the clock behavior is vital. The accurate products of the IGS enable daily point positions to the sub-cm level and continuous global clock comparisons to the sub-ns level. Time transfers are less accurate than associated positioning because of: 1) difficult-to-measure hardware

K. L. Senior; J. R. Ray

2007-01-01

411

0.84 ps Resolution Clock Skew Measurement via Subsampling  

Microsoft Academic Search

An all-digital on-chip clock skew measurement system via subsampling is presented. The clock nodes are sub- sampled with a near-frequency asynchronous sampling clock to result in beat signals which are themselves skewed in the same proportion but on a larger time scale. The beat signals are then suitably masked to extract only the skews of the rising edges of the

Bharadwaj Amrutur; Pratap Kumar Das; Rajath Vasudevamurthy

2011-01-01

412

Relativity Theory and Time Perception: Single or Multiple Clocks?  

PubMed Central

Background Current theories of interval timing assume that humans and other animals time as if using a single, absolute stopwatch that can be stopped or reset on command. Here we evaluate the alternative view that psychological time is represented by multiple clocks, and that these clocks create separate temporal contexts by which duration is judged in a relative manner. Two predictions of the multiple-clock hypothesis were tested. First, that the multiple clocks can be manipulated (stopped and/or reset) independently. Second, that an event of a given physical duration would be perceived as having different durations in different temporal contexts, i.e., would be judged differently by each clock. Methodology/Principal Findings Rats were trained to time three durations (e.g., 10, 30, and 90 s). When timing was interrupted by an unexpected gap in the signal, rats reset the clock used to time the “short” duration, stopped the “medium” duration clock, and continued to run the “long” duration clock. When the duration of the gap was manipulated, the rats reset these clocks in a hierarchical order, first the “short”, then the “medium”, and finally the “long” clock. Quantitative modeling assuming re-allocation of cognitive resources in proportion to the relative duration of the gap to the multiple, simultaneously timed event durations was used to account for the results. Conclusions/Significance These results indicate that the three event durations were effectively timed by separate clocks operated independently, and that the same gap duration was judged relative to these three temporal contexts. Results suggest that the brain processes the duration of an event in a manner similar to Einstein's special relativity theory: A given time interval is registered differently by independent clocks dependent upon the context.

Buhusi, Catalin V.; Meck, Warren H.

2009-01-01

413

PARCS: NASA's laser-cooled atomic clock in space  

Microsoft Academic Search

The Primary Atomic Reference Clock in Space (PARCS) mission is designed to perform certain tests of relativity theory, to study the performance of individual GPS space-vehicle clocks, to study the dynamics of atom motion in microgravity, to advance the state-of-the art for space clocks, and to serve as a pathfinder for precision instruments based on laser cooling of atoms. After

D. B. Sullivan; N. Ashby; E. A. Donley; T. P. Heavner; L. W. Hollberg; S. R. Jefferts; W. M. Klipstein; W. D. Phillips; D. J. Seidel

2005-01-01

414

OPTICAL METROLOGY AND QUANTUM FREQUENCY STANDARDS: Femtosecond optical clock  

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

415

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

416

Circadian autophagy rhythm: a link between clock and metabolism?  

PubMed Central

Nutrient and energy metabolism in mammals exhibits strong diurnal rhythm that aligns with the body clock. Circadian regulation of metabolism is mediated through reciprocal signaling between the clock and metabolic regulatory networks. Recent work has demonstrated that autophagy is rhythmically activated in a clock-dependent manner. As autophagy is a conserved biological process that contributes to nutrient and cellular homeostasis, its cyclic induction may provide a novel link between clock and metabolism. This review discusses the mechanisms underlying circadian autophagy regulation, the role of rhythmic autophagy in nutrient and energy metabolism, and its implications in physiology and metabolic disease.

Ma, Di; Li, Siming; Molusky, Matthew M.; Lin, Jiandie D.

2012-01-01

417

Power and Skew Aware Point Diffusion Clock Network  

NASA Astrophysics Data System (ADS)

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

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

418

Clock mutation affects circadian regulation of circulating blood cells  

PubMed Central

Background Although the number of circulating immune cells is subject to high-amplitude circadian rhythms, the underlying mechanisms are not fully understood. Methods To determine whether intact CLOCK protein is required for the circadian changes in peripheral blood cells, we examined circulating white (WBC) and red (RBC) blood cells in homozygous Clock mutant mice. Results Daytime increases in total WBC and lymphocytes were suppressed and slightly phase-delayed along with plasma corticosterone levels in Clock mutant mice. The peak RBC rhythm was significantly reduced and phase-advanced in the Clock mutants. Anatomical examination revealed hemoglobin-rich, swollen red spleens in Clock mutant mice, suggesting RBC accumulation. Conclusion Our results suggest that endogenous clock-regulated circadian corticosterone secretion from the adrenal gland is involved in the effect of a Clock mutation on daily profiles of circulating WBC. However, intact CLOCK seems unnecessary for generating the rhythm of corticosterone secretion in mice. Our results also suggest that CLOCK is involved in discharge of RBC from the spleen.

Oishi, Katsutaka; Ohkura, Naoki; Kadota, Koji; Kasamatsu, Manami; Shibusawa, Kentaro; Matsuda, Juzo; Machida, Kazuhiko; Horie, Shuichi; Ishida, Norio

2006-01-01

419

AMPK at the crossroads of circadian clocks and metabolism.  

PubMed

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 and CRY2) 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

2012-06-28

420

Crosstalk between the Circadian Clock and Innate Immunity in Arabidopsis  

PubMed Central

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

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

2013-01-01

421

Working around the clock: circadian rhythms and skeletal muscle  

PubMed Central

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

Zhang, Xiping; Dube, Thomas J.

