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1

Weyl-Eddington-Einstein affine gravity in the context of modern cosmology  

NASA Astrophysics Data System (ADS)

We propose new models of the “affine” theory of gravity in multidimensional space-times with symmetric connections. We use and develop ideas of Weyl, Eddington, and Einstein, in particular, Einstein’s proposed method for obtaining the geometry using the Hamilton principle. More specifically, the connection coefficients are determined using a “geometric” Lagrangian that is an arbitrary function of the generalized (nonsymmetric) Ricci curvature tensor (and, possibly, other fundamental tensors) expressed in terms of the connection coefficients regarded as independent variables. Such a theory supplements the standard Einstein theory with dark energy (the cosmological constant, in the first approximation), a neutral massive (or tachyonic) meson, and massive (or tachyonic) scalar fields. These fields couple only to gravity and can generate dark matter and/or inflation. The new field masses (real or imaginary) have a geometric origin and must appear in any concrete model. The concrete choice of the Lagrangian determines further details of the theory, for example, the nature of the fields that can describe massive particles, tachyons, or even “phantoms.” In “natural” geometric theories, dark energy must also arise. The basic parameters of the theory (cosmological constant, mass, possible dimensionless constants) are theoretically indeterminate, but in the framework of modern “multiverse” ideas, this is more a virtue than a defect. We consider further extensions of the affine models and in more detail discuss approximate effective (“physical”) Lagrangians that can be applied to the cosmology of the early Universe.

Filippov, A. T.

2010-06-01

2

Relativistic Variable Eddington Factor  

NASA Astrophysics Data System (ADS)

We analytically derived a relativistic variable Eddington factor in relativistic radiative flow, and found that the Eddington factor depends on the velocity gradient as well as the flow velocity. When the gaseous flow is accelerated and there is a velocity gradient, there also exists a density gradient. As a result, an unobstructed viewing range by a comoving observer, where the optical depth measured from the comoving observer is unity, is not a sphere, but becomes an oval shape elongated in the direction of the flow; we call it a one-tau photo-oval. For a comoving observer, an inner wall of the photo-oval generally emits at a non-uniform intensity, and has a relative velocity. Thus, the comoving radiation fields observed by the comoving observer becomes anisotropic, and the Eddington factor must deviate from the value for the isotropic radiation fields. In the case of a plane-parallel vertical flow, we examine the photo-oval and obtain the Eddington factor. In a sufficiently optically thick linear regime, the Eddington factor is analytically expressed as f(?,?,{d?}/{d?} = 1/3 (1 + {16/15} {d?}/{d?}), where ? is the optical depth and ? (= v/c) is the flow speed normalized by the speed of light. We also examined the linear and semi-linear regimes, and found that the Eddington factor generally depends both on the velocity and its gradient.

Fukue, Jun

2008-04-01

3

Instability & Mass Loss near the Eddington Limit  

NASA Astrophysics Data System (ADS)

We review the physics of continuum-driven mass loss and its likely role in ? Carinae and LBVs. Unlike a line-driven wind, which is inherently limited by self-shadowing, continuum driving can in principle lead to mass-loss rates up to the "photon-tiring" limit, for which the entire luminosity is expended in lifting the outflow. We discuss how instabilities near the Eddington limit give rise to a clumped atmosphere, and how the associated "porosity" can regulate a continuum-driven flow. We also summarize recent time-dependent simulations in which a mass flow stagnates because it exceeds the tiring limit, leading to complex time-dependent inflow and outflow regions. Porosity-regulated continuum driving in super-Eddington epochs can probably explain the large, near tiring-limit mass loss inferred for LBV giant eruptions. However, while these extreme flows can persist over dynamically long periods, they cannot be sustained for an evolutionary timescale; so ultimately it is stellar structure and evolution that sets the overall mass loss.

Owocki, S. P.; Shaviv, N. J.

4

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

5

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

2012-12-18

6

The Eddington Luminosity Limit for Multiphased Media  

Microsoft Academic Search

We consider the effective Eddington luminosity in a locally inhomogeneous medium by averaging out the coarse, small-scale behavior. We show that the ratio between the emitted flux and the average radiation force changes. The mean luminosity therefore can theoretically exceed the classical Eddington limit. It is further shown that acoustic modes are unstable under most relevant conditions, and they unavoidably

Nir J. Shaviv

1998-01-01

7

COSMOLOGICAL EVOLUTION OF MASSIVE BLACK HOLES: EFFECTS OF EDDINGTON RATIO DISTRIBUTION AND QUASAR LIFETIME  

SciTech Connect

A power-law time-dependent light curve for active galactic nuclei (AGNs) is expected by the self-regulated black hole growth scenario, in which the feedback of AGNs expels gas and shut down accretion. This is also supported by the observed power-law Eddington ratio distribution of AGNs. At high redshifts, the AGN life timescale is comparable with (or even shorter than) the age of the universe, which sets a constraint on the minimal Eddington ratio for AGNs on the assumption of a power-law AGN light curve. The black hole mass function (BHMF) of AGN relics is calculated by integrating the continuity equation of massive black hole number density on the assumption of the growth of massive black holes being dominated by mass accretion with a power-law Eddington ratio distribution for AGNs. The derived BHMF of AGN relics at z = 0 can fit the measured local mass function of the massive black holes in galaxies quite well, provided the radiative efficiency {approx}0.1 and a suitable power-law index for the Eddington ratio distribution are adopted. In our calculations of the black hole evolution, the duty cycle of AGN should be less than unity, which requires the quasar life timescale {tau}{sub Q} {approx}> 5 x 10{sup 8} years.

Cao Xinwu, E-mail: cxw@shao.ac.c [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road, Shanghai, 200030 (China)

2010-12-10

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

2010-07-02

9

Planning for Transport in the Wake of Stern and Eddington  

Microsoft Academic Search

Docherty I. and Mackie P. Planning for transport in the wake of Stern and Eddington, Regional Studies. The recent Stern and Eddington Reports for the UK Treasury emphasize the significance of the linkages between transport, land use, the environment, and the economy. Against that background, the purpose of this paper is to consider the future of transport planning in England

Iain Docherty; Peter Mackie

2010-01-01

10

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

2011-07-14

11

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

12

Einstein Online  

NSDL National Science Digital Library

Einstein Online provides the user with a simple, but meticulous, approach to Einstein's Theory of Relativity. In the section 'Elementary Einstein', the theories of Special and General Relativity are explained in detail, going through concepts like Relativity, Spacetime and Space Geometry. The following section, 'Spotlights on Relativity', contains applications of both theories, from the Relativity of Simultaneity, to Gravity and Gravitational Waves, to Black Holes and Cosmology, to the Quantum realm.

2007-06-18

13

Microlensing evidence for super-Eddington disc accretion in quasars  

NASA Astrophysics Data System (ADS)

Microlensing by the stellar population of lensing galaxies provides an important opportunity to resolve the accretion disc structure spatially in strongly lensed quasars. Disc sizes estimated in this way are on average larger than the predictions of the standard Shakura-Sunyaev accretion disc model. An analysis of the observational data on microlensing variability suggests that some fraction of lensed quasars (primarily smaller-mass objects) are accreting in the super-Eddington regime. Super-Eddington accretion leads to the formation of an optically thick envelope scattering the radiation formed in the disc. This makes the apparent disc size larger and practically independent of wavelength. In the framework of our model, it is possible to make self-consistent estimates of mass accretion rates and black hole masses for the cases when both amplification-corrected fluxes and radii are available.

Abolmasov, P.; Shakura, N. I.

2012-12-01

14

Super-Eddington radiation transfer in soft gamma repeaters  

NASA Astrophysics Data System (ADS)

Bursts from soft gamma repeaters (SGRs) have been shown to be super-Eddington by a factor of 1000 and have been persuasively associated with compact objects. Super-Eddington radiation transfer on the surface of a strongly magnetic (greater than or equal to 1013 G) neutron star is studied and related to the observational constraints on SGRs. In strong magnetic fields, Thompson scattering is suppressed in one polarization state, so super-Eddington fluxes can be radiated while the plasma remains in hydrostatic equilibrium. We discuss a model which offers a somewhat natural explanation for the observation that the energy spectra of bursts with varying intensity are similar. The radiation produced is found to be linearly polarized to one part in 1000 in a direction determined by the local magnetic field, and intensity variations between bursts are understood as a change in the radiating area on the source. The net polarization is inversely correlated with burst intensity. Further, it is shown that for radiation transfer calculations in limit of superstrong magnetic fields, it is sufficient to solve the radiation transfer for the low opacity state rather than the coupled equations for both. With this approximation, standard stellar atmosphere techniques are utilized to calculate the model energy spectrum.

Ulmer, Andrew

1994-12-01

15

Einsteins dream  

SciTech Connect

This book discusses the following topics: the search for meaning; Einstein's dream; curved space; Einstein and warped space-time and extreme wraping; early unified field theories; star death; beyond the white dwarf; the early universe; the hadron, Lepton, and Radiation eras; the redshift controversy; other universes; the final fate of the universe; the missing mass; bounce; fate of the open universe; the world of particles and fields; Dirac's equation; Yukawa; gauge theory; quantum chromodynamics; supergravity and superstrings; twistors and heaven; and the new Einstein.

Parker, B.

1986-01-01

16

Einstein's boxes  

NASA Astrophysics Data System (ADS)

At the 1927 Solvay conference, Albert Einstein presented a thought experiment intended to demonstrate the incompleteness of the quantum mechanical description of reality. In the following years, the experiment was modified by Einstein, de Broglie, and several other commentators into a simple scenario involving the splitting in half of the wave function of a single particle in a box. This paper collects together several formulations of this thought experiment from the literature, analyzes and assesses it from the point of view of the Einstein-Bohr debates, the EPR dilemma, and Bell's theorem, and argues for ``Einstein's Boxes'' taking its rightful place alongside similar but historically better known quantum mechanical thought experiments such as EPR and Schrödinger's Cat.

Norsen, Travis

2005-02-01

17

Einstein's Universe.  

ERIC Educational Resources Information Center

|Presents a guide to be used by students and teachers in conjunction with a television program about Einstein. Provides general information about special and general relativity, and the universe. Includes questions for discussion after each section and a bibliography. (MA)|

Carlson, Eric; Wald, Robert

1979-01-01

18

Einstein, Picasso  

Microsoft Academic Search

How the 20th century's most important scientist---Albert Einstein---and its most important artist---Pablo Picasso---made their greatest discoveries at almost the same time is a remarkable story: Einstein's relativity theory in 1905 and Picasso's Les Demoiselles d'Avignon two years later. A scientist and an artist confronted the same problem---the nature of time and simultaneity---and resolved it after realizing a new aesthetic. At

Arthur I. Miller

2004-01-01

19

The controversy between Alexander Friedmann and Albert Einstein about the possibility of a non-static world (German Title: Die Kontroverse zwischen Alexander Friedmann und Albert Einstein um die Möglichkeit einer nichtstatischen Welt)  

Microsoft Academic Search

Einstein's treatment of the cosmological problem as well as his unshakeable adherence to his own static solution of the complete field equations was throughout determined by Ernst Mach's idea of relativity of inertia. Friedmann, however, like Eddington, Weyl and others did not consider Mach's principle to be a part of general relativity, and so he regarded a time dependent developing

Georg Singer

2005-01-01

20

Einstein Revisited  

ERIC Educational Resources Information Center

|A brief description on the work and life of the great physicist scientist Albert Einstein is presented. The photoelectric paper written by him in 1905 led him to the study of fluctuations in the energy density of radiation and from there to the incomplete nature of the equipartition theorem of classical mechanics, which failed to account for…

Fine, Leonard

2005-01-01

21

Einstein's Mirror  

ERIC Educational Resources Information Center

|Reflection of light from a plane mirror in uniform rectilinear motion is a century-old problem, intimately related to the foundations of special relativity. The problem was first investigated by Einstein in his famous 1905 paper by using the Lorentz transformations to switch from the mirror's rest frame to the frame where the mirror moves at a…

Gjurchinovski, Aleksandar; Skeparovski, Aleksandar

2008-01-01

22

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

23

THE EVOLUTION AND EDDINGTON RATIO DISTRIBUTION OF COMPTON THICK ACTIVE GALACTIC NUCLEI  

SciTech Connect

Previous studies of the active galactic nuclei (AGNs) contribution to the cosmic X-ray background (CXB) consider only observable parameters such as luminosity and absorbing column. Here, for the first time, we extend the study of the CXB to physical parameters including the Eddington ratio of the sources and the black hole mass. In order to calculate the contribution to the CXB of AGN accreting at various Eddington ratios, an evolving Eddington ratio space density model is calculated. In particular, Compton thick (CT) AGNs are modeled as accreting at specific, physically motivated Eddington ratios instead of as a simple extension of the Compton thin type 2 AGN population. Comparing against the observed CT AGN space densities and log N-log S relation indicates that CT AGNs are likely a composite population of AGNs made up of sources accreting either at >90% or <1% of their Eddington rate.

Draper, A. R.; Ballantyne, D. R., E-mail: aden.draper@physics.gatech.ed [Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)

2010-06-01

24

Arthur Stanley Eddington: pioneer of stellar structure theory  

NASA Astrophysics Data System (ADS)

In 1920. Eddington pointed to the fusion of four hydrogen atoms into a helium atom as the likely energy source supplying the observed stellar luminosity. In his monumental Internal Constitution of the Stars, he argued that the luminosity could be predicted from the equations of hydrostatic equilibrium and radiative transfer. By means of a draconian approximation, which required the energy ? liberated per gram to be effectively uniform through the star, he produced his 'standard model', with the luminosity strongly dependent on the mass. Application of his theory to the observed Main Sequence confirmed this, but required also that the central temperature increase only moderately with mass, implying that ? is a strong function of temperature. This was subsequently vindicated by thermonuclear theory, but contradicts his approximation. Later work showed that his Mass-Luminosity relation is really a Mass-Luminosity-Radius relation in disguise, but with only a weak dependence on the radius. Radiative transfer effectively fixes the luminosity, and the energy balance condition fixes the radius. To get agreement with the observed luminosity, stellar material must have a substantial hydrogen content. Eddington's theory does not apply to the high-density. low-luminosity white dwarf stars. He was delighted at Fowler's application of the Pauli Exclusion Principle to show that even at zero temperature, the effectively free gas of degenerate electrons exerts a pressure able to balance the enormous gravitational force. But he never accepted the Stoner-Anderson-Chandrasekhar relativistic extension, with its prediction of a limiting mass, beyond which no cold body can exist in equilibrium. However, his claim that the Fowler equation of state remained valid at all densities failed to carry conviction: 'relativistic degeneracy' is now an essential part of our picture of stellar evolution, ensuring that we can account for the synthesis of the more massive elements, the occurrence of supernovae, the formation of neutron stars, and collapse into a black hole state.

Mestel, Leon

2004-12-01

25

Einstein Light  

NSDL National Science Digital Library

This web site is a basic, non-mathematical introduction to relativity. It covers concepts from Galileo, Newton, and Maxwell through Einstein and special relativity. The site also mentions modern topics such as the relations between gravity and quantum mechanics. The main resource is a series of Flash media files with narration and animations. Thirty detailed pages that go into specifics are included, each marked by their level of mathematics used. Questions are also available to test readers' understanding.

Wolfe, Joe; Hatsidimitris, George

2010-01-12

26

Beyond Einstein  

ScienceCinema

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.

27

Broad Absorption Line Variability on Multi-Year Timescales: Current Results and SDSS-III Prospects  

NASA Astrophysics Data System (ADS)

Over the past few years, studies of the variability of quasar Broad Absorption Lines (BALs) on multi-year rest-frame timescales have provided a number of intriguing results. These include (1) quantification of how BAL variability increases with rest-frame timescale, (2) characterization of the basic modes of multi-year BAL variability; e.g., variation often occurs in discrete regions which are only a few thousand km/s wide, and (3) tight limits upon BAL acceleration enabled by the long sampled timescales. We are aiming to transform the field of multi-year BAL variability studies into one that supplies rigorous large-sample constraints upon quasar winds using an ancillary project of the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS). BOSS is re-observing 2000 bright BAL quasars originally observed by SDSS-I/SDSS-II from 2000-2008. This sample size is 100 times larger than those of current multi-year BAL variability studies, and > 800 objects are already observed. Measured variations constrain, e.g., BAL disappearance and emergence, BAL lifetimes, the modes of multi-year BAL variability, and BAL acceleration. For example, we have already detected about 20 new examples of BAL disappearance events. Soon we will constrain the dependence of multi-year BAL variability upon luminosity, redshift, black-hole mass, Eddington fraction, and radio properties.

Niel Brandt, W.; Filiz Ak, N.; Hall, P. B.; Schneider, D. P.; BOSS Quasar Working Group

2012-05-01

28

Posing Einstein's Question: Questioning Einstein's Pose.  

ERIC Educational Resources Information Center

|Discusses the events surrounding a famous picture of Albert Einstein in which he poses near a blackboard containing a tensor form of his 10 field equations for pure gravity with a question mark after it. Speculates as to the content of Einstein's lecture and the questions he might have had about the equation. (Contains over 30 references.) (WRM)|

Topper, David; Vincent, Dwight E.

2000-01-01

29

Tunneling Effect and Hawking Radiation from a Gibbon Maeda Black Hole by Using Eddington Finkelstein Coordinates  

NASA Astrophysics Data System (ADS)

In this paper, by using well-known Eddington Finkelstein coordinates instead of Painlevè coordinates, we study the tunneling effect of black holes. As examples of special static black holes, we calculate the tunneling rates of Gibbon Maeda black holes. The result obtained by adopting Eddington Finkelstein coordinates is in agreement with the Parikh’s standard result, ?˜exp (-2Im S), which adopts the Painlevè coordinates. In addition, we discuss carefully the condition that the coordinates system in which we study the tunneling process should satisfy. In our opinion, the terms of the tunneling effect are not as strict as ones in Parikh’s paper and could be softened properly.

Ren, Jun; Zhao, Zheng

2007-12-01

30

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.

31

Timescales of the Paleomagnetic Field  

NASA Astrophysics Data System (ADS)

To mark the 70th birthday of Neil D. Opdyke, a Chapman Conference entitled "Timescales ofthe Internal Geomagnetic Field" was held at the University of Florida in Gainesville on March 9-11, 2003. This AGU Chapman Conference was sponsored by the U.S. National Science Foundation, University of Florida, Florida Museum of Natural History, and 2G Enterprises. Forty-one talks and twenty-three posters were presented during the three-day meeting. This monograph contains twenty-four of those papers, and is a balanced subset ofthe papers presented at the conference. The monograph is divided into three parts. Part 1 deals with the geocentric axial dipole (GAD) hypothesis, continental reconstruction, and long-term geomagnetic field behavior. Part 2 comprises papers on magnetic polarity stratigraphy and the acquisition of sedimentary magnetization. Part 3 deals with secular variation, paleointensity, and short-term geomagnetic field behavior. These are all topics that have been substantially impacted by Neil's scientific work.

Channell, James E. T.; Kent, Dennis V.; Lowrie, William; Meert, Joseph G.

32

Water balance variability at the interstorm timescale  

Microsoft Academic Search

The translation of rainfall variability into variability in evapotranspiration, soil moisture, or runoff depends on many factors. Previously published results indicate that the sensitivity of evapotranspiration to rainfall at the interannual timescale generally increases as catchment aridity increases. This paper generalizes these results to the interstorm timescale by calculating the variance of interstorm evapotranspiration from a stochastic model of soil

N. J. Potter; L. Zhang

2007-01-01

33

Rapid Cooling Of The Neutron Star In The Quiescent Super-Eddington Transient XTE J1701-462  

NASA Astrophysics Data System (ADS)

In the past decade the observing of cooling neutron star transients after long-duration (year or longer) outbursts has entered as a new approach to constraining the properties of matter inside neutron stars. We present Chandra and XMM-Newton observations of the super-Eddington neutron star transient XTE J1701-426 in quiescence. The observations cover the first 800 days of quiescence following the end, in August 2007, of a very luminous 19-month-long outburst. This data set represents the best-sampled cooling curve of a neutron star transient to date. We also present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the outburst. The transition from active accretion to a quiescent phase dominated by thermal emission from the neutron star is resolved with unprecedented precision compared to other cooling neutron star transients observed after extended outbursts. The observations of XTE J1701-426 represent new parameter space being covered in neutron star cooling, this source having accreted at a much higher level than other observed sources, and the length of the outburst being intermediate between regular transients (with outbursts typically lasting weeks or months) and quasi-persistent transients (which accrete for many years or decades). The inferred effective surface temperature at the start of the quiescent phase is considerably higher for XTE J1701-426 than other observed sources, and the timescale of the cooling is much faster, strongly indicating a highly conductive neutron star crust. The quiescent spectra also show a prominent non-thermal component, which has exhibited large and irregular variability. The origin of this component is uncertain; one possibility is residual accretion from the companion star.

Fridriksson, Joel K.; Homan, J.; Wijnands, R.; Mendez, M.; Cackett, E. M.; Altamirano, D.; Belloni, T. M.; Brown, E. F.; Degenaar, N.; Lewin, W. H. G.

2010-02-01

34

Rapid Cooling of the Neutron Star in the Quiescent Super-Eddington Transient XTE J1701--462  

NASA Astrophysics Data System (ADS)

In the past decade the observing of cooling neutron star transients after long-duration (year or longer) outbursts has entered as a new approach to constraining the properties of matter inside neutron stars. We present Chandra and XMM-Newton observations of the super-Eddington neutron star transient XTE J1701--426 in quiescence. The observations cover the first ?700 days of quiescence following the end, in August 2007, of a very luminous ?19-month-long outburst. This data set represents the best- sampled cooling curve of a neutron star transient to date. We also present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the outburst. The transition from active accretion to a quiescent phase dominated by thermal emission from the neutron star is resolved with unprecedented precision compared to other neutron star transients observed after extended outbursts. The observations of XTE J1701--426 represent new parameter space being covered in neutron star cooling, this source having accreted at a much higher level than other observed sources, and the length of the outburst being intermediate between regular transients (outbursts typically lasting weeks or months) and quasi-persistent transients (which accrete for many years or decades). The inferred effective surface temperature at the start of the quiescent phase is considerably higher for XTE J1701--426 than other observed sources, and the timescale of the cooling is much faster, strongly indicating a highly conductive neutron star crust. The quiescent spectra also show a prominent non-thermal component, which has exhibited large and irregular variability. The origin of this component is highly uncertain; one possibility is residual accretion from the companion star.

Fridriksson, Joel K.; Homan, Jeroen; Wijnands, Rudy; Méndez, Mariano; Cackett, Edward M.; Altamirano, Diego; Belloni, Tomaso M.; Brown, Edward F.; Degenaar, Nathalie; Lewin, Walter H. G.

2009-09-01

35

Strange stars and superbursts at near-Eddington mass accretion rates  

Microsoft Academic Search

Careful assessment of four good superburst candidates for GX 17+2 reveals that superburst is possible at near Eddington mass accretion rates. For the other seven stars, where superburst is found, there is the standard model of burning accumulated carbon from normal type I bursts of the accreting stars. However, there is the need for carbon, nitrogen and oxygen mass fraction

Monika Sinha; Subharthi Ray; Mira Dey; Jishnu Dey

2005-01-01

36

Einstein X-ray observations of cataclysmic variables  

SciTech Connect

Observations with the imaging X-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity X-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrumentation has permitted study of their short timescale variability and spectra. The data are adding significantly to our knowledge of the accretion process in cataclysmic variables and forcing some revision in our ideas concerning the origin of the optical variability in these stars.

Mason, K.O.; Cordova, F.A.

1982-01-01

37

Einstein in the City  

NASA Astrophysics Data System (ADS)

On his first trip to the United States in April 1921, Albert Einstein visited The City College of New York before he proceeded to Columbia and Princeton Universities. As a result, Einstein gave his very first scientific speech in the United States at The City College, known simply and cordially to New Yorkers as ``the City.'' That visit, however, is now rarely known. This paper will investigate why Einstein came to the City, what he spoke there, and the significance and consequences of his visit. In particular, the paper will discuss Einstein's associations with Reinhard Wetzel, a physicist, and Morris R. Cohen, a philosopher, at the City.

Hu, Danian

2007-04-01

38

The Einstein Observatory Detection of Faint X-Ray Flashes  

Microsoft Academic Search

We report on the result of an extensive search for X-ray counterparts to gamma-ray bursts (GRBs) using data acquired with the imaging proportional counter (IPC) on board the Einstein Observatory. We examine background sky fields from all pointed observations for short timescale (<~ 10 s), transient X-ray phenomena not associated a priori with detectable point sources. A total of 1.5

E. V. Gotthelf; T. T. Hamilton; D. J. Helfand

1996-01-01

39

Quasars Are Not Light Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution  

NASA Astrophysics Data System (ADS)

We use the observed distribution of Eddington ratios as a function of supermassive black hole (BH) mass to constrain models of quasar/active galactic nucleus (AGN) lifetimes and light curves. Given the observed (well constrained) AGN luminosity function, a particular model for AGN light curves L(t) or, equivalently, the distribution of AGN lifetimes (time above a given luminosity t(>L)) translates directly and uniquely (without further assumptions) to a predicted distribution of Eddington ratios at each BH mass. Models for self-regulated BH growth, in which feedback produces a self-regulating "decay" or "blowout" phase after the AGN reaches some peak luminosity/BH mass and begins to expel gas and shut down accretion, make specific predictions for the light curves/lifetimes, distinct from, e.g., the expected distribution if AGN simply shut down by gas starvation (without feedback) and very different from the prediction of simple phenomenological "light bulb" scenarios. We show that the present observations of the Eddington ratio distribution, spanning nearly 5 orders of magnitude in Eddington ratio, 3 orders of magnitude in BH mass, and redshifts z = 0-1, agree well with the predictions of self-regulated models, and rule out phenomenological "light bulb" or pure exponential models, as well as gas starvation models, at high significance (~5?). We also compare with observations of the distribution of Eddington ratios at a given AGN luminosity, and find similar good agreement (but show that these observations are much less constraining). We fit the functional form of the quasar lifetime distribution and provide these fits for use, and show how the Eddington ratio distributions place precise, tight limits on the AGN lifetimes at various luminosities, in agreement with model predictions. We compare with independent estimates of episodic lifetimes and use this to constrain the shape of the typical AGN light curve, and provide simple analytic fits to these for use in other analyses. Given these constraints, the average local BH must have gained its mass in no more than a couple of bright, near peak-luminosity episodes, in agreement with models of accretion triggering in interactions and mergers.

Hopkins, Philip F.; Hernquist, Lars

2009-06-01

40

Relativity from Galileo to Einstein.  

National Technical Information Service (NTIS)

The following topics are discussed: Galilean relativity; Cartesian relativity; Classical relativistic mechanics; Lagrangian relativity; Constitutive relativity; Einstein's special relativity; The space-time; Einstein's theory of gravitation; Consequences ...

B. Finzi

1964-01-01

41

Einstein, Bose and Bose-Einstein Statistics  

NASA Astrophysics Data System (ADS)

In June 1924, a relatively unknown Satyendra Nath Bose from Dacca, India, wrote a letter to Einstein beginning with ``Respected Sir, I have ventured to send you the accompanying article for your perusal. I am anxious to know what you think of it. You will see that I have ventured to deduce the coefficient 8??^2/c^3 in Planck's law independent of the classical electrodynamics, only assuming that the ultimate elementary regions in Phase-space have the content h^3. I do not know sufficient German to translate the paper. If you think the paper worth publication, I shall be grateful if you arrange for its publication in Zeitschrift für Physik.'' Einstein did translate the article himself and got it published. He wrote to Ehrenfest: ``The Indian Bose has given a beautiful derivation of Planck's law, including the constant [i.e.8??^2/c^3].'' Einstein extended the ideas of Bose that implied, among other things, a new statistics for the light-quanta to the molecules of an ideal gas and wrote to Ehrenfest, `from a certain temperature on, the molecules ``condense'' without attractive forces, that is, they accumulate at zero velocity. The theory is pretty, but is there also some truth to it?' Abraham Pais has called Bose's paper ``the fourth and the last revolutionary papers of the old quantum theory.'' My paper will present the works of Bose and Einstein in their historical perspective and the eventual birth of the new quantum Bose-Einstein statistics.

Wali, Kameshwar C.

2005-05-01

42

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

43

A New Einstein Ring  

NASA Astrophysics Data System (ADS)

Using the VLT, Rémi Cabanac and colleagues1 have discovered a new and very impressive Einstein ring. This cosmic mirage, dubbed FOR J0332-3557, is seen towards the southern constellation Fornax (the Furnace), and is remarkable on at least two counts. First, it is a bright, almost complete Einstein ring. Second, it is the farthest of its type ever found.

2005-09-01

44

When Art Meets Einstein  

ERIC Educational Resources Information Center

|This article deals with a pale blue sculpture entitled "A New World View", as an homage to the most famous scientist in modern history, Albert Einstein. It has 32 bas-relief squares composed of glass and steel that represent one aspect of the life and legacy of Albert Einstein. Images of children's faces peer out from behind the glass squares,…

Science Scope, 2006

2006-01-01

45

Einstein and Ehrenfest  

NASA Astrophysics Data System (ADS)

After Paul Ehrenfest's untimely death, Albert Einstein wrote about their first meeting more than twenty years earlier. ``Within a few hours we were true friends as though our dreams and aspirations were meant for each other.'' In fact, this warm friendship with a fellow theoretical physicist of his own age was unique in Einstein's life. I shall try to characterize it in this talk.

Klein, Martin J.

2005-03-01

46

Once Upon Einstein  

Microsoft Academic Search

Thibault Damour is a theoretical physicist, and a member of the French Academy of Sciences. This book is the translation, by Eric Novak, of the original French Si Einstein m'etait cont (Le Cherche Midi, 2005). It is neither a book of theoretical physics nor a biography of Einstein. It is not a book of history nor philosophy of science. In

E Giannetto

2007-01-01

47

Hawking Radiation via Tunnelling from Black Holes by Using Eddington Finkelstein Coordinates  

NASA Astrophysics Data System (ADS)

In this paper, by using well-known Eddington Finkelstein coordinates instead of Painlevè coordinates, we study the tunnelling effect of the black holes once again. As examples of the static and stationary black holes, we calculate the tunnelling rates of Schwarzschild and Kerr black holes. In addition, the result obtained by adopting Eddington Finkelstein coordinates is in agreement with the Parikh’s and Zhang’s recent work which adopts the Painlevè coordinates. At last, we discuss carefully the condition that the coordinates system in which we study the tunnelling process should satisfy. In our opinion, the terms of the tunnelling effect are not as strict as ones in Parikh’s paper and could be softened properly.

Ren, Jun; Zhao, Zheng

2006-07-01

48

V4641Sgr - A super-Eddington source enshrouded by an extended envelope  

NASA Astrophysics Data System (ADS)

Optical spectroscopy of an unusual fast transient V4641 Sgr constrains its mass to be 8.7-11.7 Msun (9.6 Msun is the best fit value) and the distance to 7.4-12.3 kpc (Orosz et al. \\cite{orosz}). At this distance the peak flux as measured by ASM/RXTE in 2-12 keV energy band implies the X-ray luminosity exceeding 2-3x 1039 erg s-1, i.e. near or above the Eddington limit for a 9.6 Msun black hole. Optical photometry shows that at the peak of the optical outburst the visual magnitude increased by Delta mV >~ 4.7m relative to the quiescent level and reached mV<~ 8.8m. An assumption that this optical emission is due to the irradiated surface of an accretion disk or a companion star with a black body spectrum would mean that the bolometric luminosity of the system exceeds >~ 3 x 1041 erg s-1 ~ 300 LEdd. We argue that the optical data strongly suggest the presence of an extended envelope surrounding the source which absorbs X-ray flux and reemits it in the optical and UV. The data also suggest that this envelope should be optically thin in UV, EUV and soft X-rays. The observed properties of V4641 Sgr at the peak of an optical flare are very similar to those of SS433. This envelope is likely the result of a near- or super-Eddington rate of mass accretion onto the black hole. The envelope vanishes during subsequent evolution of the source when the apparent luminosity drops well below the Eddington value. Thus this transient source provides us with direct proof of the dramatic change in the character of an accretion flow at the mass accretion rate near or above the critical Eddington value as predicted long ago by the theoretical models.

Revnivtsev, M.; Sunyaev, R.; Gilfanov, M.; Churazov, E.

2002-04-01

49

Quasars Are Not Light Bulbs: Testing Models of Quasar Lifetimes with the Observed Eddington Ratio Distribution  

Microsoft Academic Search

We use the observed distribution of Eddington ratios as a function of supermassive black hole (BH) mass to constrain models of quasar\\/active galactic nucleus (AGN) lifetimes and light curves. Given the observed (well constrained) AGN luminosity function, a particular model for AGN light curves L(t) or, equivalently, the distribution of AGN lifetimes (time above a given luminosity t(>L)) translates directly

Philip F. Hopkins; Lars Hernquist

2009-01-01

50

Mysticism and Marxism: A.S. Eddington, Chapman Cohen, and Political Engagement Through Science Popularization  

Microsoft Academic Search

This paper argues that that political context of British science popularization in the inter-war period was intimately tied\\u000a to contemporary debates about religion and science. A leading science popularizer, the Quaker astronomer A.S. Eddington, and\\u000a one of his opponents, the materialist Chapman Cohen, are examined in detail to show the intertwined nature of science, philosophy,\\u000a religion, and politics.

Matthew Stanley

2008-01-01

51

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

52

Timescales of seawater intrusion and retreat  

NASA Astrophysics Data System (ADS)

Quantifying the timescales associated with moving freshwater-seawater interfaces is critical for effective management of coastal groundwater resources. In this study, timescales of interface movement in response to both inland and coastal water level variations are investigated. We first assume that seawater intrusion (SWI) and retreat (SWR) are driven by an instantaneous freshwater-level variation at the inland boundary. Numerical modelling results reveal that logarithmic timescales of SWI (lnTi) and SWR (lnTr) can be described respectively by various simple linear equations. For example, SWI timescales are described by lnTi = a + blnh?f-s, where a and b are linear regression coefficients and h?f-s is the boundary head difference after an instantaneous drop of inland freshwater head. For SWR cases with the same initial conditions, but with different increases in freshwater head, lnTr = c + d?XT, where c and d are regression coefficients and ?XT is the distance of toe response that can be estimated by a steady-state, sharp-interface analytical solution. For SWR cases with the same freshwater head increase, but with different initial conditions, in contrast, lnTr = e + fln?XT, where e and f are regression coefficients. The timescale of toe response caused by an instantaneous variation of sea level is almost equivalent to that induced by an instantaneous inland head variation with the same magnitude of water level change, but opposite in direction. Accordingly, the empirical equations of this study are also applicable for sea-level variations in head-controlled systems or for simultaneous variations of both inland and coastal water levels. Despite the idealised conceptual models adopted in this study, the results imply that for a particular coastal aquifer, SWI timescales are controlled by the boundary water levels after variations, whereas SWR timescales are dominated by the distance of toe response.

Lu, Chunhui; Werner, Adrian D.

2013-09-01

53

The stolen brain of Einstein  

Microsoft Academic Search

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

Kavan Modi

2008-01-01

54

Einstein, Bose and Bose-Einstein Statistics  

Microsoft Academic Search

In June 1924, a relatively unknown Satyendra Nath Bose from Dacca, India, wrote a letter to Einstein beginning with ``Respected Sir, I have ventured to send you the accompanying article for your perusal. I am anxious to know what you think of it. You will see that I have ventured to deduce the coefficient 8piupsilo^2\\/c^3 in Planck's law independent of

Kameshwar C. Wali

2005-01-01

55

The ultraluminous state revisited: fractional variability and spectral shape as diagnostics of super-Eddington accretion  

NASA Astrophysics Data System (ADS)

Although we are nearing a consensus that most ultraluminous X-ray sources (ULXs) below 1041 erg s-1 represent stellar mass black holes accreting in a super-Eddington `ultraluminous' accretion state, little is yet established of the physics of this extreme accretion mode. Here, we use a combined X-ray spectral and timing analysis of an XMM-Newton sample of ULXs to investigate this new accretion regime. We start by suggesting an empirical classification scheme that separates ULXs into three classes based on the spectral morphologies observed by Gladstone et al.: a singly peaked broadened disc class, and two-component hard ultraluminous and soft ultraluminous regimes, with the spectra of the latter two classes dominated by the harder and softer component, respectively. We find that at the lowest luminosities (LX < 3 × 1039 erg s-1) the ULX population is dominated by sources with broadened disc spectra, whilst ULXs with two-component spectra are seen almost exclusively at higher luminosities, suggestive of a distinction between ˜Eddington and super-Eddington accretion modes. We find high levels of fractional variability are limited to ULXs with soft ultraluminous spectra, and a couple of the broadened disc sources. Furthermore, the variability in these sources is strongest at high energies, suggesting it originates in the harder of the two spectral components. We argue that these properties are consistent with current models of super-Eddington emission, where a massive radiatively driven wind forms a funnel-like geometry around the central regions of the accretion flow. As the wind provides the soft spectral component this suggests that inclination is the key determinant in the observed two-component X-ray spectra, which is very strongly supported by the variability results if this originates due to clumpy material at the edge of the wind intermittently obscuring our line-of-sight to the spectrally hard central regions of the ULX. The pattern of spectral variability with luminosity in two ULXs that straddle the hard/soft ultraluminous regime boundary is consistent with the wind increasing at higher accretion rates, and thus narrowing the opening angle of the funnel. Hence, this work suggests that most ULXs can be explained as stellar mass black holes accreting at and above the Eddington limit, with their observed characteristics dominated by two variables: accretion rate and inclination.

