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1

EINSTein  

NASA Astrophysics Data System (ADS)

Artificial Life techniques—specifically, multiagent-based models and evolutionary learning algorithms—provide a powerful new approach to understanding some of the fundamental processes of war. This chapter introduces a simple artificial “toy model” of combat called EINSTein. EINSTein is designed to illustrate how certain aspects of land combat can be viewed as self-organized, emergent phenomena resulting from the dynamical web of interactions among notional combatants. EINSTein's bottom-up, synthesist approach to the modeling of combat stands in stark contrast to the more traditional top-down, or reductionist, approach taken by conventional military models, and it represents a step toward developing a complex systems theoretic toolbox for identifying, exploring, and possibly exploiting self-organized, emergent collective patterns of behavior on the real battlefield. A description of the model is provided, along with examples of emergent spatial patterns and behaviors.

Ilachinski, Andrew

2

Maximum Entropy Eddington Factors.  

National Technical Information Service (NTIS)

A technique from statistical mechanics is applied to the problem of determining the most probable value of the Eddington tensor given the zeroth and first moment of the intensity. The result is applicable to two- and three-dimensional configurations and i...

G. N. Minerbo

1977-01-01

3

Surface Singularities in Eddington-Inspired Born-Infeld Gravity  

NASA Astrophysics Data System (ADS)

Eddington-inspired Born-Infeld gravity was recently proposed as an alternative to general relativity that offers a resolution of spacetime singularities. The theory differs from Einstein’s gravity only inside matter due to nondynamical degrees of freedom, and it is compatible with all current observations. We show that the theory is reminiscent of Palatini f(R) gravity and that it shares the same pathologies, such as curvature singularities at the surface of polytropic stars and unacceptable Newtonian limit. This casts serious doubt on its viability.

Pani, Paolo; Sotiriou, Thomas P.

2012-12-01

4

Surface singularities in Eddington-inspired Born-Infeld gravity.  

PubMed

Eddington-inspired Born-Infeld gravity was recently proposed as an alternative to general relativity that offers a resolution of spacetime singularities. The theory differs from Einstein's gravity only inside matter due to nondynamical degrees of freedom, and it is compatible with all current observations. We show that the theory is reminiscent of Palatini f(R) gravity and that it shares the same pathologies, such as curvature singularities at the surface of polytropic stars and unacceptable Newtonian limit. This casts serious doubt on its viability. PMID:23368444

Pani, Paolo; Sotiriou, Thomas P

2012-12-21

5

Eddington's Theory of Gravity and Its Progeny  

NASA Astrophysics Data System (ADS)

We resurrect Eddington’s proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington’s theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe.

Bañados, Máximo; Ferreira, Pedro G.

2010-07-01

6

Comparison of the Kepler and Eddington Missions  

NASA Technical Reports Server (NTRS)

The Kepler and Eddington missions are spaceborne photometric missions with similar apertures. Both are capable of finding Earth-size extrasolar planets and both can detect p-mode oscillations in stars. The Kepler mission is optimized to find Earth-size planets in the habitability zone of Solar-like stars and does astroseismology only as incidental science. The Eddington mission appears to be optimized for astroseismology. The Kepler design provides a very large field of view, a low measurement cadence, a heliocentric orbit, and a long mission duration. The demand for a large field-of-view results in a Schmidt design with a massive corrector. However, the use of the corrector allows a 105 square degree FOV and thereby provides 15 times the number of stars at a given magnitude than does the optical design used in Eddington. Because Kepler stares at a single FOV throughout the mission, it does much less astroseismology than Eddington. Other comparisons are also discussed.

Borucki, William J.; DeVincenzi, D. (Technical Monitor)

2002-01-01

7

Chandrasekhar vs. Eddington - An Unanticipated Confrontation.  

ERIC Educational Resources Information Center

In the 1930s, Subrahmanyan Chandrasekhar found a fundamental parameter that determines the density of stars. Although recognized as a major discovery, it was generally unaccepted by astronomers because the work was ridiculed by a preeminent astronomer (Arthur Eddington). The controversy and current understanding of stellar evolution are discussed.…

Wali, Kameshwar C.

1982-01-01

8

Eddington's theory of gravity and its progeny.  

PubMed

We resurrect Eddington's proposal for the gravitational action in the presence of a cosmological constant and extend it to include matter fields. We show that the Newton-Poisson equation is modified in the presence of sources and that charged black holes show great similarities with those arising in Born-Infeld electrodynamics coupled to gravity. When we consider homogeneous and isotropic space-times, we find that there is a minimum length (and maximum density) at early times, clearly pointing to an alternative theory of the big bang. We thus argue that the modern formulation of Eddington's theory, Born-Infeld gravity, presents us with a novel, nonsingular description of the Universe. PMID:20867432

Bañados, Máximo; Ferreira, Pedro G

2010-07-01

9

Compact stars in Eddington inspired gravity.  

PubMed

A new, Eddington inspired theory of gravity was recently proposed by Bañados and Ferreira. It is equivalent to general relativity in vacuum, but differs from it inside matter. This viable, one-parameter theory was shown to avoid cosmological singularities and turns out to lead to many other exciting new features that we report here. First, for a positive coupling parameter, the field equations have a dramatic impact on the collapse of dust, and do not lead to singularities. We further find that the theory supports stable, compact pressureless stars made of perfect fluid, which provide interesting models of self-gravitating dark matter. Finally, we show that the mere existence of relativistic stars imposes a strong, near optimal constraint on the coupling parameter, which can even be improved by observations of the moment of inertia of the double pulsar. PMID:21838345

Pani, Paolo; Cardoso, Vitor; Delsate, Térence

2011-07-15

10

BAL QSOs AND EXTREME UFOs: THE EDDINGTON CONNECTION  

SciTech Connect

We suggest a common physical origin connecting the fast, highly ionized winds (UFOs) seen in nearby active galactic nuclei (AGNs), and the slower and less ionized winds of broad absorption line (BAL) QSOs. The primary difference is the mass-loss rate in the wind, which is ultimately determined by the rate at which mass is fed toward the central supermassive black hole (SMBH) on large scales. This is below the Eddington accretion rate in most UFOs, and slightly super-Eddington in extreme UFOs such as PG1211+143, but ranges up to {approx}10-50 times this in BAL QSOs. For UFOs this implies black hole accretion rates and wind mass-loss rates which are at most comparable to Eddington, giving fast, highly ionized winds. In contrast, BAL QSO black holes have mildly super-Eddington accretion rates, and drive winds whose mass-loss rates are significantly super-Eddington, and so are slower and less ionized. This picture correctly predicts the velocities and ionization states of the observed winds, including the recently discovered one in SDSS J1106+1939. We suggest that luminous AGNs may evolve through a sequence from BAL QSO through LoBAL to UFO-producing Seyfert or quasar as their Eddington factors drop during the decay of a bright accretion event. LoBALs correspond to a short-lived stage in which the AGN radiation pressure largely evacuates the ionization cone, but before the large-scale accretion rate has dropped to the Eddington value. We show that sub-Eddington wind rates would produce an M-{sigma} relation lying above that observed. We conclude that significant SMBH mass growth must occur in super-Eddington phases, either as BAL QSOs, extreme UFOs, or obscured from direct observation.

Zubovas, Kastytis; King, Andrew, E-mail: kastytis.zubovas@ftmc.lt [Theoretical Astrophysics Group, University of Leicester, Leicester LE1 7RH (United Kingdom)

2013-05-20

11

BAL QSOs and Extreme UFOs: The Eddington Connection  

NASA Astrophysics Data System (ADS)

We suggest a common physical origin connecting the fast, highly ionized winds (UFOs) seen in nearby active galactic nuclei (AGNs), and the slower and less ionized winds of broad absorption line (BAL) QSOs. The primary difference is the mass-loss rate in the wind, which is ultimately determined by the rate at which mass is fed toward the central supermassive black hole (SMBH) on large scales. This is below the Eddington accretion rate in most UFOs, and slightly super-Eddington in extreme UFOs such as PG1211+143, but ranges up to ~10-50 times this in BAL QSOs. For UFOs this implies black hole accretion rates and wind mass-loss rates which are at most comparable to Eddington, giving fast, highly ionized winds. In contrast, BAL QSO black holes have mildly super-Eddington accretion rates, and drive winds whose mass-loss rates are significantly super-Eddington, and so are slower and less ionized. This picture correctly predicts the velocities and ionization states of the observed winds, including the recently discovered one in SDSS J1106+1939. We suggest that luminous AGNs may evolve through a sequence from BAL QSO through LoBAL to UFO-producing Seyfert or quasar as their Eddington factors drop during the decay of a bright accretion event. LoBALs correspond to a short-lived stage in which the AGN radiation pressure largely evacuates the ionization cone, but before the large-scale accretion rate has dropped to the Eddington value. We show that sub-Eddington wind rates would produce an M-? relation lying above that observed. We conclude that significant SMBH mass growth must occur in super-Eddington phases, either as BAL QSOs, extreme UFOs, or obscured from direct observation.

Zubovas, Kastytis; King, Andrew

2013-05-01

12

Variable Eddington Factors and Flux-Limiting Diffusion Coefficients.  

National Technical Information Service (NTIS)

Variable Eddington factors and flux limiting diffusion coefficients arise in two common techniques of closing the moment equations of transport. The first two moment equations of the full transport equation are still frequently used to solve many problems...

P. P. Whalen

1982-01-01

13

Optical intra-day variability timescales and black hole mass of the blazars  

NASA Astrophysics Data System (ADS)

In this paper, we have used optical intra-day variability archive data to calculate the central black hole masses and Eddington luminosities for nine blazars: 3C 66A, AO 0235+164, S5 0716+714, PKS 0735+178, OJ 287, 1215+303, 1216-010, 1308+326, PKS 1510-089, Mrk 501 and BL Lac using intra-day variability timescales and periodicity (if present). The calculated central black hole mass of these nine blazars using intra-day variability timescales are found to be in the range of 1.22-25.30 × 10 7 M ? and corresponding Eddington luminosity in the range of 1.58-32.88 × 10 45 erg s -1. The black hole mass and Eddington luminosity are in the range of 0.32-31.23 × 10 8 M ? and 1.23-31.20 × 10 46 erg s -1, respectively when optical Doppler factor is taken into account. The comparison show, our estimated values of black hole mass are consistent with earlier reported values. Periodicity were present in two blazars OJ 287 and 1216-010 which give the central black hole mass of these blazars in the range of 1.32-14.6 × 10 7 M ? and corresponding Eddington luminosity in the range of 1.60-19.0 × 10 45 erg s -1, respectively.

Gupta, S. P.; Pandey, U. S.; Singh, K.; Rani, B.; Pan, J.; Fan, J. H.; Gupta, A. C.

2012-01-01

14

Non-linear Oscillations of Massive Stars Near the Eddington Limit  

NASA Astrophysics Data System (ADS)

The physics of massive star evolution, even on the main sequence is marred by uncertainties and hence, poorly understood. The focus of our work lies on the evolution of very massive stars on the main sequence when they approach the Eddington limit. Massive stars evolving near the Eddington limit are characterized by pronounced core-halo structures (Ishii et al. 1999) with extended low density envelopes accounting for even ~ 70% of the stellar radius, and density inversions (Petrovic et al. 2006, Graefener et al. 2011). These are ideal conditions or radial oscillations called ``strange modes'' (Glatzel 2004) which have very small growth times (~ dynamical timescale). We present non-linear calculations of these pulsations using a state-of-the-art one-dimensional hydrodynamic stellar evolution code (BEC) and latest input physics. The brightness perturbations caused as a result may relate to the microvariations observed in LBVs like AG Car (Lamers et al. 2004) or in supergiants like Deneb. Moreover, the feature of inflated envelopes coupled with the dynamic pulsations can play a major role in the modelling of mass transfer in very massive binary systems. We investigate how mass loss (through RLOF or wind) from such inflated stars may affect the envelope structure.

Sanyal, Debashis; Langer, Norbert

2013-06-01

15

Centenarian Einstein  

ScienceCinema

Commémoration de A.Einstein avec 4 orateurs pour honnorer sa mémoire: le prof.Weisskopf parlera de l'homme de science engagé, Daniel Amati du climat de la physique aux années 1920, Sergio Fubini de l'heure scientifique d'A.Einstein et le prof.Berob(?)

None

2011-04-25

16

Timescales of DNAPL migration  

NASA Astrophysics Data System (ADS)

Dense, non-aqueous phase liquids such as chlorinated solvents, PCB oils, creosote, and coal tar are common soil and groundwater contaminants at sites throughout the world. Current source zone remediation approaches typically assume that the residual and pooled DNAPL of interest is no longer migrating. The motivation for partial mass removal from a DNAPL source zone varies from site to site, but is often motivated by the belief that mass removal will lead to shorter steady-state plumes, shorter longevity of the source zone, and possibly aquifer restoration in a reasonable period of time. This talk addresses the issue of DNAPL migration timescales, and illustrates that certain types of DNAPL in certain geological environments are likely still migrating at some sites. The implication of this is that remedial strategies may need to be aimed at source zone stabilization in the short term, not partial mass removal for the reasons outlined above. The timescales of DNAPL migration at a site are influenced by many factors, including fluid properties, capillary properties, relative permeability characteristics, boundary conditions, and the volume and nature of release. Accurate prediction of DNAPL migration timescales requires a model that properly accounts for both the entry and terminal pressures in the capillary pressure -- saturation constitutive relationship, and properly accounts for relative permeability characteristics. This talk will address the above issues, and will present the results of laboratory experiments and numerical simulations to illustrate the timescale of DNAPL migration in a variety of environments including fractured rock, fractured clay, and unconsolidated porous media.

Kueper, B.; Gerhard, J.; Reynolds, D.

2003-04-01

17

Software for timescale applications  

NASA Astrophysics Data System (ADS)

This paper describes some of the design considerations behind the timescale transformation software provided by the International Astronomical Union's SOFA collaboration. The solution adopted by SOFA includes two-part Julian dates, to safeguard precision, and individual treatment of specific transformations, rather than a single general-purpose routine. Correct handling of UTC leap seconds was a particular challenge.

Wallace, P. T.

2011-08-01

18

Software for timescale applications  

Microsoft Academic Search

This paper describes some of the design considerations behind the timescale transformation software provided by the International Astronomical Union's SOFA collaboration. The solution adopted by SOFA includes two-part Julian dates, to safeguard precision, and individual treatment of specific transformations, rather than a single general-purpose routine. Correct handling of UTC leap seconds was a particular challenge.

P. T. Wallace

2011-01-01

19

Celebrating Einstein  

NASA Astrophysics Data System (ADS)

The Gravity Group at Montana State University (MSU) hosted Celebrating Einstein, a free public arts and multimedia event celebrating Einstein and his ideas in Bozeman, Montana April 2-6, 2013. The products of our efforts are now available to any party interested in hosting a similar event. Celebrating Einstein is a truly interdisciplinary effort including art, film, dance, music, physics, history, and education. Events included a black hole immersive art installation, a series of public talks by physicists, and Einstein lessons in the public schools leading up to a live free public multimedia performance including a professional dance company, a live interview with a renowned physicist, and an original score composed for the MSU student symphony to be performed with an original film produced by the Science and Natural History film program at MSU. This project is funded by the Montana Space Grant Consortium, Montana State University, and the National Science Foundation.

Shapiro Key, Joey; Yunes, Nicolas

2013-04-01

20

Stellar Pulsation Theory From Arthur Stanley Eddington to Today  

NASA Astrophysics Data System (ADS)

(Abstract only) While one could question that Eddington was the pioneer in theoretical work directly addressing the pulsating variable stars, there is no doubt that his work in the first part of the 20th Century set the stage for a transformation of theoretical astrophysics. After Eddington (the 1940s to the present day) stellar pulsation theory evolved from analytic theory into the realm of computational physics. Starting from Eddington's formulation, the flexibility provided by numerical solutions enabled exploration of systematics of pulsating variable stars in vastly greater detail. In this talk, we will trace this development that led to theoretical explanations of period-luminosity relations, new mechanisms of pulsation driving, connections with mass loss and stellar hydrodyamics, and to modern asteroseismic probes of the Sun and the stars.

Kawaler, S. D.; Hansen, Carl J.

2012-06-01

21

Stellar Pulsation Theory from Arthur Stanley Eddington to Today  

NASA Astrophysics Data System (ADS)

While one could question that Eddington was the pioneer in theoretical work directly addressing the pulsating variable stars, there is no doubt that his work in the first part of the 20th Century set the stage for a transformation of theoretical astrophysics. After Eddington (the 1940s to the present day) stellar pulsation theory evolved from analytic theory into the realm of computational physics. Starting from Eddington's formulation, the flexibility provided by numerical solutions enabled exploration of systematics of pulsating variable stars in vastly greater detail. In this talk, we will trace this development that led to theoretical explanations of period-luminosity relations, new mechanisms of pulsation driving, connections with mass loss and stellar hydrodyamics, and to modern asteroseismic probes of the Sun and the stars.

Kawaler, Steven D.; Hansen, C. J.

2011-05-01

22

Einstein's meanders  

NASA Astrophysics Data System (ADS)

What does Einstein have to do with subduction? Good question. Peaceful Lake Budi, lying at the heart of an Indian reservation in the Deep South of Chile, had subsided by two meters in the 1960 mega-thrust earthquake. This unique South American salt lake was hiding an awful secret: it was actually an oxbow, not a lake. But Einstein had realized in 1926 that meanders are natural freaks. Rivers will not flow uphill, yet - he claimed - they don't flow down the path of steepest descent either. This anomaly was put at the doorstep of a weak Coriolis Force. Thus Einstein problematized the dilemma of the earth sciences. How can a non-force produce margin-parallel compression in a convergent margin where extension is expected? In fact, where does the energy for meander formation come from? Good question . . . Even Wikipedia knows that Coriolis is not a “force” but an “effect”. So is the obliquity of plate convergence in subduction. Where did Einstein err, and where was he a pioneer? Coastal ablation plus alternating subsidence and emergence in giant earthquakes may yield an answer. Einstein, A. (1926). Die Ursache der Maeanderbildung der Flusslaeufe und das sogenannte Baersche Gesetz, Naturwissenschaften, 14, fascicle II.

Lomnitz, C.

2007-05-01

23

A pulsar-based timescale  

NASA Astrophysics Data System (ADS)

I will demonstrate how pulsar observations can be used to develop a pulsar-based timescale that can be compared with terrestrial timescales. Using observations from the Parkes Pulsar Timing Array project, I will show that we can identify known issues with TAI and have a marginally significant detection of a discrepancy between our pulsar based timescale and BIPM2011.

Hobbs, George

2012-08-01

24

Einstein Light  

NSDL National Science Digital Library

This web site is a basic, non-mathematical introduction to relativity, built around the framework of Flash media files with narration and animations. Einstein Light was intended to serve a diverse range of users at a variety of levels. It explores concepts from Galileo, Newton, and Maxwell through Einstein and special relativity. The site also introduces modern topics such as binding energies in the nucleus and the relationship between gravity and quantum mechanics. Background information is provided in 30 detailed pages, organized by topic and level of mathematics required for understanding. Questions are also available to assess student comprehension.

Wolfe, Joe; Hatsidimitris, George

2007-12-08

25

Einstein's Gravity  

NSDL National Science Digital Library

In this lesson, students will read the 1919 edition of the Cosmic Times (see related resources) and respond by raising questions to be answered with further research. They will make a model of curved space to view the motion of spheres as explained by Albert Einstein's General Theory of Relativity. After presentations of their research to the class they will create an interview with Einstein. This activity is part of the Cosmic Times teachers guide and is intended to be used in conjunction with the 1919 Cosmic Times Poster.

26

Einstein's Relativity  

NSDL National Science Digital Library

These web pages contain material explaining Einstein's general and special theories of relativity. Gravity and warped spacetime are included, along with explanations of the impact on observational astronomy. This is part of Astronomy Notes, an educational resource for introductory astronomy classes.

Strobel, Nick

2004-06-13

27

BOOK REVIEW: Einsteins Kosmos. Untersuchungen zur Geschichte der Kosmologie Relativitatstheorie und zu Einsteins Wirken und Nachwirken  

NASA Astrophysics Data System (ADS)

This book collects about 15 papers (most of them by one single author) on Einstein and the history of general relativity (GR) and the foundations of relativistic cosmology. The matter not only deals with Einstein and his times, but also with pre-GR ideas, and with the interplay of Einstein and his colleagues (opposing as well as supporting personalities). As the title indicates, all papers are written in German, but they include comprehensive Abstracts both in German and English. The book is illustrated with quite a number classical - but also some far more original though not less beautiful - photographs and facsimiles of documents. The book is edited very well, though the style of references is not quite homogeneous. There is no Index. K. Hentschel covers Einstein's argumentation for the existence of graviational redshift, and the initial search for empirical support. The error analysis of observational evidence supporting relativistic light deflection is discussed in a paper by P. Brosche. In particular, H. Duerbeck and P. Flin - in their description of the life and work of Silberstein, who was quite sceptic on the significance of the observational verifications a la Eddington - include the transcription of two most revealing letters by Silberstein to Sommerfeld (1919) and to Einstein (1934). In the first letter, Silberstein clearly shows his scientific maturity and integrity by scrutinising the observational evidence supporting light deflection, presented at a joint meeting of the Royal Society and the Royal Astronomical Society. The second letter, which is more a personal letter, includes lots of political references and connotations. Some of Einstein's political views are also revealed by D.B. Herrmann on the basis of his own correspondence with E.G. Straus, a collaborator of Einstein's. In a consequent paper, S. Grundmann gives remarks on Herrmann's contribution and illustrates Einstein's attitude towards Marx, Engels, Lenin and Stalin. M. Schemmel discusses Schwarzschild's cosmological speculations, and wonders why some people do immediately grasp the meaning and consequence of newly proposed doctrines, whereas the bulk of the contemporaneous scientists respond in a rather low profile. T. Jung reviews Einstein's contribution to cosmology, leading to the Friedmann-Einstein and Einstein-de Sitter universes (with a detailed Appendix on the Friedmann-Lemaitre cosmology), and also presents the cosmological work of Selety, and his correspondence with Einstein. In a subsequent paper, H.-J. Schmidt comments on Einstein's criticism on de Sitter's solution of the Einstein field equations. Controversies with Einstein are elaborated by G. Singer (on Friedmann) and by K. Roessler (on Lemaitre). J. Renn and T. Sauer discuss Mandl's role in the publication history of Einstein's papers, notably Einstein's short paper on gravitational lensing. Finally, the book concludes with a contribution by D.B. Herrmann about the relationship between Einstein and Archenhold Observatory (where Einstein gave his first Berlin popular lecture in 1915), the transcription of H.-J. Treder's 1979 public address at the Einstein memorial plaque, and an inventory list of about 50 Einstein memorabilia - monuments, busts, plaques - compiled by W.R. Dick. This book is based on ideas approached in a historical context from the individual perspective of the authors. It is a real treasure trove of information and basic references on the history of GR, and it also covers quite some grounds with mathematical equations.

Sterken, C.; Duerbeck, H. W.; Dick, W. R.

2006-12-01

28

Beyond Einstein  

SciTech Connect

The National Academy of Sciences was commissioned in 2006 to report on how to restart the Beyond Einstein program, which includes missions to understand dark energy, test general relativity, and observe gravity waves from merging supermassive black holes. This colloquium by one of the members of the recently released Academy study will explain the research strategy that the report proposes and its implications for continued U.S. participation in the exploration of the universe.

Professor Joel Primack

2007-10-08

29

FOREWORD: Modern Applications of Timescales Modern Applications of Timescales  

Microsoft Academic Search

The development of the first atomic frequency standard by Louis Essen in the 1950s is at the origin of the adoption of the atomic definition of the SI second by the 13th General Conference on Weights and Measures in 1967 and the consequent adoption of the atomic timescale. After the short reign of ephemeris time as the world's reference timescale

E. F. Arias; W. Lewandowski

2011-01-01

30

Sources X super-Eddington dans les Galaxies Proches  

NASA Astrophysics Data System (ADS)

Un certain nombre de galaxies proches abritent, en dehors de leur noyau, des sources X extrêmement lumineuses qui, apparemment dépassent la limite d'Eddington d'un objet compact de quelques masses solaires. Nous avons réalisé une étude photométrique et spectroscopique d'un échantillon de ces sources X brillantes en utilisant pour cela le télescope de 193 cm de l'OHP, le CFHT et le NTT de l'ESO. Ceci nous a permis de mettre en évidence l'association d'une source X avec une nébuleuse hautement ionisée, il s'agit de la première identification optique d'une source X super-Eddington. cette découverte est un argument en faveur de l'existence de trous noirs de plusieurs dizaines de masses solaires dans les systèmes binaires. Nous avons également découvert des nébuleuses annulaires de quelques centaines de parsecs apparemment excitées par les sources X très lumineuses.

Mirioni, L.; Pakull, M. W.

2001-01-01

31

Timescales of Magma Residence  

NASA Astrophysics Data System (ADS)

The wide variety of approaches by which magma systems can now be imaged provide insights into the duration and dynamics of magma residence in the crust. Many steps may contribute to magma residence, including ascent and emplacement into regions of storage, and episodes of outright magma storage. It is still difficult to distinguish between the various contributions to magma residence and to compare the plumbing systems associated with different magmatic centers because constraints obtained by complementary approaches on single volcanoes are generally lacking. Another limitation of work to date is that most estimates for magma residence times are for volcanic rocks and may therefore preferentially image the most-fluid portions of a magma reservoir. That the various geochemical and geophysical approaches have fidelity for different aspects of a magmatic system is well demonstrated by the range of residence estimates obtained for magma associated with Kilauea. Nonetheless, estimates for magma residence times in mafic systems are on the order of a few thousand years at most and generally years to hundreds of years. These relatively short periods of basaltic residence could reflect the absence of shallow magma reservoirs or, where present, its small volume and/or high turnover rate. Andesitic to dacitic magmas associated with arc stratovolcanoes are complicated by magma recharge, crustal assimilation, and recycling and ascent-related resorption of crystals. Radiometric ages obtained for crystals can predate eruption considerably more than permitted by apparent crystal growth rates which, considered together with the 226Ra excesses of many arc magmas and their crystals, could require either frequent mixing and mingling between recharge melts and reservoir magmas and/or entrainment of crystals from stagnant, mush-dominated magma regimes. Moreover, to reconcile the timescales of years may require multiple magma domains to coevolve in limited geographical areas, as might occur in a subvolcanic plexus of dikes and sills. Concordance between ages of differentiation and of the onset of crystallization in more evolved magmas, and/or the magnitudes of 226Ra excesses, suggest that differentiation may occur rather rapidly (<10's of k.y.). Timescales for the generation of trachytes from their mafic precursors may be considerably longer (up to hundreds of k.y.) but it is difficult to partition the evolution from mafic to evolved compositions between differentiation, storage in a magma reservoir, and remelting of the underplated mafic magmas. Residence times of silicic magmas can be relatively long, from thousands to a few hundreds of thousands of years. It is possible, however, that once differentiated, silicic magmas solidify and are stored in the crust, only to be later remobilized by reheating. As with mafic magma centers, the same reservoir may be tapped repeatedly but silicic magma residence times seem to be dictated by when storage is interrupted by eruption rather than by the balance between supply and eruption. The several year to few thousand year residence times for the majority of magmas show that individual magma batches are very transient features of the ~0.5 to several m.y. life-spans of many individual volcanic and plutonic systems. Even the timeframes inferred for silicic magmas are short-lived with respect to repose intervals between the more voluminous silicic eruptions and therefore the duration of silicic activity at any particular volcanic system. The liquid (and mush) portions of reservoirs responsible for these magma batches may be equally ephemeral features or may be more longstanding because they are repeatedly renewed/replenished.

Reid, M. R.

2004-05-01

32

Relativistic Milne-Eddington-Type Solutions with a Variable Eddington Factor for Relativistic Plane-Parallel Flows  

NASA Astrophysics Data System (ADS)

Relativistic radiative transfer in a relativistic plane-parallel flow is examined in a fully special relativistic treatment. Under the assumption of a constant flow speed and using a variable Eddington factor, we analytically solve the relativistic moment equations in the comoving frame for several cases, such as the radiative equilibrium or local thermodynamical equilibrium, and obtain relativistic Milne-Eddington-type solutions. In all the cases, the solutions exhibit an exponential behavior on the optical depth; the solutions are expressed by the linear combination of the exponential terms. In addition, the optical depth ? in the exponential term is replaced by the apparent optical depth ? ?, where ? is a function of the flow speed v. This is the essential properties of the relativistic regime of the radiative transfer. In the case of the radiative equilibrium, the radiation energy density in the comoving frame approaches a constant value, while the radiative flux becomes zero as the optical depth increases. In addition, with uniform heating, the radiative quantity in the comoving frame generally decreases compared with that in the case without heating, whereas, if there is advection cooling, the radiative quantity generally increases. In the case of the local thermodynamic equilibrium, the radiative quantity approaches the LTE values as the optical depth increases.

Fukue, J.

2011-07-01

33

FOREWORD: Modern Applications of Timescales Modern Applications of Timescales  

NASA Astrophysics Data System (ADS)

The development of the first atomic frequency standard by Louis Essen in the 1950s is at the origin of the adoption of the atomic definition of the SI second by the 13th General Conference on Weights and Measures in 1967 and the consequent adoption of the atomic timescale. After the short reign of ephemeris time as the world's reference timescale from 1954 until 1967, Coordinated Universal Time (UTC), synchronized to universal time UT1, appeared as the best compromise for satisfying the requests of all users. At the moment of the discussion on the adoption of an atomic timescale to replace ephemeris time, the possibility of having both an astronomical time and an atomic time to serve different purposes was discussed. In the words of Essen [1], this 'would cause endless confusion as well as involving duplication of equipment'. Forty years after the adoption of the definition of Coordinated Universal Time at the International Telecommunication Union (ITU), we are close to the moment of making a decision on whether or not to decouple UTC from its tight link to the rotation of the Earth embodied in UT1. It has been a ten-year process of discussion, mainly at the ITU with the input of the International Astronomical Union, the BIPM, the Consultative Committee for Time and Frequency and other organizations. The majority opinion supported the change based on developers and users of systems that need time synchronization to a stable and continuous reference timescale; others insist on the necessity of keeping the leap-second strategy for serving some applications or just for tradition. It is our hope that, as happened in the seventies, the most appropriate definition to serve all modern applications will be adopted with the consensus of the different sectors. The redirection of international timekeeping from astronomy to metrology can be considered the benchmark that started the era of modern timescales, all based on atomic properties. The aim of this special issue of Metrologia is to review timescales in use today, either the internationally recognized references or those adapted to some specific applications, to discuss new and future developments and to present the sometimes complex procedures for making international recommendations. We are grateful to our colleagues who, without exception, accepted our invitation to contribute to this special issue. Reference Henderson D 2005 Metrologia 42 S4-29 The pdf file contains an appendix: "Glossary of acronyms related to timescales used in this issue".

Arias, E. F.; Lewandowski, W.

2011-08-01

34

Super-Eddington Atmospheres That Do Not Blow Away  

NASA Astrophysics Data System (ADS)

We show that magnetized, radiation-dominated atmospheres can support steady state patterns of density inhomogeneity that enable them to radiate at far above the Eddington limit without suffering mass loss. The inhomogeneities consist of periodic shock fronts bounding narrow, high-density regions, interspersed with much broader regions of low density. The flow of radiation avoids the dense regions, which are therefore weighed down by gravity, while gas in the low-density regions is slammed upward into the shock fronts by radiation force. As the wave pattern moves through the atmosphere, each parcel of matter alternately experiences upward and downward forces, which balance on average. We calculate the density structure and phase speed of the wave pattern and relate these to the density contrast and the factor by which the net radiation flux exceeds the Eddington limit. The presence of a magnetic field is essential for the existence of these flows since magnetic tension shares the competing forces between regions of different densities, preventing the atmosphere from blowing apart. There appears to be a broad family of modes propagating in arbitrary directions with respect to the direction of the mean magnetic field and exhibiting a range of density contrasts. While the transition from low to high density occurs through a strong shock, the gas must pass through a slow magnetosonic critical point in order to return to the low-density state. The flux of radiation escaping from the atmosphere exceeds the Eddington limit by a factor of order the square root of the ratio between maximum and minimum density. In principle, this factor can be as large as the ratio of magnetic pressure to mean gas pressure. Although the magnetic pressure must be large compared to the mean gas pressure in order to support a large density contrast, it need not be large compared to the radiation pressure. These highly inhomogeneous flows could represent the nonlinear development of the ``photon bubble'' instability discovered by Gammie. If they occur in nature, these structures could have an impact on our understanding of luminous systems such as accreting compact objects and very massive stars.

Begelman, Mitchell C.

2001-04-01

35

Evolution of anisotropies in Eddington-Born-Infeld cosmology  

SciTech Connect

Recently a Born-Infeld action for dark energy and dark matter that uses additional affine connections was proposed. At the background level, it was shown that the new proposal can mimic the standard cosmological evolution. In Bianchi cosmologies, contrary to the scalar field approach (e.g., Chaplygin gas), the new approach leads to anisotropic pressure, raising the issues of stability of the isotropic solution under anisotropic perturbations and, being stable, how the anisotropies evolve. In this work, the Eddington-Born-Infeld proposal is extended to a Bianchi type I scenario and residual post-inflationary anisotropies are shown to decay in time. Moreover, it is shown that the shears decay following a damped oscillatory pattern, instead of the standard exponential-like decay. Allowing for some fine-tuning on the initial conditions, standard theoretical bounds on the shears can be avoided.

Rodrigues, Davi C. [Departamento de Fisica, Universidad de Santiago de Chile, Casilla 307, Santiago (Chile) and Departamento de Fisica, P. Universidad Catolica de Chile, Casilla 306, Santiago (Chile)

2008-09-15

36

Genomic clocks and evolutionary timescales  

Microsoft Academic Search

For decades, molecular clocks have helped to illuminate the evolutionary timescale of life, but now genomic data pose a challenge for time estimation methods. It is unclear how to integrate data from many genes, each potentially evolving under a different model of substitution and at a different rate. Current methods can be grouped by the way the data are handled

S. Blair Hedges; Sudhir Kumar

2003-01-01

37

Spectral energy distribution of super-Eddington flows  

NASA Astrophysics Data System (ADS)

Spectral properties of super-Eddington accretion flows are investigated by means of a parallel line-of-sight calculation. The subjacent model, taken from the two-dimensional radiation hydrodynamic simulations by Ohsuga et al. (2005), consists of a disc accretion region and an extended atmosphere with high-velocity outflows. The non-grey radiative transfer equation is solved, including relativistic effects, by applying the flux-limited diffusion approximation. The calculated spectrum is composed of a thermal, blackbody-like emission from the disc which depends sensitively on the inclination angle, and of high-energy X-ray and gamma-ray emission from the atmosphere. We find mild beaming effects in the thermal radiation for small inclination angles. If we compare the face-on case with the edge-on case, the average photon energy is larger by a factor of ~1.7 due mainly to Doppler boosting, while the photon number density is larger by a factor of ~3.7 due mainly to anisotropic matter distribution around the central black hole. This gives an explanation for the observed X-ray temperatures of ULXs which are too high to be explained in the framework of intermediate-mass black holes. While the main features of the thermal spectral component are consistent with more detailed calculations of slim accretion discs, the atmosphere induces major changes in the high-energy part, which cannot be reproduced by existing models. We also conclude that, in order to interpret the observational data properly, simple approaches like the Eddington-Barbier approximation cannot be applied.

Heinzeller, D.; Mineshige, S.; Ohsuga, K.

2006-11-01

38

Einstein Books for Adults  

NSDL National Science Digital Library

This reference list has more than 15 books and articles on Einstein that are written for adults, including biographies and some of Einstein's own writings. For each title, the author's name, publisher, and publication date are included.

39

Einstein Equations and Electromagnetism.  

National Technical Information Service (NTIS)

Einstein's equations for infinitesimal gravitational fields are investigated from the standpoint of replacing Einstein's flat Minkowskian background space by a strongly agitated Riemannian lattice space, with the added demand that the perturbation field b...

C. Lanczos

1966-01-01

40

A Century of Einstein  

NSDL National Science Digital Library

This intriguing MSNBC website addresses how Einstein's theories still affect the world we live in today. Users can view a Macromedia Flash Player-enhanced slide show summarizing Einstein's life and major accomplishments. Visitors can download the five papers from 1905, Einstein's "miracle year." Students can find a helpful interactive module discussing the principles of relativity and its importance. The website discusses Einstein's personality and beliefs and hypothesizes how Einstein might have faired in today's world. Users can learn about the questions dealing with dark matter and dark energy that scientists are still trying to understand today.

41

Feedback systems and multiple time-scales  

NASA Technical Reports Server (NTRS)

A study is conducted of feedback design for systems with multiple time-scale structure uncovering an intrinsic time-scale structure for a state feedback system with full state output. From this a multiple time-scale asymptotic observer and a system with state feedback via a two time-scale asymptotic observer is considered. Finally more general results for a restricted class of systems are obtained.

Silva-Madriz, R.

1986-01-01

42

LOW-IONIZATION OUTFLOWS IN HIGH EDDINGTON RATIO QUASARS  

SciTech Connect

The broad Mg II {lambda}2800 doublet has been frequently studied in connection with its potentially important role as a virial estimator of black hole mass in high-redshift quasars. An important task, therefore, is the identification of any line components that are likely related to broadening by non-virial motions. High signal-to-noise median composite spectra (binned in the {sup f}our-dimensional eigenvector 1'' context of Sulentic et al.) were constructed for the brightest 680 Sloan Digital Sky Survey Data Release 7 quasars in the 0.4 {<=} z {<=} 0.75 range where both Mg II {lambda}2800 and H{beta} are recorded in the same spectra. Composite spectra representing 90% of the quasars confirm previous findings that FWHM(Mg II {lambda}2800) is about 20% narrower than FWHM(H{beta}). The situation is clearly different for the most extreme (Population A) sources, which are the highest Eddington radiators in the sample. In the median spectra of these sources, FWHM Mg II {lambda}2800 is equal to or greater than FWHM(H{beta}) and shows a significant blueshift relative to H{beta}. We interpret the Mg II {lambda}2800 blueshift as the signature of a radiation-driven wind or outflow in the highest accreting quasars. In this interpretation, the Mg II {lambda}2800 line width-affected by blueshifted emission-is unsuitable for virial mass estimation in Almost-Equal-To 10% of quasars.

Marziani, Paola [Also at INAF, Astronomical Observatory of Padova, Padova, Italy. (Italy)] [Also at INAF, Astronomical Observatory of Padova, Padova, Italy. (Italy); Sulentic, Jack W.; Plauchu-Frayn, Ilse; Del Olmo, Ascension, E-mail: paola.marziani@oapd.inaf.it [Instituto de Astrofisica de Andalucia, CSIC, E-18008 Granada (Spain)

2013-02-20

43

Einstein Homogeneous Riemannian Fibrations  

NASA Astrophysics Data System (ADS)

In this work we study the existence of homogeneous Einstein metrics on the total space of homogeneous fibrations such that the fibers are totally geodesic manifolds. We obtain the Ricci curvature of an invariant metric with totally geodesic fibers and some necessary conditions for such a metric to be Einstein in terms of Casimir operators. Some particular cases are studied, for instance, for normal base or fiber, symmetric fiber, Einstein base or fiber, for which the Einstein equations are manageable. We show the existence of new invariant Einstein metrics on homogeneous bisymmetric fibrations of maximal rank. For such spaces we describe explicitly the isotropy representation in terms subsets of roots and compute the eigenvalues of the Casimir operators of the fiber along the horizontal direction. Results for compact simply connected 4-symmetric spaces of maximal rank follow from this. Also, new invariant Einstein metrics are found on Kowalski n-symmetric spaces.

Araujo, Fatima

2009-05-01

44

STP Einstein Solids Program  

NSDL National Science Digital Library

The STP EinsteinSolids program displays the energy distribution of an Einstein solid in thermal contact with another Einstein solid. The purpose of this program is to explore the distribution of energy between two systems in thermal contact. The default state is two Einstein solids, system A and system B of with 4 particles each, and energies 10 and 2, respectively. Additional states and parameters can be specified using the Display|Switch GUI menu item. STP EinsteinSolids is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double clicking the stp_EinsteinSolids.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2008-05-28

45

A high Eddington-ratio, true Seyfert 2 galaxy candidate: implications for broad-line region models  

NASA Astrophysics Data System (ADS)

A bright, soft X-ray source was detected on 2010 July 14 during an XMM-Newton slew at a position consistent with the galaxy GSN 069 (z = 0.018). Previous ROSAT observations failed to detect the source and imply that GSN 069 is now ?240 times brighter than it was in 1994 in the soft X-ray band. Optical spectra (from 2001 to 2003) are dominated by unresolved emission lines with no broad components, classifying GSN 069 as a Seyfert 2 galaxy. We report here results from a ˜1 yr monitoring with Swift and XMM-Newton, as well as from new optical spectroscopy. GSN 069 is an unabsorbed, ultrasoft source in X-rays, with no flux detected above ˜1 keV. The soft X-rays exhibit significant variability down to time-scales of hundreds of seconds. The UV-to-X-ray spectrum of GSN 069 is consistent with a pure accretion disc model which implies an Eddington ratio ? ? 0.5 and a black hole mass of ? 1.2 × 106 M?. A new optical spectrum, obtained ˜3.5 months after the XMM-Newton slew detection, is consistent with earlier spectra and lacks any broad-line component. The lack of cold X-ray absorption and the short time-scale variability in the soft X-rays rule out a standard Seyfert 2 interpretation of the source. The present Eddington ratio of GSN 069 exceeds the critical value below which no emitting broad-line region (BLR) forms, according to popular models, so that GSN 069 can be classified as a bona-fide high Eddington-ratio true Seyfert 2 galaxy. We discuss our results within the framework of two possible scenarios for the BLR in AGN, namely the two-phase model (cold BLR clouds in pressure equilibrium with a hotter medium), and models in which the BLR is part of an outflow, or disc-wind. Finally, we point out that GSN 069 may be a member of a population of super-soft active galactic nuclei (AGN) whose spectral energy distribution is completely dominated by accretion disc emission, as it is the case in some black hole X-ray binary transients during their outburst evolution. The disc emission for a typical AGN with black hole mass of 107-108 M? does not enters the soft X-ray band, so that GSN 069-like objects with larger black hole mass (i.e. the bulk of the AGN population) are missed by current X-ray surveys, or misclassified as Compton-thick candidates. If the analogy between black hole X-ray binary transients and AGN holds, the lifetime of these super-soft states in AGN may be longer than 104 years, implying that the actual population of super-soft AGN may not be negligible, possibly contaminating the estimated fraction of heavily obscured AGN from current X-ray surveys.

Miniutti, G.; Saxton, R. D.; Rodríguez-Pascual, P. M.; Read, A. M.; Esquej, P.; Colless, M.; Dobbie, P.; Spolaor, M.

2013-08-01

46

A Limit Relation between Black Hole Mass and H? Width: Testing Super-Eddington Accretion in Active Galactic Nuclei  

NASA Astrophysics Data System (ADS)

We show that there is a limit relation between the black hole mass (MBH) and the width at half-maximum (?FWHM) of H? for active galactic nuclei (AGNs) with super-Eddington accretion rates. When a black hole has a super-Eddington accretion rate, the empirical relation derived from reverberation mapping can be applied in two possible ways. First, it reduces to a relation between the black hole mass and the size of the broad-line region because of photon-trapping effects inside the accretion disk. For the empirical reverberation relation of Kaspi et al., we obtain the limit relation MBH=(2.9-12.6)×106 [vFWHM/(103 km s-1)]6.67Msolar, called the Eddington limit. Second, the Eddington limit luminosity will be relaxed if the trapped photons can escape from the magnetized super-Eddington accretion disk via the photon bubble instability, and the size of the broad-line region will be enlarged according to the empirical reverberation relation, leading to a relatively narrow H? width. We call this the Begelman limit. Using this limit relation, we searched 164 AGNs for super-Eddington accretion. We find that most of them are well confined by the Eddington limit relation-that is, most have sub-Eddington accretion rates-but there are a handful of objects located between the Eddington and Begelman limit lines; they may be candidate super-Eddington accretors in a hybrid structure of photon trapping and photon bubble instability. The maximum H? width is in the range (3.0-3.8)×10 3 km s-1 for the most massive black holes with super-Eddington accretion rates among AGNs. We suggest that the FWHM(H?)-MBH relation is a reliable and convenient method to test whether a source is super-Eddington and useful to probe the structure of the super-Eddington accretion process.

Wang, Jian-Min

2003-06-01

47

Einstein in Time  

NSDL National Science Digital Library

This fun Web site is part of OLogy, where kids can collect virtual trading cards and create projects with them. Here, they are introduced to Einstein's scientific and humanitarian pursuits with two engaging, kid-friendly sections: Einstein in Time, a fascinating look at the major events in his life presented in a timeline and Everyday Einstein: Humanitarian, a quick overview of how he used his fame to draw attention to the things he believed in.

48

Neuromythology of Einstein's brain.  

PubMed

The idea that the brain of the great physicist Albert Einstein is different from "average" brains in both cellular structure and external shape is widespread. This belief is based on several studies examining Einstein's brain both histologically and morphologically. This paper reviews these studies and finds them wanting. Their results do not, in fact, provide support for the claim that the structure of Einstein's brain reflects his intellectual abilities. PMID:24836969

Hines, Terence

2014-07-01

49

RAPID COOLING OF THE NEUTRON STAR IN THE QUIESCENT SUPER-EDDINGTON TRANSIENT XTE J1701-462  

SciTech Connect

We present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the 2006-2007 outburst of the super-Eddington neutron star (NS) transient XTE J1701-462, as well as Chandra and XMM-Newton observations covering the first {approx_equal}800 days of the subsequent quiescent phase. The source transitioned quickly from active accretion to quiescence, with the luminosity dropping by over 3 orders of magnitude in {approx_equal}13 days. The spectra obtained during quiescence exhibit both a thermal component, presumed to originate in emission from the NS surface, and a non-thermal component of uncertain origin, which has shown large and irregular variability. We interpret the observed decay of the inferred effective surface temperature of the NS in quiescence as the cooling of the NS crust after having been heated and brought out of thermal equilibrium with the core during the outburst. The interpretation of the data is complicated by an apparent temporary increase in temperature {approx_equal}220 days into quiescence, possibly due to an additional spurt of accretion. We derive an exponential decay timescale of {approx_equal}120{sup +30}{sub -20} days for the inferred temperature (excluding observations affected by the temporary increase). This short timescale indicates a highly conductive NS crust. Further observations are needed to confirm whether the crust is still slowly cooling or has already reached thermal equilibrium with the core at a surface temperature of {approx_equal}125 eV. The latter would imply a high equilibrium bolometric thermal luminosity of {approx_equal}5 x 10{sup 33}ergs{sup -1} for an assumed distance of 8.8 kpc.

Fridriksson, Joel K.; Lewin, Walter H. G. [Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Homan, Jeroen [MIT Kavli Institute for Astrophysics and Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States); Wijnands, Rudy; Altamirano, Diego; Degenaar, Nathalie [Astronomical Institute 'Anton Pannekoek', University of Amsterdam, Science Park 904, 1098 XH, Amsterdam (Netherlands); Mendez, Mariano [Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700 AV, Groningen (Netherlands); Cackett, Edward M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Brown, Edward F. [Department of Physics and Astronomy, National Superconducting Cyclotron Laboratory, and Joint Institute for Nuclear Astrophysics, Michigan State University, East Lansing, MI 48824 (United States); Belloni, Tomaso M., E-mail: joelkf@mit.ed [INAF-Osservatorio Astronomico di Brera, Via E. Bianchi 46, I-23807 Merate (Italy)

2010-05-01

50

Einstein and Hilbert  

NASA Astrophysics Data System (ADS)

I will discuss the origins of their friendship, the strain put upon it in 1915 when Einstein felt that Hilbert was ``nostrifying'' [i.e., taking over and presenting as his own] some of Einstein's ideas about the general theory of relativity, and their ultimate reconciliation and lasting friendship. The nature of Hilbert's work on his own unified field theory program and its relation to Einstein's general relativity program will be considered, as will be Einstein's role in the curious ``battle of the frogs and mice,'' as he dubbed the controversy between Hilbert and Brouwer over the foundations of mathematics.

Stachel, John

2005-03-01

51

Generalized Einstein Relation in an aging colloidal glass  

NASA Astrophysics Data System (ADS)

We present an experimental investigation of the Generalized Einstein Relation (GER), a particular form of a fluctuation-dissipation relation, in an out-of-equilibrium visco-elastic fluid. Micrometer beads, used as thermometers, are immersed in an aging colloidal glass to provide both fluctuation and dissipation measurements. The deviations from the Generalized Einstein Relation are derived as a function of frequency and aging time. The observed deviations are interpreted as directly related to the change in the glass relaxation times with aging time. In our scenario, deviations are observed in the regime where the observation timescale is of the order of a characteristic relaxation time of the glass.

Abou, Bérengère; Gallet, François; Monceau, Pascal; Pottier, Noëlle

2008-06-01

52

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

53

Einstein and Boltzmann  

NASA Astrophysics Data System (ADS)

In 1916 Einstein published a remarkable paper entitled ``On the Quantum Theory of Radiation''ootnotetextA. Einstein ``On the Quantum theory of Radiation,'' Phys. Zeitschrift 18 (1917) 121. First printed in Mitteilungender Physikalischen Gesellschaft Zurich. No 18, 1916. Translated into English in Van der Waerden ``Sources of Quantum Mechanics'' (North Holland 1967) pp. 63-77. in which he obtained Planck's formula for black-body radiation by introducing a new statistical hypothesis for the emmision and absorption of electromagneic radiation based on discrete bundles of energy and momentum which are now called photons. Einstein radiation theory replaced Maxwell's classical theory by a stochastic process which, when properly interpreted, also gives well known statistics of massless particles with even spin.^2 This quantum distribution, however, was not discovered by Einstein but was communicated to him by Bose in 1924. Like Boltzmann's classical counterpart, Einstein's statistical theory leads to an irreversible approach to thermal equilibrium, but because this violates time reversal, Einstein theory can not be regarded as a fundamental theory of physical process.ootnotetextM. Nauenberg ``The evolution of radiation towards thermal equilibrium: A soluble model which illustrates the foundations of statistical mechanics,'' American Journal of Physics 72 (2004) 313 Apparently Einstein and his contemporaries were unaware of this problem, and even today this problem is ignored in contemporary discussions of Einstein's treatment of the black-body spectrum.

Nauenberg, Michael

2005-03-01

54

Einstein for Everyone  

SciTech Connect

Young Einstein was a rebel who seemed doomed to fail. How did he overcome rejection to become the most famous scientist in history? We will discuss and explain all his theories in plain English and without math, and we will discover how Einstein's achievements impact our lives through DVDs, GPS, iPods, computers and green energy.

Piccioni, Robert

2010-10-05

55

A NUMERICAL METHOD FOR STUDYING SUPER-EDDINGTON MASS TRANSFER IN DOUBLE WHITE DWARF BINARIES  

SciTech Connect

We present a numerical method for the study of double white dwarf (DWD) binary systems at the onset of super-Eddington mass transfer. We incorporate the physics of ideal inviscid hydrodynamical flow, Newtonian self-gravity, and radiation transport on a three-dimensional uniformly rotating cylindrical Eulerian grid. Care has been taken to conserve the key physical quantities such as angular momentum and energy. Our new method conserves total energy to a higher degree of accuracy than other codes that are presently being used to model mass transfer in DWD systems. We present the results of verification tests and simulate the first 20 + orbits of a binary system of mass ratio q 0.7 at the onset of dynamically unstable direct impact mass transfer. The mass transfer rate quickly exceeds the critical Eddington limit by many orders of magnitude, and thus we are unable to model a trans-Eddington phase. It appears that radiation pressure does not significantly affect the accretion flow in the highly super-Eddington regime. An optically thick common envelope forms around the binary within a few orbits. Although this envelope quickly exceeds the spatial domain of the computational grid, the fraction of the common envelope that exceeds zero gravitational binding energy is extremely small, suggesting that radiation-driven mass loss is insignificant in this regime. It remains to be seen whether simulations that capture the trans-Eddington phase of such flows will lead to the same conclusion or show that substantial material gets expelled.

Marcello, Dominic C.; Tohline, Joel E., E-mail: dmarcello@phys.lsu.edu, E-mail: tohline@phys.lsu.edu [Department of Physics and Astronomy, Louisiana State University and Agricultural and Mechanical College, 202 Nicholson Hall, Baton Rouge, LA (United States)

2012-04-01

56

Einstein and Millikan  

NASA Astrophysics Data System (ADS)

Albert Einstein traveled to America by boat during the great depression to consult with scientists at the California Institute of Technology. He was a theoretical physicist, a Nobel Prize winner, and a 20th century folk hero. Few members of the general public understood his theories, but they idolized him all the same. The invitation came from physicist Robert Millikan, who had initiated a visiting-scholars program at Caltech shortly after he became head of the school in 1921. Einstein's visits to the campus in 1931, 1932, and 1933 capped Millikan's campaign to make Caltech one of the physics capitals of the world. Mount Wilson astronomer Edwin Hubble's discovery that redshifts are proportional to their distances from the observer challenged Einstein's cosmological picture of a static universe. The big question at Caltech in 1931 was whether Einstein would give up his cosmological constant and accept the idea of an expanding universe. By day, Einstein discussed his theory and its interpretation at length with Richard Tolman, Hubble, and the other scientists on the campus. By night, Einstein filled his travel diary with his personal impressions. During his third visit, Einstein sidestepped as long as possible the question of whether conditions in Germany might prevent his return there. After the January 30 announcement that Hitler had become chancellor of Germany, the question could no longer be evaded. He postponed his return trip for a few weeks and then went to Belgium for several months instead of to Berlin. In the fall of 1933, Albert Einstein returned to the United States as an emigre and became a charter member of Abraham Flexner's new Institute for Advanced Study in Princeton, New Jersey. Why did Einstein go to Princeton and not Pasadena?

