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1

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

NASA Astrophysics Data System (ADS)

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

Grocott, A.; Milan, S. E.

2013-12-01

2

The influence of IMF clock angle timescales on the morphology of ionospheric convection  

NASA Astrophysics Data System (ADS)

We exploit a database of high-latitude ionospheric electric potential patterns, derived from radar observations of plasma convection in the Northern Hemisphere from the years 2000-2006, to investigate the timescales of interplanetary magnetic field (IMF) control of ionospheric convection and associated magnetospheric dynamics. We parameterize the convection observations by IMF clock angle, ? (the angle between geocentric solar magnetic (GSM) north and the projection of the IMF vector onto the GSM Y-Z plane), and by an IMF timescale, ?B (the length of time that a similar clock angle has been maintained prior to the convection observations being made). We find that the nature of the ionospheric convection changes with IMF clock angle, as expected from previous time-averaged studies, and that for ?B˜30 min, the convection patterns closely resemble their time-averaged counterparts. However, as ?B increases we find that the convection evolves away from the time-averaged patterns to reveal modified characteristic flow features. We discuss these findings in terms of solar wind-magnetosphere-ionosphere coupling and consider their implications for understanding the time-dependent nature of magnetospheric dynamics.

Grocott, A.; Milan, S. E.

2014-07-01

3

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

E-print Network

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

Lockwood, Mike

4

Influences of the interplanetary magnetic field clock angle and cone angle on the field-aligned currents in the magnetotail  

NASA Astrophysics Data System (ADS)

The influences of the interplanetary magnetic field (IMF) cone angle ? and clock angle ? on the field-aligned currents (FACs) at the plasma sheet boundary layers (PSBLs) have been investigated using Cluster Data. The FAC occurrence increases monotonically with IMF cone angle and has two peaks at -90° and +110° clock angle, respectively. The peak at +110° is distinctly larger than that at -90°. Overall, there are more FACs between 0° < ? < 180°, indicating that FACs occurrence is closely associated with duskward IMF. More FACs occur when 90° < |?| < 180°, implying that FAC is closely associated with southward IMF. The large FAC densities occur when 60° < |?| < 120°. The density also has two peaks and the peak at +90° clock angle (duskward IMF) is larger than that at -90° (dawnward IMF). These results indicate that the IMF influence on the FACs is from all IMF components and not only from a single component.

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

2013-10-01

5

FTE Dependence on IMF Orientation and Presence of Hall Physics in Global MHD Simulations  

NASA Astrophysics Data System (ADS)

Flux Transfer Events (FTEs) are poleward traveling flux ropes that form in the dayside magnetopause and represent significant coupling of the solar wind to the magnetosphere during times of southward IMF. In the 35 years since their discovery, FTEs have been extensively observed and modeled; however, there is still no consensus on their generation mechanism. Previous modeling efforts have shown that FTE occurrence and size depend on the resistivity model that is used in simulations and the structure of X-lines in the magnetopause. We use Hall OpenGGCM, a global Hall-MHD code, to study the formation and propagation of FTEs in the dayside magnetopause using synthetic solar wind conditions. We examine large scale FTE structure and nearby magnetic separators for a range of IMF clock angles and dipole tilts. In addition, we investigate how FTE formation and recurrence rate depends on the presence of the Hall term in the generalized Ohm's law compared with resistive MHD.

Maynard, K. M.; Germaschewski, K.; Lin, L.; Raeder, J.

2013-12-01

6

Robo Clock  

NSDL National Science Digital Library

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

AMPS GK-12 Program,

7

IMF Staff Papers  

NSDL National Science Digital Library

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

8

Measuring the IMF  

NSDL National Science Digital Library

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

9

IMF Annual Report 1998  

NSDL National Science Digital Library

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

International Monetary Fund.

1998-01-01

10

The Influence of Clocking Angle of the Projectile on the Simulated Impact Response of a Shuttle Leading Edge Wing Panel  

NASA Technical Reports Server (NTRS)

An analytical study was conducted to determine the influence of clocking angle of a foam projectile impacting a space shuttle leading edge wing panel. Four simulations were performed using LS-DYNA. The leading edge panels are fabricated of multiple layers of reinforced carbon-carbon (RCC) material. The RCC material was represented using Mat 58, which is a material property that can be used for laminated composite fabrics. Simulations were performed of a rectangular-shaped foam block, weighing 0.23-lb., impacting RCC Panel 9 on the top surface. The material properties of the foam were input using Mat 83. The impact velocity was 1,000 ft/s along the Orbiter X-axis. In two models, the foam impacted on a corner, in one model the foam impacted the panel initially on the 2-in.-long edge, and in the last model the foam impacted the panel on the 7-in.- long edge. The simulation results are presented as contour plots of first principal infinitesimal strain and time history plots of contact force and internal and kinetic energy of the foam and RCC panel.

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

2005-01-01

11

IMF Loan for Russia  

NSDL National Science Digital Library

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

Waters, Megan.

1998-01-01

12

Angles  

NSDL National Science Digital Library

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

Mr Clark

2012-10-31

13

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.

Jo Edkins

2007-01-01

14

Clock Counting  

NSDL National Science Digital Library

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

Ms. McDuffee

2008-11-12

15

IMF Working Papers  

NSDL National Science Digital Library

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

16

Angles  

NSDL National Science Digital Library

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

Dan Bunker

2011-01-01

17

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

Shodor Education Foundation

2004-01-01

18

Angles  

NSDL National Science Digital Library

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

2011-05-23

19

Understanding the IMF  

E-print Network

It is suggested that the thermal physics of star-forming clouds may play a more important role than has usually been recognized in the origin of the stellar IMF and in determining a characteristic mass scale. The importance of the thermal physics has been clearly demonstrated for the formation of the first stars in the universe, where it is well understood and results in cooling to a characteristic minimum temperature at a preferred density, and hence in a characteristic scale for fragmentation. In present-day star-forming clouds, an analogous situation may exist in that at low densities the temperature is expected to decrease with increasing density, reaching a minimum when the gas becomes thermally coupled to the dust and then rising slowly at higher densities. A minimum temperature of about 5 K is predicted to occur at a density of the order of 10^(-18) g cm^(-3), and at this point the Jeans mass is about 0.3 solar masses, similar to the mass at which the IMF peaks. If most of the fragmentation in star-forming clouds occurs in filaments, as is suggested by many simulations as well as by observations, fragmentation seems likely to occur preferentially at the density where the temperature reaches a minimum, and the Jeans mass at this point may then determine a characteristic scale for fragmentation and hence a preferred stellar mass.

Richard B. Larson

2004-08-27

20

The IMF in Starbursts  

NASA Astrophysics Data System (ADS)

We report on our ongoing study of the stellar content of starburst regions. Numerous claims have been made, both on theoretical and observational grounds, that the initial mass function (IMF) in regions of violent star formation differs significantly from the solar neighborhood. If the cloud fragmentation and accretion processes depend strongly on the environment, the resulting IMF slope as well as the upper and lower mass cut-offs may vary significantly. In order to derive the mass function in violent star forming regions we used HST/NICMOS, VLT(ANTU)/ISAAC, and ESO's ADONIS to spatially resolve their stellar content. Our study is mainly based on the two closest massive star forming regions NGC 3603 and 30 Doradus but recent ISO results indicate that these regions are likely to be representative building blocks of starburst galaxies. We find no evidence for an exotic mass function, although the slope varies locally. In particular, our spatially integrated results do not indicate a pronounced flattening or cut-off down to our detection limits.

Brandl, B.; Zinnecker, H.; Brandner, W.

1999-12-01

21

Angles  

NSDL National Science Digital Library

In this activity, students practice comparing angles when a transversal intersects two parallel lines. This activity allows students to explore the vocabulary used when comparing angles (e.g., alternate, same-side, interior, corresponding, etc.). This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

2010-01-01

22

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

NASA Technical Reports Server (NTRS)

Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walen tests, are necessary, but not sufficient, conditions, for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the SuperDARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than approximately 150 degrees. While inferred high-latitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole tilt angle increases or when IMF B(sub X) increases the effective dipole tilt.

Maynard, N. C.; Ober, D. M.; Burke, W. J.; Scudder, J. D.; Lester, M.; Dunlap, M.; Wild, J. A.; Grocott, A.; Farrugia, C. J.; Lund, E. J.; Russell, C. T.

2003-01-01

23

Recent advances on IMF research  

E-print Network

Here I discuss recent work on brown dwarfs, massive stars and the IMF in general. The stellar IMF can be well described by an invariant two-part power law in present-day star-formation events within the Local Group of galaxies. It is nearly identical in shape to the pre-stellar core mass function. The majority of brown dwarfs follow a separate IMF. Evidence from globular clusters and ultra-compact dwarf galaxies has emerged that IMFs may have been top heavy depending on the star-formation rate density. The IGIMF then ranges from bottom heavy at low galaxy-wide star formation rates to being top-heavy in galaxy-scale star bursts.

Kroupa, Pavel

2012-01-01

24

Recent Advances on IMF Research  

NASA Astrophysics Data System (ADS)

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

Kroupa, Pavel

25

International Monetary Fund (IMF) Data Mapper  

NSDL National Science Digital Library

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

International Monetary Fund

26

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

NASA Technical Reports Server (NTRS)

Flux transfer events (FTE) have been postulated to result from transient magnetic merging. If so, the ion distributions within an event should exhibit features known to result from merging. Observations of a FTE by instruments on the Polar spacecraft revealed classical merging signatures that included: 1) D-shaped, accelerated, magnetosheath ion distributions, 2) a well defined de Hoffman-Teller frame, 3) local stress balance, and 4) a P-N magnetic field signature. This FTE was observed near the magnetic equator at approx. 13 MLT under conditions of a moderately northward interplanetary magnetic field (IMF) (clock angle of less than 10 deg). The nature of the ion distributions and the consistency of the measured cutoff speed with that calculated from the measured local magnetic field and the derived de Hoffman-Teller speed show the ion injection to be local. Coupled with the northward IMF these results lead to the conclusion that component merging in the low latitude region was responsible for the FTE.

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

2003-01-01

27

Competitive Accretion and the IMF  

E-print Network

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

Ian A. Bonnell

2005-01-13

28

Clock Wise  

NSDL National Science Digital Library

In this activity, students can enter a time to be displayed on an analog clock. They can also have the clock display a time then read the clock to figure out what time it says. This activity allows students to practice reading analog clocks. This activity includes supplemental materials, including background information about the topics covered, a description of how to use the application, and exploration questions for use with the java applet.

2010-01-01

29

The IMF and Civil Society  

NSDL National Science Digital Library

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

30

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

NASA Astrophysics Data System (ADS)

A survey of dayside 557.7 and 630.0 nm auroral emission, acquired from the all-sky imagers at the Yellow River Station in Ny-Ålesund, Svalbard, shows that the dayside auroral oval could be divided into five auroral active regions: the dawnside (Da, 06:00-07:30 MLT) and duskside (Du, 15:30-17:00 MLT) green aurora sectors, the prenoon (W, 07:30-10:00 MLT) and postnoon (H, 13:00-15:30 MLT) peaks for 557.7 and 630.0 nm auroral emissions, and the midday gap (M, 10:00-13:00 MLT) for green aurora. The 630.0 nm intensities in W, M, and H nearly increase linearly with the Kan-Lee electric field. The 630.0 nm auroral emissions in W and H show a double-peak feature associated with the change of interplanetary magnetic field (IMF) clock angle: one peak at 90° and the other at 270°. The 630.0 nm emission in M, however, is dominantly excited during the clock angle of 90°-270°. It is considered that the 630.0 nm emissions in W/H and M are related to the prenoon/postnoon antiparallel reconnection at the high-latitude magnetopause and the subsolar component reconnection, respectively. Moreover, the 630.0 nm intensity in the dayside oval shows the monotonic increase with the absolute value of the north-south oriented electric field (Ez), but the increasing rate of the intensity in the postnoon (prenoon) oval is larger than that in the prenoon (postnoon) oval when IMF By is negative (positive). Only the 557.7 nm intensity in region M and H/Du increases gradually with the absolute value of negative Ez. These features should be associated with the change of interhemispheric currents produced by Ez.

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

2012-02-01

31

Clock Arithmetic  

NSDL National Science Digital Library

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

2010-01-01

32

IMF Financial Transactions Plan Quarterly Report  

NSDL National Science Digital Library

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

33

IMF Length Scales and Predictability: The Two Length Scale Medium  

NASA Technical Reports Server (NTRS)

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

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

1999-01-01

34

Primary Clock  

NSDL National Science Digital Library

This Flash applet includes a working analog clock face displaying the current time, and stating the time in text, which optionally may be spoken. Clicking on the right or left sides of the face displays the number of minutes "past" or "to" the hour, respectively. A smaller clock on the right can be set to any time specified by the user.

2012-01-01

35

The Stellar IMF from turbulent fragmentation  

NASA Technical Reports Server (NTRS)

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

Padoan, P.; Nordlund, A.

2001-01-01

36

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

37

Clock Works.  

ERIC Educational Resources Information Center

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

Markle, Sandra

1988-01-01

38

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

39

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

NASA Technical Reports Server (NTRS)

It is demonstrated that there are distinct differences in the electron precipitation patterns (or the polar cap size), geomagnetic activity, and field-aligned currents in the highest-latitude region for small and large IMF B(z) values when the IMF B(z) component is positive. First, during periods of weakly northward IMF, there is a distinct area in the highest-latitude region in which the electron precipitation is absent except for the polar rain. By contrast, during strongly northward IMF, the entire polar region is often filled with burst-type soft electron precipitations. Second, geomagnetic disturbances and field-aligned-current intensities in the highest-latitude region are less during a weak IMF B(z) condition than those during a strongly northward IMF B(z) condition. Geomagnetic activity in the auroral zone for both conditions is absent or very weak.

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

1988-01-01

40

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! ...

Ms. Troff

2008-06-23

41

Living Clocks  

NSDL National Science Digital Library

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

Nancy P. Moreno

2009-01-01

42

Atomic Clocks Ultimate Clocks, W. Wayt Gibbs  

E-print Network

Atomic Clocks Ultimate Clocks, W. Wayt Gibbs Scientific American Time 306, 60-67 (19 January 2012-75 (22 January 2014) An Atomic Clock with 10­18 Instability N. Hinkley, J. A. Sherman, N. B. Phillips, M. Rosenband, and D. J. Wineland Science 24 September 2010: 1630-1633. Two Atomic Clocks Ticking as One Bruce

Safronova, Marianna

43

Time Clocks  

NSDL National Science Digital Library

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

Stephen Greb

44

The smallest clock  

Microsoft Academic Search

If one considers bacteria as clocks they may be the smallest clocks allowed by quantum mechanical considerations. Diffusion explains why such a small clock is calibrated in minutes. Similar considerations may also limit human nanotechnology.

Peter D. Pesic

1993-01-01

45

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

46

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! ...

Miss Smith

2011-03-23

47

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

Microsoft Academic Search

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly-enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle theta\\/sub B\\/n of the interplanetary magnetic field (IMF) to the shock

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

1982-01-01

48

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

Microsoft Academic Search

Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle of the interplanetary magnetic field (IMF) to the shock normal

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

1982-01-01

49

Smart clock: a new time  

Microsoft Academic Search

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

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

1992-01-01

50

Optical Atomic Clocks  

E-print Network

Optical atomic clocks represent the state-of-the-art in the frontier of modern measurement science. In this article we provide a detailed review on the development of optical atomic clocks that are based on trapped single ions and many neutral atoms. We discuss important technical ingredients for optical clocks, and we present measurement precision and systematic uncertainty associated with some of the best clocks to date. We conclude with an outlook on the exciting prospect for clock applications.

Ludlow, Andrew D; Ye, Jun; Peik, Ekkehard; Schmidt, Piet O

2014-01-01

51

SIMULTANEOUS DEMULTIPLEXING, ELECTRICAL CLOCK RECOVERY, AND OPTICAL CLOCK GENERATION USING  

E-print Network

SIMULTANEOUS DEMULTIPLEXING, ELECTRICAL CLOCK RECOVERY, AND OPTICAL CLOCK GENERATION USING of the PLL. As a result, simultaneous demultiplexing, electrical clock recovery and optical clock generation), and Masashi Usami (2) 1 : Department of Electrical and Computer Engineering, University of California Santa

Bowers, John

52

Active Ion Optical Clock  

E-print Network

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

Zhuang, Wei; Chen, Jingbiao

2011-01-01

53

Beat The Clock!!  

NSDL National Science Digital Library

How well can you compute? Are your basic math skills up to the challenge to solve equations to beat the clock? The faster the you work, the better your score! The more you practice, the better you can become at basic math. Pick each link below, work as fast as you can, then record your score! Try each link twice beat the clock: addition equations Beat the clock: subtracting beat the clock: multiplication beat the clock: division beat the clock: two step *Bonus: Try one or two links again to improve your score ...

Mrs. Pierce

2010-10-25

54

IMF draping around the geotail - IMP 8 observations  

NASA Technical Reports Server (NTRS)

The draping pattern for the full range of IMF directions is mapped in the GSM yz-plane using a large data set for studying magnetic field draping around the tail. Based on the maps, it is concluded that the dominant pattern is draping as found by Ohtani and Kokubun (1991) and Sanchez and Siscoe (1990). A new finding is that the draping pattern is rotated relative to the plane formed by the IMF and the aberrated x-axis, with the degree of rotation varying from zero for strongly northward and southward IMF to a peak of 17 deg for moderately southward IMF. It is also found that the tail radius is bigger for southward IMF than for northward IMF.

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

1992-01-01

55

Hanle detection for optical clocks.  

PubMed

Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423?nm fluorescence, the improved 657?nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard. PMID:25734183

Zhang, Xiaogang; Zhang, Shengnan; Pan, Duo; Chen, Peipei; Xue, Xiaobo; Zhuang, Wei; Chen, Jingbiao

2015-01-01

56

Hanle Detection for Optical Clocks  

PubMed Central

Considering the strong inhomogeneous spatial polarization and intensity distribution of spontaneous decay fluorescence due to the Hanle effect, we propose and demonstrate a universe Hanle detection configuration of electron-shelving method for optical clocks. Experimental results from Ca atomic beam optical frequency standard with electron-shelving method show that a designed Hanle detection geometry with optimized magnetic field direction, detection laser beam propagation and polarization direction, and detector position can improve the fluorescence collection rate by more than one order of magnitude comparing with that of inefficient geometry. With the fixed 423?nm fluorescence, the improved 657?nm optical frequency standard signal intensity is presented. The potential application of the Hanle detection geometry designed for facilitating the fluorescence collection for optical lattice clock with a limited solid angle of the fluorescence collection has been discussed. The Hanle detection geometry is also effective for ion detection in ion optical clock and quantum information experiments. Besides, a cylinder fluorescence collection structure is designed to increase the solid angle of the fluorescence collection in Ca atomic beam optical frequency standard. PMID:25734183

Zhang, Xiaogang; Zhang, Shengnan; Pan, Duo; Chen, Peipei; Xue, Xiaobo; Zhuang, Wei; Chen, Jingbiao

2015-01-01

57

Atomic fountain clocks  

Microsoft Academic Search

We describe and review the current state of the art in atomic fountain clocks. These clocks provide the best realization of the SI second possible today, with relative uncertainties of a few parts in 1016.

R. Wynands; S. Weyers

2005-01-01

58

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

59

VLBI clock synchronization. [for atomic clock rate  

NASA Technical Reports Server (NTRS)

The potential accuracy of VLBI (very long baseline interferometry) for clock epoch and rate comparisons was demonstrated by results from long- and short-baseline experiments. It was found that atomic clocks at widely separated sites (several thousand kilometers apart) can be synchronized to within several nanoseconds from a few minutes of VLBI observations and to within one nanosecond from several hours of observations.

Counselman, C. C., III; Shapiro, I. I.; Rogers, A. E. E.; Hinteregger, H. F.; Knight, C. A.; Whitney, A. R.; Clark, T. A.

1977-01-01

60

Radioactive Counting Clocks  

Microsoft Academic Search

We report on a radioactive counting clock (RCC) based on radioactive beta emissions from nickel-63 thin films. We present a theoretical analysis of the clock that uses the radioactive source (physics package) to lock and stabilize the frequency of a voltage-to-frequency converter (local oscillator). We present frequency stability measurements of the RCC over 10 days of clock operation. We analyze

Shankar Radhakrishnan; Amit Lal

2006-01-01

61

Clipart ETC: Clock Menu  

NSDL National Science Digital Library

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

Educational Technology Clearinghouse

2010-08-20

62

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

63

Atomic clocks for astrophysical measurements  

NASA Technical Reports Server (NTRS)

It is noted that recently developed atomic hydrogen masers have achieved stability well into the 10 to the -16th domain for averaging time intervals beyond 1000 sec and that further improvements are in prospect. These devices are highly adaptable for space use in very high precision measurements of angle through Very Long Baseline Interferometry (VLBI) and of range and range-rate through Doppler techniques. Space missions that will use these clocks for measuring the sun's gravity field distribution and for testing gravitation and relativity (a project that will include a search for pulsed low-frequency gravitational waves) are discussed. Estimates are made of system performance capability, and the accuracy capability of relativistic measurements is evaluated in terms of the results from the 1976 NASA/SAO spaceborne clock test of the Einstein Equivalence Principle.