2009-01-01

422

Light induction of the clock-controlled gene ccg-1 is not transduced through the circadian clock in Neurospora crassa  

Microsoft Academic Search

Ambient light and the circadian clock have been shown to be capable of acting either independently or in an interrelated fashion to regulate the expression of conidiation in the ascomycete fungusNeurospora crassa. Recently several molecular correlates of the circadian clock have been identified in the form of the morning-specific clock-controlled genesccg-1 andccg-2. In this paper we report studies on the

G. Arpaia; J. J. Loros; J. C. Dunlap; G. Morelli; G. Macino

1995-01-01

423

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

NASA Astrophysics Data System (ADS)

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

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

2004-12-01

424

Self-clocked 80 Gbits/s optical time-domain multiplexing transmission with clock distribution based on amplitude discrimination.  

PubMed

Conventional all-optical feedback-based clock recovery techniques for optical time-domain multiplexing (OTDM) networks place restrictions on the allowed data patterns that can be transmitted. We propose a data-independent clock distribution solution based on amplitude discrimination and experimentally demonstrate it in an 80 Gbits/s self-clocked OTDM transmission. According to the method a single OTDM subchannel is used for exchanging clock information. All processing is performed all optically in low latency nonlinear-optical-loop-mirror-based switches with short (approximately 10 m) nonlinear elements. PMID:19340179

Kravtsov, Konstantin; Prucnal, Paul R

2009-04-01

425

A positive feedback loop links circadian clock factor CLOCK-BMAL1 to the basic transcriptional machinery  

PubMed Central

Circadian clocks in mammals are built on a negative feedback loop in which the heterodimeric transcription factor circadian locomotor output cycles kaput (CLOCK)-brain, muscle Arnt-like 1 (BMAL1) drives the expression of its own inhibitors, the PERIOD and CRYPTOCHROME proteins. Reactivation of CLOCK-BMAL1 occurs at a specific time several hours after PERIOD and CRYPTOCHROME protein turnover, but the mechanism underlying this process is unknown. We found that mouse BMAL1 complexes include TRAP150 (thyroid hormone receptor-associated protein-150; also known as THRAP3). TRAP150 is a selective coactivator for CLOCK-BMAL1, which oscillates under CLOCK-BMAL1 transcriptional control. TRAP150 promotes CLOCK-BMAL1 binding to target genes and links CLOCK-BMAL1 to the transcriptional machinery at target-gene promoters. Depletion of TRAP150 caused low-amplitude, long-period rhythms, identifying it as a positive clock element. The activity of TRAP150 defines a positive feedback loop within the clock and provides a potential mechanism for timing the reactivation of circadian transcription.

Lande-Diner, Laura; Boyault, Cyril; Kim, Jin Young; Weitz, Charles J.

2013-01-01

426

Time prediction accuracy for a space clock  

NASA Astrophysics Data System (ADS)

For the Galileo system it is required that a space clock time prediction be performed, covering the time interval (Tp) between two uploads. The time prediction accuracy of the space clock is therefore an important issue. The predictability of the Space Passive Hydrogen Maser (S-PHM) time error is evaluated by the RMS of the predicted time errors at the prediction time Tp: DeltaTRMS(Tp). A linear prediction model is used, corresponding to the absence of a frequency drift. The results show that: (1) the RMS time error can be evaluated from a priori knowledge of the clock's Allan deviation; (2) conversely, it is possible to extract the Allan deviation from the measurement of DeltaTRMS versus Tp; (3) the modelling of DeltaTRMS(Tp) of S-PHM based on the white frequency and flicker frequency noises appears to be particularly accurate: the difference between the model fit and the measured prediction accuracy is leq10 ps RMS for Tm = 24 h (4) for Tp = 4 h, the performance of the S-PHM is a factor of 4.5 better than the performance of the space rubidium frequency standard (S-RAFS). This has a dramatic effect on the probability of the Signal In Space Accuracy: assuming a Gaussian distribution the probability of a predicted time error DeltaTleq1.5 ns for Tp = 4 h is 89% for the S-RAFS, while the same time error constitutes an absolute upper bound for the Galileo S-PHM.

Busca, G.; Wang, Q.

2003-06-01

427

Improved master clock reference system at USNO  

NASA Astrophysics Data System (ADS)

The first phase of the NAVELEX/NRL/USNO Master Clock (MC) upgrade program has been completed with the delivery of two VLG11B hydrogen Masers to the U.S. Naval Observatory (USNO). After installation in a specially prepaid Maser Laboratory with redundant environmental control, and a ten-day burn-in operation, the masers were independently tuned. Their subsequent performance caused a review of our plans for their operational use as part of the USNO MC complex. A revised concept is the basis for system integration presently in progress.

Winkler, G. M. R.

1985-04-01

428

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

429

The Circadian Clock Modulates Enamel Development  

PubMed Central

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

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

2012-01-01

430

Precision of Genetic Oscillators and Clocks  

NASA Astrophysics Data System (ADS)

We develop a stochastic description of feedback oscillators in which functional molecules are produced by an assembly line consisting of many identical steps. The initiation rate of this assembly is regulated by its products via a negative feedback. This model is motivated by genetic oscillators such as circadian clocks. We show that precise oscillations of high quality are possible even when the number of product molecules is low and the fluctuations of amplitude are large. We discuss parameter values which can account for high quality oscillations as observed in single cells. Furthermore, we discuss effects of stochastic amplification steps on precision to account for translational bursting.

Morelli, Luis G.; Jülicher, Frank

2007-06-01

431

Testing General Relativity with Atomic Clocks  

NASA Astrophysics Data System (ADS)

We discuss perspectives for new tests of general relativity which are based on recent technological developments as well as new ideas. We focus our attention on tests performed with atomic clocks and do not repeat arguments present in the other contributions to the present issue (Space Sci. Rev. 2009, This Issue). In particular, we present the scientific motivations of the space projects ACES (Salomon et al. in CR Acad. Sci. IV-2:1313, 2001) and SAGAS (Wolf et al. in Exp. Astron. 23:651, 2009).