Erwin, Charlotte

2005-03-01

57

Einstein and 1905  

NASA Astrophysics Data System (ADS)

From March 17 to September 29, 1905, just over six months, Einstein wrote five papers that shifted the tectonic foundations of physics and changed the face of Nature. Three of these papers, the March paper presenting the particle of light, the May paper on Brownian motion, and the June paper on the Special Theory of Relativity are universally recognized as fundamental; however, the Brownian motion paper cannot be divorced from Einstein's April paper, A New Determination of the Dimensions of Molecules, and the September paper that gave the world its most famous equation, E = mc^2, cannot be separated from the June paper. These five papers reveal characteristics of Einstein's approach to physics.

Rigden, John

2005-05-01

58

The Varieties of Universal Expansion: Eddington and the Complexities of Early Cosmology  

NASA Astrophysics Data System (ADS)

A.S. Eddington was one of the handful of astronomers conversant with the many observational and theoretical factors at play in early 20th-century cosmology. Early relativistic cosmology touched on deep issues in several fields, and these diverse disciplinary requirements gave rise to a great deal of confusion about precisely what “expansion” meant and what implications that had for the construction of cosmological models. Eddington's efforts to resolve these difficulties help show the profound technical, conceptual, and philosophical difficulties that attended early ideas regarding an expanding universe.

Stanley, M.

2013-04-01

59

On the appearance of super-Eddington states in various astrophysical systems  

NASA Astrophysics Data System (ADS)

We briefly review the characteristics of super-Eddington (SED) states which arise in various astrophysical systems. These include classical nova eruptions, giant LBV eruptions, super-massive objects (SMOs) and very high accretion rate flows. The former two have ample observational data to establish the existence of SED states and learn of their behavior. When applying this understanding to the latter two, very interesting conclusions can be drawn. For example, ``super-Eddington" black hole growth through accretion is possible, but SMOs cannot provide the photoionizing radiation in the early Universe, though they can provide seed black holes.

Shaviv, Nir J.; Dotan, Calanit

60

Einstein in Wyoming.  

ERIC Educational Resources Information Center

Describes "Einstein's Adventurarium," a science center housed in an empty shopping mall in Gillette, Wyoming, created through school, business, and city-county government partnership. Describes how interactive exhibits allow exploration of life sciences, physics, and paleontology. (KDFB)

Elliot, Ian

1996-01-01

61

Once Upon Einstein  

NSDL National Science Digital Library

This book provides a description of Einstein's work through imagined scenes from his life. Topics covered include time, relativity, and quantum physics. Simple, non-mathematical analogies are used to explain the physics.

Damour, Thibault

2007-01-28

62

Albert Einstein Cancer Center  

Cancer.gov

The Albert Einstein College of Medicine at Yeshiva University was founded in 1955. In 1971, the Albert Einstein Cancer Center (AECC) was established at the medical school and in 1972, AECC became an NCI-designated Cancer Center. AECC is located in the Chanin Research Institute. The Center’s imaging facility, new mouse facilities, and expanded research programs are housed in the newly opened Price Center for Genetic and Translational Medicine.

63

Profile: Albert Einstein  

NSDL National Science Digital Library

This online article is from the Museum's Seminars on Science, a series of distance-learning courses designed to help educators meet the new national science standards. "Profile: Albert Einstein," part of the Frontiers in Physical Science seminar, briefly covers Einstein's life and work including his Special Theory of Relativity and the paper that gave the world E=mc², his Nobel Prize in Physics, his influence yet exclusion from the Manhattan Project, and his promotion of peace and human rights.

64

The use of the Milne-Eddington absorption coefficient for radiative heat transfer in combustion systems  

Microsoft Academic Search

The applicability of the Milne-Eddington absorption coefficient approximation is discussed in relation to the calculation of radiative transport involving the two distinct types of species produced in combustion systems - gases and soot particles. The approximation is found to apply well to hydrocarbon soot particles and as a result analytical closed-form solutions are derived for the radiative heat transfer inside

J. D. Felske; C. L. Tien

1977-01-01

65

The X-ray flux and spectral variability of the Einstein Extended Medium Sensitivity Survey AGN  

Microsoft Academic Search

Fifteen ROSAT PSPC observations available in the public archive are analyzed in order to study time and spectral variability of the 12 Einstein Extended Medium Sensitivity Survey (EMSS) AGN detected by ROSAT with more than 2000 net counts. Time variability was investigated on 13 different time-scales, ranging from 400 to 3.15 x 10 exp 6 s (1 yr). Of the

Paolo Ciliegi; Tommaso Maccacaro

1997-01-01

66

Dephasing and breakdown of adiabaticity in the splitting of Bose–Einstein condensates  

Microsoft Academic Search

We study the quantum dynamics of a Bose–Einstein condensate trapped in a double-well potential with a rising interwell barrier. We analytically find the characteristic timescales of the splitting process and compare our results with numerical analyses available in the literature. In the first stage of the dynamics, the relative phase of the two condensates evolves adiabatically. At a critical time

L Pezzé; A. Smerzi; G. P. Berman; A. R. Bishop; L. A. Collins

2005-01-01

67

Dephasing and breakdown of adiabaticity in the splitting of Bose Einstein condensates  

Microsoft Academic Search

We study the quantum dynamics of a Bose Einstein condensate trapped in a double-well potential with a rising interwell barrier. We analytically find the characteristic timescales of the splitting process and compare our results with numerical analyses available in the literature. In the first stage of the dynamics, the relative phase of the two condensates evolves adiabatically. At a critical

L. Pezzé; A. Smerzi; G. P. Berman; A. R. Bishop; L. A. Collins

2005-01-01

68

A Morphological Time-Scale for Rivers.  

National Technical Information Service (NTIS)

To predict changes in the geometry of a river due to human interference, a morphological time-scale, characterizing processes of degradation (erosion) and aggradation of rivers was defined. Processes of degradation and aggradation of rivers have a speed d...

M. Devries

1975-01-01

69

NOVA: Einstein's Big Idea  

NSDL National Science Digital Library

It is hard to overestimate the importance of Albert Einstein's equation, "Energy equals mass times the speed of light squared." A recent special from NOVA explores many different facets of the lasting and pervasive effects of this revolutionary statement. The website was developed to provide a host of complementary resources to the actual television program, and as such, anyone with even a trace of interest in the history of science or physics will want to take a close look. The interactive features are excellent; they include 10 top physicist's explanation of the famous equation and a timeline of Einstein's life. The essays offered here are also top-notch, and they include a piece titled "Einstein the Nobody" by David Bodanis and "Relativity and the Cosmos" by Alan Lightman.

2005-01-01

70

Discrete scale invariance connects geodynamo timescales  

NASA Astrophysics Data System (ADS)

The geodynamo exhibits a bewildering gamut of time-dependent fluctuations, on timescales from years to at least hundreds of millions of years. No framework yet exists that comprises all and relates each to all others in a quantitative sense. The technique of bootstrapped discrete scale invariance quantifies characteristic timescales of a process, based upon log-periodic fits of modulated power-law scaling of size-ranked event durations. Four independent geomagnetic data sets are analysed therewith, each spanning different timescales: the sequence of 332 known dipole reversal intervals (0-161 Ma); dipole intensity fluctuations (0-2 Ma); archeomagnetic secular variation (5000 B.C.-1950 A.D.); and historical secular variation (1590-1990 A.D.). Six major characteristic timescales are empirically attested: circa 1.43 Ma, 56 Ka, and 763, 106, 21 and 3 yr. Moreover, all detected wavelengths and phases of the detected scaling signatures are highly similar, suggesting that a single process underlies all. This hypothesis is reinforced by extrapolating the log-periodic scaling signal of any particular data set to higher timescales than observed, through which predictions are obtained for characteristic scales attested elsewhere. Not only do many confirm one another, they also predict the typical duration of superchrons and geomagnetic jerks. A universal scaling bridge describes the complete range of geodynamo fluctuation timescales with a single power law.

Jonkers, A. R. T.

2007-11-01

71

Exact solutions of Einstein's equations  

NASA Astrophysics Data System (ADS)

Einstein's General Relativity is the leading theory of space-time and gravity: it is highly nonlinear. Exact solutions of Einstein's equations thus model gravitating systems and enable exploration of the mathematics and physics of the theory.

MacCallum, Malcolm A. H.

2013-12-01

72

Eye on Einstein  

NSDL National Science Digital Library

This OLogy activity challenges students to find nine inventions that Einstein's ideas helped to create. The activity begins with an illustration of Al's Junk Shop. Mixed in with his junk are a Global Positioning System, CD player, computer, calculator, scanner, laser pointer, TV, and representations of both laser surgery and nuclear energy. After making a mental list of their nine choices, students can click to a second page to check their answers. Each invention has a rollover note about how Einstein's ideas helped pave the way for its creation. Alternately, the first page could be printed and used as a handout for an offline activity.

73

Water renewal timescales in the Scheldt Estuary  

NASA Astrophysics Data System (ADS)

Using the concepts of the Constituent-oriented Age and Residence time Theory (CART), we compute timescales related to the water renewal in the Scheldt Estuary (The Netherlands/Belgium). Three different timescales are used to better understand and characterize the dynamics of the estuary: the age of the renewing water, the residence time and the exposure time. The residence time is the time taken by a water parcel to leave the estuary for the first time while the exposure time is the total time spent by a water parcel in the estuary including re-entries. The age of a renewing water parcel is defined as the time elapsed since it entered the estuary. The renewing water was split into three types: the water originating from the sea, the water originating from the upstream fresh tidal rivers and the water originating from the different canals and docks connected to the estuary. Every timescale is computed at any time and position by means of the finite-element, unstructured-mesh model SLIM. This results in movies of the timescale fields (shown as Supplementary material), allowing a detailed analysis of their spatial and temporal variabilities. The effect of the M2 tide and the discharge regime (winter, summer or average situation) on the timescales is also investigated. Tidally-averaged timescales vary little over the width of the estuary and hence exhibit a virtually one-dimensional behaviour. However, around these average values, the timescales can vary hugely over a tidal cycle, with amplitudes that significantly depend on the space coordinates. The reason thereof has yet to be elucidated. These results underscore the need for two- or three-dimensional models with high temporal resolution for investigating the dynamics of the Scheldt Estuary.

de Brye, Benjamin; de Brauwere, Anouk; Gourgue, Olivier; Delhez, Eric J. M.; Deleersnijder, Eric

2012-06-01

74

2011 Einstein Fellows Chosen  

NASA Astrophysics Data System (ADS)

ASA has announced the selection of the 2011 Einstein Fellows who will conduct research related to NASA's Physics of the Cosmos program, which aims to expand our knowledge of the origin, evolution, and fate of the Universe. The Einstein Fellowship provides support to the awardees for three years, and the Fellows may pursue their research at a host university or research center of their choosing in the United States. The new Fellows will begin their programs in the fall of 2011. The new Einstein Fellows and their host institutions are listed below: * Akos Bogdan (Smithsonian Astrophysical Observatory, Cambridge, Mass.) * Samuel Gralla (University of Maryland, College Park, Md.) * Philip Hopkins (University of California at Berkeley) * Matthew Kunz (Princeton University, Princeton, N.J.) * Laura Lopez (Massachusetts Institute of Technology, Cambridge, Mass.) * Amy Reines (National Radio Astronomy Observatory, Charlottesville, Virg.) * Rubens Reis (University of Michigan, Ann Arbor) * Ken Shen (Lawrence Berkeley National Laboratory, Berkeley, Calif.) * Jennifer Siegal-Gaskins (California Institute of Technology, Pasadena) * Lorenzo Sironi (Harvard University, Cambridge, Mass.) NASA has two other astrophysics theme-based fellowship programs: the Sagan Fellowship Program, which supports research into exoplanet exploration, and the Hubble Fellowship Program, which supports research into cosmic origins. More information on the Einstein Fellowships can be found at: http://cxc.harvard.edu/fellows/

2011-03-01

75

Einstein Books for Kids  

NSDL National Science Digital Library

This OLogy reference list has 10 kid-friendly books on physics. A short description is given for each title, along with author name and publisher. The list includes engaging biographies covering Einstein's life and contributions, collections of easy-to-complete science experiments, and illustrated looks at energy, time and space, light, and matter.

76

From Newton to Einstein.  

ERIC Educational Resources Information Center

Discusses the history of scientific thought in terms of the theories of inertia and absolute space, relativity and gravitation. Describes how Sir Isaac Newton used the work of earlier scholars in his theories and how Albert Einstein used Newton's theories in his. (CW)

Ryder, L. H.

1987-01-01

77

Correlation of Maxima in Long-Period Variable Stars: From Eddington to Present Time  

NASA Astrophysics Data System (ADS)

Eddington during the years of pioneering in General Relativity worked also in observational statistics of variable stars, and proposed a model for Cepheids' pulsation. The statistical analysis of time series of long-period variable stars (Mira): Mira Ceti and ? Cygni made by Eddington and Plakidis in 1929 has been extended to luminosities dominion and to R Leonis and R Hydrae. The difference between consecutive maxima ?M is negatively correlated with the magnitude M of the first maximum of the pair. Bright maxima are preferentially followed by dim ones, excepted for R Hydrae. It shows a possible two-periods time pattern of its maxima, which makes easier predictions of its maxima. Our two-points correlation analysis is still not enough to give a satisfactory predictive model of maxima sequence.

Sigismondi, Costantino

2006-02-01

78

Mid-Infrared Selected Quasars I: Virial Black Hole Mass and Eddington Ratios  

NASA Astrophysics Data System (ADS)

We provide a catalog of 391 mid-infrared-selected (MIR, 24?m) broad-emission-line (BEL, type 1) quasars in the 20 square deg SWIRE Lockman Hole field. This quasar sample is selected in the MIR from Spitzer MIPS with S24 > 0.4mJy, and jointly with an optical magnitude limit of r (AB)= 22.5. The catalog is based on MMT spectroscopy to select BEL quasars, and extends the SDSS coverage to fainter magnitudes and a more complete quasar population. The MIR-selected quasar sample peaks at z ?1.4, and shows a significant and constant (20%) fraction of objects with extended SDSS photometry, previously missed by the SDSS optical point source dominant color selection. This sample also recovers a significant population of z < 3 quasars at i > 19.1, previously dropped by SDSS for efficiency consideration. We also investigate the continuum luminosity and line profile of these MIR quasars, estimate their virial black hole masses, and provide the Eddington ratios. The SMBH mass shows evidence of downsizing, though the Eddington ratios remain constant at 1 < z < 4. Compared to point sources in the same redshift range, extended sources at z < 1 show systematically lower Eddington ratios. The catalog and spectra will be publicly available online.

Dai, Yu Sophia; Elvis, Martin; Bergeron, Jacqueline; Fazio, Giovanni G.; Huang, Jiasheng; Wilkes, Belinda J.; Willmar, Christopher

2014-06-01

79

Einstein@Home  

NSDL National Science Digital Library

Bruce Allen developed this World Year of Physics 2005 project for the Laser Interferometer Gravitational Wave Observatory (LIGO) Scientific Collaboration to recruit Internet users to help determine whether gravitational wave exist. "Einstein@Home is a program that uses your computer's idle time to search for spinning neutron stars (also called pulsars) using data from the LIGO and GEO gravitational wave detectors." Users need only a computer with a fast connection to the Internet and the Einstein@Home screensaver. After learning about the program's rules and policies, visitors can create an account and download the necessary components. The website offers a user profile zone where visitors can share information and opinions as well as links to news stories about the project.

80

Einstein's Real "biggest Blunder"  

NASA Astrophysics Data System (ADS)

Albert Einstein's real "biggest blunder" was not the 1917 introduction into his gravitational field equations of a cosmological constant term ?, rather was his failure in 1916 to distinguish between the entirely different concepts of active gravitational mass and passive gravitational mass. Had he made the distinction, and followed David Hilbert's lead in deriving field equations from a variational principle, he might have discovered a true (not a cut and paste) Einstein-Rosen bridge and a cosmological model that would have allowed him to predict, long before such phenomena were imagined by others, inflation, a big bounce (not a big bang), an accelerating expansion of the universe, dark matter, and the existence of cosmic voids, walls, filaments and nodes.

Ellis, Homer G.

2012-10-01

81

The stolen brain of Einstein  

NASA Astrophysics Data System (ADS)

Pathologist Thomas Stoltz Harvey performed an autopsy on Einstein after his death in 1955. During the autopsy Harvey removed Einstein's brain, took pictures of it and then cut it into several pieces. A lot of scientific attention has been devoted to Einstein' brain, and it still comes up once in a while. We've all heard something or other about Einstein's brain, as it has become somewhat of a folk lore. What is less known is that Harvey in actuality did not have the permission to remove the brain. Only later Harvey convinced Einstein's Hans Albert Einstein son that this was for a good purpose. The brain would only be used for scientific purpose, which will be published reputable journals. I will try to describe in some detail the long journey this brain has taken in last fifty two years.

Modi, Kavan

2008-03-01

82

Einstein, Bohr, and Bell  

NASA Astrophysics Data System (ADS)

The final form of quantum physics, in the particular case of wave mechanics, was established in the years 1925-1927 by Heisenberg, Schrödinger, Born and others, but the synthesis was the work of Bohr who gave an epistemological interpretation of all the technicalities built up over those years; this interpretation will be examined briefly in Chapter 10. Although Einstein acknowledged the success of quantum mechanics in atomic, molecular and solid state physics, he disagreed deeply with Bohr's interpretation. For many years, he tried to find flaws in the formulation of quantum theory as it had been more or less accepted by a large majority of physicists, but his objections were brushed away by Bohr. However, in an article published in 1935 with Podolsky and Rosen, universally known under the acronym EPR, Einstein thought he had identified a difficulty in the by then standard interpretation. Bohr's obscure, and in part beyond the point, answer showed that Einstein had hit a sensitive target. Nevertheless, until 1964, the so-called Bohr-Einstein debate stayed uniquely on a philosophical level, and it was actually forgotten by most physicists, as the few of them aware of it thought it had no practical implication. In 1964, the Northern Irish physicist John Bell realized that the assumptions contained in the EPR article could be tested experimentally. These assumptions led to inequalities, the Bell inequalities, which were in contradiction with quantum mechanical predictions: as we shall see later on, it is extremely likely that the assumptions of the EPR article are not consistent with experiment, which, on the contrary, vindicates the predictions of quantum physics. In Section 3.2, the origin of Bell's inequalities will be explained with an intuitive example, then they will be compared with the predictions of quantum theory in Section 3.3, and finally their experimental status will be reviewed in Section 3.4. The debate between Bohr and Einstein goes much beyond a simple controversy, which is after all almost eighty years old and has been settled today. In fact, the concept introduced in this debate, that of entanglement, lies at the heart of many very important developments of modern quantum physics, in particular all those linked to quantum information (Chapter 8). Moreover, we shall see that the phenomenon of non-local correlations compels us to revise in depth our space-time representation of quantum processes. These are the two reasons why a whole chapter is devoted to this debate.

Bellac, Michel Le

2014-11-01

83

The Einstein Dossiers: Science and Politics - Einstein's Berlin Period with an Appendix on Einstein's FBI File  

NASA Astrophysics Data System (ADS)

In 1919 the Prussian Ministry of Science, Arts and Culture opened a dossier on "Einstein's Theory of Relativity." It was rediscovered by the author in 1961 and is used in conjunction with numerous other subsequently identified 'Einstein' files as the basis of this fascinating book. In particular, the author carefully scrutinizes Einstein's FBI file from 1950-55 against mostly unpublished material from European including Soviet sources and presents hitherto unknown documentation on Einstein's alleged contacts with the German Communist Party and the Comintern.

Grundmann, Siegfried

84

The Eddington Limit Upper Boudary for Cool Stars on the HR Diagram  

NASA Astrophysics Data System (ADS)

We have examined the properties of cool, low metallicity, super-massive forming stars, which may exist at high redshift. We seek to address the location of the Eddington limit and possible evolution scenarios for such stars. The location of the modified Eddington limit was determined across the Hertzsprung Russell Diagram by using Kurucz model atmospheres. Radiative acceleration and ? max = grad}/g{mass were calculated for a range of gravities at specific temperatures from model atmospheres that accounted for presence of convection zones. Results for Teff and mass gravity were converted to a location on the HR Diagram using a mass luminosity relation that fit upper main sequence stars and extrapolated to ? electron\\:scattering = 1 for very massive stars. Models were calculated for both Z/Z? = 1.0 and 0.03. On the hot side of the HR Diagram, our results agree well with the modified Eddington limit derived by Lamers and Noordhoek (1993) and Ulmer and Fitzpatrick (1998). Our results also agree well with the Humphreys-Davidson limit for the most luminous stars, reaching a minimal Lmax at about 12000 K. Our results extend to stars on the cool side of this minimum. We find that the opacity decreases well below the fully ionized electron scattering opacity allowing the upper limit to reach values 104 higher than the H-D limit at Teff = 5000 K for Z/Z? = 1 and 105 higher for Z/Z? = 0.03. This apex region might be of interest for two classes of stars. a) Luminous Blue Variables could reach the cool apex region by crossing the divide from the Blue Hypergiant region to the yellow side during their outburst phases. b) The collapse and formation of the earliest generation of super-massive stars could also lead to objects that might be found observationally only as hyperluminous cool stars and not as Wolf-Rayet type hot stars as is commonly assumed.

Mendygral, P. J.; Babler, B. L.; Cassinelli, J. P.

2002-12-01

85

GROWTH OF EARLY SUPERMASSIVE BLACK HOLES AND THE HIGH-REDSHIFT EDDINGTON RATIO DISTRIBUTION  

SciTech Connect

Using a new large-scale ({approx} 0.75 Gpc){sup 3} hydrodynamic cosmological simulation, we investigate the growth rate of supermassive black holes (BHs) in the early universe (z {approx}> 4.75). Remarkably we find a clear peak in the typical Eddington ratio ({lambda}) at BH masses of (4-8) Multiplication-Sign 10{sup 7} M{sub Sun} (typically in halos of {approx}7 Multiplication-Sign 10{sup 11} to 1 Multiplication-Sign 10{sup 12} M{sub Sun }, close to their shock heating scale), independent of redshift and indicative that most BH growth occurs in the cold-flow-dominated regime. BH growth is enhanced at high-z and by and large regulated by the cosmological evolution of gas density, with {lambda} scaling simply as (1 + z){sup 3}. The peak in {lambda} is caused by the competition between increased gas density available in more massive hosts, and a decrease due to active galactic nucleus feedback that becomes effective above the shock heating halo mass scale and at high BH masses. We show that the distribution of {lambda} among both mass-selected and luminosity-selected samples is approximately lognormal. We combine these findings into a single lognormal fitting formula for the distribution of Eddington ratios as a function of (M{sub BH}, z). This formula can be used in analytic and semianalytic models for evolving BH populations, predicting BH masses of observed quasars, and, in conjunction with the observed distribution of Eddington ratios, can be used to constrain the BH mass function.

DeGraf, C.; Di Matteo, T.; Khandai, N.; Croft, R. [McWilliams Center for Cosmology, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213 (United States)

2012-08-10

86

Accretion-driven evolution of black holes: Eddington ratios, duty cycles and active galaxy fractions  

NASA Astrophysics Data System (ADS)

We develop semi-empirical models of the supermassive black hole and active galactic nucleus (AGN) populations, which incorporate the black hole growth implied by the observed AGN luminosity function assuming a radiative efficiency ? and a distribution of Eddington ratios ?. By generalizing these continuity-equation models to allow a distribution P(? | MBH, z), we are able to draw on constraints from observationally estimated ? distributions and active galaxy fractions while accounting for the luminosity thresholds of observational samples. We consider models with a Gaussian distribution of log ? and Gaussians augmented with a power-law tail to low ?. Within our framework, reproducing the high observed AGN fractions at low redshift requires a characteristic Eddington ratio ?c that declines at late times, and matching observed Eddington ratio distributions requires a P(?) that broadens at low redshift. To reproduce the observed increase of AGN fraction with black hole or galaxy mass, we also require a ?c that decreases with increasing black hole mass, reducing the AGN luminosity associated with the most massive black holes. Finally, achieving a good match to the high-mass end of the local black hole mass function requires an increased radiative efficiency at high black hole mass. We discuss the potential impact of black hole mergers or a ?-dependent bolometric correction, and we compute evolutionary predictions for black hole and galaxy specific accretion rates. Despite the flexibility of our framework, no one model provides a good fit to all the data we consider; it is particularly difficult to reconcile the relatively narrow ? distributions and low duty cycles estimated for luminous broad-line AGN with the broader ? distributions and higher duty cycles found in more widely selected AGN samples, which typically have lower luminosity thresholds.

Shankar, Francesco; Weinberg, David H.; Miralda-Escudé, Jordi

2013-01-01

87

A LONG, LONG time ago: geologic timescales  

NSDL National Science Digital Library

Each student randomly picks a card with a geologic event (written description and an image) on it. A timeline has 11 events, not including the formation of the Earth and today. Students attach their event where they think it should go on a 45.5' timeline (in the hallway) made out of paper adding tape and mark the location on the timeline. They return to the classroom and receive a list of age dates for each event. Each group figures out the scale (1 foot = 100 million years) and then moves their events to the correct locations. Students are asked how the position of the events changed, and answer other questions that reinforce the difference between human timescales and geologic timescales. The powerpoint file below contains a template for making geologic event labels for the index cards. Instructors can tailor the geologic event list to fit their course.

Johnson, Elizabeth

88

Planetary chaotic zone clearing: destinations and timescales  

NASA Astrophysics Data System (ADS)

It is well known that there exists an annular zone in the vicinity of a planet’s orbit where circular orbits are strongly chaotic due to the overlap of first order mean motion resonances. What is the final destination of these strongly chaotic orbits? What fraction impact the star, impact the planet or escape to infinity, and on what timescales? We explore these questions within the framework of the circular, planar restricted three body problem for planet-star mass ratios in the range 10^-9 to 10^-1.5. We find that most particles from the chaotic zone collide with the planet for low masses; particles can be scattered into unbound orbits only by higher mass planets. The chaotic zone clearing timescale is found to have a broken power-law dependence on the planet's mass, with a shallower power-law at low masses transitioning to a steeper power law at larger masses.

Morrison, Sarah J.

2014-05-01

89

Galileo and Einstein  

NSDL National Science Digital Library

This website provides materials for a university-level historical astronomy course. Full lecture notes are provided, along with animations and simulations to illustrate aspects of the course. Links are provided to related supporting material. The course lecture notes are extensive and focus on two revolutions in the way humanity perceives the universe. The lectures begin with a review of important contributions from early civilizations, before focusing on the paradigm shift following Galileo's discoveries. The last part of the course discusses Einstein's contributions to astronomy and develops the theory of special relativity.

Fowler, Michael

2008-08-08

90

Passive optical limiting in long timescales  

NASA Astrophysics Data System (ADS)

From its use in medicine to measure and/or probe various physiologies to commercial applications such as data storage on optical disks, the laser has positively contributed to the lives of people around the globe. Alongside it's unique properties, the control of laser light poses significant challenges. Optical limiting, or the truncation of optical energy at particular thresholds represents one such challenge. Given the plethora of radiation sources available, it is of significant value to identify a means by which optical limiting can be achieved simultaneously for a wide berth of source parameters. That said, this document focuses on the exploration of a particular optical limiting modality applied to long timescales; That is, optical pulses with durations on the order of hundreds of nanoseconds, microseconds and up to continuous-wave. Given that this modality has been previously shown to be broadband and effective in short timescales, evidence of it's efficacy in long timescales would demonstrate the modality as an exceptional option in the design of truly robust optical limiting devices. The results of L34 optical limiting research with incident laser light at a 750nm wavelength and pulse durations in the microsecond and nanosecond regimes as well as continuous-wave light at 532nm are shown and discussed. Results are discussed for both bulk and liquid-infiltrated capillary-array arrangements and for various output light collection configurations. The mechanisms by which limiting action occurs are discussed and their optimization within various configurations is considered. Through measurement in a variety of experimental situations and device configurations, the organic liquid L34 is shown to be an effective optical limiting material in long timescales. When combined with the fiber array architecture, these results provide evidence that L34 is an excellent candidate for use as a spectrally and temporally robust optical limiting system that is easy to construct and maintain.

Stinger, Michael Vincent

91

Time-scale segmentation of respiratory sounds.  

PubMed

Respiratory sounds are composed of various events: normal and so-called adventitious sounds. These phenomena present a wide range of characteristics which make difficult their analysis with a single technique. Adapted time-frequency and time-scale techniques allow to fit best, under constraints, the accuracy of analysis of a time segmentation and, by the way, make feasible the study of complex signals. We present here new approaches based only on the wavelet packet decomposition to segment respiratory sounds. PMID:9754684

Ademovic, E; Pesquet, J C; Charbonneau, G

1998-06-01

92

Geonic black holes and remnants in Eddington-inspired Born-Infeld gravity  

NASA Astrophysics Data System (ADS)

We show that electrically charged solutions within the Eddington-inspired Born-Infeld theory of gravity replace the central singularity by a wormhole supported by the electric field. As a result, the total energy associated with the electric field is finite and similar to that found in the Born-Infeld electromagnetic theory. When a certain charge-to-mass ratio is satisfied, in the lowest part of the mass and charge spectrum the event horizon disappears, yielding stable remnants. We argue that quantum effects in the matter sector can lower the mass of these remnants from the Planck scale down to the TeV scale.

Olmo, Gonzalo J.; Rubiera-Garcia, D.; Sanchis-Alepuz, Helios

2014-03-01

93

A modified Eddington-Barbier relation in highly coherent resonance-line wings  

NASA Astrophysics Data System (ADS)

It is shown that resonance-line wings are just as useful in inferring plane-parallel stellar chromospheric SL distributions as complete redistribution (CRD) profiles. Although coherent scattering effects at a given frequency tend to average depth-dependent parameters over a larger volume than in CRD, this effect can be offset by simply looking closer to line center, where the same depth-dependent information exists as in CRD, albeit somewhat more compressed in frequency space. For resonance lines with high excitation energies such as Ly-alpha, steep Planck function gradients can invalidate the modified Eddington-Barbier approach given, but this problem also exists in CRD.

Gayley, K. G.

1992-06-01

94

A modified Eddington-Barbier relation in highly coherent resonance-line wings  

NASA Technical Reports Server (NTRS)

It is shown that resonance-line wings are just as useful in inferring plane-parallel stellar chromospheric S sub L distributions as complete redistribution (CRD) profiles. Although coherent scattering effects at a given frequency tend to average depth-dependent parameters over a larger volume than in CRD, this effect can be offset by simply looking closer to line center, where the same depth-dependent information exists as in CRD, albeit somewhat more compressed in frequency space. For resonance lines with high excitation energies such as Ly-alpha, steep Planck function gradients can invalidate the modified Eddington-Barbier approach given, but this problem also exists in CRD.

Gayley, K. G.

1992-01-01

95

Timescales of Land Surface Evapotranspiration Response  

NASA Technical Reports Server (NTRS)

Soil and vegetation exert strong control over the evapotranspiration rate, which couples the land surface water and energy balances. A method is presented to quantify the timescale of this surface control using daily general circulation model (GCM) simulation values of evapotranspiration and precipitation. By equating the time history of evaporation efficiency (ratio of actual to potential evapotranspiration) to the convolution of precipitation and a unit kernel (temporal weighting function), response functions are generated that can be used to characterize the timescales of evapotranspiration response for the land surface model (LSM) component of GCMS. The technique is applied to the output of two multiyear simulations of a GCM, one using a Surface-Vegetation-Atmosphere-Transfer (SVAT) scheme and the other a Bucket LSM. The derived response functions show that the Bucket LSM's response is significantly slower than that of the SVAT across the globe. The analysis also shows how the timescales of interception reservoir evaporation, bare soil evaporation, and vegetation transpiration differ within the SVAT LSM.

Scott, Russell; Entekhabi, Dara; Koster, Randal; Suarez, Max

1997-01-01

96

Albert Einstein 1879-1955.  

ERIC Educational Resources Information Center

Celebrates the centennial of Einstein's birth with an eight-page pictorial biography and two special articles: (1) Einstein the catalyst; and (2) Unitary field theories. His special and general theories of relativity and his contributions to quantum physics and other topics are also presented. (HM)

Physics Today, 1979

1979-01-01

97

Einstein's contributions to atomic physics  

Microsoft Academic Search

Many of the epoch-breaking papers that have been published by Einstein are remembered today as treatises dealing with various isolated phenomena rather than as direct consequences of a new unified world view. This paper traces the various ways in which ten papers published by Einstein during the period 1905-1925 influenced the development of the modern atomic paradigm, and illustrates how

Lorenzo J Curtis

2009-01-01

98

Einstein and the twin paradox  

Microsoft Academic Search

Einstein was the first to discuss and resolve the 'twin paradox', which in 1905 he did not consider paradoxical and treated as a consequence of lack of simultaneity. He maintained this view until at least 1914. However, in 1918 Einstein brought forward arguments about accelerated frames of reference that tended to overshadow his initial resolution. His earlier arguments were gradually

Peter Pesic

2003-01-01

99

Einstein Inflationary Probe (EIP)  

NASA Technical Reports Server (NTRS)

I will discuss plans to develop a concept for the Einstein Inflation Probe: a mission to detect gravity waves from inflation via the unique signature they impart to the cosmic microwave background (CMB) polarization. A sensitive CMB polarization satellite may be the only way to probe physics at the grand-unified theory (GUT) scale, exceeding by 12 orders of magnitude the energies studied at the Large Hadron Collider. A detection of gravity waves would represent a remarkable confirmation of the inflationary paradigm and set the energy scale at which inflation occurred when the universe was a fraction of a second old. Even a strong upper limit to the gravity wave amplitude would be significant, ruling out many common models of inflation, and pointing to inflation occurring at much lower energy, if at all. Measuring gravity waves via the CMB polarization will be challenging. We will undertake a comprehensive study to identify the critical scientific requirements for the mission and their derived instrumental performance requirements. At the core of the study will be an assessment of what is scientifically and experimentally optimal within the scope and purpose of the Einstein Inflation Probe.

Hinshaw, Gary

2004-01-01

100

Uncertainties of the masses of black holes and Eddington ratios in AGN  

NASA Astrophysics Data System (ADS)

Black hole (BH) masses in Active Galactic Nuclei (AGN) are determined in ˜ 40 objects through reverberation mapping of the emission line region. Scatter around the relationship between BH masses obtained by this method and host-galaxy bulge velocity dispersion, indicates that the masses are uncertain typically by a factor of about three. Systematic errors seem to be linked to the Eddington luminosity ratio and to the inclination of the line emission region. When BH masses are not known via reverberation mapping but estimated using empirical relations, the uncertainties can be larger, especially when the relations are extrapolated to high and low masses and/or luminosities. In particular they lead to small masses and consequently to Eddington ratios of the order of or larger than unity in samples of Narrow Line Seyfert 1. If these masses are correct, the optical luminosities imply sometimes accretion rates at ˜1000 RG larger than the critical rate by one or two orders of magnitude. Either accretion onto BHs is also performed at super-critical rate, resulting in rapid growth of the BH, or strong winds produced close to the BHs evacuate a large fraction of the accretion flow.

Collin, Suzy

2007-04-01

101

X-Ray Outflows and Super-Eddington Accretion in the Ultraluminous X-Ray Source Holmberg IX X-1  

NASA Astrophysics Data System (ADS)

Studies of X-ray continuum emission and flux variability have not conclusively revealed the nature of ultraluminous X-ray sources (ULXs) at the high-luminosity end of the distribution (those with L X >= 1040 erg s-1). These are of particular interest because the luminosity requires either super-Eddington accretion onto a black hole of mass ~10 M ? or more standard accretion onto an intermediate-mass black hole. Super-Eddington accretion models predict strong outflowing winds, making atomic absorption lines a key diagnostic of the nature of extreme ULXs. To search for such features, we have undertaken a long, 500 ks observing campaign on Holmberg IX X-1 with Suzaku. This is the most sensitive data set in the iron K bandpass for a bright, isolated ULX to date, yet we find no statistically significant atomic features in either emission or absorption; any undetected narrow features must have equivalent widths less than 15-20 eV at 99% confidence. These limits are far below the gsim150 eV lines expected if observed trends between mass inflow and outflow rates extend into the super-Eddington regime and in fact rule out the line strengths observed from disk winds in a variety of sub-Eddington black holes. We therefore cannot be viewing the central regions of Holmberg IX X-1 through any substantial column of material, ruling out models of spherical super-Eddington accretion. If Holmberg IX X-1 is a super-Eddington source, any associated outflow must have an anisotropic geometry. Finally, the lack of iron emission suggests that the stellar companion cannot be launching a strong wind and that Holmberg IX X-1 must primarily accrete via Roche-lobe overflow.

Walton, D. J.; Miller, J. M.; Harrison, F. A.; Fabian, A. C.; Roberts, T. P.; Middleton, M. J.; Reis, R. C.

2013-08-01

102

Cryogenics and Einstein Telescope  

NASA Astrophysics Data System (ADS)

The dominant noises which limit the present sensitivity of the gravitational wave detectors are the thermal noise of the suspended mirrors and the shot noise. For the third generation of gravitational wave detectors as the Einstein Telescope (ET), the reduction of the shot noise implies to increase the power stored in the detector at 1 MW level and, at the same time, to compensate the huge optic distortion due to induced thermal lensing. At low temperature it is possible to reduce both these effects. However, lowering the temperature of the test masses without injecting vibration noise from the cooling system is a technological challenge. We review here the thermal noise impact on the ultimate ET sensitivity limit and we discuss possible cryogenic configurations to cool the mirror.

Puppo, Paola; Ricci, Fulvio

2011-02-01

103

The Einstein tensor characterizing some Riemann spaces  

NASA Astrophysics Data System (ADS)

A formal definition of the Einstein tensor is given. Mention is made of how this tensor plays a role of expressing certain conditions in a precise form. The cases of reducing the Einstein tensor to a zero tensor are studied on its merit. An account of results, formulated as theorems, on Einstein symmetric and Einstein recurrent spaces is then presented.

Rahman, M. S.

1993-07-01

104

Einstein's Thoughts on the Ether  

NSDL National Science Digital Library

Do light waves travel through the ether like waves on a lake travel through water? In this video segment adapted from NOVA, a young Albert Einstein grapples with this question while examining the speed of light.

Foundation, Wgbh E.

2004-02-20

105

Einstein and the twin paradox  

NASA Astrophysics Data System (ADS)

Einstein was the first to discuss and resolve the 'twin paradox', which in 1905 he did not consider paradoxical and treated as a consequence of lack of simultaneity. He maintained this view until at least 1914. However, in 1918 Einstein brought forward arguments about accelerated frames of reference that tended to overshadow his initial resolution. His earlier arguments were gradually rediscovered during the subsequent controversy about this 'paradox'.

Pesic, Peter

2003-11-01

106

Hindcasting of decadal?timescale estuarine bathymetric change with a tidal?timescale model  

USGS Publications Warehouse

Hindcasting decadal-timescale bathymetric change in estuaries is prone to error due to limited data for initial conditions, boundary forcing, and calibration; computational limitations further hinder efforts. We developed and calibrated a tidal-timescale model to bathymetric change in Suisun Bay, California, over the 1867–1887 period. A general, multiple-timescale calibration ensured robustness over all timescales; two input reduction methods, the morphological hydrograph and the morphological acceleration factor, were applied at the decadal timescale. The model was calibrated to net bathymetric change in the entire basin; average error for bathymetric change over individual depth ranges was 37%. On a model cell-by-cell basis, performance for spatial amplitude correlation was poor over the majority of the domain, though spatial phase correlation was better, with 61% of the domain correctly indicated as erosional or depositional. Poor agreement was likely caused by the specification of initial bed composition, which was unknown during the 1867–1887 period. Cross-sectional bathymetric change between channels and flats, driven primarily by wind wave resuspension, was modeled with higher skill than longitudinal change, which is driven in part by gravitational circulation. The accelerated response of depth may have prevented gravitational circulation from being represented properly. As performance criteria became more stringent in a spatial sense, the error of the model increased. While these methods are useful for estimating basin-scale sedimentation changes, they may not be suitable for predicting specific locations of erosion or deposition. They do, however, provide a foundation for realistic estuarine geomorphic modeling applications.

Ganju, Neil K.; Schoellhamer, David H.; Jaffe, Bruce E.

2009-01-01

107

The NASA Beyond Einstein Program  

NASA Technical Reports Server (NTRS)

Einstein's legacy is incomplete, his theory of General relativity raises -- but cannot answer --three profound questions: What powered the big bang? What happens to space, time, and matter at the edge of a black hole? and What is the mysterious dark energy pulling the Universe apart? The Beyond Einstein program within NASA's Office of Space Science aims to answer these questions, employing a series of missions linked by powerful new technologies and complementary approaches towards shared science goals. The Beyond Einstein program has three linked elements which advance science and technology towards two visions; to detect directly gravitational wave signals from the earliest possible moments of the BIg Bang, and to image the event horizon of a black hole. The central element is a pair of Einstein Great Observatories, Constellation-X and LISA. Constellation-X is a powerful new X-ray observatory dedicated to X-Ray Spectroscopy. LISA is the first spaced based gravitational wave detector. These powerful facilities will blaze new paths to the questions about black holes, the Big Bang and dark energy. The second element is a series of competitively selected Einstein Probes, each focused on one of the science questions and includes a mission dedicated resolving the Dark Energy mystery. The third element is a program of technology development, theoretical studies and education. The Beyond Einstein program is a new element in the proposed NASA budget for 2004. This talk will give an overview of the program and the missions contained within it.

White, Nicholas E.

2006-01-01

108

Conservative 3+1 general relativistic variable Eddington tensor radiation transport equations  

NASA Astrophysics Data System (ADS)

We present conservative 3+1 general relativistic variable Eddington tensor radiation transport equations, including greater elaboration of the momentum space divergence (that is, the energy derivative term) than in previous work. These equations are intended for use in simulations involving numerical relativity, particularly in the absence of spherical symmetry. The independent variables are the lab frame coordinate basis spacetime position coordinates and the particle energy measured in the comoving frame. With an eye towards astrophysical applications—such as core-collapse supernovae and compact object mergers—in which the fluid includes nuclei and/or nuclear matter at finite temperature, and in which the transported particles are neutrinos, we pay special attention to the consistency of four-momentum and lepton number exchange between neutrinos and the fluid, showing the term-by-term cancellations that must occur for this consistency to be achieved.

Cardall, Christian Y.; Endeve, Eirik; Mezzacappa, Anthony

2013-05-01

109

From Super-Eddington to zero: following a Z source into quiescence  

NASA Astrophysics Data System (ADS)

XTE J1701-462 is probably the most luminous Galactic transient neutron star LMXB (NSXB) in the history of X-ray astronomy. Early observations have already clarified our view on the role of mass accretion rate in NSXBs. Observing XTE J1701-462 as it returns to quiescence will create a unique opportunity to study the effects of mass-accretion rate on the spectral/variability properties in a single NSXB over an unprecedented luminosity range. We propose a Chandra/XMM-Newton TOO program with two goals: 1) observe the source during the end of the decay and in quiescence, to complete what might well become a 'Rosetta stone' for NSXBs and 2) constrain the structure of neutron stars by studying the effects of near-Eddington accretion on the cooling of the crust/core in transient NSXBs.

Homan, Jeroen

2007-09-01

110

Observational discrimination of Eddington-inspired Born-Infeld gravity from general relativity  

NASA Astrophysics Data System (ADS)

Direct observations of neutron stars could tell us an imprint of modified gravity. However, it is generally difficult to resolve the degeneracy due to the uncertainties in the equation of state of neutron star matter and in gravitational theories. In this paper, we have successfully found the observational possibility to distinguish Eddington-inspired Born-Infeld gravity (EiBI) from general relativity. We show that the radii of neutron stars with 0.5M? are strongly correlated with the neutron skin thickness of Pb208 independently of the equation of state, while this correlation depends on the coupling constant in EiBI. As a result, via the direct observations of the radius of the neutron star with 0.5M? and the measurements of a neutron skin thickness of Pb208 by the terrestrial experiments, one could not only discriminate EiBI from general relativity but also estimate the coupling constant in EiBI.

Sotani, Hajime

2014-05-01

111

The curve of growth for the sun as a star in the Milne-Eddington approximation  

NASA Astrophysics Data System (ADS)

For the first time, the experimental curve of growth for the Sun as a star has been constructed in the Milne-Eddington approximation, basing on the Fe I lines. The cleanest 280 Fe I lines in the spectral region from ?4000 Å to ?7000 Å have been used. The equivalent widths have been taken from the works of Rutten and van der Zalm who had published a list of 602 clean (unblended) lines in the spectrum of the Sun as a star from Becker et al.'s atlas. Kostyk's system of absolute oscillator strengths was used. The velocity of microturbulent motion (vm = 1±0.3 km/s), excitation temperature (Tex = 5360±70K) and iron abundance (lg NFe = 7.57±0.10) in the photosphere of the Sun as a star were determined.

Kuli-Zade, D. M.; Gusejnov, K. I.

1988-06-01

112

Dark matter density profile and galactic metric in Eddington-inspired Born-Infeld gravity  

NASA Astrophysics Data System (ADS)

We consider the density profile of pressureless dark matter in Eddington-inspired Born-Infeld (EiBI) gravity. The gravitational field equations are investigated for a spherically symmetric dark matter galactic halo, by adopting a phenomenological tangential velocity profile for test particles moving in stable circular orbits around the galactic center. The density profile and the mass distribution, as well as the general form of the metric tensor is obtained by numerically integrating the gravitational field equations, and in an approximate analytical form by using the Newtonian limit of the theory. In the weak field limit, the dark matter density distribution is described by the Lane-Emden equation with polytropic index n = 1, and is nonsingular at the galactic center. The parameter ? of the theory is determined so that the theory could provide a realistic description of the dark matter halos. The gravitational properties of the dark matter halos are also briefly discussed in the Newtonian approximation.

Harko, Tiberiu; Lobo, Francisco S. N.; Mak, M. K.; Sushkov, Sergey V.

2014-03-01

113

Continuum-driven versus line-driven mass loss and the Eddington limit  

NASA Astrophysics Data System (ADS)

Basic stellar structure dictates that stars of ˜ 100 M or more will be close to the Eddington limit, with luminosities in excess of 106 L, and radiation pressure contributing prominently to the support against gravity. Although it is formally possible to generate static structure models of even more massive stars, recent studies of dense clusters show there is a sharp cutoff at masses above ˜ 150 M. This talk examines the role of extreme mass loss is limiting the masses of stars, emphasizing in particular that continuum driving, possibly associated with structural instabilities of radiation dominated envelope, can lead to much stronger mass loss than is possible by the usual line-scattering mechanism of steady stellar winds. However, population studies of very young, dense stellar clusters now suggest quite strongly that there is a sharp cutoff at masses above ca. 150 M (see, e.g., the talk by Sally Oey, in this JD 05, p. 206). This is sometimes attributed to a mass limit on star formation by accretion processes, though there are competing formation scenarios by binary or cluster merging that would seem likely to lead to formation of even higher mass stars (see talks in JD14 and S237). So given the above rough coincidence of the observational upper mass limit with the Eddington-limit domain of radiation-pressure dominance, it seems associated instabilities in stellar structure might actually be a more important factor in this upper mass limit, leading to extreme mass loss in LBV and/or giant eruption events, much as inferred from circumstellar nebulae observed around high mass stars like eta Carinae and the Pistol star.

Owocki, Stanley P.

2007-08-01

114

Bolometric luminosities and Eddington ratios of X-ray selected active galactic nuclei in the XMM-COSMOS survey  

NASA Astrophysics Data System (ADS)

Bolometric luminosities and Eddington ratios of both X-ray selected broad-line (Type-1) and narrow-line (Type-2) active galactic nuclei (AGN) from the XMM-Newton survey in the Cosmic Evolution Survey field are presented. The sample is composed of 929 AGN (382 Type-1 AGN and 547 Type-2 AGN) and it covers a wide range of redshifts, X-ray luminosities and absorbing column densities. About 65 per cent of the sources are spectroscopically identified as either Type-1 or Type-2 AGN (83 and 52 per cent, respectively), while accurate photometric redshifts are available for the rest of the sample. The study of such a large sample of X-ray selected AGN with a high-quality multiwavelength coverage from the far-infrared (now with the inclusion of Herschel data at 100 and 160 ?m) to the optical-ultraviolet allows us to obtain accurate estimates of bolometric luminosities, bolometric corrections and Eddington ratios. The kbol - Lbol relations derived in this work are calibrated for the first time against a sizable AGN sample, and rely on observed redshifts, X-ray luminosities and column density distributions. We find that kbol is significantly lower at high Lbol with respect to previous estimates by Marconi et al. and Hopkins et al. Black hole (BH) masses and Eddington ratios are available for 170 Type-1 AGN, while BH masses for Type-2 AGN are computed for 481 objects using the BH mass-stellar mass relation and the morphological information. We confirm a trend between kbol and ?Edd, with lower hard X-ray bolometric corrections at lower Eddington ratios for both Type-1 and Type-2 AGN. We find that, on average, the Eddington ratio increases with redshift for all types of AGN at any given MBH, while no clear evolution with redshift is seen at any given Lbol.

Lusso, E.; Comastri, A.; Simmons, B. D.; Mignoli, M.; Zamorani, G.; Vignali, C.; Brusa, M.; Shankar, F.; Lutz, D.; Trump, J. R.; Maiolino, R.; Gilli, R.; Bolzonella, M.; Puccetti, S.; Salvato, M.; Impey, C. D.; Civano, F.; Elvis, M.; Mainieri, V.; Silverman, J. D.; Koekemoer, A. M.; Bongiorno, A.; Merloni, A.; Berta, S.; Le Floc'h, E.; Magnelli, B.; Pozzi, F.; Riguccini, L.

2012-09-01

115

Relativistic timescale analysis suggests lunar theory revision  

NASA Astrophysics Data System (ADS)

The SI second of the atomic clock was calibrated to match the Ephemeris Time (ET) second in a mutual four year effort between the National Physical Laboratory (NPL) and the United States Naval Observatory (USNO). The ephemeris time is 'clocked' by observing the elapsed time it takes the Moon to cross two positions (usually occultation of stars relative to a position on Earth) and dividing that time span into the predicted seconds according to the lunar equations of motion. The last revision of the equations of motion was the Improved Lunar Ephemeris (ILE), which was based on E. W. Brown's lunar theory. Brown classically derived the lunar equations from a purely Newtonian gravity with no relativistic compensations. However, ET is very theory dependent and is affected by relativity, which was not included in the ILE. To investigate the relativistic effects, a new, noninertial metric for a gravitated, translationally accelerated and rotating reference frame has three sets of contributions, namely (1) Earth's velocity, (2) the static solar gravity field and (3) the centripetal acceleration from Earth's orbit. This last term can be characterized as a pseudogravitational acceleration. This metric predicts a time dilation calculated to be -0.787481 seconds in one year. The effect of this dilation would make the ET timescale run slower than had been originally determined. Interestingly, this value is within 2 percent of the average leap second insertion rate, which is the result of the divergence between International Atomic Time (TAI) and Earth's rotational time called Universal Time (UT or UTI). Because the predictions themselves are significant, regardless of the comparison to TAI and UT, the authors will be rederiving the lunar ephemeris model in the manner of Brown with the relativistic time dilation effects from the new metric to determine a revised, relativistic ephemeris timescale that could be used to determine UT free of leap second adjustments.

Deines, Steven D.; Williams, Carol A.

1995-05-01

116

Relativistic timescale analysis suggests lunar theory revision  

NASA Technical Reports Server (NTRS)

The SI second of the atomic clock was calibrated to match the Ephemeris Time (ET) second in a mutual four year effort between the National Physical Laboratory (NPL) and the United States Naval Observatory (USNO). The ephemeris time is 'clocked' by observing the elapsed time it takes the Moon to cross two positions (usually occultation of stars relative to a position on Earth) and dividing that time span into the predicted seconds according to the lunar equations of motion. The last revision of the equations of motion was the Improved Lunar Ephemeris (ILE), which was based on E. W. Brown's lunar theory. Brown classically derived the lunar equations from a purely Newtonian gravity with no relativistic compensations. However, ET is very theory dependent and is affected by relativity, which was not included in the ILE. To investigate the relativistic effects, a new, noninertial metric for a gravitated, translationally accelerated and rotating reference frame has three sets of contributions, namely (1) Earth's velocity, (2) the static solar gravity field and (3) the centripetal acceleration from Earth's orbit. This last term can be characterized as a pseudogravitational acceleration. This metric predicts a time dilation calculated to be -0.787481 seconds in one year. The effect of this dilation would make the ET timescale run slower than had been originally determined. Interestingly, this value is within 2 percent of the average leap second insertion rate, which is the result of the divergence between International Atomic Time (TAI) and Earth's rotational time called Universal Time (UT or UTI). Because the predictions themselves are significant, regardless of the comparison to TAI and UT, the authors will be rederiving the lunar ephemeris model in the manner of Brown with the relativistic time dilation effects from the new metric to determine a revised, relativistic ephemeris timescale that could be used to determine UT free of leap second adjustments.