Sutton, Andrew D.; Roberts, Timothy P.; Middleton, Matthew J.

2013-10-01

56

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

57

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.

58

A molecular timescale for vertebrate evolution  

Microsoft Academic Search

A timescale is necessary for estimating rates of molecular and morphological change in organisms and for interpreting patterns of macroevolution and biogeography. Traditionally, these times have been obtained from the fossil record, where the earliest representatives of two lineages establish a minimum time of divergence of these lineages. The clock-like accumulation of sequence differences in some genes provides an alternative

Sudhir Kumar; S. Blair Hedges

1998-01-01

59

BOOK REVIEW: Einstein's Jury: The Race to Test Relativity  

NASA Astrophysics Data System (ADS)

'I know very well that my theory rests on a shaky foundation. What attracts me to it is that it leads to consequences that seem to be accessible to experiment, and it provides a starting point for the theoretical understanding of gravitation', wrote Einstein in 1911. Einstein's Jury by Jeffrey Crelinsten—well documented, well written, and fascinating to read—describes how, from 1909 on, Einstein's two theories of relativity became known to astronomers, and how the predictions made between 1907 and 1915 were received as challenges to observers. The author gives a non-technical account of the efforts made until 1930 to test these predictions; he focuses on two of the three classical tests, namely gravitational redshift and bending of light; the 'jury' consists mainly of American observers—Adams, Campbell, Curtis, Hale, Perrin, St John, Trumpler and others—working with newly built large telescopes, and the Britons Eddington and Evershed. The major steps which, after a long struggle, convinced the majority of astronomers that Einstein was right, are narrated chronologically in rather great detail, especially the work at Lick Observatory, before and after the famous British observation of 1919, on solar eclipses, and the work at Mount Wilson and the Indian Kodaikanal Observatories to extract the gravitational redshift from the complicated spectrum of the sun. The account of the eclipse work which was carried out between 1918 and 1923 by Lick astronomers corrects the impression suggested by many historical accounts that the British expedition alone settled the light-bending question. Apart from these main topics, the anomalous perihelion advance of Mercury and the ether problem are covered. By concentrating on astronomy rather than on physics this book complements the rich but repetitive literature on Einstein and relativity which appeared in connection with the commemoration of Einstein's annus mirabilis, 2005. The well told stories include curiosities such as the Vulcan hypothesis, Evershed's Earth effect, and D C Miller's ether drift experiments. In particular, the sections on the history of the Californian observatories, their leading personalities, the differing attitudes of American and European scientists, and the influence of World War 1 on science, add interesting and informative aspects to the narrative. Those sections which report logistic and instrumental details of, for example, eclipse expeditions, were (to me) somewhat tiring. A weakness seems to be that the scientific importance of relativity problems is not stated clearly. On p43, the reader learns that Curtis quoted de Sitter's theoretical result of 7.15'' per century for Mercury's anomalous perihelion shift, but it is not mentioned that this value was due only to the special-relativistic variation of mass with velocity and already known to be much smaller than the observed value given on p88 and explained by general relativity, which includes, in particular, space curvature. In connection with light bending, the 'factor 2' is mentioned in several places without the explanation that this doubling is due to space curvature, the principal new effect whose observation created such a stir in 1919. Moreover, technical terms, for example absolute space, inertial frame, state of rest and (anomalous) dispersion, are used without explanation. Besides, readers interested as much in science as in its history would probably have appreciated a brief account of the present state of knowledge concerning the issues treated in this book and related ones. There are a few deplorable errors, for example the spectrum of the Andromeda nebula is shifted not towards the red, but towards the blue (p12); Eddington's limb deflection is given (p144) as 0.61'', while the correct value is 1.61''; misprints like that on p147 (coefficient of dr²), mistaking the astronomer Soldner (not Solden) for a physicist (p164). On p34 one reads 'Minkowski did not really grasp the physical implications of Einstein's work'—a strange judgment which contradicts the historical record. Thus reader

Ehlers, Jürgen

2007-10-01

60

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

61

Backreaction of accreting matter onto a black hole in the Eddington-Finkelstein coordinates  

NASA Astrophysics Data System (ADS)

We study backreaction of accreting matter onto a spherically symmetric black hole in a perturbative way, when accretion is in a quasi-steady state. General expressions for corrections to the metric coefficients are found in the Eddington-Finkelstein coordinates. It is shown that near the horizon of a black hole, independently of the form of the energy-momentum tensor, the leading corrections to the metric are of the Vaidya form. The relation to other solutions is discussed and particular examples are presented.

Babichev, E.; Dokuchaev, V.; Eroshenko, Yu

2012-06-01

62

Massive Stars Near the Eddington Limit: Mass Loss and Envelope Inflation  

NASA Astrophysics Data System (ADS)

When massive stars approach the Eddington limit, their outer envelopes and winds become dominated by ‘opacity peaks’, i.e. by material properties. We discuss the physical consequences, namely the formation of strong Wolf-Rayet (WR) type winds and a radial extension of the stellar envelopes. The understanding of the physical processes in this regime is of basic importance for key phases of stellar evolution, such as the WR and LBV stage, and thus for questions on how massive stars evolve and how they end their lives.

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

2012-12-01

63

Einstein’s 1935 Derivation of E= mc 2  

Microsoft Academic Search

Einstein’s 1935 derivation of mass–energy equivalence is philosophically important because it contains both a criticism of purported demonstrations that proceed by analogy and strong motivations for the definitions of the ‘new’ dynamical quantities (viz relativistic momentum, relativistic kinetic energy and relativistic energy). In this paper, I argue that Einstein’s criticism and insights are still relevant today by showing how his

Francisco Flores

1998-01-01

64

Einstein and Bose  

NASA Astrophysics Data System (ADS)

In June 1924, a relatively unknown Satyendra Nath Bose from Dacca, India, wrote a letter to Einstein beginning with ``Respected Sir, I have ventured to send you the accompanying article for your perusal. I am anxious to know what you think of it. You will see that I have ventured to deduce the coefficient 8??^2/c^3 in Planck's law independent of the classical electrodynamics, only assuming that the ultimate elementary regions in Phase-space have the content h^3. I do not know sufficient German to translate the paper. If you think the paper worth publication, I shall be grateful if you arrange for its publication in Zeitschrift für Physik.'' Einstein did translate the article himself and got it published. He wrote to Ehrenfest: ``The Indian Bose has given a beautiful derivation of Planck's law, including the constant [i.e.8??^2/c^3].'' Einstein extended the ideas of Bose that implied, among other things, a new statistics for the light-quanta to the molecules of an ideal gas and wrote to Ehrenfest, `from a certain temperature on, the molecules ``condense'' without attractive forces, that is, they accumulate at zero velocity. The theory is pretty, but is there also some truth to it?' Abraham Pais has called Bose's paper ``the fourth and the last revolutionary papers of the old quantum theory.'' My paper will present the works of Bose and Einstein in their historical perspective and the eventual birth of the new quantum Bose-Einstein statistics.

Wali, Kameshwar C.

2005-04-01

65

Conversations With Albert Einstein. II  

ERIC Educational Resources Information Center

|Discusses Einstein's views on the role of Michelson-Morley, Fizeau, and Miller experiments in the development of relativity and his attitude toward the theories of new quantum mechanics. Indicates that Einstein's opposition to quantum mechanics is beyond dispute. (CC)|

Shankland, R. S.

1973-01-01

66

Certainties and uncertainties of orbitally tuned timescales  

NASA Astrophysics Data System (ADS)

High precision timescales are often based on an integrated stratigraphical approach using several dating techniques. Because many records show an imprint of orbital climate forcing, these imprints can be used to obtain high resolution stratigraphies. However, uncertainties are hardly ever assigned to these timescales, mainly because uncertainties are not straightforward to quantify. We discuss different sources of uncertainty (the uncertainty of the astronomical parameters used for the tuning procedure, climatic response time to orbital forcing, non-constant sedimentation rates) and discuss the assignment of realistic ages and (un)certainties for chronologies based on orbital tuning. Besides discussing uncertainties, it is important to note that very most cyclostratigraphic studies are based on an integrated stratigraphic approach, and are not solely based on orbital tuning.

Zeeden, Christian; Rivera, Tiffany; Lourens, Lucas; Hilgen, Frederik

2013-04-01

67

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

68

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.

69

Effects of aerosols on the wavelength dependence of atmospheric transmission in the ultraviolet and visible 1. A ``single-scattering-separate'' delta-Eddington model  

Microsoft Academic Search

A modification to the conventional delta-Eddington radiative transfer scheme was implemented in order to create a simple and efficient model particularly suitable for handling the highly anisotropic scattering properties exhibited by cloud drops and aerosol particles in the atmosphere. The modification includes separating out the singly scattered radiation and applying the conventional Eddington approximation to the multiply scattered radiation alone.

Carynelisa Erlickand; John E. Frederick

1998-01-01

70

Times of Albert Einstein.  

National Technical Information Service (NTIS)

''The life of Albert Einstein has a dramatic quality that does not rest exclusively on his theory of relativity. The extravagant timing of history linked him with three shattering developments of the twentieth century: the rise and fall of Nazi Germany, t...

S. M. W. Ahmad

1990-01-01

71

Einstein and Singularities  

Microsoft Academic Search

Except for a few brief periods, Einstein was uninterested in analysing the nature of the spacetime singularities that appeared in solutions to his gravitational field equations for general relativity. The existence of such monstrosities reinforced his conviction that general relativity was an incomplete theory which would be superseded by a singularity-free unified field theory. Nevertheless, on a number of occasions

John Earman; Jean Eisenstaedt

1999-01-01

72

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

73

Examining the Enigmatic Einstein  

ERIC Educational Resources Information Center

|Albert Einstein is the icon of scientific genius. His is one the most recognizable faces in the history of mankind. This paper takes a cursory look at the man who is commonly perceived to be the epitome of eccentricity. We manage to sum up his salient traits which are associated with his name. The traits are based on anecdotal evidence. This…

Khoon, Koh Aik

2007-01-01

74

Einstein's Years in Switzerland  

Microsoft Academic Search

Albert Einstein left Germany, the country of his birth, in 1894 and moved to Switzerland in 1895. He studied, worked and taught there, except for a year's stay in Prague, until1914. That year he returned to Germany, where he lived until his emigration to the United States in 1933. In 1905, while living with his wife Mileva and their first

Hans S. Plendl

2005-01-01

75

Einstein and Friedman  

NASA Astrophysics Data System (ADS)

The focus of the present article is Friedman's 1922 letter to Einstein accompanied by additional evidence throwing light on their debate, and the great roles played by Yuri Krutkov and Paul Ehrenfest, both of whom Einstein knew very well (see Frenkel 1970). The debate began soon after the appearance of Friedman's first article showing the possibility of a nonstationary solution of the cosmological problem (thus laying the foundation for the theory of an expanding universe). Einstein replied to Friedman with a note in which, as aptly observed by Fock, "he said, somewhat condescendingly, that Friedman's results seemed suspicious to him, and that he had found a mistake in them which, when corrected, reduced Friedman's solution to a stationary one" (Friedman 1966). Great people's delusions are always instructive, especially when dealing with fundamental problems. The honesty of great men can also be exemplary: the debate came to an end after the publication of Einstein's second note, in which he stressed the importance of Friedman's work.

Frenkel, Viktor

76

Einstein Cannon Model  

NSDL National Science Digital Library

The Einstein Cannon model computes and displays the trajectory of cannonballs (particles) shot from a cannon in the vicinity of a black hole.  It was created for the study of Einstein's theory of general relativity and the Schwarzschild metric.  The main window displays a map of space in the vicinity of the black hole using Schwarzschild coordinates and a cannon located a distance r0 from the center black hole's center.  The position and firing angle of the cannon can be adjusted by dragging a marker and the number of cannon balls and their initial speed can be changed using input fields.  The maximum speed of the cannon ball is the speed of light c=1 in accordance with Einstein's theory.  Newton suggested that a cannon ball fired from a high mountain could fall to Earth, orbit the Earth, or fly away depending on how it was fired.  The same is true in general relativity but there are many important differences.  This model demonstrates these differences. The Einstein Cannon model is a supplemental simulation for the article "When action is not least for orbits in general relativity" by C. G. Gray and Eric Poisson in the American Journal of Physics 79(1), 43-55 (2011) and has been approved by the authors and the American Journal of Physics (AJP) editor. The simulation was developed using the Easy Java Simulations (EJS) modeling tool and is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_gr_EinsteinCannon.jar file will run the program if Java is installed.

Christian, Wolfgang

2010-10-30

77

A Porosity-Length Formalism for Photon-Tiring-Limited Mass Loss from Stars Above the Eddington Limit  

Microsoft Academic Search

We examine radiatively driven mass loss from stars near and above the\\u000aEddington limit (Ledd). We begin by reviewing the instabilities that are\\u000aexpected to form extensive structure near Ledd. We investigate how this\\u000a\\

Kenneth G. Gayley; Nir J. Shaviv

2004-01-01

78

Host galaxies, BH Masses and Eddington Ratio of Radio-Loud AGNs  

NASA Astrophysics Data System (ADS)

We compare the host galaxies properties of BL Lac objects with those of radio loud quasars (RLQs) imaged by the WFPC2 on board of HST. The considered objects (z<0.5) are always well resolved and their host galaxies satisfactorily modelled by ellipticals. After homogeneous treatment of the data we find RLQs hosts are systematically more luminous (by ~0.7 mag) with respect to the hosts of BL Lacs. Using the M_BH - L_bulge relation, derived for nearby elliptical galaxies, we have evaluated the central black hole masses of our sample of active galaxies. These data are discussed in conjunction with the nuclear luminosity and the Eddington ratio.

Treves, A.; Carangelo, N.; Falomo, R.; Urry, C. M.; O'Dowd, M.; Scarpa, R.

79

New Velocity Distribution for Cold Dark Matter in the Context of the Eddington Theory  

NASA Astrophysics Data System (ADS)

Exotic dark matter, together with the vacuum energy (associated with the cosmological constant), seems to dominate the universe. Thus, its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and velocity distribution of the LSP. The detection rate is proportional to this density in our vicinity. Furthermore, since this rate is expected to be very low, one should explore the two characteristic signatures of the process, namely, the modulation effect, i.e., the dependence of the event rate on the Earth's motion, and the correlation of the directional rate with the motion of the Sun. Both of these crucially depend on the LSP velocity distribution. In the present paper we study simultaneously density profiles and velocity distributions based on the Eddington theory.

Vergados, J. D.; Owen, D.

2003-05-01

80

EDDINGTON RATIO GOVERNS THE EQUIVALENT WIDTH OF Mg II EMISSION LINE IN ACTIVE GALACTIC NUCLEI  

SciTech Connect

We have investigated the ensemble regularities of the equivalent widths (EWs) of Mg II lambda2800 emission line of active galactic nuclei (AGNs), using a uniformly selected sample of 2092 Seyfert 1 galaxies and quasars at 0.45 <= z <= 0.8 in the spectroscopic data set of the Sloan Digital Sky Survey Fourth Data Release. We find a strong correlation between the EW of Mg II and the AGN Eddington ratio (L/L{sub Edd}): EW(Mg II) propor to (L/L {sub Edd}){sup -0.4}. Furthermore, for AGNs with the same L/L{sub Edd}, their EWs of Mg II show no correlation with luminosity, black hole mass, or line width, and the Mg II line luminosity is proportional to continuum luminosity, as expected by photoionization theory. Our result shows that Mg II EW is not dependent on luminosity, but is solely governed by L/L{sub Edd}.

Dong Xiaobo; Wang Tinggui; Wang Jianguo; Wang Huiyuan; Zhou Hongyan [Key Laboratory for Research in Galaxies and Cosmology, University of Sciences and Technology of China, Chinese Academy of Sciences, Hefei, Anhui 230026 (China); Fan Xiaohui [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Yuan Weimin, E-mail: xbdong@ustc.edu.c, E-mail: wmy@ynao.ac.c, E-mail: fan@as.arizona.ed [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, Kunming, Yunnan 650011 (China)

2009-09-20

81

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

82

Einstein's Years in Switzerland  

NASA Astrophysics Data System (ADS)

Albert Einstein left Germany, the country of his birth, in 1894 and moved to Switzerland in 1895. He studied, worked and taught there, except for a year's stay in Prague, until1914. That year he returned to Germany, where he lived until his emigration to the United States in 1933. In 1905, while living with his wife Mileva and their first son Hans Albert in Bern and working as a technical expert at the Swiss Patent Office, he published his dissertation on the determination of molecular dimensions, his papers on Brownian Motion that helped to establish the Kinetic Theory of Heat and on the Photo-Electric Effect that validated the Quantum Theory of Light, and the two papers introducing the Special Theory of Relativity. How the young Einstein could help to lay the foundations of these theories while still working on his dissertation, holding a full-time job and helping to raise a family has evoked much discussion among his biographers. In this contribution, the extent to which living within Swiss society and culture could have made this feat possible will be examined. Old and recent photos of places in Switzerland where Einstein has lived and worked will be shown.

Plendl, Hans S.

2005-11-01

83

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

NASA Astrophysics Data System (ADS)

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.

2009-12-01

84

Einstein's Jury: Trial by Telescope  

NASA Astrophysics Data System (ADS)

While Einstein's theory of relativity ultimately laid the foundation for modern studies of the universe, it took a long time to be accepted. Between 1905 and 1930, relativity was poorly understood and Einstein worked hard to try to make it more accessible to scientists and scientifically literate laypeople. Its acceptance was largely due to the astronomy community, which undertook precise measurements to test Einstein's astronomical predictions. The well-known 1919 British eclipse expeditions that made Einstein famous did not convince most scientists to accept relativity. The 1920s saw numerous attempts to measure light-bending, as well as solar line displacements and even ether-drift. How astronomers approached the ``Einstein problem'' in these early years before and after the First World War, and how the public reacted to what they reported, helped to shape attitudes we hold today about Einstein and his ideas.

Crelinsten, Jeffrey

2007-03-01

85

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

86

Timescale Measures for Irregularly Sampled, Aperiodic Light Curves  

NASA Astrophysics Data System (ADS)

We present preliminary results of a project to determine the most robust methods for identifying the characteristic timescale(s) of an aperiodic signal given noise and uneven sampling. While periodograms have been a staple of the analysis of periodic signals for decades, the analogous situation for aperiodic signals involves a mixture of competing heuristic techniques. We present both theoretical and empirical characterizations of the accuracy, precision, and robustness of a variety of techniques, and outline recommendations for the most practical timescale measures.

Findeisen, Krzysztof; Hillenbrand, L.

2013-06-01

87

Short Timescale Variations in the Atmosphere of Antares A  

NASA Astrophysics Data System (ADS)

We analyze three years of high-resolution spectroscopic data and find radial velocity variations with a characteristic timescale of 100 ± 6 days that are nearly sinusoidal. Simultaneous variations in line-depth ratios imply temperature variations of up to 100 K. No photometric variation is seen on a 100 day timescale. The timescale of the variation and its resonant nature suggest solar-like oscillations driven by large-scale convection.

Pugh, T.; Gray, David F.

2013-11-01

88

ON THE RADIATIVE EFFICIENCIES, EDDINGTON RATIOS, AND DUTY CYCLES OF LUMINOUS HIGH-REDSHIFT QUASARS  

SciTech Connect

We investigate the characteristic radiative efficiency {epsilon}, Eddington ratio {lambda}, and duty cycle P {sub 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}, {lambda}, and the normalization, scatter, and redshift evolution of the relation between black hole (BH) mass M {sub BH} and halo virial velocity V{sub 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 {lambda}, with a lower limit (based on 2{sigma} agreement with the measured z = 4 correlation length) {epsilon} {approx}> 0.7{lambda}/(1 + 0.7{lambda}), implying {epsilon} {approx}> 0.17 for {lambda}>0.25. Successful models predict high duty cycles, P{sub 0} {approx} 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 > 10{sup 47.5} erg s{sup -1} should be at z {approx} 7.5, and that all quasars with higher apparent luminosities would have to be magnified by lensing.

Shankar, Francesco; Weinberg, David H. [Astronomy Department, Ohio State University, 140 W. 18th Ave., Columbus, OH 43210 (United States); Crocce, Martin; Miralda-Escude, Jordi; Fosalba, Pablo [Institut de Ciencies de l'Espai (IEEC-CSIC), Campus UAB, Bellaterra (Spain)

2010-07-20

89

Preheating in generalized Einstein theories  

Microsoft Academic Search

We study the preheating scenario in generalized Einstein theories, considering a class of such theories which are conformally equivalent to those of an extra field with a modified potential in the Einstein frame. Resonant creation of bosons from an oscillating inflaton has been studied before in the context of general relativity taking also into account the effect of metric perturbations

Anupam Mazumdar; Luís E. Mendes

1999-01-01

90

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

91

Einstein and the "Crucial" Experiment  

ERIC Educational Resources Information Center

|Examines the widespread view that it was the crucial Michelson-Morley experiment that led Einstein to formulate the special relativity theory. From Einstein's writings, evidence is presented that no such direct genetic connection exists. The author suggests that the historian of science must resist the experimenticist's fallacy of imposing a…

Holton, Gerald

1969-01-01

92

Liouville gravity from Einstein gravity  

Microsoft Academic Search

We show that Liouville gravity arises as the limit of pure Einstein gravity in 2+epsilon dimensions as epsilon goes to zero, provided Newton's constant scales with epsilon. Our procedure - spherical reduction, dualization, limit, dualizing back - passes several consistency tests: geometric properties, interactions with matter and the Bekenstein-Hawking entropy are as expected from Einstein gravity.

D. Grumiller; R. Jackiw

2007-01-01

93

BOOK REVIEW: Once Upon Einstein  

Microsoft Academic Search

Thibault Damour is a theoretical physicist, and a member of the French Academy of Sciences. This book is the translation, by Eric Novak, of the original French Si Einstein m'etait conté (Le Cherche Midi, 2005). It is neither a book of theoretical physics nor a biography of Einstein. It is not a book of history nor philosophy of science. In

Thibault Damour

2007-01-01

94

Einstein's Jury: Trial by Telescope  

Microsoft Academic Search

While Einstein's theory of relativity ultimately laid the foundation for modern studies of the universe, it took a long time to be accepted. Between 1905 and 1930, relativity was poorly understood and Einstein worked hard to try to make it more accessible to scientists and scientifically literate laypeople. Its acceptance was largely due to the astronomy community, which undertook precise

Jeffrey Crelinsten

2007-01-01

95

A Niching Genetic Algorithm For Milne-Eddington Spectral Line Inversions  

NASA Astrophysics Data System (ADS)

Stokes profile inversions form a basis for ``measuring'' solar magnetic fields. The High Altitude Observatory (HAO) Milne-Eddington (M-E) spectral line inversions have traditionally been used as initializations to more sophisticated inversion procedures. One such code uses a genetic-algorithm initialization to search the parameter space on a more global scale, in an effort to obtain a good starting guess for a more traditional hill-climbing (e.g. Levenberg-Marquardt) algorithm. A serious drawback to the type of genetic algorithm used is that it has been shown to perform poorly on high-dimensional spaces with multiple optima. A single-component M-E model atmosphere is typically described by about 7 free parameters, indicating a fairly high parameter space dimensionality. Two-component models increase the ability to fit frequently-observed asymmetric spectral lines, at the price of nearly doubling the dimension of the parameter space. Furthermore, spectral lines for large magnetic field strengths and large inclinations are very similar to profiles for weaker field strengths and small inclinations, indicating the potential presence of multiple optima that correspond to very different physical conditions. This poster presents an initial investigation into alleviating these difficulties by incorporating a more sophisticated evolutionary strategy into the SGA, and parallelizing over multiple processors.

Harker, Brian; Balasubramaniam, K.; Sojka, Jan

2006-10-01

96

Eddington-inspired Born-Infeld gravity: Phenomenology of nonlinear gravity-matter coupling  

NASA Astrophysics Data System (ADS)

Viable corrections to the matter sector of Poisson’s equation may result in qualitatively different astrophysical phenomenology, for example, the gravitational collapse and the properties of compact objects can change drastically. We discuss a class of modified nonrelativistic theories and focus on a relativistic completion, Eddington-inspired Born-Infeld gravity. This recently proposed theory is equivalent to General Relativity in vacuum, but its nontrivial coupling to matter prevents singularities in early cosmology and in the nonrelativistic collapse of noninteracting particles. We extend our previous analysis, discussing further developments. We present a full numerical study of spherically symmetric nonrelativistic gravitational collapse of dust. For any positive coupling, the final state of the collapse is a regular pressureless star rather than a singularity. We also argue that there is no Chandrasekhar limit for the mass of a nonrelativistic white dwarf in this theory. Finally, we extend our previous results in the fully relativistic theory by constructing static and slowly rotating compact stars governed by nuclear-physics inspired equations of state. In the relativistic theory, there exists an upper bound on the mass of compact objects, suggesting that black holes can still be formed in the relativistic collapse.

Pani, Paolo; Delsate, Térence; Cardoso, Vitor

2012-04-01

97

Super-Eddington accreting massive black holes as long-lived cosmological standards.  

PubMed

Super-Eddington accreting massive black holes (SEAMBHs) reach saturated luminosities above a certain accretion rate due to photon trapping and advection in slim accretion disks. We show that these SEAMBHs could provide a new tool for estimating cosmological distances if they are properly identified by hard x-ray observations, in particular by the slope of their 2-10 keV continuum. To verify this idea we obtained black hole mass estimates and x-ray data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be the most promising SEAMBH candidates. We demonstrate that the distances derived by the new method for the objects in the sample get closer to the standard luminosity distances as the hard x-ray continuum gets steeper. The results allow us to analyze the requirements for using the method in future samples of active black holes and to demonstrate that the expected uncertainty, given large enough samples, can make them into a useful, new cosmological ruler. PMID:23473126

Wang, Jian-Min; Du, Pu; Valls-Gabaud, David; Hu, Chen; Netzer, Hagai

2013-02-19

98

Einstein: The Standard of Greatness  

ScienceCinema

Einstein's seven-month performance in 1905 has no equal in the history of physics. Beginning with his revolutionary paper, completed on March 17, and continuing to September 26, Einstein wrote a total of five papers that changed the infrastructure of physics and today, a century later, these papers remain part of the tectonic bedrock of the discipline. How Einstein approached his physics and what he accomplished certainly provided the basis for his world fame. But while the What? and the How? were, and remain, of primary importance, can they explain Einstein's celebrity standing after 1922 and his iconic status today, fifty years after his death? The question remains: Why is Einstein the standard of greatness?

99

Einstein: The Standard of Greatness  

SciTech Connect

Einstein's seven-month performance in 1905 has no equal in the history of physics. Beginning with his revolutionary paper, completed on March 17, and continuing to September 26, Einstein wrote a total of five papers that changed the infrastructure of physics and today, a century later, these papers remain part of the tectonic bedrock of the discipline. How Einstein approached his physics and what he accomplished certainly provided the basis for his world fame. But while the What? and the How? were, and remain, of primary importance, can they explain Einstein's celebrity standing after 1922 and his iconic status today, fifty years after his death? The question remains: Why is Einstein the standard of greatness?

Rigdon, John (Washington University)

2005-03-16

100

The Demographics of Broad-line Quasars in the Mass-Luminosity Plane. II. Black Hole Mass and Eddington Ratio Functions  

NASA Astrophysics Data System (ADS)

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 ~58, 000 quasars from the Sloan Digital Sky Survey (SDSS) DR7. We find that the SDSS becomes significantly incomplete at M BH <~ 3 × 108 M ? or L/L Edd <~ 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 Edd ~ 3. Consistent with our results in Shen & 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.; Shen, Yue

2013-02-01

101

Timescale phenomena in multi - fragment processes  

NASA Astrophysics Data System (ADS)

Recent experimental results on the production of intermediate mass fragments (IMF) in reactions of 12C, 18O, 20Ne, and 40Ar on natAg and 197Au at bombarding energies 30MeV <= E/A <= 84 MeV are reviewed. For all investigated reactions the average multiplicity of IMF's is <= 1.6, indicating that these reactions mark the threshold region for multi-fragment processes. Correlations between intermediate-mass fragments were measured for 18O induced reactions on natAg and 197Au at E/A = 84 MeV. An anticorrelation at low relative velocities is observed reflecting the proximity of the two IMF's at the point of creation. The timescales for IMF emission derived from these correlation functions are similar to those of binary decay modes which indicates a multi-sequential nature of multifragment emission. Furthermore, it is found that the excitation energy residing in the composite system before fragment emission is the key variable governing these processes. The results presented in this paper were obtained in several experiments performed in collaboration with E. Eckert, R. Glasow, K.D. Hildenbrand, K.H. Kampert, P. Kreutz, A. Kühmichel, U. Lynen, W.F.J. Müller, D. Pelte, H.J. Rabe, H. Sann, R. Santo, H. Stelzer, W. Trautmann, R. Trockel, R. Wada.

Pochodzalla, Josef

1988-10-01

102

Relaxation timescales for conformational substates in disordered polymers  

Microsoft Academic Search

We study the kinetics of interconversion of conformational substates in RNA folding by means of a Monte-Carlo simulation. We establish a scaling law relating the size of the barriers with the length of a random uncorrelated RNA chain. The way the relaxation timescales diverge in the thermodynamic limit coincides with the behavior of nonergodic relaxation timescales for spin glasses.

Ariel Fernández

1992-01-01

103

Multi-timescale nonlinear robust control for a miniature helicopter  

Microsoft Academic Search

This paper proposes a new nonlinear control approach which is applied to a miniature aerobatic helicopter through a multi-timescale structure. To deal with inherent unstable internal dynamics, the translational, rotational, and flapping dynamics of the helicopter are organized into a three-timescale nonlinear model. The concepts of dynamic inversion and sliding manifold are combined together. Part of the uncertainties is explicitly

Yunjun Xu

2008-01-01

104

On Einstein's 1905 Paper, E = mc 2  

Microsoft Academic Search

As we know the derivation of mass - energy equivalence which is called Einstein's relation has been derived through different ways by Einstein and appeared in his article which was published in 1905. Einstein's derivation is true under special conditions only, not in general. Hence Einstein's relation opened the door to many researchers who presented many papers about this relation.

A. K. Hariri; N. Hamdan; A. Dahan

105

Stratospheric variability and tropospheric annular mode timescales.  

NASA Astrophysics Data System (ADS)

The annular modes are the dominant modes of variability in the extra-tropical circulation of each hemisphere. In the troposphere they represent latitudinal migrations of the eddy driven mid-latitude jets. Many climate forcings such as ozone depletion and increasing greenhouse gas concentrations result in circulation changes that project strongly onto these modes. It is therefore important that the dynamics behind annular mode variability be understood and that such variability be captured correctly in climate models. Observational evidence suggests that stratospheric variability enhances annular mode timescales, although it is difficult to prove this unambiguously as other factors, such as tropospheric jet structure, vary alongside stratospheric variability. Here, experiments with the Canadian Middle Atmosphere Model (CMAM) will be presented. A free running simulation is compared with a simulation in which the zonal mean circulation of the stratosphere is nudged toward the climatology of the free simulation. These two simulations have identical climatologies but one has zonal mean stratospheric variability and the other does not. This allows us to clearly demonstrate that stratospheric zonal-mean variability significantly enhances tropospheric annular mode persistence. A common bias among climate models is that they tend to exhibit much too persistent Southern Annular Mode anomalies in the summer season. While some of this bias is attributable to stratospheric zonal-mean biases in late spring/early summer, these model experiments also reveal that, atleast for the case of CMAM, a significant proportion of this bias is internal to the troposphere. This potentially has important consequences for the ability of global climate models to simulate SH climate change in this season. Possible causes of this bias will be discussed.

Simpson, I. R.; Hitchcock, P.; Shepherd, T. G.; Scinocca, J. F.

2012-04-01

106

The jets and disc of SS 433 at super-Eddington luminosities  

NASA Astrophysics Data System (ADS)

We examine the jets and the disc of SS 433 at super-Eddington luminosities with by time-dependent two-dimensional radiation hydrodynamical calculations, assuming an ?-model for the viscosity. One-dimensional supercritical accretion disc models with mass loss or advection are used as the initial configurations of the disc. As a result, from the initial advective disc models with ? = 0.001 and 0.1, we obtain total luminosities ~2.5 × 1040 and 2.0 × 1040ergs-1. The total mass-outflow rates are ~4 × 10-5 and 10-4Msolaryr-1, and the rates of the relativistic axial outflows in a small half opening angle of ~1° are about 10-6Msolaryr-1: the values are generally consistent with the corresponding observed rates of the wind and the jets, respectively. From the initial models with mass loss but without advection, we obtain total mass-outflow and axial outflow rates smaller than or comparable to the observed rates of the wind and the jets, respectively, depending on ?. In the advective disc model with ? = 0.1, the initially radiation-pressure-dominant, optically thick disc evolves to a gas-pressure-dominated, optically thin state in the inner region of the disc, and the inner disc is unstable. Consequently, we find remarkable modulations of the disc luminosity and the accretion rate through the inner edge. These modulations manifest themselves as recurrent hot blobs with high temperatures and low densities at the disc plane, which develop outwards and upwards and produce quasi-periodic oscillations (QPOs) of the total luminosity with an amplitude of a factor of ~2 and quasi-periods of ~10-25 s. This may explain the massive jet ejection and the QPO phenomena observed in SS 433.

Okuda, T.; Lipunova, G. V.; Molteni, D.

2009-10-01

107

Eddington-limited Accretion and the Black Hole Mass Function at Redshift 6  

NASA Astrophysics Data System (ADS)

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 ~ 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 ~104 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 ~102 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.; Albert, Loic; Arzoumanian, Doris; Bergeron, Jacqueline; Crampton, David; Delorme, Philippe; Hutchings, John B.; Omont, Alain; Reylé, Céline; Schade, David

2010-08-01

108

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

109

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

110

Einstein: The Gourmet of Creativity.  

ERIC Educational Resources Information Center

|Reports a psychiatrist's analysis of Einstein's personal account of how he developed the theory of relativity. The psychiatrist cites Janusian thinking, actively conceiving two or more opposite concepts simultaneously, as a characteristic of much creative thought in general. (MA)|

Greenberg, Joel

1979-01-01

111

Factorizability of Einstein'S Field Equations.  

National Technical Information Service (NTIS)

In the two-dimensional spinor formulation, the field equations of general relativity are shown not to factor. However, since the spinor field equations have an antisymmetric part, they have more content than the Einstein field equations.

H. G. Loos

1968-01-01

112

Einstein: The Gourmet of Creativity.  

ERIC Educational Resources Information Center

Reports a psychiatrist's analysis of Einstein's personal account of how he developed the theory of relativity. The psychiatrist cites Janusian thinking, actively conceiving two or more opposite concepts simultaneously, as a characteristic of much creative thought in general. (MA)

Greenberg, Joel

1979-01-01

113

Video Gallery: Reflection on Einstein  

NSDL National Science Digital Library

This online video gallery is from the Museum's Seminars on Science, a series of distance-learning courses designed to help educators meet the new national science standards. Reflections on Einstein, part of the Frontiers in Physical Science seminar, is available in broadband and modem formats and with a printable PDF transcript. The video shows excerpts of a panel of seven scientists reflecting on Einstein's influence.