Vessot, R. F. C.; Mattison, E. M.

1982-01-01

64

Fifty Years of IMF Variation: The Intermediate-Mass Stars  

E-print Network

I track the history of star count estimates of the Milky Way field star and open cluster IMFs, concentrating on the neglected mass range from 1 to 15 M${_\\odot}$. The prevalent belief in a universal IMF appears to be without basis for this mass range. Two recent estimates of the field star IMF using different methods and samples give values of the average logarithmic slope $\\Gamma$ between -1.7 and -2.1 in the mass range 1.1 to 4 M${_\\odot}$. Two older estimates between 2 and 15 M${_\\odot}$ disagree severely; the field IMF in this range is essentially unknown from star counts. Variations in $\\Gamma$ among open cluster IMFs in this mass range have not decreased despite numerous detailed studies, even for studies using homogeneous data and reduction procedures and including only clusters with a significant mass range. These cluster variations \\textit{might} be due to the combined effects of sampling, systematic errors, stellar evolution uncertainties, dynamical evolution, and unresolved binaries. If so, then the cluster data are consistent with a universal IMF, but are also consistent with sizeable variations. The cluster data do not allow an estimate of an average IMF or $\\Gamma$ because the average depends on the choice of weighting procedure and other effects. If the spread in cluster IMFs is in excess of the effects listed above, real IMF variations must occur that do not depend much on physical conditions explored so far. The complexity of the star formation process seen in observations and simulations suggests that large realization-to-realization differences might be expected, in which case an individual cluster IMF would be in part the product of evolutionary contingency in star formation, and the function of interest is the probability distribution of IMF parameters.

John Scalo

2004-12-20

65

Optimizing Passive Quantum Clocks  

E-print Network

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

Michael Mullan; Emanuel Knill

2014-04-15

66

Optimizing passive quantum clocks  

NASA Astrophysics Data System (ADS)

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

Mullan, Michael; Knill, Emanuel

2014-10-01

67

Connection between dynamically derived IMF normalisation and stellar populations  

E-print Network

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

McDermid, Richard M

2015-01-01

68

Connection between dynamically derived IMF normalisation and stellar populations  

NASA Astrophysics Data System (ADS)

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

McDermid, Richard M.

2015-04-01

69

Clock Trees: Logical Clocks for Programs with Nested Parallelism  

Microsoft Academic Search

A vector clock is a valuable tool for maintaining run time concurrency information in parallel programs. A novel method is presented for modifying vector clocks to make them suitable for programs with nested fork join parallelism (having a variable number of tasks). The resulting kind of clock is called a clock tree, due to its tree structure. The clock tree

Koenraad Audenaert

1997-01-01

70

Magnetic field topology for northward IMF reconnection: Ion observations  

NASA Astrophysics Data System (ADS)

Ion observations from the Cluster spacecraft are used to investigate magnetopause reconnection for northward Interplanetary Magnetic Field (IMF) conditions. When the spacecraft cross the magnetopause and enter the magnetosphere at low latitudes, equatorward of the magnetospheric cusps, multiple ion populations of magnetosheath origin are almost always observed. The bulk flow velocities of these separate populations are consistent with their entry at high northern and southern latitudes. Furthermore, characteristics of the pitch angle distributions provide a means to estimate the entry point of the magnetosheath ions and the relative timing of the reconnections in opposite hemispheres. In the example presented, these entry points are poleward of both magnetospheric cusps, and the reconnections are separated by minutes. In a survey of magnetopause crossing events, most ion observations and associated electron observations are consistent with this dual-lobe reconnection process as long as the reconnections are separated in time by several minutes. A small percentage of events are not consistent with this reconnection model and may indicate reconnection at other locations, such as equatorward of the cusp.

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

2014-11-01

71

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

72

Science Nation: Biological Clocks  

NSDL National Science Digital Library

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

73

Clock Arithmetic and Cryptography  

NSDL National Science Digital Library

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

2010-01-01

74

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

75

Cryogenic optical lattice clocks  

NASA Astrophysics Data System (ADS)

The accuracy of atomic clocks relies on the superb reproducibility of atomic spectroscopy, which is accomplished by careful control and the elimination of environmental perturbations on atoms. To date, individual atomic clocks have achieved a 10?18 level of total uncertainties, but a two-clock comparison at the 10?18 level has yet to be demonstrated. Here, we demonstrate optical lattice clocks with 87Sr atoms interrogated in a cryogenic environment to address the blackbody radiation-induced frequency shift, which remains the primary source of systematic uncertainty and has initiated vigorous theoretical and experimental investigations. The systematic uncertainty for the cryogenic clock is evaluated to be 7.2?×?10?18, which is expedited by operating two such cryo-clocks synchronously. After 11 measurements performed over a month, statistical agreement between the two cryo-clocks reached 2.0?×?10?18. Such clocks' reproducibility is a major step towards developing accurate clocks at the low 10?18 level, and is directly applicable as a means for relativistic geodesy.

Ushijima, Ichiro; Takamoto, Masao; Das, Manoj; Ohkubo, Takuya; Katori, Hidetoshi

2015-03-01

76

Using circadian entrainment to find cryptic clocks.  

PubMed

Three properties are most often attributed to the circadian clock: a ca. 24-h free-running rhythm, temperature compensation of the circadian rhythm, and its entrainment to zeitgeber cycles. Relatively few experiments, however, are performed under entrainment conditions. Rather, most chronobiology protocols concern constant conditions. We have turned this paradigm around and used entrainment to study the circadian clock in organisms where a free-running rhythm is weak or lacking. We describe two examples therein: Caenorhabditis elegans and Saccharomyces cerevisiae. By probing the system with zeitgeber cycles that have various structures and amplitudes, we can demonstrate the establishment of systematic entrained phase angles in these organisms. We conclude that entrainment can be utilized to discover hitherto unknown circadian clocks and we discuss the implications of using entrainment more broadly, even in model systems that show robust free-running rhythms. PMID:25662452

Eelderink-Chen, Zheng; Olmedo, Maria; Bosman, Jasper; Merrow, Martha

2015-01-01

77

World Population Clock  

NSDL National Science Digital Library

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

David Levine

78

Quantum Clocks and Stopwatches  

Microsoft Academic Search

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

Rafael Sala Mayato; Daniel Alonso; Iñigo Egusquiza

79

Biological Clocks & Circadian Rhythms  

ERIC Educational Resources Information Center

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

Robertson, Laura; Jones, M. Gail

2009-01-01

80

Egyptian "Star Clocks"  

NASA Astrophysics Data System (ADS)

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

Symons, Sarah

81

Number Base Clocks  

NSDL National Science Digital Library

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

82

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

83

Clock drawing, clock copying, and physical abilities in geriatric rehabilitation  

Microsoft Academic Search

Ruchinskas RA, Singer HK, Repetz NK. Clock drawing, clock copying, and physical abilities in geriatric rehabilitation. Arch Phys Med Rehabil 2001;82;920-4. Objectives: To determine whether clock drawing and clock copying assess domains that are critical for successful rehabilitation and to evaluate the use of these tasks in predicting physical abilities during rehabilitation. Design: Observational survey study of geriatric cohorts. Setting:

Robert A. Ruchinskas; Hedy K. Singer; Nancy K. Repetz

2001-01-01

84

Publications Angling, Angling Records,  

E-print Network

Publications Angling, Angling Records, and Game Fish Conservation The 1982 edition of "World Record Game Fishes," published by the Inter- national Game Fish Association, 3000 East Las alas Boulevard, Fort Lauder- dale, FL 33316, continues to grow as an important reference work for the serious angler

85

Optical Atomic Clocks David Hanneke  

E-print Network

Optical Atomic Clocks David Hanneke Michelson Postdoctoral Prize Lectures 11 May 2010 #12;Hanneke Optical atomic clock 1 PHz = 1015 Hz Frequency comb http://en.wikipedia.org/wiki/ File:Scappamento.gif T Pendulum clock 103 Quartz watch 105 Optical atomic clock 1014 1/Q C. W. Chou, et al., To be published (2010

Hanneke, David

86

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

87

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

88

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

89

Real-time simulation clock  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

90

Atomic and gravitational clocks  

NASA Technical Reports Server (NTRS)

Atomic and gravitational clocks are governed by the laws of electrodynamics and gravity, respectively. While the strong equivalence principle (SEP) assumes that the two clocks have been synchronous at all times, recent planetary data seem to suggest a possible violation of the SEP. Past analysis of the implications of an SEP violation on different physical phenomena revealed no disagreement. However, these studies assumed that the two different clocks can be consistently constructed within the framework. The concept of scale invariance, and the physical meaning of different systems of units, are now reviewed and the construction of two clocks that do not remain synchronous - whose rates are related by a non-constant function beta sub a - is demonstrated. The cosmological character of beta sub a is also discussed.

Canuto, V. M.; Goldman, I.

1982-01-01

91

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

92

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

NASA Astrophysics Data System (ADS)

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

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

2005-02-01

93

Variable frequency microprocessor clock generator  

SciTech Connect

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

Branson, C.N.

1989-04-04

94

High-Latitude Ionospheric Dynamics During Conditions of Northward IMF  

NASA Technical Reports Server (NTRS)

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

Sharber, J. R.

1996-01-01

95

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

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

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

96

Somites without a clock.  

PubMed

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

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

2014-02-14

97

Somites Without a Clock  

PubMed Central

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

Belmonte, Julio M.; Glazier, James A.; Stern, Claudio D.

2014-01-01

98

Distinct Magnetospheric Responses to Southward IMF in Two Substorms  

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

99

Northwest of Suez: The 1956 Crisis and the IMF  

Microsoft Academic Search

Egypt's nationalization of the Suez Canal in 1956 and the failed attempt by France, Israel, and the United Kingdom to retake it by force constituted a serious political crisis with significant economic consequences. For the United Kingdom, it engendered a financial crisis as well. That all four of the combatants sought and obtained IMF financial assistance was highly unusual for

James Boughton

2001-01-01

100

Tutorial: Clock and Clock Systems Performance Measures  

NASA Technical Reports Server (NTRS)

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

Allan, David W.

1996-01-01

101

Iron around the clock.  

PubMed

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

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

2014-07-01

102

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

103

Iodine Clock Reaction  

NSDL National Science Digital Library

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

104

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; )

2009-10-16

105

World Food Clock  

NSDL National Science Digital Library

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

Twyman, Luke

106

Generalized gravitomagnetic clock effect  

E-print Network

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

Eva Hackmann; Claus Lämmerzahl

2014-08-28

107

Generalized gravitomagnetic clock effect  

NASA Astrophysics Data System (ADS)

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

Hackmann, Eva; Lämmerzahl, Claus

2014-08-01

108

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.

109

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

110

Thermal Physics, Cloud Geometry, and the Stellar IMF  

E-print Network

The thermal properties of star-forming clouds have an important influence on how they fragment into stars, and it is suggested in this paper that the low-mass stellar IMF, which appears to be almost universal, is determined largely by the thermal physics of these clouds. In particular, it is suggested that the characteristic stellar mass, a little below one solar mass, is determined by the transition from an initial cooling phase of collapse to a later phase of slowly rising temperature that occurs when the gas becomes thermally coupled to the dust. Numerical simulations support the hypothesis that the Jeans mass at this transition point plays an important role in determining the peak mass of the IMF. A filamentary geometry may also play a key role in the fragmentation process because the isothermal case is a critical one for the collapse of a cylinder: the collapse and fragmentation of a cylinder can continue freely as long as the temperature continues to decrease, but not if it begins to increase. The limited available results on the dependence of the thermal properties of clouds on metallicity do not suggest a strong dependence of the IMF on metallicity, but the far-infrared background radiation in starburst regions and in the early universe may significantly shift the peak mass to higher masses in these situations.

Richard B. Larson

2005-01-31

111

Modern yields per stellar generation: the effect of the IMF  

E-print Network

Gaseous and stellar metallicities in galaxies are nowadays routinely used to constrain the evolutionary processes in galaxies. This requires the knowledge of the average yield per stellar generation, $y_{\\text{Z}}$, i.e. the quantity of metals that a stellar population releases into the interstellar medium (ISM), which is generally assumed to be a fixed fiducial value. Deviations of the observed metallicity from the expected value of $y_{\\text{Z}}$ are used to quantify the effect of outflows or inflows of gas, or even as evidence for biased metallicity calibrations or inaccurate metallicity diagnostics. Here we show that $\\rm y_{\\text{Z}}$ depends significantly on the Initial Mass Function (IMF), varying by up to a factor larger than three, for the range of IMFs typically adopted in various studies. This, along with the variation of the gas mass fraction restored into the ISM by supernovae ($R$, which also depends on the IMF), may yield to deceiving results, if not properly taken into account. In particular, ...

Vincenzo, Fiorenzo; Belfiore, Francesco; Maiolino, Roberto

2015-01-01

112

Clocks in algae.  

PubMed

As major contributors to global oxygen levels and producers of fatty acids, carotenoids, sterols, and phycocolloids, algae have significant ecological and commercial roles. Early algal models have contributed much to our understanding of circadian clocks at physiological and biochemical levels. The genetic and molecular approaches that identified clock components in other taxa have not been as widely applied to algae. We review results from seven species: the chlorophytes Chlamydomonas reinhardtii, Ostreococcus tauri, and Acetabularia spp.; the dinoflagellates Lingulodinium polyedrum and Symbiodinium spp.; the euglenozoa Euglena gracilis; and the red alga Cyanidioschyzon merolae. The relative simplicity, experimental tractability, and ecological and evolutionary diversity of algal systems may now make them particularly useful in integrating quantitative data from "omic" technologies (e.g., genomics, transcriptomics, metabolomics, and proteomics) with computational and mathematical methods. PMID:25379817

Noordally, Zeenat B; Millar, Andrew J

2015-01-20

113

Molecular Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

Ultracold homonuclear molecules present a model-independent system for precision measurements, such as tests of time variations of the proton-electron mass ratio. These measurements would complement those utilizing atomic clocks or astronomical observations. Creation and manipulation of dimers based on ultracold bosonic alkaline-earth-metal atoms appears particularly attractive due to the simplicity of the zero-spin ground state molecular potentials. Furthermore, recent success with precision and accuracy of optical lattice clocks based on these atoms shows the potential of achieving extremely low systematic uncertainties in the tight-confinement regime in the lattice. We discuss specific schemes for obtaining the cold molecular sample, including the magic-frequency optical lattice technique for molecular vibrational transitions.

Zelevinsky, Tanya; Kotochigova, Svetlana; Ye, Jun

2008-05-01

114

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 hydrogen masers.

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

2001-01-01

115

A microfabricated atomic clock  

Microsoft Academic Search

Fabrication techniques usually applied to microelectromechanical systems (MEMS) are used to reduce the size and operating power of the core physics assembly of an atomic clock. With a volume of 9.5 mm3, a fractional frequency instability of 2.5×10-10 at 1 s of integration, and dissipating less than 75 mW of power, the device has the potential to bring atomically precise

Svenja Knappe; Vishal Shah; Peter D. D. Schwindt; Leo Hollberg; John Kitching; Li-Anne Liew; John Moreland

2004-01-01

116

Microchip-Based Trapped-Atom Clocks  

E-print Network

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

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

2011-04-20

117

Circadian Clocks in the Ovary  

PubMed Central

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

Sellix, Michael T.; Menaker, Michael

2010-01-01

118

An Active Ion Optical Clock  

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

119

LOW POWER DESIGN OF DIGITAL SYSTEMS USING ENERGY RECOVERY CLOCKING AND CLOCK GATING  

E-print Network

LOW POWER DESIGN OF DIGITAL SYSTEMS USING ENERGY RECOVERY CLOCKING AND CLOCK GATING A thesis work that I have read Low Power Design of Digital Systems Using Energy Recovery Clocking and Clock Gating Engineering #12;iv LOW POWER DESIGN OF DIGITAL SYSTEMS USING ENERGY RECOVERY CLOCKING AND CLOCK GATING

Mahmoodi, Hamid

120

Clock Gating and Negative Edge Triggering for Energy Recovery Clock Vishwanadh Tirumalashetty and Hamid Mahmoodi  

E-print Network

Clock Gating and Negative Edge Triggering for Energy Recovery Clock Vishwanadh Tirumalashetty>@sfsu.edu Abstract Energy recovery clocking has been demonstrated as an effective method for reducing the clock power solutions. In this paper, we propose a clock gating solution for energy recovery clocking by gating the flip

Mahmoodi, Hamid

121

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

122

Tick Tock Goes the Clock  

NSDL National Science Digital Library

Can you tell time? Play these games to find out! Begin with Set the Clock. Play this fun game 5 times then move on the next one. Can you Stop the Clock? Be quick at telling time in this exciting game. Play this game 5 times. What time is it? Do you know? I hope so because this challenging game uses an analog clock and a digital ...

Ms. Morgan

2008-04-03

123

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

124

Angle Sums  

NSDL National Science Digital Library

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

Illuminations National Council of Teachers of Mathematics

2010-05-20

125

Master/slave clock arrangement for providing reliable clock signal  

NASA Technical Reports Server (NTRS)

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

Abbey, Duane L. (Inventor)

1977-01-01

126

A Light Clock Satisfying the Clock Hypothesis of Special Relativity  

ERIC Educational Resources Information Center

The design of the FMEL, a floor-mirrored Einstein-Langevin "light clock", is introduced. The clock provides a physically intuitive manner to calculate and visualize the time dilation effects for a spatially extended set of observers (an accelerated "frame") undergoing unidirectional acceleration or observers on a rotating cylinder of constant…

West, Joseph

2007-01-01

127

Angle Practice!  

NSDL National Science Digital Library

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

Ms. Hume

2012-11-02

128

Quartz Crystal Clocks  

NASA Technical Reports Server (NTRS)

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

1976-01-01

129

Fault-tolerant clock synchronization  

Microsoft Academic Search

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

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

1984-01-01

130

The Vitamin C Clock Reaction.  

ERIC Educational Resources Information Center

Describes an iodine clock reaction that produces an effect similar to the Landolt clock reaction. This reaction uses supermarket chemicals and avoids iodate, bisulfite, and mercury compounds. Ascorbic acid and tincture of iodine are the main reactants with alternate procedures provided for vitamin C tablets and orange juice. (DDR)

Wright, Stephen W.

2002-01-01

131

Mind the Clock  

PubMed Central

Recent progress in plant genomics allows us to investigate genetic and physiological changes in genome-wide gene expression.1,2 In the past years, a large-scale service for the global expression profiling in Arabidopsis, AtGenExpress, has been designed and coordinated.2,3 By using these multiple datasets, questions about complicated biological networks are being resolved in powerful ways. For example, microarray analyses reveal orchestrated transcript expressions during circadian and diurnal time courses.4–6 It was estimated in this work that up to 20% of transcripts are circadian regulated, implying that the clock impacts most botanical processes, including light, temperature, and hormone signalling, and much of cellular metabolism.4,6 In turn, external cues are well-known to affect the circadian system.7,8 For example, we reported phytohormone regulation.9 Thus, we imagined that in the AtGenExpress datasets inclusive of stress- and hormone-treated experiments, clock genes might be altered in expression levels. PMID:19704590

Hanano, Shigeru

2007-01-01

132

The IMF of open star clusters with Tycho-2  

E-print Network

We studied the fields of nine nearby open star clusters based on the Tycho-2 catalogue. The clusters are: Blanco 1, Stock 2, the alpha Per cluster, the Pleiades, NGC 2451, IC 2391, Praesepe, IC 2602, and NGC 7092. We determined membership probabilities for the stars in the cluster fields from the stellar proper motions and used the Tycho-2 photometry to compute the initial mass function (IMF) of the clusters from the main sequence turn-off point down to approx. 1 M_sun. We found IMF slopes ranging from Gamma=-0.69 down to Gamma=-2.27 (when the Salpeter (1955) value would be Gamma=-1.35). We also studied the membership of individual stars of special astrophysical interest. In some cases previous results had to be revised. As a by-product, we investigated some general properties of the Tycho-2 catalogue; we confirmed that the Tycho-2 proper motions show only marginal deviations from the Hipparcos catalogue. On the other hand, in some regions the completeness of the catalogue seems to decrease at magnitudes brighter than claimed by Hog et al. (2000).