Deines, Steven D.; Williams, Carol A.

1995-01-01

117

Long time-scale variability in GRS1915+105  

Microsoft Academic Search

We present very high resolution hydrodynamical simulations of accretion discs\\u000ain black hole X-ray binaries accreting near the Eddington limit. The results\\u000ashow that mass loss, irradiation and tidal interactions all have a profound\\u000aeffect on the observed behaviour of long period X-ray transients. In\\u000aparticular, the interplay of all of these effects in the outer regions of the\\u000aaccretion

Michael Truss; Graham Wynn

2004-01-01

118

Rheological Behavior of Living Cells Is Timescale-Dependent  

PubMed Central

The dynamic mechanical behavior of living cells has been proposed to result from timescale-invariant processes governed by the soft glass rheology theory derived from soft matter physics. But this theory is based on experimental measurements over timescales that are shorter than those most relevant for cell growth and function. Here we report results measured over a wider range of timescales which demonstrate that rheological behaviors of living cells are not timescale-invariant. These findings demonstrate that although soft glass rheology appears to accurately predict certain cell mechanical behaviors, it is not a unified model of cell rheology under biologically relevant conditions and thus, alternative mechanisms need to be considered.

Stamenovic, Dimitrije; Rosenblatt, Noah; Montoya-Zavala, Martin; Matthews, Benjamin D.; Hu, Shaohua; Suki, Bela; Wang, Ning; Ingber, Donald E.

2007-01-01

119

Empirical distributions of Chinese stock returns at different microscopic timescales  

NASA Astrophysics Data System (ADS)

We study the distributions of event-time returns and clock-time returns at different microscopic timescales using ultra-high-frequency data extracted from the limit-order books of 23 stocks traded in the Chinese stock market in 2003. We find that the returns at the one-trade timescale obey the inverse cubic law. For larger timescales (2-32 trades and 1-5 min), the returns follow the Student distribution with power-law tails. With the decrease in timescale, the tail becomes fatter, which is consistent with the variational theory in Turbulence.

Gu, Gao-Feng; Chen, Wei; Zhou, Wei-Xing

2008-01-01

120

Timescale dependent deformation of orogenic belts?  

NASA Astrophysics Data System (ADS)

The principle aim to link geodetic, paleoseismologic and geologic estimates of fault slip is to extrapolate the respective rates from one timescale to the other to finally predict the recurrence interval of large earthquakes, which threat human habitats. This approach however, is based on two often implicitly made assumptions: a uniform slip distribution through time and space and no changes of the boundary conditions during the time interval of interest. Both assumptions are often hard to verify. A recent study, which analysed an exceptionally complete record of seismic slip for the Wasatch and related faults (Basin and Range province), ranging from 10 yr to 10 Myr suggests that such a link between geodetic and geologic rates might not exist, i.e., that our records of fault displacement may depend on the timescale over which they were measured. This view derives support from results of scaled 2D sandbox experiments, as well as numerical simulations with distinct elements, both of which investigated the effect of boundary conditions such as flexure, mechanic stratigraphy and erosion on the spatio-temporal distribution of deformation within bivergent wedges. We identified three types of processes based on their distinct spatio-temporal distribution of deformation. First, incremental strain and local strain rates are very short-lived are broadly distributed within the bivergent wedge and no temporal pattern could be established. Second, footwall shortcuts and the re-activation of either internal thrusts or of the retro shear-zone are irregularly distributed in time and are thus not predictable either, but last for a longer time interval. Third, the stepwise initiation and propagation of the deformation front is very regular in time, since it depends on the thickness of the incoming layer and on its internal and basal material properties. We consider the propagation of the deformation front as an internal clock of a thrust belt, which is therefore predictable. A deformation front advance cycle requires the longest timescale. Thus, despite known and constant boundary conditions during the simulations, we found only one regular temporal pattern of deformation in a steady active bivergent-wedge. We therefore propose that the structural inventory of an orogenic belt is hierarchically ordered with respect to accumulated slip, in analogy to the discharge pattern in a drainage network. The deformation front would have the highest, a branching splay the lowest order. Since kinematic boundary conditions control deformation front advance, its timing and the related maximum magnitude of finite strain, i.e. throw on the frontal thrust are predictable. However, the number of controlling factors, such as the degree of strain softening, the orientation of faults or fluid flow and resulting cementation of faults, responsible for the reactivation of faults increases with increasing distance from the deformation front. Since it is rarely possible to determine the complete network of forces within a wedge, the reactivation of lower order structures is not predictable in time and space. Two implications for field studies may emerge: A change of the propagation of deformation can only be determined, if at least two accretion cycles are sampled. The link between geodetic, paleoseismologic and geologic fault slip estimates can only be successfully derived if the position of the investigated fault within the hierarchical order has not changed over the time interval of interest.

Hoth, S.; Friedrich, A. M.; Vietor, T.; Hoffmann-Rothe, A.; Kukowski, N.; Oncken, O.

2004-12-01

121

Two Timescale Dispersal of Magnetized Protoplanetary Disks  

NASA Astrophysics Data System (ADS)

Protoplanetary disks are likely to be threaded by a weak net flux of vertical magnetic field that is a remnant of the much larger fluxes present in molecular cloud cores. If this flux is approximately conserved its dynamical importance will increase as mass is accreted, initially by stimulating magnetorotational disk turbulence and subsequently by enabling wind angular momentum loss. We use fits to numerical simulations of ambipolar dominated disk turbulence to construct simplified one-dimensional evolution models for weakly magnetized protoplanetary disks. We show that the late onset of significant angular momentum loss in a wind can give rise to "two timescale" disk evolution in which a long phase of viscous evolution precedes rapid dispersal as the wind becomes dominant. The wide dispersion in disk lifetimes could therefore be due to varying initial levels of net flux. Magnetohydrodynamic (MHD) wind triggered dispersal differs from photoevaporative dispersal in predicting mass loss from small (<1 AU) scales, where thermal winds are suppressed. Our specific models are based on a limited set of simulations that remain uncertain, but qualitatively similar evolution appears likely if mass is lost from disks more quickly than flux, and if MHD winds become important as the plasma ? decreases.

Armitage, Philip J.; Simon, Jacob B.; Martin, Rebecca G.

2013-11-01

122

Schwinger's Approach to Einstein's Gravity  

NASA Astrophysics Data System (ADS)

Albert Einstein was one of Julian Schwinger's heroes, and Schwinger was greatly honored when he received the first Einstein Prize (together with Kurt Godel) for his work on quantum electrodynamics. Schwinger contributed greatly to the development of a quantum version of gravitational theory, and his work led directly to the important work of (his students) Arnowitt, Deser, and DeWitt on the subject. Later in the 1960's and 1970's Schwinger developed a new formulation of quantum field theory, which he dubbed Source Theory, in an attempt to get closer contact to phenomena. In this formulation, he revisited gravity, and in books and papers showed how Einstein's theory of General Relativity emerged naturally from one physical assumption: that the carrier of the gravitational force is a massless, helicity-2 particle, the graviton. (There has been a minor dispute whether gravitational theory can be considered as the massless limit of a massive spin-2 theory; Schwinger believed that was the case, while Van Dam and Veltman concluded the opposite.) In the process, he showed how all of the tests of General Relativity could be explained simply, without using the full machinery of the theory and without the extraneous concept of curved space, including such effects as geodetic precession and the Lense-Thirring effect. (These effects have now been verified by the Gravity Probe B experiment.) This did not mean that he did not accept Einstein's equations, and in his book and full article on the subject, he showed how those emerge essentially uniquely from the assumption of the graviton. So to speak of Schwinger versus Einstein is misleading, although it is true that Schwinger saw no necessity to talk of curved spacetime. In this talk I will lay out Schwinger's approach, and the connection to Einstein's theory.

Milton, Kim

2012-05-01

123

On the Radiative Efficiencies, Eddington Ratios, and Duty Cycles of Luminous High-redshift Quasars  

NASA Astrophysics Data System (ADS)

We investigate the characteristic radiative efficiency epsilon, Eddington ratio ?, and duty cycle P 0 of high-redshift active galactic nuclei (AGNs), drawing on measurements of the AGN luminosity function at z = 3-6 and, especially, on recent measurements of quasar clustering at z = 3-4.5 from the Sloan Digital Sky Survey. The free parameters of our models are epsilon, ?, and the normalization, scatter, and redshift evolution of the relation between black hole (BH) mass M BH and halo virial velocity V vir. We compute the luminosity function from the implied growth of the BH mass function and the quasar correlation length from the bias of the host halos. We test our adopted formulae for the halo mass function and halo bias against measurements from the large N-body simulation developed by the MICE collaboration. The strong clustering of AGNs observed at z = 3 and, especially, at z = 4 implies that massive BHs reside in rare, massive dark matter halos. Reproducing the observed luminosity function then requires high efficiency epsilon and/or low Eddington ratio ?, with a lower limit (based on 2? agreement with the measured z = 4 correlation length) epsilon >~ 0.7?/(1 + 0.7?), implying epsilon >~ 0.17 for ?>0.25. Successful models predict high duty cycles, P 0 ~ 0.2, 0.5, and 0.9 at z = 3.1, 4.5, and 6, respectively, and they require that the fraction of halo baryons locked in the central BH is much larger than the locally observed value. The rapid drop in the abundance of the massive and rare host halos at z > 7 implies a proportionally rapid decline in the number density of luminous quasars, much stronger than simple extrapolations of the z = 3-6 luminosity function would predict. For example, our most successful model predicts that the highest redshift quasar in the sky with true bolometric luminosity L > 1047.5 erg s-1 should be at z ~ 7.5, and that all quasars with higher apparent luminosities would have to be magnified by lensing.

Shankar, Francesco; Crocce, Martin; Miralda-Escudé, Jordi; Fosalba, Pablo; Weinberg, David H.

2010-07-01

124

Galileo and Einstein: Physics Flashlets  

NSDL National Science Digital Library

This is a collection of Flash animations developed to support a course in introductory historical astronomy. The "Flashlets" are presented sequentially, beginning with early Greek science and Galilean motion. The series progresses through the Kepler's and Newton's Laws and culminates in Einstein's theory of special relativity and time dilation. This collection is part of a larger set of curriculum materials developed at the University of Virginia for the course "Galileo and Einstein". See Related Materials for a link to the full index, which includes lecture notes, Java simulations, and historical excerpts.

Fowler, Michael

2008-07-29

125

Einstein Solid Temperature Demon Worksheet and Model  

NSDL National Science Digital Library

A worksheet that considers an Einstein solid in contact with a temperature demon (a single oscillator thermometer that exchanges energy with the Einstein solid). The combined solid-demon system is isolated. The number of energy units in this system can be adjusted by editing the field in the main display. All of this energy is originally in the Einstein solid, but after interaction starts it is shared between the demon and the Einstein solid.

Wheaton, Spencer

2013-08-16

126

Modelling periodic oscillation of biological systems with multiple timescale networks  

Microsoft Academic Search

In this paper, we aim to develop a new methodology to model and design periodic oscillators of biological networks, in particular gene regulatory networks with multiple genes, proteins and time delays, by using multiple timescale networks (MTN). Fast reactions constitute a positive feedback-loop network (PFN), while slow reactions consist of a cyclic feedback-loop network (CFN), in MTN. Multiple timescales are

R. Wang; T. Zhou; Z. Jing; L. Chen

2004-01-01

127

Response to Deines and Williams on Astronomical Timescales  

Microsoft Academic Search

In a paper presented at this conference, Deines and Williams (DW) question the conventional determination and interpretation of the differences between astronomical timescales, such as Universal Time (UT) which deals with Earth rotation, Atomic Time (AT), and planetary ephemeride timescales such as Terrestrial Time (TT). This paper offers explanations attempting to remove some sources of confusion on the subject, in

Victor J. Slabinski

2009-01-01

128

Einstein for Schools and the General Public  

ERIC Educational Resources Information Center

In April 2005 the World Year of Physics (Einstein Year in the UK and Ireland) was celebrated with an Einstein week in Stockholm House of Science. Seven experiments illustrated Einstein's remarkable work in 1905 on Brownian motion, the photoelectric effect and special relativity. Thirteen school classes with 260 pupils, 30 teachers and 25 members…

Johansson, K. E.; Kozma, C; Nilsson, Ch

2006-01-01

129

Development of a pulsar-based time-scale  

NASA Astrophysics Data System (ADS)

Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Échelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.

Hobbs, G.; Coles, W.; Manchester, R. N.; Keith, M. J.; Shannon, R. M.; Chen, D.; Bailes, M.; Bhat, N. D. R.; Burke-Spolaor, S.; Champion, D.; Chaudhary, A.; Hotan, A.; Khoo, J.; Kocz, J.; Levin, Y.; Oslowski, S.; Preisig, B.; Ravi, V.; Reynolds, J. E.; Sarkissian, J.; van Straten, W.; Verbiest, J. P. W.; Yardley, D.; You, X. P.

2012-12-01

130

The Eddington Limit in Cosmic Rays: An Explanation for the Observed Faintness of Starbursting Galaxies  

NASA Astrophysics Data System (ADS)

We show that the luminosity of a star-forming galaxy is capped by the production and subsequent expulsion of cosmic rays from its interstellar medium. By defining an Eddington luminosity in cosmic rays, we show that the star formation rate of a given galaxy is limited by its mass content and the cosmic-ray mean free path. When the cosmic-ray luminosity and pressure reach a critical value as a result of vigorous star formation, hydrostatic balance is lost, a galactic-scale cosmic-ray-driven wind develops, and star formation is choked off. Cosmic-ray pressure driven winds are likely to produce wind velocities in proportion to and significantly in excess of the galactic escape velocity. It is possible that cosmic-ray feedback results in the Faber-Jackson relation for a plausible set of input parameters that describe cosmic-ray production and transport, which are calibrated by observations of the Milky Way's interstellar cosmic rays as well as other nearby galaxies.

Socrates, Aristotle; Davis, Shane W.; Ramirez-Ruiz, Enrico

2008-11-01

131

Eddington-inspired Born-Infeld gravity: Astrophysical and cosmological constraints  

NASA Astrophysics Data System (ADS)

In this paper we compute stringent astrophysical and cosmological constraints on a recently proposed Eddington-inspired Born-Infeld theory of gravity. We find, using a generalized version of the Zel’dovich approximation, that in this theory a pressureless, cold-dark matter fluid has a nonzero effective sound speed. We compute the corresponding effective Jeans length and show that it is approximately equal to the fundamental length of the theory R*=?1/2G-1/2, where ? is the only additional parameter of theory with respect to general relativity and G is the gravitational constant. This scale determines the minimum size of compact objects which are held together by gravity. We also estimate the critical mass above which pressureless compact objects are unstable against collapse into a black hole, showing that it is approximately equal to the fundamental mass M*=?1/2c2G-3/2, and we show that the maximum density attainable inside stable compact stars is roughly equal to the fundamental density ?*=?-1c2, where c is the speed of light in vacuum. We find that the mere existence of astrophysical objects of size R, which are held together by their own gravity, leads to the constraint ?

Avelino, P. P.

2012-05-01

132

Structure of neutron, quark, and exotic stars in Eddington-inspired Born-Infeld gravity  

NASA Astrophysics Data System (ADS)

We consider the structure and physical properties of specific classes of neutron, quark, and “exotic” stars in Eddington-inspired Born-Infeld (EiBI) gravity. The latter reduces to standard general relativity in vacuum, but presents a different behavior of the gravitational field in the presence of matter. The equilibrium equations for a spherically symmetric configuration (mass continuity and Tolman-Oppenheimer-Volkoff) are derived, and their solutions are obtained numerically for different equations of state of neutron and quark matter. More specifically, stellar models, described by the stiff fluid, radiationlike, polytropic and the bag model quark equations of state are explicitly constructed in both general relativity and EiBI gravity, thus allowing a comparison between the predictions of these two gravitational models. As a general result it turns out that for all the considered equations of state, EiBI gravity stars are more massive than their general relativistic counterparts. Furthermore, an exact solution of the spherically symmetric field equations in EiBI gravity, describing an exotic star, with decreasing pressure but increasing energy density, is also obtained. As a possible astrophysical application of the obtained results we suggest that stellar mass black holes, with masses in the range of 3.8M? and 6M?, respectively, could be in fact EiBI neutron or quark stars.

Harko, Tiberiu; Lobo, Francisco S. N.; Mak, M. K.; Sushkov, Sergey V.

2013-08-01

133

THE DEMOGRAPHICS OF BROAD-LINE QUASARS IN THE MASS-LUMINOSITY PLANE. II. BLACK HOLE MASS AND EDDINGTON RATIO FUNCTIONS  

SciTech Connect

We employ a flexible Bayesian technique to estimate the black hole (BH) mass and Eddington ratio functions for Type 1 (i.e., broad line) quasars from a uniformly selected data set of {approx}58, 000 quasars from the Sloan Digital Sky Survey (SDSS) DR7. We find that the SDSS becomes significantly incomplete at M {sub BH} {approx}< 3 Multiplication-Sign 10{sup 8} M {sub Sun} or L/L {sub Edd} {approx}< 0.07, and that the number densities of Type 1 quasars continue to increase down to these limits. Both the mass and Eddington ratio functions show evidence of downsizing, with the most massive and highest Eddington ratio BHs experiencing Type 1 quasar phases first, although the Eddington ratio number densities are flat at z < 2. We estimate the maximum Eddington ratio of Type 1 quasars in the observable universe to be L/L {sub Edd} {approx} 3. Consistent with our results in Shen and Kelly, we do not find statistical evidence for a so-called sub-Eddington boundary in the mass-luminosity plane of broad-line quasars, and demonstrate that such an apparent boundary in the observed distribution can be caused by selection effect and errors in virial BH mass estimates. Based on the typical Eddington ratio in a given mass bin, we estimate growth times for the BHs in Type 1 quasars and find that they are comparable to or longer than the age of the universe, implying an earlier phase of accelerated (i.e., with higher Eddington ratios) and possibly obscured growth. The large masses probed by our sample imply that most of our BHs reside in what are locally early-type galaxies, and we interpret our results within the context of models of self-regulated BH growth.

Kelly, Brandon C. [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93107 (United States)] [Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93107 (United States); Shen, Yue [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)] [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-51, Cambridge, MA 02138 (United States)

2013-02-10

134

Stability of the Einstein Universe.  

National Technical Information Service (NTIS)

It is shown that the Einstein Universe is stable by a large class of exact perturbations, which are made starting from a detailed exam of the topology of the model, and which include perturbations of the type considered by Lemaitre. The problem is reduced...

I. D. Soares

1983-01-01

135

4-Manifolds without Einstein Metrics  

Microsoft Academic Search

It is shown that there are infinitely many compact orientable smooth 4-manifolds which do not admit Einstein metrics, but nevertheless satisfy the strict Hitchin-Thorpe inequality 2 chi > 3 |tau|. The examples in question arise as non-minimal complex algebraic surfaces of general type, and the method of proof stems from Seiberg-Witten theory.

Claude LeBrun; SUNY Stony Brook

1995-01-01

136

Einstein Metrics on Complex Surfaces  

Microsoft Academic Search

We consider compact complex surfaces with Hermitian metrics which are Einstein but not Kaehler. It is shown that the manifold must be CP2 blown up at 1,2, or 3 points, and the isometry group of the metric must contain a 2-torus. Thus the Page metric on CP2#(-CP2) is almost the only metric of this type.

Claude LeBrun; SUNY Stony Brook

1995-01-01

137

Einstein Metrics and Mostow Rigidity  

Microsoft Academic Search

Using the new diffeomorphism invariants of Seiberg and Witten, a uniqueness theorem is proved for Einstein metrics on compact quotients of irreducible 4-dimensional symmetric spaces of non-compact type. The proof also yields a Riemannian version of the Miyaoka-Yau inequality.

Claude LeBrun; SUNY Stony Brook

1994-01-01

138

Approaching Bose-Einstein Condensation  

ERIC Educational Resources Information Center

Bose-Einstein condensation (BEC) is discussed at the level of an advanced course of statistical thermodynamics, clarifying some formal and physical aspects that are usually not covered by the standard pedagogical literature. The non-conventional approach adopted starts by showing that the continuum limit, in certain cases, cancels out the crucial…

Ferrari, Loris

2011-01-01

139

Building a Bridge to Deep Time: Sedimentary Systems Across Timescales  

NASA Astrophysics Data System (ADS)

It is increasingly important to understand the complex and interdependent processes associated with sediment production, transport, and deposition at timescales relevant to civilization (annual to millennial). However, predicting the response of sedimentary systems to global environmental change across a range of timescales remains a significant challenge. For example, a significant increase in global average temperature at the Paleocene-Eocene boundary (55.8 Ma) is interpreted to have occurred over millennial timescales; however, the specific response of sedimentary systems (e.g., timing and magnitude of sediment flux variability in river systems) to that forcing is debated. Thus, using such environmental perturbations recorded in sedimentary archives as analogs for ongoing/future global change requires improved approaches to bridging across time. Additionally, the ability to bridge timescales is critical for addressing other questions about sedimentary system behavior, including signal propagation and signal versus ';noise' in the record. The geologic record provides information that can be used to develop a comprehensive understanding of process-response behavior at multiple timescales. The geomorphic ';snapshot' of present-day erosional and depositional landscapes can be examined to reconstruct the history of processes that created the observable configurations. Direct measurement and monitoring of active processes are used to constrain conceptual and numerical models and develop sedimentary system theory. But real-time observations of active Earth-surface processes are limited to the very recent, and how such processes integrate over longer timescales to transform into strata remains unknown. At longer timescales (>106 yr), the stratigraphic record is the only vestige of ancient sedimentary systems. Stratigraphic successions contain a complex record of sediment deposition and preservation, as well as the detrital material that originated in long since denuded orogenic belts. Moreover, as the timescale of the duration of the process-response behavior and/or system age increase, additional aspects must be considered (e.g., significant tectonic regime change, rare but significant events, non-periodic global change, etc.). In this presentation we discuss several examples of sedimentary system analysis at different timescales with the goal of highlighting various approaches at one timescale and how they can (or cannot) be applied for questions at different timescales. Examples include: (1) brief review of decadal to centennial sediment budgets; (2) land-to-sea sediment budget reconstructions from southern California at millennial to multi-millennial timescales, and (3) sedimentary system response to climatic and tectonic forcings at ?105 yr timescales.

Romans, B.; Castelltort, S.; Covault, J. A.; Walsh, J. P.

2013-12-01

140

EDDINGTON-LIMITED ACCRETION AND THE BLACK HOLE MASS FUNCTION AT REDSHIFT 6  

SciTech Connect

We present discovery observations of a quasar in the Canada-France High-z Quasar Survey (CFHQS) at redshift z = 6.44. We also use near-infrared spectroscopy of nine CFHQS quasars at z {approx} 6 to determine black hole masses. These are compared with similar estimates for more luminous Sloan Digital Sky Survey quasars to investigate the relationship between black hole mass and quasar luminosity. We find a strong correlation between Mg II FWHM and UV luminosity and that most quasars at this early epoch are accreting close to the Eddington limit. Thus, these quasars appear to be in an early stage of their life cycle where they are building up their black hole mass exponentially. Combining these results with the quasar luminosity function, we derive the black hole mass function at z = 6. Our black hole mass function is {approx}10{sup 4} times lower than at z = 0 and substantially below estimates from previous studies. The main uncertainties which could increase the black hole mass function are a larger population of obscured quasars at high redshift than is observed at low redshift and/or a low quasar duty cycle at z = 6. In comparison, the global stellar mass function is only {approx}10{sup 2} times lower at z = 6 than at z = 0. The difference between the black hole and stellar mass function evolution is due to either rapid early star formation which is not limited by radiation pressure as is the case for black hole growth or inefficient black hole seeding. Our work predicts that the black hole mass-stellar mass relation for a volume-limited sample of galaxies declines rapidly at very high redshift. This is in contrast to the observed increase at 4 < z < 6 from the local relation if one just studies the most massive black holes.

Willott, Chris J.; Crampton, David; Hutchings, John B.; Schade, David [Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada); Albert, Loic [Canada-France-Hawaii Telescope Corporation, 65-1238 Mamalahoa Highway, Kamuela, HI 96743 (United States); Arzoumanian, Doris [CEA-Saclay, IRFU, SAp, 91191 Gif-sur-Yvette (France); Bergeron, Jacqueline; Omont, Alain [Institut d'Astrophysique de Paris, CNRS and Universite Pierre et Marie Curie, 98bis Boulevard Arago, F-75014 Paris (France); Delorme, Philippe [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews KY16 9SS (United Kingdom); Reyle, Celine, E-mail: chris.willott@nrc.c [Institut Utinam, Observatoire de Besancon, Universite de Franche-Comte, BP1615, 25010 Besancon Cedex (France)

2010-08-15

141

Diffusion Time-Scale of Porous Pressure-Sensitive Paint.  

National Technical Information Service (NTIS)

Pressure-sensitive paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic flows require fast time response of the paint. There are two characteristic time-scales that are rela...

T. Liu N. Teduka M. Kameda K. Asai

2001-01-01

142

Wind Power Forecasting Error Distributions over Multiple Timescales: Preprint  

SciTech Connect

In this paper, we examine the shape of the persistence model error distribution for ten different wind plants in the ERCOT system over multiple timescales. Comparisons are made between the experimental distribution shape and that of the normal distribution.

Hodge, B. M.; Milligan, M.

2011-03-01

143

A. Einstein - Image and Impact  

NSDL National Science Digital Library

This online exhibit on the life of Albert Einstein takes a somewhat less orthodox approach. How did an ordinary patent clerk with an undistinguished college record evolve into one of the most profound thinkers of all time, whose contributions to theoretical physics changed the world? Was it the structure of his brain (the exhibit delves into images of Einstein's brain taken after his death). Was it the support of key friends and family members at an early age? Was it his associations with noted physicists such as Max Planck? Einsteinâs major achievements, his public and personal life, and his philosophy are all explored in this resource produced by the American Institute of Physics. Archived speech clips, photos, quotations, and essays serve to bring the exhibit to life. A âSite Contentsâ section provides an overview and facilitates navigation within the exhibit.

Physics, American I.

2012-02-01

144

Parameterized Beyond-Einstein Growth  

SciTech Connect

A single parameter, the gravitational growth index gamma, succeeds in characterizing the growth of density perturbations in the linear regime separately from the effects of the cosmic expansion. The parameter is restricted to a very narrow range for models of dark energy obeying the laws of general relativity but can take on distinctly different values in models of beyond-Einstein gravity. Motivated by the parameterized post-Newtonian (PPN) formalism for testing gravity, we analytically derive and extend the gravitational growth index, or Minimal Modified Gravity, approach to parameterizing beyond-Einstein cosmology. The analytic formalism demonstrates how to apply the growth index parameter to early dark energy, time-varying gravity, DGP braneworld gravity, and some scalar-tensor gravity.

Linder, Eric; Linder, Eric V.; Cahn, Robert N.

2007-09-17

145

Unifying Einstein and Palatini gravities  

SciTech Connect

We consider a novel class of f(R) gravity theories where the connection is related to the conformally scaled metric g{sub {mu}{nu}=}C(R)g{sub {mu}{nu}} with a scaling that depends on the scalar curvature R only. We call them C theories and show that the Einstein and Palatini gravities can be obtained as special limits. In addition, C theories include completely new physically distinct gravity theories even when f(R)=R. With nonlinear f(R), C theories interpolate and extrapolate the Einstein and Palatini cases and may avoid some of their conceptual and observational problems. We further show that C theories have a scalar-tensor formulation, which in some special cases reduces to simple Brans-Dicke-type gravity. If matter fields couple to the connection, the conservation laws in C theories are modified. The stability of perturbations about flat space is determined by a simple condition on the Lagrangian.

Amendola, Luca; Enqvist, Kari; Koivisto, Tomi [Institut fuer Theoretische Physik, University of Heidelberg, Philosophenweg 16, 69120 Heidelberg (Germany); Physics Department, University of Helsinki, and Helsinki Institute of Physics, FIN-00014 University of Helsinki (Finland); Institute for Theoretical Physics and Spinoza Institute, Leuvenlaan 4, 3584 CE Utrecht (Netherlands)

2011-02-15

146

Quantification of Biochar's 'Stable' Carbon on Centennial Timescales  

NASA Astrophysics Data System (ADS)

A basic requirement for any biochar offset methodology is for the carbon in biochar to be stable and remain sequestered on centennial timescales. It is well known that a variable component of most biochar is labile (degradable on annual/decadal timescales) and hence only a proportion of total carbon in biochar provides long-term carbon sequestration. This stable fraction of biochar is in the form of polycyclic aromatic carbon (PAC) but small ring size compounds (

McBeath, Anna; Bird, Michael

2014-05-01

147

Multisoliton solutions to Einstein's equations  

SciTech Connect

We discuss a multisoliton solution to Einstein's equations in vacuum. The solution is interpreted as many gravitational solitons propagating and colliding on a homogeneous cosmological background. Following a previous letter, we characterize the solitons by their localizability and by their peculiar properties under collisions. Furthermore, we define an associated frame-dependent velocity field which illustrates the solitonic character of these gravitational solitons in the classical sense.

Ibaez, J.; Verdaguer, E.

1985-01-15

148

The X-ray outburst of RX J0520.5-6932 is reaching the Eddington luminosity  

NASA Astrophysics Data System (ADS)

We report on the evolution of the current X-ray outburst of the LMC Be/X-ray binary pulsar RX J0520.5-6932 (see ATel #5673) from our Swift/XRT monitoring. Since the start of the outburst (2013 Dec 28) the luminosity of the source has continued to rise to a maximum of 1.91×1038erg s-1 (0.3-10 keV band), which is close to or at the Eddington limit for a neutron star.

Vasilopoulos, G.; Sturm, R.; Maggi, P.; Haberl, F.

2014-01-01

149

Einstein as a Missionary of Science  

NASA Astrophysics Data System (ADS)

The paper reviews Einstein's engagement as a mediator and popularizer of science. It discusses the formative role of popular scientific literature for the young Einstein, showing that not only his broad scientific outlook but also his internationalist political views were shaped by these readings. Then, on the basis of recent detailed studies, Einstein's travels and their impact on the dissemination of relativity theory are examined. These activities as well as Einstein's own popular writings are interpreted in the context of his understanding of science as part of human culture.

Renn, Jürgen

2013-10-01

150

Einstein's Viscous Advice Flowed Freely Nonetheless  

NASA Astrophysics Data System (ADS)

This talk will examine a 1930 letter from Einstein to a medicinal chemistry assistant in Leiden, whose full name isn't identified in the text. I have ascertained that the letter was likely addressed to a student named Jan Lens who was writing his doctoral thesis in Utrecht on the properties of lyophilic colloids. I show how the letter refers to the Einstein relation for viscosity that first appeared in erroneous form in 1906 and corrected form in 1911. In the letter, Einstein alludes to the possibility of an extension of his formula to charged particles. It offers an interesting example of Einstein's free- flowing generosity in offering advice to students.

Halpern, Paul

2007-04-01

151

The Luminosity Function of Quasars (active Galactic Nuclei) in a Merging Model with the Eddington Limit Taken Into Account  

NASA Astrophysics Data System (ADS)

The influence of Eddington's limit on the active galactic nuclei (AGN) luminosity function within the framework of a phenomenological activity model (Kats and Kontorovich, 1990, 1991) based on angular momentum compensation in the process of galaxy merging is investigated. In particular, it is shown that in spite of the essential dependence of the galaxy merging probability on their masses in the most important and interesting case it behaves effectively as a constant, so that the abovementioned (Kats and Kontorovich, 1991) correspondence between the observed galaxy mass function (Binggeli et al., 1988) and quasar luminosity function power exponents (Boyle et al., 1988; Koo and Kron, 1988; Cristiani et al., 1993) for a constant merger probability takes place in reality. A break in the power-law dependence of the luminosity function due to Eddington's restriction (cf. Dibai, 1981; Padovani and Rafanelli, 1988) is obtained in certain cases. Possible correlation between masses of black holes in AGN and masses of their host galaxies is discussed. A more detailed paper containing the results presented at this conference was published in Pis'ma v Astron. Zh. (Kontorovich and Krivitsky, 1995). Here we have added also some additional notes and references.

Kontorovich, V. M.; Krivitsky, D. S.

152

Correlations of the IR Luminosity and Eddington Ratio with a Hard X-ray Selected Sample of AGN  

NASA Technical Reports Server (NTRS)

We use the SWIFT Burst Alert Telescope (BAT) sample of hard x-ray selected active galactic nuclei (AGN) with a median redshift of 0.03 and the 2MASS J and K band photometry to examine the correlation of hard x-ray emission to Eddington ratio as well as the relationship of the J and K band nuclear luminosity to the hard x-ray luminosity. The BAT sample is almost unbiased by the effects of obscuration and thus offers the first large unbiased sample for the examination of correlations between different wavelength bands. We find that the near-IR nuclear J and K band luminosity is related to the BAT (14 - 195 keV) luminosity over a factor of 10(exp 3) in luminosity (L(sub IR) approx.equals L(sub BAT)(sup 1.25) and thus is unlikely to be due to dust. We also find that the Eddington ratio is proportional to the x-ray luminosity. This new result should be a strong constraint on models of the formation of the broad band continuum.

Mushotzy, Richard F.; Winter, Lisa M.; McIntosh, Daniel H.; Tueller, Jack

2008-01-01

153

BINARY ASTEROID ENCOUNTERS WITH TERRESTRIAL PLANETS: TIMESCALES AND EFFECTS  

SciTech Connect

Many asteroids that make close encounters with terrestrial planets are in a binary configuration. Here, we calculate the relevant encounter timescales and investigate the effects of encounters on a binary's mutual orbit. We use a combination of analytical and numerical approaches with a wide range of initial conditions. Our test cases include generic binaries with close, moderate, and wide separations, as well as seven well-characterized near-Earth binaries. We find that close approaches (<10 Earth radii) occur for almost all binaries on 1-10 million year timescales. At such distances, our results suggest substantial modifications to a binary's semimajor axis, eccentricity, and inclination, which we quantify. Encounters within 30 Earth radii typically occur on sub-million year timescales and significantly affect the wider binaries. Important processes in the lives of near-Earth binaries, such as tidal and radiative evolution, can be altered or stopped by planetary encounters.

Fang, Julia; Margot, Jean-Luc [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)

2012-01-15

154

Diffusion Time-Scale of Porous Pressure-Sensitive Paint  

NASA Technical Reports Server (NTRS)

Pressure-sensitive paint (PSP) is an optical pressure sensor that utilizes the oxygen quenching of luminescence. PSP measurements in unsteady aerodynamic flows require fast time response of the paint. There are two characteristic time-scales that are related to the time response of PSP. One is the luminescent lifetime representing an intrinsic physical limit for the achievable temporal resolution of PSP. Another is the time-scale of oxygen diffusion across the PSP layer. When the time-scale of oxygen diffusion is much larger than the luminescent lifetime, the time response of PSP is controlled by oxygen diffusion. In a thin homogenous polymer layer where diffusion is Fickian, the oxygen concentration 1021 can be described by the diffusion equation in one-dimension.

Liu, Tianshu; Teduka, Norikazu; Kameda, Masaharu; Asai, Keisuke

2001-01-01

155

Einstein tensor characterizing some Riemann spaces.  

National Technical Information Service (NTIS)

A formal definition of the Einstein tensor is given. Mention is made of how this tensor plays a role of expressing certain conditions in a precise form. The cases of reducing the Einstein tensor to a zero tensor are studied on its merit. A lucid account o...

M. S. Rahman

1993-01-01

156

Books on Einstein--Collectors' Delight  

ERIC Educational Resources Information Center

A survey of thirteen books on Einstein is presented. Its gives an idea on how much is written about the man and how frequent are the publications. The year 2005 saw the most publications. It is the centenary for the Miraculous Year. Interestingly some books can just sustain their readers' interest with just words. Einstein comes alive with the…

Khoon, Koh Aik; Jalal, Azman; Abd-Shukor, R.; Yatim, Baharudin; Talib, Ibrahim Abu; Daud, Abdul Razak; Samat, Supian

2009-01-01

157

People Interview: Continuing Einstein's great work  

NASA Astrophysics Data System (ADS)

INTERVIEW Continuing Einstein's great work Dr Michio Kaku is a theoretical physicist, bestselling author and popularizer of science. He is the co-founder of string field theory (a branch of string theory) and continues Einstein's search to unite the four fundamental forces of nature into one unified theory. David Smith speaks to him about inspiration and education.

2009-09-01

158

Beyond Einstein: Exploring the Extreme Universe.  

National Technical Information Service (NTIS)

This paper will give an overview of the NASA Universe Division Beyond Einstein program. The Beyond Einstein program consists of a series of exploratory missions to investigate some of the most important and pressing problems in modern-day astrophysics - i...

L. M. Barbier

2005-01-01

159

Relativistic fireballs - Energy conversion and time-scales  

NASA Technical Reports Server (NTRS)

The expansion energy of a relativistic fireball can be reconverted into radiation when it interacts with an external medium. For expansion with Lorentz factors greater than or approximately equal to 1000 into a typical galactic environment, the corresponding time-scale in the frame of the observer is of the order of seconds. This mechanism would operate in any cosmological scenario of gamma-ray bursts involving initial energies of order a percent of a stellar rest mass, and implies photon energies and time-scales compatible with those observed in gamma-ray bursts.

Rees, M. J.; Meszaros, P.

1992-01-01

160

LETTER TO THE EDITOR: Generating ring currents, solitons and svortices by stirring a Bose-Einstein condensate in a toroidal trap  

Microsoft Academic Search

We propose a simple stirring experiment to generate quantized ring currents and solitary excitations in Bose-Einstein condensates in a toroidal trap geometry. Simulations of the three-dimensional Gross-Pitaevskii equation show that pure ring current states can be generated efficiently by adiabatic manipulation of the condensate, which can be realized on experimental timescales. This is illustrated by simulated generation of a ring

Joachim Brand; William P. Reinhardt

2001-01-01

161

A genomic timescale for the origin of eukaryotes  

Microsoft Academic Search

BACKGROUND: Genomic sequence analyses have shown that horizontal gene transfer occurred during the origin of eukaryotes as a consequence of symbiosis. However, details of the timing and number of symbiotic events are unclear. A timescale for the early evolution of eukaryotes would help to better understand the relationship between these biological events and changes in Earth's environment, such as the

S Blair Hedges; Hsiong Chen; Sudhir Kumar; Daniel Y-C Wang; Amanda S Thompson; Hidemi Watanabe

2001-01-01

162

On the pathways and timescales of intercontinental air pollution transport  

Microsoft Academic Search

This paper presents results of a 1-year simulation of the transport of six passive tracers, released over the continents according to an emission inventory for carbon monoxide (CO). Lagrangian concepts are introduced to derive age spectra of the tracer concentrations on a global grid in order to determine the timescales and pathways of pollution export from the continents. Calculating these

Andreas Stohl; Sabine Eckhardt; Caroline Forster; Paul James; Nicole Spichtinger

2002-01-01

163

Energetic outer zone electron loss timescales during low geomagnetic activity  

Microsoft Academic Search

Following enhanced magnetic activity the fluxes of energetic electrons in the Earth's outer radiation belt gradually decay to quiet-time levels. We use CRRES observations to estimate the energetic electron loss timescales and to identify the principal loss mechanisms. Gradual loss of energetic electrons in the region 3.0 ? L ? 5.0 occurs during quiet periods (Kp 7), indicating that the

Nigel P. Meredith; Richard B. Horne; Sarah A. Glauert; Richard M. Thorne; Danny Summers; Jay M. Albert; Roger R. Anderson

2006-01-01

164

Statistical Multiplexing of Multiple TimeScale Markov Streams  

Microsoft Academic Search

We study the problem of statistical multiplexing of cell streams which have correla- tions at multiple time-scales. Each stream is modeled by a singularly perturbed Markov- modulated process with some state transitions occurring much more infrequently than others. We develop a set of large deviations results to estimate the buffer overflow prob- abilities in various asymptotic regimes in the buffer

David N. C. Tse; Robert G. Gallager; John N. Tsitsiklis

1995-01-01

165

Short time-scale structural variation in 3C 273  

Microsoft Academic Search

The results of VLBI observations at 22 GHz and 43 GHz of the quasar 3C 273 are presented Hybrid maps and modelfitting were made to look for any short time-scale structural variation in the jet. The jet structure did not show dramatic changes during the 42 days in which 3C 273 was observed 5 times at almost 10 day intervals.

F. Mantovani; C. Valerio; W. Junor; I. McHardy

1999-01-01

166

STP Einstein Solid Heat Bath Program  

NSDL National Science Digital Library

The STP EinsteinSolidHeatBath program simulates the exchange of energy between an Einstein solid and a heat bath. The purpose of this simulation is to determine the properties of a Einstein solid at different temperature T and to compare our results with analytical calculations of the thermodynamic properties of the Einstein solid. The default state is an Einstein solid of N=20 particles in contact with a heat bath at temperature T = 2. Additional states and parameters can be specified using the Display|Switch GUI menu item. STP EinsteinSolidHeatBath is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double-clicking the stp_EinsteinSolidHeatBath.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2008-05-28

167

TIMESCALES ON WHICH STAR FORMATION AFFECTS THE NEUTRAL INTERSTELLAR MEDIUM  

SciTech Connect

Turbulent neutral hydrogen (H I) line widths are often thought to be driven primarily by star formation (SF), but the timescale for converting SF energy to H I kinetic energy is unclear. As a complication, studies on the connection between H I line widths and SF in external galaxies often use broadband tracers for the SF rate, which must implicitly assume that SF histories (SFHs) have been constant over the timescale of the tracer. In this paper, we compare measures of H I energy to time-resolved SFHs in a number of nearby dwarf galaxies. We find that H I energy surface density is strongly correlated only with SF that occurred 30-40 Myr ago. This timescale corresponds to the approximate lifetime of the lowest mass supernova progenitors ({approx}8 M{sub Sun }). This analysis suggests that the coupling between SF and the neutral interstellar medium is strongest on this timescale, due either to an intrinsic delay between the release of the peak energy from SF or to the coherent effects of many supernova explosions during this interval. At {Sigma}{sub SFR} > 10{sup -3} M{sub Sun} yr{sup -1} kpc{sup -2}, we find a mean coupling efficiency between SF energy and H I energy of {epsilon} = 0.11 {+-} 0.04 using the 30-40 Myr timescale. However, unphysical efficiencies are required in lower {Sigma}{sub SFR} systems, implying that SF is not the primary driver of H I kinematics at {Sigma}{sub SFR} < 10{sup -3} M{sub Sun} yr{sup -1} kpc{sup -2}.

Stilp, Adrienne M.; Dalcanton, Julianne J.; Weisz, Daniel R.; Williams, Benjamin F. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Warren, Steven R. [Department of Astronomy, University of Maryland, CSS Building, Room 1024, Stadium Drive, College Park, MD 20742-2421 (United States); Skillman, Evan [Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455 (United States); Ott, Juergen [National Radio Astronomy Observatory, P.O. Box O, 1003 Lopezville Road, Socorro, NM 87801 (United States); Dolphin, Andrew E. [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States)

2013-08-01

168

Timescale analysis of rule-based biochemical reaction networks  

PubMed Central

The flow of information within a cell is governed by a series of protein-protein interactions that can be described as a reaction network. Mathematical models of biochemical reaction networks can be constructed by repetitively applying specific rules that define how reactants interact and what new species are formed upon reaction. To aid in understanding the underlying biochemistry, timescale analysis is one method developed to prune the size of the reaction network. In this work, we extend the methods associated with timescale analysis to reaction rules instead of the species contained within the network. To illustrate this approach, we applied timescale analysis to a simple receptor-ligand binding model and a rule-based model of Interleukin-12 (IL-12) signaling in näive CD4+ T cells. The IL-12 signaling pathway includes multiple protein-protein interactions that collectively transmit information; however, the level of mechanistic detail sufficient to capture the observed dynamics has not been justified based upon the available data. The analysis correctly predicted that reactions associated with JAK2 and TYK2 binding to their corresponding receptor exist at a pseudo-equilibrium. In contrast, reactions associated with ligand binding and receptor turnover regulate cellular response to IL-12. An empirical Bayesian approach was used to estimate the uncertainty in the timescales. This approach complements existing rank- and flux-based methods that can be used to interrogate complex reaction networks. Ultimately, timescale analysis of rule-based models is a computational tool that can be used to reveal the biochemical steps that regulate signaling dynamics.

Klinke, David J.; Finley, Stacey D.

2012-01-01

169

Timescale analysis of rule-based biochemical reaction networks.  

PubMed

The flow of information within a cell is governed by a series of protein-protein interactions that can be described as a reaction network. Mathematical models of biochemical reaction networks can be constructed by repetitively applying specific rules that define how reactants interact and what new species are formed on reaction. To aid in understanding the underlying biochemistry, timescale analysis is one method developed to prune the size of the reaction network. In this work, we extend the methods associated with timescale analysis to reaction rules instead of the species contained within the network. To illustrate this approach, we applied timescale analysis to a simple receptor-ligand binding model and a rule-based model of interleukin-12 (IL-12) signaling in naïve CD4+ T cells. The IL-12 signaling pathway includes multiple protein-protein interactions that collectively transmit information; however, the level of mechanistic detail sufficient to capture the observed dynamics has not been justified based on the available data. The analysis correctly predicted that reactions associated with Janus Kinase 2 and Tyrosine Kinase 2 binding to their corresponding receptor exist at a pseudo-equilibrium. By contrast, reactions associated with ligand binding and receptor turnover regulate cellular response to IL-12. An empirical Bayesian approach was used to estimate the uncertainty in the timescales. This approach complements existing rank- and flux-based methods that can be used to interrogate complex reaction networks. Ultimately, timescale analysis of rule-based models is a computational tool that can be used to reveal the biochemical steps that regulate signaling dynamics. PMID:21954150

Klinke, David J; Finley, Stacey D

2012-01-01

170

Singular Kaehler-Einstein metrics  

NASA Astrophysics Data System (ADS)

We study degenerate complex Monge-Ampere equations of the form (?+dd^c\\varphi)^n = e^{t \\varphi}? where ? is a big semi-positive form on a compact Kaehler manifold X of dimension n , t in {R}^+ , and ?=f?^n is a positive measure with density fin L^p(X,?^n) , p>1 . We prove the existence and unicity of bounded ? -plurisubharmonic solutions. We also prove that the solution is continuous under a further technical condition. In case X is projective and ?=psi^*?' , where psi:Xto V is a proper birational morphism to a normal projective variety, [?']in NS_{{R}} (V) is an ample class and ? has only algebraic singularities, we prove that the solution is smooth in the regular locus of the equation. We use these results to construct singular Kaehler-Einstein metrics of non-positive curvature on projective klt pairs, in particular on canonical models of algebraic varieties of general type.

Eyssidieux, Philippe; Guedj, Vincent; Zeriahi, Ahmed

2009-07-01

171

Einstein Light: Galilean Relativity and Newtonian Mechanics  

NSDL National Science Digital Library

This animated tutorial, part of the Einstein Light website, presents the concept of relativity from a situation inspired by Galileo (an inertial reference frame). It shows the motion of a ball being dropped from two reference frames: on a moving train and on a stationary platform. How does the motion appear different to the observer on the platform and the observer on the train? The Einstein Light project is a qualitative introduction to relativity, developed for novice learners and built around the framework of Flash media files with narration, video, and animation. It explores concepts ranging from Galilean relativity through Einstein and quantum mechanics.

Wolfe, Joe; Hatsidimitris, George

2007-12-20

172

Quasar Jets on the kpc scale: Fast and Super-Eddington or Slow and Multi-TeV Accelerators?  

NASA Astrophysics Data System (ADS)

A long-standing debate exists around the nature of the anomalously high X-ray emission from the kpc-scale resolved quasar jet emission, which is related to the question of their speeds on the kpc scale. Are they fast (Lorentz factors ~10-20) and powerful (in many cases super-Eddington) or slow, sub-Eddington, and multi-TeV particle accelerators?. This question has direct bearing on the physics of cluster heating by powerful jets. Also, the slow jet case implies that the beaming-corrected radiated power of the jet on kpc scales may be comparable to, or even exceed that of the blazar (core) emission, with important implications for the GeV background radiation and the heating of intergalactic gas by TeV photons. The widely accepted model for producing the high X-ray emission has been a highly-relativistic kpc-scale jet producing inverse Compton emission by up-scattering the cosmic microwave background (IC/CMB), though the X-rays could also be synchrotron emission from a multi-TeV electron population accelerated in situ, as both models can reproduce the observed radio to X-ray spectra. We present very recent work by our group, showing that IC/CMB model is ruled out in at least two cases. In both 3C 273 PKS 0637-752, the uniquely determined GeV flux predicted by the IC/CMB model overproduces the 99.9% flux limits obtained from recent Fermi gamma-ray observations.

Meyer, Eileen T.; Georganopoulos, Markos; Sparks, William B.

2014-08-01

173

Stability of the Einstein static universe in Einstein-Cartan theory  

NASA Astrophysics Data System (ADS)

The existence and stability of the Einstein static solution have been built in the Einstein-Cartan gravity. We show that this solution in the presence of perfect fluid with spin density satisfying the Weyssenhoff restriction is cyclically stable around a center equilibrium point. Thus, study of this solution is interesting because it supports non-singular emergent cosmological models in which the early universe oscillates indeterminately about an initial Einstein static solution and is thus past eternal.

Atazadeh, K.

2014-06-01

174

Einstein/Roosevelt Letters: A Unit.  

ERIC Educational Resources Information Center

The letters in this unit of study intended for secondary students are facsimile reproductions of the correspondence between Albert Einstein and President Roosevelt on the possibility of constructing an atomic bomb. Classroom activities are also suggested. (RM)

Bodle, Walter S.

1985-01-01

175

Coleman Weinberg Model in Einstein Spacetime.  

National Technical Information Service (NTIS)

We study radiative symmetry breaking, a la Coleman-Weinberg, in the geometry of a static Einstein Universe. We prove that the symmetric ground state =0, in a non-minimally coupled massless lambda phi exp 4 theory, can become...

G. Denardo E. Spallucci

1984-01-01

176

STP Temperature Measurement Einstein Solid Program  

NSDL National Science Digital Library

The STP DemonEinsteinSolid program displays a histogram of the energy of a demon that exchanges energy with an ideal gas of particles. The purpose of this simulation is to understand how the demon acts as an ideal thermometer. The default system is an Einstein solid of N=40 particles. Additional states and parameters can be specified using the Display|Switch GUI menu item. STP DemonEinsteinSolid is part of a suite of Open Source Physics programs that model aspects of Statistical and Thermal Physics (STP). The program is distributed as a ready-to-run (compiled) Java archive. Double-clicking the stp_DemonEinsteinSolid.jar file will run the program if Java is installed on your computer. Additional programs can be found by searching ComPADRE for Open Source Physics, STP, or Statistical and Thermal Physics.

Gould, Harvey; Tobochnik, Jan; Christian, Wolfgang; Cox, Anne

2008-05-28

177

How History Helped Einstein in Special Relativity  

NASA Astrophysics Data System (ADS)

I will discuss how the German intellectual movement known as ``critical history'' motivated several physicists in the late 1900s to radically analyze the fundamental principles of mechanics, leading eventually to Einstein's special theory of relativity. Eugen Karl Dühring, Johann Bernhard Stallo, Ludwig Lange, and Ernst Mach wrote critical histories of mechanics, some of which emphasized notions of relativity and observation, in opposition to old metaphysical concepts that seemed to infect the foundations of physics. This strand of critical history included the ``genetic method'' of analyzing how concepts develop over time, in our minds, by way of ordinary experiences, which by 1904 was young Albert Einstein's favorite approach for examining fundamental notions. Thus I will discuss how history contributed in Einstein's path to relativity, as well as comment more generally on Einstein's views on history.

Martinez, Alberto

2013-04-01

178

On Einstein's opponents, and other crackpots  

Microsoft Academic Search

Einsteins Gegner: Die öffentliche Kontroverse um die Relativitätstheorie in den 1920er Jahren, Milena Wazeck. Campus Verlag, pp. 429, EUR 39.90. ISBN: 978-3593389141\\u000a\\u000a\\u000a“This world is a strange madhouse. Currently, every coachman and every waiter is debating whether relativity theory is correct. Belief in this matter depends on political party affiliation.”1 Thus begins a letter by Albert Einstein to his one

Jeroen van Dongen

2010-01-01

179

Einstein's Biggest Blunder: A Cosmic Mystery Story  

ScienceCinema

The standard model of cosmology built up over 20 years is no longer accepted as accurate. New data suggest that most of the energy density of the universe may be contained in empty space. Remarkably, this is exactly what would be expected if Einstein's cosmological constant really exists. If it does, its origin is the biggest mystery in physics and presents huge challenges for the fundamental theories of elementary particles and fields. Krauss explains Einstein's concept and describes its possible implications.