Reynaud, S.; Salomon, C.; Wolf, P.

2009-12-01

432

Automatic Multi-Stage Clock Gating Optimization Using ILP Formulation  

NASA Astrophysics Data System (ADS)

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

Man, Xin; Horiyama, Takashi; Kimura, Shinji

433

The role of clock in ethanol-related behaviors.  

PubMed

Mice with a mutation in the Clock gene (Clock?19) exhibit increased preference for stimulant rewards and sucrose. They also have an increase in dopaminergic activity in the ventral tegmental area (VTA) and a general increase in glutamatergic tone that might underlie these behaviors. However, it is unclear if their phenotype would extend to a very different class of drug (ethanol), and if so, whether these systems might be involved in their response. Continuous access voluntary ethanol intake was evaluated in Clock?19 mutants and wild-type (WT) mice. We found that Clock?19 mice exhibited significantly increased ethanol intake in a two-bottle choice paradigm. Interestingly, this effect was more robust in female mice. Moreover, chronic ethanol experience resulted in a long-lasting decrease in VTA Clock expression. To determine the importance of VTA Clock expression in ethanol intake, we knocked down Clock expression in the VTA of WT mice via RNA interference. We found that reducing Clock expression in the VTA resulted in significantly increased ethanol intake similar to the Clock?19 mice. Interestingly, we also discovered that Clock?19 mice exhibit significantly augmented responses to the sedative effects of ethanol and ketamine, but not pentobarbital. However, their drinking behavior was not affected by acamprosate, an FDA-approved drug for the treatment of alcoholism, suggesting that their increased glutamatergic tone might underlie the increased sensitivity to the sedative/hypnotic properties of ethanol but not the rewarding properties of ethanol. Taken together, we have identified a significant role for Clock in the VTA as a negative regulator of ethanol intake and implicate the VTA dopamine system in this response. PMID:23722243

Ozburn, Angela Renee; Falcon, Edgardo; Mukherjee, Shibani; Gillman, Andrea; Arey, Rachel; Spencer, Sade; McClung, Colleen A

2013-05-31

434

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

SciTech Connect

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

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

1987-04-01

435

Effects of the integrated galactic IMF on the chemical evolution of the solar neighbourhood  

NASA Astrophysics Data System (ADS)

The initial mass function determines the fraction of stars of different initial mass born per stellar generation. In this paper, we test the effects of the integrated galactic initial mass function (IGIMF) on the chemical evolution of the solar neighbourhood. The IGIMF (Weidner & Kroupa 2005) is computed from the combination of the stellar initial mass function (IMF), i.e. the mass function of single star clusters, and the embedded cluster mass function, i.e. a power law with index ?. By taking into account also the fact that the maximum achievable stellar mass is a function of the total mass of the cluster, the IGIMF becomes a time-varying IMF which depends on the star formation rate. We applied this formalism to a chemical evolution model for the solar neighbourhood and compared the results obtained by assuming three possible values for ? with the results obtained by means of a standard, well-tested, constant IMF. In general, a lower absolute value of ? implies a flatter IGIMF, hence a larger number of massive stars and larger metal ejection rates. This translates into higher type Ia and II supernova rates, higher mass ejection rates from massive stars and a larger amount of gas available for star formation, coupled with lower present-day stellar mass densities. Lower values of ? correspond also to higher metallicities and higher [?/Fe] values at a given metallicity. We consider a large set of chemical evolution observables and test which value of ? provides the best match to all of these constraints. We also discuss the importance of the present-day stellar mass function (PDMF) in providing a way to disentangle among various assumptions for ?. Our results indicate that the model adopting the IGIMF computed with ? ~= 2 should be considered the best since it allows us to reproduce the observed PDMF and to account for most of the chemical evolution constraints considered in this work.

Calura, F.; Recchi, S.; Matteucci, F.; Kroupa, P.

2010-08-01

436

High Speed Stream Activity in an IMF-By magnetosphere (Invited)  

NASA Astrophysics Data System (ADS)

A simulation of the 22-24 January 2005 high speed stream interval under obliquely southward IMF conditions compared to a variety of magnetospheric and ionospheric observations shows new features not previously associated with high speed streams, including capture of magnetosheath plasma on the dayside and field-aligned currents associated with weak field regions in the magnetotail. Magnetosheath plasma is captured on the dayside as a result of opening and then re-closing overdraped magnetospheric field lines. There is evidence that a portion of the cusp/cleft is on closed field lines and that ring current ions are being re-circulated within the magnetosphere through the cusp and mantle. A dayside peak in energetic neutral atoms (ENA) is observed throughout the three days of the event, which may be related to scattering of high-energy ions in the weak fields near the dayside cusp. On the nightside, high-energy particle injections at geosynchronous orbit are associated with peaks in solar wind Ey and thus bursts of magnetospheric convection. These injections coincide with auroral activity resembling poleward boundary intensifications in many respects rather than the recurrent substorms normally thought to be associated with high-speed stream activity. Dipole tilt variations over the day give the geosynchronous injections and auroral activity a recurrent UT-dependence. These new phenomena suggest that high-speed streams drive a continuum of magnetic activity in which features depend on the orientation and IMF bias of a particular stream. TWINS observations of newly discovered features under conditions of large IMF By will be presented.