114

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

115

Geometric structure of multiple time-scale nonlinear dynamical systems  

Microsoft Academic Search

A new methodology to analyze time-scale structure of smooth finite-dimensional nonlinear dynamical systems is developed. This approach does not assume apriori knowledge of slow and fast variables for special coordinates that simplify the form of the nonlinear dynamics. Conventional approaches to analyze time-scale structure of nonlinear dynamics such as singular perturbation theory proceed from such specialized apriori knowledge which is

Sanjay Bharadwaj

1999-01-01

116

CHEMICAL TIMESCALES IN THE ATMOSPHERES OF HIGHLY ECCENTRIC EXOPLANETS  

SciTech Connect

Close-in exoplanets with highly eccentric orbits are subject to large variations in incoming stellar flux between periapse and apoapse. These variations may lead to large swings in atmospheric temperature, which in turn may cause changes in the chemistry of the atmosphere from higher CO abundances at periapse to higher CH{sub 4} abundances at apoapse. Here, we examine chemical timescales for CO{r_reversible}CH{sub 4} interconversion compared to orbital timescales and vertical mixing timescales for the highly eccentric exoplanets HAT-P-2b and CoRoT-10b. As exoplanet atmospheres cool, the chemical timescales for CO{r_reversible}CH{sub 4} tend to exceed orbital and/or vertical mixing timescales, leading to quenching. The relative roles of orbit-induced thermal quenching and vertical quenching depend upon mixing timescales relative to orbital timescales. For both HAT-P-2b and CoRoT-10b, vertical quenching will determine disequilibrium CO{r_reversible}CH{sub 4} chemistry at faster vertical mixing rates (K{sub zz} > 10{sup 7} cm{sup 2} s{sup -1}), whereas orbit-induced thermal quenching may play a significant role at slower mixing rates (K{sub zz} < 10{sup 7} cm{sup 2} s{sup -1}). The general abundance and chemical timescale results-calculated as a function of pressure, temperature, and metallicity-can be applied for different atmospheric profiles in order to estimate the quench level and disequilibrium abundances of CO and CH{sub 4} on hydrogen-dominated exoplanets. Observations of CO and CH{sub 4} on highly eccentric exoplanets may yield important clues to the chemical and dynamical properties of their atmospheres.

Visscher, Channon [Department of Space Studies, Southwest Research Institute, Boulder, CO 80302 (United States)

2012-09-20

117

Einstein's 1919 View  

NASA Astrophysics Data System (ADS)

When Rutherford discovered the nuclear force in 1919, he felt the force he discovered reflected some deviation of Newtonian gravity. Einstein too in his 1919 paper published the failure of the general relativity and Newtonian gravity to explain nuclear force and, in his concluding remarks, he retracted his earlier introduction of the cosmological constant. Consistent with his genius, we modify Newtonian gravity as probabilistic gravity using natural Planck units for a realistic study of nature. The result is capable of expressing both (1) nuclear force [strong coupling], and (2) Newtonian gravity in one equation, implying in general, in layman's words, that gravity is the cumulative effect of all quantum mechanical forces which are impossible to measure at long distances. Non discovery of graviton and quantum gravity silently support our findings. Continuing to climb on the shoulders of the giants enables us to see horizons otherwise unseen, as reflected in our book: ``Quantum Consciousness - The Road to Reality,'' and physics/0210040, where we derive the fine structure constant as a function of the age of the universe in Planck times consistent with Gamow's hint, using natural logarithm consistent with Feynman's hint.

Goradia, Shantilal

2012-10-01

118

Reservoir timescales for anthropogenic CO2 in the atmosphere  

PubMed

Non-steady state timescales are complicated and their application to specific geophysical systems requires a common theoretical foundation. We first extend reservoir theory by quantifying the difference between turnover time and transit time (or residence time) for time-dependent systems under any mixing conditions. We explicitly demonstrate the errors which result from assuming these timescales are equal, which is only true at steady state. We also derive a new response function which allows the calculation of age distributions and timescales for well-mixed reservoirs away from steady state, and differentiate between timescales based on gross and net fluxes. These theoretical results are particularly important to tracer-calibrated "box models" currently used to study the carbon cycle, which usually approximate reservoirs as well-mixed. We then apply the results to the important case of anthropogenic CO2 in the atmosphere, since timescales describing its behavior are commonly used but ambiguously defined. All relevant timescales, including lifetime, transit time, and adjustment time, are precisely defined and calculated from data and models. Apparent discrepancies between the current, empirically determined turnover time of 30-60 years and longer model-derived estimates of expected lifetime and adjustment time are explained within this theoretical framework. We also discuss the results in light of policy issues related to global warming, in particular since any comparisons of the "lifetimes" of different greenhouse gases (CO2, CH4, N2O, CFC's etc.) must use a consistent definition to be meaningful. PMID:11541520

O'Neill, B C; Gaffin, S R; Tubiello, F N; Oppenheimer, M

1994-11-01

119

Extended timescale atomistic modeling of crack tip behavior in aluminum  

NASA Astrophysics Data System (ADS)

Traditional molecular dynamics (MD) simulations are limited not only by their spatial domain, but also by the time domain that they can examine. Considering that many of the events associated with plasticity are thermally activated, and thus rare at atomic timescales, the limited time domain of traditional MD simulations can present a significant challenge when trying to realistically model the mechanical behavior of materials. A wide variety of approaches have been developed to address the timescale challenge, each having their own strengths and weaknesses dependent upon the specific application. Here, we have simultaneously applied three distinct approaches to model crack tip behavior in aluminum at timescales well beyond those accessible to traditional MD simulation. Specifically, we combine concurrent multiscale modeling (to reduce the degrees of freedom in the system), parallel replica dynamics (to parallelize the simulations in time) and hyperdynamics (to accelerate the exploration of phase space). Overall, the simulations (1) provide new insight into atomic-scale crack tip behavior at more typical timescales and (2) illuminate the potential of common extended timescale techniques to enable atomic-scale modeling of fracture processes at typical experimental timescales.

Baker, K. L.; Warner, D. H.

2012-09-01

120

BOOK REVIEW: Once Upon Einstein  

NASA Astrophysics Data System (ADS)

Thibault Damour is a theoretical physicist, and a member of the French Academy of Sciences. This book is the translation, by Eric Novak, of the original French Si Einstein m'etait conté (Le Cherche Midi, 2005). It is neither a book of theoretical physics nor a biography of Einstein. It is not a book of history nor philosophy of science. In Damour's words it was written to encourage the reader to share with Einstein `those times when he understood some part of the hidden order of the universe'. It is a relatively short book, written in a very fluent style, but it deals with all the major problems and achievements of Einstein's works. Starting from special relativity, it continues with general relativity, quantum theories, unified field theory and a brief overview of the actual research related to Einstein's legacy. It is essentially a popular science book with some related exploration in history and philosophy to interpret physical theories. The most important problem discussed by Damour is the nature of time. On this subject, there is a very interesting short paragraph (pp 33--35) dedicated to the reception of the relativity idea by the great writer Marcel Proust and its counterpart within À la Recherche du Temps Perdu. A correct discussion of the implications of a relativistic time should imply the distinction of the different possible interpretations of this concept. Damour seems to conclude that only one interpretation is possible: `time does not exist', flowing of time is an illusion. One has to know that Einstein's ideas on time were related to Spinoza's perspective of a knowledge sub specie aeternitatis. However, other interpretations are possible and are related to the idea of time as an actuality. Damour speaks about the controversy between Einstein and Bergson, but Bergson is considered as a philosopher who did not understand relativity. This philosophical problem of relativistic time is indeed related to a historical problem briefly discussed by Damour (pp 17--21, 48--52 and related endnotes): had Henri Poincaré constructed a special relativistic dynamics before Einstein? There is a long debate on this subject in the literature. Damour's answer is negative and his conclusions seem related to the conservation of a myth of Einstein, that is, the rise of special relativity is considered as a creatio ex nihilo within Einstein's mind and Einstein is considered as the only genius able to conceive the relativity of time. Poincaré's texts are undervalued and misunderstood by Damour's cutting quotations from their context. Damour never quotes La Science et l'Hypothèse (1902): we know it was read by Einstein and here Poincaré first (within chapters already published as separate papers in 1900) stated the relativity of time and of simultaneity. Damour never quotes Poincaré's paper published on 5 June 1905, La dynamique de l'èlectron, which presents the first relativistic dynamics, invariant by Lorentz transformations. Poincaré's (July 1905) introduction of a quadrimensional space-time is considered by Damour only a mathematical artifice (p 51) and Damour never said that Minkowski took this idea from Poincaré! Poincaré's interpretation of relativistic time implies that it is not an illusion but a complex net of different real flows related to different processes. Poincaré and Einstein had different conceptions of Nature at the root of special relativity: respectively an electromagnetic conception (Poincaré) and a semi-mechanist one (Einstein). Thus, the (philosophical) meaning of relativity can be very different from the one presented by Damour. Furthermore, Damour accepts Kantian philosophy as a key to understanding relativity and quantum theories. This perspective seems to me very anachronistic and based on a misunderstanding: an interpretation of 20th century physical theories (relativity and quantum physics) is given within the framework of an 18th century philosophical perspective, created to give a foundation to Newton's theory. Relativity and quantum physics imply a breakdown of Kantian philosophy (see,

Giannetto, E.

2007-07-01

121

Comparing Broad-line Region Gas Metallicity with Black Hole Mass and Eddington Ratio Using Low-z QSOs  

NASA Astrophysics Data System (ADS)

We investigate the broad-line region (BLR) gas metallicity of a sample of 70 Palomar-Green QSOs at z < 0.5 using archival UV spectra obtained with the HST and IUE. By utilizing the flux ratio of UV emission lines (i.e., NV/CIV,(SiIV+OIV)/CIV, NV/HeII, and AlIII/CIV) as metallicity indicators, we compare BLR gas metallicity with AGN properties, i.e., black hole mass, luminosity, and Eddinton ratio. We find that BLR metallicity correlates with Eddington ratio while the dependency on black hole mass is much weaker. Although these trends of low-z AGNs appear to be different from those of high-z QSOs, the difference is partly caused by the limited dynamical range of the samples. We conclude that metal enrichment at the center of galaxies is closely connected to the accretion activity of black holes as manifested by the metallicity - Eddington ratio correlation and that the scatter of the metallicity - black hole mass correlation increases over cosmic time due to various nuclear star formation mechanism.

Woo, Jong-Hak; Shin, J.; Nagao, T.

2013-01-01

122

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.

123

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

124

Distributions of microcanonical cascade weights of rainfall at small timescales  

NASA Astrophysics Data System (ADS)

Empirical frequency distributions of multiplicative cascade weights, or breakdown coefficients, at small timescales are analyzed for 5-min precipitation time series from four gauges in Germany. It is shown that histograms of the weights, W, are strongly deformed by the recording precision of rainfall amounts. A randomization procedure is proposed to statistically remove the artifacts due to precision errors in the original series. Evolution of the probability distributions of W from beta-like for large timescales to combined beta-normal distribution with a pronounced peak at W ? 0.5 for small timescales is observed. A new 3N-B distribution built from 3 separate normal, N, distributions and one beta, B, distribution is proposed for reproduction of the empirical histograms of W at small timescales. Parameters of the 3N-B distributions are fitted for all gauges and analyzed timescales. Microcanonical cascades models with a generator based on 3N-B distributions are developed and their performance at disaggregating precipitation at 1280-min intervals down to 5-min intervals is evaluated.

Licznar, Pawe?; Schmitt, Theo G.; Rupp, David E.

2011-10-01

125

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

126

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

127

HOST GALAXIES, CLUSTERING, EDDINGTON RATIOS, AND EVOLUTION OF RADIO, X-RAY, AND INFRARED-SELECTED AGNs  

SciTech Connect

We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared (IR) wavebands. We study a sample of 585 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We select AGNs with observations in the radio at 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays from the Chandra XBooetes Survey, and mid-IR from the Spitzer IRAC Shallow Survey. The radio, X-ray, and IR AGN samples show only modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios, for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3-10 h {sup -1} Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red sequence galaxies, are strongly clustered (with M {sub halo} {approx} 3 x 10{sup 13} h {sup -1} M {sub sun}), and have very low Eddington ratios {lambda} {approx}< 10{sup -3}; (2) X-ray-selected AGNs are preferentially found in galaxies that lie in the 'green valley' of color-magnitude space and are clustered similar to the typical AGES galaxies (M {sub halo} {approx} 10{sup 13} h {sup -1} M {sub sun}), with 10{sup -3} {approx}< {lambda} {approx}< 1; (3) IR AGNs reside in slightly bluer, slightly less luminous galaxies than X-ray AGNs, are weakly clustered (M {sub halo} {approx}< 10{sup 12} h {sup -1} M {sub sun}), and have {lambda}>10{sup -2}. We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a 'quasar' phase and the growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a critical mass between {approx}10{sup 12} and 10{sup 13} M {sub sun}. After this event, star formation ceases and AGN accretion shifts from radiatively efficient (optical- and IR-bright) to radiatively inefficient (optically faint, radio-bright) modes.

Hickox, Ryan C.; Jones, Christine; Forman, William R.; Murray, Stephen S.; Brodwin, Mark; Narayan, Ramesh; Kenter, Almus; Caldwell, Nelson; Anderson, Michael E. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Kochanek, Christopher S. [Department of Astronomy and Center for Cosmology and Astroparticle Physics, Ohio State University, 140 West 18th Avenue, Columbus, OH 43210-1173 (United States); Eisenstein, Daniel [Steward Observatory, 933 North Cherry Avenue, Tucson, AZ 85721 (United States); Jannuzi, Buell T.; Dey, Arjun [National Optical Astronomy Observatory, Tucson, AZ 85726-6732 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton 3800, Victoria (Australia); Stern, Daniel; Eisenhardt, Peter R.; Gorjian, Varoujan [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Cool, Richard J. [Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001 (United States)], E-mail: rhickox@cfa.harvard.edu

2009-05-01

128

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

129

Einstein Gravity from Conformal Gravity  

Microsoft Academic Search

We show that that four dimensional conformal gravity plus a simple Neumann boundary condition can be used to get the semiclassical (or tree level) wavefunction of the universe of four dimensional asymptotically de-Sitter or Euclidean anti-de Sitter spacetimes. This simple Neumann boundary condition selects the Einstein solution out of the more numerous solutions of conformal gravity. It thus removes the

Juan Maldacena

2011-01-01

130

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

131

On the Einstein equivalence principle  

SciTech Connect

The Einstein equivalence principle, the cornerstone of our present day understanding of gravity, is used to explore a deeper connection between the deflection of starlight by a spinning object and the Lense-Thirring dragging of inertial frames. It is also noted that experiment has not established that the gravitomagnetic coupling to currents of particle rest-mass energy, to currents of electromagnetic energy, and to currents of all other types of energy are identical as predicted by the Einstein equivalence principle. The detailed analysis of how atomic physics experiments originated by Hughes and by Drever can constrain such possible violations of the Einstein equivalence principle is given. Atomic clocks are also important tools used to test local Lorentz invariance and hence one important aspect of Einstein equivalence principle. The sensitivity of atomic clocks to preferred-frame effects is studied here for the first time, and the behavior of the hydrogen-maser clocks of the Gravity Probe A experiment is analyzed to illustrate use of the techniques involved.

Gabriel, M.D.

1989-01-01

132

Spontaneous creation of Kibble-Zurek solitons in a Bose-Einstein condensate  

NASA Astrophysics Data System (ADS)

When a system crosses a second-order phase transition on a finite timescale, spontaneous symmetry breaking can cause the development of domains with independent order parameters, which then grow and approach each other creating boundary defects. This is known as the Kibble-Zurek mechanism. Originally introduced in cosmology, it applies to both classical and quantum phase transitions, in a wide variety of physical systems. Here we report on the spontaneous creation of solitons in Bose-Einstein condensates through the Kibble-Zurek mechanism. We measure the power-law dependence of defect number on the quench time, and show that lower atomic densities enhance defect formation. These results provide a promising test bed for the determination of critical exponents in Bose-Einstein condensates.

Lamporesi, Giacomo; Donadello, Simone; Serafini, Simone; Dalfovo, Franco; Ferrari, Gabriele

2013-10-01

133

On the timescales characterizing groundwater discharge at springs  

Microsoft Academic Search

In some regions, measurements made at springs can be used to study regional hydrogeologic processes, and determine hydraulic and transport properties of aquifers. Here, input–output models, spectral analysis, and time series analysis are used to identify three different timescales characterizing discharge at springs. First, the “hydraulic time scale” depends on the transmissivity of the aquifer and relates long term changes

Michael Manga

1999-01-01

134

Indirect detonation initiation using acoustic timescale thermal power deposition  

NASA Astrophysics Data System (ADS)

A fluid dynamics video is presented that demonstrates an indirect detonation initiation process. In this process, a transient power deposition adds heat to a spatially resolved volume of fluid in an amount of time that is similar to the acoustic timescale of the fluid volume. A highly resolved two-dimensional simulation shows the events that unfold after the heat is added.

Regele, J. D.; Kassoy, D. R.; Vezolainen, A.; Vasilyev, O. V.

2013-09-01

135

Multi-Timescale Nonlinear Robust Control for a Miniature Helicopter  

Microsoft Academic Search

A new nonlinear control approach, which is applied to a miniature aerobatic helicopter through a multi-timescale structure, is proposed. Because of the highly nonlinear, unstable, and underactuated nature of a miniature helicopter, it is a challenge to design an autonomous flight control system that is capable of operating in the full flight envelope. To deal with unstable internal dynamics, the

Yunjun Xu

2010-01-01

136

The time-scale of escape from star clusters  

Microsoft Academic Search

In this paper a cluster is modelled as a smooth potential (due to the cluster stars) plus the steady tidal field of the Galaxy. In this model there is a minimum energy below which stars cannot escape. Above this energy, however, the time-scale on which a star escapes varies with the orbital parameters of the star (mainly its energy) in

T. Fukushige; D. C. Heggie

2000-01-01

137

Understanding Protoplanetary Disk Structure through the Timescale of its Variability  

NASA Astrophysics Data System (ADS)

While most of our knowledge of protoplanetary disks is based on single snapshots of many systems, their evolution is in fact highly dynamic on short timescales. Previous surveys have found that the majority of young stellar objects are variable in the infrared, due to large structural perturbations of the inner disk, over the course of weeks and months. These studies of large samples of objects over two month observing windows have not been able to completely constrain the physical source of these fluctuations. We propose to use the variability timescale as a novel method for understanding the underlying physics processes setting the protoplanetary disk structure. With roughly one observation per day for 200 days, a more intensive monitoring campaign than has been previously attempted, we can distinguish between variability on the stellar rotation period (related to variable heating by star spots), the dynamical timescale (related to MRI effects and perturbation by a companion) and the thermal timescale (related to thermal waves in the disk). By focusing on a small field within the 2 Myr Chameleon star-forming region, we will obtain detailed light curves for ~16 young stellar objects, including a 15 Jupiter mass brown dwarf with a disk. This type of intensive, long baseline monitoring has not been attempted in the past, is only feasible with the observing capabilities of Spitzer, and has the potential to greatly advance our understanding of young stellar object evolution.

Flaherty, Kevin; Muzerolle, James; Balog, Zoltan; Herbst, William; Megeath, S. Thomas; Furlan, Elise; Gutermuth, Robert

2012-12-01

138

Einstein's Jury -The Race to Test Relativity  

NASA Astrophysics Data System (ADS)

It is common belief that Einstein’s general theory of relativity won worldwide acceptance after British astronomers announced in November 1919 that the sun’s gravitational field bends starlight by an amount predicted by Einstein. This paper demonstrates that the case for Einstein was not settled until much later and that there was considerable confusion and debate about relativity during this period. Most astronomers considered Einstein’s general theory too metaphysical and abstruse, and many tried to find more conventional explanations of the astronomical observations. Two American announcements before the British results appeared had been contrary to Einstein’s prediction. They came from Lick and Mt. Wilson observatories, which enjoyed international reputations as two of the most advanced astrophysical research establishments in the world. Astronomers at these renowned institutions were instrumental in swaying the court of scientific opinion during the decade of the 1920s, which saw numerous attempts to measure light-bending, as well as solar line displacements and even ether-drift. How astronomers approached the “Einstein problem” in these early years before and after the First World War, and how the public reacted to what they reported, helped to shape attitudes we hold today about Einstein and his ideas.

Crelinsten, Jeffrey

2006-12-01

139

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

140

Unifying Einstein and Palatini gravities  

NASA Astrophysics Data System (ADS)

We consider a novel class of f(R) gravity theories where the connection is related to the conformally scaled metric g^??=C(R)g?? 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

2011-02-01

141

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

142

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

143

Entropic corrections to Einstein equations  

SciTech Connect

Considering the general quantum corrections to the area law of black hole entropy and adopting the viewpoint that gravity interprets as an entropic force, we derive the modified forms of Modified Newtonian dynamics (MOND) theory of gravitation and Einstein field equations. As two special cases we study the logarithmic and power-law corrections to entropy and find the explicit form of the obtained modified equations.

Hendi, S. H. [Physics Department, College of Sciences, Yasouj University, Yasouj 75914 (Iran, Islamic Republic of); Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of); Sheykhi, A. [Research Institute for Astronomy and Astrophysics of Maragha (RIAAM), Maragha (Iran, Islamic Republic of); Department of Physics, Shahid Bahonar University, P.O. Box 76175-132, Kerman (Iran, Islamic Republic of)

2011-04-15

144

Stable Bose-Einstein correlations  

Microsoft Academic Search

The shape of Bose-Einstein (or HBT) correlation functions is determined for\\u000athe case when particles are emitted from a stable source, obtained after\\u000aconvolutions of large number of elementary random processes. The two-particle\\u000acorrelation function is shown to have a {\\\\it stretched exponential} shape,\\u000acharacterized by the L\\\\'evy index of stability $ 0 < \\\\alpha \\\\le 2$ and the\\u000ascale

S. Hegyi; W. A. Zajc; MTA KFKI RMKI

2004-01-01

145

OWL representation of the geologic timescale implementing stratigraphic best practice  

NASA Astrophysics Data System (ADS)

The geologic timescale is a cornerstone of the earth sciences. Versions are available from many sources, with the following being of particular interest: (i) The official International Stratigraphic Chart (ISC) is maintained by the International Commission for Stratigraphy (ICS), following principles developed over the last 40 years. ICS provides the data underlying the chart as part of a specialized software package, and the chart itself as a PDF using the standard colours; (ii) ITC Enschede has developed a representation of the timescale as a thesaurus in SKOS, used in a Web Map Service delivery system; (iii) JPL's SWEET ontology includes a geologic timescale. This takes full advantage of the capabilities of OWL. However, each of these has limitations - The ISC falls down because of incompatibility with web technologies; - While SKOS supports multilingual labelling, SKOS does not adequately support timescale semantics, in particular since it does not include ordering relationships; - The SWEET version (as of version 2) is not fully aligned to the model used by ICS, in particular not recognizing the role of the Global Boundary Stratotype Sections and Point (GSSP). Furthermore, it is distributed as static documents, rather than through a dynamic API using SPARQL. The representation presented in this paper overcomes all of these limitations as follows: - the timescale model is formulated as an OWL ontology - the ontology is directly derived from the UML representation of the ICS best practice proposed by Cox & Richard [2005], and subsequently included as the Geologic Timescale package in GeoSciML (http://www.geosciml.org); this includes links to GSSPs as per the ICS process - key properties in the ontology are also asserted to be subProperties of SKOS properties (topConcept and broader/narrower relations) in order to support SKOS-based queries; SKOS labelling is used to support multi-lingual naming and synonyms - the International Stratigraphic Chart is implemented as a set of instances of classes from the ontology, and published through a SPARQL end-point - the elements of the Stratigraphic chart are linked to the corresponding elements in SWEET (Raskin et al., 2011) and DBpedia to support traceability between different commonly accessed representations. The ontology builds on standard geospatial information models, including the Observations and Measurements model (ISO 19156), and GeoSciML. This allows the ages given in the chart to be linked to the evidence basis found in the associated GeoSciML features.

Cox, S. J.

2011-12-01

146

Consistency of the pulsating universe with Einstein’s field equations  

Microsoft Academic Search

Summary  It is shown that the pulsating model of the universe can be derived from Einstein’s field equations with the addition of a\\u000a traceless, negative-energy source tensor. Bounds on the negative-energy density are given. Earlier works on negative-energy\\u000a sources as well as prevention of singularities are discussed. The results support earlier findings that one can obtain a bounce\\u000a without modifying Einstein’s

F. R. Tangherlini

1993-01-01

147

Did Einstein prove E= mc 2?  

Microsoft Academic Search

Although Einstein's name is closely linked with the celebrated relation E=mc2 between mass and energy, a critical examination of the more than half dozen “proofs” of this relation that Einstein produced over a span of forty years reveals that all these proofs suffer from mistakes. Einstein introduced unjustified assumptions, committed fatal errors in logic, or adopted low-speed, restrictive approximations. He

Hans C. Ohanian

2009-01-01

148

The Einstein Observatory - New perspectives in astronomy  

Microsoft Academic Search

The impact of high-resolution, high-sensitivity X-ray measurements obtained by the Einstein Observatory (HEAO-2) on various areas of astronomical research is discussed. Following a review of the Einstein instruments based on grazing incidence focusing X-ray optics, including the telescope, imaging detectors and spectrometers, consideration is given to observations of X-ray emission from stellar systems, galaxies, and clusters of galaxies. Einstein results

R. Giacconi; H. Tananbaum

1980-01-01

149

Characteristic microvessel relaxation timescales associated with ultrasound-activated microbubbles  

PubMed Central

Ultrasound-activated microbubbles were used as actuators to deform microvessels for quantifying microvessel relaxation timescales at megahertz frequencies. Venules containing ultrasound contrast microbubbles were insonified by short 1?MHz ultrasound pulses. Vessel wall forced-deformations were on the same microsecond timescale as microbubble oscillations. The subsequent relaxation of the vessel was recorded by high-speed photomicrography. The tissue was modeled as a simple Voigt solid. Relaxation time constants were measured to be on the order of ?10??s. The correlation coefficients between the model and 38 data sets were never lower than 0.85, suggesting this model is sufficient for modeling tissue relaxation at these frequencies. The results place a bound on potential numerical values for viscosity and elasticity of venules.

Chen, Hong; Brayman, Andrew A.; Matula, Thomas J.

2012-01-01

150

A two-timescale approach to nonlinear Model Predictive Control  

SciTech Connect

Model Predictive Control (MPC) schemes generate controls by using a model to predict the plant`s response to various control strategies. A problem arises when the underlying model is obtained by fitting a general nonlinear function, such as a neural network, to data: an exorbitant amount of data may be required to obtain accurate enough predictions. We describe a means of avoiding this problem that involves a simplified plant model which bases its predictions on averages of past control inputs. This model operates on a timescale slower than- the rate at which the controls are updated and the plant outputs are sampled. Not only does this technique give better closed-loop performance from the same amount of open-loop data, but it requires far less on-line computation as well. We illustrate the usefulness of this two-timescale approach by applying it to a simulated exothermic continuously stirred tank reactor with jacket dynamics.

Buescher, K.L.; Baum, C.C.

1994-10-01

151

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

152

Chaotic dynamics of atmospheric CO2 at millennial timescales  

Microsoft Academic Search

The angle between Earth's rotational axis and the normal to the plane of its orbit (known as obliquity) varies periodically between 22.1 degrees and 24.5 degrees on about 41,000-year cycle. Such millennial timescale changes in orientation change the amount of solar radi- ation reaching the Earth in different latitudes. In high latitudes the annual mean insolation (incident solar ra- diation)

A. Bershadskii

153

APPLICATION OF CONTROL THEORY IN THE FORMATION OF A TIMESCALE  

Microsoft Academic Search

We have created a timescale that joins the short-term stability of several hydrogen masers with the long-term capabilities of an ensemble of cesium frequency standards. Control theory is utilized in a system design that combines frequency standards with varied properties. The system steers a maser ensemble with respect to a cesium ensemble while minimally perturbing the maser short-term performance. Results

P. Koppang; D. Johns; J. Skinner

154

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

155

SIMPLIFICATION OF CHEMICAL REACTION SYSTEMS BY TIMESCALE ANALYSIS  

Microsoft Academic Search

In this article, we present a model order reduction method based on time-scale analysis for chemical reaction systems. The method can be applied to any reaction system exhibiting multiple time scales and described by the set or differential equations dc\\/dl = f(c), where c (dimension n) is the vector of chemical species and f is the operator describing the kinetics.

MILES S. OKINO; MICHAEL L. MAVROVOUNIOTIS

1999-01-01

156

Minimum variability time-scales of long and short GRBs  

NASA Astrophysics Data System (ADS)

We have investigated the time variations in the light curves from a sample of long and short Fermi/GBM gamma-ray bursts (GRBs) using an impartial wavelet analysis. The results indicate that in the source frame, the variability time-scales for long bursts differ from that for short bursts, variabilities of the order of a few milliseconds are not uncommon and an intriguing relationship exists between the minimum variability time and the burst duration.

MacLachlan, G. A.; Shenoy, A.; Sonbas, E.; Dhuga, K. S.; Cobb, B. E.; Ukwatta, T. N.; Morris, D. C.; Eskandarian, A.; Maximon, L. C.; Parke, W. C.

2013-06-01

157

Resource distributions affect social learning on multiple timescales  

Microsoft Academic Search

We study how learning is shaped by foraging opportunities and self-organizing processes and how this impacts on the effects\\u000a of “copying what neighbors eat” on multiple timescales. We use an individual-based model with a rich environment, where group\\u000a foragers learn what to eat. We vary foraging opportunities by changing local variation in resources, studying copying in environments\\u000a with pure patches,

Daniel J. van der Post; Bas Ursem; Paulien Hogeweg

2009-01-01

158

Stratospheric variability and tropospheric annular-mode timescales  

NASA Astrophysics Data System (ADS)

Climate models tend to exhibit much too persistent Southern Annular Mode (SAM) circulation anomalies in summer, compared to observations. Theoretical arguments suggest this bias may lead to an overly strong model response to anthropogenic forcing during this season, which is of interest since the largest observed changes in Southern Hemisphere high-latitude climate over the last few decades have occurred in summer, and are congruent with the SAM. The origin of this model bias is examined here in the case of the Canadian Middle Atmosphere Model, using a novel technique to quantify the influence of stratospheric variability on tropospheric annular-mode timescales. Part of the model bias is shown to be attributable to the too-late breakdown of the stratospheric polar vortex, which allows the tropospheric influence of stratospheric variability to extend into early summer. However, the analysis also reveals an enhanced summertime persistence of the model's SAM that is unrelated to either stratospheric variability or the bias in model stratospheric climatology, and is thus of tropospheric origin. No such feature is evident in the Northern Hemisphere. The effect of stratospheric variability in lengthening tropospheric annular-mode timescales is evident in both hemispheres. While in the Southern Hemisphere the effect is restricted to late-spring/early summer, in the Northern Hemisphere it can occur throughout the winter-spring season, with the seasonality of peak timescales exhibiting considerable variability between different 50 year sections of the same simulation.

Simpson, I. R.; Hitchcock, P.; Shepherd, T. G.; Scinocca, J. F.

2011-10-01

159

A wavelet-based multiscale ensemble time-scale algorithm.  

PubMed

The wide-spread availability of ensembles of high-performance clocks has motivated interest in time-scale algorithms. There are many such algorithms in use today in applications ranging from scientific to commercial. Although these algorithms differ in key aspects and are sometimes tailored for specific applications and mixtures of clocks, they all share the goal of combining measured time differences between clocks to form a reference time scale that is more stable than any of the clocks in the ensemble. A new approach to forming time scales is presented here, the multiscale ensemble timescale (METS) algorithm. This approach is based on a multiresolution analysis afforded by the discrete wavelet transform. The algorithm does not assume a specific parametric model for the clocks involved and hence is well-suited for an ensemble of highly disparate clocks. The approach is based on an appealing optimality criterion which yields a reference time scale that is more stable than the constituent clocks over all averaging intervals (scales). The METS algorithm is presented here in detail and is shown in a simulation study to compare favorably with a time-scale algorithm based on Kalman filtering. PMID:22481786

Percival, Donald B; Senior, Kenneth L

2012-03-01

160

Einstein's Theory of Special Relativity  

NSDL National Science Digital Library

This concise tutorial from the Physics Classroom explores a phenomenon thatis integral to Einstein's Theory of Special Relativity. This phenomenonis known as "Relativistic Length Contraction" and occurs when "the length of objects moving at relativistic speeds undergo a contraction along the dimension of motion." This may seem complicated, but the animations included in this tutorial will help you understand this intriguing concept in no time. This a great visual resource to include in class, and is helpful for anyone seeking to understand the concept of relativistic length contraction.

2007-11-14

161

Near-infrared Spectroscopy And Photometry Of The Super-Eddington Transient XTE J1701-462 In Quiescence  

NASA Astrophysics Data System (ADS)

XTE J1701-462 is a neutron-star X-ray transient that was in outburst for nearly 19 months in 2006-2007. For a large part of its outburst the source accreted at super- or near-Eddington luminosities, possibly making it the most luminous neutron-star X-ray transient. Using the VLT, Magellan, and the CTIO 4-m we performed near-infrared spectroscopy and multi-epoch photometry in quiescence to study the properties of the secondary and constrain the binary parameters. The main goal of these observations is to understand what type of donor star powered the exceptionally long and luminous outburst of XTE J1701-462, and to compare its properties with those of the donors in other X-ray binaries. A secondary goal is to search for signatures of ongoing low-level accretion, for which we see evidence in X-rays. Here we report on the first results from our campaign.

Van Den Berg, Maureen; Homan, J.; Elenbaas, C.; Fridriksson, J.; Cackett, E.

2011-09-01

162

The Global Water Cycle Drives Volcanism on Seasonal to Millennial Timescales  

Microsoft Academic Search

Global rates of occurrence of volcanic eruptions show periodic behaviour on timescales ranging from 106 years. At long timescales (>106 to 107 years), rates of eruption are controlled by plate tectonics. At shorter timescales, the periodic nature of volcanism is forced by the global water cycle. Historical records of the rates of onset of eruption for the past 300 years

D. M. Pyle; B. G. Mason; T. E. Jupp; W. B. Dade

2005-01-01

163

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

164

What Einstein Can Teach Us about Education  

ERIC Educational Resources Information Center

|People are more likely to associate Einstein with complex scientific theories and mathematical calculations than with education theory. In fact, Einstein's own experiences of schooling and his reflections on the meaning of life and the significance of education are profound and oddly relevant to the situation that pertains in England today. It is…

Hayes, Denis

2007-01-01

165

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

166

Bose-Einstein condensation of sodium atoms  

Microsoft Academic Search

Summary form only given. Bose-Einstein condensation (BEG) has been observed in a dilute gas of sodium atoms. A Bose-Einstein condensate consists of a macroscopic population of the ground state of the system and is a coherent state of matter. In an ideal gas, this phase transition is purely quantum statistical. The study of BEC in weakly interacting systems that can

N. I. Van Druten; D. S. Durfee; K. B. Davis; M.-O. Mewes; M. R. Andrews; D. M. Kurn; W. Ketterle

1996-01-01

167

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

168

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

169

Bose-Einstein Condensation in Classical Systems  

Microsoft Academic Search

It is shown, that Bose-Einstein statistical distributions can occur not only in quantum system, but in classical systems as well. The coherent dynamics of the system, or equivalently autocatalytic dynamics in momentum space of the system is the main reason for the Bose-Einstein condensation. A coherence is possible in both quantum and classical systems, and in both cases can lead

Kestutis Staliunas

2000-01-01

170

Macroscopic superpositions of Bose-Einstein condensates  

Microsoft Academic Search

We consider two dilute gas Bose-Einstein condensates with opposite velocities from which a monochromatic light field detuned far from the resonance of the optical transition is coherently scattered. In the thermodynamic limit, when the relative fluctuations of the atom number difference between the two condensates vanish, the relative phase between the Bose-Einstein condensates may be established in a superposition state

Janne Ruostekoski; M. J. Collett; Robert Graham; Dan F. Walls

1998-01-01

171

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

172

The Hundredth Anniversary of Einstein's Annus Mirabilis  

Microsoft Academic Search

The year 2005 marks the hundredth anniversary of the pioneering contribution of Einstein's to modern physics in 1905. The discussion of Einstein's five groundbreaking fundamental papers, which change our picture of the universe and ideas about the microworld and cosmos, is given.

Roman Ya. Kezerashvili

2005-01-01

173

The Hundredth Anniversary of Einstein's Annus Mirabilis  

Microsoft Academic Search

The year 2005 marks the hundredth anniversary of the pioneering contribution\\u000aof Einstein's to modern physics in 1905. The discussion of Einstein's five\\u000agroundbreaking fundamental papers, which change our picture of the universe and\\u000aideas about the microworld and cosmos, is given.

Roman Ya. Kezerashvili

2005-01-01

174

Einstein's Jury: The Race to Test Relativity  

Microsoft Academic Search

'I know very well that my theory rests on a shaky foundation. What attracts me to it is that it leads to consequences that seem to be accessible to experiment, and it provides a starting point for the theoretical understanding of gravitation', wrote Einstein in 1911. Einstein's Jury by Jeffrey Crelinsten—well documented, well written, and fascinating to read—describes how, from

Jürgen Ehlers

2007-01-01

175

Astrophysical observations: lensing and eclipsing Einstein's theories.  