Lawrence Krauss

2010-09-01

180

CMB Polarization in Einstein-Aether Theory  

Microsoft Academic Search

We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using

Masahiro Nakashima

2011-01-01

181

CMB Polarization in Einstein-Aether Theory  

Microsoft Academic Search

We study the impact of modifying the vector sector of gravity on the CMB\\u000apolarization. We employ the Einstein-aether theory as a concrete example. The\\u000aEinstein-aether theory admits dynamical vector perturbations generated during\\u000ainflation, leaving imprints on the CMB polarization. We derive the perturbation\\u000aequations of the aether vector field in covariant formalism and compute the CMB\\u000aB-mode polarization using

Masahiro Nakashima; Tsutomu Kobayashi

2010-01-01

182

Einstein, Mach, and the Fortunes of Gravity  

NASA Astrophysics Data System (ADS)

Early in his life, Albert Einstein considered himself a devoted student of the physicist and philosopher Ernst Mach. Mach's famous critiques of Newton's absolute space and time -- most notably Mach's explanation of Newton's bucket experiment -- held a strong sway over Einstein as he struggled to formulate general relativity. Einstein was convinced that his emerging theory of gravity should be consistent with Mach's principle, which states that local inertial effects arise due to gravitational interactions with distant matter. Once completed, Einstein's general relativity enjoyed two decades of worldwide attention, only to fall out of physicists' interest during the 1930s and 1940s, when topics like nuclear physics claimed center stage. Gravity began to return to the limelight during the 1950s and especially the 1960s, and once again Mach proved to be a major spur: Princeton physicists Carl Brans and Robert Dicke introduced a rival theory of gravity in 1961 which they argued satisfied Mach's principle better than Einstein's general relativity did. The Brans-Dicke theory, and the new generation of experiments designed to test its predictions against those of general relativity, played a major role in bringing Einstein's beloved topic back to the center of physics.

Kaiser, David

2005-04-01

183

Beyond Einstein: scientific goals and missions  

NASA Astrophysics Data System (ADS)

A century ago, Albert Einstein began creating his theory of relativity, the ideas we use to understand space, time, and gravity, and he took some of the first steps towards the theory of quantum mechanics, the ideas we use to understand matter and energy. Time magazine named Einstein the “Person of the Century” because his ideas transformed civilization. But his work is not finished: spacetime is not yet reconciled with the quantum. Einstein’s general theory of relativity opened possibilities for the formation and structure of the Universe that seemed unbelievable even to Einstein himself but which have all been subsequently confirmed: that the whole Universe began in a hot, dense Big Bang from which all of space expanded; that dense matter could tie spacetime into tangled knots called black holes; and that “empty” space might contain energy with repulsive gravity. Despite these discoveries, we still do not understand conditions at the beginning of the Universe, how space and time behave at the edge of a black hole, or why distant galaxies are accelerating away from us. These phenomena represent the most extreme interactions of matter and energy with space and time. They are the places to look for clues to the next fundamental revolution in understanding - Beyond Einstein.

White, Nicholas E.

184

The effects of clock errors on timescale stability  

NASA Technical Reports Server (NTRS)

The weighting scheme for the cesium clocks and hydrogen masers constituting the USNO timing ensemble is reexamined from an empirical standpoint of maximizing both frequency accuracy and timescale uniformity. The utility of a sliding-weight relation between the masers and the cesiums is reaffirmed, but improvement is found if one incorporates inverse Allan variances for sampling times of 12 and 6 hours for the cesiums and masers, respectively, with some dependence on clock model.

Breakiron, Lee A.

1995-01-01

185

Astronomically tuned geomagnetic polarity timescale for the Late Triassic  

Microsoft Academic Search

Cycle stratigraphic and magnetostratigraphic analyses of a ~5000-m-thick composite section obtained by scientific coring in the Newark rift basin of eastern North America provide a high-resolution astronomically calibrated geomagnetic polarity timescale (GPTS) spanning over 30 m.y. of the Late Triassic and earliest Jurassic. Only normal polarity is found in ~1000 m of interbedded volcanics and continental sediments of earliest Jurassic

Dennis V. Kent; Paul E. Olsen

1999-01-01

186

Shape invariant time-scale and pitch modification of speech  

Microsoft Academic Search

The simplified linear model of speech production predicts that when the rate of articulation is changed, the resulting waveform takes on the appearance of the original, except for a change in the time scale. A time-scale modification system that preserves this shape-invariance property during voicing is developed. This is done using a version of the sinusoidal analysis-synthesis system that models

Thomas F. Quatieri; Robert J. McAulay

1992-01-01

187

Short time-scale variability in bright Seyfert galaxies  

Microsoft Academic Search

High-quality, long-slit CCD spectroscopic data were obtained to search for short time-scale (hour-day) variability in a sample of five Seyfert galaxies. The equivalent widths of all of the emission lines and the relative intensities of the Balmer lines were measured for each galaxy. No significant profile or flux variations were observed for any galaxy within errors, except for NGC 4151.

E. Xanthopoulos; M. M. De Robertis

1991-01-01

188

Response to Deines and Williams on Astronomical Timescales  

NASA Astrophysics Data System (ADS)

In a paper presented at this conference, Deines and Williams (DW) question the conventional determination and interpretation of the differences between astronomical timescales, such as Universal Time (UT) which deals with Earth rotation, Atomic Time (AT), and planetary ephemeride timescales such as Terrestrial Time (TT). This paper offers explanations attempting to remove some sources of confusion on the subject, in particular: 1) To explain large discrepancies in the determined values for the tidal deceleration of Earth spin rate, we show that the rotational acceleration producing decadal variations in Earth spin are large compared to the tidal deceleration and easily mask the latter signal in rotation data spanning less than 200 years. 2) DW argue that the absence of a leap second between 1999 Jan 1 and 2005 Dec 31 is a statistically improbable event and is an artifact of the UT formula redefinition adopted in 2003. We offer a counterexample. If the Terrestrial Time second had been defined to match the UT second at an epoch other than the effective 1819 epoch that was used, a seven year span without leap seconds can be produced in other decades, decades without a redefinition of the UT formula. This shows that several seven year spans without leap seconds are possible and thereby negates the DW statistical argument. 3) DW also argue that there is a divergence in the TT timescale because relativistic time dilation was not included in Newcomb's analysis of the Sun's apparent motion. We show by a simple analysis that any such dilation was absorbed into the observationally determined elements of Earth's solar orbit. The resulting theory then accurately predicts the Sun's position using TT as told by Earth mounted clocks without any explicit use of time dilation, that is, there is no observational indication of timescale divergence.

Slabinski, Victor J.

2009-05-01

189

Timescales of emulsion formation caused by anisotropic particles.  

PubMed

Particle stabilized emulsions have received much interest in the recent past, but our understanding of the dynamics of emulsion formation is still limited. For simple spherical particles, the time dependent growth of fluid domains is dominated by the formation of droplets, particle adsorption and coalescence of droplets (Ostwald ripening), which eventually can be almost fully blocked due to the presence of the particles. Ellipsoidal particles are known to be more efficient stabilizers of fluid interfaces than spherical particles and their anisotropic shape and the related additional rotational degrees of freedom have an impact on the dynamics of emulsion formation. In this paper, we investigate this point by means of simple model systems consisting of a single ellipsoidal particle or a particle ensemble at a flat interface as well as a particle ensemble at a spherical interface. By applying combined multicomponent lattice Boltzmann and molecular dynamics simulations we demonstrate that the anisotropic shape of ellipsoidal particles causes two additional timescales to be of relevance in the dynamics of emulsion formation: a relatively short timescale can be attributed to the adsorption of single particles and the involved rotation of particles towards the interface. As soon as the interface is jammed, however, capillary interactions between the particles cause a local reordering on very long timescales leading to a continuous change in the interface configuration and increase of the interfacial area. This effect can be utilized to counteract the thermodynamic instability of particle stabilized emulsions and thus offers the possibility to produce emulsions with exceptional stability. PMID:24888563

Günther, Florian; Frijters, Stefan; Harting, Jens

2014-07-21

190

The Galaxy Viewed at Very Short Time-Scales  

NASA Astrophysics Data System (ADS)

We present high time-resolution astronomical observations recorded with the Berkeley Visible Image Tube (BVIT) photon counting detector mounted on the 10m South African Large Telescope (SALT). Relative B and V-band photometric fluxes were obtained as a function of time for targets that included Polar-type cataclysmic variables (UZ For, OY Car, V1033Cen), low-mass X-ray binaries (GX 339-4, UY Vol), pulsars (PSR 0540-69), dMe flare stars (CN Leo) and active galactic nucleii (Mkn 618). These observations, which were recorded during several nights of engineering time at SALT in early 2009, indicate that there are many types of astrophysical processes operating over very short time-scales in a wide variety of astronomical objects. The high-time resolution capability of the BVIT detector allowed emission features occurring on time-scales as short as tens of milli-seconds to be revealed. In particular, we have measured the optical period of the PSR 0540-69 pulsar to be 0.05065018808s and we have also detected several quasi-periodic oscillations operating on time-scales of < 0.5 s in the emitted flux from the X-ray transient source, GX 339-4. These preliminary data indicate that the new field of high time-resolution astronomy is providing important new insights into the transient nature of the Universe.

Radnia, Navid; Siegmund, O.; Welsh, B.; Mcphate, J.; Rogers, D.; Charles, P.; Buckley, D.

2010-01-01

191

Einstein observations of active galaxies  

NASA Technical Reports Server (NTRS)

X-ray observations of Cen A (NGC 5128) and seven other X-ray emitting active galaxies are discussed which were made with the imaging proportional counter and the high-resolution imager aboard the Einstein Observatory. In addition to Cen A, the sources observed were the N-type galaxy 3C 120, the quasars OX 169 and 3C 273, and four Class 1 Seyfert galaxies, viz., Mkn 509, Mkn 79, NGC 6814, and NGC 4151. For Cen A, it is found that the X-ray data are dominated by a central point source of about 2 cts/sec, that X-ray elongations (possibly associated with the inner radio lobes) extend in the NE and SW directions, and that an X-ray jet exists which is aligned with the optical jet. The results for the other sources are used to derive emitting-region sizes and black-hole masses for models based on an accreting central black hole.

Tananbaum, H.

1980-01-01

192

The Importance of Rotational Time-scales in Accretion Variability  

NASA Astrophysics Data System (ADS)

For the first few million years, one of the dominant sources of emission from a low mass young stellar object is from accretion. This process regulates the flow of material and angular moments from the surroundings to the central object, and is thought to play an important role in the definition of the long term stellar properties. Variability is a well documented attribute of accretion, and has been observed on time-scales of from days to years. However, where these variations come from is not clear. Th current model for accretion is magnetospheric accretion, where the stellar magnetic field truncates the disc, allowing the matter to flow from the disc onto the surface of the star. This model allows for variations in the accretion rate to come from many different sources, such as the magnetic field, the circumstellar disc and the interaction of the different parts of the system. We have been studying unbiased samples of accretors in order to identify the dominant time-scales and typical magnitudes of variations. In this way different sources of variations can be excluded and any missing physics in these systems identified. Through our previous work with the Long-term Accretion Monitoring Program (LAMP), we found 10 accretors in the ChaI region, whose variability is dominated by short term variations of 2 weeks. This was the shortest time period between spectroscopic observations which spanned 15 months, and rules out large scale processes in the disk as origins of this variability. On the basis of this study we have gone further to study the accretion signature H-alpha, over the time-scales of minutes and days in a set of Herbig Ae and T Tauri stars. Using the same methods as we used in LAMP we found the dominant time-scales of variations to be days. These samples both point towards rotation period of these objects as being an important time-scale for accretion variations. This allows us to indicate which are the most likely sources of these variations.

Costigan, Gráinne; Vink, Joirck; Scholz, Aleks; Testi, Leonardo; Ray, Tom

2013-07-01

193

Focus on quantum Einstein gravity Focus on quantum Einstein gravity  

NASA Astrophysics Data System (ADS)

The gravitational asymptotic safety program summarizes the attempts to construct a consistent and predictive quantum theory of gravity within Wilson's generalized framework of renormalization. Its key ingredient is a non-Gaussian fixed point of the renormalization group flow which controls the behavior of the theory at trans-Planckian energies and renders gravity safe from unphysical divergences. Provided that the fixed point comes with a finite number of ultraviolet-attractive (relevant) directions, this construction gives rise to a consistent quantum field theory which is as predictive as an ordinary, perturbatively renormalizable one. This opens up the exciting possibility of establishing quantum Einstein gravity as a fundamental theory of gravity, without introducing supersymmetry or extra dimensions, and solely based on quantization techniques that are known to work well for the other fundamental forces of nature. While the idea of gravity being asymptotically safe was proposed by Steven Weinberg more than 30 years ago [1], the technical tools for investigating this scenario only emerged during the last decade. Here a key role is played by the exact functional renormalization group equation for gravity, which allows the construction of non-perturbative approximate solutions for the RG-flow of the gravitational couplings. Most remarkably, all solutions constructed to date exhibit a suitable non-Gaussian fixed point, lending strong support to the asymptotic safety conjecture. Moreover, the functional renormalization group also provides indications that the central idea of a non-Gaussian fixed point providing a safe ultraviolet completion also carries over to more realistic scenarios where gravity is coupled to a suitable matter sector like the standard model. These theoretical successes also triggered a wealth of studies focusing on the consequences of asymptotic safety in a wide range of phenomenological applications covering the physics of black holes, early time cosmology and the big bang, as well as TeV-scale gravity models testable at the Large Hadron Collider. On different grounds, Monte-Carlo studies of the gravitational partition function based on the discrete causal dynamical triangulations approach provide an a priori independent avenue towards unveiling the non-perturbative features of gravity. As a highlight, detailed simulations established that the phase diagram underlying causal dynamical triangulations contains a phase where the triangulations naturally give rise to four-dimensional, macroscopic universes. Moreover, there are indications for a second-order phase transition that naturally forms the discrete analog of the non-Gaussian fixed point seen in the continuum computations. Thus there is a good chance that the discrete and continuum computations will converge to the same fundamental physics. This focus issue collects a series of papers that outline the current frontiers of the gravitational asymptotic safety program. We hope that readers get an impression of the depth and variety of this research area as well as our excitement about the new and ongoing developments. References [1] Weinberg S 1979 General Relativity, an Einstein Centenary Survey ed S W Hawking and W Israel (Cambridge: Cambridge University Press)

Ambjorn, Jan; Reuter, Martin; Saueressig, Frank

2012-09-01

194

A statistical relation between the X-ray spectral index and Eddington ratio of active galactic nuclei in deep surveys  

NASA Astrophysics Data System (ADS)

We present an investigation into how well the properties of the accretion flow on to a supermassive black hole may be coupled to those of the overlying hot corona. To do so, we specifically measure the characteristic spectral index, ?, of a power-law energy distribution, over an energy range of 2-10 keV, for X-ray selected, broad-lined radio-quiet active galactic nuclei (AGN) up to z ˜ 2 in Cosmic Evolution Survey (COSMOS) and Extended Chandra Deep Field South (E-CDF-S). We test the previously reported dependence between ? and black hole mass, full width at half-maximum (FWHM) and Eddington ratio using a sample of AGN covering a broad range in these parameters based on both the Mg II and H? emission lines with the later afforded by recent near-infrared spectroscopic observations using Subaru/Fibre Multi Object Spectrograph. We calculate the Eddington ratios, ?Edd, for sources where a bolometric luminosity (LBol) has been presented in the literature, based on spectral energy distribution fitting, or, for sources where these data do not exist, we calculate LBol using a bolometric correction to the X-ray luminosity, derived from a relationship between the bolometric correction and LX/L3000. From a sample of 69 X-ray bright sources (>250 counts), where ? can be measured with greatest precision, with an estimate of LBol, we find a statistically significant correlation between ? and ?Edd, which is highly significant with a chance probability of 6.59× 10-8. A statistically significant correlation between ? and the FWHM of the optical lines is confirmed, but at lower significance than with ?Edd indicating that ?Edd is the key parameter driving conditions in the corona. Linear regression analysis reveals that ? = (0.32 ± 0.05) log10?Edd + (2.27 ± 0.06) and ? = (-0.69 ± 0.11) log10(FWHM/km s-1) + (4.44 ± 0.42). Our results on ?-?Edd are in very good agreement with previous results. While the ?-?Edd relationship means that X-ray spectroscopy may be used to estimate black hole accretion rate, considerable dispersion in the correlation does not make this viable for single sources, however could be valuable for large X-ray spectral samples, such as those to be produced by eROSITA.

Brightman, M.; Silverman, J. D.; Mainieri, V.; Ueda, Y.; Schramm, M.; Matsuoka, K.; Nagao, T.; Steinhardt, C.; Kartaltepe, J.; Sanders, D. B.; Treister, E.; Shemmer, O.; Brandt, W. N.; Brusa, M.; Comastri, A.; Ho, L. C.; Lanzuisi, G.; Lusso, E.; Nandra, K.; Salvato, M.; Zamorani, G.; Akiyama, M.; Alexander, D. M.; Bongiorno, A.; Capak, P.; Civano, F.; Del Moro, A.; Doi, A.; Elvis, M.; Hasinger, G.; Laird, E. S.; Masters, D.; Mignoli, M.; Ohta, K.; Schawinski, K.; Taniguchi, Y.

2013-08-01

195

Distinct mechanisms control contrast adaptation over different timescales.  

PubMed

Changes to the visual environment can happen at many timescales, from very transient to semi-permanent. To adapt optimally, the visual system also adjusts at different timescales, with longer-lasting environmental changes producing longer-lasting effects, but how the visual system adapts in this way remains unknown. Here, we show that contrast adaptation-the most-studied form of visual adaptation-has multiple controllers, each operating over a different time scale. In a series of experiments, subjects completed either a contrast matching, contrast detection, or tilt adjustment task, while adapting to contrast at one orientation. Following a relatively longer period (5 min) of adaptation to high contrast, subjects were "deadapted" for a shorter period (e.g., 40 s) to a lower contrast. Deadaptation eliminated perceptual aftereffects of adaptation, but continued testing in a neutral environment revealed their striking recovery. These results suggest the following account: Adaptation was controlled by at least two mechanisms, with initial adaptation affecting a longer-term one and deadaptation affecting a shorter-term one in the opposite direction. Immediately following deadaptation, the effects of the two mechanisms cancelled each other, but the short-term effects rapidly decayed, revealing ongoing longer-term adaptation. A single controlling mechanism cannot account for the observed recovery of effects, since once deadaptation cancels the initial longer-term adaptation, no trace of it remains. Combined with previous results at very long adaptation durations, the present results suggest that contrast adaptation is possibly controlled by a continuum of mechanisms acting over a large range of timescales. PMID:23978470

Bao, Min; Fast, Elizabeth; Mesik, Juraj; Engel, Stephen

2013-01-01

196

Multiple time-scale methods in particle simulations of plasmas  

SciTech Connect

This paper surveys recent advances in the application of multiple time-scale methods to particle simulation of collective phenomena in plasmas. These methods dramatically improve the efficiency of simulating low-frequency kinetic behavior by allowing the use of a large timestep, while retaining accuracy. The numerical schemes surveyed provide selective damping of unwanted high-frequency waves and preserve numerical stability in a variety of physics models: electrostatic, magneto-inductive, Darwin and fully electromagnetic. The paper reviews hybrid simulation models, the implicitmoment-equation method, the direct implicit method, orbit averaging, and subcycling.

Cohen, B.I.

1985-02-14

197

Low redshift AGN in the Hamburg\\/ESO Survey . II. The active black hole mass function and the distribution function of Eddington ratios  

Microsoft Academic Search

We estimated black hole masses and Eddington ratios (L\\/LEdd) for a well defined sample of local (z < 0.3) broad line AGN from the Hamburg\\/ESO Survey (HES), based on the Hbeta line and standard recipes assuming virial equilibrium for the broad line region. The sample represents the low-redshift AGN population over a wide range of luminosities, from Seyfert 1 galaxies

Andreas Schulze; Lutz Wisotzki

2010-01-01

198

Three-dimensional general relativistic radiation magnetohydrodynamical simulation of super-Eddington accretion, using a new code HARMRAD with M1 closure  

NASA Astrophysics Data System (ADS)

Black hole (BH) accretion flows and jets are dynamic hot relativistic magnetized plasma flows whose radiative opacity can significantly affect flow structure and behaviour. We describe a numerical scheme, tests, and an astrophysically relevant application using the M1 radiation closure within a new 3D general relativistic radiation magnetohydrodynamics (GRRMHD) massively parallel code called HARMRAD. Our 3D GRRMHD simulation of super-Eddington accretion (about 20 times Eddington) on to a rapidly rotating BH (dimensionless spin j = 0.9375) shows sustained non-axisymmemtric disc turbulence, a persistent electromagnetic jet driven by the Blandford-Znajek effect, a disc wind, and a polar radiation jet. The total accretion efficiency is of the order of 20 per cent, the large-scale electromagnetic jet efficiency is of the order of 10 per cent, the disc wind efficiency is less than 1 per cent, and the total radiative efficiency remains low at only of the order of 1 per cent (of order the Eddington luminosity). However, the radiation jet and the electromagnetic jet both emerge from a geometrically beamed polar region, with super-Eddington isotropic equivalent luminosities. Such simulations with HARMRAD can enlighten the role of BH spin versus discs in launching jets, help determine the origin of spectral and temporal states in X-ray binaries, help to understand how tidal disruption events work, provide an accurate horizon-scale flow structure for M87 and other active galactic nuclei (AGN), and isolate whether AGN feedback is driven by radiation or by an electromagnetic, thermal, or kinetic wind/jet. For example, the low radiative efficiency and weak BH spin-down rate from our simulation suggest that BH growth over cosmological times to billions of solar masses by redshifts of z ˜ 6-8 is achievable even with rapidly rotating BHs and 10 M? BH seeds.

McKinney, Jonathan C.; Tchekhovskoy, Alexander; Sadowski, Aleksander; Narayan, Ramesh

2014-07-01

199

Einstein database of quasars. I. (Wilkes+, 1994)  

NASA Astrophysics Data System (ADS)

We present the first volume of the Einstein quasar database. The database includes estimates of the X-ray count rates, fluxes, and luminosities for 514 quasars and Seyfert 1 galaxies observed with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory. All were previously known optically selected or radio-selected objects, and most were targets of the X-ray observations. The X-ray properties of the AGNs have been derived by reanalyzing the IPC data in a systematic manner to provide a uniform database for general use by the astronomical community. We use the database to extend earlier quasar luminosity studies which were made using only a subset of the currently available data. The database can be accessed on Internet via the SAO Einstein on-line system ("Einline") and is available in ASCII format on magnetic tape and DOS diskette. (8 data files).

Wilkes, B.; Tananbaum, H.; Worrall, D. M.; Avni, Y.; Oey, M. S.; Flanagan, J.

1994-10-01

200

Einstein, Ethics and the Atomic Bomb  

NASA Astrophysics Data System (ADS)

Einstein voiced his ethical views against war as well as fascism via venues and alliances with a variety of organizations still debated today. In 1939, he signed a letter to President Roosevelt (drafted by younger colleagues Szilard, Wigner and others) warning the U.S.government about the danger of Nazi Germany gaining control of uranium in the Belgian-controlled Congo in order to develop atomic weapons, based on the discovery of fission by Otto Hahn and Lise Meitner. In 1945, he became a member of the Princeton-based ``Emergency Committee for Atomic Scientists'' organized by Bethe, Condon, Bacher, Urey, Szilard and Weisskopf. Rare Einstein slides will illustrate Dr.Rife's presentation on Albert Einstein's philosophic and ethical convictions about peace, and public stance against war (1914-1950).

Rife, Patricia

2005-03-01

201

Bose-Einstein condensation in microgravity.  

PubMed

Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter. PMID:20558713

van Zoest, T; Gaaloul, N; Singh, Y; Ahlers, H; Herr, W; Seidel, S T; Ertmer, W; Rasel, E; Eckart, M; Kajari, E; Arnold, S; Nandi, G; Schleich, W P; Walser, R; Vogel, A; Sengstock, K; Bongs, K; Lewoczko-Adamczyk, W; Schiemangk, M; Schuldt, T; Peters, A; Könemann, T; Müntinga, H; Lämmerzahl, C; Dittus, H; Steinmetz, T; Hänsch, T W; Reichel, J

2010-06-18

202

Albert Einstein - And the Frontiers of Physics  

NASA Astrophysics Data System (ADS)

Albert Einstein did not impress his first teachers. They found him a dreamy child without an especially promising future. But some time in his early years he developed what he called "wonder" about the world. Later in life, he remembered two instances from his childhood--his fascination at age five with a compass and his introduction to the lucidity and certainty of geometry--that may have been the first signs of what was to come. From these ordinary beginnings, Einstein became one of the greatest scientific thinkers of all time. This illuminating biography describes in understandable language the experiments and revolutionary theories that flowed from Einstein's imagination and intellect--from his theory of relativity, which changed our conception of the universe and our place in it, to his search for a unified field theory that would explain all of the forces in the universe.

Bernstein, Jeremy

1997-11-01

203

Radiation hydrodynamic instability in a plane-parallel, super-Eddington atmosphere: A mechanism for clump formation  

NASA Astrophysics Data System (ADS)

In order to understand the physical processes underlying clump formation in outflow from supercritical accretion flow, we perform two-dimensional radiation hydrodynamic (RHD) simulations. We focus our discussion on the nature of RHD instability in a marginally optically thick, plane-parallel, super-Eddington atmosphere. Initially we set a two-layered atmosphere with a density contrast of 100 exposed to strong, upward continuum-radiation force; the lower layer is denser than the upper one, the condition for RHD instability. We assume non-zero but negligible gravitational force, compared with the radiation force. We find that short-wavelength perturbations grow first, followed by the growth of longer-wavelength patterns, which lead to the formation of clumpy structure. The typical size of clumps (clouds) corresponds to about one optical depth. An anti-correlation between the radiation pressure and the gas pressure is confirmed: this anti-correlation provides a damping mechanism for perturbations of longer wavelength than the typical clump size. Matter and radiation energy densities are correlated. These features are exactly what we found in the radiation-magnetohydrodynamic (radiation-MHD) simulations of supercritical outflow.

Takeuchi, Shun; Ohsuga, Ken; Mineshige, Shin

2014-04-01

204

The relationship between the Eddington limit, the observed upper luminosity limit for massive stars, and the luminous blue variables  

NASA Technical Reports Server (NTRS)

The observed upper luminosity limits in the Galaxy and the LMC are compared with the Eddington limit as estimated for plane-parallel LTE model atmospheres which include the full effects of metal line opacities in the ultraviolet. It is shown that the Humphreys-Davidson (HD) limit corresponds to the locus of extremely low effective gravities. This result suggests that stars approaching the HD limit will suffer high mass-loss rates because of the reduction of the effective gravity due to radiation pressure. These high mass-loss rates ultimtely lead to the core mass fraction reaching its critical value and the reversal of the stellar evolution tracks. It is shown that radiation pressure, as an agent for producing enhanced mass loss near the HD limit, can in a natural way explain the kink in the HD limit near T(eff) roughly 10,000 K and the upper luminosity limit for yellow and red supergiants. The high mass-loss rates of the luminous blue variables, their location in the HR diagram, and their evolutionary stage are also discussed.

Lamers, Henny J. G. L. M.; Fitzpatrick, Edward L.

1988-01-01

205

Relationship between the Eddington limit, the observed upper luminosity limit for massive stars, and the luminous blue variables  

SciTech Connect

The observed upper luminosity limits in the Galaxy and the LMC are compared with the Eddington limit as estimated for plane-parallel LTE model atmospheres which include the full effects of metal line opacities in the ultraviolet. It is shown that the Humphreys-Davidson (HD) limit corresponds to the locus of extremely low effective gravities. This result suggests that stars approaching the HD limit will suffer high mass-loss rates because of the reduction of the effective gravity due to radiation pressure. These high mass-loss rates ultimtely lead to the core mass fraction reaching its critical value and the reversal of the stellar evolution tracks. It is shown that radiation pressure, as an agent for producing enhanced mass loss near the HD limit, can in a natural way explain the kink in the HD limit near T(eff) roughly 10,000 K and the upper luminosity limit for yellow and red supergiants. The high mass-loss rates of the luminous blue variables, their location in the HR diagram, and their evolutionary stage are also discussed. 27 references.

Lamers, H.J.G.L.M.; Fitzpatrick, E.L.

1988-01-01

206

Radiation hydrodynamic instability in a plane-parallel, super-Eddington atmosphere: A mechanism for clump formation  

NASA Astrophysics Data System (ADS)

In order to understand the physical processes underlying clump formation in outflow from supercritical accretion flow, we perform two-dimensional radiation hydrodynamic (RHD) simulations. We focus our discussion on the nature of RHD instability in a marginally optically thick, plane-parallel, super-Eddington atmosphere. Initially we set a two-layered atmosphere with a density contrast of 100 exposed to strong, upward continuum-radiation force; the lower layer is denser than the upper one, the condition for RHD instability. We assume non-zero but negligible gravitational force, compared with the radiation force. We find that short-wavelength perturbations grow first, followed by the growth of longer-wavelength patterns, which lead to the formation of clumpy structure. The typical size of clumps (clouds) corresponds to about one optical depth. An anti-correlation between the radiation pressure and the gas pressure is confirmed: this anti-correlation provides a damping mechanism for perturbations of longer wavelength than the typical clump size. Matter and radiation energy densities are correlated. These features are exactly what we found in the radiation-magnetohydrodynamic (radiation-MHD) simulations of supercritical outflow.

Takeuchi, Shun; Ohsuga, Ken; Mineshige, Shin

2014-05-01

207

Misconceptions about Einstein: His Work and His Views.  

ERIC Educational Resources Information Center

Discusses eight misconceptions concerning Einstein's work and views, as part of a presentation at the Einstein Symposium held at the 178th National American Chemical Society Meetings in Washington, D.C., in September, 1979. (CS)

Resnick, Robert

1980-01-01

208

SYSTEMATIC UNCERTAINTIES IN THE SPECTROSCOPIC MEASUREMENTS OF NEUTRON-STAR MASSES AND RADII FROM THERMONUCLEAR X-RAY BURSTS. II. EDDINGTON LIMIT  

SciTech Connect

Time-resolved X-ray spectroscopy of thermonuclear bursts observed from low-mass X-ray binaries offer a unique tool to measure neutron-star masses and radii. In this paper, we continue our systematic analysis of all the X-ray bursts observed with Rossi X-ray Timing Explorer from X-ray binaries. We determine the events that show clear evidence for photospheric radius expansion and measure the Eddington limits for these accreting neutron stars using the bolometric fluxes attained at the touchdown moments of each X-ray burst. We employ a Bayesian technique to investigate the degree to which the Eddington limit for each source remains constant between bursts. We find that for sources with a large number of radius expansion bursts, systematic uncertainties are at a 5%-10% level. Moreover, in six sources with only pairs of Eddington-limited bursts, the distribution of fluxes is consistent with a {approx}10% fractional dispersion. This indicates that the spectroscopic measurements of neutron-star masses and radii using thermonuclear X-ray bursts can reach the level of accuracy required to distinguish between different neutron-star equations of state, provided that uncertainties related to the overall flux calibration of X-ray detectors are of comparable magnitude.

Guever, Tolga; Oezel, Feryal; Psaltis, Dimitrios [Department of Astronomy, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)

2012-03-01

209

Emergence of long timescales and stereotyped behaviors in Caenorhabditis elegans  

PubMed Central

Animal behaviors often are decomposable into discrete, stereotyped elements, well separated in time. In one model, such behaviors are triggered by specific commands; in the extreme case, the discreteness of behavior is traced to the discreteness of action potentials in the individual command neurons. Here, we use the crawling behavior of the nematode Caenorhabditis elegans to demonstrate the opposite view, in which discreteness, stereotypy, and long timescales emerge from the collective dynamics of the behavior itself. In previous work, we found that as C. elegans crawls, its body moves through a “shape space” in which four dimensions capture approximately 95% of the variance in body shape. Here we show that stochastic dynamics within this shape space predicts transitions between attractors corresponding to abrupt reversals in crawling direction. With no free parameters, our inferred stochastic dynamical system generates reversal timescales and stereotyped trajectories in close agreement with experimental observations. We use the stochastic dynamics to show that the noise amplitude decreases systematically with increasing time away from food, resulting in longer bouts of forward crawling and suggesting that worms can use noise to modify their locomotory behavior.

Stephens, Greg J.; Bueno de Mesquita, Matthew; Ryu, William S.; Bialek, William

2011-01-01

210

Interpreting characteristic drainage timescale variability across Kilombero Valley, Tanzania  

NASA Astrophysics Data System (ADS)

We derived the characteristic drainage timescale (K) from river discharge records across the Kilombero Valley in central Tanzania to explore seasonal variability and spatiotemporal patterns in dominant hydrologic processes. This was done using streamflow recession analysis to isolate storage-discharge relationships drawing from hydraulic groundwater theory. Such an approach may be advantageous in this and other data limited environments as it allows utilization of streamflow records with large time gaps and limited consistency. The observed K values during the wet season and for the relatively smaller catchments draining upland positions are consistent with those expected from hydraulic groundwater theory (e.g., K = 45 × 15 days). In the dry season, however, the timescales estimated for these catchments are larger than expected from hydraulic groundwater theory. Further, larger catchments draining part of the valley bottom, which is dominated by wetlands, never exhibited K values consistent with those expected from hydraulic groundwater theory. These hydrometric results are consistent with initial hydrologic tracer investigations with implications for the transit times of water moving through this upland-wetland seasonally-connected region and resultant regional groundwater recharge. Identifying these spatiotemporal shifts (i.e., isolating when general hydraulic groundwater theory may not be valid) facilitates process representation relevant for improved hydrologic modeling and water resources management in regions like Kilombero Valley.

Lyon, S. W.; Koutsouris, A.

2013-12-01

211

A Hierarchy of Time-Scales and the Brain  

PubMed Central

In this paper, we suggest that cortical anatomy recapitulates the temporal hierarchy that is inherent in the dynamics of environmental states. Many aspects of brain function can be understood in terms of a hierarchy of temporal scales at which representations of the environment evolve. The lowest level of this hierarchy corresponds to fast fluctuations associated with sensory processing, whereas the highest levels encode slow contextual changes in the environment, under which faster representations unfold. First, we describe a mathematical model that exploits the temporal structure of fast sensory input to track the slower trajectories of their underlying causes. This model of sensory encoding or perceptual inference establishes a proof of concept that slowly changing neuronal states can encode the paths or trajectories of faster sensory states. We then review empirical evidence that suggests that a temporal hierarchy is recapitulated in the macroscopic organization of the cortex. This anatomic-temporal hierarchy provides a comprehensive framework for understanding cortical function: the specific time-scale that engages a cortical area can be inferred by its location along a rostro-caudal gradient, which reflects the anatomical distance from primary sensory areas. This is most evident in the prefrontal cortex, where complex functions can be explained as operations on representations of the environment that change slowly. The framework provides predictions about, and principled constraints on, cortical structure–function relationships, which can be tested by manipulating the time-scales of sensory input.

Kiebel, Stefan J.; Daunizeau, Jean; Friston, Karl J.

2008-01-01

212

Solar irradiance, cosmic rays and cloudiness over daily timescales  

NASA Astrophysics Data System (ADS)

Although over centennial and greater timescales solar variability may be one of the most influential climate forcing agents, the extent to which solar activity influences climate over shorter time periods is poorly understood. If a link exists between solar activity and climate, it is likely via a mechanism connected to one (or a combination) of the following parameters: total solar irradiance (TSI), ultraviolet (UV) spectral irradiance, or the galactic cosmic ray (GCR) flux. We present an analysis based around a superposed epoch (composite) approach focusing on the largest TSI increases and decreases (the latter occurring in both the presence and absence of appreciable GCR reductions) over daily timescales. Using these composites we test for the presence of a robust link between solar activity and cloud cover over large areas of the globe using rigorous statistical techniques. We find no evidence that widespread variations in cloud cover at any tropospheric level are significantly associated with changes in the TSI, GCR or UV flux, and further conclude that TSI or UV changes occurring during reductions in the GCR flux are not masking a solar-cloud response. However, we note the detectability of any potential links is strongly constrained by cloud variability.

Laken, Benjamin A.; ?alogovi?, Jasa

2011-12-01

213

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing  

NASA Technical Reports Server (NTRS)

Evaluation of metal-based structures has long relied on atmospheric exposure test sites to determine corrosion resistance in marine environments. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions of the corrosive environment. Their success for correlation to atmospheric exposure is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated laboratory testing, which often focuses on the electrochemical reactions that occur during corrosion conditions, has yet to be universally accepted as a useful tool in predicting the long term service life of a metal despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard and their use is imperative, a method that correlates timescales from atmospheric exposure to accelerated testing would be very valuable. This work uses surface chemistry to interpret the chemical changes occurring on low carbon steel during atmospheric and accelerated corrosion conditions with the objective of finding a correlation between its accelerated and long-term corrosion performance. The current results of correlating data from marine atmospheric exposure conditions at the Kennedy Space Center beachside corrosion test site, alternating seawater spray, and immersion in typical electrochemical laboratory conditions, will be presented. Key words: atmospheric exposure, accelerated corrosion testing, alternating seawater spray, marine, correlation, seawater, carbon steel, long-term corrosion performance prediction, X-ray photoelectron spectroscopy.

Montgomery, Eliza L.; Calle, Luz Marina; Curran, Jerone C.; Kolody, Mark R.

2011-01-01

214

Propagating torsion in the Einstein frame  

SciTech Connect

The Einstein-Cartan-Saa theory of torsion modifies the spacetime volume element so that it is compatible with the connection. The condition of connection compatibility gives constraints on torsion, which are also necessary for the consistence of torsion, minimal coupling, and electromagnetic gauge invariance. To solve the problem of positivity of energy associated with the torsionic scalar, we reformulate this theory in the Einstein conformal frame. In the presence of the electromagnetic field, we obtain the Hojman-Rosenbaum-Ryan-Shepley theory of propagating torsion with a different factor in the torsionic kinetic term.

Poplawski, Nikodem J. [Department of Physics, Indiana University, 727 East Third Street, Bloomington, Indiana 47405 (United States)

2006-11-15

215

Bose-Einstein condensation of erbium.  

PubMed

We report on the achievement of Bose-Einstein condensation of erbium atoms and on the observation of magnetic Feshbach resonances at low magnetic fields. By means of evaporative cooling in an optical dipole trap, we produce pure condensates of 168Er, containing up to 7×10(4) atoms. Feshbach spectroscopy reveals an extraordinary rich loss spectrum with six loss resonances already in a narrow magnetic-field range up to 3 G. Finally, we demonstrate the application of a low-field Feshbach resonance to produce a tunable dipolar Bose-Einstein condensate and we observe its characteristic d-wave collapse. PMID:23003221

Aikawa, K; Frisch, A; Mark, M; Baier, S; Rietzler, A; Grimm, R; Ferlaino, F

2012-05-25

216

Hypermass generalization of Einstein's gravitation theory  

NASA Technical Reports Server (NTRS)

The curvilinear invariant quaternion formalism is examined for curved space time. Einstein's gravitation equation is shown to have a simple and natural form in this notation. The hypermass generalization of particle mass, which was generated in our studies of the Dirac equation, is incorporated in gravitation by generalizing Einstein's equation. Covariance requires that the gravitational constant be generalized to an invariant quaternion when the mass is. The modification appears minor and of no importance cosmologically, unless one begins considering time and mass dependence of G.

Edmonds, J. D., Jr.

1973-01-01

217

Beyond Einstein: Exploring the Extreme Universe  

NASA Technical Reports Server (NTRS)

This paper will give an overview of the NASA Universe Division Beyond Einstein program. The Beyond Einstein program consists of a series of exploratory missions to investigate some of the most important and pressing problems in modern-day astrophysics - including searches for Dark Energy and studies of the earliest times in the universe, during the inflationary period after the Big Bang. A variety of new technologies are being developed both in the science instrumentation these missions will carry and in the spacecraft that will carry those instruments.

Barbier, Louis M.

2005-01-01

218

Human dynamics: Darwin and Einstein correspondence patterns  

NASA Astrophysics Data System (ADS)

In an era when letters were the main means of exchanging scientific ideas and results, Charles Darwin (1809-82) and Albert Einstein (1879-1955) were notably prolific correspondents. But did their patterns of communication differ from those associated with the instant-access e-mail of modern times? Here we show that, although the means have changed, the communication dynamics have not: Darwin's and Einstein's patterns of correspondence and today's electronic exchanges follow the same scaling laws. However, the response times of their surface-mail communication is described by a different scaling exponent from e-mail communication, providing evidence for a new class of phenomena in human dynamics.

Oliveira, João Gama; Barabási, Albert-László

2005-10-01

219

Input-output description of linear systems with multiple time-scales  

NASA Technical Reports Server (NTRS)

It is pointed out that the study of systems evolving at multiple time-scales is simplified by studying reduced-order models of these systems valid at specific time-scales. The present investigation is concerned with an extension of results on the time-scale decomposition of autonomous systems to that of input-output systems. The results are employed to study conditions under which positive realness of a transfer function is preserved under singular perturbation. Attention is given to the perturbation theory for linear operators, the multiple time-scale structure of autonomous linear systems, the input-output description of two time-scale linear systems, the positive realness of two time-scale systems, and multiple time-scale linear systems.

Madriz, R. S.; Sastry, S. S.

1984-01-01

220

Hawking Radiation of Black Hole in Einstein-Proca Theory  

NASA Astrophysics Data System (ADS)

The Hawking radiation of black hole in Einstein-Proca theory is discussed in this paper. The Einstein-Proca black hole is more general than Reissner-Nordström black hole, because Proca field is massive vector field. We calculate several quantum perturbations in this spacetime, and obtain the Hawking radiation at the horizon in Einstein-Proca theory.

Yang, Shuzheng; Lin, Kai; Li, Jin

2014-05-01

221

Einstein-Yang-Mills black hole solutions in three dimensions  

Microsoft Academic Search

In this paper, a procedure which gives euclidean solutions of 3-dimensional Einstein-Yang-Mills equations when one has solutions of the Einstein equations is proposed. The method is based on reformulating Yang-Mills theory in such a way that it becomes a gravity. It is applied to find black hole solutions of the coupled Einstein-Yang-Mills equations.

V Brindejonc

1997-01-01

222

Einstein - Yang - Mills black hole solutions in three dimensions  

Microsoft Academic Search

In this paper, a procedure which gives Euclidean solutions of three-dimensional Einstein - Yang - Mills equations when one has solutions of the Einstein equations is proposed. The method is based on reformulating Yang - Mills theory in such a way that it becomes a gravity. It is applied to find black hole solutions of the coupled Einstein - Yang

Vincent Brindejonc

1998-01-01

223

CONSTRAINTS ON BLACK HOLE GROWTH, QUASAR LIFETIMES, AND EDDINGTON RATIO DISTRIBUTIONS FROM THE SDSS BROAD-LINE QUASAR BLACK HOLE MASS FUNCTION  

SciTech Connect

We present an estimate of the black hole mass function of broad-line quasars (BLQSOs) that self-consistently corrects for incompleteness and the statistical uncertainty in the mass estimates, based on a sample of 9886 quasars at 1 < z < 4.5 drawn from the Sloan Digital Sky Survey (SDSS). We find evidence for 'cosmic downsizing' of black holes in BLQSOs, where the peak in their number density shifts to higher redshift with increasing black hole mass. The cosmic mass density for black holes seen as BLQSOs peaks at z {approx} 2. We estimate the completeness of the SDSS as a function of the black hole mass and Eddington ratio, and find that at z > 1 it is highly incomplete at M {sub BH} {approx}< 10{sup 9} M {sub sun} and L/L{sub Edd} {approx}< 0.5. We estimate a lower limit on the lifetime of a single BLQSO phase to be t {sub BL} > 150 {+-} 15 Myr for black holes at z = 1 with a mass of M {sub BH} = 10{sup 9} M{sub sun}, and we constrain the maximum mass of a black hole in a BLQSO to be {approx}3 x 10{sup 10} M{sub sun}. Our estimated distribution of BLQSO Eddington ratios peaks at L/L {sub Edd} {approx} 0.05 and has a dispersion of {approx}0.4 dex, implying that most BLQSOs are not radiating at or near the Eddington limit; however, the location of the peak is subject to considerable uncertainty. The steep increase in number density of BLQSOs toward lower Eddington ratios is expected if the BLQSO accretion rate monotonically decays with time. Furthermore, our estimated lifetime and Eddington ratio distributions imply that the majority of the most massive black holes spend a significant amount of time growing in an earlier obscured phase, a conclusion which is independent of the unknown obscured fraction. These results are consistent with models for self-regulated black hole growth, at least for massive systems at z > 1, where the BLQSO phase occurs at the end of a fueling event when black hole feedback unbinds the accreting gas, halting the accretion flow.

Kelly, Brandon C.; Hernquist, Lars; Siemiginowska, Aneta [Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States); Vestergaard, Marianne; Fan Xiaohui [Department of Astronomy, University of Arizona, Tucson, AZ 85721 (United States); Hopkins, Philip, E-mail: bckelly@cfa.harvard.ed [Department of Astronomy, University of California, Berkeley, CA (United States)

2010-08-20

224

Einstein-Podolsky-Rosen Entanglement Strategies in Two-Well Bose-Einstein Condensates  

SciTech Connect

Criteria suitable for measuring entanglement between two different potential wells in a Bose-Einstein condensation are evaluated. We show how to generate the required entanglement, utilizing either an adiabatic two-mode or a dynamic four-mode interaction strategy, with techniques that take advantage of s-wave scattering interactions to provide the nonlinear coupling. The dynamic entanglement method results in an entanglement signature with spatially separated detectors, as in the Einstein-Podolsky-Rosen paradox.

He, Q. Y.; Vaughan, T. G. [ARC Centre of Excellence for Quantum-Atom Optics, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122 (Australia); Reid, M. D.; Drummond, P. D. [ARC Centre of Excellence for Quantum-Atom Optics, Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122 (Australia)] [Kirchhoff-Institut fuer Physik, Universitaet Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg (Germany); Gross, C.; Oberthaler, M. [Kirchhoff-Institut fuer Physik, Universitaet Heidelberg, Im Neuenheimer Feld 227, 69120 Heidelberg (Germany)

2011-03-25

225

Conformally related null Einstein-Maxwell fields  

NASA Astrophysics Data System (ADS)

We present a class of pairs of non-trivially conformally related solutions of Einstein-Maxwell equations that are not pp-waves. To our knowledge, this is the first such case and thus an extension of theorems by Brinkmann, Daftardar-Gejji and Van den Bergh concerning conformal transformations of solutions with null electromagnetic fields.

Hruška, J.; Žofka, M.

2013-01-01

226

Einstein equations in the null quasispherical gauge  

Microsoft Academic Search

Properties of the Einstein equations in a coordinate gauge based on expanding null hypersurfaces foliated by metric 2-spheres are described. This null quasispherical (NQS) gauge leads to particularly simple analyses of the characteristic structure of the equations and of the propagation of gravitational shocks, and clarifies the geometry of timelike boundary condition. A feature of the NQS gauge is the

Robert Bartnik

1997-01-01

227

Quantum Structures in Einstein General Relativity  

Microsoft Academic Search

We introduce the notion of a ‘quantum structure’ on an Einstein general relativistic classical spacetime M. It consists of a line bundle over M equipped with a connection fulfilling certain conditions. We give a necessary and sufficient condition for the existence of quantum structures and classify them. The existence and classification results are analogous to those of geometric quantisation (Kostant

Raffaele Vitolo; E. De Giorgi

2000-01-01

228

On the Scalar Curvature of Einstein Manifolds  

Microsoft Academic Search

We show that there are high-dimensional smooth compact manifolds which admit pairs of Einstein metrics for which the scalar curvatures have opposite signs. These are counter-examples to a conjecture considered by Besse. The proof hinges on showing that the Barlow surface has small deformations with ample canonical line bundle.

Fabrizio Catanese; Claude LeBrun

1997-01-01

229

On the Scalar Curvature of Einstein Manifolds  

Microsoft Academic Search

We show that there are high-dimensional smooth compact manifolds which admit pairs of Einstein metrics for which the scalar curvatures have opposite signs. These are counter-examples to a conjecture considered by Besse (6, p. 19). The proof hinges on showing that the Barlow surface has small deformations with ample canonical line bundle.

Fabrizio Catanese; Claude LeBrun

230

Einstein Solid with a Heat Bath Model  

NSDL National Science Digital Library

A worksheet that considers the case of an Einstein solid in thermal contact with a large reservoir or heat bath. Energy is continually exchanged between the bath and the solid, but the bath is so large that its temperature remains constant.

Wheaton, Spencer

2013-08-15

231

Entanglement concentration in Bose-Einstein condensates  

Microsoft Academic Search

We propose a scheme for demonstrating entanglement swapping (i.e., teleportation of entanglement) using trapped Bose-Einstein condensates. This is accomplished by detection of the total number of atoms leaking out of two adjacent traps. We describe how this scheme may be used to concentrate entanglement shared between two parties in the form of entangled condensates.

J. A. Dunningham; S. Bose; L. Henderson; V. Vedral; K. Burnett

2002-01-01

232

Efficient Algorithm for Computing Einstein Integrals  

Microsoft Academic Search

Analytical approximations to Einstein integrals are proposed. The approximations represented by two fast-converging series are valid for all values of their arguments. Accordingly, the algorithm can be easily incorporated into professional software like HEC-RAS or HEC-6 with minimum computational effort.

Junke Guo; Pierre Y. Julien

2004-01-01

233

DESIGN ANALYSIS OF THE EINSTEIN REFRIGERATION CYCLE  

Microsoft Academic Search

After developing the theory of relativity, Albert Einstein spent several years working with Leo Szilard on absorption refrigeration cycles. In 1930, they obtained a U.S. patent for a unique single pressure absorption cycle. The single pressure eliminates the need for a solution pump. Their cycle has only recently been rediscovered. The cycle u tilizes butane as its refrigerant, ammonia as

Sam V. Shelton; Andrew Delano; Laura A. Schaefer

1998-01-01

234

Chromohydrodynamics in Einstein-Cartan theory  

SciTech Connect

The complete dynamical system for a classical fluid endowed with non-Abelian charge density is obtained by using variational techniques. Spin density appears in a natural way, as a consequence of a usual gauge construction. Einstein-Cartan, Yang-Mills, and generalized Wong equations are explicitly shown.

Amorim, R.

1986-05-15

235

On Einstein Manifolds of Positive Sectional Curvature  

Microsoft Academic Search

Let (M, g) be a compact oriented 4-dimensional Einstein manifold. If M has positive intersection form and g has non-negative sectional curva- ture, we show that, up to rescaling and isometry, (M, g) is CP2, with its standard Fubini-Study metric.

Matthew J. Gursky; Claude LeBrun; SUNY Stony Brook

1999-01-01

236

Einstein and a century of time  

Microsoft Academic Search

In a world overabundant in information, a subject is defined by its iconography. Physics is the falling apple, the planetary atom, the laser, the mushroom cloud and the image of the later Einstein - images that represent, respectively, gravity, atomic theory, quantum theory, mass-energy and the scientist who had a hand in all four. It is therefore appropriate that World

D J Raine

2005-01-01

237

Energy in the Einstein-aether theory  

Microsoft Academic Search

We investigate the energy of a theory with a unit vector field (the aether) coupled to gravity. Both the Weinberg and Einstein type energy-momentum pseudotensors are employed. In the linearized theory we find expressions for the energy density of the 5 wave modes. The requirement that the modes have positive energy is then used to constrain the theory. In the

Christopher Eling

2006-01-01

238

Neutron stars in Einstein-aether theory  

Microsoft Academic Search

As current and future experiments probe strong gravitational regimes around neutron stars and black holes, it is desirable to have theoretically sound alternatives to general relativity against which to test observations. Here we study the consequences of one such generalization, Einstein-aether theory, for the properties of nonrotating neutron stars. This theory has a parameter range that satisfies all current weak-field

Christopher Eling; Ted Jacobson; M. Coleman Miller

2007-01-01

239

Einstein-aether gravity: a status report  

Microsoft Academic Search

This paper reviews the theory, phenomenology, and observational constraints on the coupling parameters of Einstein-aether gravity, i.e. General Relativity coupled to a dynamical unit timelike vector field. A discussion of open questions concerning both phenomenology and fundamental issues is included.

Ted Jacobson

2008-01-01

240

Type III Einstein-Yang-Mills solutions  

Microsoft Academic Search

We construct two distinct classes of exact type III solutions of the D=4 Einstein-Yang-Mills system. The solutions are embeddings of the non-Abelian plane waves in spacetimes in Kundt's class. Reduction of the solutions to type N leads to generalized pp and Kundt waves. The geodesic equations are briefly discussed.