Kozyra, J. U.; Brandt, P. C.; Buzulukova, N.; Cattell, C. A.; de Zeeuw, D.; Escoubet, C. P.; Fok, M. H.; Frey, H. U.; Goldstein, J.; Gonzalez, W. D.; Liemohn, M. W.; McComas, D. J.; Mende, S. B.; Paxton, L. J.; Perez, J. D.; Peterson, W. K.; Rastaetter, L.; Ridley, A. J.; Sotirelis, T.; Thomsen, M. F.; Tsurutani, B.; Valek, P. W.

2010-12-01

437

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

NASA Astrophysics Data System (ADS)

A unique 32 hour interval of very northward Interplanetary Magnetic Field (IMF) on October 22-24, 2003 created a exceptionally thick cold dense magnetotail plasma sheet, a small polar cap and accompanying small tail lobe. These features were detected by the Cluster DMSP and FAST spacecraft and modeled by a global simulation as described in papers by Oieroset et al. (2005) and Li et al. (2005). During the same interval the Wind spacecraft was passing through the center of the magnetotail about 130 Re downstream of Earth. Wind results will be described that reveal a very unusual magnetotail characterized by (1) continual tailward flow of 200-400 km/s with densities in the range 0.2-3/cc, both of which are clearly less than those expected in the magnetosheath, (2) a mostly northward Bz but with a predominant Bx field component with sign reversals indicating crossings between the two hemispheres of the tail, and (3) velocity waves superposed on the downstream flow with peak-to-peak amplitudes of 100 to 200 km/s, periods of 10 to 20 minutes and clockwise polarization. Low altitude DMSP and Fast measurements reveal an auroral oval with enhanced latitudinal thickness and a small polar cap filled with structured precipitating electrons and few ions. A new global MHD simulation of the event exhibits a highly elliptical tail of diminished cross-section at 130 Re with major axis aligned with the northward IMF. The tail current sheet also tends to be aligned in a north-south direction with the two tail hemispheres to the east and west with their polarities depending on prior history of the IMF. The simulation appears to be consistent with many, but not all, of the observations. High latitude cusp reconnection and subsequent downtail flow of closed field lines may explain the tail structure, but the waves are more likely due to the Kelvin-Helmholtz instability often thought to occur during northward IMF conditions. Oieroset, M., J. Raeder,T. D. Phan, S. Wing, J. P. McFadden, W. Li, M. Fujimoto, H. Re`me, and A. Balogh (2005), Geophys. Res. Lett., 32, L12S07, doi:10.1029/2004GL021523. Li, W., J. Raeder, J. Dorelli, M. Øieroset, and T. D. Phan (2005), Geophys. Res. Lett., 32, L12S08, doi:10.1029/2004GL021524.

Fairfield, D. H.; Raeder, J.; Oieroset, M.; Phan, T.; Lepping, R. P.; Newell, P.; Wing, S.

2006-12-01

438

Real-Time Station Clock Synchronization for GNSS Integrity Monitoring  

Microsoft Academic Search

Precise synchronization of monitoring station clocks is a crucial part of a real-time integrity monitoring system as foreseen for Galileo. Stringent requirements on accuracy and robustness in the presence of narrow performance margins raise the need to identify an optimal algorithm for the efficient computation of synchronization parameters. In this context several types of candidate clock filter algorithms have been

Johannes Mach; Ingrid Deuster; Robert Wolf; Theo Zink

439

Clock monitoring and control units for navigation satellites  

Microsoft Academic Search

All signal generation and transmission frequencies in the payload of a navigation satellite are typically derived from a single 10.23 MHz master clock. In case of the current payload architecture of the Galileo or other Navigation System this Master Timing Reference (MTR) is synthesized in a Clock Monitoring and Control Unit (CMCU) based on one single atomic reference. To achieve

Dirk Felbach; Francis Soualle; Lars Stopfkuchen; Alexander Zenzinger

2010-01-01

440

[The role of biological clock in glucose homeostasis].  

PubMed

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

Chro?cicki, Piotr; Usarek, Micha?; Bryla, Jadwiga

2013-06-20

441

ANALYSIS OF CLOCK MODELING TECHNIQUES FOR USNO CESIUM MEAN  

Microsoft Academic Search

The U.S. Naval Observatory (USNO) maintains an ensemble of commercial cesium frequency standards. The mean timescale generated from this ensemble is used as the long- term frequency reference for all USNO clocks. Maintenance of this mean is currently done in a post-processing fashion with clock models being adjusted as far as 75 days into the past. While this method ensures

J. Skinner; P. Koppang

442

The mercury clock of the Libros del Saber  

Microsoft Academic Search

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

A. A. Mills

1988-01-01

443

Kerberos with Clocks Adrift: History, Protocols, and Implementation  

Microsoft Academic Search

We show that the Kerberos Authentica- tion System can relax its requirement for synchronized clocks, with only a minor change which is consistent with the current protocol. Synchronization has been an important limitation of Kerberos; it imposes political costs and technical ones. Further, Kerberos' reliance on synchronization obstructs the secure initialization of clocks at bootstrap. Perhaps most important, this synchronization

Donald T. Davis; Daniel E. Geer Jr.