PubMed

Albert Einstein postulated the equivalence of energy and mass, developed the theory of special relativity, explained the photoelectric effect, and described Brownian motion in five papers, all published in 1905, 100 years ago. With these papers, Einstein provided the framework for understanding modern astrophysical phenomena. Conversely, astrophysical observations provide one of the most effective means for testing Einstein's theories. Here, I review astrophysical advances precipitated by Einstein's insights, including gravitational redshifts, gravitational lensing, gravitational waves, the Lense-Thirring effect, and modern cosmology. A complete understanding of cosmology, from the earliest moments to the ultimate fate of the universe, will require developments in physics beyond Einstein, to a unified theory of gravity and quantum physics. PMID:15705841

Bennett, Charles L

2005-02-11

176

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

177

Probing AGN Variability on 10-100 kyr Timescales  

NASA Astrophysics Data System (ADS)

Following the discovery of IC 2497 and Hanny's Voorwerp, the citizen scientists taking part in the Galaxy Zoo project have identified a sample of low-redshift galaxies with extended AGN-photoionized clouds indicative of a Seyfert- luminosity AGN. We select a sample of 7 such galaxies where the lack of infrared emission makes it plausible that the AGN phase illuminating the cloud has shut down within the light travel time to the cloud. We propose to use XMM-Newton to observe these objects, as in IC 2497, to test whether these AGN have indeed shut down and thus providing a measurement of significant AGN variability on previously inaccessible timescales.

Schawinski, Kevin

2010-10-01

178

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

179

Neuronal correlates of visual time perception at brief timescales  

PubMed Central

Successful interaction with the world depends on accurate perception of the timing of external events. Neurons at early stages of the primate visual system represent time-varying stimuli with high precision. However, it is unknown whether this temporal fidelity is maintained in the prefrontal cortex, where changes in neuronal activity generally correlate with changes in perception. One reason to suspect that it is not maintained is that humans experience surprisingly large fluctuations in the perception of time. To investigate the neuronal correlates of time perception, we recorded from neurons in the prefrontal cortex and midbrain of monkeys performing a temporal-discrimination task. Visual time intervals were presented at a timescale relevant to natural behavior (<500 ms). At this brief timescale, neuronal adaptation—time-dependent changes in the size of successive responses—occurs. We found that visual activity fluctuated with timing judgments in the prefrontal cortex but not in comparable midbrain areas. Surprisingly, only response strength, not timing, predicted task performance. Intervals perceived as longer were associated with larger visual responses and shorter intervals with smaller responses, matching the dynamics of adaptation. These results suggest that the magnitude of prefrontal activity may be read out to provide temporal information that contributes to judging the passage of time.

Mayo, J. Patrick; Sommer, Marc A.

2013-01-01

180

Neuronal correlates of visual time perception at brief timescales.  

PubMed

Successful interaction with the world depends on accurate perception of the timing of external events. Neurons at early stages of the primate visual system represent time-varying stimuli with high precision. However, it is unknown whether this temporal fidelity is maintained in the prefrontal cortex, where changes in neuronal activity generally correlate with changes in perception. One reason to suspect that it is not maintained is that humans experience surprisingly large fluctuations in the perception of time. To investigate the neuronal correlates of time perception, we recorded from neurons in the prefrontal cortex and midbrain of monkeys performing a temporal-discrimination task. Visual time intervals were presented at a timescale relevant to natural behavior (<500 ms). At this brief timescale, neuronal adaptation--time-dependent changes in the size of successive responses--occurs. We found that visual activity fluctuated with timing judgments in the prefrontal cortex but not in comparable midbrain areas. Surprisingly, only response strength, not timing, predicted task performance. Intervals perceived as longer were associated with larger visual responses and shorter intervals with smaller responses, matching the dynamics of adaptation. These results suggest that the magnitude of prefrontal activity may be read out to provide temporal information that contributes to judging the passage of time. PMID:23297217

Mayo, J Patrick; Sommer, Marc A

2013-01-07

181

Correlated Radio-Optical Variations on Intraday Timescales  

NASA Astrophysics Data System (ADS)

Correlated radio-optical variations on intraday timescales have been observed (e.g. in BLO 0716+714) and such radio intraday variability is suggested to have an intrinsic origin. Recently, multi-wavelength observations, simultaneous at radio, mm-submm, optical and hard X-rays, of 0716+714, show that during a period of intraday/interday variations at radio and mm wavelengths, the apparent brightness temperature of the source exceeded the Compton-limit (~1012 K) by 2-4 orders of magnitude, but no Compton catastrophe (or no high luminosity of inverse-Compton radiation) was detected. It is also found that the intraday/interday variations at mm-submm wavelengths are consistent with the evolutionary behavior of a standard synchrotron source and for the intraday/interday variations at centimeter wavelengths opacity effects can play a significant role, which is consistent with the interpretation suggested previously by Qian et al. Thus the apparent high brightness temperatures may probably be explained in terms of Doppler boosting effects due to bulk relativistic motion of the source. We will argue a scenario to simulate the correlations between the radio and optical variations on intraday timescales observed in BLO 0716+714 in terms of a relativistic shock propagating through a jet with a dual structure.

Qian, Shan-Jie

2008-04-01

182

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

183

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

184

Vegetation roots and fluvial ecomorphodynamics: processes and related timescales  

NASA Astrophysics Data System (ADS)

The biological dynamics of riparian and riverbed vegetation has been recognized to play a fundamental role in fluvial ecomorphodynamics. Contrarily to terrain slopes, the role of vegetation roots in alluvial (non-cohesive) sediment is quite unexplored both at the field and laboratory scales. Hydrologic and biologic growth processes can interact at certain timescales and be determinant to the colonization and successive stabilization of alluvial bedforms. This influences the reworking return period (i.e., the magnitude of impacting floods) of islands and bars in the absence of vegetation and may lead to specific riverbed morphological features. In this paper we first discuss how river hydrology may influence root tropisms and the related growing architecture at the field scale (Pasquale et al., 2012). Different root density vertical distributions can thus be determinant to uprooting and transport processes (Edmaier et al., 2011). Results from a number of laboratory experiments aimed at relating floods intertime and root growth timescales to uprooting statistics are then presented (Perona et al., 2012). We show the biomass selection mechanism operated by flow disturbances on riverbed vegetation, and discuss :i) the related impact that this process may have to select young vegetation in and among species (Crouzy and Perona, 2012; ii) two exemplary vegetation patterns that have been observed in rivers with converging boundaries and ephemeral streams. This study is a first step to better understand and model the sediment stabilization mechanism by vegetation roots in the equations of morphodynamics.

Perona, P.

2012-04-01

185

Oceanic control of Northeast Pacific hurricane activity at interannual timescales  

NASA Astrophysics Data System (ADS)

Sea surface temperature (SST) is not the only oceanic parameter that can play a key role in the interannual variability of Northeast Pacific hurricane activity. Using several observational data sets and the statistical technique of multiple linear regression analysis, we show that, along with SST, the thermocline depth (TD) plays an important role in hurricane activity at interannual timescales in this basin. Based on the parameter that dominates, the ocean basin can be divided into two sub-regions. In the Southern sub-region, which includes the hurricane main development area, interannual variability of the upper-ocean heat content (OHC) is primarily controlled by TD variations. Consequently, the interannual variability in the hurricane power dissipation index (PDI), which is a measure of the intensity of hurricane activity, is driven by that of the TD. On the other hand, in the Northern sub-region, SST exerts the major control over the OHC variability and, in turn, the PDI. Our study suggests that both SST and TD have a significant influence on the Northeast Pacific hurricane activity at interannual timescales and that their respective roles are more clearly delineated when sub-regions along an approximate north–south demarcation are considered rather than the basin as a whole.

Balaguru, Karthik; Leung, L. Ruby; Yoon, Jin-ho

2013-12-01

186

Sasaki-Einstein and paraSasaki-Einstein metrics from (?,?)-structures  

NASA Astrophysics Data System (ADS)

We prove that every contact metric (?,?)-space admits a canonical ?-Einstein Sasakian or ?-Einstein paraSasakian metric. An explicit expression for the curvature tensor fields of those metrics is given and we find the values of ? and ? for which such metrics are Sasaki-Einstein and paraSasaki-Einstein. Conversely, we prove that, under some natural assumptions, a K-contact or K-paracontact manifold foliated by two mutually orthogonal, totally geodesic Legendre foliations admits a contact metric (?,?)-structure. Furthermore, we apply the above results to the geometry of tangent sphere bundles and we discuss some geometric properties of (?,?)-spaces related to the existence of Einstein-Weyl and Lorentzian-Sasaki-Einstein structures.

Cappelletti-Montano, Beniamino; Carriazo, Alfonso; Martín-Molina, Verónica

2013-11-01

187

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

188

Cosmography with the Einstein Telescope  

NASA Astrophysics Data System (ADS)

The Einstein Telescope, a third-generation gravitational-wave detector under a design study, could detect millions of binary neutron star inspirals each year. A small fraction of these events might be observed as gamma-ray bursts, helping to measure both the luminosity distance DL to and redshift {\\bm z} of the source. By fitting these measured values of DL and {\\bm z} to a cosmological model, it would be possible to infer the dark energy equation of state to within 1.5% without the need to correct for errors in DL caused by weak lensing. This compares favourably with 0.3-10% accuracy that can be achieved with the Laser Interferometer Space Antenna (where weak lensing will need to be dealt with) as well as with dedicated dark energy missions that have been proposed, where 3.5-11% uncertainty is expected.

Sathyaprakash, B. S.; Schutz, B. F.; Van Den Broeck, C.

2010-11-01

189

Albert Einstein and Archenhold Observatory 1905 - 2005 (German Title: Albert Einstein und die Archenhold-Sternwarte 1905 -- 2005)  

Microsoft Academic Search

After Einstein came to Berlin, he gave his first popular lecture in the Archenhold Observatory, in 1915, on the special and the general theories of relativity. From then on, friendly relations grew between Archenhold and Einstein, which led to a permanent connection between the Observatory and Einstein's achievement. This contribution presents the background of the connection between Archenhold and Einstein,

Dieter B. Herrmann

2005-01-01

190

Einstein’s Legacy to Astronomy: From Black Holes to the Expanding Universe  

NASA Astrophysics Data System (ADS)

Albert Einstein placed a formidable imprint on astronomy. Not since the time of Isaac Newton, three centuries ago, has a single individual so influenced the field. Many of the great astronomical findings of the 20th century--the expanding universe, compact stars, origin of the Sun’s power, black holes, gravitational lensing, dark energy, gravity waves--are rooted in the physics that Einstein so brilliantly deduced. This illustrated presentation, the Gemant Award Lecture sponsored by the American Institute of Physics, will provide a guided tour through the cosmos and explain how our understanding of the universe was transformed by Einstein’s theories of special and general relativity.

Bartusiak, Marcia

2006-12-01

191

Modelling Factors That Control Peat Accumulation Over Different Timescales  

NASA Astrophysics Data System (ADS)

Net carbon accumulation or loss from peat soils reflect the balance between plant productivity at the surface and decomposition throughout the peat profile. This balance is affected by environmental parameters (water table depth, oxygen availability, pH, and soil temperature) that moderate biological processes such as productivity, root dynamics, and decomposition. Given the same environmental conditions, individual peatland litters differ in their susceptibility to decay, reflecting differences in organic matter composition and nutrient content. The relative importance of these internal and external controls on peat accumulation is presently only poorly understood. In this study, simulation modelling was used to examine factors that control peat accumulation over timescales from years to millennia. The model used recognizes three organic matter fractions that differ in their susceptibility to decay. Litter quality-related parameters (nutrient availability and previous decay history) have different effects on turnover rates for the different organic matter fractions, whereas external controls (temperature, pH, and oxygen availability) affect all fractions equally. Sensitivity analysis of the model shows that the relative ability of different input parameters to affect peat accumulation depends on the timescale of reference. Peat nitrogen content affected organic matter accumulation mainly within the first decade. Total NPP and several litter-quality dependent parameters were important throughout, but their effect peaked between 500 and 1000 years. A third group of parameters (including oxic:anoxic decay ratios and pH) had no or steadily increasing effects on accumulated mass over the first 1000 years. Subsequently, their effect remained constant or continued to increase. Patterns of organic matter accumulation in nine peatland types were modelled over 8,000 years, with peatland types differing in both environmental boundary conditions and the chemical quality of dominant litters. Over 8,000 years, rich fens accumulated less organic matter than other peatland types with similar water table depths. At high and medium water tables, bogs / poor fens accumulated most peat, whereas transitional fens showed highest long-term peat accumulation at low water tables. In several instances, the relative peat accumulation potential of different community types changed over time. While the specific results of this study reflect the structure of the decay model chosen, they stress the importance of defining a timescale of reference when examining organic matter accumulation. They further point towards litter-quality related parameters as important controls over organic matter dynamics in peatlands.

Bauer, I.

2002-12-01

192

Time-scales of granite magmatism: from source to emplacement  

NASA Astrophysics Data System (ADS)

Many granite (sensu-lato) bodies in the upper crust originated as partial melts in the mid- to lower crust. Their formation involves four separate, but inter-related processes: generation, segregation, ascent and emplacement. These processes were traditionally thought to occur over long time-scales (c. 1-10 M.y.), but this view has recently been challenged. Quantitative studies have suggested that melt generation following the intrusion of mantle-derived basalt, ascent of granite magma through dykes, and emplacement of tabular plutons accommodated by lateral fault opening and vertical movement of roof and floor, can occur over much shorter time-scales (c. 0.01 M.y. 1 M.y.). However, what is missing is a quantitative understanding of the time-scales over which granite melt can segregate from its partially molten protolith. Melt flow along grain edges can be driven by buoyancy, and space to accommodate the melt provided by compaction of the solid matrix. Previous studies suggested that this process is very slow, but they neglected the coupled physical and chemical processes which occur as buoyant melt migrates upwards through the steep thermal gradient above a hot basalt intrusion. A new quantitative model of melt generation and segregation via buoyancy-driven compaction includes these coupled processes, and suggests that granite magma can segregate rapidly following the onset of melting. Combining this model with magma ascent via dykes, and using reasonable values of the governing physical parameters, suggests that emplacement of a 100 km3 pluton in the upper crust can be complete within c. 50,000 y. of the onset of melting in the lower crust. Melt generation results from the intrusion of mantle-derived basalt with a thickness of 250m, over an area of 900 km2. The segregated granite magma accumulates at the top of the partially molten source region, where it flows laterally to a localised area of dyke formation and then upwards to the emplacement level. Repeated intrusion of basalt into thickening lower crust leads to the formation of multiple plutons.

Jackson, M. D.

2006-12-01

193

Einstein and General Relativity: Historical Perspectives.  

ERIC Educational Resources Information Center

|This paper presented in the 1978 Oppenheimer Memorial Lecture at Los Alamos Scientific Laboratories on August 17, 1978, discusses Einstein's contributions to physics, in particular, his discovery of the general theory of relativity. (HM)|

Chandrasekhar, S.

1979-01-01

194

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

195

Visualization of Bose-Einstein Condensates.  

National Technical Information Service (NTIS)

A Bose-Einstein condensate (BEC) is a state of matter that exists at extremely low temperatures. BECs are currently under investigation by the research community through both numerical simulation and laboratory experiments. The central goal of this visual...

P. Ketcham D. Feder W. Reinhardt C. Clark W. George

1999-01-01

196

Volume Visualization of Bose-Einstein Condensates.  

National Technical Information Service (NTIS)

Theoretical aspects of Bose-Einstein condensates are investigated by conducting computer simulations of their behavior. Scientific visualization techniques are employed in order to examine the large amount of data generated by simulation. Visualization of...

P. M. Ketcham D. L. Feder C. W. Clark S. G. Satterfield T. J. Griffin

2001-01-01

197

The Creativity of Einstein and Astronomy.  

National Technical Information Service (NTIS)

A discussion of Einstein's scientific achievements for the 100th anniversary of his birth is presented. His works dealing with thermodynamics are described, along with his quantum theory of radiation. Most of the article discusses his general theory of re...

Y. B. Zeldovich

1980-01-01

198

Vortex sorter for Bose-Einstein condensates  

SciTech Connect

We have designed interferometers that sort Bose-Einstein condensates into their vortex components. The Bose-Einstein condensates in the two arms of the interferometer are rotated with respect to each other through fixed angles; different vortex components then exit the interferometer in different directions. The method we use to rotate the Bose-Einstein condensates involves asymmetric phase imprinting and is itself new. We have modeled rotation through fixed angles and sorting into vortex components with even and odd values of the topological charge of two-dimensional Bose-Einstein condensates in a number of states (pure or superposition vortex states for different values of the scattering length). Our scheme may have applications for quantum information processing.

Whyte, Graeme; Veitch, John; Courtial, Johannes [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Oehberg, Patrik [Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

2004-07-01

199

Einstein and General Relativity: Historical Perspectives.  

ERIC Educational Resources Information Center

This paper presented in the 1978 Oppenheimer Memorial Lecture at Los Alamos Scientific Laboratories on August 17, 1978, discusses Einstein's contributions to physics, in particular, his discovery of the general theory of relativity. (HM)

Chandrasekhar, S.

1979-01-01

200

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

201

Atmosphere/Earth interaction and Earth rotation at geological timescale  

NASA Astrophysics Data System (ADS)

The length-of-day (i.e. the time of one rotation of the Earth) is deeply affected by the interaction of the Earth with the atmosphere, and consequently by the state of the atmosphere and by the climate. At very long timescale, the climate has changed deeply, due to the change of the paleogeography, to the formation/melting of icecaps, to the change of the CO2 content of the atmosphere... Those climate changes have impacted the mean rotation state of the atmosphere, which in return change the length-of-day. By analysing the outputs of more than 200 climate models of the past Earth, we have separated the effects from the CO2 changes from those of the paleogeography, and those from the ice-caps. This allows to identify the changes in the atmosphere dynamics of the different cause, and their signature in the Earth rotation.

de Viron, O.; Fluteau, F.; Le Hir, G.; Donnadieu, Y.

2010-12-01

202

Medium timescale beach rotation; gale climate and offshore island influences  

NASA Astrophysics Data System (ADS)

Beach profile surveys, gale climate and atmospheric variations were utilized to assess medium timescale morphological change at South Sands, Tenby, West Wales. Due to beach aspect in relation to offshore islands, gale wave height decreased as wave direction rotated eastwards (r = 0.83) and westwards (r = 0.88). Similarly, wave heights were in attuned to variations in positive (r = 0.68) and negative (r = - 0.72) NAO Index, showing a wave height reduction occurred during weakly negative/positive or transitory phases; morphological change was attuned to atmospheric variation at a 2-year timelag. Shelter from offshore islands is given to waves from the predominant southwesterly direction and was confirmed by negligible correlation with South Sands morphology. However, outside the shelter of these offshore islands, correlation was found between south-eastward rotating wave directions (135°-180°) and morphological change, which resulted in southern and central beach erosion and accretion to the north. With a southwesterly rotation (243°-256°) the opposite was true. Beach rotation expressed by volume change within the sub-aerial zone had a negative phased relationship between beach extremities (r = - 0.94) and a timelagged association within the intertidal zone (r = 0.55). Analyses resulted in the development of two medium timescale rotation models based on incident wave direction and climatic variability. Results have global implications for headland bays in the lee of offshore islands, as well as macro-tidal beach areas; and consequently similar models could inform local, regional and national beach management strategies

Thomas, T.; Phillips, M. R.; Williams, A. T.; Jenkins, R. E.

2011-12-01

203

Streamflow response of a small forested catchment on different timescales  

NASA Astrophysics Data System (ADS)

The hydrological response of a catchment to rainfall on different timescales is result of a complex system involving a range of physical processes which may operate simultaneously and have different spatial and temporal influences. This paper presents the analysis of streamflow response of a small humid-temperate catchment (Aixola, 4.8 km2) in the Basque Country on different timescales and discusses the role of the controlling factors. Firstly, daily time series analysis was used to establish a hypothesis on the general functioning of the catchment through the relationship between precipitation and discharge on an annual and multiannual scale (2003-2008). Second, rainfall-runoff relationships and relationships among several hydrological variables, including catchment antecedent conditions, were explored at the event scale (222 events) to check and improve the hypothesis. Finally, the evolution of electrical conductivity (EC) during some of the monitored storm events (28 events) was examined to identify the time origin of waters. Quick response of the catchment to almost all the rainfall events as well as a considerable regulation capacity was deduced from the correlation and spectral analyses. These results agree with runoff event scale data analysis; however, the event analysis revealed the non-linearity of the system, as antecedent conditions play a significant role in this catchment. Further, analysis at the event scale made possible to clarify factors controlling (precipitation, precipitation intensity and initial discharge) the different aspects of the runoff response (runoff coefficient and discharge increase) for this catchment. Finally, the evolution of EC of the waters enabled the time origin (event or pre-event waters) of the quickflow to be established; specifically, the conductivity showed that pre-event waters usually represent a high percentage of the total discharge during runoff peaks. The importance of soil waters in the catchment is being studied more deeply.

Zabaleta, A.; Antigüedad, I.

2013-01-01

204

Human dynamics: Darwin and Einstein correspondence patterns  

Microsoft Academic Search

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

João Gama Oliveira; Albert-László Barabási

2005-01-01

205

Linearized Einstein theory via null surfaces  

Microsoft Academic Search

Recently there has been developed a reformulation of general relativity (GR)—referred to as thenullsurfaceversionofGR—where instead of the metric field as the basic variable of the theory, families of three-surfaces in a four-manifold become basic. From these surfaces themselves, a conformal metric, conformal to an Einstein metric, can be constructed. A choice of conformal factor turns it into an Einstein metric.

Simonetta Frittelli; Carlos N. Kozameh; Ezra T. Newman

1995-01-01

206

Stimulated Emission and Bose-Einstein Statistics  

Microsoft Academic Search

Einstein's derivation of Planck's blackbody formula using the A and B coefficients for spontaneous and stimulated transition probabilities is reviewed. Application of the Einstein-Fowler equation for statistical fluctuations, <(DeltaE)2> = kT2(deltaE\\/deltaT), shows that two terms contribute to the fluctuations, one from the particle nature of the system and one from its wave nature. When expressed in terms of the average

J. H. Webb

1972-01-01

207

Macroscopic superpositions of Bose-Einstein condensates  

Microsoft Academic Search

We consider two dilute gas Bose-Einstein condensates with opposite velocities\\u000afrom which a monochromatic light field detuned far from the resonance of the\\u000aoptical transition is coherently scattered. In the thermodynamic limit, when\\u000athe relative fluctuations of the atom number difference between the two\\u000acondensates vanish, the relative phase between the Bose-Einstein condensates\\u000amay be established in a superposition state

Janne Ruostekoski; M. J. Collett; Robert Graham; Dan F. Walls

1998-01-01

208

Teleparallel Killing Vectors of the Einstein Universe  

NASA Astrophysics Data System (ADS)

In this paper we establish the definition of the Lie derivative of a second rank tensor in the context of teleparallel theory of gravity and also extend it for a general tensor of rank p + q. This definition is then used to find Killing vectors of the Einstein universe. It turns out that Killing vectors of the Einstein universe in the teleparallel theory are the same as in general relativity.

Sharif, M.; Amir, M. Jamil

209

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

210

Liver transplantation at Hospital Israelita Albert Einstein Transplante de fígado no Hospital Israelita Albert Einstein  

Microsoft Academic Search

Objective: To present patients and results of liver transplantation performed by the Liver Unit team at the Hospital Israelita Albert Einstein. Methods: The medical records of all patients transplanted by the team at the Liver Unit of the Hospital Israelita Albert Einstein, from January 2002 to June 2005, were analyzed. Results: During this period, 328 transplants were performed and 64.3%

Sergio Mies

211

Einstein und der Eötvös-Versuch: Ein Brief Albert Einsteins an Willy Wien  

Microsoft Academic Search

Das Aequivalenzprinzip wurde von Einstein erst 1907 in Worte gefasst. Er wendete sich 1912 brieflich an W. Wien mit der Bitte, den Unterschied der Schwingungsdauer eines Uranpendels und eines Bleipendels sowie die Proportionalität der trägen und schweren Massen eines Blei- und eines Urangewichts auszumessen, und zwar mit einer Drehwage. Der Brief macht es klar, dass Einstein bei der Aufstellung des

József Illy

1989-01-01

212

Unified Maxwell-Einstein and Yang-Mills-Einstein supergravity theories in four dimensions  

Microsoft Academic Search

We study unified Script N = 2 Maxwell-Einstein supergravity theories (MESGTs) and unified Yang-Mills Einstein supergravity theories (YMESGTs) in four dimensions. As their defining property, these theories admit the action of a global or local symmetry group that is (i) simple, and (ii) acts irreducibly on all the vector fields of the theory, including the ``graviphoton''. Restricting ourselves to the

Murat Günaydin; Sean McReynolds; Marco Zagermann

2005-01-01

213

Einstein's contribution to cosmology - an overview (German Title: Einsteins Beitrag zur Kosmologie - ein Überblick)  

NASA Astrophysics Data System (ADS)

It is well known that Einstein founded relativistic cosmology in 1917 when he published his ``Cosmological considerations in the general theory of relativity.'' He presented a static, spatially closed though unbounded cosmological model with a uniform large-scale distribution of matter. For more than a decade, he defended his Einstein model against the proposals of Friedmann (1922/23) and Lemaître (1927) who took non-static world models into consideration, as well as against the spatially infinite model worked out by Selety (1922). Only after getting acquainted with the latest observational data like Hubble's redshift-distance relation during visiting Hubble, Tolman and others in California around the turn of the year 1930, Einstein gave up his static model and began to accept expanding world models. In the aftermath, he himself proposed two expanding world models, namely the Friedmann-Einstein universe in 1931 and the Einstein-de Sitter universe in a joint paper with de Sitter in 1932. In Einstein's opinion, world models still had to be spatially closed, but the cosmological constant which he had introduced in 1917 to obtain a static cosmological model had to be abandoned. In his later years, Einstein showed scepticism against relativistic cosmology as can be seen from his remarks concerning the rotating Gödel universes (1949). Although Einstein seemed to consider relativistic cosmology as a ``fashionable disease'' the then discovered Friedmann-Lemaître models are still used to describe the large-scale evolution of the space-time background of the universe.

Jung, Tobias

214

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

215

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

216

Einstein's Revolutionary Light-Quantum Hypothesis  

NASA Astrophysics Data System (ADS)

The paper in which Albert Einstein proposed his light-quantum hypothesis was the only one of his great papers of 1905 that he himself termed ``revolutionary.'' Contrary to widespread belief, Einstein did not propose his light-quantum hypothesis ``to explain the photoelectric effect.'' Instead, he based his argument for light quanta on the statistical interpretation of the second law of thermodynamics, with the photoelectric effect being only one of three phenomena that he offered as possible experimental support for it. I will discuss Einstein's light-quantum hypothesis of 1905 and his introduction of the wave-particle duality in 1909 and then turn to the reception of his work on light quanta by his contemporaries. We will examine the reasons that prominent physicists advanced to reject Einstein's light-quantum hypothesis in succeeding years. Those physicists included Robert A. Millikan, even though he provided convincing experimental proof of the validity of Einstein's equation of the photoelectric effect in 1915. The turning point came after Arthur Holly Compton discovered the Compton effect in late 1922, but even then Compton's discovery was contested both on experimental and on theoretical grounds. Niels Bohr, in particular, had never accepted the reality of light quanta and now, in 1924, proposed a theory, the Bohr-Kramers-Slater theory, which assumed that energy and momentum were conserved only statistically in microscopic interactions. Only after that theory was disproved experimentally in 1925 was Einstein's revolutionary light-quantum hypothesis generally accepted by physicists---a full two decades after Einstein had proposed it.

Stuewer, Roger H.

2005-05-01

217

Hierarchical maximum entropy principle for generalized superstatistical systems and Bose-Einstein condensation of light  

NASA Astrophysics Data System (ADS)

A principle of hierarchical entropy maximization is proposed for generalized superstatistical systems, which are characterized by the existence of three levels of dynamics. If a generalized superstatistical system comprises a set of superstatistical subsystems, each made up of a set of cells, then the Boltzmann-Gibbs-Shannon entropy should be maximized first for each cell, second for each subsystem, and finally for the whole system. Hierarchical entropy maximization naturally reflects the sufficient time-scale separation between different dynamical levels and allows one to find the distribution of both the intensive parameter and the control parameter for the corresponding superstatistics. The hierarchical maximum entropy principle is applied to fluctuations of the photon Bose-Einstein condensate in a dye microcavity. This principle provides an alternative to the master equation approach recently applied to this problem. The possibility of constructing generalized superstatistics based on a statistics different from the Boltzmann-Gibbs statistics is pointed out.

Sob'yanin, Denis Nikolaevich

2012-06-01

218

Hierarchical maximum entropy principle for generalized superstatistical systems and Bose-Einstein condensation of light.  

PubMed

A principle of hierarchical entropy maximization is proposed for generalized superstatistical systems, which are characterized by the existence of three levels of dynamics. If a generalized superstatistical system comprises a set of superstatistical subsystems, each made up of a set of cells, then the Boltzmann-Gibbs-Shannon entropy should be maximized first for each cell, second for each subsystem, and finally for the whole system. Hierarchical entropy maximization naturally reflects the sufficient time-scale separation between different dynamical levels and allows one to find the distribution of both the intensive parameter and the control parameter for the corresponding superstatistics. The hierarchical maximum entropy principle is applied to fluctuations of the photon Bose-Einstein condensate in a dye microcavity. This principle provides an alternative to the master equation approach recently applied to this problem. The possibility of constructing generalized superstatistics based on a statistics different from the Boltzmann-Gibbs statistics is pointed out. PMID:23005064

Sob'yanin, Denis Nikolaevich

2012-06-20

219

Isotopic exchange of carbon-bound hydrogen over geologic timescales  

NASA Astrophysics Data System (ADS)

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 data from several pilot studies to investigate such issues. Published experimental estimates of exchange rates between organic hydrogen and water indicate that at warm temperatures (50-100°C) exchange likely occurs on timescales of 10 4 to 10 8 yr. Incubation experiments using organic compounds and D-enriched water, combined with compound-specific D/H analyses, provide a new and highly sensitive method for measuring exchange at low temperatures. Comparison of ?D values for isoprenoid and n-alkyl carbon skeletons in sedimentary organic matter provides no evidence for exchange in young (<1 Ma), cool sediments, but strong evidence for exchange in ancient (>350 Ma) rocks. Specific rates of exchange are probably influenced by the nature and abundance of organic matter, pore-water chemistry, the presence of catalytic mineral surfaces, and perhaps even enzymatic activity. Estimates of equilibrium fractionation factors between organic H and water indicate that typical lipids will be depleted in D relative to water by ˜75 to 140‰ at equilibrium (30°C). Thus large differences in ?D between organic molecules and water cannot be unambiguously interpreted as evidence against hydrogen exchange. A better approach may be to use changes in stereochemistry as a proxy for hydrogen exchange. For example, estimated rates of H exchange in pristane are similar to predicted rates for stereochemical inversion in steranes and hopanes. The isotopic consequences of this exchange remain in question. Incubations of cholestene with D 2O indicate that the number of D atoms incorporated during structural rearrangements can be far less than the number of C-H bonds that are broken. Sample calculations indicate that, for steranes in immature sediments, the D/H ratio imparted by biosynthesis may be largely preserved in spite of significant structural changes.

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

2004-04-01

220

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

221

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

222

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

223

Relaxation in polymer electrolytes on the nanosecond timescale.  

SciTech Connect

The relation between mechanical and electrical relaxation in polymer/lithium-salt complexes is a fascinating and still unresolved problem in condensed-matter physics, yet has an important bearing on the viability of such materials for use as electrolytes in lithium batteries. At room temperature, these materials are biphasic: they consist of both fluid amorphous regions and salt-enriched crystalline regions. Ionic conduction is known to occur predominantly in the amorphous fluid regions. Although the conduction mechanisms are not yet fully understood, it is widely accepted that lithium ions, coordinated with groups of ether oxygen atoms on single or perhaps double polymer chains, move through re-coordination with other oxygen-bearing groups. The formation and disruption of these coordination bonds must be accompanied by strong relaxation of the local chain structure. Here we probe the relaxation on a nanosecond timescale using quasielastic neutron scattering, and we show that at least two processes are involved: a slow process with a translational character and one or two fast processes with a rotational character. Whereas the former reflects the slowing-down of the translational relaxation commonly observed in polyethylene oxide and other polymer melts, the latter appears to be unique to the polymer electrolytes and has not (to our knowledge) been observed before. A clear picture emerges of the lithium cations forming crosslinks between chain segments and thereby profoundly altering the dynamics of the polymer network.

Mao, G.; Fernandez-Perea, R.; Price, D. L.; Saboungi, M.-L.; Howells, W. S.; Materials Science Division; Rutherford-Appleton Lab.

2000-05-11

224

Seven invariant classes of the Einstein equations and projective mappings  

NASA Astrophysics Data System (ADS)

By using the representation theory of groups, we define seven classes of the Einstein equations of the General Relativity Theory. Then we use this result for a more detailed study of the Einstein equations.

Stepanov, Sergey; Mikeš, Josef

2012-07-01

225

Coherence, Abstraction, and Personal Involvement: Albert Einstein, Physicist and Humanist.  

ERIC Educational Resources Information Center

|Reviews Einstein's main contributions to physics, and analyzes the importance of a coherent body of theory. Einstein's involvement in nonscientific issues such as nuclear disarmament is also included. (HM)|

Ne'eman, Yuval

1979-01-01

226

Understanding Einstein's 1905 derivation of E= Mc 2  

Microsoft Academic Search

H. C. Ohanian maintains that a consideration of the internal structure of a body reveals several mistakes in Einstein's 1905 paper on the mass–energy relation. The “mistakes” he identifies are based on misunderstandings of Einstein's argument.

N. David Mermin

2011-01-01

227

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

228

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

229

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

2012-05-21

230

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

231

Quantum corrections help Einstein gravity exit graciously  

SciTech Connect

This paper exploits the conformal equivalence between the 1-loop corrected Einstein gravity coupled to a scalar field, and linear Einstein gravity with an exponential potential, to show how the Graceful Exit Problem is solved in the context of this theory in a natural and simple way. What emerges is a scenario with a chaotic initial period followed by an era of old inflation. The resulting bubble nucleation rate is time-dependent in such a way that the second inflationary period, helped by the chaotic period, brings the Universe out of its inflationary era in a self-regulated and natural way.

Perez-Mercader, J. (Los Alamos National Lab., NM (United States))

1991-03-28

232

Resonances for coupled Bose-Einstein condensates  

SciTech Connect

The properties of a Bose-Einstein condensate in a two-well potential can be manipulated by periodic modulation of the potential parameters. We study the effects arising from modulating the barrier height and the difference in well depth. At certain modulation frequencies the system exhibits resonances, which may show up in an enhancement of the tunneling rate between the wells. Resonances can be used to control the particle distribution over the wells. Some of the effects occurring in the two-well system also arise for a Bose-Einstein condensate in an optical lattice.

Haroutyunyan, H.L.; Nienhuis, G. [Huygens Laborotarium, Universiteit Leiden, Postbus 9504, 2300 RA Leiden (Netherlands)

2004-12-01

233

Bose-Einstein Condensation of Erbium  

NASA Astrophysics Data System (ADS)

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 Er168, containing up to 7×104 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.