Andrea Fuster; Jan-Willem van Holten

2005-01-01

241

Parametric autoresonance in Bose-Einstein condensates  

Microsoft Academic Search

ó We investigate parametric autoresonant excitations in Bose-Einstein condensates under the modulation of scattering length with slowly vary- ing frequencies (adiabatic modulation). By numerically solving the Gross- Pitaevskii equation we observe a step-wise increase in the amplitude of os- cillation due to continuous phase locking between driving frequency and nonlinear frequency. Such an autoresonant excitation has been shown to exist

S. Rajendran; P. Muruganandam; M. Lakshmanan

242

Fast transport of Bose-Einstein condensates  

Microsoft Academic Search

We propose an inverse method to accelerate without final excitation the adiabatic transport of a Bose Einstein condensate. The method, applicable to arbitrary potential traps, is based on a partial extension of the Lewis-Riesenfeld invariants, and provides transport protocols that satisfy exactly the no-excitation conditions without constraints or approximations. This inverse method is complemented by optimizing the trap trajectory with

E. Torrontegui; Xi Chen; M. Modugno; S. Schmidt; A. Ruschhaupt; J. G. Muga

2011-01-01

243

Phase Separation of Bose-Einstein Condensates  

Microsoft Academic Search

We distinguish two types of spatial separation exhibited by atomic trap Bose-Einstein condensates: potential separation, in which case the condensates diffuse into each other as the trap is opened adiabatically, and phase separation, in which case the separation persists in the absence of external potentials. We discuss relevant features of the dynamics and statics of the phase separation of dilute

Eddy Timmermans

1998-01-01

244

Equilibration timescale of atmospheric secondary organic aerosol partitioning  

NASA Astrophysics Data System (ADS)

Secondary organic aerosol (SOA) formed from partitioning of oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs) accounts for a substantial portion of atmospheric particulate matter. In describing SOA formation, it is generally assumed that VOC oxidation products rapidly adopt gas-aerosol equilibrium. Here we estimate the equilibration timescale, ?eq, of SOA gas-particle partitioning using a state-of-the-art kinetic flux model. ?eq is found to be of order seconds to minutes for partitioning of relatively high volatility organic compounds into liquid particles, thereby adhering to equilibrium gas-particle partitioning. However, ?eq increases to hours or days for organic aerosol associated with semi-solid particles, low volatility, large particle size, and low mass loadings. Instantaneous equilibrium partitioning may lead to substantial overestimation of particle mass concentration and underestimation of gas-phase concentration.

Shiraiwa, Manabu; Seinfeld, John H.

2012-12-01

245

DYNAMICAL MASS SEGREGATION ON A VERY SHORT TIMESCALE  

SciTech Connect

We discuss the observations and theory of star cluster formation to argue that clusters form dynamically cool (subvirial) and with substructure. We then perform an ensemble of simulations of cool, clumpy (fractal) clusters and show that they often dynamically mass segregate on timescales far shorter than expected from simple models. The mass segregation comes about through the production of a short-lived, but very dense core. This shows that in clusters like the Orion Nebula Cluster the stars {>=} 4 M{sub sun} can dynamically mass segregate within the current age of the cluster. Therefore, the observed mass segregation in apparently dynamically young clusters need not be primordial, but could be the result of rapid and violent early dynamical evolution.

Allison, Richard J.; Goodwin, Simon P.; Parker, Richard J.; De Grijs, Richard; Kouwenhoven, M. B. N. [Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom); Portegies Zwart, Simon F. [Leiden Observatory, P.O. Box 9513, NL-2300 RA Leiden (Netherlands)], E-mail: r.allison@sheffield.ac.uk

2009-08-01

246

Reconstructing disturbances and their biogeochemical consequences over multiple timescales  

USGS Publications Warehouse

Ongoing changes in disturbance regimes are predicted to cause acute changes in ecosystem structure and function in the coming decades, but many aspects of these predictions are uncertain. A key challenge is to improve the predictability of postdisturbance biogeochemical trajectories at the ecosystem level. Ecosystem ecologists and paleoecologists have generated complementary data sets about disturbance (type, severity, frequency) and ecosystem response (net primary productivity, nutrient cycling) spanning decadal to millennial timescales. Here, we take the first steps toward a full integration of these data sets by reviewing how disturbances are reconstructed using dendrochronological and sedimentary archives and by summarizing the conceptual frameworks for carbon, nitrogen, and hydrologic responses to disturbances. Key research priorities include further development of paleoecological techniques that reconstruct both disturbances and terrestrial ecosystem dynamics. In addition, mechanistic detail from disturbance experiments, long-term observations, and chronosequences can help increase the understanding of ecosystem resilience.

McLauchlan, Kendra K.; Higuera, Philip E.; Gavin, Daniel G.; Perakis, Steven S.; Mack, Michelle C.; Alexander, Heather; Battles, John; Biondi, Franco; Buma, Brian; Colombaroli, Daniele; Enders, Sara K.; Engstrom, Daniel R.; Hu, Feng Sheng; Marlon, Jennifer R.; Marshall, John; McGlone, Matt; Morris, Jesse L.; Nave, Lucas E.; Shuman, Bryan; Smithwick, Erica A. H.; Urrego, Dunia H.; Wardle, David A.; Williams, Christopher J.; Williams, Joseph J.

2014-01-01

247

Short time-scale surface changes on Io  

NASA Technical Reports Server (NTRS)

Imaging data from the Voyager 1 and 2 encounters with the Jupiter system provide a data set for the examination of short time-scale variations of surface features on Io. Clear evidence exists for variations near the known eruption sites and for other areas which appeared to have erupted between the encounters. Regions outside the known active eruption sites were examined in order to look for variations in the surface scattering properties which is due to undetected small-scale volcanic activity. The phase functions of many areas are intercompared in order to look for regions with phase functions outside the normal range for satellite surface properties. Areas with unusual scattering properties are related to small-scale eruptions of gas or particles. Determination of the distribution of these areas has strong implications for the resurfacing rates for Io.

Terrile, R. J.

1984-01-01

248

Simulating protein folding and aggregation on the 10 second timescale  

NASA Astrophysics Data System (ADS)

Understanding how proteins self-assemble or ``fold'' is a fundamental problem in biophysics. Moreover, the ability to understand and quantitatively predict folding kinetics would have many implications, especially in the area of diseases related to protein misfolding, such as Alzheimer's Disease. However, there are many challenges to simulating folding, most notably the great computational challenges of simulating protein folding with models with sufficient accuracy to make quantitative predictions of experiments. In my talk, I will discuss our recent work to combine distributed computing with a new theoretical technique (Markov State Models) in order to simulate folding on long timescales as well as the direct and quantitative experimental tests of these methods. I will conclude with the application of these methods to the study of the Abeta peptide, whose aggregation has been directly implicated as the toxic element in Alzheimer's Disease.

Pande, Vijay

2007-03-01

249

Einstein's Foil & the Emergence of Structure  

NASA Astrophysics Data System (ADS)

Before introducing his cosmological constant, Einstein considered a difficulty with Newtonian theory: a steady-state, infinite Newtonian stellar system cannot exist at all. He continues: "It seems hardly possible to surmount these difficulties on the basis of Newtonian theory. We may ask ourselves the question whether they can be removed by a modification of the Newtonian theory. First of all we will indicate a method which does not in itself claim to be taken seriously; it merely serves as a foil for what is to follow. In place of Poisson's equation we write ?? -? ? = 4 ? ? ? where ? denotes a universal constant. If ? be the uniform density of a distribution of mass, then ?=-4? ??/? is a solution." Einstein discarded this foil because it is not compatible with his famed equation for general relativity. In 2004 I proposed a graviton of imaginary mass and a photon of real mass, both equal to 10 -25 eV. Classically this graviton satisfies Einstein's first equation with an empirical value of 2 ?/?-?=Ro/20 = 400 pc. I now suggest an equivalent absolute value -?= (1/2)EH4 2 ? G. where EH is the Hartree energy 2 × 13.6 eV and c=(h/2?) = 1. I will show why this choice and Einstein's second equation gives an emergence of structure at a lookback Z=5.65 dex, a time between nucleosynthesis and recombination when the universe was a plasma of photons, protons, electrons, and helium nuclei. The particular strong structure that I approximate is shown in Hartnett and Hirano (2008). The talk is 3 slides. There will be time for questions. References- "Analogies between electricity and gravity", Metrologia 41(2004)S115-S124. books: Laughlin (2005), Feynman(1995), Weinberg (1977), Lorentz, Einstein, Minkowski, and Weyl (English) (1923).

Bartlett, David F.

2011-01-01

250

Was Einstein Really a Pacifist? Einstein's Independent, Forward-Thinking, Flexible, and Self-Defined Pacifism  

NASA Astrophysics Data System (ADS)

Perhaps motivated by an admiration for Einstein and a desire to identify with him, combined with a majority world-view in opposition to pacifism, skeptics may often question whether Einstein was really a pacifist. They might point to the fact that his dramatic contributions to the field of physics at the beginning of the twentieth century made nuclear weapons possible, as well as his 1939 letter to President Franklin D. Roosevelt urging him to develop such weapons before the Nazis would, as examples of at least an inconsistent stance on pacifism across time on Einstein's part. However, as this paper will show, Einstein's pacifism began early in his life, was a deep-seated conviction that he expressed repeatedly across the years, and was an independent pacifism that flowed from his own responses to events around him and contained some original and impressively forward-thinking elements. Moreover, in calling himself a pacifist, as Einstein did, he defined pacifism in his own terms, not according to the standards of others, and this self-defined pacifism included the flexibility to designate the Nazis as a special case that had to be opposed through the use of military violence, in his view. As early as during his childhood, Einstein already disliked competitive games, because of the necessity of winners and losers, and disliked military discipline. In his late thirties, living in Germany during the First World War with a prestigious academic position in Berlin, yet retaining his identity as a Swiss citizen, Einstein joined a small group of four intellectuals who signed the pacifist ``Appeal to the Europeans'' in response to the militarist ``Manifesto to the Civilized World'' signed by 93 German intellectuals. In private, throughout that War, Einstein repeatedly expressed his disgust and sense of alienation at the ``war-enthusiasm'' sentiment of the majority. In the aftermath of the War, Einstein was involved in a German private commission to investigate German war crimes and the publication that it produced, and throughout the Weimar period of 1918 to 1933 Einstein continued to take public and private stances as a pacifist. As did many pacifists, Einstein also linked his advocacy for peace with a concern for social justice, which included opposition to antisemitism and advocacy for Zionism, and in 1929, after violent clashes between Jews and Arabs in Palestine, in which hundreds died on both sides, Einstein made some impressively forward-thinking statements about Jewish-Arab conciliation, and even published in an Arab newspaper his own proposal to set up a joint Jewish-Arab council for purposes of conflict resolution. But Einstein's pacifism was not forever obliterated by the Nazi era and the Holocaust, despite his well-known encouragement to Roosevelt to develop the bomb. In the United States, where he lived from 1933 on, in the first ten years after World War II, also the last decade of his life, Einstein inspired American pacifists with his strong stances against war and nuclear weapons.

Holmes, Virginia Iris

2005-03-01

251

Computational methods for time-scale analysis of nonlinear dynamical systems  

Microsoft Academic Search

Knowledge of the time-scale structure of a smooth finite dimensional nonlinear dynamical system provides the opportunity for model decomposition, if there are two or more disparate time-scales. A few benefits of such model decomposition are simplified control design and analysis and reduced computational effort in simulation. Singular perturbation theory provides the tools necessary to analyze and decompose a multiple time-scale

Shawn Iravanchy

2003-01-01

252

A Common Mechanism of Multi-timescale Abrupt Global Change  

NASA Astrophysics Data System (ADS)

The La Nina phase of the El Nino/Southern Oscillation (ENSO) is known to cause global cooling on inter- annual timescales through changes in deep convection patterns and reduced supply of water vapor to the tropical atmosphere. Two distinct means are presented here by which this mechanism may also act on timescales exceeding 100,000 years. Firstly, the hypothesis of millennial tidal forcing is revisited with the view that equatorial buoyancy frequencies and steep internal waves in the Pacific Equatorial Undercurrent make vertical mixing in the equatorial Pacific uniquely susceptible to incremental changes in tidal energy. Hourly Tropical Ocean Array subsurface temperature data show a resonant response to extreme tides associated with the 1997 and 2000 ENSO events. Complimenting the known 1,800 year peak tide cycle, a 550-600 year cycle of three-fold variation in the frequency of deep central eclipses (gamma < 0.05) is consistent with the timing of the Little Ice Age. Fortnightly eclipse triples (FET's) associated with this eclipse cycle are shown to coincide with both warm and cold phase Southern Oscillation Index (SOI) inflection points between 1876 and 2007, and notably the cold phase maxima of 1904 and 1917. In the second proposed trigger, southward migration of the intertropical convergence zone (ITCZ) in the central and eastern Pacific may periodically shift the rising branch of the Hadley circulation over the equatorial cold tongue. The resulting winter monsoon system develops an equatorially symmetric La Nina (ESLN) mode through a positive feedback between diverging surface winds and meridional rather than zonal SST gradients. Exchange of latent heat in the winter monsoon contracts the Hadley Cell, draws circumpolar westerly winds equatorward, and expands high latitude ice volume, as demonstrated in 1998. A three million year record of obliquity and August 10°N minus 10°S insolation (AUG10N-S) shows an ice volume dependence upon the mutual direction of change of these signals (rather than upon their quantity). This suggests an orbitally driven north-south ITCZ oscillator in which increasing August insolation at 10°N steepens the cross-equator meridional temperature gradient and strengthens the annual cycle when damped by southern hemisphere thermal inertia, and vice-versa. Increasing Aug10N-S is shown to constrain rapid ice loss (ESLN off). Conversely, declining AUG10N-S coupled with declining obliquity less than 23.5° triggered or maintained glaciation in 44 of 49 cases (ESLN on). The above tidal forcing means may additionally act on precessional timescales because the FET cycle has a seasonal maximum at aphelion, with a possible greatest effect when combined with equinoctial tides. Also, the lunar day at new moons is shorter (closer to 24 hours) at each equinox, thereby extending periods of luni-solar resonance at those peak tides. Tidal forcing may vary further with 100,000 and 400,000 year eccentricity cycles, both directly and by perturbation of the Moon's orbit, and through possible secular changes in the Saros cycle. It is proposed that an equatorially symmetric ITCZ is the necessary condition for a cold phase response to tidal forcing.

Duke, J. H.

2008-12-01

253

Two Versions of Gravity: Newton and Einstein  

NSDL National Science Digital Library

The goal of this lesson is for two groups of students to exchange information (e.g., through poster presentations, Podcasts, debates, or PowerPoint presentations) about how two different theories explain a natural phenomenon: Newton's Law of Gravitation and Einstein's General Theory of Relativity. The lesson will also illustrate how the scientific process allows a new, more complete theory to take the place of an older theory that does not produce accurate results for a new discovery. Students will need to have either studied both Newton's Law of Gravitation and Einstein's Theory of Relativity or be given the time and resources to look up this information. This lesson is part of the Cosmic Times teachers guide and is intended to be used in conjunction with the 1919 Cosmic Times Poster.

254

Einstein static universe in braneworld scenario  

NASA Astrophysics Data System (ADS)

The stability of Einstein static universe against homogeneous scalar perturbations in the context of braneworld scenario is investigated. The stability regions are obtained in terms of the constant geometric linear equation of state parameter ?=p/? and are studied for each evolutionary era of the universe. The results are discussed for the case of closed, open or flat universe in each era under the obtained restricting conditions. We also briefly investigate the stability against vector and tensor perturbations. Contrary to the classical general relativity, it is found that a stable Einstein static universe may exist in a braneworld theory of gravity against scalar, vector and tensor perturbations for some suitable values and ranges of the cosmological parameters.

Atazadeh, K.; Heydarzade, Y.; Darabi, F.

2014-05-01

255

Quantifying einstein-podolsky-rosen steering.  

PubMed

Einstein-Podolsky-Rosen steering is a form of bipartite quantum correlation that is intermediate between entanglement and Bell nonlocality. It allows for entanglement certification when the measurements performed by one of the parties are not characterized (or are untrusted) and has applications in quantum key distribution. Despite its foundational and applied importance, Einstein-Podolsky-Rosen steering lacks a quantitative assessment. Here we propose a way of quantifying this phenomenon and use it to study the steerability of several quantum states. In particular, we show that every pure entangled state is maximally steerable and the projector onto the antisymmetric subspace is maximally steerable for all dimensions; we provide a new example of one-way steering and give strong support that states with positive-partial transposition are not steerable. PMID:24856679

Skrzypczyk, Paul; Navascués, Miguel; Cavalcanti, Daniel

2014-05-01

256

Quantifying Einstein-Podolsky-Rosen Steering  

NASA Astrophysics Data System (ADS)

Einstein-Podolsky-Rosen steering is a form of bipartite quantum correlation that is intermediate between entanglement and Bell nonlocality. It allows for entanglement certification when the measurements performed by one of the parties are not characterized (or are untrusted) and has applications in quantum key distribution. Despite its foundational and applied importance, Einstein-Podolsky-Rosen steering lacks a quantitative assessment. Here we propose a way of quantifying this phenomenon and use it to study the steerability of several quantum states. In particular, we show that every pure entangled state is maximally steerable and the projector onto the antisymmetric subspace is maximally steerable for all dimensions; we provide a new example of one-way steering and give strong support that states with positive-partial transposition are not steerable.

Skrzypczyk, Paul; Navascués, Miguel; Cavalcanti, Daniel

2014-05-01

257

Low redshift AGN in the Hamburg/ESO Survey . II. The active black hole mass function and the distribution function of Eddington ratios  

NASA Astrophysics Data System (ADS)

We estimated black hole masses and Eddington ratios (L/LEdd) for a well defined sample of local (z < 0.3) broad line AGN from the Hamburg/ESO Survey (HES), based on the H? line and standard recipes assuming virial equilibrium for the broad line region. The sample represents the low-redshift AGN population over a wide range of luminosities, from Seyfert 1 galaxies to luminous quasars. From the distribution of black hole masses we derived the active black hole mass function (BHMF) and the Eddington ratio distribution function (ERDF) in the local universe, exploiting the fact that the HES has a well-defined selection function. While the directly determined ERDF turns over around L/LEdd ~ 0.1, similar to what has been seen in previous analyses, we argue that this is an artefact of the sample selection. We employed a maximum likelihood approach to estimate the intrinsic distribution functions of black hole masses and Eddington ratios simultaneously in an unbiased way, taking the sample selection function fully into account. The resulting ERDF is well described by a Schechter function, with evidence for a steady increase towards lower Eddington ratios, qualitatively similar to what has been found for type 2 AGN from the SDSS. Comparing our best-fit active BHMF with the mass function of inactive black holes we obtained an estimate of the fraction of active black holes, i.e. an estimate of the AGN duty cycle. The active fraction decreases strongly with increasing black hole mass. A comparison with the BHMF at higher redshifts also indicates that, at the high mass end, black holes are now in a less active stage than at earlier cosmic epochs. Our results support the notion of anti-hierarchical growth of black holes, and are consistent with a picture where the most massive black holes grew at early cosmic times, whereas at present mainly smaller mass black holes accrete at a significant rate. Based on observations collected at the European Southern Observatory, Chile (Proposal 145.B-0009).

Schulze, A.; Wisotzki, L.

2010-06-01

258

A MODEL FOR THE CORRELATION OF HARD X-RAY INDEX WITH EDDINGTON RATIO IN BLACK HOLE X-RAY BINARIES  

SciTech Connect

Observations show that there is a positive correlation between the Eddington ratio {lambda} and hard X-ray index {Gamma} for {lambda} {approx}> 0.01, and there is an anti-correlation between {lambda} and {Gamma} for {lambda} {approx}< 0.01 in black hole X-ray binaries (with {lambda} = L {sub bol}/L {sub Edd}). In this work, we theoretically investigate the correlation between {Gamma} and {lambda} within the framework of a disk-corona model. We improve the model by taking into account all cooling processes, including synchrotron and self-Compton radiations in the corona, Comptonization of the soft photons from the underlying accretion disk, and the bremsstrahlung radiations. Presuming that the coronal flow above the disk can reach up to the 0.1 Eddington rate at the outer region, we calculate the structure of the two-phase accretion flows and the emergent spectra for accretion rates from 0.003 to 0.1. We find that at accretion rates larger than bsim0.01 Eddington rate, a fraction of coronal gas condenses into the disk and an inner disk can be sustained by condensation. In this case, the X-ray emission is dominated by the scattering of the soft photon from the underlying disk in the corona. The emission from the inner disk and corona can produce the positive correlation between {lambda} and {Gamma}. While at accretion rates lower than bsim0.01 Eddington accretion rate, the inner disk vanishes completely by evaporation, and the accretion is dominated by advection-dominated accretion flows (ADAFs), in which the X-ray emission is produced by the Comptonization of the synchrotron and bremsstrahlung photons of ADAF itself. The emission from ADAFs can produce the anti-correlation between {lambda} and {Gamma}. We show that our model can roughly explain the observed evolution of {Gamma}{sub 3-25keV} with L {sub 0.5-25keV}/L {sub Edd} for the black hole X-ray transient H1743-322 in the decay of 2003 from the thermal-dominated state to low/hard state.

Qiao, Erlin; Liu, B. F., E-mail: qiaoel@nao.cas.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)

2013-02-10

259

Wave turbulence in Bose-Einstein condensates  

Microsoft Academic Search

The kinetics of nonequilibrium Bose-Einstein condensates are considered within the framework of the Gross-Pitaevskii equation. A systematic derivation is given for weak small-scale perturbations of a steady confined condensate state. This approach combines a wavepacket WKB description with the weak turbulence theory. The WKB theory derived in this paper describes the effect of the condensate on the short-wave excitations which

Yuri Lvov Sergey Nazarenko Robert West; Sergey Nazarenko; Robert West

2003-01-01

260

Bose Einstein Condensation of Ideal Bose Gases  

NASA Astrophysics Data System (ADS)

Bose Einstein condensation (BEC) is studied for ideal boson gases with a wide class of the dispersion relations. A criterion of the BEC, the transition temperature and a fraction of the condensate are calculated under the appropriate thermodynamic limits. The correspondence between the dispersion relation (spectrum) and the trap potential is shown. This gives the criterion for the trap shape and the dimensionality of the system.

Ieda, Jun'ichi; Tsurumi, Takeya; Wadati, Miki

2001-05-01

261

Einstein EMSS Survey (Gioia+ 1990, Stocke+ 1991)  

Microsoft Academic Search

The Einstein Extended Medium Sensitivity Survey (EMSS) consists of 835 serendipitous X-ray sources detected at or above 4 times the rms level in 1435 IPC fields with their centers located away from the galactic plane. Their limiting sensitivities range from ~5*10-14 to to ~ 3*10-12 erg.cm-2.s-1 in the 0.3-3.5keV band. A total area of 778 square degrees of the high

I. M. Gioia; T. Maccacaro; R. E. Schild; A. Wolter

1995-01-01

262

Hysteresis effects in Bose-Einstein condensates  

SciTech Connect

Here, we consider damped two-component Bose-Einstein condensates with many-body interactions. We show that, when the external trapping potential has a double-well shape and when the nonlinear coupling factors are modulated in time, hysteresis effects may appear under some circumstances. Such hysteresis phenomena are a result of the joint contribution of the appearance of saddle node bifurcations and the damping effect.

Sacchetti, Andrea [Faculty of Sciences, University of Modena e Reggio Emilia, Via Campi 213/B, I-41100 Modena (Italy)

2010-07-15

263

Genuine Multipartite Einstein-Podolsky-Rosen Steering  

NASA Astrophysics Data System (ADS)

We develop the concept of genuine N-partite Einstein-Podolsky-Rosen (EPR) steering. This nonlocality is the natural multipartite extension of the original EPR paradox. Useful properties emerge that are not guaranteed for genuine multipartite entangled states. In particular, there is a close link with the task of one-sided, device-independent quantum secret sharing. We derive inequalities to demonstrate multipartite EPR steering for Greenberger-Horne-Zeilinger and Gaussian continuous variable states in loophole-free scenarios.

He, Q. Y.; Reid, M. D.

2013-12-01

264

Analogue gravity from Bose-Einstein condensates  

Microsoft Academic Search

We analyse prospects for the use of Bose-Einstein condensates as condensed-matter systems suitable for generating a generic `effective metric', and for mimicking kinematic aspects of general relativity. We extend the analysis due to Garay et al (2000 Phys. Rev. Lett. 85 4643, 2001 Phys. Rev. A 63 023611). Taking a long-term view, we ask what the ultimate limits of such

Carlos Barceló; S. Liberati; Matt Visser

2001-01-01

265

Radiation damping in Einstein-aether theory  

Microsoft Academic Search

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory - an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian order are wave forms for the metric and vector fields far from a nearly Newtonian system and the rate of

Brendan Z. Foster; Brendan Z

2006-01-01

266

Radiation damping in Einstein-aether theory  

Microsoft Academic Search

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory---an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian order are wave forms for the metric and vector fields far from a nearly Newtonian system and the rate of energy radiated

Brendan Z. Foster

2006-01-01

267

Passing the Einstein-Rosen bridge  

NASA Astrophysics Data System (ADS)

A test particle moving along geodesic line in a spacetime has three physical propagating degrees of freedom and one unphysical gauge degree. We relax the requirement of geodesic completeness of a spacetime. Instead, we require test particles trajectories to be smooth and complete only for physical degrees of freedom. Test particles trajectories for Einstein-Rosen bridge are proved to be smooth and complete in the physical sector, and particles can freely penetrate the bridge in both directions.

Katanaev, M. O.

2014-05-01

268

Black Holes in Bose–Einstein Condensates  

Microsoft Academic Search

It is shown that there exist both dynamically stable and unstable dilute-gas Bose–Einstein condensates that, in the hydrodynamic limit, exhibit a behavior completely analogous to that of gravitational black holes. The dynamical instabilities involve creation of quasiparticle pairs in positive and negative energy states. We illustrate these features in two qualitatively different one-dimensional models. We have also simulated the creation

L. J. Garay

2002-01-01

269

Fast transport of Bose–Einstein condensates  

Microsoft Academic Search

We propose an inverse method to accelerate without final excitation the adiabatic transport of a Bose–Einstein condensate. The method is based on a partial extension of the Lewis–Riesenfeld invariants and provides transport protocols that satisfy exactly the no-excitation conditions without approximations. This inverse method is complemented by optimizing the trap trajectory with respect to different physical criteria and by studying

E Torrontegui; Xi Chen; M Modugno; S Schmidt; A Ruschhaupt; J G Muga

2012-01-01

270

Stellar envelope inflation near the Eddington limit. Implications for the radii of Wolf-Rayet stars and luminous blue variables  

NASA Astrophysics Data System (ADS)

Context. It has been proposed that the envelopes of luminous stars may be subject to substantial radius inflation. The peculiar structure of such inflated envelopes, with an almost void, radiatively dominated region beneath a thin, dense shell could mean that many in reality compact stars are hidden below inflated envelopes, displaying much lower effective temperatures. The inflation effect has been discussed in relation to the radius problem of Wolf-Rayet (WR) stars, but has yet failed to explain the large observed radii of Galactic WR stars. Aims: We wish to obtain a physical perspective of the inflation effect, and study the consequences for the radii of WR stars, and luminous blue variables (LBVs). For WR stars the observed radii are up to an order of magnitude larger than predicted by theory, whilst S Doradus-type LBVs are subject to humongous radius variations, which remain as yet ill-explained. Methods: We use a dual approach to investigate the envelope inflation, based on numerical models for stars near the Eddington limit, and a new analytic formalism to describe the effect. An additional new aspect is that we take the effect of density inhomogeneities (clumping) within the outer stellar envelopes into account. Results: Due to the effect of clumping we are able to bring the observed WR radii in agreement with theory. Based on our new formalism, we find that the radial inflation is a function of a dimensionless parameter W, which largely depends on the topology of the Fe-opacity peak, i.e., on material properties. For W > 1, we discover an instability limit, for which the stellar envelope becomes gravitationally unbound, i.e. there no longer exists a static solution. Within this framework we are also able to explain the S Doradus-type instabilities for LBVs like AG Car, with a possible triggering due to changes in stellar rotation. Conclusions: The stellar effective temperatures in the upper Hertzsprung-Russell (HR) diagram are potentially strongly affected by the inflation effect. This may have particularly strong effects on the evolved massive LBV and WR stars just prior to their final collapse, as the progenitors of supernovae (SNe) Ibc, SNe II, and long-duration gamma-ray bursts (long GRBs).

Gräfener, G.; Owocki, S. P.; Vink, J. S.

2012-02-01

271

Stellar mass-loss near the Eddington limit. Tracing the sub-photospheric layers of classical Wolf-Rayet stars  

NASA Astrophysics Data System (ADS)

Context. Towards the end of their evolution, hot massive stars develop strong stellar winds and appear as emission line stars, such as Wolf-Rayet (WR) stars or luminous blue variables (LBVs). The quantitative description of the mass loss in these important pre-supernova phases is hampered by unknowns, such as clumping and porosity due to an inhomogeneous wind structure and by an incomplete theoretical understanding of optically thick stellar winds. Even the stellar radii in these phases are badly understood since they are often variable (LBVs) or deviate from theoretical expectations (WR stars). Aims: In this work we investigate the conditions in deep atmospheric layers of WR stars to find out whether they comply with the theory of optically thick winds and whether we find indications of clumping in these layers. Methods: We used a new semi-empirical method to determine sonic-point optical depths, densities, and temperatures for a large sample of WR stars of the carbon (WC) and oxygen (WO) sequence. Based on an artificial model sequence we investigated the reliability of our method and its sensitivity to uncertainties in stellar parameters. Results: We find that the WR stars in our sample obey an approximate relation with Prad/Pgas ? 80 at the sonic point. This "wind condition" is ubiquitous for radiatively driven, optically thick winds, and it sets constraints on possible wind/envelope solutions affecting radii, mass-loss rates, and clumping properties. Conclusions: Our results suggest that the presence of an optically thick wind may force many stars near the Eddington limit to develop clumped, radially extended sub-surface zones. The clumping in these zones is most likely sustained by the non-linear strange-mode instability and may be the origin of the observed wind clumping. The properties of typical late-type WC stars comply with this model. Solutions without sub-surface clumping and inflation are also possible but require compact stars with comparatively low mass-loss rates. These objects may resemble the small group of WO stars with their exceptionally hot stellar temperatures and highly ionized winds. Tables 1 and 2 are available in electronic form at http://www.aanda.org

Gräfener, G.; Vink, J. S.

2013-12-01

272

Analogue gravity from Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

We analyse prospects for the use of Bose-Einstein condensates as condensed-matter systems suitable for generating a generic `effective metric', and for mimicking kinematic aspects of general relativity. We extend the analysis due to Garay et al (2000 Phys. Rev. Lett. 85 4643, 2001 Phys. Rev. A 63 023611). Taking a long-term view, we ask what the ultimate limits of such a system might be. To this end, we consider a very general version of the nonlinear Schrödinger equation (with a 3-tensor position-dependent mass and arbitrary nonlinearity). Such equations can be used, for example, in discussing Bose-Einstein condensates in heterogeneous and highly nonlinear systems. We demonstrate that at low momenta linearized excitations of the phase of the condensate wavefunction obey a (3 + 1)-dimensional d'Alembertian equation coupling to a (3 + 1)-dimensional Lorentzian-signature `effective metric' that is generic, and depends algebraically on the background field. Thus at low momenta this system serves as an analogue for the curved spacetime of general relativity. In contrast, at high momenta we demonstrate how one can use the eikonal approximation to extract a well controlled Bogoliubov-like dispersion relation, and (perhaps unexpectedly) recover non-relativistic Newtonian physics at high momenta. Bose-Einstein condensates appear to be an extremely promising analogue system for probing kinematic aspects of general relativity.

Barceló, Carlos; Liberati, S.; Visser, Matt

2001-03-01

273

Albert Einstein's Special Theory of Relativity  

NASA Astrophysics Data System (ADS)

This book analyzes one of the three great papers Einstein published in 1905, each of which would alter forever the field it dealt with. The second of these papers, "On the Electrodynamics of Moving Bodies," had an impact in a much broader field than electrodynamics: it established what Einstein sometimes referred to (after 1906) as the "so-called Theory of Relativity." Miller uses the paper to provide a window into the intense intellectual struggles of physicists in the first decade of the 20th century: the interplay between physical theory and empirical data, the fiercely held notions that could not be articulated clearly or verified experimentally, the great intellectual investment in existing theories, data, and interpretations -- and associated intellectual inertia -- and the drive to the long-sought- for unification of the sciences. Since its original publication, this book has become a standard reference and sourcebook for the history and philosophy of science; however, it can equally well serve as a text in the history of ideas or of twentieth-century philosophy. From reviews of the previous edition: ÄMillerÜ has written a superb, perhaps definitive, historical study of Einstein's special theory of relativity.... One comes away from the book with a respect for both the creative genius of the man and his nerve: he simply brushed aside much of the work that was going on around him. - The New Yorker

Miller, Arthur I.

274

Einstein's Universe - Gravity at Work and Play  

NASA Astrophysics Data System (ADS)

On Albert Einstein's seventy-sixth and final birthday, a friend gave him a simple toy made from a broomstick, a brass ball attached to a length of string, and a weak spring. Einstein was delighted: the toy worked on a principle he had conceived fifty years earlier when he was working on his revolutionary theory of gravitya principle whose implications are still confounding physicists today.Starting with this winning anecdote, Anthony Zee begins his animated discussion of phenomena ranging from the emergence of galaxies to the curvature of space-time, evidence for the existence of gravity waves, and the shape of the universe in the first nanoseconds of creation and today. Making complex ideas accessible without oversimplifying, Zee leads the reader through the implications of Einstein's theory and its influence on modern physics. His playful and lucid style conveys the excitement of some of the latest developments in physics, and his new Afterword brings things even further up-to-date.

Zee, A.

2001-07-01

275

Conformal and Einstein gravity from twistor actions  

NASA Astrophysics Data System (ADS)

We use the embedding of Einstein gravity with cosmological constant into conformal gravity as a basis for using the twistor action for conformal gravity to obtain maximal-helicity-violating (MHV) scattering amplitudes not just for conformal gravity, but also for Einstein gravity on backgrounds with non-zero cosmological constant. The new formulae for the gravitational MHV amplitude with cosmological constant arise by summing Feynman diagrams using the matrix-tree theorem. We show that this formula is well-defined (i.e., is independent of certain gauge choices) and that it non-trivially reproduces Hodges’ formula for the MHV amplitude in the flat-space limit. We give a preliminary discussion of an MHV formalism for more general amplitudes obtained from the conformal gravity twistor action in an axial gauge. We also see that the embedding of Einstein data into the conformal gravity action can be performed off-shell in twistor space to give a proposal for an Einsten twistor action that automatically gives the same MHV amplitude. These ideas extend naturally to {N}=4 supersymmetry.

Adamo, Tim; Mason, Lionel

2014-02-01

276

Thermodynamic structure of the Einstein tensor  

SciTech Connect

We analyze the generic structure of Einstein tensor projected onto a 2D spacelike surface S defined by a unit timelike and spacelike vectors u and n, respectively, which describe an accelerated observer (see text). Assuming that flow along u defines an approximate Killing vector {xi}, we then show that near the corresponding Rindler horizon, the flux j{sup a}=G{sub b}{sup a{xi}b} along the ingoing null geodesics k, i.e., j{center_dot}k, has a natural thermodynamic interpretation. Moreover, change in the cross-sectional area of the k congruence yields the required change in area of S under virtual displacements normal to it. The main aim of this paper is to clearly demonstrate how, and why, the content of Einstein equations under such horizon deformations, originally pointed out by Padmanabhan, is essentially different from the result of Jacobson, who employed the so-called Clausius relation in an attempt to derive Einstein equations from such a Clausius relation. More specifically, we show how a very specific geometric term (reminiscent of Hawking's quasilocal expression for energy of spheres) corresponding to change in gravitational energy arises inevitably in the first law: dE{sub G}/d{lambda}{proportional_to}Hd{sup 2}x{radical}({sigma}){sup (2)}R (see text)--the contribution of this purely geometric term would be missed in attempts to obtain area (and hence entropy) change by integrating the Raychaudhuri equation.

Kothawala, Dawood [Department of Mathematics and Statistics, University of New Brunswick, Fredericton, NB, E3B 5A3 (Canada)

2011-01-15

277

Relativistic Vortices in Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

We present two different approaches to the formation of vortices for a Bose-Einstein condensate in a honeycomb optical lattice. In the first approach, we consider vortices in the condensate order parameter. These are multi-component localized solutions of the nonlinear Dirac equation with nontrivial rotation about a core phase singularity [1]. They are different from ordinary spinor vortices because the Berry phase induced by the lattice background supports a remarkable boson-fermion mapping in the quasi-particle operator statistics [2]. Another type of vortex occurs when we add a mass gap by including distortions of both the nearest neighbor and next-nearest neighbor hopping, as well as a staggered chemical potential between the two sublattices. Vortices with fractional statistics emerge when the superfluid order parameter is integrated over a topological defect in the mass gap.[0pt] [1] L. H. Haddad and L. D. Carr, ``The Nonlinear Dirac Equation in Bose-Einstein Condensates: Foundation and Symmetries,'' Physica D: Nonlinear Phenomena, v. 238, p. 1413 (2009). http://arxiv.org/pdf/0803.3039v1 [2] L. H. Haddad and L. D. Carr, ``Relativistic Linear Stability Equations for the Nonlinear Dirac Equation in Bose-Einstein Condensates,'' Submitted to Europhysics Letters Jan. 2011. http://arxiv.org/abs/1006.3893

Haddad, Laith; Carr, Lincoln

2011-06-01

278

Complex Processes from Dynamical Architectures with Time-Scale Hierarchy  

PubMed Central

The idea that complex motor, perceptual, and cognitive behaviors are composed of smaller units, which are somehow brought into a meaningful relation, permeates the biological and life sciences. However, no principled framework defining the constituent elementary processes has been developed to this date. Consequently, functional configurations (or architectures) relating elementary processes and external influences are mostly piecemeal formulations suitable to particular instances only. Here, we develop a general dynamical framework for distinct functional architectures characterized by the time-scale separation of their constituents and evaluate their efficiency. Thereto, we build on the (phase) flow of a system, which prescribes the temporal evolution of its state variables. The phase flow topology allows for the unambiguous classification of qualitatively distinct processes, which we consider to represent the functional units or modes within the dynamical architecture. Using the example of a composite movement we illustrate how different architectures can be characterized by their degree of time scale separation between the internal elements of the architecture (i.e. the functional modes) and external interventions. We reveal a tradeoff of the interactions between internal and external influences, which offers a theoretical justification for the efficient composition of complex processes out of non-trivial elementary processes or functional modes.

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor

2011-01-01

279

Complex processes from dynamical architectures with time-scale hierarchy.  

PubMed

The idea that complex motor, perceptual, and cognitive behaviors are composed of smaller units, which are somehow brought into a meaningful relation, permeates the biological and life sciences. However, no principled framework defining the constituent elementary processes has been developed to this date. Consequently, functional configurations (or architectures) relating elementary processes and external influences are mostly piecemeal formulations suitable to particular instances only. Here, we develop a general dynamical framework for distinct functional architectures characterized by the time-scale separation of their constituents and evaluate their efficiency. Thereto, we build on the (phase) flow of a system, which prescribes the temporal evolution of its state variables. The phase flow topology allows for the unambiguous classification of qualitatively distinct processes, which we consider to represent the functional units or modes within the dynamical architecture. Using the example of a composite movement we illustrate how different architectures can be characterized by their degree of time scale separation between the internal elements of the architecture (i.e. the functional modes) and external interventions. We reveal a tradeoff of the interactions between internal and external influences, which offers a theoretical justification for the efficient composition of complex processes out of non-trivial elementary processes or functional modes. PMID:21347363

Perdikis, Dionysios; Huys, Raoul; Jirsa, Viktor

2011-01-01

280

A hybrid approach to model shoreline change at multiple timescales  

NASA Astrophysics Data System (ADS)

The paper describes the development of a hybrid behaviour-oriented/data-driven shoreline evolution model. The model is based on a form of advection-diffusion formulation widely known to describe shoreline change. The approach breaks down the model governing equation into two parts, one describing the contribution from time-averaged wave-driven processes through a spatially varying diffusion coefficient and the other describing time-varying wave contributions and all other processes that contribute to shoreline change, through a source function. Both the diffusion coefficient and the source function are site-specific and unknown. Historic incident wave measurements are used to determine the diffusion coefficient at a given site. The source function is derived by the inverse solution of the model governing equation using historic shoreline surveys. The method is demonstrated for Colwyn Bay beach at Conwy Bay in North Wales, UK. For drift-dominated shorelines, the technique can isolate the contributions of cross-shore and long-shore transport to shoreline change over a range of timescales, which is critical in implementing coastal defence measures.

Karunarathna, Harshinie; Reeve, Dominic E.

2013-09-01

281

Evidence of Protein Collective Motions on the Picosecond Timescale  

PubMed Central

We investigate the presence of structural collective motions on a picosecond timescale for the heme protein, cytochrome c, as a function of oxidation and hydration, using terahertz (THz) time domain spectroscopy and molecular dynamics simulations. The THz response dramatically increases with oxidation, with the largest increase for lowest hydrations, and highest frequencies. For both oxidation states the THz response rapidly increases with hydration saturating above ?25% (g H2O/g protein). Quasiharmonic vibrational modes and dipole-dipole correlation functions were calculated from molecular dynamics trajectories. The collective mode density of states alone reproduces the measured hydration dependence, providing strong evidence of the existence of these motions. The large oxidation dependence is reproduced only by the dipole-dipole correlation function, indicating the contrast arises from diffusive motions consistent with structural changes occurring in the vicinity of buried internal water molecules. This source for the observed oxidation dependence is consistent with the lack of an oxidation dependence in nuclear resonant vibrational spectroscopy measurements.

He, Yunfen; Chen, J.-Y.; Knab, J.R.; Zheng, Wenjun; Markelz, A.G.

2011-01-01

282

Modeling the Short Timescale Inner Disk Changes of HD169142  

NASA Astrophysics Data System (ADS)

Recent observations of circumstellar disks of gas and dust found around young stars present the unique opportunity for the study of planetary formation regions in their infancy. Observations dating from the early 1990s until the early 2000s on the Herbig Ae star HD169142 show changes in the 1-5 micron fluxes of up to 30%. We present two models for the disk around HD169142 - representing the two distinct flux states observed in the spectral energy distributions, that prior to the year 2000, and that post-2000. The short 10 years) timescale of the changes demands that whatever changes are made to the models occur within the inner few AU of the disk. In accordance with this and popular consensus on the origin of high near-IR flux in these disks, our models fit the change in near infrared flux by changing the puffed up inner rim by a decrease in its height and length. However, this change alone affects the shadowing of the outer disk and thus affects the far infrared flux levels. Observations from both eras lack any such change in far infrared flux. This might be due to either a tilted inner disk (so changes in shadowing of the outer disk are minimized) or because of the long thermal time scale of the outer disk. This work was supported by NASA ADAP grant NNX09AC73G, Hubble Space Telescope grant HST-GO-13032, and the IR&D program at The Aerospace Corporation.

Wagner, Kevin; Sitko, M. L.; Whitney, B.; Swearingen, J. R.; Champney, E. H.; Johnson, A. N.; Warren, C. C.; Russell, R. W.; Grady, C. A.; Fukagawa, M.; Hashimoto, J.

2014-01-01

283

Construction of Einstein-Sasaki metrics in D{>=}7  

SciTech Connect

We construct explicit Einstein-Kaehler metrics in all even dimensions D=2n+4{>=}6, in terms of a 2n-dimensional Einstein-Kaehler base metric. These are cohomogeneity 2 metrics which have the new feature of including a NUT-type parameter, or gravomagnetic charge, in addition to..' in addition to mass and rotation parameters. Using a canonical construction, these metrics all yield Einstein-Sasaki metrics in dimensions D=2n+5{>=}7. As is commonly the case in this type of construction, for suitable choices of the free parameters the Einstein-Sasaki metrics can extend smoothly onto complete and nonsingular manifolds, even though the underlying Einstein-Kaehler metric has conical singularities. We discuss some explicit examples in the case of seven-dimensional Einstein-Sasaki spaces. These new spaces can provide supersymmetric backgrounds in M theory, which play a role in the AdS{sub 4}/CFT{sub 3} correspondence.

Lue, H.; Pope, C. N. [George P. and Cynthia W. Mitchell Institute for Fundamental Physics, Texas A and M University, College Station, Texas 77843-4242 (United States); Vazquez-Poritz, J. F. [Department of Physics, University of Cincinnati, Cincinnati Ohio 45221-0011 (United States)

2007-01-15

284

RCBR: A Simple and Efficient Service for Multiple TimeScale Traffic  

Microsoft Academic Search

Compressed video traffic is expected to be a significant component of the traffic mix in integrated services networks. This traffic is hard to manage, since it has strict delay and loss requirements, but at the same time, exhibits burstiness at multiple time-scales. In this paper, we observe that slow time-scale variations can cause sustained peaks in the source rate, substantially

Matthias Grossglauser; Srinivasan Keshav; David N. C. Tse

1995-01-01

285

Time Dilation and the Length of the Second: Why Timescales Diverge  

Microsoft Academic Search

We show that the timescale divergence between Universal Time (UT1) and international atomic time (TAI), which is compensated for by the occasional addition of a leap second, is due to the fact that the Système Internationale (SI) second is shorter than the UT second. Celestial mechanicians saw the necessity of introducing a timescale that eliminated the discrepancy between the observed

Steven D. Deines; Carol A. Williams

2007-01-01

286

a Review of Einstein's Theory of Special Relativity  

NASA Astrophysics Data System (ADS)

Using only the descriptions and the results of the 'thought experiment' contained in Einstein's seminal 1905 paper, proofs are offered which show that the transformation equations of Einstein's special relativity apply only to the joint use in his experiment of point sources of light and point reflectors. Further, it is shown that two different special relativities could have been invented by Einstein and, because they possess differing space and time contraction factors, they cannot co-exist and, therefore, both must be discarded.

Mott, Gerald

287

A connection between the Einstein and Yang-Mills equations  

Microsoft Academic Search

It is our purpose here to show an unusual relationship between the Einstein equations and the Yang-Mills equations. We give a correspondence between solutions of the self-dual Einstein vacuum equations and the self-dual Yang-Mills equations with a special choice of gauge group. The extension of the argument to the full Yang-Mills equations yields Einstein's unifield equations. We try to incorporate

L. J. Mason; E. T. Newman

1989-01-01

288

Accessing correlated electron motion on the attosecond timescale  

NASA Astrophysics Data System (ADS)

In the last decade, there have been tremendous advances in the production of coherent ultrashort light pulses as short as 80 attoseconds (1 as = 10-18 s). The availability of these pulses has led to the development of the field of attosecond physics, which aims to follow and control electron motion on its natural timescale (1 atomic unit of time is about 24 attoseconds). One of the major goals of attosecond physics is to access correlated electron dynamics. This requires a description of the target system that goes beyond the commonly used single-active-electron approximation. The large bandwidth of ultrashort pulses and many-photon absorption in strong infrared fields make such a description extremely challenging. I will discuss our work on the full numerical solution of the two-electron Schr"odinger equation for helium, which already displays rich correlation effects. I will focus on two applications: The first is attosecond streaking, in which temporal information about the photoionization process in an attosecond pulse is mapped into a momentum shift by a synchronized infrared pulse. This promises to give access to the Eisenbud-Wigner-Smith time delay of photoionization. I will discuss the additional effects that are induced by the infrared field, and how these have to be taken into account for attosecond streaking to fulfill its promise. I will then discuss the possibility of accessing two-electron wave packet dynamics in doubly excited states of helium by an attosecond pump-attosecond probe setup. Such experiments have been called the ``holy grail'' of attosecond physics and should come within reach in the near future. I will discuss our recent proposal of using two-photon absorption from a single pulse as a coherent reference wave, which can be used to increase the experimental signal by almost two orders of magnitude. This provides direct access to time-dependent observables (e.g., the distance between the two electrons) of the two-electron wave packet.

Feist, Johannes

2012-02-01

289

Time domain modeling of plasmas at RF time-scales  

NASA Astrophysics Data System (ADS)

Results from tokamak experiments such as PPPL's NSTX indicate that significant anomalous power absorption can occur in the edge of the fusion plasma. Understanding of this phenomenon is a critical issue for analysis of RF heating scenarios on the ITER fusion experiment. Two probable edge absorption candidates, rf sheath losses and parametric decay instability, are both inherently non-linear, and likely to depend significantly on non-axi-symmetric geometric detail in the vicinity of the antenna structures. Analysis of these phenomenon is beyond the capabilities of existing axi-symmetric frequency-domain linear-solvers used for analysis of heating and current drive in core fusion plasma, and so we are augmenting our analysis capability with the time-domain 3-D general-geometry electromagnetic and particle-in-cell simulation framework, Vorpal [1]. This framework is a modern object-oriented software package, which has demonstrated fast scalable operation on clusters of over 1000 cpu's, a necessity for this type of calculation. We have successfully introduced into this framework an implicit plasma solver [2], in order to accurately treat electromagnetic plasma wave characteristics in the wide range of plasma conditions occurring from edge plasma to core plasma, including situations where the plasma frequency is not resolvable at the rf time-scales of interest, and including sharp plasma resonances and cutoff behaviours common in the rf regime. We present benchmarking of this new plasma solver for 1-D, 2-D, and 3-D scenarios. We also discuss implementation plans for non-linear sheath boundary models, non-linear edge-plasma conditions leading to parametric decay, and also tracking of high-energy particles in core-heating scenarios, where issues of finite-banana-width effects and superadiabaticity remain outside the scope of the existing frequency-domain solvers.

Smithe, David N.

2007-07-01

290

Science at the Time-scale of the Electron  

NASA Astrophysics Data System (ADS)

Replace this text with your abstract Ever since the invention of the laser 50 years ago and its application in nonlinear optics, scientists have been striving to extend coherent laser beams into the x-ray region of the spectrum. Very recently however, the prospects for tabletop coherent sources, with attosecond pulse durations, at very short wavelengths even in the hard x-ray region of the spectrum at wavelengths < 1nm, have brightened considerably. These advances are possible by taking nonlinear optics techniques to an extreme, and are the direct result of a new ability to manipulate electrons on the fastest, attosecond, time-scales of our natural world. My talk will discuss new experimental data that demonstrates high harmonic generation of laser-like, fully coherent, 10 attosecond duration, soft x-ray beams at photon energies around 0.5keV. Several applications will also be discussed, including making a movie of how electron orbitals in a molecule change shape as a molecule breaks apart, following how fast a magnetic material can flip orientation, understanding how fast heat flows in a nanocircuit, or building a microscope without lenses. [4pt] [1] T. Popmintchev et al., ``Phase matched upconversion of coherent ultrafast laser light into the soft and hard x-ray regions of the spectrum'', PNAS 106, 10516 (2009). [0pt] [2] C. LaOVorakiat et al., ``Ultrafast Soft X-Ray Magneto-Optics at the M-edge Using a Tabletop High-Harmonic Source'', Physical Review Letters 103, 257402 (2009). [0pt] [3] M. Siemens et al. ``Measurement of quasi-ballistic heat transport across nanoscale interfaces using ultrafast coherent soft x-ray beams'', Nature Materials 9, 26 (2010). [0pt] [4] K. Raines et al., ``Three-dimensional structure determination from a single view,'' Nature 463, 214 (2010). [0pt] [5] W. Li et al., ``Time-resolved Probing of Dynamics in Polyatomic Molecules using High Harmonic Generation'', Science 322, 1207 (2008).

Murnane, Margaret

2010-03-01

291

A genomic timescale for the origin of eukaryotes  

PubMed Central

Background Genomic sequence analyses have shown that horizontal gene transfer occurred during the origin of eukaryotes as a consequence of symbiosis. However, details of the timing and number of symbiotic events are unclear. A timescale for the early evolution of eukaryotes would help to better understand the relationship between these biological events and changes in Earth's environment, such as the rise in oxygen. We used refined methods of sequence alignment, site selection, and time estimation to address these questions with protein sequences from complete genomes of prokaryotes and eukaryotes. Results Eukaryotes were found to evolve faster than prokaryotes, with those eukaryotes derived from eubacteria evolving faster than those derived from archaebacteria. We found an early time of divergence (~4 billion years ago, Ga) for archaebacteria and the archaebacterial genes in eukaryotes. Our analyses support at least two horizontal gene transfer events in the origin of eukaryotes, at 2.7 Ga and 1.8 Ga. Time estimates for the origin of cyanobacteria (2.6 Ga) and the divergence of an early-branching eukaryote that lacks mitochondria (Giardia) (2.2 Ga) fall between those two events. Conclusions We find support for two symbiotic events in the origin of eukaryotes: one premitochondrial and a later mitochondrial event. The appearance of cyanobacteria immediately prior to the earliest undisputed evidence for the presence of oxygen (2.4–2.2 Ga) suggests that the innovation of oxygenic photosynthesis had a relatively rapid impact on the environment as it set the stage for further evolution of the eukaryotic cell.