1996-01-01

444

Temperature Regulates Transcription in the Zebrafish Circadian Clock  

Microsoft Academic Search

It has been well-documented that temperature influences key aspects of the circadian clock. Temperature cycles entrain the clock, while the period length of the circadian cycle is adjusted so that it remains relatively constant over a wide range of temperatures (temperature compensation). In vertebrates, the molecular basis of these properties is poorly understood. Here, using the zebrafish as an ectothermic

Kajori Lahiri; Daniela Vallone; Srinivas Babu Gondi; Cristina Santoriello; Thomas Dickmeis; Nicholas S Foulkes

2005-01-01

445

Performance, Modeling, and Simulation of Some Cesium Beam Clocks  

Microsoft Academic Search

Summary With the availability of a new primary frequency standard, NBS-5 at the National Bureau of Standards, we have been able to evaluate with greater confidence than in the past the performance characteristics of the commercial cesium beam clocks used in the AT(NBS) atomic time scale. Two other techniques have also been employed to evaluate a clock's performance, viz., interclock

David W. Allan; D. J. Glaze; H. E. Machlan; A. E. Wainwright; Helmut Hellwig; J. A. Barnes; James E. Gray

1973-01-01

446

Transcriptional oscillation of canonical clock genes in mouse peripheral tissues  

Microsoft Academic Search

BACKGROUND: The circadian rhythm of about 24 hours is a fundamental physiological function observed in almost all organisms from prokaryotes to humans. Identification of clock genes has allowed us to study the molecular bases for circadian behaviors and temporal physiological processes such as hormonal secretion, and has prompted the idea that molecular clocks reside not only in a central pacemaker,

Takuro Yamamoto; Yasukazu Nakahata; Haruhiko Soma; Makoto Akashi; Takayoshi Mamine; Toru Takumi

2004-01-01

447

Multi-clock domain TDF ATPG testing: An innovative approach  

Microsoft Academic Search

With the rapid advancement of fab process technology into the nanometer node era, there is an increasing trend in the manifestation of deep submicron (DSM) marginal defects in integrated circuit (IC) fabrication. Despite transition delay fault (TDF) tests providing reasonable coverage against DSM marginal defects, this methodology is hampered in designs with multiple clock domains where the lowest operating clock

Chin Hai Ang

2008-01-01

448

Move over, quartz: the atomic clock gets smaller and cheaper  

Microsoft Academic Search

While the standard quartz watch maybe less expensive, engineers still prefer to use atomic clocks because of the many advantages they offer. A good example is the new atomic clock that operates using a radio signal linked to the atomic standard. Its core is the size of a grain of rice, i.e. chip-scale, because it is made with standard microelectronic

L. Geppert

2005-01-01

449

Coordination of the maize transcriptome by a conserved circadian clock  

Microsoft Academic Search

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

Sadaf Khan; Scott C Rowe; Frank G Harmon

2010-01-01

450

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 ...

451

Resetting the clock: Dexras1 defines a path.  

PubMed

The signaling pathways by which light and activity shift the circadian clock are not well understood. In this issue of Neuron, Cheng et al. analyze mice lacking Dexras1 (a Ras family GTPase protein) and demonstrate an important role for G(i/o) signaling mediating both photic and nonphotic phase shifts of the circadian clock. PMID:15339641

Van Gelder, Russell N

2004-09-01

452

The Circadian Clock-Controlled Transcriptome of Developing Soybean Seeds.  

Technology Transfer Automated Retrieval System (TEKTRAN)

A number of metabolic and physiological processes in plants are controlled by the circadian clock, which enables the plant to anticipate daily changes in the environment. Microarray expression profiling was used to identify circadian clock controlled genes expressed in developing soybean seeds. 1.8...

453

Coexisting chaotic and periodic dynamics in clock escapements  

Microsoft Academic Search

This paper addresses the nature of noise in machines. As a concrete example, we examine the dynamics of clock escapements from experimental, historical and analytical points of view. Experiments on two escapement mechanisms from the Reuleaux kinematic collection at Cornell University are used to illustrate chaotic-like noise in clocks. These vibrations coexist with the periodic dynamics of the balance wheel

Francis C. Moon; Preston D. Stiefel

2006-01-01

454

Clock Skew Scheduling with Delay Padding for Prescribed Skew Domains  

Microsoft Academic Search

Clock skew scheduling is a technique that intentionally in- troduces skews to memory elements to improve the perfor- mance of a sequential circuit. It was shown in (21) that the full optimization potential of clock skew scheduling can be reliably implemented using a few skew domains. In this paper we present an optimal skew scheduling algorithm for sequential circuits with

Chuan Lin; Hai Zhou

2007-01-01

455

Saving Power by Synthesizing Gated Clocks for Sequential Circuits  

Microsoft Academic Search

Portable devices demand low power consumption to prolong battery life. Gating the clock is one strategy for saving power. The authors' technique identifies self-loops in an FSM and uses the function described by the self-loops to gate the clock. Applying these techniques to standard benchmarks achieved an average 25% less power dissipation at a cost of only 5% more area.

Luca Benini; Polly Siegel; Giovanni De Micheli

1994-01-01

456

Genetic Differences in Human Circadian Clock Genes Among Worldwide Populations  

PubMed Central

The daily biological clock regulates the timing of sleep and physiological processes that are of fundamental importance to human health, performance, and well-being. Environmental parameters of relevance to biological clocks include (i) daily fluctuations in light intensity and temperature, and (ii) seasonal changes in photoperiod (daylength) and temperature; these parameters vary dramatically as a function of latitude and locale. In wide-ranging species other than humans, natural selection has genetically optimized adaptiveness along latitudinal clines. Is there evidence for selection of clock gene alleles along latitudinal/photoperiod clines in humans? A number of polymorphisms in the human clock genes Per2, Per3, Clock, and AANAT have been reported as alleles that could be subject to selection. In addition, this investigation discovered several novel polymorphisms in the human Arntl and Arntl2 genes that may have functional impact upon the expression of these clock transcriptional factors. The frequency distribution of these clock gene polymorphisms is reported for diverse populations of African Americans, European Americans, Ghanaians, Han Chinese and Papua New Guineans (including five subpopulations within Papua New Guinea). There are significant differences in the frequency distribution of clock gene alleles among these populations. Population genetic analyses indicate that these differences are likely to arise from genetic drift rather than from natural selection.