J. Sanner; M. Geffert

2001-02-12

133

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

134

Clocks around Sgr A*  

NASA Astrophysics Data System (ADS)

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

Angélil, Raymond; Saha, Prasenjit

2014-11-01

135

Synchronizing clocks in the presence of faults  

Microsoft Academic Search

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

Leslie Lamport; P. M. Melliar-Smith

1985-01-01

136

spiral inductors power/clock mesh  

E-print Network

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

137

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

E-print Network

GPS clock calibration using an atomic clock Shuei YAMADA,Hans Gerd BERNS Abstract Time di#11;ernece of GPS at SK and KEK was measured by making reference to an atomic clock. Following value was obtained and atomic clock at MIZU- SAWA (1999 Oct 19th), 2. measured time di#11;erence of GPS and atomic clock at KEK

Berns, Hans-Gerd

138

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

Microsoft Academic Search

Circadian timing is generated through a unique series of autoregulatory interactions termed the molecular clock. Behavioral rhythms subject to the molecular clock are well characterized. We demonstrate a role for Bmal1 and Clock in the regulation of glucose homeostasis. Inactivation of the known clock components Bmal1 (Mop3) and Clock suppress the diurnal variation in glucose and triglycerides. Gluconeogenesis is abolished

R. Daniel Rudic; Peter McNamara; Anne-Maria Curtis; Raymond C. Boston; Satchidananda Panda; John B. Hogenesch; Garret A. FitzGerald

2004-01-01

139

Temporal and spatial expression patterns of canonical clock genes and clock-controlled genes in the  

E-print Network

Temporal and spatial expression patterns of canonical clock genes and clock-controlled genesB)-containing cells is retinorecipient and the cells therein lack rhythmic expression of clock genes and electrical of expression of the canonical clock genes Per1, Per2 and vasopressin mRNA, a clock-controlled gene

Silver, Rae

140

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

NASA Astrophysics Data System (ADS)

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

Chen, Ning; Xu, Xinye

2015-01-01

141

Angles (elementary)  

NSDL National Science Digital Library

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

2011-05-23

142

Acceleration effects on atomic clocks  

E-print Network

We consider a free massive particle inside a box which is dragged by Rindler observers. Admitting that the particle obeys the Klein-Gordon equation, we find the frequencies of the stationary states of this system. Transitions between the stationary states are employed to set a standard frequency for a toy atomic clock. Comparing the energy spectrum of the accelerated system with the energy spectrum of an identical system in an inertial frame, we determine the influence of the instantaneous acceleration on the rate of atomic clocks. We argue that our result does not violate the clock hypothesis.

F. Dahia; P. J. Felix de Araujo

2014-12-16

143

Acceleration effects on atomic clocks  

E-print Network

We consider a free massive particle inside a box which is dragged by Rindler observers. Admitting that the particle obeys the Klein-Gordon equation, we find the frequencies of the stationary states of this system. Transitions between the stationary states are employed to set a standard frequency for a toy atomic clock. Comparing the energy spectrum of the accelerated system with the energy spectrum of an identical system in an inertial frame, we determine the influence of the instantaneous acceleration on the rate of atomic clocks. We argue that our result does not violate the clock hypothesis.

Dahia, F

2014-01-01

144

Biological Clocks and Circadian Rhythms  

NSDL National Science Digital Library

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

Laura Robertson

2009-02-01

145

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

PubMed

In this article, we interrogate the policy response of the International Monetary Fund (IMF) to the global financial crisis, and discuss the likely global health implications, especially in low-income countries. In doing so, we ask if the IMF has meaningfully loosened its fiscal deficit targets in light of the economic challenges posed by the financial crisis and adjusted its macro-economic policy advice to this new reality; or has the rhetoric of counter-cyclical spending failed to translate into additional fiscal space for IMF loan-recipient countries, with negative health consequences? To answer these questions, we assess several post-crisis IMF lending agreements with countries requiring financial assistance, and draw upon recent academic studies and civil society reports examining policy conditionalities still being prescribed by the IMF. We also reference recent studies examining the health impacts of these conditionalities. We demonstrate that while the IMF has been somewhat more flexible in its crisis response than in previous episodes of financial upheaval, there has been no meaningful rethinking in the application of dominant neoliberal macro-economic policies. After showing some flexibility in the initial crisis response, the IMF is pushing for excessive contraction in most low and middle-income countries. We conclude that there remains a wide gap between the rhetoric and the reality of the IMF's policy and programming advice, with negative implications for global health. PMID:22504946

Ruckert, Arne; Labonté, Ronald

2013-09-01

146

Reconguration and closure of lobe ux by reconnection during northward IMF: possible evidence for signatures  

E-print Network

IMF would reconnect in one hemisphere only, thereby driving a circulation of open ¯ux within that polar cap. A catalogue of other topological possibilities was presented by Cowley (1981, 1983 times for any one sheath ®eld line. The ®rst observational evidence that this north- ward-IMF lobe

Paris-Sud XI, Université de

147

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

148

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

149

Clocking design and analysis for a 600MHz Alpha microprocessor  

Microsoft Academic Search

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

Daniel W. Bailey; Bradley J. Benschneider

1998-01-01

150

Clock genes and female reproduction   

E-print Network

The involvement of clock genes in the temporal regulation of the function and lifespan of the corpus luteum (CL) has not been investigated in detail. Immunohistochemistry and real-time quantitative PCR techniques were used ...

Chen, Cynthia

2009-01-01

151

History of early atomic clocks  

Microsoft Academic Search

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

Norman F. Ramsey

2005-01-01

152

Right Angle  

NSDL National Science Digital Library

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

Paul Goldenberg

2011-06-09

153

O+ transport in the dayside magnetosheath and its dependence on the IMF direction  

NASA Astrophysics Data System (ADS)

Recent studies have shown that the escape of oxygen ions (O+) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O+ transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O+ flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O+ is transported downstream. In contrast, for northward IMF we observe O+ flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O+ and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O+ to be 5%, a small number considering that ion flux calculations are rough estimates. The total O+ escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O+ cusp outflow.

Slapak, R.; Nilsson, H.; Westerberg, L. G.; Larsson, R.

2015-03-01

154

Molecular Mechanisms Underlying the Arabidopsis Circadian Clock  

PubMed Central

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

Nakamichi, Norihito

2011-01-01

155

Dual reference signal post-silicon reconfigurable clock distribution networks  

E-print Network

traveling in opposite directions to perform clock synchronization on a daisy- chained (serial) clock that is impossible without our daisy-chained clock network. We investigate a clock network that emphasizes

Zilic, Zeljko

156

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.

157

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

NASA Astrophysics Data System (ADS)

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

Cnossen, Ingrid; Richmond, Arthur D.

2012-10-01

158

Proposal of atomic clock in motion: Time in moving clock  

E-print Network

The time in an atomic clock in motion is discussed using the analogy of a sing around sound source. Sing around frequency is modified according to the motion of the sing around sound source, using the Lorentz transformation equation. Thus, if we use the sing around frequency as a reference, we can define the reference time. We propose that the time delay of an atomic clock in motion be derived using the sing around method. In this letter, we show that time is defined by a combination of light speed and motion.

Masanori Sato

2004-11-22

159

Synchronous clock stopper for microprocessor  

NASA Technical Reports Server (NTRS)

A synchronous clock stopper circuit for inhibiting clock pulses to a microprocessor in response to a stop request signal, and for reinstating the clock pulses in response to a start request signal thereby to conserve power consumption of the microprocessor when used in an environment of limited power. The stopping and starting of the microprocessor is synchronized, by a phase tracker, with the occurrences of a predetermined phase in the instruction cycle of the microprocessor in which the I/O data and address lines of the microprocessor are of high impedance so that a shared memory connected to the I/O lines may be accessed by other peripheral devices. The starting and stopping occur when the microprocessor initiates and completes, respectively, an instruction, as well as before and after transferring data with a memory. Also, the phase tracker transmits phase information signals over a bus to other peripheral devices which signals identify the current operational phase of the microprocessor.

Kitchin, David A. (Inventor)

1985-01-01

160

A critique of vole clocks  

NASA Astrophysics Data System (ADS)

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

Martin, Robert A.

2014-06-01

161

Primary Atomic Clock Reference System  

NASA Technical Reports Server (NTRS)

An artist's concept of the Primary Atomic Clock Reference System (PARCS) plarned to fly on the International Space Station (ISS). PARCS will make even more accurate atomic time available to everyone, from physicists testing Einstein's Theory of Relativity, to hikers using the Global Positioning System to find their way. In ground-based atomic clocks, lasers are used to cool and nearly stop atoms of cesium whose vibrations are used as the time base. The microgravity of space will allow the atoms to be suspended in the clock rather than circulated in an atomic fountain, as required on Earth. PARCS is being developed by the Jet Propulsion Laboratory with principal investigators at the National Institutes of Standards and Technology and the University of Colorado, Boulder. See also No. 0100120.

2001-01-01

162

Primary Atomic Clock Reference System  

NASA Technical Reports Server (NTRS)

An artist's concept of the Primary Atomic Clock Reference System (PARCS) plarned to fly on the International Space Station (ISS). PARCS will make even more accurate atomic time available to everyone, from physicists testing Einstein's Theory of Relativity, to hikers using the Global Positioning System to find their way. In ground-based atomic clocks, lasers are used to cool and nearly stop atoms of cesium whose vibrations are used as the time base. The microgravity of space will allow the atoms to be suspended in the clock rather than circulated in an atomic fountain, as required on Earth. PARCS is being developed by the Jet Propulsion Laboratory with principal investigators at the National Institutes of Standards and Technology and the University of Colorado, Boulder. See also No. 0103191

2001-01-01

163

A Clock Reaction Based on Molybdenum Blue  

E-print Network

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

Neuenschwander, Ulrich

164

PLL-based active optical clock distribution  

E-print Network

Reducing the timing uncertainty associated with clock edges has become an exceedingly difficult problem as clock frequencies in high-performance processors increase past several gigahertz. Absolute quantities of skew and ...

Kern, Alexandra M., 1979-

2004-01-01

165

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

166

Multiwavelength all-optical clock recovery  

E-print Network

Multiwavelength clock recovery is especially desirable in systems that use wavelength-division-multipleged technology. A multiwavelength clock-recovery device can greatly simplify costs by eliminating the need to have a ...

Johnson, C.; Demarest, Kenneth; Allen, Christopher Thomas; Hui, Rongqing; Peddanarappagari, K. V.; Zhu, B.

1999-07-01

167

The US Naval Observatory Clock Time Reference and the Performance of a Sample of Atomic Clocks  

Microsoft Academic Search

The US 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 × 10-14 for very long intervals are being achieved together with utmost reliability of the time scale. Individual clocks differ widely in their performance and are carefully selected for

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

1970-01-01

168

Circadian molecular clocks and cancer.  

PubMed

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

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

2014-01-01

169

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

170

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

NASA Astrophysics Data System (ADS)

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

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

171

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

E-print Network

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

Carsten Weidner; Pavel Kroupa

2004-09-30

172

Single-transistor-clocked flip-flop  

DOEpatents

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

Zhao, Peiyi; Darwish, Tarek; Bayoumi, Magdy

2005-08-30

173

Optimized multiparty quantum clock synchronization  

SciTech Connect

A multiparty protocol for distributed quantum clock synchronization has been claimed to provide universal limits on the clock accuracy, viz., that accuracy monotonically decreases with the number n of party members. But this is only true for synchronization when one limits oneself to W states. This work shows that the usage of Z (Symmetric Dicke) states, a generalization of W states, results in improved accuracy, having a maximum when Left-Floor n/2 Right-Floor of its members have their qubits with a |1> eigenstate.

Ben-Av, Radel; Exman, Iaakov [Software Engineering Department, Jerusalem College of Engineering, POB 3566, Jerusalem, 91035 (Israel)

2011-07-15

174

Massive Elliptical Galaxies: BH Scouring or a Bottom-Heavy IMF?  

NASA Astrophysics Data System (ADS)

We present indirect constraints on the stellar initial-mass-function (IMF) in nine massive elliptical galaxies with ? ~ 300 km/s, via a comparison of dynamical and stellar-population based stellar masses. We use adaptive-optics assisted, high resolution kinematical data from the SINFONI Search for Supermassive Black Holes that allow us to constrain the dynamical stellar mass-to-light ratio in the very centre of each galaxy. Hence we measure the IMF in a galaxy region where the stellar mass dominates over dark matter, minimising any potential degeneracy between the two mass components. In six of our galaxies - those which have depleted stellar cores - we find an IMF consistent with the one measured in the Milky-Way via direct star counts. The three remaining, power-law galaxies have instead stellar masses about a factor of two times larger than expected from a Milky-Way type IMF, indicating either a more bottom-heavy IMF (like, e.g., the Salpeter IMF) or a dark-matter distribution that is degenerate with the stellar mass down to the very centres of these galaxies. The bottom-light IMF in our core galaxies is surprising in view of previous studies that suggested a systematic IMF variation where early-type galaxies with ? ~ 300 km/s have a Salpeter or even more dwarf-dominated IMF. Core galaxies are particularly important since their unique central orbital structure offers an independent crosscheck for the dynamical models. Our models with a bottom-light IMF are consistent with the distribution of orbits predicted by SMBH-binary core-formation models. This indicates that spatially well resolved central kinematical data are important for determining unbiased dynamical stellar mass-to-light ratios. Our results imply either that the IMF in massive galaxies varies over a wider range than previously anticipated, and is not the same in core and power-law ellipticals, or else that there are systematic variations in the distribution of dark matter among massive early-type galaxies.

Thomas, Jens; Saglia, Roberto; Bender, Ralf; Erwin, Peter; Fabricius, Maximilian

2015-04-01

175

Oxygen ion escape from Venus: The acceleration mechanisms and the escape rate under different IMF configurations  

NASA Astrophysics Data System (ADS)

Using data obtained from ASPERA-4 (Analyser of Space Plasma and Energetic Atoms) and MAG (magnetometer) experiments onboard Venus Express, we investigate the acceleration mechanisms, the escape rate of the oxygen ions from the Venus upper atmosphere, and the contribution of the upstream condition to them. We first produce spatial distribution maps of O+ fluxes (>100 eV) around Venus for two different convection electric fields, namely the solar wind electric field (SWEF; Esw = -Vsw x Bsw) and the local convection electric field (LCEF; EL = -VL x BL where VL and BL are the local proton velocity and the local magnetic field that obtained over one-scan (192 s)). Comparison between the two distributions, we find that the O+ fluxes are frequently observed in the hemisphere where LCEF orients. Moreover, such structure can be identified regardless of the upstream interplanetary magnetic field (IMF) direction. Thus we conclude that the O+ ions are accelerated more effectively by LCEF rather than SWEF in the Venusian upper atmosphere. In the induced magnetosphere, O+ fluxes are frequently associated with Bx reversals where the IMF curvature is strong. It indicates that a magnetic tension force also contributes to O+ acceleration. We also investigate the dependency of the O+ escape rates on the upstream IMF directions. Here, the IMF condition is classified into two cases: the perpendicular IMF case and the parallel IMF case, where IMF directs nearly perpendicular to the Venus-Sun line (60° < ? < 120°) and nearly parallel to it (0° < ? < 30° or 150° < ? < 180°). During the data period between 20 Jun 2006 and 20 Dec 2009 we have obtained 141 perpendicular IMF cases and 71 parallel IMF cases. Using these data, total O+ escape rates are estimated by integrating the anti-sunward fluxes in the nightside region. We find that the total escape rates between the two IMF cases are of the same order, and thus we conclude that the upstream IMF direction does not significantly affect to the total amount of O+ outflow from the Venusian upper atmosphere.

Masunaga, K.; Futaana, Y.; Yamauchi, M.; Barabash, S.; Zhang, T.; Fedorov, A.; Okano, S.; Terada, N.

2012-12-01

176

Naming Analog Clocks Conceptually Facilitates Naming Digital Clocks  

ERIC Educational Resources Information Center

This study investigates how speakers of Dutch compute and produce relative time expressions. Naming digital clocks (e.g., 2:45, say ''quarter to three'') requires conceptual operations on the minute and hour information for the correct relative time expression. The interplay of these conceptual operations was investigated using a repetition…

Meeuwissen, Marjolein; Roelofs, Ardi; Levelt, Willem J. M.

2004-01-01

177

Proposal of atomic clock in motion: Time in moving clock  

Microsoft Academic Search

The time in an atomic clock in motion is discussed using the analogy of a sing around sound source. Sing around frequency is modified according to the motion of the sing around sound source, using the Lorentz transformation equation. Thus, if we use the sing around frequency as a reference, we can define the reference time. We propose that the

Masanori Sato

2004-01-01

178

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

179

Collisionally Induced Atomic Clock Shifts and Correlations  

E-print Network

We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts and blackbody radiation effects for atomic clock transitions using a density matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Results for a finite temperature ${}^{87}$Sr ${}^1S_0$ ($F = 9/2$) atomic clock in a magic wavelength optical lattice are presented.

Y. B. Band; I. Osherov

2011-06-23

180

Spin squeezing in a Rydberg lattice clock.  

PubMed

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

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

2014-03-14

181

Quasars as very-accurate clock synchronizers  

NASA Technical Reports Server (NTRS)

Quasars can be employed to synchronize global data communications, geophysical measurements, and atomic clocks. It is potentially two to three orders of magnitude better than presently-used Moon-bounce system. Comparisons between quasar and clock pulses are used to develop correction or synchronization factors for station clocks.

Hurd, W. J.; Goldstein, R. M.

1975-01-01

182

Microwave Cavity Clocks On Space Station  

NASA Technical Reports Server (NTRS)

We describe the status of a microwave cavity clock experiment to perform improved tests of Local Position Invariance and Lorentz Invariance on the International Space Station in conjunction with atomic clocks. Significant improvements over present bounds are expected in both cases. The oscillators can also be used to enhance the performance of atomic clocks at short time scales for other experiments.

Lipa, J. a.; Nissen, J. A.; Wang, S.; Stricker, D. A.; Avaloff, D.

2003-01-01

183

Heterogeneous Genomic Molecular Clocks in Primates  

E-print Network

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

Yi, Soojin

184

VCSEL polarization control for chip-scale atomic clocks.  

SciTech Connect

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

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

2007-01-01

185

Saturation of IMF Bz influence on the position of dayside magnetopause  

NASA Astrophysics Data System (ADS)

The dayside magnetopause moves closer to the Earth with increasing southward IMF Bz. Is the response of magnetopause to solar wind parameters, southward IMF Bz, and dynamic pressure Dp linear or nonlinear? GOES observations on 6 April 2000 shows that the magnetopause is still outside of geosynchronous orbit even though the southward IMF Bz is greater than 25 nT and Dp is near 8 nPa. We suggest that the earthward motion of the dayside magnetopause saturates for large southward IMF Bz. Magnetosheath encounters observed by GOES satellites during 1999-2000 are used as a database for selecting a functional form of the saturation effect based on the calculations of the modified magnetopause model of [2002]. To obtain a relationship of the threshold of southward IMF Bz for saturation occurring as a function of Dp, an iteration procedure is used to minimize the false alarm rate (FAR) and maximize the probability of prediction (PoP). The relationship B'z = -8.1 - 12.0 × log (Dp + 1) is obtained where B'z is the threshold of IMF Bz for saturation. This relationship is applied to a modified [2002] model and the new model is compared against magnetosheath encounters observed by the LANL MPA instruments on 31 March 2001.

Yang, Y.-H.; Chao, J. K.; Dmitriev, A. V.; Lin, C.-H.; Ober, D. M.

2003-03-01

186

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

NASA Technical Reports Server (NTRS)

On May 23, 2000, proton auroras observed by IMAGE (Imager for Magnetopause to Aurora Global Exploration) FUV (Far Ultraviolet) on the dayside were very dynamic. Auroral pattern in the cusp is well correlated with Interplanetary Magnetic Field (IMF) and solar wind parameters. When IMF were northward, cusp proton aurora appeared at high latitude poleward from the auroral oval. A high-latitude proton aurora brightened after solar wind ion temperature increased and it disappeared after IMF turned southward. Under the southward IMF condition, auroral activity occurred only in the dayside auroral oval. As IMF $B_z$ reverted to northward, cusp proton aurora reappeared at high latitude. The magnetic local time of the cusp proton aurora changes with the IMF $B_y$ polarity, consistent with previous reports. These results suggest an upstream source of the high-latitude cusp proton aurora for this event. One possible explanation is that bow shock energetic ions are transported into the cusp via the high-latitude magnetic merging process to induce optical emissions in the ionosphere.