Hedges, S Blair; Chen, Hsiong; Kumar, Sudhir; Wang, Daniel YC; Thompson, Amanda S; Watanabe, Hidemi

2001-01-01

292

On the pathways and timescales of intercontinental air pollution transport  

NASA Astrophysics Data System (ADS)

This paper presents results of a 1-year simulation of the transport of six passive tracers, released over the continents according to an emission inventory for carbon monoxide (CO). Lagrangian concepts are introduced to derive age spectra of the tracer concentrations on a global grid in order to determine the timescales and pathways of pollution export from the continents. Calculating these age spectra is equivalent to simulating many (quasi continuous) plumes, each starting at a different time, which are subsequently merged. Movies of the tracer dispersion have been made available on an Internet website. It is found that emissions from Asia experience the fastest vertical transport, whereas European emissions have the strongest tendency to remain in the lower troposphere. European emissions are transported primarily into the Arctic and appear to be the major contributor to the Arctic haze problem. Tracers from an upwind continent first arrive over a receptor continent in the upper troposphere, typically after some 4 days. Only later foreign tracers also arrive in the lower troposphere. Assuming a 2-day lifetime, the domestic tracers dominate total tracer columns over all continents except over Australia where foreign tracers account for 20% of the tracer mass. In contrast, for a 20-day lifetime even continents with high domestic emissions receive more than half of their tracer burden from foreign continents. Three special regions were identified where tracers are transported to, and tracer dilution is slow. Future field studies therefore should be deployed in the following regions: (1) In the winter, the Asia tracer accumulates over Indonesia and the Indian Ocean, a region speculated to be a stratospheric fountain. (2) In the summer, the highest concentrations of the Asia tracer are found in the Middle East. (3) In the summer, the highest concentrations of the North America tracer are found in the Mediterranean.

Stohl, Andreas; Eckhardt, Sabine; Forster, Caroline; James, Paul; Spichtinger, Nicole

2002-12-01

293

In the limelight of stars. Einstein, Mandl, and the origins of gravitational lens research (German Title: Im Rampenlicht der Sterne. Einstein, Mandl und die Ursprünge der Gravitationslinsenforschung)  

Microsoft Academic Search

Einstein's paper on gravitational lensing from 1936 was published only as a result of insistent prodding by the Czech amateur scientist Rudi Mandl. We discuss Mandl's role for the publication history of Einstein's paper and point out striking similarities between Mandl's situation in 1936 and Einstein's own position in 1912. At that time, Einstein himself had already considered the idea

Jürgen Renn; Tilman Sauer

2005-01-01

294

The density and temperature dependence of the cooling timescale for fragmentation of self-gravitating disks  

NASA Astrophysics Data System (ADS)

The purpose of this paper is to explore the influences of cooling timescale on fragmentation of self-gravitating protoplanetary disks. We assume the cooling timescale, expressed in terms of the dynamical timescale ? tcool, has a power-law dependence on temperature and density, ? tcool ? ??aT?b, where a and b are constants. We use this cooling timescale in a simple prescription for the cooling rate, du/dt = ?u/tcool, where u is the internal energy. We perform our simulations using the smoothed particle hydrodynamics method. The simulations demonstrate that the disk is very sensitive to the cooling timescale, which depends on density and temperature. Under such a cooling timescale, the disk becomes gravitationally unstable and clumps form in the disk. This property even occurs for cooling timescales which are much longer than the critical cooling timescale, ? tcool ? 7. We show that by adding the dependence of a cooling timescale on temperature and density, the number of clumps increases and the clumps can also form at smaller radii. The simulations imply that the sensitivity of a cooling timescale to density is more than to temperature, because even for a small dependence of the cooling timescale on density, clumps can still form in the disk. However, when the cooling timescale has a large dependence on temperature, clumps form in the disk. We also consider the effects of artificial viscosity parameters on fragmentation conditions. This consideration is performed in two cases, where ? tcool is a constant and ? tcool is a function of density and temperature. The simulations consider both cases, and results show the artificial viscosity parameters have rather similar effects. For example, using too small of values for linear and quadratic terms in artificial viscosity can suppress the gravitational instability and consequently the efficiency of the clump formation process decreases. This property is consistent with recent simulations of self-gravitating disks. We perform simulations with and without the Balsara form of artificial viscosity. We find that in the cooling and self-gravitating disks without the Balsara switch, the clumps can form more easily than those with the Balsara switch. Moreover, in both cases where the Balsara switch is present or absent, the simulations show that the cooling timescale strongly depends on density and temperature.

Faghei, Kazem

2014-06-01

295

Bose-Einstein condensate general relativistic stars  

NASA Astrophysics Data System (ADS)

We analyze the possibility that due to their superfluid properties some compact astrophysical objects may contain a significant part of their matter in the form of a Bose-Einstein condensate. To study the condensate we use the Gross-Pitaevskii equation with arbitrary nonlinearity. By introducing the Madelung representation of the wave function, we formulate the dynamics of the system in terms of the continuity and hydrodynamic Euler equations. The nonrelativistic and Newtonian Bose-Einstein gravitational condensate can be described as a gas, whose density and pressure are related by a barotropic equation of state. In the case of a condensate with quartic nonlinearity, the equation of state is polytropic with index one. In the framework of the Thomas-Fermi approximation the structure of the Newtonian gravitational condensate is described by the Lane-Emden equation, which can be exactly solved. The case of the rotating condensate is briefly discussed. General relativistic configurations with quartic nonlinearity are studied numerically with both nonrelativistic and relativistic equations of state, and the maximum mass of the stable configuration is determined. Condensates with particle masses of the order of two neutron masses (Cooper pair) and scattering length of the order of 10-20 fm have maximum masses of the order of 2M?, maximum central density of the order of 0.1-0.3×1016g/cm3 and minimum radii in the range of 10-20 km. In this way we obtain a large class of stable astrophysical objects, whose basic astrophysical parameters (mass and radius) sensitively depend on the mass of the condensed particle, and on the scattering length. We also propose that the recently observed neutron stars with masses in the range of 2-2.4M? are Bose-Einstein condensate stars. We discuss the connection of our results with previous boson star models based on scalar field theory.

Chavanis, Pierre-Henri; Harko, Tiberiu

2012-09-01

296

Bose-Einstein Condensation in Extended Microgravity  

NASA Astrophysics Data System (ADS)

The setup and the envisaged experiment timeline of the QUANTUS-III experiment onboard a sounding rocket to be started in the near future are presented. The major intention of QUANTUS-III is the stable generation of a number of Bose-Einstein condensates as a source for atom interferometry during several minutes of microgravity onboard the sounding rocket. Later missions aim at the realization of atom interferoemeters as precursor satellite missions. These condesates will be generated serially, allowing a large number of repeatable tests. Within such Bose-Einstein condensates, millions of atoms lose their identity and can be described by a single macroscopic wave function. During the expansion over several seconds, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter. Cold quantum gases and, in particular, Bose-Einstein condensates represent a new state of matter which is nowadays established in many laboratories. They offer unique insights into a broad range of fundamental physics as well as prospects for novel quantum sensors. Microgravity will substantially extend the science of quantum gases towards nowadays inaccessible regimes at lowest temperatures, to macroscopic dimensions, and to unequalled durations of unperturbed evolution of these distinguished quantum objects. Right now, the QUANTUS-III experiment is in the development phase, taking heritage from QUANTUS-I and QUANTUS-II. Major components of the engineering model are available. Boundary conditions of the rocket, requirements of the experiment and interface considerations are presented. This include laser stabilization, vacuum technology and magnetic shielding. The planned trajectory of the rocket will have an apogee of 200 - 300 km and a total microgravity time of 4 - 7 minutes, both depending on the total experiment mass.

Scharringhausen, Marco; Quantus Team; Rasel, Ernst Maria

2012-07-01

297

Infrared fixed point in quantum Einstein gravity  

NASA Astrophysics Data System (ADS)

We performed the renormalization group analysis of the quantum Einstein gravity in the deep infrared regime for different types of extensions of the model. It is shown that an attractive infrared point exists in the broken symmetric phase of the model. It is also shown that due to the Gaussian fixed point the IR critical exponent ? of the correlation length is 1/2. However, there exists a certain extension of the model which gives finite correlation length in the broken symmetric phase. It typically appears in case of models possessing a first order phase transitions as is demonstrated on the example of the scalar field theory with a Coleman-Weinberg potential.

Nagy, S.; Krizsan, J.; Sailer, K.

2012-07-01

298

Einstein equations in the null quasispherical gauge  

NASA Astrophysics Data System (ADS)

Properties of the Einstein equations in a coordinate gauge based on expanding null hypersurfaces foliated by metric 2-spheres are described. This null quasispherical (NQS) gauge leads to particularly simple analyses of the characteristic structure of the equations and of the propagation of gravitational shocks, and clarifies the geometry of timelike boundary condition. A feature of the NQS gauge is the use of the standard 0264-9381/14/8/017/img1 (`edth') operator on 0264-9381/14/8/017/img2 to express angular derivatives, and the consequent use of spin-weighted spherical harmonic decompositions of the metric fields.

Bartnik, Robert

1997-08-01

299

Wormholes in Einstein-Born-Infeld theory  

SciTech Connect

Spherically symmetric thin-shell wormholes are studied within the framework of Einstein-Born-Infeld theory. We analyze the exotic matter content, and find that for certain values of the Born-Infeld parameter the amount of exotic matter on the shell can be reduced in relation to the Maxwell case. We also examine the mechanical stability of the wormhole configurations under radial perturbations preserving the spherical symmetry. In addition, in the Appendix the repulsive or attractive character of the wormhole geometries is briefly discussed.

Richarte, Martin G.; Simeone, Claudio [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellon I, 1428 Buenos Aires (Argentina)

2009-11-15

300

Einstein-Regge equations in spinfoams  

NASA Astrophysics Data System (ADS)

We consider spinfoam quantum gravity on a spacetime decomposition with many 4-simplices, in the double scaling limit in which the Immirzi parameter ? is sent to zero (flipped limit) and the physical area in Planck units (? times the spin quantum number j) is kept constant. We show that the quantum amplitude takes the form of a Regge-like path integral and enforces Einstein equations in the semiclassical regime. In addition to quantum corrections which vanish when the Planck constant goes to zero, we find new corrections due to the discreteness of geometric spectra which is controlled by the Immirzi parameter.

Perini, Claudio

2012-05-01

301

Signature transition in Einstein-Cartan cosmology  

NASA Astrophysics Data System (ADS)

In the context of Einstein-Cartan theory of gravity, we consider a Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological model with Weyssenhoff perfect fluid. We focus attention on those classical solutions that admit a degenerate metric in which the scale factor has smooth behavior in the transition from a Euclidean to a Lorentzian domain. It is shown that the spin-spin contact interaction enables one to obtain such a signature changing solutions due to the Riemann-Cartan (U4) structure of space-time.

Vakili, Babak; Jalalzadeh, Shahram

2013-10-01

302

Multimessenger astronomy with the Einstein Telescope  

NASA Astrophysics Data System (ADS)

Gravitational waves (GWs) are expected to play a crucial role in the development of multimessenger astrophysics. The combination of GW observations with other astrophysical triggers, such as from gamma-ray and X-ray satellites, optical/radio telescopes, and neutrino detectors allows us to decipher science that would otherwise be inaccessible. In this paper, we provide a broad review from the multimessenger perspective of the science reach offered by the third generation interferometric GW detectors and by the Einstein Telescope (ET) in particular. We focus on cosmic transients, and base our estimates on the results obtained by ET's predecessors GEO, LIGO, and Virgo.

Chassande-Mottin, Eric; Hendry, Martin; Sutton, Patrick J.; Márka, Szabolcs

2011-02-01

303

Rydberg excitation of Bose-Einstein condensates.  

PubMed

Rydberg atoms provide a wide range of possibilities to tailor interactions in a quantum gas. Here, we report on Rydberg excitation of Bose-Einstein condensed 87Rb atoms. The Rydberg fraction was investigated for various excitation times and temperatures above and below the condensation temperature. The excitation is locally blocked by the van der Waals interaction between Rydberg atoms to a density-dependent limit. Therefore, the abrupt change of the thermal atomic density distribution to the characteristic bimodal distribution upon condensation could be observed in the Rydberg fraction. The observed features are reproduced by a simulation based on local collective Rydberg excitations. PMID:18232977

Heidemann, Rolf; Raitzsch, Ulrich; Bendkowsky, Vera; Butscher, Björn; Löw, Robert; Pfau, Tilman

2008-01-25

304

Extragalactic counterparts to Einstein slew survey sources  

NASA Technical Reports Server (NTRS)

The Einstein slew survey consists of 819 bright X-ray sources, of which 636 (or 78 percent) are identified with counterparts in standard catalogs. The importance of bright X-ray surveys is stressed, and the slew survey is compared to the Rosat all sky survey. Statistical techniques for minimizing confusion in arcminute error circles in digitized data are discussed. The 238 slew survey active galactic nuclei, clusters, and BL Lacertae objects identified to date and their implications for logN-logS and source evolution studies are described.

Schachter, Jonathan F.; Elvis, Martin; Plummer, David; Remillard, Ron

1992-01-01

305

IUE and Einstein observations of NGC5204  

NASA Technical Reports Server (NTRS)

The use of both the Einstein and IUE observations of NGC5204 to test some of the hypotheses put forward as a result of an X-ray survey of blue peculiar late type galaxies is discussed. In particular the hypothesis that binary X-ray sources of Pop I progenitors are responsible for most of the X-ray emission, is strengthened by the IUE short wavelength spectrum of NGC5204. This spectrum suggests a number of OB stars in agreement with the inferred from the X-ray luminosity. It also shows an ultraviolet excess in agreement with the large X-ray to blue flux ratio.

Fabbiano, G.; Panagia, N.

1982-01-01

306

Quenching of Einstein-coefficients by photons  

SciTech Connect

Experimental evidence is presented for the change of Einstein's A- coefficients for spontaneous transitions from the upper laser level of argon ion laser discharge due to the presence of the high- intensity laser flux. To demonstrate that this quenching effect cannot be attributed to a reduction in self-absorption of the strong spontaneous emission line, absorption and line profile measurements have been performed. Computer modelling of the reduction of self absorption due to Rabi splitting also indicated that this effect is too small to explain the observed quenching of spontaneous line emissions. 13 refs., 11 figs.

Aumayr, F. (Technische Univ., Vienna (Austria). Inst. fuer Allgemeine Physik); Lee, W.; Skinner, C.H.; Suckewer, S. (Princeton Univ., NJ (USA). Plasma Physics Lab.)

1991-03-01

307

Timescales in creep and yielding of attractive gels.  

PubMed

The stress-induced yielding scenario of colloidal gels is investigated under rough boundary conditions by means of rheometry coupled with local velocity measurements. Under an applied shear stress ?, the fluidization of gels made of attractive carbon black particles dispersed in a mineral oil is shown to involve a previously unreported shear rate response ? dot above(t) characterized by two well-defined and separated timescales ?c and ?f. First ? dot above decreases as a weak power law strongly reminiscent of the primary creep observed in numerous crystalline and amorphous solids, coined the "Andrade creep". We show that the bulk deformation remains homogeneous at the micron scale, which demonstrates that whether plastic events take place or whether any shear transformation zone exists, such phenomena occur at a smaller scale. As a key result of this paper, the duration ?c of this creep regime decreases as a power law of the viscous stress, defined as the difference between the applied stress and the yield stress ?c, i.e. ?c ? (? - ?c)(-?), with ? = 2-3 depending on the gel concentration. The end of this first regime is marked by a jump of the shear rate by several orders of magnitude, while the gel slowly slides as a solid block experiencing strong wall slip at both walls, despite rough boundary conditions. Finally, a second sudden increase of the shear rate is concomitant with the full fluidization of the material which ends up being homogeneously sheared. The corresponding fluidization time ?f robustly follows an exponential decay with the applied shear stress, i.e. ?f = ?0?exp(-?/?0), as already reported for smooth boundary conditions. Varying the gel concentration C in a systematic fashion shows that the parameter ?0 and the yield stress ?c exhibit similar power-law dependences with C. Finally, we highlight a few features that are common to attractive colloidal gels and to solid materials by discussing our results in the framework of theoretical approaches of solid rupture (kinetic, fiber bundle, and transient network models). PMID:24651869

Grenard, Vincent; Divoux, Thibaut; Taberlet, Nicolas; Manneville, Sébastien

2014-03-14

308

Deformation associated with faulting within geologic and interseismic timescales  

NASA Astrophysics Data System (ADS)

This dissertation consists of several distinct studies that use numerical modeling to better constrain deformation due to faulting over disparate timescales. Field mapping reveals a segment of the Lake Mead fault system, the Pinto Ridge fault, and a cluster of west-dipping normal faults located near Pinto Ridge. I suggest that this strike-slip segment was kinematically related to the Bitter Spring Valley fault, created the normal fault cluster at Pinto Ridge, and utilized these normal faults as linking structures between fault segments. Modeling results demonstrate that the location and orientations of the normal faults are consistent with having formed in the perturbed stress field around the slipping Pinto Ridge fault. Calculations of mechanical efficiency suggest that a preferred dip of normal faults in the region may reflect a crustal anisotropy at depth, such as a detachment. I present a methodology for simulating interseismic deformation in complex regions. I derive an analytical model of interseismic deformation that is equivalent to the conventional model. Based on this model, I formulate a two-step numerical simulation of geologic and interseismic deformation. I apply this technique to the Los Angeles region and find that model results match well both geologic slip rate estimates and geodetic velocities. Model results suggest that the Puente Hills thrusts are currently slipping at rates that are compatible with geologic estimates and that localized contraction in the San Gabriel basin is dominantly due to deep slip on the Sierra Madre fault. To assess the control of fault geometry and mechanical interactions on fault slip in a natural system, I create models of the Ventura region, California, using both planar and non-planar faults. I find that incorporating geologically-constrained fault surfaces into numerical models results in a better match to available geologic slip rate data than models utilizing planar faults. Because slip rates at most locations along the surface traces of Ventura faults are not likely to represent average values for the entire fault surface, I propose that well-constrained models can be used to predict slip rates at specific locations and determine whether existing slip rate estimates are representative of average fault slip rates.

Marshall, Scott T.

309

Characteristic Timescales of Shoreface Response to Sea-Level Rise  

NASA Astrophysics Data System (ADS)

On open ocean, wave-dominated, sandy coasts, the response of the shore to sea-level rise is dominated not by inundation, but rather by the dynamic response of sediment transport processes to perturbations of the sea level. In a regime of sea level change, the predominant response of the wave-dominated shoreface depends upon the time-dependent response of the shoreface itself to changes in sea level as well as the potential changes to the shoreline. On a barrier coast, persistent, long-term changes to the shoreline are caused by storm overwash, which transports marine sediment landward, moving the shoreline boundary. Raised sea levels increase the impact and frequency of this overwash as relative barrier elevation is reduced. Overall, sediment transport processes on the shoreface remain poorly understood, complicating predictions of equilibrium shoreface shapes and even net sediment transport directions. However, presuming an equilibrium geometry, energetics-based, time-averaged relationships for cross-shore sediment transport provide a framework to understand the characteristic rates and types of shoreface response to perturbations to either the sea level or the shoreline boundary. In the case of a sea-level rise, we find that the dominant perturbation for a barrier system is not the sea-level rise itself, but rather the movement of the shoreline by overwash. The characteristic response time of the shoreface itself increases significantly at depth, suggesting that the lower shoreface response to a sea level change can be significantly delayed. We estimate the importance of extreme events on shoreface evolution by analyzing decade-long data series of wave characteristics along different open ocean coasts with barriers (Florida Gulf Coast, North Carolina, Marthas Vineyard). Analogous to the effect of floods in fluvial systems, although storm events can move significant sediment, the infrequency of the larger events limits their effect on the shoreface-the morphologically significant event for shoreface evolution has a return interval of less than two years. However, numerical simulations of tens of thousands of synthetic storm strikes at the same locations suggest that the return interval of storm events expected to cause significant overwash is longer, on the order of at least 50 years. To study the interactions between the characteristic timescales of shoreface evolution and barrier overwash, we apply a numerical model of barrier profile evolution that couples shoreface evolution with barrier overwash. This integrated model provides a tool to understand the response of barrier systems to changes in sea level over the late Holocene to the modern. The model also investigates the potential behavior of barrier systems as they (and their human occupants) respond to predicted increased rates of sea-level rise over the coming centuries.

Ashton, A. D.; Ortiz, A.; Lane, P.; Donnelly, J. P.

2011-12-01

310

Colloquium: Bulk Bogoliubov excitations in a Bose-Einstein condensate  

SciTech Connect

Bogoliubov theory for excitations in Bose-Einstein condensates was formulated over 50 years ago to qualitatively explain strongly interacting superfluids. Quantitative experimental verification of this theory came with the long-awaited realization of gaseous, weakly interacting condensates. This Colloquium reviews recent experimental advances in the study of Bogoliubov bulk excitations in Bose-Einstein condensates, obtained using two-photon Bragg scattering.

Ozeri, R.; Katz, N.; Steinhauer, J.; Davidson, N. [Department of Physics of Complex Systems, Weizmann Institute of Science, Rehovot 76100 (Israel)

2005-01-01

311

Modifying the Einstein equations off the constraint hypersurface  

SciTech Connect

A new technique is presented for modifying the Einstein evolution equations off the constraint hypersurface. With this approach the evolution equations for the constraints can be specified freely. The equations of motion for the gravitational field variables are modified by the addition of terms that are linear and nonlocal in the constraints. These terms are obtained from solutions of the linearized Einstein constraints.

Brown, J. David; Lowe, Lisa L. [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695 (United States)

2006-11-15

312

Quantum Mechanics of the Einstein-Hopf Model.  

ERIC Educational Resources Information Center

The Einstein-Hopf model for the thermodynamic equilibrium between the electromagnetic field and dipole oscillators is considered within the framework of quantum mechanics. Both the wave and particle aspects of the Einstein fluctuation formula are interpreted in terms of the fundamental absorption and emission processes. (Author/SK)

Milonni, P. W.

1981-01-01

313

Bose-Einstein condensation in dilute atomic gases  

Microsoft Academic Search

Bose-Einstein condensation is one of the most curious and fascinating phenomena in physics. It lies at the heart of such intriguing processes as superfluidity and superconductivity. However, in most cases, only a small part of the sample is Bose-condensed and strong interactions are present. A weakly interacting, pure Bose-Einstein condensate (BEC) has therefore been called the \\

J. J. Arlt; K. Bongs; K. Sengstock; W. Ertmer

2002-01-01

314

Time-Scales for Non-Inductive Current Buildup in Low-Aspect-Ratio Toroidal Geometry  

SciTech Connect

The fundamental differences between inductive and non-inductive current buildup are clarified and the associated time-scales and other implications are discussed. A simulation is presented whereby the plasma current in a low-aspect-ratio torus is increased primarily by the self-generated bootstrap current with only 10% coming from external current drive. The maximum obtainable plasma current by this process is shown to scale with the toroidal field strength. The basic physics setting the time-scales can be obtained from a 1D analysis. Comparisons are made between the timescales found here and those reported in the experimental literature.

S.C. Jardin

1999-11-01

315

Gravity Before Einstein and Schwinger Before Gravity  

NASA Astrophysics Data System (ADS)

Julian Schwinger was a child prodigy, and Albert Einstein distinctly not; Schwinger had something like 73 graduate students, and Einstein very few. But both thought gravity was important. They were not, of course, the first, nor is the disagreement on how one should think about gravity that is being highlighted here the first such dispute. The talk will explore, first, several of the earlier dichotomies: was gravity capable of action at a distance (Newton), or was a transmitting ether required (many others). Did it act on everything or only on solids (an odd idea of the Herschels that fed into their ideas of solar structure and sunspots)? Did gravitational information require time for its transmission? Is the exponent of r precisely 2, or 2 plus a smidgeon (a suggestion by Simon Newcomb among others)? And so forth. Second, I will try to say something about Scwinger's lesser known early work and how it might have prefigured his "source theory," beginning with "On the Interaction of Several Electrons (the unpublished, 1934 "zeroth paper," whose title somewhat reminds one of "On the Dynamics of an Asteroid," through his days at Berkeley with Oppenheimer, Gerjuoy, and others, to his application of ideas from nuclear physics to radar and of radar engineering techniques to problems in nuclear physics. And folks who think good jobs are difficult to come by now might want to contemplate the couple of years Schwinger spent teaching elementary physics at Purdue before moving on to the MIT Rad Lab for war work.

Trimble, Virginia L.

2012-05-01

316

Bose-Einstein condensation in quantum magnets  

NASA Astrophysics Data System (ADS)

This article reviews experimental and theoretical work on Bose-Einstein condensation in quantum magnets. These magnets are natural realizations of gases of interacting bosons whose relevant parameters such as dimensionality, lattice geometry, amount of disorder, nature of the interactions, and particle concentration can vary widely between different compounds. The particle concentration can be easily tuned by applying an external magnetic field which plays the role of a chemical potential. This rich spectrum of realizations offers a unique possibility for studying the different physical behaviors that emerge in interacting Bose gases from the interplay between their relevant parameters. The plethora of other bosonic phases that can emerge in quantum magnets, of which the Bose-Einstein condensate is the most basic ground state, is reviewed. The compounds discussed in this review have been intensively studied in the last two decades and have led to important contributions in the area of quantum magnetism. In spite of their apparent simplicity, these systems often exhibit surprising behaviors. The possibility of using controlled theoretical approaches has triggered the discovery of unusual effects induced by frustration, dimensionality, or disorder.

Zapf, Vivien; Jaime, Marcelo; Batista, C. D.

2014-04-01

317

Radiation damping in Einstein-aether theory  

NASA Astrophysics Data System (ADS)

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory—an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian order are wave forms for the metric and vector fields far from a nearly Newtonian system and the rate of energy radiated by the system. The expressions depend on the quadrupole moment of the source, as in standard general relativity, but also contain monopolar and dipolar terms. There exists a one-parameter family of Einstein-aether theories for which only the quadrupolar contribution is present, and for which the expression for the damping rate is identical to that of general relativity to the order worked to here. This family cannot yet be declared observationally viable, since effects due to the strong internal fields of bodies in the actual systems used to test the damping rate have not yet been determined.

Foster, Brendan Z.

2006-05-01

318

Radiation damping in Einstein-aether theory  

SciTech Connect

This work concerns the loss of energy of a material system due to gravitational radiation in Einstein-aether theory - an alternative theory of gravity in which the metric couples to a dynamical, timelike, unit-norm vector field. Derived to lowest post-Newtonian order are wave forms for the metric and vector fields far from a nearly Newtonian system and the rate of energy radiated by the system. The expressions depend on the quadrupole moment of the source, as in standard general relativity, but also contain monopolar and dipolar terms. There exists a one-parameter family of Einstein-aether theories for which only the quadrupolar contribution is present, and for which the expression for the damping rate is identical to that of general relativity to the order worked to here. This family cannot yet be declared observationally viable, since effects due to the strong internal fields of bodies in the actual systems used to test the damping rate have not yet been determined.

Foster, Brendan Z. [Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)

2006-05-15

319

Dual giant gravitons in Sasaki Einstein backgrounds  

NASA Astrophysics Data System (ADS)

We study the dynamics of a BPS D3-brane wrapped on a three-sphere in AdS×L, a so-called dual giant graviton, where L is a Sasakian five-manifold. The phase space of these configurations is the symplectic cone X over L, and geometric quantisation naturally produces a Hilbert space of L-normalisable holomorphic functions on X, whose states are dual to scalar chiral BPS operators in the dual superconformal field theory. We define classical and quantum partition functions and relate them to earlier mathematical constructions by the authors and S.-T. Yau, [D. Martelli, J. Sparks, S.-T. Yau, Sasaki-Einstein manifolds and volume minimisation, hep-th/0603021]. In particular, a Sasaki-Einstein metric then minimises an entropy function associated with the D3-brane. Finally, we introduce a grand canonical partition function that counts multiple dual giant gravitons. This is related simply to the index-character of the above reference, and provides a method for counting multi-trace scalar BPS operators in the dual superconformal field theory.

Martelli, Dario; Sparks, James

2006-12-01

320

Core Formation Timescale, Silicate-Metal Equilibration, and W Diffusivity  

NASA Astrophysics Data System (ADS)

The extent to which material accreted to the proto-Earth and segregated to form the core was chemically and isotopically equilibrated with the silicate mantle is an outstanding problem in planetary science. This is particularly important when attempting to assign a meaningful age for planetary accretion and core formation based on Hf-W isotope systematics. The Earth and other terrestrial planets likely formed by accretion of previously differentiated planetesimals. For the planetesimals themselves the most important energy source for metal-silicate differentiation is the combined radioactive heating due to decay of 26Al (half-life 0.7 Ma) and 60Fe (half-life 1.5 Ma). It is expected that the fractionation of Hf and W during planetesimal core formation will lead to a divergence in the W isotopic compositions of the core and silicate portions of these bodies. This expectation is supported by the enormously radiogenic 182W signatures reported for basaltic eucrites. The observation that the W isotopic compositions of the silicate portions of Earth, Moon and Mars are similar and markedly less radiogenic than eucrites suggests that during planet accretion the pre-differentiated metallic core material containing low 182W must have equilibrated extensively with the more radiogenic (high 182W) silicate material to subdue the ingrowth of 182W in the silicate mantle of the planets. The standard theory of planet formation predicts that after runaway and oligarchic growth, the late stage of planet formation is characterized by impact and merging of Mars-sized objects. This is a tremendously energetic process estimated to raise the temperature of the proto-Earth to about 7000K (a temperature equivalent to a mass spectrometer's plasma source, which indiscriminately ionizes all incoming elements). After the giant impacts, the proto-Earth had a luminosity and surface temperature close to a low mass star for a brief period of time. Stevenson (1990) argued that emulsification caused by large-scale Rayleigh-Taylor instabilities following giant impacts breaks up the metallic core of the impactor into centimeter-sized droplets within minutes. We have constructed a simple model to study the kinetics of isotope equilibration between metal-silicate during the "rain-fall" of metal droplets descending through the terrestrial magma ocean. This model highlights the importance of the kinetics of ion mobility of W for assessing quantitatively the degree of metal-silicate equilibration during core formation. We have determined for the first time that the W self-diffusion coefficient in basaltic liquid is 4.98E-7 cm2/s at 3GPa, 1500 C. We assume this is a minimum value in the magma ocean scenario, and the equilibration is rate-limited by diffusion in the silicate liquid. Applying this value and taking a reasonable estimate of viscosity for silicate liquids from the literature, we show that the degree of equilibration asymptotically approaches 100% within the timescale of metal-silicate segregation when the metallic droplets are <20 cm in diameter.

Yin, Q.; Jacobsen, B.; Tinker, D.; Lesher, C.

2004-12-01

321

Audio watermarking robust against time-scale modification and MP3 compression  

Microsoft Academic Search

In continuation to earlier work where the problem of time-scale modification (TSM) has been studied [S. Xiang, J. Huang, R. Yang, Time-scale invariant audio watermarking based on the statistical features in time domain, in: Proceedings of the 8th Information Hiding Workshop (IH 2006), Lecture Notes in Computer Science, vol. 4437, Springer, Berlin, pp. 93–108] by modifying the shape of histogram

Shijun Xiang; Hyoung-joong Kim; Jiwu Huang

2008-01-01

322

Short time-scale radiative transfer in light-emitting porous silicon  

Microsoft Academic Search

In this work, a five level system is proposed to model the short time-scale radiative transfer in light-emitting porous silicon. Equations are derived for the various energy levels. The model is applied to picosecond differential transmission measurements made on porous silicon. A picture of short time-scale carrier dynamics is drawn considering the unique properties of confinement, high surface-to-volume ratio and

M. Cynthia Hipwell; C. L. Tien

1999-01-01

323

Short time-scale variability in the Faint Sky Variability Survey  

Microsoft Academic Search

We present the V-band variability analysis of the point sources in the Faint Sky Variability Survey on time-scales from 24 min to tens of days. We find that about one per cent of the point sources down to V = 24 are variables. We discuss the variability-detection probabilities for each field depending on field sampling, amplitude and time-scale of the

L. Morales-Rueda; P. J. Groot; T. Augusteijn; G. Nelemans; P. M. Vreeswijk; E. J. M. van den Besselaar

2006-01-01

324

COMPARING THE ACCRETION DISK EVOLUTION OF BLACK HOLE AND NEUTRON STAR X-RAY BINARIES FROM LOW TO SUPER-EDDINGTON LUMINOSITY  

SciTech Connect

Low-mass X-ray binaries (LMXBs) are systems in which a low-mass companion transfers mass via Roche-lobe overflow onto a black hole (BH) or a weakly magnetized neutron star (NS). It is believed that both the solid surface and the magnetic field of an NS can affect the accretion flow and show some observable effects. Using the disk emission dominant data, we compare the disk evolution of the two types of systems from low luminosity to super-Eddington luminosity. As the luminosity decreases the disk in the NS LMXB 4U1608-522 begins to leave the innermost stable circular orbit (ISCO) at much higher luminosity ({approx}0.1 L{sub Edd}), compared with BH LMXBs at much lower luminosity ({approx}0.03 L{sub Edd}), due to the interaction between the NS magnetosphere and accretion flow. However, as the luminosity increases above a critical luminosity, the disks in BH and NS LMXBs trace the same evolutionary pattern, because the magnetosphere is restricted inside ISCO, and then both the NS surface emission and (dipole) magnetic field do not significantly affect the secular evolution of the accretion disk, which is driven by the increased radiation pressure in the inner region. We further suggest that the NS surface emission provides additional information about the accretion disk not available in BH systems. Through the observed NS surface emission, we argue that the disk thickness H/R is less than 0.3-0.4, and that the significant outflow from the inner disk edge exists at a luminosity close to Eddington luminosity.

Weng Shanshan; Zhang Shuangnan, E-mail: wengss@ihep.ac.cn, E-mail: zhangsn@ihep.ac.cn [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China)

2011-09-20

325

On the Nature of the Prototype Luminous Blue Variable AG Carinae. II. Witnessing a Massive Star Evolving Close to the Eddington and Bistability Limits  

NASA Astrophysics Data System (ADS)

We show that the significantly different effective temperatures (T eff) achieved by the luminous blue variable AG Carinae during the consecutive visual minima of 1985-1990 (T eff ~= 22,800 K) and 2000-2001 (T eff ~= 17,000 K) place the star on different sides of the bistability limit, which occurs in line-driven stellar winds around T eff ~ 21,000 K. Decisive evidence is provided by huge changes in the optical depth of the Lyman continuum in the inner wind as T eff changes during the S Dor cycle. These changes cause different Fe ionization structures in the inner wind. The bistability mechanism is also related to the different wind parameters during visual minima: the wind terminal velocity was 2-3 times higher and the mass-loss rate roughly two times smaller in 1985-1990 than in 2000-2003. We obtain a projected rotational velocity of 220 ± 50 km s-1 during 1985-1990 which, combined with the high luminosity (L sstarf = 1.5 × 106 L sun), puts AG Car extremely close to the Eddington limit modified by rotation (?? limit): for an inclination angle of 90°, ?? >~ 1.0 for M sun <~ 60. Based on evolutionary models and mass budget, we obtain an initial mass of ~100 M sun and a current mass of ~60-70 M sun for AG Car. Therefore, AG Car is close to, if not at, the ?? limit during visual minimum. Assuming M = 70 M sun, we find that ?? decreases from 0.93 to 0.72 as AG Car expands toward visual maximum, suggesting that the star is not above the Eddington limit during maximum phases.

Groh, J. H.; Hillier, D. J.; Damineli, A.

2011-07-01

326

COMPARISON OF KEPLER PHOTOMETRIC VARIABILITY WITH THE SUN ON DIFFERENT TIMESCALES  

SciTech Connect

We utilize Kepler data to study the precision differential photometric variability of solar-type and cooler stars at different timescales, ranging from half an hour to three months. We define a diagnostic that characterizes the median differential intensity change between data bins of a given timescale. We apply the same diagnostics to Solar and Heliospheric Observatory data that has been rendered comparable to Kepler. The Sun exhibits similar photometric variability on all timescales as comparable solar-type stars in the Kepler field. The previously defined photometric ''range'' serves as our activity proxy (driven by starspot coverage). We revisit the fraction of comparable stars in the Kepler field that are more active than the Sun. The exact active fraction depends on what is meant by ''more active than the Sun'' and on the magnitude limit of the sample of stars considered. This active fraction is between a quarter and a third (depending on the timescale). We argue that a reliable result requires timescales of half a day or longer and stars brighter than M{sub Kep} of 14, otherwise non-stellar noise distorts it. We also analyze main sequence stars grouped by temperature from 6500 to 3500 K. As one moves to cooler stars, the active fraction of stars becomes steadily larger (greater than 90% for early M dwarfs). The Sun is a good photometric model at all timescales for those cooler stars that have long-term variability within the span of solar variability.

Basri, Gibor [Astronomy Department, University of California, Hearst Field Annex, Berkeley, CA 94720 (United States); Walkowicz, Lucianne M. [Department of Astrophysical Sciences, Princeton University, Peyton Hall, 4 Ivy Lane, Princeton NJ 08534 (United States); Reiners, Ansgar [Georg-August-University Goettingen, Institute for Astrophysics, Friedrich-Hund-Platz 1, DE D-37077, Goettingen (Germany)

2013-05-20

327

Time-scale invariance as an emergent property in a perceptron with realistic, noisy neurons  

PubMed Central

In most species, interval timing is time-scale invariant: errors in time estimation scale up linearly with the estimated duration. In mammals, time-scale invariance is ubiquitous over behavioral, lesion, and pharmacological manipulations. For example, dopaminergic drugs induce an immediate, whereas cholinergic drugs induce a gradual, scalar change in timing. Behavioral theories posit that time-scale invariance derives from particular computations, rules, or coding schemes. In contrast, we discuss a simple neural circuit, the perceptron, whose output neurons fire in a clockwise fashion (interval timing) based on the pattern of coincidental activation of its input neurons. We show numerically that time-scale invariance emerges spontaneously in a perceptron with realistic neurons, in the presence of noise. Under the assumption that dopaminergic drugs modulate the firing of input neurons, and that cholinergic drugs modulate the memory representation of the criterion time, we show that a perceptron with realistic neurons reproduces the pharmacological clock and memory patterns, and their time-scale invariance, in the presence of noise. These results suggest that rather than being a signature of higher-order cognitive processes or specific computations related to timing, time-scale invariance may spontaneously emerge in a massively-connected brain from the intrinsic noise of neurons and circuits, thus providing the simplest explanation for the ubiquity of scale invariance of interval timing.

Buhusi, Catalin V.; Oprisan, Sorinel A.

2013-01-01

328

Time-scale invariance as an emergent property in a perceptron with realistic, noisy neurons.  

PubMed

In most species, interval timing is time-scale invariant: errors in time estimation scale up linearly with the estimated duration. In mammals, time-scale invariance is ubiquitous over behavioral, lesion, and pharmacological manipulations. For example, dopaminergic drugs induce an immediate, whereas cholinergic drugs induce a gradual, scalar change in timing. Behavioral theories posit that time-scale invariance derives from particular computations, rules, or coding schemes. In contrast, we discuss a simple neural circuit, the perceptron, whose output neurons fire in a clockwise fashion based on the pattern of coincidental activation of its input neurons. We show numerically that time-scale invariance emerges spontaneously in a perceptron with realistic neurons, in the presence of noise. Under the assumption that dopaminergic drugs modulate the firing of input neurons, and that cholinergic drugs modulate the memory representation of the criterion time, we show that a perceptron with realistic neurons reproduces the pharmacological clock and memory patterns, and their time-scale invariance, in the presence of noise. These results suggest that rather than being a signature of higher order cognitive processes or specific computations related to timing, time-scale invariance may spontaneously emerge in a massively connected brain from the intrinsic noise of neurons and circuits, thus providing the simplest explanation for the ubiquity of scale invariance of interval timing. PMID:23518297

Buhusi, Catalin V; Oprisan, Sorinel A

2013-05-01

329

Six-Degree-of-Freedom Trajectory Optimization Utilizing a Two-Timescale Collocation Architecture  

NASA Technical Reports Server (NTRS)

Six-degree-of-freedom (6DOF) trajectory optimization of a reentry vehicle is solved using a two-timescale collocation methodology. This class of 6DOF trajectory problems are characterized by two distinct timescales in their governing equations, where a subset of the states have high-frequency dynamics (the rotational equations of motion) while the remaining states (the translational equations of motion) vary comparatively slowly. With conventional collocation methods, the 6DOF problem size becomes extraordinarily large and difficult to solve. Utilizing the two-timescale collocation architecture, the problem size is reduced significantly. The converged solution shows a realistic landing profile and captures the appropriate high-frequency rotational dynamics. A large reduction in the overall problem size (by 55%) is attained with the two-timescale architecture as compared to the conventional single-timescale collocation method. Consequently, optimum 6DOF trajectory problems can now be solved efficiently using collocation, which was not previously possible for a system with two distinct timescales in the governing states.

Desai, Prasun N.; Conway, Bruce A.

2005-01-01

330

Nonlinear interaction of light with a Bose-Einstein condensate: Methods to generate sub-Poissonian light  

NASA Astrophysics Data System (ADS)

We consider a ? -type model of the Bose-Einstein condensate of sodium atoms interacting with the light. Coefficients of the Kerr nonlinearity in the condensate can achieve large and negative values, providing the possibility for effective control of group velocity and dispersion of the probe pulse. We find a regime when the observation of the “slow” and “fast” light propagating without absorption becomes achievable due to the strong nonlinearity. An effective two-level quantum model of the system is derived and studied. Our approach is based on a possibility of establishing a connection of the underlying algebra with the su(2) algebra within the formalism of the polynomial algebras of excitations (PAE). We propose an efficient way for the generation of sub-Poissonian fields in the Bose-Einstein condensate at time-scales much shorter than the characteristic decay time in the system. We show that the quantum properties of the probe pulse can be controlled in BEC by the classical coupling field.

Vadeiko, I.; Prokhorov, A. V.; Rybin, A. V.; Arakelyan, S. M.

2005-07-01

331

Einstein, race, and the myth of the cultural icon.  

PubMed

The most remarkable aspect of Einstein's 1946 address at Lincoln University is that it has vanished from Einstein's recorded history. Its disappearance into a historical black hole symbolizes what seems to happen in the creation of a cultural icon. It is but one of many political statements by Einstein to have met such a fate, though his civil rights activism is most glaringly missing. One explanation for this historical amnesia is that those who shape our official memories felt that Einstein's "controversial" friends like Paul Robeson and activities like co-chairing the anti-lynching crusade might tarnish Einstein as an icon. That icon, sanctified by Time magazine when it dubbed Einstein "Person of the Century" at the end of 1999, is a myth, albeit a marvelous one. Yet it is not so much the motive for the omission but the consequence of it that should concern us. Americans and the millions of Einstein fans around the world are left unaware that he was an outspoken, passionate, committed antiracist. PMID:16011298

Jerome, Fred

2004-12-01

332

Einstein, race, and the myth of the cultural icon  

NASA Astrophysics Data System (ADS)

The most remarkable aspect of Einstein's 1946 address at Lincoln University is that it has vanished from Einstein's recorded history. Its disappearance into a historical black hole symbolizes what seems to happen in the creation of a cultural icon. It is but one of many political statements by Einstein to have met such a fate, though his civil rights activism is most glaringly mission. One explanation for this historical amnesia is that those who shape our official memories felt that Einstein's "controversial" friends like Paul Robeson and activities like co-chairing the anti-lynching crusade might tarnish Einstein as an icon. That icon, sanctified by Time magazine when it dubbed Einstein "Person of the Century" at the end of 1999, is a myth, albeit a marvelous one. Yet it is not so much the motive for the omission but the consequence of it that should concern us. Americans and the millions of Einstein fans around the world are left unaware that he was an outspoken, passionate, committed antiracist.

Jerome, Fred

2004-12-01

333

Noncommutative Einstein-Maxwell pp-waves  

SciTech Connect

The field equations coupling a Seiberg-Witten electromagnetic field to noncommutative gravity, as described by a formal power series in the noncommutativity parameters {theta}{sup {alpha}}{sup {beta}}, is investigated. A large family of solutions, up to order one in {theta}{sup {alpha}}{sup {beta}}, describing Einstein-Maxwell null pp-waves is obtained. The order-one contributions can be viewed as providing noncommutative corrections to pp-waves. In our solutions, noncommutativity enters the spacetime metric through a conformal factor and is responsible for dilating/contracting the separation between points in the same null surface. The noncommutative corrections to the electromagnetic waves, while preserving the wave null character, include constant polarization, higher harmonic generation, and inhomogeneous susceptibility. As compared to pure noncommutative gravity, the novelty is that nonzero corrections to the metric already occur at order one in {theta}{sup {alpha}}{sup {beta}}.

Marculescu, S.; Ruiz, F. Ruiz [Fachbereich Physik, Universitaet Siegen, D-57068 Siegen (Germany); Departamento de Fisica Teorica I, Universidad Complutense de Madrid, 28040 Madrid (Spain)

2006-11-15

334

Towards Nonperaturbative Renormalizability of Quantum Einstein Gravity  

NASA Astrophysics Data System (ADS)

We summarize recent evidence supporting the conjecture that four-dimensional Quantum Einstein Gravity (QEG) is nonperturbatively renormalizable along the lines of Weinberg's asymptotic safety scenario. This would mean that QEG is mathematically consistent and predictive even at arbitrarily small length scales below the Planck length. For a truncated version of the exact flow equation of the effective average action we establish the existence of a non-Gaussian renormalization group fixed point which is suitable for the construction of a nonperturbative infinite cutoff-limit. The cosmological implications of this fixed point are discussed, and it is argued that QEG might solve the horizon and flatness problem of standard cosmology without an inflationary period.

Lauscher, O.; Reuter, M.

335

Einstein observations of the galactic centre  

NASA Technical Reports Server (NTRS)

A description is presented of the X-ray observations made with the Einstein Observatory Imaging Proportional Counter of a 1 x 1 degree field centered near the galactic nucleus. In the direction of the galactic center the interstellar medium is generally opaque to all radiation between the visual and extreme ultraviolet due to the large column density of the intervening gas and dust. The importance of this X-ray study lies in the fact that it opens up a new window in which the central regions of the Milky Way Galaxy can be observed. The X-ray image is clearly dominated by a bright, central region of emission elongated along the galactic plane. Also presented are a number of unresolved sources.

Watson, M. G.; Willingale, R.; Hertz, P.; Grindlay, J. E.

1981-01-01

336

Energy in the Einstein-aether theory  

NASA Astrophysics Data System (ADS)

We investigate the energy of a theory with a unit vector field (the aether) coupled to gravity. Both the Weinberg and Einstein type energy-momentum pseudotensors are employed. In the linearized theory we find expressions for the energy density of the 5 wave modes. The requirement that the modes have positive energy is then used to constrain the theory. In the fully nonlinear theory we compute the total energy of an asymptotically flat spacetime. The resulting energy expression is modified by the presence of the aether due to the nonzero value of the unit vector at infinity and its 1/r falloff. The question of nonlinear energy positivity is also discussed, but not resolved.

Eling, Christopher

2006-04-01

337

Energy in the Einstein-aether theory  

SciTech Connect

We investigate the energy of a theory with a unit vector field (the aether) coupled to gravity. Both the Weinberg and Einstein type energy-momentum pseudotensors are employed. In the linearized theory we find expressions for the energy density of the 5 wave modes. The requirement that the modes have positive energy is then used to constrain the theory. In the fully nonlinear theory we compute the total energy of an asymptotically flat spacetime. The resulting energy expression is modified by the presence of the aether due to the nonzero value of the unit vector at infinity and its 1/r falloff. The question of nonlinear energy positivity is also discussed, but not resolved.

Eling, Christopher [Department of Physics, University of Maryland, College Park, Maryland 20742-4111 (United States)

2006-04-15

338

What about Albert Einstein? Using Biographies to Promote Students' Scientific Thinking  

ERIC Educational Resources Information Center

Who hasn't heard of Einstein? Science educators everywhere are familiar with Einstein's genius and general theory of relativity. Students easily recognize Einstein's image by his white flyaway hair and bushy mustache. It is well known that Einstein was a brilliant physicist and an abstract thinker who often used his creativity and imagination in…

Fingon, Joan C.; Fingon, Shallon D.

2009-01-01

339

Computational methods for time-scale analysis of nonlinear dynamical systems  

NASA Astrophysics Data System (ADS)

Knowledge of the time-scale structure of a smooth finite dimensional nonlinear dynamical system provides the opportunity for model decomposition, if there are two or more disparate time-scales. A few benefits of such model decomposition are simplified control design and analysis and reduced computational effort in simulation. Singular perturbation theory provides the tools necessary to analyze and decompose a multiple time-scale nonlinear system, provided that it is in standard form. This dissertation contributes to the development of a systematic approach for determining the time-scales and the associated geometric structure in the state-space for a differential equation model in general form. The development began with the Ph.D. research of Bharadwaj[32] and was extended further in the paper by Mease, Bharadwaj, and Iravanchy[31]. The approach proceeds from investigating the behavior of the linear variational dynamics associated with a nonlinear system. By analyzing the propagation of a hyper-sphere of initial conditions which evolves into an hyper-ellipsoid in the tangent space, the time-scale information may be quantified. The time-scale information is characterized by the Lyapunov exponents and vectors, and they are related to the principal axes of the hyper-ellipsoid. The Lyapunov spectrum characterizes the average exponential rates of expansion or decay of nearby trajectories and their associated directions. It is known that the classical eigenspace analysis does not provide the correct information, i.e., eigenvalues and eigenvectors of the linearized dynamics. In this thesis the theory is extended to include dynamical systems that operate in non-Euclidean space, since a state transformation may effectively change the metric. The presentation of the entire theory provides the background for presenting the primary new contributions in this dissertation: the development and application of numerical methods for time-scale analysis. A systematic procedure is developed to diagnose, analyze, and extract the time-scale information for the system under study. The procedure includes the detection of the time-scales and their uniformity, the computation of the time-scale information, and the identification of a slow manifold. The algorithms are analyzed to better understand the error behavior, convergence rates, their geometric representation in state space, and the effect of state transformations. (Abstract shortened by UMI.)

Iravanchy, Shawn

340

EDITORIAL: Squeeze transformation and optics after Einstein  

NASA Astrophysics Data System (ADS)

With this special issue, Journal of Optics B: Quantum and Semiclassical Optics contributes to the celebration of the World Year of Physics held in recognition of five brilliant papers written by Albert Einstein in 1905. There is no need to explain to the readers of this journal the content and importance of these papers, which are cornerstones of modern physics. The 51 contributions in this special issue represent current trends in quantum optics —100 years after the concept of light quanta was introduced. At first glance, in his famous papers of 1905, Einstein treated quite independent subjects—special relativity, the nature and statistical properties of light, electrodynamics of moving bodies and Brownian motion. We now know that all these phenomena are deeply related, and these relations are clearly shown in many papers in this issue. Most of the papers are based on the talks and poster contributions from participants of the 9th International Conference on Squeezed States and Uncertainty Relations (ICSSUR'05), which took place in Besançon, France, 2-6 May, 2005. This was the continuation of a series of meetings, originating with the first workshops organized by Professor Y S Kim at the University of Maryland, College Park, USA, in 1991 and by Professor V I Man'ko at the Lebedev Physical Institute, Moscow in 1992. One of the main topics of ICSSUR'05 and this special issue is the theory and applications of squeezed states and their generalizations. At first glance, one could think that this subject has no relation to Einstein's papers. However, this is not true: the theory of squeezed states is deeply related to special relativity, as far as it is based on the representations of the Lorentz group (see the paper by Kim Y S and Noz M E, S458-S467), which also links the current concepts of entanglement and decoherence with Lorentz-covariance. Besides, studies of the different quantum states of light imply, after all, the study of photon (or photo-electron) statistics and fluctuations of the electromagnetic field, whose importance was first emphasized by Einstein in 1905. The squeezed states can also be considered as a generalization of the concept of coherent states, which turned out to be one of the most important theoretical tools for solving the numerous problems of quantum optics. It seems highly symbolical that the printed version of this special issue will appear in the same month when one of the prominent creators of the theory of coherent states and modern quantum optics—Professor Roy J Glauber—will receive his Nobel Prize in Stockholm. ICSSUR'05 was opened by the invited talk of R J Glauber, `What makes a quantum jump?', and we take great pleasure in congratulating him on this well deserved award. We are sure that all participants of ICSSUR'05 and all readers of this special issue share our feelings. Two other Nobel Prize winners of 2005—Professor J L Hall and Professor T W H\\"ansch—also made great contributions to quantum optics. In particular, in 1986, J L Hall with collaborators, performed the first experiments on the generation of squeezed states by parametric down conversion, having obtained squeezing at the 50% level (Wu L A, Kimble H J, Hall J L and Wu H 1986 Phys. Rev. Lett. 57 2520). Another area, which has attracted the attention of many researchers in the past decade and which is well represented in this special issue, is related to the problems of quantum correlations, entanglement and quantum nonlocality. It is also connected with the name of Einstein due to his famous `EPR' paper of 1935 written together with Podolsky and Rosen. For several decades this was an area of `thought experiments' only, but now this field is becoming a new part of physics, known as `quantum information'. The reader can find several papers which introduce new concepts in this area, such as applications of the Galois algebras and discrete Wigner functions. Solutions of different problems of the interaction between light and matter (which also take their origin in Einstein's paper of 1905), stationary and nons

Kim, Young S.; Man'ko, Margarita A.; Planat, Michel

2005-12-01

341

Stochastic Quantization of Einstein-Cartan Gravitational Theory  

NASA Astrophysics Data System (ADS)

We apply the stochastic quantization method to Einstein-Cartan gravitational theory. The stochastic propagators are calculated and the cooperation of modes in such a theory is investigated. It was shown that in equilibrium limit our result is equivalent to the propagator for the symmetric part of tetrads.Translated AbstractStochastische Quantisierung der Einstein-Cartanschen GravitationstheorieWir wenden die stochastischen Quantisierungsmethode auf die Einstein-Cartansche Gravitationstheorie an. Die stochastischen Propagatoren werden bestimmt und die Kooperation der Moden in einer solchen Theorie untersucht. Es wird gezeigt, daß im Gleichgewichts-grenzfall unser Resultat äquivalent zum Propagator des symmetrischen Teils der Tetraden ist.