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

2012-05-01

234

Conceptual Development of Einstein's Mass-Energy Relationship  

ERIC Educational Resources Information Center

|Einstein's special theory of relativity was published in 1905. It stands as one of the greatest intellectual achievements in the history of human thought. Einstein described the equivalence of mass and energy as "the most important upshot of the special theory of relativity" (Einstein, 1919). In this paper, we will discuss the evolution of the…

Wong, Chee Leong; Yap, Kueh Chin

2005-01-01

235

Einstein, Newton and the empirical foundations of space time geometry  

Microsoft Academic Search

Einstein intended the general theory of relativity to be a generalization of the relativity of motion and, therefore, a radical departure from previous spacetime theories. It has since become clear, however, that this intention was not fulfilled. I try to explain Einstein's misunderstanding on this point as a misunderstanding of the role that spacetime plays in physics. According to Einstein,

Robert DiSalle

1992-01-01

236

On Certain Conceptual Anomalies in Einstein's Theory of Relativity  

Microsoft Academic Search

There are a number of conceptual anomalies occurring in the Standard expo- sition of Einstein's Theory of Relativity. These anomalies relate to issues in both mathematics and in physics and penetrate to the very heart of Einstein's theory. This paper reveals and amplifies a few such anomalies, including the fact that Einstein's field equations for the so-called static vacuum configura-

Stephen J. Crothers

237

Einstein, race, and the myth of the cultural icon  

Microsoft Academic Search

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

Fred Jerome

2004-01-01

238

Time-scale modelling of the invasive species Robinia pseudoacacia  

NASA Astrophysics Data System (ADS)

Our contribution is part of the TransEcoNet project (Transnational Ecological Networks in Central Europe) that aims to investigate transboundary ecological networks across Central Europe. An objective of this project is to contribute towards awareness rising on the value and role of ecological networks. This poster presents the activities that are carried out in Pomurje region, Slovenia as our case study area. Pomurje region borders with Austria in the north, to Hungary in the east, and to Croatia in the south. We are investigating the spread of the invasive species Robinia pseudacacia and the underlying causes, and assess landscape scale ecological dynamics (e.g. Mura River floodplains) in ecological networks. The study comprises investigation and mapping of the R. pseudacacia spread with time-series analysis to understand its spatial dynamics. The preliminary studies show that the R. pseudacacia had the most expanded in the region since 1980s. Some of the surfaces were cut and converted back to fields. This reflects the socioeconomic situation in the region. The further study will include statistic, GIS (geographical information systems) and remote sensing techniques. We will apply various character data: satellite imagery, IR-orthophotos, digital elevation models, including LIDAR, contemporary and historical maps, and other spatial/non-spatial data sources. The outputs will include reconstruction of R. pseudacacia-dynamics in the recent decade, modelling the distribution of R. pseudacacia in relation to abiotic environmental factors and land use, and modelling (prediction) the expected distribution of R. pseudacacia in case of climate and land use change. Keywords: invasive species, Robinia pseudacacia, spatial analysis, time-scale analysis, remote sensing, land use change, climate change

Tomaž, Podobnikar; Andraž, Ä.?Arni; Imelda, Somodi

2010-05-01

239

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

240

Einstein-Lorentz Comparison and Its Interpretations. 3. The Einstein Heuristics.  

National Technical Information Service (NTIS)

In order to examine, from the philosophical point of view, the relation between Einstein's relativity theory and Lorentz's aether theory the Zahar interpretation about this theme is transcribed with the aim of clarify some dark aspects. (Atomindex citatio...

A. Villani

1981-01-01

241

Evolution of Modeling Strategies for Operational Hydrologic Models with Changing Timescales  

NASA Astrophysics Data System (ADS)

Hydrologic forecasting models are used at a range of timescales: at short timescales for flood forecasting, at intermediate timescales for seasonal flow forecasting, and long timescales for decadal to century scale for global change predictions. Often models are developed for each of these purposes rather independently, sometimes in an ad hoc manner, leading to inefficiencies and leaving no room for flexibility and continuous refinement. In this paper we present a consistent framework for the development of distributed models at each of these timescales that enable a seamless transition as we transition from small to large timescales and accommodate the cascading of variability across the full range of timescales as well as, where needed, the interactions between water flow processes and other land-forming and life sustaining processes. This framework accommodates a synthesis of both bottom-up and top-down approaches to modeling that enable inclusion of laws of mass, momentum and energy balances, as well as the ability to embrace the learning from patterns in observed hydrologic responses. The proposed approach is a synthesis of the REW approach to distributed modeling proposed by Reggiani et al. (1998, 1999), and the data-based top-down approach to modeling reviewed by Sivapalan et al. (2003). We will articulate these ideas with respect to model development efforts in Australia for short, intermediate and long term streamflow forecasting at regional and continental scales as part of the WIRADA project.

Sivapalan, M.

2011-12-01

242

Timescales of Multineuronal Activity Patterns Reflect Temporal Structure of Visual Stimuli  

PubMed Central

The investigation of distributed coding across multiple neurons in the cortex remains to this date a challenge. Our current understanding of collective encoding of information and the relevant timescales is still limited. Most results are restricted to disparate timescales, focused on either very fast, e.g., spike-synchrony, or slow timescales, e.g., firing rate. Here, we investigated systematically multineuronal activity patterns evolving on different timescales, spanning the whole range from spike-synchrony to mean firing rate. Using multi-electrode recordings from cat visual cortex, we show that cortical responses can be described as trajectories in a high-dimensional pattern space. Patterns evolve on a continuum of coexisting timescales that strongly relate to the temporal properties of stimuli. Timescales consistent with the time constants of neuronal membranes and fast synaptic transmission (5–20 ms) play a particularly salient role in encoding a large amount of stimulus-related information. Thus, to faithfully encode the properties of visual stimuli the brain engages multiple neurons into activity patterns evolving on multiple timescales.

Jurjut, Ovidiu F.; Nikolic, Danko; Singer, Wolf; Yu, Shan; Havenith, Martha N.; Muresan, Raul C.

2011-01-01

243

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

244

New Einstein-Sasaki and Einstein spaces from Kerr-de Sitter  

Microsoft Academic Search

In this paper, which is an elaboration of our results in Phys. Rev. Lett. 95:071101, 2005 (hep-th\\/0504225), we construct new Einstein-Sasaki spaces Lp,q,r1,…,rn?1 in all odd dimensions D = 2n+1 ? 5. They arise by taking certain BPS limits of the Euclideanised Kerr-de Sitter metrics. This yields local Einstein-Sasaki metrics of cohomogeneity n, with toric U(1)n+1 principal orbits, and n

M. Cvetiÿc; H. Lü; Don N. Page; C. N. Pope

2009-01-01

245

Skyrme-Einstein closed cosmic chiral strings  

SciTech Connect

Within the theory of general relativity, the configuration of a closed string (vortex) characterized by a topological charge of the degree type is described for the Skyrme-Einstein SU (2) chiral model. In the approximation of a large vortex-closure radius (a), a solution to equations of motion is obtained, along with estimates for the vortex energy and radius.

Rybakov, Yu. P., E-mail: soliton4@mail.ru; Ivanova, I. S. [Peoples' Friendship University (Russian Federation)

2007-07-15

246

Quantum metrology with Bose-Einstein condensates  

Microsoft Academic Search

We show how a generalized quantum metrology protocol can be implemented in a two-mode Bose-Einstein condensate of n atoms, achieving a sensitivity that scales better than 1\\/n and approaches 1\\/n3\\/2 for appropriate design of the condensate.

Sergio Boixo; Animesh Datta; Matthew J. Davis; Steven T. Flammia; Anil Shaji; Alexandre B. Tacla; Carlton M. Caves

2009-01-01

247

Type III Einstein-Yang-Mills solutions  

SciTech Connect

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.

Fuster, Andrea; Holten, Jan-Willem van

2005-07-15

248

Einstein Observations of Galactic supernova remnants  

SciTech Connect

This paper summarizes the observations of Galactic supernova remnants with the imaging detectors of the Einstein Observatory. X-ray surface brightness contours of 47 remnants are shown together with gray-scale pictures. Count rates for these remnants have been derived and are listed for the HRI, IPC, and MPC detectors. 118 refs.

Seward, F.D. (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (USA))

1990-08-01

249

[Albert Einstein and his abdominal aortic aneurysm].  

PubMed

The interesting case of Albert Einstein's abdominal aortic aneurysm is presented. He was operated on at age 69 and, finding that the large aneurysm could not be removed, the surgeon elected to wrap it with cellophane to prevent its growth. However, seven years later the aneurysm ruptured and caused the death of the famous scientist. PMID:21412401

Cervantes Castro, Jorge

250

Linearized Einstein theory via null surfaces  

Microsoft Academic Search

Recently there has been developed a reformulation of General Relativity - referred to as {\\\\it the null surface version of GR} - where instead of the metric field as the basic variable of the theory, families of three-surfaces in a four-manifold become basic. From these surfaces themselves, a conformal metric, conformal to an Einstein metric, can be constructed. A choice

Simonetta Frittelli; Carlos N. Kozameh; Ezra T. Newman

1995-01-01

251

The Excellence of Einstein's Theory of Gravitation.  

ERIC Educational Resources Information Center

|This article is adapted from a presentation made in 1978 at the symposium on the Impact of Modern Scientific Ideas on Society organized by UNESCO in Ulm, West Germany. It discusses Einstein's theory of gravitation and how it started a new line of activity for physicists. (HM)|

Dirac, P. A. M.

1979-01-01

252

Henri Poincare and Einstein's Theory of Relativity  

Microsoft Academic Search

Contrary to the opinion of some who have written on the history of relativity, the author argues that Henri Poincaré did not anticipate Einstein's special theory of relativity; but rather, that Poincaré was intent on an entirely different program-the perfection of the Lorentz theory of electrons. It is also suggested that Poincaré was not consistent in his use of the

Stanley Goldberg

1967-01-01

253

Can you do quantum mechanics without Einstein?  

SciTech Connect

The present form of quantum mechanics is based on the Copenhagen school of interpretation. Einstein did not belong to the Copenhagen school, because he did not believe in probabilistic interpretation of fundamental physical laws. This is the reason why we are still debating whether there is a more deterministic theory. One cause of this separation between Einstein and the Copenhagen school could have been that the Copenhagen physicists thoroughly ignored Einstein's main concern: the principle of relativity. Paul A. M. Dirac was the first one to realize this problem. Indeed, from 1927 to 1963, Paul A. M. Dirac published at least four papers to study the problem of making the uncertainty relation consistent with Einstein's Lorentz covariance. It is interesting to combine those papers by Dirac to make the uncertainty relation consistent with relativity. It is shown that the mathematics of two coupled oscillators enables us to carry out this job. We are then led to the question of whether the concept of localized probability distribution is consistent with Lorentz covariance.

Kim, Y. S. [Department of Physics, University of Maryland, College Park, Maryland 20742 (United States); Noz, Marilyn E. [Department of Radiology, New York University, New York, New York 10016 (United States)

2007-02-21

254

Atom optics with Bose-Einstein condensates  

Microsoft Academic Search

We use optical, stimulated Raman transitions to coherently split and transfer momentum to Bose-Einstein condensates of sodium atoms. With this technique, we have demonstrated a highly directional, quasi-continuous atom laser and four-wave mixing of matter-waves

L. Deng; E. Hagley; K. Helmerson; Y. Ovchinnikov; W. D. Philips; S. L. Rolston; J. Simsarian

1999-01-01

255

CEGO: China Einstein gravitational wave observatory  

Microsoft Academic Search

Gravitational waves were predicted by Einstein's general relativity. Up to now there has been no direct evidence for gravitational waves. Since the 1990's, laser interferometers have become the dominant detectors for gravitational wave detection, LIGO, Virgo, GEO600 and TAMA300 are the major laser interferometer gravitational wave observatories in the world. Chinese scientists would like to join the international club on

Keyun Tang; Fei Kang; R. DeSalvo; Jun Xu; Yang Zhang; Zonghong Zhu

2004-01-01

256

The Excellence of Einstein's Theory of Gravitation.  

ERIC Educational Resources Information Center

This article is adapted from a presentation made in 1978 at the symposium on the Impact of Modern Scientific Ideas on Society organized by UNESCO in Ulm, West Germany. It discusses Einstein's theory of gravitation and how it started a new line of activity for physicists. (HM)

Dirac, P. A. M.

1979-01-01

257

BOSE-EINSTEIN CONDENSATION OF EXCITONS  

Microsoft Academic Search

Whether quasi-particles, such as excitons, i.e., nonlocalized excited ; states of solids, can fulfill necessary conditions for a Bose-Einstein ; condensation and whether such condensation can be observed are discussed. ; Although uncertainties of data on excitons preclude precise numerical ; predictions, it is concluded that under certain experimentally attainable ; circumstances excitons fulfill the necessary conditions, i.e., condensation is

John Blatt; K. W. Boeer; Werner Brandt

1962-01-01

258

Stability of Attractive Bose–Einstein Condensates  

Microsoft Academic Search

We propose the critical nonlinear Schrödinger equation with a harmonic potential as a model of attractive Bose–Einstein condensates. By an elaborate mathematical analysis we show that a sharp stability threshold exists with respect to the number of condensate particles. The value of the threshold agrees with the existing experimental data. Moreover with this threshold we prove that a ground state

Jian Zhang

2000-01-01

259

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

260

Bose-Einstein Condensation in Complex Networks  

Microsoft Academic Search

The evolution of many complex systems, including the World Wide Web, business, and citation networks, is encoded in the dynamic web describing the interactions between the system's constituents. Despite their irreversible and nonequilibrium nature these networks follow Bose statistics and can undergo Bose-Einstein condensation. Addressing the dynamical properties of these nonequilibrium systems within the framework of equilibrium quantum gases predicts

Ginestra Bianconiand; Albert-László Barabási

2001-01-01

261

Vortices in a Bose Einstein condensate  

Microsoft Academic Search

Summary form only given. Since the first observations of Bose Einstein condensates (BEC) in dilute atomic gases, there has been considerable interest in observing effects in atomic BEC akin to the hallmark effects associated with a superfluid, in particular persistent, quantized circulation of the fluid. Using a method proposed by Williams and Holland' we have prepared vortices, macroscopic quantum states

P. C. Haljan; B. P. Anderson; Michael Matthews; David Hall; Carl Wieman; Eric Cornell

2000-01-01

262

A REAPPRAISAL OF THE EINSTEIN MODEL  

Microsoft Academic Search

A wave exists only in its propagating medium but Einstein erred to discard the medium for 'light-wave' and introduce 4-D spacetime continuum. It denied him the chance to address wave- quantum Unity of light and to predict the existence of 'basic substance' to compose all forms of E & m so compellingly demanded by E=mc2, otherwise E & m could

Rati Ram Sharma

263

Selfdual Einstein metrics with torus symmetry  

Microsoft Academic Search

It is well known that any 4-dimensional hyperkahler metric with two commuting Killing fields may be obtained explicitly, via the Gibbons-Hawking Ansatz, from a harmonic function invariant under a Killing field on R^3. In this paper, we find all selfdual Einstein metrics of nonzero scalar curvature with two commuting Killing fields. They are given explicitly in terms of a local

David M. J. Calderbank; Henrik Pedersen

2001-01-01

264

Topics in conformally compact Einstein metrics  

Microsoft Academic Search

We discuss a number of topics in the area of conformally compact Einstein\\u000ametrics, mostly centered around the global existence question of finding such\\u000ametrics with an arbitrarily prescribed conformal infinity. The paper is partly\\u000aa survey of this area but also presents new results and a number of open\\u000aproblems.

Michael T. Anderson

2005-01-01

265

Disembodied boundary data for Einstein's equations  

NASA Astrophysics Data System (ADS)

A strongly well-posed initial boundary value problem based upon constraint-preserving boundary conditions of the Sommerfeld type has been established for the harmonic formulation of the vacuum Einstein’s equations. These Sommerfeld conditions have been previously presented in a four-dimensional geometric form. Here we recast the associated boundary data as three-dimensional tensor fields intrinsic to the boundary. This provides a geometric presentation of the boundary data analogous to the three-dimensional presentation of Cauchy data in terms of three-metric and extrinsic curvature. In particular, diffeomorphisms of the boundary data lead to vacuum spacetimes with isometric geometries. The proof of well-posedness is valid for the harmonic formulation and its generalizations. The Sommerfeld conditions can be directly applied to existing harmonic codes which have been used in simulating binary black holes, thus ensuring boundary stability of the underlying analytic system. The geometric form of the boundary conditions also allows them to be formally applied to any metric formulation of Einstein’s equations, although well-posedness of the boundary problem is no longer ensured. We discuss to what extent such a formal application might be implemented in a constraint-preserving manner to 3+1 formulations, such as the Baumgarte-Shapiro-Shibata-Nakamura system which has been highly successful in binary black hole simulation.

Winicour, Jeffrey

2009-12-01

266

Quantum metrology with Bose-Einstein condensates  

SciTech Connect

We show how a generalized quantum metrology protocol can be implemented in a two-mode Bose-Einstein condensate of n atoms, achieving a sensitivity that scales better than 1/n and approaches 1/n{sup 3/2} for appropriate design of the condensate.

Boixo, Sergio [Institute for Quantum Information, Caltech, Pasadena, California, 91125 (United States); Datta, Animesh [Institute for Mathematical Sciences, 53 Prince's Gate, Imperial College, London, SW7 2PG (United Kingdom); QOLS, Blackett Laboratory, Imperial College, London, Prince Consort Road, SW7 2BW (United Kingdom); Davis, Matthew J. [School of Physical Sciences, University of Queensland, Brisbane, Queensland 4072 (Australia); Flammia, Steven T. [Perimeter Institute for Theoretical Physics, 31 Caroline Street N., Waterloo, ON N2L 2Y5 (Canada); Shaji, Anil; Tacla, Alexandre B.; Caves, Carlton M. [Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM, 87131 (United States)

2009-04-13

267

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

268

On the consequences of Einstein locality  

Microsoft Academic Search

After some considerations about the equivalence of the objective local theories to the deterministic theories of Bell's type, a simple and systematic way to deduce inequalities from Einstein locality is introduced: All the inequalities deduced by Bell and by other authors, as well as several new ones, are so obtained. Some theorems are proven which show how striking the difference

F. Selleri

1978-01-01

269

Einstein oscillators that impede thermal transport  

NASA Astrophysics Data System (ADS)

The Einstein model of a solid usually lacks a clear illustration in introductory solid-state physics courses because most solids are much better described by the Debye model. Filled antimony skutterudites, materials that have recently attracted much attention because of their potential for thermoelectric applications, provide a canonical illustration of the Einstein model. The filling atoms are loosely bound in the atomic cage formed by their neighbors, and hence their description as independent harmonic oscillators is adequate. Simple models for the heat capacity and thermal conductivity of a solid are introduced, with emphasis on the density of vibrational states. These models are used in conjunction with experimental results obtained from heat capacity and inelastic neutron scattering measurements to demonstrate the applicability of the concept of the Einstein oscillator to the filling guests in antimony skutterudites. The importance of these Einstein oscillators for impeding thermal transport is discussed and some simple problems involving the heat capacity, thermal conductivity, and inelastic neutron scattering are proposed.

Hermann, Raphaël P.; Grandjean, Fernande; Long, Gary J.

2005-02-01

270

Solving Einstein's Riddle Using Spreadsheet Optimization  

Microsoft Academic Search

A solution to Einstein's Riddle is presented using spreadsheet modelling and optimization. Various versions of this problem have been used in intro- ductory management science (MS) classes either as an assignment or as a take-home exam. This riddle has proved to be a challenging problem, since it simultaneously integrates many of the elements that are taught throughout the semester. Namely,

Julian Scott Yeomans

2003-01-01

271

ASYMPTOTIC SELF-SIMILAR SOLUTIONS WITH A CHARACTERISTIC TIMESCALE  

SciTech Connect

For a wide variety of initial and boundary conditions, adiabatic one-dimensional flows of an ideal gas approach self-similar behavior when the characteristic length scale over which the flow takes place, R, diverges or tends to zero. It is commonly assumed that self-similarity is approached since in the R {yields} {infinity}(0) limit the flow becomes independent of any characteristic length or timescales. In this case, the flow fields f(r, t) must be of the form f(r,t)=t{sup {alpha}}{sub f}F(r/R) with R {proportional_to} ({+-}t){sup {alpha}}. We show that requiring the asymptotic flow to be independent only of characteristic length scales implies a more general form of self-similar solutions, f(r,t)=R{sup {delta}}{sub f}F(r/R) with R-dot {proportional_to}R{sup {delta}}, which includes the exponential ({delta} = 1) solutions, R {proportional_to} e {sup t/{tau}}. We demonstrate that the latter, less restrictive, requirement is the physically relevant one by showing that the asymptotic behavior of accelerating blast waves, driven by the release of energy at the center of a cold gas sphere of initial density {rho} {proportional_to} r {sup -{omega}}, changes its character at large {omega}: the flow is described by 0 {<=} {delta} < 1, R {proportional_to} t {sup 1/(1-{delta})}, solutions for {omega} < {omega}{sub c}, by {delta}>1 solutions with R {proportional_to} (-t){sup 1/({delta}-1)} diverging at finite time (t = 0) for {omega}>{omega}{sub c}, and by exponential solutions for {omega} = {omega}{sub c} ({omega}{sub c} depends on the adiabatic index of the gas, {omega}{sub c} {approx} 8 for 4/3 < {gamma} < 5/3). The properties of the new solutions obtained here for {omega} {>=} {omega}{sub c} are analyzed, and self-similar solutions describing the t>0 behavior for {omega}>{omega}{sub c} are also derived.

Waxman, Eli [Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Rehovot 76100 (Israel); Shvarts, Dov [Department of Physics, Nuclear Research Center Negev, P.O. Box 9001, Beer-Sheva 84015 (Israel)

2010-10-01

272

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.

273

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

274

On the X-ray and gamma-ray emergent spectrum and hydrodynamics of super-Eddington explosion of very massive star. Application to spectral appearances of gamma-ray bursts  

Microsoft Academic Search

In the framework of super-Eddington explosion of a very massive star (M ¿ 100 solar masses) we offer a hydrodynamical solution of the relativistic outflow formation along with the solution for the relativistic Green's (response) function to the injection of seed photons to this relativistic outflow (ROF). We demonstrate that outflow with relativistic velocities cannot be formed close to the

Lev Titarchuk; Ruben Farinelli

2010-01-01

275

Einstein-Rosen “bridge” needs lightlike brane source  

NASA Astrophysics Data System (ADS)

The Einstein-Rosen “bridge” wormhole solution proposed in the classic paper (Einstein and Rosen (1935) [1]) does not satisfy the vacuum Einstein equations at the wormhole throat. We show that the fully consistent formulation of the original Einstein-Rosen “bridge” requires solving Einstein equations of bulk D=4 gravity coupled to a lightlike brane with a well-defined world-volume action. The non-vanishing contribution of Einstein-Rosen “bridge” solution to the right-hand side of Einstein equations at the throat matches precisely the surface stress-energy tensor of the lightlike brane which automatically occupies the throat (“horizon straddling”) — a feature triggered by the world-volume lightlike brane dynamics.

Guendelman, Eduardo; Kaganovich, Alexander; Nissimov, Emil; Pacheva, Svetlana

2009-11-01

276

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

277

Einstein and a century of time  

NASA Astrophysics Data System (ADS)

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 Year of Physics is called Einstein Year in the UK. Of course one can argue that progress in science depends on the contributions of many people; that there are other geniuses in physics, even some colourful personalities. Nevertheless there are fundamental reasons why Einstein's early achievements stand out even in their company. When at last the thought came to him that 'time itself was suspect', Einstein had found a new insight into the nature of the physical universe. It is this: that the universal properties of material objects tell us about the nature of space and time, and it is through these properties, not philosophical logic or common sense, that we discover the structure of spacetime. The later Einstein turned this successful formula on its head and sought to use the properties of spacetime to define those of material objects, thereby seeking to abolish matter entirely in favour of geometry. Before I introduce this special feature of European Journal of Physics I will say a few words about what is not here. Like all great geniuses Einstein can be seen as the climax of what went before him and the initiation of what was to follow. Looking back we can see the influence of Mach's positivism, according to which the role of science is to relate observations to other observations; hence only observations can tell us what is 'real'. But Einstein also grew up with the family electromechanical businesses, which testifies to the reality of the Maxwellian electromagnetic fields: thus only theory can tell us what is real! As is well known, Einstein himself refused to accept the full consequences of this pivotal insight into the role of theory when it came to quantum mechanics. Much has been written about this and we do not add to it in this collection. Quantum theory is a consistent description of nature whatever Einstein may think of 'god' for making it so. Many of us would side with Einstein in hoping it will yet turn out not to be a complete description. This will not happen, as Einstein hoped throughout his later work, from a return to classical field theory. But quantum behaviour is a universal property of matter and may therefore be expected, according to Einstein's way of thought, to have a geometrical origin. The advent of non-commutative quantum geometries may turn out to be a step in this direction. My own introduction to Einstein's physics was through what has come to be known as Mach's principle. My research supervisor, Dennis Sciama, in what he always claimed was probably Einstein's last significant scientific conversation, talked with him on this subject, during which Einstein explained that he had abandoned the idea of Mach's principle. This principle had been a guiding thought in the development of general relativity, but superfluous to its final exposition. It can be interpreted variously as the determination of the local compass of inertia by the distant stars, the non-rotation of the Universe or, more restrictedly, as requiring a critical density universe (to generate the right amount of inertia). This last formulation amounts to G??2 approx 1, where ? is the density of the Universe at time ?. This appears to be a classical expression, which would probably be sufficient to relegate Mach's principle to mere historical interest along with the classical unified field theories. It is also usually considered to be accounted for by inflation, which drives the Universe to ?=1. However, we can also think of the expression as saying that the Universe has a Planck mass in a Planck volume at the Planck time: G=(hc / G)1/2(c3 / Gh)3/2(Gh / c5)=1. This suggests that Mach's principle may yet have a surprising role in expressing the fact that the U

Raine, D. J.

2005-09-01

278

Dependence of evaporation on meteorological variables at different time-scales and intercomparison of estimation methods  

Microsoft Academic Search

This paper consists of two parts. In the first part, the significance of five major factors, including solar radiation, vapour pressure deficit, relative humidity, wind speed and air temperature, that control evaporation were evaluated comparatively at different time-scales using the data from Changines station in Switzerland. The comparative evaluation was made at hourly, daily, 10-day and monthly time-scales. It was

C.-Y. Xu; V. P. Singh

1998-01-01

279

Time-scales, Meaning, and Availability of Information in a Global Brain  

Microsoft Academic Search

We note the importance of time-scales, meaning, and availability of information for the emergence of novel information meta-structures at a global scale. We discuss previous work in this area and develop future perspectives. We focus on the transmission of scientific articles and the integration of traditional conferences with their virtual ext ensions on the I nternet, their time-scales, and av

Carlos Gershenson; Gottfried Mayer-Kress; Atin Das; Pritha Das; Matus Marko

2003-01-01

280

An improved whitecap timescale for sea spray aerosol production flux modeling using the discrete whitecap method  

NASA Astrophysics Data System (ADS)

The discrete whitecap method (DWM) to model the sea spray aerosol (SSA) production flux explicitly requires a whitecap timescale, which up to now has only considered a whitecap decay timescale, ?decay. A reevaluation of the DWM suggests that the whitecap timescale should account for the total whitecap lifetime (?wcap), which consists of both the formation timescale (?form) and the decay timescale (timescale definitions are given in the text). Here values of ?form for 552 oceanic whitecaps measured at the Martha's Vineyard Coastal Observatory on the east coast of the USA are presented, and added to the corresponding values of ?decay to form 552 whitecap timescales. For the majority of whitecaps, ?form makes up about 20-25% of ?wcap, but this can be as large as 70% depending on the value of ?decay. Furthermore, an area-weighted mean whitecap timescale for use in the DWM (?DWM) is defined that encompasses the variable nature of individual whitecap lifetimes within a given time period, and is calculated to be 5.3 s for this entire data set. This value is combined with previously published whitecap coverage parameterizations and estimates of SSA particle production per whitecap area to form a size-resolved SSA production flux parameterization (dF(r80)/dlog10r80). This parameterization yields integrated sea-salt mass fluxes that are largely within the range of uncertainty of recent measurements over the size range 0.029 µm < r80 < 0.580 µm. Physical factors controlling whitecap lifetime such as bubble plume lifetime and surfactant stabilization are discussed in the context of SSA production from whitecaps.

Callaghan, Adrian H.

2013-09-01

281

Rotating trapped Bose-Einstein condensates  

SciTech Connect

After reviewing the ideal Bose-Einstein gas in a box and in a harmonic trap, the effect of interactions on the formation of a Bose-Einstein condensate are discussed, along with the dynamics of small-amplitude perturbations (the Bogoliubov equations). When the condensate rotates with angular velocity {Omega}, one or several vortices nucleate, leading to many observable consequences. With more rapid rotation, the vortices form a dense triangular array, and the collective behavior of these vortices has additional experimental implications. For {Omega} near the radial trap frequency {omega}{sub perpendicular}, the lowest-Landau-level approximation becomes applicable, providing a simple picture of such rapidly rotating condensates. Eventually, as {Omega}{yields}{omega}{sub perpendicular}, the rotating dilute gas is expected to undergo a quantum phase transition from a superfluid to various highly correlated (nonsuperfluid) states analogous to those familiar from the fractional quantum Hall effect for electrons in a strong perpendicular magnetic field.

Fetter, Alexander L. [Geballe Laboratory for Advanced Materials and Departments of Physics and Applied Physics, Stanford University, Stanford, California 94305-4045 (United States)

2009-04-15

282

Bose-Einstein condensation of chromium.  

PubMed

We report on the generation of a Bose-Einstein condensate in a gas of chromium atoms, which have an exceptionally large magnetic dipole moment and therefore underlie anisotropic long-range interactions. The preparation of the chromium condensate requires novel cooling strategies that are adapted to its special electronic and magnetic properties. The final step to reach quantum degeneracy is forced evaporative cooling of 52Cr atoms within a crossed optical dipole trap. At a critical temperature of T(c) approximately 700 nK, we observe Bose-Einstein condensation by the appearance of a two-component velocity distribution. We are able to produce almost pure condensates with more than 50,000 condensed 52Cr atoms. PMID:15904199

Griesmaier, Axel; Werner, Jörg; Hensler, Sven; Stuhler, Jürgen; Pfau, Tilman

2005-04-29

283

How Einstein confirmed E0=mc2  

NASA Astrophysics Data System (ADS)

The equivalence of mass m and rest-energy E0 is one of the great discoveries of all time. Despite the current wisdom, Einstein did not derive this relation from first principles. Having conceived the idea in the summer of 1905 he spent more than 40 years trying to prove it. We briefly examine all of Einstein's conceptual demonstrations of E0=mc2, focusing on their limitations and his awareness of their shortcomings. Although he repeatedly confirmed the efficacy of E0=mc2, he never constructed a general proof. Leaving aside that it continues to be affirmed experimentally, a rigorous proof of the mass-energy equivalence is probably beyond the purview of the special theory.

Hecht, Eugene

2011-06-01

284

Einstein metrics and Brans-Dicke superfields  

SciTech Connect

It is obtained here a space conformal to the Einstein space-time, making the transition from an internal bosonic space, constructed with the Majorana constant spinors in the Majorana representation, to a bosonic ''superspace,'' through the use of Einstein vierbeins. These spaces are related to a Grassmann space constructed with the Majorana spinors referred to above, where the ''metric'' is a function of internal bosonic coordinates. The conformal function is a scale factor in the zone of gravitational radiation. A conformal function dependent on space-time coordinates can be constructed in that region when we introduce Majorana spinors which are functions of those coordinates. With this we obtain a scalar field of Brans-Dicke type. 11 refs.

Marques, S.

1988-01-01

285

Particle losses in Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

The two mode coherent atomic state, so called SU(2) state, evolves in the presence of particle interactions to highly entangled state. The Fisher information increases in the evolution to its maximal possible value. Thus, the system may be useful in the interferometry. Here we study its Fisher information decay due to particle losses. We explain in details new phenomena caused by these processes and finally their effect on the ``usefulness'' of two mode Bose-Einstein condensate for ultra precise measurements.

Pawlowski, Krzysztof; Spehner, Dominique; Ferrini, Giulia; Hekking, Frank; Minguzzi, Anna

2012-06-01

286

Embeddings for solutions of Einstein equations  

NASA Astrophysics Data System (ADS)

We study isometric embeddings of some solutions of the Einstein equations with sufficiently high symmetries into a flat ambient space. We briefly describe a method for constructing surfaces with a given symmetry. We discuss all minimal embeddings of the Schwarzschild metric obtained using this method and show how the method can be used to construct all minimal embeddings for the Friedmann models. We classify all the embeddings in terms of realizations of symmetries of the corresponding solutions.

Paston, S. A.; Sheykin, A. A.

2013-06-01

287

The einstein observatory medium sensitivity survey  

Microsoft Academic Search

Results are presented from an X-ray survey of ~50 square degrees of the high galactic latitude sky at sensitivities in the range 7·10-14 – 5·10-12 erg\\/cm2 sec (0·3–3·5 keV) carried out with the Imaging Proportional Counter (IPC) aboard the Einstein Observatory. The extragalactic sample consists of 48 sources which have been used to determine the number flux relation. The content

T. Maccacaro; E. D. Feigelson; R. Giacconi; I. M. Gioia; R. E. Griffiths; J. Liebert; S. S. Murray; J. Stocke; G. Zamorani

1981-01-01

288

Bose-Einstein Condensation of Atomic Hydrogen  

Microsoft Academic Search

We have observed Bose-Einstein condensation (BEC) of trapped atomic hydrogen, and studied it by two-photon spectroscopy of the 1S-2S transition. In these lecture notes we briefly review the history of spin-polarized atomic hydrogen and describe the final steps to BEC. Laser spectroscopy, which probes the difference in mean field energy of the 1S and 2S states, is used to study

Daniel Kleppner; Thomas J. Greytak; Thomas C. Killian; David Landhuis; Lorenz Willmann

1998-01-01

289

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

290

Bose-Einstein condensation in complex networks  

Microsoft Academic Search

The evolution of many complex systems, including the world wide web, busi- ness and citation networks is encoded in the dynamic web describing the interactions between the system's constituents. Despite their irreversible and non-equilibrium nature these networks follow Bose statistics and can undergo Bose-Einstein condensation. Addressing the dynamical properties of these non-equilibrium systems within the framework of equilibrium quantum gases

Ginestra Bianconiand; Albert-Laszlo Barabasi

291

Microchip traps and Bose–Einstein condensation  

Microsoft Academic Search

.   The article gives an overview of the rapidly evolving field of magnetic microchip traps (also called ‘atom chips’) for neutral\\u000a atoms. Special attention is given to Bose–Einstein condensation in such traps, to the particular properties of microchip trap\\u000a potentials, and to practical considerations in their design. Scaling laws are developed, which lead to an estimate of the\\u000a ultimate confinement

J. Reichel

2002-01-01

292

Molecules in a Bose-Einstein Condensate  

Microsoft Academic Search

State-selected rubidium-87 molecules were created at rest in a dilute Bose- Einstein condensate of rubidium-87 atoms with coherent free-bound stimu- lated Raman transitions. The transition rate exhibited a resonance line shape with an extremely narrow width as small as 1.5 kilohertz. The precise shape and position of the resonance are sensitive to the mean-field interactions between the molecules and the

Roahn Wynar; R. S. Freeland; D. J. Han; C. Ryu; D. J. Heinzen

2000-01-01

293

Vortices in a Bose-Einstein Condensate  

Microsoft Academic Search

We have created vortices in two-component Bose-Einstein condensates. The\\u000avortex state was created through a coherent process involving the spatial and\\u000atemporal control of interconversion between the two components. Using an\\u000ainterference technique, we map the phase of the vortex state to confirm that it\\u000apossesses angular momentum. We can create vortices in either of the two\\u000acomponents and have

D. S. Hall; C. E. Wieman; E. A. Cornell

1999-01-01

294

Bose–Einstein condensation of atomic hydrogen  

Microsoft Academic Search

.   The recent creation of a Bose–Einstein condensate of atomic hydrogen has added a new system to this exciting field. The differences\\u000a between hydrogen and the alkali metal atoms require other techniques for the initial trapping and cooling of the atoms and\\u000a the subsequent detection of the condensate. The use of a cryogenic loading technique results in a larger number

L. Willmann; D. Kleppner; D. G. Fried; T. C. Killian; David Landhuis; Stephen C. Moss

1999-01-01

295

Bose-Einstein Condensation of Molecules  

Microsoft Academic Search

We report on the Bose-Einstein condensation of more than 105 Li2 molecules in an optical trap starting from a spin mixture of fermionic lithium atoms. During forced evaporative cooling, the molecules are formed by three-body recombination near a Feshbach resonance and finally condense in a long-lived thermal equilibrium state. We measured the characteristic frequency of a collective excitation mode and

S. Jochim; M. Bartenstein; A. Altmeyer; G. Hendl; S. Riedl; C. Chin; J. Hecker Denschlag; R. Grimm

2003-01-01

296

Einstein Spaces with a Conformal Group  

Microsoft Academic Search

.  The pseudo-Riemannian Einstein spaces with a (local or global) conformal group of strictly positive dimension can be classified.\\u000a In this article we give a straightforward and systematic proof. As a common generalization, this includes the global theorem\\u000a of Yano and Nagano in the Riemannian case (1959, published in the Annals of Mathematics) and a pseudo-Riemannian analogue\\u000a proved by Kerckhove in

Wolfgang Kühnel; Hans-Bert Rademacher

2009-01-01

297

Theoretical studies of Bose-Einstein condensates  

Microsoft Academic Search

This thesis is a theoretical study of Bose-Einstein Condensation (BEC) in harmonically-trapped, weakly-interacting dilute gases. The motivation for this study is the experimental realization of BEC in trapped alkali gases since 1995. The weak inter-particle interactions and diluteness of the gases allow for a fairly accurate mean-field treatment and justifies a discrete quasi-particle description as we use in this work.