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

2002-01-01

187

Ultra-stable Laser Clock  

Microsoft Academic Search

Summary The Air Force has requirements for both high accuracy timing sources and precision inertial navigation systems for advanced fighter aircraft. The author has devised a method of using a multi-frequency ring laser gyro (RLC) simultaneously as a gyro and as a clock. This device uses a rnutli-frequency RLG with an auxiliary detector to sense a 583 MHz beat frequency,

Lieutenant Roger Facklam; Wright-Patterson AFB

1982-01-01

188

Stochastic Models for Atomic Clocks  

Microsoft Academic Search

Most workers in the field of atomic clocks encounter frequency and time instabilities which can be character- ized ( or model led) as random fluctuations. These random f 1 uctuations typical ly display a power spectral density which varies as a power-law over some signisicant range of (Fourier) frequencies (e. q. , 5 (f) = h f , where Y

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

189

Atomic clocks and inertial sensors  

Microsoft Academic Search

We show that the language of atom interferometry provides a unified picture for microwave and optical atomic clocks as well as for gravito-inertial sensors. The sensitivity and accuracy of these devices is now such that a new theoretical framework common to all these interferometers is required that includes: (a) a fully quantum mechanical treatment of the atomic motion in free

Ch J Bordé

2002-01-01

190

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

191

Our Future Clocks and Watches  

Microsoft Academic Search

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

Edward L. Garbett

1885-01-01

192

Clock Award Recipients Spring 2013  

E-print Network

Clock Award Recipients Spring 2013 College of Natural Sciences Deborah "Didi" Smith Department of Art and Art History Dr. Jeffrey Smith Dr. Louis Waldman Department of Classics Dr. Richard Buxton Johnson Department of History Dr. Frank Guridy Dr. Emilio Zamora Department of Human Ecology Dr. Cynthia

Texas at Austin, University of

193

Isolation of an internal clock  

Microsoft Academic Search

Investigated in 5 experiments with 10 male albino Norway rats the presence of an internal clock that measures time on the order of seconds. A procedure was used in which 2 types of trials were randomly mixed: (a) On food trials, the 1st response (leverpress) after a fixed time was rewarded with food; the trial then ended; and (b) on

Seth Roberts

1981-01-01

194

Biological Clocks: Riding the Tides  

PubMed Central

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

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

2015-01-01

195

[Circadian clock disruption and diabetes mellitus].  

PubMed

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

Ando, Hitoshi; Fujimura, Akio

2013-12-01

196

Robust Clock Synchronization in Wireless Sensor Networks  

E-print Network

Exchange Mechanism Without Clock Skew Assuming no clock skew, a number of N two-way message exchanges or sender- receiver synchronization (SRS) exchanges are graphically shown in Figure 2.1. T1,k and T4,k represent the timestamps measured by the local... clock of node A, while T2,k and T3,k represent the timestamps measured by the local clock of node B at the kth message exchange. Figure 2.1: Two-way message exchange mechanism which assumes only clock offset Based on the above pairwise message...

Saibua, Sawin

2010-10-12

197

Analysis of a Magnetically Trapped Atom Clock  

E-print Network

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.

D. Kadio; Y. B. Band

2006-12-12

198

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

199

Building a Better Atomic Clock  

NASA Astrophysics Data System (ADS)

Since 1967, the Second has been defined by the CGPM as 9,192,631,770 periods of oscillation corresponding to a transition between two hyperfine levels in a Cesium atom with zero external fields. Key to this definition was the fact that as experimentalists found new and more precise ways to measure this frequency, the definition of the second would become more and more accurate with time. However, in the last 30 years, new technologies based on tunable lasers addressing optical transitions in atoms, ions, and molecules have offered an entirely new approach to defining the Second with significantly higher precision and accuracy. Here, I will show that by trapping thousands of atoms inside a specially engineered optical lattice one can create an extremely accurate frequency standard with 2 orders of magnitude improvement over current Cs standards. Furthermore, I will explain that standards based on this technology are fundamentally more stable than the primary standard by 3 orders of magnitude. Leapfrogging the currently held accuracy records of ion clocks, this work documents the first optical lattice clock to best all other atomic clock implementations, a mere 8 years after the first proof of principle experiments. In this thesis I will describe how we have overcome a number of important systematic uncertainties to achieve these results. This revolution in accuracy and precision opens the door for new experiments utilizing the clock as a probe of quantum many-body physics. To this end, a new apparatus has been designed that combines the unprecedented precision of clock experiments with the amazing progress attained in quantum gas experiments.

Bloom, Benjamin J.

200

IMF control of the location of Venusian bow shock: The effect of the magnitude of IMF component tangential to the bow shock surface  

NASA Astrophysics Data System (ADS)

The interplanetary magnetic field (IMF) frozen in the solar wind, together with the solar EUV radiation, can significantly affect the location of Venusian bow shock. To recognize the IMF effect on the Venusian bow shock, we investigated 1680 bow shock crossings recorded by Venus Express during the unusually long-lasting solar minimum (May 2006 to December 2010), of which the effect of solar EUV variation was significantly decreased. Our analysis shows that during the unusually long-lasting solar minimum, the effect of the solar EUV flux on the Venusian bow shock location is negligible. Neither solar wind dynamic pressure nor solar wind velocity has observable effect on the Venusian bow shock location. However, the IMF magnitude has a strong control of the Venusian bow shock location. We found that the size of Venusian bow shock linearly increases with the magnitude of the IMF component tangential to the bow shock surface, and this relationship can account for the perpendicular-parallel asymmetry and magnetic pole-equator asymmetry found in previous researches, as well as the magnetic dawn-dusk asymmetry discerned in this study.

Chai, Lihui; Fraenz, Markus; Wan, Weixing; Rong, Zhaojin; Zhang, Tielong; Wei, Yong; Dubinin, Eduard; Zhong, Jun; Han, Xiuhong; Barabash, Stas

2014-12-01

201

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

E-print Network

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

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

2006-03-17

202

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

NSDL National Science Digital Library

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

National Action Council for Minorities in Engineering

2002-01-01

203

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

PubMed

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

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

2014-09-01

204

Evidence That IMF Fluctuations During High-Speed Solar Wind Steams Substantially Affect the Strength of Dayside Ionospheric Convection  

NASA Astrophysics Data System (ADS)

The orientation and magnitude of the interplanetary magnetic field (IMF) and solar wind dynamic pressure are known to affect the strength of ionospheric convection. However, the high-speed solar wind streams during the IPY have provided the opportunity to investigate whether the ULF waves of the IMF during high- speed streams can have a substantial contribution to the strength of convection. We have examined ionospheric convection in the dayside polar cap measured by the Sondrestrom radar under various solar wind conditions. Using an extensive radar data set, we find that ULF power in the IMF is closely associated with the strength of dayside ionospheric convection. Convection flows during periods of large north-south IMF fluctuations are observed to be as strong as for steady and large southward IMF periods. Enhanced convection can be also observed even for northward IMF intervals, but only if the interplanetary magnetic field exhibits high ULF power. These observations thus suggest that IMF wave activity can significantly influence ionospheric convection. Comparisons with events with substantial ULF power not occurring during high-speed streams indicate that the ULF power is effective, independent of any direct affect from the solar wind speed. We speculate that resonance between IMF fluctuations and natural magnetospheric oscillation frequencies might be responsible for the connection between ionospheric convection and IMF ULF power. We have also found some evidence for a connection between the ULF power in the solar wind density and the strength of convection.

Kim, H.; Lyons, L. R.; Boudouridis, T.; Zou, S.; Heinselman, C.; McCready, M.

2008-12-01

205

Genomic clocks and evolutionary timescales  

NASA Technical Reports Server (NTRS)

For decades, molecular clocks have helped to illuminate the evolutionary timescale of life, but now genomic data pose a challenge for time estimation methods. It is unclear how to integrate data from many genes, each potentially evolving under a different model of substitution and at a different rate. Current methods can be grouped by the way the data are handled (genes considered separately or combined into a 'supergene') and the way gene-specific rate models are applied (global versus local clock). There are advantages and disadvantages to each of these approaches, and the optimal method has not yet emerged. Fortunately, time estimates inferred using many genes or proteins have greater precision and appear to be robust to different approaches.

Blair Hedges, S.; Kumar, Sudhir

2003-01-01

206

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

207

The IMF of Field OB Stars in the Small Magellanic Cloud  

NASA Astrophysics Data System (ADS)

The population of field OB stars is an important component of a galaxy's stellar content, representing 20-30% of the massive stars. To study this population, we have undertaken the Runaways and Isolated O Type Star Spectroscopic Survey of the SMC (RIOTS4). RIOTS4 surveys a spatially complete sample of >350 field OB stars in the Small Magellanic Cloud and will serve as a key probe of runaways, binaries, and the stellar IMF in the field massive star population. Here, we focus on the field IMF, which provides an empirical probe of the star-forming process and is a fundamental property of a stellar population. Together with photometry from the OGLE survey, RIOTS4 will yield a definitive stellar IMF for the SMC field massive star population. We present preliminary results that suggests the field IMF is much steeper, ? = 2.9, than the canonical stellar IMF of ? = 1.35. Despite the steep slope, we see no evidence of a stellar upper mass limit, up to our highest mass star of 65M?.

Lamb, J. B.; Oey, M. S.; Graus, A. S.; Segura-Cox, D. M.

2012-12-01

208

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

NASA Astrophysics Data System (ADS)

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

Lei, Y.; Zhao, D. N.

2014-05-01

209

The Mercury Ion Optical Clock  

Microsoft Academic Search

The search for accurate and stable frequency standards has led to the development of trapped-ion optical clocks. In our system, a single ^199Hg^+ ion is confined in a cryogenic, spherical, radio-frequency (Paul) trap and is cooled on the dipole transition at 194 nm. The electric-quadrupole ^2S_1\\/2 (F=0) rightarrow ^2D_5\\/2 (F=2,m_F=0) transition at 282 nm serves as the reference for the

W. H. Oskay; T. Rosenband; U. Tanaka; C. E. Tanner; S. A. Diddams; L. Hollberg; W. M. Itano; J. C. Bergquist

2004-01-01

210

Our Future Clocks and Watches  

Microsoft Academic Search

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

H. H. Clayton

1885-01-01

211

The LASSO experiment. [clock synchronization  

NASA Technical Reports Server (NTRS)

An international coordinated experimental assessment of a system which promises to provide a synchronization of clocks bound to time and frequency standard laboratories, with an accuracy of one nanosecond using existing or near ground-based laser stations via a geostationary satellite (SIRIO-2) is detailed. The system performance and the technical details concerning the on-board equiment, the ground segment, and the operational configuration are discussed. Finally, the future prospects of the LASSO experiment and possible implementations are examined together.

Serene, B.

1979-01-01

212

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

E-print Network

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

M. Bauer

2014-03-25

213

Sun Watching Lesson 4: Making a Sun Clock  

E-print Network

29 Sun Watching Lesson 4: Making a Sun Clock Lesson 4: Making a Sun Clock A major factor;31 Sun Watching Lesson 4: Making a Sun Clock 6. Before going outside to use the Sun Clocks, check the time on a clock or watch. If it is daylight saving time (depending on your locale, between the first

Maxwell, Bruce D.

214

Molecular components of the mammalian circadian clock  

PubMed Central

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

Buhr, Ethan D.; Takahashi, Joseph S.

2013-01-01

215

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

216

Precise time dissemination via portable atomic clocks  

NASA Technical Reports Server (NTRS)

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

Putkovich, K.

1982-01-01

217

Future Laser-Cooled Microwave Clock Performance  

NASA Technical Reports Server (NTRS)

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

Gibble, Kurt

1997-01-01

218

The Circadian Clock Coordinates Ribosome Biogenesis  

PubMed Central

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

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

2013-01-01

219

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

E-print Network

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

Thies, Ingo; Kroupa, Pavel; Marks, Michael

2015-01-01

220

Continuous reconnections inferred from observations by TC-1 during IMF Bz?0  

NASA Astrophysics Data System (ADS)

During a one-hour interval of IMF Bz?0, the equatorial spacecraft Double Star named TC-1 encountered magnetopause multi times at MLT of 08:00, latitude = -27 degrees. During each encounter, reconnection jets were oberserved with velocities up to more than 500 km/s, significantly higher than the background flows of the magnetosheath. The fast flows match the theoretical prediction of Alfvenic acceleration well. The mainly southward and tailward flow of the jets indicate that the spacecraft was located south of the reconnection site, consistent with models of reconnection with such IMF conditions. The accelerated flows were observed lasting for about one hour, with some modulation by the oscillation of the magnetopause, but no reversals in the direction of Vz were found during the interval, implying that reconnection at magnetopause northward to the spacecraft might be continuously active under such IMF conditions.

Yan, G.; Mozer, F.; Phan, T. D.; Chen, T.; Reme, H.; Carr, C.

2012-12-01

221

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

222

Molecular origin of the kidney clock.  

PubMed

Increasing evidence suggests that a functional circadian clock in the kidney contributes to the regulation of renal function including blood pressure and sodium balance. When does this kidney clock begin ticking? Mészáros et al. provide the first evidence that the endogenous molecular machinery of the circadian clock begins oscillating in the late fetal kidney. These findings have important implications for our understanding of how homeostasis is maintained in early life. PMID:25360489

Gumz, Michelle L

2014-11-01

223

Collisionally induced atomic clock shifts and correlations  

SciTech Connect

We develop a formalism to incorporate exchange symmetry considerations into the calculation of collisional frequency shifts for atomic clocks using a density-matrix formalism. The formalism is developed for both fermionic and bosonic atomic clocks. Numerical results for a finite-temperature {sup 87}Sr {sup 1}S{sub 0} (F=9/2) atomic clock in a magic wavelength optical lattice are presented.

Band, Y. B.; Osherov, I. [Departments of Chemistry and Electro-Optics and the Ilse Katz Center for Nano-Science, Ben-Gurion University, Beer-Sheva 84105 (Israel)

2011-07-15

224

Clock Routing for High-Performance ICs  

Microsoft Academic Search

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

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

1990-01-01

225

Posttranslational Mechanisms Regulate the Mammalian Circadian Clock  

Microsoft Academic Search

We have examined posttranslational regulation of clock proteins in mouse liver in vivo. The mouse PERIOD proteins (mPER1 and mPER2), CLOCK, and BMAL1 undergo robust circadian changes in phosphorylation. These proteins, the cryptochromes (mCRY1 and mCRY2), and casein kinase I epsilon (CKI?) form multimeric complexes that are bound to DNA during negative transcriptional feedback. CLOCK:BMAL1 heterodimers remain bound to DNA

Choogon Lee; Jean-Pierre Etchegaray; Felino R. A. Cagampang; Andrew S. I. Loudon; Steven M. Reppert

2001-01-01

226

Huygens synchronization of two pendulum clocks  

E-print Network

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

Henrique M. Oliveira; Luís V. Melo

2014-10-29

227

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

228

Spin-1/2 Optical Lattice Clock  

SciTech Connect

We experimentally investigate an optical clock based on {sup 171}Yb (I=1/2) atoms confined in an optical lattice. We have evaluated all known frequency shifts to the clock transition, including a density-dependent collision shift, with a fractional uncertainty of 3.4x10{sup -16}, limited principally by uncertainty in the blackbody radiation Stark shift. We measured the absolute clock transition frequency relative to the NIST-F1 Cs fountain clock and find the frequency to be 518 295 836 590 865.2(0.7) Hz.

Lemke, N. D.; Ludlow, A. D.; Barber, Z. W.; Fortier, T. M.; Diddams, S. A.; Jiang, Y.; Jefferts, S. R.; Heavner, T. P.; Parker, T. E.; Oates, C. W. [National Institute of Standards and Technology, 325 Broadway, Boulder, Colorado 80305 (United States)

2009-08-07

229

A transportable strontium optical lattice clock  

NASA Astrophysics Data System (ADS)

We report on a transportable optical clock, based on laser-cooled strontium atoms trapped in an optical lattice. The experimental apparatus is composed of a compact source of ultra-cold strontium atoms including a compact cooling laser setup and a transportable ultra-stable laser for interrogating the optical clock transition. The whole setup (excluding electronics) fits within a volume of <2 m3. The high degree of operation reliability of both systems allowed the spectroscopy of the clock transition to be performed with 10 Hz resolution. We estimate a relative uncertainty of the clock of 7 × 10-15.

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

2014-12-01

230

Low velocity limits of cold atom clocks  

E-print Network

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

J. Muñoz; I. Lizuain; J. G. Muga

2009-09-08

231

Song I-Yeong's Armillary Clock  

NASA Astrophysics Data System (ADS)

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

Kim, Sang Hyuk; Lee, Yong Sam

232

The Circadian Clock in Arabidopsis Roots Is a Simplified Slave Version of the Clock in Shoots  

Microsoft Academic Search

The circadian oscillator in eukaryotes consists of several interlocking feedback loops through which the expression of clock genes is controlled. It is generally assumed that all plant cells contain essentially identical and cell-autonomous multiloop clocks. Here, we show that the circadian clock in the roots of mature Arabidopsis plants differs markedly from that in the shoots and that the root

Allan B. James; José A. Monreal; Gillian A. Nimmo; Ciarán L. Kelly; Pawel Herzyk; Gareth I. Jenkins; Hugh G. Nimmo

2008-01-01

233

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.

234

Effects of Pinealectomy on Hypothalamic Metabolic and Clock Gene Rhythms  

E-print Network

by comparing the affects of pinealectomy on 2DG uptake and canonical "clock" gene expression in the hypothalamus of house sparrows, Passer domesticus. Since other brain structures exhibit metabolic and clock gene rhythms, investigation of clock gene expression...

Clauson, Amanda

2006-07-11

235

Synchronization: from pendulum clocks to chaotic lasers and chemical oscillators  

E-print Network

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

Potsdam, Universität

236

Triangle Geometry: Angles  

NSDL National Science Digital Library

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

Math Cove

2007-12-12

237

Improving Governance and Fighting Corruption in the Baltic and CIS CountriesThe Role of the IMF  

Microsoft Academic Search

This paper examines the indirect role the IMF plays in combating corruption in the Baltic and CIS countries by promoting structural reforms that help improve economic governance and thus reduce opportunities for rent-seeking behavior. The analysis draws on examples of actual experience with corruption and outlines some of the structural measures under IMF-supported arrangements, which, if successfully implemented, can be

Thomas Wolf; Emine G?rgen

2000-01-01

238

Gigabit Ethernet Asynchronous Clock Compensation FIFO  

NASA Technical Reports Server (NTRS)

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

Duhachek, Jeff

2012-01-01

239

The circadian clock in Arabidopsis roots is a simplified slave version of the clock in shoots.  

PubMed

The circadian oscillator in eukaryotes consists of several interlocking feedback loops through which the expression of clock genes is controlled. It is generally assumed that all plant cells contain essentially identical and cell-autonomous multiloop clocks. Here, we show that the circadian clock in the roots of mature Arabidopsis plants differs markedly from that in the shoots and that the root clock is synchronized by a photosynthesis-related signal from the shoot. Two of the feedback loops of the plant circadian clock are disengaged in roots, because two key clock components, the transcription factors CCA1 and LHY, are able to inhibit gene expression in shoots but not in roots. Thus, the plant clock is organ-specific but not organ-autonomous. PMID:19095940

James, Allan B; Monreal, José A; Nimmo, Gillian A; Kelly, Ciarán L; Herzyk, Pawel; Jenkins, Gareth I; Nimmo, Hugh G

2008-12-19

240

A clock distribution network for microprocessors  

Microsoft Academic Search

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

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

2001-01-01

241

"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

242

THE INTRINSIC CIRCADIAN CLOCK WITHIN THE CARDIOMYOCYTE  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

243

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

244

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

245

Entrainment of the Neurospora Circadian Clock  

Microsoft Academic Search

Neurospora crassa has been systematically investigated for circadian entrainment behavior. Many aspects of synchronization can be investigated in this simple, cellular system, ranging from systematic entrainment and drivenness to masking. Clock gene expression during entrainment and entrainment without clock genes suggest that the known transcription\\/ translation feedback loop is not alone responsible for entrainment in Neurospora. .

Martha Merrow; Cornelia Boesl; Jan Ricken; Marlies Messerschmitt; Manfred Goedel; Till Roenneberg

2006-01-01

246

Development of a compact cold atom clock  

Microsoft Academic Search

HORACE is a compact cold atom clock where the atoms are cooled inside the microwave interrogation cavity. About 108 atoms can be cooled at kinetic temperatures as low as 2.5 ?K. We report, for the first time, a Ramsey pattern observed with a 14 Hz linewidth and fringe contrast better than 80%. Since this clock is designed for space applications,

S. Tremine; S. Guerandel; D. Holleville; A. Clairon; N. Dimarcq

2004-01-01

247

GPS SIGNAL INTEGRITY DEPENDENCIES ON ATOMIC CLOCKS  

Microsoft Academic Search

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

Marc Weiss; Pradipta Shome; Ron Beard

248

Entrainment of the Neurospora circadian clock.  

PubMed

Neurospora crassa has been systematically investigated for circadian entrainment behavior. Many aspects of synchronization can be investigated in this simple, cellular system, ranging from systematic entrainment and drivenness to masking. Clock gene expression during entrainment and entrainment without clock genes suggest that the known transcription/translation feedback loop is not alone responsible for entrainment in Neurospora. PMID:16687281

Merrow, Martha; Boesl, Cornelia; Ricken, Jan; Messerschmitt, Marlies; Goedel, Manfred; Roenneberg, Till

2006-01-01

249

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

250

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

251

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

252

Constraining fossil calibrations for molecular clocks  

E-print Network

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

Kumar, Sudhir

253

The field-aligned currents in the magnetotail response to the interplanetary magnetic field orientation  

NASA Astrophysics Data System (ADS)

The influences of the interplanetary magnetic field (IMF) cone angle theta and clock angle phi on the field-aligned currents (FACs) at the plasma sheet boundary layers (PSBLs) have been investigated using Cluster Data. The FAC occurrence increases monotonically with IMF cone angle, and has two peaks at -90º and +110º clock angle, respectively. The peak at +110º is distinctly larger than that at -90º. Overall, there are more FACs between 0ºIMF. More FACs occur when 90ºIMF. The large FAC densities occur when 60ºIMF clock angle is a good parameter to determine the FAC with large density in the magnetotail. The density also has two peaks and the peak at +90º clock angle (duskward IMF) is larger than that at -90º (dawnward IMF). These results indicate that the IMF influence on the FACs is from all IMF components and not only from a single component.