Ciarleglio, Christopher M.; Ryckman, Kelli; Servick, Stein V.; Hida, Akiko; Robbins, Sam; Wells, Nancy; Hicks, Jennifer; Larson, Sydney A.; Wiedermann, Joshua P.; Carver, Krista; Hamilton, Nalo; Kidd, Kenneth K.; Kidd, Judith R.; Smith, Jeffrey R.; Friedlaender, Jonathan; McMahon, Douglas G.; Williams, Scott; Summar, Marshall L.; Johnson, Carl Hirschie

2008-01-01

457

Posttranslational modifications regulate the ticking of the circadian clock  

Microsoft Academic Search

Getting a good night's sleep is on everyone's to-do list. So is, no doubt, staying awake during late afternoon seminars. Our internal clocks control these and many more workings of the body, and disruptions of the circadian clocks predispose individuals to depression, obesity and cancer. Mutations in kinases and phosphatases in hamsters, flies, fungi and humans highlight how our timepieces

Monica Gallego; David M. Virshup

2007-01-01

458

AMPK Regulates the Circadian Clock by Cryptochrome Phosphorylation and Degradation  

Microsoft Academic Search

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

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

2009-01-01

459

Orchestrating time: arrangements of the brain circadian clock  

Microsoft Academic Search

Daily oscillations in physiology and behavior are regu- lated by a brain clock located in the suprachiasmatic nucleus (SCN). Individual cells within this nucleus contain an autonomous molecular clock. Recent dis- coveries that make use of new molecular and genetic data and tools highlight the conclusion that the SCN is a heterogeneous network of functionally and phenotypi- cally differentiated cells.

Michael C. Antle; Rae Silver

2005-01-01

460

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)).

Castillo-Secilla, Jose Maria; Palomares, Jose Manuel; Olivares, Joaquin

2013-01-01

461

Temperature-compensated clock skew adjustment.  

PubMed

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

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

2013-08-20

462

The Renaissance or the cuckoo clock.  

PubMed

'…in Italy, for thirty years under the Borgias, they had warfare, terror, murder and bloodshed, but they produced Michelangelo, Leonardo da Vinci and the Renaissance. In Switzerland, they had brotherly love, they had five hundred years of democracy and peace-and what did that produce? The cuckoo clock'. Orson Welles as Harry Lime: The Third Man. Orson Welles might have been a little unfair on the Swiss, after all cuckoo clocks were developed in the Schwartzwald, but, more importantly, Swiss democracy gives remarkably stable government with considerable decision-making at the local level. The alternative is the battling city-states of Renaissance Italy: culturally rich but chaotic at a higher level of organization. As our understanding of the cell cycle improves, it appears that the cell is organized more along the lines of Switzerland than Renaissance Italy, and one major challenge is to determine how local decisions are made and coordinated to produce the robust cell cycle mechanisms that we observe in the cell as a whole. PMID:22084388

Pines, Jonathon; Hagan, Iain

2011-12-27

463

Circadian clocks in human red blood cells.  

PubMed

Circadian (?24 hour) clocks are fundamentally important for coordinated physiology in organisms as diverse as cyanobacteria and humans. All current models of the molecular circadian 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, which have no nucleus (or DNA) and therefore cannot perform transcription. Our results show that transcription is not required for circadian oscillations in humans, and that non-transcriptional events seem to be sufficient to sustain cellular circadian rhythms. Using red blood cells, we found that peroxiredoxins, highly conserved antioxidant proteins, undergo ?24-hour redox cycles, which persist for many days under constant conditions (that is, in the absence of external cues). Moreover, these rhythms are entrainable (that is, tunable by environmental stimuli) and temperature-compensated, both key features of circadian rhythms. We anticipate that 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

2011-01-27

464

Circadian clock-regulated physiological outputs: dynamic responses in nature.  

PubMed

The plant circadian clock is involved in the regulation of numerous processes. It serves as a timekeeper to ensure that the onset of key developmental events coincides with the appropriate conditions. Although internal oscillating clock mechanisms likely evolved in response to the earth's predictable day and night cycles, organisms must integrate a range of external and internal cues to adjust development and physiology. Here we introduce three different clock outputs to illustrate the complexity of clock control. Clock-regulated diurnal growth is altered by environmental stimuli. The complexity of the photoperiodic flowering pathway highlights numerous nodes through which plants may integrate information to modulate the timing of flowering. Comparative analyses among ecotypes that differ in flowering response reveal additional environmental cues and molecular processes that have developed to influence flowering. We also explore the process of cold acclimation, where circadian inputs, light quality, and stress responses converge to improve freezing tolerance in anticipation of colder temperatures. PMID:23435352

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

2013-02-20

465

Epigenetic Control of Circadian Clock Operation during Development  

PubMed Central

The molecular players of circadian clock oscillation have been identified and extensively characterized. The epigenetic mechanisms behind the circadian gene expression control has also been recently studied, although there are still details to be illucidated. In this review, we briefly summarize the current understanding of the mammalian clock. We also provide evidence for the lack of circadian oscillation in particular cell types. As the circadian clock has intimate interaction with the various cellular functions in different type of cells, it must have plasticity and specicity in its operation within different epigenetic environments. The lack of circadian oscillation in certain cells provide an unique opportunity to study the required epigenetic environment in the cell that permit circadian oscillation and to idenfify key influencing factors for proper clock function. How epigenetic mechansims, including DNA methylaiton and chromatin modifications, participate in control of clock oscillation still awaits future studies at the genomic scale.