Kunal Kashyap Das

2001-01-01

298

On Relativistic Bose-Einstein Condensation  

Microsoft Academic Search

We discuss the properties of an ideal relativistic gas of events possessing\\u000aBose-Einstein statistics. We find that the mass spectrum of such a system is\\u000abounded by $\\\\mu \\\\leq m\\\\leq 2M\\/\\\\mu _K,$ where $\\\\mu $ is the usual chemical\\u000apotential, $M$ is an intrinsic dimensional scale parameter for the motion of an\\u000aevent in space-time, and $\\\\mu _K$ is an

L. Burakovsky; L. P. Horwitz; W. C. Schieve

1995-01-01

299

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

300

On Relativistic Bose-Einstein Condensation  

Microsoft Academic Search

We discuss the properties of an ideal relativistic gas of events possessing Bose-Einstein statistics. We find that the mass spectrum of such a system is bounded by $\\\\mu \\\\leq m\\\\leq 2M\\/\\\\mu _K,$ where $\\\\mu $ is the usual chemical potential, $M$ is an intrinsic dimensional scale parameter for the motion of an event in space-time, and $\\\\mu _K$ is an

L. Burakovsky; L. P. Horwitz; W. C. Schieve

1995-01-01

301

Gravity Probe B: Testing Einstein's Universe  

NSDL National Science Digital Library

Gravity Probe B is the relativity gyroscope experiment being developed by NASA and Stanford University to test two extraordinary, unverified predictions of Albert Einstein's general theory of relativity. The experiment will use changes in the direction of spin of four gyroscopes contained in an Earth satellite to measure how space and time are warped by the presence of the Earth, and, more profoundly, how the Earth's rotation drags spacetime around with it.

Everitt, C. W.

2003-10-10

302

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

303

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

304

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

305

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

306

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

307

The extended conformal Einstein field equations with matter: The Einstein–Maxwell field  

NASA Astrophysics Data System (ADS)

A discussion is given of the conformal Einstein field equations coupled with matter whose energy–momentum tensor is trace-free. These resulting equations are expressed in terms of a generic Weyl connection. The article shows how in the presence of matter it is possible to construct a conformal gauge which allows to know a priori the location of the conformal boundary. In vacuum this gauge reduces to the so-called conformal Gaussian gauge. These ideas are applied to obtain (i) a new proof of the stability of Einstein–Maxwell de Sitter-like spacetimes; (ii) a proof of the semi-global stability of purely radiative Einstein–Maxwell spacetimes.

Lübbe, Christian; Valiente Kroon, Juan Antonio

2012-06-01

308

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

309

Einstein–Weyl structures on contact metric manifolds  

Microsoft Academic Search

In this paper we study Einstein-Weyl structures in the framework of contact metric manifolds. First, we prove that a complete\\u000a K-contact manifold admitting both the Einstein-Weyl structures W\\u000a ± = (g, ±?) is Sasakian. Next, we show that a compact contact metric manifold admitting an Einstein-Weyl structure is either K-contact or the dual field of ? is orthogonal to the Reeb vector

Amalendu Ghosh

2009-01-01

310

Einstein-Podolsky-Rosen Correlations via Dissociation of a Molecular Bose-Einstein Condensate  

SciTech Connect

Recent experimental measurements of atomic intensity correlations through atom shot noise suggest that atomic quadrature phase correlations may soon be measured with a similar precision. We propose a test of local realism with mesoscopic numbers of massive particles based on such measurements. Using dissociation of a Bose-Einstein condensate of diatomic molecules into bosonic atoms, we demonstrate that strongly entangled atomic beams may be produced which possess Einstein-Podolsky-Rosen (EPR) correlations in field quadratures in direct analogy to the position and momentum correlations originally considered by EPR.

Kheruntsyan, K.V.; Drummond, P.D. [ARC Centre of Excellence for Quantum-Atom Optics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia); Olsen, M.K. [ARC Centre of Excellence for Quantum-Atom Optics, School of Physical Sciences, University of Queensland, Brisbane, Qld 4072 (Australia); Instituto de Fisica da Universidade Federal Fluminense, Boa Viagem 24210-340, Niteroi - Rio de Janeiro (Brazil)

2005-10-07

311

On the Energy-Momentum Problem in Static Einstein Universe  

NASA Astrophysics Data System (ADS)

The energy-momentum distributions of Einstein's simplest static geometrical model for an isotropic and homogeneous universe are evaluated. For this purpose, Einstein, Bergmann Thomson, Landau Lifshitz (LL), Møller and Papapetrou energy-momentum complexes are used in general relativity. While Einstein and Bergmann Thomson complexes give exactly the same results, LL and Papapetrou energy-momentum complexes do not provide the same energy densities. The Møller energy-momentum density is found to be zero everywhere in Einstein's universe. Also, several spacetimes are the limiting cases considered here.

Aygün, S.; Tarhan, I.; Baysal, H.

2007-02-01

312

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

313

A one-to-one correspondence between the static Einstein-Maxwell and stationary Einstein-vacuum space-times  

Microsoft Academic Search

A one-to-one correspondence is established between the static solutions of the Einstein-Maxwell equations and the stationary solutions of the Einstein-vacuum equations, that enables one to directly write down a solution for the one from a known solution of the other, and conversely, by a simple transcription. The directness of the correspondence is achieved by writing the metric for static Einstein-Maxwell

Subrahmanyan Chandrasekhar

1989-01-01

314

The magnitude-timescale relationship of surface temperature feedbacks in climate models  

NASA Astrophysics Data System (ADS)

Because of the fundamental role feedbacks play in determining the characteristics of climate it is important we are able to specify both the magnitude and response timescale of the feedbacks we are interested in. This paper employs three different climate models driven to equilibrium with a 4 × CO2 forcing to analyze the magnitude and timescales of surface temperature feedbacks. These models are a global energy balance model, an intermediate complexity climate model and a general circulation model. Rather than split surface temperature feedback into characteristic physical processes, this paper adopts a linear systems approach to split feedback according to their time constants and corresponding feedback amplitudes. The analysis reveals that there is a dominant net negative feedback realised during the first year. However, this is partially attenuated by a spectrum of positive feedbacks for time constants in the range 10 to 1000 years. This attenuation was composed of two discrete phases which are attributed to the effects of ''diffusive - mixed layer'' and ''circulatory - deep ocean'' ocean heat equilibration processes. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 % of the overall ocean heat equilibration feedback, whilst the circulatory feedback operated on a centennial timescale and accounted for the remaining 20 to 25 % of the response. It is important to quantify these decadal and centennial feedback processes to understand the range of climate model projections on these longer timescales.

Jarvis, A.

2011-07-01

315

The magnitudes and timescales of global mean surface temperature feedbacks in climate models  

NASA Astrophysics Data System (ADS)

Because of the fundamental role feedbacks play in determining the response of surface temperature to perturbations in radiative forcing, it is important we understand the dynamic characteristics of these feedbacks. Rather than attribute the aggregate surface temperature feedback to particular physical processes, this paper adopts a linear systems approach to investigate the partitioning with respect to the timescale of the feedbacks regulating global mean surface temperature in climate models. The analysis reveals that there is a dominant net negative feedback realised on an annual timescale and that this is partially attenuated by a spectrum of positive feedbacks with characteristic timescales in the range 10 to 1000 yr. This attenuation was composed of two discrete phases which are attributed to the equilibration of "diffusive - mixed layer" and "circulatory - deep ocean" ocean heat uptake. The diffusive equilibration was associated with time constants on the decadal timescale and accounted for approximately 75 to 80 percent of the overall ocean heat feedback, whilst the circulatory equilibration operated on a centennial timescale and accounted for the remaining 20 to 25 percent of the response. This suggests that the dynamics of the transient ocean heat uptake feedback first discussed by Baker and Roe (2009) tends to be dominated by loss of diffusive heat uptake in climate models, rather than circulatory deep ocean heat equilibration.

Jarvis, A.

2011-12-01

316

Colocalization of fast and slow timescale dynamics in the allosteric signaling protein CheY.  

PubMed

It is now widely recognized that dynamics are important to consider for understanding allosteric protein function. However, dynamics occur over a wide range of timescales, and how these different motions relate to one another is not well understood. Here, we report an NMR relaxation study of dynamics over multiple timescales at both backbone and side-chain sites upon an allosteric response to phosphorylation. The response regulator, Escherichia coli CheY, allosterically responds to phosphorylation with a change in dynamics on both the microsecond-to-millisecond (?s-ms) timescale and the picosecond-to-nanosecond (ps-ns) timescale. We observe an apparent decrease and redistribution of ?s-ms dynamics upon phosphorylation (and accompanying Mg(2+) saturation) of CheY. Additionally, methyl groups with the largest changes in ps-ns dynamics localize to the regions of conformational change measured by ?s-ms dynamics. The limited spread of changes in ps-ns dynamics suggests a distinct relationship between motions on the ?s-ms and ps-ns timescales in CheY. The allosteric mechanism utilized by CheY highlights the diversity of roles dynamics play in protein function. PMID:23648838

McDonald, Leanna R; Whitley, Matthew J; Boyer, Joshua A; Lee, Andrew L

2013-05-03

317

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

PubMed Central

Supereruptions violently transfer huge amounts (100 s–1000 s km3) 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 ?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, Alfred T.; Sutton, Stephen R.; Rivers, Mark L.

2012-01-01

318

Timescales of quartz crystallization and the longevity of the Bishop giant magma body.  

PubMed

Supereruptions violently transfer huge amounts (100 s-1000 s km(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 ~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. PMID:22666359

Gualda, Guilherme A R; Pamukcu, Ayla S; Ghiorso, Mark S; Anderson, Alfred T; Sutton, Stephen R; Rivers, Mark L

2012-05-30

319

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

320

A Search for Short-Timescale Microvariability in Active Galactic Nuclei in the Ultraviolet  

NASA Astrophysics Data System (ADS)

We observed four active galactic nuclei (AGNs) (the type 1 Seyfert systems 3C 249.1, NGC 6814, and Mrk 205, and the BL Lac object 3C 371) using the High Speed Photometer on the Hubble Space Telescope (HST) to search for short-timescale microvariability in the UV. Continuous observations of ~3000 s duration were obtained for each system on several consecutive HST orbits using a 1 s sample time in a 1400-3000 Å bandpass. No photometric variability greater than 0.3% (0.003 mag) was detected in any AGN on timescales shorter than 1500 s. The distribution of photon arrival times observed from each source was consistent with Poisson statistics. Because of HST optical problems, the limit on photometric variability at longer timescales is less precise. These results restrict the masses of black holes as the central engines of AGNs and the diskoseismic oscillations of any accretion disk around such a black hole.

Dolan, Joseph F.; Clark, L. Lee

2004-05-01

321

Albert Einstein - Chief Engineer of the Universe: 100 Authors for Einstein Essays  

Microsoft Academic Search

In 1905, Albert Einstein published five scientific articles that fundamentally changed the world-view of physics: The Special Theory of Reativity revolutionized our concept of space and time, E=mc² became the best-known equation in physics. On the occasion of the 100th aniversary of his \\

Jürgen Renn

2005-01-01

322

Einstein’s Investigations of Galilean Covariant Electrodynamics Prior to 1905  

Microsoft Academic Search

Einstein learned from the magnet and conductor thought experiment how to use field transformation laws to extend the covariance of Maxwell’s electrodynamics. If he persisted in his use of this device, he would have found that the theory cleaves into two Galilean covariant parts, each with different field transformation laws. The tension between the two parts reflects a failure not

John D. Norton

2004-01-01

323

Bose-Einstein condensation of photons  

NASA Astrophysics Data System (ADS)

In recent work, we have observed Bose-Einstein condensation (BEC) of a two-dimensional photon gas in an optical microcavity [1]. Here, the transversal motional degrees of freedom of the photons are thermally coupled to the cavity environment by multiple absorption-fluorescence cycles in a dye medium, with the latter serving both as a heat bath and a particle reservoir. The photon energies in this system are found to follow a Bose-Einstein distribution at room temperature. Upon reaching a critical total photon number, a condensation into the transversal ground state of the resonator sets in, while the population of the transversally excited modes roughly saturates. The critical photon number is experimentally verified to agree well with theoretical predictions. Owing to particle exchange between the photon gas and the dye molecules, grandcanonical experimental conditions can approximately be realized in this system. Under these conditions, two markedly different condensate regimes are theoretically expected [2]. On the one hand, this includes a condensate with Poissonian photon number statistics, being the analog to present atomic Bose condensates. Additionally, we predict a second regime with anomalously large condensate fluctuations accompanied by a Bose-Einstein-like photon number distribution that is not observed in present atomic BEC experiments. The crossover between these two regimes, corresponding to the emergence of second-order coherence, depends on the size of the molecular reservoir (e.g. the dye concentration) and is expected to occur at a temperature below the BEC phase transition. In my talk, I will give an update on our experimental work.[4pt] [1] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010)[0pt] [2] J. Klaers, J. Schmitt, T. Damm, F. Vewinger, and M. Weitz, Phys. Rev. Lett. 108, 160403 (2012)

Klaers, Jan

2013-03-01

324

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

325

Einstein Light: Inertial frames and Newtonian mechanics  

NSDL National Science Digital Library

This web page describes inertial and non-inertial frames of reference, the latter being frames where Newton's laws do not hold. The text explains "fictitious forces", the centrifugal force and the Coriolis force, that enable Newton's laws to describe motion in a non-inertial frame. An animation shows the motion of a ball rolling on a merry-go-round as seen both from the merry-go-round and from the ground. This is part of a large web site, EinsteinLight, that explains relativity at a qualitative level from Galileo through the intersection with quantum mechanics.

Wolfe, Joe

2007-11-29

326

Generalised Einstein relation for hot Brownian motion  

NASA Astrophysics Data System (ADS)

The Brownian motion of a hot nanoparticle is described by an effective Markov theory based on fluctuating hydrodynamics. Its predictions are scrutinized over a wide temperature range using large-scale molecular dynamics simulations of a hot nanoparticle in a Lennard-Jones fluid. The particle positions and momenta are found to be Boltzmann distributed according to distinct effective temperatures THBM and Tk. For THBM we derive a formally exact theoretical prediction and establish a generalised Einstein relation that links it to directly measurable quantities.

Chakraborty, D.; Gnann, M. V.; Rings, D.; Glaser, J.; Otto, F.; Cichos, F.; Kroy, K.

2011-12-01

327

Uniqueness and nonuniqueness in the Einstein constraints.  

PubMed

The conformal thin-sandwich (CTS) equations are a set of four of the Einstein equations, which generalize the Laplace-Poisson equation of Newton's theory. We examine numerically solutions of the CTS equations describing perturbed Minkowski space, and find only one solution. However, we find two distinct solutions, one even containing a black hole, when the lapse is determined by a fifth elliptic equation through specification of the mean curvature. While the relationship of the two systems and their solutions is a fundamental property of general relativity, this fairly simple example of an elliptic system with nonunique solutions is also of broader interest. PMID:16197202

Pfeiffer, Harald P; York, James W

2005-08-26

328

Analog gravity from Bose-Einstein condensates  

Microsoft Academic Search

We analyze prospects for the use of Bose-Einstein condensates as\\u000acondensed-matter systems suitable for generating a generic ``effective\\u000ametric'', and for mimicking kinematic aspects of general relativity. We extend\\u000athe analysis due to Garay et al, [gr-qc\\/0002015, gr-qc\\/0005131]. Taking a long\\u000aterm view, we ask what the ultimate limits of such a system might be. To this\\u000aend, we consider

Carlos Barcelo; Stefano Liberati; Matt Visser

2000-01-01

329

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

330

Rydberg Excitation of Bose-Einstein Condensates  

SciTech Connect

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 {sup 87}Rb 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.

Heidemann, Rolf; Raitzsch, Ulrich; Bendkowsky, Vera; Butscher, Bjoern; Loew, Robert; Pfau, Tilman [5. Physikalisches Institut, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart (Germany)

2008-01-25

331

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

2008-01-22

332

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

333

Bose-Einstein Condensation of Strontium  

SciTech Connect

We report on the attainment of Bose-Einstein condensation with ultracold strontium atoms. We use the {sup 84}Sr isotope, which has a low natural abundance but offers excellent scattering properties for evaporative cooling. Accumulation in a metastable state using a magnetic-trap, narrowline cooling, and straightforward evaporative cooling in an optical trap lead to pure condensates containing 1.5x10{sup 5} atoms. This puts {sup 84}Sr in a prime position for future experiments on quantum-degenerate gases involving atomic two-electron systems.

Stellmer, Simon; Huang Bo; Grimm, Rudolf [Institut fuer Quantenoptik und Quanteninformation (IQOQI), Oesterreichische Akademie der Wissenschaften, 6020 Innsbruck (Austria); Institut fuer Experimentalphysik und Zentrum fuer Quantenphysik, Universitaet Innsbruck, 6020 Innsbruck (Austria); Tey, Meng Khoon; Schreck, Florian [Institut fuer Quantenoptik und Quanteninformation (IQOQI), Oesterreichische Akademie der Wissenschaften, 6020 Innsbruck (Austria)

2009-11-13

334

On the mode switching timescales of pulsar PSR B0329+54  

NASA Astrophysics Data System (ADS)

Chen et al. (2011) found that the durations (timescales) of the normal and abnormal modes of PSR B0329+54 follow a gamma distribution, and constrained the parameters of the distribution function. In this paper, we perform a further analysis on the relationship between the timescales of the two modes. The ratio between the durations of a normal mode and the succeeding abnormal mode is calculated for 54 such pairs. It is found that the cumulative distribution function (CDF) of the ratio is consistent with the CDF obtained by assuming random mode switching, suggesting that the two modes work independently.

Wang, Hong-Guang; Chen, Jian-Ling; Wen, Zhi-Gang; Pi, Fei-Peng

2013-03-01

335

Sensor location selection for structures via identifiability analysis in the time-scale domain  

NASA Astrophysics Data System (ADS)

Sensor location selection for structures is demonstrated via identifiability analysis. The sensitivities of sensor outputs to structural stiffness coefficients are computed by a model and transformed via continuous wavelet transforms into the time-scale domain to characterize their shape attributes and accentuate their differences. Regions are then sought in the time-scale plane wherein the wavelet coefficient of an output sensitivity surpasses all the others' as indication of the sensitivity's uniqueness. This yields a comprehensive account of identifiability by each output for individual stiffness coefficients as the basis for output selection. The proposed output selection strategy is demonstrated for an eight-storey building frame model.

Danai, Kourosh; Civjan, Scott A.; Styckiewicz, Matthew M.

2013-11-01

336

Albert Einstein's 1916 Review Article on General Relativity  

Microsoft Academic Search

The first comprehensive overview of the final version of the general theory of relativity was published by Einstein in 1916 after several expositions of preliminary versions and latest revisions of the theory in November 1915. A historical account of this review paper is given, of its prehistory, including a discussion of Einstein's collaboration with Marcel Grossmann, and of its immediate

Tilman Sauer; Einstein Papers Project

2004-01-01

337

Beyond Einstein: From the Big Bang to Black Holes  

Microsoft Academic Search

Beyond Einstein is a science-driven program of missions, education and outreach, and technology, to address three questions: What powered the Big Bang? What happens to space, time, and matter at the edge of a Black Hole? What is the mysterious Dark Energy pulling the universe apart? To address the science objectives, Beyond Einstein contains several interlinked elements. The strategic missions

N. White

2002-01-01

338

Focus: The elusive icon: Einstein, 1905-2005 - Introduction  

Microsoft Academic Search

As Einstein's portrait comes increasingly to resemble an icon, we lose more than detail - his writings and actions lose all reference. This is as true for his physics as it is for his philosophy and his politics; the best of recent work aims to remove Einstein's interventions from the abstract sphere of Delphic pronouncements and to insert them in

Peter Galison

2004-01-01

339

[Photoeffects, Einstein's light quanta and the history of their acceptance].  

PubMed

It is generally supposed, that the discovery of the efficacy-quantum by Planck was the impetus to Einstein's hypothesis of lightquanta. With its help Einstein could explain the external light-electrical effect. But even years before Einstein had worked at the photoeffect and already made experiments on it. For that reason the article gives a short survey about the history of the lightelectric effects. Lenard's basical work about the release of the photoelectrons is dealt with in detail, without which Einstein would scarcely have found his lightquanta. Furthermore it is shown how difficult it was for the physicists to give up--at least partially--the traditional view of the undulation-nature of light, and how they searched to explain the great energies of the photoelectrons. On the other side it is set forth how Einstein's formula of lightquanta was gradually confirmed. The tragical development of Einstein's personal relations with Johannes Stark and Philipp Lenard are briefly described. Stark was one of the few who supported Einstein's ideas at the beginning. Only with the Compton-effect, which could only be quantitatively interpreted by means of lightquanta and the special theory of relativity 1923, the way was free for the general acceptance of the lightquanta. Einstein did not agree to the obtained dualism of undulation and corpuscle; he had a different solution in mind about the fusion of the two forms of appearance of light. PMID:17338401

Wiederkehr, Karl Heinrich

2006-01-01

340

The Lorentz Theory of Electrons and Einstein's Theory of Relativity  

ERIC Educational Resources Information Center

|Traces the development of Lorentz's theory of electrons as applied to the problem of the electrodynamics of moving bodies. Presents evidence that the principle of relativity did not play an important role in Lorentz's theory, and that though Lorentz eventually acknowledged Einstein's work, he was unwilling to completely embrace the Einstein

Goldberg, Stanley

1969-01-01

341

a Review of Einstein's Theory of Special Relativity  

Microsoft Academic Search

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

Gerald Mott

2006-01-01

342

A Demonstration of Einstein's Equivalence of Gravity and Acceleration  

ERIC Educational Resources Information Center

|In 1907, Einstein described a "Gedankenexperiment" in which he showed that free fall in a gravitational field is indistinguishable from a body at rest in an elevator accelerated upwards in zero gravity. This paper describes an apparatus, which is simple to make and simple to operate, that acts as an observable footnote to Einstein's example. It…

Newburgh, Ronald

2008-01-01

343

Quenching of Einstein's A-coefficients by photons  

SciTech Connect

We present evidence for the quenching of Einstein A-coefficients in an Ar-ion laser discharge due to the presence of a high intensity laser flux. The reduction in spontaneous emission intensity when lasing occurs was found to be dependent on the Einstein A-coefficient for transitions originating from the same upper level. 9 refs., 3 figs.

Aumayr, F.; Hung, J.; Suckewer, S.

1989-05-01

344

Einstein X-Ray Observations of Cataclysmic Variables.  

National Technical Information Service (NTIS)

Observations with the imaging x-ray detectors on the Einstein Observatory have led to a large increase in the number of low luminosity x-ray sources known to be associated with cataclysmic variable stars (CVs). The high sensitivity of the Einstein instrum...

K. O. Mason F. A. Cordova

1982-01-01

345

The Einstein@Home search for new neutron stars  

NASA Astrophysics Data System (ADS)

Einstein@Home is a volunteer distributed computing project with more than a quarter-million participants. I will describe the current status of its search for new neutron stars, using data from radio telescopes and gravitational wave observatories. I will also talk about the first Einstein@Home discoveries, of new radio pulsars found in data from the Arecibo Observatory.

Allen, Bruce

2011-04-01

346

A nonlinear Poisson transform for Einstein metrics on product spaces  

Microsoft Academic Search

We consider the Einstein deformations of the reducible rank two symmetric spaces of noncompact type. If $M$ is the product of any two real, complex, quaternionic or octonionic hyperbolic spaces, we prove that the family of nearby Einstein metrics is parametrized by certain new geometric structures on the Furstenberg boundary of $M$.

Olivier Biquard; Rafe Mazzeo

2007-01-01

347

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

348

BOOK REVIEW: Einstein's Jury: The Race to Test Relativity  

Microsoft Academic Search

'I know very well that my theory rests on a shaky foundation. What attracts me to it is that it leads to consequences that seem to be accessible to experiment, and it provides a starting point for the theoretical understanding of gravitation', wrote Einstein in 1911. Einstein's Jury by Jeffrey Crelinsten---well documented, well written, and fascinating to read---describes how, from

Jeffrey Crelinsten

2007-01-01

349

The Lorentz Theory of Electrons and Einstein's Theory of Relativity  

ERIC Educational Resources Information Center

Traces the development of Lorentz's theory of electrons as applied to the problem of the electrodynamics of moving bodies. Presents evidence that the principle of relativity did not play an important role in Lorentz's theory, and that though Lorentz eventually acknowledged Einstein's work, he was unwilling to completely embrace the Einstein

Goldberg, Stanley

1969-01-01

350

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

351

Bose-Einstein condensation of photons  

NASA Astrophysics Data System (ADS)

Bose-Einstein condensation, the macroscopic ground state accumulation of particles with integer spin (bosons) at low temperature and high density, has been observed in several physical systems, including cold atomic gases and solid state physics quasiparticles. However, the most omnipresent Bose gas, blackbody radiation (radiation in thermal equilibrium with the cavity walls) does not show this phase transition. The photon number is not conserved when the temperature of the photon gas is varied (vanishing chemical potential), and at low temperatures photons disappear in the cavity walls instead of occupying the cavity ground state. Here I will describe an experiment observing a Bose-Einstein condensation of photons in a dye-filled optical microcavity [1]. The cavity mirrors provide both a confining potential and a non-vanishing effective photon mass, making the system formally equivalent to a two-dimensional gas of trapped, massive bosons. By multiple scattering of the dye molecules, the photons thermalize to the temperature of the dye solution. In my talk, I will begin with a general introduction and give an account of current work and future plans of the Bonn photon gas experiment. [4pt] [1] J. Klaers, J. Schmitt, F. Vewinger, and M. Weitz, Nature 468, 545 (2010).

Weitz, Martin

2012-02-01

352

Disembodied boundary data for Einstein's equations  

SciTech Connect

A strongly well-posed initial boundary value problem based upon constraint-preserving boundary conditions of the Sommerfeld type has been established for the harmonic formulation of the vacuum Einstein's equations. These Sommerfeld conditions have been previously presented in a four-dimensional geometric form. Here we recast the associated boundary data as three-dimensional tensor fields intrinsic to the boundary. This provides a geometric presentation of the boundary data analogous to the three-dimensional presentation of Cauchy data in terms of three-metric and extrinsic curvature. In particular, diffeomorphisms of the boundary data lead to vacuum spacetimes with isometric geometries. The proof of well-posedness is valid for the harmonic formulation and its generalizations. The Sommerfeld conditions can be directly applied to existing harmonic codes which have been used in simulating binary black holes, thus ensuring boundary stability of the underlying analytic system. The geometric form of the boundary conditions also allows them to be formally applied to any metric formulation of Einstein's equations, although well-posedness of the boundary problem is no longer ensured. We discuss to what extent such a formal application might be implemented in a constraint-preserving manner to 3+1 formulations, such as the Baumgarte-Shapiro-Shibata-Nakamura system which has been highly successful in binary black hole simulation.

Winicour, Jeffrey [Department of Physics and Astronomy University of Pittsburgh, Pittsburgh, Pennsylvania 15260 (United States); Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, 14476 Golm (Germany)

2009-12-15

353

On the Typical Timescale for the Chemical Enrichment from Type Ia Supernovae in Galaxies  

Microsoft Academic Search

We calculate the Type Ia supernova (SN) rate for different star formation histories in galaxies by adopting the most popular and recent progenitor models. We show that the timescale for the maximum in the SN Ia rate, which corresponds also to time of the maximum enrichment, is not unique but is a strong function of the adopted stellar lifetimes, initial

Francesca Matteucci; Simone Recchi

2001-01-01

354

Star Formation Timescale in the Circumnuclear Starburst Ring of Barred Galaxy NGC 7552  

NASA Astrophysics Data System (ADS)

We present the multiple line observations carried out with interferometry. We observed the circumnuclear region of the barred galaxy NGC 7552 in molecular lines tracing diffuse molecular gas (12CO J = 2 - 1; observed by SMA) and relatively dense molecular gas (HCN J = 1 - 0; observed by ATCA). We also reprocessed a published HI image which covers the entire galaxy to gain an analytical image with higher resolution. The displacement between HCN (J = 1 - 0) and radio knots (3 cm continuum; ATCA archive data) is clearly seen in the circumnuclear starburst ring of NGC 7552. The propagation time derived from 12CO J = 2 - 1 and HI based rotation curve between the HCN (J = 1 - 0) and radio knots implies the timescale between the formation and death of massive stars. The timescale of NGC 7552 is about an order of magnitude shorter than 5 - 10 Myr timescale for OB stars to become supernovae. It is possible that star formation in the ring is top heavy, resulting in a shorter timescale.

Pan, Hsi-An; Lim, Jeremy; Matsushita, Satoki; Wong, Tony

2012-07-01

355

A Short-timescale Channel of Dissipation of the Strong Solar Wind Turbulence  

Microsoft Academic Search

Hybrid numerical simulations of a turbulent cascade nearly perpendicular to the background magnetic field are carried out at the proton kinetic scales. It is shown that the cascade produces exponentially growing current sheets previously observed in fluid simulations. In the kinetic limit, the sheets are developing on a timescale as fast as the proton gyration. The rapid variations of the

S. A. Markovskii; Bernard J. Vasquez

2011-01-01

356

Relationships between global precipitation and surface temperature on interannual and longer timescales (1979-2006)  

Microsoft Academic Search

Associations between global and regional precipitation and surface temperature anomalies on interannual and longer timescales are explored for the period of 1979-2006 using the GPCP precipitation product and the NASA-GISS surface temperature data set. Positive (negative) correlations are generally confirmed between these two variables over tropical oceans (lands). ENSO is the dominant factor in these interannual tropical relations. Away from

Robert F. Adler; Guojun Gu; Jian-Jian Wang; George J. Huffman; Scott Curtis; David Bolvin

2008-01-01

357

Relationships between global precipitation and surface temperature on interannual and longer timescales (1979–2006)  

Microsoft Academic Search

Associations between global and regional precipitation and surface temperature anomalies on interannual and longer timescales are explored for the period of 1979–2006 using the GPCP precipitation product and the NASA-GISS surface temperature data set. Positive (negative) correlations are generally confirmed between these two variables over tropical oceans (lands). ENSO is the dominant factor in these interannual tropical relations. Away from

Robert F. Adler; Guojun Gu; Jian-Jian Wang; George J. Huffman; Scott Curtis; David Bolvin

2008-01-01

358

THE COLORADO PLATEAU CORING PROJECT: THE TIMESCALE AND TEMPO OF BIOTIC CHANGE OF THE EARLY MESOZOIC  

Microsoft Academic Search

The proposed Colorado Plateau Coring Project (CPCP) is an interdisciplinary, multi-institutional coring project designed to recover continuous core through mostly continental strata spanning ~100 million years of the Triassic and Jurassic. Its principal purpose is to tie the incredibly rich faunas, floras, and environmental record of this interval to a rigorously developed timescale and thus to biotic, environmental, and tectonic

P. E. Olsen; D. V. Kent; R. Mundil; R. Irmis; J. W. Geissman; J. Martz; W. Parker

2009-01-01

359

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

360

Anti-control of chaos of single time-scale brushless DC motor.  

PubMed

Anti-control of chaos of single time-scale brushless DC motors is studied in this paper. In order to analyse a variety of periodic and chaotic phenomena, we employ several numerical techniques such as phase portraits, bifurcation diagrams and Lyapunov exponents. Anti-control of chaos can be achieved by adding an external constant term or an external periodic term. PMID:16893797

Ge, Zheng-Ming; Chang, Ching-Ming; Chen, Yen-Sheng

2006-09-15

361

Multiple-timescale quantum dynamics of many interacting bosons in a dimer  

Microsoft Academic Search

The full quantum dynamics of many bosons that are initially completely localized on one site of a symmetric dimer is investigated in the small tunnelling amplitude regime. The number difference of bosons between the two equivalent sites of the dimer exhibits rich behaviour on different timescales, ranging from small amplitude oscillations and collapses and revivals, to coherent tunnelling. We show

G. Kalosakas; A. R. Bishop; V. M. Kenkre

2003-01-01

362

A Cenozoic Time-Scale. Some Implications for Regional Geology and Paleobiogeography.  

National Technical Information Service (NTIS)

Recent data generally substantiate the most recent incarnation of the Cenozoic time-scale. Newly obtained dates in the type section of the Chattian (Upper Oligocene) support a previous suggestion that a hiatus may separate the top of the stratotype Chatti...

W. A. Berggren

1972-01-01

363

Climate and landscape controls on water balance model complexity over changing timescales  

Microsoft Academic Search

A systematic approach is described for determining the minimum level of model complexity required to predict runoff in New Zealand catchments, with minimal calibration, at decreasing timescales. Starting with a lumped conceptual model representing the most basic hydrological processes needed to capture water balance, model complexity is systematically increased in response to demonstrated deficiencies in model predictions until acceptable accuracy

S. E. Atkinson; R. A. Woods; M. Sivapalan

2002-01-01

364

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

365

Modelling the effect of form and profile adjustments on channel equilibrium timescales  

Microsoft Academic Search

A model for describing river channel profile adjustments through time is developed and applied to a river responding to base- level lowering in order to examine the effect of channel widening and downstream aggradation on equilibrium timescales. Across a range of boundary conditions, downstream aggradation controlled how quickly a channel reached equilibrium. Channel widening either increased or decreased the equilibrium

Martin W. Doyle; Jon M. Harbor

2003-01-01

366

Two approaches to timescale modeling for proxy series with chronological errors.  

NASA Astrophysics Data System (ADS)

A substantial part of proxy series used in paleoclimate research has chronological uncertainties. Any constructed timescale is therefore only an estimate of the true, but unknown timescale. An accurate assessment of the timing of events in the paleoproxy series and networks, as well as the use of proxy-based paleoclimate reconstructions in GCM model scoring experiments, requires the effect of these errors to be properly taken into account. We consider two types of the timescale error models corresponding to the two basic approaches to construction of the (depth-) age scale in a proxy series. Typically, a chronological control of a proxy series stemming from all types of marine and terrestrial sedimentary archives is based on the use of 14C dates, reference horizons or their combination. Depending on the prevalent origin of the available fix points (age markers) the following approaches to timescale modeling are proposed. 1) 14C dates. The algorithm uses Markov-chain Monte Carlo sampling technique to generate the ordered set of perturbed age markers. Proceeding sequentially from the youngest to the oldest fixpoint, the sampler draws random numbers from the age distribution of each individual 14C date. Every following perturbed age marker is generated such that condition of no age reversal is fulfilled. The relevant regression model is then applied to construct a simulated timescale. 2) Reference horizons (f. ex. volcanic or dust layers, T bomb peak) generally provide absolutely dated fixpoints. Due to a natural variability in sedimentation (accumulation) rate, however, the dating uncertainty in the interpolated timescale tends to grow together with a span to the nearest fixpoint. The (accumulation, sedimentation) process associated with formation of a proxy series is modelled using stochastic Levy process. The respective increments for the process are drawn from the log-normal distribution with the mean/variance ratio prescribed as a site(proxy)- dependent external parameter. The number of generated annual increments corresponds to a time interval between the considered reference horizons. The simulated series is then rescaled to match the length of the actual core section being modelled. Within each method the multitude of timescales is generated creating a number of possible realisations of a proxy series or a proxy based reconstruction in the time domain. This allows consideration of a proxy record in a probabilistic framework. The effect of accounting for uncertainties in chronology on a reconstructed environmental variable is illustrated with the two case studies of marine sediment records.

Divine, Dmitry; Godtliebsen, Fred

2010-05-01

367

A Comparison of Solar Energetic Particle Event Timescales with Properties of Associated Coronal Mass Ejections  

NASA Astrophysics Data System (ADS)

The dependence of solar energetic proton (SEP) event peak intensities Ip on properties of associated coronal mass ejections (CMEs) has been extensively examined, but the dependence of SEP event timescales is not well known. We define three timescales of 20 MeV SEP events and ask how they are related to speeds v CME or widths W of their associated CMEs observed by LASCO/SOHO. The timescales of the EPACT/Wind 20 MeV events are TO, the onset time from CME launch to SEP onset; TR, the rise time from onset to half the peak intensity (0.5Ip); and TD, the duration of the SEP intensity above 0.5Ip. This is a statistical study based on 217 SEP-CME events observed during 1996-2008. The large number of SEP events allows us to examine the SEP-CME relationship in five solar-source longitude ranges. In general, we statistically find that TO declines slightly with v CME, and TR and TD increase with both v CME and W. TO is inversely correlated with log Ip, as expected from a particle background effect. We discuss the implications of this result and find that a background-independent parameter TO+TR also increases with v CME and W. The correlations generally fall below the 98% significance level, but there is a significant correlation between v CME and W which renders interpretation of the timescale results uncertain. We suggest that faster (and wider) CMEs drive shocks and accelerate SEPs over longer times to produce the longer TR and TD SEP timescales.

Kahler, S. W.