Cheng, Zhengwei; Dunlop, Malcolm; Liu, Zhenxing; Shi, Jiankui

254

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

E-print Network

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

Lummerzheim, Dirk

255

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

E-print Network

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

California at Berkeley, University of

256

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

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

257

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

E-print Network

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

Paris-Sud XI, Université de

258

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

E-print Network

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

California at Berkeley, University of

259

Transpolar auroras, their particle precipitation, and IMF B sub y component  

SciTech Connect

Transpolar auroras, their associated particle precipitation, and their occurrence with respect to the IMF B{sub y} polarity are examined on the basis of DMSP F6 auroral images and the corresponding particle data. It is found that the transpolar arcs are located in the poleward edge of the soft particle precipitation region extending from either the dawn or dusk part of the auroral oval precipitation; they are not embedded in the polar rain region. This finding suggests that the transpolar arcs are located along the poleward boundary of the closed field line region (or the equatorward boundary of the open region) as suggested by Meng. Further, the appearance of the extended precipitation region from the oval depends on the polarity of the IMF B{sub y}, in the northern hemisphere morning sector for IMF B{sub y} < 0 or in the evening sector for IMF B{sub y} > 0. In general, the precipitating particle flux in the extended precipitation region is not high enough to produce appreciable luminosity. Thus only the transpolar arcs (associated with relatively intense precipitation) near the poleward boundary tend to become much more luminous, forming the so-called theta aurora.

Makita, K. (Takushoku Univ., Tokyo (Japan)); Meng, C.I. (Johns Hopkins Univ., Laurel, MD (United States)); Akasofu, S.I. (Univ. of Alaska, Fairbanks (United States))

1991-08-01

260

Adoption, Implementation and Impact of IMF Programmes: A Review of the Issues and Evidence1  

Microsoft Academic Search

This paper evaluates the literature on the lending programmes of the International Monetary Fund (IMF). The first section deals with the initiation of a Fund program, which has been shown to be influenced by political and institutional variables. A second focus of research analyses the design and implementation of Fund-supported polices, since many programmes are often not successfully completed. The

Joseph P Joyce

261

Adoption, Implementation and Impact of IMF Programmes: A Review of the Issues and Evidence  

Microsoft Academic Search

This paper evaluates the literature on the lending programmes of the International Monetary Fund (IMF). The first section deals with the initiation of a Fund program, which has been shown to be influenced by political and institutional variables. A second focus of research analyses the design and implementation of Fund-supported polices, since many programmes are often not successfully completed. The

Joseph P Joyce

2004-01-01

262

Simulations of observed auroral brightening caused by solar wind dynamic pressure enhancements under different IMF conditions  

NASA Astrophysics Data System (ADS)

Solar wind dynamic pressure enhancements (P_{dyn}) have been observed to cause large-scale auroral brightening. The mechanism for this kind of auroral brightening is still a topic of current space research. Using the global PPMLR-MHD simulation model, we investigate three auroral brightening events caused by dynamic pressure enhancement under different interplanetary magnetic field (IMF) conditions, (1) B_z<0, and B_y>0 on 11 August 2000, (2) B_z<0, and B_y<0 on 8 May 2001, and (3) B_z&ge&q0 on 21 January 2005. We show that the auroral location depends on the IMF conditions. Under southward IMF conditions, when B_y is negative, the duskside aurora is located more equatorward at around 70° magnetic latitude (MLAT) for all MLTs, when B_y is positive, the duskside aurora can even reach beyond 80° MLAT. A smaller and more localized response is seen when the IMF B_z is nearly zero or northward as shown in previous studies. Our simulation results are consistent with these observations, indicating that the observed aurora activities could be caused by solar wind dynamic pressure enhancements. The simulation results suggest that the enhancement of P_{dyn} can increase the ionospheric transpolar potential and the corresponding field-aligned currents (FACs), leading to the observed auroral brightening.

Peng, Zhong; Hu, Youqiu; Kan, J. R.; Yang, Yafen; Wang, Chi

2012-07-01

263

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

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

264

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

2013-05-30

265

The Ozone-Iodine-Chlorate Clock Reaction  

PubMed Central

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

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

2013-01-01

266

The Mercury Ion Optical Clock  

NASA Astrophysics Data System (ADS)

The search for accurate and stable frequency standards has led to the development of trapped-ion optical clocks. In our system, a single ^199Hg^+ ion is confined in a cryogenic, spherical, radio-frequency (Paul) trap and is cooled on the dipole transition at 194 nm. The electric-quadrupole ^2S_1/2 (F=0) rightarrow ^2D_5/2 (F=2,m_F=0) transition at 282 nm serves as the reference for the frequency standard. This transition is probed by a stabilized dye laser that derives its short-term stability from an isolated Fabry-Pérot cavity. Over longer time scales, a servo loop steers the laser frequency to the atomic resonance. The stable light from this optical frequency standard is phase-coherently compared with signals from other frequency standards by means of an octave-spanning, optical frequency comb. In the past year, we have moved the clock system into an improved laboratory and resumed progress towards evaluating the uncertainties of the system. We now summarize the current status of the system and describe our recent progress towards these evaluations.

Oskay, W. H.; Rosenband, T.; Tanaka, U.; Tanner, C. E.; Diddams, S. A.; Hollberg, L.; Itano, W. M.; Bergquist, J. C.

2004-05-01

267

Measuring the IMF and Detailed Abundance Patterns from the Integrated Light of Old Stellar Systems  

NASA Astrophysics Data System (ADS)

The spectral energy distributions (SEDs) of unresolved stellar systems holds key information regarding the detailed abundance pattern, star formation history, dust properties, and initial mass function (IMF) of the underlying stellar population(s). This information can only be extracted with the aid of stellar population synthesis (SPS) models. Such models have been employed to estimate basic properties such as the star formation rate, metallicity (Z, and in certain contexts, alpha-enhancement), and total stellar mass (assuming an IMF). However, much more information is available in the SED than can be extracted by the current generation of SPS models because existing models are plagued by incomplete and poorly calibrated ingredients. The proposers request funds to develop a next generation SPS model capable of measuring the IMF and detailed abundance patterns from the SEDs of composite stellar systems. In particular, we intend to develop an SPS model that makes accurate predictions for the SEDs (from 0.1-3mu m at a resolving power of ~5,000) of composite systems as a function of the IMF, stellar age, metallicity, and individual elemental abundances (including C, N, O, Na, Mg, Ca, Ti, Cr, Mn, Fe, Sr, and Ba). This will require the construction of a new synthetic stellar spectral library and a new isochrone library. This new model will be the first to make predictions for the full SED shape as a function of individual abundance ratios, age, and the IMF. We will extensively calibrate the model predictions against data on individual stars and globular clusters. The new model will be essential for interpreting optical-NIR spectra obtained from the James Webb Space Telescope as well as both present and future ground-based facilities.

Conroy, Charlie

268

Multi-fault detection of rolling element bearings under harsh working condition using IMF-based adaptive envelope order analysis.  

PubMed

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

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

2014-01-01

269

EVIDENCE FOR A CONSTANT IMF IN EARLY-TYPE GALAXIES BASED ON THEIR X-RAY BINARY POPULATIONS  

NASA Astrophysics Data System (ADS)

A number of recent studies have proposed that the stellar initial mass function (IMF) of early type galaxies varies systematically as a function of galaxy mass, with higher mass galaxies having steeper IMFs. These steeper IMFs have more low-mass stars relative to the number of high mass stars, and therefore naturally result in proportionally fewer neutron stars and black holes. In this paper, we specifically predict the variation in the number of black holes and neutron stars in early type galaxies based on the IMF variation required to reproduce the observed mass-to-light ratio trends with galaxy mass. We then test whether such variations are observed by studying the field low-mass X-ray binary populations (LMXBs) of nearby early-type galaxies. These binaries are field neutron stars or black holes accreting from a low-mass donor star. We specifically compare the number of field LMXBs per K-band light in a well-studied sample of elliptical galaxies, and use this result to distinguish between an invariant IMF and one that is Kroupa/Chabrier-like at low masses and steeper at high masses. We discuss how these observations constrain the possible forms of the IMF variations and how future Chandra observations can enable sharper tests of the IMF.

Zepf, Stephen E.; Maccarone, T. J.; Kundu, A.; Gonzalez, A. H.; Lehmer, B.; Maraston, C.

2014-01-01

270

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

PubMed Central

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

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

2014-01-01

271

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

NASA Astrophysics Data System (ADS)

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

Kullen, Anita; Fear, Rob; Milan, Steve

2014-05-01

272

Circadian clocks are designed optimally  

E-print Network

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

Hasegawa, Yoshihiko

2014-01-01

273

Decentralized Fault-Tolerant Clock Pulse Generation in VLSI Chips  

E-print Network

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

Szmolyan, Peter

274

The circadian clock in cancer development and therapy  

Technology Transfer Automated Retrieval System (TEKTRAN)

Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The...

275

Zero-dead-time operation of interleaved atomic clocks.  

PubMed

We demonstrate a zero-dead-time operation of atomic clocks. This clock reduces sensitivity to local oscillator noise, integrating as nearly 1/? whereas a clock with dead time integrates as 1/?(1/2) under identical conditions. We contend that a similar scheme may be applied to improve the stability of optical clocks. PMID:24206471

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

2013-10-25

276

Magic wavelengths for terahertz clock transitions  

NASA Astrophysics Data System (ADS)

Magic wavelengths for laser trapping of boson isotopes of alkaline-earth metal atoms Sr, Ca, and Mg are investigated while considering terahertz clock transitions between the 3P0, 3P1, and 3P2 metastable triplet states. Our calculation shows that magic wavelengths for laser trapping do exist. This result is important because those metastable states have already been used to make accurate clocks in the terahertz frequency domain. Detailed discussions for magic wavelengths for terahertz clock transitions are given in this article.

Zhou, Xiaoji; Xu, Xia; Chen, Xuzong; Chen, Jingbiao

2010-01-01

277

Molecular Architecture of the Mammalian Circadian Clock  

PubMed Central

Circadian clocks coordinate physiology and behavior with the 24-hour solar day to provide temporal homeostasis with the external environment. The molecular clocks that drive these intrinsic rhythmic changes are based on interlocked transcription/translation feedback loops that integrate with diverse environmental and metabolic stimuli to generate internal 24-hour timing. In this review we highlight recent advances in our understanding of the core molecular clock and how it utilizes diverse transcriptional and post-transcriptional mechanisms to impart temporal control onto mammalian physiology. Understanding the way in which biological rhythms are generated throughout the body may provide avenues for temporally-directed therapeutics to improve health and prevent disease. PMID:23916625

Partch, Carrie L.; Green, Carla B.; Takahashi, Joseph S.

2013-01-01

278

Using Atomic Clocks to Detect Gravitational Waves  

E-print Network

Atomic clocks have recently reached a fractional timing precision of $atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

Abraham Loeb; Dan Maoz

2015-01-28

279

Atomic Clock Based On Linear Ion Trap  

NASA Technical Reports Server (NTRS)

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

Prestage, John D.; Dick, G. John

1992-01-01

280

Feynman's Clock for open quantum systems  

E-print Network

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

David G. Tempel; Alan Aspuru-Guzik

2014-06-21

281

Magic wavelengths for terahertz clock transitions  

SciTech Connect

Magic wavelengths for laser trapping of boson isotopes of alkaline-earth metal atoms Sr, Ca, and Mg are investigated while considering terahertz clock transitions between the {sup 3}P{sub 0}, {sup 3}P{sub 1}, and {sup 3}P{sub 2} metastable triplet states. Our calculation shows that magic wavelengths for laser trapping do exist. This result is important because those metastable states have already been used to make accurate clocks in the terahertz frequency domain. Detailed discussions for magic wavelengths for terahertz clock transitions are given in this article.

Zhou Xiaoji; Xu Xia; Chen Xuzong; Chen Jingbiao [School of Electronics Engineering and Computer Science, Peking University, Beijing 100871 (China)

2010-01-15

282

Using Atomic Clocks to Detect Gravitational Waves  

E-print Network

Atomic clocks have recently reached a fractional timing precision of $atomic clocks, distributed along the Earth's orbit around the Sun, will have the sensitivity needed to detect the time dilation effect of mHz gravitational waves (GWs), such as those emitted by supermassive black hole binaries at cosmological distances. Simultaneous measurement of clock-rates at different phases of a passing GW provides an attractive alternative to the interferometric detection of temporal variations in distance between test masses separated by less than a GW wavelength, currently envisioned for the eLISA mission.

Loeb, Abraham

2015-01-01

283

a Mercury-Ion Optical Clock  

NASA Astrophysics Data System (ADS)

We have developed an optical clock based on a laser whose frequency is locked to a single, laser-cooled 199Hg+ ion and that uses a femtosecond laser and microstructure fiber to phase-coherently divide the optical frequency to a countable microwave frequency. The measured short-term stability in the optical domain is about an order of magnitude higher than the best cesium-fountain clock. The estimated value of the electric-quadrupole frequency shift of the 2S1/2 (F = 0, mF = 0) - 2D5/2 (F = 2, mF = 0) clock transition is given.

Bergquist, J. C.; Tanaka, U.; Drullinger, R. E.; Itano, W. M.; Wineland, D. J.; Diddams, S. A.; Hollberg, L.; Curtis, E. A.; Oates, C. W.; Udem, Th.

2002-04-01

284

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

285

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

286

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

287

Circadian and Circalunar Clock Interactions in a Marine Annelid  

PubMed Central

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

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

2013-01-01

288

Clock Drawing in Spatial Neglect: A Comprehensive Analysis of Clock Perimeter, Placement, and Accuracy  

PubMed Central

Clock drawings produced by right-brain-damaged (RBD) individuals with spatial neglect often contain an abundance of empty space on the left while numbers and hands are placed on the right. However, the clock perimeter is rarely compromised in neglect patients’ drawings. By analyzing clock drawings produced by 71 RBD and 40 healthy adults, this study investigated whether the geometric characteristics of the clock perimeter reveal novel insights to understanding spatial neglect. Neglect participants drew smaller clocks than either healthy or non-neglect RBD participants. While healthy participants’ clock perimeter was close to circular, RBD participants drew radially extended ellipses. The mechanisms for these phenomena were investigated by examining the relation between clock-drawing characteristics and performance on six subtests of the Behavioral Inattention Test (BIT). The findings indicated that the clock shape was independent of any BIT subtest or the drawing placement on the test sheet and that the clock size was significantly predicted by one BIT subtest: the poorer the figure and shape copying, the smaller the clock perimeter. Further analyses revealed that in all participants, clocks decreased in size as they were placed farther from the center of the paper. However, even when neglect participants placed their clocks towards the center of the page, they were smaller than those produced by healthy or non-neglect RBD participants. These results suggest a neglect-specific reduction in the subjectively available workspace for graphic production from memory, consistent with the hypothesis that neglect patients are impaired in the ability to enlarge the attentional aperture. PMID:22390278

Chen, Peii; Goedert, Kelly M.

2012-01-01

289

Optical atomic clocks with suppressed blackbody-radiation shift  

NASA Astrophysics Data System (ADS)

We study a wide range of neutral atoms and ions suitable for ultraprecise atomic optical clocks with naturally suppressed blackbody-radiation shift of clock transition frequency. Calculations show that scalar polarizabilities of clock states cancel each other for at least one order of magnitude for the considered systems. Results for calculations of frequencies, quadrupole moments of the states, clock transition amplitudes, and natural widths of upper clock states are presented.

Kozlov, A.; Dzuba, V. A.; Flambaum, V. V.

2014-10-01

290

Optical atomic clocks with suppressed black body radiation shift  

E-print Network

We study a wide range of neutral atoms and ions suitable for ultra-precise atomic optical clocks with naturally suppressed black body radiation shift of clock transition frequency. Calculations show that scalar polarizabilities of clock states cancel each other for at least one order of magnitude for considered systems. Results for calculations of frequencies, quadrupole moments of the states, clock transition amplitudes and natural widths of upper clock states are presented.

Kozlov, Alexander; Flambaum, Victor

2014-01-01

291

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

NASA Astrophysics Data System (ADS)

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

Perreault, Paul D.

292

Techniques for low jitter clock multiplication  

E-print Network

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

Helal, Belal M., 1971-

2008-01-01

293

Method and system for downhole clock synchronization  

DOEpatents

A method and system for use in synchronizing at least two clocks in a downhole network are disclosed. The method comprises determining a total signal latency between a controlling processing element and at least one downhole processing element in a downhole network and sending a synchronizing time over the downhole network to the at least one downhole processing element adjusted for the signal latency. Electronic time stamps may be used to measure latency between processing elements. A system for electrically synchronizing at least two clocks connected to a downhole network comprises a controlling processing element connected to a synchronizing clock in communication over a downhole network with at least one downhole processing element comprising at least one downhole clock. Preferably, the downhole network is integrated into a downhole tool string.

Hall, David R.; Bartholomew, David B.; Johnson, Monte; Moon, Justin; Koehler, Roger O.

2006-11-28

294

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

295

Avian Circadian Organization: A Chorus of Clocks  

PubMed Central

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

Cassone, Vincent M

2013-01-01

296

Connecting the Circadian Clock with Chemosensation  

E-print Network

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

Chatterjee, Abhishek

2012-07-16

297

Clock synchronization for mobile ad hoc networks  

E-print Network

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

Chandra, Rajan

2013-02-22

298

Biological clocks and the practice of psychiatry  

PubMed Central

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

Schulz, Pierre

2007-01-01

299

The IGIMF and other IMFs in dSphs: the case of Sagittarius  

E-print Network

We have studied the effects of various initial mass functions (IMFs) on the chemical evolution of the Sagittarius dwarf galaxy (Sgr). In particular, we tested the effects of the integrated galactic initial mass function (IGIMF) on various predicted abundance patterns. The IGIMF depends on the star formation rate and metallicity and predicts less massive stars in a regime of low star formation, as it is the case in dwarf spheroidals. We adopted a detailed chemical evolution model following the evolution of $\\alpha$-elements, Fe and Eu, and assuming the currently best set of stellar yields. We also explored different yield prescriptions for the Eu, including production from neutron star mergers. Although the uncertainties still present in the stellar yields and data prevent us from drawing firm conclusions, our results suggest that the IGIMF applied to Sgr predicts lower [$\\alpha$/Fe] ratios than classical IMFs and lower [hydrostatic/explosive] $\\alpha$-element ratios, in qualitative agreement with observations...

Vincenzo, Fiorenzo; Recchi, Simone; Calura, Francesco; McWilliam, Andrew; Lanfranchi, Gustavo A

2015-01-01

300

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

301

a Mercury-Ion Optical Clock  

Microsoft Academic Search

We have developed an optical clock based on a laser whose frequency is locked to a single, laser-cooled 199Hg+ ion and that uses a femtosecond laser and microstructure fiber to phase-coherently divide the optical frequency to a countable microwave frequency. The measured short-term stability in the optical domain is about an order of magnitude higher than the best cesium-fountain clock.

J. C. Bergquist; U. Tanaka; R. E. Drullinger; W. M. Itano; D. J. Wineland; S. A. Diddams; L. Hollberg; E. A. Curtis; C. W. Oates; Th. Udem

2002-01-01

302

Circadian Clock Proteins in Mood Regulation  

PubMed Central

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

Partonen, Timo

2015-01-01

303

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

304

Coronal Open Magnetic Flux - Comparing two models to the IMF at 1 AU  

NASA Astrophysics Data System (ADS)

We present results of two extrapolation techniques for modeling the magnitude of solar coronal open magnetic flux at 1 AU: PFSS (Potential field – source surface) and HCCSSS (Horizontal current – current sheet – source surface). SDO/HMI photospheric magnetic field data from August 2010 through July 2014 are used as input. We compare the modeling results to the interplanetary magnetic field (IMF) data contained in the OMNI database. We discuss temporal variations in magnitude over the rising part of solar cycle 24.

Arden, William; Norton, Aimee A.

2015-04-01

305

Circadian clocks, food intake, and metabolism.  

PubMed

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

Challet, Etienne

2013-01-01

306

The aging biological clock in Neurospora crassa.  