Li, Chengwei; Gong, Changxia; Yu, Shuang; Wu, Jianguo; Li, Xiaodong

2012-01-01

466

Clock Synchronization in Wireless Sensor Networks: An Overview  

PubMed Central

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

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

2009-01-01

467

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

468

Cocaine self-administration behaviors in Clock?19 mice  

PubMed Central

Rationale A key role has been identified for the circadian locomotor output cycles kaput (Clock) gene in the regulation of drug reward. Mice bearing a dominant negative mutation in the Clock gene (Clock?19 mice) exhibit increased cocaine-induced conditioned place preference, reduced anxiety- and depression-like behavior, increased sensitivity to intracranial self-stimulation, and increased do-paminergic cell activity in the ventral tegmental area. Objectives We sought to determine if this hyperhedonic phenotype extends to cocaine self-administration and measures of motivation. Methods Two separate serial testing procedures were carried out (n=7–10/genotype/schedule). Testing began with acquisition of sucrose pellet self-administration, implantation of intravenous catheter, acquisition of cocaine self-administration, and dose–response testing (fixed ratio or progressive ratio). To evaluate diurnal variations in acquisition behavior, these sessions occurred at Zeitgeber 2 (ZT2) or ZT14. Results WT and Clock?19 mice exhibited similar learning and readily acquired food self-administration at both ZT2 and ZT14. However, only Clock?19 mice acquired cocaine self-administration at ZT2. A greater percentage of Clock?19 mice reached acquisition criteria at ZT2 and ZT14. Clock?19 mice self-administered more cocaine than WT mice. Using fixed ratio and progressive ratio schedules of reinforcement dose–response paradigms, we found that cocaine is a more efficacious reinforcer in Clock?19 mice than in WT mice. Conclusion Our results demonstrate that the Clock gene plays an important role in cocaine reinforcement and that decreased CLOCK function increases vulnerability for cocaine use.

Ozburn, Angela Renee; Larson, Erin Beth; Self, David W.; McClung, Colleen A.

2013-01-01

469

Aspect and Deviation Angle.  

National Technical Information Service (NTIS)

The purpose of this paper is twofold: first, an attempt is made to define aspect angle and deviation angle in a logical and acceptable manner; second, a graphical calculator is supplied in the hope that it will make the calculation of these angles so simp...

T. A. Croft

1964-01-01

470

Galileo payload 10.23 MHZ master clock generation with a clock monitoring and control unit (CMCU)  

Microsoft Academic Search

The system concept of the Galileo navigation satellite payload requires a clock monitoring and control unit (CMCU) to provide a master timing reference for the generation of the navigation signal. This frequency is synthesized from one of four atomic clocks, selected by the CMCU to provide a 10 MHz reference. High requirements have to be applied to the frequency synthesizers

D. Felbach; D. Heimbuerger; P. Herre; P. Rastetter

2003-01-01

471

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

NASA Astrophysics Data System (ADS)

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

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

2007-07-01

472

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

SciTech Connect

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

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

1986-01-01

473

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

474

Bow shock current closure for large IMF By: The unipolar generator  

NASA Astrophysics Data System (ADS)

It has long been known that large IMF By significantly impacts ionospheric plasma convection and produces asymmetric polar cap potentials. In particular, the plasma circulation known as lobe cell convection is associated with large By and interhemispheric asymmetries, and it is generally attributed to high latitude reconnection. We argue that lobe cell convection may not powered by reconnection, but rather by a direct transfer of mechanical energy extracted from the solar wind at the bowshock into the ionosphere on open field lines via the magnetic shear generated at the bow shock. When the solar wind crosses the bow shock, the transverse components of the magnetic field are compressed. The presence of this magnetic shear means that a large current must flow on the bow shock. For primarily east-west IMF this current flows north-south. The magnetic shear generated at the bow shock extends throughout the magnetosheath. Some of the current from the bow shock flows directly into the polar cap, appearing as an up or down Birkeland current at low altitude. These Birkeland currents drive plasma convection on open field lines as a unipolar generator with opposite polarity in the two hemispheres. We present both simulation results and observations to support our line of argument, and highlight the importance of the bow shock generator in solar wind-magnetosphere energy transfer and the generation of interhemispheric asymmetry.

Lopez, R. E.; Mitchell, E. J.; Bruntz, R. J.; Allen, R.; Anderson, P. C.; Hairston, M. R.; Wiltberger, M. J.; Lyon, J.

2009-12-01

475

Observations of draping plasma accelerations in the magnetosheath under IMF Bz North  

NASA Astrophysics Data System (ADS)

Accelerations in the magnetosheath due to draping of the Interplanetary Magnetic Field (IMF) around the magnetosphere is a rich topic of renewed interest. Here, we study these draping events in the first statistical study of draping related accelerations in the magnetosheath. We present a methodology to unambiguously identify draping related accelerations from reconnection, and present several case studies of 34 identified events. To discourage reconnection, we focus on the IMF Bz northward phase of ICMEs identified by Cane and Richardson [2010] from 1997-2010, and spacecraft that are low in the ecliptic plane to avoid reconnection at high latitudes. We study the effect of upstream MA and Magnetic Local Time (MLT) on the ratio at which the magnetosheath speeds exceed the speed of the solar wind, and compare with theory. We find that the ratio of magnetosheath speed to speed of the solar wind increases with decreasing MA, and show the suggested positional dependance along the magnetopause of this ratio with respect to the east-west terminator as well as global trends.

Harris, B. S.; Farrugia, C. J.

2011-12-01

476

Identification of the IMF sector structure in near-real time by ground magnetic data  

NASA Astrophysics Data System (ADS)

A method is proposed to determine in near-real time the interplanetary magnetic field (IMF) sector structure (SS) effect on geomagnetic data from polar cap stations. To separate the SS effect, whose polarity is invariant within an interval from some days to 2 weeks, from the disturbed solar wind effects with periodicity from minutes to hours, the daily median values of geomagnetic H (or D) component are estimated. Then the median values for 9 days preceding the current day are subjected to 3-days running averages and the interpolation procedure is applied to these smoothed averages. Comparisons of the sector structure reconstructed from the ground magnetic data with the actual variations of the GSM IMF By component measured onboard the ACE spacecraft in the summer months of 1990 and 2001 demonstrate their good agreement with coefficient of correlation R=0.96-0.97 for the H-component and R=0.93-0.95 for the D-component. The proposed simple method makes possible identification of the SS effect in the same near real-time regime as the derivation of the quiet daily curve and as level of reference for the polar cap magnetic disturbances in the calculation of the polar cap magnetic activity PC index.