2013-06-01

368

Co-evolution of Soils and Landforms: Erosion Modelling over Decadal Timescales for Disturbed Lands  

NASA Astrophysics Data System (ADS)

Landform evolution models (LEMs) have largely ignored temporal changes in the soils. Likewise fluvial erosion models have typically ignored temporal changes in soils. In both cases these changes in soils and erosion rates may be independent of (e.g. weathering of soils/rock particles), or dependent on (e.g. armouring due to selective entrainment) the fluvial erosion process. Typically, LEMs and erosion models have implicitly assumed that soils are constant in time and at equilibrium. This may be true for undisturbed sites but is unlikely to be true for disturbed sites. The high erosion rates on poorly managed agricultural lands typically lead to coarsening of the surface (i.e. desertification) over relatively short periods of time such as decades, so ought to be considered as part of any erosion assessment. For unnatural constructed landforms the issue is even more dramatic. Many of the mine and nuclear waste rehabilitation problems examined by the authors using LEMs over the last 20 years show, in the field, significant evolution of the surface erodibility at the decadal timescale. We conclude that the evolution of soils must be modeled explicitly to be able to predict landscape evolution over the decadal timescale. Some insights based on our recent work in quantitative pedogenesis models will be presented and we will show how current approaches used in LEMs are deficient, and propose a route forward. We will show that there are two important pedogenic timescales, (1) the surface of the soil and (2) the entire soil profile. We conclude that we must consider several timescales for soil evolution, that for the entire profile, and that for the surface alone. The evolution of the soil surface is an order of magnitude faster process than that of the entire profile. The evolution of the soil surface is likely to be dominant at the decadal timescale.

Willgoose, G. R.; Hancock, G. R.; Cohen, S.

2011-12-01

369

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

370

On Einstein clusters as galactic dark matter haloes  

NASA Astrophysics Data System (ADS)

We consider global and gravitational lensing properties of the recently suggested Einstein clusters of weakly interacting massive particles (WIMPs) as galactic dark matter haloes. Being tangential pressure dominated, Einstein clusters are strongly anisotropic systems which can describe any galactic rotation curve by specifying the anisotropy. Due to this property, Einstein clusters may be considered as dark matter candidates. We analyse the stability of the Einstein clusters against both radial and non-radial pulsations, and we show that the Einstein clusters are dynamically stable. With the use of the Buchdahl type inequalities for anisotropic bodies, we derive upper limits on the velocity of the particles defining the cluster. These limits are consistent with those obtained from stability considerations. The study of light deflection shows that the gravitational lensing effect is slightly smaller for the Einstein clusters as compared to the singular isothermal density sphere model for dark matter. Therefore, lensing observations may discriminate, at least, in principle, between Einstein cluster and the other dark matter models.

Böhmer, C. G.; Harko, T.

2007-07-01

371

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

372

Observation of Bose-Einstein condensation of molecules.  

PubMed

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic 6Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into 6Li2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900 000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation. PMID:14754098

Zwierlein, M W; Stan, C A; Schunck, C H; Raupach, S M F; Gupta, S; Hadzibabic, Z; Ketterle, W

2003-12-15

373

Generalized Einstein-Aether theories and the Solar System  

NASA Astrophysics Data System (ADS)

It has been shown that generalized Einstein-Aether theories may lead to significant modifications to the nonrelativistic limit of the Einstein equations. In this paper we study the effect of a general class of such theories on the Solar System. We consider corrections to the gravitational potential in negative and positive powers of distance from the source. Using measurements of the perihelion shift of Mercury and time delay of radar signals to Cassini, we place constraints on these corrections. We find that a subclass of generalized Einstein-Aether theories is compatible with these constraints.

Bonvin, Camille; Durrer, Ruth; Ferreira, Pedro G.; Starkman, Glenn; Zlosnik, Tom G.

2008-01-01

374

Vortex Molecules in Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

Stable vortex dimers are known to exist in coherently coupled two component Bose-Einstein condensates (BECs). We construct stable vortex trimers in three component BECs and find that the shape can be controlled by changing the internal coherent (Rabi) couplings. Stable vortex N-omers are also constructed in coherently coupled N-component BECs. We classify all possible N-omers in terms of the mathematical graph theory. Next, we study effects of the Rabi coupling in vortex lattices in two-component BECs. We find how the vortex lattices without the Rabi coupling known before are connected to the Abrikosov lattice of integer vortices with increasing the Rabi coupling. In this process, vortex dimers change their partners in various ways at large couplings. We then find that the Abrikosov lattices are robust in three-component BECs.

Nitta, Muneto; Eto, Minoru; Cipriani, Mattia

2013-10-01

375

Polarized entangled Bose-Einstein condensation  

SciTech Connect

We consider a mixture of two distinct species of atoms of pseudospin (1/2) with both intraspecies and interspecies spin-exchange interactions and find all the ground states in a general case of the parameters in the effective Hamiltonian. In general, corresponding to the two-species and two-pseudospin states, there are four orbital wave functions into which the atoms condense. We find that in certain parameter regimes, the ground state is the so-called polarized entangled Bose-Einstein condensation; that is, in addition to condensation of interspecies singlet pairs, there are unpaired atoms with spins polarized in the same direction. The interspecies entanglement and polarization significantly affect the generalized Gross-Pitaevskii equations governing the four orbital wave functions into which the atoms condense, as an interesting interplay between spin and orbital degrees of freedom.

Wang Jinlong; Shi Yu [State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai, 200433 (China)

2010-12-15

376

Nonlinear interferometry with Bose-Einstein condensates  

SciTech Connect

We analyze a proposed experiment [Boixo et al., Phys. Rev. Lett. 101, 040403 (2008)] for achieving sensitivity scaling better than 1/N in a nonlinear Ramsey interferometer that uses a two-mode Bose-Einstein condensate (BEC) of N atoms. We present numerical simulations that confirm the analytical predictions for the effect of the spreading of the BEC ground-state wave function on the ideal 1/N{sup 3/2} scaling. Numerical integration of the coupled, time-dependent, two-mode Gross-Pitaevskii equations allows us to study the several simplifying assumptions made in the initial analytic study of the proposal and to explore when they can be justified. In particular, we find that the two modes share the same spatial wave function for a length of time that is sufficient to run the metrology scheme.

Tacla, Alexandre B. [Center for Quantum Information and Control, MSC 07-4220, University of New Mexico, Albuquerque, New Mexico 87131-0001 (United States); Boixo, Sergio [Institute for Quantum Information, California Institute of Technology, Pasadena, California 91125 (United States); Datta, Animesh [Clarendon Laboratory, Department of Physics, University of Oxford, OX1 3PU (United Kingdom); Shaji, Anil [School of Physics, Indian Institute of Science Education and Research, College of Engineering Trivandrum Campus, Thiruvananthapuram, Kerala 695016 (India); Caves, Carlton M. [Center for Quantum Information and Control, MSC 07-4220, University of New Mexico, Albuquerque, New Mexico 87131-0001 (United States); School of Mathematics and Physics, University of Queensland, Brisbane, Queensland 4072 (Australia)

2010-11-15

377

Optomechanics of Antiferromagnetic Bose-Einstein Condensates  

NASA Astrophysics Data System (ADS)

We investigate the matter-wave analog of rotational optomechanics. That is, in stead of considering the optomechanical coupling of a rotating mechanical element, we study the optomechanical effects associated with spin-wave excitations of a macroscopic mode in an antiferromagnetic Bose-Einstein condensate (BEC) inside a unidirectional ring cavity, relying on the well established fact that the antiferromagnetic BEC can be effectively described as a single quantum rotor characterized by angular momentum and angular displacement. We show that under suitable conditions the optomechanical coupling can be quadratic in angular displacement, and demonstrate how one can measure its eigen-energy nondestructively by observation of the cavity output signal. This model opens the door to the observation of spin-wave quantum jumps, as well as to controllable entanglement between a quantum spin gas and a mechanical element.

Jing, Hui; Goldbaum, Dan; Buchmann, Lukas; Meystre, Pierre

2011-06-01

378

An Introduction to the Einstein Toolkit  

NASA Astrophysics Data System (ADS)

We give an introduction to the Einstein Toolkit, a mature, open-source computational infrastructure for numerical relativity based on the Cactus Framework, for the target group of new users. This toolkit is composed of several different modules, is developed by researchers from different institutions throughout the world and is in active continuous development. Documentation for the toolkit and its several modules is often scattered across different locations, a difficulty new users may at times have to struggle with. Scientific papers exist describing the toolkit and its methods in detail, but they might be overwhelming at first. With these lecture notes we hope to provide an initial overview for new users. We cover how to obtain, compile and run the toolkit, and give an overview of some of the tools and modules provided with it.

Zilhão, Miguel; Löffler, Frank

2013-09-01

379

Faraday waves in Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

Motivated by recent experiments on Faraday waves in Bose-Einstein condensates we investigate both analytically and numerically the dynamics of cigar-shaped Bose-condensed gases subject to periodic modulation of the strength of the transverse confinement. We offer a fully analytical explanation of the observed parametric resonance, based on a Mathieu-type analysis of the non-polynomial Schrödinger equation. The theoretical prediction for the pattern periodicity versus the driving frequency is directly compared to the experimental data, yielding good qualitative and quantitative agreement between the two. These results are corroborated by direct numerical simulations of both the one-dimensional non-polynomial Schrödinger equation and of the fully three-dimensional Gross-Pitaevskii equation.

Nicolin, Alexandru I.; Carretero-González, R.; Kevrekidis, P. G.

2007-12-01

380

Einstein - Weyl structures in the conformal classes of LeBrun metrics  

NASA Astrophysics Data System (ADS)

We study the Einstein - Weyl equations for diagonal Bianchi IX metrics and give new non-trivial Einstein - Weyl structures in the conformal classes of Bianchi IX scalar-flat Kähler metrics. These solutions offer examples of metrics admitting both Einstein and Einstein - Weyl structures and give also examples of self-dual Einstein - Weyl structures which can appear on both sides of the dichotomy established by Pedersen and Swann.

Bisbjerg Madsen, Anders

1997-09-01

381

Addendum to 'Interface tension of Bose-Einstein condensates'  

SciTech Connect

In this addendum to our paper [B. Van Schaeybroeck, Phys. Rev. A 78, 023624 (2008)] we present an exact solution of the interface tension of Bose-Einstein condensates in a particular parameter regime.

Van Schaeybroeck, Bert [Instituut voor Theoretische Fysica, Katholieke Universiteit Leuven, Celestijnenlaan 200 D, B-3001 Leuven (Belgium)

2009-12-15

382

Interacting Einstein Solids and Entropy Worksheet and Model  

NSDL National Science Digital Library

A worksheet that uses two small Einstein solid model to illustrate that at equilibrium not all micropartitions are equally likely. The Metropolis method is used to sample according to the distribution given by the multiplicities.

Wheaton, Spencer

2013-08-15

383

Persistent Currents in a Bose-Einstein Condensate.  

National Technical Information Service (NTIS)

This research program explored matter wave optics and rotating Bose- Einstein condensates (BECs). High sensitivity inertial sensors based on matter waves may benefit greatly from the coherence properties of condensates. We explored rotating BECs using Bra...

C. Raman

2009-01-01

384

Einstein supergravity amplitudes from twistor-string theory  

NASA Astrophysics Data System (ADS)

This paper gives a twistor-string formulation for all tree amplitudes of Einstein (super-)gravities for {N}=0 and 4. Formulae are given with and without cosmological constant and with various possibilities for the gauging. The formulae are justified by use of Maldacena's observation that conformal gravity tree amplitudes with Einstein wavefunctions and non-zero cosmological constant will correctly give the Einstein tree amplitudes. This justifies the construction of Einstein gravity amplitudes at {N}=0 from twistor-string theory and is extended to {N}=4 by requiring the standard relation between the MHV-degree and the degree of the rational curve for Yang-Mills this systematically excludes the spurious conformal supergravity gravity contributions. For comparison, BCFW recursion is used to obtain twistor-string-like formulae at degree 0 and 1 (anti-MHV and MHV) for amplitudes with {N}=8 supersymmetry with and without cosmological constant.

Adamo, Tim; Mason, Lionel

2012-07-01

385

On the Bose-Einstein distribution and Bose condensation  

Microsoft Academic Search

For a system of identical Bose particles sitting on integer energy levels, we give sharp estimates for the convergence of the sequence of occupation numbers to the Bose-Einstein distribution and for the Bose condensation effect.

V. P. Maslov; V. E. Nazaikinskii

2008-01-01

386

Reduction of type IIB on squashed Sasaki-Einstein manifolds  

NASA Astrophysics Data System (ADS)

We present a consistent truncation of type IIB supergravity on squashed Sasaki-Einstein manifolds, leading to half-maximal gauged supergravity in five dimensions. We comment on the holographic picture of consistency.

Cassani, D.

2011-07-01

387

Bose-Einstein condensation in low-dimensional traps  

NSDL National Science Digital Library

The authors demonstrate the possibility of Bose-Einstein condensation of an ideal Bose gas confined by one- and two-dimensional power-law traps. Problem 6.66 in Gould & Tobochnik is based on this paper.

Bagnato, Vanderlei; Kleppner, Daniel

2011-05-26

388

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

389

Estimating Black Carbon Aging Time-Scales with a Particle-Resolved Aerosol Model  

SciTech Connect

Understanding the aging process of aerosol particles is important for assessing their chemical reactivity, cloud condensation nuclei activity, radiative properties and health impacts. In this study we investigate the aging of black carbon containing particles in an idealized urban plume using a new approach, the particleresolved aerosol model PartMC-MOSAIC. We present a method to estimate aging time-scales using an aging criterion based on cloud condensation nuclei activation. The results show a separation into a daytime regime where condensation dominates and a nighttime regime where coagulation dominates. For the chosen urban plume scenario, depending on the supersaturation threshold, the values for the aging timescales vary between 0.06 hours and 10 hours during the day, and between 6 hours and 20 hours during the night.

Riemer, Nicole; West, Matt; Zaveri, Rahul A.; Easter, Richard C.

2010-01-13

390

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

391

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

392

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

393

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

394

Kähler-Einstein metrics with positive scalar curvature  

Microsoft Academic Search

.   In this paper, we prove that the existence of Khler-Einstein metrics implies the stability of the underlying Khler manifold\\u000a in a suitable sense. In particular, this disproves a long-standing conjecture that a compact Khler manifold admits Khler-Einstein\\u000a metrics if it has positive first Chern class and no nontrivial holomorphic vector fields. We will also establish an analytic\\u000a criterion for

Gang Tian

1997-01-01

395

Phase separation of two-component Bose-Einstein condensates  

SciTech Connect

Recently, coupled systems of nonlinear Schroedinger equations have been used extensively to describe mixtures Bose-Einstein condensates. In this paper, we study the distribution of two different hyperfine spin states of a binary mixture of three dimensional Bose-Einstein condensates. In a double condensate, an interface may occur due to large intraspecies and interspecies scattering lengths. We prove that there is an asymptotic separation of different phases in the strong coupling (Thomas-Fermi) limit.

Liu, Zuhan [Department of Mathematics, Xuzhou Normal University, Xuzhou 221116 (China)

2009-10-15

396

The Einstein Observatory and future X-ray telescopes  

Microsoft Academic Search

A history of the events leading to the development and flight of the Einstein Observatory is given. The advantages of using grazing-incidence telescopes for solar and extrasolar X-ray astronomy is first discussed and followed by a description of the HEAO program. The Einstein Observatory marks a departure from the manner in which X-ray investigations are carried out, from individual experiments

R. Giacconi; P. Gorenstein; S. S. Murray; E. Schreier; F. Seward; H. Tananbaum; W. H. Tucker; L. van Speybroeck

1981-01-01

397

X-ray studies of quasars with the Einstein Observatory  

Microsoft Academic Search

Results of an investigation of the X-ray properties of quasars conducted using the Einstein Observatory (HEAO 2) are reported. The positions, fluxes and luminosities of 35 known quasars were observed by the Einstein high-resolution imaging detector and the imaging proportional counter. Assuming optical redshifts as valid distance indicators, 0.5-4.5 keV X-ray luminosities ranging from 10 to the 43rd to 10

H. Tananbaum; Y. Avni; G. Branduardi; M. Elvis; G. Fabbiano; E. Feigelson; R. Giacconi; J. P. Henry; J. P. Pye; A. Soltan; G. Zamorani

1979-01-01

398

Circular orbits in Einstein-Gauss-Bonnet gravity  

SciTech Connect

The stability under radial and vertical perturbations of circular orbits associated to particles orbiting a spherically symmetric center of attraction is studied in the context of the n-dimensional: the Newtonian theory of gravitation, Einstein's general relativity, and the Einstein-Gauss-Bonnet theory of gravitation. The presence of a cosmological constant is also considered. We find that this constant as well as the Gauss-Bonnet coupling constant are crucial to have stability for n>4.

Rosa, Valeria M.; Letelier, Patricio S. [Departamento de Matematica, Universidade Federal de Vicosa, 36570-000 Vicosa, M.G. (Brazil); Departamento de Matematica Aplicada-IMECC, Universidade Estadual de Campinas, 13083-970 Campinas, S.P. (Brazil)

2008-10-15

399

Optical Confinement of a Bose-Einstein Condensate  

Microsoft Academic Search

Bose-Einstein condensates of sodium atoms have been confined in an optical dipole trap using a single focused infrared laser beam. This eliminates the restrictions of magnetic traps for further studies of atom lasers and Bose-Einstein condensates. More than 5×106 condensed atoms were transferred into the optical trap. Densities of up to 3×1015 cm-3 of Bose condensed atoms were obtained, allowing

D. M. Stamper-Kurn; M. R. Andrews; A. P. Chikkatur; S. Inouye; H.-J. Miesner; J. Stenger; W. Ketterle

1998-01-01

400

Observation of Bose-Einstein Condensation of Molecules  

Microsoft Academic Search

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic 6Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into 6Li2 molecules. Below 600nK, a Bose-Einstein condensate of up to 900 000molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the

M. W. Zwierlein; C. A. Stan; C. H. Schunck; S. M. Raupach; S. Gupta; Z. Hadzibabic; W. Ketterle

2003-01-01

401

Dynamics of Bose-Einstein condensates in optical lattices  

Microsoft Academic Search

Matter waves inside periodic potentials are well known from solid-state physics, where electrons interacting with a crystal lattice are considered. Atomic Bose-Einstein condensates inside light-induced periodic potentials (optical lattices) share many features with electrons in solids, but also with light waves in nonlinear materials and other nonlinear systems. Generally, atom-atom interactions in Bose-Einstein condensates lead to rich and interesting nonlinear

Oliver Morsch; Markus Oberthaler

2006-01-01

402

Einstein metrics, hypercomplex structures and the Toda field equation  

Microsoft Academic Search

We obtain explicitly all solutions of the SU(?) Toda field equation with the property that the associated Einstein–Weyl space admits a 2-sphere of divergence-free shear-free geodesic congruences. The solutions depend on an arbitrary holomorphic function and give rise to new hyperKähler and selfdual Einstein metrics with one-dimensional isometry group. These metrics each admit a compatible hypercomplex structure with respect to which

David M. J. Calderbank; Paul Tod

2001-01-01

403

Cohomogeneity-one Einstein–Weyl structures: a local approach  

Microsoft Academic Search

We analyse in a systematic way the (non-) compact n-dimensional Einstein–Weyl spaces equipped with a cohomogeneity-one metric. In that context, with no compactness hypothesis for the manifold on which lives the Einstein–Weyl structure, we prove that, as soon as the (n?1)-dimensional space is a homogeneous reductive Riemannian space with a unimodular group of left-acting isometries G:•there exists a Gauduchon gauge

Guy Bonneau

2001-01-01

404

Communications: The fractional Stokes-Einstein equation: Application to water  

Microsoft Academic Search

Previously [K. R. Harris, J. Chem. Phys. 131, 054503 (2009)] it was shown that both real and model liquids fit the fractional form of the Stokes-Einstein relation [fractional Stokes-Einstein (FSE)] over extended ranges of temperature and density. For example, the self-diffusion coefficient and viscosity of the Lennard-Jones fluid fit the relation (D\\/T)=(1\\/?)t with t=(0.921+\\/-0.003) and a range of molecular and

Kenneth R. Harris

2010-01-01

405

Communications: The fractional Stokes–Einstein equation: Application to water  

Microsoft Academic Search

Previously [K. R. Harris, J. Chem. Phys. 131, 054503 (2009)] it was shown that both real and model liquids fit the fractional form of the Stokes–Einstein relation [fractional Stokes–Einstein (FSE)] over extended ranges of temperature and density. For example, the self-diffusion coefficient and viscosity of the Lennard-Jones fluid fit the relation (D\\/T)=(1\\/&eegr;)t with t=(0.921±0.003) and a range of molecular and

Kenneth R. Harris

2010-01-01

406

Soliton Creation During a Bose-Einstein Condensation  

SciTech Connect

We use the stochastic Gross-Pitaevskii equation to study dynamics of Bose-Einstein condensation. We show that cooling into a Bose-Einstein condensate (BEC) can create solitons with density given by the cooling rate and by the critical exponents of the transition. Thus, counting solitons left in its wake should allow one to determine the critical exponents z and {nu} for a BEC phase transition. The same information can be extracted from two-point correlation functions.

Damski, Bogdan; Zurek, Wojciech H. [Theoretical Division, Los Alamos National Laboratory, MS-B213, Los Alamos, New Mexico 87545 (United States)

2010-04-23

407

Nonequilibrium Bose-Einstein condensation of hot magnons  

SciTech Connect

We present an analysis of the emergence of a nonequilibrium Bose-Einstein-type condensation of magnons in radio-frequency pumped magnetic thin films, which has recently been experimentally observed. A complete description of all the nonequilibrium processes involved is given. It is demonstrated that the phenomenon is another example of the emergence of Bose-Einstein-type condensation in nonequilibrium many-boson systems embedded in a thermal bath, a phenomenon evidenced decades ago by the renowned late Herbert Froehlich.

Vannucchi, Fabio Stucchi; Vasconcellos, Aurea Rosas; Luzzi, Roberto [Condensed Matter Physics Department, Institute of Physics 'Gleb Wataghin', State University of Campinas (UNICAMP), 13083-859 Campinas, SP (Brazil)

2010-10-01

408

Observation of Bose-Einstein Condensation of Molecules  

Microsoft Academic Search

We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic ^6Li atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into ^6Li2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes

Martin W. Zwierlein; Claudiu A. Stan; Christian H. Schunck; Sebastian M. F. Raupach; Subhadeep Gupta; Zoran Hadzibabic; Wolfgang Ketterle

2004-01-01

409

The Bose-einstein Condensation of Positronium in Submicron Cavities  

Microsoft Academic Search

We have considered the possibility of creating a matter-antimatter Bose-Einstein condensate in the laboratory and concluded\\u000a that a committed and focussed program could succeed in making this new “extraordinary” material available for scientific study.\\u000a In this paper we describe the experimental requirements of the scheme and the mechanisms by which a positronium Bose-Einstein\\u000a condensate may be both formed and observed.

D. B. Cassidy; J. A. Golovchenko

410

The geocenter motion from decadal to geological time-scales: geophysical modelling  

NASA Astrophysics Data System (ADS)

Among the coefficients of the spherical harmonics expansion of elasto-gravitational deformations, the degree-one has particular characteristics related to geodesy as well as to mechanics. It is linked to the position of the Earth centre of mass and is strongly dependent on the choice of the origin of the reference frame. We investigate here the geocenter motion, that is to say the geometric centre of the translated external surface with respect to the centre of mass, for different internal excitation sources at different time-scales. At decadal time-scale, we find that the geocenter motion induced by geostrophic pressures within the fluid core acting at both the core-mantle and inner core boundaries is at a level of 0.1 mm/yr. At secular time-scale, geocenter motions induced by post-glacial rebound have been shown to be at the level of -0.4 - 0.2 mm/yr Finally, at geological time-scale, we quantify degree-one deformations induced by internal loads within the mantle. We use a simple model in which we assume that subducted plates sink vertically through the mantle, and in which upwelling domes are stable over the last 120 Ma. We found that, although the associated geocenter secular motion is one order of magnitude smaller than the one induced by post-glacial rebound, there is a significant discrepancy of about a few hundred meters between the centre of figure and the centre of mass of the Earth. Is it possible to detect, at the present time, with geodetic measurements, such a permanent translation?

Greff-Lefftz, M.; Métivier, L.

2012-04-01

411

Linkage between mei-yu precipitation and North Atlantic SST on the decadal timescale  

Microsoft Academic Search

This paper investigates the relationship between mei-yu and North Atlantic sea surface temperature anomalies (SSTA). Results\\u000a show that they are significantly associated with each other on the decadal timescale. Both mei-yu precipitation and mei-yu\\u000a duration are characterized by significant decadal variability. Their decadal components are closely correlated with a triple\\u000a mode of North Atlantic SSTA in the preceding winter. Regression

Wei Gu; Chongyin Li; Xin Wang; Wen Zhou; Weijing Li

2009-01-01

412

The effect of mass ratio on the morphology and time-scales of disc galaxy mergers  

NASA Astrophysics Data System (ADS)

The majority of galaxy mergers are expected to be minor mergers. The observational signatures of minor mergers are not well understood; thus, there exist few constraints on the minor merger rate. This paper seeks to address this gap in our understanding by determining if and when minor mergers exhibit disturbed morphologies and how they differ from the morphology of major mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying galaxy mergers via projected separation and quantitative morphology (the Gini coefficient G, asymmetry A and the second-order moment of the brightest 20 per cent of the light M20) depends on the merger mass ratio, relative orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1 baryonic mass ratio mergers as 1:1 mergers, with observability time-scales of ~0.2-0.4Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios between 4:1 and 1:1 (assuming local disc galaxy gas fractions). Asymmetry time-scales for moderate gas-fraction major disc mergers are ~0.2-0.4Gyr and less than 0.06Gyr for moderate gas-fraction minor mergers. The relative orientations and orbits have little effect on the time-scales for morphological disturbances. Observational studies of close pairs often select major mergers by choosing paired galaxies with similar luminosities and/or stellar masses. Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs) are sensitive to galaxy mergers of different mass ratios. By comparing the frequency of mergers selected by different techniques, one may place empirical constraints on the major and minor galaxy merger rates.

Lotz, Jennifer M.; Jonsson, Patrik; Cox, T. J.; Primack, Joel R.

2010-05-01

413

On multi-timescale variability of temperature in China in modulated annual cycle reference frame  

Microsoft Academic Search

The traditional anomaly (TA) reference frame and its corresponding anomaly for a given data span changes with the extension\\u000a of data length. In this study, the modulated annual cycle (MAC), instead of the widely used climatological mean annual cycle,\\u000a is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface\\u000a air temperature (SAT)

Cheng Qian; Zhaohua Wu; Congbin Fu; Tianjun Zhou

2010-01-01

414

Non-parametric techniques for pitch-scale and time-scale modification of speech  

Microsoft Academic Search

Time-scale and, to a lesser extent, pitch-scale modifications of speech and audio signals are the subject of major theoretical and practical interest. Applications are numerous, including, to name but a few, text-to-speech synthesis (based on acoustical unit concatenation), transformation of voice characteristics, foreign language learning but also audio monitoring or film\\/soundtrack post-synchronization. To fulfill the need for high-quality time and

Eric Moulines; Jean Laroche

1995-01-01

415

Mixed TimeScale Generalized Fair Scheduling for Amplify-and-Forward Relay Networks  

Microsoft Academic Search

We devise an optimization framework for generalized proportional fairness (GPF) under different time scales for amplify-and-forward (AF) relay networks. In GPF scheduling, a single input parameter is used to change the fairness from throughput optimal, to proportionally fair and asymptotically to max-min fair. We extend the GPF scheduling to include a new input parameter, which determines the time-scale of fairness

Alireza Sharifian; Petar Djukic; Halim Yanikomeroglu; Jietao Zhang

2010-01-01

416

Assessment of chemical disequilibria in oil reservoirs: Implications for production- and diagenetic-timescale geochemical modelling  

Microsoft Academic Search

The accurate prediction of reservoir fluid-rock interaction in oil reservoirs is important in both production engineering and reservoir geology. Produced and\\/or mixed brine scaling tendencies, formation damage and production treatments all require a knowledge of mineral dissolution and precipitation both close to the well-bore and in the interwell volume. This can be carried forward into the longer timescale over which

J. R. Bunney; K. S. Sorbie; M. M. Jordan

1996-01-01

417

Search for Ultra--High-Energy Point-Source Emission over Various Timescales  

NASA Astrophysics Data System (ADS)

A method has been developed to search for pulsed and/or unpulsed ultra-high-energy (UHE) emission from point sources over a range of time scales. This method has been applied to data accumulated with the CYGNUS extensive air-shower array to search for episodic emission from Cyg X-3, Her X-1, the Crab Nebula, and a collection of 48 secondary source candidates. An examination of timescales ranging from minutes to years has yielded results consistent with background fluctuations.

Biller, S.; Alexandreas, D. E.; Allen, G. E.; Berley, D.; Burman, R. L.; Cavalli-Sforza, M.; Chang, C. Y.; Chen, M. L.; Chumney, P.; Coyne, D.; Dion, C.; Dion, G. M.; Dorfan, D.; Ellsworth, R. W.; Goodman, J. A.; Haines, T. J.; Harmon, M.; Hoffman, C. M.; Kelley, L.; Klein, S.; Nagle, D. E.; Schaller, S. C.; Schmidt, D. M.; Schnee, R.; Shoup, A.; Sinnis, C.; Stark, M. J.; Weeks, D. D.; Williams, D. A.; Wu, J.-P.; Yang, T.; Yodh, G. B.; Zhang, W.

1994-03-01

418

Ocean-atmosphere partitioning of anthropogenic carbon dioxide on multimillennial timescales  

Microsoft Academic Search

Ocean-sediment and weathering interactions exert the primary control on how much anthropogenic-emitted CO2 remains in the atmosphere on timescales longer than about 1 kyr. Analytical theory is presented which predicts, from initial conditions, the remaining atmospheric fraction of emitted CO2 after equilibrium with CaCO3 burial in deep-sea sediments but before silicate weathering removes all excess CO2 on a >100 kyr

Philip Goodwin; Andy Ridgwell

2010-01-01

419

Assessment of chemical disequilibria in oil reservoirs: Implications for production- and diagenetic-timescale geochemical modelling  

SciTech Connect

The accurate prediction of reservoir fluid-rock interaction in oil reservoirs is important in both production engineering and reservoir geology. Produced and/or mixed brine scaling tendencies, formation damage and production treatments all require a knowledge of mineral dissolution and precipitation both close to the well-bore and in the interwell volume. This can be carried forward into the longer timescale over which diagenetic processes occur to predict reservoir quality and to trace migration pathways. Geochemical packages which are available to model such processes are based on equilibrium thermodynamics. However, during the relatively short timescale of oilfield production, the introduction of large volumes of external brines generally causes the fluid-rock system to be far from equilibrium. In order to apply quantitative geochemical modelling to prediction of production chemistry, the degree of chemical disequilibrium must be assessed. The Oilfield Scale Research Group at Heriot-Watt University has conducted an extensive series of flooding experiments in which many ([approx]40) reservoir cores have been reconditioned to reservoir conditions and seawater (or produced brine) has been injected over long time periods (up to months) at elevated temperatures. The composition of injection fluid and effluent are monitored throughout the flood and the full mineralogical analysis of the core both before and after these floods has been established. We are able to quantify the fluid-rock interaction. Both carbonate and aluminosilicate systems have been examined. Comparing the experimental core flooding data with thermodynamic simulations of those systems illuminates the degree of disequilibria present over production timescales. The results from many core floods in various mineralogical systems have been analyzed and will be presented. Certain reactions can be assigned to be rate independent over the timescale in question, by either occurring spontaneously or not at all.

Bunney, J.R.; Sorbie, K.S.; Jordan, M.M. (Heriot-Watt Univ., Edinburgh, Scotland (United Kingdom))

1996-01-01

420

Charge sensing in carbon-nanotube quantum dots on microsecond timescales  

Microsoft Academic Search

We report fast, simultaneous charge sensing and transport measurements of gate-defined carbon nanotube quantum dots. Aluminum radio-frequency (rf) single electron transistors capacitively coupled to the nanotube dot provide single-electron charge sensing on microsecond timescales. Simultaneously, rf reflectometry allows the fast measurement of transport through the nanotube dot. Charge stability diagrams for the nanotube dot in the Coulomb blockade regime show

M. J. Biercuk; D. J. Reilly; T. M. Buehler; V. C. Chan; J. M. Chow; R. G. Clark; C. M. Marcus

2006-01-01

421

A biologically plausible model of time-scale invariant interval timing  

Microsoft Academic Search

The temporal durations between events often exert a strong influence over behavior. The details of this influence have been\\u000a extensively characterized in behavioral experiments in different animal species. A remarkable feature of the data collected\\u000a in these experiments is that they are often time-scale invariant. This means that response measurements obtained under intervals\\u000a of different durations coincide when plotted as

Rita Almeida; Anders Ledberg

2010-01-01

422

Oceanic Climate Variability at Millennial Time-Scales: Models of Climate Connections  

Microsoft Academic Search

One of the most exciting questions in palaeoclimatology is the study of the complex interactions between the different components\\u000a of the climate system in order to understand how climate changes occur at Milankovitch as well as at millennial and centennial\\u000a time-scales. The primary objective of this paper is to place the PEP III transect palaeo-data within a global climate context

Laurence Vidal; Helge Arz

423

North–South Precipitation Patterns in Western North America on Interannual-to-Decadal Timescales  

Microsoft Academic Search

The overall amount of precipitation deposited along the West Coast and western cordillera of North America from 258 to 558N 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

Michael D. Dettinger; Daniel R. Cayan; Henry F. Diaz; David M. Meko

1998-01-01

424

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

425

The effect of gas fraction on the morphology and time-scales of disc galaxy mergers  

NASA Astrophysics Data System (ADS)

Gas-rich galaxy mergers are more easily identified by their disturbed morphologies than mergers with less gas. Because the typical gas fraction of galaxy mergers is expected to increase with redshift, the under-counting of low gas-fraction mergers may bias morphological estimates of the evolution of galaxy merger rate. To understand the magnitude of this bias, we explore the effect of gas fraction on the morphologies of a series of simulated disc galaxy mergers. With the resulting g-band images, we determine how the time-scale for identifying major and minor galaxy mergers via close projected pairs and quantitative morphology (the Gini coefficient G, the second-order moment of the brightest 20 per cent of the light M20 and asymmetry A) depends on baryonic gas fraction fgas. Strong asymmetries last significantly longer in high gas-fraction mergers of all mass ratios, with time-scales ranging from <=300Myr for fgas ~ 20 per cent to >=1Gyr for fgas ~ 50 per cent. Therefore, the strong evolution with redshift observed in the fraction of asymmetric galaxies may reflect evolution in the gas properties of galaxies rather than the global galaxy merger rate. On the other hand, the time-scale for identifying a galaxy merger via G-M20 is weakly dependent on gas fraction (~200-400Myr), consistent with the weak evolution observed for G-M20 mergers.

Lotz, Jennifer M.; Jonsson, Patrik; Cox, T. J.; Primack, Joel R.

2010-05-01

426

Cumulative Number of Cell Divisions as a Meaningful Timescale for Adaptive Laboratory Evolution of Escherichia coli  

PubMed Central

Adaptive laboratory evolution (ALE) under controlled conditions has become a valuable approach for the study of the genetic and biochemical basis for microbial adaptation under a given selection pressure. Conventionally, the timescale in ALE experiments has been set in terms of number of generations. As mutations are believed to occur primarily during cell division in growing cultures, the cumulative number of cell divisions (CCD) would be an alternative way to set the timescale for ALE. Here we show that in short-term ALE (up to 40–50 days), Escherichia coli, under growth rate selection pressure, was found to undergo approximately 1011.2 total cumulative cell divisions in the population to produce a new stable growth phenotype that results from 2 to 8 mutations. Continuous exposure to a low level of the mutagen N-methyl-N?-nitro-N-nitrosoguanidine was found to accelerate this timescale and led to a superior growth rate phenotype with a much larger number of mutations as determined with whole-genome sequencing. These results would be useful for the fundamental kinetics of the ALE process in designing ALE experiments and provide a basis for its quantitative description.

Barrett, Christian L.; Palsson, Bernhard ?.