Ivanenko, D.; Budylin, S.; Pronin, P.

342

BOOK REVIEW: A Student's Guide to Einstein's Major Papers A Student's Guide to Einstein's Major Papers  

NASA Astrophysics Data System (ADS)

The core of this volume is formed by four chapters (2-5) with detailed reconstructions of the arguments and derivations in four of Einstein's most important papers, the three main papers of his annus mirabilis 1905 (on the light quantum, Brownian motion, and special relativity) and his first systematic exposition of general relativity of 1916. The derivations are given in sufficient detail and in sufficiently modernized notation (without any serious distortion of the originals) for an undergraduate physics major to read and understand them with far less effort than it would take him or her to understand (English translations of) Einstein's original papers. Each of these four papers is accompanied by a detailed introduction, which covers the conceptual development of the relevant field prior to Einstein's contribution to it and corrects some of the myths surrounding these papers that still have not been fully eradicated among physicists. (One quibble: though Kennedy correctly points out that the goal of the light quantum paper was not to explain the photoelectric effect, it is also not quite right to say that 'it was written to explain the Wien region of blackbody radiation' (p. xv). Einstein used this explanatory feat as the central argument for his light quantum hypothesis.) These four chapters then are the most valuable part of the volume. They could be used, independently of one another, but preferably in conjunction with Einstein's original texts, in courses on quantum mechanics, statistical mechanics, electrodynamics, and general relativity, respectively, to add a historical component to such courses. As a historian of science embedded in a physics department who is regularly called upon to give guest lectures in such courses on the history of their subjects, I can highly recommend the volume for this purpose. However, I would not adopt this volume as (one of) the central text(s) for a course on the history of modern physics. For one thing, chapter 1, which in just 26 pages (not counting six pages of notes and references) covers everything from Copernicus, Galileo, Kepler and Newton to Maxwell and Lorentz to Einstein's early biography to a cardboard version of Popper versus Kuhn, is too superficial to be useful for such a course. To a lesser extent, this is also true for chapter 6, which compresses the development of quantum theory after Einstein's 1905 paper into 20 pages (plus seven pages of notes and references) and for chapter 7, a brief epilogue. However, this is not my main worry. One could easily supplement or even replace the bookends of the volume with other richer sources and use this volume mainly for its excellent detailed commentaries on some Einstein classics in the four chapters in between. My more serious reservation about the use of the volume as a whole in a history of physics course, ironically, comes from the exact same feature that made me whole-heartedly recommend its core chapters for physics courses. This is especially true for the chapters on special and general relativity. How useful is it for a student to go through, in as much detail as this volume provides, the Lorentz transformation of Maxwell's equations in vector form? I can see how a student in an E&M class (with a section on special relativity) might benefit from this exercise. The clumsiness of the calculations in vector form by Lorentz and Einstein could help a student encountering Maxwell's equations in tensor form for the first time appreciate the advantages of the latter formalism. Similarly, it would be useful for a student in a GR class to go through the basics of tensor calculus in the old-fashioned but not inelegant mathematical introduction of Einstein's 1916 review article on general relativity. This could reinforce mastery of material that a student in a GR class will have to learn anyway (though Einstein's presentation of the mathematics of both special and general relativity in The Meaning of Relativity would seem to be more suitable for these purposes). It is not so clear what benefit a student in a history of phy

Janssen, Michel

2013-12-01

343

Dynamic hyporheic exchange at intermediate timescales: testing the relative importance of evapotranspiration and flood pulses  

USGS Publications Warehouse

Hyporheic fluxes influence ecological processes across a continuum of timescales. However, few studies have been able to characterize hyporheic fluxes and residence time distributions (RTDs) over timescales of days to years, during which evapotranspiration (ET) and seasonal flood pulses create unsteady forcing. Here we present a data-driven, particle-tracking piston model that characterizes hyporheic fluxes and RTDs based on measured vertical head differences. We used the model to test the relative influence of ET and seasonal flood pulses in the Everglades (FL, USA), in a manner applicable to other low-energy floodplains or broad, shallow streams. We found that over the multiyear timescale, flood pulses that drive relatively deep (?1 m) flow paths had the dominant influence on hyporheic fluxes and residence times but that ET effects were discernible at shorter timescales (weeks to months) as a break in RTDs. Cumulative RTDs on either side of the break were generally well represented by lognormal functions, except for when ET was strong and none of the standard distributions applied to the shorter timescale. At the monthly timescale, ET increased hyporheic fluxes by 1–2 orders of magnitude; it also decreased 6 year mean residence times by 53–87%. Long, slow flow paths driven by flood pulses increased 6 year hyporheic fluxes by another 1–2 orders of magnitude, to a level comparable to that induced over the short term by shear flow in streams. Results suggest that models of intermediate-timescale processes should include at least two-storage zones with different RTDs, and that supporting field data collection occur over 3–4 years.

Larsen, Laurel G.; Harvey, Judson W.; Maglio, Morgan M.

2014-01-01

344

Time Dilation and the Length of the Second: Why Timescales Diverge  

NASA Astrophysics Data System (ADS)

We show that the timescale divergence between Universal Time (UT1) and international atomic time (TAI), which is compensated for by the occasional addition of a leap second, is due to the fact that the Système Internationale (SI) second is shorter than the UT second. Celestial mechanicians saw the necessity of introducing a timescale that eliminated the discrepancy between the observed and calculated longitudes of the Moon, Sun, and planets. This timescale, called ephemeris time (ET), was measured and used to calibrate the length of the SI second. It has been shown that ET and TAI are equivalent for all practical purposes. We show that the length of the ET second (and consequently the length of the SI second) was shorter than the length of the UT second at the beginning of the tropical year 1900.0, even though it was intended that the ET second would equal this length. We further show that this difference in the lengths of the UT and SI seconds is due to time dilation. The ET (or equivalently the SI) second is a measure of the scale of coordinate time, while the UT second is a measure of proper time for an observer moving with the Earth. Our calculation of the time dilation effect matches both the difference between the SI and UT seconds and also the leap-second insertion rate to within 0.2% since atomic time began in 1958 up to 2000, when UT was redefined. The deceleration of Earth's rotation contributes less than 1% of this timescale divergence according to the measurements from paleontological records of tidal friction. One possible method to convert from the TAI timescale is to use a multiplicative scalar to obtain a UT timescale. This method would necessitate the insertion of a leap second into the UT timescale only once in approximately 14 decades to account for tidal friction.

Deines, Steven D.; Williams, Carol A.

2007-07-01

345

A dynamic multi-timescale method for combustion modeling with detailed and reduced chemical kinetic mechanisms  

SciTech Connect

A new on-grid dynamic multi-timescale (MTS) method is presented to increase significantly the computation efficiency involving multi-physical and chemical processes using detailed and reduced kinetic mechanisms. The methodology of the MTS method using the instantaneous timescales of different species is introduced. The definition of the characteristic time for species is examined and compared with that of the computational singular perturbation (CSP) and frozen reaction rate methods by using a simple reaction system. A hybrid multi-timescale (HMTS) algorithm is constructed by integrating the MTS method with an implicit Euler scheme, respectively, for species with and without the requirement of accurate time histories at sub-base timescales. The efficiency and the robustness of the MTS and HMTS methods are demonstrated by comparing with the Euler and VODE solvers for homogenous ignition and unsteady flame propagation of hydrogen, methane, and n-decane-air mixtures. The results show that both MTS and HMTS reproduce well the species and temperature histories and are able to decrease computation time by about one-order with the same kinetic mechanism. Compared to MTS, HMTS has slightly better computation efficiency but scarifies the stability at large base time steps. The results also show that with the increase of mechanism size and the decrease of time step, the computation efficiency of multi-timescale method increases compared to the VODE solver. In addition, it is shown that the integration of the multi-timescale method with the path flux analysis based mechanism reduction approach can further increase the computation efficiency. Unsteady simulations of outwardly propagating spherical n-decane-air premixed flames demonstrate that the multi-timescale method is rigorous for direct numerical simulations with both detailed and reduced chemistry and can dramatically improve the computation efficiency. (author)

Gou, Xiaolong [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); College of Power Engineering, Chongqing University, Chongqing 400030 (China); Sun, Wenting; Ju, Yiguang [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); Chen, Zheng [Department of Mechanical and Aerospace Engineering, Princeton University, NJ 08544 (United States); School of Engineering, Peking University, Beijing 100871 (China)

2010-06-15

346

From the Einstein-Szilard Patent to Modern Magnetohydrodynamics.  

ERIC Educational Resources Information Center

Examines present-day and future prospects of the applications of modern magnetohydrodynamics in a number of countries. Explains how the electromagnetic pump, which was invented by Einstein and Leo Szilard, led to the development of applied magnetohydrodynamics. (HM)

Povh, I. L.; Barinberg, A. D.

1979-01-01

347

Knots in a Spinor Bose-Einstein Condensate  

SciTech Connect

We show that knots of spin textures can be created in the polar phase of a spin-1 Bose-Einstein condensate, and discuss experimental schemes for their generation and probe, together with their lifetime.

Kawaguchi, Yuki [Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); Nitta, Muneto [Department of Physics, Keio University, Hiyoshi, Yokohama, Kanagawa 223-8521 (Japan); Ueda, Masahito [Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551 (Japan); ERATO Macroscopic Quantum Control Project, JST, Tokyo 113-8656 (Japan)

2008-05-09

348

On Rotating Reference Systems in Einsteins Theory of Gravitation.  

National Technical Information Service (NTIS)

Solutions to the equations of motion of a mass point, solving (in Einstein's linear approximation) for the gravitational field created by a rotating shell, in order to determine if the centrifugal and coriolis forces are relativistic in rotating systems o...

L. Pietronero

1971-01-01

349

A comparative analysis of perspectives of Mileva Maric Einstein  

NASA Astrophysics Data System (ADS)

This dissertation examines the controversy surrounding Mileva Maric Einstein and the allegations subsequent to the publication of love letters during the time that Mileva Maric and Albert Einstein were students and during the early years of their marriage. It also examines the role of women in science from a historical perspective. Chapter One surveys the history of women in science from antiquity to the late nineteenth century and the patterns of gender related and restricting practices such as education, publication, the problem of mentoring and the issue of the lack of historical recognition. Chapter Two provides a comparative analyses between the lives of Mileva Maric Einstein and Marie Sklodowska Curie. Both had very similar social and educational backgrounds yet Marie Curie was able to work and publish jointly with her husband and received (although belatedly) international recognition for her work. On the other hand, Mileva Maric Einstein was never able to complete her degree and lived a life of obscurity and unfulfilled professional dreams. Both highly educated and intelligent women, but with drastically different outcomes in their professional and personal lives. Chapter Three examines the one book devoted to the life of Mileva Maric Einstein, Im Schatten Albert Einsteins: Das Tragische Leben der Mileva Einstein-Maric (In The Shadow of Albert Einstein: The Tragic Life of Mileva Maric), by Desanka Trbuhovic-Gjuric, Paul Haupt Publishers, 1985. It addresses the subjective as well as constructive and destructive criticisms of the various critical camps and provides examples of the statements made by the author which prompted a controversy within the academic and scientific communities. Appropriate responses are provided from various members of the scientific community to reflect the diversity of opinion and the intensity of the debate. Chapter Four addresses the problem of historicity and various interpretations of evidence which might suggest that the role of Mileva Maric was indeed more than just emotional spousal support for the scientific ideas of Albert Einstein. This chapter also details various lines and quotes from the book on Maric Einstein and also from the love letters shared between she and Albert Einstein to provide an indepth account of what evidence we have of possible professional collaboration.

Barnett, Carol C.

350

Timescales of Quartz Crystallization and the Longevity of the Bishop Giant Magma Body  

SciTech Connect

Supereruptions violently transfer huge amounts (100 s-1000 s km{sup 3}) of magma to the surface in a matter of days and testify to the existence of giant pools of magma at depth. The longevity of these giant magma bodies is of significant scientific and societal interest. Radiometric data on whole rocks, glasses, feldspar and zircon crystals have been used to suggest that the Bishop Tuff giant magma body, which erupted {approx}760,000 years ago and created the Long Valley caldera (California), was long-lived (>100,000 years) and evolved rather slowly. In this work, we present four lines of evidence to constrain the timescales of crystallization of the Bishop magma body: (1) quartz residence times based on diffusional relaxation of Ti profiles, (2) quartz residence times based on the kinetics of faceting of melt inclusions, (3) quartz and feldspar crystallization times derived using quartz+feldspar crystal size distributions, and (4) timescales of cooling and crystallization based on thermodynamic and heat flow modeling. All of our estimates suggest quartz crystallization on timescales of <10,000 years, more typically within 500-3,000 years before eruption. We conclude that large-volume, crystal-poor magma bodies are ephemeral features that, once established, evolve on millennial timescales. We also suggest that zircon crystals, rather than recording the timescales of crystallization of a large pool of crystal-poor magma, record the extended periods of time necessary for maturation of the crust and establishment of these giant magma bodies.

Gualda, Guilherme A.R.; Pamukcu, Ayla S.; Ghiorso, Mark S.; Anderson, Jr. , Alfred T.; Sutton, Stephen R.; Rivers, Mark L. (OFM Res.); (Vanderbilt); (UC)

2013-04-08

351

Solar radiation-induced changes in ionospheric height and the Schumann resonance waveguide on different timescales  

NASA Astrophysics Data System (ADS)

This study draws together the available observations in the Schumann resonance frequency range to examine the general issue of sensitivity of ionospheric height variations to changes in ionizing radiation from the Sun on different timescales. Ionospheric height can be formally defined, and two characteristic heights are recognized in the Schumann resonance frequency range. In general, order of magnitude changes in radiation are needed to cause relative changes in ionospheric height as large as 10%, as is the case on both the diurnal and 11-year timescales. Changes in EUV radiation are probably insufficiently strong to account for either the 27-day or the 11-year variation in ionospheric height. More ionization-effective X radiation is needed, but much smaller height changes are expected on the solar rotation timescale because the variations in X radiation on this timescale are only tens of percent and not orders of magnitude. The annual variation in radiation from the Sun is only 7%, with an expected height variation less than 100 m, and this remains to be verified by observations. The general insensitivity of the Schumann resonance cavity to changes in ionizing radiation lends stability to the medium that is valuable toward quantifying absolute changes in the global lightning activity on various timescales within the cavity.

Williams, E. R.; SáTori, G.

2007-04-01

352

Rough Solutions of Einstein Vacuum Equations in CMCSH Gauge  

NASA Astrophysics Data System (ADS)

In this paper, we consider very rough solutions to the Cauchy problem for the Einstein vacuum equations in CMC spatial harmonic gauge, and obtain the local well-posedness result in H s , s > 2. The novelty of our approach lies in that, without resorting to the standard paradifferential regularization over the rough, Einstein metric g, we manage to implement the commuting vector field approach to prove Strichartz estimate for geometric wave equation directly.

Wang, Qian

2014-06-01

353

Toric Sasaki-Einstein metrics on S2 × S3  

Microsoft Academic Search

We show that by taking a certain scaling limit of a Euclideanised form of the Plebanski-Demianski metrics one obtains a family of local toric Kahler-Einstein metrics. These can be used to construct local Sasaki-Einstein metrics in five di- mensions which are generalisations of the Y p,q manifolds. In fact, we find that these metrics are diffeomorphic to those recently found

Dario Martelli; James Sparks

354

Some forgotten features of the Bose-Einstein correlations  

SciTech Connect

Notwithstanding the visible maturity of the subject of Bose-Einstein correlations (BEC), as witnessed nowadays, we would like to bring to one's attention two points which apparently did not receive the attention they deserve: the problem of the choice of the form of C{sub 2}(Q) correlation function when effects of partial coherence of the hadronizing source are to be included and the feasibility to model effects of Bose-Einstein statistics, in particular, the BEC, by direct numerical simulations.

Kozlov, G. A. [Joint Institute for Nuclear Research, Bogolyubov Laboratory of Theoretical Physics (Russian Federation); Utyuzh, O. V.; Wilk, G., E-mail: wilk@fuw.edu.p [Andrzej Soltan Institute for Nuclear Studies (Poland); Wlodarczyk, Z. [Swietokrzyska Academy, Institute of Physics (Poland)

2008-09-15

355

Observation of Vortex Pinning in Bose-Einstein Condensates  

SciTech Connect

We report the observation of vortex pinning in rotating gaseous Bose-Einstein condensates. Vortices are pinned to columnar pinning sites created by a corotating optical lattice superimposed on the rotating Bose-Einstein condensates. We study the effects of two types of optical lattice: triangular and square. In both geometries we see an orientation locking between the vortex and the optical lattices. At sufficient intensity the square optical lattice induces a structural crossover in the vortex lattice.

Tung, S.; Schweikhard, V.; Cornell, E. A. [JILA, National Institute of Standards and Technology, and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440 (United States)

2006-12-15

356

Gravitational spectrum of black holes in the Einstein Aether theory  

NASA Astrophysics Data System (ADS)

Evolution of gravitational perturbations, both in time and frequency domains, is considered for a spherically symmetric black hole in the non-reduced Einstein-Aether theory. It is shown that real oscillation frequency and damping rate are larger for the Einstein-Aether black hole than for the Schwarzschild black hole. This may provide an opportunity to observe aether in the forthcoming experiments with new generation of gravitational antennas.

Konoplya, R. A.; Zhidenko, A.

2007-05-01

357

Bose-Einstein correlations in W-pair decays  

Microsoft Academic Search

Bose-Einstein correlations are studied in semileptonic (WW?qq???) and fully hadronic (WW?qq?qq?) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned

S. R. Armstrong; P. Elmer; D. P. S. Ferguson; Y. Gao; S. González; O. J. Hayes; H. Hu; S. Jin; J. Kile; P. A. McNamara III; J. Nielsen; W. Orejudos; Y. B. Pan; Y. Saadi; I. J. Scott; J. Walsh; J. H. von Wimmersperg-Toeller; S. L. Wu; X. Wu; G. Zobernig; M. Martinez; G. Merino; R. Miquel; L. M. Mir; P. Morawitz; A. Pacheco; I. Riu; H. Ruiz; A. Colaleo; D. Creanza; M. de Palma; G. Iaselli; G. Maggi; M. Maggi; S. Nuzzo; A. Ranieri; G. Raso; F. Ruggieri; G. Selvaggi; L. Silvestris; P. Tempesta; A. Tricomi; G. Zito; X. Huang; J. Lin; Q. Ouyang; T. Wang; Y. Xie; R. Xu; S. Xue; J. Zhang; L. Zhang; W. Zhao; D. Abbaneo; G. Boix; O. Buchmüller; M. Cattaneo; F. Cerutti; V. Ciulli; G. Davies; G. Dissertori; H. Drevermann; R. W. Forty; M. Frank; F. Gianotti; T. C. Greening; A. W. Halley; J. B. Hansen; J. Harvey; P. Janot; B. Jost; M. Kado; O. Leroy; P. Maley; P. Mato; A. Minten; A. Moutoussi; F. Ranjard; L. Rolandi; D. Schlatter; M. Schmitt; O. Schneider; P. Spagnolo; W. Tejessy; F. Teubert; E. Tournefier; A. Valassi; A. E. Wright; Z. Ajaltouni; F. Badaud; G. Chazelle; O. Deschamps; S. Dessagne; A. Falvard; C. Ferdi; P. Gay; C. Guicheney; P. Henrard; J. Jousset; B. Michel; S. Monteil; J.-C. Montret; D. Pallin; J. M. Pascolo; P. Perret; F. Podlyski; J. D. Hansen; P. H. Hansen; B. S. Nilsson; B. Rensch; A. Wäänänen; G. Daskalakis; A. Kyriakis; C. Markou; E. Simopoulou; A. Vayaki; A. Blondel; J.-C. Brient; F. Machefert; A. Rougé; M. Swynghedauw; R. Tanaka; H. Videau; E. Focardi; G. Parrini; K. Zachariadou; M. Corden; C. Georgiopoulos; A. Antonelli; G. Bencivenni; G. Bologna; F. Bossi; P. Campana; G. Capon; V. Chiarella; P. Laurelli; G. Mannocchi; F. Murtas; G. P. Murtas; L. Passalacqua; M. Pepe-Altarelli; M. Chalmers; J. Kennedy; J. G. Lynch; P. Negus; V. O'Shea; B. Raeven; D. Smith; P. Teixeira-Dias; A. S. Thompson; J. J. Ward; R. Cavanaugh; S. Dhamotharan; C. Geweniger; P. Hanke; V. Hepp; E. E. Kluge; G. Leibenguth; A. Putzer; K. Tittel; S. Werner; M. Wunsch; R. Beuselinck; D. M. Binnie; W. Cameron; P. J. Dornan; M. Girone; S. Goodsir; N. Marinelli; E. B. Martin; J. Nash; J. Nowell; H. Przysiezniak; A. Sciabà; J. K. Sedgbeer; J. C. Thompson; E. Thomson; M. D. Williams; V. M. Ghete; P. Girtler; E. Kneringer; D. Kuhn; G. Rudolph; C. K. Bowdery; P. G. Buck; G. Ellis; A. J. Finch; F. Foster; G. Hughes; R. W. L. Jones; N. A. Robertson; M. Smizanska; M. I. Williams; I. Giehl; F. Hölldorfer; K. Jakobs; K. Kleinknecht; M. Kröcker; A.-S. Müller; H.-A. Nürnberger; G. Quast; B. Renk; E. Rohne; H.-G. Sander; S. Schmeling; H. Wachsmuth; C. Zeitnitz; T. Ziegler; A. Bonissent; J. Carr; P. Coyle; A. Ealet; D. Fouchez; P. Payre; D. Rousseau; A. Tilquin; M. Aleppo; M. Antonelli; S. Gilardoni; F. Ragusa; V. Büscher; H. Dietl; G. Ganis; K. Hüttmann; G. Lütjens; C. Mannert; W. Männer; H.-G. Moser; S. Schael; R. Settles; H. Seywerd; H. Stenzel; W. Wiedenmann; G. Wolf; P. Azzurri; J. Boucrot; O. Callot; S. Chen; M. Davier; L. Duflot; J.-F. Grivaz; P. Heusse; A. Jacholkowska; J. Lefrançois; L. Serin; J.-J. Veillet; I. Videau; J.-B. de Vivie de Régie; D. Zerwas; G. Bagliesi; T. Boccali; C. Bozzi; G. Calderini; R. Dell'Orso; I. Ferrante; A. Giassi; A. Gregorio; F. Ligabue; P. S. Marrocchesi; A. Messineo; F. Palla; G. Rizzo; G. Sanguinetti; G. Sguazzoni; R. Tenchini; A. Venturi; P. G. Verdini; G. A. Blair; J. Coles; G. Cowan; M. G. Green; D. E. Hutchcroft; L. T. Jones; T. Medcalf; J. A. Strong; D. R. Botterill; R. W. Clifft; T. R. Edgecock; P. R. Norton; I. R. Tomalin; B. Bloch-Devaux; P. Colas; B. Fabbro; G. Faïf; E. Lançon; M.-C. Lemaire; E. Locci; P. Perez; J. Rander; J.-F. Renardy; A. Rosowsky; P. Seager; A. Trabelsi; B. Tuchming; B. Vallage; S. N. Black; J. H. Dann; C. Loomis; H. Y. Kim; N. Konstantinidis; A. M. Litke; M. A. McNeil; G. Taylor; C. N. Booth; S. Cartwright; F. Combley; P. N. Hodgson; M. Lehto; L. F. Thompson; K. Affholderbach; A. Böhrer; S. Brandt; C. Grupen; J. Hess; A. Misiejuk; G. Prange; U. Sieler; C. Borean; G. Giannini; B. Gobbo; J. Putz; J. Rothberg; S. Wasserbaech; R. W. Williams; P. Elmer; Y. B. Pan; J. Walsh

2000-01-01

358

The Einstein-Vlasov system\\/Kinetic theory  

Microsoft Academic Search

The main purpose of this article is to provide a guide to theorems on global\\u000aproperties of solutions to the Einstein-Vlasov system. This system couples\\u000aEinstein's equations to a kinetic matter model. Kinetic theory has been an\\u000aimportant field of research during several decades in which the main focus has\\u000abeen on nonrelativistic and special relativistic physics, {\\\\it i.e.} to

Hakan Andreasson

2005-01-01

359

Bose-Einstein condensation in a Ioffe-Pritchard trap  

Microsoft Academic Search

Since its first observation in 1995, Bose-Einstein condensation (BEC) experiments in dilute gases have been performed with only a few different kinds of magnetic traps. We have performed a BEC experiment with 87Rb atoms in a Ioffe-Pritchard magnetic potential, which opens up the possibility to study, e.g., Bose-Einstein condensates released in only one dimension. Our trap consists of a clip-like

U. Ernst; A. Marte; F. Schreck; J. Schuster; G. Rempe

1998-01-01

360

Bose-Einstein condensation of excitons in Cu2O  

Microsoft Academic Search

We present a parameter-free model that estimates the density of excitons in Cu2O, related to experiments that have tried to create an excitonic Bose-Einstein condensate. Our study demonstrates that the triplet-state excitons move along adiabats and obey classical statistics, while the singlet-state excitons are a possible candidate for forming a Bose-Einstein condensate. Finally we show that the results of this

G. M. Kavoulakis

2002-01-01

361

Asymptotic behavior of solutions to Einstein's equation  

NASA Astrophysics Data System (ADS)

This dissertation is a report of research on the properties of cosmological solutions to Einstein's equation near the singularity. In the first part of this work methods from dynamical systems analysis are used to prove that the presence of a magnetic field perpendicular to the two commuting Killing vector fields in spatially homogeneous solutions of Bianchi type VI0 changes the dynamics from asymptotically velocity term dominated to oscillatory. In particular, it is shown that the ?-limit set (for the time direction that puts the singularity in the past) of any of these magnetic solutions contains at least two Kasner points. Previous work by others provides evidence that these spacetimes are not only oscillatory but indeed mixmaster. However, this has never been proven. In the second part of this work evidence for mixmaster behavior in a class of solutions which is a spatially inhomogeneous generalization of locally homogeneous magnetic Bianchi VI0 is presented. In this generalization spatial variation is allowed in the direction of the magnetic field. These spacetimes are much like the Gowdy models, except for the presence of the magnetic field and a different spatial topology. Numerical results combined with qualitative analysis show that the presence of the magnetic field changes the dynamics from asymptotically velocity term dominated to mixmaster. These are the first results that provide clear evidence of the occurrence of mixmaster evolution in spatially inhomogeneous solutions to Einstein's equation. The evolution toward the singularity at almost every spatial point asymptotically approaches the evolution of some magnetic Bianchi VI0 spacetime. The evolution at different spatial points approaches the evolution of different magnetic Bianchi VI0 spacetimes. This behavior is in agreement with the description by Belinskii, Khalatnikov and Lifshitz of the oscillatory approach to the singularity. Using the same methods to study the Gowdy models having T 3 spatial topology leads to the conjecture that the presence of a magnetic field perpendicular to the symmetry directions changes the dynamics from asymptotically velocity term dominated to mixmaster. Finally, indications of oscillatory behavior in the vacuum (no magnetic field) T 2 symmetric spacetimes with nonvanishing twist are obtained by these methods.

Weaver, Marsha Jane

1999-10-01

362

Bose-Einstein Condensation in Microgravity  

NASA Astrophysics Data System (ADS)

Quantum matter gives unique insights into a broad range of phenomena in fundamental physics as well as it offers interesting prospects for novel quantum sensors. Reaching ever-new frontiers in low temperature physics and achieving full control of these elementary quantum systems were part of the central motivations for research on cooling and manipulation of atoms. The breaking of temperature records opened the way to many new scientific achievements, like atom interferometers and atomic clocks with highest accuracy, novel phase transitions or atom lasers. It is interesting to speculate if quantum degenerate gases will be of advantage for metrological applications. The perfect control of the external degrees of freedom is mandatory for a better control of systematic errors. Microgravity can extend the science of quantum gases towards inaccessible regimes of lowest temperatures below picokelvins, macroscopic dimensions, and unequalled durations of the un-perturbed evolution of these distinguished quantum objects. These conditions set the stage for the study of the physics of ultra-dilute gases and giant matter-waves and the control of these macroscopic quantum objects and mixtures in an environment unbiased by gravity. In particu-lar, microgravity is of high relevance for matter-wave as it permits the extension the unperturbed free fall of these test particles in a low-noise environment. This is a prerequisite for fundamen-tal tests in the quantum domain such as the equivalence principle or the realisation of ideal reference systems. The QUANTUS team, formed by a consortium of the Leibniz University of Hanover, the University of Hamburg, Berlin, Ulm and ZARM as well as the Max-Planck Institute and ENS, realised a compact facility to study a Rubidium Bose-Einstein Condensate in the extended free fall at the drop tower in Bremen and during parabolic flights. The facil-ity will permit to study the generation and outcoupling of BEC in microgravity, the study of decoherence and atom interferometry. The remote controlled and miniaturised facility, which produces Bose-Einstein condensates of Rubidium, is in operation since November 2007. The QUANTUS -Team is formed by the LUH, Univ. of Hamburg/Univ. of Birmingham, MPQ/ENS,Univ. Ulm, AvH zu Berlin. The project is funded on behalf of the BMWI on the grant number DLR 50 WM 0346.

Rasel, Ernst Maria

363

Bose-Einstein Condensation in Microgravity  

NASA Astrophysics Data System (ADS)

Quantum matter gives unique insights into a broad range of phenomena in fundamental physics as well as it offers interesting prospects for novel quantum sensors. Reaching ever-new frontiers in low temperature physics and achieving full control of these elementary quantum systems were part of the central motivations for research on cooling and manipulation of atoms. The breaking of temperature records opened the way to many new scientific achievements, like atom interferometers and atomic clocks with highest accuracy, novel phase transitions or atom lasers. It is interesting to speculate if quantum degenerate gases will be of advantage for metrological applications. The perfect control of the external degrees of freedom is mandatory for a better control of systematic errors. Microgravity can extend the science of quantum gases towards inaccessible regimes of lowest temperatures below picokelvins, macroscopic dimensions, and unequalled durations of the un-perturbed evolution of these distinguished quantum objects. These conditions set the stage for the study of the physics of ultra-dilute gases and giant matter-waves and the control of these macroscopic quantum objects and mixtures in an environment unbiased by gravity. In particular, microgravity is of high relevance for matter-wave as it permits the extension the unperturbed free fall of these test particles in a low-noise environment. This is a prerequisite for fundamental tests in the quantum domain such as the equivalence principle or the realisa-tion of ideal reference systems. The QUANTUS team, formed by a consortium of the Leibniz University of Hanover, the University of Hamburg, Berlin, Ulm and ZARM as well as the Max-Planck Institute and ENS, realised a compact facility to study a Rubidium Bose-Einstein Condensate in the extended free fall at the drop tower in Bremen and during parabolic flights. The facility will permit to study the generation and outcoupling of BEC in microgravity, the study of decoherence and atom interferometry. The remote controlled and miniaturised facility, which produces Bose-Einstein condensates of Rubidium, is in operation since November 2007. The QUANTUS -Team is formed by the LUH, Univ. of Hamburg/Univ. of Birmingham, MPQ/ENS,Univ. Ulm, AvH zu Berlin. The project is funded on behalf of the BMWI on the grant number DLR 50 WM 0346.

Rasel, Ernst Maria

364

Guided Plasmaspheric Hiss Interactions with Superthermal Electrons. Part 1; Resonance Curves and Timescales  

NASA Technical Reports Server (NTRS)

Under the proper conditions, guided plasmaspheric hiss is shown to be more efficient than Coulomb collisions at scattering electrons in the superthermal energy range of 50 to 500 eV. Broadband, whistler mode hiss becomes guided by plasma density gradients, intensifying the wave energy densities and focusing the wave normal angles. These waves are shown to interact through Cherenkov (Landau) resonance with electrons below 500 eV, and the presented equatorial plane timescales for pitch angle, energy, and mixed diffusion are shown to be faster than Coulomb collision timescales for typical values at the inner edge of the plasmapause and in detached plasma regions. In the latter case, energy diffusion timescales of less than 100 s for small pitch angle electrons between 250 and 500 eV indicate that these waves have the potential to dramatically change the distribution function.

Liemohn, M. W.; Khazanov, G. V.; Kozyra, J. U.

1997-01-01

365

A Hierarchy of Timescales in Protein Dynamics is Linked to Enzyme Catalysis  

SciTech Connect

The synergy between structure and dynamics is essential to the function of biological macromolecules. Thermally driven dynamics on different timescales have been experimentally observed or simulated, and a direct link between micro- to milli-second domain motions and enzymatic function has been established. However, very little is understood about the connection of these functionally relevant, collective movements with local atomic fluctuations, which are much faster. Here we show that pico- to nano-second timescale atomic fluctuations in hinge regions of adenylate kinase facilitate the large-scale, slower lid motions that produce a catalytically competent state. The fast, local mobilities differ between a mesophilic and hyperthermophilic adenylate kinase, but are strikingly similar at temperatures at which enzymatic activity and free energy of folding are matched. The connection between different timescales and the corresponding amplitudes of motions in adenylate kinase and their linkage to catalytic function is likely to be a general characteristic of protein energy landscapes.

Henzler-Wildman,K.; Lei, M.; Thai, V.; Jordan Kerns, S.; Karplus, M.; Kern, D.

2007-01-01

366

ON THE NATURE OF THE PROTOTYPE LUMINOUS BLUE VARIABLE AG CARINAE. II. WITNESSING A MASSIVE STAR EVOLVING CLOSE TO THE EDDINGTON AND BISTABILITY LIMITS  

SciTech Connect

We show that the significantly different effective temperatures (T{sub eff}) achieved by the luminous blue variable AG Carinae during the consecutive visual minima of 1985-1990 (T{sub eff} {approx_equal} 22,800 K) and 2000-2001 (T{sub eff} {approx_equal} 17,000 K) place the star on different sides of the bistability limit, which occurs in line-driven stellar winds around T{sub eff} {approx} 21,000 K. Decisive evidence is provided by huge changes in the optical depth of the Lyman continuum in the inner wind as T{sub eff} changes during the S Dor cycle. These changes cause different Fe ionization structures in the inner wind. The bistability mechanism is also related to the different wind parameters during visual minima: the wind terminal velocity was 2-3 times higher and the mass-loss rate roughly two times smaller in 1985-1990 than in 2000-2003. We obtain a projected rotational velocity of 220 {+-} 50 km s{sup -1} during 1985-1990 which, combined with the high luminosity (L{sub *} = 1.5 x 10{sup 6} L{sub sun}), puts AG Car extremely close to the Eddington limit modified by rotation ({Omega}{Gamma} limit): for an inclination angle of 90{sup 0}, {Gamma}{sub {Omega}} {approx}> 1.0 for M{sub sun} {approx}< 60. Based on evolutionary models and mass budget, we obtain an initial mass of {approx}100 M{sub sun} and a current mass of {approx}60-70 M{sub sun} for AG Car. Therefore, AG Car is close to, if not at, the {Omega}{Gamma} limit during visual minimum. Assuming M = 70 M{sub sun}, we find that {Gamma}{sub {Omega}} decreases from 0.93 to 0.72 as AG Car expands toward visual maximum, suggesting that the star is not above the Eddington limit during maximum phases.

Groh, J. H. [Max-Planck-Institut fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany); Hillier, D. J. [Department of Physics and Astronomy, University of Pittsburgh, 3941 O'Hara Street, Pittsburgh, PA 15260 (United States); Damineli, A., E-mail: jgroh@mpifr.de [Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, 05508-900, Sao Paulo, SP (Brazil)

2011-07-20

367

Spatial and seasonal variability of the air-sea equilibration timescale of carbon dioxide  

NASA Astrophysics Data System (ADS)

The exchange of carbon dioxide between the ocean and the atmosphere tends to bring near-surface waters toward equilibrium by reducing the partial pressure gradient across the air-water interface. However, the equilibration process is not instantaneous; in general there is a lag between forcing and response. The timescale of air-sea equilibration depends on several factors involving the depth of the mixed layer, temperature, salinity, wind speed, and carbonate chemistry. In this work, we use a suite of observational datasets to generate climatological and seasonal composite maps of the air-sea equilibration timescale. The relaxation timescale exhibits considerable spatial and seasonal variations, which are largely set by changes in mixed layer depth and wind speed. The net effect is dominated by the mixed layer depth; the gas exchange velocity and carbonate chemistry parameters only provide partial compensation. Broadly speaking, the adjustment timescale tends to increase with latitude. We compare the observationally-derived air-sea gas exchange timescale with a model-derived surface residence time and a data-derived horizontal transport timescale, which allows us to define two non-dimensional metrics of gas exchange efficiency. These parameters highlight the Southern Ocean, equatorial Pacific, and North Atlantic as regions of inefficient air-sea equilibration where carbon anomalies are likely to form and persist. The efficiency parameters presented here can serve as simple tools for understanding regional air-sea disequilibrium in both observations and models. This work is distributed under the Creative Commons Attribution 3.0 Unported License together with an author copyright. This license does not conflict with the regulations of the Crown Copyright.

Jones, Daniel; Ito, Takamitsu; Takano, Yohei; Hsu, Wei-Ching

2014-05-01

368

Response of vegetation to drought time-scales across global land biomes.  

PubMed

We evaluated the response of the Earth land biomes to drought by correlating a drought index with three global indicators of vegetation activity and growth: vegetation indices from satellite imagery, tree-ring growth series, and Aboveground Net Primary Production (ANPP) records. Arid and humid biomes are both affected by drought, and we suggest that the persistence of the water deficit (i.e., the drought time-scale) could be playing a key role in determining the sensitivity of land biomes to drought. We found that arid biomes respond to drought at short time-scales; that is, there is a rapid vegetation reaction as soon as water deficits below normal conditions occur. This may be due to the fact that plant species of arid regions have mechanisms allowing them to rapidly adapt to changing water availability. Humid biomes also respond to drought at short time-scales, but in this case the physiological mechanisms likely differ from those operating in arid biomes, as plants usually have a poor adaptability to water shortage. On the contrary, semiarid and subhumid biomes respond to drought at long time-scales, probably because plants are able to withstand water deficits, but they lack the rapid response of arid biomes to drought. These results are consistent among three vegetation parameters analyzed and across different land biomes, showing that the response of vegetation to drought depends on characteristic drought time-scales for each biome. Understanding the dominant time-scales at which drought most influences vegetation might help assessing the resistance and resilience of vegetation and improving our knowledge of vegetation vulnerability to climate change. PMID:23248309

Vicente-Serrano, Sergio M; Gouveia, Célia; Camarero, Jesús Julio; Beguería, Santiago; Trigo, Ricardo; López-Moreno, Juan I; Azorín-Molina, César; Pasho, Edmond; Lorenzo-Lacruz, Jorge; Revuelto, Jesús; Morán-Tejeda, Enrique; Sanchez-Lorenzo, Arturo

2013-01-01

369

Dynamics of Separating Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

When a Bragg laser pulse (two counterpropagating beams with slightly different frequencies) is applied to a gaseous Bose-Einstein condensate (BEC), it is possible to transfer momentum to a controllable fraction of the condensate atoms. A Bragg pulse that imparts momentum to half of the condensate atoms is termed a ?/2 pulse while a pulse that imparts momentum to all of the atoms is called a ? pulse. Such pulses split the BEC into two clouds that eventually separate. While the clouds are overlapped, however, their interaction alters both the density and phase profiles of the individual clouds in a nontrivial way. While this process can be modeled using the time-dependent Gross-Pitaevskii (GP) equation, the solution of the full three--dimensional GP equation for large momentum transfer can be a challenging computational task. We have studied the dynamics of two separating BEC's using a Lagrangian variational technique that provides equations of motion for time-dependent variational parameters contained in a specified wavefunction ansatz for the GP solution. We compare the results of these models with data from a recent experiment performed at NIST.

Edwards, Mark; Simsarian, J. E.; Denschlag, J.; Helmerson, K.; Rolston, S. E.; Phillips, W. D.; Clark, Charles W.

2000-06-01

370

Bose-Einstein condensation of exciton polaritons.  

PubMed

Phase transitions to quantum condensed phases--such as Bose-Einstein condensation (BEC), superfluidity, and superconductivity--have long fascinated scientists, as they bring pure quantum effects to a macroscopic scale. BEC has, for example, famously been demonstrated in dilute atom gas of rubidium atoms at temperatures below 200 nanokelvin. Much effort has been devoted to finding a solid-state system in which BEC can take place. Promising candidate systems are semiconductor microcavities, in which photons are confined and strongly coupled to electronic excitations, leading to the creation of exciton polaritons. These bosonic quasi-particles are 10(9) times lighter than rubidium atoms, thus theoretically permitting BEC to occur at standard cryogenic temperatures. Here we detail a comprehensive set of experiments giving compelling evidence for BEC of polaritons. Above a critical density, we observe massive occupation of the ground state developing from a polariton gas at thermal equilibrium at 19 K, an increase of temporal coherence, and the build-up of long-range spatial coherence and linear polarization, all of which indicate the spontaneous onset of a macroscopic quantum phase. PMID:17006506

Kasprzak, J; Richard, M; Kundermann, S; Baas, A; Jeambrun, P; Keeling, J M J; Marchetti, F M; Szyma?ska, M H; André, R; Staehli, J L; Savona, V; Littlewood, P B; Deveaud, B; Dang, Le Si

2006-09-28

371

Nonminimal Einstein-Maxwell-Vlasov-axion model  

NASA Astrophysics Data System (ADS)

We establish a new self-consistent system of equations accounting for a nonminimal coupling of the cooperative gravitational, electromagnetic and pseudoscalar (axion) fields in a multi-component relativistic plasma. The axionic extension of the nonminimal Einstein-Maxwell-Vlasov theory is based on two consistent procedures. First, we use the Lagrange formalism to obtain nonminimal equations for the gravitational, electromagnetic and pseudoscalar fields with the additional sources generated in plasma. Second, we use the Vlasov version of the relativistic kinetic theory of the plasma, guided by the cooperative macroscopic electromagnetic, gravitational and axionic fields, to describe adequately the response of the plasma on the variations of these fields. In order to show the self-consistency of this approach we check directly the compatibility conditions for the master equations for the cooperative fields. Using these compatibility conditions we reconstruct the ponderomotive force, which acts on the plasma particles, and discuss the necessary conditions for existence of the distribution function of the equilibrium type.

Balakin, Alexander B.; Muharlyamov, Ruslan K.; Zayats, Alexei E.

2014-01-01

372

Spinor Bose-Einstein condensates of positronium  

NASA Astrophysics Data System (ADS)

Bose-Einstein condensates (BECs) of positronium (Ps) have been of experimental and theoretical interest due to their potential application as the gain medium of a ?-ray laser. Ps BECs are intrinsically spinor due to the presence of ortho-positronium (o-Ps) and para-positronium (p-Ps), whose annihilation lifetimes differ by three orders of magnitude. In this paper, we study the spinor dynamics and annihilation processes in the p-Ps/o-Ps system using both solutions of the time-dependent Gross-Pitaevskii equations and a semiclassical rate-equation approach. The spinor interactions have an O(4) symmetry which is broken to SO(3) by an internal energy difference between o-Ps and p-Ps. For an initially unpolarized condensate, there is a threshold density of ?1019 cm-3 at which spin mixing between o-Ps and p-Ps occurs. Beyond this threshold, there are unstable spatial modes accompanied by spin mixing. To ensure a high production yield above the critical density, a careful choice of external field must be made to avoid the spin mixing instability.

Wang, Yi-Hsieh; Anderson, Brandon M.; Clark, Charles W.

2014-04-01

373

Einstein observations of the Orion Nebula  

NASA Technical Reports Server (NTRS)

A single 3.5 hour observation on 1979 March 6 with the imaging proportional counter aboard the Einstein Observatory has revealed the presence of numerous low-luminosity (10 to the 31st ergs/s) X-ray sources in a region centered near the Trapezium in the Orion Nebula. In addition to the Trapezium, 22 discrete sources have been detected in a 1 x 1 deg field at or above the 4 sigma level. These sources are clearly associated with star formation, as indicated by the similarity of their spatial distribution with that of the nebular variables, a class of pre-main-sequence stars. Because the field is quite crowded, however, individual identifications of these sources are difficult. In addition to the discrete sources, there is evidence for diffuse or unresolved emission from two ridges extending 16 deg to the north and 15 deg to the west of the Trapezium. The nature of the discrete sources and of the diffuse emission is discussed.

Ku, W. H.-M.; Chanan, G. A.

1979-01-01

374

Direct radiometric dating of the Devonian-Mississippian time-scale boundary using the Re-Os black shale geochronometer  

Microsoft Academic Search

Many Phanerozoic time-scale boundaries are characterized by oceanic anoxia and mass extinction events with the deposition of black shale. The Re-Os isotope system in black shale can be used to provide depositional ages for these rocks, thus yielding direct radiometric ages for time-scale boundaries. We demonstrate that the Re-Os black shale geochronometer can yield precise ages useful for time-scale research

David Selby; Robert A. Creaser

2005-01-01

375

Framework and Research Methodology of Short-Timescale Pulsed Power Phenomena in High-Voltage and High-Power Converters  

Microsoft Academic Search

Various short-timescale transients exist in power electronic converters, particularly in high-voltage and high-power systems. The timescales of these transients are from nanoseconds to microseconds, including a switching transition of power semiconductor devices, commutating processes, and drive signal transmissions. These transient processes directly affect the performance and reliability of power electronic systems. Therefore, it is necessary to study these short-timescale processes.

Hua Bai; Zhengming Zhao; Chris Mi

2009-01-01

376

Einstein energy associated with the Friedmann-Robertson-Walker metric  

NASA Astrophysics Data System (ADS)

Following Einstein’s definition of Lagrangian density and gravitational field energy density (Einstein in Ann Phys Lpz 49:806, 1916, Einstein in Phys Z 19:115, 1918, Pauli in Theory of Relativity, B.I. Publications, Mumbai, 1963), Tolman derived a general formula for the total matter plus gravitational field energy ( P 0) of an arbitrary system (Tolman in Phys Rev 35:875, 1930, Tolman in Relativity, Thermodynamics & Cosmology, Clarendon Press, Oxford, 1962, Xulu in hep-th/0308070, 2003). For a static isolated system, in quasi-Cartesian coordinates, this formula leads to the well known result {P_0 = int sqrt{-g} (T_0^0 - T_1^1 - T_2^2 - T_3^3) d^3 x,} where g is the determinant of the metric tensor and {T^a_b} is the energy momentum tensor of the matter. Though in the literature, this is known as “Tolman Mass”, it must be realized that this is essentially “Einstein Mass” because the underlying pseudo-tensor here is due to Einstein. In fact, Landau-Lifshitz obtained the same expression for the “inertial mass” of a static isolated system without using any pseudo-tensor at all and which points to physical significance and correctness of Einstein Mass (Landau, Lifshitz in The Classical Theory of Fields, Pergamon Press, Oxford, 1962)! For the first time we apply this general formula to find an expression for P 0 for the Friedmann-Robertson-Walker (FRW) metric by using the same quasi-Cartesian basis. As we analyze this new result, it transpires that, physically, a spatially flat model having no cosmological constant is preferred. Eventually, it is seen that conservation of P 0 is honoured only in the static limit.

Mitra, Abhas

2010-03-01

377

In the limelight of stars. Einstein, Mandl, and the origins of gravitational lens research (German Title: Im Rampenlicht der Sterne. Einstein, Mandl und die Ursprünge der Gravitationslinsenforschung)  

NASA Astrophysics Data System (ADS)

Einstein's paper on gravitational lensing from 1936 was published only as a result of insistent prodding by the Czech amateur scientist Rudi Mandl. We discuss Mandl's role for the publication history of Einstein's paper and point out striking similarities between Mandl's situation in 1936 and Einstein's own position in 1912. At that time, Einstein himself had already considered the idea of gravitational lensing, as had been discovered some years ago through the identification of research notes from that period. Other early discussions of gravitational lensing by Lodge, Chwolson, Tikhov, Zwicky, Russell, and others were either only perceived or only written after Mandl had succeeded to persuade Einstein into publication.

Renn, Jürgen; Sauer, Tilman

378

The softest Einstein AGN (active galactic nuclei)  

SciTech Connect

We have undertaken a coarse spectral study to find the softest sources detected with the Imaging Proportional Counter (IPC) on the Einstein Observatory. Of the nearly 7700 IPC sources, 226 have color ratios that make them candidate ultrasoft'' sources; of these, 83 have small enough errors that we can say with confidence that they have a spectral component similar to those of the white dwarfs Sirius and HZ 43, nearby stars such as {alpha} Cen and Procyon, and typical polar'' cataclysmic variables. By means of catalog searches and ground-based optical and radio observations we have thus far identified 96 of the 226 candidate soft sources; 37 of them are active galactic nuclei (AGN). In the more selective subset of 83 sources, 47 have been identified, 12 of them with AGN. The list of 47 identifications is given in Cordova et al. For one QSO in our sample, E0132.8--411, we are able to fit the pulse-height data to a power-law model and obtain a best fit for the energy spectral index of 2. 2{sub {minus}0.4}{sup +0.6}. For the remainder of the AGN in the higher confidence sample we are able to infer on the basis of their x-ray colors that they have a similar spectral component. Two-thirds of the AGN are detected below 0.5 keV only, while the remainder evidence a flatter spectral component in addition to the ultra-soft component. 14 refs., 5 figs.

Cordova, F.A.; Kartje, J.; Mason, K.O.; Mittaz, J.P.D. (Los Alamos National Lab., NM (USA); Chicago Univ., IL (USA); University Coll., London (UK). Mullard Space Science Lab.)

1989-01-01

379

Studying planet populations with Einstein's blip.  

PubMed

Although Einstein originally judged that 'there is no great chance of observing this phenomenon', the 'most curious effect' of the bending of starlight by the gravity of intervening foreground stars--now commonly referred to as 'gravitational microlensing'--has become one of the successfully applied techniques to detect planets orbiting stars other than the Sun, while being quite unlike any other. With more than 400 extra-solar planets known altogether, the discovery of a true sibling of our home planet seems to have become simply a question of time. However, in order to properly understand the origin of Earth, carrying all its various life forms, models of planet formation and orbital evolution need to be brought into agreement with the statistics of the full variety of planets like Earth and unlike Earth. Given the complementarity of the currently applied planet detection techniques, a comprehensive picture will only arise from a combination of their respective findings. Gravitational microlensing favours a range of orbital separations that covers planets whose orbital periods are too long to allow detection by other indirect techniques, but which are still too close to their host star to be detected by means of their emitted or reflected light. Rather than being limited to the Solar neighbourhood, a unique opportunity is provided for inferring a census of planets orbiting stars belonging to two distinct populations within the Milky Way, with a sensitivity not only reaching down to Earth mass, but even below, with ground-based observations. The capabilities of gravitational microlensing extend even to obtaining evidence of a planet orbiting a star in another galaxy. PMID:20603366

Dominik, Martin

2010-08-13

380

THE EFFECT OF EXTERNAL AND INTERNAL FOSSIL CALIBRATIONS ON THE AVIAN EVOLUTIONARY TIMESCALE  

Microsoft Academic Search

Molecular clocks can provide insights into the evolutionary timescale of groups with unusually biased or fragmentary fossil records, such as birds. In those cases, it is advantageous to establish internal anchor points—molecular time estimates—using the best external fossil calibrations. In turn, those anchor points can be used as calibrations for more detailed time estimation within the group under study. This

MARCEL van TUINEN; S. BLAIR HEDGES

2004-01-01

381

Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic  

Microsoft Academic Search

Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous\\/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and

S. C. Cande; D. V. Kent

1995-01-01

382

Antarctic circumpolar transport and the southern mode: a model investigation of interannual to decadal timescales  

NASA Astrophysics Data System (ADS)

It is well-established that, at periods shorter than a year, variations in Antarctic circumpolar transport are reflected in a barotropic mode, known as the southern mode, in which sea level and bottom pressure varies coherently around Antarctica. Here, we use two multidecadal ocean model runs to investigate the behaviour of the southern mode at timescales on which density changes become important, leading to a baroclinic component to the adjustment. We find that the concept of a southern mode in bottom pressure remains valid, and remains a direct measure of the circumpolar transport, with changes at the northern boundary playing only a small role even on decadal timescales. However, at periods longer than about 5 years, density changes start to play a role, leading to a surface intensification of the vertical profile of the transport. We also find that barotropic currents on the continental slope account for a significant fraction of the variability, and produce surface intensification in the meridional-integral flow. Circumpolar sea level and transport are related at all investigated timescales. However, the role of density variations results in a ratio of sea level change to transport which becomes larger at longer timescales. This means that any long-term transport monitoring strategy based on present measurement systems must involve multiplying the observed quantity by a factor which depends on frequency.