PubMed

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

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

2014-09-01

307

Nuclear spin effects in optical lattice clocks  

SciTech Connect

We present a detailed experimental and theoretical study of the effect of nuclear spin on the performance of optical lattice clocks. With a state-mixing theory including spin-orbit and hyperfine interactions, we describe the origin of the {sup 1}S{sub 0}-{sup 3}P{sub 0} clock transition and the differential g factor between the two clock states for alkaline-earth-metal(-like) atoms, using {sup 87}Sr as an example. Clock frequency shifts due to magnetic and optical fields are discussed with an emphasis on those relating to nuclear structure. An experimental determination of the differential g factor in {sup 87}Sr is performed and is in good agreement with theory. The magnitude of the tensor light shift on the clock states is also explored experimentally. State specific measurements with controlled nuclear spin polarization are discussed as a method to reduce the nuclear spin-related systematic effects to below 10{sup -17} in lattice clocks.

Boyd, Martin M.; Zelevinsky, Tanya; Ludlow, Andrew D.; Blatt, Sebastian; Zanon-Willette, Thomas; Foreman, Seth M.; Ye Jun [JILA, National Institute of Standards and Technology and University of Colorado, Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2007-08-15

308

The aging biological clock in Neurospora crassa  

PubMed Central

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

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

2014-01-01

309

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

NASA Astrophysics Data System (ADS)

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

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

2014-11-01

310

On the Effect of IMF Turning on Ion Dynamics at Mercury  

NASA Technical Reports Server (NTRS)

We investigate the effect of a rotation of the Interplanetary Magnetic Field (IMF) on the transport of magnetospheric ion populations at Mercury. We focus on ions of planetary origin and investigate their large-scale circulation using three-dimensional single-particle simulations. We show that a nonzero Bx component of the IMF leads to a pronounced asymmetry in the overall circulation pattern . In particular, we demonstrate that the centrifugal acceleration due to curvature of the E x B drift paths is more pronounced in one hemisphere than the other, leading to filling of the magnetospheric lobes and plasma sheet with more or less energetic material depending upon the hemisphere of origin. Using a time-varying electric and magnetic field model, we investigate the response of ions to rapid (a few tens of seconds) re-orientation of the IMF. We show that, for ions with gyroperiods comparable to the field variation time scale, the inductive electric field should lead to significant nonadiabatic energization, up to several hundreds of eVs or a few keVs. It thus appears that IMP turning at Mercury should lead to localized loading of the magnetosphere with energetic material of planetary origin (e.g., Na+).

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

2011-01-01

311

Two regimes of Turbulent Fragmentation and the stellar IMF from Primordial to Present Day Star Formation  

E-print Network

The Padoan and Nordlund model of the stellar initial mass function (IMF) is derived from low order statistics of supersonic turbulence, neglecting gravity (e.g. gravitational fragmentation, accretion and merging). In this work the predictions of that model are tested using the largest numerical experiments of supersonic hydrodynamic (HD) and magneto-hydrodynamic (MHD) turbulence to date (~1000^3 computational zones) and three different codes (Enzo, Zeus and the Stagger Code). The model predicts a power law distribution for large masses, related to the turbulence energy power spectrum slope, and the shock jump conditions. This power law mass distribution is confirmed by the numerical experiments. The model also predicts a sharp difference between the HD and MHD regimes, which is recovered in the experiments as well, implying that the magnetic field, even below energy equipartition on the large scale, is a crucial component of the process of turbulent fragmentation. These results suggest that the stellar IMF of primordial stars may differ from that in later epochs of star formation, due to differences in both gas temperature and magnetic field strength. In particular, we find that the IMF of primordial stars born in turbulent clouds may be narrowly peaked around a mass of order 10 solar masses, as long as the column density of such clouds is not much in excess of 10^22 cm^-2.

Paolo Padoan; AAke Nordlund; Alexei G. Kritsuk; Michael L. Norman; Pak Shing Li

2007-04-23

312

Hydrogen Maser Clock (HMC) Experiment  

NASA Technical Reports Server (NTRS)

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

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

1997-01-01

313

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

314

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

315

Evolutionary Links Between Circadian Clocks and Photoperiodic Diapause in Insects  

PubMed Central

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

Meuti, Megan E.; Denlinger, David L.

2013-01-01

316

Health Sciences New Employee Orientation Home Department Clock In/ Out Clock Code  

E-print Network

_labor_relations/agency_fee/fschart.html MANDATORY ONLINE COURSES: UCSD Learning: http://blink.ucsd.edu/HR/training/resources/web/index.html NewEmployee Health Sciences New Employee Orientation Home Department Clock In/ Out Clock Code 1(in) or 9(out employee ID. " Enter your employee ID. Your employee ID is 2 zeroes followed by the 6-digit number you

Gleeson, Joseph G.

317

A high-speed photonic clock and carrier regenerator  

NASA Technical Reports Server (NTRS)

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

Yao, X. S.; Lutes, G.

1995-01-01

318

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

E-print Network

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

Olivier Besida

2011-10-13

319

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

E-print Network

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

Besida, Olivier

2011-01-01

320

Compact, Highly Stable Ion Atomic Clock  

NASA Technical Reports Server (NTRS)

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

Prestage, John

2008-01-01

321

Nuclear receptors rock around the clock.  

PubMed

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

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

2014-05-01

322

Clock synchronization on the RAX spacecraft  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

323

Dating Phylogenies with Hybrid Local Molecular Clocks  

PubMed Central

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

Aris-Brosou, Stéphane

2007-01-01

324

Nuclear receptors rock around the clock  

PubMed Central

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

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

2014-01-01

325

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

326

Small angle spectrometers: Summary  

SciTech Connect

Aspects of experiments at small angles at the Superconducting Super Collider are considered. Topics summarized include a small angle spectrometer, a high contingency spectrometer, dipole and toroid spectrometers, and magnet choices. (LEW)

Courant, E.; Foley, K.J.; Schlein, P.E.; Rosner, J.; Slaughter, J.; Bromberg, C.; Jones, L.; Garren, A.; Groom, D.; Johnson, D.E.

1986-01-01

327

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.

Michael W. Davidson

2006-06-15

328

Supporting Family Awareness with the Whereabouts Clock  

NASA Astrophysics Data System (ADS)

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

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

329

The Deep Space Atomic Clock Mission  

NASA Technical Reports Server (NTRS)

The Deep Space Atomic Clock (DSAC) mission will demonstrate the space flight performance of a small, low-mass, high-stability mercury-ion atomic clock with long term stability and accuracy on par with that of the Deep Space Network. The timing stability introduced by DSAC allows for a 1-Way radiometric tracking paradigm for deep space navigation, with benefits including increased tracking via utilization of the DSN's Multiple Spacecraft Per Aperture (MSPA) capability and full ground station-spacecraft view periods, more accurate radio occultation signals, decreased single-frequency measurement noise, and the possibility for fully autonomous on-board navigation. Specific examples of navigation and radio science benefits to deep space missions are highlighted through simulations of Mars orbiter and Europa flyby missions. Additionally, this paper provides an overview of the mercury-ion trap technology behind DSAC, details of and options for the upcoming 2015/2016 space demonstration, and expected on-orbit clock performance.

Ely, Todd A.; Koch, Timothy; Kuang, Da; Lee, Karen; Murphy, David; Prestage, John; Tjoelker, Robert; Seubert, Jill

2012-01-01

330

Models of the Primordial Standard Clock  

NASA Astrophysics Data System (ADS)

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

Chen, Xingang; Namjoo, Mohammad Hossein; Wang, Yi

2015-02-01

331

Sharp World Clock 4.55  

NSDL National Science Digital Library

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

Wallroth, Johannes

332

Tick Tock: New Clues about Biological Clocks and Health  

MedlinePLUS

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

333

Watching the clock: Studying variation in rates of molecular evolution  

E-print Network

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

Hohenlohe, Paul A.

334

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...

335

Reference-Based Clock Distribution Architectures Atanu Chattopadhyay  

E-print Network

-directional clock line is daisy-chained using specially designed switches at each tap in the distribution. Daisy strategy achieves a set of skew-tolerant clocks at each tap in a daisy- chain. The design provides simple

Zilic, Zeljko

336

Clock mechanisms and their effects, leads into steam engine  

E-print Network

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

Dugan, David

2004-08-17

337

Review article Circadian clocks -from genes to complex behaviour  

E-print Network

Review article Circadian clocks - from genes to complex behaviour Till Roenneberg Martha Merrow (Received 4 February 1999; accepted 16 April 1999) Abstract - Circadian clocks control temporal structure, molecular mechanisms that underlie this endogenous temporal programme. The generation of circadian rhythms

Paris-Sud XI, Université de

338

Angles All Around  

NSDL National Science Digital Library

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

Mrs. Bennett

2011-12-14

339

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

PubMed Central

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

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

2014-01-01

340

Planar clock routing for high performance chip and package co-design  

Microsoft Academic Search

A new concept of chip and package co-design for the clock network is presented in this paper. We propose a two level clock distribution scheme which partitions the clock network into two levels. First, the clock terminals are partitioned into a set of clusters. For each cluster, a local on-chip clock tree is used to distribute the clock signal from

Qing Zhu; Wayne Wei-ming Dai

1996-01-01

341

Sample-Clock Phase-Control Feedback  

NASA Technical Reports Server (NTRS)

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

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

2012-01-01

342

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

343

Simultaneous observations of polar cap patches and Sun-aligned arcs during transitions of the IMF  

NASA Astrophysics Data System (ADS)

This paper presents the first observations of simultaneous polar cap patches and polar cap arcs in a single common 1000-km field of view, and identifies a model that explains the interplanetary magnetic field (IMF) dependencies of the observed phenomenology. To study the characteristics of the polar cap optical emissions in the 630.0 nm line during transitions of the IMF Bz, we have scanned images taken at Qaanaaq, Greeland, between 1989 and 1994. We found that on a few occasions, when Bz changed from a south to a north orientation, a particular pattern of polar cap patches and Sun-aligned arcs coexisted. No similar pattern of coexisting arcs and patches was found during north-to-south IMF transitions. The detailed analyses of three of these events are presented here in which patches and polar cap arcs are clearly identified to reside simultaneously within the Qaanaaq imager field of view. The digisonde located also at Qaanaaq is used to confirm that the optical patches correspond to enhancements in the number density and a simultaneous decrease of the hmF2 value. These two factors increase the capability of the imager to differentiate between patches and the background airglow. Data collected by the DMSP F8 satellite during one of the events reaffirm the appearance of polar cap precipitation during the Bz positive period. The J4 sensor on board DMSP F8 detected typical electron fluxes commonly associated with polar cap arcs. The coexistence of patches and arcs is due to a slower response of the patches in exiting the polar cap, and then the relatively sudden appearance of polar cap arcs presumably driven by dayside reconnection between the IMF and open flux drawn initially equatorward toward the cusp. This model, of dayside reconnection switching from equatorward of the cusp for Bz south to poleward of the cusp for Bz north, likewise explains why arcs and patches are seen by the imager to coexist for rapid Bz reversals only from south to north and not from north to south.

Valladares, C. E.; Fukui, K.; Sheehan, R.; Carlson, H. C., Jr.; Bullett, T.

1998-11-01

344

Quantum time-of-flight measurements: Kicked clock versus continuous clock  

SciTech Connect

The measurement of time durations or instants of occurrence of events has been frequently modeled 'operationally' by coupling the system of interest to a ''clock.'' According to several of these models, the operational approach is limited at low energies because the perturbation of the clock does not allow to reproduce accurately the corresponding ideal time quantity, defined for the system in isolation. We show that, for a time-of-flight measurement model that can be set to measure dwell or arrival times, these limitations may be overcome by extending the range of energies where the clock works properly using pulsed couplings rather than continuous ones.

Alonso, Daniel; Sala Mayato, R.; Muga, J.G. [Departamento de Fisica Fundamental y Experimental, Electronica y Sistemas, Universidad de La Laguna, La Laguna, Tenerife (Spain); Departamento de Fisica Fundamental II, Universidad de La Laguna, La Laguna, Tenerife (Spain); Departamento de Quimica-Fisica, Universidad del Pais Vasco, Apartado Postal 644, 48080 Bilbao (Spain)

2003-03-01

345

Timescale algorithms combining cesium clocks and hydrogen masers  

NASA Technical Reports Server (NTRS)

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

Breakiron, Lee A.

1992-01-01

346

Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock  

E-print Network

We study experimentally the lifetime of a special class of entangled states in an atomic clock, squeezed spin states. In the presence of anisotropic noise, their lifetime is strongly dependent on squeezing orientation. We measure the Allan deviation spectrum of a clock operated with a phase-squeezed input state. For integration times up to 50 s the squeezed clock achieves a given precision 2.8(3) times faster than a clock operating at the standard quantum limit.

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

2010-04-10

347

Orientation-Dependent Entanglement Lifetime in a Squeezed Atomic Clock  

SciTech Connect

We study experimentally the application of a class of entangled states, squeezed spin states, to the improvement of atomic-clock precision. In the presence of anisotropic noise, the entanglement lifetime is strongly dependent on squeezing orientation. We measure the Allan deviation spectrum of a clock operated with a phase-squeezed input state. For averaging times up to 50 s the squeezed clock achieves a given precision 2.8(3) times faster than a clock operating at the standard quantum limit.

Leroux, Ian D.; Schleier-Smith, Monika H.; Vuletic, Vladan [Department of Physics, MIT-Harvard Center for Ultracold Atoms and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2010-06-25

348

Satellite virtual atomic clock with pseudorange difference function  

Microsoft Academic Search

Satellite atomic clocks are the basis of GPS for the control of time and frequency of navigation signals. In the Chinese Area\\u000a Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed.\\u000a Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic\\u000a clocks are used

Xiaohui Li; Haitao Wu; Yujing Bian; Danni Wang

2009-01-01

349

Positional Cloning of the Mouse Circadian Clock Gene  

Microsoft Academic Search

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

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

1997-01-01

350

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

351

Caring around the Clock: rounding in practice.  

PubMed

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

Hutchings, Marie

352

Detection of the gravitomagnetic clock effect  

E-print Network

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

A. Tartaglia

1999-09-16

353

A relativistic analysis of clock synchronization  

NASA Technical Reports Server (NTRS)

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

Thomas, J. B.

1974-01-01

354

Weather Alarm Clock 2.1  

NSDL National Science Digital Library

This handy application is fairly self-explanatory: It displays both the weather and tells the time. Now, it does so in a visually pleasing manner, and for that alone it should be praised. It comes with a few customized skins, and users can create alarms which can be accompanied by pop-up messages. Finally, for those who are quite particular about the exact time, the clock feature can be synchronized with various omnipotent atomic clock servers. This version is compatible with computers running Windows 2000, XP, and 2003.

2007-01-01

355

Quantum Clock Synchronization with a Single Qudit  

PubMed Central

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

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

2015-01-01

356

Quantum Clock Synchronization with a Single Qudit  

NASA Astrophysics Data System (ADS)

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

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

2015-01-01

357

Lu-176 - Cosmic clock and stellar thermometer  

NASA Astrophysics Data System (ADS)

The s-process nucleosynthesis of the isobar pair Lu-176/Hf-176, a long-lived cosmic clock, is examined in conjunction with the s-only isotopes Sm-148,150, Gd-154, Dy-160, Yb-170, Os-186, and Pt-192. Expressions are derived which make it possible to calculate the s-process age from measured quantities alone. A formula is specified which does not contain the population probability P of the 3.68 hr isomeric state in Lu-176. This makes it possible to decide if Lu-176 is, in addition to a cosmic clock, also a stellar thermometer.

Beer, H.

1982-11-01

358

The Large Water-Clock of Amphiaraeion  

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

359

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

SciTech Connect

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

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

2013-07-01

360

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

361

Clock generation and distribution for the first IA64 microprocessor  

Microsoft Academic Search

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

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

2000-01-01

362

Minimal Skew Clock Embedding Considering Time Variant Temperature Gradient  

E-print Network

- ing points can be shifted with presence of the temperature gradient. As a result, it requires a clockMinimal Skew Clock Embedding Considering Time Variant Temperature Gradient Hao Yu, Yu Hu, Chunchen-aware clock embedding assumes a time-invariant temperature gradient. However, it is not solved how to find

He, Lei

363

Molecular genetics of the fruit-fly circadian clock  

Microsoft Academic Search

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

Ezio Rosato; Eran Tauber; Charalambos P Kyriacou

2006-01-01

364

PARCS: a Primary Atomic Reference Clock in Space  

Microsoft Academic Search

NIST, in collaboration with the Jet Propulsion Laboratories (JPL), the University of Colorado, Politecnico di Torino and Harvard Smithsonian Center for Astrophysics (SAO) is building a laser-cooled cesium-beam atomic clock for flight on the International Space Station (ISS). The clock, named PARCS (Primary Atomic Reference Clock in Space) is designed to perform certain tests of relativity and fundamental physics and

S. R. Jefferts; T. P. Heavner; L. W. Hollberg; J. Kitching; D. M. Meekhof; T. E. Parker; W. Phillips; S. Rolston; H. G. Robinson; J. H. Shirley; D. B. Sullivan; F. L. Walls; N. Ashby; W. M. Klipstein; L. Maleki; D. Seidel; R. Thompson; S. Wu; L. Young; R. F. C. Vessot; A. DeMarchi

1999-01-01

365

Microchip-based trapped-atom clocks Vladan Vuletic  

E-print Network

1 1 Microchip-based trapped-atom clocks Vladan Vuleti´c Ian D. Leroux Monika H. Schleier-Smith 1 , the fractional stability improves with higher transi- tion frequency. #12;2 1 Microchip-based trapped-atom clocks 1.2 Atomic-fountain versus trapped-atom clocks In the absence of other fields, particles fall under

Vuletic, Vladan

366

The effect of humidity on commercial cesium beam atomic clocks  

Microsoft Academic Search

Control of humidity is studied in one of the environmental chambers for the NBS cesium beam clock ensemble. The relative humidity was changed from a few percent to 48%. All of the clocks underwent a change in frequency. The resulting frequency changes were of different sign and of varying magnitudes among the clocks. In some, the changes were an order

J. E. Gray; H. E. Machlan; D. W. Allan

1988-01-01

367

Blackbody radiation shifts and magic wavelengths for atomic clock research  

E-print Network

Blackbody radiation shifts and magic wavelengths for atomic clock research M. S. Safronova of interest to atomic clock development are reported. We also calculated the blackbody radiation shift The operation of atomic clocks is generally carried out at room temperature, whereas the definition

Safronova, Marianna

368

Atomic clocks of the future: using the ultrafast and ultrastable'  

E-print Network

Atomic clocks of the future: using the ultrafast and ultrastable' Leo Hollberg, Scott Diddanis based on laser cooled and trapped atoms. In contrast to today's atomic clocks that are based on electronic oscillators locked to microwave transitions in atoms, the nest generation of atomic clocks

369

A new fault-tolerant algorithm for clock synchronization  

Microsoft Academic Search

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

Jennifer Lundelius; Nancy A. Lynch

1984-01-01

370

Origin and evolution of the anchor clock escapement  

Microsoft Academic Search

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

M. V. Headrick

2002-01-01

371

Restoration of an 18th century English clock  

Microsoft Academic Search

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

Daniel Curtit; Jean-Michel Piguet

1992-01-01

372

Self Calibrating Clocks for Globally Asynchronous Locally Synchronous Systems  

E-print Network

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

Mullins, Robert

373

An Upper Bound on Expected Clock Skew in Synchronous Systems  

Microsoft Academic Search

A statistical model is considered for clock skew in which the propagation delays on every source-to-processor path are sums of independent contributions, and are identically distributed. Upper bounds are derived for expected skew, and its variance, in tree distribution systems with N synchronously clocked processing elements. The results are applied to two special cases of clock distribution. In the first,

Steven D. Kugelmass; Kenneth Steiglitz

1990-01-01

374

Synchronization of Cellular Clocks in the Suprachiasmatic Nucleus  

Microsoft Academic Search

Individual cellular clocks in the suprachiasmatic nucleus (SCN), the circadian center, are integrated into a stable and robust pacemaker with a period length of about 24 hours. We used real-time analysis of gene expression to show synchronized rhythms of clock gene transcription across hundreds of neurons within the mammalian SCN in organotypic slice culture. Differentially phased neuronal clocks are topographically

Shun Yamaguchi; Hiromi Isejima; Takuya Matsuo; Ryusuke Okura; Kazuhiro Yagita; Masaki Kobayashi; Hitoshi Okamura

2003-01-01

375

INTRODUCTION Most living organisms possess an endogenous circadian clock  

E-print Network

INTRODUCTION Most living organisms possess an endogenous circadian clock that runs, in constant the endogenous clock to a 24-hour period, or, stated otherwise, set the phase of the clock daily to solar time) comprise two subsets of cells that express the products of the period (per) and timeless (tim) genes

Rouyer, Francois

376

Time zones: a comparative genetics of circadian clocks  

Microsoft Academic Search

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

Michael W. Young; Steve A. Kay

2001-01-01

377

Modeling the circadian clock: from molecular mechanism to  

E-print Network

Modeling the circadian clock: from molecular mechanism to physiological disorders Jean of circadian rhythms, a computa- tional model for the mammalian circadian clock is used to examine the dynamical bases of circadian-clock-related physiological disorders in humans. Entrainment by the light

Goldbeter, Albert

378

10GHz clock distribution using coupled standing-wave oscillators  

Microsoft Academic Search

A global clock network comprised of coupled, standing-wave oscillators is prototyped in a 0.18?m 6M CMOS process. The clock network operates from 9.8 to 10.5 GHz with 0.6ps skew and contributes only 0.5ps jitter when referencing a clock source with 1.4ps rms jitter.