2011-01-01

427

Optical Variability Timescales in Seyfert Galaxies: Relationships with Black Hole Mass and Luminosity  

NASA Astrophysics Data System (ADS)

The Lick AGN Monitoring Project (LAMP) targeted 13 nearby Seyfert 1 galaxies with the goal of measuring their black hole masses using reverberation mapping. The AGNs in the sample were selected to have black holes with masses between 106 and 3*107 solar masses. In order to measure the AGN continuum variability, we obtained broad-band B and V images on most nights from February through May 2008. Having regularly sampled light curves with a daily cadence over the course of a few months not only is useful for obtaining the broad-line reverberation lag and black hole mass, but also allows us to examine the characteristics of the continuum variability. Using the light curve data, we measured variability structure functions and determined the characteristic break timescales. Combining our results with previous results from the literature for higher-mass reverberation-mapped AGNs, we find that the characteristic timescale is strongly correlated with both black hole mass and AGN luminosity. We derive a new relationship between characteristic timescale, black hole mass, and luminosity that fits the properties of Seyfert galaxies and quasars over nearly four orders of magnitude in black hole mass. Such a relationship can provide a new method for estimating black hole masses in Seyfert galaxies and quasars using optical light curves measured from future synoptic variability surveys.

Walsh, Jonelle; LAMP Collaboration

2009-05-01

428

Relaxation Kinetics and the Glassiness of Native Proteins: Coupling of Timescales  

PubMed Central

We provide evidence that the onset of functional dynamics of folded proteins with elevated temperatures is associated with the effective sampling of its energy landscape under physiological conditions. The analysis is based on data describing the relaxation phenomena governing the backbone dynamics of bovine pancreatic trypsin inhibitor derived from molecular dynamics simulations, previously reported by us. By representing the backbone dynamics of the folded protein by three distinct regimes, it is possible to decompose its seemingly complex dynamics, described by a stretch exponential decay of the backbone motions. Of these three regimes, one is associated with the slow timescales due to the activity along the envelope of the energy surface defining the folded protein. Another, with fast timescales, is due to the activity along the pockets decorating the folded-state envelope. The intermediate regime emerges at temperatures where jumps between the pockets become possible. It is at the temperature window where motions corresponding to all three timescales become operative that the protein becomes active.

Baysal, Canan; Atilgan, Ali Rana

2005-01-01

429

Event and time-scale characteristics of heart-rate dynamics  

NASA Astrophysics Data System (ADS)

The cardiac system shows various scale dynamic activities from secondly to yearly. Therefore multiple time-scale characteristics of heart dynamics have received much attention for understanding and distinguishing healthy and pathological cardiac systems. In this paper we expand the multiple time-scale analysis into event and time scales to investigate scale characteristics in healthy and pathologic cardiac systems. To do this, we define a measure based on symbolic dynamics, which calculates complexity at each time and event scale, called the unit time block entropy (UTBE). This measure allows a reliable comparison of experimental data through matching the number of words and the total measurement time at the same time for all RR interval sequences which are composed of the time durations between consecutive R waves of electrocardiograms. We apply the UTBE to the healthy heart-rate (HR) group and pathological HR groups and find that the RR interval acceleration is more effective than the RR interval in distinguishing each group. And we also find that the normal and pathological HR groups are clearly distinguished in some specific event and time-scale regions.

Lee, Uncheol; Kim, Seunghwan; Yi, S. H.

2005-06-01

430

Multiwavelength Observations of Short-Timescale Variability in NGC 4151. I. Ultraviolet Observations  

NASA Astrophysics Data System (ADS)

We present the results of an intensive ultraviolet monitoring campaign on the Seyfert I galaxy NGC 4151, as part of an effort to study its short-timescale variability over a broad range in wavelength. The nucleus of NGC 4151 was observed continuously With the International Ultraviolet Explorer for 9.3 days, yielding a pair of LWP and SWP spectra every ~70 minutes, and during 4 hr periods for 4 days Prior to and 5 days after the continuous-monitoring period. The sampling frequency of the observations is an order of magnitude higher than that of any previous UV monitoring campaign on a Seyfert galaxy. The continuum fluxes in bands from 1275 to 2688 A went through four significant and well-defined events of duration 2-3 days during the continuous-monitoring period. We find that the amplitudes of the continuum variations decrease with increasing wavelength, which extends a general trend for this and other Seyfert galaxies to smaller timescales (i.e., a few days). The continuum variations in all the UV bands are simultaneous to within an accuracy of ~0.15 days, providing a strict constraint on continuum models. The emission-line light curves show only one major event during the continuous monitoring (a slow rise followed by a shallow dip) and do not correlate well with continuum light curves over the short duration of the campaign, because the timescale for continuum variations is apparently smaller than the response times of the emission lines.

Crenshaw, D. M.; Rodriguez-Pascual, P. M.; Penton, S. V.; Edelson, R. A.; Alloin, D.; Ayres, T. R.; Clavel, J.; Horne, K.; Johnson, W. N.; Kaspi, S.; Korista, K. T.; Kriss, G. A.; Krolik, J. H.; Malkan, M. A.; Maoz, D.; Netzer, H.; O'Brien, P. T.; Peterson, B. M.; Reichert, G. A.; Shull, J. M.; Ulrich, M.-H.; Wamsteker, W.; Warwick, R. S.; Yaqoob, T.; Balonek, T. J.; Barr, P.; Bromage, G. E.; Carini, M.; Carone, T. E.; Cheng, F.-Z.; Chuvaev, K. K.; Dietrich, M.; Doroshenko, V. T.; Dultzin-Hacyan, D.; Filippenko, A. V.; Gaskell, C. M.; Glass, I. S.; Goad, M. R.; Hutchings, J.; Kazanas, D.; Kollatschny, W.; Koratkar, A. P.; Laor, A.; Leighly, K.; Lyutyi, V. M.; MacAlpine, G. M.; Malkov, Yu. F.; Martin, P. G.; McCollum, B.; Merkulova, N. I.; Metik, L.; Metlov, V. G.; Miller, H. R.; Morris, S. L.; Oknyanskij, V. L.; Penfold, J.; Perez, E.; Perola, G. C.; Pike, G.; Pogge, R. W.; Pronik, I.; Pronik, V. I.; Ptak, R. L.; Recondo-Gonzalez, M. C.; Rodriguez-Espinoza, J. M.; Rokaki, E. L.; Roland, J.; Sadun, A. C.; Salamanca, I.; Santos-Lleo, M.; Sergeev, S. G.; Smith, S. M.; Snijders, M. A. J.; Sparke, L. S.; Stirpe, G. M.; Stoner, R. E.; Sun, W.-H.; van Groningen, E.; Wagner, R. M.; Wagner, S.; Wanders, I.; Welsh, W. F.; Weymann, R. J.; Wilkes, B. J.; Zheng, W.

1996-10-01

431

Wormholes Supported by a Combination of Normal and Quintessential Matter in Einstein and Einstein-Maxwell Gravity  

NASA Astrophysics Data System (ADS)

It is shown in the first part of this paper that a combined model comprising ordinary and quintessential matter can support a traversable wormhole in Einstein-Maxwell gravity. Since the solution allows zero tidal forces, the wormhole is suitable for a humanoid traveler. The second part of the paper shows that the electric field can be eliminated (Einstein gravity), but only by tolerating enormous tidal forces. Such a wormhole would still be capable of transmitting signals.

Kuhfittig, Peter K. F.

432

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

433

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

434

Variability in quasar broad absorption line outflows - III. What happens on the shortest time-scales?  

NASA Astrophysics Data System (ADS)

Broad absorption lines (BALs) in quasar spectra are prominent signatures of high-velocity outflows, which might be present in all quasars and could be a major contributor to feedback to galaxy evolution. Studying the variability in these BALs allows us to further our understanding of the structure, evolution and basic physical properties of the outflows. This is the third paper in a series on a monitoring programme of 24 luminous BAL quasars at redshifts 1.2 < z < 2.9. We focus here on the time-scales of variability in C IV ?1549 BALs in our full multi-epoch sample, which covers time-scales from 0.02 to 8.7 yr in the quasar rest frame. Our sample contains up to 13 epochs of data per quasar, with an average of seven epochs per quasar. We find that both the incidence and the amplitude of variability are greater across longer time-scales. Part of our monitoring programme specifically targeted half of these BAL quasars at rest-frame time-scales ?2 months. This revealed variability down to the shortest time-scales we probe (8-10 d). Observed variations in only portions of BAL troughs or in lines that are optically thick suggest that at least some of these changes are caused by clouds (or some type of outflow substructures) moving across our lines of sight. In this crossing cloud scenario, the variability times constrain both the crossing speeds and the absorber locations. Specific results also depend on the emission and absorption geometries. We consider a range of geometries and use Keplerian rotational speeds to derive a general relationship between the variability times, crossing speeds and outflow locations. Typical variability times of the order of ˜1 yr indicate crossing speeds of a few thousand km s-1 and radial distances ˜1 pc from the central black hole. However, the most rapid BAL changes occurring in 8-10 d require crossing speeds of 17 000-84 000 km s-1 and radial distances of only 0.001-0.02 pc. These speeds are similar to or greater than the observed radial outflow speeds, and the inferred locations are within the nominal radius of the broad emission-line region.

Capellupo, D. M.; Hamann, F.; Shields, J. C.; Halpern, J. P.; Barlow, T. A.

2013-03-01

435

Timescales and topographic expression of lithospheric extension in the western Great Basin, NV, USA  

NASA Astrophysics Data System (ADS)

One of the goals of the Plate Boundary Observatory is to determine how continental lithosphere responds to changes in driving forces. Because many geodynamic processes occur on timescales much longer than geodetic recording time intervals, longer term deformation measurements are required. On what timescale, however, should these longer term (geological) measurements be made to allow a meaningful integration with geodetic time series? Traditional geological and tectonic studies appear to indicate that continental fault systems are active continuously for millions of years, whereas more precise paleoseismological measurements often document irregular fault displacement. In order to study the evolution of individual fault systems, measurements are needed on an intermediate timescale: long enough to average over many seismic cycles, but short enough to provide the incremental strain history. For continental fault systems such as those of the Basin and Range Province (c. 10 nstrain at present, e.g., Bennett et al., TECTONICS 2003, Friedrich et al., JGR 2003), the expected time interval is on the order of a few hundred thousand years and the expected signal size should range from several to a few hundred meters. In climatically sensitive regions, such as the Great Basin, such surface deformation features (fault trace in alluvial sediments, triangular facets, etc.) may, on one hand, be preserved extremelly well over several hundred thousand years; On the other hand, however, such regions are also sensitive to weather extremes and medium-term climatic variations (tens of ka) as exhibited during wet periods. In the Great Basin, both cases are represented. For example, (1) on the 10 ka timescale, many internally drained basins filled to large lakes (Bonneville and Lahontan) which left thick sedimentary sections covering most pre-existing fault traces; and (2) on the 500 ka timescale, growth or reactivation of faults affected drainage, erosion and deposition patterns. We document such tectonogeomorphic features along the W-flank of the Shoshone Range and Cortez Mountains and surrounding region. We speculate that these features are the expression of active crustal or lithospheric thinning.

Friedrich, A. M.; Gaudemer, Y.; King, G.; Armijo, R.; Strecker, M.

2004-12-01

436

Chaotic variability of the meridional overturning circulation on subannual to interannual timescales  

NASA Astrophysics Data System (ADS)

Observations and numerical simulations have shown that the meridional overturning circulation (MOC) exhibits substantial variability on sub- to interannual timescales. This variability is not fully understood. In particular it is not known what fraction of the MOC variability is caused by processes such as mesoscale ocean eddies and waves which are ubiquitous in the ocean. Here we analyse twin experiments performed with a global ocean model at eddying (1/4°) and non-eddying (1°) resolutions. The twin experiments are forced with the same surface fluxes for the 1958 to 2001 period but start from different initial conditions. Our results show that on subannual to interannual timescales a large fraction of MOC variability directly reflects variability in the surface forcing. Nevertheless, in the eddy-permitting case there is an initial-condition-dependent MOC variability (hereinafter referred to as "chaotic" variability) of several Sv (1Sv = 106 m3 s-1) in the Atlantic and the Indo-Pacific. In the Atlantic the chaotic MOC variability represents up to 30% of the total variability at the depths where the maximum MOC occurs. In comparison the chaotic MOC variability is only 5-10% in the non-eddying case. The surface forcing being almost identical in the twin experiments suggests that mesoscale ocean eddies are the most likely cause for the increased chaotic MOC variability in the eddying case. The exact formation time of eddies is determined by the initial conditions which are different in the two model passes, and as a consequence the mesoscale eddy field is decorrelated in the twin experiments. In regions where eddy activity is high in the eddy-permitting model, the correlation of sea surface height variability in the twin runs is close to zero. In the non-eddying case in contrast, we find high correlations (0.9 or higher) over most regions. Looking at the sub- and interannual MOC components separately reveals that most of the chaotic MOC variability is found on subannual timescales for the eddy-permitting model. On interannual timescales the amplitude of the chaotic MOC variability is much smaller and the amplitudes are comparable for both the eddy-permitting and non-eddy-permitting model resolutions. Whereas the chaotic MOC variability on interannual timescales only accounts for a small fraction of the total chaotic MOC variability in the eddy-permitting case, it is the main contributor to the chaotic variability in the non-eddying case away from the Equator.

Hirschi, J. J.-M.; Blaker, A. T.; Sinha, B.; Coward, A.; de Cuevas, B.; Alderson, S.; Madec, G.

2013-09-01

437

Discrete breathers in Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

Discrete breathers, originally introduced in the context of biopolymers and coupled nonlinear oscillators, are also localized modes of excitation of Bose-Einstein condensates (BEC) in periodic potentials such as those generated by counter-propagating laser beams in an optical lattice. Static and dynamical properties of breather states are analysed in the discrete nonlinear Schrödinger equation that is derived in the limit of deep potential wells, tight-binding and the superfluid regime of the condensate. Static and mobile breathers can be formed by progressive re-shaping of initial Gaussian wave-packets or by transporting atomic density towards dissipative boundaries of the lattice. Static breathers generated via boundary dissipations are determined via a transfer-matrix approach and discussed in the two analytic limits of highly localized and very broad profiles. Mobile breathers that move across the lattice are well approximated by modified analytical expressions derived from integrable models with two independent parameters: the core-phase gradient and the peak amplitude. Finally, possible experimental realizations of discrete breathers in BEC in optical lattices are discussed in the presence of residual harmonic trapping and in interferometry configurations suitable to investigate discrete breathers' interactions.

Franzosi, Roberto; Livi, Roberto; Oppo, Gian-Luca; Politi, Antonio

2011-12-01

438

Consistent cosmological modifications to the Einstein equations  

SciTech Connect

General relativity is a phenomenologically successful theory that rests on firm foundations, but has not been tested on cosmological scales. The deep mystery of dark energy (and possibly even the requirement of cold dark matter), has increased the need for testing modifications to general relativity, as the inference of such otherwise undetected fluids, depends crucially on the theory of gravity. In this work I outline a general scheme for constructing consistent and covariant modifications to the Einstein equations. This framework is such that there is a clear connection between the modification and the underlying field content that produces it. I argue that this is mandatory for distinguishing modifications of gravity from conventional fluids. I give two nontrivial examples, the first of which is a simple metric-based modification of the fluctuation equations for which the background is exact {lambda}CDM and the second has a Dvali-Gabadadze-Porrati background but differs from it in the perturbations. I present their impact on observations of the cosmic microwave background radiation.

Skordis, Constantinos [Perimeter Institute, Waterloo, Ontario N2L 2Y5 (Canada)

2009-06-15

439

The einstein observatory: new perspectives in astronomy.  

PubMed

High-sensitivity x-ray measurements with the recently launched Einstein Observatory are having a major impact on wide areas of astronomical research. The x-ray luminosity of young O, B, and A stars and late K and M stars is found to be several orders of magnitude greater than predicted by current theories of coronal heating. Detailed x-ray images and spectra of supernova remnants are providing new information on the temperature, composition, and distribution of material ejected in supernova explosions as well as of the material comprising the interstellar medium. Observations of galaxies are yielding insights on the formation and evolution of stellar systems and galaxies over a wide range of variables. X-ray time variations are being used to probe the underlying energy source in quasars and active galactic nuclei. The distribution of mass in clusters of galaxies is being traced through detailed x-ray images, and the data are being used to classify clusters and trace their formation and evolution. Substantial progress is being made in several areas of cosmological research, particularly in the study of the diffuse x-ray background. PMID:17810974

Giacconi, R; Tananbaum, H

1980-08-22

440

Gravitational dynamics in Bose-Einstein condensates  

SciTech Connect

Analogue models for gravity intend to provide a framework where matter and gravity, as well as their intertwined dynamics, emerge from degrees of freedom that have a priori nothing to do with what we call gravity or matter. Bose-Einstein condensates (BEC) are a natural example of an analogue model since one can identify matter propagating on a (pseudo-Riemannian) metric with collective excitations above the condensate of atoms. However, until now, a description of the 'analogue gravitational dynamics' for such model was missing. We show here that in a BEC system with massive quasiparticles, the gravitational dynamics can be encoded in a modified (semiclassical) Poisson equation. In particular, gravity is of extreme short range (characterized by the healing length) and the cosmological constant appears from the noncondensed fraction of atoms in the quasiparticle vacuum. While some of these features make the analogue gravitational dynamics of our BEC system quite different from standard Newtonian gravity, we nonetheless show that it can be used to draw some interesting lessons about 'emergent gravity' scenarios.

Girelli, F.; Liberati, S.; Sindoni, L. [SISSA and INFN, Sezione di Trieste Via Beirut 2-4, 34014 Trieste (Italy)

2008-10-15

441

Rotating trapped Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

Trapped Bose-Einstein condensates (BECs) differ considerably from the standard textbook example of a uniform Bose gas. In an isotropic harmonic potential V( r) = ½ M?2 r 2, the single-particle ground state introduces a new intrinsic scale of length [the ground-state size d = ? ?/( M?)] and energy [the ground-state energy E 0 = frac{3} {2} ??]. When the trap rotates at a low angular velocity, the behavior of a single vortex illustrates the crucial role of discrete quantized vorticity. For more rapid rotation, the condensate contains a vortex array. The resulting centrifugal forces expand the condensate radially and shrink it axially; thus, the condensate becomes effectively two dimensional. If the external rotation speed approaches the frequency of the radial harmonic confining potential, the condensate enters the "lowest-Landau-level" regime, and a simple description again becomes possible. Eventually, the system is predicted to make a quantum phase transition to a highly correlated state analogous to the fractional quantum Hall states of electrons in a strong magnetic field.

Fetter, A. L.

2008-01-01

442

Rotating trapped Bose-Einstein condensates  

NASA Astrophysics Data System (ADS)

I review free and trapped Bose-Einstein condensates (BECs) [1, 2, 3, 4, 5]. In an isotropic harmonic potential V(r) = 12M?2r2, the single-particle ground state introduces a new intrinsic scale of length [the ground-state size d = ?/(M?)] and energy [the ground-state energy E0 = 32??]. When the trap rotates [6, 7, 8], there is a critical angular velocity for the appearance of one or a few quantized vortices. For more rapid rotation [9, 10, 11, 12, 13] the condensate contains a vortex array. The resulting centrifugal forces expand the condensate radially and shrink it axially; thus the condensate becomes effectively two-dimensional. If the external rotation speed approaches the frequency of the radial harmonic confining potential, the condensate enters the ``lowest-Landau-level'' regime, and a simple description again becomes possible [14, 15]. Eventually, the system is predicted to make a quantum phase transition to a highly correlated state analogous to the fractional quantum Hall states of electrons in a strong magnetic field [16, 17, 18, 19, 20].

Fetter, Alexander L.

2008-03-01

443

Twistor Theory and the Einstein Equations  

NASA Astrophysics Data System (ADS)

R. Penrose (in Advances in twistor theory, pp. 168-176, and in Cosmology and gravitation; Nato advanced study institute series, pp. 287-316 (1980). New York: Plenum Press) has argued that the goal of twistor theory with regard to the vacuum Einstein equations ought to consist of some kind of unification of twistor-theoretic descriptions of anti-self-dual (a.s.d.) and self-dual (s.d.) space-times. S.d. space-times currently possess a description only in terms of dual twistor space, however, rather than twistor space. In this paper, suggestions due to Penrose for providing a purely twistor space description of s.d. space-times are investigated. It is shown how the points of certain s.d. space-times define mappings on twistor space and the geometry of these mappings is studied. The families of mappings for two particular s.d. space-times are presented explicitly.

Law, P. R.

1985-05-01

444

EINSTEIN SSS Observations of Two Intermediate Polars  

NASA Astrophysics Data System (ADS)

We present the Einstein Solid State Spectrometer (SSS) observations of two Intermediate Polars, EX Hydrae and TV Columbae. These data have revealed a new soft X-ray component in the spectra of both the objects. The spectrum of EX Hya is modeled with two temperature components, ~ 9 keV and ~ 0.74 keV optically thin plasma in collisional ionization equilibrium. The variation in the spectrum in phase with the 67 minute pulsation can be interpreted as arising due to excess absorbing material covering 40% of the emission region at the minimum phase, a modification of the ``accretion curtain model''. The spectrum of TV Col also reveals an excess at soft energies above the previously accepted thermal model ( ~ 15 keV), with a patchy absorber. This excess can be modeled with two optically thin thermal components with kT ~ 0.18 and ~ 0.75 keV. The spectrum is found to vary with the phase of the ~ 4 day period found in the optical photometry of this source. There is also evidence for the 32 minute pulsation, interpreted as the white dwarf spin period. The variation in the spectrum due to the 32 minute pulsation will be compared to the variations found in EX Hya due to the 67 minute pulsations.

Singh, J.; Swank, J. H.

1992-12-01

445

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

446

Impacts of multi-scale solar activity on climate. Part II: Dominant timescales in decadal-centennial climate variability  

NASA Astrophysics Data System (ADS)

Part II of this study detects the dominant decadal-centennial timescales in four SST indices up to the 2010/2011 winter and tries to relate them to the observed 11-yr and 88-yr solar activity with the sunspot number up to Solar Cycle 24. To explore plausible solar origins of the observed decadal-centennial timescales in the SSTs and climate variability in general, we design a simple one-dimensional dynamical system forced by an annual cycle modulated by a small-amplitude single- or multi-scale "solar activity." Results suggest that nonlinear harmonic and subharmonic resonance of the system to the forcing and period-doubling bifurcations are responsible for the dominant timescales in the system, including the 60-yr timescale that dominates the Atlantic Multidecadal Oscillation. The dominant timescales in the forced system depend on the system's parameter setting. Scale enhancement among the dominant response timescales may result in dramatic amplifications over a few decades and extreme values of the time series on various timescales. Three possible energy sources for such amplifications and extremes are proposed. Dynamical model results suggest that solar activity may play an important yet not well recognized role in the observed decadal-centennial climate variability. The atmospheric dynamical amplifying mechanism shown in Part I and the nonlinear resonant and bifurcation mechanisms shown in Part II help us to understand the solar source of the multi-scale climate change in the 20th century and the fact that different solar influenced dominant timescales for recurrent climate extremes for a given region or a parameter setting. Part II also indicates that solar influences on climate cannot be linearly compared with non-cyclic or sporadic thermal forcings because they cannot exert their influences on climate in the same way as the sun does.

Weng, Hengyi

2012-07-01

447

Lagged processes and critical timescales in boreal forest response to climate  

NASA Astrophysics Data System (ADS)

Long-term eddy covariance datasets have recorded the response of boreal ecosystems to climate on timescales up to decadal (Dunn et al. 2006, Barr et al. 2006). Carbon balances in these forests are very dynamic, responding to climatic anomalies on timescales of months to years. A boreal black spruce forest in central Manitoba, Canada, was a source of carbon to the atmosphere in the mid-1990s (55 g C m^{- 2} y-1, 1995-1997), but switched to a sink in recent years (-25 g C m-2 y-1, 2003-2005). The short-term carbon exchange at this site was strongly controlled by temperature, but on long timescales the water balance was more important (Dunn et al. 2006). In a boreal aspen forest in central Saskatchewan, Canada, temperature was the main driver of phenology and canopy duration, but drought status, and especially the persistence of drought over multiple years, was a critical control on ecosystem respiration and resultant carbon balance (Barr et al. 2006). Lagged processes are especially important in the boreal forest: Dunn et al. (2006) found that carbon balances, and especially ecosystem respiration, were strongly controlled by the integrated water balance over preceding years, suggesting that the effects of climatic anomalies are expressed slowly in these forests. Rocha et al. (2006) found similar evidence in tree-ring cores from the NOBS site, which showed a strong correlation with lagged water balances, suggesting that wood growth in these forests is a process integrating over prior years. In a tree-ring analysis across aspen stands in western Canada, Hogg et al. (2005) found that current and lagged (up to four years) moisture status were critical factors regulating ecosystem carbon balance. These results from long-term boreal datasets suggest that the vulnerability of these forests to climate change will be strongly dependent on the future balance between precipitation and temperature. Persistent perturbations to the local climate will likely shift overall biome carbon balance.

Wofsy, S. C.; Dunn, A. L.; Amiro, B. D.; Barr, A.; Rocha, A. V.; Goulden, M. L.

2006-12-01

448

The cascading effects of absolute reference frames and geomagnetic polarity timescales on global plate motions  

NASA Astrophysics Data System (ADS)

Global plate motion models use Africa and the Pacific as the base of plate rotation hierarchies, with many other plates moving relative to them. Relative plate motions in the Mesozoic are generally well resolved where seafloor spreading histories are preserved to the present-day. However, the choice of absolute reference frames, whether they are fixed-hotspot, moving-hotspot, true-polar wander-corrected or pure paleomagnetic, can have significant consequences for the absolute plate velocities of smaller plates that are at the mercy of the cascading effects of movement within a complex plate motion hierarchy. We use GPlates to sample plate velocities through time at equally spaced mesh nodes that are contained within continuously closing plate polygons. We calculate root-mean square plate velocities to isolate the effects of different absolute reference frames on absolute plate velocity trends. Apart from being a quality-control tool for the creation of global plate motion models, this approach allows us to track the source of plate velocity spikes, some of which may be indicative of plate reorganisation events. We use a similar approach to test whether alternative geomagnetic polarity time-scales introduce or help reduce anomalous plate velocity fluctuations in global plate motion models. The choice of timescales can affect the seafloor spreading rates partitioned across stage rotations and models of sea level change. Such a workflow may help test alternative timescales, in order to study the model-dependence and controversies that have recently surfaced regarding proposed plate reorganisation events and the mid-Cretaceous seafloor spreading pulse.

Zahirovic, S.; Seton, M.; Müller, R. D.; Torsvik, T. H.

2011-12-01

449

What controls the variability of the South American summer monsoon on paleoclimate timescales? (Invited)  

NASA Astrophysics Data System (ADS)

In most of tropical South America south of the equator, including much of the Amazon basin, the Altiplano and central Andes, the Chaco, and the Pantanal, the majority of precipitation arrives as a result of the South American summer monsoon (SASM) system. Along the northeastern coast of Brazil, the majority of precipitation results from convection in the ITCZ, and the peak of this activity is delayed by about one season from that of the SASM. During the past century or so, which encompasses the entire instrumental period, a significant fraction (but not the majority) of the inter-annual precipitation variability in these regions was extrinsically forced, and ENSO, PDO, and tropical Atlantic variability have been implicated as major forcing factors. On lower frequency timescales, using paleoclimatic proxies, one can identify far larger changes in precipitation amount than those observed in the instrumental period. The spatial patterns of this precipitation variability and the dependence of these patterns on temporal scale (orbital or millennial) are becoming known. We posit that three major extrinsic climate-forcing factors can explain most of the observed (or not yet observed) precipitation variability on paleoclimate timescales: top-of-the atmosphere southern subtropical summer insolation, north-south Atlantic sea-surface temperature (SST) gradients, and east-west equatorial Pacific SST gradients. Using the best available paleo-SST data sets, the calculated values of insolation, and a subjective spatial weighting, we construct a simple spatio-temporal forcing model that we believe represents the history of precipitation over the region on millennial timescales for the past ca. 4,000,000 years. Our model effectively explains precipitation in the heart of the SASM region as inferred from speleothem records that span the last ~100,000 years BP and eventually will be tested using much older speleothem records dated by U-Pb chronologies.

Baker, P. A.; Fritz, S. C.; Rigsby, C. A.

2010-12-01

450

Decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano.  

PubMed

Caldera-forming volcanic eruptions are low-frequency, high-impact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days, with devastating effects on local and global scales. Because no such eruption has been monitored during its long build-up phase, the precursor phenomena are not well understood. Geophysical signals obtained during recent episodes of unrest at calderas such as Yellowstone, USA, and Campi Flegrei, Italy, are difficult to interpret, and the conditions necessary for large eruptions are poorly constrained. Here we present a study of pre-eruptive magmatic processes and their timescales using chemically zoned crystals from the 'Minoan' caldera-forming eruption of Santorini volcano, Greece, which occurred in the late 1600s BC. The results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption. Despite the large volume of erupted magma (40-60 cubic kilometres), and the 18,000-year gestation period between the Minoan eruption and the previous major eruption, most crystals in the Minoan magma record processes that occurred less than about 100 years before the eruption. Recharge of the magma reservoir by large volumes of silicic magma (and some mafic magma) occurred during the century before eruption, and mixing between different silicic magma batches was still taking place during the final months. Final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period, with major growth phases immediately before eruption. These observations have implications for the monitoring of long-dormant, but potentially active, caldera systems. PMID:22297973

Druitt, T H; Costa, F; Deloule, E; Dungan, M; Scaillet, B

2012-02-01

451

Length of day variations due to mantle dynamics at geological timescale  

NASA Astrophysics Data System (ADS)

The geological evolution of length of day (LOD) variations is mainly controlled by the frictional tidal torque responsible for the secular slowdown of the Earth's rotation and for the receding of the Moon. Superimposed on this variation, which has existed since the early history of the planet, there are, at shorter timescales (less than 1 Myr), LOD perturbations induced by the glaciation-deglaciation cycles. In this paper, we investigate the influence of mantle dynamics on LOD at the geological timescale. We use the complete non-linear equations to compute the influence of mantle density heterogeneities on the angular velocity of the rotation, that is to say on the LOD. We discuss the degree zero coefficient of the spherical harmonic expansion of the mantle mass anomaly, which is strongly dependent on the conservation of mass of the Earth. We first compute the effects induced by upwelling domes and subducted plates sinking into the mantle, which are known to induce geological variations in the orientation of the rotation axis with respect to a fixed terrestrial frame (the so-called True Polar Wander). We find that the time-variable mantle density heterogeneities associated with the large-scale pattern of plate tectonic motions since 120 Ma and with the upwelling domes can perturb LOD by about ? per year, that is, with an order of magnitude smaller than the effects induced by the last deglaciation. Superimposed on this linear trend, we show that there are fluctuations around 0.1-0.2 s Myr-1 on a timescale of a few tens of millions of years. We then combine a spherical model of mantle circulation with solutions for the equations governing the rotation of a viscous planet, to improve the constraint of mantle mass conservation. Finally, we compare our results with other effects.

Greff-Lefftz, Marianne

2011-11-01

452

Emergence of Functional Hierarchy in a Multiple Timescale Neural Network Model: A Humanoid Robot Experiment  

PubMed Central

It is generally thought that skilled behavior in human beings results from a functional hierarchy of the motor control system, within which reusable motor primitives are flexibly integrated into various sensori-motor sequence patterns. The underlying neural mechanisms governing the way in which continuous sensori-motor flows are segmented into primitives and the way in which series of primitives are integrated into various behavior sequences have, however, not yet been clarified. In earlier studies, this functional hierarchy has been realized through the use of explicit hierarchical structure, with local modules representing motor primitives in the lower level and a higher module representing sequences of primitives switched via additional mechanisms such as gate-selecting. When sequences contain similarities and overlap, however, a conflict arises in such earlier models between generalization and segmentation, induced by this separated modular structure. To address this issue, we propose a different type of neural network model. The current model neither makes use of separate local modules to represent primitives nor introduces explicit hierarchical structure. Rather than forcing architectural hierarchy onto the system, functional hierarchy emerges through a form of self-organization that is based on two distinct types of neurons, each with different time properties (“multiple timescales”). Through the introduction of multiple timescales, continuous sequences of behavior are segmented into reusable primitives, and the primitives, in turn, are flexibly integrated into novel sequences. In experiments, the proposed network model, coordinating the physical body of a humanoid robot through high-dimensional sensori-motor control, also successfully situated itself within a physical environment. Our results suggest that it is not only the spatial connections between neurons but also the timescales of neural activity that act as important mechanisms leading to functional hierarchy in neural systems.

Yamashita, Yuichi; Tani, Jun

2008-01-01

453

Timescale dependence of glacial erosion rates: A case study of Marinelli Glacier, Cordillera Darwin, southern Patagonia  

NASA Astrophysics Data System (ADS)

Erosion rates have been estimated for a number of glaciated basins around the world, mostly based on modern observations (last few decades) of sediment fluxes to fjords. We use time-constrained sediment volumes delivered by Marinelli Glacier (55°S), an outlet glacier of the Cordillera Darwin ice cap, southern Patagonian Andes, Tierra del Fuego, to determine erosion rates across different timescales. Sediment volumes are derived using a dense grid of high- and low-frequency single channel seismic data and swath bathymetry data along with piston and Kasten cores. Our results show dramatic differences in erosion rates over different timescales. Erosion rates at Marinelli Glacier diminish about 80% (or by factor of ˜5) with each ten-fold increase in the time span over which erosion rates are averaged: 29.3 mm/yr for the last 45 years, 5.3 mm/yr for the last 364 years, and 0.5 mm/yr for the last 12,500 years. These results indicate that modern sediment yields and erosion rates from temperate tidewater glaciers can exceed long-term values over the time of deglaciation after the Last Glacial Maximum (centennial and millennial timescales) by up to 2 orders of magnitude. In view of the low exhumation rates of Cordillera Darwin (˜0.07 mm/yr average for the last 30 Myr), modern erosion rates could be up to 3 orders of magnitude higher than rates over geological time. We conclude that the pattern of erosion rate variation with time reflects the sensitivity of glaciers to climate variability.

Fernandez, Rodrigo A.; Anderson, John B.; Wellner, Julia S.; Hallet, Bernard

2011-03-01

454

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

455

Search for Short Variability Timescale of the GEV Gamma-Ray-Loud Blazars  

NASA Astrophysics Data System (ADS)

In this paper we report a brief description of 13 ?-ray-loud blazars as the second batch of the results of our blazar monitoring program. Six of the monitored objects show significant rapid variations. We found the typical minimum variability timescale to be about 1 hr. We have analyzed the relationships between optical variability and ?-ray variability and found that during 1995-1996 the TeV ?-ray emission of Mrk 501 correlated to its optical emission, based on our monitoring data in the optical band. This result will provide a strong constraint to the emission models.

Xie, G. Z.; Li, K. H.; Bai, J. M.; Dai, B. Z.; Liu, W. W.; Zhang, X.; Xing, S. Y.

2001-02-01

456

Observation of Optical Pulse and Material Dynamics on the Femtosecond Time-Scale  

SciTech Connect

The widespread availability of lasers that generate pulses on the femtosecond scale has opened new realms of investigation in the basic and applied sciences, rendering available excitations delivering intensities well in excess of 10{sup 21} W/cm{sup 2}, and furnishing probes capable of resolving molecular relaxation timescales. As a consequence and a necessity, sophisticated techniques to examine the pulse behavior on the femtosecond scale have been developed and are of crucial importance to gain insight on the behavior of physical systems. These techniques will be discussed with specific application to guided pulse propagation and ionization dynamics of noble gases.

Omenetto, F.; Luce, B.; Siders, C.W.; Taylor, A.J.

1999-09-13

457

Investigations of Variability on Multi-Year Timescales in a Venus Atmosphere GCM  

NASA Astrophysics Data System (ADS)

We have developed a Venus atmosphere general circulation model (GCM) based on the NCAR CAM Earth climate model. In our simulations we use a simpified thermal relaxation scheme, similar to that used in other Venus GCMs, and linear friction at the lower boundary, with a sponge layer in the upper levels to prevent possible reflection from the upper boundary. We use a high resolution of around 1 degree by 1 degree in latitude and longitude, which allows us to simulate variations on small spatial scales which may be important in Venus' atmosphere. We generate superrotation with mean zonal wind magnitudes comparable with those observed using probes, and around 50 to 60 percent of those measured using cloud-tracking techniques. We find periodic variations in the magnitude of the zonal winds in our simulations at cloud top heights and below, with a timescale of around 10 years. We also find a vacillation cycle in our results, in which the westward winds at cloud level alternate between mid latitude zonal jets and a single equatorial maximum. Analysis of angular momentum transport within our simulations suggests that there is no single simple Hadley cell circulation that transports angular momentum between the surface and cloud levels, but that there is a more complex flow below around 40 km altitude. Observations of Venus' cloud top winds suggest there may be variations in the zonal wind structure over multi-year timescales. Measurements of the atmosphere above the cloud tops also show changes in carbon monoxide content and temperature with timescales of around 10 years. Variations with timescales of tens of years have also been found in the sulphur dioxide content ab