Hughes, C. W.; Williams, Joanne; Coward, A. C.; de Cuevas, B. A.

2014-04-01

383

The Timescale Effects of Corporate Governance Measure on Predicting Financial Distress  

Microsoft Academic Search

This study aims to investigate the timescale effects of the corporate governance measure on predicting financial distress of corporations. A new corporate governance measure is adopted in the logistic regression model. Historical data of the companies listed on the Taiwan Stock Exchange Corporation (TSEC) were used in the empirical analysis. The analysis was based on three different prediction horizons comprising

Hsin-Hung Chen

2008-01-01

384

Automatic fault diagnosis of rotating machines by time-scale manifold ridge analysis  

NASA Astrophysics Data System (ADS)

This paper explores the improved time-scale representation by considering the non-linear property for effectively identifying rotating machine faults in the time-scale domain. A new time-scale signature, called time-scale manifold (TSM), is proposed in this study through combining phase space reconstruction (PSR), continuous wavelet transform (CWT), and manifold learning. For the TSM generation, an optimal scale band is selected to eliminate the influence of unconcerned scale components, and the noise in the selected band is suppressed by manifold learning to highlight the inherent non-linear structure of faulty impacts. The TSM reserves the non-stationary information and reveals the non-linear structure of the fault pattern, with the merits of noise suppression and resolution improvement. The TSM ridge is further extracted by seeking the ridge with energy concentration lying on the TSM signature. It inherits the advantages of both the TSM and ridge analysis, and hence is beneficial to demodulation of the fault information. Through analyzing the instantaneous amplitude (IA) of the TSM ridge, in which the noise is nearly not contained, the fault characteristic frequency can be exactly identified. The whole process of the proposed fault diagnosis scheme is automatic, and its effectiveness has been verified by means of typical faulty vibration/acoustic signals from a gearbox and bearings. A reliable performance of the new method is validated in comparison with traditional enveloping methods for rotating machine fault diagnosis.

Wang, Jun; He, Qingbo; Kong, Fanrang

2013-10-01

385

A new astronomical timescale for the loess deposits of Northern China  

Microsoft Academic Search

Here, we present a refined timescale for the entire sequence of Quaternary Chinese loess, which relies upon the correlation of detailed monsoon records to the astronomical solution of Laskar (1990) and the oceanic ODP677 ?18O record of Shackleton et al. (1990). The chronological scheme considers in detail the relative structures of the palaeoclimatic and palaeomagnetic records to produce an accurate

D. Heslop; C. G. Langereis; M. J. Dekkers

2000-01-01

386

TIMESCALE FOR CLIMATIC EVENTS OF SUBBOREAL\\/SUBATLANTIC TRANSITION RECORDED AT THE VALAKUPIAI SITE, LITHUANIA  

Microsoft Academic Search

Oxbow lake deposits of the Neris River at the Valakupiai site in Vilnius (Lithuania) have been studied by dif- ferent methods including radiocarbon dating. A timescale was attained for the development of the oxbow lake and climatic events recorded in the sediments. 14C dates obtained for 24 samples cover the range 990-6500 BP (AD 580 to 5600 BC). Medieval human

Jacek Pawlyta; Algirdas Gaigalas; Anna Pazdur; Aleksander Sanko

2007-01-01

387

North Atlantic Ocean control on surface heat flux on multidecadal timescales.  

PubMed

Nearly 50 years ago Bjerknes suggested that the character of large-scale air-sea interaction over the mid-latitude North Atlantic Ocean differs with timescales: the atmosphere was thought to drive directly most short-term--interannual--sea surface temperature (SST) variability, and the ocean to contribute significantly to long-term--multidecadal--SST and potentially atmospheric variability. Although the conjecture for short timescales is well accepted, understanding Atlantic multidecadal variability (AMV) of SST remains a challenge as a result of limited ocean observations. AMV is nonetheless of major socio-economic importance because it is linked to important climate phenomena such as Atlantic hurricane activity and Sahel rainfall, and it hinders the detection of anthropogenic signals in the North Atlantic sector. Direct evidence of the oceanic influence of AMV can only be provided by surface heat fluxes, the language of ocean-atmosphere communication. Here we provide observational evidence that in the mid-latitude North Atlantic and on timescales longer than 10 years, surface turbulent heat fluxes are indeed driven by the ocean and may force the atmosphere, whereas on shorter timescales the converse is true, thereby confirming the Bjerknes conjecture. This result, although strongest in boreal winter, is found in all seasons. Our findings suggest that the predictability of mid-latitude North Atlantic air-sea interaction could extend beyond the ocean to the climate of surrounding continents. PMID:23887431

Gulev, Sergey K; Latif, Mojib; Keenlyside, Noel; Park, Wonsun; Koltermann, Klaus Peter

2013-07-25

388

Optimal structured feedback policies for ABR flow control using two-timescale SPSA  

Microsoft Academic Search

Optimal structured feedback control policies for rate-based flow control of available bit rate service in asynchronous transfer mode networks are obtained in the presence of information and propagation delays, using a numerically efficient two-timescale simultaneous perturbation stochastic approximation algorithm. Models comprising both a single bottleneck node and a network with multiple bottleneck nodes are considered. A convergence analysis of the

Shalabh Bhatnagar; Michael C. Fu; Steven I. Marcus; Pedram J. Fard

2001-01-01

389

Application of markov state models to simulate long timescale dynamics of biological macromolecules.  

PubMed

Conformational changes of proteins are an*Author contributed equally with all other contributors. essential part of many biological processes such as: protein folding, ligand binding, signal transduction, allostery, and enzymatic catalysis. Molecular dynamics (MD) simulations can describe the dynamics of molecules at atomic detail, therefore providing a much higher temporal and spatial resolution than most experimental techniques. Although MD simulations have been widely applied to study protein dynamics, the timescales accessible by conventional MD methods are usually limited to timescales that are orders of magnitude shorter than the conformational changes relevant for most biological functions. During the past decades great effort has been devoted to the development of theoretical methods that may enhance the conformational sampling. In recent years, it has been shown that the statistical mechanics framework provided by discrete-state and -time Markov State Models (MSMs) can predict long timescale dynamics from a pool of short MD simulations. In this chapter we provide the readers an account of the basic theory and selected applications of MSMs. We will first introduce the general concepts behind MSMs, and then describe the existing procedures for the construction of MSMs. This will be followed by the discussions of the challenges of constructing and validating MSMs, Finally, we will employ two biologically-relevant systems, the RNA polymerase and the LAO-protein, to illustrate the application of Markov State Models to elucidate the molecular mechanisms of complex conformational changes at biologically relevant timescales. PMID:24446356

Da, Lin-Tai; Sheong, Fu Kit; Silva, Daniel-Adriano; Huang, Xuhui

2014-01-01

390

Improving the readability of time-frequency and time-scale representations by the reassignment method  

Microsoft Academic Search

In this paper, the use of the reassignment method, first applied by Kodera, Gendrin, and de Villedary (1976) to the spectrogram, is generalized to any bilinear time-frequency or time-scale distribution. This method creates a modified version of a representation by moving its values away from where they are computed, so as to produce a better localization of the signal components.

Franqois Auger; Patrick Flandrin

1995-01-01

391

Short time-scale \\/less than 2 hour\\/ wind variations observed with the Garchy meteor radar  

Microsoft Academic Search

The good altitude definition and the great abundance of wind data (up to 1200 individual measurements per day) given by the Garchy meteor radar facility yield a good opportunity to study short time-scale motions (periods less than 2 hours) in the 80-100 km altitude region. A statistical study of the differences between zonal wind values measured at close points in

J. L. Fellous; M. Glass

1976-01-01

392

Short time-scale X-ray variability of Active Galactic Nuclei  

Microsoft Academic Search

In this work we investigated the short time-scale variability of NGC 4051 and NGC 4388. A quasi-steady QPO of 3922±17 sec was detected for NGC 4051. For NGC 4388, we investigated the rapid spectral variability with a new “Moving Fit” method for processing of the dynamic X-ray spectra.

Alexander V. Halevin

2004-01-01

393

Short time-scale heating of the Earth's mantle by ice-sheet dynamics  

Microsoft Academic Search

We have studied the possibility of short time-scale energy transfer from the ice sheet loading and unloading processes to the Earth's interior via viscous dissipation associated with the transient viscoelastic flow in the mantle. We have focussed on the magnitude of glacially induced deformations and the corresponding shear heating for an ice sheet of the spatial extent of Laurentide region

Ladislav Hanyk; Ctirad Matyska; D. A. Yuen

2005-01-01

394

Fluid and Kinetic Modelling on Timescales Longer than the Confinement Time in Bounded Systems  

SciTech Connect

The problem of fluid modelling on timescales longer than the confinement time is addressed as a problem of decay of high order moments without sources. Several mechanisms for the decay of higher order moments are discussed and very strong experimental evidence is given for toroidal plasmas.

Weiland, Jan [Chalmers University of Technology and EURATOM-VR Association, Gothenburg (Sweden); Zagorodny, Anatoly; Zasenko, Volodymyr [Bogoliubov Institute for Theoretical Physics, Kiev (Ukraine)

2009-10-08

395

Integrated Isotopic Dating and Geospeedometry: Timescales of Rhyolite Rejuvenation and Crystallization at Yellowstone  

NASA Astrophysics Data System (ADS)

Two techniques have been primarily used to quantify the timescales associated with the evolution and residence of voluminous rhyolitic magmas: 1) isotopic dating, especially using U-Th-Pb dating of accessory minerals, and 2) "geospeedometry" using the diffusional relaxation of intra-crystal zoning of trace element or isotope composition. These methods can resolve different aspects magma evolution over short and long timescales, yet few studies have combined both. To evaluate the timescales associated with crystallization, storage, and rejuvenation of rhyolitic magma at Yellowstone caldera, we have applied ion microprobe 238U-230Th dating of zircon and geospeedometry using zoned sanidine and pyroxene phenocrysts from the ~260 ka Scaup Lake flow (SLF). The SLF is one of the youngest and most-evolved lavas of the Upper Basin Member, rhyolites which mainly erupted 100 kyr after the 0.6 Ma caldera-forming Lava Creek Tuff, and well before the effusion of the voluminous Central Plateau Member lavas between 170 and 70 ka. SLF zircons yield a 230Th-corrected U-Pb age of 312±45 ka (2?, n=19, MSWD=2.7), suggesting magma generation on the order of 104-105 years before eruption. Most SLF sanidines have significant intra-crystal zoning with multiple resorption surfaces and rims with relatively high Ba and Sr concentrations. Clinopyroxene cores contain exsolution lamellae and are overgrown by inclusion-free rims. Quartz phenocrysts have rims with higher Ti concentrations than their cores. These petrographic observations suggest recycling of subsolidus residue from earlier intrusions and renewed crystallization in new and hotter melt. Diffusion profiles for trace elements across resorption boundaries near sanidine cores yield timescales on the order of 103-104 years, assuming temperatures of 850° C. Profiles across near-rim boundaries suggest insignificant diffusion and that rims formed immediately prior to eruption. Timescales from Fe-Mg diffusion between clinopyroxene cores and rims are similar to those from sanidine. Application of both isotopic dating and geospeedometry to SLF minerals yields timescales over several orders of magnitude, which reflect different aspects of magma evolution. The ages of SLF zircons are likely to reflect a mixture of recycled crystal residue and renewed crystallization. Contrasting timescales from geospeedometry are dependent on petrographic context and reflect different evolutionary "milestones" in the chronology of the SLF magma.

Vazquez, J. A.; Boyce, J. W.; Kyriazis, S. F.; Reid, M. R.

2008-12-01

396

Echoing Citizen Einstein in the East: Andrei Sakharov  

NASA Astrophysics Data System (ADS)

As if a handing of the torch, Andrei Sakharov saw his dissidence acquire initial impetus from nuclear tests that it was clear were becoming out of control in the hands of an unscrupulous regime in 1955, the very year Einstein died. He had of course drawn from the latter's science for the realization of the Soviet H-bomb. From then on, however, it would be the humanistic views of Einstein that would lead his way. Not only was he not an anti-Semite like many in official circles in the Soviet Union at the time but through experiences in his young age and later in his work on the bomb where he had many Jewish colleagues, Sakharov had come to admire Jewish culture and particularly its inclination towards intellectual life. It was with a fully open mind then that he got acquainted with Einstein's ideas on how the great man saw the world. Sakharov would divulge his own vision of the world in an essay titled ``Progress, Peaceful Coexistence and Intellectual Freedom'' in 1968. The Albert Einstein Peace Prize he would be awarded in 1988 for his relentless advocacy of peace would come as a confirmation of the spiritual linkage between the two men. This paper scrutinizes traces of Einstein's thinking in Sakharov's own. It focuses particularly on their convergent understanding of the notion of world government.

Rhéaume, Charles

2006-11-01

397

The Deep Lens Survey Transient Search. I. Short Timescale and Astrometric Variability  

NASA Astrophysics Data System (ADS)

We report on the methodology and first results from the Deep Lens Survey (DLS) transient search. We utilize image subtraction on survey data to yield all sources of optical variability down to 24th magnitude. Images are analyzed immediately after acquisition, at the telescope, and in near-real time, to allow for follow-up in the case of time-critical events. All classes of transients are posted to the World Wide Web upon detection. Our observing strategy allows sensitivity to variability over several decades in timescale. The DLS is the first survey to classify and report all types of photometric and astrometric variability detected, including solar system objects, variable stars, supernovae, and short timescale phenomena. Three unusual optical transient (OT) events were detected, flaring on 1000 s timescales. All three events were seen in the B passband, suggesting blue color indices for the phenomena. One event (OT 20020115) is determined to be from a flaring Galactic dwarf star of spectral type dM4. From the remaining two events, we find an overall rate of ?=1.4 events deg-2 day-1 on 1000 s timescales, with a 95% confidence limit of ?<4.3. One of these events (OT 20010326) originated from a compact precursor in the field of galaxy cluster A1836, and its nature is uncertain. For the second (OT 20030305) we find strong evidence for an extended extragalactic host. A dearth of such events in the R passband yields an upper 95% confidence limit on short-timescale astronomical variability in the range 19.5

Becker, A. C.; Wittman, D. M.; Boeshaar, P. C.; Clocchiatti, A.; Dell'Antonio, I. P.; Frail, D. A.; Halpern, J.; Margoniner, V. E.; Norman, D.; Tyson, J. A.; Schommer, R. A.

2004-08-01

398

Bose-Einstein Condensation of Magnons in Superfluid 3He  

NASA Astrophysics Data System (ADS)

The possibility of Bose-Einstein condensation of excitations has been discussed for a long time. The phenomenon of the phase-coherent precession of magnetization in superfluid 3He and the related effects of spin superfluidity are based on the true Bose-Einstein condensation of magnons. Several different states of coherent precession has been observed in 3He-B: homogeneously precessing domain (HPD); persistent signal formed by Q-balls at very low temperatures; coherent precession with fractional magnetization; and a mode of the coherent precession in compressed aerogel. The coherent precession has been also found in 3He-A in compressed aerogel. Here we demonstrate that all these cases are examples of a Bose-Einstein condensation of magnons, with the magnon interaction term in the Gross-Pitaevskii equation being provided by different types of spin-orbit coupling in the background of the coherent precession.

Bunkov, Yuriy M.; Volovik, Grigory E.

2008-02-01

399

Bose-Einstein correlations in W-pair decays  

NASA Astrophysics Data System (ADS)

Bose-Einstein correlations are studied in semileptonic (WW-->qq¯l?) and fully hadronic (WW-->qq¯qq¯) W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189 GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einstein correlations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW-->qq¯l? events. The same Monte Carlo reproduces the correlations in the WW-->qq¯qq¯ channel assuming independent fragmentation of the two W's. A variant of this model with Bose-Einstein correlations between decay products of different W's is disfavoured.

Barate, R.; Decamp, D.; Ghez, P.; Goy, C.; Jezequel, S.; Lees, J.-P.; Martin, F.; Merle, E.; Minard, M.-N.; Pietrzyk, B.; Alemany, R.; Bravo, S.; Casado, M. P.; Chmeissani, M.; Crespo, J. M.; Fernandez, E.; Fernandez-Bosman, M.; Garrido, L.; Graugés, E.; Juste, A.; Martinez, M.; Merino, G.; Miquel, R.; Mir, L. M.; Morawitz, P.; Pacheco, A.; Riu, I.; Ruiz, H.; Colaleo, A.; Creanza, D.; de Palma, M.; Iaselli, G.; Maggi, G.; Maggi, M.; Nuzzo, S.; Ranieri, A.; Raso, G.; Ruggieri, F.; Selvaggi, G.; Silvestris, L.; Tempesta, P.; Tricomi, A.; Zito, G.; Huang, X.; Lin, J.; Ouyang, Q.; Wang, T.; Xie, Y.; Xu, R.; Xue, S.; Zhang, J.; Zhang, L.; Zhao, W.; Abbaneo, D.; Boix, G.; Buchmüller, O.; Cattaneo, M.; Cerutti, F.; Ciulli, V.; Davies, G.; Dissertori, G.; Drevermann, H.; Forty, R. W.; Frank, M.; Gianotti, F.; Greening, T. C.; Halley, A. W.; Hansen, J. B.; Harvey, J.; Janot, P.; Jost, B.; Kado, M.; Leroy, O.; Maley, P.; Mato, P.; Minten, A.; Moutoussi, A.; Ranjard, F.; Rolandi, L.; Schlatter, D.; Schmitt, M.; Schneider, O.; Spagnolo, P.; Tejessy, W.; Teubert, F.; Tournefier, E.; Valassi, A.; Wright, A. E.; Ajaltouni, Z.; Badaud, F.; Chazelle, G.; Deschamps, O.; Dessagne, S.; Falvard, A.; Ferdi, C.; Gay, P.; Guicheney, C.; Henrard, P.; Jousset, J.; Michel, B.; Monteil, S.; Montret, J.-C.; Pallin, D.; Pascolo, J. M.; Perret, P.; Podlyski, F.; Hansen, J. D.; Hansen, J. R.; Hansen, P. H.; Nilsson, B. S.; Rensch, B.; Wäänänen, A.; Daskalakis, G.; Kyriakis, A.; Markou, C.; Simopoulou, E.; Vayaki, A.; Blondel, A.; Brient, J.-C.; Machefert, F.; Rougé, A.; Swynghedauw, M.; Tanaka, R.; Videau, H.; Focardi, E.; Parrini, G.; Zachariadou, K.; Corden, M.; Georgiopoulos, C.; Antonelli, A.; Bencivenni, G.; Bologna, G.; Bossi, F.; Campana, P.; Capon, G.; Chiarella, V.; Laurelli, P.; Mannocchi, G.; Murtas, F.; Murtas, G. P.; Passalacqua, L.; Pepe-Altarelli, M.; Chalmers, M.; Kennedy, J.; Lynch, J. G.; Negus, P.; O'Shea, V.; Raeven, B.; Smith, D.; Teixeira-Dias, P.; Thompson, A. S.; Ward, J. J.; Cavanaugh, R.; Dhamotharan, S.; Geweniger, C.; Hanke, P.; Hepp, V.; Kluge, E. E.; Leibenguth, G.; Putzer, A.; Tittel, K.; Werner, S.; Wunsch, M.; Beuselinck, R.; Binnie, D. M.; Cameron, W.; Dornan, P. J.; Girone, M.; Goodsir, S.; Marinelli, N.; Martin, E. B.; Nash, J.; Nowell, J.; Przysiezniak, H.; Sciabà, A.; Sedgbeer, J. K.; Thompson, J. C.; Thomson, E.; Williams, M. D.; Ghete, V. M.; Girtler, P.; Kneringer, E.; Kuhn, D.; Rudolph, G.; Bowdery, C. K.; Buck, P. G.; Ellis, G.; Finch, A. J.; Foster, F.; Hughes, G.; Jones, R. W. L.; Robertson, N. A.; Smizanska, M.; Williams, M. I.; Giehl, I.; Hölldorfer, F.; Jakobs, K.; Kleinknecht, K.; Kröcker, M.; Müller, A.-S.; Nürnberger, H.-A.; Quast, G.; Renk, B.; Rohne, E.; Sander, H.-G.; Schmeling, S.; Wachsmuth, H.; Zeitnitz, C.; Ziegler, T.; Bonissent, A.; Carr, J.; Coyle, P.; Ealet, A.; Fouchez, D.; Payre, P.; Rousseau, D.; Tilquin, A.; Aleppo, M.; Antonelli, M.; Gilardoni, S.; Ragusa, F.; Büscher, V.; Dietl, H.; Ganis, G.; Hüttmann, K.; Lütjens, G.; Mannert, C.; Männer, W.; Moser, H.-G.; Schael, S.; Settles, R.; Seywerd, H.; Stenzel, H.; Wiedenmann, W.; Wolf, G.; Azzurri, P.; Boucrot, J.; Callot, O.; Chen, S.; Davier, M.; Duflot, L.; Grivaz, J.-F.; Heusse, P.; Jacholkowska, A.; Lefrançois, J.; Serin, L.; Veillet, J.-J.; Videau, I.; de Vivie de Régie, J.-B.; Zerwas, D.; Bagliesi, G.; Boccali, T.; Bozzi, C.; Calderini, G.; Dell'Orso, R.; Ferrante, I.; Giassi, A.; Gregorio, A.; Ligabue, F.; Marrocchesi, P. S.; Messineo, A.; Palla, F.; Rizzo, G.; Sanguinetti, G.; Sguazzoni, G.; Tenchini, R.; Venturi, A.; Verdini, P. G.; Blair, G. A.; Coles, J.; Cowan, G.; Green, M. G.; Hutchcroft, D. E.; Jones, L. T.; Medcalf, T.; Strong, J. A.; Botterill, D. R.; Clifft, R. W.; Edgecock, T. R.; Norton, P. R.; Tomalin, I. R.; Bloch-Devaux, B.; Colas, P.; Fabbro, B.; Faïf, G.; Lançon, E.; Lemaire, M.-C.; Locci, E.; Perez, P.; Rander, J.; Renardy, J.-F.; Rosowsky, A.; Seager, P.; Trabelsi, A.; Tuchming, B.; Vallage, B.; Black, S. N.; Dann, J. H.; Loomis, C.; Kim, H. Y.; Konstantinidis, N.; Litke, A. M.; McNeil, M. A.; Taylor, G.; Booth, C. N.; Cartwright, S.; Combley, F.; Hodgson, P. N.; Lehto, M.; Thompson, L. F.; Affholderbach, K.; Böhrer, A.; Brandt, S.; Grupen, C.; Hess, J.; Misiejuk, A.; Prange, G.; Sieler, U.; Borean, C.; Giannini, G.; Gobbo, B.; Putz, J.; Rothberg, J.; Wasserbaech, S.; Williams, R. W.; Armstrong, S. R.; Elmer, P.; Ferguson, D. P. S.; Gao, Y.; González, S.; Hayes, O. J.; Hu, H.; Jin, S.; Kile, J.; McNamara, P. A., III; Nielsen, J.; Orejudos, W.; Pan, Y. B.; Saadi, Y.; Scott, I. J.; Walsh, J.; von Wimmersperg-Toeller, J. H.; Wu, S. L.; Wu, X.; Zobernig, G.

2000-04-01

400

Radiating black hole solutions in Einstein-Gauss-Bonnet gravity  

SciTech Connect

In this paper, we find some new exact solutions to the Einstein-Gauss-Bonnet equations. First, we prove a theorem which allows us to find a large family of solutions to the Einstein-Gauss-Bonnet gravity in n-dimensions. This family of solutions represents dynamic black holes and contains, as particular cases, not only the recently found Vaidya-Einstein-Gauss-Bonnet black hole, but also other physical solutions that we think are new, such as the Gauss-Bonnet versions of the Bonnor-Vaidya (de Sitter/anti-de Sitter) solution, a global monopole, and the Husain black holes. We also present a more general version of this theorem in which less restrictive conditions on the energy-momentum tensor are imposed. As an application of this theorem, we present the exact solution describing a black hole radiating a charged null fluid in a Born-Infeld nonlinear electrodynamics.

Dominguez, Alfredo E. [FaMAF, Ciudad Universitaria, Universidad Nacional de Cordoba (5000), Cordoba (Argentina); Instituto Universitario Aeronautico, Avenida Fuerza Aerea km 6.5. (5000), Cordoba (Argentina); Gallo, Emanuel [FaMAF, Ciudad Universitaria, Universidad Nacional de Cordoba (5000), Cordoba (Argentina)

2006-03-15

401

Einstein-Podolsky-Rosen argument and Bell inequalities for Bose-Einstein spin condensates  

SciTech Connect

We discuss the properties of two Bose-Einstein condensates in different spin states, represented quantum mechanically by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions (perpendicular to the spin quantization axis), giving access to the relative phase of the two macroscopically occupied states. Before the first spin measurement, the phase is completely undetermined; after a few measurements, a more and more precise knowledge of its value emerges under the effect of the quantum measurement process. This naturally leads to the usual notion of a quasiclassical phase (Anderson phase) and to an interesting transposition of the Einstein-Podolsky-Rosen argument to macroscopic physical quantities. The purpose of this paper is to discuss this transposition, as well as situations where the notion of a quasiclassical phase is no longer sufficient to account for the quantum results, and where significant violations of Bell-type inequalities are predicted. Quantum mechanically, the problem can be treated exactly: the probability for all sequences of results can be expressed in the form of a double integral, depending on all parameters that define the experiment (number of particles, number and angles of measurements). We discuss the differences between this case and the usual two-spin case. We discuss the effect of the many parameters that the experimenters can adjust for their measurements, starting with a discussion of the effect of the angles of measurement (the 'settings'), and then envisaging various choices of the functions that are used to obtain violation of Bell-Clauser-Horne-Shimony-Holt inequalities. We then discuss how the 'sample bias loophole' (often also called 'efficiency loophole') can be closed in this case, by introducing a preliminary sequence of measurements to localize the particles into 'measurement boxes'. We finally show that the same nonlocal effects can be observed with distinguishable spins.

Laloee, F. [Laboratoire Kastler Brossel, Ecole Normale Superieure, Universite Pierre et Marie Curie, CNRS, 24 rue Lhomond, 75005 Paris (France); Mullin, W. J. [Department of Physics, University of Massachusetts, Amherst, Massachusetts 01003 (United States)

2008-02-15

402

The Stokes-Einstein relation at moderate Schmidt number.  

PubMed

The Stokes-Einstein relation for the self-diffusion coefficient of a spherical particle suspended in an incompressible fluid is an asymptotic result in the limit of large Schmidt number, that is, when momentum diffuses much faster than the particle. When the Schmidt number is moderate, which happens in most particle methods for hydrodynamics, deviations from the Stokes-Einstein prediction are expected. We study these corrections computationally using a recently developed minimally resolved method for coupling particles to an incompressible fluctuating fluid in both two and three dimensions. We find that for moderate Schmidt numbers the diffusion coefficient is reduced relative to the Stokes-Einstein prediction by an amount inversely proportional to the Schmidt number in both two and three dimensions. We find, however, that the Einstein formula is obeyed at all Schmidt numbers, consistent with linear response theory. The mismatch arises because thermal fluctuations affect the drag coefficient for a particle due to the nonlinear nature of the fluid-particle coupling. The numerical data are in good agreement with an approximate self-consistent theory, which can be used to estimate finite-Schmidt number corrections in a variety of methods. Our results indicate that the corrections to the Stokes-Einstein formula come primarily from the fact that the particle itself diffuses together with the momentum. Our study separates effects coming from corrections to no-slip hydrodynamics from those of finite separation of time scales, allowing for a better understanding of widely observed deviations from the Stokes-Einstein prediction in particle methods such as molecular dynamics. PMID:24320370

Balboa Usabiaga, Florencio; Xie, Xiaoyi; Delgado-Buscalioni, Rafael; Donev, Aleksandar

2013-12-01

403

The Stokes-Einstein relation at moderate Schmidt number  

NASA Astrophysics Data System (ADS)

The Stokes-Einstein relation for the self-diffusion coefficient of a spherical particle suspended in an incompressible fluid is an asymptotic result in the limit of large Schmidt number, that is, when momentum diffuses much faster than the particle. When the Schmidt number is moderate, which happens in most particle methods for hydrodynamics, deviations from the Stokes-Einstein prediction are expected. We study these corrections computationally using a recently developed minimally resolved method for coupling particles to an incompressible fluctuating fluid in both two and three dimensions. We find that for moderate Schmidt numbers the diffusion coefficient is reduced relative to the Stokes-Einstein prediction by an amount inversely proportional to the Schmidt number in both two and three dimensions. We find, however, that the Einstein formula is obeyed at all Schmidt numbers, consistent with linear response theory. The mismatch arises because thermal fluctuations affect the drag coefficient for a particle due to the nonlinear nature of the fluid-particle coupling. The numerical data are in good agreement with an approximate self-consistent theory, which can be used to estimate finite-Schmidt number corrections in a variety of methods. Our results indicate that the corrections to the Stokes-Einstein formula come primarily from the fact that the particle itself diffuses together with the momentum. Our study separates effects coming from corrections to no-slip hydrodynamics from those of finite separation of time scales, allowing for a better understanding of widely observed deviations from the Stokes-Einstein prediction in particle methods such as molecular dynamics.

Balboa Usabiaga, Florencio; Xie, Xiaoyi; Delgado-Buscalioni, Rafael; Donev, Aleksandar

2013-12-01

404

Obstructions to the Existence of Sasaki-Einstein Metrics  

NASA Astrophysics Data System (ADS)

We describe two simple obstructions to the existence of Ricci-flat Kähler cone metrics on isolated Gorenstein singularities or, equivalently, to the existence of Sasaki-Einstein metrics on the links of these singularities. In particular, this also leads to new obstructions for Kähler-Einstein metrics on Fano orbifolds. We present several families of hypersurface singularities that are obstructed, including 3-fold and 4-fold singularities of ADE type that have been studied previously in the physics literature. We show that the AdS/CFT dual of one obstruction is that the R-charge of a gauge invariant chiral primary operator violates the unitarity bound.

Gauntlett, Jerome P.; Martelli, Dario; Sparks, James; Yau, Shing-Tung

2007-08-01

405

Einstein–Weyl geometry, dispersionless Hirota equation and Veronese webs  

NASA Astrophysics Data System (ADS)

We exploit the correspondence between the three-dimensional Lorentzian Einstein-Weyl geometries of the hyper-CR type, and the Veronese webs to show that the former structures are locally given in terms of solutions to the dispersionless Hirota equation. We also demonstrate how to construct hyper-CR Einstein--Weyl structures by Kodaira deformations of the flat twistor space $T\\CP^1$, and how to recover the pencil of Poisson structures in five dimensions illustrating the method by an example of the Veronese web on the Heisenberg group.

Dunajski, Maciej; Kry?ski, Wojciech

2014-07-01

406

No-go theorem for ergodicity and an Einstein relation  

NASA Astrophysics Data System (ADS)

We provide a simple no-go theorem for ergodicity and the generalized Einstein relation for anomalous diffusion processes. The theorem states that either ergodicity in the sense of equal time and ensemble averaged mean squared displacements (MSD) is broken, and/or the generalized Einstein relation for time averaged diffusivity and mobility is invalid, which is in complete contrast to normal diffusion processes. We also give a general relation for the time averages of drift and MSD for ergodic (in the MSD sense) anomalous diffusion processes, showing that the ratio of these quantities depends on the measurement time. The Lévy walk model is used to exemplify the no-go theorem.

Froemberg, D.; Barkai, E.

2013-08-01

407

Bose-Einstein condensates in optical quasicrystal lattices  

SciTech Connect

We analyze the physics of Bose-Einstein condensates confined in two dimensional (2D) quasiperiodic optical lattices, which offer an intermediate situation between ordered and disordered systems. First, we analyze the time-of-flight interference pattern that reveals quasiperiodic long-range order. Second, we demonstrate localization effects associated with quasidisorder as well as quasiperiodic Bloch oscillations associated with the extended nature of the wave function of a Bose-Einstein condensate in an optical quasicrystal. In addition, we discuss in detail the crossover between diffusive and localized regimes when the quasiperiodic potential is switched on, as well as the effects of interaction000.

Sanchez-Palencia, L. [Laboratoire Charles Fabry, Institut d'Optique, Universite Paris-Sud XI, F-91403 Orsay (France); Institut fuer Theoretische Physik, Universitaet Hannover, D-30167 Hannover (Germany); Santos, L. [Institut fuer Theoretische Physik III, Universitaet Stuttgart, D-70569 Stuttgart (Germany)

2005-11-15

408

Einstein, the Universe, and All That: An Introduction to Relativity  

NASA Technical Reports Server (NTRS)

Black holes) an expanding universe) space and time inextricably tied together) GPS ... What was this Einstein guy thinking?!? In this tutorial) I'll give an overview of Einstein's theories of relativity and the wild things they say about our Universe. What really happens when a particle crosses an event horizon? What is the future of the Universe? And how can we know it? Wh I'll try to touch on these questions and in so doing) give the talks in the Cosmology) Gravitation and Relativity sessions some context.

Prescod-Weinstein, Chandra

2011-01-01

409

Modeling Bose-Einstein correlations via elementary emitting cells  

SciTech Connect

We propose a method of numerical modeling Bose-Einstein correlations by using the notion of the elementary emitting cell (EEC). They are intermediary objects containing identical bosons and are supposed to be produced independently during the hadronization process. Only bosons in the EEC, which represents a single quantum state here, are subjected to the effects of Bose-Einstein (BE) statistics, which forces them to follow a geometrical distribution. There are no such effects between particles from different EECs. We illustrate our proposition by calculating a representative number of typical distributions and discussing their sensitivity to EECs and their characteristics.

Utyuzh, Oleg; Wilk, Grzegorz; Wlodarczyk, Zbigniew [Andrzej Soltan Institute for Nuclear Studies, Hoza 69, 00-681 Warsaw (Poland); Institute of Physics, Swietokrzyska Academy, Swietokrzyska 15, 25-405 Kielce (Poland)

2007-04-01

410

Black hole stability in Jordan and Einstein frames  

NASA Astrophysics Data System (ADS)

We investigate the classical stability of Schwarzschild black hole in Jordan and Einstein frames that are related by the conformal transformations. For this purpose, we introduce two models of the Brans-Dicke theory and Brans-Dicke-Weyl gravity in the Jordan frame and two corresponding models in the Einstein frame. The former model is suitable for studying the massless spin-2 graviton propagating around the Schwarzschild black hole, while the latter is designed for the massive spin-2 graviton propagating around the black hole. It turns out that the black hole (in)stability is independent of the frame which shows that the two frames are equivalent to each other.

Myung, Yun Soo; Moon, Taeyoon

2014-05-01

411

Bose-Einstein condensation of excitons in Cu2O  

Microsoft Academic Search

We present a parameter-free model which estimates the density of excitons in\\u000aCu$_2$O, related to experiments that have tried to create an excitonic\\u000aBose-Einstein condensate. Our study demonstrates that the triplet-state\\u000aexcitons move along adiabats and obey classical statistics, while the\\u000asinglet-state excitons are a possible candidate for forming a Bose-Einstein\\u000acondensate. Finally we show that the results of this

G. M. Kavoulakis

2001-01-01

412

The cerebral cortex of Albert Einstein: a description and preliminary analysis of unpublished photographs  

PubMed Central

Upon his death in 1955, Albert Einstein’s brain was removed, fixed and photographed from multiple angles. It was then sectioned into 240 blocks, and histological slides were prepared. At the time, a roadmap was drawn that illustrates the location within the brain of each block and its associated slides. Here we describe the external gross neuroanatomy of Einstein’s entire cerebral cortex from 14 recently discovered photographs, most of which were taken from unconventional angles. Two of the photographs reveal sulcal patterns of the medial surfaces of the hemispheres, and another shows the neuroanatomy of the right (exposed) insula. Most of Einstein’s sulci are identified, and sulcal patterns in various parts of the brain are compared with those of 85 human brains that have been described in the literature. To the extent currently possible, unusual features of Einstein’s brain are tentatively interpreted in light of what is known about the evolution of higher cognitive processes in humans. As an aid to future investigators, these (and other) features are correlated with blocks on the roadmap (and therefore histological slides). Einstein’s brain has an extraordinary prefrontal cortex, which may have contributed to the neurological substrates for some of his remarkable cognitive abilities. The primary somatosensory and motor cortices near the regions that typically represent face and tongue are greatly expanded in the left hemisphere. Einstein’s parietal lobes are also unusual and may have provided some of the neurological underpinnings for his visuospatial and mathematical skills, as others have hypothesized. Einstein’s brain has typical frontal and occipital shape asymmetries (petalias) and grossly asymmetrical inferior and superior parietal lobules. Contrary to the literature, Einstein’s brain is not spherical, does not lack parietal opercula and has non-confluent Sylvian and inferior postcentral sulci.

Lepore, Frederick E.; Noe, Adrianne

2013-01-01

413

On the local structure of Lorentzian Einstein manifolds with parallel distribution of null lines  

NASA Astrophysics Data System (ADS)

We study transformations of coordinates on a Lorentzian Einstein manifold with a parallel distribution of null lines and show that the general Walker coordinates can be simplified. In these coordinates, the full Lorentzian Einstein equation is reduced to equations on a family of Einstein Riemannian metrics. Dedicated to Dmitri Vladimirovich Alekseevsky on his 70th birthday.

Galaev, Anton S.; Leistner, Thomas

2010-11-01

414

Fission time-scale in experiments and in multiple initiation model  

SciTech Connect

Rate of fission for highly-excited nuclei is affected by the viscose character of the systemmotion in deformation coordinates as was reported for very heavy nuclei with Z{sub C} > 90. The long time-scale of fission can be described in a model of 'fission by diffusion' that includes an assumption of the overdamped diabatic motion. The fission-to-spallation ratio at intermediate proton energy could be influenced by the viscosity, as well. Within a novel approach of the present work, the cross examination of the fission probability, time-scales, and pre-fission neutron multiplicities is resulted in the consistent interpretation of a whole set of the observables. Earlier, different aspects could be reproduced in partial simulations without careful coordination.

Karamian, S. A., E-mail: karamian@nrmail.jinr.ru [Joint Institute for Nuclear Research (Russian Federation)

2011-12-15

415

Intrinsic dynamics of heart regulatory systems on short timescales: from experiment to modelling  

NASA Astrophysics Data System (ADS)

We discuss open problems related to the stochastic modelling of cardiac function. The work is based on an experimental investigation of the dynamics of heart rate variability (HRV) in the absence of respiratory perturbations. We consider first the cardiac control system on short timescales via an analysis of HRV within the framework of a random walk approach. Our experiments show that HRV on timescales of less than a minute takes the form of free diffusion, close to Brownian motion, which can be described as a non-stationary process with stationary increments. Secondly, we consider the inverse problem of modelling the state of the control system so as to reproduce the experimentally observed HRV statistics of. We discuss some simple toy models and identify open problems for the modelling of heart dynamics.

Khovanov, I. A.; Khovanova, N. A.; McClintock, P. V. E.; Stefanovska, A.

2009-01-01

416

Slow Cortical Dynamics and the Accumulation of Information over Long Timescales  

PubMed Central

SUMMARY Making sense of the world requires us to process information over multiple timescales. We sought to identify brain regions that accumulate information over short and long timescales and to characterize the distinguishing features of their dynamics. We recorded electrocorticographic (ECoG) signals from individuals watching intact and scrambled movies. Within sensory regions, fluctuations of high-frequency (64–200 Hz) power reliably tracked instantaneous low-level properties of the intact and scrambled movies. Within higher order regions, the power fluctuations were more reliable for the intact movie than the scrambled movie, indicating that these regions accumulate information over relatively long time periods (several seconds or longer). Slow (<0.1 Hz) fluctuations of high-frequency power with time courses locked to the movies were observed throughout the cortex. Slow fluctuations were relatively larger in regions that accumulated information over longer time periods, suggesting a connection between slow neuronal population dynamics and temporally extended information processing.

Honey, Christopher J.; Thesen, Thomas; Donner, Tobias H.; Silbert, Lauren J.; Carlson, Chad E.; Devinsky, Orrin; Doyle, Werner K.; Rubin, Nava; Heeger, David J.; Hasson, Uri

2012-01-01

417

Protein robustness promotes evolutionary innovations on large evolutionary time-scales  

PubMed Central

Recent laboratory experiments suggest that a molecule's ability to evolve neutrally is important for its ability to generate evolutionary innovations. In contrast to laboratory experiments, life unfolds on time-scales of billions of years. Here, we ask whether a molecule's ability to evolve neutrally—a measure of its robustness—facilitates evolutionary innovation also on these large time-scales. To this end, we use protein designability, the number of sequences that can adopt a given protein structure, as an estimate of the structure's ability to evolve neutrally. Based on two complementary measures of functional diversity—catalytic diversity and molecular functional diversity in gene ontology—we show that more robust proteins have a greater capacity to produce functional innovations. Significant associations among structural designability, folding rate and intrinsic disorder also exist, underlining the complex relationship of the structural factors that affect protein evolution.

Ferrada, Evandro; Wagner, Andreas

2008-01-01

418

Timescales of Coherent Dynamics in the Light Harvesting Complex 2 (LH2) of Rhodobacter sphaeroides  

PubMed Central

The initial dynamics of energy transfer in the light harvesting complex 2 from Rhodobacter sphaeroides were investigated with polarization controlled two-dimensional spectroscopy. This method allows only the coherent electronic motions to be observed revealing the timescale of dephasing among the excited states. We observe persistent coherence among all states and assign ensemble dephasing rates for the various coherences. A simple model is utilized to connect the spectroscopic transitions to the molecular structure, allowing us to distinguish coherences between the two rings of chromophores and coherences within the rings. We also compare dephasing rates between excited states to dephasing rates between the ground and excited states, revealing that the coherences between excited states dephase on a slower timescale than coherences between the ground and excited states.

Fidler, Andrew F.; Singh, Ved P.; Long, Phillip D.; Dahlberg, Peter D.; Engel, Gregory S.

2013-01-01

419

Decade time-scale modulation of low-mass X-ray binaries  

NASA Astrophysics Data System (ADS)

Regular observations by the All-Sky Monitor aboard the Rossi X-ray Timing Explorer satellite have yielded well-sampled light curves with a time baseline of over 10 years. We find that up to eight of the 16 brightest persistent low-mass X-ray binaries (LMXBs) show significant, possible sinusoidal, variations with periods of the order of 10 years. We speculate on its possible origin and prevalence in the population of LMXBs, and we find the presence of a third object in the system, or long-period variability intrinsic to the donor star, as being attractive origins for the X-ray flux modulation we detect. For some of the objects in which we do not detect a signal, there is substantial short-term variation which may hide modest modulation on long time-scales. Decade time-scale modulations may thus be even more common.

Durant, Martin; Cornelisse, Remon; Remillard, Ron; Levine, Alan

2010-01-01

420

North-South precipitation patterns in western North America on interannual-to-decadal timescales  

USGS Publications Warehouse

The overall amount of precipitation deposited along the West Coast and western cordillera of North America from 25??to 55??N varies from year to year, and superimposed on this domain-average variability are varying north-south contrasts on timescales from at least interannual to interdecadal. In order to better understand the north-south precipitation contrasts, their interannual and decadal variations are studied in terms of how much they affect overall precipitation amounts and how they are related to large-scale climatic patterns. Spatial empirical orthogonal functions (EOFs) and spatial moments (domain average, central latitude, and latitudinal spread) of zonally averaged precipitation anomalies along the westernmost parts of North America are analyzed, and each is correlated with global sea level pressure (SLP) and sea surface temperature series, on interannual (defined here as 3-7 yr) and decadal (>7 yr) timescales. The interannual band considered here corresponds to timescales that are particularly strong in tropical climate variations and thus is expected to contain much precipitation variability that is related to El Nino-Southern Oscillation; the decadal scale is defined so as to capture the whole range of long-term climatic variations affecting western North America. Zonal EOFs of the interannual and decadal filtered versions of the zonal-precipitation series are remarkably similar. At both timescales, two leading EOFs describe 1) a north-south seesaw of precipitation pivoting near 40??N and 2) variations in precipitation near 40??N, respectively. The amount of overall precipitation variability is only about 10% of the mean and is largely determined by precipitation variations around 40??-45??N and most consistently influenced by nearby circulation patterns; in this sense, domain-average precipitation is closely related to the second EOF. The central latitude and latitudinal spread of precipitation distributions are strongly influenced by precipitation variations in the southern parts of western North America and are closely related to the first EOF. Central latitude of precipitation moves south (north) with tropical warming (cooling) in association with midlatitude western Pacific SLP variations, on both interannual and decadal timescales. Regional patterns and zonal averages of precipitation-sensitive tree-ring series are used to corroborate these patterns and to extend them into the past and appear to share much long- and short-term information with the instrumentally based zonal precipitation EOFs and moments.The overall amount of precipitation deposited along the West Coast and western cordillera of North America from 25?? to 55 ??N varies from year to year, and superimposed on this domain-average variability are varying north-south contrasts on timescales from at least interannual to interdecadal. In order to better understand the north-south precipitation contrasts, their interannual and decadal variations are studied in terms of how much they affect overall precipitation amounts and how they are related to large-scale climatic patterns. Spatial empirical orthogonal functions (EOFs) and spatial moments (domain average, central latitude, and latitudinal spread) of zonally averaged precipitation anomalies along the westernmost parts of North America are analyzed, and each is correlated with global sea level pressure (SLP) and sea surface temperature series, on interannual (defined here as 3-7 yr) and decadal (>7 yr) timescales. The interannual band considered here corresponds to timescales that are particularly strong in tropical climate variations and thus is expected to contain much precipitation variability that is related to El Nino-Southern Oscillation; the decadal scale is defined so as to capture the whole range of long-term climatic variations affecting western North America. Zonal EOFs of the interannual and decadal filtered versions of the zonal-precipitation series are remarkably similar. At both tim

Dettinger, M. D.; Cayan, D. R.; Diaz, H. F.; Meko, D. M.

1998-01-01

421

Elucidation of the timescales and origins of quantum electronic coherence in LHCII  

NASA Astrophysics Data System (ADS)

Photosynthetic organisms harvest sunlight with near unity quantum efficiency. The complexity of the electronic structure and energy transfer pathways within networks of photosynthetic pigment-protein complexes often obscures the mechanisms behind the efficient light-absorption-to-charge conversion process. Recent experiments, particularly using two-dimensional spectroscopy, have detected long-lived quantum coherence, which theory suggests may contribute to the effectiveness of photosynthetic energy transfer. Here, we present a new, direct method to access coherence signals: a coherence-specific polarization sequence, which isolates the excitonic coherence features from the population signals that usually dominate two-dimensional spectra. With this polarization sequence, we elucidate coherent dynamics and determine the overall measurable lifetime of excitonic coherence in the major light-harvesting complex of photosystem II. Coherence decays on two distinct timescales of 47 fs and ~800 fs. We present theoretical calculations to show that these two timescales are from weakly and moderately strongly coupled pigments, respectively.

Schlau-Cohen, Gabriela S.; Ishizaki, Akihito; Calhoun, Tessa R.; Ginsberg, Naomi S.; Ballottari, Matteo; Bassi, Roberto; Fleming, Graham R.

2012-05-01

422

Slow cortical dynamics and the accumulation of information over long timescales.  

PubMed

Making sense of the world requires us to process information over multiple timescales. We sought to identify brain regions that accumulate information over short and long timescales and to characterize the distinguishing features of their dynamics. We recorded electrocorticographic (ECoG) signals from individuals watching intact and scrambled movies. Within sensory regions, fluctuations of high-frequency (64-200 Hz) power reliably tracked instantaneous low-level properties of the intact and scrambled movies. Within higher order regions, the power fluctuations were more reliable for the intact movie than the scrambled movie, indicating that these regions accumulate information over relatively long time periods (several seconds or longer). Slow (<0.1 Hz) fluctuations of high-frequency power with time courses locked to the movies were observed throughout the cortex. Slow fluctuations were relatively larger in regions that accumulated information over longer time periods, suggesting a connection between slow neuronal population dynamics and temporally extended information processing. PMID:23083743

Honey, Christopher J; Thesen, Thomas; Donner, Tobias H; Silbert, Lauren J; Carlson, Chad E; Devinsky, Orrin; Doyle, Werner K; Rubin, Nava; Heeger, David J; Hasson, Uri

2012-10-18

423

The Verwey transition in Fe3O4: lattice distortions on a fs time-scale  

NASA Astrophysics Data System (ADS)

Magnetite, Fe3O4, displays a strong decrease in resistivity upon heating above TC= 123 K: the Verwey transition. This transition is accompanied by a structural change from monoclinic to cubic symmetry. Despite decades of research and indications that charge and orbital ordering play an important role, the mechanism behind the Verwey transition is yet unclear. Using pump-probe soft X-ray scattering at the new LCLS SXR beamline, we have studied the role of the structural transition for the Verwey transition on ultra-fast time-scales. Focusing off-resonance on the high T forbidden (001) lattice reflection, we find a lattice response on time-scales t< 250 fs. The response displays a pump fluence threshold indicative of a phase transition. This strongly suggests that the lattice, via coupling to certain low energy phonon modes, plays a crucial role for the Verwey transition in Fe3O4.

Kukreja, R.; de Jong, S.; Hossain, M.; Back, C.; Scherz, A.; Zhu, D.; Schlotter, W.; Turner, J.; Lee, W.; Chuang, Y.; Moore, R.; Krupin, O.; Trigo, M.; Dürr, H.; Patthey, L.; Pontius, N.; Kachel, T.; Föhlisch, A.; Beye, M.; Sorgenfrei, F.; Wurth, W.; Chang, C.; Döhler, M.; Trabant, C.; Schüssler-Langeheine, C.

2011-03-01

424

Recent fluid deformation closure for velocity gradient tensor dynamics in turbulence: Timescale effects and expansions  

NASA Astrophysics Data System (ADS)

In order to model pressure and viscous terms in the equation for the Lagrangian dynamics of the velocity gradient tensor in turbulent flows, Chevillard & Meneveau [L. Chevillard, C. Meneveau, Lagrangian dynamics and geometric structure of turbulence, Phys. Rev. Lett. 97 (174501) (2006) 1-4] introduced the Recent Fluid Deformation closure. Using matrix exponentials, the closure allows us to overcome the unphysical finite-time blow-up of the well-known Restricted Euler model. However, it also requires the specification of a decorrelation timescale of the velocity gradient along the Lagrangian evolution, and when the latter is chosen too short (or, equivalently, the Reynolds number is too high), the model leads to unphysical statistics. In the present paper, we explore the limitations of this closure by means of numerical experiments and analytical considerations. We also study the possible effects of using time-correlated stochastic forcing instead of the previously employed white-noise forcing. Numerical experiments show that reducing the correlation timescale specified in the closure and in the forcing does not lead to a commensurate reduction of the autocorrelation timescale of the predicted evolution of the velocity gradient tensor. This observed inconsistency could explain the unrealistic predictions at increasing Reynolds numbers. We perform a series expansion of the matrix exponentials in powers of the decorrelation timescale, and we compare the full original model with a linearized version. The latter is not able to extend the limits of applicability of the former but allows the model to be cast in terms of a damping term whose sign gives additional information about the stability of the model as a function of the second invariant of the velocity gradient tensor.

Martins Afonso, Marco; Meneveau, Charles

2010-07-01

425

Isotopic exchange of carbon-bound hydrogen over geologic timescales 1 1 Associate editor: J. Horita  

Microsoft Academic Search

The increasing popularity of compound-specific hydrogen isotope (D\\/H) analyses for investigating sedimentary organic matter raises numerous questions about the exchange of carbon-bound hydrogen over geologic timescales. Important questions include the rates of isotopic exchange, methods for diagnosing exchange in ancient samples, and the isotopic consequences of that exchange. This article provides a review of relevant literature data along with new

Alex L. Sessions; Sean P. Sylva; Roger E. Summons; John M. Hayes

2004-01-01

426

Multiscale Modeling and TimeScale Analysis of a Human Limb  

Microsoft Academic Search

A multi-scale modeling approach is proposed in this paper that assists the user in constructing musculoskeletal system models from sub-models describing various mechanisms on different levels on the length scale. In addition, dynamic time-scale analysis has been performed on the developed multi-scale models of various parts of a human limb: on wrist, elbow and shoulder characterized by different maximal muscle

Csaba Fazekas; ORGY KOZMANN; Katalin M. Hangos

2007-01-01

427

An investigation of the controls on Irish precipitation ? 18 O values on monthly and event timescales  

Microsoft Academic Search

This two-year study investigates the relative influence of meteorological variables (precipitation amount and temperature),\\u000a atmospheric circulation, air mass history, and moisture source region on Irish precipitation oxygen isotopes (?18Op) on event and monthly timescales. Single predictor correlations reveal that on the event scale, 20% of ?18Op variability is attributable to the amount effect and 7% to the temperature effect while

Lisa M. BaldiniFrank; Frank McDermott; James U. L. Baldini; Matthew J. Fischer; Martin Möllhoff

2010-01-01