Janzhura, A. S.; Troshichev, O. A.

2011-08-01

477

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

PubMed

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

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

2012-11-19

478

Comparative analysis of teleost fish genomes reveals preservation of different ancient clock duplicates in different fishes.  

PubMed

Clock (Circadian locomotor output cycle kaput) was the first vertebrate circadian clock gene identified in a mouse forward genetics mutagenesis screen. It encodes a bHLH-PAS protein that is highly conserved throughout evolution. Tetrapods also have the second Clock gene, Clock2 or Npas2 (Neuronal PAS domain protein 2). Conversely, the fruit fly, an invertebrate, has only one clock gene. Interrogation of the five teleost fish genome databases revealed that the zebrafish and the Japanese pufferfish (fugu) each have three clock genes, whereas the green spotted pufferfish (tetraodon), the Japanese medaka fish and the three-spine stickleback each have two clock genes. Phylogenetic and splice site analyses indicated that zebrafish and fugu each have two clock1 genes, clock1a and clock1b and one clock2; tetraodon also have clock1a and clock1b but do not have clock2; and medaka and stickleback each have clock1b and one clock2. Genome neighborhood analysis further showed that clock1a/clock1b in zebrafish, fugu and tetraodon is an ancient duplicate. While the dN/dS ratios of these three fish clock duplicates are all <1, indicating that purifying selection has acted upon them; the Tajima relative rate test showed that all three fish clock duplicates have asymmetric evolutionary rates, implicating that one of these duplicates have been under positive selection or relaxed functional constraint. These results support the view that teleost fish clock genes were generated from an ancient genome-wide duplication, and differential gene loss after the duplication resulted in retention of different ancient duplicates in different teleost fishes, which could have contributed to the evolution of the distinct fish circadian clock mechanisms. PMID:21798156

Wang, Han

2008-08-08

479

Projectile entry angle determination.  

PubMed

Small angles of projectile entry are difficult to determine in two-dimensional targets or in three-dimensional targets where internal deflection has taken place. This results from the fact that small errors in measurement lead to large errors in the calculation of the sine function used in the estimation of the angular projection of a circle onto an inclined plane at angles of less than 20 degrees from the normal. The use of a bullet tip scale, constructed to the dimensions of the entering projectile, allows a significantly more accurate determination of small angles of entry in targets not subject to stretching. A comparison of the relative error inherent in calculating entry angle using the sine function and measuring the angle using the bullet tip scale demonstrates the suitability of using the tip scale at angles less than 20 degrees and the sine function at entry angles greater than 20 degrees. PMID:3944581

Cashman, P J

1986-01-01

480

Phase measurement system using a dithered clock  

DOEpatents

In interferometry, a reference signal is compared to a measured signal. The difference between the frequencies of these two signals is used to determine the velocity of an object. The phase difference between these two signals is used to determine the position of the object. The invention relates to an apparatus used to precisely measure cumulative phase differences between high frequency signals. The invention would also be useful in areas outside of interferometry, wherever precision measurements of cumulative phase differences between high frequency signals is desired. This paper presents a phase measurement system 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. 3 figs.

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

1989-11-17

481

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

482

Formal development of a clock synchronization circuit  

NASA Astrophysics Data System (ADS)

This talk presents the latest stage in formal development of a fault-tolerant clock synchronization circuit. The development spans from a high level specification of the required properties to a circuit realizing the core function of the system. An abstract description of an algorithm has been verified to satisfy the high-level properties using the mechanical verification system EHDM. This abstract description is recast as a behavioral specification input to the Digital Design Derivation system (DDD) developed at Indiana University. DDD provides a formal design algebra for developing correct digital hardware. Using DDD as the principle design environment, a core circuit implementing the clock synchronization algorithm was developed. The design process consisted of standard DDD transformations augmented with an ad hoc refinement justified using the Prototype Verification System (PVS) from SRI International. Subsequent to the above development, Wilfredo Torres-Pomales discovered an area-efficient realization of the same function. Establishing correctness of this optimization requires reasoning in arithmetic, so a general verification is outside the domain of both DDD transformations and model-checking techniques. DDD represents digital hardware by systems of mutually recursive stream equations. A collection of PVS theories was developed to aid in reasoning about DDD-style streams. These theories include a combinator for defining streams that satisfy stream equations, and a means for proving stream equivalence by exhibiting a stream bisimulation. DDD was used to isolate the sub-system involved in Torres-Pomales' optimization. The equivalence between the original design and the optimized verified was verified in PVS by exhibiting a suitable bisimulation. The verification depended upon type constraints on the input streams and made extensive use of the PVS type system. The dependent types in PVS provided a useful mechanism for defining an appropriate bisimulation.

Miner, Paul S.

1995-06-01

483

IMF; Planning for Use of Gold Sales Profits Under Way, but No Decision Made for Using a Portion of the Profits.  

National Technical Information Service (NTIS)

The International Monetary Fund (IMF) has historically financed its operating costs with income earned from the interest that member governments pay to borrow its funds.1 However, a rapid reduction in IMF lending in the mid-2000s significantly decreased t...

2012-01-01

484

Response time of the high-latitude dayside ionosphere to sudden changes in the north-south component of the IMF  

Microsoft Academic Search

The time scale of the response of the high-latitude dayside ionospheric flow to changes in the north-south component of the IMF is studied by examining the time delays between corresponding sudden changes obtained from simultaneous