F. O'Mahony; C. P. Yue; M. Horowitz; S. Simon Wong

2003-01-01

379

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

E-print Network

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

Ramakrishnan, Sundararajan

2010-10-12

380

Identifying Variations to the IMF at High-z Through Deep Radio Surveys  

NASA Astrophysics Data System (ADS)

In this article I briefly describe how deep radio surveys may provide a means to identify variations in the upper end of the initial mass function (IMF) in star-forming galaxies at high redshifts (i.e., z ? 3). At such high redshifts, I argue that deep radio continuum observations at frequencies ?10 GHz using next generation facilities (e.g., EVLA, MeerKAT, SKA/NAA) will likely provide the most accurate measurements for the ionizing photon rates (star formation rates; SFRs) of normal galaxies since their non-thermal emission should be highly suppressed due to the increased inverse Compton (IC) losses from the cosmic microwave background (CMB), leaving only thermal (free-free) emission detectable. Thus, a careful analysis of such observations in combination with future ALMA and JWST data, measuring the rest-frame far-infrared and UV emission from the same population of galaxies, may yield the best means to search for variability in the stellar IMF at such epochs.

Murphy, E. J.

2011-06-01

381

Test-particle simulations of SEP propagation in IMF with large-scale fluctuations  

NASA Astrophysics Data System (ADS)

The results of full-orbit test-particle simulations of SEPs propagating through an IMF which exhibits large-scale fluctuations are presented. A variety of propagation conditions are simulated - scatter-free, and scattering with mean free path, ?, of 0.3 and 2.0 AU - and the cross-field transport of SEPs is investigated. When calculating cross-field displacements the Parker spiral geometry is accounted for and the role of magnetic field expansion is taken into account. It is found that transport across the magnetic field is enhanced in the ? =0.3 AU and ? =2 AU cases, compared to the scatter-free case, with the ? =2 AU case in particular containing outlying particles that had strayed a large distance across the IMF. Outliers are catergorized by means of Chauvenet's criterion and it is found that typically between 1 and 2% of the population falls within this category. The ratio of latitudinal to longitudinal diffusion coefficient perpendicular to the magnetic field is typically 0.2, suggesting that transport in latitude is less efficient.

Kelly, J.; Dalla, S.; Laitinen, T.

2012-11-01

382

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

SciTech Connect

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

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

1996-03-01

383

Biochemical basis for the biological clock  

NASA Technical Reports Server (NTRS)

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

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

2002-01-01

384

Supplemental Data Connecting the Navigational Clock  

E-print Network

Supplemental Data Connecting the Navigational Clock to Sun Compass Input in Monarch Butterfly Brain replicates out of 500 in which a particular node is supported. Red indicates cloned monarch opsin cDNAs. Gen butterfly (A­C). Flight records in the presence of a UV-interference filter are colored red. The UV

385

Circadian clock function in the mammalian ovary.  

PubMed

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

Sellix, Michael T

2015-02-01

386

Gradient Clock Synchronization in Wireless Sensor Networks  

E-print Network

Gradient Clock Synchronization in Wireless Sensor Networks Philipp Sommer Computer Engineering- olution. Without doubt, time is a first-class citizen in wireless sensor networks. Without accurate time if the nodes in the wireless sensor network manage to have an adequate agreement of time. Indeed

387

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

388

U. S. and World Population Clocks  

NSDL National Science Digital Library

These population clocks from the U.S. Census Bureau show population estimates for the United States and world. Estimates are projected to the current date and time; there are also component settings for U. S. population (one birth every X seconds, one death every X seconds), and monthly population figures for the world.

389

Precision synchronization of computer network clocks  

Microsoft Academic Search

This paper builds on previous work involving the Network Time Protocol, which is used to synchronize computer clocks in the Internet. It describes a series of incremental improvements in system hardware and software which result in significantly better accuracy and stability, especially in primary time servers directly synchronized to radio or satellite time services. These improvements include novel interfacing techniques

David L. Mills

1994-01-01

390

Improved Algorithms for Synchronizing Computer Network Clocks  

Microsoft Academic Search

The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementa- tions. Most of the estimated deployment of 100,000 NTP servers and

David L. Mills

1994-01-01

391

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

392

Oscillatory Mechanisms Underlying the Murine Circadian Clock  

NSDL National Science Digital Library

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

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

2003-11-18

393

Blackbody radiation shifts in optical atomic clocks.  

PubMed

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

Safronova, Marianna; Kozlov, Mikhail; Clark, Charles

2012-03-01

394

Testing General Relativity with Atomic Clocks  

E-print Network

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 volume. In particular, we present the scientific motivations of the space projects ACES and SAGAS.

S. Reynaud; C. Salomon; P. Wolf

2009-03-06

395

Distant clock synchronization using entangled photon pairs  

SciTech Connect

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

Valencia, Alejandra; Scarcelli, Giuliano; Shih, Yanhua [Department of Physics, University of Maryland, Baltimore County, Baltimore, Maryland 21250 (United States)

2004-09-27

396

Compact microwave cavity for hydrogen atomic clock  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

397

Caesium atomic clocks: function, performance and applications  

Microsoft Academic Search

For more than four decades, caesium atomic clocks have been the backbone in a variety of demanding applications in science and technology. Neither satellite based navigation systems, like the US Global Positioning System, nor the syntonization of telecommunication networks at the presently prescribed levels, would function without them. Recent years have brought major breakthroughs in the development, operation and mutual

Andreas Bauch

2003-01-01

398

European plans for new clocks in space  

NASA Technical Reports Server (NTRS)

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

Leschiutta, Sigfrido M.; Tavella, Patrizia

1995-01-01

399

Rank clocks and plant community dynamics.  

PubMed

Summarizing complex temporal dynamics in communities is difficult to achieve in a way that yields an intuitive picture of change. Rank clocks and rank abundance statistics provide a graphical and analytical framework for displaying and quantifying community dynamics. We used rank clocks, in which the rank order abundance for each species is plotted over time in temporal clockwise direction, to display temporal changes in species abundances and richness. We used mean rank shift and proportional species persistence to quantify changes in community structure in long-term data sets from fertilized and control plots in a late successional old field, frequently and infrequently burned tallgrass prairie, and Chihuahuan desert grassland and shrubland communities. Rank clocks showed that relatively constant species richness masks considerable temporal dynamics in relative species abundances. In the old field, fertilized plots initially experienced high mean rank shifts that stabilized rapidly below that of unfertilized plots. Rank shifts were higher in infrequently burned vs. annually burned tallgrass prairie and in desert grassland compared to shrubland vegetation. Proportional persistence showed that arid grasslands were more dynamic than mesic grasslands. We conclude that rank clocks and rank abundance statistics provide important insights into community dynamics that are often hidden by traditional univariate approaches. PMID:19137958

Collins, Scott L; Suding, Katharine N; Cleland, Elsa E; Batty, Michael; Pennings, Steven C; Gross, Katherine L; Grace, James B; Gough, Laura; Fargione, Joe E; Clark, Christopher M

2008-12-01

400

Systems Biology of the Mammalian Circadian Clock  

E-print Network

Systems Biology of the Mammalian Circadian Clock Hanspeter Herzel Institute for Theoretical Biology Molecular Chronobiology #12;The circadian oscillator Circadian rhythm Oster et al., 2002 Feedback loopsOscillations Reppert and Weaver, 2001 #12;Simplified model of the circadian core oscillator S. Becker-Weimann, J. Wolf

Spang, Rainer

401

Longitudinal light clock vs special relativity  

E-print Network

In order to respect the Principle of Relativity, the analysis of the behavior of the longitudinal light clock reveals the necessity to extend the Doppler effect also to space and time. As a consequence, the bodies in inertial motion must dilate along the direction of their movement.

Giovanni Zanella

2012-12-10

402

The mammalian retina as a clock  

NASA Technical Reports Server (NTRS)

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

Tosini, Gianluca; Fukuhara, Chiaki

2002-01-01

403

Current Status of the Molecular Clock Hypothesis  

ERIC Educational Resources Information Center

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

Hermann, Gilbert

2003-01-01

404

The peripheral clock regulates human pigmentation.  

PubMed

Although the regulation of pigmentation is well characterized, it remains unclear whether cell-autonomous controls regulate the cyclic on-off switching of pigmentation in the hair follicle (HF). As human HFs and epidermal melanocytes express clock genes and proteins, and given that core clock genes (PER1, BMAL1) modulate human HF cycling, we investigated whether peripheral clock activity influences human HF pigmentation. We found that silencing BMAL1 or PER1 in human HFs increased HF melanin content. Furthermore, tyrosinase expression and activity, as well as TYRP1 and TYRP2 mRNA levels, gp100 protein expression, melanocyte dendricity, and the number gp100+ HF melanocytes, were all significantly increased in BMAL1 and/or PER1-silenced HFs. BMAL1 or PER1 silencing also increased epidermal melanin content, gp100 protein expression, and tyrosinase activity in human skin. These effects reflect direct modulation of melanocytes, as BMAL1 and/or PER1 silencing in isolated melanocytes increased tyrosinase activity and TYRP1/2 expression. Mechanistically, BMAL1 knockdown reduces PER1 transcription, and PER1 silencing induces phosphorylation of the master regulator of melanogenesis, microphthalmia-associated transcription factor, thus stimulating human melanogenesis and melanocyte activity in situ and in vitro. Therefore, the molecular clock operates as a cell-autonomous modulator of human pigmentation and may be targeted for future therapeutic strategies. PMID:25310406

Hardman, Jonathan A; Tobin, Desmond J; Haslam, Iain S; Farjo, Nilofer; Farjo, Bessam; Al-Nuaimi, Yusur; Grimaldi, Benedetto; Paus, Ralf

2015-04-01

405

Building a Capillary Action Water Clock.  

ERIC Educational Resources Information Center

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

Tracy, Dyanne M.

2002-01-01

406

On the Sun, Earth, and Clocks.  

ERIC Educational Resources Information Center

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

Easton, D.

1985-01-01

407

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

NASA Astrophysics Data System (ADS)

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

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

2014-02-01

408

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

PubMed

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

Lee, Euna; Kim, Eun Young

2014-09-01

409

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

PubMed Central

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

Lee, Euna

2014-01-01

410

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

E-print Network

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

Sawa Manoff

2005-05-12

411

s-Wave collisional frequency shift of a fermion clock.  

PubMed

We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, ?(1). The fermion shift instead depends strongly on the second pulse area ?(2). It allows the shift to be canceled, nominally at ?(2)=?/2, but correlations perturb the null to slightly larger ?(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589

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

2013-04-19

412

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

413

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

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

414

Molecular-clock methods for estimating evolutionary rates and timescales.  

PubMed

The molecular clock presents a means of estimating evolutionary rates and timescales using genetic data. These estimates can lead to important insights into evolutionary processes and mechanisms, as well as providing a framework for further biological analyses. To deal with rate variation among genes and among lineages, a diverse range of molecular-clock methods have been developed. These methods have been implemented in various software packages and differ in their statistical properties, ability to handle different models of rate variation, capacity to incorporate various forms of calibrating information and tractability for analysing large data sets. Choosing a suitable molecular-clock model can be a challenging exercise, but a number of model-selection techniques are available. In this review, we describe the different forms of evolutionary rate heterogeneity and explain how they can be accommodated in molecular-clock analyses. We provide an outline of the various clock methods and models that are available, including the strict clock, local clocks, discrete clocks and relaxed clocks. Techniques for calibration and clock-model selection are also described, along with methods for handling multilocus data sets. We conclude our review with some comments about the future of molecular clocks. PMID:25290107

Ho, Simon Y W; Duchêne, Sebastián

2014-12-01

415

Neuron, Vol. 46, 457467, May 5, 2005, Copyright 2005 by Elsevier Inc. DOI 10.1016/j.neuron.2005.03.014 Connecting the Navigational Clock  

E-print Network

.03.014 Connecting the Navigational Clock to Sun Compass Input in Monarch Butterfly Brain Ivo Sauman,2,5 Adriana D migration, North Ameri- can monarch butterflies (Danaus plexippus) use a time-Ceske Budejovice Czech Previous studies suggest that monarch butterflies can use the angle of plane polarized light (e

416

Satellite virtual atomic clock with pseudorange difference function  

NASA Astrophysics Data System (ADS)

Satellite atomic clocks are the basis of GPS for the control of time and frequency of navigation signals. In the Chinese Area Positioning System (CAPS), a satellite navigation system without the satellite atomic clocks onboard is successfully developed. Thus, the method of time synchronization based on satellite atomic clocks in GPS is not suitable. Satellite virtual atomic clocks are used to implement satellite navigation. With the satellite virtual atomic clocks, the time at which the signals are transmitted from the ground can be delayed into the time that the signals are transmitted from the satellites and the pseudorange measuring can be fulfilled as in GPS. Satellite virtual atomic clocks can implement the navigation, make a pseudorange difference, remove the ephemeris error, and improve the accuracy of navigation positioning. They not only provide a navigation system without satellite clocks, but also a navigation system with pseudorange difference.

Li, Xiaohui; Wu, Haitao; Bian, Yujing; Wang, Danni

2009-03-01

417

Photoperiodic plasticity in circadian clock neurons in insects  

PubMed Central

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

Shiga, Sakiko

2013-01-01

418

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

419

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

Microsoft Academic Search

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

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

1993-01-01

420

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

E-print Network

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

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

2014-01-01

421

The mammalian circadian clock protein period counteracts cryptochrome in phosphorylation dynamics of circadian locomotor output cycles kaput (CLOCK).  

PubMed

The circadian transcription factor CLOCK exhibits a circadian oscillation in its phosphorylation levels. Although it remains unclear whether this phosphorylation contributes to circadian rhythm generation, it has been suggested to be involved in transcriptional activity, intracellular localization, and degradative turnover of CLOCK. Here, we obtained direct evidence that CLOCK phosphorylation may be essential for autonomous circadian oscillation in clock gene expression. Importantly, we found that the circadian transcriptional repressors Cryptochrome (CRY) and Period (PER) showed an opposite effect on CLOCK phosphorylation; CRY impaired BMAL1-dependent CLOCK phosphorylation, whereas PER protected the phosphorylation against CRY. Interestingly, unlike PER1 and PER2, PER3 did not exert a protective action, which correlates with the phenotypic differences among mice lacking the Per genes. Further studies on the regulatory mechanism of CLOCK phosphorylation would thus lead to elucidation of the mechanism of CRY-mediated transcriptional repression and an understanding of the true role of PER in the negative feedback system. PMID:25271155

Matsumura, Ritsuko; Tsuchiya, Yoshiki; Tokuda, Isao; Matsuo, Takahiro; Sato, Miho; Node, Koichi; Nishida, Eisuke; Akashi, Makoto

2014-11-14

422

What's My Angle?  

NSDL National Science Digital Library

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

2011-01-01

423

Reading Angles in Maps  

ERIC Educational Resources Information Center

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

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

2014-01-01

424

Polygon Angle Applet  

NSDL National Science Digital Library

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

Nicholas Exner

2000-05-31

425

Special Angle Pairs Discovery Activity  

NSDL National Science Digital Library

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

Barbara Henry

2012-04-16

426

Global Auroral Energy Deposition during Substorm Onset Compared with Local Time and Solar Wind IMF Conditions  

NASA Technical Reports Server (NTRS)

The global images made by the Ultraviolet Imager (UVI) aboard the IASTP/Polar Satellite are used to derive the global auroral energy deposited in the ionosphere resulting from electron precipitation. During a substorm onset, the energy deposited and its location in local time are compared to the solar wind IMF conditions. Previously, insitu measurements of low orbiting satellites have made precipitating particle measurements along the spacecraft track and global images of the auroral zone, without the ability to quantify energy parameters, have been available. However, usage of the high temporal, spatial, and spectral resolution of consecutive UVI images enables quantitative measurement of the energy deposited in the ionosphere not previously available on a global scale. Data over an extended period beginning in January 1997 will be presented.

Spann, J. F.; Brittnacher, M.; Fillingim, M. O.; Germany, G. A.; Parks, G. K.

1998-01-01

427

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

E-print Network

.65E-02 4.65E-02 4.65E-02 U234 1.28E-06 7.03E-07 1.71E-06 U235 9.08E-04 1.85E-04 1.85E-04 U236 0.00E+00 1.14E-04 1.14E-04 U238 2.23E-02 2.16E-02 2.16E-02 Np237 0.00E+00 1.53E-05 1.61E-05 Pu238 0.00E+00 6.40E-06 5.93E-06 Pu239 0.00E+00 1.41E-04 1... ....................... 39 5.4 Isotopics Discharge Concentrations for Single Reflected IMF Pin ............. 40 6.1 Pu Vector as a Function of Number of Recyclings for MOX M-R ............. 42 xi FIGURE...

Zhang, Yunhuang

2011-02-22

428

Statistical Properties of the Solar Wind and IMF at 1 AU  

NASA Astrophysics Data System (ADS)

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

McPherron, R. L.

2006-12-01

429

Glucocorticoids entrain molecular clock components in human peripheral cells.  

PubMed

In humans, shift work induces a desynchronization between the circadian system and the outside world, which contributes to shift work-associated medical disorders. Using a simulated night shift experiment, we previously showed that 3 d of bright light at night fully synchronize the central clock to the inverted sleep schedule, whereas the peripheral clocks located in peripheral blood mononuclear cells (PBMCs) took longer to reset. This underlines the need for testing the effects of synchronizers on both the central and peripheral clocks. Glucocorticoids display circadian rhythms controlled by the central clock and are thought to act as synchronizers of rodent peripheral clocks. In the present study, we tested whether the human central and peripheral clocks were sensitive to exogenous glucocorticoids (Cortef) administered in the late afternoon. We showed that 20 mg Cortef taken orally acutely increased PER1 expression in PBMC peripheral clocks. After 6 d of Cortef administration, the phases of central markers were not affected, whereas those of PER2-3 and BMAL1 expression in PBMCs were shifted by ?9.5-11.5 h. These results demonstrate, for the first time, that human peripheral clocks are entrained by glucocorticoids. Importantly, they suggest innovative interventions for shift workers and jet-lag travelers, combining synchronizing agents for the central and peripheral clocks.-Cuesta, M., Cermakian, N., Boivin, D. B. Glucocorticoids entrain molecular clock components in human peripheral cells. PMID:25500935

Cuesta, Marc; Cermakian, Nicolas; Boivin, Diane B

2015-04-01

430

Circadian clock proteins regulate neuronal redox homeostasis and neurodegeneration  

PubMed Central

Brain aging is associated with diminished circadian clock output and decreased expression of the core clock proteins, which regulate many aspects of cellular biochemistry and metabolism. The genes encoding clock proteins are expressed throughout the brain, though it is unknown whether these proteins modulate brain homeostasis. We observed that deletion of circadian clock transcriptional activators aryl hydrocarbon receptor nuclear translocator–like (Bmal1) alone, or circadian locomotor output cycles kaput (Clock) in combination with neuronal PAS domain protein 2 (Npas2), induced severe age-dependent astrogliosis in the cortex and hippocampus. Mice lacking the clock gene repressors period circadian clock 1 (Per1) and period circadian clock 2 (Per2) had no observed astrogliosis. Bmal1 deletion caused the degeneration of synaptic terminals and impaired cortical functional connectivity, as well as neuronal oxidative damage and impaired expression of several redox defense genes. Targeted deletion of Bmal1 in neurons and glia caused similar neuropathology, despite the retention of intact circadian behavioral and sleep-wake rhythms. Reduction of Bmal1 expression promoted neuronal death in primary cultures and in mice treated with a chemical inducer of oxidative injury and striatal neurodegeneration. Our findings indicate that BMAL1 in a complex with CLOCK or NPAS2 regulates cerebral redox homeostasis and connects impaired clock gene function to neurodegeneration. PMID:24270424

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

2013-01-01

431

Regulated DNA Methylation and the Circadian Clock: Implications in Cancer  

PubMed Central

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

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

2014-01-01

432

Tissue-specific clocks in Arabidopsis show asymmetric coupling  

PubMed Central

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

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

2014-01-01

433

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

NASA Astrophysics Data System (ADS)

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

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

1993-07-01

434

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

NASA Technical Reports Server (NTRS)

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

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

1993-01-01

435

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

NASA Astrophysics Data System (ADS)

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

Tang, Baitian; Worthey, Guy

2015-01-01

436

Case Study of Solar Wind and IMF Influence on Ionospheric Outflow  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

437

Carbon-Enhanced Hyper-metal-poor Stars and the Stellar IMF at Low Metallicity  

E-print Network

The two known ``hyper-metal-poor'' (HMP) stars, HE0107-5240 and HE1327-2326, have extremely high enhancements of the light elements C, N, and O relative to Fe and appear to represent a statistically significant excess population relative to the halo metallicity distribution extrapolated from [Fe/H] > -3. This study weighs the available evidence for and against three hypothetical origins for these stars: (1) that they formed from gas enriched by a primordial ``faint supernova'', (2) that they formed from gas enriched by core-collapse supernovae and C-rich gas ejected in rotation-driven winds from massive stars, and (3) that they formed as the low-mass secondaries in binary systems at Z ~ 10^{-5.5} Zsun and acquired their light-element enhancements from an intermediate-mass companion as it passed through an AGB phase. The observations interpreted here, especially the depletion of lithium seen in HE1327-2326, favor the binary mass-transfer hypothesis. If HE0107-5240 and HE1327-2326 formed in binary systems, the statistically significant absence of isolated and/or C-normal stars at similar [Fe/H] implies that low-mass stars could form at that metallicity, but that masses M ~< 1.4 Msun were disfavored in the IMF. This result is also explained if the abundance-derived top-heavy IMF for primordial stars persists to [Fe/H] ~ -5.5. This finding indicates that low-mass star formation was possible at extremely low metallicity, and that the typical stellar mass may have had a complex dependence on metallicity rather than a sharp transition driven solely by gas cooling.

Jason Tumlinson

2007-07-05

438

The suprachiasmatic nuclei as a seasonal clock.  

PubMed

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

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

2014-11-20

439

Molecular Clock on a Neutral Network  

NASA Astrophysics Data System (ADS)

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.

Raval, Alpan

2007-09-01

440

An Iodine Fluorescence Quenching Clock Reaction  

NASA Astrophysics Data System (ADS)

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

Weinberg, Richard B.

2007-05-01

441

Analysis of atom-interferometer clocks  

E-print Network

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

Peil, Steven

2014-01-01

442

Frequency measurements of cold-atom clocks  

NASA Astrophysics Data System (ADS)

The frequency comb created by a femtosecond mode-locked laser and a microstructured optical fiber has been used to phase coherently measure the frequencies of the laser-cooled Hg+ and Ca optical standards with unprecedented precision. For the Hg+ standard the statistical uncertainty in the measurement is essentially limited by our knowledge of the SI second at 2e-15. The high precision and high demonstrated stability of the standards combined with the straightforward femtosecond-laser-based clockwork suggest Hg+ and Ca as excellent references for future all-optical clocks. Indeed, we have recently demonstrated an optical clock based on a single Hg+ ion reference which employs the femtosecond-laser-based clockwork to divide the stable optical frequency down to the microwave regime.

Diddams, Scott A.

2001-04-01

443

Optimal Implementations for Reliable Circadian Clocks  

NASA Astrophysics Data System (ADS)

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

Hasegawa, Yoshihiko; Arita, Masanori

2014-09-01

444

Clock-Driven Quantum Thermal Engines  

E-print Network

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

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

2014-12-03

445

Metabolism and the Circadian Clock Converge  

PubMed Central

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

Eckel-Mahan, Kristin

2013-01-01

446

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.

447

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

448

Optimal Prediction of Clocks from Finite Data  

NASA Technical Reports Server (NTRS)

This talk is about optimal linear prediction of processes with stationary dth increments, which serve as a class of models for random clock disturbances. The predictor is obtained by orthogonal projection on the affine space of estimators whose errors are invariant to additive polynomials of degree < d. The projection conditions give a system of linear equations thatcan be solved straightforwardly for the regression coefficients. If the data are equally spaced, then the predictor can be obtained by an extension of Levinson's algorithm.

Greenhall, Charles A.

2005-01-01

449

Intense, Narrow Atomic-Clock Resonances  

Microsoft Academic Search

We present experimental and theoretical results showing that magnetic resonance transitions from the ``end'' sublevels of maximum or minimum spin in alkali-metal vapors are a promising alternative to the conventional 0-0 transition for small-size gas-cell atomic clocks. For these ``end resonances,'' collisional spin-exchange broadening, which often dominates the linewidth of the 0-0 resonance, decreases with increasing spin polarization and vanishes

Y.-Y. Jau; A. B. Post; N. N. Kuzma; A. M. Braun; M. V. Romalis; W. Happer

2004-01-01

450

A Manufacturable Chip-Scale Atomic Clock  

Microsoft Academic Search

Several factors are converging to enable atomic clocks to be manufactured with very small dimensions and run at low operating power. MOEMS technology, high-speed vcsels, microelectronics, wafer-scale packaging, and the all-optical CPT method of exciting atomic transitions are key ingredients in the quest to make precision time-keeping devices with chip-scale dimensions. In this paper we report on the design and

D. W. Youngner; L. Lust; D. R. Carlson; S. T. Lu; L. J. Forner; H. M. Chanhvongsak; T. D. Stark

2007-01-01

451

Atomic clocks with suppressed blackbody radiation shift.  

PubMed

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

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

2011-07-15

452

Radium single-ion optical clock  

E-print Network

We explore the potential of the electric quadrupole transitions $7s\\,^2S_{1/2}$ - $6d\\,^2D_{3/2}$, $6d\\,^2D_{5/2}$ in radium isotopes as single-ion optical frequency standards. The frequency shifts of the clock transitions due to external fields and the corresponding uncertainties are calculated. Several competitive $^A$Ra$^+$ candidates with $A=$ 223 - 229 are identified. In particular, we show that the transition $7s\\,^2S_{1/2}\\,(F=2,m_F=0)$ - $6d\\,^2D_{3/2}\\,(F=0,m_F=0)$ at 828 nm in $^{223}$Ra$^+$, with no linear Zeeman and electric quadrupole shifts, stands out as a relatively simple case, which could be exploited as a compact, robust, and low-cost atomic clock operating at a fractional frequency uncertainty of $10^{-17}$. With more experimental effort, the $^{223,225,226}$Ra$^+$ clocks could be pushed to a projected performance reaching the $10^{-18}$ level.

Versolato, O O; Jungmann, K; Timmermans, R G E; Willmann, L; Wilschut, H W

2011-01-01

453

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

454

Viewing angle changeable display  

NASA Astrophysics Data System (ADS)

Viewing angle changeable display can change the display viewing angle as needed: In the public place the display could have a narrow viewing angle for privacy, while in the private place the displays could have a wide viewing angle for the convenience of the operation and better viewing experience. This article propose a novel adjustable optical transmission device to realize the viewing angle changes for LCD by using the principle of guest- host effect of liquid crystal. The major technology is to insert a special equipment between the backlight and the LCD, through which the backlight will display either parallel or scattered features to get an either narrow or wide viewing angle. The equipment is an adjustable transmission cell (ATC) which is actually a black G-H LC cell. This ATC is the main focus of our invention. The ATC consists of a polarizer sheet and a special guest-host liquid crystal device filled with the two-phase dye (called as GH-LC in this report), to achieve the viewing angle change in the LCD. When an electrical field charges to the ATC, only the so-called near-axis lights can pass through the ATC within a relatively small angle, while the other scattered lights are absorbed sequentially by GH-LC and the polarizer sheet. On the other hand, when there is no electrical charge to the ATC, the cell behaves like a normal polarizer; and the scattered light can pass through the cell and polarizer in a normal way. This paper describes the principle and structure of the device, applies the electric field on the sample to observe the electro-optical properties, combine the theoretical and experimental research, getting the viewing angle effects of the display.

Leng, Jinbi; Huang, Ziqiang; Yang, Wenjun; Chen, Xiaoxi

2010-10-01

455

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

E-print Network

Cold Atoms and Stable Lasers: The Clocks of the Future Today Leo Hollberg National Institute laser and length metrology Richard Fox #12;Types of Clocks Ruler Clock Decay Stable Oscillator Atomic 158 Counter Generic Atomic Clock Atoms #12;Atomic Beam Clock Ramsey Method Cs Signal # of Atoms d

Van Stryland, Eric

456

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

457

Laser angle sensor development  

NASA Technical Reports Server (NTRS)

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

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

1980-01-01

458

Clock Auto-synchronizing Method for BES III ETOF Upgrade  

E-print Network

An automatic clock synchronizing method implemented in field programmable gate array (FPGA) is proposed in this paper. It is developed for the clock system which will be applied in the end-cap time of flight (ETOF) upgrade of the Beijing Spectrometer (BESIII). In this design, an FPGA is used to automatically monitor the synchronization circuit and deal with signals coming from external clock synchronization circuit. By testing different delay time of the detection signal and analyzing state signals returned, the synchronization windows will be found automatically in FPGA. The new clock system not only retains low clock jitter which is less than 20ps root mean square (RMS), but also demonstrates automatic synchronization to the beam bunches. So far, the clock auto-synchronizing function has been working successfully under a series of tests. It will greatly simplify the system initialization and maintenance in the future.

Si-Yu, Wang; Shu-Bin, Liu; Qi, An

2015-01-01

459

Clock Auto-synchronizing Method for BES III ETOF Upgrade  

E-print Network

An automatic clock synchronizing method implemented in field programmable gate array (FPGA) is proposed in this paper. It is developed for the clock system which will be applied in the end-cap time of flight (ETOF) upgrade of the Beijing Spectrometer (BESIII). In this design, an FPGA is used to automatically monitor the synchronization circuit and deal with signals coming from external clock synchronization circuit. By testing different delay time of the detection signal and analyzing state signals returned, the synchronization windows will be found automatically in FPGA. The new clock system not only retains low clock jitter which is less than 20ps root mean square (RMS), but also demonstrates automatic synchronization to the beam bunches. So far, the clock auto-synchronizing function has been working successfully under a series of tests. It will greatly simplify the system initialization and maintenance in the future.

Wang Si-Yu; Cao Ping; Liu Shu-Bin; An Qi

2015-03-09

460

Wetting and Contact Angle  

NSDL National Science Digital Library

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

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

461

Higher Pole Linear Traps for Atomic Clock Applications  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

462

OPTICAL METROLOGY AND QUANTUM FREQUENCY STANDARDS: Femtosecond optical clock  

Microsoft Academic Search

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

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

2004-01-01

463

Integrated power clock generators for low energy logic  

Microsoft Academic Search

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

D. Maksimovic; V. G. Oklobdzija

1995-01-01

464

Daily coordination of cancer growth and circadian clock gene expression  

Microsoft Academic Search

Background.Circadian coordination in mammals is accomplished, in part, by coordinate, rhythmic expression of a series of circadian clock genes in the central clock within the suprachiasmatic nuclei (SCN) of the hypothalamus. These same genes are also rhythmically expressed each day within each peripheral tissue.Methods.We measured tumor size, tumor cell cyclin E protein, tumor cell mitotic index, and circadian clock gene

Shaojin You; Patricia A. Wood; Yin Xiong; Minoru Kobayashi; Jovelyn Du-Quiton; William J. M. Hrushesky

2005-01-01

465

Ground control system for the midcourse space experiment UTC clock  

NASA Technical Reports Server (NTRS)

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

Dragonette, Richard

1994-01-01

466

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

SciTech Connect

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

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

2013-01-01

467

Micromagic Clock: Microwave Clock Based on Atoms in an Engineered Optical Lattice  

SciTech Connect

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

Beloy, K.; Derevianko, A.; Dzuba, V. A.; Flambaum, V. V. [Department of Physics, University of Nevada, Reno, Nevada 89557 (United States); School of Physics, University of New South Wales, Sydney, 2052 (Australia)

2009-03-27

468

'Magic Angle Precession'  

SciTech Connect

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

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

2008-01-21

469

On-Line Schemes For Computing Rotation Angles For SVDS  

NASA Astrophysics Data System (ADS)

Two floating-point radix-2 schemes using on-line arithmetic for implementing the direct two-angle method for SVDs are presented. The first scheme is an on-line variant of the cosine/sine approach and is the fastest of the schemes considered: it performs the 2x2 SVD step in about 2n clock cycles. However, it requires a relatively large number of modules; this number is reduced when some modules are reused, resulting in a time of 3n clock cycles. The number of modules of this on-line version is still larger than that of the conventional one, but this is compensated by the smaller number of bit-slices per module and by the digit-serial communication among modules. The corresponding speed-up ratios are of 5 and 3 with respect to a conventional arithmetic implementation. The second scheme uses an on-line CORDIC approach and performs the 2x2 SVD in about 7n clock cycles and is advantageous because it is more time-area efficient. It results in a speed-up of about 2.5 with respect to the conventional CORDIC implementation.

Ercegovac, Milos D.; Lang, Tomas

1988-01-01

470

On chip clock synchronization for large digital systems  

E-print Network

is distributed to the various elements using such an architecture. This type of network has been successfully used in the Alpha chip [3]. A large buffer is used to drive a single wire laid across the chip. Several of the buffer ? wire are connected in Vin 1... ' A Metal 2 Metal 3 B , Clock Drivers Figure 3. Single Wire Clock Network. on the alpha chip indicate that the skew increases exponentially as the size of the chip grows. 1. 4 H ? Tree Clock Distribution The H ? tree clock distribution...

Brueske, Daniel

1994-01-01

471

Continuous Nondemolition Measurement of the Cs Clock Transition Pseudospin  

SciTech Connect

We demonstrate a weak continuous measurement of the pseudospin associated with the clock transition in a sample of Cs atoms. Our scheme uses an optical probe tuned near the D{sub 1} transition to measure the sample birefringence, which depends on the z component of the collective pseudospin. At certain probe frequencies the differential light shift of the clock states vanishes, and the measurement is nonperturbing. In dense samples the measurement can be used to squeeze the collective clock pseudospin and has the potential to improve the performance of atomic clocks and interferometers.

Chaudhury, Souma; Smith, Greg A.; Schulz, Kevin; Jessen, Poul S. [College of Optical Sciences, University of Arizona, Tucson, Arizona 85721 (United States)

2006-02-03

472

Prospects for Optical Clocks with a Blue-Detuned Lattice  

SciTech Connect

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

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

2009-02-13

473

Clock distribution and synchronization in large digital systems  

E-print Network

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

Hung, Tzu-Chien

1991-01-01

474

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

475

Clocks And Dynamics In Quantum Mechanics  

E-print Network

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

Michael York

2014-07-11

476

Using Inscribed Angles and Polygons  

NSDL National Science Digital Library

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

Mrs. Neubert

2011-03-10

477

Laser Cooled Atomic Clocks in Space  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

478

Comparisons of Synchronous-Clocking SFQ Adders  

NASA Astrophysics Data System (ADS)

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

Takagi, Naofumi; Tanaka, Masamitsu

479

Clock tree synthesis for prescribed skew specifications  

E-print Network

. : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 8 Examples of merging subtrees without wire snaking in (a) and with wire snaking when delay-target tj at vj is signi?cantly greater than delay-target tk at vk in (b). : : : : : : : : : : : : : : : : : : : : 12 9 Construction of merging segment with...6 S5 S2 S1 S2 S6 SOURCE S5 S3 Fig. 4. An example of balanced bu?er insertion (a) abstract tree; (b) physical tree. 9 CHAPTER II PRELIMINARY Same as other clock routing works, we adopt the Elmore delay model for delay com- putation [25]. The wire cost...

Chaturvedi, Rishi

2005-08-29

480

High-Accuracy Measurement of Atomic Polarizability in an Optical Lattice Clock  

NASA Astrophysics Data System (ADS)

Presently, the Stark effect contributes the largest source of uncertainty in a ytterbium optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock’s sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels ?clock=36.2612(7)kHz(kV/cm)-2. The clock’s uncertainty due to room temperature blackbody radiation is reduced by an order of magnitude to 3×10-17.

Sherman, J. A.; Lemke, N. D.; Hinkley, N.; Pizzocaro, M.; Fox, R. W.; Ludlow, A. D.; Oates, C. W.

2012-04-01

481

What's the Angle?  

NSDL National Science Digital Library

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

482

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

E-print Network

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

Lars Mattsson

2008-08-15

483

Velocity response curves demonstrate the complexity of modeling entrainable clocks.  

PubMed

Circadian clocks are biological oscillators that regulate daily behaviors in organisms across the kingdoms of life. Their rhythms are generated by complex systems, generally involving interlocked regulatory feedback loops. These rhythms are entrained by the daily light/dark cycle, ensuring that the internal clock time is coordinated with the environment. Mathematical models play an important role in understanding how the components work together to function as a clock which can be entrained by light. For a clock to entrain, it must be possible for it to be sped up or slowed down at appropriate times. To understand how biophysical processes affect the speed of the clock, one can compute velocity response curves (VRCs). Here, in a case study involving the fruit fly clock, we demonstrate that VRC analysis provides insight into a clock?s response to light. We also show that biochemical mechanisms and parameters together determine a model?s ability to respond realistically to light. The implication is that, if one is developing a model and its current form has an unrealistic response to light, then one must reexamine one?s model structure, because searching for better parameter values is unlikely to lead to a realistic response to light. PMID:25193284

Taylor, Stephanie R; Cheever, Allyson; Harmon, Sarah M

2014-12-21

484

Environmental stimulus perception and control of circadian clocks  

Microsoft Academic Search

Circadian rhythms are regulated by clocks located in specific structures of the central nervous system, such as the suprachiasmatic nucleus (SCN) in mammals, and by peripheral oscillators present in various other tissues. Recent discoveries have elucidated the control of central and peripheral clocks by environmental signals. The major synchroniser in animals is light. In mammals, a subset of retinal ganglion

Nicolas Cermakian; Paolo Sassone-Corsi

2002-01-01

485

Clocked quantum-dot cellular automata shift register  

Microsoft Academic Search

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

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

2003-01-01

486

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

E-print Network

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

487

General framework for removal of clock network pessimism  

Microsoft Academic Search

The paper presents a simple yet powerful general theoretical framework and efficient implementation for removal of clock network timing pessimism. We address pessimism in static timing analysis (STA) tools caused by considering delay variation along common segments of clock paths. The STA tools compute setup (hold) timing slack based on conservative combinations of late (early) launching and early (late) capturing

Jindrich Zejda; Paul Frain

2002-01-01

488

Local receptors as novel regulators for peripheral clock expression  

PubMed Central

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

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

2014-01-01

489

A mathematical model for the atomic clock error  

Microsoft Academic Search

A mathematical model for the clock phase and frequency deviation based on the theory of stochastic differential equations (SDEs) is discussed. In particular, we consider a model that includes what are called the `white and random walk frequency noises' in time metrology, which give rise in a mathematical context to a Wiener and an integrated Wiener process on the clock

L. Galleani; L. Sacerdote; P. Tavella; C. Zucca

2003-01-01

490

Detection of Anomalies in the Behavior of Atomic Clocks  

Microsoft Academic Search

In this paper, the problem of identifying variations in the nature of atomic clock noise is addressed. Two methods are proposed. One method is based on a generalized likelihood ratio test (GLRT), and the other is based on the dynamic Allan variance (DAVAR), which is a representation of the instantaneous clock stability that is able to point out possible nonstationary

Emilia Nunzi; Lorenzo Galleani; Patrizia Tavella; Paolo Carbone

2007-01-01

491

A Heuristic Model of Long-Term Atomic Clock Behavior  

Microsoft Academic Search

Summary A class of conceptually simple models for the long-term frequency variations of atomic clocks is presented. The basic model simulates the average fractional frequency deviation of a frequency standard as the sum of a normally distributed random variable, E and a random variable, l~ , which represents the spontaneous changes in the mean frequency of an atomic t clock

D. B. Percival

1976-01-01

492

Atomic clocks: new prospects in metrology and geodesy  

E-print Network

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

Pacôme Delva; Jérôme Lodewyck

2013-08-29

493

Nuclear magnetic resonance implementation of a quantum clock synchronization algorithm  

SciTech Connect

The quantum clock synchronization (QCS) algorithm proposed by Chuang [Phys. Rev. Lett. 85, 2006 (2000)] has been implemented in a three qubit nuclear magnetic resonance quantum system. The time difference between two separated clocks can be determined by measuring the output states. The experimental realization of the QCS algorithm also demonstrates an application of the quantum phase estimation.

Zhang Jingfu; Long, G.C; Liu Wenzhang [Key Laboratory For Quantum Information and Measurements, Tsinghua University, Beijing, 100084 (China); Department of Physics, Tsinghua University, Beijing 100084 (China); Deng Zhiwei [Testing and Analytical Center, Beijing Normal University, Beijing, 100875 (China); Lu Zhiheng [Department of Physics, Beijing Normal University, Beijing, 100875 (China)

2004-12-01

494

Atomic-based stabilization for laser-pumped atomic clocks  

Microsoft Academic Search

We describe a novel technique for stabilizing frequency shifts in laser-interrogated vapor-cell atomic clocks. The method suppresses frequency shifts due to changes in the laser frequency, intensity, and modulation index as well as atomic vapor density. The clock operating parameters are monitored by using the atoms themselves, rather than by using conventional schemes for laser frequency and cell temperature control.

V. Gerginov; V. Shah; S. Knappe; L. Hollberg; J. Kitching

2006-01-01

495

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